Human Anatomy: Villi in the Small Intestine

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Questions and Answers

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

To increase surface area for nutrient absorption (correct)

To absorb water from the food

To produce digestive enzymes

To transport waste materials

What structural feature characterizes villi?

Long and tubular form

Spherical bladders

Finger-like projections (correct)

Flat and broad shape

Why are blood vessels important in the function of villi?

They remove toxins from the intestine

They facilitate the digestion of proteins

They help in the movement of food

They enable the absorption of nutrients into the bloodstream (correct)

Where in the human body would you find villi?

In the inner lining of the small intestine Signup and view all the answers

How do villi contribute to nutrient absorption?

By increasing the surface area available for absorption Signup and view all the answers

What is the primary mechanism by which the substance enters the epithelial cells?

Passive diffusion Signup and view all the answers

What is the difference between how the substance enters and leaves the epithelial cells?

The substance enters passively and leaves actively. Signup and view all the answers

Which membrane is responsible for the substance's entry into epithelial cells?

Luminal membrane Signup and view all the answers

Which process requires energy to move the substance across the cell membrane?

Exit from the cells. Signup and view all the answers

What is the final destination of the substance after it leaves the epithelial cells?

Bloodstream Signup and view all the answers

What ions are involved in the absorption process described within the intestine?

Sodium ions Signup and view all the answers

How many sodium ions are transported along with one glucose molecule?

Two sodium ions Signup and view all the answers

What type of carriers facilitate the transport of sodium ions and glucose in the intestine?

Na+ linked carriers Signup and view all the answers

Where does the absorption of sodium ions and glucose take place in the body?

Within the lumen of the intestine Signup and view all the answers

What is the primary role of sodium ions in the absorption of glucose?

They are linked to glucose transport by carriers. Signup and view all the answers

Which of the following substances is NOT known to inhibit iron absorption?

Vitamin C Signup and view all the answers

What is the most prevalent theory regarding the mechanism of iron absorption?

Secretion of a globular protein called apoferritin Signup and view all the answers

What is the primary source of phytic acid, known to inhibit iron absorption?

Cereals Signup and view all the answers

The text mentions two possible mechanisms for iron absorption. What are they?

Active transport and secretion of apoferritin Signup and view all the answers

Which of the following is NOT a known inhibitor of iron absorption?

Bile Signup and view all the answers

What happens to Na+ after it enters the cells?

It is pumped out at the basolateral membrane. Signup and view all the answers

How is glucose transported out of the cells?

By facilitated diffusion into the capillaries of the villus. Signup and view all the answers

Which membrane is referred to as the basolateral membrane?

The membrane closest to the bloodstream. Signup and view all the answers

What process is used to move glucose from the cell into the bloodstream?

Facilitated diffusion. Signup and view all the answers

What role does the basolateral membrane play in nutrient absorption?

It enables the transport of glucose and Na+ to the bloodstream. Signup and view all the answers

What is the primary role of the hormone mentioned in the colon?

To conserve water and Na+ during dehydration Signup and view all the answers

What does the absorption of Cl- primarily occur?

In the upper part of the small intestine Signup and view all the answers

Why is the conservation of Na+ and water vital during dehydration?

To maintain blood pressure and volume Signup and view all the answers

Which condition is primarily addressed by this hormone?

Dehydration Signup and view all the answers

What component is mostly conserved by this hormone in the colon during periods of dehydration?

Sodium ions (Na+) Signup and view all the answers

Study Notes

Digestion and Absorption

Digestion breaks down carbohydrates, proteins, and lipids using enzymes.
Absorption involves specialized epithelial cells.
Most absorption occurs in the small intestine; some in the stomach, and none in the esophagus.
The small intestine's structure (mucosal folds, villi, microvilli) increases surface area for absorption, about 600 folds.
The colon absorbs water and electrolytes.

Carbohydrate Digestion and Absorption

Carbohydrates are ingested as starch, sucrose, lactose, and cellulose.
Cellulose is indigestible.
Digestion starts in the mouth with salivary amylase (ptyalin), partially breaking down starch into smaller glucose polymers.
Pancreatic amylase continues this process in the small intestine.
Brush border enzymes (lactase, sucrase, maltase, and alpha-dextranase) further break down disaccharides into monosaccharides (glucose, fructose, and galactose).
These monosaccharides are absorbed via active transport or facilitated diffusion.

Protein Digestion and Absorption

Protein digestion starts in the stomach with pepsin and HCl, initially breaking down large proteins.
Proteolytic enzymes (endopeptidases and exopeptidases) in the small intestine further break down peptides into smaller peptides and amino acids.
Brush border enzymes (peptidases) in the small intestine break down peptides into amino acids.
Amino acids are absorbed via active transport across the intestinal epithelial cells.

Lipid Digestion and Absorption

Bile salts emulsify fats in the duodenum.
Pancreatic lipase breaks down triglycerides into free fatty acids and monoglycerides.
These products combine with bile salts, phospholipids, cholesterol, and form micelles.
Free fatty acids, monoglycerides, and other components pass through the intestinal cell membrane via passive diffusion.
Chylomicrons (combined lipids and proteins) are then formed and released from the cells.
Cholesterol, glycerol, and fatty acids are absorbed through the bloodstream.

Water and Electrolyte Absorption

Water passively follows the sodium gradient into epithelial cells.
Electrolytes (sodium, chloride, potassium) are actively absorbed in the small intestine and colon, sometimes exchanged across the membrane for sodium.
Sodium absorption can also be regulated by the hormone aldosterone.

Iron Absorption

Iron absorption occurs primarily in the upper part of the small intestine.
Ferrous iron (Fe++) is more readily absorbed than ferric iron (Fe+++).
Factors like vitamin C increase iron absorption, while phosphates, oxalates, and phytic acid can inhibit absorption.

Vitamin Absorption

Water-soluble vitamins are absorbed passively, except for vitamin C, B1, and B12.
B12 requires intrinsic factor for absorption.
Lipid-soluble vitamins are absorbed similarly to lipids (with micelles and chylomicrons).

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Description

This quiz explores the structure and function of villi in the small intestine. You'll learn about their role in nutrient absorption, the mechanisms involved, and the importance of blood vessels. Test your knowledge on how substances are transported across epithelial cells.