PSL Final

Question 1

how do the pancreas, small intestine, and liver work together in digestion?

Answer 1

Liver: bile salts + bilirubin
Pancreas: bicarbonate + enzymes

Secreted to SI

Question 2

role of small intestine in digestion?

Answer 2

peristalsis, main site for nutrient absorption, digests many nitrients

Question 3

role of large intestine (colon) in digestion?

Answer 3

mass mvmt, absorb water + electrolytes, store fecal matter

Question 4

how is the wall of the GI tract structured?

Answer 4

Four layers:
1. mucosa
2. submucosa
3. muscularis
4. serosa

also has enteric nervous system

Question 5

what are the specialized cells of the mucosa?

Answer 5

transport: secrete acid + bicarbonate, absorbs water + nutrients + vitamins

enteroendocrine: secrete hormones to blood

exocrine:
goblet - secrete mucous
paneth - secrete antimicrobial compounds

Question 6

how does nervous regulation of the digestive system work?

Answer 6

a:
external stimuli (smell food) -> sensory receptor -> cephalic brain -> neurons of myenteric and submucosal plexus -> smooth muscle or secretory cells (effectors) -> digestive system responses

b:
local stimulus (pH, stretch, etc) -> sensory receptors and neurons -> interneoruouns + cephalic brain -> same as above

c:
local stimulus -> efffectors -> same as above

Question 7

what are the structures of the enteric nervous system?

Answer 7

myenteric (A, motility) and submucosal plexus (M, secretion and absorption) -> neurons

Question 8

describe the mechanism of parasympathetic control of the digestive system

Answer 8

“Rest and Digest”
Vagus nerve (X) synapses on enteric system neurons -> acetylcholine release from postganglionic fibers -> (») gut muscle activity + relax sphincters + increase secretion

Question 9

describe the mechanism of sympathetic control of the digestive system

Answer 9

“Fight or Flight” -> no digestion
postganglionic neurons innervate GI tract _> noradrenaline release-> inhibit gut movement + constrict sphincters + reduce secretion

Question 10

how does the GI regulate its own activity?

Answer 10

pH, physical and chemical stimulation -> hormone release + other effects (peristalsis, etc)

Question 11

what is the splanchnic circulation?

Answer 11

blood goes from aorta -> hepatic artery -> capillaries throughout entire tract -> hepatic portal vein in liver -> inferior vena cava

Question 12

which arteries supply the GI tract?

Answer 12

stomach: celiac artery
SI: superior mesenteric artery
LI: super and infer m arteries

Question 13

what absorbs fats into the lymphatic system?

Answer 13

central lacteals

Question 14

how does blood flow in the liver?

Answer 14

1. hepatocytes clean blood
2. blood from hepatic portal vein and hepatic artery pools in sinusoids
3. blood goes to central veins, drains into hepatic vein, returns to heart

Question 15

how do GI smooth muscle cells operate as a single unit?

Answer 15

gap junctions join cells + action potentials travel in all directions

Question 16

how do GI smooth muscle cells exhibit electrical properties?

Answer 16

slow waves, when they reach threshold -> action potential (slow wave determines frequency) -> contraction (also force of contraction and duration)

(1) interstitial cells of Cajal = pacemaker cells-> random AP via pacemaker potential (Ca triggers) -> spread AP to other non-pacemaker cells

Question 17

compare and contrast heart and Cajal pacemaker cells.

Answer 17

Heart: uniform, depolarize 80 times per minute

Cajal: slow waves, deploraize 3/min(stomach) or 12/min(duodenum) via Ca entry

Question 18

how is GI smooth muscle potential modulated?

Answer 18

depolarization: relaxes sphincters, stim by
- acetylcholine, stretch, parasympathetics

hyperpolarization: constrict sphincters, stim by
- noradrenaline, sympathetics

Question 19

describe how deglutition (swallowing) works

Answer 19

1. tongue pushes bolus against soft palate and back of mouth -> swallow reflex
2. upper esophageal sphincter relaxes, epiglottins closes
3. food goes to esophagus via peristalsis and gravity

Question 20

describe the cranial nerves involved in voluntary and involuntary swallowing

Answer 20

Voluntary: CN 5, 9, 10, 12 (V, IX, X, XII) -> tongue moves against hard palette, respiration inhibited

Involuntary: CN 5, 7, 9, 10, 12 (V, VII, IX, XII) -> upward movement of soft palette, epiglottis closes, bases of tongue pushes food.

swallowing center in medulla and pons

Question 21

how does food from the esophagus to the stomach?

Answer 21

food stimulates vagus nerve + swallowing center -> myenteric plexus -> peristalsis and relaxation of lower esophageal sphincter -> food in stomach

Question 22

how does peristalsis move food?

Answer 22

1. contraction of circular muscles behind food
2. contraction of longitudinal muscles ahead of food (see diagram)
3. circular muscle layer contraction -> food moves forward via rhythmic pulsation

Question 23

how does the stomach accommodate and move food?

Answer 23

the vagovagal reflex links stretch of stomach to brain-> brain adjusts stomach size

peristalsis waves mix chyme -> stomach empties into duodenum

Question 24

what does segmentation in the SI do?

Answer 24

• contractions at intervals along SI
• circular muscle contract + longitudinal muscle relax -> food mixes

Question 25

how does ileocecal valve ensure one way movement from the S-LI?

Answer 25

• prevents backflow
• distension of ileum + gastroilieal reflex
• closed by distention of colon

Question 26

how does the large intestine control mass movement?

Answer 26

waves of contraction -> slow movement (5-20cm/hour)

controlled by enteric nervous system:
- PNS&raquo_space; motility
- SNS &laquo_space;motility

Question 27

how does brain trigger vomiting (emesis)?

Answer 27

vagus:
increase salvation + relax esophagus + contract pylorus

spinal nerves:
inspiration and contraction of abdominal muscles

phrenic nerve:
diaphragm descends

stomach:
undergoes reverse peristalsis