Anatomy & Physiology 2 Exam 3 Review

Gluconeogenesis

"Making glucose from new sources". Stimulated by cortisol and glucagon. Making glucose from fats and proteins aka non sugar sources. *Formation of glucose from non-carbohydrate sources, e.g. glycerol or amino acids.* This occurs during long periods of fasting or starvation where all glycogen is depleted and blood sugar levels are very low. -Glycerol and fatty acids can enter Kreb's cycle by a process of oxidation. -Ketone bodies are end products and they lead to acidosis (commoncomplication in hypoglycemic ketoacidosis in diabetics) -Amino acids can also enter Kreb's cycle by transamination (transfer of amine group).

Blood Circulation of the Liver

*Hepatic Artery (from celiac trunk)* - Brings oxygenated blood to the liver. *Hepatic Portal Vein* - Brings nutrient-rich blood from intestines to liver. *Right and Left Hepatic Veins* - Drain venous blood from the liver to the IVC

Functions of the Digestive System

-Food intake -Digestion (breaking down of food into nutrients) -Absorption -Elimination of waste products

Functions of the Liver

1. *Hepatocytes produce bile* 2. *Phagocytosis:* Sinusoids contain Kupffer cells which are macrophages 3. *Carbohydrate metabolism:* Stores glucose as glycogen 4.*Protein metabolism*: Uses amino acids to synthesize plasma proteins 5. *Stores fat-soluble vitamins* 6. *Detoxification: Especially converting ammonia (by-product of protein breakdown) to urea, which is excreted by body. Removes and breaks down circulating drugs and toxins. *

List 3 structures within the small intestine that increase the surface area

1. *Mucosal folds:* the inner surface of the small intestine is not flat, but thrown into circular folds, which not only increase surface area, but aid in mixing the ingesta by acting as baffles. 2. *Villi:* the mucosa forms multitudes of projections which protrude into the lumen and are covered with epithelial cells. 3. *Microvilli:* the lumenal plasma membrane of absorptive epithelial cells is studded with densely-packed microvilli.

Mesentery Proper

A broad fan-shaped fold of peritoneum suspending the jejunum and the ileum from the dorsal wall of the abdomen. Functions: -Allows movement -Anchors jejunum and ileum to post wall

Oxidation-Reduction (Redox)

A type of chemical reaction that involves a transfer of electrons between two species. An oxidation-reduction reaction is any chemical reaction in which the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron.

Metabolism During Postabsorptive State

About 4 hours after the last meal absorption in small intestine nearly complete *Blood glucose levels start to fall* Main metabolic challenge to maintain normal blood glucose levels: *Glucose production* -Breakdown of liver glycogen, lipolysis, and gluconeogenesis *Glucose conservation* -Oxidation of fatty acids, lactic acid, amino acids, ketone bodies and breakdown of muscle glycogen

Pharynx

Allows passage of food from mouth to the esophagus

Carbohydrates

Broken down to glucose to provide energy. Cellular Uses: Glucose is the main source of ATP especially for neurons and RBCs Dietary Sources: Monosaccharides (Sugars), Disaccharides (Sugars), Polysaccharides (Starch)

Six Main Classes of Nutrients

Carbohydrates, lipids, proteins, vitamins, minerals, water

Lipids

Cellular Uses: 1. Absorb fat-soluble vitamins 2. Triglycerides are energy source for skeletal muscle and hepatocytes 3. Phospholipids form myelin sheath and cell membrane 4. Cholesterol forms part of cell membrane. It is also a precursor of bile salts and steroid hormones. 5. Fats are protective to internal organs. 6. Insulation Dietary Sources: -Saturated fats: meat and dairy products -Unsaturated fats: seeds, nuts, and vegetable oils -Cholesterol: egg-yolk, meat, and full fat milk

Proteins

Cellular Uses: 1. Structural component of skin keratin; collagen and elastin in connective tissue and muscles. 2. Enzymes or hormones Dietary Sources: -Animal products contain all essential amino acids: eggs, milk and meats -Vegetable products lack some essential amino acids: legumes, nuts, and cereal

Cortisol

Cortisol is produced by your adrenal glands and is released in response to stress. It has many primary functions in the metabolism realm and basically functions to make energy available if needed for quick use, like if you need to escape from a risky situation (also known as the fight or flight response) Cortisol is within a class of hormones called glucocorticoid and it increases blood glucose levels: -It works against insulin to keep glucose around and breaks down glucose from stored fat to release energy (through a process called gluconeogenesis). I-t reduces protein uptake (those proteins are used in gluconeogenesis) by the muscles. So, if cortisol is around for long periods of time, it can lead to a reduction in lean muscle mass. -The release of cortisol increases blood pressure. -Cortisol suppresses the immune system because those functions aren't vital to surviving an immediate threat or stressful situation.

Where does Glycolysis occur?

Cytoplasm

Function of the Small Intestine

Digestion & Absorption 1. *Mechanical Digestion:* - Mixing food with digestive juices by segmentation 2. *Chemical Digestion* . -Brush border enzymes digest carbohydrates, proteins and nucleic acids. -Cholecystokinin (CCK) secretion is stimulated by fatty meals. Stimulates the gallbladder to contract releasing its stored bile into the duodenum. Stimulates the pancreas to release pancreatic juice into the duodenum. -Intestinal secretin stimulates secretion of bicarbonate from the pancreas. -Pancreatic juice from the pancreas completes digestion of all classes of food. -Bile from the liver and gall bladder emulsifies fats 3. *Absorption products of digestion:* -Amino acids, glucose and galactose, fatty acids) are absorbed. 4. *Paneth cells secrete lysozymes and are capable of phagocytosis.*

List the 3 regions of the small intestine in order at the beginning of the pyloric sphincter

Duodenum, jejunum, and ileum.

FAD

Electron carrier FAD is reduced to FADH2 in Citric Acid cycle, and entesr ETC and gives 2 ATP for every FADH2.

Vitamin A

Fat-soluble vitamin Source: -Beta-carotenes which are in deep yellow & green vegetables -Vit. A in fish-liver oil Importance: -Integrity of skin and mucosa -Bone and tooth development

Vitamin K

Fat-soluble vitamin Source: *Synthesized by bacteria in large intestine* Importance: *Blood clotting*

Glycogenolysis

Glycogen breakdown. When blood sugar level decreases, stored glycogen can be broken down into glucose to provide energy. Stimulated by glucagon and epinephrine. Process: Occurs when blood glucose is low. Inside the liver there are going to be some enzymes that are going to break down and release some blood glucose from inside the liver back out to the blood.

What are the 3 primary veins that send blood back to the liver via the hepatic portal vein?

Inferior mesenteric vein Superior mesenteric vein Splenic vein

Where does the Kreb's Cycle occur?

Matrix of the mitochondria

Describe physiological functions of each organ in the digestive system.

Mouth: Function: Mastication/chewing which is mechanical digestion. Chemical digestion starts here with salivary amylase enzymes which digest starch. Stomach: -Digestion. Pancreas -Chemical digestion. Gallbladder: -Chemical digestion. Liver: -Bile production for chemical digestion. Small Intestine: -Digestion and absorption. Large Intestine: -Very little digestion; but absorption of water mainly and good bacteria that work on food residue (undigested food) and some bacteria that produce vitamin K (good for blood clotting).

What substances do the goblet cells in the mucosa of the digestive tract secrete? What are two important functions of this secretion?

Mucus. Protection/movement of food.

What is the final electron acceptor in the Electron transport Chain?

Oxygen to form water

Catabolism

Reactions involved in breaking down Produces energy For example: Glycogen broken down to glucose.

Anabolism

Reactions involved in building up Consumes energy For example: Protein molecules are formed from amino acids.

Gallbladder

Small muscular organ on ventral surface of liver *Only function is storage of bile* Bile leaves gallbladder via cystic duct *Cholecystokinin* secreted by small intestine stimulates gallbladder to contract and release bile.* This occurs when fatty chyme enters the duodenum.

Minerals

Sources are milk, egg yolk and fish Stored in teeth and bones. Important for transmission of nerve impulses, muscle contraction, and blood clotting

Tooth

Structure of the Mouth Enamel: Hard outer part. Dentine: Tissue. Pulp: Located in pulp cavity. Where the blood vessels and the nerves are Gingiva: Gum Tissue Root Canal: In a root canal the pulp is removed and the nerve supply is removed.

Accessory Digestive Organs

Teeth, tongue, gallbladder, salivary glands, liver, pancreas

What is the function of the gall bladder in the digestive process? If the gall bladder is removed is there a loss of function? Why or why not?

The gall bladder stores excess bile secreted from the liver. If the gall bladder is removed excess bile cannot be stored and therefore a low-fat diet should be followed after gall bladder removal until the body can adjust.

Describe the characteristics of the blood that is carried to the liver in the hepatic portal vein

The hepatic portal vein supplies 75% of the blood to the liver, while the hepatic arteries supply the remaining 25%. Approximately half of the liver's oxygen demand is met by the hepatic portal vein, and half is met by the hepatic arteries. The hepatic portal system connects the capillaries of the gastrointestinal tract with the capillaries in the liver. Nutrient-rich blood leaves the gastrointestinal tract and is first brought to the liver for processing before being sent to the heart.

What is the importance of pancreatic acinar cells in digestion?

The pancreatic acinar cell is the functional unit of the exocrine pancreas. It synthesizes, stores, and secretes digestive enzymes.

Metabolism

The sum of all chemical reactions in the body

What is the function of the esophagus?

To carry food, liquids, and saliva from the mouth to the stomach

Fat-Soluble Vitamins

Vitamins A, D, E, K -Absorbed with fats -Stored in the body, so overdose can be harmful.

Water-Soluble Vitamins

Vitamins C and B -Absorbed in water in the GI tract -Excreted in urine, not stored in the body

Alimentary Canal (GI Tract)

aka Digestive tube Functions: Responsible for receiving, digesting and absorbing food. Includes: -Mouth -Pharynx -Esophagus -Stomach -Small intestine -Large intestine -Rectum -Anus

Liver Bile

*Bile is formed in the liver* and *drains through the common hepatic duct that joins the cystic duct (from the gallbladder) to form the common bile duct.* -The *porta hepatis* is the region on the ventral aspect where *vessels and ducts enter or leave the liver.* - *Bile has one main function which is emulsification of fats.* -Yellow-green alkaline solution consisting mainly of bile salts and bile pigment. Bile Salts: -Cholic acid and chenodeoxycholic acid Function: Emulsify fats i.e. large globules of fat entering the intestine are broken down into small fatty "emulsion" droplets that are easier to digest. Facilitate fat and cholesterol absorption. Bile Pigment: *Bilirubin* -Produced by breakdown of heme molecule which is part of hemoglobin -Metabolized in small intestine by resident bacteria and one of the products is *urobilinogen.* -Urobilinogen is excreted in feces and gives it its brown color. -Obstruction of bile duct will therefore prevent fat digestion and absorption, and result in undigested fat in feces. -If food entering small intestine is high in fat content, it stimulates secretion of intestinal secretin, which in turn increases bile secretion by liver.

Glucose Catabolism/Cellular Respiration

*Glycolysis* 1. Oxidation of glucose into pyruvic acid involves ten step of chemical reactions 2. Can occur in presence or absence of oxygen 3. Occurs in the cytoplasm of the cell 4. Final products: *Glucose → 2 pyruvic acid + 2 NADH (reduced coenzyme) + 2 ATP* *Kreb's cycle (Tricarboxylic acid cycle- TCA):* 1. Starts with pyruvic acid and involves eight steps of chemical reactions 2. *Requires oxygen: Occurs in matrix of the mitochondria* 3. End product: *Pyruvic acid → Acetyl CoA + 10 molecules of reduced coenzyme (NADH and FADH2) + 2 ATP* Electron Transport Chain (ETC) and Oxidative Phosphorylation: 1. Requires oxygen 2. Reduced coenzyme + oxygen → oxidized coenzyme + H2O 3. Transfer of electrons (H⁺) to oxygen releases large amounts of energy 4. Occurs in the inner mitochondrial membrane 5 .This energy is used to synthesize ATP ATP synthase ADP + Pi (inorganic phosphate----------→ ATP 5. *Aerobic Oxidation of one glucose molecule will result in net gain of up to 36 molecules of ATP.*

Hepatopancreatic sphincter

AKA Hepatopancreatic sphincter AKA Sphincter of Oddi AKA Ampulla of Vater AKA Hepatopancreatic ampulla Dilatation or opening formed by the common bile duct and pancreatic duct(s) as they enter the duodenum, where they empty bile and pancreatic enzymes that assist in the digestive process.

Coenzyme A

Acetyl-CoA is an important biochemical molecule in cellular respiration. It is produced in the second step of aerobic respiration after glycolysis and carries the carbon atoms of the acetyl group to the TCA cycle to be oxidized for energy production.

What is the outer layer of the esophagus called?

Adventitia Function: Protection

Pancreatic Juice

Components: 1. *Water* 2. *Enzymes:* -Proteases that digest proteins are produced in an inactive form in the pancreas thenbecome activated in the small intestine. This protects the pancreas from digesting itself. Trypsinogen → Trypsin -Amylase -Lipase -Nuclease 3. *Bicarbonate ion:* -Gives pancreatic juice its high pH to neutralize the acidic chyme that reaches the duodenum from the stomach. -*Intestinal secretin is produced by the small intestine in response to acidity of chyme coming from the stomach.* -*Intestinal secretin stimulates the pancreatic duct cells to secrete bicarbonate.*

What two activities occur in the small intestine?

Digestion and absorption

Functions of the Upper GI Organs

Digestion begins in the mouth by salivary amylase, which digests polysaccharides (carbohydrates) into smaller glucose units. The pharynx and esophagus have no digestive function, but are merely passages for food. Mastication (Chewing): Food is broken down into smaller particles is the function of the teeth aided by lips, cheek, and tongue. Deglutition (Swallowing): Controlled by the swallowing center in the medulla oblongata. It involves 22 different muscle groups and several nerves and occurs in two phases: 1. Buccal phase is under voluntary control and it is carried out by the tongue contracting against the hard palate and propelling the food bolus into the oropharynx. 2. Pharyngeal-esophageal phase is involuntary and is controlled by swallowing center in medulla and pons. Once food enters the oropharynx, all routes except the esophagus are closed: a. Tongue blocks mouth b. Soft palate blocks the nasopharynx c. Epiglottis closes the larynx and trachea Food passes down the esophagus by peristalsis, and as it reaches the gastro-esophageal sphincter, the latter relaxes and food enters the stomach.

Stomach

Digestion of proteins starts in the stomach where food is broken down into a creamy paste called *chyme.* Anatomy: *The entrance of the stomach is called the cardia* which is *followed by an upward dome called the fundus.* -This leads to the *body* and pyloric region -Ends in the *pyloric sphincter (gastro-duodenal sphincter).* Function: *Controls stomach into the duodenum.* -The lateral convex surface of the stomach is called the *greater curvature* where the *greater omentum* is attached, while the medial concave surface is termed the *lesser curvature* where the *lesser omentum* is attached. -The interior lining of the stomach contains folds called *rugae* that *increase the surface area of the stomach and allows it to expand.*

Glucagon

Hormone secreted from islets of Langerhans from pancreas. Secreted when there is a fall in blood glucose level from the normal range. Stops insulin secretion during low blood glucose levels. Increases blood glucose levels by breaking down stored glycogen and triglycerides. Overall effect: Stimulate glucose synthesis, use of ketone bodies as fuel.

Where does the Electron Transport Chain occur?

Inner mitochondrial membrane

What vessels are found within the villi? What function do these vessels serve?

Lacteals. Lacteals are part of the lymphatic system. Any fats, fat soluble vitamins and excess liquids absorbed by the villi are first moved into the lymph fluid circulation before being emptied into the blood stream. The villus structures are also involved in digestion.

Lipoproteins

Lipoproteins categorized and named according to density (ratio of lipids to proteins) Chylomicrons -Form in small intestine mucosal epithelial cells -Dietary lipids that are absorbed when we take them in, they are going to go into the adipose tissue and deposit there. Very low-density lipoproteins (VLDLs) -Form in hepatocytes -Transport endogenous lipids to adipocytes -Bad cholesterol, want low levels Low-density lipoproteins (LDLs) - "bad" cholesterol -Carry 75% of total cholesterol in blood -Can deposit cholesterol in fatty plaques -Bad cholesterol, want low levels High-density lipoproteins (HDLs) - "good" cholesterol -Remove excess cholesterol from body cells and blood -Deliver to liver for elimination -Want high levels of HDLs

Histology of the Liver

Liver is divided into liver lobules that are hexagonal in shape. In the center of each lobule runs the central vein. At each of the six corners of the lobule is the portal triad which consists of: 1. Branch of hepatic artery 2. Branch of hepatic portal vein 3. Bile duct *How things move in and out* Liver Cells: -Hepatocytes are organized in rows with liver blood-filled channels called sinusoids between the rows. -*Sinusoids also contain the hepatic fixed macrophages known as Kupffer cells that remove bacteria and debris.* -Blood from hepatic artery and portal vein percolates through sinusoids and drains into the central vein. -All central veins will eventually collect into right and left hepatic veins that drain into the inferior vena cava.

Muscularis Externa (Stomach Layers)

Longitudinal: Outer layer. Runs Vertically. Circular: Middle Layer. Thick with circular muscle. Oblique: *The innermost layer of the stomach muscle, the inner oblique layer, aids in digestion by grinding the food together with digestive juices.*

Microscopic Anatomy of the Stomach (Cells of Gastric Glands)

Muscularis externa has an additional innermost layer of oblique muscles that provides the stomach with extra strength for churning and mixing food. Mucosa has pockets called gastric pits which are lined with columnar epithelium with many goblet cells that secrete alkaline mucus. Gastric pits lead into the gastric glands that contain 4 different types of cells that secrete gastric juice: 1. Mucous Neck Cells -Secretes mucus; protects the stomach from being eroded from high levels of HCl. Important to have high levels of mucous neck cells. 2. Parietal (Oxynic) Cells: -Secretes intrinsic factor (important for absorption of vitamin b12) and hydrochloric acid (converts pepsinogen to pepsin and kills microbes). 3. Chief (Zymogenic) Cells: -Secretes pepsinogen (inactive form that needs to be activated) cannot digest proteins. The peptide bonds need to be broken to break down the proteins. Needs to be converted to pepsin so that proteins can be digested. 4. G (Enteroendocrine) Cells -Produces a hormone called gastrin. Gastrin is absorbed by the blood and stimulates gastric glands to secrete more juice (HCl and pepsinogen) and stimulates motility (stomach contractions) of the stomach. Want this to happen when we are eating.

Briefly discuss the vascular supply and neural control of the GI system

Nervous Regulation of the Digestive Tract: -There is a *plexus of nerves between the layers of the muscularis externa* called the *myenteric plexus* - Myenteric plexus *controls the motility and secretions of the digestive tract.* -*Myenteric plexus is controlled by the autonomic nervous system (ANS)* -*Parasympathetic stimulation via the vagus nerve will increase motility and secretion.* Blood Supply of the GI Tract: -Hepatic, splenic and left gastric arteries supply the liver, spleen, and stomach -The superior mesenteric artery supplies blood to the small intestine and the inferior mesenteric artery supplies blood to the large intestine. -*The hepatic portal circulation collects nutrient-rich venous blood from the intestine and conveys it to the liver for metabolic processing and storage.*

Retroperitoneal Organs

Posterior to the peritoneum; covered by peritoneum only anteriorly. Include: Duodenum, pancreas and parts of the large intestine.

Greater Omentum, Lesser Omentum, Mesentery

*Greater Omentum* -Big, thick double fold that lines the stomach. -Looks like a big curtain covering the parts of the GI tract. - Histology: Serous membrane with simple squamous ET. -Hangs from the lower border of the stomach (greater curvature of the stomach) -Has adipose tissue for fat storage and provides cushioning. -People with a lot of stomach fat; sticking on the greater omentum. *Lesser Omentum* - Smaller fold of peritoneum that extends between the liver and lesser curvature of the stomach (look for the gallbladder) Mesentery: -Peritoneum is going to make a continuous membrane which is called the mesentery. -The mesentery is tissue that is a double layer of peritoneum that loops in a certain way; so the loops of the small intestine don't move. -Prevent the long intestine from being twisted or tangled during contractions. -The mesenteries also provide passage blood vessels and nerves that supply to these organs. There is a dorsal and ventral mesentery. - Seen under the greater omentum (retracted) Function: Keeps the shape and has the pathway for arterial blood supply (artery and veins and nerves) traveling to the loops.

Major Digestive Processes

*Ingestion:* -Food intake *Propulsion*: -Movement of food distally down the GI tract by swallowing and peristalsis. -*Swallowing is a voluntary process, peristalsis is involuntary.* -Peristalsis is a wave of muscular contractions of adjacent segments of the GI tract that squeezes food down the tract. *Mechanical Digestion:* -*Chewing, mixing and churning of food.* -In the intestine, mixing of food with the digestive juices occurs by a process called *segmentation*, where non-adjacent segments of the GI tract *contract and relax* alternately to *push the bolus of food up and down within the same segment.* -The effect is to knead and churn the contents. *Chemical Digestion:* -Catabolic breakdown of food by enzymes *Absorption:* - Digested nutrients leave the GI tract and are *absorbed by blood and lymph* *Defecation:* -Undigested waste products leave the body in the form of feces.

Lipid Metabolism

*Lipid catabolism: lipolysis* Triglycerides split into glycerol and fatty acids Done in muscle, liver, and adipose tissue Enhanced by epinephrine and norepinephrine *Lipid anabolism: lipogenesis* Liver cells and adipose cells synthesize lipids from glucose or amino acids Occurs when more calories are consumed than needed for ATP production Condensed: Hormones regulate how much you break down or build up. Lipolysis: Breaking down triglycerides through exercise enhanced by hormones epinephrine and norepinephrine. Lipogenesis: If you ingest more calories then you are going to burn then it is going to end up in your fat cells.

Functions of the Large Intestine

*Main function is defecation which is movement of waste products to the outside and water absorption.* Most of food absorption occurs in the small intestine before reaching the large intestine. *There are no folds, no villi, and no cells that secrete enzymes.* *The large intestine contains mucus secreting goblet cells that facilitate movement of feces.* Good Bacteria: -The large intestine is *inhabited by bacterial flora that provide a good balance in the body against harmful bacteria.* -Some of these bacteria synthesize vitamin K (good for blood clotting) which will be absorbed by the colon. - The good bacteria works on food residue (undigested food)

Describe the histology of the visceral and parietal peritoneum.

*Peritoneum*: -Serous membrane lining the abdomino-pelvic cavity *Parietal Peritoneum:* -Layer that lines the wall of the abdominal (body) cavity. -Serous membrane that lines the parietal layer. -Serous fluid in between. *Visceral Peritoneum:* -Continuous layer that covers the external surfaces of the stomach, small and large intestine and the loops.

Thermoregulation

*The control center that functions as the body's thermostat is the hypothalamus* If core body temp is lower: Skin is going to vasoconstrict to keep warmth inside - Thyroid hormones secrete - Cellular metabolism increases Shivering so the muscles move quickly to increase the temperature If temperature is higher: -Blood vessels dilate in the skin - Sweating occurs - Metabloc rate lowered - Less thyroid hormones produced

Esophagus

-25 cm long tube that receives food from the oropharynx. -Lies posterior to trachea. -Lined with stratified squamous E.T. -Descends in the mediastinum, passes through an opening in the diaphragm and enters the abdomen. Upper Esophageal Sphincter: -Opening: Allow food to enter the stomach -Closure: Prevent esophageal air insufflation during inspiration and to prevent esophagopharyngeal/laryngeal reflux during esophageal peristalsis. Lower Esophageal (Gastro-esophageal) Sphincter: -Connects to the stomach -Prevents food from regurgitating into the esophagus and this protects the esophagus from the corrosive effect of stomach acid. -The lining epithelium changes from stratified squamous (protective) to simple columnar which is secretory in function. -The submucosa contains esophageal glands that secrete mucus to aid food in gliding down the esophagus.

Regulation of Gastric Secretion (Three Phases)

1. *Cephalic Phase (Reflex):* -Before food reaches stomach, it responds to sight, smell or thought of food. Receptors are olfactory (smell) and taste buds. -*Vagus nerve stimulates gastric secretion before food is even swallowed.* 2. *Gastric Phase:* -*Begins with the arrival of food into the stomach.* -Stretch receptors are stimulated when the stomach is distended with food. -Parasympathetic system activated to produce more gastric juice and stomach contraction. -Chemoreceptors in the mucosa of the stomach are stimulated by proteins, small quantities of alcohol, and caffeine, which will also enhance gastric secretion. 3. *Intestinal Phase:* -Starts several hours after food has been mixed and churned in the stomach.* -Each time the pylorus contracts, a small amount of chyme squirts through the pyloric sphincter and enters the duodenum. -*The function of the intestinal phase is to moderate and control the rate of gastric emptying.* -*This allows the intestine to digest smaller amounts of chyme at a time and protects the intestine from excessive acidity.* -When the intestine distends with chyme, the entero-gastric reflex is activated which will lead to: *Inhibition of Gastrin secretion* (will lead to less gastric juice and decrease in gastric motility) and *contraction of pyloric sphincter* so that the content in the stomach can be digested.

Metabolic Functions of Liver

1. Carbohydrate metabolism: -Glycogenesis -Glycogenolysis -Gluconeogenesis 2. Fat metabolism -Breakdown of fatty acids -Formation of ketone bodies c -Cholesterol synthesis -Storage of fats 3. Protein Metabolism -Transamination -Synthesis of plasma proteins -Detoxification of ammonia into urea 4. Vitamin metabolism -Stores Vitamins A, D, B12, and iron

Vitamins

1. Most vitamins act as coenzymes (help an enzyme to complete a chemical reaction). 2. Most vitamins are not made in body and need to be supplied in food Exceptions: -Vitamin D synthesized in skin -Vitamin K synthesized by intestinal bacteria 3. Some provitamins (from food) are converted in body into vitamins, e.g. beta-carotenes from carrots are converted into Vitamin A 4. Vitamins can be either water-soluble or fat-soluble. 5. Vitamins A, C, and E are antioxidants that remove free radicals from body.

Pancreas

Anatomy: - Head, body and tail. -*Pancreatic duct*: Opens into the duodenum of small intestine. *Supplies pancreatic juice which aids in digestion.* - *Hepatopancreatic sphincter (Sphincter of Oddi)*: Valvelike muscular sheath surrounding the distal pancreatic and common bile ducts as they enter the duodenum together. *Controls the flow of juices through the duodenum.* Histology: *Acini* -Secretory cells. Full of zymogen granules that *synthesize the digestive enzymes.* *Pancreatic islets (islets of Langerhans)* -Endocrine glands that *secrete insulin (beta cells) and glucagon (alpha cells)*. Play an important role in carbohydrate metabolism. Endocrine part of the Pancreas. *Duct Cells* - Secrete bicarbonate

Large Intestine

Anatomy: -Starts from ileocecal valve to the anus. -Called large because it is larger in diameter but not in length. Subdivided into: -Cecum and appendix -Colon (ascending, transverse, descending, and sigmoid) -Rectum -Anal canal -The colon has two flexures: the hepatic flexure on right side and the splenic flexure on the left side. -The outer wall of the colon shows creases that *create the appearance of a series of pouches called haustra*. -*Smooth muscle bands called teaniae coli traverse the length of the colon.* -The epiploic appendices are small pouches of the peritoneum filled with fat and situated along the colon, but are absent in the rectum.

Liver

Anatomy: Divided into four lobes: 1. *Right Lobe* (A) 2. *Left Lobe* (B) Right and Left lobe are separated by *Falciform ligament (C)* 3. *Caudate Lobe* (visible on the inferior view) 4. *Quadrate Lobe* (visible on the inferior view) -Situated in right hypochondrium and epigastrium.

NAD

Electron carrier It plays a key role in energy metabolism by accepting and donating electrons. NAD is reduced to NADH in CItric Acid Cycle and glycolysis, it then transfers electrons into electron transport chain.

Vitamin D

Fat-soluble vitamin Source: Produced in skin by UV light Importance: *Hormone responsible for calcium absorption* and mobilization of calcium from bones to blood

Vitamin E

Fat-soluble vitamin Source: Vegetable oils, nuts, whole grains Importance: *Antioxidant*

Why is increased surface area necessary in the small intestine?

Food/nutrient absorption

Intraperitoneal Organs

GI organs are enclosed by mesentery on both sides. Include: Stomach, spleen, liver, jejunum, ileum, transverse colon, and sigmoid colon.

Glycogenesis

Glycogen synthesis. Most glucose is used to generate ATP. Excess glucose is stored in the liver in the form of glycogen. Process: Insulin is going to take some of this blood glucose and take it inside the cell and it is going to make glycogen molecules out of many of those glucose molecule and store it inside the cell in the form of glycogen. Lack of insulin will have high blood glucose. Happens inside liver and muscle cells and where excess glucose is stored.

What is the function of the lymphatic tissue that is observed throughout the digestive tract?

Gut-associated lymphoid tissue (GALT) is a component of the mucosa-associated lymphoid tissue (MALT) which works in the immune system to protect the body from invasion in the gut. For example: Peyer's patches in the ileum of the small intestine. Function: -The digestive tract is an important component of the body's immune system. In fact, the intestine possesses the largest mass of lymphoid tissue in the human body. -The GALT is made up of several types of lymphoid tissue that store immune cells, such as T and B lymphocytes, that carry out attacks and defend against pathogens.

Insulin

Hormone secreted by beta cells in the islets of Langerhans from pancreas. Elevated blood glucose levels lead to secretion of insulin. Anabolic functions; reduces high blood glucose levels.

Protein Metabolism

Protein Synthesis: 1. Occurs in ribosomes 2. Regulated by hormones especially growth hormone, sex hormones, and thyroid hormones. 3. Both essential and non-essential amino acids are used in synthesis 4. Essential amino acids must be provided in diet, but the non-essential amino acids are produced in the liver. Protein Catabolism: -Breakdown of amino acids will produce ammonia which is toxic to the cells. -In the liver, ammonia is converted into urea which is eventually excreted in urine.

Basal Metabolic Rate

Rate at which metabolic reactions use energy. Whatever the metabolic rate, heat is a constant by-product of metabolic reactions, and can be expressed in calories: -A calorie (cal) is the amount of heat required to raise 1 gram of water 1°C. A Kcal is the amount of energy (heat) required to raise 1000 g of water 1°C The thyroid releases a hormone that is responsible for the basal metabolic rate. *Core body temperature comes from basal metabolic rate*: -Despite wide fluctuations in environmental temperatures, homeostatic mechanisms maintain a normal range for internal (core) body temperature at 37°C (98.6°F) -Body temperature is maintained by hormonal regulation of the BMR, exercise, and sympathetic nervous system stimulation

Mouth

Roof: Hard and Soft Palate Functions: Soft palate and uvula are mobile and they function to close off the nasopharynx during swallowing, preventing food from going back to the nose. Floor: Tongue (Surrounded by teeth) Anterior: Lips Posterior: Oropharynx Lining: *Stratified squamous epithelium* which can secrete an *antimicrobial peptide called defensin*.

Name the major food substrates and the products of the chemical process of digestion

Salivary Glands: *Salivary amylase* Function: Digests starch Esophagus: *Mucus* Function: Food movement Stomach: 1. *Hydrochloric acid (HCl)* Function: Converts pepsinogen to pepsin and kills microbes. Secreted by parietal cell. 2. *Intrinsic Factor* Function:Vitamin B12 absorption. Secreted by parietal cell. 3. *Pepsinogen* Function: Converts to *pepsin* which *digests proteins*. Secreted by chief cell. 4. *Lipase* Function: Converts triglycerides (lipids) into *glycerol and fatty acids* 5. *Mucus* Function: Protects the stomach from pepsin and HCl. Secreted by mucous neck cell. 6. *Gastrin* Function: G cell produces a hormone called *gastrin*.Gastrin is absorbed by the blood and stimulates gastric glands to secrete more juice (HCl and pepsinogen). Stimulates stomach contractions. This happens when we are eating. Pancreas: 1. *Pancreatic amylase* Function: Digests starch 2. *Trypsin and Chymotrypsin* Function: Digest proteins into peptides 3. *Lipase* Function: Converts triglycerides (lipids) into *glycerol and fatty acids* 4. *Nuclease* Function: Digestion of nucleic acids 5. *Bicarbonate* Function: Neutralizes HCl from stomach Small Intestine 1. *Brush Border Enzymes*: Maltase, Sucrase, Lactase, Peptidase (Sugars) 2. *Secretin* Function: Enteroendocrine cell secretes hormone called *secretin* which is stimulated by the acidic chyme duodeunum. Secretin stimulates release of bicarbonate which comes from the pancreas to neutralize acidic food. 3. *CCK* Function: Enteroendocrine cell secretes *CCK hormone*. Stimulated when fatty food reaches the intestine. CCK causes contraction of the gallbladder where bile is; *bile has the ability to break down fat.* -Stimulates pancreas to secrete basic bicarbonate; will stimulate pancreas to contract to release its pancreatic juice into duodenum for chemical digestion. Liver *Bile* Function: *Emulsifies fat* (breaks down larger fat globs into smaller ones for lipase to digest) Gall Bladder *Stores excess bile secreted from liver* Large Intestine *Mucus* Function: *Aids in movement of food*

The Absorptive State

Soon after a meal glucose, amino acids, and lipid nutrients enter the blood. Triglycerides enter the blood carried in large lipoproteins called chylomicrons. There are 2 metabolic hallmarks of this state: Glucose is oxidized to produce ATP in all body cells Any excess fuel molecules are stored in hepatocytes, adipocytes, and skeletal muscle cells Pancreatic cells begin to release insulin to promote entry of glucose and amino acids into cells Summary: Ate, digested, and the nutrients are being absorbed in the blood. In about 4 hours, the food has been used and some have been stored some have been absorbed.

Small Intestine

Starts at the pyloric sphincter and ends at the ileocecal valve where it joins the large intestine. Divided into 3 main parts: Duodenum, jejunum, and ileum. Duodenum: -C-shaped and it curves around the head of the pancreas. -Opening called hepato-pancreatic sphincter that opens into the duodenum that carries bile from the gall bladder and pancreatic juice from the pancreas. Ducts: -The cystic duct draining bile from the gall bladder joins the hepatic duct leaving the liver, and both form the common bile duct. -The common bile duct and the pancreatic duct will join and open together in the duodenum. Jejunum and Ileum: -The jejunum and ileum form long winding loops and they are the *main site for chemical digestion and nutrient absorption.*

In what organ of the digestive tract does the muscularis have three layers?

Stomach Longitudinal: Outer layer. Runs Vertically. Circular: Middle Layer. Thick with circular muscle. Extra Stomach Layer: Oblique: The innermost layer of the stomach muscle, the inner oblique layer, aids in digestion by grinding the food together with digestive juices.

Tongue

Structure of the Mouth -Made of skeletal muscle and it mixes food with saliva to form a bolus. *It also initiates swallowing and has a role in speech* Papillae on tongue: -Filiform papillae: When we eat they are for licking. Especially ice cream this is where you use filiform papillae. Cone shaped. Rough texture. Mechanical only. -Fungiform papillae: Specialized taste buds. Mushroom shaped. Taste receptors there is a nerve attached that goes to the brain that tells what kind of food we are eating. -Circumvallate: Surrounded by a furrow, present in one row on a V-shaped line that divides the tongue into an anterior 2/3rd and posterior 1/3rd areas. *Contains taste buds.*

Saliva

Structure of the Mouth Composed of: -97-99% water -Acidic pH (6.75-7.00) -Electrolytes (Na, K, Cl, HCO3) -Digestive enzymes: Salivary amylase and lipase -Proteins: Mucin (mucus), IgA antibody, lysozyme Functions: -Defense against microorganisms (acidity, IgA, lysozyme) - Cleanses the mouth - Dissolves food - Moistens food and forms it into a bolus Regulation of Salivary Secretion: -Salivary glands are constantly producing a small amount of saliva, a process called salivation. -*Normal daily output is 1-1.5 liters/day.* -*Parasympathetic stimulation increases secretion of saliva*. Ingested food will stimulate chemoreceptors and pressure receptors in the mouth which will *lead to increased salivary secretion.* -*Sympathetic stimulation (anxiety) inhibits salivation* and *leads to dryness of the mouth.*

Nasopharynx, Oropharynx, Laryngopharynx

Structure of the Mouth Three Regions of the Pharynx: 1. Nasopharynx: -Passage of Air (Breathing) 2. Oropharynx: -Passage of Food/Air 3. Laryngopharyx: -Passage of Food/Air

Parotid Gland

Structure of the Mouth: Salivary Gland -Anterior to ear, duct opens next to second upper molar. Can be felt in front of ear. -In children this gland may become infected by a virus causing mumps -Secretes saliva

Submandibular Gland

Structure of the Mouth: Salivary Gland -Duct opens under the tongue. Located under the mandible. -Secretes saliva

Sublingual Gland

Structure of the Mouth: Salivary Gland -Situated under the tongue, it opens by 10-12 ducts in the floor of the mouth. -Secretes saliva

Deglutination

Swallowing is controlled by the swallowing center in the medulla oblongata. It involves 22 different muscle groups and several nerves and occurs in two phases: 1. *Buccal Phase* -Voluntary control -The tongue contracts against the hard palate and propels the food bolus into the oropharynx. 2. *Pharyngeal-Esophageal Phase* -Involuntary -Controlled by swallowing center in medulla and pons -Once food enters the oropharynx, all routes except the esophagus are closed in this order: 1. Tongue blocks mouth 2. Soft palate blocks the nasopharynx 3. Epiglottis closes the larynx and trachea - Food passes down the esophagus by peristalsis, and as it reaches the gastro-esophageal sphincter, the latter relaxes and food enters the stomach. Deglutition Animation: http://www.linkstudio.info/images/portfolio/medani/Swallow.swf

What is the function of the cardiac and pyloric sphincters? What occurs if they function inadequately?

The cardiac sphincter is located at the upper portion (cardia) of the stomach. This sphincter prevents the acidic contents of the stomach from moving upward into the esophagus. The pyloric sphincter is a ring of smooth muscle at the end of the pyloric canal which lets food pass from the stomach to the duodenum (small intestine). *It controls the outflow of gastric contents into the duodenum.* If the cardiac sphincter functions inadequately then you would have GERD; or acid reflux into the esophagus and then into the mouth. If the pyloric sphincter functions inadequately then regurgitation of chyme would happen from the duodenum into the stomach.

What is the function of the mesentery?

The mesentery is formed by a double layered fold of peritoneum. Functions: -Suspends the small and large intestine from the posterior abdominal wall; anchoring them in place, whilst still allowing some movement. -Provides a conduit for blood vessels, nerves and lymphatic vessels. -Postulated to play a pathological role in inflammatory bowel diseases such as Crohn's disease.

Mesocolon

The mesentery that attaches the colon to the dorsal abdominal wall; it is called ascending, descending or transverse, according to the portion of the colon to which it attaches.

Where in the digestive tract does chemical digestion first take place?

The mouth. Salivary amylase breaks down starch.

Microscopic Anatomy of Small Intestine

The mucosa and submucosa of the small intestine form circular folds or plicae circularis that force chyme to move slowly, thus allowing enough time for absorption. VillI: In cross section these folds are made of finger-like projections called villi. -*Villi are lined by columnar epithelium with goblet cells* and *each receives a rich blood supply and has lymphatic drainage via lacteals*. -*On the free surface of villi are tiny projections called microvilli.* -Because of their fuzzy appearance they are referred to as *brush border*, and they *secrete brush border enzymes*. -Brush border enzymes complete the digestion of carbohydrates and proteins. -Between the villi are the *intestinal crypts (crypts of Lieberkuhn)* whose *cells secrete intestinal juice. Watery secretion that *aids in absorbing nutrients from chyme.* - *Duodenum also contains special duodenal glands that secrete alkaline mucus which neutralizes stomach acidity.*

Describe the tissue composition of the four layers of the alimentary canal (the mucosa, submucosa, muscularis externa, and serosa (visceral peritoneum), and discuss the general function of each layer.

Tissue Composition of the Four Layers of the Alimentary Canal: *Mucosa:* -The first innermost layer that is in direct contact with food is called the mucosa and is a type of epithelium that lines sits on a basement membrane called the *lamina propria* -Has *simple columnar ET with goblet cells that secrete mucus* to *ease passage of food down the tract.* -Only the mouth, esophagus and distal part of the anal canal are lined by stratified squamous epithelium which protects from abrasions - *Lamina propria*: underlies the epithelium and it contains loose areolar connective tissue. *Contains the lymphatic tissue (MALT) of GI tract.* - *Muscularis mucosa: smooth muscle layer* *Submucosa:* - The second layer. Esophageal gland. *This is the layer where the blood vessels are.* - Dense connective tissue containing elastic fibers. - Carries the blood and lymph vessels, lymph nodes and nerves. *Muscularis Externa:* -Third layer consisting of two layers: 1.*Inner circular (transverse)*: Circular layer 2. *Outer longitudinal layer*: Lengthwise/vertical layer -Responsible for: *Peristalsis and Segmentation* *Serosa (Visceral Peritoneum):* -Continuous layer that covers the stomach, small and large intestine and then loops and becomes the mesentery. In the esophagus it is called adventitia. -Function: *Protection*

Lipolysis

Triglycerides are broken down into fatty acids and glycerol in tissues by the help of two hormones, epinephrine and cortisol. Both glycerol and fatty acids can be further metabolized to produce energy. If the body is deprived of carbohydrates (starvation or low carbohydrate diets), lipolysis may be a major pathway for production of ATP. Excessive breakdown of fatty acids will lead to the production of larger amounts of ketone bodies which are acidic in nature. Ketosis is a condition caused by increase in the concentration of ketone bodies in the blood above normal values. This may result in acidosis (decreased blood pH) which is a potentially life threatening condition.

Vitamin C

Water-Soluble Vitamin *Ascorbic Acid* Source: *Citrus Fruits*/Vegetables Importance: *Antioxidant*

Vitamin B6

Water-Soluble Vitamin *Pyridoxine* Source: Milk, yeast, liver Importance: Conversion of tryptophan to niacin; *formation of hemoglobin*

Vitamin B2

Water-Soluble Vitamin *Riboflavin* Source: -Milk, yeast, liver Importance: - *Coenzyme FAD*

Vitamin B1

Water-Soluble Vitamin *Thiamine* Source: -Meat, liver, fish, leafy green vegetables Importance: -Coenzyme in carbohydrate metabolism; *conversion of pyruvic acid to acetyl CoA*

Vitamin B12

Water-Soluble Vitamin Source: Liver, meat, poultry. *Intrinsic factor in stomach is essential for absorption of B12* Importance: *Coenzyme in all cells, essential for DNA synthesis*

Folic Acid

Water-Soluble Vitamin Source: Liver, orange juice, green vegetables Importance: *Essential for normal neural tube development in embryo*

Niacin

Water-Soluble Vitamin Source: Most proteins (tryptophan in diet converted to niacin) Source: -*Constituent of FAD coenzyme*