Secretory Functions of the Alimentary Tract

Question 1

Name 4 things which can stimulate mucous cells to secrete mucous

Answer 1

1. Chemical Irritation
2. Tactile stimulation
3. Distention of the gut wall
4. Glandular cell secretion of hormones

Question 2

What does parasympathetic stimulation do to the rate of secretion?

Answer 2

Increases

Question 3

What is the parasympathetic innervation to the upper GI tract?

Answer 3

Glossopharyngeal and Vagus Nerve

Question 4

What is the parasympathetic innervation to the distal large intestine?

Answer 4

Pelvic parasympathetic nerves

Secrete due to mechanical stimulation

Question 5

What does sympathetic stimulation do to the rate of secretion?

Answer 5

Increases secretions and vasoconstrict the vessels supplying the gland

If parasympathetic innervation is already present then secretion is reduced

Question 6

Water and Electrolyte Secretion

- What does nerve stimulation cause?

Answer 6

1. Influx of chloride ions and an influx of +ve ions e.g. sodium
2. Osmotic gradient resulting in water influx
3. Cell swells
4. Increased pressure causes minute openings of the secretory border of the cell
5. Water/Electrolytes/Organic Materials exit the secretary surface of the glandular cell

Question 7

What secretion type do the parotid gland produce?

Answer 7

Serous

Question 8

What secretion type do the submandibular glands produce?

Answer 8

Serous and mucous

Question 9

What secretion type do the sublingual glands produce?

Answer 9

Serous and mucous

Question 10

What secretion type do the buccal glands produce?

Answer 10

Mucous only

Question 11

What enzyme is present in saliva which digests starch?

Answer 11

alpha-amylase

Question 12

Salivary glands: Acini

• What secretion do these produce?
• What ions comprise this secretion?

Answer 12

Produce isotonic plasma like primary secretion

Ions: sodium, chloride, bicarbonate and water

Question 13

Salivary glands: Ducts

- What happens in the ducts?

Answer 13

Reabsorption of NaCl

1. Excess reabsorption of sodium ions Vs potassium ions
2. Results in lumenal -70mV
3. Chloride ions are passively reabsorbed from lumen to increase the mV
4. [chloride ions] decreases to match the [sodium ions] decrease
5. Small [HCO3-] secreted into the lumen due to Cl-/HCO3- exchanger

Question 14

In a resting salivary gland what is the concentration of:

• NaCl
• K
• HCO3

Answer 14

15 mEq/L

30mEq/L

50-70mEq/L

Question 15

Why does the concentration of the saliva change during maximal salivation?

Answer 15

Rate of primary secretion increases by 20x

Acinar secretion flows through ducts so rapidly that the ductal reabsorption of NaCl is considerably decreased

Question 16

What two things does saliva contain to promote oral hygiene?

Answer 16

Thiocyanate ions (bacteriocidal)

Proteolytic enzymes (lysosome)

Question 17

What is the main control of salivation?

Answer 17

Parasympathetic stimulation from the superior and inferior salivatory nuclei in the brainstem

Question 18

Parasympathetic stimulation of salivation

• What type of saliva results?
• Which cranial nerves stimulate this?
• What type of receptors are involved?
• What intracellular signalling pathway is involved?

Answer 18

1. Watery
2. CN 7 and 9
3. Muscarinic receptors
4. IP3 intracellular pway

Question 19

Sympathetic stimulation of salivation

• What type of saliva results?
• Which nerves are involved?

Answer 19

1. Viscous

2. T1-T3 nerves of the superior cervical ganglion