III. Homeostasis

A. Basic principles

1. Homeostasis is the condition in which the body’s internal

environment remains within certain physiological limits

2. The extracellular fluid is considered to be the body’s internal environment

3. An organism is said to be in homeostasis when its internal environment…

a. Contains optimal concentration of gases, nutrients, ions, or water

b. Has optimal temperature

c. Has optimal volume for the health of cells

B. Stress and homeostasis

1. Stress is any external or internal stimulus that creates an imbalance in internal environment

2. The body attempts to counteract effects and bring things back to

normal

3. Homeostasis is maintained by the nervous and endocrine systems

a. Nervous system uses nerve impulses to correct (quick)

b. Endocrine system uses hormones (slow)

4. Regulate through feedback loopsa. Loops- cycle of events in

which info about the status of a condition is continually monitored by a central control region

b. Have three components:1. Control center- sets and

controls standard2. Receptor- notices

change, inputs to c.c.3. Effector- gets output

from c.c and responds

Control Center

Receptor Effector

c. Two types of feedback loops

1. Positive loop- enhances the

original stimulusa. Labor-

uterian cells stretch> send input to hypothalamus>

release oxytocin> more forceful

contraction

2.negative loop- reverses original stimulus

a. B.P.- B.P. rises> input to brain>

impulse to heart> heart rate decreases ( also dilates blood vessels)

C. Homeostatic imbalance

1. Disease is any change from a state of health

a. Local- limited areab. Systemic- entire body or

several partsc. Signs- observable,

measurable changesd. Symptoms- unobservable

changes