Lecture 2: Renal Physiology: Body Fluid Composition Flashcards
Kidney Lobe
Cortex: Glomerulus + Parts of Distal and Proximal Tubule
Medulla: Collecting ducts + Loops of Henle
Nephrons: lie from deep –> outer locations
- close to junction of medulla and cortex
Collecting Ducts fuse –> Large size for larger volume –> Renal Papillae
Medullary Rays: CD + Prox. + Distal Tubule Straight bundles. Centre of Lobule. In Cortex, going too and from Medulla.
Defined by Interlobar blood vessels. - Define but not continuous
What types of loves do cats and mice have?
Unilobar kidneys
Arterial Blood supply to the kidney
Renal artery –> Interlobar arteries –> Arcuate (Arching) artery –> Interlobular artery –> Afferent arterioles
Function of Arterial Outer Renal Corpuscles
Corpusles Located in cortex
1. Efferent arterioles –> forms Peritubular capillary bed
2. Venous return logically in reverse order: (Interlobular –> arcuate –> interlobar)
Overall: Renal a –> Interlobar a –> arcuate a –> interlobular a –> afferent a/g –> efferent v/g –> interlobular v –> arcuate v –> interlobar v –> Renal v
Function of Arterial Inner Renal Corpuscles
Corpuscles Located in Medulla
1. Arterial Vasa Recta:
a) Long and straight vessels
b) bundled with Collecting duct + Loop of Henle
c) Branches to capillary bed around loops
3. Venous return occurs via the Vasa Recta (also bundled)
Overall: Renal a –> afferent a/g –> arterial vasa recta –>efferent v –> acruate v –> venous vasa recta –> Renal v
Function of Arterial Peritubular capillaries
Wrap around proximal tubules
- Reabsorb the nutrients which kidney’s filter
- Later returning to venous capillary bed
Location of nephron to outer/inner renal corpuscles
Nephron sits within the Outer corpuscles Peritubular capillaries and within the Inner corpuscles Vasa Recta
- Allows countercurrent relationship of tubules (creating urine) and capillaries/vasa recta (creating blood supply)
What is the reasoning behind the Looping of the Vascular Vasa Recta and the Urinary Loop of Henle?
Looping preserves the medullary salt gradient
Allows:
1. Preservation of salt levels in the urine –> Able to concentrate urine when leaving the medulla
2. Medullary salt gradient –> Water extraction from nephron and reabsorption into vascular vasa recta –> preserves salt deposited in the medulla
Overall Flow of Outer Renal Corpuscle Arterial system
Renal a –> Interlobar a –> arcuate a –> interlobular a –> afferent a/g –> efferent v/g –> interlobular v –> arcuate v –> interlobar v –> Renal v
Overall Flow of Inner Renal Corpuscle Arterial system
Renal a –> afferent a/g –> arterial vasa recta –>efferent v –> arcuate v –> venous vasa recta –> Renal v
Cellular components of the Ureter and Bladder
- Mucous membrane: a) lubrication b) protection for acidic urine + pathogens
- Transitional epithelium: (when folded permits expansion and contraction)
- Sub-epithelial CT/ Elastic Lamina Propria: allows epithelium to open and close again
- Smooth muscle layers: ILOC 2x layers allowing for peristatic contraction
- Outer Adventitia: a) elastic b) harbours blood supply (vasovasorum)
Smooth muscle components of the Ureter and Bladder
2x layers: ILOC
Inner Longitudinal + Outer Circular
= Allows for peristaltic contraction and hence movement of fluid
Bladder Epithelium
Bladder is a continuation of the ureter but on a larger scale
Relaxed Bladder epithelium: Folded back on itself
Contracted Bladder epithelium: Single layer
Urethral Epithelium
Urethra’s epithelium will change according to how close it is to the external environment/outside of the body –> becomes increasingly protective
- Initial Transitional epithelial lining –>
- Stratified Columnar –>
- Stratified Squamous
Fat cells and Water
Fat cells dont pack that much water
Reason for proportional quantities of body water: Larger quantity of fat cells (females and elderly) = Small amount of body water (50%)
Variation in Levels of Human Body Water and reasoning
Average Human: 50-70% water - Babies: 70% - Males: 60% (42L) - Elderly and Females: 50% (30L) Reason for proportional quantities of body water: Quantity of fat cells --> Fat cells dont pack that much water --> therefore larger quantity of fat cells (females and elderly) = Small amount of body water (50%)
Where is water located in the body?
- Inside cells/ Intracellular fluid/ ICF (28L)
2. Outside cells/ Extracellular fluid/ ECF (14L) –> (80% Interstitial fluid 11L + 20% Plasma 3L)
How does the water move between compartments?
All the membranes in the body are permeable to water
- with exception of Kidneys, Ureters and Bladder –> due to tight membranes/ inbuilt mechanisms
Water moves for a high to low concentration of Osmotically active molecules
Directionality of water movement
Water moves from a high to low concentration of osmotically active molecules
Osmolality
Number of osmotically active particles per UNIT WEIGHT of SOLVENT
mOsmol/kg of solvent (e.g. water)
e.g. 13 solute particles + 1 kg water
= Osmotic pressure exerted by a solution across a membrane
Osmolarity
Number of osmotically active particles per LITRE of TOTAL SOLUTION
e.g. 13 solute particles + (1 kg water - 13 solut particles = to make combined 1 L of total solution)
mOsmol/L
Comparison b/w osmolality and osmolarity
Molal solution is Approximately equal to a Molar solution
Although osmolality and osmolarity differ,
Osmolality: expression of osmotic activity per weight (kg)
Osmolarity: expression of osmotic activity per L of total solution
for clinical purposes they are similar
Osmolality has now largely replaced Osmolarity
Tonicity
Osmotic pressure a solute exerts across a cell membrane DUE TO BEING IMPERMEABLE–> creates water movement
- created by NON-osmotically active compounds
- Property of Solution in reference to a particular membrane
- Tonicity is NON-readily measurable mmHg (unlike osmolality)
Why is tonicity important
- Cell membrane is a permeable membrane
- Bodies are full of salt and water
- Bodes are full of impermeable molecules –> exert pressure (as part of the solute) on cell membranes –> creates water movement
Plasma Membranes and Tonicity
Plasma membranes: SEMIpermeable –> Permeable to water but NOT permeable to charged molecules
Cells are full of proteins which are osmotically active but impermeable to the membrane (e.g. proteins) –> compensate by exerting pressure on membrane –> creates water movement towards the charged protein molecules
3x solution tonicity types
- Hypotonic: make cells swell (water moves in as higher concentration inside cell)
- Isotonic: cell stay the same size (water movement in and out of the cell at the same rate)
- Hypertonic: make cells shrink (water moves out of cell as lower concentration inside cell)
Gibbs-Donnan Equilibrium
Charged particles separated by a semi-permeable membrane can fail to distribute evenly across the membrane due to the presence of a non-diffusible ion
Gibbs-Donnan Equilibrium in motion
- Negative ions want to move down their concentration gradient
- Positive ions want to follow negative ions (to balance charge) –> so remains electrogenic
- -> now have lots of osmotically active particles on one side - Negative protein is drawing in molecules –> but these ions want to go back again due to THEIR OWN CONCENTRATION gradients –> -ve Charged protein molecules are still unable to cross membrane
Gradients involved in the Gibbs-Donnan Equation
- Competing electrical and concentration gradients –> At Equilibrium –> Side with proteins is More negatively charged –> creates voltage gradient
- More osmotically active particles are on the protein side (greater osmolality) –> water flow to the protein side (oncotic pressure)
- Cells need to balance osmotic pressures across their membranes otherwise they’ll burst –> Solution: Pump osmotically active ions (Na+) out using the Na+/K+ ATPase transporter
- Creates 2x Opposing Donn and Gibb equilibriums, BOTh of which H2O is a part of (High Na vs High K& High Protein) –> Balanced water movement equal across membranes
- Intracellular movement slows and ECF becomes isotonic –> ICF and ECF compartments have identical osmolality (300mOsmol/kg), regardless of having different compositions
Osmolarity b/w bodily compartments
Despite differences in composition, the ICF and ECF compartments have identical osmolality (300mOsmol/kg)
Inside cell: lots of K and charged protein
Outside cell: lots of Na
- All due to Na/K ATPase
Note: plasma is similar to interstitium, except greater amount of protein (albumin/immune complexes) being pushed around
Hypotonic ECF osmolality
Decreased Na concentration outside of cells –> Relatively greater Na concentration of osmotically active particles inside of cells –> Water moves via osmosis into cell –> cells swell –> try to return to equilibrium –> (If swell excessively –> burst –> Death)
Note: swollen brain = painful
Remove water from ECF to dilute
e.g. Excessive water consumption –> body needs to remove the H2O in order to concentrate the NA –> maintains isotonic environment
What are concentration gradients referring to?
Relatively greater number of osmotically active particles
Water movement occurs to try and reach equilibrium again/ isotonic environment
Hypertonic ECF osmolality
Increased Na concentration outside of cells –> Relatively smaller Na concentration of osmotically active particles inside of cells –> Water moves via osmosis out of cell into ECF –> cells shrink –> try to return to equilibrium –> (If shrink excessively –> Death)
Note: shrunk brain = painful
Add water to ECF to dilute
Control of ECF Osmolality
ECF osmolality control is critical for cell survival --> tightly controlled --> varies 1-2% ECF osmolality (salt concentration) is largely regulated by altering water levels --> more rapid response to water levels > salt levels
How is the Tight control of ECF osmolality regulated?
Altering water levels
- -> as ECF volumes (H2O content) is primarily dependant on the amount of Na –> as Na is the most osmotically active solute in the ECF
- -> results in ECF volume levels being less tightly controlled (more dynamic range of 15% regulation)
Maintenance of compartment sizes
- Kidney: major regulator of water and salt homeostasis (i.e. ECF osmolality and volume)
- Starling Forces:
- change in plasma protein levels –> change in oncotic pressure – change in starling forces
Oedema
Causes: Inflammation, Obstruction (lymphatic or venous), sodium retention, Low serum albumin
–> Changes in charged/osmotically active plasma protein levels –> change in starling forces in plasma –> fluid movement into the interstitial space –> Abnormal expansion of the interstitial fluid compartment
Can be localised or general
Balance b/w daily intake and output for an adult at room temperature
What goes in (salt and water) = Has to come out Water intake: Total: 2.5L 1. Drinking 1.2L 2. In Food 1L 3. Metabolism 300mL Water Out-take: Total 2.5 L 1. Insensible 700mL 2. Sweat 100mL 3. Faeces 200mL 4. URINE 1.5L = MAJORITY URINE AND SALT OUTPUT of the body
Role of urine
Urine = largest components of the balanced 2.5L daily water outake = 1.5L = as urine contains the majority of urine and salt output of the body
Urine ouput and urine Osmolality VARIES –> in order to balance water and salt levels
–> allows water intake to be completely balanced by water output
Note: if water intake isnt balanced by water output –> expansion –> change in osmolality outside of 1-2% tightly regulated range –> need dialysis
