Exam 3 slides 5

Question 1

List the three subdivisions of the SI in order from proximal to distal.

Answer 1

o The major organ of digestion and absorption
o A convoluted tube – approximately 20 feet long in a cadaver, but 7 to 13 feet long in life
o Small Diameter: ~1 to 1.6in
o Extends from the pyloric sphincter to the ileocecal sphincter
o Primary arterial supply: SMA
o Three Subdivisions
 Duodenum
 Jejunum
 Ileum

Question 2

Contrast the diameters and lengths of the SI and LI.

Answer 2

o LI
 Diameter = ~2.8in, greater than the SI
 Length = ~5 feet
o SI
 A convoluted tube – approximately 20 feet long in a cadaver, but 7 to 13 feet long in life
 Small Diameter: ~1 to 1.6in

Question 3

Define circular folds. What is their functional importance?

Answer 3

Circular Folds: permanent folds; bumps to slow/alter the flow of chyme

Question 4

What is contained within a villus? Review what a lacteal is.

Answer 4

o Villi: fingerlike projections of mucosa
 1mm high – narrow and shorten through the length of the SI
 Core contains a dense capillary bed + a lacteal

Question 5

Define brush border. What is its physiological role?

Answer 5

o Microvilli: cytoplasmic extensions of each mucosal cell – give a fuzzy appearance called the brush border
 Brush border enzymes complete final carbohydrate + protein digestion

Question 6

List the 5 types of cells found in the SI’s villi and crypts. What is the essential function or role of each of these cell types?

Answer 6

o Enterocytes: make up the bulk of the epithelium
 In the villi, absorb nutrients and electrolytes
 In the crypts, produce intestinal juice
o Goblet Cells: secrete mucus in the villi and crypts
o Enteroendocrine: source of enterogastrones – hormones that inhibit secretion
o Paneth Cells: secretory cells found deep in the crypts – secrete antimicrobial agents
o Stem Cells: continuously divide to produce other cell types – epithelium is renewed every 2-4 days

Question 7

What is a Peyer’s Patch? A duodenal gland?

Answer 7

o MALT: protects intestine from microorganisms
 Individual Lymphoid Follicles
 Peyer’s Patches: aggregate lymphoid nodules, located in the lamina propria
* Found in greater numbers in the distal SI – along with large numbers of IgA secreting plasma cells
o Submucosa
 Duodenal Glands: secrete alkaline mucus to neutralize acidic chyme and prevent duodenal ulcers

Question 8

Contrast intestinal juice with digestive juice.

Answer 8

o 1-2L are secreted daily in response to distension or irritation of the mucosa
o Production stimulated by acidic chyme
o Slightly alkaline, isotonic with blood plasma
o Largely water + mucus from the duodenal glands and goblet cells

Question 9

Why is the slow pace of chyme entering the SI crucial? – there’s a couple reasons!

Answer 9

o Regulation of Chyme Entry
 Chyme entering the duodenum is hypertonic – to avoid water loss from blood, chyme entry must be slow
 Additionally, acidic chyme must be neutralized
 It takes time for chyme to be mixed with bile and pancreatic juices
o The enterogastric reflex and enterogastrones prevent overfilling by controlling movement of food into the duodenum

Question 10

What valve controls the entrance of chyme into the LI?

Answer 10

o Ileocecal Valve: typically closed; relaxes to admit chyme into the LI; closes to prevent regurgitation

Question 11

Define the gastroileal reflex.

Answer 11

o Gastroileal Reflex: a long neural reflex triggered by stomach activity – force of segmentation is increased in the ileum and the ileocecal valve relaxes

Question 12

What are the key functions of the LI? What types of vitamins are produced in the LI and why are they important?

Answer 12

o Functions: reabsorb most of the remaining water from indigestible food residue, temporarily store residue, absorb metabolites produced by resident bacteria, and eliminate residue from the body as semisolid feces

Question 13

Describe tenae coli, haustra, and haustral contractions.

Answer 13

o Teniae Coli: 3 bands of longitudinal smooth muscle in the muscularis
o Haustra: pocketlike sacs caused by the muscular tone of the teniae coli
o Epiploic Appendages: fat-filled pouches of visceral peritoneum
o Haustral Contractions: primary contractions of the colon; slow, segmenting movements primarily in the ascending and transverse colon; haustra sequentially contract in response to distension

Question 14

Be prepared to label the subdivisions and major landmarks of the LI.

Answer 14

o Cecum: 1st part of the LI, continuous with the ileum of the SI
o Appendix: contains masses of lymphoid tissue
 Part of MALT
 Storehouse for bacteria, capable of recolonizing gut when necessary
 Susceptible to blockages because of twisted shape
o Colon: has several regions, some regions are retroperitoneal, but the transverse and sigmoid portions are peritoneal
 Ascending Colon: travels up the R side of the abdominal cavity
 Ends in R angle turn = right colic (hepatic) flexure
 Transverse Colon: travels across the abdominal cavity
 Ends in R angle turn = left colic (splenic) flexure
o Colon (Continued)
 Descending Colon: travels down L side of the abdominal cavity
 Sigmoid Colon: S-shaped portion that travels through the pelvis
o Rectum: three rectal valves or transverse folds
o Anal Canal: last segment, opens to the exterior, well developed muscularis
 Internal Anal Sphincter: smooth muscle
 External Anal Sphincter: skeletal muscle

Question 15

List the functions of the appendix.

Answer 15

Appendix: contains masses of lymphoid tissue
Part of MALT
Storehouse for bacteria, capable of recolonizing gut when necessary
Susceptible to blockages because of twisted shape

Question 16

Which of the anal sphincters is under voluntary control? Involuntary control?

Answer 16

Parasympathetic signals stimulate contraction, and the internal anal sphincter relaxes
The external anal sphincter requires voluntary relaxation

Question 17

Appreciate the roles of the goblet cells, stratified epithelium, and the anal columns in the LI.

Question 18

What does your gut microbiome do? What impacts might it have on your health? List some things that determine the unique composition of your gut microbiome.

Answer 18

o Mounting evidence supports findings that the kinds and proportions of our gut bacteria can influence our:
 Body weight
 Susceptibility to various diseases – diabetes, atherosclerosis, fatty liver disease
 Allergies
 Moods/mental health

Question 19

Define the gastrocolic reflex.

Answer 19

o Gastrocolic Reflex: initiated by the presence of food in the stomach; causes mass movements: slow, powerful peristaltic waves that are activated 3-4 times/day

Question 20

What causes diverticula?

Answer 20

o A low-fiber diet can result in low residue volume and a narrowed colon – contractions became more powerful and increase pressure on the colon’s walls
o Diverticula: herniations of mucosa through the colon’s walls
o Diverticulosis: presence of diverticula
 Most common in the sigmoid colon
 50% of people over 70 years old
o Diverticulitis: inflammations of diverticula – may rupture and leak into the peritoneal cavity. Can be life threatening.

Question 21

Know the causes and implications of diarrhea and constipation.

Answer 21

o Diarrhea: watery, loose stools; LI does not have time to absorb remaining water
 Causes: irritation of the colon by bacteria, jostling of digestive viscera
 Prolonged diarrhea may result in dehydration and electrolyte imbalances
o Constipation: food residue remains in the colon for extended periods of time; too much water is absorbed
 Stool becomes hard and difficult to pass
 Causes: insufficient fiber and/or fluid in the diet, improper bowel habits, lack of exercise, or laxative abuse