5.1.2 Excretion and Homeostatic Control Flashcards
What is excretion ?
•The process of removing metabolic (eg CO2 and nitrogen based biproducts) to maintain metabolism.
•It enables organisms to maintain pH balance and regulate osmotic pressure.
Describe the gross structure of the mammalian liver
•Liver lobules : cylinders of hepatocytes arranged in rows and connected at the centre. They connect to the hepatic vein
•Hepatic vein : takes deoxygenated blood away from the liver & is attached to hepatic portal vein
•Hepatic portal vein : contains products of digestion
•Hepatic artery : supplied liver with oxygenated blood via sinusoid capillaries.
Outline the functions of the mammalian liver.
•Site of gluconeogenesis, glycosis and glycogenesis
•Stores glycogen
•Deanimates amino acids, forming ammonia organic acids
•Detoxifies chemicals eg ethanol -> ethanal -> acetic acid.
Describe the gross structure of a mammalian kidney.
Fibrous capsule : protects the kidney
Cortex : outer region of Bowman’s capsule, convoluted tubules and blood vessels
Medulla : inner region of collecting ducts, loop of Henle and blood vessels.
What are the components of a nephron
•Glomerulus
•Bowman’s capsule
•Proximal convoluted tubule
•Collecting duct
•Loop of henle
•Distal convoluted tubule
Describe the process of ultrafiltration
•Occurs in the bowman’s capsule
•High hydrostatic pressure in glomerulus forces small molecules out of capillaries against osmotic gradient
•Basement membrane acts as a filter, large proteins (>69,000) stay in capillary.
How are the cells of the Bowman’s capsule adapted for ultrafiltration ?
•There are pores between the epithelial cells of the capillaries
•Fluid can pass between and under podocytes.
State what happens during selective reabsorption and where it occurs
•Useful molecules from glomerular filtrate e.g. glucose are re absorbed into the blood
•This occurs in the proximal convoluted tubule (PCT)in the kidneys.
Outline the transport process involved in selective reabsorption
•Glucose from glomerular filtrate is co-transported with Na+ to the cell lining of PCT
•Active transport takes it to the intercellular spaces
•Diffusion then takes it to the capillaries.
How does the kidney produce urine ?
•After selective reabsorption, filtrate passes through Loop of Henle which acts as a countercurrent
•It then passes through the distal convoluted tubule where water and mineral ions are re absorbed
•More water is reabsorbed in the collecting duct, remaining fluid is urine.
What happens in the loop of Henle ?
•Active transport of Na+ and Cl- ions out of ascending limb
•Water potential of interstitial fluid decreases
•Osmosis of water out of descending limb (ascending is impermeable to water)
•Water potential of filtrate decreases going down the ascending limb
Explain the function of the distal convoluted tubule
Reabsorption of :
Water via osmosis
Ions via active transport (determined by ADH)
Define osmoregulation
The control of plasma water potential via negative feedback homeostatic mechanisms
Explain the role of the hypothalamus in osmoregulation
•Osmosis of water out of osmoreceptors (due to water potential of plasma) causes them to shrink
•This triggers the hypothalamus to produce more ADH.
Explain the role of the pituitary gland in osmoregulation
Stores and secretes ADH produced by the hypothalamus
Explain the role of ADH in osmoregulation
•The hormone binds to receptors on cell surfaces in collecting duct, where it triggers activation of cAMP as a secondary messenger
•This triggers cellular processes that form aquaporins that increase reabsorption of water
•This makes urine more concentrated
How does ADH increase reabsorption of water ?
•It makes the cells lining the collecting duct more permeable to water (causes vesicles with aquaporins to fuse with membrane)
•Makes cells lining collecting duct more permeable to urea, making water potential on interstitial fluid decrease.
What can cause kidney failure ?
•Kidney infections cause inflammatory damage = change in glomerular filtration rate
•Kidney stones
•Diabetes
•High blood pressure, damages walls of glomerulus.
Describe the effects of kidney failure
•Build up of toxic waste products e.g. urea causes symptoms like vomiting
•If kidneys cannot remove excess water swelling occurs
Name potential treatments for kidney failure
•Dialysis (haemodialysis / peritoneal), short term treatment that must be repeated regularly
•Kidney transplant, long term treatment but must be followed by immunosuppressants.
Describe haemodialysis
•Removes blood from the body and passes it through machine
•Blood runs countercurrent to dialysis fluid, separated by artificial membrane (diffusion gradient)
•Blood thinning agent prevents clotting outside of body.
Describe peritoneal dialysis
•Dialysis fluid is put into body cavity
•The exchange of molecules happens across the body’s peritoneal membrane
•Fluid must be drained and replaced regularly.
How can urine samples be used to test for pregnancy ?
•Monoclonal antibodies bind to the hormone hCG in the urine of pregnant women
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How can urine samples be tested for drugs such as anabolic steroids ?
•Gas chromatography measures the time taken for urine to pass through a column
•This is compared to how long it takes a steroid to pass through.
