Gi Physiology Lecture 2 Wittingham

Front 1

What is Gastrin?

What is it secreted by?

Back 1

Gastrin is several related short-chain polypeptide hormones.

It is secreted by G cells of the stomach and duodenum.

Front 2

What stimulates the secretion of gastrin?

Back 2

Presence of food in the stomach or duodenum.

Front 3

What does gastrin stimulate?

Back 3

Gastric release of HCl and, to a lesser extent, pepsinogen (the inactive precursor to proteolytic enzyme pepsin).

Front 4

What is Somatostatin?

What is it released by?

Back 4

Somatostatin is a mixture of several related polypeptides.

Released by cells in gastric glands and also by cells of the pancreas (as well as hypothalamic cells).

Front 5

What is the function of somatostatin?

Back 5

To inhibit secretions of the stomach (Gastrin and HCl), duodenum (Secretin & Cholecystokinin), and pancreas (Glucagon).

Therefore, release of somatostatin tends to reduce the rate of nutrient absorption from the digestive tract (it slows digestion).

Front 6

What is Secretin?

Where is it released?

Back 6

It is a polypeptide that is released by cells of the duodenum in response to the presence of low pH (chyme entering the duodenum).

Front 7

What are the functions of secretin?

Back 7

Stimulates the pancreas to release bicarbonate--neutralizing chyme and thereby allowing activation of digestive enzymes.

Also starts to inhibit further acid secretion by the stomach and slows peristalsis.

Front 8

What is Cholecystokinin (CCK)?

Where is it secreted?

Why is it secreted?

Back 8

CCK is a group of small polypeptides which are secreted by cells of the duodenum and jejunum?

It is secreted in response to the presence of lipids and their catabolites.

Front 9

Cholecystokinin's cascade of effects is what?

Back 9

CCK stimulates gall bladder contraction, releasing bile into the duodenum for the emulsification of lipids.

This allows fats to be digested efficiently, stimulates the pancreas to secrete digestive enzymes, slows the rate of gastric emptying (fats take longer to digest), and also stimulates the satiety center.

Front 10

What is Vasactive Intestinal Polypeptide (VIP)?

Where is it released?

Back 10

VIP is a polypeptide hormone that is released at 'loose' synapses.

Front 11

What is the function of Vasactive Intestinal Polypeptide?

Back 11

It produces vasodilation in vessels of the gi tract during digestion. This allows for the active cells to receive sufficient oxygen and sufficient plasma (needed for enterocytes and mucous secretions), as well as better nutrient absorption.

Front 12

The central nervous system plays an important role in regulating gi function. The outflow for this regulation is carried by way of the ____________ nervous system. This outflow doesn't directly innervate gi cells, but instead moderates the activity of the _________ nervous system.

Back 12

autonomic

enteric

Front 13

What are the 2 layers of the enteric nervous system?

What are their functions?

Back 13

1. Myenteric (Auerbach's) Plexus: Primarily regulates contractions of smooth muscle that results in peristalsis and sphincter control.

2. Submucosal (Meissner's) Plexus: Regulation of secretions and blood flow along the length of the digestive tract.

Front 14

In the GI tract what is the function of:
Motor neurons?

Interneurons?

Sensory neurons?

Back 14

Motor: producing muscle contractions and secretions.

Interneurons: coordinating function (local control).

Sensory neurons: provide info from the gut back to the CNS.

Front 15

What do the sensory neurons in the enteric nervous system respond to?

Back 15

Mechanical stimuli (stretch and tension)

Thermal stimuli

Osmotic stimuli

Chemical stimuli (glucose and amino acids)

Front 16

How is the sensory information conveyed to the CNS?

Back 16

Along the afferent fibers of the Vagus.

Parasympathetic outflow to the gut includes the Glossopharyngeal (IX) and Facial (VII) nerves innervating salivary glands, the vagus innervating much of the length of the digestive tract and sacral nerves innervating the colon.

Front 17

Sympathetic innervation of the salivary glands travels through the _________ ________ ________, while the _________ _______ conduct impulses to much of the rest of the GI tract.

Back 17

superior cervical ganglion

splanchnic nerves

Front 18

How are the digestive reflexes named?

Back 18

The site of initiation followed by the site affected. ie: The gastrocolic reflex refers to how food entering the stomach results in increased motility of the colon.

Front 19

Significant secretions of the mouth?

Back 19

Saliva.

Front 20

Significant secretions of the esophagus?

Back 20

Mucus throughout its length. The mucus is thicker and contains a higher level of bicorbonate at its gastric end.

Lubricates and protects from scraping and acid erosion.

Front 21

Significant secretions of the stomach?

Back 21

Gastrin

HCl

Pepsinogen

Mucus

Gastroferrin (facilitates iron absorption)

Intrinsic Factor (essential for Vit. B12 absorption)

Front 22

Significant secretions of the small intestine (duodenum, jejunum, ileum)?

Back 22

Secretin & Cholecystokinin: released into blood

Released into lumen of SI:
Serous mucus

Bicarbonate-enriched mucus

Lysozyme & Defensins-Antibacterial functions

Front 23

Significant secretions of the colon?

Back 23

Mucin-rich mucus

Front 24

Significant secretions of the pancreas?

Back 24

Insulin, glucagon and somatostain into blood.

Into the lumen of gi tract:
Trypsinogen
Chymotrypsinogen
Procarboxypeptidase A and B
Pro-elastase
These are all inactive precursors of proteolytic enzymes.

Pancreatic lipase
Pancreatic amylase
Ribonucleases.

Also about 2 liters/day of bicarbonate-rich fluid.

Front 25

Significant secretions of the liver?

Back 25

Into Blood:
Plasma proteins

VLDLs (very low density lipoproteins)

HDLs

Into Lumen:
Bile--concentrated in gall bladder, contains bile salts and bile acids for lipid emulsification, and also serves as an avenue for excretion of bilirubin from heme breakdown.