FLUID COMPARTMENTS EXTRA CELLUAR FLUID INTRA CELLULAR FLUID INTERSTITIAL FLUID PLASMA TRANSCELLULAR FLUID CSF Intra ocular Pleural Peritoneal Synovial Digestive Secretions

Transcellular fluid: is a small compartment that represents all those body fluids which are formed from the transport activities of cells. It is contained within epithelial lined spaces. It includes CSF, GIT fluids, bladder urine, aqueous humour and joint fluid.

Composition Of Body Fluids  The solutes in ICF and ECF body fluids are organic and inorganic.  Organic :compounds of small molecular sizes such as glucose, urea, uric acid.  Inorganic electrolytes such as Na +, K +  Cl - ……..

COMPOSITION OF BODY FLUIDS CATIONS (mmol/l)PlasmaInterstitialIntracellular Na K Ca Mg ANIONS (mmol/l) Cl HCO Protein HPO

Interstitial Fluid: Interstitial fluid consists of a water solvent containing amino acids, sugars, fatty acids, coenzymes, hormones, neurotransmitters, salts, as well as waste products from the cells. The composition of tissue fluid depends upon the exchanges between the cells in the biological tissue and the blood. This means that tissue fluid has a different composition in different tissues and in different areas of the body. Physiological Function Of The ISF: Interstitial fluid bathes the cells of the tissues. Thus providing a media through which materials and metabolic waste are exchanged between the cells and blood,and acting as a media for intercellular communication.cellstissues

Interstitial Fluid: Interstitial fluid consists of a water solvent containing amino acids, sugars, fatty acids, coenzymes, hormones, neurotransmitters, salts, as well as waste products from the cells. It is similar in composition to blood plasma, except for a relatively low protein content (due to the low permeability of capillaries to plasma proteins). Physiological Function Of The ISF: Interstitial fluid bathes the cells of the tissues. Thus providing a media through which materials and metabolic waste are exchanged between the cells and blood,and acting as a media for intercellular communication.cellstissues

Intracellular Fluid:  The cytosol or intracellular fluid is the liquid found inside the cells.  Physiological Function :  The cytosol has no single function and is instead the site of multiple cell processes including metabolic processes (such as glycolysis,gluconeogenesis, PPP). It is also involved in signal transduction from the cell membrane to sites within the cell.

Homeostasis: Refers to the variety of mechanisms that have evolved for regulation of the volume and composition of the body fluids within fairly narrow limits. Osmosis: Refers to the movement of water across membranes in response to differences in osmotic pressure between the two sides of the membrane.Water generally migrates from the side of the membrane with the more dilute solute to that containing the concentrated solute. Since water passes freely across cell membranes,the volumes of the various fluid compartments are determined by unique solutes that are confined to each space. Which is the plasma proteins in the intravascular volume,sodium in the ECF compartment and Potassium in the ICF compartment.

Homeostasis:  The osmolarity of ICF is determined mainly by its K + concentration while that of the ECF by Na + concentration The volume of both compartments is maintained at constant levels through mechanisms that provide adjustments in the excretion of water, Na +, and K + in response to variations in the enviroment.  These adjustments are accomplished mainly by the kidneys.

Homeostatic Regulatorty Mechanisms:  The regulatory mechanism involves  - a sensor.  - a controller.  - an affector.

Regulatory Mechanisms; 1-Existance of receptors sensitive to variations in osmolar concentration of the ECF comopartment 2- The alterations in production and release of key hormones such as ADH antidiuretic hormone and aldosterone which regulate the excretion of water Na + and K +. 3-The Intrarenal mechanisms concerned with excretion of water and solutes.

How does it work ?  Blood diluted sensed by osmoreceptors in the brain will inhibit ADH secretion which lead to excretion of water from the renal tubules resulting in the excretion of a large volume of diluted urine.  Blood concentrated (dehydration) sensed by osmoreceptors stimulate ADH secretion promoting water reabsorption from the kidney tubules more water is returned to blood thus decreasing blood osmolarity.

Control Of Body Fluid Volume(Homeostasis):  In health the volume and composition of various body fluid compartments are maintained within physiological limits even in face of wide variations in intake of water and solutes.

 Antidiuretic hormone is produced by the hypothalamus,stored in the pituitary gland and causes the reabsorption of water from the distal tubules,collecting tubules and parts of loops of henle.  Aldosterone produced by the adrenal cortex and is responsible for 95% of all Na + tubular reabsorption from the distal tubules ,collecting tubules and part of loop henle.