Lecture 33

Question 1

List some of the accessory organs of the GI tract, as well as what an accessory organ is

Answer 1

functionally associated, no material passes through
pancreas
liver
gall bladder
salivary glands

Question 2

List the different GI tract organs and their functions

Answer 2

oral cavity = digestion
esophagus = transport from mouth to stomach
stomach = continued digestion 
small intestine = absorption and digestion
large intestine (colon/rectum) = absorb water, hold feces

Question 3

Describe the tissue layers of the GI tract

Answer 3

mucosa = 1 thin layer of epithelial cells (secretory, transport, stem cells), then lamina propria (nerve fibers, blood supply, lymphatic vessels, connective tissue), then muscularis mucosa (thin layer of muscle to change the SA of mucosa)
submucosa (nerve trunks, blood supply, lymphatic vessels, submucosal plexus in the SI)
muscularis externa = circular muscle fibers to constrict lumen then longitudinal muscle fibers to shorten lumen (oblique muscle fibers in the stomach), myenteric plexus between layers
serosa = outer covering of GI tract, continuous with peritoneal membrane, lubricates/protects/suspends, made of secretory epithelium and connective tissue

Question 4

Describe the 4 basic GI functions

Answer 4

digestion = chemical/mechanical breakdown of food into units ready for absorption
absorption = movement of material from lumen to ECF
motility = movement of material through GI tract
secretion = movement of material from cells to ECF/lumen

Question 5

Describe the two modes of motility

Answer 5

peristaltic contraction = contraction just behind the bolus

segmental contraction = churning/mixing

Question 6

How is GI function regulated? List 3 ways, and how the PNS/SNS acts

Answer 6

Short reflexes: sensed by distension in stomach, presence of food, osmolarity or pH change. sensory receptors send signal to interneurons within enteric nervous system to the GI effectors (smooth muscle and secretory) which respond with altered motility and secretions
Long reflexes: same sensory inputs, or feedforward process (sight/smell/thought of food) leads to input to the GI effectors
GI peptides: caused by inputs from local stimuli or the enteric nervous system outputs to release GI peptides from the secretory cells, causes same effects on GI effectors, also modulates behaviour in the brain, causes release of insulin/decreased glucagon in the pancreas

PNS = enhances GI function, SNS = inhibits