Adrenal glands Flashcards
explain the structure of the adrenal glands
Adrenal cortex: The outer layer of the adrenal gland, the adrenal cortex, is divided into three zones, each of which produces different types of hormones:
Zona glomerulosa: This layer produces mineralocorticoids, primarily aldosterone, which regulates salt and water balance in the body.
Zona fasciculata: This layer produces glucocorticoids, primarily cortisol, which regulates metabolism and immune function in the body.
Zona reticularis: This layer produces androgens, such as dehydroepiandrosterone (DHEA), which are precursors to male and female sex hormones.
Adrenal medulla: The inner layer of the adrenal gland, the adrenal medulla, produces catecholamines, such as epinephrine (adrenaline) and norepinephrine (noradrenaline), which play important roles in the body’s response to stress.
Synthesis of steroid hormones
The synthesis of steroid hormones begins with the conversion of cholesterol to pregnenolone, which is catalyzed by an enzyme called cholesterol side-chain cleavage enzyme (CYP11A1). Pregnenolone is then converted to other steroid hormones through a series of enzymatic reactions, which differ depending on the specific hormone being synthesized.
For example, the synthesis of cortisol, a glucocorticoid hormone, involves the conversion of pregnenolone to progesterone by the enzyme 3β-hydroxysteroid dehydrogenase (3β-HSD). Progesterone is then converted to 17α-hydroxyprogesterone by the enzyme 17α-hydroxylase. Finally, 17α-hydroxyprogesterone is converted to cortisol by the enzyme 21-hydroxylase.
The synthesis of aldosterone, a mineralocorticoid hormone, involves the conversion of pregnenolone to progesterone by 3β-HSD, followed by the conversion of progesterone to deoxycorticosterone by the enzyme 21-hydroxylase. Deoxycorticosterone is then converted to aldosterone by the enzyme aldosterone synthase.
The synthesis of sex hormones such as estrogen and testosterone involves more complex pathways. In females, estrogen is synthesized primarily in the ovaries, where it is produced from androgens such as testosterone. The synthesis of testosterone, on the other hand, occurs primarily in the testes in males.
explain The major physiological actions of corticosteroid
Anti-inflammatory and immunosuppressive effects: Corticosteroids are potent anti-inflammatory agents that can reduce inflammation and swelling in various tissues throughout the body. They also suppress the immune system, which can be beneficial in certain autoimmune disorders.
Gluconeogenesis: Corticosteroids promote the production of glucose from non-carbohydrate sources, such as amino acids and fatty acids, in the liver. This helps to maintain adequate blood sugar levels in the body during times of stress.
Protein catabolism: Corticosteroids increase the breakdown of protein in muscle tissue, which can lead to muscle wasting and weakness.
Sodium and water retention: Corticosteroids promote the reabsorption of sodium and water in the kidneys, which can lead to fluid retention and hypertension.
Anti-allergic effects: Corticosteroids can be used to treat allergies by reducing inflammation in the airways and suppressing the immune response that causes allergic reactions.
Suppression of the hypothalamic-pituitary-adrenal axis: Long-term use of corticosteroids can suppress the body’s natural production of cortisol, leading to a range of side effects including adrenal insufficiency and increased risk of infections.
The regulation of adrenocortical function
The hypothalamus secretes corticotropin-releasing hormone (CRH), which stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH) into the bloodstream. ACTH then travels to the adrenal cortex, where it stimulates the production and secretion of cortisol and other steroid hormones.
Cortisol, in turn, acts on the hypothalamus and pituitary gland to inhibit the release of CRH and ACTH, respectively, thereby regulating its own production. This negative feedback system helps to maintain normal cortisol levels in the body.
Other factors that can affect adrenocortical function include stress, illness, and certain medications. Chronic stress, for example, can lead to prolonged activation of the hypothalamic-pituitary-adrenal (HPA) axis and elevated cortisol levels, which can have negative health effects over time.
Additionally, certain medications, such as glucocorticoids, can suppress the HPA axis and decrease adrenal function. This can lead to adrenal insufficiency if the medication is not tapered off slowly, as the body may become dependent on the medication to produce cortisol.
Adrenal disorders
drenal insufficiency: Also known as Addison’s disease, adrenal insufficiency occurs when the adrenal glands do not produce enough cortisol and sometimes aldosterone. Symptoms can include fatigue, weight loss, low blood pressure, and salt cravings.
Cushing’s syndrome: This is a condition caused by an excess of cortisol in the body, either due to overproduction by the adrenal glands or prolonged use of corticosteroid medications. Symptoms can include weight gain, high blood pressure, and a round, “moon-shaped” face.
Congenital adrenal hyperplasia: This is a genetic condition in which the adrenal glands produce too much androgen, a male sex hormone. This can cause a variety of symptoms in both males and females, including ambiguous genitalia in newborns, early puberty, and irregular periods in females.
Pheochromocytoma: This is a rare tumor of the adrenal gland that causes the gland to produce too much adrenaline and noradrenaline, which can lead to high blood pressure, headaches, and sweating.
