Chapter 66- Digestion and Absorption in the Gastrointestinal Tract

What is the process of breaking down carbohydrates during digestion?

Hydrolysis, which converts large polysaccharides or disaccharides back to monosaccharides by adding water.

What are triglycerides composed of?

Three fatty acids and a glycerol backbone, formed via condensation.

How are triglycerides digested?

Through hydrolysis, where fat-digesting enzymes add three molecules of water to split fatty acids from glycerol.

What is the role of hydrolysis in protein digestion?

It breaks down peptide bonds by adding water to separate amino acids.

What common process is involved in the digestion of carbohydrates, fats, and proteins?

Hydrolysis.

What type of molecules are all digestive enzymes?

Proteins.

Name a source of carbohydrates that is a disaccharide found in milk.

Lactose.

What is sucrose commonly known as?

Table sugar, a disaccharide.

What are starches?

Large polysaccharides present in nonanimal foods, particularly in potatoes and grains.

List one other type of carbohydrate besides sucrose and lactose.

Amylose, glycogen, or alcohol.

What is the main function of hydrolysis in digestion?

To separate macromolecules into their smaller building blocks by adding water.

What is the significance of condensation in the formation of triglycerides?

It involves the removal of water to join three fatty acids to a glycerol backbone.

What is the role of ptyalin in carbohydrate digestion?

Ptyalin (alpha amylase) hydrolyzes starch into disaccharide maltose and small glucose polymers.

Where does the digestion of carbohydrates begin?

In the mouth and stomach.

What percentage of starches can be hydrolyzed to maltose before reaching the stomach?

30-40%.

What enzyme in the small intestine is similar to salivary alpha amylase?

Pancreatic alpha amylase.

What are the end products of carbohydrate digestion?

Monosaccharides, primarily glucose, with some galactose and fructose.

What enzyme splits lactose into galactose and glucose?

Lactase.

What is the primary function of pepsin in protein digestion?

Pepsin initiates protein digestion by breaking down proteins into smaller peptides.

What are the main pancreatic proteolytic enzymes involved in protein digestion?

Trypsin, chymotrypsin, carboxypolypeptidase, and elastase.

What is the final product of protein digestion?

Individual amino acids.

What is the role of bile salts in fat digestion?

Bile salts emulsify fat globules to increase surface area for enzyme action.

What enzyme is responsible for digesting triglycerides in the small intestine?

Pancreatic lipase.

What are micelles?

Small spherical structures composed of bile salts that facilitate the absorption of fatty acids and monoglycerides.

How are free fatty acids absorbed into the bloodstream?

They diffuse out of micelles and into the epithelial cells of the intestine.

What is the primary site for nutrient absorption in the gastrointestinal tract?

The small intestine.

What anatomical features increase the absorptive surface area of the small intestine?

Folds of Kerckring, villi, and microvilli.

What is the role of aldosterone in sodium absorption?

Aldosterone increases sodium absorption in the kidneys and intestines, promoting water retention.

What is the mechanism of sodium absorption in the intestines?

Active transport through Na+/K+ ATPase and secondary active transport with glucose and amino acids.

How is water absorbed in the intestines?

By osmosis, following the osmotic gradient created by ion absorption.

What is the primary method of chloride ion absorption in the small intestine?

Chloride ions are absorbed by diffusion and through chloride/bicarbonate exchangers.

What is the significance of vitamin K produced by intestinal bacteria?

Vitamin K is essential for blood coagulation.

What are the components of feces?

Water, dead bacteria, fat, inorganic matter, protein, and undigested food.

What causes the brown color of feces?

Stercobilin and urobilin, which are derivatives of bilirubin.

What is the role of bicarbonate in the large intestine?

Bicarbonate neutralizes acidic products formed by bacteria.

What is the primary function of the large intestine?

Absorption of water and electrolytes, and storage of feces.

What happens to sodium and chloride absorption during dehydration?

Aldosterone secretion increases sodium and chloride absorption to conserve water.

How are dipeptides and tripeptides absorbed in the small intestine?

Through secondary active transport mechanisms similar to amino acids.

What is the role of the central lacteal in the intestinal villus?

The central lacteal absorbs fats into the lymphatic system.

What happens to excess fluid entering the large intestine?

If it exceeds absorptive capacity, it appears in the feces as diarrhea.

What is the effect of cholera toxins on intestinal absorption?

Cholera toxins cause extreme fluid loss through diarrhea.

What is the absorption mechanism for glucose in the small intestine?

Glucose is absorbed via sodium-glucose co-transporters (SGLT1) and facilitated diffusion through GLUT2.

What is the primary function of peptidases in the small intestine?

Peptidases break down remaining peptides into amino acids for absorption.

What is the role of actin filaments in intestinal absorption?

Actin filaments maintain the movement of microvilli, enhancing exposure to intestinal fluid.

How does the absorption of potassium and magnesium occur?

Through active transport mechanisms across the intestinal mucosa.

What is the primary absorption site for calcium ions?

The duodenum, regulated by parathyroid hormone and vitamin D.

What is the significance of the tight junctions in the large intestine?

Tight junctions prevent back diffusion of ions, enhancing absorption efficiency.

What is the composition of bile salts?

Bile salts consist of a sterol backbone that is fat-soluble and a polar group that is water-soluble.

What happens to dietary fats after absorption in the intestine?

They are transported in the blood as chylomicrons after being reassembled into triglycerides.

What is the function of the Na+/H+ exchanger in the intestine?

It secretes H+ into the lumen while reabsorbing sodium, facilitating bicarbonate absorption.

What is the role of pinocytic vesicles in the intestine?

They absorb small amounts of fluids through the process of pinocytosis.

What is the primary mechanism for fructose absorption?

Facilitated diffusion through GLUT5 and GLUT2, without sodium co-transport.

What is the role of dietary fibers in digestion?

Dietary fibers are not digested by humans and contribute to fecal bulk.