Lecture 27

Question 1

GI secretions are classified into 2 parts. What are they?

Answer 1

endocrine secretions and exocrine secretions

Question 2

What is the purpose of endocrine secretions? Give examples

They are for the regulation of __________ and ____________ eg. _________ stimulation of stomach ________ and _________ acid secretion. __________ and _______ inhibition for _______ motility and stimulation of _______ secretions

Answer 2

They are for the regulation of motility and secretion eg. gastrin stimulation of stomach motility and gastric acid secretion. CCK and secretin inhibition for stomach motility and stimulation of pancreatic secretions

Question 3

What are the purposes of exocrine secretions?

Prepare ________ for __________ by:

• diluting it to the _________ of the plasma
• altering _________ for optimal ________
• digesting ________
• protection/________

Answer 3

Prepare food for digestion by:

• diluting it to the osmolarity of the plasma
• altering pH for optimal digestion
• digesting food
• protection/lubrication

Question 4

What are the 4 major components of GI secretions?

Answer 4

• mucus
• enzymes
• electrolytes
• serous solutions

Question 5

How many litres of saliva do we secrete per day?

Answer 5

1.5 L

Question 6

Is saliva hypertonic, hypotonic or isosmotic? What is its osmolarity?

Answer 6

hypotonic with an osmolarity of 100 mOsmolL-1

Question 7

What is the main ion in saliva?

Answer 7

Na+

Question 8

What are five functions of saliva?

Answer 8

1. oral hygiene
2. helps with talking
3. chewing and swallowing by moistening and dissolving food
4. makes food isosmotic
5. has amylase for starch digestion

Question 9

What condition happen as a result of a lack of saliva?

Answer 9

xerostomia

Question 10

Is food acidic or basic?

Answer 10

acidic

Question 11

What is in saliva that protects us from the acidic food?

Answer 11

HCO3-

Question 12

Does the sympathetic system increase or decrease saliva secretion.

Answer 12

Decrease

Question 13

What are 6 examples of things we can analyse using saliva?

Answer 13

1. DNA
2. cancer
3. heart attack
4. infections (HIV)
5. homeopathy
6. COVID-19 testing

Question 14

How many pairs of salivary glands are there?

Answer 14

3

Question 15

What are the three main pairs of salivary glands? What sort of secretion do each of these have?

Answer 15

• parotid (serous)
• submandibular (mixture of mucous and serous)
• sublingual (mucous)

Question 16

As well as the three main pairs of salivary glands, where are the minor ones located?

Answer 16

there are minor buccal glands in the mouth, pharynx and oesophagus

Question 17

Where are the parotid salivary glands located?

Answer 17

behind the ears

Question 18

Where are the submandibular salivary glands located?

Answer 18

in the jaw

Question 19

Where are the sublingual salivary glands located?

Answer 19

under the tongue

Question 20

What are the two important types of cells in the salivary glands?

Answer 20

acinar cells

duct cells

Question 21

Describe the acinar cells in the salivary glands

Answer 21

There are little acinar cells that form a ball and make an acinus. They have leaky epithelium as they mostly move H2O. You can have more serous or more mucous acinar cells depending on the type of salivary gland.

Question 22

What is the purpose of the acinar cells?

Answer 22

They are producing primary saliva which is an isotonic NaCl solution

Question 23

What are the two different types of duct cells?

Answer 23

• intercalated duct cells

- striated duct cells

Question 24

What sort of epithelium are the duct cells? (both types)

Why is this?

Answer 24

tight because they have no movement of H2O, it is mostly for the movement of electrolytes

Question 25

When we are stimulated, by how much can saliva secretion increase?

Answer 25

10-fold

Question 26

What is the composition of saliva?

Answer 26

- mucous (mainly from the sublingual, submandibular and buccal glands) - digestive enzymes such as α-amylase from the parotid gland, lingual lipase from the salivary glands on the tongue - serous secretion (primarily the parotid gland)

Question 27

What is the composition of the serous solution secreted mainly by the parotid glands? It is _______-osmotic solution of _______ with a slightly elevated ________ and ________ but the composition varies with the rate of ________

Answer 27

It is hypo-osmotic solution of NaCl with a slightly elevated K+ and HCO3- but the composition varies with the rate of secretion

Question 28

Saliva is always _______ and _________

Answer 28

hypo-osmotic | hypotonic

Question 29

How do the concentrations of Na+, Cl-, K+ and HCO3- in the saliva differ from those in plasma?

Answer 29

[Na+] and [Cl-] are lower in the saliva and higher in plasma [K+] is higher in the saliva and less in the plasma [HCO3-] is higher in the saliva and less in the plasma

Question 30

What increases as the rate of secretion increases?

Answer 30

osmolarity

Question 31

Why does the composition of the saliva vary with the rate of secretion?

Answer 31

The rate of secretion depends on how the salivary glands is perfused and this depends on whether or not it is regulated by parasympathetic and sympathetic system.

Question 32

The rate of secretion by the acini is variable/constant whereas the rate of secretion by the duct cells is variable/constant

Answer 32

variable | constant

Question 33

Explain the slow rates of saliva secretions

Answer 33

The primary fluid is in contact wth the duct epithelium for an extended period of time so there is a greater absorption of NaCl

Question 34

Explain the high rates of secretion

Answer 34

The primary fluid passes through the ducts rapidly and so there is limited absorption of NaCl

Question 35

Saliva A. is hypertonic during stimulation of secretion. B. helps digesting starch. C. contains enzymes such as pepsin. D. contains less bicarbonate than plasma. E. is rich in NaCl.

Answer 35

B. helps digesting starch.

Question 36

What is the two step process for the formation of saliva? First, the __________ fluid is produced which is an __________ NaCl solution with __________ and __________. Then there is the modification of the fluid by the reabsorption of _______ and ________ by both _______ cells. _________ is not reabsorbed because the duct cells have ________ epithelia. There is limited amount of _________ and _____________ secretion depending on the species, and ________ is secreted from the _________ cells

Answer 36

First, the primary fluid is produced which is an isotonic NaCl solution with amylase and mucous. Then there is the modification of the fluid by the reabsorption of Na+ and Cl- by both duct cells. Water is not reabsorbed because the duct cells have tight epithelia. There is limited amount of K+ and HCO3- secretion depending on the species, and mucous is secreted from the duct cells

Question 37

Describe the secretion from the acinar cells

Answer 37

There is an NKCC1 (not NKCC2), Na+/K+ ATPase and K+ channel in the basolateral membrane. Cl- comes in the basolateral membrane from the NKCC1 which is driven by the Na+ gradients set up by Na+/K+ ATPase. Cl- in now in the cell and it leaks out of an apical Cl- channel due to the electrical gradient which has ben built up in the cell. Na+ follows paracellulary do keep the charge in the lumen neutral and H2O follows into the lumen

Question 38

Explain the reabsorption by the duct cells.

Answer 38

Na+ is reabsorbed in the apical membrane via ENaC. The more saliva we produce, the less we reabsorb via ENaC. K+ is secreted (apically) through K+ channels. H2O can't move through because it is tight epithelium. HCO3- can come in from the blood via a Na+/HCO3- cotransporter. It is also made from the CA reaction and is secreted apically via the Cl-/HCO3- exchanger. CFTR is driving Cl- secretion to maintain this exchanger

Question 39

Describe the parasympathetic regulation of salivary secretion

Answer 39

This is the main system (rest and digest stimulates secretion). ACh is released which helps stimulate blood flow to perfuse the salivary gland so that more water is delivered to the salivary gland so more blood is there to produce high amounts of serous saliva.

Question 40

Describe the sympathetic regulation of salivary secretion

Answer 40

Noradrenaline binds to α1 and β2 receptors and this causes vasoconstriction which inhibits blood flow and so there is only a low amount of mucous saliva

Question 41

What is saliva secreted in response to? (4)

Answer 41

- thought of food - approach of food - food in the mouth - the parasympathetic nervous system

Question 42

What are the two reflexes involved in the secretion of saliva? Explain them

Answer 42

- conditioned reflex: this is due to the sight and smell of food (Pavlov's learned response) - unconditioned reflex: due to the presence of food in the mouth and in response to taste receptors

Question 43

Secretion of a hypotonic salivary solution A. depends on sympathetic activation. B. requires a basolateral chloride and bicarbonate channel in acini. C. requires para-cellular re-absorption of Na+ in acini. D. requires leaky acinar epithelium. E. requires an apical Na+/K+/2Cl- co-transporter to re-absorb Na+ in duct cells.

Answer 43

D. requires leaky acinar epithelium.