Excretion And Homeostatic Control Flashcards
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 the centre) are connected to :
Hepatic vein takes deoxygenated blood away from the liver and is attached to the hepatic portal vein (contains products of digestion) and the hepatic artery (supplies oxygenated blood via sinusoid capillaries
Bile duct: transports bile to gall bladder for storage
Outline the functions of the mammalian liver
Site of gluconeogenesis, glycolysis and glycogenesis
Stores glycogen
Deaminates excess amino acids, forming ammonia and organic acids. Acids can be respired or converted in glycogen. Ammonia is detoxified by the addition of CO2 in the ornithine cycle
Detoxifies chemicals e.g. converts alcohol to ethanal then to acetic acid
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, Convoluted tubules and blood vessels
Medulla: inner region consists of collecting ducts, loops of Henle and blood vesselsq
Describe the structure of a nephron
Glomerulus
Bowmans capsule
PCT
Collecting duct
Afferent arteriole
Efferent arteriole
Loop of Henle
DCT
Describe the blood vessels associated with a nephron
Wide afferent arteriole from renal artery enters renal capsule and forms glomerulus, a branched knot of capillaries which combine to form narrow efferent arterioles
Efferent arteriole branches to form capillary network that surrounds tubules
Describe the histology of the kidney
- Glomerulum
- Proximal tubule
- Distal tubule
Describe the sections of a nephron
Bowman’s capsule at the 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 microvilli
Loop of Henle: hairpin loop extends from cortex into medulla
Distal convoluted tubule: similar to PCT but fewer 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 glomerulus forces small molecules (urea, water, glucose, mineral ions) out of capillary fenestrations AGAINST osmotic gradient
Basement membrane acts as filter. Blood cells & large molecules e.g. proteins 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 during selective reabsorption and where it occurs
Useful molecules from glomerular filtrate e.g. glucose are reabsorbed into the blood
Occurs in proximal convoluted tubule
Outline the transport processes involved in selective reabsorption
Glucose from glomerular filtrate
I Co-transport with Na+ ions
V
Cells lining poroximal convoluted tubule
I Active transport
V
Intercellular spaces
I Diffusion
V
Blood capillary lining tubule
How does the kidney produce urine
After selective reabsorption, filtrate passes through Loop of Henle, which acts as countercurrent multiplier and then through 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
- Active transport of Na+ and 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 ascending limb: lowest in medullary region, highest at top of ascending limb
Explain the role of the distal convoluted tubule
Reabsorption:
a. of water via osmosis
b. 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 antidiuretic hormone (ADH)
Explain the role of the posterior pituitary gland in osmoregulation
Stores and secretes 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. 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 interstitial 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 toxic waste products e.g. urea causes symptoms such as vomiting
If kidneys cannot remove excess water from the 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: haemodialysis / peritoneal dialysis (short term solution repeated several times a week so toxic waste products do not accumulate
Kidney transplant (long-term solution, but difficult to find suitable donor with same blood / tissue type and patient requires immunosuppressants)
