Week 4 – Homeostasis 1
OBJ 1 – Define homeostasis, explain its importance and specify three conditions that must
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
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 bt 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