By: Dr shahrokhi

CELL is the functional unit of the body - The body made of ~ 100 trillion plus cells, all surrounded by fluid, (extra-cellular fluid, ECF) PROTOPLASM - is the different substances that make- up the cell - Has 5 basic components; WATER, ELECTROLYTE, PROTEINS, LIPIDS, and CARBOHYDRATES.

WATER: 60% to 75% ELECTROLYTES : important (inside the cell) are K +, Mg 2+, Phosphate, Bicarbonate, and small quantities of Na +, Cl - and Ca 2+ PROTEINS: - Constitutes ~ 10% -20% of cell mass. - 2 types; i) STRUCTURAL PROTEINS ii) GLOBULAR PROTEINS LIPIDS : most important are phospholipids and cholesterol which make-up ~2% of total cell mass Phospholipids and cholesterol are mainly insoluble in water and are used to form cell membrane CARBOHYDRATE : structural role is limited. Major role is nutrition - especially in the form of dissolve glucose in the surrounding extra- cellular fluid.

Composition of the human body Water: 60% Protein: 18% Fats: 18% Minerals: 4%

Cytoplasm Components: Cytosol – gel-like fluid Storage substances Cell organelles Cytoskeleton – network of filaments and fibers

The internal environment The cell is surrounded by tissue fluid (Internal Environment). The composition of the internal environment should remain constant within narrow limits.

Homeostasis Maintaining constancy of internal environment. Dynamic constancy. Within a certain normal range. Regulatory mechanisms: Intrinsic: Within organ being regulated. Extrinsic: Outside of organ, such as nervous or hormonal systems.

Negative Feedback Figure 1.5

Action of effectors amplifies the changes. Is in same direction as change. Examples: –Oxytocin (parturition). –Voltage gated Na + channels (depolarization). –blood clotting Positive Feedback

Feed Forward Control When response has to occur rapidly, the brain uses a principle called feed forward control. Seen mainly in nervous system. Eg: Conditioned reflex Adaptive control.

Body Water Content Infants have low body fat, low bone mass, and are 73% or more water Total water content declines throughout life Healthy males are about 60% water; healthy females are around 50% This difference reflects females’: Higher body fat Smaller amount of skeletal muscle In old age, only about 45% of body weight is water

INTRACELLULAR FLUID (ICF) EXTRACELLULAR FLUID (ECF ) Interstitial fluid Transcellular fluid - cerebrospinal, pericardial, synovial Major Compartments for Fluids

Extracellular fluid: It is the internal environment that immediately surround the units of life of the whole body Intravascular: within the vascular system Interstitial: lies between the cells Transcellular : secreted by epithelial lining e.g., CSF, pleural fluid,peritoneal fluid, joint fluid,…. Large volumes are present in disease states, pleural effusion, ascites. Large losses in diarrhea and vomiting leads to dehydration and electrolyte disturbances.

Fluid Compartments Figure 26.1

Extra cellular fluidIntracellular fluid ISFPlasmaICF CATIONS mmol/L Na 44145K 551Ca 2240Mg ANIONS mmol/L Cl HCO HPO Proteins Osmolality mOsmol/L

Electrolyte Composition of Body Fluids Figure 26.2