Flashcards in Renal System 3 Deck (53):
What is blood flow to the kidney like, and how does it affect glomerular filtration rate?
Blood flow is tightly regulated, so the glomerular filtration rate is relatively constant
What is urine output directly proportional to?
What is special about the glomerular capillaries?
It has arterioles before and after it
What does arterioles on either side of the glomerular capillaries (glomerulus) allow for ?
Tight regulation of pressure gradients to maintain near constant glomerular filtration rates
What can control the glomerular filtration rate when there's an increase in arterial pressure?
It can be buffered by the vasoconstriction of afferent arterioles
How can glomerular filtration rate remain constant when there's a decrease in arterioles pressure?
It can be buffered by the vasoconstriction of efferent arteriole
What do you not want glomerular filtration to respond to?
Rapid blood pressure change
When does glomerulus pressure drop?
When there's constriction upstream (afferent)
When does glomerulus pressure increase?
When there's constricted efferent arterioles downstream
What is glomerular pressure equal to?
Exactly between the afferent and efferent arteriole pressures
What is afferent and efferent arteriole pressure if glomerular pressure is 55mmHg?
What is efferent/afferent pressure if glomerular pressure is 52.5
What is afferent/efferent pressure if glomerular pressure is 57.5?
What is glomerular filtration determined by?
Net filtration pressure
What does net filtration pressure equal?
Glomerular (blood) hydrostatic pressure - blood colloid osmotic pressure - capsular hydrostatic pressure
What is average glomerular (blood) hydrostatic pressure?
What is blood colloid osmotic pressure?
What does net filtration determine?
How much water and small dissolved dilutes leave the blood
What is glomerular blood hydrostatic pressure?
The mechanical pressure between the afferent and efferent arterioles (ie within the glomerulus; drives the plasma filtrate from the capillaries of the glomerulus into the capsules space)
What is capsular hydrostatic pressure?
The pressure exerted on the plasma filtrate by the elastic recoil of the glomerular capsule
What is blood colloid osmotic pressure?
The osmotic force which is of the proteins left in the plasma; the proteins exert an increasing osmotic "pull" on the water filter in the plasma filtrate
What is autoregulation of glomerular filtration?
What is neural regulation of the glomerular filtration?
Increased sympathetic nerve activity leads to vasoconstriction
What is hormonal regulation of glomerular filtration?
Angiotensin 2 via vasoconstriction of afferent and efferent arterioles
Atrial naturetic peptide via relaxation of mesangial cells, increasing surface area available for filtration
What regulates the glomerular filtration?
Anything that alters the glomerular hydrostatic blood pressure (eg pressure of the afferent artery) and anything that alters the surface areas available for filtration
What are the two types of nephrons?
1. Cortical nephrons (dilute urine)
2. Juxamedullary nephron (important in production of concentrated urine)
What is the medulla like?
Has a high concentration of urea and salts
What occurs at the proximal convoluted tubule?
The largest amount of solute and water reabsorption from fluid
Percentages of solute and water reabsorption in proximal convoluted tubule?
60% glomerular filtrate
60% NaCl and water
What is the proximal convoluted tubule like?
Highly active in membrane transport process with reabsorption of water, ions and glucose
What is the proximal convoluted tubule characterised by?
The presence of a highly developed brush border increasing surface area
What maintains the Na gradient in the proximal convoluted tubule?
The Na/K ATPase pump on the basal surface of epithelial cells
How does Na move into tubule cells in the proximal convoluted tubule?
Via symporters (Na/glucose) and antiporters (Na/H allowing H to be secreted), so glucose and other solute can diffuse down their gradients
What allows water movement via osmosis in the proximal convoluted tubule?
What is the osmolarity in the proximal convoluted tubule like?
Similar to plasma, 290 mOsmol/L
What has a low permeability to ions and urea but high permeability to water?
Descending loop of henle
Why does water move out of the descending loop of henle via osmosis?
Because the interstitial fluid is highly concentrated in the medulla of the kidney
Where in the descending loop of henle is the filtrate very concentrated?
At the bottom of the loop- 1200mOsmol/L
What is impermeable to water?
The thick ascending limb
What is actively absorbed in the thick ascending limb?
Na, K and Cl
What is the concentration of filtrate at the tip of the loop of Henle like?
Very dilute- 100 mOsmol/L
Where is Na pumped out actively?
Thick ascending limb
What has a countercurrent mechanism?
The loop of henle
How is the loop of henle a countercurrent mechanism?
Descending limb is impermeable to NaCl, while the ascending limb is impermeable to water, and the interstitial fluid is very concentrated in the tip of the medulla
Where is there additional reabsorption of NaCl?
In the diluted convoluted tubule and collecting duct
What is water permeability in the diluted convoluted tubule and collecting duct dependent on?
Antidiuretic hormone (ADH)
When is urine dilute?
In the absence of ADH
What is vasopressin?
What does ADH act on?
Vasopressin acts on the last part of the convoluted distal tubule and the collecting duct
What does ADH do?
Stimulates the insertion of aquaporin-2 containing vesicles into the apical membrane
What is aquaporin 2 and what does it do?
It's a water channel so water can now move from the tubule into the cell and because the basolateral membrane is always relatively permeable to water, water is ultimately reabsorbed into the blood
What does ADH facilitate?
The reabsorption of water resulting in very concentrated urine