18-Kidney

Mammalian Kidney

Osmoregulating and excretory organs that eliminate excess substances and maintain body composition.

Nephron

The functional subunit of the kidney, consisting of a long epithelial tube involved in urine formation.

Glomerular filtration

The process by which plasma is filtered from the blood through the glomerulus into the Bowman’s capsule.

Tubular reabsorption

The process of moving valuable substances from the nephron back into the bloodstream, primarily occurring in the renal tubules.

Tubular secretion

The active transport of substances from the bloodstream into the tubular fluid in the nephron.

Renal regulation of pH

The kidneys help maintain acid-base balance by secreting or reabsorbing hydrogen ions and bicarbonate.

Hemodialysis

A medical process that filters the blood through an artificial membrane to remove waste and excess fluids.

Glomerulus

A tuft of capillaries involved in the filtration of blood at the start of nephron function.

Bowman's capsule

The sac-like structure that encases the glomerulus and collects the filtrate from blood.

Loop of Henle

A section of the nephron that plays a crucial role in concentrating urine.

Juxtamedullary nephron

A type of nephron with glomeruli located deep in the kidney cortex, important for urine concentration.

Cortical nephron

A type of nephron with glomeruli in the outer cortex and shorter loops of Henle.

Antidiuretic hormone (ADH)

A hormone that regulates water reabsorption in the kidneys, influencing urine concentration.

Renin-angiotensin system

A hormone system that regulates blood pressure and fluid balance through the secretion of renin and angiotensin.

Aquaporins

Water channels in the membrane that facilitate water reabsorption in the kidney.

Glomerular filtration rate (GFR)

The rate at which fluid is filtered through the glomeruli, a measure of kidney function.

Ultrafiltrate

The fluid that is filtered through the glomerulus, containing water and small solutes but not blood cells or large proteins.

Renal Cortex

The outer region of the kidney, containing renal corpuscles and convoluted tubules.

Renal Medulla

The inner region of the kidney, consisting of renal pyramids and containing loops of Henle and collecting ducts.

Renal Pelvis

The funnel-shaped basin that collects urine from the calyces and channels it into the ureter.

Ureters

Tubes that transport urine from the renal pelvis of the kidneys to the urinary bladder.

Urinary Bladder

A muscular sac that temporarily stores urine before it is expelled from the body.

Urethra

The tube that carries urine from the urinary bladder to outside the body.

Renal Corpuscle

Composed of the glomerulus and Bowman's capsule, where blood filtration begins.

Proximal Convoluted Tubule (PCT)

The segment of the nephron responsible for most reabsorption of water, ions, and organic nutrients from the filtrate.

Distal Convoluted Tubule (DCT)

A segment of the nephron involved in fine-tuning reabsorption and secretion, particularly for sodium, potassium, and acid-base balance.

Collecting Duct

A tube that receives urine from several nephrons and is involved in final water reabsorption under hormonal control.

Vasa Recta

Capillaries that run parallel to the loop of Henle in juxtamedullary nephrons, maintaining the medullary osmotic gradient.

Peritubular Capillaries

Capillaries surrounding the renal tubules in cortical nephrons, involved in reabsorption and secretion.

Juxtaglomerular Apparatus (JGA)

A specialized structure near the glomerulus that regulates blood pressure and GFR through renin secretion and tubuloglomerular feedback.

Macula Densa

Specialized cells in the DCT that sense sodium chloride concentration in the filtrate and contribute to tubuloglomerular feedback.

Granular Cells (Juxtaglomerular Cells)

Specialized smooth muscle cells in the afferent arteriole that synthesize and release renin.

Net Filtration Pressure (NFP)

The sum of hydrostatic and oncotic pressures that determines the net movement of fluid out of the glomerulus into Bowman's capsule.

Autoregulation of GFR

Intrinsic mechanisms within the kidney that maintain a relatively constant GFR despite fluctuations in systemic blood pressure.

Myogenic Mechanism

An intrinsic autoregulatory mechanism where afferent arterioles constrict in response to increased blood pressure, protecting the glomerulus from pressure fluctuations.

Tubuloglomerular Feedback

An intrinsic autoregulatory mechanism involving the macula densa, which adjusts afferent arteriolar resistance based on filtrate composition and flow rate in the DCT.

Countercurrent Multiplier

The mechanism involving the loop of Henle that establishes and maintains the vertical osmotic gradient in the renal medulla.

Countercurrent Exchanger

The mechanism involving the vasa recta that maintains the medullary osmotic gradient by minimizing solute washout.

Medullary Osmotic Gradient

A progressively increasing solute concentration from the cortex to the inner medulla, crucial for concentrating urine.

Urea Recycling

The movement of urea from the collecting duct into the medullary interstitium and then back into the loop of Henle, contributing to the osmotic gradient.

Aldosterone

A hormone secreted by the adrenal cortex that promotes sodium reabsorption and potassium secretion in the DCT and collecting duct, influencing blood pressure and volume.

Atrial Natriuretic Peptide (ANP)

A hormone secreted by the atria of the heart in response to high blood volume, promoting sodium and water excretion and decreasing blood pressure.

Erythropoietin (EPO)

A hormone produced by the kidneys that stimulates red blood cell production in the bone marrow.

Renin

An enzyme secreted by the granular cells of the JGA that initiates the renin-angiotensin-aldosterone system by converting angiotensinogen to angiotensin I.

Angiotensin II

A potent vasoconstrictor and stimulator of aldosterone release, key in regulating blood pressure and fluid balance.

Sodium Reabsorption

The active transport of sodium ions out of the tubular fluid, creating an osmotic gradient for water reabsorption.

Glucose Reabsorption

The process by which glucose is reabsorbed from the filtrate in the PCT, primarily via SGLT and GLUT transporters.

Renal Threshold for Glucose

The plasma concentration of glucose above which glucose begins to appear in the urine because the transport maximum (Tm) for glucose reabsorption has been exceeded.

Amino Acid Reabsorption

The transport of amino acids from the tubular fluid back into the blood, mainly occurring in the PCT.

Urea Excretion

The elimination of urea, a waste product of protein metabolism, from the body via urine.

Creatinine Clearance

A measure used to estimate GFR, representing the volume of plasma cleared of creatinine per unit time.

Potassium Secretion

The active transport of potassium ions from the peritubular capillaries into the tubular fluid, mainly in the DCT and collecting duct, regulated by aldosterone.

Hydrogen Ion Secretion

The process by which kidneys excrete excess hydrogen ions into the urine to maintain acid-base balance.

Bicarbonate Reabsorption

The process by which bicarbonate ions are reabsorbed from the filtrate, crucial for buffering blood pH.

Renal Clearance

The volume of plasma completely cleared of a substance by the kidneys per unit time.

Excretion

The process of eliminating metabolic waste products and other unwanted substances from the body.

Micturition

The process of urinating, involving the coordinated contraction of the detrusor muscle and relaxation of urethral sphincters.

Detrusor Muscle

The smooth muscle layer in the wall of the urinary bladder that contracts to expel urine.

Internal Urethral Sphincter

An involuntary smooth muscle that prevents urine leakage between voiding and relaxes during micturition.

External Urethral Sphincter

A voluntary skeletal muscle that allows conscious control over urination.