Recall that Felix had problems maintaining normal blood pressure. His blood pres
ID: 3472498 • Letter: R
Question
Recall that Felix had problems maintaining normal blood pressure. His blood pressure was low, a condition called hypotension, and would drop further when he got out of bed or up from a chair, a type of low blood pressure called orthostatic hypotension.
(a) Describe how the endocrine system regulates fluid homeostasis under normal conditions.
(b) Low blood plasma volume can cause hypotension. Describe how the endocrine system normally regulates low blood plasma volume.
(c) Explain why Felix’s endocrine system was unable to respond to episodes of hypotension appropriately. What is the normal role of aldosterone?
Explanation / Answer
Before going into the questions let us understand the meaning of the key words involved in the below discussion .
Fluid homeostasis- is balance between the volume of fluid and the solutes present in the fluid.
Solute -particles present fluid which is not visible to naked eye
Osmolarity of a fluid- measure of solutes present in a solution measured in terms of -particles per litre.
a) Four organs mainly involved in fluid homeostasis namely Hypothalamus ,posterior pituitary,adrenal cortex,kidney.
Hypothalamus is a endocrine organ which has osmoreceptors which sense the osmotic pressure of bbody fluids and acts accordingly ,osmotic pressure is a gradiet through which fluids can pass from low lower concentration to higher concentration(eg :plain water diffuses into salty water when separated via semipermeable membrane).Hypothalamus hence plays a major role as a osmoreceptors and keeps a watch on the osmotic pressure of the fluid and if any disturbances will act accordingly explained in part 2 answer.
Posterior posterior pituitary releases hormone on recieving signal from hypothalamus .
Adrenal gland is an endocrine gland again has a major role in fluid homeostasis ,which produces mineralocorticoid and help to maintain balance between electrolytes and the water by maintaining osmolarity .
Kidney endocrine function is to sense the signals received by hypothalamus and adrenal cortex and maintain fluid homeostasis.
b)Hypothalamus is a osmoreceptors which senses disturbances in osmotic pressure in fluid and sends signal to posterior pituitary to release antidiuretic hormone which in turn acts on kidney and increases further water reabsorption .
And also stretch receptors in heart sense the low venous return and sends stimuli to the endocrine organs via the chemical messengers.
Baroreceptors present in aorta and carotids sense low blood pressure and which acts as a negative feedback indicator to central nervous system which in turn regulates the vascular resistance of blood vessels .
Adrenal cortex-releases aldosterone when body has decreased levels of sodium hence aldosterone acts on distal nephrons to retain sufficient amount of sodium in deficiencies
Kidney releases angiotensin 2 via jg cells which sense the decrease osmolarity and in turn stimulate the adrenal cortex-releases to release aldosterone.
Note :when plasma is concentrated aldosterone is released.
c)As per the short history Felix could be old man who is dealing with his old age hypotension,as in old age vascular resistance of blood vessels decreases and at the same time baroreceptors also wanes due to to age,causing orthostatic hypotension.
or
He could be suffering from Addison's deficiency of aldosterone hormone,leading to disturbance in fluid homeostasis in turn causing hypotension.
Role of aldosterone:
Aldosterone is released by adrenal gland via the stimuli received from stretch receptors due to low blood pressure and in turn causes reabsorption of sodium from kidneys to maintain normal osmolarity.,and normalise the blood pressure .and also aldosterone is activated via renin angiotensin system ,and causes to reabsorb sodium further .
Hence aldosterone is required physiologically to maintain the blood pressure and osmolarity of the fluid in the body.
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