Lecture 1
What is meant by homeostasis?
Meaning =Unchanging + standing. Homeostasis is a stable internal environment, coordinated by processes that maintain the internal environment within a narrow range of limits, achieved by balancing inputs and outputs.
Hierarchy of biological organisation
Cell-tissue-organ-organ system-organism
Homeostatic mechanism.
Many physiological mechanisms of varying complexity. Virtually every organ system plays a part in maintaining homeostasis. A wide range of thermal, chemical and neural factors must act and interact in complex ways to maintain a dynamic state of equilibrium. Most homeostatic mechanisms are negative feedback mechanisms. Blood pressure, waste disposal and blood nutrient levels must be monitored. No single organ system has total control over any homeostatic mechanism.
Fundamental components of a homeostatic mechanism
The fundamental component is FEEDBACK- the return of some of the output of a system as input so as to exert some control in the process. Stimulus- receptor-input-control centre-output-response. Going in it is the afferent pathway going out the efferent pathway.
Negative feedback
A sensing mechanism detects a change in conditions beyond specific limits. The control centre evaluates the change and activates a second mechanism to correct the condition. When the control centre determines that conditions have returned to normal the corrective action is discontinued. E.g. the regulation of glucose in the blood.
Positive feedback
Response of the system amplifies the effect of the original stimulus provides short term control over environment. Associated with processes that occur infrequently. Relative minor role in maintenance of homeostasis. E.g. labour.
Homeostatic failure
Values of physiological parameters drift outside normal range. Consequences include disease and death. Occurs when the negative feedback mechanisms are overwhelmed and the destructive positive feedback mechanisms take over like in heart failure.
Principle cause of homeostatic failure.
Infection, neoplasia, inherited disorders, autoimmune disease, environmental hazards, nutritional factors and ageing.

Lecture 2
Define atom- atoms are clusters of protons neutrons and electrons. A central nucleus contains the protons and neutrons tightly bound together then shells of orbiting electron clouds
Element- are atoms composed of different numbers of electrons, protons and neutrons; they differ in atomic weight, mass and number.
Molecule- a combination of two or more atoms held together by chemical bonds.
Compound-when two or more atoms of different elements combined to make a molecule
Valency- describes the capacity of an atom to combine with other atoms to form molecules. The electrons in the outer most shell are the valence electrons. There is a tendency to combine with atoms that will fill the outer shell and produce a stable number of valence electrons
Atomic number- equal to the number of protons in the nucleus written in a subscript to the left
Atomic mass- sum of the mass of the protons and neutrons
Atomic weight-The average of the relative weights (mass numbers) of all the isotopes of a given element, usually the atomic mass of its most abundant isotope.
Isotope- elements which have the same number of protons and electrons but differ in number of neutrons
Electron shell- within the electron cloud there are ordered energy shells occupied by orbiting electrons. Spaces for 2, 8, 8 electrons.
Inert atom- the outer electron shell is complete e.g. Noble gases
Reactive atom- the outer electron shell is incomplete so the atom is reactive
Inorganic- without carbon atoms include water oxygen and salt
Organic- have carbon atoms include carbohydrate, proteins, lipids and nucleic acids exceptions to the carbon rule include carbonates and CO2
Describe atomic structure – nucleus containing protons and neutrons (except Hydrogen that just has one proton and no neutrons)