Physiology of Tubular Reabsorption

The intrinsic ability of the tubules to increase their reabsorption rate in response to increased filtered load (GFR). This balance primarily occurs in the proximal tubules and to a lesser extent in the loop of Henle.

The physical forces that help move fluids between the peritubular capillaries and the renal interstitium. These forces primarily include hydrostatic pressure and colloid osmotic pressure.

Changes in arterial pressure can directly impact urine output. The body has mechanisms to regulate this, known as pressure-natriuresis and pressure-diuresis.

Hormones play a significant role in regulating tubular reabsorption. These hormones can either increase or decrease the reabsorption of water and solutes.

Sympathetic nerve activity can increase the reabsorption of sodium ions from the tubules. This is part of the body's fight-or-flight response.

The process by which substances are filtered from the blood into the tubules and then excreted in the urine.

The ability of the kidneys to regulate the concentration of urine, producing either concentrated or dilute urine depending on the body's needs.

The kidneys play a key role in regulating the osmolarity of the extracellular fluid (ECF), maintaining a stable balance of water and electrolytes.

The force that drives the movement of fluid between the blood and interstitial spaces. It's influenced by the hydrostatic pressure (pushing force) and osmotic pressure (pulling force) of both the blood and interstitial fluid.

The pressure exerted by the fluid inside blood vessels, pushing fluid out into the interstitium.

The pressure exerted by the fluid in the interstitial space, opposing the outward movement of fluid from the blood vessels.

The pressure exerted by proteins and other solutes in the blood, pulling fluid from the interstitial space into the blood.

The pressure exerted by proteins and other solutes in the interstitial fluid, opposing the inward movement of fluid from the interstitial space into the blood.

The process of increasing the excretion of sodium in urine, leading to increased water excretion as well.

The process of increasing the excretion of urine. It often occurs alongside natriuresis due to increased sodium excretion.

The ability of the kidneys to maintain a relatively constant glomerular filtration rate even when blood pressure fluctuates. This helps to ensure stable urine production.

A substance freely filtered by the glomerulus and neither reabsorbed nor secreted by the renal tubules. Its clearance rate accurately reflects the GFR.

A polysaccharide used to measure GFR. It is not produced by the body and must be administered intravenously.

A by-product of muscle metabolism used clinically to estimate GFR. It is filtered by the glomerulus and slightly secreted by the tubules.

If the clearance rate of a substance is less than inulin's, it indicates reabsorption by the renal tubules.

If the clearance rate of a substance is greater than inulin's, it indicates secretion by the renal tubules.

The process of maintaining a stable osmolarity of the extracellular fluid (ECF), primarily through the regulation of sodium ions.

Water intake comes from food and drink, as well as cellular respiration. Water output occurs through urine, feces, and evaporation from the skin and lungs.

Normal daily sodium intake should match the daily output, which is typically 10-20 mEq.

When the body's fluid is too concentrated (high osmolarity), the kidneys produce small amounts of concentrated urine to conserve water.

When the body's fluid is too diluted (low osmolarity), the kidneys produce large amounts of dilute urine to get rid of excess water.

A hormone released by the posterior pituitary gland that increases the permeability of the collecting ducts to water, leading to reabsorption of water and the production of concentrated urine.

The mechanism by which the kidney creates a concentration gradient in the medulla, allowing it to concentrate urine. It involves the countercurrent flow of fluid in the loop of Henle.

The process by which the ascending limb of the Loop of Henle pumps out salt, creating a hyperosmotic environment in the medulla.

The daily minimum volume of urine that needs to be excreted to remove metabolic waste products.

The kidneys play a crucial role in maintaining the balance of water and electrolytes in the body, regulating the osmolarity of the extracellular fluid.

Angiotensin II (Ang II) increases sodium and water reabsorption, especially in the proximal tubule, through three main mechanisms: 1) stimulating aldosterone release, 2) constricting efferent arterioles to increase peritubular capillary osmotic pressure, and 3) stimulating sodium pumps and transporters on the basolateral and luminal membranes.

Antidiuretic hormone (ADH) is produced by the posterior pituitary gland and acts on water channels (aquaporins) in the distal tubules and collecting ducts to increase water reabsorption, leading to concentrated urine.

Atrial natriuretic peptide (ANP) is produced by the heart's atria in response to increased blood volume. It acts on the collecting ducts to decrease sodium and water reabsorption, leading to increased urine excretion to lower blood volume.

Parathyroid hormone (PTH) is produced by the parathyroid glands and acts on the thick ascending limb of Henle's loop and distal tubules to increase calcium and magnesium reabsorption while decreasing phosphate reabsorption.

Sympathetic activity increases tubular sodium reabsorption by constricting renal arterioles, decreasing GFR, and increasing renin release and Angiotensin II formation.

Renal clearance is the volume of plasma completely cleared of a substance by the kidneys per unit time. It's used to measure kidney function, blood flow, and filtration, reabsorption, and secretion rates.

Renal clearance of a substance (Cs) is calculated by dividing the urinary excretion rate (Us × V) by the plasma concentration (Ps), where Us is the urine concentration, and V is the urine flow rate.

Glomerular filtration, tubular reabsorption, and tubular secretion are the three basic functions of the kidneys.

The process where the ascending limb of Henle's loop actively transports salt out of the tubular lumen, increasing the interstitial osmolarity. This creates a gradient that draws water out of the descending limb, concentrating the tubular fluid. This cycle repeats, continuously concentrating the interstitial fluid in the medulla.

The vasa recta are blood vessels that run alongside the loop of Henle. They act as countercurrent exchangers, preventing the washout of the concentrated interstitial fluid. As blood descends, water diffuses out, and solutes diffuse in, making the blood hyperosmotic. As it ascends, the process reverses.

The ability of the kidneys to produce urine of varying concentrations, ranging from very dilute to highly concentrated, depending on the body's hydration needs. This is achieved by the countercurrent mechanism.

The descending limb of the loop of Henle is permeable to water but not to salts. As the concentrated interstitial fluid draws water out, the tubular fluid becomes more concentrated.

The ascending limb of Henle's loop is impermeable to water, but actively transports salts out of the tubular fluid into the interstitial space. This contributes to the hyperosmotic environment of the medulla.

The ability of the kidneys to regulate the concentration of urine, producing either concentrated or dilute urine depending on the body's needs. This is achieved by the countercurrent mechanism.

The thick ascending loop of Henle actively transports Na+ and Cl- out of the tubular fluid into the interstitial space, creating a high osmotic gradient. This process requires energy and contributes to urine concentration.

The thin descending loop of Henle is highly permeable to water but impermeable to salts. Water moves passively out of the tubule, concentrating the tubular fluid.