Lecture 27 Flashcards
GI secretions are classified into 2 parts. What are they?
endocrine secretions and exocrine secretions
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
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
What are the purposes of exocrine secretions?
Prepare ________ for __________ by:
- diluting it to the _________ of the plasma
- altering _________ for optimal ________
- digesting ________
- protection/________
Prepare food for digestion by:
- diluting it to the osmolarity of the plasma
- altering pH for optimal digestion
- digesting food
- protection/lubrication
What are the 4 major components of GI secretions?
- mucus
- enzymes
- electrolytes
- serous solutions
How many litres of saliva do we secrete per day?
1.5 L
Is saliva hypertonic, hypotonic or isosmotic? What is its osmolarity?
hypotonic with an osmolarity of 100 mOsmolL-1
What is the main ion in saliva?
Na+
What are five functions of saliva?
- oral hygiene
- helps with talking
- chewing and swallowing by moistening and dissolving food
- makes food isosmotic
- has amylase for starch digestion
What condition happen as a result of a lack of saliva?
xerostomia
Is food acidic or basic?
acidic
What is in saliva that protects us from the acidic food?
HCO3-
Does the sympathetic system increase or decrease saliva secretion.
Decrease
What are 6 examples of things we can analyse using saliva?
- DNA
- cancer
- heart attack
- infections (HIV)
- homeopathy
- COVID-19 testing
How many pairs of salivary glands are there?
3
What are the three main pairs of salivary glands? What sort of secretion do each of these have?
- parotid (serous)
- submandibular (mixture of mucous and serous)
- sublingual (mucous)
As well as the three main pairs of salivary glands, where are the minor ones located?
there are minor buccal glands in the mouth, pharynx and oesophagus
Where are the parotid salivary glands located?
behind the ears
Where are the submandibular salivary glands located?
in the jaw
Where are the sublingual salivary glands located?
under the tongue
What are the two important types of cells in the salivary glands?
acinar cells
duct cells
Describe the acinar cells in the salivary glands
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.
What is the purpose of the acinar cells?
They are producing primary saliva which is an isotonic NaCl solution
What are the two different types of duct cells?
- intercalated duct cells
- striated duct cells
What sort of epithelium are the duct cells? (both types)
Why is this?
tight because they have no movement of H2O, it is mostly for the movement of electrolytes
When we are stimulated, by how much can saliva secretion increase?
10-fold
What is the composition of saliva?
- 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)
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 ________
It is hypo-osmotic solution of NaCl with a slightly elevated K+ and HCO3- but the composition varies with the rate of secretion
Saliva is always _______ and _________
hypo-osmotic
hypotonic
How do the concentrations of Na+, Cl-, K+ and HCO3- in the saliva differ from those in plasma?
[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
What increases as the rate of secretion increases?
osmolarity
Why does the composition of the saliva vary with the rate of secretion?
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.
The rate of secretion by the acini is variable/constant whereas the rate of secretion by the duct cells is variable/constant
variable
constant
Explain the slow rates of saliva secretions
The primary fluid is in contact wth the duct epithelium for an extended period of time so there is a greater absorption of NaCl
Explain the high rates of secretion
The primary fluid passes through the ducts rapidly and so there is limited absorption of NaCl
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.
B. helps digesting starch.
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
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
Describe the secretion from the acinar cells
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
Explain the reabsorption by the duct cells.
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
Describe the parasympathetic regulation of salivary secretion
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.
Describe the sympathetic regulation of salivary secretion
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
What is saliva secreted in response to? (4)
- thought of food
- approach of food
- food in the mouth
- the parasympathetic nervous system
What are the two reflexes involved in the secretion of saliva? Explain them
- 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
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.
D. requires leaky acinar epithelium.
