Homeostasis

Question 1

What are the physiological control mechanisms for dynamic balance (4)

Answer 1

1. Sensor - sensory input conveyed centrally via Afferent paths
2. Central integrator - typically the hypothalamus: determines the level of output appropriate to correct the sensation of deviations from a “set point”
3. Effector - “motor” output signals conveyed via Efferent paths
4. Feedback inhibition - self-limiting - tending to attenuate, promoting dynamic equilibrium (balance) at the “set point”.

Question 2

How is the Solute/water balance maintained (5)

Answer 2

1. Body water is lost leading to osmolarity (hypertonic plasma), decreased volume (hypovolemic plasma), and low blood pressure (hypotension)
2. This is sensed by osmoreceptors (hypothalamus; ileum) and volume receptors (veins, arteries, right atrium and digestive tract)
3. These sensors trigger the central integrator (hypothalamus)
4. The hypothalamus responds by releasing control of thirst and the antidiuretic hormone (ADH/AVP) which decreases water loss by urinary excretion
5. Baroceptors sense the failure of pressure in the kidney, releasing renin, which leads to the production of the angiotensin system that triggers the adrenal glands to produce aldosterone, which decreases salt loss by urinary excretion, meaning water has to be retained in the kidney, correcting the ADH mechanism

Question 3

How is core temperature maintained with the pituitary (8)

Answer 3

1. decrease in temp
2. hypothalamus
3. pituitary
4. thyroid
5. promoted cellular metabolism (BMR)
6. Feedback inhibition by correction of difference from set point
7. core temperature is reached
8. Nerves feedback info to the hypothalamus to turn the system off

Question 4

How is core temperature maintained with the ANS and SNS (8)

Answer 4

1. decrease in temp
2. hypothalamus
3. Brain stem
4. ANS
5. SNS promotes BMR, Brown adipose tissue (a non-shivering way to produce heat), Vasoconstriction, and stop sweating.
6. Feedback inhibition by correction of difference from set point
7. core temperature is reached
8. Nerves feedback info to the hypothalamus to turn the system off

Question 5

How is core temperature maintained with the ANS and PsNS (8)

Answer 5

1. decrease in temp
2. hypothalamus
3. Brain stem
4. ANS
5. PsNS promots vasocontriction
6. Feedback inhibition by correction of difference from set point
7. core temperature is reached
8. Nerves feedback info to the hypothalamus to turn the system off

Question 6

How is core temperature maintained with the Limbic system (7)

Answer 6

1. decrease in temp
2. hypothalamus
3. Limbic
4. Somatic promotes skeletal muscles to start shivering movement activity
5. Feedback inhibition by correction of difference from set point
6. core temperature is reached
7. Nerves feedback info to the hypothalamus to turn the system off

Question 7

How are trophic changes regulated - Cortisol (5)

Answer 7

1. A stress triggers the hypothalamus
2. The hypothalamus releases the corticotropin-releasing hormone (CRH) to the anterior pituitary gland
3. The pituitary gland produces corticotropin (ACTH)
4. ACTH causes the growth of the adrenal causing the release of cortisol
5. the presence of cortisol turns off the adrenal, pituitary and hypothalamus.

Question 8

How are trophic changes regulated - Thyroid hormone (4)

Answer 8

1. the hypothalamus produces a thyroid-releasing hormone to the pituitary
2. pituitary releases thyroid stimulating hormone (TSH) to thyroid gland
3. thyroid gland releases thyroid hormone (TH)
4. The presence of thyroid turns off the thyroid gland, pituitary and hypothalamus

Question 9

How are trophic changes regulated - testosterone (4)

Answer 9

1. hypothalamus produces gonadotropin-releasing hormone to the anterior pituitary gland
2. pituitary releases luteinising hormone (LH) to the testes
3. testes produce testosterone
4. The presence of testosterone turns off the testes, pituitary and hypothalamus

Question 10

How are blood glucose levels maintained (8)

Answer 10

1. too much glucose in the blood
2. beta-pancreatic cells produce insulin which enters the blood
3. insulin turns glucose into glycogen to be absorbed by body cells
4. Blood glucose is reduced
5. too little glucose in the blood
6. pancreatic alpha cells produce glucagon which enters the blood
7. glucagon turns glycogen to glucose to be absorbed by body cells
8. blood glucose is increased

Question 11

How are blood calcium levels maintained - kidneys (4)

Answer 11

1. calcium levels decrease
2. parathyroid glands release parathyroid hormones to the kidney
3. kidney activates calcitriol (the hormonally active metabolite of Vitamin D) in the small intestine
4. Calcium absorption in the blood increases

Question 12

How are blood calcium levels maintained - bone (4)

Answer 12

1. calcium levels decrease
2. parathyroid glands release parathyroid hormones to the bone
3. osteoclasts breakdown and transfer calcium and potassium from the bone to the blood
4. Calcium absorption in the blood increases

Question 13

How is blood pressure maintained (10)

Answer 13

1. blood pressure decreases
2. angiotensinogen is released from the liver
3. renin from the kidney converts angiotensinogen to angiotensin i
4. angiotensin-converting enzymes (ACE) are released from the lungs converting angiotensin I to angiotensin ii
5. angiotensin ii increases:
   
   1. blood pressure sympathetic activity
   2. tubular Na+, Cl- reabsorption and K+ excretion and H2O retention
   3. tells the adrenal gland cortex to secrete aldosterone retaining H2O
   4. increases blood pressure through arteriolar vasoconstriction
   5. tells the pituitary gland to secrete ADH, causing H2O reabsorption at the collecting duct