5.1.1 and 5.1.2 Homeostasis Flashcards
What is homeostasis?
Maintenance of a constant internal environment by physiological control systems.
Define negative feedback mechanisms.
When a deviation from the set limits is detected by the body by receptors so a mechanism is put in place to restore conditions back into set limits.
Define positive feedback mechanisms.
When a deviation from set limits triggers a response to increase the deviation further.
Describe the nervous response through which endotherms regulate their temperature.
Peripheral receptors in the skin detect an external temperature change.
This sends an impulse along a sensory neuron to the brain where the hypothalamus coordinates a response.
This triggers a response in glands and muscles.
What responses may be triggered to regulate an endotherms body temperature?
Sweating
Shivering
Vasodilation
Vasoconstriction
Hairs lie flat
Hairs stand on end
Behaviour modification
What is excretion?
The removal of (toxic) waste products e.g. carbon dioxide and nitrogenous waste.
Functions of the liver
glycogen storage, detoxification and formation of urea
How is the liver supplied with blood?
Receives oxygenated blood via the hepatic artery and blood leaves via the hepatic vein.
Hepatic portal vein also supplies the liver with blood from the digestive system.
Where does blood delivered to the liver mix?
Blood delivered from the hepatic artery and hepatic portal veins mixes in sinusoids (spaces surrounded by hepatocytes).
Why is it important that blood delivered to liver lobules mixes?
Blood delivered by hepatic artery is highly oxygenated and can mix with blood from the hepatic portal vein to provide partially oxygenated blood.
What vessels does the liver contain?
- Hepatic artery (deliver oxygenated blood)
- Hepatic vein (take deoxygenated blood away)
- Hepatic portal vein (connects liver to intestines)
- Bile duct (takes bile from liver to gall bladder for storage)
Describe liver structure
- Liver is made up of cylindrical structure called lobules.
- Lobules made up of hepatocytes that radiate from central vein.
- Central vein connects to hepatic portal vein and artery via special capillaries = sinusoids.
- Also connects to bile duct via tubes = canaliculi
What happens as blood moves through sinusoids?
Hepatocytes convert toxic substance into less harmful molecules.
What are Kupffer cells?
Cells attached to sinusoid walls that break down RBC’s + remove bacteria from blood stream.
What is the ornithine cycle?
How excess amino acids are converted to urea (can’t be stored and may damage tissues)
Describe the ornithine cycle
- Amino acids deaminated (amino group removed = ammonia + organic acids)
- Organic acids respired/stored as glycogen
- Ammonia combined with CO2 which converts to urea in cyclical reaction
- Urea released into blood stream, filtered by kidneys and excreted in urine
Mammalian kidney function
responsible for excretion of nitrogenous waste and osmoregulation
Describe kidney structure
- Inner part called medulla, outer part = cortex
- Renal pelvis = cavity that collects urine
- Blood arrives via renal artery + leaves via renal vein
- Structures that filter blood = nephrons
Nephron structure
Glomerulus
Bowman’s (renal) capsule
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
Blood vessels in nephron
Afferent arteriole (supplies glomerulus)
Glomerulus
Efferent arteriole (carries blood away from glomerulus)
Capillaries around PCT, DCT and loop of Henle
Describe ultrafiltration
- Blood enter glomerulus via afferent arteriole
- Leaves via smaller efferent arteriole = high hydrostatic pressure
- Forces molecules out of blood = glomerulus filtrate
- Fluid passes through basement membrane (network of collagen fibres and proteins)
- Podocytes in BC wall w/extensions = pedicels filter blood
- Filtered fluid collects in BC
Adaptations of epithelial cells in PCT
Microvilli
Basal infoldings
Numerous mitochondria
Co-transporter proteins in plasma membrane
Steps for reabsorption in the PCT
- Na+ ions actively transported into blood capillaries reducing Na+ conc. in epithelial cells in PCT
- Na+ moves from PCT lumen to epithelial cells down conc. grad.
- Na+ cotransported with glucose/amino acids into epithelial cells.
- Reabsorbed molecules diffuse into blood capillaries.
How is water reabsorbed in the loop of Henle?
- Ascending limb is permeable to ions but impermeable to water.
- At the top of ascending limb, Na+ + Cl- is actively pumped into medulla lowering water potential
- Water moves out from descending limb (permeable to water, impermeable to ions) by osmosis
- As water moves out, filtrate becomes more concentrated
- Na+ / Cl- move out of nephron at ascending limb by facilitated diffusion
- Lowers water potential further causing water to move out of DCT and collecting duct by osmosis
- Water in medulla moves to capillary
Why do organisms in dry conditions have an extra long loop of henle?
More ions can be pumped into the medulla encouraging more water out of the nephron by osmosis
Describe role of hypothalamus
Changes in water potential of blood are detected by osmoreceptors here.
What happens if water potential of blood is too low?
Water leaves osmoreceptors by osmosis causing them to shrivel stimulating the hypothalamus to produce more ADH
Where is ADH produced and released?
produced by hypothalamus then moves to posterior pituitary gland where it is released into capillaries + blood
Describe mechanism when blood water potential drops
- Osmoreceptors detect low water potential
- Hypothalamus signals posterior pituitary gland to secrete ADH
- ADH increases DCT and collecting duct permeability (incorporates aquaporins into cell membranes)
- Water moved out of DCT/collecting duct by osmosis and reabsorbed into blood stream increasing water potential
- Smaller vol. of conc. urine produced.
What happens when ADH binds to complementary receptors on target cells of DCT/collecting duct?
- Activates adenyl cyclase to make cAMP
- Activates an enzyme which causes vesicles containing aquaporins to fuse with the membrane
Describe why urine can be used in diagnosis
Because substances removed from blood end up in urine, it can be used to test for drugs, diabetes, anabolic steroids and pregnancy
How do pregnancy tests work?
- Absorbent end of test submerged in urine
- Mobile monoclonal antibody with coloured dye attached bind to complementary HCG
- Second complementary antibody immobilised
- Third antibody complementary to constant region of first antibody (control strip)
What causes kidney failure?
Infection, high blood pressure, physical damage, genetic conditions
What happens when kidneys are infected/damaged?
- Tubules, podocytes, basement membranes, epithelial cells = damaged
- Large substances can filter out of blood
How is kidney failure diagnosed?
Glomerular filtration rate (GFR) = rate at which blood is filtered from BC
Low GFR = Kidney failure
What can kidney failure mean?
waste products build up, electrolyte/ion imbalance, accumulation of fluids, anaemia, mortality
Treatment for kidney failure
(Haemo)Dialysis
- Blood passed through partially permeable membrane surrounded by dialysis fluid
- Urea out of blood into fluid
- Glucose, salt and water move between blood and dialysis fluid to restore levels
