Ch 1, 5, Homeostasis

Question 1

homeostasis

Answer 1

maintenance of a relatively stable internal environment despite continuous outside changes–a dynamic state of equilibrium

Question 2

homeostatic control mechanisms

Answer 2

1. involve continuous monitoring and regulation of many factors (variables)
2. nervous and endocrine systems accomplish the communication via nerve impulses and hormones

Question 3

components of a control mechanism

Answer 3

1. stimulus-variable, a change in internal or external environment
2. Receptor (sensor)- senses the change (stimulus) and transmits info to the control center via a afferent pathway (sensory neuron)
3. control center- analyzes input and decides on response
   - sends command to the effector via efferent pathway (motor neuron)
   - decides the normal value at which the variable should be maintained
4. effector- muscle or gland responds to the command from the control center
5. response- action carried out by the effector
   - acts to reduce or enhance the stimulus (feedback)

Question 4

negative feedback control

Answer 4

the response reduces or shuts of the original stimulus–response is the opposite direction to the original stimulus (or reduces intensity)

Question 5

example of negative feedback; Regulation of blood volume by ADH

Answer 5

a. receptors sense decreased blood volume
b. control center in hypothalamus stimulates pituitary gland to release antidiuretic hormone (ADH)
c. ADH causes the kidneys (effectors) to return more water to the blood
d. response is increased blood volume
e. return to normal c=volume sensed by receptors
f. control center in hypothalamus stops stimulation of pituitary gland
g. pituitary gland stops release of ADH

Question 6

Positive feedback control

Answer 6

1. the response increases or exaggerates the original stimulus- if original stimulus is an increase in some parameter, the response will be a even greater increase in the parameter which will result in a ever greater response
2. May exhibit a cascade or amplifying effect
3. results in an unstable situation which is either a normal self-limiting event or results in an abnormal disease function
   a. normal self-limiting: child birth, hemostasis
   b. abnormal pathogenic condition: hyper tension leads to heart failure

Question 7

childbirth

Answer 7

a normal self limiting feed back mechanism
stretching of cervix, releases oxytocin, uterus contracts, more oxytocin, more contraction, oxytocin etc
culminates in both which ends in a positive feedback cycle
pressure is increased, oxytocin is increased

Question 8

hemostasis (blood clotting)

Answer 8

1. break or tear in blood vessel wall
2. platelets adhere to site and release chemicals
3. released chemicals attract more platelets
4. platelet plug is formed( end of cycle)

Question 9

homeostatic imbalance

Answer 9

disturbance of homeostasis

a. increases risk of disease
b. contributes to changes associated with aging
c. may allow destructive positive feedback mechanisms to take over eg, heart failure

plaque build up in vessels-decreased diameter of vessels-inflammation of vessels-more plaque build up-increased restriction to flow-increased blood pressure-stress on heart-heart failure