Anatomy - Digestive System

Describe the pancreas and state its functions in digestion. Discriminate between exocrine and endocrine functions of the pancreas. Define zymogen and state how pancreatic zymogens are activated in the duodenal lumen. Describe pancreatic juice and list its functional enzymes. Describe how pancreatic juice secretion is regulated: state the activities of CCK and secretin in this process.

- Pancreas: tadpole shaped, extends from tail to head, accessory exocrine digestive organ, produces many enzymes and breaks down all categories of food, releases pancreatic juice through pancreatic duct which fuses with the bile duct, acini within pancreas is full of RER, also has an endocrine function of islets that release insulin and glucagon - zymogen: pancreas secretes zymogens partly to prevent the enzymes from digesting proteins in the cells in which they are synthesised - Pepsinogen is activated when chief cells release it into the gastric acid, whose hydrochloric acid partially activates it. Another partially activated pepsinogen completes the activation by removing the peptide, turning the pepsinogen into pepsin. Accidental activation of zymogens can happen when the secretion duct in the pancreas is blocked by a gallstone resulting in acute pancreatitis. - pancreatic juice: clear, 1.5 L a day, pH 8, functional enzymes are protease, pancreatic amylase, lipase, nucleases - pancreatic juice is regulated the same way bile enters into the duodenum

Compare and contrast the two propulsive processes: peristalsis and segmentation.

- Peristalsis: Adjacent segments of the alimentary canal organs alternatively contract and relax, food is moved distally along the tract, primarily propulsive; some mixing may occur - Segmentation: nonadjacent segments of the alimentary canal organs alternatively contract and relax, food is moved backward then forward, primarily mixes food then breaks it down mechanically; some propulsion may occur

Describe bile: include the function and description of bile salts. Define emulsion and emulsify. Describe, give the location, and state the functions of the gall bladder. Trace the path of the bile from gall bladder to duodenum. State what a gallstone is.

- bile: yellow, green alkaline solution composed of bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes - bile salts: cholesterol derivatives, distribute fats throughout watery intestinal contents (emulsify), provide a large surface area for fat-digesting enzymes to work on, facilitate fat and cholesterol absorption, recycled through enterohepatic circulation and returned to liver via hepatic portal blood (resecreted in newly formed bile) - emulsion: a mixture of two or more liquids that are not mixable - emulsify: to mix and convert the two liquids

Describe short and long neural reflex pathways involved in changing contractile or secretory activity of the GI tract. Describe how stimuli from both within and outside the GI tract initiate these short and long neural reflexes.

- both short and long reflexes are initiated by stimuli found both within and outside the GI tract - short reflexes are mediated entirely by enteric nervous system plexuses in response to stimuli within the GI tract, pacemaker cells and reflex arcs - long reflexes involve CNS integration centers and extrinsic autonomic nerves. The enteric nervous system sends information to the central nervous system via afferent visceral fibers. Long reflexes are initiated by stimuli arising inside or outside of the GI tract

Saliva

- 97% water (hypo-osmotic) - slightly acidic - electrolytes (Na, K, Cl, PO4-, HCO3-) - salivary amylase (breakdown of starch and glycogen) - glycoprotein mucin - lysozyme - IgA - metabolic wastes

List, identify, and briefly state the functions of the organs of the digestive system including all the parts of the alimentary canal, the accessory digestive organs, and the accessory glands.

- Alimentary canal: digests and absorbs, includes the mouth, pharynx, esophagus, stomach, small intestine and large intestine - Accessory organs: teeth, tongue, gallbladder (stores bile) - Accessory glands: salivary glands, liver, pancreas

Describe the large intestine. Compare and contrast the large and small intestinal mucosa. State the functions of the large intestine (colon).

- Major function — absorb H2O from indigestible food residues and eliminate them from body as feces - mucosa is simple columnar epithelium (no circular folds, villi, nor digestive enzyme-secreting cells) - mucosa is thicker in small intestine, deep crypts with mucus-producing goblet cells give ease of feces movement and protects wall from acids and gases produced by bacteria in colon - anal columns are lined by stratified columnar epithelium

Describe the mesentery and state its functions. Define peritoneum and retroperitoneal. State which organs of the digestive system can be positioned retroperitoneal. Define peritonitis.

- Mesentery: double layer of peritoneum, provides routes for blood vessels, lymphatics, nerves, holds organs in place and stores fats - Peritoneum: serous membrane lining the abdominal cavities - Retroperitoneal: organs that have lost their mesentery during development (parts of small and large intestine, pancreas) - Peritonitis: inflammation of peritoneum and causes include burst of the appendix or a piercing abdominal wound

State where chemical digestion ends. Describe how and where carbohydrates are digested and how the monomers produced are absorbed. Describe how and where proteins are digested and how the monomers produced are absorbed. Describe sodium co-transport or secondary active transport. Describe how and where fats are digested and how the monomers produced are absorbed. Describe the role of bile salts in fat absorption.

- chemical digestion breaks down food molecules into chemical building blocks that can be absorbed (monomers) - ends in small intestine - carbohydrates are digested in the mouth and small intestine, glucose and galactose are absorbed via cotransport with Na+, fructose passes via facilitated diffusion, all monosaccharides leave the epithelial cells via facilitated diffusion and enter the capillary blood in the villi then are transported to the liver via the hepatic portal vein - proteins are digested in the stomach and small intestine and amino acids are absorbed via cotransport with Na+, some dipeptides and tripeptides are absorbed via cotransport with H+ and hydrolyzed to amino acids within the cell, transcytosis of small peptides occur, amino acids leave the epithelial cells by facilitated diffusion and enter the capillary blood in the villi and are transported to the liver via hepatic portal vein -

Define chime and state how much is emitted from the stomach at a time during gastric emptying. Describe how gastric emptying is controlled and how long the process usually takes. State the sources and actions of the following: secretin, cholecystokinin, VIP. Describe the process of vomiting.

- chime: partially digested food and stomach moves 3 ml at a time - stomach and duodenum work together for gastric emptying - stomach normally empties within 4 hours of a meal - secretin: stimulated by acidic chyme and secreted by duodenal enteroendocrine cells - cholecystokinin: stimulated by proteins and fats in chyme and secreted by duodenal enteroendocrine cells - VIP: vasoactive intestinal peptide - vomiting: sensory impulses to medullary emetic center

Describe the three structural modifications of the small intestine specialized for facilitating absorption. Define plicae circulares, brush border, and lacteal.

- circular folds: a.k.a plicae circulares (large valvular flaps projecting into the lumen of the small intestine) - villi: epithelia = absorptive columnar enterocytes - microvilli: create a brush border (the microvilli-covered surface of simple cuboidal epithelium and simple columnar epithelium cells) - lacteal: the lymphatic vessels of the small intestine that absorb digested fats.

Define and describe the process of deglutition. Include descriptions of the voluntary and involuntary phases and how the involuntary phase is controlled.

- deglutition: (swallowing) coordination of tongue, soft palate, pharynx, esophagus, and over 22 muscle groups - voluntary - involuntary: controlled by swallowing center in medulla and lower pons

Describe the digestive processes of the small intestine: state what is required, what kind of movement is used, what initiates this movement, and how PSNS and SNS impacts this movement.

- digestion and absorption of fats, carbohydrates and proteins - relies on bile, digestive enzymes, and bicarbonate ions released from liver and pancreas - segmentation is the most common movement which is initiated by interstitial cells of Cajal and those in duodenum depolarize more frequently than those in ileum (contents get moved toward ileocecal valve) - Intensity of segmentation altered by long and short reflexes and hormones, parasympathetic increases and sympathetic decreases - true peristalsis occurs after absorption

gall bladder

- green musclular sac size of a kiwi - found on ventral surface of liver - stores bile that is not immediately needed for digestion - concentrates bile by absorbing water and ions - bile is expelled through cystic duct and then flows into bile duct - too much cholesterol or too few bile salts results in crystallization of cholesterol to form gallstones

Name the largest gland in the body (location, # of lobes, and how it is suspended). Describe this gland's digestive function. Describe the functional microscopic anatomy: define lobule, portal triad, and sinusoid. State what is carried to this gland by the portal blood.

- liver is the largest gland in the body - accessory organ associated with the small intestine - 4 lobes (right, left, caudate, and quadrate) - produces bile for export to duodenum - falciform ligament suspends the liver and and separates the left and right lobes anteriorly - lobule: a small lobe - portal triad: consists of a hepatic artery branch, a hepatic portal vein branch that carries nutrients from digestive viscera, and a bile duct - sinusoid: small blood vessel found in liver

Describe the histological architecture of the alimentary canal including each of the four major layers (Mucosa, Submucosa, Muscularis externa and the Serosa).

- mucosa: epithelium, lamina propria, muscularis mucosae - submucosa: areolar connective tissue - muscularis externa: circular layer, longitudinal layer - serosa: connective tissue, epithelium (mesothelium)

Describe the oral cavity and state its functions in digestion. Describe how the tongue is used in sensing taste, digestion, and speech.

- oral cavity: site for chewing, mixing, and moistening food, is made of stratified squamous epithelium, and mucosal cells produce defensins on injury - tongue: repositions food between teeth while chewing, helps form food bolus, helps form consonant sounds, fungiform and circumvallate papillae house taste buds

Describe the epithelium and muscle content of the oro- and laryngopharynx. Describe the esophagus and state why the gastroesophageal sphincter is considered a physiological sphincter. Define GERD and state what causes this disease. Define metaplasia; state why Barrett's esophagitis is a good example of metaplasia.

- oropharnyx and laryngopharynx is composed of stratified squamous epithelium and has an outer layer of skeletal muscle that propels food into esophagus - esophagus: pierces diaphragm at esophageal hiatus, enters stomach at cardiac orifice - gastroesophageal sphincter: physiological sphincter, kept closed by diaphragm when food is not being swallowed - heartburn: first symptom of gastroesophageal reflux disease, acidic gastric juice refluxes into esophagus (GERD) - metaplasia: presence of goblet cells in the esophagus (Barret's - damage to the lower part of the esophagus)

Describe the 3 major extrinsic salivary glands and state what kind of product each of these glands contributes to saliva. Thoroughly describe the contents and properties of saliva and state the influences of the PSNS and SNS on control of saliva production.

- parotid salivary glands: only serous glands (water, enzymes, ions, mucins) - submandibular: serous and mucous (produce mucous) glands - sublingual: mostly mucous glands - salivation is increased by the PSNS (serous, enzyme rich saliva) - SNS stimulation (mucin rich saliva release) - Extremely strong sympathetic stimulation (very dry mouth)

Describe gastric contractile activity. Define propulsion, grinding, and retropulsion. Include the location and function of the Interstitial cells of Cajal and state what other factors control gastric motility.

- peristaltic waves act primarily in pyloric region to mix and move chyme through pyloric valve (about 3 ml at a time) - interstitial cells of Cajal in longitudinal muscle layer and the pacemaker cells set BER (basic electrical rhythm) at 3 waves per minute - factors increasing secretory activity also increase strength of stomach contraction - propulsion: peristaltic waves move from the fundus towards the pylorus - grinding: the most vigorous peristalsis and mixing occur close to the pylorus. The pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum - retropulsion: the peristaltic wave closes the pyloric valve, forcing most of the contents of the pylorus back into the stomach

Describe the microscopic anatomy of the stomach wall; type of epithelium, source of protective alkaline mucous, and gastric glands. Describe and state the functions and list the products of the 4 types of secretory cells that can be seen in the gastric glands.

- simple columnar epithelium - composed of mucus cells that secrete protective - gastric glands that produce gastric juice - mucus neck cells produce acidic mucus - parietal cells produce HCl which activates pepsin and also produces intrinsic factor which produces glycoprotein that is required for vitamin B12 absorption - chief cells produce pepsin - enteroendocrine cells: release hormones directly into lamina propria and produces gastrin, histamine, endorphins, serotonin, cholecystokinin, and somatostatin

State the site where virtually all absorption of digested nutrients takes place. State the names of the first, second, and third parts of the small intestine.

- site where virtually all absorption of digested nutrients takes place: small intestine - duodenum - jejunum - ileum

State the anatomical location of the stomach. State the capacity of the stomach when empty and when full.

- upper left quadrant - 50 ml when empty - 4 L when full

Pathway of bile to duodenum

1) CCK and secretin are secreted by duodenal enteroendocrine cells - CCK release is stimulated by proteins and fats in chyme - Secretin release is stimulated by acidic chyme - CCK and secretin enter circulation and cause the following four events 2) Pancreatic secretion: - CCK induces secretion by duct cells of HCO3- rich pancreatic juice - Vagus nerve weakly stimulates during cephalic and gastric phases 3) Bile secretion by liver - Bile salts returning from enterohepatic circulation are the most powerful stimulus for bile secretion - Secretin is a minor stimulus 4) Gallbladder contraction - CCK causes gallbladder contraction - Vagus nerve stimulates weak gallbladder contraction during cephalic and gastric phases 5) Hepatopancreatic sphincter relaxation - CCK causes hepatopancreatic sphincter to relax. Bile and pancreatic juice enter duodenum,

Briefly describe each of the six processes involved in digestion and state where each of these processes takes place. Explain why the digestive tract can be considered a "disassembly line".

1) Ingestion - where food is put into the mouth and swallowed 2) Propulsion - movement of food down the esophagus and contracts the food (peristalsis) 3) Mechanical digestion - in the mouth (chewing) and when the stomach, esophagus, and intestines break the food apart into particles, small intestine (segmentation) 4) Chemical digestion - in mouth where salivary amylase breaks down starch to form bolus, and in stomach where Hcl and pepsin forms chyme 5) absorption - nutrients that pass through the intestinal wall into the bloodstream 6) defecation - poop - disassembly line because as food is carried down, the body is taking what it needs as it goes

Describe how gastric secretion is regulated (stimulated and inhibited) by each of the 3 major phases (cephalic, gastric, and intestinal). State the function and source of gastrin.

cephalic phase: - stimulated by sight and thought of food, stimulation of receptors, increase in parasympathetic activity - inhibited by decrease in parasympathetic activity, loss of appetite gastric phase: - stimulated by stomach distention which activates stretch receptors, food chemicals and rising pH activate chemoreceptors - inhibited by excessive acidity and emotional stress intestinal phase: - stimulated by presence of partially digested foods in duodenum or distension of the duodenum when stomach begins to empty - inhibited: distension of duodenum presence of fatty, acidic or hypertonic chyme - gastrin: Gastrin is a peptide hormone that stimulates secretion of gastric acid by the parietal cells of the stomach and aids in gastric motility.