Human Physiology - UNIT 1

What does physiology mean?

• Short answer: The science of the fxn of living systems.

• Long answer: the science of the mechanical, physical, bioelectrical, and biochemical functions of < organism of interest > in good health, their organs, and the cells of which they are composed.

Function vs. Mechanism

• Function represent the “why”

• Mechanism represent the “how”

What is Homeostasis?

• It’s the maintenance of a relatively stable internal environment (especially extracellular fluid)

• oscillation around a set point

whats an example of a negative and a positive feedback loop?

• negative: body temp regulation

• positive: childbirth

Study of homeostatic mechanisms….

physiology

failure to compensate for change…

diease

study of failure to compensate for change…

pathophysiology

Local Control

• occurs a site of stimulus

• uses paracrine (beside) or autocrine (self)

• affects nearby cells ONLY

• no nervous or endocrine system

• EXAMPLE: low O2 → local vasodilation

• Local “stays here”

Relex Control

• Long distance signalling

• uses nervous and endocrine system

• pathway: stimulus → integration centre → response

• can affect distant organs

• EXAMPLE: blood pressure reflex

• Reflex “goes to brain or hormones”

What is the response loop pathway?

Stimulus → Sensor → input signal → integrating centre → output signal → target → response

What are the feedback mechanisms?

• negative feedback

• feedforward control

• positive feedback

Negative feedback

• negative feedback stabilizes variable

- reverses the change to bring things back to normal

- keeps body stable (homeostasis)

- EX: body temp regulation

Feedforward control

• feedforward control anticipates change

- anticipates change before it happens

- EX: heart rate increases before exercise

Positive feedback

• Positive feedback reinforces stimulus - not homeostatic

- amplifies the change instead of reversing it

- not homeostatic

- EX: contractions during childbirth