19. Chapter 21- The Digestive System

Question 1

What is the primary function of the digestive system?

Answer 1

Move nutrients, water and electrolytes from the external environment into the body’s internal environment
Main thing needed for regulation and integration of metabolic processes throughout the body
Proper functioning needed for homeostasis
10% of health care costs are GI system

Question 2

What is the anatomy of the digestive system?

What is the GI tract?

Answer 2

Extends from mouth to large intestine (15 feet length average)
GI tract: long tube with muscular walls lined by transporting and secretory epithelial (digestion primarily occurs here)
Stomach to anus is the gut!
So it’s mouth to anus

Question 3

What do the three pairs of salivary glands do with the beginning of digestion in the mouth? (4 things)

Answer 3

1. Moisten and lubricate food
2. Amylase partially digests polysaccharides
3. Dissolve some food molecules (taste)
4. Lysozyme kills bacteria

Slide 5 Feb 25

Question 4

What is the esophagus?

What parts are skeletal and smooth muscle?

Answer 4

Passageway from mouth to stomach
Upper and lower esophageal sphincters
Top 1/3 is skeletal muscle, bottom 2/3 is smooth muscle

Moves food via peristaltic waves

Slide 6 Feb 25

Question 5

What is the small intestine? (3 parts)

What is the large intestine? (3 parts)

Answer 5

Small intestine- majority of digestion takes place here
First 25 cm is duodenum
Then jejunum
Then ileum
Slide 7 Feb 25
Large intestine- (colon) larger diameter but shorter, made of ascending colon, transverse colon, and descending colon
Water and electrolytes removes to create semisolid feces
Feces entering the terminal section of the large intestine (rectum) trigger a defecation reflex

Question 6

What are the GI layers? (4 of them)

Slide 9-10 Feb 25!

Answer 6

Slide 9-10 Feb 25
Mucosa
Submucosa
Muscularis externa
Serosa

Question 7

What is mucosa?

What’s it made of? (3 things)

Answer 7

First layer of GI tract
Epithelium- transporting epithelial cells, endocrine and exocrine secretory cells, shirt life span always making new cells
Lamina propia- contains nerve fibres, small blood vessels and lymph vessels
Muscularis mucosae- thin layer of smooth muscle that can alter surface area available for absorption
Slide 11-12 Feb 25

Question 8

What is the submucosa?

Answer 8

Seconds part of GI tract below mucosa
Middle distensible layer containing larger vessels (lymph and blood) and the submucosal plexus; one of the major nerve networks in the enteric nervous system
Slide 15 Feb 25

Question 9

What is the muscularis externa?

What is the serosa?

Answer 9

Muscularis externa: 2 layers of smooth muscle: circular decrease diameter, longitudinal shortens the tube, contains myenteric plexus
Serosa- outer covering of connective tissue that is a continuation of the peritoneal membrane, sheets of mesentary hold intestines in place
Slide 16 Feb 25

Question 10

What are the 4 steps of the digestive function and processes?

Answer 10

1. Digestion- chemical and mechanical breakdown of food into absorbable units
2. Secretion- movement of material from cells into lumen or ECF
3. Absorption- movement of material from GI lumen to ECF
4. Motility- movement of material through the GI tract as a result of muscle contraction
   Slide 17 Feb 25

Question 11

What are the 3 fluid secretions?

Answer 11

Water- ions transported from ECF into the lumen
Digestive enzymes- exocrine glands and epithelial cells in stomach and small intestine
Mucus- viscous glycoprotein (mucins) secretions that protect GI cells and lubricate the contents

Question 12

What is motility in the digestive system?

Answer 12

1. Moves food from mouth to anus
2. Mechanically mixing food breaks it into uniformly small particles
   This is determined by properties of smooth muscle and modified by chemical input

Slow waves originate in a network of cells known as interstitial cells of cajal (ICC)
Modified smooth muscle cells serve as pacemaker for slow wave activity

Question 13

What are the 3 basic patterns of contraction that occur in the GI system bringing about different types of movement?

Answer 13

1. Migrating motor complex (motilin)
   Between meals
   Begins in the stomach and slowly passes from section to section, sweeps food remnants and bacteria out of upper GI tract and into the large intestine
2. Peristaltic contractions- responsible for forward movement
3. Segmental contractions- responsible for mixing
   Slide 9-10 Feb 27

Question 14

What are enteric nervous system (ENS) reflexes? (Short and long reflexes)

Answer 14

Short reflexes originate in the enteric nervous system and are carried out entirely within the wall of the gut
Long reflexes are integrated in the CNS, some long reflexes originate outside the GI tract but others originate in the enteric nervous system

Question 15

What are GI peptides?

Answer 15

Hormones, peptides and cytokines
Can act as hormones or paracrine signals
Excite or inhibit motility and secretion
Can be secreted in to lumen to act on apical membrane receptors or ECF to act on neighbouring cells

Question 16

What are the 3 hormone families?

Answer 16

Gastrin family- gastrin, cholecystokinin
Secretin family- secretin, vasoactive intestinal peptide, gastric inhibitory peptide
Other- motilin

Question 17

What are the 3 phases of integrated function within the digestive system?

Answer 17

1. Cephalic/oral phase- digestive processes occurring before food enters the stomach
   Long reflexes beginning in the brain, increased parasympathetic output from medulla to salivary glands and to the enteric nervous system
2. Gastric phase- digestive processes in the stomach, 3.5L of food drink and saliva enter the stomach each day, storage digestion and defence are the functions of the stomach
3. Intestinal phase- digestive processes in the intestines

Question 18

How does mechanical digestion start?

Answer 18

Begins with mastication (chewing) of food by teeth
Tongue and lips he’ll manipulate food
Joined by a flood of saliva from the three pies of salivary glands (exocrine secretion) 1.5L/day 99.5% water 0.5% solutes

Question 19

What is the parotid gland, submandibular gland, and sublingual gland?

Answer 19

Parotid gland- watery solution with amylase
Submandibular- similar to parotid plus some mucus
Sublingual- mainly mucus

Slide 9 Mar 1

Question 20

What is deglutition? 3 steps

Answer 20

Reflex that pushes a bolus of food or liquid into the esophagus

1. Tongue pushes bolus against soft palate and back of mouth, triggering swallowing reflex
2. Breathing is inhibited as the bolus passes the closed pathway
3. Food moves downward into the esophagus, propelled by peristaltic waves and aided by gravity

Question 21

What is the gastroesophageal reflux disease (heartburn)?

Answer 21

Churning action if stomach contraction can cause backflow
Negative intrapleural pressure during inspiration can cause esophagus to expand drawing gastric acid and pepsin from the stomach
Slide 12 Mar 1

Question 22

What happens to the stomach upon swallowing food?

Answer 22

Parasympathetic neurons to the ENS cause the fundus if the stomach to relax: receptive relaxation
Distension of stomach enhances motility

Weak peristaltic waves (15-25 seconds) that increase in force proceeding down to the antrum moves chyme toward pylorus and then larger particles are moved back to the body

Slide 14-15 Mar 1

Question 23

What is the stimuli for acid secretion?

Answer 23

Apical H+/K+ ATPase, Cl- and K+ transporters stored in vesicles

Stimuli cause exocytosis and insertion of apical transporters

Slide 4 Mar 4

Question 24

What is digestive enzyme secretion?

Answer 24

Stimulated by acid secretion via short reflex

Chief cell

Slide 7 Mar 4

Question 25

What is paracrine secretion?

Answer 25

ECL- histamine Activated H2 receptors on parietal cells to stimulate HCl secretion Parietal cell- intrinsic factor - forms a complex with Vit B12 so it can be absorbed D cell- somatostatin - negative feedback for acid secretions (G cells, parietal cells and ECL cells) - inhibits pepsinogen release Slide 8-9 Mar 4

Question 26

What is mucus secretion?

Answer 26

Mucus and HCO3- secreted from mucous cells - mucus secretion stimulated by parasympathetic input and irritation - HCO3- by parasympathetic input and H+ Slide 10 Mar 4

Question 27

What is a peptic ulcer?

Answer 27

A sore or break in the lining of the stomach or duodenum Helicobacter pylori Slide 11 Mar 4

Question 28

What is the intestinal phase of digestion?

Answer 28

5.5 L of food fluid and secretions enter small intestine and 3.5 L form hepatic pancreatic and intestinal Combo of segmental and peristaltic contractions mix the chyme with enzymes and expose digested nutrients to mucosal epithelium for absorption Plicae and villi (secrete mucus) increase surface area Crypts contain hormone and fluid secretory cells + stem cells Most nutrients absorbed into capillaries in the villi Slides 15-17 Mar 4

Question 29

What does the pancreas do?

Answer 29

Contains endocrine secretory epithelium (islets): insulin and glucagon Exocrine secretory epithelium: digestive enzymes and NaHCO3 Many pancreatic digestive enzymes released as zymogens Trypsin activates zymogens Bicarbonate produced in duct cells neutralizes acid entering stomach Slide 5-8 Mar 6

Question 30

What does the liver do?

Answer 30

Slides 9-10 Mar 6 Largest internal organ lying under diaphragm Bike: a non enzymatic solution secreted from hepatocytes 3 components: bile salts, bile pigments, cholesterol

Question 31

What is fat digestion?

Answer 31

Fats and related molecules (triacylglycerols, cholesterol, phospholipids, ling chain fatty acids, fat soluble vitamins) are put into fat droplets then a coarse emulsion of large fat droplets in chyme broken to smaller, stable particles by bile salts Slides 11-12 Mar 6

Question 32

What is fat absorption? (5 steps)

Answer 32

1. Bile salts from liver cost fat cells 2. Pancreatic lipase and colipase break down fats into monoglycerides and fatty acids stored in micelles 3a. Monoglycerides and fatty acids move out of micelles and enter cells by diffusion 3b. Cholesterol is transported into cells 4. Absorbed fats combine with cholesterol and proteins in the intestinal cells to form chylomicrons 5. Chylomicrons are removed by the lymphatic system Slide 13 mar 6

Question 33

What are gallstones?

Answer 33

Hardened deposits likely due to excess cholesterol or bilirubin Upper right abdominal pain, jaundice Gallbladder removal Slide 14 Mar 6

Question 34

What is carbohydrate digestion and absorption?

Answer 34

Slides 15-16 Mar 6 Digestion: starch and sucrose Amylase break down glucose polymers to disaccharides, then these are broken down by intestinal brush border enzymes (disaccharidases) Absorption: glucose galactose fructose Normally glucose is phosphorylated when entering a cell, but enterocytes primarily use glutamine so glucose 6 phosphate is not formed and free glucose stays high facilitating transport

Question 35

What is protein digestion?

Answer 35

Slide 17 mar 6 and slide 3 Mar 8 Not all proteins are digestible Attack peptide bonds in the amino chain forming fragments Results primarily in free amino acids, dipeptides and tripeptides

Question 36

What is protein absorption?

Answer 36

Proteins absorbed mostly as free amino acids, a few di and tripeptides are absorbed Single AA’s on Na cotransporters (apical) and Na exchangers (basolateral) Di and tripeptides on oligopeptide transporter (H+ transporter) Slide 4-5 Mar 8

Question 37

What is vitamin and mineral absorption? | What is ion and water absorption?

Answer 37

Slide 6 Mar 8 Fat soluble vitamins (A, D, E and K) absorbed with fats Water soluble (C and most B) are absorbed by mediated transport B12 is absorbed in the ileum after forming a complex with intrinsic factor released from parietal cells Slide 7 Mar 8 Most water absorbed in the small intestine This same mechanism exists in the colon

Question 38

How is the intestinal phase regulated?

Answer 38

Regulated by distension, acidity, and digestive products in the small intestine through short and long reflexes and endocrine signaling Reduces motility and secretions in the stomach, increases in the intestine Slide 9 Mar 8 Intestinal motility primarily by ENS neurons Mo cell-motilin (migrating motor complex) S cell: secretin I cells: cholecystokinin K cells: glucose-dependent insulinoteopic peptide (GIP) L cells: glucagon like peptide 1 (GLP-1)

Question 39

``` What are S cells? What are I cells? What are K cells? What are L cells? Slides 10-13 Mar 6 ```

Answer 39

S cells- secretin, stimulated by acid entering the duodenum from the stomach (primary role is regulation of pH) (stimulates bicarbonate secretion from pancreas and inhibition of gastric acid secretion) I cells- cholecystokinin (CCK) stimulated by presence of fatty acids and amino acids in chyme. Regulates pancreatic enzyme secretion and regulates bile secretion K cells- GIP, glucose homeostasis, inhibit gastric acid secretion L cells- GLP-1, glucose homeostasis, inhibit gastric acid secretion

Question 40

How is gastric and intestinal phase integrated?

Answer 40

Enterogastric reflex Acid, enzymes and digested food results in hyperosmotic chyme that inhibits gastric emptying

Question 41

Which intestine concentrates waste?

Answer 41

The large intestine stores and concentrates fecal manner 1.5 L of chyme proceed through ileocecal valve (valve relaxes as contraction proceeds through ileum, food in stomach causes contraction of ileum and relaxation of ileocecal valve (gastroileal reflex)) Slide 15 Mar 8

Question 42

What are secretions and digestions?

Answer 42

Secretions- minimal and primarily consists of mucus from goblet cells Digestion- traditionally believed that zero digestion occurs in the large intestine Slide 16 Mar 8