Physiology of Salivary and Gastric Secretion and Gastric Motility

Question 1

State the three main pairs of salivary glands and the nature of their secretions in relation to mucous content

Answer 1

Parotid - low mucous
Submandibular - medium mucous
Sublingual - high mucous

Question 2

State the structure of salivary glands`

Answer 2

Salivary glands consist of:
External capsule
Septae separating lobes and lobules
Lobules composed of salivons

Question 3

State the structure of a salivon

Answer 3

The salivon is the functional unit of a salivary gland. It comprises:
Acinus formed from serous and mucous cells
Contractile myoepithelial cells surrounding the acini
Serous demilunes - secrete lysozyme
Intercalated duct
Striated duct

Question 4

State the main functions of saliva and explain how saliva does these functions

Answer 4

Lubrication - saliva aids movement, facilitates speech and helps swallowing
Protection - see next flashcard
Digestion - saliva liberates chemicals from food to stimulate taste buds and alpha-amylase in saliva initiates digestion of complex carbohydrates
Facilitating suckling by infants
Increasing secretion before vomiting to protect against gastric acid reflux

Question 5

Explain how saliva protects the body

Answer 5

Bicarbonate, phosphate and mucous in saliva buffer metabolic acids
High Ca2+ content helps prevent demineralisation of enamel
Lysozyme attacks bacteria cell walls
Lactoferrin chelates iron and limits iron availability to bacteria
IgA in saliva contributes to immunity

Question 6

List the electrolyte constituents of saliva and state which constituents are found at higher concentrations than plasma

Answer 6

Fe2+
K+ - higher than plasma
Cl-
I-
HCO 3- - higher than plasma
Ca2+
Na+
PO2 4-

Question 7

Describe the different contents of the secretion by different glands

Answer 7

Parotid - secretion is watery and alpha-amylase rich
Submandibular - more viscous than parotid
Sublingual - mucous-rich secretion

Question 8

Name the first stage of formation of saliva and explain what happens in it

Answer 8

The first stage in the formation of saliva is called primary secretion
The Na+/K+ pump drives inward movement of Cl- into the lumen
Na+ and K+ diffuses into the duct and water follows by osmosis

Question 9

Name the second stage of saliva production and explain what happens in it

Answer 9

The second stage of saliva production is called secondary modification
Striated, intercalated and excretory ducts remove Na+ and Cl- from the solution and add K+ and HCO3-
The movement of Na+ and Cl- is greater meaning the solution is diluted

Question 10

State the mechanisms through which saliva secretion is controlled by reflexes

Answer 10

Salivary reflexes are learned reflexes. Once they are, the cerebral cortex stimulates the salivary glands through extrinsic parasympathetic fibres in CN VII (submandibular and sublingual) and CN IX (parotid)

Question 11

Explain when parasympathetic stimulation is dominant in saliva secretion, and what it causes

Answer 11

Parasympathetic stimulation is dominant in normal saliva secretion. It causes
Increased synthesis and secretion of alpha-amylase
Increased contraction of myoepithelial cells
Increased blood flow to glands

This causes large volume, watery and enzyme-rich saliva

Question 12

Explain when sympathetic stimulation is dominant in saliva secretion and its effects

Answer 12

Sympathetic stimulation is dominant in stressful saliva production. It causes
Increases secretion of alpha-amylase, K+ and HCO3-
Increased contraction of myoepithelial cells
Decreased blood flow to the glands

This causes small volume, mucous-rich and thick saliva

Question 13

State the divisions of the secretory mucousa

Answer 13

Oxyntic mucosa

Pyloric gland area

Question 14

Name the secreting cells within the pyloric gland area, their secretions and the functions of their secretions

Answer 14

D cells - produce somatostatin, which inhibits HCl secretion

G cells - produce gastrin, which stimulates HCl secretion

Question 15

Name the secreting cells within the oxyntic mucosa, what they secrete and the functions of their secretions

Answer 15

Chief cells - produce pepsinogen, an inactive precursor of pepsin
Enterochromoffin-like cells - produce histamine, which stimulates HCl secretion
Parietal cells - secrete intrinsic factor, which binds to vitamin B12 allowing absorption in the terminal ileum, and secretes HCl, which activates pepsinogen to pepsin

Question 16

Name the pump responsible for secreting HCl and the substances which enhance the action of the pump

Answer 16

The H+/K+ATPase pump is crucial in secreting HCl

It is enhanced by ACh, histamine and gastrin

Question 17

Describe what happens in the cephalic phase of gastric secretion

Answer 17

The cephalic phase of gastric secretion is ‘in the head’, where vagal activation leads to increased secretion of gastric acid

Question 18

Describe what happens in the gastric phase of gastric secretion

Answer 18

The gastric phase is when the food is in the stomach, and the amount of secretion depends upon the nutrient content of food

Question 19

Describe what happens in the intestinal phase of gastric secretion

Answer 19

In the intestinal phase of gastric secretion, signals originate from the duodenum which inhibit gastric acid secretion