Homeostasis

Homeostasis

To maintain nearly constant conditions in the internal environment (bodily functions and chemical compositions like electrolytes)

Extracellular fluid (whatever is around the cell) is often called internal environment

Blood Pressure Control

Blood pressure increase, receptors in blood vessels, nerve impulses input to brain (control center), nerve impulses output to heart and blood vessels (effectors)

This causes a decrease in heart rate and the dilation of blood vessels cause blood pressure to decrease (negative feedback)

Sympathetic activation increases blood pressure

Parasympathetic activation decreases blood pressure

Feedback Mechanism Steps

1. Senses the parameter using sensor/receptor (needs stimulus)

2. Compares the parameter to the normal operating value (set-point)

3. Sensor produces an output signal to a control center

4. Output signal from the control center then activates the effector to bring the parameter closer to the set-point

Sympathetic and Parasympathetic Activation

Symp- increase blood pressure (vasoconstriction) (supress when blood pressure too high)

Parasymp (vagal)- activation decreases blood pressure

Arterial Blood Pressure System (Negative Feedback)

• increase in arterial pressure

• detected by the baroreceptors

• send impulses to the medulla of the brain

• these impulses inhibit the vasomotor center

• decrease the sympathetic activities

• decrease cardiac pumping activity and dilate blood vessels (arterial blood pressure back to normal)

Positive Feedback

• increase stimulus intensity

• the response reinforces the stimulus, sending the variable farther from the setpoint

Negative Feedback

• decreases stimulus intensity

• the response counteracts the stimulus, shutting off the response loop