Osmoregulation Flashcards
Homeostasis
Maintenance of the internal environment of the body at a stable/ constant level despite external changes
Importance of homeostasis
Optimal conditions for reactants and products in metabolic reactions and protects cells from changes in environment
Negative Feedback
- Movement of condition away from the normal leads to a set of processes/ response to make it normal again
Stimulus -> Receptor -> Co-ordinator/ control centre -> Effector (muscle/ gland) -> response
- Glucose: high = insulin secreted which converts it to glycogen snd low = glucagon secreted and converts glycogen to glucose
Positive feedback
Movement of condition away from the normal causes further movement away from the normal
Oxytocin stimulates uterus contraction during birth
Platelets when they form blood clots
Hormones
- Molecules secreted by endocrine gland directly into the bloodstream and travel to the target organ
- Target cells have receptors in cell membrane complementary to hormone molecules so only respond to them
Types of gland
- Endocrine: ductless gland that secretes hormones directly into the blood
- Exocrine: secretes substances into ducts lined by epithelial cells
Less water intake
- Low water potential/ levels of blood detected by osmoreceptors in hypothalamus
- More ADH (antidiuretic hormone) secreted by the posterior pituitary gland into the blood
- ADH travels to the CD and DCT
- Increases permeability of DCT and CD walls to WATER (inserts more aquaporins)
- More water absorbed by osmosis as walls become more permeable
- Into tissue fluid because medulla has a low w.p and high salt conc
- Preserves water and low volumes of concentrated urine
- Removed by capillaries/ vasa recta
After drinking water
- Water absorbed into blood and w.p rises
- Osmoreceptors in hypothalamus detect it
- Posterior pituitary gland secretes less ADH
- DCT/ CD walls less permeable to water
- Less water absorbed and large volumes of dilute urine produced
What can stimulate ADH?
- Low blood pressure and volume
- Severe diarrhoea
- Vomiting
- Blood loss
Thirst cause
- Upto certain point, ADH can achieve sufficient water reabsorption
- After this point, water needs to be taken in by drinking to avoid dehydration
Length of Loop of Henle
- Dry habitat = longer loop so more time to reabsorb water in descending limb and pump ions (lower w.p in medulla to conserve more water)
- Higher conc of ions in medulla so lower water potential
- Conserves water: small volumes of conc urine - Short length in fresh water animals as water readily available so low w.p not needed
Cortical nephron
- Glomerulus in cortex
- Short loop penetrates medulla
- Humans (most), beavers and muskrats
- More water availability and low risk of dehydration
- Dilute urine
Juxtamedullary nephron
- Bowman’s capsule closer to cortex boundary
- Long loop penetrates deep into medulla
- Dry habitat animals have high proportion
- Low water potential generated in medulla
- Conc urine and water preserved
Aquaporins
- ADH binds to complementary receptors on the basal membrane of DCT and CD wall cells
- Signals secondary messengers to travel through cytoplasm
- Causes vesicles containing aquaporins to move towards apical membrane
- Vesicle fuses with apical memb and aquaporins embedded
- Water moves through aquaporins by osmosis and then through basal aquaporins into medulla and blood (maintains gradient)
[Urea] filtrate vs urine
- Water (osmosis) and Na+ ions reabsorbed from filtrate in PCT
- Urea not reabsorbed
- Active transport of Na+ ions in ascending limb and water reabsorbed in descending limb (permeable)
- Lowers w.p of medulla and water reabsorbed in CD
- [Urea] increases
