Homeostasis Maintenance of relatively stable internal environment HOMEOSTASIS

Homeostasis Maintenance of relatively stable internal environment.

HOMEOSTASIS • Homeostasis is the maintenance of a steady state in the body despite changes in the external environment • The steady state is the optimum level for the body functions © 2008 Paul Billiet ODWS

HOMEOSTASIS – REGULATION OF INTERNAL CONDITIONS • The term “milieu interieur” was coined by Claude Bernard. • The actual environment of the body cells is the interstitial component of the extracellular fluid (ECF) • The term “homeostasis” was coined by WB Cannon in 1929 to mean constancy of the internal environment after its distortion by external stresses.

HOMEOSTASIS – REGULATION OF INTERNAL CONDITIONS • Regulation of fluid, electrolytes and acid-base balance is concerned with total body water (TBW), and concentrations of substances distributed between different fluid compartments. • Maintaining homeostasis or constancy of the internal environment is a function of many organ systems. • It follows that malfunction of any of them can disturb fluid, electrolyte, and acid-base balance.

Homeostasis depends on feedback circuits • Three components Receptor – detects a change in internal environment Control Center – process information from receptor, directs signal to the effector Effector – brings about the change to normal condition.

Negative feedback control system Cause and response are in opposite direction. v The sensor detects deviations from normal set point. v Signals from the sensor trigger compensatory changes that continue until the set point is again reached v. The response to the initiating stimulus is negative. v

Secretion of insulin entry of glucose to peripheral tissue Increase in blood sugar level Blood sugar to cause or stimulus normal level response /effect

• • Positive feedback control system Response is in the direction of stimulus. Amplifying system. Each successive cycle shall be stronger than previous cycle. Egs. Parturition Milk ejection reflex Blood coagulation.

Positive Feedback: Blood Clotting

Body composition • In average young adult male: Body composition % of body weight Protein, & related substances 18% Fat 15% Mineral 7% Water 60%

TOTAL BODY WATER(TBW) • 60% OF THE BODY WEIGHT IN ADULT MALE • 50% OF THE BODY WEITH IN ADULT FEMALE

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

Body Fluids • Water content in body is divided into 2 compartments: 1. Extracellular fluid (ECF): (internal environment or the milieu intérieur) • Fluid outside the cells. • ECF=14 liters • 20% of body weight • Interstitial fluid between cell is 80% of ECF. • Plasma in blood is 20% of ECF • Also includes lymph, cerebrospinal fluid, synovial fluid, aqueous humor, vitreous body, endolymph, per lymph, pleural, pericardial, and peritoneal fluids

2. Intracellular fluid (ICF): - Fluid inside the cells. - ICF=28 liters. 40% 0 f body weight.

Total Body Water ECF Blood ICF Interstitial ICF BLOOD ICF

VOLUME OF BODY FLUIDS IN 70 kg MAN TOTAL VOLUME 42 L INTRA CELLUAR FLUID 28 L(ROUGHLY 2/3 OF TBW) EXTRA CELLULAR FLUID 14 L(ROUGHLY 1/3 OF TBW) PLASMA 4 L (ROUGHLY ¼ OF ECF)

CATIONS (mmol/l) Na Plasma Interstitial Intracellular 142 OF BODY 139 COMPOSITION FLUIDS 14 K 4. 2 4. 0 140 Ca 1. 3 1. 2 0 Mg 0. 8 0. 7 20 Cl 108 4. 0 HCO 3 24. 0 28. 3 10 Protein 1. 2 0. 2 4. 0 HPO 4 2. 0 11 ANIONS (mmol/l)

MEASUREMENT OF BODY FLUID COMPARTMENT INTERSTITIAL FLUID ECF – Plasma Volume INTRACELLULAR FLUID TBW – ECF

VOLUME MEASUREMENT OF VARIOUS FLUIDS COMPARTMETNS • Dye Dilution Principle TOTAL BODY WATER (TBW) SUBSTANCE USED • DEUTERIUM OXIDE (D 2 O) • TRITIATED WATER • ANTIPYRINE • AMINOPYRINE

VOLUME MEASUREMENT OF VARIOUS FLUIDS COMPARTMETNS • EXTRACELLUR FLUID • SUBSTANCES USED : TWO MAJOR TYPES: – SACCHARIDES e. g. SUCROSE, INULIN, MANNITOL – DIFFUSIBLE INONS e. g. SULPHATE, SODIUM, THIOSULPHATE, BROMIDE, CHLORIDE

VOLUME MEASUREMENT OF VARIOUS FLUIDS COMPARTMETNS BLOOD PLASMA. • EVAN’S BLUE • RADIOACTIVE LABELED 125 I ALBUMIN TOTAL BLOOD VOLUME PLASME VOL X 100 -HCT