Human Homeostasis – Kidney Structure & Function

40 vocabulary flashcards summarising key terms related to kidney structure, function, and mechanisms of osmoregulation and excretion in humans.

Homeostasis

The maintenance of stable internal conditions within narrow limits despite external changes.

Excretion

Removal of toxic waste products of metabolism from the body, chiefly nitrogenous wastes.

Osmoregulation

Regulation of osmotic concentration (osmol L⁻¹) of body fluids to keep water and solute balance constant.

Kidney

Paired organ that carries out excretion and osmoregulation; supplied by a renal artery and drained by a renal vein.

Nephron

Microscopic functional unit of the kidney responsible for filtering blood and forming urine.

Renal Cortex

Outer region of the kidney where most ultrafiltration and selective reabsorption occur.

Renal Medulla

Inner region of the kidney containing loops of Henle and collecting ducts; key site of osmoregulation.

Renal Pelvis

Funnel-shaped cavity that collects urine from collecting ducts and channels it to the ureter.

Renal Artery

Blood vessel delivering oxygen-rich blood containing wastes to the kidney.

Renal Vein

Blood vessel carrying filtered, ‘clean’ blood away from the kidney back to the heart.

Ureter

Tube that transports urine from the kidney to the bladder.

Glomerulus

High-pressure capillary knot that forces plasma out of the blood during ultrafiltration.

Bowman’s Capsule

Cup-shaped structure surrounding the glomerulus; collects the filtrate formed by ultrafiltration.

Ultrafiltration

Non-selective filtration of blood plasma under pressure in the glomerulus into Bowman’s capsule.

Fenestrations

100 nm pores in glomerular capillary endothelium allowing passage of plasma but retaining blood cells.

Basement Membrane

Negatively charged glycoprotein mesh around glomerular capillaries that blocks plasma proteins >65 kDa.

Podocytes

Specialised cells of Bowman’s capsule with foot-like processes and filtration slits that allow filtrate through.

Glomerular Filtrate

Fluid entering the nephron containing water, ions, glucose, amino acids, urea, but lacking cells & big proteins.

Proximal Convoluted Tubule (PCT)

First twisted tubule where selective reabsorption of glucose, salts and water back into blood occurs.

Selective Reabsorption

Process by which useful solutes are actively or passively transported from filtrate back to blood in the PCT.

Microvilli (in PCT)

Membrane projections that increase surface area for rapid reabsorption.

Mitochondria (in PCT cells)

Organelles providing ATP for active transport of Na⁺ and other solutes during reabsorption.

Loop of Henle

Hairpin-shaped section of nephron creating a solute gradient in the medulla for water conservation.

Descending Limb

Water-permeable part of the loop of Henle where water leaves filtrate by osmosis into hypertonic medulla.

Ascending Limb

Water-impermeable part actively transporting Na⁺ and Cl⁻ out, raising medullary solute concentration.

Countercurrent Multiplier

Mechanism of the loop of Henle where opposite flow directions amplify medullary solute gradient.

Vasa Recta

Capillary network paralleling loops of Henle, maintaining medullary gradient by countercurrent exchange.

Distal Convoluted Tubule (DCT)

Nephron segment performing fine pH adjustment and regulated secretion or reabsorption of ions.

Collecting Duct

Channel carrying filtrate through medulla; variable water reabsorption controlled by ADH.

Antidiuretic Hormone (ADH)

Hormone from posterior pituitary that increases water permeability of collecting ducts via aquaporins.

Osmoreceptors

Hypothalamic sensors detecting blood solute concentration and regulating ADH secretion.

Aquaporins

Water-channel proteins inserted into collecting-duct membranes to facilitate water reabsorption.

Urea

Main nitrogenous waste in mammals, produced in liver from ammonia and excreted in urine.

Uric Acid

Non-water-soluble nitrogenous waste produced by birds and reptiles, conserving water.

Active Transport

Energy-requiring movement of substances against a concentration gradient, e.g., Na⁺ pumps in PCT.

Osmol (osmol/L)

Unit expressing osmotic concentration; number of moles of solute particles per litre of solution.

Countercurrent System

Arrangement of two fluids flowing in opposite directions to maintain concentration gradients, as in the loop of Henle.

Vasoconstriction

Narrowing of blood vessels to reduce blood flow to an organ.

Vasodilation

Widening of blood vessels to increase blood flow to an organ.

Relative Medullary Thickness (RMT)

Measure of medulla size relative to kidney size, correlating with maximum urine solute concentration.