Homeostasis (Sept 5)

Question 1

What system is dedicated to the process of homeostasis?

Answer 1

Autonomic nervous system

Question 2

Variable in homeostasis

Answer 2

something to regulate (eg. temp, glucose, etc.)

Question 3

Detector/receptor

Answer 3

detects change in the variable from its set point

Question 4

stimulus

Answer 4

movement of the system away from its set point (eg. blood pressure going up or down)

Question 5

control centre

Answer 5

figures out what to do when stimulus is detected

Question 6

effector

Answer 6

moves the variable back to normal (deprives the system of the stimulus and terminates the feedback loop)

Question 7

disease

Answer 7

departure from homeostasis

Question 8

Glucose regulation

Answer 8

1. Eat meal with sugar (glucose is variable)
2. Cells in pancreas detect sugar in blood (detector)
3. Pancreas (control centre)
4. Pancreas releases insulin to liver
5. Liver takes glucose out of blood and makes it into glycogen (effector)
6. Glucose can go to adipocytes as well (effector)

Question 9

Temperature regulation (decrease in temperature)

Answer 9

1. Stimulus decreases body temperature
2. Thermoreceptors in skin and hypothalamus detect temp change (Hypothalamic nuclei measure temperature)
3. Hypothalamus (control centre) sends messages to effectors
4. Blood vessels in skin constrict to decrease heat loss through the skin, adrenal medulla releases hormones that increase cellular metabolism, skeletal muscles contract (shiver), thyroid gland releases thyroid hormones which increases metabolic rate

Question 10

Deviating far from homeostasis

Answer 10

Body loses its ability to bring you back (eg. get too hot, body loses its ability to cool you down)

Question 11

Temperature regulation (increase in temperature)

Answer 11

1. Stimulus increases body temperature
2. Skin and hypothalamic temp sensors detect increase and relay message to hypothalamus
3. Hypothalamus stimulates effectors (control centre)
4. Blood vessels in skin dilate and sweat glands are activated (along with release of hormones and other things)
   Increased evaporation/conduction/convection decreases body temp

Question 12

Positive feedback

Answer 12

way to maintain homeostasis when a distinct event will facilitate the return to homeostasis

Question 13

Effector in positive feedback

Answer 13

brings the variable further from the starting point (increases the stimulus)

Question 14

Examples of positive feedback

Answer 14

blood clotting, action potential in neuron (message needs to be discrete so message making is done by positive feedback), ovulation (to produce an egg- positive feedback mechanism with estrogen that causes ovary to push egg out then stops and resets itself), Orgasm (sensory nervous input associated with sexual response causes you to become more sensitive until you have the orgasm), uterine contractions in labour (the more the uterus contracts, the more irritable it becomes and the more likely it is to be contracting until the baby is delivered)

Question 15

Lactation

Answer 15

1. Stimulus: suckling on breast
2. Detectors: touch receptors in nipple sense pressure and send nervous signal to hypothalamus
3. Control centre: hypothalamus
4. Release of oxytocin into the blood by the posterior pituitary (into pituitary portal circulation)
5. Contracting myoepithelium of breast (effector)
   When breast starts to express the milk, baby starts suckling harder, causes more receptors to be stimulated, more oxytocin, more lactation, etc.
   Baby stops eating and that finishes this process

Question 16

Blood clotting

Answer 16

1. Broken blood vessel exposes collagen which excites blood (platelets)
2. Platelets detect and stick to the collagen (detector)
3. Platelets release chemicals to cause a blood clot (control centre)
4. Clotting proteins are released which attract more platelets (effector) such as ADP and TXA2
5. Bring in more platelets, they release more chemicals, which attracts more platelets
6. Clot is made and you begin to release anticlotting things but you have now covered up the collagen which was the initial stimulus (anticlotting: prostaglandin, prostacyclin)

Question 17

DIC (disseminated intravascular coagulation)

Answer 17

• start clotting everywhere

- die because without clotting proteins in blood stream, fluid leaks out of bloodstream (petechiae- red dots everywhere)

Question 18

Example of pathology resulting from positive feedback

Answer 18

neurons firing recruit more neurons until they are all firing together in one part of the brain which causes a seizure (epilepsy). can be motor if motor neurons are recruited or psychological if neurons in the cortex are involved.