Excretion and the Human Urinary System

Comprehensive vocabulary flashcards defining key physiological and anatomical terms relating to human excretion, the urinary system, nephron function, osmoregulation, and renal pathologies.

Metabolism

The sum total of all the chemical reactions that continuously occur in a cell.

Excretion

The removal of metabolic wastes from the body.

Egestion

The removal of undigested substances from the body that are not products of metabolism and were never inside cells.

Secretion

The release of useful substances produced by cells for important functions, such as digestive juices, hormones, and milk.

Deamination

The chemical process occurring in the liver that breaks down excess amino acids to form urea.

Uric acid

A nitrogenous waste product formed as the end product of the metabolism of nucleic acids.

Creatinine

A nitrogenous waste product formed from creatinine phosphate in body cells.

Bile pigments

Metabolic waste substances formed in the liver during the breakdown of haemoglobin, which pass into the small intestine and are excreted as bile salts in faeces.

Kidneys

A pair of excretory organs located in the abdominal cavity on either side of the vertebral column, just below the diaphragm, that excrete urine.

Ureters

Two tubes in the urinary system that transport urine from the kidneys to the bladder.

Urinary bladder

A thin-walled muscular sac that temporarily stores urine before excretion.

Urethra

The passage that carries urine from the bladder to the exterior of the body, controlled by a sphincter.

Renal artery

A blood vessel branching from the aorta that transports oxygenated blood rich in metabolic wastes to the kidney.

Renal vein

The blood vessel that carries deoxygenated, purified blood away from the kidney to merge with the inferior vena cava.

Nephron

The microscopic structural and functional unit of the kidney, with approximately $1\times 10^6$ present in each kidney.

Malpighian body

The filtration unit situated in the cortex of the kidney, composed of Bowman's capsule and the glomerulus.

Bowman's capsule

A double-walled, cup-shaped structure situated at one end of the nephron in the cortex that encloses the glomerulus.

Glomerulus

A network of capillary blood vessels lined with a single endothelial layer of squamous epithelium with pores, situated inside Bowman's capsule.

Afferent arteriole

The wider blood vessel branching from the renal artery that brings blood into the glomerulus under high pressure.

Efferent arteriole

The narrower blood vessel that carries deoxygenated, filtered blood away from the glomerulus and divides into the peritubular capillary network.

Podocytes

Specialised epithelial cells with projections lining the inner wall of Bowman's capsule, forming filtration slits between the projections.

Filtration slits

Small openings between the projections of podocytes in Bowman's capsule that permit only small solutes and fluid to filter through.

Renal tubule

A long convoluted tube situated partially in the cortex and partially in the medulla, composed of the proximal convoluted tubule, loop of Henle, and distal convoluted tubule.

Proximal convoluted tubule

The widest part of the renal tubule, located in the cortex directly after Bowman's capsule, lined with cuboidal epithelium featuring a brush border of microvilli and abundant mitochondria.

Loop of Henle

A hairpin-shaped section of the renal tubule located in the medulla, comprising a descending limb that extends into the medulla and an ascending limb that extends back to the cortex.

Distal convoluted tubule

A convoluted segment of the renal tubule situated in the renal cortex that opens into a collecting duct.

Ducts of Bellini

Large collecting tubes formed by the convergence of multiple collecting ducts that form renal pyramids and open into the renal calyces.

Peritubular capillary network

A capillary network branching from the efferent arteriole that surrounds the renal tubule to facilitate reabsorption and tubular excretion.

Glomerular filtration

The non-selective, pressure-driven process occurring in Malpighian bodies where plasma solutes are forced through pores and filtration slits into the cavity of Bowman's capsule.

Glomerular filtrate

The fluid filtered into Bowman's capsule containing water, glucose, amino acids, vitamins, salts, and nitrogenous wastes, but lacking blood cells and plasma proteins.

Tubular reabsorption

The selective process by which useful substances and water in the glomerular filtrate are transported from the renal tubule back into the peritubular bloodstream.

Sodium pump

An active transport mechanism in the ascending limb of the loop of Henle that pumps sodium ions into the tissue fluid of the medulla against a concentration gradient.

Tubular excretion

The process whereby substances such as hydrogen ions, potassium ions, creatinine, drugs, and food colourants are actively secreted from peritubular capillaries into the renal tubule.

Osmoregulation

The homeostatic regulation of the water content of the blood, primarily mediated by antidiuretic hormone (ADH).

Aldosterone

A hormone secreted by the adrenal gland that increases sodium ion reabsorption from the distal convoluted tubule and collecting duct into the blood.

Antidiuretic hormone (ADH)

A hormone released by the hypophysis (pituitary gland) that increases the water permeability of the distal convoluted tubule and collecting duct.

Negative feedback mechanism

A control cycle in which a detected deviation from a normal physiological setpoint triggers a response that opposes the change to restore normal levels.

Kidney stones

Solid crystals formed when nitrogenous wastes and mineral salts fail to dissolve in urine, which can obstruct the ureter if larger than $4.5\,\text{mm}$ in diameter.

Cystitis

A bacterial bladder infection marked by painful urination, frequent urges to urinate, cloudy or bloody urine, fever, and nausea.

Bilharzia

A parasitic disease caused by the flatworm Schistosoma, requiring both humans and freshwater snails to complete its life cycle, causing bladder ulceration and renal damage.

Acute renal failure

A sudden loss of kidney function commonly resulting from injury, surgical complications, drug overdose, or the overuse of certain painkillers.

Chronic renal failure

A slow, progressive deterioration of kidney function most commonly caused by diabetes, untreated high blood pressure, or genetics.

Dialysis

An artificial process of purifying blood using a kidney machine, separating small molecules from large molecules across a selectively permeable membrane.

Heparin

An anticoagulant substance added to a patient's blood as it leaves the arm to prevent clotting inside the kidney machine.

Counter-current system

The operational design in a kidney machine in which dialysis fluid flows around the fine tubes in the opposite direction to blood flow to maximise substance exchange.

Kidney transplant

A surgical procedure for end-stage renal failure where a diseased kidney is replaced by a healthy donor kidney, requiring lifelong immunosuppressants.