Chapter 23

Question 1

Peristalis

Answer 1

Adjacent segments of GI tract organs alternately contract and relax moving food distally.

Question 2

Segmentation

Answer 2

Nonadjacent segments of alimentary tract organs alternately contract and relax, moving food forward then backward.
Food mixing and slow food propulsion occur.

Question 3

Alimentary Canal

Answer 3

Gastrointestinal tract

Question 4

What do GI mechanoreceptors and chemoreceptors respond to?

Answer 4

Respond to stretch, changes in osmolarity, pH, and presence of substrate and end products in digestion.

Question 5

What do GI mechanoreceptors and chemoreceptors do in digestion?

Answer 5

Initiate reflexes, activate and inhibit digestive glands, stimulate smooth muscle to mix and move contents in lumen

Question 6

What is peritonitis

Answer 6

Inflammation of the peritoneum via piercing wound, perforating ulcer, ruptured appendix, peritoneal coverings sticking together.

Question 7

3 layers of Mucosa

Answer 7

Epithelium - simple columnar epithelium and mucous secreting cells. Secretes mucus: Protects organs from enzyme and eases food passage. May secrete enzymes and hormones (e.g., in stomach and small intestine)

Lamina Propria - Loose areolar connective tissue, Capillaries for nourishment, absorption 
Lymphoid follicles (part of MALT), Defend against microorganisms

Muscularis Mucosae - smooth muscle – local movements of mucosa

Question 8

Submucosa

Answer 8

Areolar connective tissue surrounds mucosa

Blood and lymphatic vessels, lymphoid follicles, and submucosal nerve plexus

Question 9

Muscularis Externa

Answer 9

• Segmentation and peristalsis
• Inner circular, outer longitudinal layers
• Circular layer thickens sphincters
• Myenteric nerve plexus between layers

Question 10

Serosa

Answer 10

Visceral peritoneum
• Areolar connective tissue covered with mesothelium in most organs
• Replaced by adventitia in esophagus

Question 11

Hard palate

Answer 11

palatine bones and maxillae

Corrugated to create friction with tongue

Question 12

Soft palate

Answer 12

Mostly of skeletal muscle
Closes nasopharynx during swallowing
Uvula projects downward from free edge

Question 13

Tongue

Answer 13

Skeletal muscle
Repositioning,mixing food during chewing
Formation of bolus
Initiation of swallowing, speech, and taste
Lingual lipase is secreted by serous cells
Fat-digesting enzyme functional in stomach

Question 14

Functions of Saliva

Answer 14

Cleanses mouth
Dissolves food
Moistens food
Enzyme breakdown starch

Question 15

Two types of secretory cells in the salivary gland

Answer 15

Serous cells- Watery, enzymes, ions, bit of mucin

Mucous cells- Mucus

Question 16

Composition of Saliva

Answer 16

97–99.5% water, slightly acidic
Electrolytes: Na+, K+, Cl–, PO4 2–, HCO3–
Salivary amylase and lingual lipase
Mucin
Metabolic wastes: urea and uric acid
Lysozyme, IgA, defensins, and a cyanide compound protect against microorganisms

Question 17

Dental Caries

Answer 17

Cavities - - demineralization of enamel and dentin from bacterial action

Question 18

Teeth

Answer 18

Tear and grind food for digestion
- 20 deciduous teeth erupt (6–24months)
Roots resorbed, teeth fall out (6-12years)
Permanent dentitions formed by age21
- Third molars at 17–25, or may not erupt

Question 19

Gingivitis

Answer 19

Plaque calcifies to form calculus (tartar) which disrupts seal between gingivae and teeth
Anaerobic bacteria infect gums

Question 20

Periodontitis

Answer 20

(from neglected gingivitis)
Immune cells attack intruders, tissues
Destroy periodontal ligament
Activate osteoclasts  dissolve bone
Possible tooth loss; may promote atherosclerosis and clot formation in coronary and cerebral arteries

Question 21

Esophagus

Answer 21

Flat muscular tube from laryngopharynx to stomach
Pierces diaphragm at esophageal hiatus
Joins stomach at cardial orifice
Gastroesophageal (cardiac) sphincter

Question 22

Heartburn

Answer 22

Stomach acid regurgitates into esophagus

Excess food/drink, extreme obesity, pregnancy, hiatal hernia: Part of stomach above diaphragm

Question 23

Cellular Layers of Esophagus

Answer 23

Mucosa
Submucosa
Muscularis Externa
Adventitia (fibrous connective tissue)

Question 24

Deglutition

Answer 24

Swallowing

Question 25

Step 1: Buccal Phase of Eating

Answer 25

``` During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. ```

Question 26

Step 2: pharyngeal-esophageal phase of eating

Answer 26

The pharyngeal-esophageal phase begins as the uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus.

Question 27

Step 3: of Eating

Answer 27

``` The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters. ```

Question 28

Step 4: of eating

Answer 28

Peristalsis moves food through the esophagus to the stomach.

Question 29

Step 5: of eating

Answer 29

The gastroesophageal sphincter surrounding the cardial oriface opens, and food enters the stomach.

Question 30

Mesentaries

Answer 30

Tether stomach

Question 31

Parietal Cells

Answer 31

Secrete: Hydrochloric acid (HCl) pH 1.5–3.5 denatures protein, activates pepsin, breaks down plant cells, kills bacteria Intrinsic factor: Required for absorption of vitamin B12 in small intestine

Question 32

Chief cell

Answer 32

secretions: Pepsinogen - inactive enzyme Activated to pepsin by HCl and by pepsin itself (positive feedback) Lipases - Digest ~15% of lipids

Question 33

Enteroendocrine cell

Answer 33

secretions: Chemical messengers into lamina propria that act as paracrines Serotonin and histamine Hormones: Somatostatin and gastrin

Question 34

Mechanisms to Protect Stomach from itself

Answer 34

``` Harsh digestive conditions in stomach Has mucosal barrier to protect Thick layer of bicarbonate-rich mucus Tight junctions between epithelial cells Damaged epithelial cells quickly replaced by division of stem cells ```

Question 35

Digestive Processes in the Stomach

Answer 35

Physical digestion Denaturation of proteins by HCl Enzymatic digestion of proteins by pepsin (milk protein by rennin, infants) Lingual lipase digests some triglycerides Delivers chyme to small intestine Lipid-soluble alcohol and aspirin absorbed Only stomach function essential to life: - Secretes intrinsic factor for vit. B12 absorption mature red blood cells - Lack of intrinsic factor: pernicious anemia, treated with B12 injections

Question 36

3 phases of Gastric Secretion

Answer 36

Cephalic (reflex) phase – conditioned reflex triggered by aroma, taste, sight. Gastric phase – lasts 3–4 hours Stimulated by distension, peptides, low acidity, gastrin (major stimulus) Enteroendocrine G cells stimulated by caffeine, peptides, rising pH gastrin Intestinal Phase: Stimulatory component: Partially digested food enters small intestine brief intestinal gastrin release Inhibitory effects: Chyme with H+, fats, peptides, irritating substances Enterogastrones released Secretin, cholecystokinin (CCK), vasoactive intestinal peptide (VIP)

Question 37

Stimuli of Gastric Phase

Answer 37

Gastrin enzyme and HCl release Low pH inhibits gastrin secretion (as between meals) Buffering action of ingested proteins -- rising pH -- gastrin secretion Three chemicals - ACh, histamine, and gastrin - stimulate parietal cells

Question 38

Structural Modifications of Small Intestine

Answer 38

Circular folds: Force chyme to slowly spiral through lumen more nutrient absorption Villi: Extensions of mucosa with capillary bed and lacteal for absorption Microvilli: (brush border) – contain enzymes for carb. and protein digestion

Question 39

Cells of Intestinal Crypts

Answer 39

Intestinal crypt epithelium renewed every 2-4 days, containn secretory cells: Enteroendocrine cells: enterogastrones Intraepithelial lymphocytes: Release cytokines that kill infected cells Paneth cells: antimicrobial agents (defensins and lysozyme)

Question 40

Peyer's patches

Answer 40

protect especially distal part of small intestines against bacteria

Question 41

hepatocytes

Answer 41

``` Liver Cells increased rough & smooth ER, Golgi, peroxisomes, mitochondria Process bloodborne nutrients Store fat-soluble vitamins Perform detoxification Produce ~900 ml bile per day ```

Question 42

Hepatitis

Answer 42

Usually viral infection, drug toxicity, wild mushroom poisoning Hep C - IV Drugs, Sex, etc. Hep A - Pathogen, Ingested, replicates in liver CDC

Question 43

Cirrhosis

Answer 43

Progressive inflammation from chronic hepatitis or alcoholism Liver fatty, fibrous -- portal hypertension

Question 44

Bile

Answer 44

Secreted by the liver and stored in the Gallbladder. Yellow-green, alkaline solution Bile salts - cholesterol derivatives that function in fat emulsification and absorption Bilirubin - pigment formed from heme Cholesterol, neutral fats, phospholipids, and electrolytes

Question 45

Gallstones

Answer 45

High cholesterol; too few bile salts Obstruct flow of bile from gallbladder May cause obstructive jaundice Treated with drugs, ultrasound (lithotripsy), laser vaporization, surgery

Question 46

Pancreas

Answer 46

Endocrine function: Pancreatic islets secrete insulin and glucagon Exocrine function: Acini (clusters of secretory cells) secrete pancreatic juicev

Question 47

Pancreatic Juice

Answer 47

1200 – 1500 ml/day Alkaline solution (pH 8) neutralizes chyme Electrolytes (primarily HCO3–) Enzymes: Amylase, lipases, nucleases Proteases secreted in inactive form

Question 48

Appendix

Answer 48

Part of MALT of immune system Bacterial storehouse recolonizes gut when necessary Appenticitis: Blocked or twisted  enteric bacteria accumulate and multiply

Question 49

Large Intestine

Answer 49

Thicker mucosa of simple columnar epith. - No circular folds, villi, digestive secretions - Abundant deep crypts with goblet cells

Question 50

Bacterial Flora: Colonize colon

Answer 50

Synthesize B complex vitamins, vit. K Metabolize host-derived molecules (mucin, heparin, hyaluronic acid) Ferment indigestible carbohydrates Release acids and gases (~500 ml/day)

Question 51

Processes of Large Intestine

Answer 51

Residue remains in large intest.12–24 hrs. No food breakdown except by bacteria Vitamins (made by bacterial flora), water, and electrolytes (Na+ and Cl–) reclaimed Propulsion of feces to anus; defecation

Question 52

Haustral contractions

Answer 52

Most contractions Large Intestines Slow segmenting movements Haustra sequentially contract in response to distension

Question 53

Gastrocolic reflex

Answer 53

Initiated by presence of food in stomach | Activates three to four slow powerful peristaltic waves per day in colon (mass movements)

Question 54

Defecation

Answer 54

Assisted by Valsalva's maneuver Closing of glottis, contraction of diaphragm and abdominal wall muscles increased intra-abdominal pressure Levator ani muscle contracts  anal canal lifted superiorly  feces leave

Question 55

Diverticulitis

Answer 55

Inflamed diverticula; may rupture and leak into peritoneal cavity.

Question 56

Irritable bowel syndrome

Answer 56

Recurring abdominal pain, stool changes, bloating, flatulence, nausea Stress common precipitating factor

Question 57

Digestion of Carbohydrates

Answer 57

Monosaccharides absorbed as ingested Glucose, fructose, galactose Digestive enzymes Salivary amylase, pancreatic amylase, dextrinase, glucoamylase, lactase, maltase, and sucrase Break down disaccharides sucrose, lactose, maltose; polysaccharides glycogen and starch

Question 58

Absorption of Carbohydrates

Answer 58

Glucose and galactose Secondary active transport (cotransport) with Na+ epithelial cells Move out of epithelial cells by facilitated diffusion capillary beds in villi Fructose Facilitated diffusion to enter and exit cells

Question 59

Digestion and absorption of Proteins

Answer 59

Digestion begins in the stomach with HCl denaturing the proteins and pepsin breaking down the proteins. Pancreatic proteases (trypsin, chymotrypsin, and carboxypeptidase), and by brush border enzymes (carboxypeptidase, aminopeptidase, and dipeptidase) of mucosal cells also break down proteins even further. The amino acids are then absorbed by active transport into the apical membrane of microvilli, and move to the basal side. The amino acids leave the villi via facilitated diffusion and enter the capillary via intercellular clefts.

Question 60

Emulsification, digestion, and absorption of fats.

Answer 60

Bile salts in the duodenum emulsify large fat globules (physically break them up into smaller fat droplets). Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. These then associate with bile salts to form micelles which “ferry” them to the intestinal mucosa. Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other fatty substances and proteins to form chylomicrons. Chylomicrons are extruded from the epithelial cells by exocytosis. The chylomicrons enter lacteals and are carried away from the intestine in lymph.

Question 61

Absorption of Vitamins

Answer 61

In small intestine Fat-soluble vitamins (A, D, E, and K) Water-soluble vitamins (C and B vit.) Vitamin B12, binds with intrinsic factor In large intestine Vitamin K and B vitamins from bacterial metabolism are absorbed

Question 62

Absorption of Electrolytes

Answer 62

Most ions along length of small intestine Iron and calcium in duodenum Na+ coupled with active absorption of glucose and amino acids Cl– transported actively K+ diffuses in response to osmotic gradients; lost if poor water absorption

Question 63

Absorption of Water

Answer 63

9L water, most from GI tract secretions, enter small intestine 95% absorbed in the small intestine Most of rest absorbed in large intestine Water uptake coupled with solute uptake

Question 64

Celiac Disease

Answer 64

Immune reaction to gluten Gluten causes immune cell damage to intestinal villi and brush border Treated by eliminating gluten from diet