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BISC 101 (55)

Unit 8 - Homeostasis

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Simon Fraser University
Biological Sciences
BISC 101
Derek Bingham

Week 4 – Homeostasis 1 OBJ 1 – Define homeostasis, explain its importance and specify three conditions that must be fulfilled. The human body has an internal environment, distinct from its external environment  Maintenance of the internal environment is conceptualized as homeostasis Homeostasis – the condition in which body’s internal environment remains relatively constant, within limits  Chemicals/enzymes involved in complex chemical reactions operate within a narrow range of conditions  Constancy of reactions is important for allowing chemical reactions to take place at the necessary rates o If conditions weren’t constant  reactions would occur slowly or not at all causing illness/death Three Conditions: ONE  There must be a proper concentration of gases, nutrients, water and salts.  Oxygen – cellular respiration that produces energy  Nutrients– raw materials for chemical reactions  Carbon dioxide – waste product of cellular respiration bt Water and salts– fluid and electrolyte balance of the body also used for other processes (determines its chemistry) TWO  Optimum temperature (37 C) O  Rates of chemical reactions are temperature dependent  Shapes of many enzymes are temperature dependent  if they overheat they break down THREE  Optimum pressure  Concentrations of various substances in the body, and the rates at which they move, are dependent on pressure o The pressures must be correct in order to maintain proper concentrations of the substances. OBJ 2 – Define “internal environment” and explain its relationship to ECF, ICF, plasma, interstitial fluid, and lymph. The body consists of cells and large amounts of extracellular material (mainly fluid). The cells are responsible for controlling bodily activities and composition of material surrounding them. The IE is defined as fluid inside the body, but outside the cells. A – Extracellular fluid  Fluid outside cells such as plasma, lymph, synovial fluid, cerebrospinal fluid, aqueous and vitreous humour  1/3 of the fluids in the body B – Intracellular fluid  Cells are primarily composed of cytoplasm (the fluid inside the cells)  2/3 of total body fluids  Although the ECF and ICF are two distinct fluid compartments, they constantly exchange materials. o Cells receive nutrients, waste materials are taken away from them, and gas exchange takes place o Once outside, cell materials move through the ECF  Most important organ system moving materials through the extracellular compartment is the circulatory system o Contains blood + arteries and veins that move it through the body o Materials are exchanged between blood and fluid in surrounding tissues in capillaries  Finely divided vessels at the ends of arteries  Thin enough to allow materials to exchange between blood and tissues C – Plasma  Blood is composed of cells (RBC + WBC), platelets (cell fragments), and a fluid called plasma.  Materials in the plasma are exchanged with the fluids in tissues in the capillary region. D – Interstitial fluid  Fluid in the tissues = intercellular fluid (because it is found between cells) = tissue fluid o Interstitial fluid is partly derived from plasma Week 4 – Homeostasis 2 o Components of the plasma move into tissues o Tissue fluid is also in contact with cells and partly derived from ICF but unique in composition E – Lymph  ISF must be returned to circulatory system so waste can be removed by the kidneys and other processes  ISF is under less pressure than the plasma in the capillaries, difficult for it to return directly to the blood  85% of ISF is returned to the circulatory system via capillaries and 15% is returned indirectly through lymph vessels o Lymphatic vessels originate as closed vessels associated with the tissues o Components of ISF move across walls of these lymphatic vessels o Fluid in these vessels = lymph = derived from tissue fluid but different in composition o Lymph collected into larger lymphatic vessels that drain into veins close to the heart OBJ 3 – Define “stress” and give two examples of stress originating from the external environment (EE) and two examples originating from the interna
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