BIOL244 Digestive System Part B

What is the function of the stomach?

temporary storage tank, starts chemical digestion of proteins, and converts food into chyme.

What are the major regions of the stomach?

Cardial part (cardia), fundus, body, pyloric part.

What are the stomach curvatures and their significance?

Greater curvature (convex lateral surface), lesser curvature (concave medial surface); these serve as attachment sites for mesenteries.

What structure allows the stomach to expand from ~50ml to 4L?

Rugae, the folds of the stomach mucosa.

What are the three layers of the stomach’s muscularis externa?

Circular, longitudinal, and oblique layers.

What is the function of gastric pits and gastric glands?

Gastric pits lead into gastric glands, which produce gastric juice for digestion.

Name the four types of gastric gland cells and their secretions.

Mucous neck cells, Parietal cells, chief cells, and enteroendocrine cells

Mucous neck cell

thin acidic mucus

Parietal cells

HCl, activates pepsinogen into pepsin, required for absorption of vitamin b12 to small intestine, ONLY FUNCTION THAT IS VITAL TO LIFE

Chief Cells

Secretes pepsinogen, protein chemical digestion begins

When are protein digestive enzymes activated?

When mixed with chyme

Enteroendocrine cells

Secretes gastric hormone

Gastrin

targets parietal cells, acts as local chemical messenger and circulating hormone

What is the only function of the stomach essential for life?

Secretion of intrinsic factor for vitamin B12 absorption.

How is gastric secretion regulated?

Through neural (vagus nerve) and hormonal (gastrin) mechanisms.

What are the three phases of gastric secretion?

Cephalic phase, gastric phase, intestinal phase.

What inhibits gastric secretion during the gastric phase?

A drop in stomach pH inhibits gastrin release.

What is the enterogastric reflex?

It inhibits stomach activity when chyme enters the duodenum.

What is the function of the liver in digestion?

Produces bile, which emulsifies fats.

What are the four main lobes of the liver?

Right, left, caudate, quadrate.

What is the function of the gallbladder?

Stores and concentrates bile.

What are the main components of bile?

Bile salts, bilirubin, cholesterol, phospholipids.

What is the function of the pancreas in digestion?

Secretes digestive enzymes and bicarbonate to neutralize stomach acid.

What are the key pancreatic enzymes?

Proteases, Amylase, and Lipase

Proteases

Digest protein

Only major nutrient absorbed in stomach

Water

Intrinsic factor

required for absorption of vitamin B12, only function vital for life

Things absorbed in the blood from the stomach

lipid-soluble alcohol, aspirin, and water

What is B12 used for?

production of red blood cells in red bone marrow

Cephalic Phase

triggered by aroma, taste, sight, and thought

stimulates production of gastric juices

Gastric Phase

provides 2/3 of the gastric juice, stimulated by rise of pH

What inhibits gastric secretion?

Low pH between meals or during digestion as negative feedback

Intestinal Phase

stimulated by brief release of intestinal gastrin from duodenal enteroendocrine cells

Primary effect of intestinal phase

inhibition of gastric juice secretion

4 factors in duodenum that causes inhibition of gastric secretions

Distension of duodenum, presence of acidic, fatty, or hypertonic chyme

What are two ways inhibition is activated in the intestinal phase?

Enterogastric reflex and enterogastrones

Enterogastrones

release two circulating hormones that inhibit gastric secretion: secretin & cholecystokinin

Basic electrical rhythm

set by enteric pacemaker cells that automatically depolarize 3x/min

What controls overfilling of chyme in the stomach

Duodenum

Emulsification

form of physical digestion that breaks down fat droplets

Largest gland of the body

Liver, 3 lbs

Falciform ligament

separates right and left lobes

Hepatic portal vein

carries nutrient-rich blood from small intestine to liver

Common hepatic duct

combination of right and left hepatic duct

Cystic Duct

leads from common hepatic duct to gallbladder

Bile duct

common hepatic duct + cystic ducts; carries bile to the duodenum

Hepatocytes

produce bile, process bloodborne nutrients, store fat-soluble vitamins, and perform detoxifcation

Enterohepatic circulation

conserves bile salts