21-24 Flashcards
What does extracellular fluid composition show about historical settings?
that it was probably similar in composition
- so mainly a solution of sodium salts
- mainly NaCl
What is osmosis?
The tendency of a solvent to pass through a selectively permeable membrane from a dilute to a more concentrated solution
What is osmotic pressure (π)?
The pressure that has to be applied to a concentrated solution in order to stop solvent moving into is from a more dilute solution across a selectively permeable membrane
- colligative property
GRAPH
π = ρ x h x g
ρ=fluid density
What is water potential?
Suction needed to prevent movement of water into concentrated solution
= -π
What is an osmole?
1 mole of osmotically active particles
What is isomostic?
solutions with the same osmotic pressure
Hyperosmotic
if has higher osmotic pressure than the other
Hyposmotic
lower osmotic pressure compared to the other
What is an ineffective osmole?
When a solute cannot exert an effective osmotic pressure as it can move across the membrane
What is an effective osmole?
A solute that cannot pass through the membrane and so can exert an effective osmotic pressure
What is the tonicity of a solution?
The effect of a solution on the volume of a cell
- related to osmolality but depends on whether effective of ineffective osmoles are involved
What does isotonic mean?
Solution does not change volume of cell
Hypertonic?
Causes cell to shrink
Hypotonic?
Causes cell to swell
What is colloid osmotic pressure?
= oncotic pressure
The osmotic pressure exerted by colloidal molecules such as proteins
- one of starlings forces determining fluid movement in capillaries
What is the principle of balance?
The maintenance of homeostasis
- as substances added must equal rate at which they are removed
What are obligatory and regulated exchanges?
Obligatory = unregulated
- like tears, sweating, breathing, faeces
Regulated = urine
What are osmoregulatory organs?
Formed by ransport epithelia found in gills, skin, kidneys or gut
- functionally polarised so the two exposed surfaces have different roles
- OUTSIDE = luminal (apical)
- INSIDE = Adluminal (Basolateral)
Osmoregulatory organs in mammals.
Marine mammals survive on metabolic water alone
- KIDNEYYYY
Osmoregulation in a typical mammal
GRAPH
-
Osmoregulation in a desert mammal
PICTURE
The urinary system
PICTURE
Gross structure of the kidney
FIgure 5 pg 5
The renal tubule diagram
DIAGRAM
- Nephron (includes Bowman’s capsule)
- Collecting duct system
- Each human has roughly 1 million nephrons
- Proximal tubule = often convoluted and straight parts together
What are the two types of nephron?
Cortical = renal corpuscles in cortex Juxtamedullary = also in cortex but close to junction with the medulla
What does the inner medulla contain?
Thin limbs of juxtamedullary nephrons
large collecting ducts
What does the outer medulla contain?
upper portions of the loops of Henle of juxtamedullary nephrons
- including all the thick ascending limbs
all of the loops of the cortical nephrons
What happens in outer stripe of outer medulla?
Where proximal straight tubules of the juxtamedullary nephrons penetrate the medulla
What are the medullary rays?
Finger-like extensions of medulla up into cortex
- contain cortical parts of collecting ducts, some straight proximal tubules of cortical nephons
- some thick ascending limb of cortical nephron loop of henle
Diagram of cortical and juxtamedullary nephrons
DIAGRAM
Renal blood supply
25% cardiac output reaches kidneys in renal arteries
What is the order of blood vessels the blood goes through the kidney in?
- Renal Artery
- Interlobar Arteries
- Arcuate Arteries
- Cortical radial arteries
- Afferent arterioles
- Glomerular capillaries
- 20% plasma out - Efferent arterioles
- Peritubular capillaries
- CORTICAL = cortical capillaries
- JUXTAMEDULLARY = capillaries in medulla - Juxtamedullary form vascular bundle and then some vasa recta
- Cortical radial veins
- Arcuate veins
- Interlobar veins
- Renal Veins
Distribution of renal blood flow.
- 90% though what
- 9%
- 1%
90% = cortical peritubular capillary network
9% = Vascular bundles of outer medulla
1% = Vasa recta
Graph showing the NaCl and urea concentration in the kidney?
Graph
How do cells in the medulla cope with large changes in osmotic pressure?
Match solute content to surroundings - produce compatible solutes such as sorbitol and betaine
- dont disturb the hydration shell of proteins
How does the vasa recta allow solute and water absorbed into the medulla to be removed?
- doesnt destroy the osmotic gradient created by the loop of Henle
- GRAPH
- As blood flows down into medullary interstitial fluid with higher osmotic pressure
- Water out and solute in
- Blood flows up and water in and solute out
- maintains medullary gradient
Structure of ADH
diagram
- cyclic nonapeptide
- Mr 1084
- Half-life = 6-10 min
On what does ADH act?
Regulates permeability of the collecting duct
- also increases the urea permeability of the inner medullary collecting duct
- V2 receptors are osmoregulatory = high affinity
- V1 are vasoconstrictor = low affinity
- Principal cells of collecting ducts
Regulation of ADH release
GRAPH
Neurosecretion of ADH
- synthesised in magnocellular neurones
- Cell bodies in hypothalamus
- Endings in posterior pituitary gland
- Calcium dependent exocytosis
How does ADH work on principal cells in collecting ducts?
V2 receptors on basolateral membranes
- G protein coupled receptors
- Adenylyl cyclase activated
- cAMP activates PKA
- Phosphorylates AQP2 on serine residue 256
- Vesicle with AQP2 into luminal membrane
- Increase water permeability
GRAPH
How does ADH increases urea permeability?
Inner medullary collecting duct by stimulating the phosphorylation and so activate urea transporters
- In luminal membrane
- UT-A1 is main transporter
What are the main solutes in urine?
- Urea
- (SO4)2-
- (HPO4)2-
need to produce 0.5 L per day in humans
Why cant humans drink seawater
1000mOsm is seawater (L)
- urea mean 600mOsm can be removed per L
- so need 1.67L urine to remove 1L urine and so become dehydrated
Are marine invertebrates and ascidians isosmotic with sea water?
yes
- hagfish rare example of isosmotic vertebrate
How do marine elasmobranchs osmoregulate?
- isosmotic with seawater
- lower conc of salts - make up with Urea and TMAO (urea is an effective osmole and TMAO opposes urea denaturation of proteins)
- NaCl across gills and in with food
- Rectal gland secretes NaCl
- Urine isosmotic with seawater
What is the structure of elasmobranch rectal gland
- diagram of cell
many blind-ended tubules which empty into intestine near rectum
- salt-secreting cells secrete fluid into tubular lumen which is isosmotic with ECF but higher [NaCl] than seawater
DIAGRAM OF HOW
How do marine teleost fish osmoregulate?
hyposmotic to seawater
- water loss across gills replaced by ingested seawater
DIAGRAM
Marine reptiles and marine birds?
DIAGRAM
hyposmotic to seawater
- nasal salt glands or turtles secrete into ducts by eyes
Glomerular filtration
About 20% of plasma filtered into Bowman’s capsule
Tubular reabsorption
Most filtered material reabsorbed
- 2 thirds in proximal tubule
- rest in later segments
Tubular secretion?
Some substances secrete into tubule and so are drawn out of the capillaries due to diffusion gradient
Urinary excretion
Fluid leaving the collecting ducts carrying anything not reabsorbed
into ureters and then bladder before excreted
What is ultrafiltration
Bulk flow of water and substances in solution across a filter
- Molecular weights >70,000Da not filtered
- <7000Da freely filtered
PROCESS = SIEVING
GRAPH OF RENAL CORPUSCLE
What are the 3 sections of the filtration barrier?
- Fenestrations in capillary endothelium
- Basement membrane
- Filtration slits between interdigitating processes of podocytes
GRAPH
What are the factors that affect filtration of a solute?
- Size
- Charge
- All three components are negatively charged
- neg macromolecules filtered less - good for proteins which are predominantly negative in physiological pH (so even small proteins low filterability)
GRAPH TO ILLUSTRATE
Filtration pressures
Starling forces
- sum of hydrostatic and colloid osmotic pressures across endothelium
Pc = Hydrostatic pressure in capillary Pb = Hydrostatic pressure in Bowman’s capsule
πc = Colloid osmotic in capillary πb = Colloid in Bowman’s capsule
NET PRESSURE = (Pc-Pb) - (πc - πb)
(do for both afferent and efferent and the difference is pressure)
Glomerular filtration rate
GFR depends on net filtration pressure
Kf = filtration coefficient = hydraulic permeability x surface area
GFR = Kf[(Net filtration pressure)]
How do marine mammals osmoregulate
Body fluids hyposmotic to the environment
- entirely metabolic water
- dont drink seawater
- kidney concentrates urine
- urine very hyperosmotic to blood
- much like desert rats
How do freshwater teleosts osmoregulate?
Hyperosmotic to environment
- gain water across gills so dont drink water
- lose salts across gills
- so actively absorbs salts across gills
- kidney reabsorbs salt - very dilute urine
Na+ absorption by a pavement cells in freshwater teleost fish
DIAGRAM
How do migratory fish such as salmon more from seawater to freshwater
leads to down-regulation of the H+-ATPase in pavement cells
- increase in number and secretory activity of chloride cells
How do amphibians osmoregulate?
Body fluids hyperosmotic to environment
- lose salts across skin
- gain water across skin
- skin actively absorb salts
URINE = very hyposmotic to blood
- skin and kidney are osmoregulators
How do terrestrial animals osmoregulate?
Suffer water loss
- must be compensated
- only mammals and birds have kidneys that allow more concentrated (hyperosmotic) urine to blood
Invertebrate osmoregulation
metabolic water and some from water
- some can extract water from air
- water loss limited by wax layer
- initial urine highly concentrated in hind gut
Haemolymph is not significantly pressurised, urine formation is not possible by filtration
- instead by secretion in malpighian tubules
How do insects produce urine?
Urine by secretion in malpighian tubules
- lie in haemocoel
- flows into hindgut
- water reabsorption and ionic modification occur in the rectum
DIAGRAM
Excretion of nitrogenous waste
amino acid catabolism yields toxic nitrogenous waste
- must be removed
- needs water
- method removed reflects water balance of organism
NH4+ most toxic
NH3 by diffusion sufficient water available = ammonotelic - 500ml
Urea = ureotelic animals - 50ml
Uric acid = uricotelic - 1ml - low solubility in water so as white precipitate
What happens in the proximal convoluted tubule?
- 65% NaCl reabsorbed
- 65% of water
- This is isosmotic fluid reabsorption (so the tubular fluid remains isosmotic with plasma along tubule)
Loop of Henle
- Overview
- 10% filtered water
- 25% NaCl absorbed
- Fluid leaving is hyposmotic to plasma
- Uncoupling of NaCl and water reabsorption
- excess solute reabsorbed raises osmotic pressure of medullary interstitial fluid
- allows for regulated reabsorption of water from collecting ducts in area
- counter-current multiplication
- thick ascending limb = actively reabsorb Na+ (Cl- follows)
- raises osmotic pressure so water leaves thin ascending limb by osmosis - Increases the concentration of solute in tubular fluid left behind
- When reaches the thick ascending limb, solute gradient between tubule lumen and interstitium reduced - more NaCl can be actively reabsorbed
- More water leaves the thin ascending limbs and so more concentrated fluid enters the thick ascending limb
What happens in the DCT?
The distal convoluted tubule
- and connecting duct
- more NaCl reabsorbed in these segments but little water
- Na+ reabsorption regulated by hormone aldosterone
What happens in the CCD
Cortical collecting duct
- water permeability regulated by ADH
- fluid entering the CCD is hyposmotic to plasma
- when ADH levels = high - water reabsorbed due to higher osmotic pressure of the cortical peritubular
- this is always isosmotic with the plasma
- so tubule fluid becomes isosmotic
- some NaCl absorbed in CCD
- causes further isosmotic fluid reabsorption when permeability to water is high
WHEN CONCENTRATING
- ccs returns tubular fluid to being isosmotic with plasma before concentrating in the medullary collecting duct
What happens in medullary collecting duct
- ADH high - duct water permeable
- water out by osmosis due to high osmotic pressure of medullary interstitial fluid
- urine hyperosmotic to the plasma
- when ADH low - medullary collecting duct reduce permeability
- so hyposmotic to plasma
Water handling by the kidney
DIAGRAM
Isosmotic reabsorption in proximal convoluted tubule
Fig 15 a-c
NaCl and water reabsorption in thick ascending limb
- actively reabsorbs NaCl
- impermeable to water
- so doesnt follow making is hyposmotic
- Na+ actively pumped across basolateral membrane and enters across the luminal membrane via NKCC2 transported
- K+ and Cl- across BM via symporter
- some K+ re-enters lumen by K+ channel - positive transepithelial potential
- so Na+ reabsorption paracellularly by tight junctions
DIAGRAM
The thin limbs of the loop of henle - absorption
DIAGRAM
- only a difference of 200mOsm
Thin descending limb
- does not reabsorb solute
- permeable to water
- fluid down it
- water out as medullary interstitial fluid solute conc increases created by thick ascending limb
- fluid then through apex of loop
Thin ascending limb
- does not actively reabsorb solute
- permeable to NaCl
- relatively impermeable to water
- urea - more water out
