Physiology: Net Reabsorption Pressure G28-3

The force that drives fluid back into the peritubular capillaries from the interstitial space.

Capillary hydrostatic pressure minus interstitial hydrostatic pressure, plus capillary osmotic pressure minus interstitial osmotic pressure.

The pressure inside the capillaries pushing fluid outward.

The pressure outside the capillaries pushing fluid inward.

The pressure created by the concentration of proteins in the capillaries, pulling fluid inward.

The pressure created by the concentration of proteins in the interstitial space, pulling fluid outward.

The ability of capillaries to filter fluid, influenced by hydraulic conductivity and surface area.

The proportion of plasma filtered at the glomerulus that is then reabsorbed by the peritubular capillaries.

Increased pressure in the fluid surrounding the renal tubules, forcing solutes back into the tubules.

Increased reabsorption of water and solutes from the tubules back into the blood.

A decrease in the amount of water and solutes reabsorbed from the renal tubules.

A hormone produced by the adrenal glands that regulates sodium and water balance.

A substance that stimulates aldosterone production.

The process of moving sodium and water back into the bloodstream from the renal tubules, increasing blood volume.

The process of removing sodium and water from the body through urine production.

The process of removing excess sodium and water from the blood by the kidneys.

The amount of plasma filtered through the glomerulus, expressed as a fraction of the total plasma flow. A higher filtration fraction means more fluid is filtered.

The process of moving fluid and solutes from the tubular capillaries back into the blood.

The reabsorption process is influenced by the pressure gradients between the tubular capillaries and the interstitium. Increasing hydrostatic pressure or decreasing colloid osmotic pressure in the capillaries reduces reabsorption.

Solutes enter the interstitial space either by active transport (requiring energy) or passive diffusion (moving down a concentration gradient). Water then follows by osmosis.

Solutes within the interstitial space can be reabsorbed into the peritubular capillaries or diffuse back into the tubular lumen.

Decreased reabsorption in the peritubular capillaries can occur due to increased hydrostatic pressure or decreased colloid osmotic pressure. This ultimately reduces fluid and solute uptake from the interstitial space and from the tubular lumen.

Creatinine is a waste product of muscle metabolism that is filtered by the glomerulus but not reabsorbed. Since its production is relatively constant, the amount of creatinine excreted in the urine can be used to estimate the rate at which the glomerulus filters blood.

The amount of a substance cleared from the plasma by the kidneys is equal to the volume of plasma that is completely cleared of that substance per unit of time. For example, if a substance is completely cleared from the plasma at a rate of 100 mL/min, then 100 mL of plasma is completely cleared of that substance every minute.

The filtration fraction is the proportion of plasma that is filtered by the glomerulus. It is calculated by dividing the glomerular filtration rate (GFR) by the renal plasma flow (RPF). For example, if GFR is 100 mL/min and RPF is 500 mL/min, the filtration fraction is 0.2 or 20%.

If the rate of excretion of a substance is less than the rate of filtration, then some of that substance must have been reabsorbed from the tubules back into the blood. Conversely, if the rate of excretion is greater than the rate of filtration, then some of that substance must have been secreted from the blood into the tubules.

The kidneys can remove substances from the blood through both filtration and secretion. Filtration occurs at the glomerulus, where a portion of the plasma is filtered into the renal tubules. Secretion occurs at the tubules, where specific substances are moved from the blood into the tubules for excretion.

ANP, a hormone released by the heart, inhibits sodium and water reabsorption in the renal tubules, leading to increased urinary excretion. This helps regulate blood volume.

Parathyroid hormone increases the reabsorption of calcium in the renal tubules, decreasing phosphate reabsorption, and promoting magnesium absorption.

Sympathetic nervous activation increases renin release and angiotensin II formation, which can decrease sodium excretion.

The renal clearance of a substance is the volume of plasma completely cleared of that substance by the kidneys per unit time. It offers a measure of kidney function.

If a substance is freely filtered by the kidneys and neither reabsorbed nor secreted, then the amount excreted in urine equals the substance's filtration rate. This is used for calculating GFR.

GFR (glomerular filtration rate) can be calculated using inulin because it is freely filtered by the kidneys and neither reabsorbed nor secreted.

Creatinine, a waste product from muscle metabolism, is mostly cleared by glomerular filtration. It is widely used to clinically estimate GFR.

Angiotensin II is a powerful vasoconstrictor hormone released in response to low blood pressure or low extracellular fluid volume. It plays a pivotal role in regulating blood pressure and fluid balance by promoting sodium and water retention.

Aldosterone, a hormone produced by the adrenal glands, is stimulated by Angiotensin II. It acts on the kidneys to increase sodium reabsorption and potassium excretion, ultimately leading to increased blood volume and pressure.

Addison's disease is characterized by the deficiency of cortisol and aldosterone. This results in significant sodium loss and potassium accumulation due to the lack of aldosterone's sodium-retaining and potassium-excreting actions.

Conn's syndrome, also known as primary hyperaldosteronism, is characterized by the excessive production of aldosterone by the adrenal glands. This leads to sodium retention and potassium loss, causing high blood pressure and low potassium levels.

Angiotensin II promotes sodium and water retention primarily through three mechanisms: constriction of arterioles, increased sodium reabsorption in the proximal tubules, loops of Henle, distal tubules, and collecting tubules, and stimulating sodium transport across the epithelial cell membranes.

Antidiuretic hormone (ADH), also known as vasopressin, is primarily responsible for increasing the water permeability of the collecting ducts in the kidney. This allows for reabsorption of water, returning it to the bloodstream and preventing excessive urine production.

Diabetes insipidus is a condition characterized by the inability to concentrate urine due to a deficiency of ADH. This leads to excessive production of dilute urine, resulting in frequent urination and dehydration.

Atrial natriuretic peptide (ANP) is a hormone produced by the heart's atrial cells in response to increased plasma volume and atrial blood pressure. It acts on the kidneys to promote sodium excretion and vasodilation, ultimately reducing blood volume and blood pressure.