Introduction to GIT Function

Question 1

The digestive system consists of?

Answer 1

1. neuronal and muscular tissues
2. epithelia with absorptive and secretory functions 3. endocrine cells
3. target cells for the gastrointestinal hormones

Question 2

Name the 2 components of the digestive system?

Answer 2

1. gastrointestinal tract 2. accessory digestive organs

Question 3

Describe the course of the digestive system?

Answer 3

extends from mouth to anus - 9 m long

Question 4

Name the organs of the GIT?

Answer 4

1. oral cavity 2. pharynx 3. oesophagus 4. stomach 5. small intestine 6. large intestine

Question 5

Name the accessory digestive organs?

Answer 5

1. teeth 2. tongue 3. salivary glands 4. liver 5. gall bladder 6. pancreas

Question 6

What are the 7 functions of the GIT?

Answer 6

1. ingestion
2. mechanical digestion and chemical digestion
3. secretion
4. absorption
5. motility/peristalsis
6. excretion
7. immune and protective role of GIT

Question 7

What is ingestion?

Answer 7

when materials enter the digestive tract via the mouth

Question 8

Describe ingestion?

Answer 8

is an active process involving conscious choice and decision making

Question 9

What is mechanical digestion?

Answer 9

physical manipulation and distortion through the actions of the teeth, tongue, and palatal surfaces

Question 10

Describe mechanical digestion?

Answer 10

Tearing and crushing with teeth followed by squashing and compaction by the tongue (preliminary mechanical processing) - may or not be required before ingestion

Question 11

What is the importance of mechanical digestion?

Answer 11

1. make food easier to propel along the digestive tract

2. increases the surface area for enzymatic attack

Question 12

What is chemical digestion?

Answer 12

chemical breakdown of food into small organic fragments suitable for absorption by the digestive epithelium

Question 13

What is the purpose of chemical digestion?

Answer 13

to break down food into simple molecules - simple molecules in food such as glucose can be absorbed intact, but large molecules e.g. polysaccharides or triglycerides cannot be absorbed

Question 14

What are the 2 types of secretions?

Answer 14

1. endocrine 2. exocrine

Question 15

Describe exocrine secretions?

Answer 15

the release of saliva, acids, digestive enzymes, buffers and salts by the epithelium of the digestive tract

Question 16

Describe endocrine secretions?

Answer 16

secretion of hormones that regulate the digestive system

Question 17

What is absorption?

Answer 17

The movement of organic substrates, electrolytes (inorganic ions), vitamins and water across the digestive epithelium into the interstitial fluid of the digestive tract

Question 18

What is motility/peristalsis?

Answer 18

The rhythmic wavelike contractions of the smooth muscle of the intestines that move food through the GI tract.

Question 19

What is excretion?

Answer 19

elimination of waste products from the body - The digestive tract and glandular organs secrete waste products in secretions discharged into the lumen of the tract

Question 20

Waste products are ejected through?

Answer 20

defecation/egestion

Question 21

Waste products are ejected as?

Answer 21

faeces - waste products + indegestable residue

Question 22

Describe the protective role of the lining of the GIT?

Answer 22

1. Corrosive effects of the digestive acids and enzymes
2. Mechanical stresses such as abrasion
3. Bacteria that either is swallowed with food or reside inside the digestive tract
4. Bacteria reaching the underlying tissues are attacked by macrophages and other cells of the immune system

Question 23

The activities of the digestive system are regulated by?

Answer 23

neural, hormonal and local mechanisms

Question 24

What is the nervous system of the GI tract?

Answer 24

enteric nervous system - 100 million neurons

Question 25

What does the enteric nervous system consist of?

Answer 25

1. myenteric plexus 2. submucosal plexus

Question 26

Where is the myenteric plexus? (Auerbachs plexus)

Answer 26

lies between the longitudinal and circular muscles

Question 27

Function of the myenteric plexus?

Answer 27

controls mainly GI movements

Question 28

Where is the submucosal plexus? (Meissners plexus)

Answer 28

lies in the submucosa

Question 29

Function of the submucosal plexus?

Answer 29

regulates GI blood flow and epithelial cell function (local intestinal secretion and absorption)

Question 30

Nerve plexuses near the GI tract initiate what? (intrinsic)

Answer 30

short reflexes

Question 31

What are the extrinsic controls of the GI tract?

Answer 31

1. sympathetic 2. parasympathetic 3. somatic

Question 32

Extrinsic controls initiate what?

Answer 32

long reflexes arising within or outside the GI tract

Question 33

What do motor neurons that terminate in the smooth muscle do?

Answer 33

stimulate contractions

Question 34

What do motor neurons that terminate on the intestinal crypts do?

Answer 34

stimulate salt and water secretion into lumen

Question 35

What does the parasympathetic nervous system do?

Answer 35

stimulates motility + secretions by the GI tract

Question 36

What does the sympathetic nervous system do?

Answer 36

1. reduces peristalsis + secretory activity 2. stimulate the contraction of sphincter muscles along the GI tract - inhibit GI functions

Question 37

What are the receptors of the GIT?

Answer 37

1. mechanoreceptors 2. chemoreceptors

Question 38

What do these receptors of the GIT respond to?

Answer 38

1. stretch 2. presence of substrate 3. osmolarity 4. pH 5. end product of digestion

Question 39

Receptors of the Git initiate reflexes that?

Answer 39

1. activate or inhibit digestive glands | 2. mix lumen contents and move them along

Question 40

Describe long reflexes?

Answer 40

- provide a higher level of control that coordinates activities along the length of the digestive tract - generally control large scale peristaltic waves that move materials from one region of the digestive tract to another - may involve motor fibres in the glossopharyngeal, vagus, or pelvic nerves that synapse in the myenteric plexus

Question 41

How can neural commands be affected?

Answer 41

the sensitivity of the smooth muscle cells to neural commands can be enhanced or inhibited by digestive hormones

Question 42

Function of gastrin?

Answer 42

stimulates acid production

Question 43

Function of secretin?

Answer 43

stimulates pancreatic bicarbonate secretion

Question 44

Function of chlocystokinin?

Answer 44

stimulates gall bladder contractility

Question 45

Describe local/paracrine mechanisms?

Answer 45

prostaglandins, histamine and other chemicals released into the interstitial fluid affect cells within a small segment of the digestive system

Question 46

Function of these mechansims?

Answer 46

these local messengers are important in coordinating a response to conditions that affect a portion of the digestive tract (e.g. pH) - for example histamine in the lamina propria of the stomach stimulates secretion of acid by cells in the adjacent epithelium