Control of Reabsorption and Secretion Flashcards
What is active transport?
Process that moves solutes against an electrochemical gradient and requires energy derived from metabolism (ATP)
What is the function of the sodium potassium pump in the kidney tubules
It transports sodium from the interior wall of the cell across the basolateral membrane creating a low intracellular sodium concentration and negative intracellular electrical potential. This causes sodium to diffuse from the tubular lumen into the epithelial cells through the brush boarder
What is secondary active transport?
Two or more substances interact with a specific membrane protein and are transported across the membrane. As one of the substances diffuses along its electrochemical gradient (sodium), the energy is released and used to drive another substance (glucose) against its chemical gradient.
Name some examples of secondary active transport in the kidneys
SGLT, Na/amino acid transporter and NHE-Na/H exchanger.
Describe the cellular ultrastructure and primary transport of proximal tubule
- 65% of sodium and water reabsorbed,
- Sodium pump driven,
- A lot of co-transport,
- Secretion,
- Organic acids/bases,
- Metabolic products,
- Drugs and toxins
Describe the cellular ultrastructure and transport characteristics of the loop of Henle
- 20% of filtered water, 25% of filtered sodium, chloride and potassium reabsorbed.
- Descending segment is permeable to water,
- Ascending limb is impermeable to water, (thick limb has active transporters for sodium chloride and potassium, can be inhibited by loop diuretics)
Describe the cellular ultrastructure and transport characteristics of early and late distal convoluted tubule
- Early section is impermeable to water.
- Absorbs sodium, chloride and potassium just
- Urine becomes more dilute.
- Last section has 2 cell types; Principle cells that absorb water and sodium, but secrete potassium. Intercalated cells which absorb potassium and secrete hydrogen ions or bicarbonate.
What is the role of alpha-intercalated cells?
Mediates acid secretion and net potassium and bicarbonate absorption.
What is the role of beta-intercalated cells
mediates bicarbonate (alkaline) secretion and net proton absorption
Describe the cellular ultrastructure and transport characteristics of the medullary collecting ducts
- Vital to producing dilute or concentrated urine.
- Impermeable to water unless ADH is present.
- Permeable to urea and has urea transporters if ADH is present.
- Can secrete H+ ions so plays a role in acid/base balance
What are the different hormones that effect tubular reabsorption?
- Aldosterone (Increases NaCl and water reabsorption and K+ secretion),
- Angiotensin 2 (Increases NaCl and water reabsorption and K+ secretion),
- Antidiuretic hormone ( Increases H2O reabsorption),
- Atrial natriuretic peptide (Decreases NaCl reabsorption),
- Parathyroid hormone (increases Ca reabsorption)
Describe features of aldosterone
Released from adrenal cortex. It stimulates sodium-potassium ATPase on basolateral side of cortical collecting tubule membrane and increases sodium permeability of the luminal side of principle cells. Also stimulates H+-ATPase in alpha intercalated cells resulting in proton secretion.
Describe features of angiotensin 2
It stimulates aldosterone release from adrenal cortex, constricts afferent and efferent arterioles in kidney, stimulates sodium reabsorption in PCT, loops of Henle, DCT and collecting ducts.
Describe some features of the antidiuretic hormone
Increases water permeability of DCT, collecting tubule and collecting duct. It binds to V2 receptors and stimulates movement of aquaporin 2 to the apical surface. This is reversible to allow control of water permeability
Describe features of the atrial natriuretic peptide hormone
It is secreted by the cardiac atria when it is distended due to increased blood volume. It inhibits the reabsorption of sodium and water by renal tubules.
