Video 1 - Urinary Physiology – Nephron & Filtration

Vocabulary flashcards covering major structures, pressures, processes, and hormones involved in renal filtration, reabsorption, secretion, and blood-pressure regulation.

Glomerulus

A tuft of fenestrated capillaries inside the renal corpuscle where blood filtration begins.

Podocytes

Foot-like cells that wrap around glomerular capillaries, forming slit pores that add an extra filtration layer.

Bowman’s (Glomerular) Capsule

The double-walled capsule surrounding the glomerulus; collects the filtrate entering the nephron.

Capsular Space

The fluid-filled gap between glomerulus and Bowman’s capsule that opposes filtration via hydrostatic pressure.

Fenestrated Capillary

Capillary with small pores that allow plasma solutes to pass but retain cells and large proteins.

Blood Hydrostatic Pressure (BHP)

The pushing force exerted by blood in glomerular capillaries that drives filtration (≈55 mm Hg).

Capsular Hydrostatic Pressure

Pressure from existing fluid in the capsular space that opposes further filtration (≈15 mm Hg).

Colloid Osmotic Pressure

Osmotic pull created by plasma proteins that draws water back into glomerular blood (≈30 mm Hg).

Net Filtration Pressure (NFP)

BHP minus capsular and colloid pressures; determines whether filtrate is formed (≈10 mm Hg normally).

Glomerular Filtration Rate (GFR)

Volume of filtrate produced per minute by both kidneys (≈100–125 mL/min).

Proximal Convoluted Tubule (PCT)

First nephron segment, lined by simple cuboidal cells; reabsorbs ~99 % of filtrate volume and secretes some wastes.

Reabsorption

Transport of filtered substances (e.g., water, ions, bicarbonate) from nephron back to blood.

Secretion

Active transfer of solutes (e.g., H⁺, drugs, urea) from peritubular blood into the nephron lumen.

Nephron Loop (Loop of Henle)

U-shaped part of nephron with thin descending limb and thick ascending limb that creates medullary gradient.

Descending Limb

Thin, squamous portion of nephron loop permeable to water but not salts; water exits by osmosis.

Thick Ascending Limb

Cuboidal segment that actively pumps Na⁺, K⁺, Cl⁻ into interstitium but is impermeable to water.

Countercurrent Multiplier

Process in nephron loop where salt pumping in ascending limb draws water from descending limb, concentrating medulla.

Positive Feedback (Loop of Henle)

More salt pumped → higher medullary osmolarity → more water pulled out → allows even more salt pumping.

Distal Convoluted Tubule (DCT)

Segment that fine-tunes filtrate; secretes K⁺, H⁺, toxins and reabsorbs Na⁺, Ca²⁺ under hormonal control.

Calcitonin

Hormone that promotes Ca²⁺ secretion in DCT when blood calcium is high.

Parathyroid Hormone (PTH)

Hormone that stimulates Ca²⁺ reabsorption in DCT when blood calcium is low.

Collecting Duct

Final tubular segment receiving filtrate from many nephrons; variable water reabsorption generates concentrated or dilute urine.

Hypertonicity (Medullary)

High solute concentration in kidney medulla that drives water reabsorption from collecting ducts.

Aquaporins

Water channel proteins inserted into collecting-duct membranes in response to ADH to increase water reabsorption.

Antidiuretic Hormone (ADH)

Posterior pituitary hormone that promotes water retention by adding aquaporins to collecting-duct cells.

Aldosterone

Adrenal cortex hormone that increases Na⁺ reabsorption (and K⁺ secretion) in nephron, aiding water retention.

Renin

Enzyme released by juxtaglomerular apparatus that initiates the RAAS pathway to raise blood pressure.

Juxtaglomerular Apparatus (JGA)

Structure where DCT contacts afferent arteriole; contains macula densa & granular cells that monitor BP and release renin.

Macula Densa

DCT cells in JGA that sense NaCl concentration and signal renin release when filtrate osmolarity is low.

Granular (Juxtaglomerular) Cells

Baroreceptor cells in afferent arteriole wall that secrete renin in response to low blood pressure.

Hyperreninemia in Hypertension

Paradoxical elevation of renin (and thus aldosterone) in some high-BP patients, leading to excess fluid retention and K⁺ loss.