removal of harmful and unwanted waste products derived from the organisms own metabolic activities is excretion.
organs of excretion
- kidney- removes urea, uric acid, ammonia, excess water and salts
- liver- bile pigments are broken down and expelled with some undigested food
- skin - removes salt, water and traces of urea
- lungs - removes carbon dioxide.
external structure of the urinary system
- renal artery- entering the kidney is the renal arty which branches from the aorta bringing oxygenated blood contain nitrogenous wastes
- renal vein- exiting the kidney, it carries de oxygenated but pure blood
- ureter- emerges from the medial surface of each kidney and connects to the base of the urinary bladder. it transports urine from the kidneys to the urinary bladder
- urinary bladder- situated at the lower end of the abdomen. the urinary bladder temporarily stores the urine until it can be discharged.
- urethra- short muscular tube leading the urinary bladder to the outside.
LS of kidney
- a kidney is made up of cells known as nephrons
- what are the main functions of the kidney?
| renal cortex |
renal medula |
| it forms the outer portion of the kidney |
it forms the inner portion of the kidney |
| it is dark red in colour |
it is light red |
| contains the malpighian corpuscle, PCT & DCT |
contains elements of henle’s loop and the collecting tubules |
- why is the renal cortex dotted?
- why is the medulla striated?
structure of a nephron
- malpighian corpuscle
- bowman’s capsule- receives the glomerular capillaries
- glomerulus- formed by the efferent and afferent arteriole.
- renal tubule-
- proximal convoluted tubule [permeable]
- distal convoluted tubule [impermeable]
- collecting tubule - DCT open into the collecting tubule which produce a common duct [renal pelvis] which open into the ureter.
mechanism of urine formation
- ultrafiltration- this takes place under tremendous pressure. it contains uric acid, urea, amino acids, and large amounts of water. primary urine is formed.
- tubular reabsorption / selective reabsorption- usable material such as some water, amino acids and glucose are reabsorbed into the blood stream
- tubular secretion- this adds minerals from the blood into the urine- creatien, ammonia.
| afferent arteriole |
efferent arteriole |
| formed by branching of renalk artery |
formed by fusion of glomerular capilaries |
| diameter is 2x of the efferent arteriole |
half the size of the afferent arterole |
| brings oxygenated blood into the kidney |
carries oxygenated blood away from the bowman’s capsule |
| large amounts of water and metabolic wastes |
thick blood with toxic wastes |
urine excretion
- induced by gravity and uretal peristalsis
bladder sphincter- exit of bladder
urethral sphincter- below bladder sphincter
expelled by simultaneous contraction of the bladder sphincter and relaxation of the urethral sphincter.
variations in urine volume
- diet & water intake- consumption of diuretics will slow down the production of urine
- physical activity- urine output is reduced during physical activity as sweat is produced
- day & night factor- not much urine is produced at night due to the decreased arterial pressure and the inhibited functioning of the organism
- environmental conditions- less urine when hot as body loses water through sweat.
- ADH- if adh is secreted more water is absorbed from the blood stream
micturition- is the act of expelling urine.