b5 exam 2 cell bio review

Afferent arteriole

Small renal artery branch delivering blood to the glomerulus; its constriction reduces GFR, while dilation increases it, part of renal autoregulation.

Efferent arteriole

Vessel leaving the glomerulus; constriction increases glomerular pressure and filtration fraction, influencing GFR and RBF.

Juxtaglomerular (JG) cells

Renin-secreting cells in the afferent arteriole wall; stimulated by reduced flow/osmolality to activate RAAS.

Macula densa

Tall, specialized cells in the distal tubule that sense NaCl transport; modulates renin release from JG cells and GFR.

Renin

Enzyme released by JG cells that cleaves angiotensinogen to angiotensin I, initiating the RAAS cascade.

Angiotensin I

Inactive decapeptide formed from angiotensinogen; converted to angiotensin II by ACE.

Angiotensin II

Potent vasoconstrictor; raises blood pressure, stimulates aldosterone release, and promotes Na+ and water retention.

Aldosterone

Mineralocorticoid that reabsorbs Na+ and secretes K+ in the collecting ducts, increasing water retention.

ADH (vasopressin)

Hormone that promotes water reabsorption via aquaporin-2 in collecting ducts; release triggered by high plasma osmolarity or Ang II.

Aquaporin-2 (AQP2)

Water channel in the apical membrane of collecting duct principal cells; inserted into the membrane by ADH.

Calcidiol

25-hydroxyvitamin D, liver-produced inactive precursor of vitamin D.

Calcitriol

Active form of vitamin D (1,25-dihydroxyvitamin D) produced in the kidney; essential for calcium homeostasis.

Cholecalciferol

Vitamin D3; formed in skin or obtained in diet; precursor to calcidiol.

Ergocalciferol (Vitamin D2)

Plant-based form of vitamin D; converted to calcidiol in the liver.

Vitamin D hydroxylation

Liver converts vitamin D to calcidiol; kidney converts calcidiol to calcitriol.

Glomerular filtration rate (GFR)

Volume of filtrate produced by the glomeruli per minute; ~125 mL/min in healthy adults.

Inulin clearance

Gold standard for measuring GFR; inulin is freely filtered and neither reabsorbed nor secreted.

PAH clearance

Used to estimate renal plasma flow; para-aminohippurate is filtered and secreted but minimally reabsorbed.

Filtration fraction (FF)

Proportion of plasma that is filtered at the glomerulus; calculated as GFR/RPF.

Renal blood flow (RBF)

Volume of blood delivered to the kidneys per minute; ~1 L/min in adults.

Tubuloglomerular feedback (TGF)

Autoregulatory mechanism where the macula densa senses NaCl and modulates GFR via JG apparatus.

Myogenic mechanism

Intrinsic vessel response to stretch; helps maintain GFR by constricting/dilating afferent arteriole.

Autoregulatory range

MAP range (about 60–180 mm Hg) where GFR is kept relatively constant via autoregulation.

Bowman’s space

Space surrounding the glomerulus where filtrate collects before entering proximal tubule.

Glomerulus

Tuft of capillaries where plasma is filtered into Bowman's capsule; glomerular capillaries are fenestrated.

Podocyte

Visceral epithelial cell with foot processes forming filtration slits; key to barrier selectivity.

Slit diaphragm

Filtration barrier between podocyte foot processes; contributes to charge- and size-selectivity.

Basement membrane (glomerular BM)

Charged layer in the filtration barrier between endothelium and podocytes.

Endothelial fenestrae

Pores in glomerular capillary endothelium that allow filtration while restricting cells.

Filtration barrier

Composite barrier (endothelium, BM, slit diaphragms) that regulates what filters into Bowman's space.

Peritubular capillaries

Capillary network surrounding renal tubules that supports reabsorption and secretion.

Vasa recta

Capillary network around loop of Henle involved in countercurrent exchange and concentrating mechanism.

Nephron

Functional unit of the kidney comprising glomerulus and renal tubule.

Cortex

Outer region of the kidney where most glomeruli and proximal/distal tubules reside.

Medulla

Inner renal region containing loops of Henle and collecting ducts; site of urine concentration.

Renal pyramid

Cone-shaped structures in the renal medulla containing collecting ducts and loops of Henle.

Minor calyx

Cup-like chamber that collects urine from papillae; drains into major calyx.

Major calyx

Convergence of several minor calyces; drains into renal pelvis.

Renal pelvis

Funnel-shaped chamber that collects urine and channels it into the ureter.

Renal artery

Main artery supplying the kidney; branches into segmental, lobar, interlobar, and arcuate arteries.

Interlobar artery

Renal artery branches running between renal pyramids; part of arterial tree.

Arcuate artery

Arteries at the corticomedullary junction that give rise to interlobular arteries.

Interlobular artery

Small arteries in the renal cortex that give rise to afferent arterioles.

Afferent arteriole (repeat for emphasis)

Arteriole delivering blood to the glomerulus; tone controls GFR.

Efferent arteriole (repeat for emphasis)

Arteriole draining the glomerulus; constriction raises glomerular pressure and FF.

Renin–angiotensin–aldosterone system (RAAS)

Hormonal system that regulates blood pressure and sodium balance via renin, Ang II, and aldosterone.

Atrial natriuretic peptide (ANP)

Hormone not detailed in notes here; often mentioned in volume regulation as opposing RAAS.

GFR vs RPF relationship

GFR is filtered volume; RPF is renal plasma flow; FF = GFR/RPF.

TF/P ratio (tubular fluid to plasma)

Ratio showing how solute concentration in tubular fluid changes relative to plasma along nephron.

Isosmotic, hyperosmotic, hypotonic

Terms describing whether fluids have equal, higher, or lower osmolality than plasma, affecting water movement.

Osmolarity

Total concentration of osmotically active particles per liter of solution.

Tonicity

Concentration of impermeant solutes that governs water movement across a membrane.

Osmolarity estimation (Osm = 2 x [Na+])

Rule-of-thumb to estimate plasma/osmolarity using sodium concentration.

Darow–Yannet diagram

Diagrammatic tool to visualize changes in volume and osmolarity across body compartments.

Hypertonic saline effect on RBCs

Causes cell shrinkage (crenation) due to increased extracellular osmolality.

Glucose reabsorption in proximal tubule

Sodium-coupled transport reabsorbs most filtered glucose via SGLT transporters.

Transport maximum (Tm) for glucose

Maximum rate of glucose reabsorption; when exceeded, glucose appears in urine.

Glucosuria

Excretion of glucose in urine due to filtered load exceeding Tm or transporter defect.

Splay (in glucose reabsorption)

Variation in saturation points across nephrons causing glucose to appear in urine before all nephrons saturate.

Isotonic/isotonic solution

Same osmolarity as plasma; no net water movement across membranes.

Hypertonic solution

Higher osmolarity than plasma; draws water out of cells.

Hypotonic solution

Lower osmolarity than plasma; water moves into cells.

Loop diuretics

Drugs (e.g., furosemide) that inhibit NKCC2 in TAL, increasing excretion of Na+, K+, Cl−.

Thiazide diuretics

Drugs that inhibit NaCl reabsorption in distal convoluted tubule, causing natriuresis.

Sodium–potassium–chloride cotransporter (NKCC2)

Transporter in TAL blocked by loop diuretics; critical for diluting segment function.

Sodium–chloride cotransporter (NCC)

Apical NaCl transporter in distal tubule; target of thiazide diuretics.

Na+/K+-ATPase

Basolateral pump maintaining Na+ gradient essential for reabsorption.

AQP1

Water channels in proximal tubule and descending limb; facilitate water reabsorption.

AQP2

Vasopressin-regulated water channel in collecting duct apical membrane.

Aldosterone action site

Principal cells in collecting duct; increases Na+ reabsorption and K+ secretion via ENaC and Na+/K+-ATPase.

Alpha-intercalated cells

Collecting duct cells that secrete H+ and reabsorb bicarbonate; important for acid-base balance.

Beta-intercalated cells

Collecting duct cells that reabsorb bicarbonate and secrete H+ differently; role in acid-base balance.

PTH in kidney

Parathyroid hormone inhibits phosphate reabsorption in PCT and modulates Ca2+ reabsorption in DCT.

Urea transporters (UT-A1)

Facilitate urea reabsorption in inner medullary collecting ducts, contributing to osmotic gradient.

Urea recycling

Movement of urea between collecting ducts and loop of Henle helping to maintain medullary osmolality.

Phosphate handling in kidney

PTH reduces Na+/phosphate reabsorption in proximal tubule increasing phosphate excretion.

Kimmelstiel–Wilson nodules

Nodular mesangial expansion seen in diabetic nephropathy.

Diabetic kidney disease (DKD)

Kidney damage from long-standing diabetes; BM thickening, nodular sclerosis, and proteinuria.

Minimal change disease (MCD)

Nephrotic syndrome with normal LM; podocyte foot-process effacement; loss of negative charge.

Focal segmental glomerulosclerosis (FSGS)

Glomerulosclerosis with segmental hyalinosis and podocyte injury; may be steroid-resistant.

Membranous nephropathy

Immunoglobulin deposits in the GBM with thickening; spike-and-dome appearance.

Post-streptococcal GN (PSGN)

Nephritic syndrome after GAS infection; starry-sky IF with C3 deposition.

IgA nephropathy (Berger disease)

IgA deposition in mesangium; hematuria; often after mucosal infections.

Alport syndrome

Genetic defect in type IV collagen causing basket-weave GBM on EM and hematuria.

Nephritic syndrome

Glomerulonephritis with inflammation, hematuria, and variable proteinuria; often HTN.

Nephrotic syndrome

Proteinuria (>3.5 g/day), hypoalbuminemia, edema, hyperlipidemia; protean renal disease.

KIDNEY autoregulation range (MAP)

Autoregulatory gut: maintains GFR between roughly 60–180 mm Hg MAP.

Renal autoregulation mechanisms

Myogenic response and tubuloglomerular feedback maintain stable GFR.

GFR and oncotic pressure along capillary

NFP changes along glomerulus; increasing π_GC toward efferent end reduces net filtration.

Angiotensin II selective efferent constriction effect

Constricts efferent arteriole; increases FF and sometimes GFR, but can reduce RBF.

Renal vascular resistance

Resistance within renal vasculature affecting RBF and GFR.

Hyperkalemia and hypokalemia in collecting duct

K+ secretion mainly in principal cells; aldosterone enhances K+ secretion.

PCT reabsorption scope

Reabsorbs ~65–80% Na+ and water; reabsorbs glucose, amino acids, bicarbonate, and many solutes.

Proximal tubule transporters (NHE3)

Na+/H+ exchanger important for Na+ reabsorption and bicarbonate reclamation.

Paracellular water movement

Water reabsorption via tight junctions between cells (paracellular route) driven by osmotic gradients.

Transcellular reabsorption

Solutes pass through cells via transporters and channels during reabsorption.

Tm (transport maximum) concept

Point at which transporters become saturated and solutes begin to appear in urine.

Sodium TF/P ratio along PCT

TF/P for Na+ remains near 1 because Na+ reabsorption tracks water movement in the PCT.

GFR decline with altered NFP

GFR falls when net filtration pressure decreases or Kf changes; RAAS and autoregulation modulate NFP.

Indicator-dilution principle

Method to measure fluid volumes by injecting an indicator and applying C1V1=C2V2.