Physiology of the kidney. Summary Nephrons are the functional units of the kidneys. The result is the primary ultrafiltrate. Secretion of urea : ADH increases the number of urea transporters.
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Hypertension 70 , — List the conditions that can affect the glomerular filtration rate GFR in kidneys and the manner of its regulation. Glomerular filtration rate GFR is the measure that describes the total amount of filtrate formed by all the renal corpuscles in both kidneys per minute. The glomerular filtration rate is directly proportional to the pressure gradient in the glomerulus, so changes in pressure will change GFR.
GFR is also an indicator of urine production, increased GFR will increase urine production, and vice versa. The filtration constant is based on the surface area of the glomerular capillaries, and the hydrostatic pressure is a pushing force exerted from the flow of a fluid itself; osmotic pressure is the pulling force exerted by proteins.
Many factors can change GFR through changes in hydrostatic pressure, in terms of the flow of blood to the glomerulus. GFR is most sensitive to hydrostatic pressure changes within the glomerulus. A notable body-wide example is blood volume. The increased blood volume with its higher blood pressure will go into the afferent arteriole and into the glomerulus, resulting in increased GFR.
Conversely, those with low blood volume due to dehydration will have a decreased GFR. Pressure changes within the afferent and efferent arterioles that go into and out of the glomerulus itself will also impact GFR.
Vasodilation in the afferent arteriole and vasconstriction in the efferent arteriole will increase blood flow and hydrostatic pressure in the glomerulus and will increase GFR.
Conversely, vasoconstriction in the afferent arteriole and vasodilation in the efferent arteriole will decrease GFR. An example of this is a ureter obstruction to the flow of urine that gradually causes a fluid buildup within the nephrons.
Osmotic pressure is the force exerted by proteins and works against filtration because the proteins draw water in. Increased osmotic pressure in the glomerulus is due to increased serum albumin in the bloodstream and decreases GFR, and vice versa.
GFR is the rate at which is this filtration occurs. GFR is one of the many ways in which homeostasis of blood volume and blood pressure may occur. In particular, low GFR is one of the variables that will activate the renin—angiotensin feedback system, a complex process that will increase blood volume, blood pressure, and GFR.
This system is also activated by low blood pressure itself, and sympathetic nervous stimulation, in addition to low GFR. Tubular reabsorption is the process by which solutes and water are removed from the tubular fluid and transported into the blood.
The fluid filtered from blood, called filtrate, passes through the nephron, much of the filtrate and its contents are reabsorbed into the body. Reabsorption is a finely tuned process that is altered to maintain homeostasis of blood volume, blood pressure, plasma osmolarity, and blood pH.
Reabsorbed fluids, ions, and molecules are returned to the bloodstream through the peri-tubular capillaries, and are not excreted as urine. Tubular secretion : Diagram showing the basic physiologic mechanisms of the kidney and the three steps involved in urine formation. Namely filtration, reabsorption, secretion, and excretion. Reabsorption in the nephron may be either a passive or active process, and the specific permeability of the each part of the nephron varies considerably in terms of the amount and type of substance reabsorbed.
The mechanisms of reabsorption into the peri-tubular capillaries include:. These processes involve the substance passing though the luminal barrier and the basolateral membrane, two plasma membranes of the kidney epithelial cells, and into the peri-tubular capillaries on the other side.
The substances that are secreted into the tubular fluid for removal from the body include:. Tubular secretion : Diagram showing the basic physiologic mechanisms of the kidney and the three steps involved in urine formation. Many pharmaceutical drugs are protein-bound molecules thatDiagram showing the basic physiologic mechanisms of the kidney and the three steps involved in urine formation. Tubular secretion occurs throughout the different parts of the nephron, from the proximal convoluted tubule to the collecting duct at the end of the nephron.
The movement of these ions also helps to conserve sodium bicarbonate NaHCO 3. The typical pH of urine is about 6. Urine that is formed via the three processes of filtration, reabsorption, and secretion leaves the kidney through the ureter, and is stored in the bladder before being removed through the urethra.
At this final stage it is only approximately one percent of the originally filtered volume, consisting mostly of water with highly diluted amounts of urea, creatinine, and variable concentrations of ions.
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