Excretion in Humans

Vocabulary practice flashcards reviewing the human excretory system, kidney function, nephron structure, ultrafiltration, reabsorption, and liver deamination based on Cambridge IGCSE Biology content.

Excretion

The removal from the body of waste products of metabolic reactions, toxic substances, and substances in excess of requirements.

Egestion

The expulsion of undigested food waste from the anus.

Metabolic reactions

The chemical reactions that take place inside cells.

Excretory system

A group of organs in humans specialized for the removal of certain excretory products, with the lungs and kidneys being two important organs in the system.

Carbon dioxide excretion

The excretion of carbon dioxide (a waste product of aerobic respiration) by the lungs during exhalation to prevent it from forming an acidic solution that lowers cellular $pH$ and reduces enzyme activity.

Kidney

Two bean-shaped organs located in the back of the abdomen that filter blood, regulate water content, and excrete excess water, salts, and urea through the formation of urine.

Ureter

The tube connecting the kidney to the bladder that carries urine from the kidneys to the bladder.

Bladder

The organ that stores urine (excess water, salts, and urea) as it is produced by the kidney.

Urethra

The tube that connects the bladder to the exterior of the body, where urine is released.

Nephron

A tiny structure (also known as a kidney tubule or renal tubule) in the kidney where filtration and reabsorption occur; each kidney contains around $1\,million$ nephrons.

Cortex

The outer region of the kidney where nephrons originate and return to after looping down into the medulla.

Medulla

The inner region of the kidney into which nephrons loop down before heading back up to the cortex.

Glomerulus

A knot of capillaries located inside the Bowman's capsule where high blood pressure forces small molecules out of the blood.

Bowman's capsule

The cup-shaped start of a nephron that collects filtrate forced out of the capillaries in the glomerulus.

Ultrafiltration

The process in which high pressure in the glomerulus forces small molecules (glucose, water, urea, and salts) out of blood capillaries into the Bowman's capsule to form filtrate.

Proximal convoluted tubule

The first convoluted section of the nephron tubule after the Bowman's capsule where all glucose is reabsorbed back into the blood by active transport.

Loop of Henle

The U-shaped section of the nephron where necessary salts are reabsorbed into the blood by diffusion and active transport, with water following by osmosis.

Collecting duct

The final part of the nephron tubule where variable amounts of water are reabsorbed by osmosis depending on body requirements, leaving concentrated urine.

Assimilation

The process where digested food molecules absorbed into the blood are converted into other molecules that the body needs.

Deamination

The process in the liver where the nitrogen-containing amino group ($-NH_2$) is removed from excess amino acids and turned into toxic ammonia, which is then immediately converted to urea.

Urea

A less toxic nitrogenous waste product produced in the liver from ammonia during deamination, carried in the blood, and excreted by the kidneys in urine.

Consequences of high urea levels

Pathological conditions caused by high concentrations of unexcreted urea, including cell death, reduced response to insulin (potentially leading to diabetes), and deposits inside blood vessels.

Urinary glucose testing in diabetes

A diagnostic check for diabetes based on detecting glucose in urine, which occurs when abnormally high blood glucose levels exceed the capacity of active transport gates in the proximal convoluted tubule.

Structure of a Human Kidney

Diagram showing the main anatomy of the kidney, including the cortex, medulla, renal artery, renal vein, ureter, and adrenal gland.

Structure of a Nephron

Diagram showing the key parts of a nephron: glomerulus, Bowman's capsule, proximal convoluted tubule, Loop of Henle, distal convoluted tubule, and collecting duct.

Chemical Structure of an Amino Acid

Diagram showing the molecular components of an amino acid: an amino group ($-NH_2$), a central carbon with a hydrogen atom and R group, and a carboxylic acid group ($-COOH$).