GI Secretions

Question 1

Composition of Secretions

Answer 1

• water
• ions
• mucous
• enzymes

Question 2

Components of Saliva

Answer 2

• Amylase: Amylase is an enzyme that helps digest carbohydrates. Breaks down starch
• Bicarbonate: present as a buffer, especially in ruminant
• pH 6.5
• Lubrication
• Digestion (enzymes that get taken down with food)
• Autonomic-Parasympathetic control (not a lot of voluntary control)

Question 3

Stomach Secretions

Answer 3

• Gastric Pits!
• Gastric Gland: chief cells, parietal cells
• cheif cells: Produce pepsinogen, precursor to pepsin–> digestive enzyme. HCl cleaves pepsinogen into pepsin. If in active form can start to digest things within the cell, not desirable
• Parietal cells: produce HCl
• Goblet cells: secrete mucus-protecting mech
• Stimulated by Acetylcholine, Gastrin (released from stomach), Histamine (paracrine agent_

Question 4

3 phases of regulation of secretion

Answer 4

1. cephalic (vagus nerve)–> HCl and pepsinogen release
2. Gastric (arrival of food)–> gastin and histamine release. negative feedback if pH is below 3
3. Intestinal –> passage of particles into intestine (inhibit acid secretion and motility by releasing secretin, GIP, and CCK)

Question 5

Small intestine secretion

Answer 5

• Succus entericus: :highly variable in constitution, and contains especially various enzymes (breakdown!)
• enterokinase
• carboxy- and aminopeptidases
• maltase
• lactase
• sucrase
• lipase
• nucleases

-ph 7-8 (Slightly above neutral to increase low ph of stomach)

• Alkaline Mucoid Fluid from Brunners glands (no enzymes)

*confers tissue protection in an acidic environment, such as in the stomach

Question 6

Glycocalyx

(small intestine)

Answer 6

• Meant to trap enzymes being released and particles being broken down with food and hold it close to cell so that digestion and absorption can occur properly
• ​The glycocalyx also enables some bacteria to adhere to environmental surfaces (rocks, root hairs, teeth, etc.), colonize, and resist flushing

Question 7

Liver Secretions

Answer 7

• secretes into intestine as well
• Fats and FA’s
• bile salts and pigments
• Cholesterol
• pH 7-8 (Again just above neutral, RAISE pH)
• Control of secretions:
• prescence of food in the duodenum
• return of bile acids to the liver: Bile is made by cells of the liver, released by the gallbladder into the intestine
• mediated by CCK: CCK stimulates digestion of fats and protein

Question 8

Compostition of Bile

Answer 8

*Bile acids from cholesterol in smooth ER of hepatocytes (cell of the liver)

*Hydrophilic and Hydrophobic sides–> detergent

*Secreted into canaliculi as sodium salts-this draws water into bile by osmosis and electrolytes

*Also takes phospholipids and cholesterol from cell membrane

*Bicarbonate is secreted from duct cells into bile

*Bile pigments are excreted through this route-the main one being bilirubin (from red blood cell turnover) –> gives fecal matter its brown color

• Have detergent nature
• Create little particles of fat
• excretory route

Question 9

Entero-hepatic Circulation

Answer 9

• 90% of bile salts are resorbed from the small intestine and returned to the hepatocytes via the portal circulation for re-excretion
• Enterohepatic circulation refers to the circulation of biliary acids, bilirubin, drugs, or other substances from the liver to the bile, followed by entry into the small intestine, absorption by the enterocyte and transport back to the liver –> Like drugs and bile (pharm)
• Bile salts: function of bile salts in the duodenum is to solubilize ingested fat and fat-soluble vitamins, facilitating their digestion and absorption

Question 10

Pancreatic Secretions

Answer 10

• Exocrine Secretions responsible for digestion of complex nutrients
• Acinar cells secrete enzymes
• Centroacinar cells and duct cells secrete sodium bicarbonate
• Secretions of these cells happens by nerve supply but also,
• stimulated by acetylcholine, cholecystokinin, and secretin
• Secretions:

​-glucagon

• insulin
• Trypsinogen
• Chymotrypsinogen
• Carboxy and aminopeptidase
• Lipase
• Amylase
• Maltase
• Nucleases
• Bicarbonate pH 7-8

Question 11

Myenteric Plexus

Answer 11

• ENTERIC NERVOUS SYSTEM (neural control)
• Can feed back locally
• can cause local control of blood flow, etc. without feedback to CNS
• Can act locally depending on feedback it is getting
• can autonomically control Secretion, tone, blood supply, absorption, and motility without feeding back to CNS and acts locally
• one of the main divisions of the autonomic nervous system and consists of a mesh-like system of neurons that governs the function of the gastrointestinal tract. ENS is largely independent of the CNS
• Main process of digestion is not governed by the CNS, but rather by the plexuses of the submucosa and muscularis (ENS)