Survival needs & homeostasis What we need to live and how we stay balanced

First a few terms & such Anatomy – the study of the structures and shape of the body and it’s organs Physiology – the study of how organs function and the relationship between systems Pathology – the study of diseases Levels of structural organization Atoms  cells  tissues  organ  organ system  organism

Survival needs Nutrients – chemical substances taken into the body for energy and cell building. Oxygen – all the chemical rxns in our bodies require oxygen Water – most abundant chemical in our bodies, provides the fluid environment required for mobility and rxns Body temperature – chemical rxns required for life occur around 37 o C (98 o F). Below this temp rxns slow to stop, while above this temp proteins are destroyed. Atmospheric pressure – breathing and exchanging O 2 & CO 2 requires a certain value of pressure

Homeostasis Ability to maintain relatively stable conditions Most 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 thermostat The 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 system Afferent 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 imbalance A disturbance in homeostasis Caused 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.