Reabsorption: Reabsorption is the movement of water and solutes back into the plasma from renal tubules. Filtration: Filtration is governed by the hydrostatic pressure. Reabsorption: Reabsorption is governed by osmotic pressure as well as oncotic pressure. Filtration: Filtration is a passive process. Reabsorption: Reabsorption is an active process.
Filtration: Filtration is a physical process. Reabsorption: Reabsorption is a selective process. Filtration: Filtration is the initial event of the formation of urine. Reabsorption: Reabsorption follows filtration. Filtration: Filtration produces a diluted filtrate.
Reabsorption: The filtrate is concentrated by reabsorption. Filtration and reabsorption are two subsequent processes occurring in the kidney nephrons during the formation of urine. The main difference between filtration and reabsorption is the function of the each process during the formation of urine.
Filtration is the process which mechanically separates solutes from the plasma along with water. 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.
Some substances can also pass through tiny spaces in between the renal epithelial cells, called tight junctions. As filtrate passes through the nephron, its osmolarity ion concentration changes as ions and water are reabsorbed.
Finally, in the distal convoluted tubule and collecting duct, a variable amount of ions and water are reabsorbed depending on hormonal stimulus. The final osmolarity of urine is therefore dependent on whether or not the final collecting tubules and ducts are permeable to water or not, which is regulated by homeostasis. Reabsorption throughout the nephron : A diagram of the nephron that shows the mechanisms of reabsorption.
Hydrogen, creatinine, and drugs are removed from the blood and into the collecting duct through the peritubular capillary network. Tubular secretion is the transfer of materials from peritubular capillaries to the renal tubular lumen; it is the opposite process of reabsorption.
This secretion is caused mainly by active transport and passive diffusion. Usually only a few substances are secreted, and are typically waste products. Urine is the substance leftover in the collecting duct following reabsorption and secretion. The mechanisms by which secretion occurs are similar to those of reabsorption, however these processes occur in the opposite direction. Renal secretion is different from reabsorption because it deals with filtering and cleaning substances from the blood, rather than retaining them.
The substances that are secreted into the tubular fluid for removal from the body include:. 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. Privacy Policy. Skip to main content. Urinary System. Search for:. When moving from the blood to the interstitium, bulk flow is termed filtration. When moving from the interstitium to the blood, bulk flow is termed re-absorption. The kidney is a major site of bulk flow where waste products are filtered from the blood.
Key Terms filtration : In bulk flow, this refers to the movement of proteins or other large molecules from the blood into the interstitium. Bulk Flow Process Bulk flow is used by small, lipid-insoluble solutes in water to cross the the capillary wall and is dependent on the physical characteristics of the capillary. The Kidneys and Bulk Flow The kidney is a major site for bulk flow transport.
Reabsorption is a two-step process beginning with the active or passive extraction of substances from the tubule fluid into the renal interstitium, and then the transport of these substances from the interstitium into the bloodstream Tubular Secretion : Diagram showing the basic physiologic mechanisms of the kidney and the three steps involved in urine formation. Authored by : Boundless. Provided by : Boundless. Provided by : Wikipedia. Located at : en.
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