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Homeostasis: process of maintaining consistent composition of body’ composition of body’s extracellular s extracellular fluid • Extracellular fluid (ECF) – Fluid environment in which the cells live (fluid outside the cells) – Major components: • Plasma • interstitial fluid – Minor ECF components – Lymph, transcellular fluid,cerebrospinal fluid, Intraocular fluid, synovial fluid, pericardial, intrapleural, and peritoneal fluids,digestive juices • Intracellular fluid (ICF) – Fluid contained within all body cells Fig. 1-5, p. 7 1 = capillary membrane separating plasma from interstitial fluid Barriers Separating Body‐Fluid Compartments • Barrier between plasma and interstitial fluid – Blood vessel walls • Barrier between ECF and ICF – Cellular plasma membranes 2 2 = cell membrane separating ICF and ECF 3 = interstitial fluid 1 Blood= plasma + cells 4 = intracellular fluid 5 5 = plasma, which is a part of blood; ECF trapped in capillary vessels 3 4 Plasma Barriers Separating Body‐Fluid Compartments HCO3– 150 Capillary wall Na+ HCO3– Plasma membrane • Presence of cell proteins in ICF that cannot permeate the cell membrane to leave the cells • Unequal distribution of Na+ and K+ and their attendant ions • Overall electric (charge) balance between intracellular and extracellular fluid • Overall osmotic balance between intracellular and extracellular fluid 200 Milliequivalents per liter of H2O – Major differences between Extracellular Interstitial Fluid and Intracellular Fluid (ICF) Intracellular fluid (skeletal muscle) Interstitial fluid PO43– K+ 100 Na+ Cl– Na+ Cl– 50 Protein anions 0 Protein K+ anions Other Other Cations Anions Other K+ Other Cations Anions Other Cations Anions Fig. 14-2, p. 419 What is the expected volume of each compartment in a person weighing weighing XXX pounds who is normally hydrated? Total Body Water (liters) = 60% of body weight kg ► Convert pounds to kilograms, ► multiply by .6 Liters/kg body weight to estimate Liters of Total Body Water ICF = 2/3 of TBW ECF = 1/3 of TBW › Interstitial fluid = 75 – 80% of ECF Use 75% › Plasma = 20-25% of ECF Use 25% 40% of body weight is intracellular fluid 20% of body weight is extracellular fluid (Your body weight / 2) - 10% of answer = your weight in kg 160 lbs / 2 = 80 actual conversion160/2.2= 72.72 80 – (10% of 80) ~ 72 kg The primary extracellular fluid (ECF) cation is sodium The primary intracellular fluid (ICF) cation is potassium. This difference is maintained by the Na+/K+ ATPase , which transport three Na+ 160/2.2026 = 72.64 molecules out of the cell in exchange for two K+ molecules transported into the cell. A balance of positive and negative charges is maintained in each compartment, but by different ions. Assume 1 kg weight = 1 liter fluid 60% of 72kg, in liters 72 kg 28.8 43.2 10.8 14.4 3.6 Homeostasis Maintain • Factors homeostatically regulated include Homeostasis (consistency of ECF) Body systems Which is essential for function (1- 6, + specialized) of that make up Cells Cell activity upsets (disorders) and restores (orders) ECF Fig. 1-6, p. 7 – – – – – – – Concentration of nutrient molecules Concentration of O2 and CO2 Concentration of waste products pH (concentration of free H+ or protons) Concentration of water, salt, and other electrolytes Blood volume and blood pressure Body Temperature Body System Contributions to Homeostasis • Circulatory system – Carries materials from one part of the body to another • Digestive system – Breaks down dietary food into smaller molecules that can be distributed to body cells – Transfers water and electrolytes from external environment to internal environment – Eliminates undigested food residues to external environment in the feces Body System Contributions to Homeostasis • Skeletal system – Provides support and protection for soft tissues and organs – Serves as storage reservoir for calcium – Along with muscular system enables movement of body and its parts – Bone marrow is ultimate source of blood cells • Muscular system – Moves the bones Body System Contributions to Homeostasis • Respiratory system – Gets O2 from and eliminates CO2 to the external environment – Important in maintenance of proper pH of internal environment • Urinary system – Removes excess water, salt, acid, and other electrolytes from plasma and eliminates them in urine; balances fluid and electrolytes Body System Contributions to Homeostasis • Integumentary system – Serves as outer protective barrier – Important in regulating body temperature • Immune system – Defends against foreign invaders and against body cells that have become cancerous – Paves way for repairing or replacing injured or worn‐out cells Body System Contributions to Homeostasis Body System Contributions to Homeostasis • Nervous system – Controls and coordinates bodily activities that require rapid responses – Detects and initiates reactions to changes in external environment • Endocrine system • Reproductive system – Not essential for homeostasis (not essential for survival of individual) – Is essential for perpetuating the species – Secreting glands of endocrine regulate activities that require duration rather than speed – Controls concentration of nutrients and, by adjusting kidney function, controls internal environment’s volume and electrolyte composition Homeostatic Control Systems • In order to maintain homeostasis, control system must be able to – Detect deviations from normal in the internal environment that need to be held within narrow limits – Integrate this information with other relevant information – Make appropriate adjustments in order to restore factor to its desired value Fig. 1-7, p. 12