Hormone axis physiology Flashcards
What are hormones and what is their role in the body?
Hormones are messenger chemicals that travel in the blood between organs and tissues, regulating various processes in the body.
What is a hormone axis?
A hormone axis is a system that controls the amount of a hormone in the system. It helps maintain proper hormone levels, as both too much or too little can have significant consequences.
What hormones are released by the anterior pituitary gland?
The anterior pituitary releases:
* Thyroid-stimulating hormone (TSH)
* Adrenocorticotropic hormone (ACTH)
* Follicle-stimulating hormone (FSH)
* Luteinising hormone (LH)
* Growth hormone (GH)
* Prolactin
What hormones are released by the posterior pituitary gland?
The posterior pituitary releases:
* Oxytocin
* Antidiuretic hormone (ADH)
How does the thyroid axis work?
The hypothalamus releases thyrotropin-releasing hormone (TRH), which stimulates the anterior pituitary to release thyroid-stimulating hormone (TSH). TSH stimulates the thyroid to release triiodothyronine (T3) and thyroxine (T4). When T3 and T4 levels rise, they suppress the release of TRH and TSH (negative feedback), regulating thyroid hormone levels.
What is negative feedback in the context of hormone regulation?
Negative feedback occurs when the end hormone (e.g., T3, T4, or cortisol) suppresses the release of the controlling hormones (e.g., TRH, TSH, or CRH), helping to maintain hormone levels within a normal range.
What is the role of cortisol in the body?
Cortisol, released by the adrenal glands, is a stress hormone that has diurnal variation. It increases alertness, inhibits the immune system, inhibits bone formation, raises blood glucose, and increases metabolism.
How does the adrenal axis work?
The hypothalamus releases corticotropin-releasing hormone (CRH), which stimulates the anterior pituitary to release adrenocorticotropic hormone (ACTH). ACTH stimulates the adrenal glands to release cortisol. The release of cortisol is regulated by negative feedback.
What are the functions of growth hormone (GH)?
Growth hormone (GH), released by the anterior pituitary, stimulates:
* Muscle growth
* Increases bone density
* Stimulates cell regeneration
* Promotes the growth of internal organs
What is the role of parathyroid hormone (PTH)?
Parathyroid hormone (PTH) increases serum calcium levels by:
* Increasing osteoclast activity to release calcium from bone
* Stimulating calcium reabsorption in the kidneys
* Promoting conversion of vitamin D into its active form (calcitriol), enhancing calcium absorption in the intestines
How does the renin-angiotensin-aldosterone system (RAAS) work?
Renin is released by the kidneys in response to low blood pressure. Renin converts angiotensinogen to angiotensin I, which is converted to angiotensin II in the lungs. Angiotensin II causes vasoconstriction, increases blood pressure, and stimulates aldosterone release.
What are the actions of aldosterone?
Aldosterone increases sodium reabsorption, potassium secretion, and hydrogen ion secretion in the kidneys, leading to increased water retention and higher blood pressure.
How does the renin-angiotensin-aldosterone system impact blood pressure?
Angiotensin II increases blood pressure by vasoconstriction and stimulating aldosterone release, which leads to increased sodium reabsorption and water retention, raising intravascular volume and blood pressure.
What is the clinical significance of ACE inhibitors and angiotensin II receptor blockers?
ACE inhibitors and angiotensin II receptor blockers reduce blood pressure by inhibiting vasoconstriction and aldosterone release. This reduces sodium reabsorption and water retention. However, these medications can cause hyperkalemia due to reduced potassium secretion in the kidneys.
