9- osmoregulation and temperature regulation Flashcards
production of urea- in the liver
• Urea is synthesised in the liver from excess amino acids.
• It is a way for the body to dispose of nitrogen, a by-product of amino acid breakdown.
process of production of urea
- The amino acids are deaminated (the -NH2 group is removed).
- The amino group is converted to ammonia.
- Ammonia is highly toxic, so it combines with CO2 to form urea.
- Urea is less toxic. It is filtered out the body by the kidneys and excreted in urine.
ultrafiltration
Ultrafiltration is the process by which small molecules are filtered from the bloodstream.
glomerular structure
• Each nephron has a bowman’s capsule containing the glomerulus.
• The glomerulus is a knot of capillaries.
• Blood is supplied by arterioles branching from the renal artery.
glomerular filtration process
• Afferent arteriole is wider than efferent arteriole, creating hydrostatic pressure.
• The pressure forces small molecules out of the capillaries through 3 layers:
• Capillary endothelium with pores.
• Basement membrane acting as a filter.
• Bowman’s capsule epithelium with podocytes (projections with gaps).
• Large cells and proteins remain in the blood due to size exclusion.
composition of glomerular filtrate
• Includes amino acids, glucose, urea, and inorganic ions (Na+, K+, CI-).
• Does not include red and white blood cells, platelets, or large proteins.
selective reabsorption in the proximal convoluted tubules- adaptations
• Microvilli increase surface area for absorption.
• Co-transporter proteins allow selective reabsorption of solutes (i.e. glucose).
• Mitochondria provide ATP for active transport mechanisms.
selective reabsorption in the proximal convoluted tubules- process
• Glucose reabsorption via sodium-glucose co-transporters.
• Amino acids, vitamins, and ions are also actively and passively reabsorbed.
• Water potential gradient drives osmotic water movement into capillaries.
• Urea partially passively diffuses back into blood following its concentration gradient.
loop of Henle- descending limb
• Thin walls.
• Permeable to water.
• Penetrates deep into the medulla.
loop of Henle- ascending limb
• Thicker walls.
• Relatively impermeable to water.
• Returns to the cortex.
loop of Henle method for filtering some salt and water
• The descending limb allows water to exit, concentrating filtrate.
• The ascending limb actively transports Na+ and Cl- out.
• The high solute concentration created draws water from the descending limb.
• The filtrate is hypotonic by the time it exits the ascending limb.
loop of Henle- counter current multiplier
• The opposite flow of filtrate maximises NaCl concentration.
• The loop’s length allows even higher concentrations of NaCl to build up.
• This lowers the water potential and maximises water reabsorption.
release of ADH when blood water potential is low
- Receptor: Osmoreceptors in the hypothalamus.
- Coordinator: Hypothalamus.
- Effector: Posterior pituitary gland.
- Response: ADH, a peptide hormone, is released by the posterior pituitary gland.
effect of ADH
- ADH travels in the bloodstream to the collecting duct to increase its permeability.
- ADH binds to the receptor proteins in the cell membranes of collecting duct cells.
- Aquaporins are phosphorylated.
The phosphorylation of aquaporins allows for their incorporation into vesicles. - Vesicles move towards luminal membranes of collecting duct cells.
- Vesicles fuse with the luminal membranes.
- Water moves through the aquaporins and is reabsorbed.
kangaroo rats
• They live in a dry environment and thus need to conserve water.
• They excrete little water and produce highly concentrated urine.
kidney adaptations in kangaroo rats
• Their medulla tissues must have low water potential so more water is reabsorbed.
• Their medullas are thus relatively thick, and accommodate longer loops of Henle in order to establish a greater concentration gradient.
other adaptions in kangaroo rats
• No sweat glands.
• No evaporation of water from the tongue.
• Lives in burrows which provide shelter.
endotherm
Relies on heat energy released by internal metabolism for thermoregulation.
endotherm advantages
• Can survive in a wider range of temperatures.
• Can be more active at night and during winter - an advantage over predators and prey.
ectotherm
• Relies on external heat sources for thermoregulation.
• All animals except for mammals and birds.
ectotherm advantages
• Uses less energy.
• Requires less food.
ectotherm disadvantages
• At cooler points in the day, their reactions will be very slow and they move very slowly. They are thus more likely to be eaten.
temperature regulation
- Receptor: Thermoreceptors in hypothalamus.
- Coordinator: Hypothalamus.
skin capillaries response to high temps
vasodilation increases skin capillary diameter and blood flow
skin capillaries response to low temps
vasoconstriction decreases skin capillary diameter and blood flow. less heat is lost through radiation
sweat glands response to high temps
sweat glands secrete sweat to cool the body by evaporation
sweat glands response to low temps
less sweating as evaporation of sweat provides a cooling affect which is unwarranted
skeletal muscles response to low temps
muscle contracts and relax, releasing heat by friction and respiration
erector pili muscles in the skin response to high temps
skin hairs lie flat, air circulates, and heat leaves by radiation
erector pili muscles in the skin response to low temps
skin hairs are pulled upwards, air is trapped and acts as an insulator
