Excretory System Flashcards
Types of metabolic waste produced by living systems
○ Digestive waste
○ Respiratory waste
○ Excess water and salt waste
○ Nitrogenous waste
Excretion
○ The removal of wastes produced by metabolism within cells
○ The main organs of excretion are
□ Lungs
- Carbon dioxide and water
□ Sweat glands
- Water, salt, and urea
□ Alimentary canal
- Water and bile pigments
□ Kidneys
- Water, salt, and urea
Elimination
- The removal of undigested materials from the body
- The bulk of feces is elimination (except for bile pigments)
Functions of the organs
○ Kidneys
- Filter blood to remove wastes and produces urine
○ Ureters
- Transports urine from the kidney to the bladder
○ Bladder
- Temporary storage of urine and contracts to ‘squeeze’ urine out of the body
○ Urethra
- Transports urine from the bladder to outside the body
Basic kidney structure
- Capsule (outside)
□ Clear
□ Smooth/skin like - Cortex (outer)
□ Where the filtration occurs
□ Light reddish brown
□ Granular - Medulla (middle)
□ Where useful substances are reabsorbed
□ Dark brown/red
□ Striated - Pelvis (inside)
□ Where the urine collects before traveling down the bladder
□ Centre
□ White/yellow
□ Smooth
Microscopic structure of the kidney
○ The structural and functional unit of the kidney is the nephron
○ There are approximately 1 million per kidney
Three basic parts of the nephron
□ Glomerulus
□ Kidney - cortex
□ Tubules
□ Kidney - medulla
□ Collecting duct
□ Kidney - pelvis
Formation of urine in the nephron
Three major stages - glomerular filtration, reabsorption, and tubular secretion
Glomerular filtration
□ Blood enters the glomerulus via the afferent arteriole and is connected to a knot of capillaries called the glomerulus.
□ The glomerulus is surrounded by the glomerular capsule
□ Some of the liquid parts of blood is forced into the glomerular capsule - the red and white blood cells and plasma proteins are left behind and leave via the efferent arteriole
□ The liquid in the glomerular capsule is now called filtrate
Reabsorption
□ The filtrate passes into the proximal convoluted tubule – many useful substances are reabsorbed into the peritubular capillaries
□ The filtrate then passes through the Loop of Henle and the distal convoluted tubule where further reabsorption of useful substances occurs
□ The Loop of Henle is particularly important for water reabsorption
- E.g. water, glucose, salts
Tubular secretion
□ Tubular secretion adds substances to the filtrate
□ The food you eat is slightly acidic, but blood needs to have a pH of 7.4-7.5
□ Hydrogen and ammonium ions are added to the filtrate so that blood pH remains stable (the body will lose these ions via the urine, and so the pH of the blood will rise)
□ Other materials such as potassium and some drugs are also removed from the body this way
□ The fluid is now called urine and passes into the collecting duct and to the ureter