Renal Physiology

• Active reabsorption of sodium in the proximal tubule increases the hydrostatic pressure gradient and facilitates the passive reabsorption of bicarbonate.
• The regulated movement of molecules in the nephron involves the renal corpuscle, distal convoluted tubule, and collecting duct.
• The renal corpuscle regulates filtration.
• The distal convoluted tubule is involved in regulated reabsorption.
• The collecting duct is part of the nephron and is involved in regulated reabsorption.
• The site of urine volume production in the nephron is the renal corpuscle.
• The renal corpuscle has two types of regulation: intrinsic regulation and regulation of filtration.
• Intrinsic regulation in the renal corpuscle alters the glomerular filtration rate.
• Inherent to the structure of the glomerular capillaries and glomerular/bowman's capsule are sensors that respond to changes in blood pressure.
• A decrease in blood pressure results in dilation of the afferent arteriole, increased blood flow into the glomerular capillary, and decreased glomerular filtration.
• An increase in blood pressure increases GFR, causing the afferent arteriole to constrict and decrease the flow of blood into the glomerular capillaries, resulting in a decreased GFR.
• Exercise increases GFR, causing the afferent arteriole to constrict and decrease the flow of blood into the glomerular capillaries, resulting in a decreased GFR.
• Extrinsic regulation of the nephron involves the autonomic nervous system, specifically the sympathetic division.
• Dropped blood pressure or increased blood pressure (exercise) results in increased sympathetic stimulation, increased cardiac output, and increased mean arterial pressure, which drives glomerular filtration rate up.
• Autoregulatory mechanisms in the nephron counter increased blood pressure with exercise, preventing increased urinary output.
• Vasoconstriction of afferent arterioles, induced by sympathetic stimulation, drives GFR down.
• Exercise causes the body to conserve blood volume by preserving blood volume.
• The juxtaglomerular apparatus consists of cells found at the interface between the afferent arteriole and the ascending limb of the loop of henle.
• There are two cell types in the juxtaglomerular apparatus: granular cells and macula densa cells.
• The location of the juxtaglomerular apparatus includes the afferent arteriole, which enters into the renal corpuscle, and the ascending limb of the loop of henle.
• The juxtaglomerular apparatus consists of two populations of cells: granular juxtaglomerular cells, which are sensitive to volume changes, and sympathetic (beta adrenergic) + macula densa, which are minor pathways.
• Granular juxtaglomerular cells respond to changes in blood volume.
• A drop in blood volume stimulates granular juxtaglomerular cells, leading to the secretion of renin.
• Renin is an enzyme, not a hormone, and the amount of enzyme determines the impact on reaction rate.
• The reaction catalyzed by renin is plasma protein, angiotensinogen, which converts into angiotensinogen I.
• Increased renin levels increase the conversion into angiotensin I.
• ACE, or angiotensin converting enzyme, is responsible for converting angiotensin I into angiotensin II.
• More angiotensin I increases the conversion into angiotensin II.
• Aldosterone is a hormone responding to increased angiotensin II.
• Aldosterone acts on the distal convoluted tubule and collecting duct of the kidney, targeting sodium transport.
• Increased sodium reabsorption leads to increased water reabsorption, decreased volume, and decreased urination.
• Potassium is detrimental to cardiac function if too high.
• More sodium reabsorption removes excess potassium, a process that also increases water reabsorption and decreases volume and urination.
• Mineralocorticoid is a hormone that acts on the distal convoluted tubule and collecting duct of the kidney, targeting sodium transport.
• Elevated potassium stimulates the adrenal cortex, leading to increased aldosterone and increased water reabsorption.
• Less aldosterone in the distal convoluted tubule/collecting duct slows down or stops reabsorbing sodium, leading to less water reabsorption and increased water in the filtrate, larger urine volume, and increased urination.
• The third regulatory hormone pathway is atrial natriuretic factor (HORMONE) (SODIUM → NATRIUM) → new 30-50 years.
• Atrial natriuretic factor (ANH) acts on the posterior pituitary to inhibit ADH production, leading to lower urine production.
• Atrial natriuretic factor (ANH) acts on the adrenal gland to inhibit aldosterone production, leading to lower urine production.
• Inhibiting both hormones increases urine production.