BIOH12012 – Urinary System Anatomy & Physiology (Week 3)

Vocabulary flashcards covering kidney functions, nephron anatomy, filtration dynamics, hormonal regulation, and major electrolyte concepts from Week 3 urinary system lecture.

Kidney – Primary Functions

Maintains fluid, electrolyte, and acid–base balance; performs endocrine roles such as renin, erythropoietin, and calcitriol secretion.

Nephron

Microscopic functional unit of the kidney that forms urine; consists of renal corpuscle and renal tubule.

Renal Corpuscle

Initial filtration portion of the nephron, composed of the glomerulus and the glomerular (Bowman’s) capsule.

Glomerulus

Tuft of fenestrated capillaries within the renal corpuscle where blood filtration begins.

Afferent Arteriole

Small artery that brings blood into the glomerulus; diameter influences glomerular pressure and GFR.

Efferent Arteriole

Vessel carrying blood away from the glomerulus; its constriction raises glomerular hydrostatic pressure.

Filtration Membrane

Tri-layer barrier of fenestrated endothelium, basement membrane, and podocyte slits that filters plasma into the capsule.

Podocyte

Specialised epithelial cell of the visceral glomerular capsule with foot processes that create filtration slits.

Juxtaglomerular Complex (JGC)

Region where the distal convoluted tubule contacts the afferent arteriole; regulates blood pressure and GFR.

Macula Densa

Chemoreceptive cells of the DCT that sense tubular NaCl concentration and modulate afferent arteriole tone.

Granular (Juxtaglomerular) Cells

Modified smooth-muscle cells in arteriole walls that act as mechanoreceptors and release renin.

Extraglomerular Mesangial Cells

Cells between arterioles and tubule that provide structural support and signalling within the JGC.

Glomerular Filtration Rate (GFR)

Volume of filtrate produced per minute by both kidneys (~120 mL min⁻¹ in adults).

Net Filtration Pressure (NFP)

Driving force for filtration; NFP = HPgc – (OPgc + HPcs).

Hydrostatic Pressure (HPgc)

Blood pressure inside glomerular capillaries that promotes filtration (~55 mm Hg).

Colloid Osmotic Pressure (OPgc)

Pulling pressure exerted by plasma proteins that opposes filtration (~30 mm Hg).

Capsular Hydrostatic Pressure (HPcs)

Pressure of filtrate in Bowman’s capsule opposing filtration (~15 mm Hg).

Tubuloglomerular Feedback

Intrinsic autoregulatory mechanism whereby macula densa alters afferent arteriole resistance in response to NaCl.

Myogenic Mechanism

Intrinsic response of afferent arteriole smooth muscle to stretch, stabilising GFR despite BP changes.

Proximal Convoluted Tubule (PCT)

First renal tubule segment; reabsorbs ~65 % of water, Na⁺, K⁺, all glucose and amino acids.

Loop of Henle – Descending Limb

Permeable to water but not solutes; water reabsorption concentrates tubular fluid.

Loop of Henle – Ascending Limb

Impermeable to water; actively reabsorbs Na⁺ and Cl⁻, diluting tubular fluid.

Distal Convoluted Tubule (DCT)

Tubule segment under hormonal control; reabsorbs Na⁺, secretes K⁺, variably reabsorbs water.

Collecting Duct

Final tubule that adjusts urine concentration; site of ADH-controlled water reabsorption and acid–base regulation.

Countercurrent Multiplier

Process in juxtamedullary nephrons where opposing flow in loop limbs creates medullary osmotic gradient.

Vasa Recta (Countercurrent Exchanger)

Peritubular capillaries paralleling the loop of Henle that preserve the medullary gradient while supplying blood.

Filtration

Movement of water and small solutes from glomerular blood into the capsular space.

Reabsorption

Transfer of substances from tubular fluid back into blood or interstitium.

Secretion

Active transport of substances from peritubular capillaries into the renal tubule for excretion.

Renin–Angiotensin–Aldosterone System (RAAS)

Hormonal cascade that elevates blood pressure and volume via vasoconstriction and Na⁺/water retention.

Renin

Enzyme released by granular cells that converts angiotensinogen to angiotensin I.

Angiotensin II

Potent vasoconstrictor that stimulates aldosterone and ADH release, raising BP.

Aldosterone

Adrenal cortical hormone that increases Na⁺ reabsorption and K⁺ secretion in DCT/collecting duct.

Antidiuretic Hormone (ADH)

Posterior pituitary hormone that inserts aquaporins in collecting ducts, conserving water.

Natriuretic Peptides (ANP & BNP)

Cardiac hormones that promote Na⁺ and water excretion, opposing RAAS and lowering blood volume.

Sodium (Na⁺)

Major extracellular cation (135–145 mmol L⁻¹) crucial for ECF volume, nerve conduction, and acid–base balance.

Hyponatraemia

Serum Na⁺ < 135 mmol L⁻¹ causing cellular swelling, confusion, seizures, hypotension.

Hypernatraemia

Serum Na⁺ > 145 mmol L⁻¹ causing cellular dehydration, thirst, neuromuscular irritability.

Potassium (K⁺)

Primary intracellular cation (3.5–5.2 mmol L⁻¹) essential for resting membrane potential and action potentials.

Hypokalaemia

Serum K⁺ < 3.5 mmol L⁻¹ leading to muscle weakness, arrhythmias, metabolic alkalosis.

Hyperkalaemia

Serum K⁺ > 5.2 mmol L⁻¹ leading to cardiac arrest risk, muscle cramps, diarrhoea.

Calcium (Ca²⁺)

Ion vital for bone, muscle contraction, clotting; normal serum 2.25–2.75 mmol L⁻¹.

Hypocalcaemia

Serum Ca²⁺ < 2.1 mmol L⁻¹ causing tetany, seizures, cardiac dysrhythmia.

Hypercalcaemia

Serum Ca²⁺ > 2.6 mmol L⁻¹ causing weakness, kidney stones, cardiac arrhythmias.

Peritubular Capillaries

Low-pressure capillaries surrounding cortical nephron tubules that reclaim filtered solutes.

Papillary Duct

Channel that delivers urine from collecting ducts to a minor calyx.