L15 physiology

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Questions and Answers

What is one of the primary functions of segmental contractions in the small intestine?

Mixing contents with digestive juices (correct)

Regulation of intestinal blood flow

Stimulating peristalsis in the colon

Propulsion of contents into the large intestine

Which hormone is primarily associated with migrating motility complexes (MMC)?

Motilin (correct)

Cortisol

Insulin

Serotonin

What triggers mass movements in the large intestine?

Hormonal secretion from the pancreas

Irritation of the intestinal wall

Food intake and gastrocolic reflex (correct)

Excessive hydration

How often do mass movements typically occur in the large intestine?

1 to 3 times per day Signup and view all the answers

What is the main consequence of irritation to the small intestine mucosa?

Powerful and rapid peristalsis Signup and view all the answers

What is the primary function of the lower esophageal sphincter during swallowing?

To allow the bolus to enter the stomach Signup and view all the answers

What is the primary role of haustration in the colon?

To mix and absorb intestinal contents Signup and view all the answers

What process enhances the stomach's ability to accommodate food volume during a meal?

Receptive relaxation Signup and view all the answers

What causes the transit time in the small intestine to last 8-9 hours?

Complexity of digestion and absorption processes Signup and view all the answers

What physiological response is initiated by the distension of the rectum?

Initiation of the defecation reflex Signup and view all the answers

What is the primary function of mastication?

To break down food into smaller pieces Signup and view all the answers

Which of the following best describes the characteristics of the phase of retropulsion in gastric mixing?

Retaining large particles in the terminal antrum Signup and view all the answers

Which factor does NOT contribute to the regulation of gastric emptying?

Increase in sympathetic impulses Signup and view all the answers

Which phase of swallowing is considered voluntary?

Oral phase Signup and view all the answers

Which structure in the brain coordinates the swallowing process?

Medulla oblongata Signup and view all the answers

What initiates vomiting or emesis?

Distention or irritation of the GIT Signup and view all the answers

What distinguishes segmentation from peristalsis in small intestine motility?

Segmentation is a mixing action, while peristalsis is a wave-like motion that propels food. Signup and view all the answers

What initiates the peristaltic contractions in the esophagus?

Entry of food bolus into the esophagus Signup and view all the answers

What role does saliva play in the swallowing process?

It acts as a lubricant and facilitates the movement of food Signup and view all the answers

What is NOT a characteristic of gastric storage?

Allows for rapid gastric emptying Signup and view all the answers

Which of the following is NOT a function of the gastric motility phases?

Immediate digestion of nutrients Signup and view all the answers

Which structure is closed off during the pharyngeal phase of swallowing?

Nasopharynx Signup and view all the answers

What is the primary type of muscle involved in peristalsis?

Circular smooth muscle Signup and view all the answers

During the swallowing process, what happens to the epiglottis?

It closes to cover the larynx Signup and view all the answers

Study Notes

Gastrointestinal Motility

Gastrointestinal motility is the movement of food through the digestive system.
Learning objectives include describing the organization of the enteric intrinsic nervous system, defining peristalsis, describing deglutition (swallowing) mechanisms, stomach motility, small and large intestine movements, and the defecation reflex.

Basic Structure of the Alimentary Canal

Mucosa: Epithelium, lamina propria (areolar connective tissue and lymphatic tissue), and muscularis mucosae (smooth muscle).
Submucosa: Areolar connective tissue, blood and lymphatic vessels, and submucosal plexus (neurons).
Muscularis: Smooth muscle, myenteric (Auerbach's) plexus (neurons), and circular and longitudinal muscle layers.
Serosa: Areolar connective tissue and epithelium (visceral peritoneum).

Motility in the Mouth (Mastication)

Chewing is a voluntary process.
Teeth cut food into smaller pieces.
Saliva mixes with food to soften and lubricate it.
Saliva contains amylase, an enzyme that begins carbohydrate digestion.

Swallowing (Deglutition)

Swallowing moves food from the mouth to the stomach.
It's facilitated by saliva and mucus.
It involves the mouth, pharynx, and esophagus.
Coordinated by the swallowing center in the medulla oblongata and lower pons.
Swallowing has three phases: oral, pharyngeal, and esophageal.

Phases of Swallowing

Oral phase: Voluntary movement of the tongue forces the bolus (food mass) to the back of the oral cavity and into the pharynx.
Pharyngeal phase: Involuntary phase. The soft palate elevates, closing the nasopharynx. The epiglottis and vocal cords close off the larynx. Peristaltic waves begin.
Esophageal phase: Involuntary phase. Peristaltic wave contractions move the bolus through the esophagus.

Lower Esophageal Sphincter (Cardiac Sphincter)

Located at the lower end of the esophagus.
Relaxes to allow the bolus to enter the stomach.
Usually closed to prevent gastric reflux (backflow of stomach contents).

Stomach Motility

Gastric filling: The stomach accommodates a large volume of food.
Gastric storage: Temporary holding area.
Gastric mixing: Mixing of food with gastric secretions.
Gastric emptying: Release of chyme (partially digested food) into the small intestine.

Gastric Filling and Storage

The stomach expands 20-fold during a meal.
Receptive relaxation allows the stomach to accommodate the food bolus.
The lower esophageal sphincter (LES) opens as food passes through.
Circular muscles of the proximal stomach relax.
Peristalsis begins in the lower portion of the stomach.

Gastric Mixing and Emptying

The gastric pump has three stages: propulsion, emptying, and retropulsion/grinding.
Propulsion involves rapid flow of liquids and suspended small particles into the small intestine.
Emptying involves the release of liquids and small particles into the small intestine, while large particles remain in the stomach.
Retropulsion/grinding mixes and grinds food particles.

Regulation of Gastric Emptying

Stomach distension stimulates gastrin secretion and parasympathetic impulses.
These stimulate contraction of the lower esophageal sphincter and increase stomach motility.
The pyloric sphincter relaxes, allowing chyme to enter small intestine.

Vomiting (Emesis)

A forceful expulsion of stomach contents.
A protective mechanism initiated by the vomiting center in the medulla oblongata.
Triggered by: Distension or irritation in the GI tract, various stimuli (sight, smell, pain), vestibular system stimulation, or increased intracranial pressure.

Motility of the Small Intestine

Two primary motility patterns are segmentation and peristalsis.
Segmentation mixes chyme with digestive juices and brings it into contact with intestinal cells for absorption.
Peristalsis propels chyme into the large intestine.
Transit time in the small intestine is 8-9 hours.
Irritations in the small intestine cause intense and powerful peristalsis.

Small Intestine Motility (Segmentations)

Nonadjacent segments of the small intestine contract and relax alternately.
Mixes contents causing exposure to intestinal cells for absorption.
Does not propel contents along the tract.

Migrating Motility Complexes (MMCs)

A type of peristalsis beginning in the lower stomach.
Pushes chyme along the small intestine.
Lasting approximately 10 minutes each, with Motilin hormone as a player and intrinsic plexus stimulation.

Motility of the Large Intestine (Haustrations)

Slow segmenting movements (haustra) move the contents.
Average transit time is 12-72 hours.
Mass movements propel feces towards the rectum.
Triggered by gastrocolic and duodenocolic reflexes, irritation, and parasympathetic stimulation.

Defecation Reflex

Rectal distension initiates the reflex.
Rise in pressure in the rectum initiates the urge to defecate.
Stretch receptors stimulate the sacral spinal cord.
Relaxation of the internal anal sphincter occurs via the pelvic nerve (parasympathetic).
External anal sphincter is a somatic muscle (voluntary) and can be controlled.
Relaxation of both anal sphincters releases feces.

Learning Resources

Textbook: Marieb EN. Human Anatomy and Physiology, 9th Edition, Pearson International Education; 2014. Chapter 23, pages 863-866.
Powerpoint slides available on Moodle.

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Description

This quiz covers gastrointestinal motility, including the movement of food through the digestive system, mechanisms of swallowing, and various types of motility in the alimentary canal. You'll also learn about the basic structure of the digestive organs and their functions.