Tubular Reabsorption: Mechanisms and Selectivity

The process by which large molecules, like proteins, are reabsorbed from the tubular lumen back into the blood.

The movement of substances from the tubular lumen, through the tubular epithelial cells, into the interstitial fluid, and finally back into the bloodstream.

The amount of fluid filtered by the glomerulus is much greater than the volume of urine excreted. This highlights the significant role of tubular reabsorption in regulating fluid balance.

Changes in tubular reabsorption have a large impact on urinary excretion because most of the filtered fluid is reabsorbed.

The process of transporting substances across the tubular epithelial membrane from the tubular lumen into the interstitial fluid. It can involve active or passive transport.

The mechanism of tubular reabsorption allows for selective reabsorption or secretion of individual substances, depending on the body's needs.

The movement of substances through the tubular epithelial cells, from the tubular lumen into the interstitial fluid.

The movement of substances between the cells, from the tubular lumen into the interstitial fluid.

The movement of substances across a membrane from an area of high concentration to an area of low concentration, requiring no energy.

Movement of substances across a membrane against their concentration gradient, requiring energy.

A type of active transport that uses energy from the breakdown of ATP to move substances across a membrane.

A type of active transport that indirectly uses energy stored in an electrochemical gradient to move substances across a membrane.

A protein that actively transports sodium ions out of the cell and potassium ions into the cell, using energy from ATP.

The movement of fluid and dissolved substances across a membrane by pressure differences.

Connections between epithelial cells that regulate the passage of substances between cells.

The fluid that surrounds cells in tissues, providing nutrients and removing waste products.

Creatinine is a waste product produced by muscle metabolism. Since it's almost entirely filtered by the glomerulus and not actively reabsorbed, it's a good indicator of glomerular filtration rate (GFR).

Creatinine clearance is a measure of how efficiently the kidneys remove creatinine from the blood. It's calculated by comparing the concentration of creatinine in urine to the concentration in blood, considering the urine flow rate.

The filtration fraction represents the proportion of renal plasma flow that gets filtered by the glomerulus. It's calculated by dividing GFR by renal plasma flow.

If the amount of a substance excreted in urine is less than what was filtered by the glomerulus, then some of it must have been reabsorbed by the tubules. Conversely, if the amount excreted exceeds what was filtered, then there must have been tubular secretion.

Substances completely cleared from the plasma during kidney function have a clearance rate equal to the total renal plasma flow. However, most substances are not fully cleared, indicating reabsorption or secretion in the tubules.

The maximum rate at which a substance can be transported across a membrane. It is determined by the number of carrier proteins available in the membrane and the rate at which they can bind and release the substance.

The process by which water moves across a semipermeable membrane from an area of high water concentration to an area of low water concentration.

A type of protein that allows water to move across cell membranes.

A hormone that increases the permeability of the distal tubules and collecting ducts to water. This leads to increased water reabsorption and concentrated urine.

The portion of the nephron where the tight junctions between epithelial cells become less permeable to water, reducing water reabsorption. This is important for regulating urine concentration.

The portion of the nephron where the tight junctions between epithelial cells are very permeable to water. This allows water to be reabsorbed from the filtrate, leading to increased volume in the peritubular capillaries.

The portion of the nephron where the permeability to water is regulated by ADH. This allows for fine-tuning of urine concentration.

The process by which substances are transported from the filtrate in the nephron back into the blood. This is essential for maintaining fluid and electrolyte balance in the body.

A peptide hormone secreted by the heart atria that helps regulate blood volume by increasing sodium and water excretion in the urine. It is released when the atria are stretched due to increased blood volume.

The process by which the kidneys filter waste products from the blood and produce urine. It involves the filtration of blood in the glomerulus, followed by the reabsorption and secretion of substances in the renal tubules.

The rate at which a substance is filtered from the blood by the glomeruli, expressed as milliliters of plasma cleared per minute. It is a useful measure of kidney function.

A substance that is neither reabsorbed nor secreted by the renal tubules, so its excretion rate directly reflects the rate at which it is filtered by the glomerulus.

A by-product of muscle metabolism that is readily filtered by the glomeruli and can be used to estimate GFR.

The difference between pressure pushing fluid out of a capillary (capillary hydrostatic pressure) and the pressure pushing fluid back in (interstitial hydrostatic pressure, capillary colloid osmotic pressure and interstitial fluid colloid osmotic pressure).

A force that pulls water back into the capillary by drawing water from the interstitial fluid. It results from differences in the concentration of proteins in the blood and interstitial fluid.

The outward pressure exerted by fluid within the capillary, driving fluid out of the capillary.

The pressure opposing filtration, stemming from fluid in the interstitial space pushing back against the capillary.

The process of moving fluid from the tubular lumen back into the bloodstream.

The ability of a capillary to filter fluid, determined by its permeability and surface area.

The pressure in the capillaries surrounding the renal tubules, driven by the arterial pressure and influencing reabsorption.