5.2 Excretion as an example of homeostatic control Flashcards
(29 cards)
What is excretion?
-Process of removing metabolic wastes e.g carbon dioxide and nitrogen based by-products to maintain metabolism
-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 centre) are connected to
-Hepatic vein: takes deoxygenated blood away from liver, and is attached to
-Hepatic portal vein: contains products of digestion
-Hepatic artery: supplies oxygenated blood via sinusoid capillaries
-Bile duct: transports bile to gall blader for storage
Outline the function of the mammalian liver
-Site of glycogenesis, glycolysis and gluconeogenesis
-stores glycogen
-Deaminates excess amino acids, forming ammonia and organic acids
-Acids can be respired or converted into glycogen, ammonia is detoxifed by addition of co2 in the orthine cycle
-detoxifies chemicals
Describe the gross structure of the mammalian urinary system
-Kidney
-Renal vein
-Renal artery
-Ureter
-Urethra
-Bladder
Describe the gross structure of the mammalian kidney.
Fibrous capsule: Protects kidney
Cortex: Outer region consists of bowman’s capsules, convulated tubes and blood vessels
Medulla: Inner region consists of collecting ducts, loop of henle and blood vessels.
Describe structure of a nephron
-Glomerus of capillaries inside the bowmans capsule
-Leads to proximal convoluted tubule
-PCT goes down into the loop of henle, consisting of a descending and ascending limb
-ascending limb leads to the distal convoluted tubule then into the collecting duct
Describe the blood vessels associated with a nephron
Wide afferent arteriole from renal artery enters renal capsule and forms the glomerus (a branched knot of capillaries) which combine to form a narrow efferent arteriole
-Efferent arteriole branches to form a capillary network outside the nephron
Describe the sections of a nephron.
-Bowmans capsule at start of nephron: cup shaped, surrounds glomerus with an inner layer of podocytes
-Proximal convoluted tubule: series of loops surrounded by capillaries, walls made of epithelial cells with microvilli
-Loop of henle: hairpin loop extends from cortex to medulla
-Distal convoluted duct: similar to PCT, less capillaries
-Collecting duct: DCT from several nephrons empty into collecting duct, which leads into pelvis of kidney
Describe the process of ultrafiltration
-Occurs in bowman’s capsule
-High hydrostatic pressure in glomerus, forces small molecules out of capillary fenestrations against osmotic pressure
-The basement membrane acts as a filter, blood cells and large molecules remain in capillary.
How are cells of the Bowman’s capsule adapted for ultrafiltration?
-Fenestrations between epithelial cells of capillaries
-fluid can pass between and under folded membrane of podocytes
State what happens in selective reabsorption and where it occurs.
-Useful glomerular filtrate e.g glucose are reabsorbed into the blood
-Occurs in the proximal convoluted tubule
Outline the transport process involved in selective reabsorption.
-Glucose from glomerular filtrate moves into cells lining the proximal convoluted tubule by co-transport with Na+ ions
-Then move from those cells into intracellular spaces using active transport
-Move from intracellular spaces into a blood capillary lining tubule via diffusion
How does the kidney produce urine?
-After selective reabsorption, filtrate passes through Loop of Henle, which acts as countercurrent multiplier, and then through the distal convoluted tubule, where water and mineral ions are reabsorbed
-More water is reabsorbed in collecting duct. Remaining fluid (urine) contains only waste materials and water
What happens in the loop of henle?
1) Active transport of Na+ and Cl- out of ascending limb
2) Water potential of interstital fluid decreases
3) Osmosis of water out of descending limb (ascending limb impermeable to water)
4) Water potential of filtrate decreases going down descending limb: lowest in medullary region, highest at top of ascending limb
Explain the role of the distal convoluted tubule
Reabsorption of water via osmosis, of ions via active transport
-permeability of walls determined by action of hormones
Define osmoregulation
Control of plasma water potential via negative feedback homeostatic mechanisms
Explain the role of the hypothalamus in osmoregulation
1) Osmosis of water out of osmoreceptors in hypothalamus causes them to shrink
2) This triggers hypothalamus to produce more antidiuretic hormone (ADH)
Explain the role of the posterior pituitary gland in osmoregulation
Stores and secreted the ADH produced by the hypothalamus
Explain the role of ADH in osmoregulation
Forms hormone-receptor complex on surface membrane of cells in collecting duct
-This triggers the activation of cAMP as secondary messenger
-Triggers cellular processes that increase reabsorption of water. Urine becomes more concentrated
How does ADH increase reabsorption of water
1) Makes cells lining collecting duct more permeable to water
Binds to a receptor which activates Phosphorylase. This then causes vesicles with aqua-porins on membrane to fuse with cell-surface membrane
2) This makes cells lining collecting duct more permeable to urea: water potential in interstitial fluid decreases
What can cause kidney failure?
-Kidney infections cause inflammatory damage which changes the glomerular filtration rate
-Kidney stones
-Uncontrolled diabetes
-High blood pressure damages capillaries of glomeruli, this means larger molecules pass into urine
Describe the effects of kidney failure
-Build up of toxic waste products e.g urea causes symptoms such as vomiting
-If kidneys cannot remove excess water from blood, fluid accumulation leads to swelling
-Disruption to electrolyte balance can make bones more brittle or increase water retention
Name potential treatments for kidney failure
-Renal dialysis: A short term solution repeated several times a week so toxic waste products do not accumulate
-Kidney transplant: A long term solution, difficult to find a suitable donor with same blood/tissue type, patient may need immunosuppressants afterwards
Describe haemodialysis
Removes blood from body and pumps it through a machine
-Blood runs countercurrent to dialysis fluid. Artificial membrane separates fluids. the diffusion gradient enables molecules to move
-The addition of a blood thinning agent can avoid clotting outside body
