L4 - Urinary Flashcards
1) How does water move across a semi-permeable membrane
2) What happens to cells in a hypotonic environment?
3) What happens to cells in a hypertonic environment?
4) Why must the osmolarity of the extracellular fluid (ECF) be carefully regulated?
1) Water moves passively from an area of low osmolarity (fewer solutes) to an area of high osmolarity (more solutes).
2) water moves into cells, causing them to swell
3) water moves out of cells, causing them to shrink.
4) to maintain an isotonic state, preventing cells from swelling or shrinking.
1) What is osmolarity?
2) Which ion accounts for 90% of extracellular fluid (ECF) osmolarity?
3) Why is urea considered an “ineffective osmole”?
4) How do you calculate plasma osmolarity?
1) concentration of osmotically active particles in a solution, determined by the total concentration of solutes that cannot cross cell membranes.
2) Sodium (Na⁺)
3) can easily cross cell membranes, so it does not contribute significantly to water movement between compartments.
Explanation for diagram:
IVF: Intravascular fluid (inside the blood vessels)
ISF: Interstitial fluid (the fluid between cells and outside the blood vessels)
ICF: Intracellular fluid (inside the cells)
Water moves freely across both capillary walls and cell membranes.
Urea can diffuse through both capillaries and cell membranes.
Glucose and sodium can cross capillary walls but need special transport mechanisms to enter cells.
Proteins remain inside the blood vessels and do not cross capillary walls.
1) How do the kidneys help control osmolarity?
2) Why is continuous water loss necessary
3) What happens when body does not have enough water to dilute soltutes?
4) What determines the total fluid volume in the body?
1) Regulate amount of solutes + water in ECF, indirectly affects ICF
2) Continuous water loss necessary to get rid of body waste via kidneys. Insensible losses (sweating, breathing) pushes body towards dehydration. Dehydration increases osmolarity of ECF
3) To maintain isotonicity (osmotic balance), body needs enough water to dilute solutes (primarily Na+) in ECF. If not enoigh water to dilite ECF, osmolarity increases, leading imbalance
4) Total fluid volyme of body determined by total amount solutes (mainly Na+) present in each compartment (ECF, ICF)
1) Which ion determines ECF volume?
2) Which ion determines ICF volume?
3) Which ion generates colloid osmotic pressure?
4) What pushes water out of capillaries?
5) What opposes hydrostatic pressure?
6) Why can’t Na⁺ diffuse through the plasma membrane?
Sodium (Na⁺): Determines ECF volume by pulling water into the ECF.
Potassium (K⁺): Pulls water into the cells (ICF).
Albumin: Remains in the intravascular compartment and helps retain water in the plasma through colloid osmotic pressure.
Hydrostatic pressure (P_H) pushes water out of capillaries, while osmotic pressure (π) pulls water back in.
6) requires transport mechanisms like the Na⁺/K⁺ pump to cross it.
1) How sensitive is the body to changes in ECF osmolarity?
2) What is the body’s response when the ECF becomes hypertonic?
3) What happens when the ECF becomes hypotonic?
1) body can detect changes in ECF osmolarity as small as ±1-2%.
2) Hypertonic = more solutes, less water. Body releases ADH to conserve water (reduce ueine output) + stimulate thirst, drink water
3) Body excretes excess water, produces dilute urine (DIURESIS)
1) What determines the amount of water reabsorbed in the kidneys from tubular fluid?
2) Which hormone increases permeability of collecting ducts to water?
3) What type of hormone is arginine vasopressin?
4) Where is ADH / arginine vasopressin released?
5) How does ADH work?
1) permeability of the epithelial cells lining the connecting tubule and collecting duct. Determines ow much water returned to body and excreted as urine
2) ARGININE VASOPRESSIN - ADH
3) Peptide
4) Posterior pituitary gland
5) Release controlled by osmoreceptors in hypothalamys, detect changes in blood osmolarity. Increases water permeabilityt of collecting ducts, more water reabsorption, less water loss in urine
1) How does vasopressin affect AQP2 channels in the kidneys?
2) What effect does vasopressin have on blood vessels?
3) How does vasopressin affect urea permeability in the kidneys?
4) How does vasopressin help regulate blood volume and blood pressure?
1) Stimulates insertion of AQP2 channels in principal cells in collecting duct. Increases permeability of tubules to water
2) vasoconstriction, which increases blood pressure.Important during dehydration or blood loss
3) increases urea permeability in the collecting duct, which aids in water reabsorption and maintaining osmotic balance.
4) By increasing water reabsorption, vasopressin helps to maintain proper blood volume and blood pressure.
1) Out of the 13 types of aquaporins, how many are expressed in the kidneys?
2) What is the location and function of aquaporin 1-4?
1) 7
How does AQP2 (Aquaporin-2) carry out its function?
What type of epithelium is present in collecting ducts?
How can water leave principal cells?
What happens when vasopressin is removed?
Why os the basolateral membrane always permeable to water?
- Apical mebrane of principal cells lining collecting duct impermeable to water
- Vasopressin reaches principal cells, AQP2 channels inserted into apical membranes of cuboidal epithelium in collecting duct
- Water enters cells via AQP2 channels, exits via AQP3, AQP4 channels.
- Vasopressin then removed, AQP2 channel retrieved via endocytosis
- Basolateral membrane alwats contains AQP3, 4, so always permeable to water
What is the mechanism for detection of plasma osmolarity?
Osmoreceptors in hypothalamus in supraoptic nuclei
detect increases in ECF osmolarity
Induce thirst
1) Why are OVLT and SON regions of hypothalamus important for detecting osmolarity changes?
2) How do osmoreceptors respond when plasma osmolarity increases by 1-2%?
1) Lack normal blood brain barrier
This allows direct exposure of neurones to blood plasma
Makes them sensitive to changes in osmolarity
2) smoreceptor cells shrink and fire action potentials, signaling the need to restore osmotic balance.
1) What triggers the activation of hypothalamic osmoreceptors?
1) Hypertonic plasma (high osmolarity) which also means low blood volume causes the hypothalamic osmoreceptors to shrink, triggering activation.
How does shrinkage lead to activation?
Shrinkage activates TRPV Cation channels, allowing +ve ions to flow into ECF
Influx of Na+ through TRPV channels causes depolarisation of osmoreceptor cells
Depolaristion generates APs, sent to posterior pituitary
Posterior pituitary releases preformed vasopressin into blood
Basopressin acts on kidneys to increase water reabsorption, helping to correct high plasma osmolarity
In addition, osmoreceptors stimulate thirst: behavioural response to drink water
1) Where is vasopressin synthesised?
2) How is transported after synthesised?
Synthesised within NEUROSECRETORY cells in SON, PVN
Transported down axons of neuroens to posterioor pituitary, where it is stored until relase
What receptor on principal cells does ADH act on to increase permeability of collecting duct?
- V2 Receptors on Prinicpal cells on basolateral membrane
- Stimulates signalling cascade, inducing aquaporins to be transported to apical luminal side ofo membrane via exocytosis.
1) How is dilute urine produced in the nephron?
2) Where does the active removal of solutes occur in the nephron?
3) Why is the thick ascending limb (TAL) referred to as the “diluting segment”?
1) active removal of solutes (via NaK2Cl co-transporters) from the tubular fluid in parts of the nephron that are impermeable to water
2) TAL of Loop of Henle (aka diluting segment)
3) impermeable to water, which leads to a dilution of the filtrate.
Diagram showing renal medulla and renal cortex. Know the positioning
Osmolarity of ISF in renal medulla increases progressively from outer renal medulla to inner renal medulla
UNDERSTANDING: As you move deeper into kidney, osmolarity increases significantly, due to koop of henle.
