excretory system Flashcards
excretory system function
to remove toxic materials and substances in excess of requirements from the organism
liver
- the body is not able to store proteins or amino acids so any excess amino acids are broken down by deamination in the liver
- the nitrogen component is converted to urea which can be toxic if its level in the blood gets too high, so it is excreted by the kidneys.
- the liver also breaks down haemoglobin from red blood cells, producing a yellow/green bile pigment called bilirubin. This is excreted with bile into the small intestine and expelled with faeces.
lungs
-remove carbon dioxide from the body (waste product of respiration)
skin
-the skin produces sweat, which consists of sodium chloride and traces of urea dissolved in water
kidneys-roles
- removal of urea (which could poison enzymes)
- adjustment of the ion content
- adjustment of the water content.
urine
- the mixture of substances removed from the blood plasma by the kidneys (the filtrate) is called urine
- it passes down a ureter to the bladder, where it is stored
- a sphincter muscle at the base of the bladder controls the release of urine through the urethra
- when the sphincter muscle relaxes, the muscle wall of the bladder contracts to expel the urine
regions of the kidneys
- cortex (outermost)
- medulla
- pelvis (innermost)
nephron structure
- blood enters a kidney through a renal artery which divides into arterioles and capillaries in the cortex
- each capillary becomes knotted to form a glomerulus, which is surrounded by a Bowman’s capsule.
- the proximal convoluted tubule passes down into the medulla, where it forms the loop of Henle, returning to a distal convoluted tubule in the cortex again
- the tubule joins a collecting duct, which passes down through the medulla into the pelvis of the kidney
nephron functioning
- the wall of the capillary of the glomerulus acts as a filter
- as blood enters the glomerulus, its pressure increases
- large structures and molecules, (e.g. blood cells and proteins) are retained within the capillary, but smaller molecules (water, ions, glucose and urea) are forced out by ultrafiltration (i.e. filtration under pressure)
- the filtrate is collected by the Bowman’s/renal capsule and passes into the proximal tubule -> Loop of Henle -> distal tubule
- as the filtrate passes along the tubule, selective reabsorption takes place into the capillaries surrounding the tubule
- glucose is reabsorbed by diffusion and active transport
- water is reabsorbed by osmosis
- some salts are reabsorbed by diffusion and active transport
- this maintains the correct concentration of substances in the blood.
- salts, urea and water continue into a collecting duct in the medulla and then to the pelvis, where the urine passes into a ureter to transfer it to the bladder for storage
high temp effect on urine
hot day:-more sweating occurs to maintain a constant body temperature, so more water is lost in sweat
- more ADH produced
- more water reabsorbed
- smaller volume of concentrated urine produced
low temp effect on urine
cold day:-less sweating occurs so less water is lost in sweat
- less ADH produced
- larger volume of dilute urine produced
- without this mechanism, the body could become over-hydrated
How will the composition of blood leaving a kidney be different from the composition of blood entering it?
blood leaving the kidney will contain: -less water -fewer salts -less urea -less oxygen -more carbon dioxide ...than blood entering the kidney
difference between ureter and urethra
- ureter carries urine from the kidneys to the bladder
- urethra carries urine from the bladder to be expelled from the body
where is urea made
liver
proximal convoluted tubule
- water reabsorption into the bloodstream occurs by both passive diffusion and active transport
- approx 2/3 of salt and water are reabsorbed
- 100% of the glucose is reabsorbed
