5.1.2 Excretion as an example of homeostatic control Flashcards
(19 cards)
Waste
Removal of waste products - excretion
-Carbon dioxide + nitrogenous waste
Overview function of the liver
- Glycogen storage, detoxification + formation of urea
- Receives oxygenated blood through hepatic artery
- Blood leaves through hepatic vein
- Hepatic portal vein supplies liver with blood from digestive system (full of nutrients)
Structure and histology of the liver
Liver cells - hepatocytes
Many mitochondria, large nuclei, prominent Golgi - enable high metabolic rate
- Blood delivered through hepatic portal vein + hepatic artery mixes in sinusoids (spaces surrounded by hepatocytes)
- Blood from hepatic artery highly oxygenated - mixes with blood from HPV
Within the liver (K-cells + bile)
Kupffer cells within sinusoids - like macrophages, engulfing any foreign particles
Hepatocytes produce bile using products from breaking down old blood
Bile secreted into spaces (canaliculi)the passed through bile ducts the stored in gall bladder
Function of the liver
- Responding to insulin + glucagon to bring blood glucose levels back to normal:
Hepatocyte responds to insulin + absorbs excess glucose from blood + convert to glycogen
Responds to glucagon, hepatocytes hydrolyse glycogen to glucose + into blood - Detoxification - ornithine cycle
Detoxification
- Neutralisation + breakdown of unwanted chemicals (alcohol, drugs, hormones, toxins produced in chemical reactions)
Liver contains enzymes to break toxins into non-toxic substances
Ornithine cycle (urea cycle)
- Urea is produced from ammonia to be transported into kidneys + excreted
- Excess proteins from diet cannot be stored - delivered to liver to be deaminated
- Deamination: amine group removed from amino acids - converting to ammonia (very toxic) then converted to urea (toxic in high conc) to be transported in the blood
Kidney key info
- Excretion of nitrogenous waste + osmoregulation
- Renal artery supplies kidney with blood for filtering
- Renal vein carries filtered blood away from kidney
- 3 layers:
1. Cortex - dark outer layer, contains many capillary networks carrying blood from renal arteries to nephrons
2. Medulla - contains nephrons
3. Pelvis - urine collects before leaving the kidney + going to the ureter
Overview of nephron
- Structures within kidney where blood is filtered + useful substances are reabsorbed into the blood
- Blood filtered here to remove waste + selectively reabsorb useful substances back into the blood
Structure of nephron
- Glomerulus: contains Bowman’s capsule - filters small solutes from blood (ultrafiltration)
- Proximal convoluted tubule (PCT): reabsorbs ions, water, nutrients, removes toxins + adjusts filtrate pH - glucose reabsorbed
- Descending Loop of Henle: aquaporins allow water to pass from filtrate into interstitial fluid
- Ascending Loop of Henle: reabsorbs Na+, Cl- from filtrate into interstitial fluid
- Distal tubule: selectively secretes + absorbs ions to maintain blood pH + electrolyte balance
- Collecting duct: reabsorbs solutes + water from filtrate
Ultrafiltration
- Blood enters through afferent arterioles + splits into smaller capillaries - glomerulus
- Causes high hydrostatic pressure of blood - water + small molecules forced out of capillaries + form glomerulus filtrate
- Filtrate passes through basement membrane (network of collagen fibres + proteins)
- Basement membrane + capillary act like a sieve
- Podocytes in Bowman’s capsule wall - additional filters - large protein + blood cells too big to fit through so remain in the blood
- Blood leaves via efferent arteriole
Selective reabsorption
- Occurs in PCT - most glomerular filtrate reabsorbed into blood - leaves urea + excess mineral ions + water
- Conc of Na+ in PCT decreased - actively transported out of PCT cells + into blood in capillaries
-Conc gradient - Na+ diffuse down gradient from lumen of PCT into cells lining PCT (co-transport - carries glucose with Na+ in proteins) - Glucose diffuse from PCT epithelial cell into blood
- Change in water potential caused by glucose - 80% of water in PCT moves back into blood
Loop of Henle - maintaining sodium and chloride ion gradient
- Filtrate passes into LoH - sodium + chloride ion gradient maintained in medulla to enable reabsorption
- Mitochondria in walls of cells provide energy to actively transport Na+, Cl- out of ascending LoH
- Accumulation of ions in medulla lowers water potential
- Water diffuses out by osmosis into interstitial space then blood capillaries
- Base of ascending limb, some Na+, Cl- transported out by diffusion - very dilute solution due to all water moving out
Hypothalamus & Posterior Pituitary Gland
Hypothalamus - changes in water potential of blood detected by osmoreceptors
- If water potential too low, water leaves osmoreceptors + shrivel > stimulates hypothalamus to produce more ADH
- If water potential too high, water enters osmoreceptors by osmosis > stimulates hypothalamus to produce less ADH
- ADH produced in hypothalamus then moves to posterior pituitary + released into blood
ADH - Antidiuretic hormone
- Binds to complementary receptors located on target cells at DCT & CD
- Activates adenyl cyclase to make cAMP
- Activates an enzyme which causes vesicles containing aquaporins to fuse with the membrane
- Aquaporins - channel proteins that allow water to transport across the membrane
- Membrane becomes more permeable to water + more will leave to be reabsorbed back into blood
- Urine more concentrated
Urine for Diagnosis
- Test for diabetes, pregnancy, anabolic steroids, drugs
Pregnancy test - uses monoclonal antibodies to detect presence of human growth hormone - present in pregnant women
Pregnancy test:
A - Urine sample tested - absorbent end of test submerged in urine
B - First mobile antibody - complementary to HGH has coloured dye attached
C - Second antibody - complementary to antigen is immobilised in the test
D - Third antibody immobilised + complementary to first antibody
Kidney failure
- Kidney infections + high BP can damage tubules, podocytes, epithelial cells, basement membranes - results in large molecules filtering out of blood (proteins + RBC)
- Completely fails, blood won’t be filtered out properly - lead to build-up of urea in blood + electrolyte imbalance
- Glomerular Filtration Rate (GFR) - affected by kidney failure. Measured indirectly by testing blood for creatinine levels (breakdown product of muscles) increase X
Treatment of kidney failure - Haemodialysis
- Dialysis machine
- Blood enters machine, parallel is dialysis fluid separated by partially permeable membrane
- Dialysis fluid contains no urea - steep conc gradient so all urea diffuses out of blood
- Dialysis fluid has normal plasma levels for glucose + ions - no net movement of glucose out of blood + only excess ions removed
- Takes many hours, multiple times a week, patient has to have a careful diet + keep blood levels as constant as possible
- Long term can have harmful side effects - best is kidney transplant but lack of donors + risk rejection
