Intestine Function and Structure

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Questions and Answers

What is the main function of the segmenting contractions in the large intestine?

To inhibit the release of digestive enzymes

To stimulate the release of digestive enzymes

To facilitate fluid and electrolyte secretion

To facilitate fluid and electrolyte absorption (correct)

What type of Cl− channels is activated by the ENS neurotransmitter vasoactive intestinal peptide?

Na+-activated Cl− channels

cAMP-activated Cl− channels (correct)

K+-activated Cl− channels

Ca2+-activated Cl− channels

What is the definition of diarrhea?

A decrease in stool frequency of less than 3 times a day

A decrease in stool fluid volume of less than 100 mL within 24 hours

An increase in stool fluid volume of more than 200 mL within 24 hours (correct)

An increase in stool frequency of more than 5 times a day

What is the name of the strips of smooth muscle in the large intestine that cause the formation of haustra?

Teniae coli Signup and view all the answers

What is the region of the large intestine where the ileocecal sphincter is located?

Cecum Signup and view all the answers

What is the function of acetylcholine from ENS neurons in the small intestine?

To stimulate Cl− secretion Signup and view all the answers

What is the name of the process by which the fecal contents are gradually turned over in the large intestine?

Haustral shuttling Signup and view all the answers

What is the function of serotonin from EC cells in the small intestine?

To stimulate Cl− secretion Signup and view all the answers

What is the primary function of the migrating motor complex (MMC) in the stomach during fasting?

To move indigestible food components into the small intestine Signup and view all the answers

What is the role of the vagovagal reflexes in gastric motility?

Mediating receptive relaxation and accommodation of food Signup and view all the answers

What is the role of retropulsion in gastric digestion?

To break down food particles by forcefully reflecting them back from the pyloric sphincter Signup and view all the answers

Which of the following mechanisms is responsible for the mixing of food with gastric juice in the distal stomach?

Antral systole Signup and view all the answers

What is the primary determinant of gastric emptying of liquids?

The intragastric pressure determined by the tonic contraction of the proximal stomach Signup and view all the answers

What is the role of the pyloric sphincter in gastric digestion?

To regulate the flow of food from the stomach to the small intestine Signup and view all the answers

Which of the following is NOT a function of the stomach?

Digesting carbohydrates Signup and view all the answers

What is the main function of the mucus-bicarbonate barrier in the stomach?

To protect the stomach lining from the corrosive effects of gastric juice Signup and view all the answers

What is the primary role of the crypt in a villus?

It secretes intestinal fluid. Signup and view all the answers

Which type of motility in the small intestine is responsible for mixing foodstuffs with digestive secretions?

Segmentation contractions Signup and view all the answers

What is a key function of the mature enterocytes located at the villus tip?

Absorption of nutrients and electrolytes. Signup and view all the answers

In the small intestine, which type of contraction mainly facilitates the propulsion of material?

Peristalsis Signup and view all the answers

Which factor is crucial for the mechanism of fluid secretion in the small intestine from crypt enterocytes?

Opening of Cl− channels Signup and view all the answers

What predominant motor activity occurs in the small intestine during the fed state?

High motor activity Signup and view all the answers

What is a consequence of fluid secretion in the intestines?

Coupling Na+ to nutrient absorption Signup and view all the answers

What is one of the three main functions of intestinal motility during the fed state?

Distribution of contents for absorption Signup and view all the answers

Study Notes

Fluid Secretion in the Small Intestine

Two types of chloride (Cl−) channels are vital for intestinal fluid secretion: cAMP-activated and Ca2+-activated.
Vasoactive intestinal peptide serves as a secretagogue for cAMP-activated Cl− channels.
Acetylcholine and serotonin stimulate Ca2+-activated Cl− channels in the enteric nervous system (ENS).

Structure and Function of the Large Intestine

The large intestine is wider than the small intestine, extending from the ileocecal sphincter to the anus.
It comprises the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal.
The teniae coli are three longitudinal strips of smooth muscle that create bulges called haustra through contractions.

Colonic Motility

Motility patterns include segmentation and peristalsis, which aid in fluid and electrolyte absorption.
Haustral shuttling, characterized by segmenting contractions, helps in gradually processing fecal contents.

Diarrhea

Defined as an increase in stool fluid volume exceeding 200 mL in 24 hours.
Functional continuum exists within a villus: crypts for fluid secretion, the maturation zone for enzyme expression and absorption, and the villus tip for nutrient and fluid absorption.

Small Intestine Motility During the Fed State

Increased motor activity includes mixing food with digestive secretions, distributing contents for absorption, and propelling materials aborally.
Major motility types are segmentation contractions for mixing and peristalsis for propulsion.

Fluid Secretion Mechanism in the Small Intestine

Both small and large intestines secrete fluids from crypt cells necessary for lubrication and nutrient absorption.
Chloride channels' opening in crypt enterocytes plays a crucial role in fluid secretion.
Intrinsic factor, a glycoprotein essential for vitamin B12 absorption, is secreted along with mucus to form a protective barrier against gastric acid.

Gastric Motility Patterns

Stomach experiences quiescence during fasting, interrupted by the migrating motor complex every 90 minutes.
Receptive relaxation occurs as food enters, allowing the stomach to accommodate food volume.
Proximal stomach exhibits sustained tonic contractions to progressively move food toward the distal stomach.

Mechanisms of Food Processing in the Stomach

Tonic contractions regulate intragastric pressure, influencing gastric emptying rates for liquids.
Antral systole results in rhythmic contractions that mix food with gastric juice, reducing particle size.
Retropulsion contributes to the formation of chyme, a semi-liquid mixture of food and gastric juices.

Peristaltic Activity in the Distal Stomach

Peristaltic waves occur at a frequency of 3–4 per minute during antral contractions, facilitating mixing and processing of ingested food.

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Description

This quiz covers the function and structure of the small and large intestines, including chloride channels and secretagogues.