composition of body fluid

volume of body fluid

osmolality controlled in order to: maintain cell volume, carry on normal cardiovascular function.

 Done by regulating excretion of water and NaCl

Inorganic Ions: Na, K, Cl, HCO3, H, Ca, P

Organic Ions: citrate, succinate excretion must match intake

Metabolic wastes (Amino acids to Urea (50% of nitrogen products), Nucleic acid to uric acid, Phosphocreatine to creatine, Metabolites to hormones, hemoglobin end products) 

  Foreign substances: - chemicals in food - drugs - insecticides and herbicides

Elimination rate matches production

proteolytic enzyme

activates renin-angiotensin-aldosterone system

 regulates blood pressure with Na-K balance 

stimulates RBC production by bone marrow, indirectly controlling O2 carrying capacity of blood

Anemia can be caused by dietary insufficiency of Fe or erythropoeitin problem

accumulation of nitrogenous wastes in blood

can result in uremia (diarrhea, vomiting, arrhythmia) leads to convulsion, coma, and death

The amount of a substance dissolved in a solution relative to its molecular weight

 mmol/L = mM used for uncharged solutes

For charged solutes such as NaCl which dissociates in solution refers to interaction between cations and anions

Molarity multiplied by valence mEq or ions/L

Passage of water from a region of high water concentration to low water concentration through a semi-permeable membrane

 Osmotic pressure difference is driving force for movement of water across cell membranes

Experiment: - high concentration of particles in chamber A - low concentration of particles in chamber B - H2O moves into A by osmotic pressure - At equilibrium, hydrostatic pressure (pressure of water volume in chamber) stops movement of water from B to A and is equal and will be opposite the osmotic pressure exerted by solute particles in chamber A

osmotic pressure =  = nCRT

n = number of dissociable particles per molecule

C = total solute concentration (mol/L)

R = gas constant

T = temp (degrees Kelvin)

Number of dissociable particles per L of solvent

Esxpressed as milliosmoles/L

(mOsm/L)

Number of solute particles per Kg solvent

not temperature dependent (based on mass rather than volume)

Expressed as Osm/kg H2O but

mOsm/kgH2O in physiology

Solutions effect on the volume of a cell

Hypotonic solution: causes cell to swell

Hypertonic: solution causes cell to shrink (crenate)

factors that affect tonicity:

permeability, osmolality

Not permiable to cell membrane. Exerts an osmotic pressure equal and opposite to the osmotic pressure generated by the contents of Rbc

Ex. Glucose

permeates cell membrane cannot exert osmotic pressure to balance that generated by solutes of ICF

ex. Urea

 = a(nCRT)

a= reflection/osmotic coefficient  (ability to cross a cell membrane)

 a = 0 solute freely crosses, no osmotic pressure exerted

a = 1 solute cannot cross cell membrane

Weight of volume of solution divided by the weight of equal volume distilled H2O

specific gravity of human plasma: 1.008-1.010

used to assess the concentrating ability of the kidneys varies in proportion to its osmolality depends on both the number and weight of solute particles

provides a measure of ECF and ICF because water is in osmotic equilibrium across capillary endothelium and cell membrane

Rough estimate: 2X plasma [Na+]

1. Hydrostatic pressure – from pumping of heart; across capillary wall only

2. Oncotic pressure = osmotic pressure due to plasma proteins; across capillary wall and cell membrane

vary among tissues and organs 

Fluid movement = Kf[(Pc – Pi) – σ(πc – πi)]

Kf = filtration coefficient of capillary wall

Pc = hydrostatic pressure in cap lumen (force for mvmt of fluid from lumen to interstitium)

πc = oncotic pressure of plasma (retards mvmt of fluid out of cap)

Pi = hydrostatic pr of interstitium (normally moves fluid out of cap)

πi = oncotic pr of the ISF – proteins that leak out of cap move fluid out of cap into interstitium

σ = reflection coefficient for proteins across the cap wall (value for ability of solute to cross cell membrane values for typical skeletal muscle capillary bed drawing

1. 5% albumin used to increase patient’s vascular volume – albumin molecules don’t readily cross cap, volume retained

2. 0.9% NaCl (isotonic saline solution) used to expand ECF – entire volume of infused sol’n remains in ECF

3. hypotonicsolutions

(0.45% NaCl or D5W) used for patients with hyperosmotic body fluids – increases both ICF and ECF 4. hypertonic solutions (3% or 5% NaCl) used for patients with hypoosmotic body fluids – expand ECF volume, decrease ICF volume

paired, retroperitoneal

115-170 g each (<.5 % of total body weight)

11cmX6cmX3cm thick

 Composed of nephrons, blood vessels, lymphatics, and nerves.

Long hairpin-shaped vessels

Follows course of loop of Henle  Function: concentrate/dilute urine

Functional unit of the kidney

1.2 million nephrons in each kidney Consists of: 1. glomerular capillaries (capillary tufts from afferent arteriole inside bowmans membrane, site of ultrafiltration of blood into Bowman’s capsule)

2. Bowman's membrane

Formed of:

Endothelium- fenustrated, allowing water Na+, urea, glucose, and small protiens through

Basement membrane- pourous matrix of extracellular proteins, type IV collagen, Laminin, Fibronectin, and other negative charged proteins

Filtration slits-Retard filtration of some macromolecules, 40-140 A

consists of:

1. Mesangial Cells-

phagocytic

Secrete prostaglandins and cytokines

Can contact and influence GFR

2. Mesangial marix

lined with epithelial cells, specialized for transport functions Segments:

1. proximal tubule

2. Henle’s Loop . descending thin limb . ascending thin limb . thick ascending limb (with macula densa) 3. distal tubule

4. cortical collecting duct (from 2 or more nephrons)

5. collecting duct . principal cells – invaginated basolateral membrane, few mitochondria . intercalated cells – high density of mitochondria

present only in proximal tubule 

Extensions of cell membrane which increase surface area for reabsorption

Dense in mitochondria

1. Superficial Cortical Nephrons - glomerulus located in outer cortex - short loop of Henle extends only into outer medullary region

2. Juxtamedullary Nephrons - glomerulus located near corticomedullary boder - larger renal corpuscle, long loop of Henle extend deep into inner medullary region - function to concentrate urine

comprised of:

1. macula densa of thick ascending limb; actually a plaque in its walls

2. extraglomerular mesangial cells

3. granular cells of afferent arteriole involved in autoregulation of blood pressure through tubuloglomerular feedback mechanism

Kidney response to homeostatic need

Urine may be diluted 50m OSM/L

Concentrated 120m OSM/L 

The ballance of starling forces across muscle capillaries

The filtered fluid is then returned to circulation via lymphatics

Transmembrane protein of slit diaphragm

Mutation in Nephrin gene causes abnormal slit diaphragm and leads to massive proteinuria and renal failure