BI 233- Lecture exam 2 digestive system and metabolism

digestion of fat soluble vitamins

(A, D, E, and K) need to be dissolved into fat before they can be absorbed into the body. When bile acids break down the fat the vitamins are dissolved, and they move with the fat through the intestinal wall into the body then end up in the liver in the body fat where they are stored until needed. Don't require daily consumptions. Fat soluble vitamins can be stored and build up in your system.

regulation of small intestine

-Chyme stimulates duodenal enteroendocrine cells to release secretin (stimulate release of bicarbonate and water from pancreas- helps neutralize pH of chyme) and CCK (in response to presence of fats and proteins- cause contraction of gallbladder to release bile and secretions of pancreatic enzymes). They stimulate pancreas and gallbladder as well as suppress gastric secretion (next phase of digestion is beginning). Bile salts and pancreatic enzymes helps with fat digestion. -Pyloric sphincter contracts tightly to limit chyme entering duodenum. Controls amount of chyme entering small intestine (1-2 teaspoons per contraction). -Enteroendocrine cells secrete GIP (stimulate insulin to secreted from pancreas; liver cells have receptors for insulin which triggers cells to take in and store glucose as glycogen).

regulation of small intestine (release of pancreatic juice and bile)

1. Ach: secreted from vagus and enteric nerves. Stimulates acini to secrete their enzymes during the cephalic phase of gastric control even before food is swallowed. (neural control) 2. CCK: secreted by mucosa of duodenum in response to arrival of fats in small intestine. Strongly stimulates gallbladder- induces contractions of the gallbladder and relaxation of the hepatopancreatic sphincter causing discharge of bile into the duodenum. (Hormonal control) 3. Secretin: released from the duodenum in response to acidic chyme arriving from the stomach. Stimulates ducts of both liver and pancreas to secrete more sodium bicarbonate. (Hormonal control)

steps of deglutition

1. Tongue compresses food against palate to form a bolus. 2. Bolus passes into pharynx. Misdirection of bolus is prevented by tongue blocking oral cavity, soft palate blocking nasal cavity, and epiglottis blocking larynx. 3. Upper esophageal sphincter constricts, and bolus passes downward. 4. Peristalsis drives bolus down esophagus. Esophagus constricts above bolus and dilates and shortens below it. 5. Lower esophageal sphincter relaxes to admit bolus to stomach.

digestive tract (alimentary canal)

1. mouth, pharynx, esophagus, stomach, small intestine, and large intestine. GI tract is the stomach and intestines. GI tract is a tube approximately 30 ft long extends from mouth to anus. Mouth is for biting, chewing, and swallowing. Pharynx and esophagus is a transport mechanism. Stomach allows for mechanical disruption and absorption of water and alcohol. Small intestine continues mechanical and chemical digestion as well as absorption. Large intestine aids in absorption of electrolytes and vitamins B & K.

pathway of bile secretion

1. parasympathetic impulses along vagus nerves stimulate bile production by liver. 2. Fatty acids and amino acids in chyme entering duodenum stimulate secretion of CCK into the blood. Acidic chyme entering duodenum stimulates secretion of secretin into the blood. 3. CCK causes contraction of gallbladder. 4. Secretin enhances flow of bile rich of bicarbonate ions from liver. Bile canniculi (narrow channels where liver secretes bile) -> bile ductules of triads-> right/left hepatic ducts -> common hepatic duct -> bile duct (cystic duct from gallbladder joins common hepatic duct) -> lesser omentum towards duodenum -> bile duct joins duct of pancreas and forms hepatic pancreatic ampulla terminates in fold of tissue of major duodenal papilla on duodenal wall (contains sphincter of Oddi - regulates passage of bile and pancreatic juices into duodenum).

absorptive cell of small intestine

AKA enterocytes predominant epithelial cell type lining lumen of small intestine and colon. Specialized for absorption of nutrients across plasma membrane. Nutrients diffuse into connective tissue space and into capillaries/lacteals. Surface area increased due to microvilli (brush border enzyme contribute to digestion breakdown). Golgi apparatus so nutrients absorbed and can be processed for transport. Life span is minimal- several days

What is the role of hepatocytes after a meal?

After a meal, hepatocytes absorb from the blood- glucose, amino acids, iron, vitamins, and other nutrients for metabolism or storage. Remives and degrades hormones, toxins, bile pigments, and drugs. Secretes into the blood albumin, lipoproteins, clotting factors, angiotensinogen, and other products. Between meals, hepatocytes break down stored glycogen and release glucose into the blood. Liver can store when it needs to, use, or deliver to other locations. LFT's used to see if chemicals released by the liver cells and see if there is any disease/damage. Common causes include NASAID, cholesterol lowering medications, antibiotics, alcohol, diabetes, infection, gallstones, tumors of the liver, and excessive use of certain herbal supplements.

secreting cells in stomach

Cardia & Pylorus cells= mucus secreting Pyloric antrum cells= mucus & gastrin Stomach fundus & body cells= larger stomach secretions (mucous neck cells, parietal cells, chief cells, and enteroendocrine cells). Typically, paracrine actions of these secretions.

neural control of stomach

Chemical messengers: gastric and pyloric glands have various kinds of enteroendocrine cells that produce as many as 20 chemical messengers. Some are hormones that enter blood and stimulate distant cells. Others are paracrine secretions that stimulate neighboring cells. Several are peptides produced in both the digestive tract and the CNS (gut-brain peptides- substance P, secretin, gastric inhibitory peptide, and cholecystokinin/CCK). Substance P: encourage rapid contraction of smooth muscles of digestive tract. Released by neurons of digestive tract or vagus nerves. CCK and serotonin: enhance substance P's release. Opioids reduce release of this. Secretin: released from the duodenum. Communicate with pancreas to secrete water and bicarbonate helping with buffering of chyme from the stomach. CCK: released by duodenum. Inhibits gastric emptying. Communicates with pancreas to release digestive enzymes to help further breakdown components of chyme. GIP (glucose dependent insulin tropic peptide): decreases stomach secretions and inhibits GI motility.

sublingual gland

Deep to the tongue located in the floor of the mouth. Has multiple ducts that empty posterior to the papilla of the submandibular duct. Same secretions but more mucous. Triggers by same.

protein digestion begin

HCl transforms pepsinogen into pepsin that breaks peptide bonds between certain amino acids. Triggered by gastrin and secreted by parietal cells.

how is pepsinogen activated

Hydrochloric acid acts by removing amino acids which forms pepsin which is an active enzyme that digests protein. Some pepsin is formed and will convert some pepsinogen into more pepsin. Both protein and lipid digestion will be completed in the small intestine.

zymogen

Inactive enzyme that when encounters hydrochloric acid it will remove some of the amino acids and convert to its active state.

overview of stomach

Ingested food buffers stomach acid. Rise in pH stimulates G cells G cells secrete gastrin Gastrin stimulates chief cells- secretes pepsinogen and parietal cells to secrete hydrochloric acid. Hydrochloric acid converts pepsinogen to pepsin. Pepsin digests dietary proteins. Protein buffers stomach acid (positive feedback).

liver and pancreas functions

Liver- secretion of bile. Pancreas- endocrine (insulin) and exocrine (pancreatic juices aid with digestion). Main duct joins common bile duct from liver. Sphincter of Odii controls content from bile in pancreas into small intestine. Opens below the pyloric sphincter. Pancreatic acini- clusters of cells part of exocrine component.

gallbladder

Made up of simple columnar epithelium. No submucosal layers. Three layers of smooth muscle- serosa, visceral peritoneum. Contraction squeezes bile out into the cystic duct through common bile duct. CCK will relax sphincter of Odii which allows bile to flow into the duodenum. Secretin stimulates liver to replace what is being used for digestion. Function is to store and concentrate bile by a factor of 20 by absorbing water and electrolytes. Hepatocytes continually secrete bile, inc production and secretion when portal blood contains more bile acid which happens with digestion absorption in small intestines. Between meals, bile flows into gallbladder for storage. Sphincter of Oddi closes entrance to duodenum. Gallstones occur if bile contains insufficient bile salts or excess cholesterol. Cholesterol may crystallize to form gallstones- can grow in size and number. Can affect bile flow and potentially result in obstruction from gallbladder to duodenum.

motor neurons and control in GI tract

Motor neurons supply longitudinal and circular smooth muscle layers of muscularis. Controls GI tract motility, frequency, and stretch of muscularis. Motor neurons of submucosa supply secretory cells of epithelium controlling secretions of organs of GI tract. Interneurons connect myenteric and submucosal plexuses. Sensory neurons function as chemoreceptors activated by the presence of certain chemicals of food in lumen. Also has stretch receptors activated when food distends wall of GI organ. Short reflexes entirely by enteric nervous system. Stimulated within GI tract. Controlled by segmentation and peristalsis (smooth muscle contraction). Segmentation is another way of helping slosh the nutrients or digested particles with enzymes. Does have pacemaker cells to keep rhythm of muscle contractions. Long reflexes of CNS and extrinsic autonomic nerves send a signal to CNS via afferent visceral fibers. Motor fibers enter small intestine wall and stimuli from inside or outside of GI tract.

List the enzymes from the pancreas and small intestines which break down nucleic acids.

Nucleic acids broken down by pancreatic ribonuclease and deoxyribonuclease (from pancreas in the small intestine and brush border enzymes in the small intestine) into pentose sugar, N-containing bases, and phosphate ions.

enzyme needed to break down proteins in stomach

Pepsin

List the enzyme from the stomach, pancreas, & small intestines breaks down proteins?

Proteins are broken down by pepsin (stomach in the presence of HCl) into large polypeptides which are broken down by proteases (pancreas) into small polypeptides and small peptides. Aminopeptidase (brush border enzyme in small intestine) breaks those down into amino acids. Simplest form that body can absorb and use.

List the flow of nutrients absorbed from the small intestine to the liver. How does the blood supply get from the liver to the heart?

Sinusoids receive oxygenated blood from hepatic artery and nutrients/deoxygenated blood from hepatic portal vein (nutrient rich blood from stomach, spleen, and intestines). Oxygen and nutrients taken up by hepatocytes. Brings venous blood from GI organs and spleen into liver. Sinusoids go to central vein -> hepatic veins- > inferior vena cava -> right atrium of the heart Liver is often for a site of metastasis for cancers originating in the GI tract.

small intestine divisions

Small intestine has a large surface area for majority of absorption. 3 parts- duodenum (first section approx. 10 inches begins at pyloric valve, receives major and minor pancreatic ducts and arches around head of pancreas ends at sharp), jejunum (3-6 feet long where most of digestion and nutrient absorption occurs), and ileum (6-12 feet in length, absorbs mainly the vitamin B12, water soluble vitamins, bile salts, and nutrients missed by the jejunum). Smaller diameter than large intestine. Almost all chemical digestion and nutrient absorption occurs. It is a coiled mass filling most of abdominal cavity inferior to stomach and liver.

Describe how the contents from the gallbladder and pancreas enter the duodenum. What is the name of the sphincter that control the movement into the duodenum.

Sphincter of Oddi. Pancreatic duct runs lengthwise through the middle of the gland. Joins the bile duct at the hepatopancreatic ampulla (store contents from gallbladder and pancreas). Hepatopancreatic sphincter controls release of both bile and pancreatic juice into the duodenum. Chyme (acid, proteins, and fats) will trigger the sphincter. Cephalic phase also triggers this sphincter (secretions with bicarbonate with help neutralize the chyme). Accessory pancreatic duct is the smaller duct that branches from the main pancreatic duct that opens independently of the duodenum. It bypasses the sphincter and allows pancreatic juice to be released into the duodenum even when bile is not.

List what enzymes are released by the mouth and pancreas which breakdown starch & disaccharides. What are the brush border enzymes which breakdown lactose, maltose, & sucrose?

Starch and disaccharides are broken down by salivary amylase (mouth) and pancreatic amylase (pancreas) into oligosaccharides and disaccharides which is then broken down into lactose, maltose, and sucrose. Brush border enzymes in small intestine (lactase, maltase, and sucrase) break down into galactose, glucose, and fructose which can then be absorbed and used by the body.

stomach protection

Stomach is protected from harsh acid via mucus coat (thick, highly alkaline which resists acid and enzymes). Epithelial cells joined together by tight junctions which prevents gastric juices to secrete between them and digesting connective tissue of the lamina propria and beyond. Epithelial cell replacement- replace every 3-6 days which are sloughed off into chyme and replaced rapidly.

List the enzymes from the mouth, stomach, and pancreas responsible for breaking down triglycerides & lipids.

Triglycerides/lipids broken down by lingual lipase (mouth), gastric lipase (stomach), and pancreatic lipase (pancreas works in small intestines) into fatty acids.

anatomical structures of small intestine

Two layers of muscularis- longitudinal and circular. Mucosal film. Vascular network and lymphatic network (not as much lymphatic vessels in stomach because they help with absorption of fats). Most absorption occurs in small intestines. Simple columnar epithelium and microvilli which increases surface area.

peritonitis

acute inflammation of peritoneum. Caused by contamination, infectious microbes during surgery, or rupture of abdominal organs.

esophagus

collapsed muscular tube C6 and cricoid cartilage. Lower esophageal sphincter allows food to pause at this point because of this constriction. Prevents stomach contents from regurgitating into the esophagus. Protects esophageal mucosa from erosive effect of stomach acid. Esophagus and small intestine are not made for acidic environment. Can erode the esophagus or cause cancer. Upper third is made of skeletal muscle. Middle has skeletal and smooth. Lower 1/3 is smooth muscle. Some voluntary control in upper portion. Has upper and lower esophageal sphincter- prominent in circular muscle. Adventia blending with surrounding connective tissue. No peritoneum. No enzymes released and no absorption occurs. Just a passageway. Salivary amylase will continue to break down starch as the food is travelling through the esophagus. Will denature in stomach.

mesentery

connective tissue sheet that loosely suspend stomach and intestine from abdominal wall. Allow them to undergo strenuous contractions, freedom of movement, holds abdominal viscera in proper relation, pertaining to small bowl mesentery which anchors small intestines to back of abdominal wall. Blood vessel nerves branch through mesentery and supply intestines.

muscularis externa

consists of two layers of muscles near outer surface= inner circular layer (thickens to form valves or sphincters that regulate passage of material through tract) and outer longitudinal layer (responsible for motility that propels food and residue through the tract).

anatomical subdivisions

digestive tract and accessory organs

pharynx

funnel-shaped tube extending from internal nares to esophagus. Allows food to move down the esophagus and prevents it from moving into the trachea and towards the lungs.

fat digestion in stomach

gastric lipase and lingual lipase split the triglycerides in milk fat. Most effective at pH 5-6 which is what infants stomach is.

regulation of gastric function

gastric secretion is stimulated by three chemicals. Period in which swallowed food and semi-digested proteins activate gastric activity. Ingested food stretches stomach which activates short reflexes via myenteric nerve plexus and activation of long reflexes via vagus nerve and brainstem. Stimulated by increasing pH of its contents. 1. Acetylcholine (Ach)- secreted by parasympathetic nerve fibers of both reflexes. 2. Histamine- a paracrine secretion from enteroendocrine cells in gastric glands. 3. Gastrin- a hormone produced by enteroendocrine G cells in pyloric glands These stimulate parietal cells to secrete hydrochloric acid and intrinsic factor. Stimulate chief cells to secrete pepsinogen and stimulate secretion of mucus.

peptic ulcer

gastritis, inflammation of the stomach, can lead to a peptic ulcer as pepsin and hydrochloric acid erode the stomach wall. Most ulcers are caused by acid-resistant Helicobacteria pylori, that can be treated with antibiotics and pepto-bismol. Can be diagnosed via blood, stool, and stomach sample. Treatment is avoiding acidic food and drinks down. Increase in pH of stomach can affect its ability to digest proteins and fats.

Submucosal (Meissner's) Plexus

in submucosa. Controls glandular secretion of mucosa and movements of muscularis mucosae.

pancreatitis

inflammation of pancreas occurring with the mumps

rugae

intestinal folds which allows it to extend and retract.

smooth muscle of digestive tract

involuntary control. Inner circular fibers and outer longitudinal fibers. Mixes, crushes, and propels food along by peristalsis.

pylorospasm

involves the muscle fibers of the sphincter fail to relax trapping food in the stomach. Vomiting occurs to relieve pressure. Can occur in adults associated with excess nicotine, morphine, fatigue, stress, and stomach ulcers. Can lead to gastric outlet obstruction- contents cannot enter the duodenum so it's going to be released via vomiting.

bile flow from liver to duodenum

liver secretes bile in bile ducts which goes to hepatic ducts to common hepatic duct joins cystic duct from gallbladder which will join bile ducts descends through lesser omentum and joins duct of pancreas move into hepato0pancreatic ampulla this terminates in folds of the tissue. The sphincter of Oddi will regulate passage of bile and pancreatic juices into the duodenum.

parotid gland

located beneath the skin anterior to the earlobe. Secretes watery, serous liquid containing salivary amylase. Mumps is an inflammation and swelling of the parotid gland caused by a virus.

bolus

mass swallowed as a result of saliva binding food particles into a soft, slippery, easily swallowed mass.

chief cells

most numerous. In lower half of gastric glands. Made of cuboidal cells. Absent in pyloric and cardiac glands. Secrete gastric lipase and pepsinogen. Stimulate by PNS- vagus nerve which activates the submucosal plexus. Gastric and lingual lipase play a minor role in digesting dietary fats- 10-15%. Pepsinogen is a zymogen which is a digestive enzyme secreted in an inactive protein. Hydrochloric acid acts by removing amino acids which forms pepsin which is an active enzyme that digests protein. Some pepsin is formed and will convert some pepsinogen into more pepsin. Both protein and lipid digestion will be completed in the small intestine.

mucous neck cells

mucus cells in gastric glands since they are concentrated in neck of gland. Produce thin, acidic mucus and open to gastric pits. Predominate in cardiac and pyloric regions involved in lubrication, protection, barrier, and trapping. Stimulated by parasympathetic (Vagus nerve) which activates the submucosal plexus.

stomach

muscular sac in upper left abdominal cavity immediately inferior to the diaphragm. Primarily functions as a food storage organ. J-shaped with greater and less curvature (cardiac region, fundic region, and body). Smooth muscle has longitudinal, circular, and oblique which allows more vigorous churning component. Mechanically breaks up food particles, liquifies food, and begins chemical digestion of protein and fat. Produces a substance called Chyme- soupy mixture of semi-digested food. Most of digestion will not occur in the stomach but after the Chyme passes into the small intestines.

bile

one quart of bile is produced per day by the liver. Yellow green in color and pH 7.6 to 8.6. Components: water, cholesterol, bile salts (Na +, K+ salts of bile acids which aids in emulsification of large lipid globules into small lipids- large SA which allow pancreatic lipase to rapidly digest. Bile salts are steroids synthesized from cholesterol. Bile is concentrated between meals. Bile salts are primarily reabsorbed), bile pigments (bilirubin from hemoglobin molecule. Globin= reusable portion. Heme= broken down into iron and bilirubin). Bilirubin secreted into bile, broken down in intestines, and metabolized by bacteria into urobilinogen which gives feces brown color.

peritoneal cavity

potential space containing a bit of serous fluid.

liver

second largest organ after skin. Secretion of bile is only function involved in digestion. Sits below diaphragm. Right lobe is larger, and gallbladder sits in right lobe. Size causes right kidney to be lower than the left. Gallbladder in depression of posterior surface and stores/concentrates bile. Has fundus, body, and neck. Regulation of pancreatic secretions occurs when you have normal amounts of HCL in stomach exact balance by amount of bicarbonates secreted by pancreas. As bicarbonate is secreted into the pancreatic juice's, hydrogen ions enter the blood. Venous blood to heart remains unchanged because alkaline blood draining from the stomach is neutralized by acidic blood draining from the pancreas.

submandibular gland

secretes more mucous (thicker). Located halfway along the body of the mandible. Its duct empties at the side of the lingual frenulum. Near the lower central incisors. Salivary nuclei in medulla oblongata and pons which are triggered by the presence of food. Oversight, thought, and smell adds to triggering salivary glands.

goblet cell in small intestine

secretes mucus which will facilitate passage of material through bowels. Few in duodenum but they will vary as they move to the colon. Many more in the colon- aids in lubrication.

enteroendocrine secretions in small intestine

secretin (digestive hormone; stimulated by chyme triggers pancreas to release bicarbonate ions and water to neutralize acidity of chyme; inhibits gastrin from stomach; stimulates liver to release bicarbonate into bile which is a neutralizer of pH), CCK (digestive hormone; triggered by amino acids, fatty acids, and hydrochloric acid of chyme; enter bloodstream - > pancreas-> stimulate to release digestive enzymes to help with breakdown; stimulate contraction of smooth muscle of gallbladder to release bile; relax hepatopancreatic sphincter where bile from liver and contents from pancreas are stored- when relaxed allows the contents to be released into small intestine; activate hypothalamus and give fullness feeling), GIP (inhibit gastrin motility and secretions of acids; pancreas release insulin preparing for increased glucose), gastrin. Paneth cells secrete lysozyme (antibacterial protein which protects stem cells)

cephalic phase

stomach being controlled by brain. Receptors for sight, smell, and taste of food activated. Thoughts of food. Preparation phase. Mechanisms- neural via vagus nerve and submucosal plexus. Stimulates mucus, enzymes, acid production (increases gastric juices), and gastrin release.

gastric phase

stomach controlling itself. Continued breakdown of food occurs. Stretch receptors detect distension of stomach. Chemoreceptors detect increased pH of gastric juice. G cells secrete gastrin into blood which increased gastric juices, gastric peristalsis, and emptying into duodenum.

lipid metabolism

store triglycerides, break down fatty acids to generate ATP, synthesis lipoproteins which transport fatty acids/triglycerides and cholesterol, synthesize cholesterol, and use it to make bile salts.

accessory organs

teeth, tongue, salivary glands, liver, gallbladder, and pancreas. Salivary gland creates enzymes for breakdown and protection from bacteria. Liver and gallbladder help with alkalinity (substance moving from stomach to small intestines). Pancreas helps with alkalinity and has digestive enzymes.

pyloric stenosis

the narrowing of sphincter indicated by projectile vomiting. Must be corrected surgically- incision in longitudinal and circular muscle of pylorus. More common in males by 2-6 weeks.

mechanical digestion

the physical breakdown of food into smaller particles via cutting and grinding action of the teeth, churning action of stomach and small intestines, and exposes more food surface to the action of digestive enzymes (beginning with salivary amylase which breaks down starch, lingual lipase which breaks down lipids, and pancreatic amylase breaks down starch, maltase breaks down grains occurs in intestines). Pepcin is from the stomach and gives trypsin which is from the stomach and pancreas for protein breakdown.

activation of pancreatic enzymes in small intestine

trypsinogen is secreted into the intestinal lumen and converted to trypsin (breaks down proteins) by an enterokinase - enzyme secreted by mucosa of small intestine. Trypsin converts trypsinogen into more trypsin (positive feedback mechanism). Chymotrypsinogen is precursor to chymotrypsin by trypsin. Procarboxypeptidase is converted to carboxypeptidase (hydrolyzes protein peptide bonds) by trypsin. Important to reuse proteins.

carbohydrate metabolism

turn proteins and triglycerides into glucose. Turn excess glucose into glycogen and store in liver. Turn glycogen back to glucose as needed. Liver is important in maintain blood glucose levels. Can convert sugars like fructose and lactose into glucose.

What nerve is responsible of activating the submucosal plexus?

vagus nerve

absorption in stomach

very little mainly due to protective mechanism of the stomach. Epithelial cells are impermeable to most materials which prevents acidic environment to seep into abdominopelvic area. If it's cold, then water is absorbed faster which may be beneficial in athletic events. Some drugs (especially aspirin and alcohol- alcohol dehydrogenase which breaks down alcohol into acetyl-aldehyde which is involved with dehydration & hang over). Fat content in stomach slows passage of alcohol. Females make 60% less of this enzyme than males. Gastric mucosal cells contain alcohol dehydrogenase that converts some alcohol to acetaldehyde.

peritoneum

visceral layer covers organs. Parietal layer lines the walls of body cavity. Serous membrane lines wall of abdominal cavity. Forms dorsal mesentery (translucent membrane extending to digestive tract. Layers pass around forming a serosa. Continues as a sheet of tissue called ventral mesentery. *** Peritoneum is largest serous membrane of body contains large folds that weave between viscera which binds organs to one another and walls of abdominal cavity. Contains blood vessels and nerves which supply abdominal organs. Five falciform ligaments which attach liver to anterior abdominal wall and diaphragm.

skeletal muscle of digestive tract

voluntary control in mouth, pharynx, upper esophagus, and anus. Control over swallowing and defecation.

secretions by G cells

("get out of here"): secrete hormones and paracrines that are concentrated in lower end of gastric pits. - Gastrin: releases more gastric juice, increase gastric motility, relax pyloric sphincter, and constrict esophageal sphincter preventing entry. Most numerous endocrine cells. Initiates digestive actions, detects harmful substances, and initiates protective responses. Gastric juices produced by gastric glands 2-4 L per day. Peptide hormone stimulates parietal cells to secrete hydrochloric acid, gastric motility, stimulated by presence of protein, and cephalic phase in preparation. Cephalic phase is the head (thought process, smell of food, anticipation, etc). stimulates gastrin to be released in preparation for food. When food moves down to the stomach, it causes the pH to increase. Stretch of stomach (presence of food and increased pH stimulate cells to release gastrin). Gastrin kills bacteria entering with food therefore minimalizing infection. Can stimulate gallbladder to empty bile and pancreas to secrete digestive enzymes. Both gallbladder and pancreas have ducts that lead into duodenum. Small intestine does not have same protective measures that the stomach does. Helps with churning. - Histamine: stimulated by food. Activates parietal cells. Paracrine measurement - Serotonin: stimulated by food. Targets stomach. Works on contractions of muscles and act locally as a paracrine. Stimulate by PNS- vagus nerve which activates submucosal plexus and by presence of food. - Somatostatin: inhibits gastrin release and emptying of the stomach. Acidic environment will be turned off therefore decreasing gastrin release. Acts locally as a hormone by diffusing into the blood to influence digestive systems target organs. Released from stomach and small intestine. Stimulated by food and sympathetic nervous system. Targets stomach which inhibits gastrin secretions. Inhibits pancreatic secretions. Inhibits gastric blood flow and absorption in small intestine. Communicates with gallbladder and liver. Inhibits contraction and release of bile. Stimulated by SNS & food

digestion of water-soluble vitamins

(C and B) have active transport for absorption. Molecules pick them up in the small intestine and are carried through the intestinal wall and deposited in the body where they can enter the blood stream. Since they are dissolvable in water, they leave the body through urine every day and need to be replenished via diet. Vitamin B needs an intrinsic factor from the stomach to be absorbed.

summary of digestive hormones

- Gastrin: stimulated by food and Ach. It's made in the stomach and its target is the stomach. Increases secretory activities, HCl secretions, and involved in gastric emptying. Also targets small intestines for contractions of the small intestines to move food out. Targets ileocecal valve and relaxes it- this is where the small intestines meets the large intestines. Targets large intestines for mass movement for excretion. -GIP: promotes secretion of gastric juices which mix with ingested foods to produce chyme. Insulin will be released from pancreas to prepare liver for increase in glucose. - Secretin: stimulated by acidic chyme. Target is stomach. Inhibits gastric gland secretions and gastric motility during gastric phase. Targets pancreas to increase output of pancreatic juice rich in bicarbonate ions and enhance the actions of CCK. Targets liver to increase bile output. - CCK: stimulated by fatty component of chyme and partially digested proteins. Its target is the gallbladder and pancreas to begin their secretions. Targets pancreas for pancreatic enzymes and gallbladder for contraction/expulsion of bile. Target sphincter of Oddi to relax and allows bile/pancreatic juices into small intestines. - Serotonin: stimulated by food in the stomach. Targets stomach and contractions of the stomach. - Histamine: stimulated by food in the stomach. Targets stomach and activates parietal cells to release HCl. - Somatostatin: stimulated by food in the food and the sympathetic nervous system. Targets stomach: inhibits gastric secretions and gastric motility/emptying. Targets pancreas and inhibits secretions. Targets small intestines inhibiting intestinal absorption and gallbladder to inhibit contraction of bile release.

causes of GERD

- If the lower sphincter fails to open: distension of esophagus feels like chest pain or heart attack - If lower esophageal sphincter fails to close: stomach acids enter esophagus and cause heart burn (weak sphincter). Tx: no large meals or laying down while eating, smoking/alcohol make the sphincter which makes it weaker, avoid triggers. Take Pepcid or omeprazole to neutralize acid. Problem if you neutralize your stomach too much too often it can affect your nutrition.

neural regulation stomach

- Short (myenteric reflexes): stretch or chemical stimulation acts through myenteric plexus. Stimulates parastaltic contractions of swallowing. Located between longitudinal and circular smooth muscle layers of muscularis. Stretch receptors due to food coming into the stomach -> signal medulla oblongata and endocrine cells in stomach - > stomach secretes gastrin -> enters circulatory system and come back to stomach - > promote secretions of gastric juices. - Long (vasovagal reflexes): parasympathetic stimulation of digestive motility and secretion. Utilizes autonomic nerves afferent and efferent of vagus nerve. Carries info from digestive tract to brainstem -> motor commands sent back to GI tract to encourage motility and breakdown of components

modifications for stomach muscularis and mucosa

- circular and longitudinal layers + oblique moves food, churns, mixes, and pummels food - mucosa lining= goblet cells. Protective 2-layer alkaline mucus coat. - gastric pits: depressions in gastric mucosa lined with simple columnar epithelium. 2-3 tubule glands which open into the bottom of each gastric pits (cardiac, pyloric, and gastric glands).

glycogenolysis pathway

1. glycogen phosphorylase forms glucose-1 phosphate 2. glucose 1 phosphate converted to glucose-6 phosphate (enzyme transfers phosphate group to other) 3. in the liver, glucose-6 phosphatase hydrolyzes glucose 6 phosphate forming glucose that is exported into the circulation leading to increase in blood glucose level.

pancreatic juices

1.5 quarts per day at pH 7.1 to 8.2. Contains water, enzymes, and sodium bicarbonate. Digestive enzymes (pancreatic amylase- breaks down carbohydrates, pancreatic lipase- breaks down triglycerides, proteases- protein digesting enzyme released from pancreas in inactive form and activated in duodenum, ribonuclease- breaks down nucleic acids, and deoxyribonuclease). Buffer acidicity of chyme. Stops secretion of pepsin. Protects small intestines. Enzymes become active when exposed to bile.

krebs cycle

2 carbon acetic acid joins the existing 4 carbon molecule. End up with 6 carbon molecules (Citric acid). Acids rearranged to produce different intermediate compounds. Decarboxylation occurs where acidic acid is broken apart by carbon and oxidized by removing H+. NAD and FAD accepting hydrogen ions. End up with 4 carbon molecule. Yields: six CO2 two converting to acetyl group and 4 in citric acid cycle. 10 enzymes: two NADH's from acetyl group, 6 from citric acid, and two FADH2 from citric acid cycle. Two ATP from citric acid cycle.

purpose of enteric nervous system

A nervous network in the esophagus, stomach, and intestines that regulated digestive tract motility, secretion, and blood flow. Thought to have over 100 million neurons. More than the spinal cord. Functions completely independently of the CNS (although the CNS exerts a significant influence on its action). Enteric nervous system contains sensory neurons that monitor tension in the gut wall and conditions in the lumen. Extends from esophagus to anus. Myenteric and submucosal. In house nerve supply of alimentary canal communicate to regulate GI activity. Plexus's interconnect like chicken wire. ENS embedded in lining of GI system. Known as second brain but usually communicates with CNS through PNS and SNS.

regulation of digestive system

CNS can and dose influence it but it is not a requirement. It can only be regulated by local control- stomach & intestinal muscles are self-pacing, GI tract's intrinsic nerve plexus carry out reflex activity, and enteroendocrine cells more important than neural influences in controlling activity.

chemical digestion

a series of hydrolysis reactions that breaks down dietary macromolecules into their monomers. Carried out by digestive enzymes produced by salivary glands, stomach, pancreas, and small intestine. Results: Polysaccharides into monosaccharaides (via salivary amylase, pancreatic amylase, maltase) Proteins into amino acids (via pepcin, trypsin, and peptidase from intestines) Fats into monoglycerides and fatty acids (via lipase from salivary gland and pancreas) Nucleic acids into nucleotides (via nuclease)

peristalsis

a wave of muscular contraction that pushes the bolus ahead of it. The circular fibers behind the bolus and longitudinal fibers in front of it which shortens the distance of travel. Entirely voluntary reflex. When standing or sitting upright, food drops to esophagus by gravity faster than peristalsis. Peristalsis ensures you can swallow despite body position. Liquids reach stomach in approximately 1-2 seconds and food reaches stomach in 4-8 seconds. When it reaches the lower end, the lower esophageal sphincter relaxes to let the food pass into the stomach.

lesser and greater omentum

double layer of fatty tissue covers and supports intestines and organs in lower abdomen. Lesser connected to lesser curvature of stomach. Connects stomach and intestines to liver. Greater omentum attached to greater curvature of stomach. Important for storage and fat deposits. Fat deposited in omentum is part of visceral fat. Rest is embedded between organs. Excess fat gives rise to central obesity, metabolic disturbances, increased risk of cardiovascular disease, and diabetes.

enteric reflexes that respond to presence of chyme

increase intestinal motility, VIP (vasoactive intestinal polypeptide) stimulates the production of intestinal juice. Segmentation depends on distension which sends impulses to the enteric plexus and CNS. Distension produces more vigorous peristalsis. Sympathetic impulses decrease motility.

Phenylketonuria (PKU)

lack enzyme to breakdown phenylalanine which is present in all food proteins. Lack of defective enzyme and cannot convert amino acids to tyrosine. Elevated levels of phenylalanine are converted to harmful substances that can create a problem with mental functioning. PKU is due to mutated genes which prevent enzymes from breaking it down.

ketogenesis

liver converts acetyl CoA into ketone bodies. Amino acids deaminated to make acetyl CoA. Ketone bodies released into blood and used by brain, heart, kidney, and skeletal muscles. They are organic acids.

enterogastric reflex

regulates amount released into intestines. Distension of duodenum and contents of chyme. Sensory impulses sent to medulla inhibit parasympathetic stimulation of stomach but increase secretion of CCK and stimulate sympathetic impulses. Increases secretions of CCK. Inhibition of gastric emptying results in decrease of gastric motility.

regulation of gastric emptying

release of chyme is regulated by neural and hormonal reflexes. Distension and stomach contents increase secretion of gastrin hormone and vagal nerve impulses. Generates parasympathetic impulse which stimulate net effect of gastric emptying. Stimulate contraction of esophageal sphincter and stomach and relaxation of pyloric sphincter. Ensures stomach doesn't release enough chyme that the intestine can process.

chemical digestion in the mouth

sends signals by way of autonomic fibers in the facial and glossopharyngeal nerves to the glands. Parasympathetics stimulate the glands to produce an abundance of thin, enzyme- rich saliva. Sympathetic stimulation stimulates the glands to produce less, and thicker, saliva with more mucus (dominates during stress- results in dry mouth). Extrinsic salivary gland secretes about 1 to 1.5 liters of saliva per day. Its swallowed and helps moisten esophagus. Most of saliva is reabsorbed to prevent fluid loss. Chemicals in food stimulate receptors in taste buds of tongue and pulses conveyed to salivary nuclei in brain stem. Returning impulses in fibers stimulate secretion of saliva. Controlled by autonomic nervous system. Keeps mucus system moist and lubricates lips/tongue during speech. Ducts empty into oral cavity (exocrine).

absorption of lipids

small fatty acids enter cells and blood by simple diffusion. Larger lipids exist only within micelles (bile salts coating). Lipids enter cells by simple diffusion leaving bile salts behind in gut. Bile salts are reabsorbed into blood and reformed into bile in the liver. Fat-soluble vitamins are able to enter cells since they were within micelles. lipids leave the micelles and move via simple diffusion. Free fatty acids and monoglycerides enter epithelial cells. The smooth ER converts them back to triglycerides and combine with lecithin and other phospholipids/cholesterol to form a water-soluble chylomicron which is too large to pass through plasma membrane. They enter the lacteals via endocytosis. Then they are emptied into venous blood at the thoracic duct. Fat absorption completed in the ileum of the small intestines. Chylomicrons are lipoproteins that transport lipids in the circulation and released by exocytosis. They are too large to enter capillaries, but they enter lacteals which are lymphatic capillaries. They enter circulation via lymphatic vessels which drain into the large subclavian veins. They are hydrolyzed lipoprotein lipase which is found in the capillaries of the endothelial cells.

fate of glucose

ATP production, converted to one of several amino acids (used as building blocks for new protein or broken down further for production of ATP, glycogenesis (hundreds of glucose molecules combined to form glycogen for storage in liver and skeletal muscles), and lipogenesis (triglyceride synthesis- converted to glycerol and fatty acids within liver and sent to fat cells). Excess ATP leads to accumulation of acetyl coenzyme A and glyceraldehyde 3 which is channeled into triglycerides synthesis pathway. Some energy is lost as heat but most remains in pyruvic acid.

make up of pancreatic juices

Alkaline mixture of water, enzymes, zymogens, sodium bicarbonate, and other electrolytes. Basic to buffer acidic chyme. Intestine does not have protection against an acidic environment. Acini secrete enzymes and zymogens (help with breakdown of proteins- trypsinogen, chymotryopsinogen, and procarboxypeptidase; become active once reach small intestine so they don't breakdown the pancreas). Ducts secrete bicarbonate. Other pancreatic enzymes: pancreatic amylase (digests starch), pancreatic lipase (digests fat), ribonuclease and deoxyribonuclease (digest RNA and DNA respectively).

anatomy of large intestine

Begins at cecum inferior to ileocecal valve. Ascending and descending colon, cecum and appendix, rectum is the last 8 inches of the GI tract anterior to the sacrum and coccyx, anal canal is the last 1 inch of GI trat. Sigmoid colon is S-shaped portion leading down to the bowl. The internal sphincter is smooth muscle and involuntary while the external sphincter is skeletal muscle and under voluntary control. Receives 500 mL indigestible residue and reduces to 150 mL of feces by absorbing water and salts.

What stimulates the release of CCK & secretin from the small intestines?

Bile and pancreatic juices stimulated by parasympathetic stimulation and inhibited by sympathetic stimulation. Regulated neurally and hormonally. During cephalic and gastric phases, parasympathetic communicates with pancreas stimulating it to increase secretion of pancreatic enzymes. Acidic chyme will equal a sympathetic impulse. Secretin: acidity in intestine causes increased sodium bicarbonate release. Secreted by duodenum and stimulates pancreas secretions rich in digestive enzymes and trigger contraction of gallbladder to release bile. Relaxation of sphincter of Oddi so bile and pancreatic juices can move into small intestines. GIP: fatty acids and sugar causes increased insulin release. Stimulate endocrine component of pancreas and release insulin by pancreatic beta cells to ready liver for rise in glucose. CCK: fats and proteins cause increased digestive enzyme release. Encourage bicarbonate ions in pancreas and stimulate release from bile to neutralize chyme.

regions of stomach

Cardiac region (cardia)- small area within about 3 cm of the cardiac orifice. Food content passes from esophagus to here. Cells within this region are responsible for mucus. Fundic region (fundus)- dome shaped portion superior to esophageal attachment. Stores undigested food and gases released from chemical digestion of foods. Belching is due to these gases, but also due to air being swallowed which is stored here as well. Body (corpus)- makes up the greatest part of the stomach. Bulk of food is partially digested. Pyloric region- narrower pouch at the inferior end. Subdivided into the funnel-like antrum. Narrower pyloric canal that terminates at the pylorus which is a narrow passage to the duodenum of the small intestine. Pyloric (gastroduodenal) sphincter- regulates passage of chyme into the duodenum. Controlled neurally based on volume, composition, and physical state of duodenum content. Food will not move until the duodenum is free of its previous content.

Explain how Acetyl Coenzyme A is formed. Where does this happen?

Coenzymes become temporary carries of energy extracted from glucose. Enzymes remove electrons as H+ from intermediate compounds and transfer H+ to coenzymes which donate to other compounds. Enzymes cannot function without coenzymes. Formation of water releases energy used to make ATP. Pyruvic acid (anion) enters the mitochondria via active transport. 1. Decarboxylation: removal of a carbon molecule by pyruvate dehydrogenase. Release of CO2 which diffuses out of cell into blood and exhaled by lungs. 2. Oxidation: remove H+ leaves acetic acid. NAD+ picks up H+. 3. Formation of acetyl CoA: acetic acid + CoA (derived from vitamin B; waits in mitochondria) gives acetyl CoA.

Are fat & water soluble vitamins absorbed in the same fashion? Explain.

Fat-soluble (A, D, E, K): travel in micelles and absorbed by simple diffusion. If ingested without fat, they are not absorbed at all but passed through the feces and eliminated. Water-soluble (B and C): absorbed by simple diffusion. B12: combines with intrinsic factor before it is transported into cells via receptor mediated endocytosis.

examples of thermoregulation

Fever is normal protective mechanism should be allowed to run its course if it not excessively high. Can result in dangerous positive feedback loop. Heat cramps are painful muscle spasms due to electrolyte imbalances from excessive sweating occurs during relaxation after strenuous exercise. Heat exhaustion can occur from severe water/electrolyte loss due to profuse sweating. Can result in hypotension, dizziness, vomiting, and sometimes syncope. Heat stroke is the state in which core body temperature is over 104 degrees brought about by prolonged heat wave with high humidity. Skin is hot and dry. Individual stops sweating. Nervous system dysfunctions can result in deliria, convulsions, coma, tachycardia, hyperventilation, or multiorgan dysfunction can occur as well as death. Hypothermia can cause life-threatening positive feedback loops. If core temperature drops below 91 degrees metabolic rate drops so low that the heat production cannot keep pace with heat loss. Temperature falls even more. Death is from cardiac fibrillation and occurs below 90 degrees F. Below 75 F is usually fatal. Dangerous to give alcohol to hypothermic as a result of heat loss by dilating cutaneous blood vessels.

transamintation, deamination, ammonia, and urea

Glutamic acid can travel to the liver. The -NH2 I removed which becomes ammonia (toxic and cannot be allowed to accumulate). Urea cycle- liver combines ammonia with CO2 to produce less toxic waste and urea. Urea is excreted in the urine as one of the body's wastes. Protein is inefficient as fuel source. Continued use of protein will result in high urea levels. Deamination: amine group is removed results in molecule converting to pyruvic acid or keto-acid intermediates. Transamination: amine group and convert to citric acid Quito cycle to form glutamic acid. Original amino acid replaces amine group with oxygen (keto-acid).

What is the difference between pyruvic acid and pyruvate? Lactic acid vs. lactate?

If O2 shortage in cell, pyruvic acid is reduced to lactic acid. Rapidly diffuse out of cell to blood. Liver cells remove it from blood and convert it back to pyruvic acid. NADH transfers electrons to pyruvate to lactic acid. NAD+ is available for glycolysis. Lactate is repurposed in the liver. Its presence creates an oxygen debt and can be removed by increasing supply of oxygen to the tissue. Lactic acid builds up and causes soreness. Its made with anaerobic activities. Performing aerobic activities helps remove hydrogen ions and soreness. Lactate clears within 30-60 minutes of exercise. Soreness is due to trauma to muscles in connective tissue, inflammation, and hydrogen ion concentration. Pyruvate is an anion while pyruvic acid is a neutral molecule. Lactate is an anion while lactic acid is neutral.

structures in small intestine that increase surface area

Lumen lined with simple columnar epithelium with microvilli. Muscularis (circular layer is much thicker) and longitudinal is thinner which plays a role in segmentation (mixes contents of duodenum with chyme). - Plica circularis: permanent ½ inch tall folds that contain part of submucosal layer. Increase SA by 2 or 3. Found in lower duodenum and jejunum. Causes chyme to flow in spiral paths causing more contact with mucus and promotes more thorough mixing with nutrient absorption. Largest folds of intestinal wall up to 11 mm in height. - Villi: contains vascular capillaries and lacteals (lymphatic capillaries). Increase SA by factor of 10. Finger-like projections 1 mm in height. Covered with absorptive cells and goblet cells for mucus. Epithelial joined by tight junctions prevent digestive enzymes from seeping between them. Core is filled with areolar tissue which makes up lamina propria. Embedded are arterial and capillary networks. - Microvilli (cell surface feature known as brush border). Increase SA by factor of 20. Fuzzy border on apical surface of absorptive cells is considered the brush border. Significant cell division produces new cells that move up, rupture, and release digestive enzymes and proteins.

metabolic rate

Metabolic rate: rate of kilocalorie consumption needed. Rate at which metabolic reactions use energy (energy used to produce heat or ATP). Basal metabolic rate reflects energy to perform essential activities (breathing, organ function). Measurements made under certain conditions (quiet, resting, and fasting condition). Important: amount of calories needed per day to survive, Metabolic rate depends on: physical activity, mental state, absorptive and postabsorptive status, thyroid hormone, and other hormones. BMR: baseline/standard that minimizes effect of activity, feeding, and hormone levels. Females have lower body and muscle mass so lower caloric intake than males. Total metabolic rate: sum of BMR and total expenditures for voluntary activities. Raised by physical activity, pregnancy, anxiety, fever, eating, catecholamines, and thyroid hormones. Higher in children and decreases with age as metabolism wanes. Lowered by apathy, depression, and prolonged starvation. Reduced food intake results in lower metabolic rate to conserve weight mass.

digestion of lipids

Mouth- lingual lipase Small intestine- emsulfication via bile (breaking larger globules into smaller ones for absorption) Pancreatic lipase will split lipids into fatty acids and monoglycerides. No brush border enzymes for lipids. Hydrophobic quality of lipids that makes digestion/absorption harder. Lingual lipase is active in the mouth but more active in stomach due to acidic environment. Pancreatic lipase will work in small intestine to digest most of fats. Globules need to be broken into smaller emulsification droplets (via bile involving lecithin and bile acids). Agitation by segmentation breaks fats into droplets. Coating of lecithin and bile acid keeps broken up exposing surface to enzymatic actions. Enough pancreatic lipase to digest fat intake. Lipase acts on triglyceride by removing first and third fatty acids from glycerol. Product of lipase action are two free fatty acids and monoglyceride. Micelles include bile, phospholipid, and cholesterol which diffuse into center of micelle to form pore. Micelles past down bile duct into the duodenum where they absorb fat soluble vitamins, more cholesterol, free fatty acids, and monoglycerides. Digestion depend on micelles which are consisting of 20-40 bile acid molecules aggregated with hydrophilic side out and hydrophobic facing inwards. Bile, phospholipids, and cholesterol diffuse into the center of the micelles which is a bile acid coating to form the core. The micelles pass down bile duct into the duodenum where they transport lipids to the intestinal absorptive cells. The lipids leave the micelles and diffuse through the plasma membrane into the cell. The micelles are reused to transport other lipids.

digestion of carbohydrates

Mouth- salivary amylase (starch into oligosaccharides) Intestine and stomach- no enzymes Duodenum - pancreatic amylase Brush border enzymes - maltase, sucrase, and lactase (contained in plasma membrane of microvilli). Contact digestion- chyme must come into contact with brush border for digestion to occur. Intestinal churning ensures contact of chyme with mucosa. They work on disaccharides. - produces monosaccharides (fructose, glucose, and galactose) - lactose intolerance (no lactase enzyme; bacteria ferment sugar which results in gas and diarrhea)

electron transport chain

Oxygen needed to make ATP. Harvest energy to make ATP. Hydrogen ions carried through ETC via coenzymes NAD and FAD. Proteins embedded in membrane of mitochondria. Electrons passed from one to another from less electronegative to more. As they pass its an exergonic reaction which creates a proton gradient and releases mall amounts of energy which will be used to make ATP. Electron carries become reduced when receives one electron pair and oxidized when it passes electron to next carrier. At the end of the electron transport chain, electrons transferred to molecular oxygen which splits in half to make water. Hydrogen ions go down concentration gradient back into matrix through ATP synthase and enzyme. Harness flow of protons to synthesize ATP. Net result will be approximately 34 ATP.

digestion of nucleic acids

Pancreatic juice contains 2 nucleases ribonuclease digests RNA and deoxyribonuclease digests RNA. Nucleotides produced are further digested by brush border enzymes (nucleosidase and phosphatase into pentose, phosphate, and nitrogenous bases which are absorbed by active transport).

substances secreted in saliva

Saliva is a hypotonic solution of water (97% water). Salivary amylase (starch digestion), lingual lipase (digests fat and activated by stomach acid), mucus (helps lubricate food to move around easily and formed into a ball and swallowed), lysozyme (kills bacteria), immunoglobulin A (inhibits bacterial growth), and electrolytes (Na+, K+, Cl-, phosphate, and bicarbonate- buffers acidic foods to maintain pH). pH is 6.8-7.0 in mouth. Saliva dissolves gases, organic substances including urea and uric acid. Helps remove waste molecules from body. Saliva wets food for easier swallowing, helps dissolve food for tasting, bicarbonate ions buffer acidic foods, and chemical digestion of starch begins with salivary amylase secretion of lysozyme helps with bacteria with a rinsing action. Tonicity measures osmotic gradient of two solutes separated by semi-permeable membrane. Hypotonic indicates it has a lesser concentration of solute in surroundings. Water will rush into the cell causing it to cell. Amylase begins starch digestion in neutral pH. When bolus hits pH in stomach hydrolysis will cease as the enzyme is denatured. Lingual lipase begins breakdown of triglycerides into fatty acids and glycerol. Lipase works in acidic environment and will not work until it reaches the stomach. Amylase predominantly released from parotid gland with small amounts from others. Lipase is secreted by sublingual gland.

1. Explain how the small intestines regulates secretions from the pancreas.

Small intestine receives chyme from stomach. Also, secretions from liver and pancreas (enter digestive tract near the junction of the stomach and small intestine). Secretions are an important part of the digestive process.

gluconeogenesis

Stimulated by cortisol (adrenal gland) and glucagon (pancreas). Occurs when there is too little glucose available for ATP synthesis during fasting, starving, low carbohydrate diets, or intense exercise. Process by which glucose is synthesized from non-carbohydrate precursors (glycerol, lactic acid, and amino acid- 60% availability). Takes place in the liver. Liver and kidney are major organs where this occurs. 90% in the liver and 10% in kidneys during overnight fasting. During prolonged fasting, 40% occurs in kidneys. Prevents hypoglycemia. Cortisol stimulates breakdown of proteins freeing amino acids. Thyroid mobilizes triglycerides from adipose tissue. Glycerol is formed from hydrolysis of triglycerides in adipose tissue and transferred to liver via blood. Glycerol is phosphorylated to glycerol phosphate by glycerol kinase enzyme. Then glycerol phosphate is oxidized to dihydraoxyacetonephosphate (intermediate of glycolysis). Lactate is derived from anaerobic glycolysis in exercising skeletal muscle and in cells that lack mitochondria and delivered by blood to the liver. Lactate is reconverted to pyruvate through oxygen debt that form glucose via this pathway. Glucogenic amino acids can be converted to glucose and formed from hydrolysis of proteins. Deamination of amino acids is where amino acids from amine group are removed and can be converted to pyruvic acid and to form glucose. Major precursor are pyruvate, lactate, glycerol, and glucogenic amino acids. Some tissues such as brain, renal, medulla, erythrocytes, lens, and cornea of eyes require continuous supply of glucose as metabolic fuel. Excessive cortisol (Cushing's disease) is going to result in rapid weight gain. Not enough cortisol (Addison's disease) can cause low BP, weakness, etc.

digestion of proteins

Stomach: HCl/acidic environment denatures or unfolds proteins. Pepsin turns proteins into peptides. Pepsin is inactivated in the duodenum when mixed with alkalinity of the pancreatic juices. Pancreatic enzymes: trypsin and chymotrypsin continue protein breakdown and digestion (split peptide bonds into different amino acids). Brush border enzymes: aminopeptidase or dipeptidase will split off the amino acid at the amino end of the molecule or split the dipeptide.

Explain what the role is for a coenzyme and list the two involved with ATP synthesis.

Store high energy electrons- NADH and FADH2. NAD plays a role in every cell in the body. Transfers energy in mitochondria. FAD is a derivative of Vitamin B12 which accepts and donates electrons. Some energy is captured within the cell when ATP is formed.

submucosa of small intestine

Submucosal layer includes blood vessels and lacteals has duodenal glands (secretes alkaline mucus). Mucosal layer contains intestinal glands (crypts of Lierberjuhn- numerous pores open into tubular gland on floor of small intestine, similar to gastric gland- upper half enterocytes and goblet cells; lower half dominated by dividing stem cells; similar life span 3-6 days; new cells migrate into crypts where it is sloughed off and digested). Secretes intestinal juice 1-2 qt/per day at pH 7.6. Brush border enzymes. Paneth cells secrete lysozyme which kills bacteria. Secrete phospholipase is hydrolyzes phospholipids

overview of cellular respiration

a. Glycolysis (1 glucose molecule oxidized giving 2 pyruvates, 2 ATP molecules, and two NADH which will be coenzyme). Occurs in cytoplasm. Does not require oxygen (anaerobic respiration). b. Formation of acetyl coenzyme A which is a transition step that prepares pyruvic acid to enter Krebs cycle. c. Krebs cycle: oxidized acetyl coenzyme A process. Incorporates CO2, ATP, coenzymes (NADH and FADH2). d. Electron transport chain: NADH and FADH2 transfer high energy electrons e. Phosphorylating is addition of phosphate group to molecule to inc potential energy. Phosphate added to ADP with input of energy which makes ATP. As far as substrate. Transfer of high energy phosphate group from intermediate phosphorylated metabolic compound goes directly to ADP. Oxidative component will pass through electron acceptors which is ETC and end up with molecules of oxygen. Phosphorylation occurs in light absorbing pigments.

steps of glycolysis

a. Phosphorylation: glucose is converted to glucose 6-phosphate using 1 ATP. Which keeps intracellular concentration of glucose low favoring continued diffusion of glucose into the cell. Prevents sugar from leaving the cell since phosphorylated compounds cannot pass through the membrane. Glucose 6- phosphate can be converted to fat or amino acids, polymerize to form glycogen, or oxidized to extract energy. b. Priming: glucose 6-phosphate is rearranged and phosphorylated to become fructose 1, 6-diphosphate using 1 ATP. c. Cleavage: fructose 1,6 diphosphate lyses or splits into 2-3 carbon molecules. Two molecules of phosphoglyceraldehyde. d. Oxidation: each PGAL oxidize by removing H+. electrons picked up by NAD+ yielding NADH. Phosphate group added to each 3-carbon molecule to free phosphate ions. e. Dephosphorylation: phosphate groups taken from glycolysis intermediates and added to ADP to make ATP. Three carbon compound becomes pyruvic acid. Fate of pyruvic acid depends on oxygen availability. If anaerobic- converted to lactic acid. If aerobic, go to Krebs cycle. series of conversions occur when glucose enters the cell. occurs in the cytosol. Breakdown of six-carbon glucose molecule into 2 three-carbon molecules of pyruvic acid. Nets 2 ATP as 4 ATP produced, and 2 ATP used. 2 NAD+ molecules as H+ acceptors. When oxygen is available, NADH goes to ETC in mitochondria. Without oxygen, NADH unloads hydrogen ions back to pyruvic acid to make lactic acid.

absorption in large intestine and feces formation

absorb water and some electrolytes (sodium and chloride). After 3 to 10 hours 90% of water has been removed from chyme. Feces are semisolid by the time reaches transverse colon. Feces consists of dead epithelial cells, undigested foods such as cellulose, and bacteria (live and dead). Hostile contractions occur every 30 minutes. Colonic motility is a form of segmentation and distension of haustrum stimulates its contractions. Filling of stomach and duodenum stimulates motility of colon and moves residue with each contraction. Function of large intestines include absorption of vitamins made by bacteria living there (commensal bacteria that break down undigested polypeptide or fibers into short chains of fatty acids which can be absorbed through passive diffusion). Bacteria produce gas which is a mixture of nitrogen and carbon dioxide with small amounts of gases of hydrogen, methane, and hydrogen sulfide. These results from bacteria fermentation of undigested polysaccharides. Bacteria also produce large amounts of vitamins. Most important are vitamin K and B. when vitamin intake is low this can be an important source of these vitamins.

digestion of nutrients

amino acids move in the cell by way of sodium bound transporters. Minerals like Ca2+ in the small intestines will be absorbed by active and passive transport. Iron in small intestine is broken down into ferrous by brush order enzymes. Cholesterol in small intestine 1/3 is through the diet, bulk of cholesterol comes from bile and other cells. Water net movement occurs by osmosis depends on absorption of solutes especially Na+.

oxidation/deamination in liver

amino group of glutamic acid is removed as ammonia and citric acid keto-acid is regenerated. Ammonia combines with CO2 to give urea and water. Urea excreted in urine. Keto-acid modification is when keto acids are altered to enter krebs cycle. Liver plays a role in metabolism. Degeneration of the liver (ex. Hepatitis, cirrhosis, and cancer) are life threatening. Proteins can be broken down to amino acids which can be used as building blocks of new proteins. When one is chronically starved the use of amino acids for energy production can lead to wasting away of the body as more and more proteins are broken down.

acute pancreatitis

associated with heavy alcohol intake or biliary tract obstruction. Appears suddenly and lasts for days. Can have chronic pancreatitis. Severe cases can cause life threatening complications. Acute pancreatitis is caused by gallstones or heavy alcohol uses, medications, metabolic disorders, surgery. In acute pancreatitis, patients secrete trypsin in the pancreas and begin digesting itself.

thermoregulation

balance between heat production and loss. Metabolically active tissues give off heat. Enzymes depend on optimal temperature as heat loss much match heat generation. Hypothermia can slow metabolism and cause death. High body temperature can disrupt coordinate metabolic pathways and can cause death. At rest most heat is generated in the- liver, heart, brain, kidneys, and endocrine organs. Changes with muscle activity. Most heat is generated by nutrient oxidation and ATP use. Skeletal muscles contribute 20-30% of total resting heat. During vigorous exercises, produce 30-40 times more heat than the rest of the body. TRH can contribute to heat by causing vasoconstriction to the skin, communicate with adrenal gland to stimulate cell metabolic rate triggering shivering and release of more thyroid hormone which raises BMR.

intestinal phase overview

begins when the chyme enters the duodenum. The duodenum responds and moderates gastric activity through hormones and nervous reflexes. Duodenum initially enhances gastric secretion but soon inhibits it (trigger stomach to send contents into small intestine then inhibits to slow down for absorption and digestion to occur). Chyme is acidic and small intestine does not have protective measures of the stomach- need time for buffering components of pancreas and gallbladder to mix with chyme to protect the small intestine. Stretching of duodenum accentuates vasovagal reflex that stimulates the stomach. Peptides and amino acids in chyme stimulate G cells of the duodenum to secrete more gastrin which further stimulates the stomach. Duodenum sends inhibitory signal to stomach via enteric nervous system signals medulla oblongata triggered by contents of chime, acid, semi-digested fats, and proteins. It inhibits vagal nuclei to reduce vagal stimulation of stomach. Inhibits stomach. Involves afferent and efferent.

myenteric nerve plexus

between longitudinal and circular smooth muscle layers. Enteric neurons main nerve supply to GI tract wall and controls motility (in house nerve supply of alimentary canal) communicates to regulate digestive system activity).

Myenteric (Auerbach's) plexus

both parasympathetic and sympathetic innervation of circular and longitudinal smooth muscle layers. parasympathetic ganglia and nerve fibers between the two layers of the muscularis interna. Controls peristalsis and other contractions of muscularis externa.

glycogenolysis

breakdown of glycogen to glucose or glucose 6-phosphate in muscle. Occurs within cytoplasm of cells. Glucose release is not a simple reversal of steps. Glycogen is the major storage mainly in the liver and skeletal muscles. In the liver, glycogenolyis occurs during periods of fasting to maintain blood glucose levels. In skeletal muscle, glycogenolysis occurs during active exercise to provide glucose 6-phosphate for glycolysis in response for need of ATP. Muscle glycogen does not directly provide free glucose due to lack of glucose-6 phosphatase enzyme in muscle. This enzyme removes a phosphate which happens in the liver (via glucose-6 phosphatase- remove phosphate group which allows glucose to go across cell membrane). In muscle, does not have this enzyme and glucose cannot go past cell membrane. Therefore, it remains in the skeletal muscles. Stimulated by glucagon and epinephrine.

lipolysis

breaking down fat for fuel (glycerol and fatty acids) using enzyme lipase. Uses sodium hydroxide and water to break apart. Glycerol and fatty acids released into blood for fuels. Body accelerates this if carb intake is low. Glycerol is easily converted to glyceraldehyde 3-phosphate which will be converted to pyruvic acid and acetyl CoA which enters krebs cycle. Net result is 15 ATP per one glycerol as glyceraldehyde is equal to half a glucose molecule. PGAL is the first stage in fatty acid catabolism in a series of reactions called beta oxidation. Fatty acids are broken down into two carbon molecules. Beta oxidation is the major pathway for catabolism in mitochondria. Two carbons removed from carboxyl end producing acetyl CoA, NADH, and FADH2. Fatty acid broken between alpha and beta carbon atoms. Enters Krebs cycle and ETC; this is an aerobic process which requires oxygen. Fatty acid oxidation generates 129 ATP (fatty acids= 16 carbons). Acetyl CoA is synthesized by beta oxidation and may be oxidized to CO2 via CAC produces large amounts of energy, precursors for synthesis of cholesterol/steroids, used to synthesize ketone bodies in live important fuels for prolonged fasting state. Muscle, liver, and adipose tissue routinely use lipolysis to produce ATP. Stimulated by epinephrine, norepinephrine, glucocorticoids, thyroid hormone, and growth hormone. Excess fats stored in liver or adipose; used for plasma membranes, lipoproteins to transport cholesterol, thromboplastin for blood clotting, myelin sheath to speed up nerve conduction, cholesterol to synthesize bile salts and steroid hormones. 50% of excess fat stored in adipose sites under skin whereas rest in adipocytes in other tissues/organs.

mastication

breaks food into pieces which increases surface area. Mixes with saliva to form a bolus. (Oral cavity includes ingestion, chewing, and chemical digestion, swallowing, speech, and respiration). Food stimulates oral receptors to trigger involuntary chewing reflex (tongue, buccinator, and orbicularis oris manipulate food. Masseter and temporalis elevate teeth to crush food. Mouth enclosed by cheeks, lips, palate, and tongue). Amylase and lipase released from salivary glands.

ketone bodies

byproducts of breaking down fat for energy. Low glucose availability. Glycogen depleted. Always present in blood. Levels rise with fasting and prolonged exercise. Overnight, ketone bodies use 2-6% of bodies energy requirements. 30-40% used after 3 day fast.

hepatitis

can be caused by alcohol consumption, health conditions, or medications. Also, may be a viral origin. Tx: certain types may require antiviral medications, corticosteroids (prednisone). Prevention: vaccines, safe sex, don't share needles, and good personal hygiene.

histology of large intestine

circular longitudinal muscularis layer, blood vessels, and lacteals. The muscular outer layer contains taeniae coli (longitudinal fibers concentrated in three thickened ribbon like strips), haustra (pouches caused by muscle tone of taeniae coli), and epiploic appendages. The serosa is the visceral peritoneum. The appendix contains large amounts of lymphatic tissue. In the pits there are two cells- absorptive cells (absorbs water) and goblet cells (secrete mucous). Mucous helps in reducing acidity and protecting from infections. Mucosa secretes bicarbonate to neutralize acidity from formation of fatty acids and other digestive components at earlier parts in the intestine. Mucosa layer acts as barrier and protects from microbial invasions. Large intestines (appendix) is confluence of lymphoid tissues which play a role in immunity. This also helps in production of antibodies and antibodies. Normal non-harmful bacteria may help prevent infections as well. In children, appendix makes amines and hormones. It assists with maturation of B lymphocytes and immunoglobulins. Exposes WBCs and promotes local immunity. In adults has immune functions (lymphoid tissue accumulates then decreases). Appendicitis is inflammation of the appendix due to blockage of the lumen by chyme, foreign bodies, carcinoma, stenosis, or kinking. Infection may progress to gangrene and perforation. If it ruptures, its contents and contents of large intestines will be expelled into the abdominopelvic area. Rectum ends at anal canal (three curves and infoldings called transverse rectal folds/valves). Anal canal passes through levator ani muscle and pelvic floor terminating at the anus. Sinuses exude mucus to lubricate during defecation. Large hemorrhoidal veins form superficial plexus - distended veins protruding into anal canal or form bulges external to the anus.

protein metabolism

deamination (removes amine group from amino acids so can use what is left as energy source). Converts resulting toxic ammonia into urea for excretion by the kidneys. Synthesizes plasma proteins (globulins, albumin, prothrombin, and fibrinogen) utilized in the clotting mechanism and immune system. Convert one amino acid into another.

factors that relate to adult digestive issues

decreased secretory mechanisms, decreased motility, loss of strength & tone of muscular tissue, changes in neurosensory feedback, and diminished response to pain and internal stimuli. Symptoms: sores, loss of taste, periodontal disease, difficulty swallowing, hernia, gastritis, ulcers, malabsorption, jaundice, cirrhosis, pancreatitis, hemorrhoids, and constipation. Cancer of the colon or rectum is common.

other functions of liver

detoxifies the blood by removing or altering drugs and hormones (thyroid and estrogen). Removes the waste product (bilirubin). Releases bile salts help digestion by emulsification. Stores fat soluble vitamins (A, B12, D, E, K). Stores iron and copper. Phagocytizes worn out blood cells and bacteria. Activates vitamin D (the skin can also do this with 1 hr of sunlight a week).

diverticulitis

diverticula develop at naturally weak places in colon that give in to pressure. When these tear this results in inflammation and possibly infection. TX: diet modifications, antibiotics, and possibly surgery. Prevention: regular exercise, eat more fiber, increase fluids, and avoid smoking.

regenerative stem cells in stomach

divide rapidly and produce continually supply of new cells to replace the cells that die. Stem cells are undifferentiated. Pluripotent stem cells found in embryos can give rise to all cells. Multipotent cells are more limited in their capacity. Development is limited to cells that make up organ system that they belong to. Found in base of the pit and in the neck of the gland.

electron transport

electrons travel in pairs along ETC. each carrier becomes reduced when receives an electron pair and oxidized when it passes along to the next carrier. Each oxygen atom accepts tow electrons and two protons from mitochondrial matrix forming water. Must have oxygen. ETC fuels respiratory enzyme complexes and pumps proteins from matrix to intermediate space. Creates steep gradient for hydrogen ions to cross inner mitochondrial membranes. Inner membrane is not permeable to hydrogen ions and only channel protein called ATP synthase allows hydrogen ions to move to inside. Chemiosmotic membrane is hydrogen ions rushing back through the ATP synthase which drives ATP synthesis.

ketosis

elevated ketone bodies leads to metabolic acidosis. Buffering system cannot keep up pace if pH is low. Breathing increase as compensation (blow off CO2 to inc pH). Does not correct problem. Occurs in diabetics since triglycerides used for ATP production instead of glucose and insulin inhibits glycolysis. (Ketourea- ketones present in urine). Typically associated with gluconeogenesis. Low carb diets use another fuel source as glucose is not available (ketones). Ketone bodies make 21 ATP.

colorectal cancer

exact cause is unknown. Risk factors include hereditary, diet, tobacco smoking, and heavy alcohol use. Tx: chemotherapy, surgery. Prevention: increase physical activity, modify diet, avoid smoking and excessive alcohol use.

parietal cells

found mostly in the upper half of the gland. Secrete: hydrochloric acid (acidity pH as low at 0.8). Contain carbonic anhydrase: CO2 moves from blood into cells, join with water, with carbonic anhydrase will convert to carbonic acid which is broken down into bicarbonate and hydrogen ions. Bicarbonate exchange with chloride- chloride shift of blood plasma. Bicarbonate into blood- used as buffer elsewhere. Chloride will be pumped into the lumen of the gastric gland and joined with hydrogen ions==== hydrochloric acid. Elevated bicarbonate ions in blood will cause alkalinity to increase blood pH. Activates pepsinogen to pepsin (breakdown proteins) and activation of lingual lipase (breakdown fats, released from sublingual and salivary glands- activates with acidic environment). Breaks connective tissue and plant cell walls. Kills bacteria (nonspecific immune defense by destroying most invaders) and converts ferric irons to ferrous ions. Ferrous ions used for hemoglobin synthesis. Intrinsic factor which breaks down vitamin B12 in intestine. B12 needed for RBC formation and growth. Deficiency results in pernicious anemia. B12 released from ingested proteins and bind with intrinsic factor. Receptors in ileum of small intestine for intrinsic factor, once it binds it will absorb the B12. Also required for nerve health and DNA replication. A hunger hormone called grehlin- hunger hormone increases appetite and stimulates growth hormones. Can act on hypothalamus and amygdala. Regulates food intake and rise just before eating and when fasting. Stimulate protein and carbohydrate ingestion and fat as well. Stimulated by PNS- vagus nerve which activates submucosal plexus.

mechanical digestion of stomach

gentle mixing waves every 15-25 seconds (mixes bolus with 2 quarts/day of gastric juice to turn it into chyme (a thin liquid)). More vigorous waves travel from body of stomach to pyloric region. Intense waves near pylorus which open and squirt 1-2 teaspoons full with each wave.

histology of liver

hepatocytes (perform metabolic, secretory, and endocrine functions) arranged in lobules fill interior of liver. Central vein passes down core. Surround central vein in radiating sheet (hepatocytes- epithelium 1-2 cells thick). Hepatic laminae are plates bordered by endothelial lined. Secrete bile into canaliculi- small ducts which move to ducts from gallbladder to form common bile duct which enters small intestines. Sinusoids fill spaces between sheets lined by fenestrated epithelium. Brush border contains microvilli that projects into this space. Blood filtered in sinusoids and comes directly from stomach and intestines. Kupffer cells are macrophages that phagocytize microbes in sinusoids.

carbohydrate loading

long-term athletic events can exhaust glycogen stored in liver and skeletal muscles. Eating large amounts of complex carbohydrates. Can store 1,800-2,000 cals as glycogen fuels 90-120 min of vigorous exercise. This maximizes glycogen availability for ATP production. Glycogen stores in liver and muscle. Carbs eventually transform to glucose. Fats and carbs are oxidized directly to produce cellular energy. While protein can be used to supply energy only after converted to a carbohydrate intermediate. Max out muscle and liver glycogen stores 2-3 days prior. Glucose catabolism through aerobic respiration is a function of this reaction and transfer energy from one glucose to 2 ATP.

segmentation

movement in which stationary ring-like contractions appear in several places along intestines. Purpose is to mix and churn not to move material along as in peristalsis. Most common kind of intestinal contraction. There are pacemaker cells in the muscularis externa which sets the rhythm of segmentation. Typical contractions in duodenum are 12x per minute and in ileum 8-9x per minute. When most of the nutrients have been absorbed then segmentation will decline then peristalsis begins (gradual movement of contents towards colon). Peristaltic waves begin in the duodenum and travel 3 inches to over 2 feet until another wave will pick up then it carries on down the tract. Is has a migrating motor complex successive overlapping waves of contraction milks chyme towards colon over a period of 2 hours. The ileocecal valve is usually closed (where the small intestines meets the large intestines). Food in the stomach will trigger the gastroileo-reflex which enhances segmentation in the ileum then relaxes the ileocecal valve. As the cecum fills with residue, the presence will pinch off the valve which prevents regurgitation of cecal contents into the lumen.

chemical digestion in large intestine

no enzymes are secreted only mucous. Bacteria ferment undigested carbohydrates into carbon dioxide and methane gas, undigested proteins into simpler substances (odor), and turn bilirubin into simpler substances that produce color. Bacteria only produce vitamin K and B in colon. 800 species of bacteria help digest cellulose and other carbohydrates, absorb sugars, synthesize vitamin B and K.

absorptive state

nutrients entering bloodstream. Glucose major fuel: remake degraded body protein, ATP production, and excess stored as fat. 4 hours for absorption of each meal. Regulated by insulin. Carbohydrates: absorbed sugars go to the liver (become available to most cells). Fructose and galactose converted to glucose. Released in blood and converted to glycogen/fat. Excess glucose is stored as glycogen or fat. Glycogen in liver and fat in adipose tissue. Fat is synthesized in the liver and transported by lipoproteins into blood and to adipose for storage. Glucose not taken into the liver will enter blood cells to make energy. Excess glucose in skeletal muscles is stored as glycogen. Triglycerides: enters lymph (as chylomicrons) where they are hydrolyzed to fatty acids and glycerol. Primary energy for hepatocytes, adipocytes, and muscle cell. Most enter adipose tissue. Amino acids: most pass through the liver to other cells. Absorbed and delivered by the liver: deaminated (ketone bodies to CAC to make ATP), or converted as fat stores, used to synthesize plasma proteins. Usually, last resort for fuel source as breaking down protein elsewhere. Most individuals with anorexia nervosa die from cardiac arrest as protein from the heart muscle is broken down as a fuel source.

glycogenesis

occurs when there are high level of ATP. Stimulated by insulin. Synthesizes glycogen- as glucose enters cell it is phosphorylated. Glycogen is our only stored carbon in the body. The first step is phosphorylation of glucose. Hydrolyzes ATP to ADP + P. Glucose is converted to glucose-6 phosphate. Occurs in both liver and skeletal muscle. Glucose 6-phophate I converted to glucose-1 phosphate. Transfer of phosphate group on glucose monomer from position six to one. Phosphate group reacts with uridine triphosphate and form an active nucleotide glucose (UDP). UDP is an active form of glucose. UDP required in the cell for cell wall biosynthesis. Glycogen synthase is the enzyme that catalyzes the synthesis of glycogen.

absorption of carbohydrates

oligosaccharides and maltose come in contact with brush border enzymes which converts into glucose. Lactose is indigestible due to decline in lactase. Plasma membrane of absorptive cells can transport proteins once brush border enzymes release them. 80% absorbed sugar in form of glucose and are taken up by sodium glucose transport proteins (SGTP). Glucose transported out of absorptive cells into ECF by facilitated diffusion. Sugars entering ECF increase its osmolarity and draws water from lumen of intestines through leaky tight junctions between epithelial cells. Water carries more glucose and other nutrients with it by the solvent drag. SGLT absorbs galactose, fructose, and is absorbed by facilitated diffusion. Absorbed by blood capillaries in villus and go to the hepatic portal system to the liver.

postabsorptive/fasting state

prevails in late mornings, late afternoons, and overnight. Stomach and intestines are empty. Regulates blood glucose levels between meals to 90-100 mg/dcl (maintaining a steady blood glucose level is critical especially for brain). Carbohydrates (glucose from glycogen reserves or gluconeogenesis). Fats (adipocytes and hepatocytes hydrolyze and convert glycerol to glucose; free fatty acids are oxidized by the liver to ketone bodies which other cells absorb and use as their source of energy leaving glucose for the brain). Proteins (used as fuel source when glycogen and fat reserves are depleted). Regulated by sympathetic nervous system and glucagon or sympathoadrenal system (epinephrine, cortisol, and growth hormone). Cachexia: extreme wasting away seen in cancer and other chronic diseases resulting from lack of appetite, anorexia, and altered metabolism. As blood glucose levels drop then insulin secretions decline. The pancreatic alpha cells secrete glucagon which promotes glycogenolysis and gluconeogenesis to raise blood glucose levels. Also promotes lipolysis and rise of free fatty acid levels make both glucose and lipids available for fuel. Sympathoadrenal system also supports gluconeogenesis and lipolysis especially under injury, fear, anger, and stress. Adipose tissue are richly innervated by sympathetic nervous system. Hepatocytes, adipocytes, and muscle cells responds to epinephrine from adrenal medulla which mobilizes stored energy reserves to meet demands of tissue repair. Cortisol promotes fat and protein catabolism as well as gluconeogenesis. Growth hormone secreted in response to rapid drop in glucose levels, opposes insulin and raises blood glucose concentrations.

anorexia nervosa

primary cause is unknown may be due to biological, psychological, and environmental factors. Tx: psychotherapy, medication, nutrition counselling. Prevention: build self-esteem, encourage them, and inform them on the dangers of dieting.

chemiosmosis

proton-motive force. H+ needs channel to move back into inner matrix using ATP synthase. ATP turns catalyzes ADP + P to ATP. Hydrogen ions pump from inner matrix to intermediate space which creates electrochemical gradient. Hydrogen ions cannot pass through phospholipid bilayer. ATP synthase is turned by flow of hydrogen ions as they move down concentration gradient. ATP synthase turns and catalyzes addition of phosphate to ADP capturing energy to form ATP. Average 34 ATP made.

What is the name of the structure which controls the amount of chyme released from the stomach into the small intestines?

pyloric sphincter

mechanical digestion in large intestine

smooth muscle (mechanical digestion) involves peristaltic waves. Hastrual churning: relaxed pouches are filled from below by muscular contractions. Gastroilial reflex: when stomach is full, gastrin hormone relaxes ileocecal sphincter so small intestine will empty and make room. Increase ileal motility and opening of valve. Gastrocolic reflex: when stomach fills, a strong peristaltic wave fills, a strong peristaltic wave moves contents of the transverse colon into the rectum. Increases intestinal peristalsis after food enters empty stomach. Emptying large intestine to make way for new food to come through. Parasympathetic defecation reflex involves spinal cord. Stretching of rectum sends sensory signals to spinal cord. Pelvic nerves send signals intensifying peristalsis and relaxing internal anal sphincter. Defecation occurs only if external anal sphincter is voluntary relaxed. Valsalva maneuver (defecation) increases the abdominal pressure of levator ani and opens anal canal outward.

absorption of electrolytes

sources of electrolytes (GI secretions, ingested foods, and liquids). Enter epithelial cells by diffusion and secondary active transport (sodium/potassium move through Na+/K+ pumps while chloride, iodide, and nitrate passively follow. Iron, magnesium, and phosphate ions enter via active transport). Intestinal calcium absorption requires vitamin D and parathyroid hormone. Electrolytes are absorbed all along the small intestine. Na+ used as co-transporter with sugars and amino acids. Chloride is exchanged for bicarbonate reversing chloride/bicarbonate exchange occurring in the stomach. Iron and calcium is absorbed as needed. Iron absorption is mainly stimulated by the liver hormone hepcidin. Absorptive cells bind ferrous ions and internalize via active transport. Unable to absorb ferric ions, but stomach acid reduces ferric ions into ferrous ions which can be absorbed. Transferrin transports iron in blood to bone marrow, muscle, and liver. Calcium is absorbed by different mechanisms- active transport in duodenum (enters through Ca+ channels in apical cell of the membrane; binds to proteins so concentration gradient continues to favor calcium influx; then actively transported out the base of the cell into the bloodstream by calcium ATPase and sodium-calcium anti-port; diffusion between epithelial cells occurs in jejunum and ileum), parathyroid hormone secreted in response to blood calcium levels, stimulates kidneys to synthesize vitamin D, vitamin D affects absorptive cells of duodenum by increasing number of calcium channels, increase amount of calbindin, and increases number of calcium ATPase pumps. Parathyroid hormone increases the level of calcium in the blood.

intestinal phase

stomach being controlled by small intestine. Stretch receptors detect distension of duodenum. Chemoreceptors detect fatty acids and glucose in duodenum (G cells secrete CCK and secretin. Reflex via medulla). Stomach contents into small intestines and absorption occurs. Release of gastrin stimulated by presence of undigested proteins. Feedback inhibition of gastric acid & pepsinogen production; reduction of gastric motility.

lipogenesis

synthesis of triglycerides by liver cells. Converts carbohydrates and amino acids to fatty acid. Glycerol and fatty acids will be recombined into triglycerides for storage. 50% of remaining fats deposited subcutaneously. Liver cells convert amino acids to fatty acids, ketone bodies, or glucose. New fats are stored for later use. When ATP and glucose levels are high lipogenesis occur. Stimulated by insulin when eating excess calories. Amino acids are converted to acetyl CoA by a deamination process and go into kreb cycle. Acetyl CoA is starting point of fatty acids. Glucose is easily converted to fat. Excess ATP leads to accumulation of acetyl CoA and glyceraldehyde 3-phosphate, so they are channeled into triglyceride synthesis pathway. Acetyl CoA join to form fatty acids (via beta oxidation where two carbons and hydrogen added while water is removed). Glyceraldehyde 3 phosphate is converted to glycerol by phosphorylation. Glycerol plus 3 fatty acid molecules and dehydration synthesis gives triglycerides.

biological reduction

the addition of electrons (hydrogen atoms to a molecule). Increase in potential energy to a molecule. Pyruvic acid to lactic acid. These reactions are coupled in the body.

biological oxidation

the loss of electrons by dehydrogenation reactions. Requires coenzymes to transfer hydrogen atoms to another compound. Common coenzymes of living cells that carry H are NAD and FAD. Energy is found in bonds between atoms. Oxidation is decrease in energy content of a molecule.

absorption of proteins

transported across via active transport process. There are transport molecules specific for amino acids depending on R group. With help of sodium transports grab single amino acid, pull inside cell, and release it. A different transport picks it up then carries side of cell near blood stream then deposits into capillaries where it enters general circulation. Amino peptidase of brush border enzymes removes amino acid from amino end of protein. Dipeptidase spits dipeptide bonds into separate amino acids which will move through cell and ultimately into bloodstream (either by sodium dependent or co-transporters). Then into capillaries through facilitated diffusion.

peptic ulcers

typically caused by H. pylori infection and long-term use of NSAID's. Tx: antibiotics, antacids, medications to reduce acid production, and promote lining of stomach/small intestine. Prevention: reduce excessive alcohol use, don't mix alcohol with medications, wash hands frequently, and reduce use of NSAID's.

dental caries and periodontal disease

typically caused by poor brushing and flossing habits that allow plaque (sticky film of bacteria) to build up on teeth and harden. In advanced stages, it leads to sore, bleeding gums, painful mastication, and tooth loss. Tx: scaling (removes tartar and bacteria), root planning, and antibiotics. Preventative measure: tooth brushing and flossing.

absorption of water

via osmosis through cell walls into vascular capillaries inside villi. Receives 9 L of water per day- 8 is absorbed by small intestine and 0.8 in large intestine. Rest is voided. Diarrhea occurs when large intestine absorbs too little water and feces passes through too quickly if intestine is irritated. Feces contains high concentration of the solute lactose. Constipation occurs when fecal movement is slow and too much water gets absorbed. Feces becomes hardened.

absorption in small intestine

villi provide massive contact surface for absorption which slip through the walls into the blood vessels to be delivered to the liver. Gluten is a protein associated with wheat, barley, and rye. Genetic problems in villi with inability to process/absorb gluten molecules.