GI: Functional Anatomy

Question 1

What comprises the GI tract?

Answer 1

• alimentary tract

- accessory glands

Question 2

List the main functions of the GI tract.

Answer 2

• motility
• secretion
• digestion
• absorption
• excretion
• immunological functions

Question 3

Describe the motility function of the GI tract. What are the outcomes?

Answer 3

• smooth muscle contractions of the GI tract propel food through the tract
• reduces food particle sizes => increased surface area for chemical enzymatic digestion
• mixes foods with enzymes
• rate of motility is optimized for digestion and absorption

Question 4

Describe the secretion function of the GI tract.

Answer 4

GI tract and glands release enzymes, mucus, water, and ions to aid in digestion and absorption

Question 5

Describe the digestion function of the GI tract.

Answer 5

Since macromolecules can’t be absorbed, the GI tract breaks them down into smaller molecules (carbs, amino acids, lipids)

Question 6

Describe the absorption function of the GI tract.

Answer 6

absorbed particles = nutrients, electrolytes, water
function = energy, catabolism, reactions, metabolism

Question 7

What does the GI tract excrete?

Answer 7

• food waste

- liver waste

Question 8

Describe the immunological functions of the GI tract.

Answer 8

• largest immune system because constantly exposed to external environment

Question 9

Track the segments of the GI tract.

Answer 9

mouth => pharynx => esophagus => stomach => duodenum => jejunum => ileum => colon => rectum => anus

Question 10

List the accessory glandular organs.

Answer 10

• salivary
• pancreas
• liver
• gallbladder
• endocrine cells

Question 11

List the sphincters in order.

Answer 11

• upper esophageal (between pharynx and esophagus)
• lower esophageal (between esophagus and stomach)
• pyloric (between stomach and duodenum)
• sphincter of Oddi (connects liver/gallbladder, pancreas, and duodenum)
• ileocecal
• external and internal anal sphincters

Question 12

How much of CO enters splanchnic circulation?

Answer 12

25%

Question 13

List the major splanchnic arteries and what organs they supply.

Answer 13

• celiac = stomach, liver, spleen
• superior mesenteric = pancreas, small intestine, ascending/transverse colon
• inferior mesenteric = descending colon

Question 14

Describe portal circulation.

Answer 14

venous blood goes first to the liver via the portal vein and then to the heart via the hepatic vein => IVC

Question 15

Describe lymphatic drainage

Answer 15

• important for lipid soluble molecules that are too large for systemic circulation
• enter the lymph vessels => thoracic duct => systemic

Question 16

List the layers of the GI tract.

Answer 16

• mucosa
• submucosa
• muscularis externa
• serosa

Question 17

List the layers of the mucosal lining.

Answer 17

• epithelium
• lamina propria
• muscularis mucosae

Question 18

Describe the following cells of the epithelial lining:

• absortive enterocytes
• enteroendocrine cells
• gastric mucosal cells
• mucin-producing cells

Answer 18

• absorptive enterocytes - vital for digestion and absorption
• enteroendocrine cells - regulation of GI tract via peptides and amines
• gastric mucosal cells - produce protons
• produce mucin

Question 19

Compare esophageal vs intestinal epithelium.

Answer 19

• esophageal = no absorptive cells; peristalsis movement

- intestinal = villi and crypts for absorption

Question 20

Describe GI lining renewal.

Answer 20

• proliferative stem cells reside in the crypts (bottom of villus)
• they travel along the villus as they grow and mature
• at the tip of the villus, they die and slough off after 3-5 days

Question 21

Describe the structure of a villus

Answer 21

crypts

microvilli brush border

Question 22

What happens if you have an impaired surface area of the villi?

Answer 22

malabsorption

ex: celiac’s disease

Question 23

Describe the lamina propria.

Answer 23

• just below epithelium
• rich in connective tissue
• contains glands: nerves, vessels, lymph

Question 24

Describe the muscular mucosae.

Answer 24

• below the lamina propria

- contraction aids in movement

Question 25

Describe the submucosal layer.

Answer 25

- rich in connective tissue - rich in nerves, lymph, and blood vessels - contains Meissner's/submucosal nerve plexus = enteric nervous system.

Question 26

Describe the muscularis externa.

Answer 26

2 layers - inner circular - outer longitudinal - contains Auerbach's/myenteric nerve plexus

Question 27

Describe the serosa layer.

Answer 27

- lines and suspends the organs | - secretes fluid to reduce friction during contraction/relaxation.

Question 28

Describe the enteric nervous system

Answer 28

- Meissner's = submucosal | - Myenteric/Auerbach's = muscularis externa