Digestion

Question 1

Briefly describe the neural control of digestion (e.g. what branches/divisions enhance and inhibit digestion).

Answer 1

Control: neural (autonomic/involuntary)
Parasympathetic (rest & repair) & Enteric: enhances digestion
Sympathetic (fight or flight): inhibits digestion

Question 2

Describe the secretions from the cephalic phase.

Answer 2

oral secretion: saliva

gastric secretions:
chief cells secrete pepsinogen
Goblet cells secrete mucous

Question 3

During the gastric phase, describe what distension and/or protein stimulates the release of and the downward effects.

Answer 3

Stimulates the secretion of gastrin and histamine.

Gastrin stimulates:
–> goblet cells: mucous
and
–> chief cells: pepsinogen

Histamine stimulates:
–> parietal cells: HCl acid

HCl catalyzes pepsinogen intp pepsin

Low pH activates pepsin (thanks to HCl)

• peak activity pH .5 to 3.0
• denatures when pH > 5.0

Question 4

Phase 3: Intestinal Secretions
Describe the feedback system involving the hormones released by the duodenum depending on the composition of the food leaving the stomach.

In regards to the STOMACH
Low pH and food in general
Fats and sugars
Low pH & Fats
Protein

Answer 4

Stimulates or inhibits stomach depending

INHIBITS Acid secretion in stomach
Low pH and food in general: SECRETIN
Fats & sugars: Gastric Inhibitory Peptide (GIP)

Low pH & Fats: Vasoactive Inhibitory Peptide (VIP)

STIMULATES acid secretion in stomach
Protein: Enteric Gastrin

Question 5

Phase 3: Intestinal Secretions
Describe the feedback system involving the hormones released by the duodenum depending on the composition of the food leaving the stomach.

In regards to the PANCREAS and/or GALLBLADDER
Low pH and food in general
Low pH & Fats
Amino-acids and Fatty acids

Answer 5

Stimulates (exocrine) pancreas and/or gallbladder

Low pH & Food in general: Secretin (again)
- STIMULATES

Low pH & Fats: Vasoactive Inhibitory Peptide (VIP) (again)

• STIMULATES:
  pancreas: bicarb & water secretion (raise pH)
  liver: bile production

Amino-acids and Fatty acids: Cholecystokinin (CCK)
- STIMULATES:
Pancreas: pancreatic enzyme secretion
gall bladder contraction; bile secretion

Question 6

What are the different ways different nutrients are absorbed?

Answer 6

Simple diffusion
Facilitated diffusion
Active transport (often co-transport)

Question 7

What enzyme catalyzes alpha-bond hydrolysis of starch? At what two sites/locations?

Answer 7

amylase

1) salivary amylase in the buccal cavity/esophagus
2) pancreatic amylase in the duodenum and small intestine
(recall: starch = amylose)

Question 8

What are the major functions of the liver?

Answer 8

metabolic storage & distribution
metabolite interconversion
poison detoxification
bile fluid (emulsifier); gall bladder, released via bile duct