Digestion of Carbs and Lipids

Question 1

Saliva

Answer 1

2 types –> hypertonic always

1) Serous - watery secretion containing a-amylase (ptyalin)
2) Mucous - contains mucin - lubrication

secrete 800-1500 mL/day!! (4mL/min)

• As flow rate increases, HCO3 stays elevated because salivary agonists stimulate secretion!
• always hypertonic but osmolarity increases as flow rate increases.

Question 2

Ptyalin

Answer 2

a-amylase

Question 3

Salivary Glands

Answer 3

4 Glands

1) Parotid - serous
2) Submandibular - mucous/serous
3) Sublingual - mucous/serous
4) Buccal - mucous

90% = parotid & submandibular

Question 4

Saliva Formation and the Pancreas

Answer 4

2 stages

1) Acini - primary secretion (Cl- is principle ion secreted)
2) Salivary Ducts - modifies saliva as it passes through ducts

Fluid goes from:
Acini –> to intercalated ducts –> to interlobular ducts

Question 5

Pancreas

Answer 5

As chyme floods SI . . . Pancreas must

• neutralize acids
• digest macronutrients

2 Glands
1) Endocrine 
- islets of langerhans (4 cells): 
a (glucagon)
B (insulin)
S (somatostatin),                                             
F (pancreatic polypeptide)         
2) Exocrine - secretes digestive enzymes and bicarb

Question 6

Carbohydrate Digestion

Answer 6

1) Pancreatic amylase (only luminal enzyme for carbs)

- converts starches and glycogen to disaccharides

Question 7

Protein Digestion

Answer 7

Proteolytic Enzymes:

1) Trypsin (cleaves proteins to polypeptides)
2) Chymotrypsin (cleaves proteins to polypeptides)
3) Carboxypeptidase (cleaves polypeptides to aa)

Question 8

Fat Digestion

Answer 8

1) Pancreatic Lipase - fat –> FA + monoglycerides
2) Phosphsoliapse - phospholipids –> FA
3) Cholesterol Esterase - cholesterol esters –> FA

Question 9

Pancreatic Acinar Cell

Answer 9

Secretory Protein Synthesis (must phosphorylate first, then secrete)

1) Acini - grape like cluster of cells that store and secretive digest enzymes in the pancreas
2) Salivary Ducts –> secrete bicarbonate

• secretes isotonic plasma like fluid

CCK & Carbachol - regulated secretion
But. . . CCK + VIP = MOST AMYLASE!!!!!!

CCK and cholinergic neurotransmitter ACh = stimulate Cl- secretion!

Question 10

Bicarb Secretion

Answer 10

• *Most powerful? Secretin! - activates adenylyl cyclase to raise cAMP to simulate protein kinase A and phosphorylate CFTR
• CO2 + CHO3 needed to enter pancreatic duct
• Secretin needed to allow Cl- and HCO3 to exit pancreatic duct INTO LUMEN

(also requiem Na+ & H2O)

Question 11

Secretin

Answer 11

**Most powerful? Secretin! - activates adenylyl cyclase to raise cAMP to simulate protein kinase A and phosphorylate CFTR

Secretin = bicarb, CCK and pancreatic fluid

• Acid from stomach releases secretin from duodenum and fats/AA release CCK
• Vagus nerve stimulates enzyme release into acini
• Secretin and CCK are absorbed in blood stream

Question 12

Cephalic, Gastric & Intestinal Phases

Answer 12

Cephalic - sight/taste of food
Gastric - food in stomach
Intestinal - H+ stimulates S cells to secrete secretin which acts on receptors to release bicarb AND protein/fat breakdown stimulates I cells to secrete CCK to act on acinar cells to release enzymes

Vagus nerve = sends GRP signal to bind to G cell to release Gastrin to acing cell!

Question 13

Pancreatitis

Answer 13

digestion is abnormal when pancreas fails to secrete normal amounts of enzymes

without enzymes: 60% of fat not absorbed (steatorrhea) and 30-40% of protein/carb not absorbed