Lecture 2: Renal Physiology: Body Fluid Composition

Question 1

Kidney Lobe

Answer 1

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

Question 2

What types of loves do cats and mice have?

Answer 2

Unilobar kidneys

Question 3

Arterial Blood supply to the kidney

Answer 3

Renal artery –> Interlobar arteries –> Arcuate (Arching) artery –> Interlobular artery –> Afferent arterioles

Question 4

Function of Arterial Outer Renal Corpuscles

Answer 4

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

Question 5

Function of Arterial Inner Renal Corpuscles

Answer 5

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

Question 6

Function of Arterial Peritubular capillaries

Answer 6

Wrap around proximal tubules

• Reabsorb the nutrients which kidney’s filter
• Later returning to venous capillary bed

Question 7

Location of nephron to outer/inner renal corpuscles

Answer 7

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)

Question 8

What is the reasoning behind the Looping of the Vascular Vasa Recta and the Urinary Loop of Henle?

Answer 8

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

Question 9

Overall Flow of Outer Renal Corpuscle Arterial system

Answer 9

Renal a –> Interlobar a –> arcuate a –> interlobular a –> afferent a/g –> efferent v/g –> interlobular v –> arcuate v –> interlobar v –> Renal v

Question 10

Overall Flow of Inner Renal Corpuscle Arterial system

Answer 10

Renal a –> afferent a/g –> arterial vasa recta –>efferent v –> arcuate v –> venous vasa recta –> Renal v

Question 11

Cellular components of the Ureter and Bladder

Answer 11

1. Mucous membrane: a) lubrication b) protection for acidic urine + pathogens
2. Transitional epithelium: (when folded permits expansion and contraction)
3. Sub-epithelial CT/ Elastic Lamina Propria: allows epithelium to open and close again
4. Smooth muscle layers: ILOC 2x layers allowing for peristatic contraction
5. Outer Adventitia: a) elastic b) harbours blood supply (vasovasorum)

Question 12

Smooth muscle components of the Ureter and Bladder

Answer 12

2x layers: ILOC
Inner Longitudinal + Outer Circular
= Allows for peristaltic contraction and hence movement of fluid

Question 13

Bladder Epithelium

Answer 13

Bladder is a continuation of the ureter but on a larger scale
Relaxed Bladder epithelium: Folded back on itself
Contracted Bladder epithelium: Single layer

Question 14

Urethral Epithelium

Answer 14

Urethra’s epithelium will change according to how close it is to the external environment/outside of the body –> becomes increasingly protective

1. Initial Transitional epithelial lining –>
2. Stratified Columnar –>
3. Stratified Squamous

Question 15

Fat cells and Water

Answer 15

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%)

Question 16

Variation in Levels of Human Body Water and reasoning

Answer 16

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%)

Question 17

Where is water located in the body?

Answer 17

1. Inside cells/ Intracellular fluid/ ICF (28L)

2. Outside cells/ Extracellular fluid/ ECF (14L) –> (80% Interstitial fluid 11L + 20% Plasma 3L)

Question 18

How does the water move between compartments?

Answer 18

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

Question 19

Directionality of water movement

Answer 19

Water moves from a high to low concentration of osmotically active molecules

Question 20

Osmolality

Answer 20

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

Question 21

Osmolarity

Answer 21

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

Question 22

Comparison b/w osmolality and osmolarity

Answer 22

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

Question 23

Tonicity

Answer 23

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)

Question 24

Why is tonicity important

Answer 24

1. Cell membrane is a permeable membrane
2. Bodies are full of salt and water
3. Bodes are full of impermeable molecules –> exert pressure (as part of the solute) on cell membranes –> creates water movement

Question 25

Plasma Membranes and Tonicity

Answer 25

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

Question 26

3x solution tonicity types

Answer 26

1. Hypotonic: make cells swell (water moves in as higher concentration inside cell) 2. Isotonic: cell stay the same size (water movement in and out of the cell at the same rate) 3. Hypertonic: make cells shrink (water moves out of cell as lower concentration inside cell)

Question 27

Gibbs-Donnan Equilibrium

Answer 27

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

Question 28

Gibbs-Donnan Equilibrium in motion

Answer 28

1. Negative ions want to move down their concentration gradient 2. Positive ions want to follow negative ions (to balance charge) --> so remains electrogenic - -> now have lots of osmotically active particles on one side 3. 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

Question 29

Gradients involved in the Gibbs-Donnan Equation

Answer 29

1. Competing electrical and concentration gradients --> At Equilibrium --> Side with proteins is More negatively charged --> creates voltage gradient 2. More osmotically active particles are on the protein side (greater osmolality) --> water flow to the protein side (oncotic pressure) 3. 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 4. 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 5. Intracellular movement slows and ECF becomes isotonic --> ICF and ECF compartments have identical osmolality (300mOsmol/kg), regardless of having different compositions

Question 30

Osmolarity b/w bodily compartments

Answer 30

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

Question 31

Hypotonic ECF osmolality

Answer 31

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

Question 32

What are concentration gradients referring to?

Answer 32

Relatively greater number of osmotically active particles | Water movement occurs to try and reach equilibrium again/ isotonic environment

Question 33

Hypertonic ECF osmolality

Answer 33

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

Question 34

Control of ECF Osmolality

Answer 34

``` 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 ```

Question 35

How is the Tight control of ECF osmolality regulated?

Answer 35

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)

Question 36

Maintenance of compartment sizes

Answer 36

1. Kidney: major regulator of water and salt homeostasis (i.e. ECF osmolality and volume) 2. Starling Forces: - change in plasma protein levels --> change in oncotic pressure -- change in starling forces

Question 37

Oedema

Answer 37

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

Question 38

Balance b/w daily intake and output for an adult at room temperature

Answer 38

``` 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 ```

Question 39

Role of urine

Answer 39

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