Introduction to HPA Flashcards
HPA stand for
Hypothalamic Pituitary Adrenal Axis
overview of HPA
– Term used to represent the interaction between the hypothalamus, pituitary gland and the adrenal gland.
– Pathway is key to our body’s repones to stress.
– Most important repones to the initiation of this pathway is the release of cortisol from the adrenal cortex.
– The aim of the stress response is to provide energy in the form of glucose.
mechanism of HPA
hypothalamus sends a signal (CRH) to pituitary gland–> releases ACTH
ACTH Travels to the Adrenal Glands, which sit on top of your kidneys.
Adrenal Glands Release Cortisol:
Cortisol helps your body by making more glucose (energy), speeding up your heart, and focusing your body on handling the stress.
Negative Feedback Loop Kicks In:
Once the stress is handled, Cortisol inhibits the release of CRH (corticotropin-releasing hormone) from the hypothalamus and ACTH (adrenocorticotropic hormone) from the anterior pituitary.
Central Endocrine Glands
Those within or in close association with the brain
– Hypothalamus
– Pituitary gland
– Pineal gland
Posterior pituitary
just an extension to the hypothalamus
neurohormone is packaged in cell body, and transported down in vesicles. They are stored in the posterior pituitary and then released into the blood.
produces oxytocin and anti-diuretic hormone (ADH)/ also known as vasopressin
Anterior pituitary
In contrast to the posterior pituitary, hormones are produced and secreted from the anterior pituitary
– BUT are under the direct control of hypothalamic hormones
– “True” endocrine gland
Hypothalamic hormones
dopamine, TRH, CRH, GHRH, somatostatin, GnRH
Anterior pituitary hormones
prolactin, TSH, ACTH, GH, FSH, LH
releases both tropic and non tropic hormones
Feedback loops of Anterior pituitary hormones
**Dominant Form is Long-Loop Negative Feedback:
**
Mechanism: Hormones produced by target glands (e.g., cortisol from the adrenal cortex) inhibit the release of hypothalamic or anterior pituitary hormones. Hormone’s effects inhibit the release of the hormone at the level of the hypothalamus or anteriorpituitary gland.
**Less Common Short-Loop Negative Feedback:
**
Short-loop negative feedback is a mechanism where the trophic hormone itself inhibits its own release at the level of the hypothalamus.
Mechanism: Tropic hormones from the anterior pituitary inhibit the release of their respective hypothalamic releasing hormones.
Example: ACTH inhibits the release of CRH from the hypothalamus.
Adrenocorticotropic hormone (ACTH) and cortisol
– Acts on adrenal cortex to promote the synthesis and release of cortisol
– Cortisol has a strong negative feedback effect on the anterior pituitary to inhibit ACTH secretion
– Cortisol provides the body with glucose –> gluconeogenesis
– Fight or flee a stressor
Anatomy of the adrenal gland
– An adrenal gland is made up of two parts: outer cortex and inner medulla.
- Medulla secretes catecholamines
– The cortex is the largest part of the adrenal gland and it secretes steroids
– Cortex is divided into three zones: Zona glomerulosa, zona fasciculata and zona reticularis.
– Each Zone is responsible for producing specific hormones.
zones of the adrenal glands
Zona glomerulosa, zona fasciculata and zona reticularis.
Function of the Adrenal medulla
– Secretes catecholamines
– adrenaline (epinephrine), noradrenaline (norepinephrine) and dopamine
function of zona glomerulosa
mineralcorticoids such as aldosterone
(regulate mineral balance)
function of zona fasisculata
glucocorticoids such as mainly cortisol
(regulate glucose metabolism)
function of zona reticularis
androgens [male stuff] such as Dehydroepiandrosterone (DHEA)
(stimulate masculinisation)
Actions of cortisol on skeletal muscle
CRH (hypothalamus) –> ACTH (anterior pituitary) –> cortisol (adrenal medulla)
DECREASE glucose uptake, glycogen, protein synthesis
INCREASE protein breakdown
Actions of cortisol on liver
CRH (hypothalamus) –> ACTH (anterior pituitary) –> cortisol (adrenal medulla)
DECREASE glycogenogenesis
INCREASE gluconeogenesis
Actions of cortisol on adipose tissue
CRH (hypothalamus) –> ACTH (anterior pituitary) –> cortisol (adrenal medulla)
INCREASE lipolysis, release of NEFAs (Non-Esterified Fatty Acids) and TGs (Triglycerides)
effects of cortisol
↑ Appetite
↑ Blood pressure
↑ Insulin resistance
↑ Gluconeogenesis, lipolysis
↓ Wound healing
↓ Inflammatory activity
↓ Bone formation
IMMUNE SYSTEM : function suppressed
LIVER : gluconeogenesis
MUSCLE : protein catabolism
ADIPOSE TISSUE : lipolysis
Abnormal cortisol secretion
Hyper-cortisolism (excess cortisol):
Cushing’s syndrome: A condition characterized by high levels of cortisol due to various causes, such as prolonged use of corticosteroid medication or tumors.
Tumors of adrenal gland or pituitary: Tumors in these glands can produce excessive amounts of cortisol.
Exogenous administration: The use of corticosteroid medications can lead to elevated cortisol levels.
Hypo-cortisolism (insufficient cortisol):
Not as common: Low cortisol levels are less common compared to high cortisol levels.
Addison’s disease: A disorder where the adrenal glands do not produce enough cortisol.
Congenital adrenal hyperplasia: A genetic condition affecting cortisol production.
Cushing’s Syndrome
– Cortisol levels are constantly elevated.
– Due exogenous steroid medications for a long period of time.
– Could also result from pituitary adenoma (excess ACTH).
– Severe muscle, bone and skin breakdown (major protein stores of
the body).
– Dampens the inflammatory and immune response.
– Affects mood and brain function.
– Increases blood pressure.
– Increase blood glucose levels.
– Increases obesity.
