Saliva and gastric secretions

Question 1

What are the functions of saliva ?

Answer 1

• digestion
• protection
• lubrication
• antibacterial roles
• blood clotting
• calcification of teeth

Question 2

Describe how saliva carries out digestion

Answer 2

• amylase cleaves the 1,4-glycosidic bonds
• lingual lipase hydrolyses lipids

Question 3

Describe how saliva carries out protection

Answer 3

• it prevents drying of the oral cavity (drying causes weakening of the oral tissue)

Question 4

Describe how saliva carries out lubrication

Answer 4

• its involved in the swallowing of bolus

Question 5

Describe how saliva has antibacterial roles

Answer 5

• lactoferrin chelates iron as a lot of bacteria require iron to survive
• lysozymes are involved in the degradation of bacterial cell walls
• it contains immunoglobulins

Question 6

Describe how saliva carries out blood clotting

Answer 6

• prevents gum disease
• promotes wound healing

Question 7

Describe how saliva calcifies the teeth

Answer 7

• acids from food decalcify the teeth and so calcium phosphates and phosphoproteins buffer these acids

Question 8

What are the major salivary glands ?

Answer 8

• parotid glands
• submaxillary glands
• sublingual glands

Question 9

Describe the secretion of the parotid gland

Answer 9

• secretes 25% of saliva
• serous and watery secretion

Question 10

Describe the secretion of the submaxillary gland

Answer 10

• secretes 70% of saliva
• serous and mucous secretion

Question 11

Describe the secretion of the sublingual gland

Answer 11

• predominantly mucous secretion

Question 12

Give some examples of conditions associated with producing less saliva

Answer 12

• xerostomia
• Sjogren’s syndrome
• hyperaldosteronism

Question 13

Describe xerostomia

Answer 13

• significant reduction or absence of saliva
• leads to a decrease in chewing, swallowing and digesting
• caused by some medications, congenital diseases and cranial nerve damage

Question 14

Describe Sjogren’s syndrome

Answer 14

• autoimmune inflammatory disease
• blocked ducts causes atrophy of glands

Question 15

Describe hyperaldosteronism

Answer 15

• can be primary or secondary
• increase in aldosterone secretion
• causes include hypertension and hypokalaemia

Question 16

What is hypokalaemia ?

Answer 16

• low potassium in the blood
• impacts the sodium content of the saliva

Question 17

What are the 2 types of saliva secretion ?

Answer 17

• basal secretion : happening continuously
• stimulated secretion : increase in secretion upon stimulation of the salivary glands

Question 18

What is the rate of saliva secretion ?

Answer 18

0.5 - 7 ml/min

Question 19

How is saliva secreted ?

Answer 19

• regulation of salivary secretion is controlled by the autonomic nervous system
• sensory receptors relay information to salivatory nuclei in the medulla

Question 20

What is the effect of parasympathetic stimulation on the secretion of saliva ?

Answer 20

• promotes watery saliva
• rich in amylase and mucins

Question 21

What is the effect of sympathetic stimulation on the secretion of saliva ?

Answer 21

• has a variable effect
• can increase or inhibit secretion of saliva

Question 22

Describe the formation of saliva

Answer 22

1) parasympathetic stimulation will bring in chloride ions into the acinar cells through a cotransporter protein
2) sodium ions and potassium ions will also move into the cells via the cotransporter
3) chloride ions are pumped out of the cell into the acinus region and this makes the acinus region have a slightly negative potential
4) this negative potential drives the movement of water and sodium ions into the acinus region through paracellular channels
5) sodium ions are pumped out of the acinar cells in exchange for potassium ions so sodium ions can move paracellularly
6) potassium ions are pumped out of the acinar cells so they can come in with chloride ions or in exchange for sodium ions

Question 23

What is meant by paracellular movement ?

Answer 23

movement between cells

Question 24

Describe the how saliva is modified

Answer 24

• the ducts are relatively impermeable to water and this allows saliva to change from isotonic to hypotonic
• the removal of chloride ions and sodium ions will change the saliva from isotonic to hypotonic

Question 25

How does the flow rate of saliva from the acinus region to the duct affect affect the modification of saliva ?

Answer 25

- a fast flow rate will mean there is less time for the removal of sodium and chloride ions and so the saliva at the duct will be more isotonic and less modification has occurred - a slow flow rate will mean more modification can be done

Question 26

What are the receptors found on the basolateral membrane of the acinar cells ?

Answer 26

- muscarinic cholinergic receptors : bind acetylcholine - α adrenergic receptors : bind noradrenaline - substance P receptors : bind substance P

Question 27

What is the effect of the receptors on the acinar cells ?

Answer 27

- receptors result in an influx of calcium ions into the acinar cells - this will increase the the internal calcium ion concentration - this results in exocytosis of amylase into the saliva

Question 28

Describe the ion composition of isotonic saliva

Answer 28

- very similar composition to plasma in terms of sodium ion and chloride ion concentration

Question 29

Describe the ion composition of hypotonic saliva

Answer 29

- low concentration of sodium ions and chloride ions

Question 30

What are the different regions of the stomach ?

Answer 30

- Cardia region - Fundus - Body or Corpus - Antrum - Pylorus

Question 31

What is the function of the pylorus ?

Answer 31

regulates the food exiting the stomach and entering the small intestine

Question 32

Describe the structure of the antrum

Answer 32

it is more muscular than any other region - has a much thicker smooth muscle

Question 33

What are the different gastric glands ?

Answer 33

- cardiac glands - oxyntic glands - pyloric glands

Question 34

Describe the structure and function of the rugae

Answer 34

- folds - allow the stomach to take in food contents without increasing the pressure

Question 35

What do the cardiac glands secrete ?

Answer 35

- mucus : eases friction

Question 36

What do the oxyntic glands secrete ?

Answer 36

- mucus : lines the stomach cells to protect the stomach from chyme - HCl - pepsinogen : pepsin precursor - intrinsic factor : important in the absorption of vitamin B12

Question 37

What do the pyloric glands secrete ?

Answer 37

- pepsinogen

Question 38

What are the different cells found in the gastric glands ?

Answer 38

- mucous neck cells - parietal cells - chief cells - enteroendocrine cells or G cells - enterochromaffin cells or mast cells or H cells

Question 39

What is the function of the mucus neck cells ?

Answer 39

they empty mucus into the stomach lumen

Question 40

What is the function of the parietal cells ?

Answer 40

secrete HCl when needed and intrinsic factor

Question 41

What is the function of the chief cells ?

Answer 41

- secrete pepsinogen - make up 25% of all gastric cells

Question 42

What is the function of the G cells ?

Answer 42

they produce gastrin

Question 43

What is the function of the H cells ?

Answer 43

produce histamine

Question 44

Describe the structure of parietal cells in the resting state

Answer 44

- acid secretion is low - tubulovesicles are present in the cell and they contain H+ pumps - tubulovesicles are relatively impermeable to potassium ions which prevents the H+ pump from being activated

Question 45

Describe the structure of parietal cells in the active state

Answer 45

- tubulovesicles fuse with canaliculus which increases the surface area - H+ pumps and chloride ions and potassium ions are inserted into the canalicular membrane - this increases acid secretion

Question 46

Why do parietal cells have lots of mitochondria ?

Answer 46

Secreting HCl requires lots of energy