Salivary and Pancreatic Secretions Flashcards
What are the functions of saliva?
As the saliva moves down the salivon from acinus –> intercalated duct –> secretory duct –> excretory duct, how is its composition changing?
Begins very similar to ECF
Na+ and Cl- reabsorbed from saliva along way to entering mouth and K+ and HCO3- secreted into saliva
How does the CNS regulate saliva secretion?
Let’s say that I’m a serous acinar cell in the submandibular salivary gland. I’ve just received input from the PSNS.
- What NTs are being released and what are their effects on my cell?
- How would this change if I received input from the SNS?
- What am I going to secrete in response to these signals?
PSNS –> post-ganglionic neurons release substance P, Ach, and VIP onto cells in submandibular ganglion
- Substance P (@ NK1) and Ach (@M3): stimulate pathway resulting in IP3, Ca2+ release, and PKC activity –> cells secrete water, Na+, K+, Cl- and HCO3-
- VIP (@VIP1): stimulate pathway resulting in PKA and cAMP also enhanced by Ca2+ release from other two NTs –> cells secrete alpha amylase
SNS –> post-ganglionic neurons release NE onto cells in submandibular ganglion
- NE (@alpha1): inhibit pathways resulting in IP3 and Ca2+ –> decreased secretion of water and ions, also less alpha amylase secreted due to less Ca2+
- NE (@beta1): inhibit pathways resulting in increase in cAMP and PKA activity –> alpha amylase secretion inhibited
Salivary gland cell will release kallikrein, which cleaves kininogen to bradykinin which is a vasodilator. Additionally, PSNS –> VIP –> vasodilation and PSNS –> Ach act on endothelial cell to release NO –> vasodilation. The response of the cell is to cause vasodiation b/c it needs increased blood flow to salivary gland to obtain the ions and water to secrete from ECF into saliva.
- What neurotransmitters are released from PSNS post-ganglionic cells onto salivary cells?
- What receptors do they bind to?
Substance P –> NK1
Ach –> M3
VIP –> VIP1
- What neurotransmitters are released from SNS post-ganglionic cells onto salivary cells?
- What receptors do they bind to?
NE –> alpha 1 –> stimulate IP3 and Ca2+ release –> secrete water and ions
NE –> beta 1 –> stimulate cAMP and PKA –> secrete alpha amylase
Mucous acinar cells are primarily controlled by the […] NS
Parasympathetic
PSNS activation of mucous acinar cells results in what signaling pathway response in order to secrete mucous?
Ach –> M3 receptor –> increased IP3 –> increased Ca2+ –> increased PKC activity –> mucous secretion
Describe the transport mechanisms by which Na+, K+, Cl- and HCO3- are secreted from ECF to saliva.
- Na+/K+ ATPase removes Na+ from inside cell and into blood to make intracellular [Na+] low and create positive electrochemical driving force for Na+ to enter cell
- Na+ enters cell via:
- Na+/H+ antiporter
- Na+/K+/2Cl- co-transporter
- Na+ is secreted into saliva via:
- No transporter shown
- Diffuse from ECF to saliva via paracellular route driven by high [Na+] and high + charge in blood compared to saliva
- K+ enters via:
- Na+/K+ ATPase
- Na+/K+/2Cl- co-transporter
- K+ is leaves cell via:
- Basolateral K+ leak channel
- Apical K+ leak channel –> likely leaves primarily through this one due to high [K+] in blood relative to saliva
- Cl- enters cell:
- Na+/K+/2Cl- co-transporter
- Cl- leaves cell:
- Negative ion leak channel apical membrane
- HCO3- is made likely via CO2 + H2O inside cell, H+ leaves in antiporter with Na+, HCO3- leaves through apical negative ion transporter
Describe electrolyte secretion in the ductal portion of the salivon.
Ductal electrolyte transport is primarily under […] control
PSNS
What effect can aldosterone have on salivary electrolyte secretion?
Due to Na+/K+ ATPase (basolateral) and apical ENac, aldosterone can increase NaCl reabsorption, thereby decreasing NaCl in saliva
Saliva is […]tonic compared to blood
Hypo
What volume of saliva do we produce daily?
1.5 L/day
Other than ions, what compounds are found in saliva?
Alpha-amylase
Lysozyme
IgA
Describe the composition of pancreatic secretions.
Acinar cells secrete NaCl and digestive enzymes into duct such that fluid is isotonic with ECF. As fluid travels along duct to reach GI tract, NaHCO3 is added to fluid in large amounts. The fluid remains isotonic but this helps provide buffering potential for the pancreatic secretions once they reach the gut because the HCO3- can neutralize the stomach acid present in the chyme.
Describe pancreatic acinar cell secretion.
Describe pancreatic ductal secretion.
What are the 3 phases of pancreatic secretion control?
Cephalic - secretion occurs before food enters stomach, anticipatory
Gastic - secretion occurs when food is in stomach
Intestinal - secretion occurs when food is in intestine
What hormones are the major regulators of pancreatic secretion in the acinus?
What hormones are the minor regulators of pancreatic secretion in the acinus?
Major
- Ach
- GRP
- CCK
Minor
- Secretin
- VIP
What hormones are the major regulators of pancreatic secretion in the ducts?
What hormones are the minor regulators of pancreatic secretion in the ducts?
Major
- Secretin
- Ach
Minor
- VIP
- In a pancreatic acinar cell, when a major regulating hormone binds to the cell, what is the signaling result?
- In a pancreatic acinar cell, when a minor regulating hormone binds to the cell, what is the signaling result?
How do the contents of the intestines affect CCK and secretin secretion?
Cells lining intestines sample contents, fatty acid and amino acid content leads to secretion of CCK into blood stream to exert effects throughout body and acid from stomach leads to secretion of secretin, which enters blood and exerts effects as major secretory regulator for pancreatic ducts and minor secretory regulator for pancreatic acini.
Once intestines secrete CCK into blood, how does it exert its effects to increase pancreatic secretions?
Presence of FA and AA in intestines stimulate enterocytes to secrete CCK releasing protein. Pancreas has already released monitor peptide which combines with CCKRP to stimulate I-cells in intestinal lining to release CCK into blood. CCK can act locally on enteric neurons to talk via vagus to CNS to release Ach onto pancreas to increase pancreatic acinar and duct secretions. CCK also act systemically by going to pancreas via blood and stimulating acinar secretion on its own as well.
A: portal vein
B: hepatic artery
C: bile duct
B: The classic liver lobule is used to examine the blood flow and excretory function of the liver
A points to the central vein, B points to a portal triad
The circled cells are in zone 1 of the liver acinus. These cells are the most metabolically active of the 3 zones, and stain darker due to higher glycogen content.
Recall that these cells receive blood that is most oxygen-rich and nutrient dense.
Ischemic injury in the cells of zone 3
Oxygen and nutrients are depleted as blood passes through zones 1, 2, and 3 on its way to the central vein. As such the hepatocytes in zone 3 are most susceptible to ischemic injury in low oxygen settings
Identify the following:
- sinusoid
- Kupffer cell
- hepatocyte
- bile cancaliculus
Purple – hepatocyte
Red – bile canaliculus
Blue – Kupfer cell
Green - sinusoid
D: Kuppfer cells are resident macrophages in the sinusoids and are derived from monocytes. They are responsible for clearing pathogens in the sinusoids, as well as break down or senescent red blood cells by phagocytic action
A: discontinuous endothelial cell
B: This is the space of Disse, which allows hepatocytes to access blood plasma for exchange of materials. The microvilli increase the surface area of the hepatocytes to plasma by as much as 6-fold. Proteins (albumin, fibronectin, C-reactive protein, several globulins) and lipoproteins synthesized by hepatocytes are secreted into the space.
Identify the layers of the gallbladder wall.
Note - No submucosa or muscularis mucosa
C
When food containing fats enters the duodenum and jejunum, I cells release CCK which stimulates gall bladder contraction.
B
A
The intercalated duct modifies pancreatic secretions by adding sodium bicarbonate-rich fluid to neutralize the acidic contents entering the duodenum from the stomach.
These are zymogen granules containing digestive enzymes in their precursor forms
Enteropeptidase (also called enterokinase) in the glycocalyx of enterocytes of the duodenum cleaves trypsinogen to activate it to trypsin. Trypsin then cleaves more trypsinogen as well as all the other zymogens
Secretin – stimulates the duct cells to secrete a high HCO3- fluid.
CCK – stimulates acinar cells to release zymogen.
The pancreas also receives autonomic innervation. The sympathetic nervous system controls pancreatic blood flow. The parasympathetic nervous system stimulates activity of acinar and centroacinar cells
