Digestion & Metabolism 2

Flashcards covering key concepts from Digestion & Metabolism Reading 2, including carbohydrate, protein, and lipid digestion and absorption, vitamin and mineral absorption, and water absorption.

What is the primary goal of nutrient absorption in the small intestine?

To move more nutrients from the lumen of the small intestine into the blood of capillaries.

What is the generic term for enzymes that break down polysaccharides?

Amylase

Where are amylase enzymes synthesized and secreted for carbohydrate digestion?

Salivary glands and pancreas

What are the initial products of starch/glycogen digestion by amylase?

Maltose and limit dextrins

What brush border enzymes further break down maltose and limit dextrins?

Maltase and dextrinase

What is the role of the Sodium/Potassium pump in GI tract absorption?

It pumps 3 Na+ out and 2 K+ in, using the Na+ gradient to bring in nutrients via co-transport mechanisms.

How are glucose and galactose absorbed across the apical membrane of GI tract cells?

Co-transport with Na+

How are glucose and galactose absorbed across the basolateral membrane of GI tract cells?

Facilitated diffusion

How is fructose absorbed across the apical and basolateral membranes of GI tract cells?

Facilitated diffusion

What is the typical daily protein consumption compared to the required amount?

Typical diet is 125 grams/day, but only 40-50 grams are required.

What are the sources of proteins digested and absorbed?

Proteins consumed in the diet, secreted into the lumen (e.g., enzymes), and sloughed off with cells lining the intestinal tract (e.g., enterocytes).

What is the generic term for enzymes that break down proteins?

Protease

What are the final products of protein digestion?

Amino acids, dipeptides, and tripeptides.

What do endopeptidases do during protein digestion?

They split polypeptides at interior peptide bonds, producing small peptide fragments.

What do exopeptidases do during protein digestion?

They cleave off amino acids from one end of a polypeptide, producing amino acids.

What are zymogens?

Inactive proteases.

What are some examples of pancreatic proteases?

Trypsin, chymotrypsin, and carboxypeptidase.

Which protease is involved in protein digestion in the stomach, and how is it activated?

Pepsin, which is activated from its inactive form pepsinogen by HCl.

Which enzyme initiates the activation of pancreatic zymogens in the small intestine?

Enterokinase (Enteropeptidase) activates trypsinogen to trypsin.

How are amino acids absorbed across the apical membrane of enterocytes?

Co-transport with Na+.

How are amino acids transported out of enterocytes across the basolateral membrane?

Facilitated diffusion.

How are dipeptides and tripeptides absorbed across the apical membrane of enterocytes?

Co-transport with H+.

What happens to dipeptides and tripeptides once inside the enterocyte?

They are broken down into amino acids by cytoplasmic peptidases.

What special problem do lipids face during digestion and absorption?

They are not water-soluble and do not mix with stomach or intestinal contents, forming fat droplets.

What is the role of bile salts in lipid digestion?

Bile salts emulsify fats by breaking large fat droplets into smaller ones, increasing the surface area for lipase digestion.

What is the role of co-lipase in lipid digestion?

Co-lipase helps load lipase onto the lipid by moving bile salts out of the way.

What are the main enzymes involved in lipid digestion?

Lingual lipase, gastric lipase, and pancreatic lipase.

Where are bile salts produced and stored?

Produced in the liver and stored in the gallbladder.

What are the steps of lipid absorption from the lumen into the lymphatic system?

Micelles release glycerol and free fatty acids, which cross the apical membrane via simple diffusion, reassemble into triglycerides in the smooth ER, combine with other lipids and protein in the Golgi apparatus to form chylomicrons, which then cross the basolateral membrane via exocytosis and enter the lacteal of the lymphatic system.

What happens to bile salts after aiding lipid digestion and absorption?

They are absorbed in the ileum of the small intestine and recycled by the liver through enterohepatic circulation.

How are fat-soluble vitamins (A, D, E, K) absorbed?

They are absorbed with lipids, dissolving in micelles and passing via simple diffusion.

How are water-soluble vitamins (B and C) absorbed?

They require special carrier proteins.

What is required for the absorption of Vitamin B12?

It must be bound to intrinsic factor.

Where is calcium actively absorbed in the GI tract?

In the duodenum and jejunum.

What is the role of calcium-binding protein in calcium absorption?

It binds calcium at the brush border and transports it into the epithelial cell.

How is water absorbed in the GI tract?

Water absorption is passive and follows the absorption of solutes by osmosis.

Where does most water absorption occur in the GI tract?

The large intestine.