Introduction to the Urinary System

Comprehensive vocabulary flashcards covering the anatomy, physiology, and hormonal regulation of the urinary system based on the provided lecture notes.

Primary function of the Urinary System

To maintain blood composition, blood volume, and blood pressure by removing metabolic wastes and producing urine.

Excretion

The removal of metabolic wastes from body fluids.

Elimination

The discharge of waste products from the body.

Homeostatic regulation

The maintenance of blood volume and solute concentration by adjusting the loss of water (via filtration, ADH, and Aldosterone) and ions.

Calcitriol

A form of Vitamin D whose synthesis by the kidneys helps control calcium ion levels.

Kidney dimensions and weight

Approximately $10\,cm$ long, $5.5\,cm$ wide, and $3\,cm$ thick, weighing about $150\,g$.

Hilum

A prominent medial indentation on the kidney that serves as the entry point for the renal artery and renal nerves, and the exit point for the renal vein and ureter.

Renal circulation volume

Kidneys receive $20-25\%$ of total cardiac output, with approximately $1200\,mL$ of blood flowing through them each minute.

Intraglomerular mesangial cells

Specialized cells derived from smooth muscle located among glomerular capillaries that provide support, filtration, phagocytosis, and control of capillary diameter.

Proximal convoluted tubule (PCT)

The first segment of the renal tubule, composed of simple cuboidal epithelium with microvilli; its primary function is the reabsorption of ions.

Distal convoluted tubule (DCT)

A segment of the renal tubule where epithelial cells lack microvilli; its primary functions are water/ion reabsorption and the active secretion of undesirable substances.

Nephron loop

A segment whose primary function is to concentrate urine and conserve water by establishing a high salt concentration in the kidney medulla.

Juxtaglomerular complex (JGC)

The collective structure that helps regulate blood pressure and filtrate formation, consisting of the macula densa, juxtaglomerular cells, and extraglomerular mesangial cells.

Cortical nephrons

The $85\%$ of all nephrons located mostly within the superficial cortex, characterized by relatively short nephron loops.

Juxtamedullary nephrons

The $15\%$ of nephrons with loops that extend deep into the medulla and efferent arterioles connected to the vasa recta.

Urea

The most abundant organic metabolic waste produced by the body.

Creatinine

A metabolic waste produced from the breakdown of creatine phosphate.

Filtration

A passive process where blood pressure forces water and solutes across the walls of glomerular capillaries into the capsular space.

Reabsorption

The movement of water and solutes recovery from the filtrate back into the peritubular fluid and blood.

Secretion

The transport of solutes from the peritubular fluid across the tubular epithelium into the tubular fluid.

Net filtration pressure (NFP)

The pressure calculated by the difference between Net Hydrostatic Pressure (NHP) and Blood Colloid Osmotic Pressure (BCOP), typically yielding $10\,mm\,Hg$ ($35\,mm\,Hg - 25\,mm\,Hg$).

Glomerular filtration rate (GFR)

The amount of filtrate kidneys produce each minute, averaging $125\,mL/min$ or about $180\,L/day$.

Renin stimuli

Released by the JGC in response to decreased blood pressure at the glomerulus, sympathetic stimulation, or decreased osmotic concentration of tubular fluid at the macula densa.

Atrial natriuretic peptide (ANP)

A hormone released by the heart atria that increases GFR and urine production while decreasing sodium reabsorption to lower blood volume and pressure.

Transport maximum ($T_m$)

The concentration at which all available carrier proteins for a specific nutrient are saturated, determining the renal threshold.

Glucosuria

The appearance of glucose in the urine, which occurs when plasma glucose levels exceed the renal threshold of $180\,mg/dL$.

Aldosterone

A hormone from the adrenal cortex that stimulates sodium pump synthesis in the DCT and collecting duct to reduce sodium loss in urine.

Hypokalemia

A dangerous reduction in plasma potassium concentration that can be produced by prolonged aldosterone stimulation.

Obligatory water reabsorption

Water movement that cannot be prevented and usually recovers $85\%$ of filtrate volume.

Facultative water reabsorption

Controlled water reabsorption along the DCT and collecting system, representing about $15\%$ of filtrate volume ($27\,L/day$).

Antidiuretic hormone (ADH)

A hormone that increases water permeability in the DCT and collecting system by causing the insertion of aquaporins.

Urobilin

The yellow pigment generated in the kidneys from urobilinogens that gives urine its characteristic color.

Creatinine clearance

A test comparing creatinine levels in urine and blood to estimate the Glomerular Filtration Rate (GFR).

Peristaltic contractions

Muscular movements occurring about every $30\,seconds$ to move urine from the renal pelvis through the ureters to the bladder.

External urethral sphincter

A circular band of skeletal muscle under voluntary control via the perineal branch of the pudendal nerve that permits urination upon relaxation.

Urine voiding reflex

A reflex initiated when the bladder contains about $200\,mL$ of urine, involving the pontine micturition center to trigger detrusor contraction and sphincter relaxation.

Incontinence

The inability to control urination voluntarily.