Marieb Human Anatomy & Physiology Chapter 25: The Urinary System

A set of vocabulary flashcards covering the key structures, functions, and physiological processes of the urinary system based on Marieb's Human Anatomy & Physiology.

Kidneys

Organs that maintain the body’s internal environment by regulating water volume, solute and ion concentrations, and long-term acid-base balance, while also excreting metabolic wastes.

Ureters

Slender, retroperitoneal tubes that transport urine from the kidneys to the urinary bladder.

Urinary bladder

A smooth, collapsible, muscular sac that serves as a temporary storage reservoir for urine.

Urethra

A thin-walled muscular tube that transports urine from the urinary bladder out of the body.

Erythropoietin

A hormone produced by the kidneys that regulates red blood cell (RBC) production.

Renin

An enzyme produced by the kidneys needed to synthesize Angitionsten, a hormone involved in blood pressure regulation.

Renal hilum

A deep cleft on the concave medial surface of the kidney where ureters, blood vessels, lymphatics, and nerves enter and exit.

Hematuria

An important clinical sign of renal injury characterized by the presence of blood in the urine.

Renal cortex

The light-colored, superficial region of the kidney with a granular appearance.

Renal medulla

The darker, reddish-brown region deep to the cortex, consisting of cone-shaped medullary pyramids separated by renal columns.

Renal pelvis

A funnel-shaped tube continuous with the ureter that receives urine from major and minor calyces.

Pyelonephritis

Infection or inflammation of the kidney, often caused by fecal bacteria spreading to the urethra or blood-borne bacteria.

Nephrons

The structural and functional units of the kidney that filter blood and form urine; there are approximately $1 \text{ million}$ per kidney.

Glomerulus

A tuft of fenestrated capillaries in the renal corpuscle that provides efficient formation of filtrate from plasma.

Glomerular capsule (Bowman’s capsule)

A cup-shaped, hollow structure surrounding the glomerulus consisting of a parietal layer and a visceral layer of podocytes.

Podocytes

Highly modified branching epithelial cells in the visceral layer of the glomerular capsule that form filtration slits with their foot processes.

Proximal convoluted tubule (PCT)

The portion of the renal tubule closest to the renal corpuscle, featuring dense microvilli that form a brush border to increase surface area for reabsorption.

Nephron loop (Loop of Henle)

A U-shaped structure of the renal tubule consisting of a descending limb and an ascending limb.

Distal convoluted tubule (DCT)

The portion of the renal tubule further from the renal corpuscle that drains into a collecting duct.

Principal cells

Cells in the collecting duct responsible for maintaining the body's water and $Na^+$ balance.

Intercalated cells

Cells in the collecting duct that help maintain the acid-base balance of the blood.

Cortical nephrons

Nephrons that make up $85\text{\%}$ of all nephrons, located almost entirely in the cortex with short loops.

Juxtamedullary nephrons

Nephrons originating close to the cortex-medulla junction with long loops essential for producing concentrated urine.

Peritubular capillaries

Low-pressure, porous capillaries surrounding renal tubules in the cortex that pick up water and solutes reabsorbed from filtrate.

Vasa recta

Long, thin-walled vessels parallel to long nephron loops in the medulla that preserve the medullary osmotic gradient.

Juxtaglomerular complex (JGC)

A region in each nephron containing the macula densa and granular cells, important in regulating filtrate formation rate and blood pressure.

Macula densa

A group of tall cells in the distal ascending limb that act as chemoreceptors to monitor the $NaCl$ content of filtrate.

Granular cells (JG cells)

Large, granular smooth muscle cells in the afferent arteriole that act as mechanoreceptors to monitor blood pressure and secrete renin.

Glomerular filtration

A passive process in which hydrostatic pressure forces fluids and solutes through a filtration membrane into the glomerular capsule.

Glomerular filtration rate (GFR)

The volume of filtrate formed per minute by both kidneys, directly proportional to net filtration pressure, surface area, and membrane permeability.

Renal autoregulation

Intrinsic controls by which the kidneys maintain a stable GFR despite regular fluctuations in blood pressure, using myogenic and tubuloglomerular feedback mechanisms.

Anuria

Abnormally low urinary output of less than $50 \text{ ml/day}$, which may indicate that glomerular blood pressure is too low for filtration.

Aquaporins

Water-filled pores that allow the passive tubular reabsorption of water by osmosis.

Transport maximum ($T_m$)

The limit for transcellular transport systems of reabsorbed substances, reflecting the number of available transport proteins.

Antidiuretic hormone (ADH)

A hormone from the posterior pituitary that inhibits diuresis by causing principal cells to insert aquaporins into their apical membranes.

Aldosterone

A hormone from the adrenal cortex that increases $Na^+$ reabsorption and water conservation to raise blood volume and pressure.

Countercurrent multiplier

The interaction between filtrate flow in the descending and ascending limbs of long nephron loops that creates the medullary osmotic gradient.

Countercurrent exchanger

The flow of blood in the vasa recta that preserves the medullary osmotic gradient by exchanging $NaCl$ and water with the interstitial fluid.

Specific gravity

The ratio of the mass of a substance to the mass of an equal volume of distilled water; for urine, it typically ranges from $1.001\text{ to }1.035$.

Renal calculi

Commonly known as kidney stones, these are crystallized calcium, magnesium, or uric acid salts that can obstruct urine flow.

Trigone

The smooth triangular area on the floor of the urinary bladder outlined by the openings for the ureters and the urethra.

Detrusor

The thick muscular layer of the bladder wall consisting of three layers of smooth muscle.

Internal urethral sphincter

An involuntary sphincter composed of circular smooth muscle at the bladder-urethra junction controlled by the autonomic nervous system.

External urethral sphincter

A voluntary sphincter of skeletal muscle surrounding the urethra as it passes through the deep perineal space.