Overview of the Urinary System and Its Functions

Kidneys

Organs responsible for filtration and excretion, water volume regulation, osmolality regulation, ion concentration regulation, long-term acid-base balance, producing EPO, producing renin, vitamin D conversion, and gluconeogenesis.

Nephrons

Structural and functional units of the kidneys, with each kidney containing approximately 1 million nephrons that filter blood and make urine.

Renal Corpuscle

Part of the nephron consisting of the glomerulus and glomerular capsule (Bowman's capsule) where filtration begins.

Glomerulus

A network of fenestrated capillaries within the renal corpuscle that filters blood.

Renal Tubule

Part of the nephron that processes filtrate and includes the proximal convoluted tubule, nephron loop, and distal convoluted tubule.

Proximal Convoluted Tubule

Segment of the renal tubule lined with cuboidal cells containing large mitochondria and a brush border.

Nephron Loop (Loop of Henle)

Part of the nephron that consists of descending and ascending limbs, involved in concentrating urine.

Distal Convoluted Tubule

Segment of the renal tubule that is cuboidal but lacks microvilli.

Collecting Ducts

Ducts that receive urine from multiple nephrons and converge at the papilla.

Cortical Nephrons

Type of nephron that makes up 85% of nephrons, located mostly in the cortex.

Juxtamedullary Nephrons

Nephrons that originate close to the cortex/medullary junction and play an important role in concentrating urine.

Glomerular Filtration Rate (GFR)

Volume of filtrate formed each minute by all 2 million glomeruli combined.

Filtration Membrane

Structure composed of fenestrated endothelium, basement membrane, and podocytes that facilitates glomerular filtration.

Hydrostatic Pressure (HPgc)

Pressure exerted by blood in the glomerular capillaries that drives filtration.

Capsular Space

The space surrounding the glomerulus where filtrate collects.

Tubular Reabsorption

Process of selective movement of substances from filtrate back into the blood, beginning as filtrate enters proximal tubules.

Transcellular Route

Pathway for tubular reabsorption that involves movement through the cell membranes.

Sodium Reabsorption

The process of reclaiming sodium ions from the filtrate back into the bloodstream.

Water Reabsorption

The process of reclaiming water from the filtrate back into the bloodstream.

Nutrient Reabsorption

The process of reclaiming nutrients and ions from the filtrate back into the bloodstream.

Filtration Pressure

The net pressure that drives filtration in the glomerulus, influenced by changes in arteriolar diameter and total surface area for filtration.

Renin

An enzyme produced by granular cells in the arteriolar walls that plays a role in blood pressure regulation.

Water Reabsorption

Process by which water is reabsorbed from the filtrate back into the bloodstream.

Nutrients & Ions Reabsorption/Secretion

The process of reabsorbing essential nutrients and ions while secreting waste products.

PCT

Proximal Convoluted Tubule, the site most active in reabsorption.

Nephron Loop

Part of the nephron where water is not coupled with solutes in the descending limb but is opposite for solutes.

DCT & Collecting Duct

Regions where hormones fine-tune the reabsorption of water and solutes.

Secretion

The process of tubular secretion where selected substances are filtered and secreted.

K+ Importance

Potassium's role in disposal and elimination, control of blood pH, and maintaining osmotic gradient homeostasis.

Osmotic Gradient

The difference in solute concentration, typically around 300 mOsm, that regulates urine concentration and volume.

Countercurrent Multiplier

Mechanism that creates an osmotic gradient extending from the cortex to the medulla.

Countercurrent Exchanger

Vasa Recta, which preserves the osmotic gradient without creating it.

Urea Recycling

Process where urea enters the filtrate and is recycled back into the ascending limb of the nephron loop.

ADH

Antidiuretic hormone that increases urea recycling and strengthens the osmotic gradient.

Diuretics

Chemicals that enhance urinary output, including types like alcohol and loop diuretics.

Renal Clearance

Volume of plasma the kidneys completely remove a particular substance from in a set amount of time (1 min).

Inulin

Substance used to measure GFR, freely filtered and neither reabsorbed nor secreted.

Chronic Renal Disease

Condition where GFR is less than 60 mL/min for at least 3 months.

Renal Failure

Condition where GFR is less than 15 mL/min, leading to uremia.

Urine Chemical Composition

95% volume is water; 5% volume is solutes.

Ureter

Structure that transports urine to the bladder, beginning at level L2.

Renal Calculi

Kidney stones formed from high concentrations of calcium salts, magnesium salts, or uric acid.

Bladder

Organ for temporary storage of urine, with layers including mucosa, muscularis, and adventitia.

Micturition

The act of emptying the bladder involving simultaneous detrusor contraction and sphincter relaxation.