Excretion Flashcards
Define metabolism
The sum of all chemical reactions in the body
Define excretion
Excretion is the removal of toxic materials and waste products of metabolism from organisms
Define egestion
Egestion is the elimination of undigested materials from the alimentary canal
What is a catabolic reaction
A catabolic reaction is a reaction that breaks up complex molecules into simpler molecules
What is an anabolic reaction
An anabolic reaction is a reaction that builds up simpler molecules into complex molecules
Why must metabolic waste products be removed from the body
Can be harmful and prevent homeostasis of body if accumulated
What are some examples of excretory products
- CO2
- Excess water
- Excess minerals and salts
- Bile pigments
What is the kidney
- Contains numerous nephrons
- Responsible for osmoregulation
What is the ureter
Tube connecting kidney to bladder
What is the bladder
Muscular bag that stores urine
What does a nephron consist of
- Glomerulus
- Bowman’s capsule
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
What is the urethra
Muscular tube for urine to flow from bladder to exterior
Define ultrafiltration
Ultrafiltration is a non-selective filtering process which occurs at the glomerulus
What are the processes involved in urine formation
- Ultrafiltration
- Selective reabsorption
Describe the process of ultrafiltration
- Renal artery splits into numerous arterioles, and each arteriole splits into a glomerulus
- Lumen of afferent arteriole bringing blood towards glomerulus is larger than that of efferent arteriole bringing blood away from glomerulus
- Blood enters glomerulus more readily than it leaves, causing blood to build up and result in high blood pressure
- This provides the main force required for ultrafiltration
- Pressure forces blood plasma out of glomerular capillaries and into the Bowman’s capsule
- Blood plasma forced out contains water and small molecules, forming filtrate in Bowman’s capsule
- Blood cells, platelets, blood proteins and fats remain in the blood and leaves glomerulus via efferent arteriole
What is the glomerulus
A network of blood capillaries
What is the average composition of urine
- 96% water
- 2% urea
- 1.8% salts
- 0.2% nitrogenous substances
Define selective reabsorption
Selective reabsorption is the transport of useful substances from the filtrate back into the bloodstream
Describe the process of selective reabsorption
- Selective reabsorption is usually completed at the proximal convoluted tubule
- All glucose, amino acids and vitamins are reabsorbed
- 85% of sodium ions, chloride ions and water are reabsorbed at the proximal convoluted tubule
- Some water and ions are reabsorbed at the loop of Henle
- Water and smaller concentrations of ion are reabsorbed at the distal convoluted tubule
- Remaining water required is reabsorbed at collecting duct
How are useful solutes reabsorbed back into blood during selective reabsorption
- Facilitated diffusion
- Active transport
How can urine composition vary
- Protein-rich diet > more urea
- Water-rich diet > more urine
- Salty food > more salts
- Cold temperature > more urine
- Diabetes > glucose present
Why is there glucose present in urine of a diabetic
- Diabetic patient unable to store excess glucose as glycogen in body
- Blood has high glucose concentration
- Glucose is all filtered at glomerulus
- Nephrons are unable to reabsorb glucose fast enough
- Glucose passes out in urine
Define osmoregulation
Osmoregulation is the maintenance of a constant water potential in the body
What controls volume of water in blood
Anti-diuretic hormone (ADH)
What is ADH
- Produced by hypothalamus
- Released by pituitary gland
- Target organ in kidney
What happens when water potential of blood increases beyond the norm
- Osmoreceptors in hypothalamus detect increase in blood water potential
- Osmoreceptors send nerve impulses to hypothalamus
- Hypothalamus sends nerve impulses to pituitary gland
- Pituitary gland releases less ADH into bloodstream
- Walls of distal convoluted tubule and collecting duct become less permeable to water so less water is reabsorbed back into blood
- Negative feedback sent to hypothalamus via osmoreceptors once water potential of blood decreases back to the norm
What happens when water potential of blood decreases below the norm
- Osmoreceptors in hypothalamus detect the decrease in blood water potential
- Osmoreceptors send nerve impulses to hypothalamus
- Hypothalamus sends nerve impulses to pituitary gland
- Pituitary gland releases more ADH into the bloodstream
- Walls of distal convoluted tubule and collecting duct become more permeable to water
- More water is reabsorbed back into the blood
- Negative feedback sent to hypothalamus via osmoreceptors once water potential of blood increases back to the norm
What are the features of a dialyser
- Narrow tubing speeds up rate of diffusion between blood and dialysis fluid
- Direction of dialysis fluid flow is opposite to direction of blood flow, maintaining concentration for removal of waste products
Where is blood drawn from for haemodialysis
Fistula in patient’s arm
