Renal 1 - Intro, diffusion, tonicity, fluid movement

Functions of kidney

1. Regulate blood volume/pressure

2. Regulate acid base balance

3. Excretion

4. Synthesis of glucose (gluconeogenesis)

5. Secretion of hormones

Kidney excretion function

- Excrete urea, uric acid, creatinine, bilirubin

- Remove foreign chemicals (drugs, food additives, pesticides)

Hormones secreted by the kidney

EPO, Renin, 1,25-dihydroxy vitamin D

Where is uric acid fro

Nitrogenous base breakdown

Where is urea from

Protein breakdown

What % of body weight is water

60%

What percent is extracellular fluid of total body weight

20%

Components of extracellular fluid

Plasma, interstitial fluid

When do fluid volume changes occur in the body

- Health disorders (dehydration, diarrhea)

How does fluid volume changes occur

Osmosis - rapid movement of water

How is plasma volume altered

- Intake of water in GIT (increase plasma)

- Loss through urine, expiration, sweat, skin evaporation

Body fluid components

intracellular and extracellular (plasma + interstitial)

Is sodium higher or lower in ECF than ICF

Higher (140 > 12 mM)

Is Potassium higher or lowe in ECF than ICF?

Low (5 < 150 mM)

Is chloride higher or lower in ECF than ICF

Higher (follows sodium) (100 >7)

Major solutes of ECF

Na+, Cl-, HCO3-

Major solutes of ICF

K+. Phosphate, Protein

Role of aquaporins

Channels allowing for water diffusion

Osmole

1 mole of dissolved particles

Osmolarity

Number of solutes per unit volume of solution measured in mol/L

What unit is water concentration measured in?

Osmolarity (mol/L)

Why is water measured in osmolarity

Water contains dissolved solutes - concertation of water depends on soluble substances in water

If a solution is low osmolarity, what is the water concentration

High concentration

If a solution is high osmolarity, what is the water concentration

Low concentration

Effect on water concentration if you add more solute

Decreased concentration (and vice versa)

Diffusion

Movement of molecules from one location to another as result of random thermal motion

Steps of diffusion

1. Higher concentration of molecules move toward lower concentration

2. Solute molecule evenly distribute

3. Diffusional equilibrium

Diffusional equlibrium

Concentration of solute in solvent is equal throughout volume

Diffusion of water through cell membrane (steps)

1. Water diffuses to side with higher osmolarity (lower water concentration), Solute moves to area with lower osmolarity

2. Diffusional equilibrium - movement of water and solute has equalized concentrations

Osmosis

Net diffusion of water across a selectively permeable membrane from a region of higher to lower water concentration

Osmotic pressure

Opposing pressure required to stop osmosis completely

Steps of osmosis

1. Partition between components is permeable to water only. Water moves from high to low concentration

2. Diffusional equilibrium occurs, equalizing solute concentration

How is tonicity determiend

Concentration of non-penetrating solutes of an extracellular solution relative to the intracellular environment of the cell

Effect of tonicity

Changes in cell volume

Three conditions of tonicity

Isotonic, hypertonic, hypotonic

Isotonic

Same osmolarity inside and outside of the cell

Hyper tonic

Higher osmolality outside the cell than inside the cell

Hypotonic

Lower osmolarity outside the cell than inside the cell

Normal osmolarity inside a cell

300 mOsm/L

Difference between isotonic and isosmotic

Isosmotic = solutes are penetrating membrane

Why is isotonic saline given to patients

Prevents RBC explosion or shrinking

Effect of hypotonic solution on RBC

Cell swells

Effect of isotonic solution on RBC

No change in cell volume

Effect of hypertonic solution on RBC

Cell shrinks

Systemic capillary permeability

Highly permeable to water and most plasma solutes (exchange between plasma and interstitial fluid)

Absorption

Movement of solute/water into the blood (plasma) from interstitial fluid

Filtration

Movement of solute/water out of the blood (plasma) into the interstitial fluid

Capillary hydrostatic pressure

Pressure exerted by fluid inside capillary walls (pushes fluid out of capillary into interstitial fluid)

Interstitial fluid hydrostatic pressure

Pressure exerted by IF onto capillary wall (exterior)

Osmotic force due to plasma concentration

Negatively charged plasma proteins cause water to move into capillary

Osmotic force due to interstitial fluid protein concentration

Some plasma proteins escape capillary and end up in IF - proteins pull water with them

Is filtration or absorption favored at arterial end of capillary

Filtration favored

Is filtration or absorption favored at venous end of capillary

Absorption favored

Change in starling forces across capillary

Capillary hydrostatic pressure decreases from arterial to venous end. Other pressures stays the same

Homeostasis

Total body balance of any substance

- Gain via ingestion/metabolism balanced with loss via excretion/metabolism

What do kidneys do with excess water

Excrete in urine

What do kidneys do if dehydrated

Keep water in plasma