Physiology lecture 1 - gastrointestinal A

Question 1

Alimentary tract provide body with what?

Answer 1

water
electrolytes
nutrients

Question 2

Functions of alimentary tract

Answer 2

1. Movement of food through the alimentary tract
2. secretion of digestive juices and digestion of the food
3. absorption of water, various electrolytes, vitamins and digestive products
4. circultation of blood through the gastrointestinal organs to carry away the absorbed substances
5. control of all these functions by nervous and hormonal system

Question 3

What is the motor function of the gut performed by?

Answer 3

by different layers of smooth muscle

Question 4

What are slow waves?

Answer 4

A slow wave potential is a rhythmic electrophysiological event in the gastrointestinal tract. The normal conduction of slow waves is one of the key regulators of gastrointestinal motility. generated and propagated by pacemaker cells called Cajal, which also act as intermediates between nerves and smooth muscle cells

Question 5

How much does the resting poteintial vary?

Answer 5

Between 5 and 15 millivolts.

Question 6

What is the frequency of slow waves in different parts of the GI tract?

Answer 6

About 3 per minute in stomach

12 in duodenum and 8 to 9 in terminal ileum

Question 7

How does food trigger spikes?

Answer 7

• The bolus distends the gut, stretching its walls.
• Stretching stimulates nerves in the wall of the gut to release neurotransmitters into smooth muscle at the site of distension - the membrane potential of that section of muscle becomes “more depolarized.”
• When a slow wave passes over this area of sensitized smooth muscle, spike potentials form and contraction results.
• The contraction moves around and along the gut in the coordinated manner because the muscle cells are electrically coupled through gap junctions.

Question 8

What is and also stimulates depolarization?

Answer 8

When the potential becomes less negative is called depolarization of the membrane, the muscle fibers become more excitable.

1. stretching of muscles
2. stimulation by acetylcholine released from the endings of parasympathetic nerves,
3. stimulation by several specific gastrointestinal hormones

Question 9

What is hyperpolarization and what triggers it?

Answer 9

When potential becomes more negative, the fibers become less excitable

1. the effect of norepinephrine or epinephrine on the fiber membrane
2. stimulation of the sympathetic nerves that secrete mainly norepinephrine at their endings

Question 10

Were is myenteric plexus and submucosal plexus and what do they do?

Answer 10

Myenteric plexus lies between the longitudinal and the circular muscle layers
(submuscosal plexus lies in the submucosa)
The myenteric plexus controls mainly the gastrointestinal movements and the submucosal plexus controls mainly gastrointestinal secretion and local blood flow.

Question 11

What stimulate gastrointestinal activity ?

Answer 11

Acetylcholine secreation by parasympathic

Question 12

What inhibits contraction

Answer 12

Norepinephrine
Epinephrine
By sympathic

Question 13

Sensory nerves going from epithelium to prevertebral ganglia, spinal cord and brain can be stimulated by what?

Answer 13

1. irritation of the gut mucosa
2. excessive distention of the gut
3. the presence of specific chemical substances in the gut

Signals transmitted through fibers can then casue excitition or under other conditions inhibition of intestinal movements or intestinal secretion
Can be used ex. during foodsickness.

Question 14

Which ion initiates depolarization?

Answer 14

Ca2+
Upon stimuli a particular membrane ion channel, L-type Ca2+ channels, are activated, resulting in calcium influx and initiation of motility

Question 15

When does sympathic system inhibit the gut movement?

Answer 15

During severe stress ex. hunted by a lion

Question 16

What is peristalsis and how is it refulated?

Answer 16

The propulsive movement which cause food to move forward and along the tract to accommodate digestion and absorption.
Stimulated by distention of gut, chemical or physical irritations regulated by myenteric plexus.
Mixing movements which keep intestinal contents mixed.

Question 17

What happens to the blood that passes through the liver?

Answer 17

It is filtered.
Bacteria is removed as well as other particulate matters that have entered fron GI tract.
Also half of three quarters of nutrients are absorbed by liver

Question 18

What happens to absorbed fats?

Answer 18

Almost all fats absorbed from the intestinal tract are absorbed into the intestinal lymphatics and then conducted to the systematic circulating blood by way of the thoracic duct, bypassing the liver

Question 19

What happens with the blood flow after ingestion of food?

Answer 19

blood flow in gastrintestinal tract increases to support:

motor, secretory and absorptive activity

Question 20

What is the different between hunger and appetite?

Answer 20

Hunger - the amount of food a person ingests - determined principally by intrinsic desire for food
Appetite - type of food that a person preferentially seeks

Question 21

Why is chewing important?

Answer 21

Fruits and raw vegetables have indigestable cellulose membranes around their nutrient portions that must be broken before the food can be digested

Digestive enzymes act only on the surface of food particles; so rate of digestion is dependent on total surface area exposed to the digestive secretion

Question 22

What happens upon swallowing?

Answer 22

The swallowing center inhibits the respiratory center halting respiration to allow swallowing to proceed

Question 23

What happens when food reach lower end of esophagus?

Answer 23

Entire stomach and even duodenum become relaxed and prepared to receive food

Question 24

Where is the Pyloric sphincter?

Answer 24

Between stomach and duodenum

Question 25

What is chyme?

Answer 25

a semifluid mix of food and gastric secretions- made in stomach

Question 26

What desides the rate of which the stomach is emptied?

Answer 26

It is regulated by both signals from stomach and duodenum.
However duodenum has by far more potent signals! is in charge.
Depends on the rate the food can be digested and absorbed in the small intestines

Question 27

Despite normal contraction of the pyloric sphincter, the pylorus is usually open enough for what?

Answer 27

For water and other fluids to empty from the stomach.

Question 28

What effect the constriction of the pylorus?

Answer 28

nervous and hormonal signals

can increase or decrease constriction

Question 29

Duodenal factors that inhibit stomach emptying.

Answer 29

1. distention of the duodenum
2. the presence of any iriitation of the duodenal mucosa
3. acidity of the duodenal chyme
4. osmolality of the chyme
5. the presence of certain breakdown products in the chyme, especially breakdown products of proteins and perhaps to a lesser extent of fat

Question 30

How does CCK give hormonal feedback from duodenum to inhibit gastric emptying ?

Answer 30

Cholecystokinin (CKK) is released from mucosa of jejunum in response to fatty substances. CCK is carried by blood to stomach, where it inhibits the pyloric pump and at the same time increase the strength of contraction of the pyloric sphincter

Question 31

How does secretin give hormonal feedback from duodenum to inhibit gastric emptying ?

Answer 31

Secretin is released mainly from the duodenal mucosa in response to gastric acid passed from the stomach through the pylorus (inhibit)

Question 32

How does GIP give hormonal feedback from duodenum to inhibit gastric emptying ?

Answer 32

GIP has a general but weak effect of decreasing gastrointestinal motility

Question 33

What nervous and hormonal signals from small intestines enhances intestinal motility?
(peristalsis)

Answer 33

Gastrin, CCK, insulin, motilin and serotonin

Question 34

What nervous and hormonal signals from small intestine inhibits intestinal motility

Answer 34

secretin and glucagon

Question 35

What happens in the colon?

Answer 35

1. absorption of water and electrolytes from the chyme to form solid feces
2. storage of fecal matter until it can be expelled