Microscopic Anatomy of the Kidney – Vocabulary Review

A set of vocabulary flashcards covering the structures, cells, and processes involved in the microscopic anatomy of the kidney as presented in the lecture notes.

Nephron

Functional unit of the kidney that converts a simple blood filtrate into urine through filtration, reabsorption, and secretion.

Filtration

Process in which plasma components move from glomerular capillaries into Bowman’s capsule to begin forming urine.

Reabsorption

Return of useful solutes and water from forming urine back into the bloodstream within the nephron.

Secretion

Addition of wastes or excess ions from the blood into forming urine along the nephron.

Renin

Enzyme released by juxtaglomerular cells that initiates conversion of angiotensinogen to angiotensin I.

Erythropoietin (EPO)

Kidney-derived hormone that stimulates red blood cell production.

Calcitriol

Active form of vitamin D produced by the kidney; promotes calcium absorption.

Renal corpuscle

Structure composed of the glomerulus and Bowman’s capsule where blood filtration occurs.

Glomerulus

High-pressure capillary tuft positioned between afferent and efferent arterioles.

Bowman’s (glomerular) capsule

Double-walled capsule surrounding the glomerulus that captures the filtrate.

Parietal layer (Bowman’s capsule)

Outer simple squamous epithelium forming the wall of Bowman’s capsule.

Visceral layer (Bowman’s capsule)

Inner layer composed of podocytes that closely envelop glomerular capillaries.

Podocyte

Specialized epithelial cell with finger-like pedicels forming filtration slits on glomerular capillaries.

Pedicel

Fine cytoplasmic extension of a podocyte that interdigitates with pedicels of adjacent podocytes.

Filtration slit

Narrow gap between interdigitating pedicels through which plasma is filtered.

Filtration membrane

Barrier formed by fenestrated endothelium, shared basement membrane, and podocyte filtration slits.

Fenestration

Approximately 70-nm pore in glomerular endothelial cells permitting rapid filtrate passage while blocking cells.

Basement membrane (renal)

Shared layer between endothelium and podocytes that prevents filtration of medium-to-large proteins.

Mesangial cell

Contractile cell within the filtration membrane that helps regulate the glomerular filtration rate.

Juxtaglomerular apparatus (JGA)

Region where the distal convoluted tubule contacts afferent/efferent arterioles, regulating GFR and renin release.

Macula densa

Cluster of distal convoluted tubule cells in the JGA that senses Na⁺ concentration and flow rate.

Juxtaglomerular cell

Modified smooth muscle cell of the afferent arteriole that contracts or releases renin in response to macula densa signals.

Angiotensin I

Peptide produced when renin cleaves angiotensinogen; inactive precursor of angiotensin II.

Angiotensin-converting enzyme (ACE)

Lung-derived enzyme that converts angiotensin I to active angiotensin II.

Angiotensin II

Potent systemic vasoconstrictor that elevates blood pressure and stimulates aldosterone release.

Aldosterone

Adrenal cortex hormone that promotes Na⁺ reabsorption and consequent water retention by the kidney.

Proximal convoluted tubule (PCT)

Nephron segment of simple cuboidal cells with dense microvilli (brush border) specialized for bulk reabsorption and secretion.

Brush border

Thick layer of microvilli on PCT cells that greatly increases surface area for transport.

Loop of Henle (nephron loop)

U-shaped nephron segment with descending and ascending limbs differing in thickness and epithelial type.

Descending thick limb

Initial portion of the descending loop composed of simple cuboidal epithelium similar to the PCT.

Descending thin limb

Long segment of the descending loop lined by simple squamous epithelium.

Ascending thin limb

Initial segment of the ascending loop lined by simple squamous epithelium.

Ascending thick limb

Long cuboidal segment of the ascending loop resembling the distal convoluted tubule.

Distal convoluted tubule (DCT)

Short, tortuous nephron segment of simple cuboidal cells with fewer microvilli involved in selective reabsorption and secretion.

Collecting duct

Tubule receiving filtrate from several nephrons; responds to ADH to concentrate or dilute urine.

Antidiuretic hormone (ADH)

Hormone that triggers insertion of aquaporin channels in collecting-duct cells to enhance water reabsorption.

Aquaporin

Membrane water channel protein allowing only water to cross lipid bilayers via osmosis.

Glomerular filtration rate (GFR)

Rate at which filtrate is formed by all renal corpuscles; kept relatively constant by JGA actions.