Survival needs & homeostasisWhat we need to live and how we stay balanced

First a few terms & suchAnatomy – the study of the structures

and shape of the body and it’s organsPhysiology – the study of how organs

function and the relationship between systems

Pathology – the study of diseases

Levels of structural organizationAtoms cells tissues organ organ

system organism

Survival needsNutrients – chemical substances taken into the

body for energy and cell building. Oxygen – all the chemical rxns in our bodies

require oxygenWater – most abundant chemical in our bodies,

provides the fluid environment required for mobility and rxns

Body temperature – chemical rxns required for life occur around 37oC (98oF). Below this temp rxns slow to stop, while above this temp proteins are destroyed.

Atmospheric pressure – breathing and exchanging O2 & CO2 requires a certain value of pressure

HomeostasisAbility to maintain relatively stable

conditionsMost body systems operate within

a small range Eg. Waste cannot accumulate,

blood sugar must not be too high or low, blood pressure

If a stimulus stresses the body it responds to the stress in a way that returns the system back to normal.

Not static, but constantly changing or dynamic

Analogy: Room thermostatThe temperature in the room is regulated by the

thermostat. If the temperature gets too hot, then the system

turns on to cool the room.The system shuts off when it reaches an acceptable

temp.

Homeostatic control systemAfferent pathway – takes

information to the control center (approaches). Afferent means to go toward

Control center – determines the appropriate level of the variable & whether a response is required

Effector – information travels away from the control center and responds to the stimulus.

INCLUDE Fig 1.4 pg 10, marieb essentials

Body system example

Negative feedback mechanisms

Similar to the thermostat.The way most homeostatic control

mechanisms in the body operate, as in the previous example.

Stimulus disrupts homeostasis, homeostatic control responds opposite to (the negative of) the stimulus. If outside gets cold, body acts to warm.

Examples: blood glucose, heart rate, blood pressure, breathing rate, blood levels of gases & nutrients.

Positive feedback mechanisms

Few mechanisms in the body operate in this manner.

Stimulus disrupts homeostasis, homeostatic control does the same thing as the stimulus. Exaggerates the effect of the stimulus. Has potential to get out of control.

Examples: blood glucose, heart rate, blood pressure, breathing rate, blood levels of gases & nutrients.

Blood clotting: damage occurs platelets cling to injury release chemicals that attract more platelets more platelets pile up.

Homeostatic imbalanceA disturbance in homeostasisCaused by illness or disease.Viruses and bacteria cause an

imbalance.As we age our organs and control

systems become less efficient & put us at risk for imbalances & thus illness.