Physiology 31 Lecture

Chapter 21 - Digestive Physiology

I. Overview

A. Introduction to the Digestive System

B. Serous Membranes & Tunics of the GI Tract

C. Motility

D. Regulation of GI Function

E. The Cephalic, Gastric, and Intestinal Phases

F. The Large Intestine

G. Disorders of the Digestive System

II. Introduction to the Digestive System

A. The food we eat must be mechanically and chemically ______to smaller molecules that can be

1. ______ through the intestinal wall

2. ______ to the cells by the blood

B. The digestive system functions to ______food, extract nutrients from it, and eliminate the residue. The stages include:

1. ______ - taking food into the mouth

2. ______digestion - chewing food; churning it in the stomach and small intestine

3. ______– movement of food through the alimentary canal; includes swallowing and ______(wavelike contractions of the GI tract)

4. ______digestion - chemical hydrolysis of macromolecules to their absorbable monomers (proteins  amino acids; carbohydrates  monosaccharides; fats  fatty acids, & glycerol; nucleic acids  nucleotides)

5. ______Secretion of enzymes, hormones and other products that carry out or regulate digestion.

6. ______ - passage of food molecules through the small intestine mucous membrane into blood and lymph capillaries for distribution to cells

7. ______ - discharge of indigestible wastes (feces) from the GI tract

C. Gut-associated lymphoid tissue (______) in the walls of the GI tract protects the body from ingested pathogens

D. Each region of the GI tract has specific ______in preparing food for utilization

5. ______cavity - grinds food and mixes it with saliva; initiates carbohydrate digestion and forms a food ______ which is swallowed and passed from pharynx to

6. ______- transports bolus to stomach by peristalsis; lower esophageal (cardiac) sphincter prevents food backflow

7. ______ - churns the bolus with gastric juices; initiates protein digestion; has some absorption; moves partially digested food (______) into the small intestine

8. _____ intestine – consists of the duodenum, jejunum, and ileum

a. ______mechanically & chemically breaks down chyme with secretions from the liver & pancreas

b. ______absorbs digested nutrients into the blood

c. ______transports indigestible matter via peristalsis to the

9. ______intestine - receives undigested wastes, absorbs water & electrolytes; forms, stores, and expels feces

E. It takes about ____-___ hrs for food to pass through the GI tract.

III. Serous membranes Tunics of the GI tract

A. ______membrane characteristics

1. Parietal ______ lines the wall of the cavity

a. Forms a double layered peritoneal fold called the ______ that holds the intestines together so they don’t become tangled during peristalsis

b. The greater & lesser ______contain many nerves, blood and lymphatic vessels, and lymph nodes that fight abdominal infections

2. ______peritoneum covers the intestinal organs

a. Peritoneal ______ is the space between the parietal and visceral peritoneum

b. ______fluid produced by the peritoneal membranes allows smooth movement of the intestines within the cavity

3. ______ is an infection of the peritoneal membranes

B. ______ of the GI Tract, from the inside out, include the mucosa, submucosa, muscularis externa, and serosa

1. ______ - thin layer that lines the GI tract lumen; consists mostly of simple columnar epithelium with goblet cells plus

b. Lamina ______ - layer of CT that contains lymphoid tissue and lies deep to the epithelial layer

c. ______mucosa – deep to the lamina propria, a thin layer of smooth muscle

2. ______ - thick, CT & vascular layer that serves the mucosa

a. Absorbed food molecules pass through the mucosa into the ______vessels or ______vessels of the submucosa

b. Also contains glands and the submucosal (Meissner) ______, that provides ANS innervation to the muscularis mucosa

3. ______externa – consists of an inner circular & outer longitudinal layer of smooth muscle

a. Rhythmic contraction of these muscles (______) moves, pulverizes, and churns food with digestive enzymes

b. ______plexus between the muscle layers provides the major ANS nerve supply to the GI tract

4. ______– visceral peritoneum that covers the intraperitoneal organs

IV. ______– smooth muscle contractions mix and move food through the GI tract

A. GI tract smooth muscle contracts ______

1. The GI tract contains ______-unit smooth muscle, with cells connected by ______junctions

2. Regions such as the anterior stomach and sphincters have sustained ______contractions

3. ______contractions of a few seconds occur in the posterior stomach and intestines

B. GI smooth muscle exhibits different patterns of ______

1. Between meals, a slow ______motor complex moves food remnants from the upper GI tract to the large intestine

2. ______meals, two types of GI contractions occur

a. ______- wave-like contractions propel food through the tract

b. ______– alternating contractions of the longitudinal and circular layers mixes food in the tract

V. ______of the digestive tract – motility and secretion is controlled by neural, hormonal, and paracrine mechanisms

A. The ______Nervous System (ENS) is an independent division of the ANS

1. Consists of the submucosal and ______plexuses

2. Can control the GI tract without _____ input

B. Neural controls include ______reflexes called short reflexes and long reflexes

1. ______reflexes involve stretching or chemical stimulation of the GI tract acting through the ______plexus to stimulate the muscularis externa for peristaltic contractions

2. ______(vasovagal) reflexes act through ANS nerve fibers that carry sensory signals to the CNS and motor commands back to the GI tract.

a. Parasympathetic innervation generally ______digestive motility and secretion

b. Sympathetic innervation usually ______digestive functions

C. Peptide ______ produced by the GI tract include gastrin, cholecystokinin (CCK), GIP, motilin, and secretin that stimulate digestive function

D. ______ secretions, such as histamine and prostaglandins, diffuse through the tissue fluids and stimulate nearby target cells

VI. The Cephalic, Gastric, and Intestinal Phases

A. Regulation of digestive function is accomplished by the nervous and ______systems during three phases: cephalic, gastric, and intestinal

B. ______phase – mental and ______stimuli lead to gastric secretion and motility via the hypothalamus, medulla oblongata, and vagus nerves

1. Chemical & Mechanical Digestion begin in the ______

a. Teeth and tongue grind food into a moist mass (______)

b. Salivary glands secrete ______, a watery solvent that cleanses teeth and dissolves food particles. Solutes include

1) Salivary ______ - enzyme that breaks starch into maltose

2) Lingual ______- enzyme that is activated by stomach acid and digests some fat after food is swallowed

3) _____, which lubricates the food mass and aids swallowing

4) ______ – enzyme that kills bacteria

5) ______globulins - proteins that inhibit bacteria and viruses

6) ______, including Na+, K+, Cl-, phosphate, and HCO3-

7) pH is about ______

2. Swallowing (______) moves food from the mouth down the esophagus to the stomach during two phases

a. ______phase – the tongue pushes the bolus against the soft palate, which signals the swallowing center in the ______oblongata, which causes the ______to cover the larynx

b. Pharyngeal-______phase – the bolus is driven downward by gravity, pharyngeal muscle contractions, and esophageal peristalsis mediated by the ______nerve plexus

c. Lower esophageal (______) sphincter between esophagus & stomach usually prevents regurgitation of food from stomach

d.Gastroesophageal reflux disease (____) involves weakness of the cardiac sphincter; allows stomach acids into the esophagus

C. Gastric phase

1. Three functions of the ______are

a. ______ food and regulates its movement through the pyloric sphincter into the small intestine

b. ______- both mechanical (churning) and chemical (initiates ______digestion)

c. ______– the acidic environment destroys many ingested pathogens; mucus protects the stomach lining

2. Swallowed food and semidigested ______stimulate gastric activity through short and long reflexes

3. Gastric ______in the gastric pits of the stomach mucosa release mucus, HCl, hormones, and some enzymes for chemical digestion

a. Mucous cells secrete ______and bicarbonate to protect the stomach lining from digestion by HCl and pepsin

b. ______cells – secrete both HCl and intrinsic factor when stimulated to do so by the vagus nerve, gastrin, or histamine

1) _____ - strong acid produced with H+ ions liberated from H2CO3 and Cl- ions exchanged for HCO3- ions during a Cl- ion shift. ______of HCl are

a) Activates ______and lingual lipase

b) Breaks up ______tissues and plant cell walls

c) Destroys ingested ______and other pathogens

2) ______factor - necessary for vit. B12 absorption in the small intestine.

3) B12 deficiency or lack of gastric intrinsic factor leads to ______anemia due to insufficient RBC production

c. ______(zymogenic) cells - secrete pepsinogen, which is cleaved to protein-digesting ______by HCl

d. G cells secrete the hormone ______when stimulated by the vagus nerve, peptides and amino acids

1) Gastrin and histamine stimulate ______secretion

2) Gastrin also stimulates the pancreas to release ______enzymes into the small intestine

3) Gastrin release is ______by somatostatin

e. D cells secrete the paracrine somato______, which inhibits HCl secretion

f. Enterochromaffin-like (ECL) cells – secrete the paracrine ______, which stimulate HCl secretion

g. Regenerative (______) cells – divide to replace cells that die

4. Gastric ______– stomach movements have two phases

a. Receptive-______response – arriving food stretches the stomach, causing it to relax

b. ______contractions of the smooth muscle churns the bolus and mixes it with gastric juices, then moves the chyme through the pyloric sphincter into the ______

5. A small amount of ______and absorption occur in the stomach

a. Salivary and gastric enzymes partially digest ______and some starch and fat in the stomach, but most digestion and nutrient absorption occurs in the small ______

b. The stomach does absorb aspirin and some lipid soluble drugs (including ______)

6. Peptic ______can occur if HCL and pepsin erode the stomach wall. The most common causes are excess aspirin and infection by the bacterium Heliobacter______, that erodes the stomach mucosa

D. Intestinal phase – acidic ______in the duodenum stimulates hormonal and nervous reflexes that initially ______the stomach, and later activate an enterogastric reflex that ______the stomach

1. Duodenal ______cells secrete the hormones secretin, cholecystokinin, and gastric inhibitory peptide

a. ______stimulates the pancreas and liver to release HCO3- into the duodenum (duodenal glands also release HCO3-)

b. Cholecystokinin (____), released when fats are present, slows gastric motility and acid secretion; also stimulates ______ release from the liver and pancreatic digestive ______

c. Gastric Inhibitory Peptide (__), secreted when carbohydrates are present, stimulates ______release from the pancreas

2. Most chemical ______and ______occurs in the small intestine. Carbohydrates, proteins, and fats are degraded and absorbed in the following manner

a. Carbohydrate (______) digestion is accomplished by the following enzymes

1) ______amylase begins starch digestion in the mouth and stomach

2) ______amylase continues starch digestion in the small intestine, hydrolyzing it into oligosaccharides and maltose

3) Small intestine ______ ______enzymes sucrase, lactase, and maltase break down sucrose, lactose, and maltose, respectively

b. Carbohydrate ______ of the resulting monosaccharides (glucose, galactose, and fructose) is facilitated across SI epithelium into the blood in the following manner

1). Monosaccharides can be transported across the ______membrane via the sodium-glucose transport protein (______), facilitated transport, or by solvent drag, in which the molecules are pulled between the cells with water

2) Once inside the epithelial cells, monosaccharides are transported through the ______membrane via a ______ facilitated diffusion transporter into the capillaries of the intestinal villus

3)The nutrients are then transported via the hepatic ______vein to the liver, where toxins are removed

c. Protein digestion

1) ______ begins protein (polypeptide) digestion in the stomach

2) ______and chymotrypsin from the pancreas continue peptide digestion in the duodenum

3) Intestinal brush border enzymescalled ______ (proteases) disassemble the resulting peptides one amino acid at a time

d. Amino acid ______is accomplished in a manner similar to that of monosaccharides (______cotransport across apical surface facilitated diffusion across basal surface villus blood capillaries  hepatic ______vein  liver)

e. Fat digestion

1) Begins with ______lipase in saliva, activated in the stomach

2) Most fat (triglyceride) is digested by ______lipase in the duodenum

3) ______salts from the liver and gall bladder help form fat into emulsification droplets

4) ______ breaks the triglycerides into free fatty acids and monoglycerides, which collect with cholesterol and fat soluble vitamins in bile-coated droplets called ______

f. Fat absorption

1) Micelles transport the lipids into intestinal ______cells

2) The absorptive cells repackage the fats into ______ droplets coated with phospholipid and protein

3) Chylomicrons are secreted from the absorptive cells and taken into lymphatic ______ in the intestinal villi

4)Chylomicrons travel in ______in the lymphatic vessels and enter the bloodstream in the subclavian veins

g. ______are not digested; they are absorbed unchanged

1) ___-soluble vitamins (__, __, __, K) are absorbed with lipids

2) Most ______-soluble vitamins (__ complex and __) are absorbed by facilitated diffusion

3) Vitamin B12 binds to ______factor, and is then absorbed by receptor mediated endocytosis

h. Minerals (______) are usually absorbed via active transport

i. Water is absorbed by ______, following an osmotic gradient established by the absorption of salts and organic nutrients

VII. The Large Intestine concentrates ______for excretion

A. Undigested ______from the ileum moves via intestinal contractions from the cecum through the ascending, transverse, descending, and sigmoid colon, into the rectum and out the anus

B. Secretion and absorption of ______and electrolytes occurs

1. Most of the water remaining in the chyme is usually ______into the blood

2. ______stimulates the absorption of Na+ and the secretion of K+ across the LI walls (as in the kidney)

3. ______results in excess secretion or inadequate reabsorption of water in the LI; and can cause ______, and even death in some cases

C. Bacterial Flora & Intestinal Gas

1. The large intestine contains numerous species of bacteria, collectively called bacterial ______

2. Bacteria ______cellulose, other undigested carbohydrates, and fats; they also synthesize ___ vitamins and vitamin ___, necessary for blood clotting

3. The average person expels about 500 ml of flatus (____) per day

E. ______ is facilitated by the following reflexes

1. Stretching of the ______triggers the intrinsic defecation reflex, mediated by the ______nerve plexus, which drives feces downward and relaxes the internal anal sphincter

2. A stronger ______sympathetic defecation reflex involves a reflex arc through the spinal cord and parasympathetic fibers of the pelvic nerve

3. These reflexes cause ______, although voluntary control of the external anal sphincter can prevent defecation

VIII. Disorders of the Digestive System

A. Viral ______– long term liver inflammation; 3 major types:

1. Hepatitis ___ – spread by _____-____ route; does not usually cause permanent damage; preventive vaccines available

2. Hepatitis ___ – transmitted by infected ______or body fluids; infection can lead to liver cancer; preventive vaccine available

3. Hepatitis ___ – transmitted by body ______; no short term symptoms; can lead to cirrhosis and liver ______; no vaccine

B. Pancreatitis – inflammation of the ______

C. ______itis – inflammed herniations (diverticula) of the colon, which can rupture. Associated with low ______diets

D. ______disease – inflammation of the small and large intestines, producing granular lesions and fibrosis of the intestines, diarrhea, and lower abdominal pain