The GI tract

Question 1

Mechanical function of the GI tract

Answer 1

To breakdown and propel food to sites of absorption and expulsion

Question 2

Membrane transport in the GI tract

Answer 2

Large surface area for absorption - fat-soluble substances diffuse through GI tract walls, and water-soluble substances are transported by transport proteins

Question 3

Immunological function of the GI tract

Answer 3

Generates protective inflammatory response to protect against toxins and pathogens
Gastointestinal associated lymphoid tissue (GALT) - Peyer’s patches and plasma cells

Question 4

Secretory function of the GI tract (4)

Answer 4

1. hormones that aid and regulate digestion
2. acid that helps in breakdown and sterilisation of food
3. mucous that protects GI tract’s inner wall
4. secretions that neutralise stomach acid

Question 5

Function of the mouth (4)

Answer 5

1. Digests mechanically (chewing) and chemically (amylase - carbs)
2. Secretes saliva
3. Absorbs drugs
4. Has immunological properties

Question 6

3 stages of swallowing

Answer 6

1. Voluntary - bolus passes to oropharynx
2. Pharyngeal - involuntary passage of bolus through the pharynx into the oesophagus
3. Oesophageal - involuntary passage of bolus through the oesophagus into the stomach

Question 7

How is food in the airway prevented?

Answer 7

As the tongue moves upwards against the palate, it causes the epiglotis to move over the trachea

Question 8

Functions of the oesophagus (2)

Answer 8

1. Food is moved via peristalsis

2. Secretes mucus to aid passage of food

Question 9

Gastric secretions chemically aid digestion of…

Answer 9

fats and proteins

Question 10

Protein digestion is aided by…

Answer 10

hydrochloric acid, which is controlled by histamine, gastrin, and acetylcholine

Question 11

Functions of the stomach (3)

Answer 11

1. Motility - makes chyme from saliva, food and gastric juice
2. Secretion - gastric juice, pepsin, intrinsic factor, lipase, mucus, gastrin
3. Absorption - water, alcohol and drugs

Question 12

Pepsin

Answer 12

Breaks proteins down into peptides, then again into essential, dispensible, and conditionally dispensible amino acids

Question 13

Lipase

Answer 13

Active in an acidic environment

Breaks down triglycerrides into di- and monoglycerrides

Question 14

Saturated vs unsaturated fats

Answer 14

Saturated fats have no double bonds and form in a straight structure; unsaturated have double bonds and form a bend structure

Question 15

Amylase

Answer 15

Breaks carbohydrates into simple sugars or monosaccharides so they can be transported across membranes

Question 16

Villi

Answer 16

Developed surface of the epithelium in the small intestine
Increase surface area to aid absorption
Microvilli on villi surface agitate fluid around villi to ensure micronutrients can access cell surface

Question 17

Functions of the small intestine

Answer 17

Digestion: so substances can be facilitated across membrane
Absorption
Protection: Paneth cells are immunological tissues

Question 18

Hepatic portal system

Answer 18

1. Small intestine absorbs products of digestion
2. Nutrients travel via the hepatic portal vein to the liver
3. Liver liberates or stores nutrients according to blood levels
4. Nutrents enter general circulation via the hepatic vein

Question 19

Functions of the large intestine

Answer 19

Removes water from chyme to produce faeces

Contents is dryer and with more fibrous material than small intestine

Question 20

Positive feedback loop of defecation

Answer 20

1. Peristalsis forces faeces into rectum
2. Stretch receptors in spinal cord send signal to spinal cord
3. Involuntary muscle in rectum contracts

Question 21

Neural control of the GI tract

Answer 21

ANS - parasympathetic nervous system, using acetylecholine

SNS inhibits via adrenaline/noradrenaline

Question 22

Institial cajal cells

Answer 22

‘Pacemakers’

Stimulated by acetylecholine and stretch

Question 23

Myenteric plexus

Answer 23

Network of nerve fibres between circular and longitudinal GI muscle layers - coordinates peristalsis contraction

Question 24

Muscularis mucosae

Answer 24

Muscle tissue between GI epithelium and submucosa that agitates epithelial layer to liberate glandular crypts and enhance contact between epithelium and tract contents