Kidney Function & Osmoregulation – Vocabulary Review

These vocabulary flashcards summarize the key terms and definitions related to the kidney’s role in osmoregulation, excretion, nephron structure, hormonal control, and blood-flow adaptations covered in the lecture notes.

Homeostasis

The process by which living organisms maintain stable internal conditions despite external changes.

Osmoregulation

Regulation of the body’s osmotic concentration (osmol L⁻¹) to keep water and solute levels within narrow limits.

Excretion

Removal of toxic metabolic waste products, such as nitrogenous compounds, from the body.

Osmotic Concentration

Measure of solute concentration expressed in osmoles per litre (osmol L⁻¹).

Kidney

Organ that carries out osmoregulation and excretion; each served by a renal artery and vein and drained by a ureter.

Nephron

Microscopic functional unit of the kidney that filters blood and forms urine.

Glomerulus

High-pressure capillary bed in each nephron where blood plasma is first filtered.

Bowman’s Capsule

Cup-shaped structure surrounding the glomerulus that collects the filtrate produced by ultrafiltration.

Ultrafiltration

Non-selective, pressure-driven filtering of plasma from glomerular capillaries into Bowman’s capsule, removing molecules <65 kDa.

Proximal Convoluted Tubule (PCT)

Highly folded first tubule segment where most selective reabsorption of water, ions and all glucose occurs.

Selective Reabsorption

Active and passive uptake of needed solutes and water from filtrate back into blood, mainly in the PCT.

Loop of Henle

Hairpin-shaped region creating a solute gradient in the medulla to enable water conservation.

Countercurrent Multiplier

System in the loop of Henle where opposing fluid flows generate a steep medullary osmotic gradient.

Vasa Recta

Capillary network paralleling the loop of Henle that preserves the medullary gradient while supplying blood.

Descending Limb

Water-permeable segment of the loop of Henle where water exits filtrate by osmosis into the medulla.

Ascending Limb

Water-impermeable segment of the loop; actively transports Na⁺ and Cl⁻ into the medulla to raise solute concentration.

Medulla (of Kidney)

Inner region with high solute concentration; site of most osmoregulation and loops of Henle.

Cortex (of Kidney)

Outer kidney region containing glomeruli, Bowman’s capsules, and convoluted tubules; site of ultrafiltration and fine adjustment.

Collecting Duct

Final tubular segment where water reabsorption is regulated by ADH as filtrate passes through the medulla.

Antidiuretic Hormone (ADH)

Posterior pituitary hormone that increases permeability of collecting ducts to water by inserting aquaporins, reducing urine volume.

Osmoreceptors

Hypothalamic cells that detect plasma solute concentration and modulate ADH release accordingly.

Aquaporins

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

Distal Convoluted Tubule (DCT)

Nephron segment responsible for fine pH adjustment, ion balance (Na⁺, K⁺), and additional water reabsorption.

Uric Acid

Insoluble nitrogenous waste excreted by birds and some reptiles; conserves water but requires high energy to produce.

Urea

Primary nitrogenous waste in mammals, formed in the liver from ammonia and excreted by the kidneys.

Ammonia

Highly toxic nitrogenous waste that must be quickly converted to urea or uric acid or diluted in water.

Renal Artery

Blood vessel delivering oxygen-rich, unfiltered blood containing toxins and ions to each kidney.

Renal Vein

Vessel that drains cleansed, filtered blood away from the kidney back to the heart.

Ureter

Duct that carries urine from each kidney to the bladder.

Urethra

Tube leading urine from the bladder to the exterior of the body.

Renal Pelvis

Central collecting space in the kidney where urine gathers before entering the ureter.

Podocytes

Specialized Bowman’s-capsule cells with foot processes that create filtration slits for plasma passage.

Fenestrations

100-nm pores in glomerular capillary endothelium that allow passage of plasma but retain blood cells.

Basement Membrane (Glomerulus)

Negatively charged glycoprotein mesh filtering out plasma proteins while letting smaller molecules through.

Active Transport (in Nephron)

Energy-requiring movement of ions such as Na⁺ and Cl⁻ across nephron cells, crucial for reabsorption and osmotic gradients.

Relative Medullary Thickness (RMT)

Ratio describing medulla thickness to kidney size; correlates with maximum urine concentration capability.

Maximum Solute Concentration (MSC)

Highest osmolarity a species can achieve in its urine, reflecting its water-conservation efficiency.

Vasoconstriction

Narrowing of blood vessels by contraction of smooth muscle, reducing blood flow to an organ.

Vasodilation

Widening of blood vessels, increasing blood flow to an organ.

Autoregulation of Renal Blood Flow

Mechanisms that keep kidney perfusion relatively constant despite systemic blood-pressure changes to maintain filtration.