SMALL INTESTINE PHYSIOLOGY

Priyanca Patel

What are the secretions of the exocrine pancreas and small intestine?

• There are 5 things to remember• A pneumonic may help? – Warwick Males Are Horny Dicks…

– Water– Mucus– Alkali– Hormones– Digestive enzymes

Mucus- Brunner’s glands in duodenal mucosa - Neutralises duodenal contents - Isotonic solution rich in HCO3

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Water- Intestinal epithelium secretes Na+, Cl- and HCO3

- and water follows by osmosis

Hormones Some Medic Girls are Very Cliquey - Secretin- Motilin- Gastric Inhibitory Peptide (GIP)- Vasoactive intestinal peptide (VIP)- Cholecystokinin (CCK)

Digestive enzymes:

- Trypsin- Chymotrypsin- Carboxypentidase- Pancreatic amylase- Lipases - Other enzymes inc. phospholipase, cholesterol

esterases and ribonucleases

Where do the pancreatic secretions originate from?

• DUCT CELLS:– Secrete alkali– Simulated by secretin and

potentiated by CCK and ACh (Vagal tone)

• ACINAR CELLS– Secrete enzymes into the

duodenum– Stimulated by CCK and

acetylcholines from parasympathetic, postganglionic neurons of Vagus

REST & DIGEST

What is digested in the SI and where?

• Occurs in the duodenum and small intestine

– FATS: Digested by pancreatic lipase monoglceride and fatty acids

– STARCH: completed by pancreatic amylase. Disaccharides monosacchardies by brush border enzymes

– PROTEINS: Broken down to peptide fragments by trypsin and chymotrypsin amino acids by carboxypeptidase (pancreas) and aminopepsidase (luminal membrane of SI epithelial cells)

Digestion and absorption of fats

1. Emulsification of fats by - Bile salts- Phospholipids

2. Fats digested by pancreatic lipase

- Products are held in micelles combined with the bile salts and phospholipids

3. Micelles diffuse into an “unstirred layer” next to the surface of epithelial cells

- Fatty acids and monoglycerides then diffuse into the cell membrane

- Once inside the cell, fatty acids and monoglycerides are reassembled into fats

- Triglyceride droplets are packaged into chylomicrons (with cholesterol and proteins)

- Chylomicrons are exported across the basolateral membrane and leave the intestinal vessel via its lymph vessel

How are monosaccharaides transported in the SI?

• Facilitated diffusion (GLUT5 & GLUT 2) and active transport (SGLT1)

OVERVIEW: Digestion in the SI