10. Cellular and Glandular mechanisms of secretions

Question 1

Describe the mechanisms involved in the cellular secretion of H+ in a kidney tubule cell.

Answer 1

• Hydrogen is added to the filtrate in the PCT, DCT and Colecting ducts of the nephron. The secretion rate depends upon the acidity of the body but essentially the end goal is to ensure that an homeostatic acid/base balance is kept.
• So basically the Bicarbonate and hydrogen within the tubular lumen form carbonic acid which is then acted upon by carbonic anhydrase to give water and carbon dioxide, both of which happily diffuse through the apical surface of the PCT cell. Once inside the PCT cell carbonic anhydrase recombines water and CO2 into carbonic acid which will basically just dissolve within the ICF to give hydrogen and bicarbonate. whilst the sodium bicarbonate transporter then actively pumps sodium and bicarbonate out of the basal membrane into the ECF and ultimately the peritubular capillary (which is the shit we arent fkn interested in right now), the sodium hydrogen antiporter (an exchanger, on the apical membrane) brings hydrogen into the PCT cell in exchange for hydrogen. wipes sweat off keyboard

Question 2

Describe the mechanisms involved in the cellular secretion of K+ in a kidney tubule cell.

Answer 2

• All filtered potassium is totally reabsorbed in the PCT, however 10-15% of that potassium is then secreted back into the filtrate in the DCT and CD.
• The factors influencing the rate of this are:
  
  • 1. Degree/state of acidosis; when the body is in acidosis the level of K+ excretion is decreased (and inversely for alkalosis)
  • 2. The levels of aldosterone in the bloodsteam (thus linked to Na+ balance). An increase in aldosterone triggers an increase in K+ secretion and visa versa.

As far as the mechanism goes, potassium secretion is mainly controlled by the sodium potassium pump (shocker, crazy, wow) so as the potassium within the peritubular capilaries is diffused through the basolateral membrane of the tubular cell (DCT or CD) via the sodium potassium pump. So now we have more potassium within the

Question 3

What are the components of gastric juice and what is their function?

Answer 3

• salts, water
• HCl (parietal cells) → activate pepsinogen, fight pathogens
• Intrinsic factor (parietal cells) → enables body to absorb B12
• pepsin (chief cells release pepsinogen) → protein degradation
• mucous (mucous neck cells) → prevention of damage to internal stomach
• gastrin (entero-endocrine cells) → increase HCl secretion & motility

Question 4

Briefly compare and contrast the 3 phases of gastric acid secretion.

Answer 4

• Cephalic Phase: Stimulating → food stimulates hypothal., PNS stimulation
• Gastric Phase: Stimulating and Continuing → distention stomach, increased gastrin secretion leading to increased pH
• Intestinal Phase: Inhibitory → distention duodenum; regulate chyme flow

Question 5

Describe the basic process of eccrine sweat secretion.

Answer 5

• Cholinergic (ACh) innervation → parasympathetic stimulation initiates
  
  • apocrine → adrenergic innervation
• purpose - body temp