Excretion And Homeostatic Control Flashcards
What is excretion ?
-Process of removing metabolic wastes e.g. carbon dioxide & nitrogen based byproducts to maintain metabolism
-Enables organism to maintain pH balance & regulate osmotic pressure
Describe the gross structure of the mammalian liver
-Liver Lobules: (Cylinders of hepatocytes arranged in rows & connected at the centre) are connected to:
-Hepatic Vein: Takes deoxygenated blood away from the liver & is attached to - hepatic portal vein:contains products of digestion & Hepatic artery supplies oxygenated blood via Sinusoid capillaries
-Bile Duct: Transports bile to the gall bladder for storage
Outline the functions of the mammalian liver
- Site of gluconeogenesis, glycolysis, glycogeneisis
- Stores glycogen
- Deaminates excess amino acids, forming ammonia & organic acids. ACids can be respired or converted into glycogen. Ammonia is detoxified by addition of Co² in ornithine cycle
- Detoxifies chemicals e.g. converts alcohol to ethanal then acetic acid
Describe the gross structure of the mammalian kidney
- Fibrous Capsule: Protects kidney
- Cortex: Outer region consists if the bowman’s capsules, convoluted tubules, blood vessels
-
Medulla: inner region consists of collecting ducts, loops of Henle, Blood vessels
Refer to Goodnotes
Describe the structure of the nephron
**Refer to Goodnotes*
Describe the blood vessels associated with a nephron
Wide afferent arteriole from renal artery enters Renal capsule & forms glomerulus: branched knot of capillaries which combine to form narrow efferent arteriole
Efferent arteriole branches to form capillary network that surrounds tubules
Describe the histology of the kidney
Refer to Goodnotes
Describe the sections of a nephron
Bowmans capsule at start of nephron: cup-shaped, surrounds glomerulus, inner layer of podocytes
Proximal convoluted tubule (PCT): series of loops surrounded by capillaries, walls made of epithelial cells with micro villi
Loop of Henle: Hairpin loop extends from cortex into medulla
Distal convoluted tubule: Similar to the PCT but fewer capillaries
Collecting Ducts: DCT from several nephrons empty into collecting duct, which leads into the pelvis of the kidney
Describe the process of ultrafiltration
First Process
- Occurs in Bowmans Capsule
- High *Hydrostatic pressure in glomerulus** forces small molecules (urea, water, glucose, mineral ions) out of capillary fenestration’s against osmotic gradient
- Basement Membrane acts as a filter. Blood cells & large molecules e.g. proteins remain in capillary
How are cells of the Bowman’s capsule adapted for ultrafiltration ?
- Fenestartions between epithelial cells of capillaries
- Fluid can pass between & under folded membrane of podocytes
State what happens during selective re absorption and where it occurs
- Useful molecules from glomerular filtrate e.g. glucose re absorbed into the blood
- Occurs in proximal convoluted tubule
Outline the transport processes involved in selective reabsorption
Refer to GoodNotes
How does the kidney produce urine ?
- After selective reabsorption, filtrate passes through Loop of Henle, which acts as a counter current multiplier & then through distal convoluted tubule, where water & minerals are reabsorbed
- More water is reabsorbed in collecting duct. Remaining fluid only contains waste Minerals & water
What happens in the loop of Henle ?
- Active Transport of Na+ & Cl- out of ascending limb
- Water potential of interstitial fluid decreases
- Osmosis of water out of descending limb (ascending limb is impermeable to water)
- 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 is 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
- Osmosis of water out of osmoreceptors in hypothalamus causes them to shrink
- This triggers 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
- Forms hormone-receptor complex on the surface membrane of cells in collecting duct. Triggers 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 ?
- Makes cells lining collecting duct more permeable to water:
Binds to receptor —> activates phosphorylase —> vesicles with aquaporins on membrane fuse with cell-surface membrane - Makes cells lining collecting duct more permeable to urea: water potential in intersistital fluid decreases
What can cause Kidney Failure ?
- Kidney infections cause inflammatory damage = change in glomerular filtration rate (rate at which filtrate flows through kidney)
- Kidney Stones
- Uncontrolled diabetes
- High Blood pressure damages capillaries of glomeruli = 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 kidneys failure
- Renal dialysis: hameodialysis/ peritoneal dialysis, short term solution repeated several times a week so toxic waste products do not accumulate
- Kidney Transplants: (long term solution but difficult to find suitable donor with Same blood/tissue type & patient requires immunosuppressants)
Describe haemodialysis
- Removes blood from body & pumps it trough the machine
- Blood runs countercurrent to dialysis fluid. Artificial membrane separates fluids = diffusion gradient enables molecules to move
- Add blood thinning agent to avoid clotting outside body
