Chapter 23: The Digestive System Objectives

Trace the path of the bile from gallbladder to duodenum:

1. Bile duct 2. Hepatic duct 3. Pancreatic duct 4. duodenum

Describe how bile release into the duodenum is regulated: state the roles of cholecystokinin and secretin in this process:

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 the circulation 2. Bile secretion by liver: Bile salts returning from enterohepatic circulation are the most powerful stimulus for bile secretion. Secretin is a minor stimulus 3. Gallbladder contraction: CCK causes gallbladder contraction Vagus nerve stimulates weak gallbladder contraction during cephalic and gastric phases 4. Hepatopancreatic sphincter relaxation: CCK causes hepatopancreatic sphincter to relax. Bile and pancreatic juice enter duodenum.

How much is emitted from the stomach at a time during gastric emptying:

3 ml is released into the duodenum from the stomach

State the capacity of the stomach when empty and when full:

50 ml empty 4 L full

Describe the three structural modifications of the small intestine specialized for facilitating absorption:

Circular folds (plicae circulares): deep circular fold of mucosa; move chyme along; increase in absorption Villi: greater surface area for more absorption Microvilli: increase in absorption; increase in surface area create brush border: what makes it look fuzzy

Describe pancreatic juice and list its functional enzymes:

Clear, 1.5 L/ day: amylase lipase nucleas water, enzymes, bicarbonate ions (by epithelial cells lining the ducts) regulated by CCK and secretin pH 8

Define and describe the process of deglutition:

Coordination of tongue, soft palate, pharynx, esophagus, and over 22 separate muscle groups

Describe the digestive processes of the small intestine: state what is required, what kind of movement is used, what initiates 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 most common movement Food entering duodenum is going to stimulate

State the names of the first, second, and third parts of the small intestine:

First portion: duodenum Second portion: jejunum Third portion: ileum

Describe the epithelium and muscle content of the oro- and laryngopharynx:

Food passes into oropharynx, then laryngopharynx: stratified squamous epithelium outer layer of skeletal muscle propel food into esophagus

Define GERD and state what causes this disease:

Heartburn, the first symptom of gastroesophageal reflux disease (GERD), is the burning, radiating substernal pain that occurs when stomach acid regurgitates into the esophagus.

Briefly describe each of the six processes involved in digestion and state where each of these processes takes place:

Ingestion is taking food into the digestive tract (eating) Propulsion, which moves food through the alimentary canal, including swallowing Mechanical digestion increases the surface area of ingested food preparing for digestion Chemical digestion, enzymes secreted into the lumen of the alimentary canal Absorption is the passage of digested end products from the lumen of the GI tract Defecation eliminates indigestible substances from the body via the anus in the form of feces

Thoroughly describe the contents and properties of saliva and state the influences of the PSNS and SNS on control of saliva production:

Largely water (97% water) acidic electrolytes (Na, K, Cl, PO4, HCO3) salivary amylase (breakdown of starch and glycogen) glycoprotein mucin Lysozyme IgA metabolic wastes

Describe the large intestine:

Major function: absorb H2O from indigestible food residues and eliminate them from body as feces Anal columns lined by stratified squamous epithelium

Compare and contrast the large and small intestinal mucosa:

Mucosa is simple columnar epithelium: no circular folds, villi, nor digestive enzyme-secreting cells Mucosa thicker than in small intestine: deep crypts with mucus-producing goblet cells ease of feces movement protects wall from acids and gases produced by bacteria in colon

Describe the 3 major extrinsic salivary glands and state what kind of product each of these glands contributes to saliva:

Parotid: only serous glands (water, enzymes, ions, mucin) Submandibular: serous and mucous (produce mucous) glands Sublingual: mostly mucous glands

Describe gastric contractile activity:

Peristaltic waves act primarily in pyloric region to mix and move chyme through pyloric valve (about 3 ml at a time)

Describe the esophagus

Pierces diaphragm at esophageal hiatus enters stomach at cardiac orifice

How PSNS and SNS impacts this movement:

SNS: doesn't help sementation-has own rhythm (PSNS and SNS change it) PSNS: helps digestion

Describe the microscopic anatomy of the stomach wall:

Simple columnar lining epithelium composed of mucous cells secrete protective alkaline

Describe the pancreas and state its functions in digestion:

Tadpole-shaped, extends from tail (abuts spleen) to head it produces enzymes that break down all categories of foodstuffs

Name the largest gland in the body:

The liver digestive function: produce bile for export to duodenum Located primarily in upper right quadrant, under diaphragm protected by ribs Suspended by falciform ligament: connect to abdominal wall and diaphragm Superficially has 4 lobes: right, left, caudate, and quadrate

Define peritoneum:

The peritoneum of the abdominopelvic cavity is the most extensive of these membranes

State the site where virtually all absorption of digested nutrients takes place:

The small intestine

State what a gallstone is:

Too much cholesterol or too few bile salts-crystallization of cholesterol

Include descriptions of voluntary and involuntary phases and how involuntary phase is controlled:

Voluntary buccal phase: occurs in the mouth. It ends when a food bolus or a "bit of saliva" leaves the mouth and stimulates tactile receptors in the posterior pharynx, initiating the next phase The pharyngeal-esophagus phase is involuntary and is controlled by the swallowing center in the brain stem (medulla and lower pons)+

Explain why the digestive tract can be considered a "disassembly line".

We can view the digestive tract as a "disassembly line" in which food becomes less complex at each step of processing and its nutrients become available to the body

Epithelia:

absorptive columnar enterocytes

Peristalsis:

adjacent segments of the alimentary canal organs alternately contract and relax Food is moved distally along the tract Primarily propulsive; some mixing may occur

state why Barret's esophagitis is a good example of metaplasia:

because you can see the change in tissue

Define emulsify:

break down into smaller fluids and dilate into a fluid

Define zymogen and state how pancreatic zymogens are activated in the duodenal lumen:

cells that contain the inactivated enzymes brush border has protase, activates tripsinogen to tripsin other enzymes require ions and bile to increase activity

Define metalplasia:

changes from stratified squamous to simple columnar

Include the function and description of bile salts:

cholesterol derivatives, distribute fats throughout water intestinal contents (emulsify)

Alimentary canal (GI Tract):

digests and absorbs mouth, pharynx, esophagus, stomach, small intestine, large intesting, anus

Describe the mesentery and and state its functions:

double layer of peritoneum provides routes for blood vessels, lymphatics, nerves Holds organs in place stores fat

Discriminate between exocrine and endocrine functions of the pancreas:

exocrine: pancreatic juices it secretes endocrine: insulin and glucogon

Describe, give the location, and state the functions of the gallbladder:

green muscular sac, size of kiwi fruit found on ventral surface of liver stores bile that is not immediately needed for digestion concentrates bile by absorbing water and ions Bile expelled through its cystic duct, then flows into bile duct

Include the location and function of the Interstitial cells of Cajal and state what other factors control gastric motility:

in longitudinal muscle layer pacemaker cells set BER (Basic electrical rhythm) cyclic slow waves of stomach 3 waves/min

Define peritonitis:

inflammation of peritoneum

Lacteal:

lymphatic capillary in villi

State the sources and actions of VIP:

made by enteric neurons, stimulated by regular chyme, results in an increased pancreatic activity, slow down stomach, prepares the small intestine for absorption

State the sources and actions of secretin:

made in duodenum as a result of acidic chyme causes stomach to slow down, increases pancreatic activity, as well as liver activity

State the sources and actions of CCK (cholecystokinin):

made in duodenum, result of fatty chyme, slow down stomach, increase liver, pancreas, gallbladder

Describe and state the functions and list the products of the 4 types of secretory cells that can be seen in the gastric glands:

mucous neck cells (acidic mucus)-It is not yet understood what special function this acidic mucus performs Parietal cells secrete hydrochloric acid and intrinsic factor, activates pepsin Intrinsic factor: glycoprotein required for vit B12 absorption Chief cells produce pepsinogen Enteroendocrine cells release hormones directly into lamina propria: gastrin, histamine, endorphins, serotonin, cholecystokinin, and somatostatin (regulate stomach by secretions)

Segmentation:

nonadjacent segment of the alimentary canal organs contract and relax Food is moved forward, then backward Primarily mixes food and breaks it down mechanically; some propulsion may occur

State what is carried to the liver by portal blood:

nutrient rich blood carried to the liver

Define portal triad:

one artery, one vein, one bile duct

Retroperitoneal organs:

parts of small and large intestine, pancreas These organs, which include most of the pancreas and duodenum and parts of the large intestine

Define propulsion:

peristaltic waves move from the fondus toward pyloris

Gastric glands:

produce gastric juice

Describe how the tongue is used in sensing taste, digestion, and speech:

repositions food between teeth during chewing Helps form food bolus Helps form consonant sounds Fungiform and circumvallate papillae house taste buds

Accessory glands:

salivary glands, liver, pancreas

Describe the process of vomiting (emesis):

sensory impulses to medullary emetic center cause a reverse in the GI system, increase in abdominal pressure

Define sinusoid:

sinus veins that connects the portal triad to the central vein

Describe the oral cavity and state its function in digestion:

site for chewing, mixing, and moistening food

Describe how gastric emptying is controlled and how long the process usually takes:

stomach and duodenum work in tandem Stomach normally empties within 4 hours after a meal

Define chyme:

stomach enzymes and partially digested food

Accessory digestive organs:

teeth, tongue, gallbladder

Define lobule:

the function unit of the liver, hexagonal each have a central vein, six portal triads

State why the gastroesophageal sphincter is considered a physiological sphincter:

the gastroesophageal sphincter is used to stop back flow of food; prevents stomach acid to going up

Define grinding:

the most vigorous peristalsis and mixing action occur close to the pylorus. The pyloric end of the stomach acts a pump that delivers small amounts of chyme into the duodenum

Define retropulsion:

the peristaltic wave closes the pyloric valve, forcing most of the contents of the pylorus backward into the stomach

Pharyngeal-esophageal phase begins:

the tongue blocks the mouth the soft palate and its uvula rise, closing off the nasopharynx The larynx rises so that the epiglottis blocks the trachea. The upper esophageal sphincter relaxes; food enters the esophagus.

Buccal phase:

the upper esophageal sphincter is contracted (closed) The tongue presses against the hard palate, forcing the food bolus into the oropharynx

State the anatomical location of the stomach:

upper left quadrant of the peritoneal cavity, nearly hidden by the liver and diaphragm

Describe bile:

yello-green alkaline solution composed of bile salts, bile pigments, cholesterol, neutral fats, phospholipids, electrolytes