The Urinary System and Fluid Balance

Comprehensive vocabulary flashcards covering the anatomy and physiology of the urinary system, nephron function, fluid compartments, hormonal regulation, and fluid balance based on lecture notes and worksheets.

Kidneys

The dark red, fist-sized principal organs of the urinary system that remove metabolic wastes, excess water, and salts from the blood to produce urine.

Erythropoietin

A hormone produced by the kidneys that regulates the production of red blood cells.

Renin

An enzyme secreted by the juxtaglomerular apparatus when blood pressure falls; it is important in regulating blood pressure by acting on a plasma protein to convert it to angiotensin I.

Uric acid

A nitrogenous waste product formed from the breakdown of nucleic acids.

Nitrogenous wastes

Metabolic waste products that contain nitrogen.

Excretion

The discharge from the body of metabolic waste products and excess solutes.

Elimination

The discharge of undigested or unabsorbed food from the digestive tract.

Sweat glands

Accessory excretory structures that excrete $5\%$ to $10\%$ of all metabolic wastes.

Retroperitoneal

The anatomical position describing the kidneys, located behind the peritoneum lining the abdominal cavity, just below the diaphragm and protected by the lower ribs.

Hilum

The notch on the medial border of each kidney where the renal artery, renal vein, and ureters connect.

Renal capsule

A tough casing of fibrous connective tissue covering the exterior of the kidney.

Renal papilla

The tip of each renal pyramid that contains several pores, which are the openings of the collecting ducts.

Minor calyx

A small tube in the kidney that receives urine from each collecting duct through a renal papilla; several unite to form a major calyx.

Renal pelvis

A large cavity formed by the major calyces that serves as an exit funnel collecting urine before it passes into the ureter.

Nephron

The microscopic structural and functional unit of the kidney that filters blood and produces urine.

Renal corpuscle

The portion of the nephron where blood is filtered, composed of the glomerulus and Bowman's capsule.

Glomerulus

A cluster of capillaries within the renal corpuscle where blood flows under high pressure to produce filtrate.

Bowman's capsule

A cuplike structure surrounding the glomerulus that captures filtered fluid.

Afferent arteriole

The vessel that transports blood directly into the glomerulus.

Efferent arteriole

The vessel that carries blood away from the glomerulus and delivers it to the peritubular capillaries.

Peritubular capillaries

Capillaries that surround the renal tubule, participating in tubular reabsorption and tubular secretion.

Proximal convoluted tubule

The coiled first section of the renal tubule extending from Bowman's capsule.

Loop of Henle

The hairpin-shaped portion of the renal tubule where filtrate flows after leaving the proximal convoluted tubule.

Distal convoluted tubule

The coiled section of the renal tubule where filtrate enters from the loop of Henle and contacts the afferent arteriole.

Juxtaglomerular apparatus

The specialized structure formed where the distal convoluted tubule curves upward and contacts the afferent arteriole; its cells secrete renin when blood pressure falls.

Glomerular filtration

The initial step of urine formation in which blood flows through the glomerular capillaries under high pressure, filtering plasma into Bowman's capsule.

Glomerular filtrate

The fluid filtered from the renal corpuscle, consisting of blood plasma containing ions and small dissolved molecules.

Tubular reabsorption

A highly selective process in the renal tubules that returns about $99\%$ of the filtrate back into the peritubular capillary blood.

Tubular secretion

The process by which substances are actively transported from the blood in the peritubular capillaries into the filtrate within the renal tubules.

Hydrogen ion secretion

An active transport process in the renal tubules that serves as an important homeostatic mechanism for regulating blood pH.

Urine

A fluid produced and excreted by the kidneys, composed of approximately $96\%$ water, $2.5\%$ nitrogenous waste, $1.5\%$ salts, and traces of other substances.

Ureters

Paired muscular tubes approximately $25\,\text{cm}$ long that gently squeeze and propel urine from the renal pelvis to the urinary bladder by peristaltic contractions.

Urinary bladder

A hollow, stretchy, temporary storage sac lined with mucous membrane folds called rugae and detrusor muscle, permitting it to hold up to $800\,\text{mL}$ of urine.

Detrusor muscle

The smooth muscle in the urinary bladder wall that contracts during micturition and relaxes to permit bladder expansion.

Rugae

Folds in the mucous membrane lining of the urinary bladder that allow it to stretch as it fills with urine.

Micturition

The process of emptying the bladder and expelling urine from the body, also known as urination.

Micturition reflex

A spinal reflex initiated when bladder stretch receptors are stimulated at a volume of about $300\,\text{mL}$, sending messages to the sacral spinal cord to contract the detrusor muscle and relax the internal urethral sphincter.

Internal urethral sphincter

An involuntary ring of smooth muscle at the neck of the bladder that relaxes during the micturition reflex.

External urethral sphincter

A voluntary ring of skeletal muscle around the urethra that is relaxed consciously to allow urination.

Urethra

The single duct through which urine leaves the bladder and is conveyed to the outside of the body.

Angiotensin-converting enzyme (ACE)

An enzyme that converts the prehormone angiotensin I into its active vasoconstrictor form, angiotensin II.

ACE inhibitors

A class of pharmaceutical agents that block the production of angiotensin II, commonly used to reduce hypertension.

Angiotensin II

The active hormone product of the renin-angiotensin-aldosterone pathway that stimulates the adrenal cortex to secrete aldosterone.

Aldosterone

A mineralocorticoid hormone secreted by the adrenal cortex that regulates salt excretion and water retention, resulting in a lower volume of urine.

Atrial natriuretic peptide (ANP)

A hormone that increases sodium excretion and decreases blood pressure, acting antagonistically to the renin-angiotensin-aldosterone system.

Antidiuretic hormone (ADH)

A hormone synthesized in the hypothalamus and released by the posterior pituitary that makes the distal tubules and collecting ducts more permeable to water, increasing water reabsorption into the blood.

Diabetes insipidus

A disorder diagnosed when the posterior pituitary fails to produce sufficient ADH, resulting in poor water reabsorption and the excretion of large volumes of dilute urine.

Diuretics

Substances found in coffee, tea, and alcoholic beverages that inhibit the reabsorption of water in the kidneys, leading to increased urine volume.

Intracellular fluid

Body fluid located inside cells, constituting approximately two-thirds ($\frac{2}{3}$) of all body fluid.

Extracellular fluid

Body fluid located outside cells, constituting approximately one-third ($\frac{1}{3}$) of total body fluid; it includes interstitial fluid, blood plasma, lymph, and fluid in special compartments.

Dehydration

A physiological condition that occurs when fluid output exceeds fluid intake, raising blood osmotic pressure and stimulating the hypothalamic thirst center.