Structure and function of GI tract 2

Question 1

Two purposes of motility

Answer 1

Moving food from mouth to the anus

Mechanically mixing food to break it down into small particles

Question 2

How is GI motility controlled

Answer 2

Determined by properties of GI smooth muscle

Modified by chemical inputs from nerves, hormones and paracrine signals

Question 3

What are the different types of contraction

Answer 3

Tonic contraction - sustained for minutes/hours; occur in some SM sphincters and anterior stomach
Phasic contractions - contraction - relaxation cycles lasting only a few seconds; occur in posterior stomach and in SI

Question 4

Where do slow wave potentials originate

Answer 4

Interstitial cells of Cajal

Question 5

How do slow waves spread

Answer 5

Through gap junctions

Question 6

What happens when slow waves reach threshold value

Answer 6

Voltage gated Ca2+ open

Ca2+ enters and cell fires one or more action potential

Question 7

What are the 3 patterns of muscle contraction

Answer 7

Migrating motor complex
Peristalsis
Segmental

Question 8

WHat is the migrating motor complex

Answer 8

Occurs between meals when the tract is largely empty; each contraction takes around 90 minutes to reach large intestine; sweeps food remnants and bacteria out of upper GI tract into large intestine

Question 9

What is peristalsis

Answer 9

Progressive waves of contraction that move form one section of the GI tract to the next; circular muscles contract behind a mass of food which pushes the mass into a receiving segment where circular muscles are releaxed; receiving segment then contracts pushing mass furthur forward

Question 10

Segmental muscle contraction

Answer 10

Short segment of intestine alternately contract and relax; circular muscles contract while longitudinal muscles relax; can occur both randomly and at regular intervals; these alternating contractions churn the intestinal contents, mixing them and keeping them in contact with the absorptive epithelium

Question 11

Functions of gastric acid

Answer 11

Causes release and activation of pepsin
Triggers somatostatin release from D cells
Denatures proteins by breaking bonds within their tertiary structure
Kills bacteria and microoganisms
Inactivates salivary amylse, halting carbohydtae digestion

Question 12

What is the acid secretion pathway

Answer 12

H+ ions from water inside parietal cells is pumped into the stomach via H+ -K+ -ATPase in exchange for K+ entering the cell
Cl- follows the gradient created and moves thorugh open chloride channels
Net result of HCL secretion by cell

Question 13

How is HCl produced in pairetal cells

Answer 13

Via H+/K+ ATPases

Question 14

What 3 neurohormonal secretagogues increase acid production

Answer 14

Histamine
Gastrin
Acetylcholine

Question 15

What decreases acid production

Answer 15

SOmatostatin - inhibition of gastrin, hisamine and parietal cells
Prostaglandin - decrease basal and stimulated acid secretion

Question 16

What are the two enzymes produced by the stomach

Answer 16

Pepsin - initially pepsinogen then cleaved to form pepsin

GAstric lipase - cosecreted with pepsin

Question 17

What are the paracrine secretion in stomach

Answer 17

Histamine - stimulates acid secretion
Intrinsic factor - complexes with vit B12 to help it’s absorption in intestine
SOmatostatin - stops acid secretion and inhibits pepsinogen secretion

Question 18

What are intestinal secretions

Answer 18

Digestive enzymes
Bile
Bicarbonate secretion
Mucus
Isotonic NaCl solution

Question 19

What is mucus

Answer 19

Viscous secretion composed primarily of glycoproteins collectively known as mucins

Question 20

Function of mucus

Answer 20

Primary function of mucus are to form protective coating over GI mucosa and lubricate contents of the gut
Infection and inflammation causes substantial secretion of mucus

Question 21

What is the mucus bicarbonate barrier

Answer 21

while acid is being secreted into lumen, bicarbonate is formed and absorbed in the blood
Buffering action of HCO3- makes blood leaving stomach less acidic
Bicarbonate neutralizes acid and protects the gastric mucosa from autodigestion
Mucus forms a physical barrier and bicarbonate forms chemical barrier

Question 22

What is bicarbonate secreted via

Answer 22

Cl- — HCO3- exchanger

Question 23

Course or chlorine ion in bicarbonate secretion

Answer 23

Chlorine enters cells by indirect active transport and leaves the apical side through a CFTR channel Cl- then reenters the cell in exchange for HCO3-