water and ion balance 2 Flashcards
What is the fish gill composed of? Which cells likely carry out transport?
*not for walter final
Chloride cells (PNA+ with many mitochondria) and Pavement cells (some with many mitochondria others with very little, both PNA-). Transport likely done by the mitochondria rich cells
What type of capillaries are found in the glomerulus of each nephron?
Fenestrated capillaries for leakage of molecules and fluid
What path do molecules follow as they pass through the nephron and get excreted?
Blood > Afferent Arteriole > Glomerulus > Bowman’s capsule > PCT > Loop of Henle > DCT > Collecting duct > Minor calyx > Major calyx > Ureter > Bladder > Urethra
What is the purpose of the Renin-Angiotensin-Aldosterone (RAA) pathway? How is this achieved?
To cause the juxtaglomerular cells to secrete Renin when either blood pressure or glomerular filtration rate is lower than usual. This in turn causes the production of angiotensin I from inactive angiotensinogen in the blood, which is then converted to angiotensin II by ACE on the vessel epithelia.
Angiotensin II is a potent vasoconstrictor (raises blood pressure) and causes the release of vasopressin and aldosterone
What is the purpose of the Macula densa?
*Not for Walter final exam
To stimulate the juxtaglomerular cells next the the afferent arteriole via paracrine signalling (when Na+ concentration in the DCT is low)
What is the function of the osmotic gradient in the nephron?
Acts as a “countercurrent multiplier” to improve water reabsorption. Filtrate becomes more and more concentrated the deeper into the renal medulla it gets.
What is the difference between transcellular transport and paracellular transport?
Transcellular: solute moves through the cell by transporters and channels in the membrane
Paracellular: Solute passes between the cell junctions which are loose enough to allow leakage
What is the “renal threshold”?
The system gets saturated if Na+ and glucose levels are elevated, therefore less and less gets reabsorbed
What is a podocyte?
Cells in the bowman’s capsule that wrap around the capillaries of the glomerules, restrict the passage of large macromolecules
What is a nephron? What is it composed of?
The functional unit of the kidney
Composed of…
Vasculature, Glomerulus, ball of capillaries, surrounded by bowman’s capsule, capillary beds surrounding renal tubule, renal tubule and lined with transport epithelium
What is a mesangial cell?
Between the capillaries in the glomerulus. Like smooth muscle, capable of contracting to restrict blood flow
What are the 4 functional processes of the nephron?
- Filtration: at the glomerulus (7.5 L/hr in humans)
- Reabsorption: ~99% of filtrate reabsorbed
- Secretion: some molecules removed from the blood and added to the filtrate. Ex: K+, H+, NH4+, pharmaceuticals
- Excretion: 1% of everything that is filtered is expelled from the body (no proteins ever excreted!)
How much fluid does the kidney excrete per hour? What percentage of total fluid is this?
7.5 mL/hour, approximately 1%.
In the nephron, what is the function of the proximal convoluted tubule?
Does most of the solute and water reabsorption, also does secretion of organic anions, organic cations, drugs, and toxins
In the nephron, what is the function of the Loop of Henle? (Ascending vs Descending)
Descending limb: water reabsorption, concentrates urine to form gradient
Ascending limb: ion reabsorption, impermeable to water, dilutes urine to restore gradient
