A+P Digestive LOs

What are the 6 essential nutrients?

Carbohydrates Proteins Lipids Minerals Vitamins water -essential nutrients: indicates substances that must constitute part of the diet for survival

Describe the bacterial action that takes place in the large intestine

numerous normal bacteria flora inhabit the large intestine, called the indigenous microbiota -if this gets out of the large intestine, this can cause sepsis and death -responsible for the chemical breakdown of complex carbohydrates, proteins, and lipids that remain in the chyme -produce CO2, H+, and other substances, as well as B vitamins and vitamin K which are then absorbed from the large intestine into the blood -feces is the final product formed and then eliminated from the GI tract -feces: composed of water, salts, epithelial cells, bacteria, and undigested material

Describe the histology of the small intestine.

-2 layer of muscle -the epithelium and lamina propria of each is like a glove (epithelium) to a finger (lamina porpria) -each contains an arteriole, a rich blood capillary network, and a venule -a lacteal is a type of lymphatic capillary also within the villus that is responsible for absorbing lipids and lipid-soluble vitamins, taking lipis to the liver -the microvilli appear as a brush border -extensions of the simple columnar epithelial cells lining the small intestine -located within close proximity and embedded within the plasma membrane are the required proteins for membrane transport of digested molecules -between intestinal villi are invaginations of the mucosa called intestinal glands that secrete intestinal juice -extend to the base of the mucosa -have many immune cells (MALT) in lymphatic nodules -thicker mucosal layer than submucosal -have goblet cells secreting mucin -have intestinal cells and enteropeptidase is part of protein breakdown

List the features that increase small intestine surface area.

-3 structures increase the surface area: -circular folds: macroscopic structures that are formed by the musical and submucosal tunics of the small intestine -they also act as speed bumps to slow down the movement of chyme and ensure that it remains within the small intestine for maximal nutrient absorption -more numerous in the duodenum and jejunum -there are villi with smaller microvilli on top; substances are mixed back and forth over this large surface area to increase digestion

Describe the makeup of salvia and its functions.

-99.5% water and a mixture of solutes, and 1.0-1.5 L is secreted daily, mostly produced during mealtime -salivary amylase, mucin, and lysozyme are added -functions: -moistens ingested food as it is formed into a bolus -initiates the chemical breakdown of starch in the oral cavity because of the salivary amylase it contains -acts as a watery medium into which food molecules are dissolved so taste receptors may be stimulated -cleanses the oral cavity structures -helps inhibit bacterial growth in the oral cavity because it contains antibacterial substances, such as lysozyme and IgA antibodies

List examples of how both water-soluble and fat-soluble vitamins function in the body.

-B-Complex Vitamins: serve as coenzymes in various enzymatic chemical reactions -For example: vitamin B3 is a necessary hydrogen carrier in mitochondria during ATP synthesis -Vitamin C: required for the synthesis of collagen, which is an important protein in connective tissue. Also functions as an antioxidant by removing free radicals -Vitamin A: precursor molecule for the formation of visual pigment retinal -Vitamin D: modified to form calcitriol which increases calcium absorption from the GI tract -Vitamin E: helps stabilize and prevent damage to cell membranes -Vitamin K: required for the synthesis of specific blood-clotting proteins

Describe the transport of lipids within the blood.

-VLDLs contain various types of lipid (triglycerides, cholesterol) packages within the protein. They are assembled within the liver and released into the blood to release triglycerides to all cells of peripheral tissues, but primarily adipose. -LDLs have high amounts of cholesterol. They deliver cholesterol to cells. LDLs bind to LDL receptors within the plasma membranes of cells and are engulfed by receptor-mediated endocytosis. Cholesterol is incorporated into the plasma membrane of cells or is used by certain tissues to produce steroid hormones -HDLs are associated with the transport of lipids from peripheral tissues to the liver. They are produced in stages and have a function opposing VLDLs and LDLs. Proteins are formed in the liver and released into the blood without the addition of lipid. HDL molecules circulate throughout the blood and fill with lipid from peripheral tissues and the lining of arterial walls. They transport these to the liver

Explain the processing in the oral cavity that initiates carbohydrate digestion.

-chemical digestion of carbohydrates involves (a) the breakdown of starch into individual glucose molecules and (b) the breakdown of disaccharides into the individual monosaccharides that compose them -digestion of starch in the oral cavity is catalyzed by salivary amylase that is synthesized and released from the salivary glands -this breaks the chemical bonds between glucose molecules within the starch molecule -salivary amylase is inactivated by the low pH of the stomach when the bolus is swallowed, typically occurring within 15-20 mins after the bolus enters the stomach -after entrance into the stomach, starches are not digested again until entry into the small intestine

Describe the anatomy of the small intestine.

-a long tube that extends from the stomach to the large intestine -about 9 to 10 liters of ingested food, water, and digestive system secretions enter the small intestine daily -finishes chemical digestion and is responsible for absorbing almost all of the nutrients and a large percentage of water, electrolytes, and vitamins -contains 3 segments: -duodenum: forms the first segment, part of the upper GI -about 25 cm long and originates at the pyloric sphincter -most is retroperitoneal, but the very initial portion is intraperitoneal -receives (a) acidic chyme from the stomach and (b) the secretions from the abdominal accessory organs, including bile from the liver and gallbladder and pancreatic juice from the pancreas -within the lumen, all these substances are mixed and digestive enzymes have constant with ingested molecules and chemical digestion primarily occurs -jejunum: middle region -primary region for nutrient absorption -ileum: last region -distal end terminates at the ileocecal valve, a sphincter that controls the entry of materials from the small intestine into the large intestine -absorption of digested materials continues along with the absorption of bile salts and vitamin B12 -both the ileum and jejunum are intraperitoneal organs and are suspended within the abdomen by mesentery proper

Identify and briefly describe the numerous roles of the liver in metabolism.

-a summary of liver functional categories includes: -carbohydrate metabolism -protein metabolism -transport of lipids -other functions (e.g, storage, drug detoxification)

Describe the functions of the large intestine.

-absorbs water and electrolytes from remaining digested materials -watery chyme is compacted into feces -stores feces until eliminated through defecation

Briefly describe the general process of absorption.

-absorption occurs when substances are moved through the simple columnar epithelial cells that line the GI tract wall and are absorbed into the blood or lymphatic capillaries located with the lamina propria of the mucosa layer

List the accessory organs and structures involved in the digestive process.

-accessory glands produce secretions that empty into the lumen of the GI tract and include the salivary glands, liver, and pancreas -others include the teeth and tongue and the gallbladder

Define how energy is obtained and measured.

-all macronutrients provide fuel for cellular respiration to form ATP -the energy is measured in calories -calorie: the amount of heat required to raise the temperature of 1 g of water by 1 degree C -kilocalorie is 1,000 calroies, or 1 Calorie

Describe Celiac Disease.

-an autoimmune disorder affecting 1% of the US population -gluten is a protein in wheat, rye, and barley that will stimulate an immune response that damages villi of the small intestine, interfering with absorption -symptoms: abdominal pain, diarrhea, nutrient deficiencies

Explain how both basal metabolic rate and total metabolic rate is measured and the variables that influence each.

-basal metabolic rate (BMR) is the amount of energy expended to keep the body functioning when an individual is at rest and not eating -rest conditions: the individual has not eaten for 12 hrs, is reclining and relaxed, and is exposed to specific environmental conditions, including a room temperature above 20 degrees C -can be measured by a calorimeter, a water-filled chamber into which an individual is placed. The heat released from the body alters the temp of the water, and a change in temp is measured. This is a direct method -can be measured by a respirometer, an instrument to measure oxygen consumption. Indirectly measured BMR because a relationship exists between heat and oxygen consumption. -varies based on sex, age, lean body mass, and levels of various hormones in the blood. -decreases as we age- 3% decline at each decade beginning at 30 -greater lean body mass have higher BMR (males have higher than females) -thyroid hormone increases BMR with an accompanying increase in lipolysis -the greater surface area of the skin means greater BMR due to heat lost -total metabolic rate (TMR) is the amount of energy used by the body, including the energy needed by physical activity, so it is BMR plus metabolism associated with physical activity. Varies depending on: -the amount of skeletal muscle and its activity: a rapid elevation of TMR occurs in vigorous exercise and stays elevated for several hrs after exercise -food intake: increases following ingestion of a meal but decreases after absorption of materials is done -changing environmental conditions: metabolic rate increases when one is exposed to cold to try and maintain normal body temperature, for example

Explain the details of vitamin B12 absorption.

-because of its large molecular size, must be absorbed by receptor-mediated endocytosis -requires intrinsic factors released from parietal cells of the stomach -during its transport, it binds vitamin B12 within chyme to form a B12-intrinsic factor complex -within the distal ileum these complexes bind to receptors on the epithelial cell lining and are taken up by receptor-mediated endocytosis -lack of intrinsic factor prevents the binding and absorption of the vitamin B12 that is required for erythrocyte formation, resulting in the development of pernicious anemia

Compare long reflexes and short reflexes that regulate the digestive system.

-both the ENS and ANS control the GI tract wall through nerve reflexes in response to receptor input -sensory input detected by either baroreceptors or chemoreceptors is relayed to neurons, causing reflexes to be initiated -a short reflex is a local reflex that only involves the ENS, coordinating small segments of the GI tract -a long reflex involves sensory input relayed to the CNS and autonomic motor output -coordinates GI tract motility, secretions, and accessory digestive organs

Describe pancreatic cancer.

-cancer of the pancreatic cells, typically exocrine cells -prognosis is good with early detection, but early detection is difficult because there is not screening test and absence of signs and symptoms in early stages of the diease -symptoms in later stages include abdominal pain, jaundice, loss of appetite, and weight loss -pancreatic cancer is often fatal because usually detected late

Name the three classes of carbohydrates.

-carbohydrates are organized based on the number of repeating units of simple sugars -monosaccharides (glucose+fructose), disaccharides (sucrose+maltose), polysaccharides (starch+cellulose) -these are digested in the oral cavity and small intestine -starch is broken down into individual glucose molecules -disaccharides are broken down into individual monosaccharides

Explain the difference between a complete protein and an incomplete protein.

-complete proteins contains all of the essential amino acids -incomplete proteins do not contain all of the essential amino acids -animal proteins (meat, poultry, eggs, milk, cheese, yogurt) are complete proteins -plant proteins (legumes, vegetables, grains) lack one or more of the essential amino acids

Describe constipation and diarrhea.

-constipation: -temporary impaired ability to defecate with compacted feces that is difficult to eliminate -from lower fiber, dehydration, lack of exercise, poor bowel habits, or anesthesia -diarrhea: -disruption in normal mechanism to absorb intestinal water -e.g. From osmotically active solutes that move large volumes of water into the colon

Define core body temperature, and explain why it must be maintained.

-core body temperature: the temperature of the vital portions of the body, or the core, which consists of the head and torso -the temperature of these regions is kept relatively constant, or stable, to ensure that life is maintained. This generally occurs by allowing fluctuations in peripheral regions, such as the limbs

Describe Diverticulosis and Diverticulitis.

-diverticulosis: -small bulges in the intentional lining called diverticula are typically formed when the colon narrows in response to low fiber -diverticulitis: -inflammation of diverticula that may be life-threatening is diverticula rupture and leak of intestinal contents into the abdominal cavity

Describe the difference between essential and nonessential vitamins

-essential vitamins must be provided in the diet -if an essential vitamin is lacking in uptake, or its absorption is impaired, then a vitamin deficiency results (avitaminosis), including vitamin C and A -nonessential vitamins are cofactors that the body is able to produce and recycle as needed -include the NADH and FADH2 involved in the citric acid cycle

Explain the relationship between dietary intake of cholesterol and the level of cholesterol synthesis in the liver. Describe cholesterol formation.

-fatty acids within the liver are transported from a liver sinusoid to enter hepatocytes, where they are broken down into numerous two-carbon units; each is formed into acetyl CoA -this process is beta-oxidation -acetyl CoA molecules are used to synthesize cholesterol in an enzymatic pathway that includes a specific enzyme called HMG-CoA reductase -liver produces cholesterol at a basal level that varies among individuals -adjusted inversely to his/her diet -a low dietary intake results in lower blood cholesterol and less cholesterol entering hepatocytes, so cholesterol synthesis by the liver increases -following its synthesis, cholesterol is (a) released into the blood as a component of VLDLs, or (b) is synthesized into bile salts and released as a component of the bile into the small intestine -the majority of bile salts are released back into the blood, primarily while moving through the ileum -a small amount continues into the large intestine and is removed as feces, providing a means of eliminating cholesterol from the body and lowering cholesterol levels

List the glands found in the small intestine and their secretions.

-four types of cells of the intestinal epithelium contribute to the process of digestion. Three secrete and produce intestinal juice, and the fourth secretes hormones: -goblet cells within the simple columnar epithelium produce mucin that, when hydrated, turns to mucus, lubricating and protecting the intestinal lining. These cells increase in number from the duodenum to the ileum because more lubrication is needed as digested materials and water are absorbed and undigested materials and less water remain in the lumen -enteroendocrine cells aer in pits release hormones like CCK and secretin into the blood that oppose gastrin -paneth cells are located only in the base of the intestinal crypts. Assist with the function of the innate immune system by secreting lyoszyme as well as some other antimicrobial agents, to help protect against potentially harmful substances within the small intestine -duodenal submucosal gland is housed within the submucosal layer and is only in the proximal duodenum. Produces a viscous, alkaline mucous secretion that protects the duodenum from the acidic chyme entering from the stomach

Describe gallstones.

-gallstones in gallbladder or biliary apparatus -risk factors: female sex, obestiy, age, Causasian -caused by condensation of cholesterol or calcium and bile salts -majority is asymptomatic until lodges in the neck to the cystic ducts -gallbaldder inflamed is cholecystitis -severe pain in the right hypochondriac region, nausea, vomiting, indigestion, bloating, with symptoms worsening after a fatty meal -most requrie surgical remvoal, cholecystectomy

Describe the gross anatomy and histology of the stomach.

-has a larger convex inferolateral surface called the greater curvature and a smaller, concave superomedial surface called the lesser curvature -composed of 4 regions: -cardia: small, narrow, superior entryway into the stomach lumen from the esophagus. The internal opening where the cardia meets the esophagus is the cardiac orifice, which is the location of the esophageal sphincter -fundus: dome-shaped lateral region lateral and superior to the esophageal connection with the stomach. Its superior surface connects to the inferior surface of the thoracic diaphragm. Has weaker muscle contractions and a higher pH in its lumen area than other regions of the stomach -body: largest region; inferior to the cardiac orifice and the fundus and extends to the pylorus -pylorus: narrow, funnel-shaped terminal region of the stomach. It opens into the duodenum of the small intestine and is the pyloric orifice. Surrounding this orifice is a thick ring of circular smooth muscle called the pyloric sphincter, regulating the movement of material from the stomach into the small intestine -internal stomach lining is composed of numerous gastric folds -the lining is indented by numerous depressions called gastric pits -several gastric glands extend deep into the mucosa from the base of each -cells here produce gastric secretions -inlcude surface mucous cells, mucous neck cells, parietal cells, chief cells, and G-cells -two serous membrane structures are associated with the stomach: -greater omentum: extends inferiorly from the greater curvature of the stomach, forming the fatty apron that covers the anterior surface of the abdominal organs -lesser omentum: extends superiorly from the lesser curvature of the stomach and duodenum to attach these structures to the liver -the mucosa of the stomach is only about 1.5mm thick at its thickest region. The inner lining has three significant features: -the stomach mucosa is composed of a simple columnar epithelium supported by lamina propria. The transition from stratified squamous in the esophagus to simple columnar in the stomach is abrupt. The cells are replaced often because of the harsh acidic environment of the stomach -the muscularis here is composed of 3 smooth muscle layers -the presence of the third (oblique) layer assists the continued churning and blending of the bolus to mechanically digest the food. -muscularis becomes thicker and stronger as it progresses from the body to the pylorus -outermost lining is serosa that produces serous fluid that lubricates the external surface of the stomach to decrease friction due to stomach motility

Describe some heat-related illnesses.

-heat cramps: -involuntary muscle spasms from excessive loss of fluid -intense physical activity in hot, humid weather -heat exhaustion: -core body temp up to 104 degrees F -headache, weakness, rapid HR, nausea, vomiting -heatstroke: -severe: may result from untreated heat exhaustion -body temp over 104 degrees F or higher; unable to control it -fever, lack of sweating, confusion, rapid breathing -can be fatal

Describe Cirrhosis of the liver.

-hepatocytes are replaced by fibrous scar tissues that compresses blood vessel -causes hepatic portal hypertension -compressses bile ducts in the liver, caused by chronic injury to hepatocytes -chronic alcholism, liver disease, drugs or toxins -most frequently viral infection from hepatitis B or C -symptoms: fatigue, weight loss, nausea, pain in right upper quadrant, jaundice, endema, ascites, itching, tosin accumulation, dialted veins of esophagus

Describe blood cholesterol levels.

-highs levels of LDLs or total cholesterol, and low levels of HDLs: -risk factors for cardiovascular diseases -above 200 mg, dL total cholesterol is considered high -LDLs: excess cholesterol deposited on inner arterial walls -HDLs: transport lipids from the arterial wall to the liver -risk factors include high saturated fat intake, cigarette smoking, caffeine intake, and stress

Describe cold-related illness.

-hypothermia: -care body temp below 95 degrees F -decreased HR, slow breathing, confusion, drowsiness, fatigue -frostbite: -damage to superficial cells due to extreme cold -skin white with possible loss of sensation -dry gangrene: -maybe caused by severe frostbite -body part dry, distinct in color, shriveled -due to extensive vasoconstriction of blood vessels -oxygen deprivation and tissue death

Describe Appendicitis.

-inflammation of the appendix, most due to fecal matter obstructing the appendix -appendix swells, blood supply compromised, and bacterial growth -may burst if untreated, causing dangerous infection and peritonitis -pain initially referred to T10 around the umbilicus from smooth muscle, but eventually involves peritoneum -pain localized to right lower quadrant -nausea or vomiting, abdominal tenderness, fever -surgically removed through an appendectomy

Describe reflux esophagitis and gastroesophageal reflux disease.

-inflammation of the esophagus due to acidic chyme refulxing into the espohagus -causes pain posterior to the sternum called heartburn -seen most frequently in overweight individuals, smokers, or after large meals -hiatal hernias is a portion of the stomach protruding through the diaphragm -the cells may change from stratified squamous to columnar secretory epithelium, called a Barrett esophagus -this increases the risk of cancerous growth -traments includes lifestyle changes, head elevation, and limiting meal size

What is Peritonitis?

-inflammation of the peritoneum that causes abdominal pain -the most common cause is GI tract perforation -this allows contents to contact the peritoneum -may result from within (ulcer, ruptured appendix) or without (gunshot wound, surgery)

Describe IBS.

-inflammatory bowel disease: -autoimmune disorders, both with region of inflamed intestine, affecting 1 in 5 Americans -Chron disease: -young adults, intermittent adn relapsing episodes of cramping adn diarrhea -ulcerative colitis: -simialr to Chron's but only involves large intestine

Describe the physiologic advantages of the ability to interconvert nutrient biomolecules.

-interconversion of nutrient biomolecules is the changing of one nutrient biomolecule to another and is possible because of the biochemical pathways associated with cellular respiration -for example, if ATP is not needed, glucose can be broken down into acetyl CoA, which is then synthesized into triglycerides and stored instead of entering the citric acid cycle -this allows someone who is not getting adequate portions of something in their diet to synthesize this molecule and continue to function normally

Describe iron deficiency.

-iron is required in hemoglobin and myoglobin and is a component of electron transport proteins -needed to synthesize certain hormones, neurotransmitters, and amino acids -obtained from meat, poultry, fish, dark leafy vegetables, nuts, and whole grains -most common nutritional deficiency and results in fatigue, weakness, pale skin, and sensitivity to cold -there is insufficient intake or iron loss (example: excessive loss from bleeding)

Describe the sources and functions of cholesterol.

-it is required as a component of the plasma membrane of cells -also the precursor molecule for the formation of steroid hormones, bile salts, and vitamin D -either made available through our diet (a component of animal-based products, including meat, eggs, and milk) or synthesized by metabolic pathways in the liver

Explain lipid breakdown in the stomach.

-lingual lipase is a component of saliva in the oral cavity -not activated until it reaches the stomach -triglycerides undergo limited digestion by both lingual lipase and gastric lipase -acidic lipases digest about 30% of the triglycerides to diglyceride and a fatty acid -gastric lipase is released by chief cells -neither of these requires the participation of bile salts

Explain the role of bile salts in the mechanical digestion of lipids and the role of pancreatic lipase in the chemical digestion of triglycerides.

-lipids are hydrophobic and do not dissolve in the luminal fluids of the digestive system, and instead form large lipid masses -so, the lipid molecules must by mechanically separated into smaller droplets before chemical digestion by pancreatic lipase can effectively occur -emulsification: the mechanical digestion process associated with lipids in the small intestine of separating large lipid droplets into smaller droplets -occurs by the action of bile salts, which are a part of the bile -bile salts are amphipathic molecules composed of a polar head and a nonpolar tail -the nonpolar tail positions itself around the lipid droplets with the polar head next to the aqueous fluid in the lumen. This structure is called a micelle -the function of bile salts is the emulsify lipids so that pancreatic lipase, which is produced and secreted from the pancreas into the duodenum, has greater "access" to the triglyceride molecules and may more effectively chemically digest the triglyceride molecules -each triglyceride is chemically digested by pancreatic lipase into a monoglyceride and two free fatty acids

Describe lipids.

-lipids are not water-soluble and have highly variable structures -they include triglycerides that is a glycerol and 3 fatty acids, and cholesterol which does not need to be broken down for absorption

Define a lipoprotein, and provide a general overview of its function in the body.

-lipoprotein: a general category of structures containing triglycerides, cholesterol, and phospholipids within the "confines" of a protein, providing a means of lipid transport in the body -chylomicron is a type of lipoprotein that is formed within epithelial cells during the absorption of lipids from the small intestine -three broad categories of lipoproteins are: -(A) VLDLs, containing the most lipid -(B) LDLs, with somewhat less lipid -(C) HDLs, with the least amount of lipid -these function in the transport of lipids between the liver and peripheral tissues

List and describe the six general functions of the digestive system.

-listed in order of occurrence, with the first four main functions happening almost exclusively in the upper GI tract: -ingestion: the introduction of solid and liquid nutrients into the oral cavity. It is the first step in the process of digesting and absorbing nutrients -motility: voluntary muscular contractions (by skeletal muscle) and involuntary muscular contractions (by smooth muscle) for mixing and moving materials through the GI tract -secretion: the process of producing and releasing substances that facilitate both digestion and movement of contents within the GI tract. Secretions are produced by both the accessory digestive glands (salivary glands, liver, pancreas) and the wall of the GI tract and include digestive enzymes, acid, and bile -digestion: the breakdown of ingested food into smaller components that may be absorbed by the GI tract. This is categorized as either mechanical or chemical digestion -mechanical: breaking of ingested material into smaller pieces without changing its chemical structure. This is chewing and mixing. -chemical: the activity of specific enzymes to break down complex molecules into smaller molecules so that they can be absorbed. -absorption: involved membrane transport of digested molecules, electrolytes, vitamins, and water across the epithelial lining of the GI tract into blood or lymph. Occurs primarily within the small intestine -elimination: the expulsion of ingested components that are not absorbed through the anal canal; this is the lower GI tract

Describe a fecal transplant.

-low-cost, low-risk procedure used to treat Clostridium difficile colitis -fecal matter from a donor is placed in the colon of the patient (enema or colonoscopy) -may help treat Chron disease, ulcerative colitis, or IBS

Distinguish macronutrients from micronutrients and essential from nonessential nutrients.

-macronutrients: must be consumed in relatively large quantities; carbs, lipids, proteins or micronutrients: must be consumed in relatively small quantities; vitamins and minerals -essential nutrients: must be obtained in the diet and absorbed by the process of the digestive system, and this it is required that these be a part of dietary intake, including some macronutrients and micronutrients, or nonessential nutrients: can be adequately provided by biochemical processes within the body, and for this reason, they are not required to be part of dietary intake

Distinguish between major minerals and trace minerals.

-major minerals: needed at levels greater than 100 mg per day -calcium, chloride, magnesium, phosphorous, potassium, sodium, sulfur -minor minerals: required at less than 100 mg a day -chromium, cobalt, copper, fluoride, iodine, iron, manganese, molybdenum, selenium, zinc

Explain the process of mastication.

-mechanical digestion in the oral cavity is mastication, or chewing -requires the coordinated efforts of teeth, skeletal muscles in lips, tongue, cheeks, and jaws that are controlled within the medulla oblongata and pons, collectively called the mastication center -the primary function of chewing is to mechanically reduce its bulk into smaller particles to facilitate swallowing -chemical digestion and absorption are affected very little by chewing except that the surface area of the food is increased -also promotes salivation to help soften and moisten the food to form a bolus -medications made of small, nonpolar molecules can be placed under the tingue, where they pass through the epithelium by simple diffusion (ntiroglycerin)

Explain the function of the mesentery, and describe the five individual mesenteries of the abdominopelvic cavity.

-mesentery: double layer of the peritoneum that attaches to the posterior abdominal wall and supports, suspends and stabilizes the intraperitoneal GI tract organs -blood vessels, lymph vessels, and nerves are sandwiched between folds -it is associated with specific organs -types of the mesentery: -greater omentum: extends inferiorly from the inferolateral space of the stomach and covers most of the abdominal organs. Often accumulates large amounts of adipose tissue, insulating the abdominal organs and storing fat called a fatty apron -lesser omentum: connects the superomedial surface of the stomach and the proximal end of the duodenum to the liver, cushions these organs some -falciform ligament: flat, thin, crescent-shaped peritoneal fold that attaches the liver to the internal surface of the anterior abdominal wall -mesentery proper: a fan-shaped fold of peritoneum that suspends most of the small intestine from the internal surface from the posterior abdominal wall -mesocolon: a fold of the peritoneum that attaches the large intestine to the posterior abdominal wall. Have several distinct sections named for the portion of the colon it suspends

Define metabolic rate.

-metabolic rate: the measure of energy used in a given period of time -two means of expressing metabolic rate: basal and total metabolic rate

Discuss the process by which lipids are absorbed.

-micelles transport lipids to the simple columnar epithelial lining of the small intestine -they enter the epithelial cells by simple diffusion, whereas the bile salts remain in the small intestine lumen -eventually, in the last portion of the ileum, bile salts are recovered from the GI tract back into the blood by active transport and recycled to the liver for reuse -new bile salts are synthesized by hepatocytes to replace those lost in the elimination of feces -chylomicrons are formed within the epithelial cells lining the small intestine -within these cells, fatty acids are reattached to monoglyceride to re-form triglycerides -triglycerides, cholesterol, and other lipid molecules are then "wrapped" with protein to form a chylomicrons -the Golgi apparatus packages chylomicrons into secretory vesicles that merge with the plasma membrane of epithelial cells to release chylomicrons by exocytosis -they enter lacteals, the lymphatic capillaries of the small intestine -chylomicrons enter the blood and deliver lipids to the liver and other tissues

Define minerals, and list examples of how minerals absorbed in the small intestine function in the body.

-minerals are inorganic irons such as iron, calcium, sodium, potassium, iodine, zinc, magnesium, and phosphorus that must be obtained from the diet -iron is present in hemoglobin within erythrocytes where it binds oxygen and in the mitochondria in the electron transport system to bind electrons -calcium is required for the formation and maintenance of the skeleton, muscle contraction, exocytosis of neurotransmitters, and blood clotting -sodium and potassium function to maintain an RMP in excitable cells and are required for propagation of an action potential -iodine is needed to produce thyroid hormone -zinc has roles in both protein synthesis and wound healing

Identify the anatomic structures of the oral cavity.

-mouth is the entrance to the GI tract -two distinct spatial regions: -vestibule which is the space between the gums, lips, and cheeks -oral cavity proper which lies central to the teeth, leading posteriorly to the oropharynx -the cheeks have buccinator that compress the cheeks to hold solid material while chewing -fauces are opening between the oral cavity and oropharynx -bound by paired muscular folds: the anterior palatoglossal arch and the posterior palatopharyngeal arch -palatine tonsils are housed between the arches that serve as an early line of defense aganist foreign antigens -the tongue is formed primarily of skeletal muscle with extrinsic and intrinsic muscles -lingual tonsils on posterionferior tongus region -attaches to the floor of the mouth by a membrane, the lingual frenulum -mainpulated and mixes materials during chewing -imporant functions in swallowing and speaking -numerous small projections called papillae cover the surface of the tongue and are involved in the sense of taste

Explain the neural and hormonal controls of temperature regulation.

-nervous control of body temp is mediated primarily through the hypothalamus -motor pathways extend from the hypothalamus to sweat glands, skeletal muscles, and peripheral blood vessels -the hypothalamus detects changes in body temp either by monitoring the temp of blood as it passes through the hypothalamus or by monitoring nerve signals received from the skin -an increase in metabolic rate causes an increase in body temp and heat must be released -hypothalamus stimulated sweat glands to release sweat and stimulates vasodilation of peripheral blood vessels to bring heat to the skin's surface -when metabolic rate decreases, the opposite happens -conscious changes in behavior that are initiated by the cerebral cortex can help regulate body temp -temp regulation also mediated by hormones, including thyroid hormone, EPI, NE, growth hormone, and testosterone -thyroid hormone establishes the metabolic rate, causing us to produce a certain amount of heat to keep warm -as body temp drops, the hypothalamus releases THR that stimulates the anterior pituitary to release TSH, which stimulates the thyroid gland to relase thyroid hormone, which increases the metabolic rate of all cells, especially neurons -neurons specifically increase their number of Na+/K- pumps, making more energy be utilized as ATP is required to move the ions, then more heat is produced

Describe the digestion of nucleic acids.

-nucleic acids: polymers of nucleotides -nucleic acid digestion occurs in the small intestine -nucleases (deoxyribonuclease and ribonuclease) are synthesized and released by the pancreas to begin the digestion of nucleic acids -each breaks to phosphodiester bond between the individual necolotides of DNA and RNA -nucleotides are the products: deoxyribonucleotides from DNA and ribonucleotides from RNA -breakdown of nucleotides is accomplished by brush border enzymes embedded in the epithelial lining of the small intestine, including: -phosphatase, breaking the holding bonds phosphate to the rest of the nucleotide -nucleotidase, breaking the bond between sugar and the nitrogenous base, releasing them -all nucleic acid building blocks are absorbed across the epithelium of the small intestine into the blood -include phosphate, sugar, and nitrogenous bases

Define both nutrition and nutrients.

-nutrition: is the study of the means by which living organisms obtain and utilize the nutrients they need to grow and sustain life -nutrients: include most biological macromolecules, vitamins, and minerals that the body needs for development and growth, maintenance of anatomic structures and physiologic processes, and repair of damaged tissues

Distinguish between intraperitoneal and retroperitoneal organs.

-organs within the abdomen completely surrounded by the visceral peritoneum are intraperitoneal organs. -the outermost layer of each of these organs is a serosa -include the stomach, most of the small intestine, parts of the large intestine, and most of the liver -retroperitoneal organs lie outside of the parietal peritoneum directly against the posterior abdominal wall, so only their anterolateral portions are covered by the parietal peritoneum -these organs are not completely enveloped by a visceral peritoneum -the outermost layer of these organs is an adventitia -include the pancreas, esophagus, most of the duodenum, parts of the large intestine, and the rectum

Describe the phases that regulate motility and secretion in the stomach.

-pacemaker cells are specialized cells within the GI tract wall -in the stomach, they are located in the longitudinal layer of smooth muscle and initiate smooth muscle contraction -electrical signals spread via gap junctions between the smooth muscle cells in the muscularis layer of the stomach -regulated by both nervous reflexes and hormones, which alter force but not rate of contraction. The secretory activity of gastric glands is also altered. -there are 3 phases: -cephalic phase: primarily involves the cephalic reflex, which is a nervous system reflex initiated by the thought, smell, sight, or taste of food -nerve signals from the higher regions of the brain are sent to the hypothalamus, which then relays signals to the medulla oblongata -medulla increases parasympathetic stimulation of the stomach via the vagus nerve, causing an increase in contractile force in the gastric wall and secretory activity of the gastric glands -gastric phase: involves processes that begin after the bolus reaches the stomach -regulated by both the nervous system via the gastric reflex and the endocrine system through the release of gastrin -gastric reflex: nervous system reflex initiated as food enters the stomach -baroreceptors in the wall of the stomach detect increased digestion in its wall, and chemoreceptors detect the presence of protein and an increase in pH in the stomach -nerve signals are relayed along sensory neurons to the medulla, resulting in nerve signals relayed along motor neurons to the stomach to cause the same effects as described in the cephalic reflex -the presence of food, especially protein, also causes the release of gastrin from enteroendocrine cells -gastrin enters the blood and circulates back to the stomach to further stimulate the contractile activity of the muscle in the stomach wall and to primarily increase the release of HCl from parietal cells -also stimulates contraction of the pyloric sphincter to slow stomach emptying, allowing time for completion of digestive activities in the stomach -intestinal phase: involves the processes following the chyme reaching the small intestine, regulated by both the nervous system and endocrine system -involves both the intestinal reflex and the release of two significant hormones from the duodenum: CCK and secretin -intestinal reflex: nervous system reflex that opposes the other two reflexes -protects the small intestine from being overloaded with chyme -initiated with the entry of acidic chyme into the duodenum, which causes a decrease in nerve signals released to the medulla -so, vagal stimulation to the stomach is decreased, lessening motility and secretory activity -CCK: hormone released by the enteroendocrine cells of the duodenum for contraction -primarily in response to fatty chyme -causes a decrease in stomach motility -secretin: hormone released by the enteroendocrine cells of the duodenum, proximity in response to the presence of acidic chyme in the small intestine -causes a decrease in secretory activity of the stomach -both CCK and secretion also inhibit the release and oppose of gastrin -this slows down the emptying of the stomach, allowing the small intestine to continue its digestive process before additional chyme is added -an increase in small intestine secretion means a decrease in stomach secretions

Describe Colorectal Cancer.

-second most common type of cancer in the US -malignant growth anywhere along the large intestine, rectum -most arises from polyps -polyps: outgrowth from colon mucosa -risk factors include low fiber, family history, age, history of ulcerative colitis -rectal bleeding, abdominal pain, weight loss -must be removed surgically and is screened through fecal occult blood test, sigmoidoscopy, or colonoscopy

Describe the histology of the oral cavity.

-the epithelial lining of the oral cavity is the stratified squamous epithelium that protects against the abrasive activities associated with chewing -keratinized type lines the lips, portions of the tongue, and a small region of the hard palate -this doesn't have layers because the oral cavity does not have the tube shape of the rest of the digestive system

Describe the chemical digestion of carbohydrates that occurs in the small intestine.

-pancreatic amylase, which is produced and secreted from the pancreas into the small intestine continues the digestion of starch into shorter strands of glucose, maltose, and individual glucose molecules. This is a component of pancreatic juice -the completion of starch breakdown is accomplished by brush border enzymes embedded within the lining of the small intestine -enzymes include dextrinase and glucoamylase, breaking bonds between glucose subunits of oligosaccharides, and maltase which breaks the bonds between the two glucose molecules that compose maltose. These are brush border enzymes as a whole; Peart claims we do not need to know specific names -digestion of other disaccharides requires one enzyme each: -lactase digests lactose to glucose and galactose (a reduction or lack of this is lactose intolerance) -sucrase digests sucrose to glucose and fructose -the monosaccharides relased from enzymes include glucose, fructose, and galactose and are absorbed across the epithelial lining into the blood -all venous blood is transported through the hepatic portal vein to the liver where fructose and galactose is converted to glucose -glucose can become part of blood glucose, be taken up by any cell to be oxidized through cellular respiration, be taken up by liver and muscle cells and be synthesized into glycogen and stored, or be converted into fat (triglycerides) and stored in adipose connective tissue. So converted to energy or stored -cellulose, a carbohydrate of plant cells walls, is not chemically digested because we lack the enzymes required to do so -this is a fiber that adds "bulk" to contents within the lumen and facilitates its moving through the GI tract

Describe the three components of the lower gastrointestinal tract.

-process of digestion and absorption continues; elimination of indigestible and non absorbable material -small intestine: very long -3 regions (duodenum, jejunum, ileum) -the duodenum is considered part of the upper GI tract because it works hand-in-hand with the stomach, secreting hormones opposing gastrin -most chemical digestion of macromolecules and absorption of water, nutrients, and electrolytes occur here -accessory digestive organs: -liver, gallbladder, and pancreas -their collective secretions include bile and pancreatic juice -bile is produced by the liver and then stored, concentrated, and released by the gallbladder -pancreatic juice contains numerous digestive enzymes and is produced and released by the pancreas -these secretions contain HCO3-, which neutralizes acidic chyme entering the duodenum -large intestine: -primarily absorbs water, electrolytes, and vitamins -the digestive process is completed as a semifluid mass of partially digested food is converted to feces and then eliminated via the anus -different segments of the large intestine are the rectum and anus

Identify the enzyme that initiates protein digestion in the stomach, and explain its activation and action.

-protein: polymers composed of amino acid subunits linked by peptide bones; digestion releases individual amino acids; broken down by enzymes -all enzymes that digest proteins are collectively called proteolytic enzymes or proteases -these target peptide bonds between amino acids -protein digestion begins in the stomach lumen -they are released inactively -HCl formed from parietal cells causes a low pH within the stomach that denatures proteins to facilitate their chemical breakdown and activates the formation of pepsin from pepsinogen -pepsin is a proteolytic enzyme that chemically digests proteins into shorter stands of amino acids; made from pepsinogen

Discuss nitrogen balance, and include the difference between a positive nitrogen balance.

-proteins are a source of nitrogen that is needed for synthesizing other nitrogen-containing molecules, like the bases of nucleic acids and porphyrin -adequate availability of nitrogen is expressed as nitrogen balance -nitrogen balance occurs when equilibrium exists between dietary intake and its loss in urine and feces -input of nitrogen must equal output to maintain nitrogen balance -positive nitrogen balance is when someone absorbs more nitrogen than is excreted, as occurs in people who are growing, pregnant, or recovering from injury -negative nitrogen balance occurs from malnutrition or blood loss; more is excreted than absorbed and can be fatal

Explain the deamination of proteins.

-proteins are made of amino acids, which contain nitrogen in an amine group (-NH2) -the amine group is removed in a process called deamination within hepatocytes in the liver -the amine group is a "contaiminant" that must be taken off in order for the amino acids to be used in cellular respiration to generate ATP -the amine group is converted into urea (urea cycle) and is eliminated through the kidneys as a component of urine

Describe why protein is required in our diet and the general amount that is needed.

-proteins are the most structurally and functionally diverse molecules -proteins are synthesized from 20 different amino acids -adequate dietary intake of protein provides the amino acids required to synthesize new proteins to replace body protein structures -a specific amount of protein needed for one's diet is dependent upon age, sex, and body composition -required protein increases when fighting an infection, after injury, under conditions of stress, and during pregnancy. Infants and children need more protein to grow -8 of 20 amino acids are essential amino acids

Describe the structure and function of salivary glands and how the release of saliva is regulated.

-salivary glands produce saliva -intrinsic salivary glands are unicellular exocrine glands that continuously release small amounts of secretions independent of the presence of food. Within oral cavity -only secretions from these contain lingual lipase, an enzyme that beings the digestion -most saliva is produced from multicellular glands outside of the oral cavity called extrinsic salivary glands -3 pairs of multicellular salivary glands are located external to the oral cavity: parotid, submandibular, and sublingual glands -parotid: largest. Each is anterior and inferior to the ear. Produce about 25-30% of saliva, which is transported through the parotid duct to the oral cavity, extending from gland across the masseter, opening near the second upper molar. Infection of the paratiod glands causes mumps -submandibular: produce most of the salvia (60-70%). Inferior to the oral cavity floor and medial to mandible body. A submandibular duct opens from each gland through a papilla in the floor of the oral cavity -sublingual: Inferior to the tongue and medial and anterior to submandibular glands. Each extends multiple tiny sublingual ducts that open to the inferior surface of the oral cavity, posterior to the submandibular duct papilla. Only contribute 3-5% of total salvia -two types of secretory cells are located within the large, paired salivary glands and collectively produce components of salvia: -mucous cells: secrete mucin, forming mucous upon hydration -serous cells: secrete a watery fluid containing electrolytes and salivary amylase -parotid glands secrete serous secretions, whereas the submandibular and sublingual glands secrete both mucous and serous secretions

List the major hormones that regulate the processes of digestion.

-several hormones participate in the regulation of the process of digestion -include circulating hormones: released into the blood and local hormones that are released and influence adjacent cells -Gastrin: the stimulus for release is bolus in the stomach, especially if it contains protein, and stimulates the stomach motility and release of gastric secretions from parietal and chief cells -Cholecystokinin (CCK): the stimulus is chyme entering the duodenum- especially if chyme contains fatty acids -stomach: inhibits stomach motility and gastric secretions -gallbladder: stimulates the release of bile -pancreas: stimulates the release of enzyme-rich pancreatic juice -hepatopancreatic sphincter: causes relaxation -ileocecal valve: causes relaxation -secretin: the stimulus is chyme entering the duodenum- especially if its acidic chyme -stomach: inhibits stomach motility and gastric secretions -liver: stimulates the secretion of HCO3- -pancreas: stimulates the secretion of HCO3- from pancreatic duct -motilin: the stimulus is increased amounts later in the intestinal phase. The small intestine regulates migrating motility complex to move contents within the lumen from the small intestine into the large intestine

Describe motility and regulation within the large intestine (defection).

-several types of movements are noted in the large intestine: -peristalsis of the large intestine is usually weak and sluggish, but otherwise, it resembles that of the wall of the small intestine -haustral churning occurs after a relaxed haustrum fills with digested or fecal matter until its distension stimulates reflex contractions in the muscularis, which increase churning and move material more to the distal haustra -mass movements are powerful, peristaltic-like contractions involving the teniae coli, which propel fecal matter toward the rectum. A wave of contraction begins in the middle of the transverse colon, forcing a large amount of fecal matter into the descending colon, sigmoid colon, and rectum. Occurs two or three times a day, often right after or during a meal -two major reflexes of the nervous system are associated with motility: -gastrocolic reflex is initiated by stomach distension to cause a mass movement -defecation reflex is the involuntary component in the elimination of feces from the GI tract by the process of defecation. Filling of the rectum initiates the urge to defecate, resulting in the transmission of nerve signals from the receptors along sensory neurons to the spinal cord. In response, increased nerve signals are relayed along parasympathetic motor neurons, causing both the sigmoid colon and rectum to contract and the internal sphincter to relax -these result in voluntary defection -learned about age 3, involving the Valsalva maneuver -involves relaxation of external (voluntary) anal sphincter

Explain motility within the small intestine and how it is regulated.

-smooth muscle activity within the small intestine wall has three primary functions: (a) mixing chyme with accessory gland secretions, (b) moving the chyme continually against the brush border, and © propelling the contents through the small intestine toward the large intestine -at first, segmentation mixes chyme with secretions from the accessory digestive organs through a back-and-forth motion and is more prominent at the beginning of the small intestine, early in the intesintal phase -peristalsis then propels material within the GI lumen by alternating contraction of the circular and longitudinal muscle layers in small regions. The rhythm of muscle contractions is more frequent in the duodenum than ileum so net movement is towards the large intestine . This is late in the intesintal phase and is initiated by motilin released from the duodenum in enteroendocrine areas, initiating these activities. -the small intestine is the primary GI portion for the (a) chemical digestion, and (b) absorption of these smaller, simpler molecules. So, for these functions to be optimal, small intestine motility is highly regulated. This occurs during the intestinal phase and can be broken into two phases: -early intestinal phase and segmentation: segmentation is more present in the early intestinal phase so that chyme is thoroughly mixed with accessory digestive organ secretions and intestinal juices released from the small intestine -muscular contractions are initiated by pacemaker cells located between smooth muscle layers of the muscularis within the small intestine wall -electrical signals spread through muscularis cells via gap junctions to allow contracting, establishing a basic rhythm of muscle contraction to cause segmentation -this allows contraction to occur more in the proximal portion of the small intestine, so there is a slow net movement of chyme to the ileum and allowing time for digestion and absorption -the force of the contractions can be altered by short reflexes involving the enteric nervous system and long reflexes involving the ANS. The frequency is unchanged -late intestinal phase and peristalsis: preistalis is more prevalent late in the intestinal phase after most substances have been digested and absorbed -the function of peristalsis is to move the remaining undigested material, sloughed-off epithelial cells, and bacteria toward the ileum, initiated by motilin released from the duodenum in progressively greater amounts late in the intestinal phase. -these successive waves of contraction are called migrating motility complex, requiring about 2 hours from duodenum to ileum, repeating until all contents are moved to the large intestine -also regulated by the enteric nervous system and long reflexes involving the ANS -gastrolileal reflex: the ileum contracts -the ileocecal sphincter relaxes (CCK helps cause this) and cecum relaxes -moves contents from ielum to cecum in response to food in stomach -ileocecal valve contract to prevent backflow

Explain the two general functional activities of the stomach.

-smooth muscle in the stomach wall has two primary functions: -mixing the bolus with gastric juices to form chyme -emptying chyme from the stomach into the small intestine -gastric mixing is a form of mechanical digestion that changes the semi-digested bolus into chyme -chyme has the consistency of a pastelike soup -contractions of the stomach's thick muscularis layer churn and mixes the bolus with the gastric secretions, leading to a reduction in the size of the swallowed particles -gastric emptying is the movement of acidic chyme from the stomach through the pyloric sphincter into the duodenum -this movement is facilitated by the progressive thickening of the muscularis layer in the pyloric region -as a wave of peristaltic muscle contraction moves through the pylorus toward the pyloric sphincter, a pressure gradient is established that drives chyme toward the duodenum -the peristaltic wave establishes a greater pressure on the contents in the pylorus than the pressure exerted by the pyloric sphincter to remain closed and prevent movement -so, a few mm of cyme are emptied into the duodenum -after the peristaltic wave has moved past the pyloric sphincter, the pressure of the sphincter is one greater than the pressure on the contents, and the pyloric sphincter closes -as this sphincter closes, stomach contents are squeezed back toward the stomach body -this reverse flow is called retropulsion -results in the prevention of further chyme moving into the small intestine but also contributes to additional mixing of stomach contents

Identify the categories that are dietary sources of carbohydrates, and give examples of each category.

-sugars: include both the monosaccharides glucose, fructose, and galactose and the disaccharides sucrose (table sugar, maple syrup, fruits), lactose (milk sugar), and maltose (cereals). Other sugars (or sweeteners) include dextrose, brown sugar, honey, malt syrup, corn syrup, corn sweetener, high fructose corn syrup, invert sugar, molasses, raw sugar, turbinado sugar, and trehalose -starch: polysaccharide polymer of glucose molecules found within tubers, grains, beans, and peas. Bread and pasta are also primarily composed of starch. Refined starches are sometimes added as thickness and stabilizers. Cornstarch is a refined starch -fiber: includes polysaccharides (cellulose) of both plants and animals that cannot be chemically digested and absorbed by the GI tract. Sources include vegetables, lentils, peas, beans, whole grains, oatmeal, berries, and nuts -sugars and starch are usually converted to glucose -glucose is not considered an essential nutrient because it can be synthesized within hepatocytes from other monosaccharides and noncarbohydrate molecules by glucogenesis -fiber adds bulk, stimulating peristalsis of the large intestine -some types of fiber decrease low-density lipoprotein (LDL) cholesterol levels

Explain the types of secretory cells of the gastric epithelium.

-surface mucous cells: line the stomach lumen and extend to the gastric pits at the very top -continuously secrete alkaline mucin onto the gastric surface -mucin becomes hydrated, producing a 1-3mm mucus layer that coats the epithelial lining that helps protect the simple columnar cells -mucous neck cells: located immediately deep to the base of the gastric pit and are interspersed among the parietal cells -release less alkaline mucin that differs structurally and functionally from the alkaline mucin -this fluid is not HCl -has lubricating properties to protect the stomach lining -chief cells: most numerous secretory cells within the gastric glands -produce and secrete packets of zymogen granules, containing pepsinogen -pepsinogen: inactive precursor of the proteolytic enzyme pepsin that breaks down chains of proteins -pepsin must be produced in this inactive form to prevent the destruction of chief cell proteins -pepsinogen is activated into pepsin following its release into the stomach, activated by the HCl and active pepsin molecules present within the stomach -pepsin chemically digests denatured proteins in the stomach into smaller peptide fragments -also produce the enzyme gastric lipase: one of the acidic lipases that have a limited role in fat digestion -parietal cells: responsible for the addition of two substances into the lumen of the stomach: -intrinsic factor: the production and release of intrinsic factors (a glycoprotein) is the only essential function performed by the stomach. Required for absorption of vitamin B12 in the ileum -hydrochloric acid (HCL): the parietal cell forms H+ and releases both H+ and Cl- into the stomach lumen. HCl causes the stomach's low pH (1.5-2.5) and activates pepsinogen. This facilitates the digestive processes of the stomach, including food breakdown, protein denaturation, pepsin activation, and enhanced enzymatic activity. The low pH of the stomach also protects from infections -the first four make gastric juice; G-cells secretes gastrin into the blood -G-cells: a type of enteroendocrine cell that is hormone-producing in the gastric glands of the stomach -secrete the hormone gastrin into the blood, and it travles to higher brain centers that stimulate stomach motility and secretions -other enteroendocrine cells produce other types of hormones, like somatostatin that modulate the function of nearby enteroendocrine and exocrine cells

Discuss the structure and development of the teeth.

-teeth are collectively known as dentition. -a tooth has an exposed crown, a constricted neck, and one or more roots that anchor it to the jaw -these fit tightly into dental alveoli, sockets within alveolar processes -the roots, the dental alveoli, and the periodontal membranes that bind the roots to the alveolar process make up a gomphosis joint -the roots are made of dense regular connective tissue -2 sets of teeth erupt and develop in a normal lifetime: -infants have 20 deciduous teeth that erupt between 6-30 months of age -these are lost and replaced by 32 permanent teeth, adding more mashing and chewing teeth -more anteriorly placed permanent teeth tend to appear first, followed by posteriorly placed teeth -the last teeth to erupt are the third molars (wisdom teeth) in the late teens or early 20s. The mouth often does not have enough room for these molars, and they emerge only partially or grow at an angle and become impacted. -the most anteriorly placed teeth are incisors that have a single root and are designed for slicing or cutting into food -immediately posterior are the canines, which have a singular pointed tip for puncturing food -premolars are located posterolateral to the canines and anterior to the molars' that crush and grind ingested materials; may have one or two roots -molars are the thickest and most posteriorly placed teeth and are adapted for grinding and crushing food

Explain the distinguishing histologic features of the large intestine.

-teniae coli are thin, distinct, longitudinal bundles of smooth muscle -act like an elastic waistband- they help bunch up the large intestine into many sacs, called haustra -hanging off the external surface of the haustra are lobules of fat called omenta appendages that act as a cushion and protection mechanism -the mucosa of the large intestine is lined by simple columnar epithelium with numerous goblet cells -large intestine mucosa lacks intestinal villi with epithelial cells and numerous intestinal glands that extend inward toward the muscularis mucosae -has goblet cells secreting mucin to reduce friction -has to absorb small amounts of water and electrolytes, so the epithelium is not stratified -regular submucosa -covered on the front with visceral peritoneal -they secrete mucin into the lumen to lubricate the undigested material and facilitate its passage through the large intestine -many lymphoid nodules and immune cells occupy the lamina propria -the muscularis of the cecum and colon has two layers of smooth muscle, but the outer longitudinal layer is discontinuous and does not completely surround the colon and cecum -instead, these longitudinal smooth muscle fibers form the teniae coli

List and describe the four tunics (layers) that make up the gastrointestinal wall.

-the GI tract is made up of hollow tubes with 4 concentric layers called tunics -mucosa is the inner-lining mucous membrane -the epithelium of the mucosa is in contact with the contents in the lumen. It is a simple columnar epithelium for most of the GI tract, which allows for secretion and absorption. The portions of the GI tracts that must withstand abrasion (like the esophagus) are lines by nonkeratinized, stratified squamous epithelium. -the underlying lamina propria is made of areolar connective tissue containing small blood, lymph vessels, and nerves. Absorption occurs when substances are moved through the simple columnar epithelial cells that line the GI tract wall and are absorbed into the blood or lymphatic capillaries here. -the muscularis mucosae is smooth muscle deep to the lamina propria. Contractions of this smooth muscle layer cause slight movements in the mucosa to gently "shake things up", which (a) facilitates the release of secretions from the mucosa into the lumen and (b) increases the contact of materials in the lumen with the epithelial layer of the mucosa for more efficient absorption. -submucosa: -composed of areolar and dense irregular connective tissue, the amounts of both depending on the area of the GI tract. Many blood vessels, lymph vessels, nerves, and glands are within the submucosa. The submucosal nerve plexus innervates both the smooth muscle and the glands of the mucosa and submucosa -the areolar connective tissue of both the lamina propria of the mucosa and the submucosa house mucosa-associated lymphoid tissue (MALT) that prevents ingested microbes from crossing GI tract wall. In the distal small intestine, larger aggregates of lymphoid nodules in the submucosa are called Peyer patches. -muscularis: -composed of smooth muscle tissue. -smooth muscle cells arranged in an inner circular layer, which contains muscle cells orientated circumferentially within the GI tract wall that constrict the tube lumen, and an outer longitudinal layer, which is composed of muscle cells orientated lengthwise within the GI tract wall that shortens the tube. -located between these two layers of smooth muscle are axons and ganglia, which are the myenteric nerve plexus that control the contractions of the muscularis -the collective constrictions of these smooth muscle layers are associated with two primary types of motility: mixing and propulsion -mixing is a "backward-and-forward" motion that blends secretions with ingested materials but does not result in directional movement of the lumen contents. Mixing includes mixing waves (by the stomach) and segmentation (by the small intestine) -propulsion is the directional movement of materials through the GI tract, occurring by the muscularis of the GI tract by peristalsis. Peristalsis is the sequential contraction of the muscularis within the GI tract wall that moves like a wave within different regions of the GI tract. -these actions are controlled by the ENS and increased by parasympathetic innervation -the inner circular muscle layer is generally thickened at several locations along the GI tract to form a sphincter. Typically positioned between regions of the GI tract. Rings of smooth muscle relax (open) and contract (close) to (a) control the movement of materials into the next section of the GI tract and (b) prevent its backflow -adventitia or serosa: -an adventitia is composed of areolar connective tissue with dispersed elastic and collagen fibers and is found outside of the peritoneal cavity; the diaphragm is the divider -a serosa is the adventitia plus a complete outer covering of a serous membrane called the visceral peritoneum. Within peritoneal cavity.

Explain how both blood and bile flow through the liver.

-the cells of the liver receive blood from two sources: -hepatic artery is a branch of the celiac trunk that extends off the descending aorta and transported oxygenated blood to the liver -hepatic portal vein is part of the hepatic portal system that transports deoxygenated and nutrient-rich blood from the capillary beds of the GI tract, spleen, and pancreas toward hepatic lobules -blood then drains into the central vein of the lobule -central veins collect the blood from each lobule and merge throughout the liver to form left and right hepatic veins that empty into the inferior vena cava -as blood is transported through hepatic sinusoids: nutrients are absorbed and enter hepatocytes, oxygen is delivered to hepatocytes for aerobic cellular respiration, and stellate cells engage in phagocytosis of potentially harmful substances -bile is a yellowish-green, alkaline fluid containing mostly water, bicarbonate ions, bile salts, bile pigments, cholesterol, lecithin, and mucin. Hepatocytes produce about 0.5-1 L per day -bile is released from hepatocytes into bile canaliculi -these small channels transport bile to the bile ducts of portal triads -bile within the bile ductules flow into progressively larger bile ducts until reaching either the left or right hepatic duct -the ducts of the biliary apparatus transport bile to the duodenum -biles functions: neutralizing acidic chyme within the small intestine through bicarbonate ions, emulsification of lipids by bile salts and lecithin, and elimination of bilirubin, a waste product of erythrocyte destruction -bile does not contain digestive enzymes for the chemical breakdown of nutrients -instead, a component of bile are dividing the larger aggregates of lipid into smaller aggregates of lipid by mechanical digestion, allowing for more effective chemical digestion by pancreatic lipase

Describe the general function of the enteric and autonomic nervous systems in regulating the digestive system.

-the enteric nervous system (ENS) is both sensory and motor neurons within submuscoal plexus and myentertic plexus -innervates smooth muscle and glands of the GI tract and coordinates the reflexes for mixing and the propulsion of materials through the GI tract. -the autonomic nervous system (ANS) innervates the GI tract wall through both sympathetic and sympathetic divisions. -parasympathetic innervation promotes GI tract activity: it stimulates GI motility and release of secretions and relaxes GI sphincters -sympathetic innervation opposes GI tract activity: inhibits GI tract motility and release of secretions, contacts GI sphincters, and vasoconstrictors blood vessels within the GI tract wall.

Describe where the following nutrient molecules enter the metabolic pathway of cellular respiration: glucose, the breakdown products of triglycerides, and amino acids.

-the first step of cellular respiration is glycolysis, occurring in the cytosol of the cell without oxygen. Glucose is oxidized to form two pyruvate molecules. Two ATP molecules are produced in substrate-level phosphorylation, and hydrogen is transferred to two NAD+ molecules to form NADH. -the other stages include the intermediate stage, the citric acid cycle, and the electron transport system -triglycerides are made of glycerol and fatty acids that can enter the cellular respiration pathway at certain stages and release their chemical energy to make ATP. -glycerol specifically enters during glycolysis where it is converted to glucose through gluconeogenesis in the liver -fatty acids are removed two at a time to form acetyl CoA through beta-oxidation and are used in the citric acid cycle -amino acids that compose a protein may be used at various stages to cellular respiration. They contain nitrogen in an amine group. They can enter at: -into the pathway of glycolysis -at the intermediate stage -at specific points in the citric acid cycle

Describe the chemical digestion of proteins that occurs in the small intestine.

-the high pH of the small intestine inhibits further action of pepsin on protein shortly following the entry of chyme into the small intestine -three of the enzymes that continue protein digestion are synthesized and released from the pancreas into the small intestine in inactive forms: -trypsinogen, chymotrypsinogen, and procarboxypeptidase -once they reach the small intestine: -trypsinogen is activated by endopeptidase, an enzyme synthesized by the small intestine and released into its lumen, activating trypsinogen to trypsin -trypsin activated additional trypsin, as well as chymotrypsinogen to chymotrypsin and procarboxypeptidase into carboxypeptidase -trypsin and chymotrypsin break the bonds between specific amino acids to produce smaller strands of amino acids called peptides -carboxypeptidase breaks the bond between an amino acid on the carboxyl end and the remaining protein. Dipeptides and free amino acids are the breakdown products of carboxypeptidase -the brush border enzyme dipeptidase breaks the final peptide bond between the two amino acids of dipeptides to release two amino acids and the brush border enzyme aminopeptidase generates free amino acids from the amino ends of peptides -amino acids are then absorbed across the small intestine epithelial lining and enter the blood -can be used as building blocks of new proteins by cells, or it excess amino acids are absorbed, they are either (a) converted into glucose or (b) deaminated and used a fuel for cellular respiration

Discuss the regulation of the accessory digestive glands associated with the small intestine.

-the increase of vagal stimulation in the cephalic phase and gastric phase of the stomach activates the pancreas to release pancreatic juice -in the intestinal phase, CCK and secretin are released. CCK is released from the small intestine in response to fatty chyme, and functions to: -stimulate smooth muscle within the gallbladder wall to strongly contract, causing the release of concentrated bile -stimulating the pancreas to release enzyme-rich pancreatic juice -relaxing the smooth muscle within the hepatopancreatic ampulla, allowing entry of bile and pancreatic juice into the small intestine -secretin is released from the small intestine in response to an increase in chyme activity. Secretin causes: -the release of an alkaline solution containing bicarbonate from the liver and ducts of the pancreas that helps neutralize the acidic chyme -inhibits gastrin secretions and motility

Distinguish the action of the muscularis mucosae from that of the muscularis tunic.

-the muscularis tunic is made of smooth muscle and participates in the mixing and propulsion of food through the GI tract -the muscularis mucosae is found in the mucosa and is directly adjacent to the submucosa. It is also made of a layer of smooth muscle. Contractions of this muscle cause slight movements of the mucosa to gently "shake things up", facilitating the release of secretions from the mucosa into the lumen and increasing contact of materials in the lumen with the epithelial layer of the mucosa for more efficient absorption

Identify the six organs that make up the gastrointestinal (GI) tract.

-the oral cavity (mouth), pharynx (throat), esophagus, stomach, small intestine, large intestine, and anus

Describe the components of the upper gastrointestinal tract.

-the oral cavity, pharynx, esophagus, stomach, and duodenum -oral cavity and salivary glands: mechanical digestion begins here. -saliva secreted from salivary glands in response to food -mixed with the ingested materials to form a bolus -one component of saliva is salivary amylase which initiates the chemical digestion of starch -pharynx: bolus is moved into the pharynx during swallowing, directed toward the oropharynx and laryngopahrynx by the epiglottis -mucus secreted in salvia in the superior part of the pharynx provides lubrication to facilitate swallowing -esophagus: bolus transported from the pharynx into the stomach -mucus secretions by the esophagus lubricate the passage of the bolus -stomach: bolus is mixed with gastric secretions by smooth muscle contractions as the muscularis in the stomach wall contracts -secretions are produced and released into the stomach lumen by epithelial cells of the stomach mucosa and include acid, digestive enzymes, and mucin -chyme is formed from mixing -the duodenum is considered part of the GI tract

Discuss the anatomy of the pharynx and esophagus and their complementary activities in the process of swallowing.

-the pharynx and esophagus connect the oral cavity to the stomach -the pharynx is a funnel-shaped, muscular passageway with distensible lateral walls that serve as the passageway for both food and air - formed by three skeletal muscle pairs called the superior, middle, and inferior pharyngeal constrictors form the wall of the pharynx -the oropharynx and laryngopharynx are lined with nonkeratinized stratified squamous epithelium protecting against abrasion -the esophagus is a normally collapsed, tubular passageway, beginning at the level or cricoid cartilage directly anterior to vertebral bodies -passes through an opening in the diaphragm called the esophageal hiatus -the inferior end connects to the stomach -the last 1.5 cm is in the abdomen -the superior esophageal sphincter is a contracted ring of circular skeletal muscle at the inferior end of the esophagus. This is where the esophagus and pharynx meet. Closed during the inhalation of air so air does not enter the esophagus -the inferior esophageal sphincter is a contracted ring of circular smooth muscle at the inferior end of the esophagus. This is not strong enough alone to prevent materials from refluxing back into the esophagus; instead, the muscles of the diaphragm at the esophageal opening contract -a bolus of food is quickly forced from the pharynx into the esophagus by smooth and skeletal muscle movement in both

How are salivary secretions regulated?

-the salivary nuclei within the pons regulates salivation. -a basal level of salivation in response to parasympathetic innervation ensures the oral cavity remains moist -input to the salivary nuclei is received from chemoreceptors or baroreceptors in the upper GI tract, being especially sensitive to acids -if one eats spoiled food, bacterial toxins within the stomach stimulate receptors that initiate sensory nerve signals to the salivary nuclei -input is also received by the salivary glands from higher brain centers in response to thought, smell, or sight of food -stimulation of salivary nuclei results in increased nerve signals relayed along parasympathetic neurons -sympathetic stimulation, occurring in exercise or when someone is excited or anxious, results in a more viscous salvia by decreasing the water content -this is because sympathetic stimulation results in vasoconstriction, decreasing the fluid added to salvia

Describe the structure of the serous membranes associated with the GI tract.

-the serous membrane associated with the abdominopelvic cavity is the peritoneum -parietal peritoneum: lines the inner surface of the abdominal wall -visceral peritoneum: serous membrane reflecting over and covering the internal organs' surface -between these layers is a potential space called the peritoneal cavity, which contains serous fluid -the fluid is produced by both the parietal and visceral peritoneum -lubricates the abdominal wall and external organ surfaces. Allows abdominal organs to move freely and reduces friction resulting from this movement

Describe the absorption of water, electrolytes, and vitamins.

-the small intestine is the location of most water, electrolytes, and vitamin absorption from the diet -the amount of water that enters the small intestine daily is 8-9 L -small intestine functions to absorb almost all of the water that enters the small intestine -thus, the daily water content of chyme entering the large intestine is only about 2 L. -the large intestine will absorb about 1.8 L, which leaves 0.2L of water lost in feces -water is absorbed across the epithelial lining of the small and large intestines into the blood capillaries by osmosis -electrolytes enter the GI tract through ingestion and as components of accessory digestive gland secretions -small intestine absorbs almost all of the electrolytes that enter the small intestine -mostly unregulated and is dependent upon the amount of the diet -iron is unusual in that its absorption is controlled -hormone hepcidin is released from the liver in response to iron levels -it inhibits the absorption of iron -when iron levels are low, hepcidin release is decreased, which removes this inhibition, allowing for greater iron absorption -vitamins are organic molecules categorized as (a) fat-soluble or (b) water-soluble -fat-soluble vitamins (A, D, E, K) are absorbed from the small intestine lumen into epithelial cells with lipids in micelles -require lipids for their absorption- without them, they are lost through the feces -water-soluble vitamins (B and C) are absorbed through simple diffusion and active transport

Describe the steps and processes involved with swallowing.

-the voluntary phase occurs after ingestion -controlled by the cerebral cortex -ingested materials and salvia mix in the oral cavity -chewing forms a bolus that is mixed and manipulated by the tongue and then pushed superiorly against the hard palate -transverse palatine folds help direct the bolus posteriorly toward the oropharynx -the arrival of the bolus at the oropharynx initiates the swallowing reflex of the pharyngeal phase -involuntary -tactile sensory receptors around the facues are stimulated by the bolus and initiate nerve signals along sensory neurons to the swallowing center in the medulla oblongata -nerve signals are relayed to cause: -entry of the bolus into the oropharynx -elevation of the soft palate and uvula to block passage between the oropharynx and nasopharynx -elevation of the larynx by extrinsic muscles that move the larynx anteriorly and superiorly, resulting in the epiglottis covering the laryngeal inlet, preventing ingested materials from entering the trachea -nerve signals are also relayed to the respiratory center to ensure no breath is taken during swallowing -the bolus passes quickly to the esophagus in about 1 second -sequential contraction of the pharynx constrictors decrease the diameter of the pharynx, beginning at the superior end toward the inferior end. This creates a pressure difference, forcing swallowed materials from the pharynx into the esophagus -esophageal phase is also involuntary -time during which the bolus passes through the esophagus and into the stomach (about 5-8secs) -the presence of the bolus within the lumen of the esophagus stimulates sequential waves of muscular contraction that assist in propelling the bolus toward the stomach -higher pressure occurs in the superior region of the esophagus relative to the inferior region -the superior and inferior esophageal sphincters, which are normally closed, open when the bolus is swallowed, allowing it to pass through the esophagus. The inferior esophageal sphincter contracts after the passage of the bolus, helping to prevent reflux from the stomach

Explain why the proteolytic enzymes of the stomach and pancreas are synthesized in inactive forms.

-they are released from the stomach and pancreas as inactive enzymes, which must be activated -this is because the proteolytic enzymes would destroy the proteins within the cells the produce them and would destory the cells lining the main and accessory pancreatic ducts

Describe a peptic ulcer.

-this is a solitary erosion of a portion of the stomach duodenum -gastric ulcers are in the stomach and duodenal ulcers are in the duodenum -symptoms of gnawing, burning pain in epigastic region, nausea, vomiting, and bleeding -may erode and cause perforation, a medical emergency -Helicoboacter pyloria causes erosion of the gastric lining -treatment similar to that of gastric reflux

Describe a gastric bypass.

-this is a surgical treatment for obesity. -a small part of the stomach sectioned off and attached to the lower part of the small intestine -less nutrients are absorbed and there is reduced appetite -there is an altered response to hormones like insulin -can induce remission of type 2 diabetes within a few days of surgery

Explain when the postabsorptive state occurs and how nutrient levels are regulated during this time.

-this is the fasting state in the time between meals when the body relies on its stores of nutrients because no further absorption of nutrients is occurring -the challenge is to maintain homeostatic levels of many nutrients as these substances decrease in the blood -glucagon is the major regulatory hormone that is released in this state -pancreas releases glucagon in response to decreasing blood glucose levels -glucagon: -simulates liver cells to engage in the catabolism of glycogen to glucose by increasing glycogenesis; may also increase the formation of glucose from noncarbohydrate sources by stimulating glucogenesis -causes adipose connective tissue to break down triglycerides to glycerol and fatty acids by stimulating lipolysis -glucose is released from the liver, and fatty acids (and glycerol) are released from adipose connective tissues in response to the glucagon stimulation. The levels of the molecules increase in the blood

Explain when the absorptive state occurs and how nutrient levels are regulated during this time.

-this is the fed state that includes the time you are eating, digesting, and absorbing nutrients -the concentrations of glucose, triglycerides, and amino acids are increasing within the blood as they are absorbed from the GI tract. The body must maintain homeostatic values during this time -insulin is the major regulatory hormone released during the fed state -released from the pancreas occurring in response to an increase in blood glucose levels -insulin: -stimulates liver and muscle cells to form the polysaccharide glycogen from glucose by increasing glycogenesis -causes adipose connective tissue to increase the uptake of triglycerides from blood and decreases the breakdown of triglycerides by stimulating lipogenesis and inhibiting lipolysis -stimulates most cells (especially muscle cells) to increase amino acid uptake causing an accelerated rate of protein synthesis -consequently, the release of insulin results in a decrease in all energy-relating molecules in the blood, an increase in the storage of glycogen and triglycerides, and the formation of protein within body tissues

Describe vomiting.

-this is the rapid expulsion of gastric contents through the oral cavity -controlled by the vomiting cetner in the medulla oblongata -responde to head injury, motion sickness, infection, toxicity, and food iritation -closure of the nasal passages and the glottis -skeletal muscle contraction increasing introgastric pressure -gastric contents are forced into and through the esophagus -danger of aspiration

Describe the accessory digestive organs associated with the small intestine and the contributions of each to digestive processes.

-three accessory organs are associated with the small intestine: the liver, gallbladder, and pancreas -ducts that deliver secretions from the accessory organs to the duodenum include the: -biliary apparatus from the liver and gallbladder -pancreatic duct from the pancreas -right and left hepatic ducts merge to form a common hepatic duct -common hepatic duct and cystic ducts merge to form a common bile duct -main pancreatic duct merges with the common bile duct at the hetatopancreatic ampulla which extends into the deodenum -bile and pancreatic juices enter the duodenum at the major duodenal papilla -pancreatic ducts: main pancreatic duct and accessory pancreatic duct -main pancreatic duct transports the majority of pancreatic juice -joins with the common bile duct to form the hepatopancreatic ampulla -accessory pancreatic duct is a smaller duct whereby limited amounts of pancreatic juice may enter the duodenum -this duct penetrates the duodenal wall, creating the minor duodenal papilla -hepatopancreatic ampulla: a swelling either adjacent to or within the posterior duodenal wall, penetrating through the duodenal wall, forming the major duodenal papilla -this receives bile from the common bile duct and pancreatic juice from the main pancreatic duct -the release of these secretions is regulated by the hepatopancreatic sphincter within the ampulla -this is normally closed and relaxation is stimulated by CCK -LIVER: the main function in digestion is the production of bile -major lobes: right and left -right is separated from left by the falcirofrm ligament, a peritoneal fold that secures the liver to the internal surface of the anterior abdominal wall -in the inferior free edge of the falciform ligament lies the round ligament of the liver, representing the remanent of the umbilical vein -within the right lobes are the caudate and quadrate lobes -on the inferior surface lie the gallbladder, inferior vena cava, and superior vena cava -the liver connective tissue branches throughout the organ and forms septa that partition the liver into thousands of hepatic lobules, which are the structural and functional units of the liver -within the lobules are liver cells called hepatocytes that produce bile -at the periphery of each lobule are several portal triads, composed of a bile ductule, and microscopic branches of the hepatic portal vein and hepatic artery -at the center of each lobule is a central vein that drains the blood flow from the lobule -central veins merge throughout the liver to form the left and right hepatic veins that empty into the inferior vena cava -hepatocytes are bordered by hepatic sinusoids, which transport blood -GALLBLADDER: stores, concentrates, and releases bile into the duodenum that the liver produces -bile breaks down lipids -three tunics: -an inner mucosa -a middle muscularis -and an external serosa -the mucosa is thrown into folds that permit distension of the wall as the gallbladder fills with bile -concentrated bile is transported from the gallbladder through the cystic duct and then the common bile duct through the hepatopancreatic ampulla into the duodenum -PANCREAS: has both endocrine and exocrine functions -controls blood glucose levels: as blood glusoce goes up, absorption increases -endocrine cells produce and secrete hormones like insulin and glucagon -exocrine cells produce pancreatic juice -isoltes are cicirulcar areas releasing hormones (endocrine function) -contains modified simple cuboidal epithelia cells called acinar cells arranged in sacklike acini -these cells are organized into large clusters called lobules -acinar cells release and produce pancreatic juices and bicarbonate -small ducts lead from each acinus to larger ducts that empty into the main or accessory pancreatic duct, which leads to the duodenum -the acinar lining the pancreatic ducts secrete alkaline fluid containing the bicarbonate ion that functions in neutralizing acidic chyme entering the small intestine -the secretions of acinar cells and cells lining the pancreatic ducts form pancreatic juice

Identify the types and dietary sources of triglycerides, and describe their function.

-triglycerides is one of the two types of lipids (the other is cholesterol) -triglycerides (or fats) are composed of glycerol and fatty acids. Fatty acids are put into three categories, depending on their degree of saturation: -saturated fatty acids have no double bonds (each C in the fatty acid chain is totally saturated with H atoms). Generally solid at room temperature, and dietary sources include fat in meat, milk, cheese, coconut oil, and palm oil -unsaturated fatty acids have one double bond. Typically liquid at room temperature. Dietary sources include nut oils and certain vegetable oils (olive oil, canola oil). -polyunsaturated fatty acids have two or more double bonds. Liquid at room temperature, and dietary sources include some vegetable oils (soybean oil, corn oil, safflower oil). -triglycerides are a primary nutrient supplying energy to cells -oxidation of triglyceride molecules yields about 9 kilocalories of energy per gram of fat- more than twice that of glucose. -fats are necessary for the absorption of fat-soluble vitamins

Distinguish between water-soluble and fat-soluble vitamins.

-vitamins are organic molecules required for normal metabolism, yet they are present in only small amounts in food and drink -categorized into water-soluble or fat-soluble and essential or nonessential -water-soluble vitamins dissolve in water -include B-complex vitamin and vitamin C -these vitamins, except vitamin B12, are easily absorbed into the blood from the digestive tract -if dietary intake exceeds the need, they are excreted in the urine -fat-soluble vitamins dissolve in fat -include vitamins A, D, E, and K -absorbed from the gastrointestinal tract within the lipid micelles and ultimately enter the lymphatic capillaries -if an excess is consumed, it is stored within body fat and may reach toxic levels (hypervitaminosis)-vitamins are organic molecules required for normal metabolism, yet they are present in only small amounts in food and drink

Name the three major regions of the large intestine and four segments of the colon of the large intestine

-wide tube, shorter than the small intestine, in the abdominal and pelvic cavities -spans from the ileocecal junction to termination at the anus -the three major regions of the large intestine are the: -cecum: a blind sac -the first portion of the large intestine located in the right abdominal quadrant -extends inferiorly from the ileocecal valve -cyme enters from the ileum -projecting inferiorly from the posteromedial region is the vermiform appendix, which is a thin, finger-like sac lined by lymphocyte-filled lymphoid nodules -both the cecum and vermiform appendix are intraperitoneal organs -the appendix may serve as a reservoir of bacteria that are beneficial to the function of the colon -colon: begins and forms an inverted U-shaped arch -partitioned into four segments: -the ascending colon originates at the ileocecal valve and extends superiorly from the superior edge of the cecum along the right lateral border of the abdominal cavity. It is retroperitoneal, since its posterior wall adheres directly to the posterior abdominal wall, and only its anterior surface is covered with peritoneum. As it approaches the inferior surface of the liver, it makes a 90-degree turn toward the left side of the body, called the right colic flexure -the transverse colon originates at the right colic flexure and curves slightly anteriorly as it projects horizontally left across the anterior region of the abdominal cavity. It is intraperitoneal. As it approaches the spleen in the left upper quadrant of the abdomen, it makes a 90-degree turn inferiorly and posteriorly, called the left colic flexure -the descending colon is retroperitoneal and originates at the left colic flexure. It is at the left side of the abdominal cavity and is slightly posterior. It descends vertically to the sigmoid colon -the sigmoid colon originates at the sigmoid flexure and turns inferomedially into the pelvic cavity. It is intraperitoneal and terminates at the rectum. A type of mesentery, called mesocolon, attaches each section of the colon to the posterior abdominal wall, for which each region of the mesocolon is specifically named. -rectum: a retroperitoneal structure extending from the sigmoid colon -the muscular tube that readily expands to store accumulated fecal material prior to defecation -three thick transverse folds of the rectum, called rectal valves, ensure that fecal material is retained in the passing of gas -the anal canal makes up the terminal few cms of the large intestine -lined by a stratified squamous epithelium and it passes through an opening in the levator ani muscles (innervated by the parasympathetic system) of the pelvic floor and terminates at the anus -the internal lining of the anal canal contains thin longitudinal ridges, called anal columns, between which are small depressions called anal sinuses -as fecal matter passes through, pressure on the anal sinuses causes their cells to release mucin to form mucus, which lubricates the anal canal during defecation -at the base of the anal canal are the involuntary smooth muscle internal anal sphincter and voluntary skeletal muscle external anal sphincter, which close off the opening to the anal canal

Describe the histology of the esophagus.

the mucosa of the esophagus is lined with nonkeratinized stratified squamous epithelium. -protects this region from abrasion as food is swallowed -esophageal submucosa is thick and composed of abundant elastic fibers -this permits distension during swallowing -also houses numerous mucous glands that provide thick, lubricated mucus for the epithelium -the ducts of these glands project through the mucosa and open into the lumen -the muscularis of the esophagus is composed of both smooth and skeletal muscle -the two layers of muscle in the superior one-third of the muscularis are skeletal to ensure that swallowed material moved rapidly out of the pharynx and into the esophagus before the next respiratory cycle begins -skeletal and smooth muscle intermingles in the middle one-third of the muscularis, and only smooth muscle is found in the wall of the inferior one-third. This transition marks the beginning of a continuous smooth muscle muscularis that extends throughout the stomach and large intestines to the anus -the outmost layer of the esophagus is an adventitia