Cellular and Glandular Mechanisms of Secretion Flashcards
Describe the mechanisms involved in the cellular secretion of H+ in a kidney tubule cell.
Regulates the Acd/Base Balance.
H+ Secretion in PCT and CD
Apical Membrane: Na+ in H+ out (antiport), CO2 diffuses in (metabolic reactions)
Inside cell: CO2+H2O+CA=H2CO3 ->H+ + HCO3-
Basal membrane: HCO3- out (channel), Na+ out (active transport) CO2 in diffuse
Describe the mechanisms involved in the cellular secretion of K+ in a kidney tubule cell.
K+ Is actively reabsorbed in the PCT. Active secretion in the DCT and CD
All filtered is reabsorbed and 10-15% is excreted.
High cell [K+] favours net diffusion -> Lumen
What are the components of gastric juice and what is their function?
Gastric juice = salts, water, Oxyritic cells secrete HCl + intrinsic factor, Zymogenic cells secrete pepsinogen (pepsin), Interstital fluid, Mucous neck cells secrete mucous, Gastro-endocrine cells secrete Gastrins. Ionic composition deends on the secretion rate.
Increased secretion = Increased [H+], decreased secretion = decreased [H+] and increased [Na+}
Describe the morphological changes that occur in the parietal cell to ‘activate it’
- Parietal cells ave elaborate system of cannaliculi (secretory villi)
- Connected via common outlet of cells luminal surface
- These are lined with microvilli
- Extensive network of tubules and vesicles = Tubuloveicular system.
- When stimuulated to secrete, TV system fuses w/ plasma membrane of secretory cannaliculi = increased surface area.
- TV system contains Hcl secretory apparatus and fusion w/ cannaliculi = increase number of pumping sites available.
Describe the mechanisms involved in the cellular secretion of HCl in a parietal cell, beginning with CO2.
CO2 (from metabolic reactions in cell or from blood) combines with OH- (and carbonic anhydrase) -> HCO3-.
Apical Membrane: H+,K+-ATPase (H+ out, K+ in, primary proton pump.) K+ diffused down ECG back into lumen of stomach. Depends on high [K+] in stomach. (Cl- out)
When H+ is pumped out of cell, HCO3- is left behind. flows down ECG -> baso-lateral membrane in exchange for Cl-.
Cl- leaves apical membrane via electrochemical channel.
Briefly compare and contrast the 3 phases of gastric acid secretion.
Cephalic Stage (Excitatory)
- Receptors for sight, taste, smell activated (thoughts of food)
- Cerebal cortex->Medulla->Vagus->Submucosal Plexus= Increased Gastric Juice + Increased Gastric Peristalsis + Entero-endocrine cells secrete gastrin.
Gastric Phase (Excitatory and continuing)
- Receptors for stretch + distention of stomach, chemorecptors detect increased ph of gastric juice
- Sumucosal plexus-> Inc. Gastric juice, inc. entero-E secretions, inc. peristalsis -> increased gastric emptying
Intestinal Phase (Inhibitory)
- Stretch receptors in duodenum, Chemorecptors detect glu. and FA in duo.
- Enteroendocrine secretion. CCK-> inhibits peristalsis
- Secretin -> inhibit peristalsis and inhibit gastric juice
- Enterogastric reflex inhib gastric juice and peristalsis
Where do ACh come from, and how does it influence HCl secretion in the parietal cell?
Ach arises form parasypathetic nerves
Ach binds to receptor on parietal cells -> open Ca2+ channels -> increase intracellular [Ca2+] -> Increase HCl secretion
Where do histamine come from, and how does it influence HCl secretion in the parietal cell?
Histamine arises from mast cells in gastric muscosa and it diffuses to the parietal cells.
Histamne binds to H2 receptors to activate adenyl cyclase -> increase [cAMP] -> increase HC secretions.
Most potent
Where does gastrin come from, and how does it influence HCl secretion in the parietal cell?
Gastrin comes from G cells of the mucosa of gastric antrum and duodenum and reaches pareital cells via the bloodstream.
Describe the basic process of eccrine sweat secretion.
Eccrine Sweat: Cholinergic innervation, sweat to reduce body core termperature.
- Simple coiled structures.
- Primary secretion = isotonic to blood, by the time it is at surface of skin = hypotonic.
- Subdermal portion of gland produces primary secretion;[Na+] 142mMo; [Cl-] 104mMol.
- Slight stimulation= almost all NaCl reabsorbed (5mMol sweat), OP falls = water reabsorbed, leaving wastes
- Strong Stimulation = 50% reabsorption (60mMol) can = large loss of NaCl
Describe the cellular transport mechanisms of a salivary acinar cell.
Acini produce isotonic primary secretion w/ amylase. Serous acina cells have zymogen granules containing salivary amylase.
- Na++K++2Cl- co transport mech. brings K- and Cl- into cell from ECF.
- Na+ secreted via paracellular transport.
- Produce primary secretion of Na+, K+, HCO3- and Cl-. increased [Cl-] in cell sets up gradient for Cl- to move through apical membrane. This electrical force brings Na+ through leaky tight junctions.
- HCO3- secreted via electrogenic ionic channel in apical membrane.
Describe the cellular transport mechanisms of a salivary duct cell.
Reabsorbes Na+ and Cl-, secretes K+ and HCO3-.
- Parallel transporters: Na+K+ exchange and Cl-HCO3- exchange results in uptake NaCl and secretion CL-, HCO3-
- K brough in on baso-lateral symporter using Na+K+ ATP ase transporter.
- As saliva flows down the ducts it progressively gets more hypotonic.
What contribution does each component (acinar & duct cell) make to the final secretion?
Acinar Portion contributes: Na+, CL-, HCO3-, K+ and H2O
Duct portion contributes: HCO3- and K+
Describe the structure and function of the pancreas.
Structure: Resembles salivary gland tissue. Acinar and islets of langerhans innervated by vagus. PostG Symp innervate BVs. Parasymp stimulates.
Function: Acts as endocrine gland exocrine gland.
Endocrine: Glucagon and Insulin secretion for regulation of blood sugar levels.
Exocrine (Digestion): Aqueous component rich in HCO3- for neutraliasation of chyme. Enzyme component for digestion of CHOs
What are the constituents of pancreatic juice (PJ)?
Enzyme component: Acinar cell secertions composed of proteases released from cells in their inacive form and contins alpha-amylases and pancreatic lipases. Stimulated by cholecystokinin. Trypsin inhibitor prevents the premature activation of proteolytic enzymes in pancreatic ducts.
Aqueous: Produced by acinar cells and modified by duct cells. Isotonic to plasma at all flowrates. [Na+] and [K+] similar to plasma; [Cl-] varies reciprocally with [HCO3-]. [HCO3] varies from60-120mMol which is dependent on secretin dn PJ secretion rates
