LESSON 25 cortas

The activity of the adrenal medulla is regulated by the hypothalamus through sympathetic endings of the splanchnic nerves. Upon receiving stimuli, the sympathetic nerves release acetylcholine, which stimulates the chromaffin cells of the adrenal medulla. These cells then secrete adrenaline and norepinephrine to capillaries, increasing the plasma concentration of adrenaline up to 300 times, leading to increased heart rate, tissue irrigation, and the release of glucose, among other actions. Norepinephrine also increases blood pressure.

a) Norepinephrine (noradrenaline) producing cells, and b) cells that produce epinephrine (adrenaline).

These cells contain large, spherical nuclei, numerous secretory granules with an electrodense nucleus, abundant RER, mitochondria, and Golgi complex.

They are larger than the norepinephrine producing cells, and their secretory granules are of lower electron density and more homogeneous.

Catecholamines.

Chromaffin cells have a very basophilic cytoplasm with granules that stain brown with chromium salts. They are called chromaffin cells because of this characteristic.

Sympathetic ganglion cells are found, singly or in groups, between the strands of chromaffin cells.

The adrenal medulla produces adrenaline and norepinephrine in these situations, which have various physiological effects such as increasing heart rate, tissue irrigation, release of glucose, and increasing blood pressure.

Thyroid hormones are produced through synthesis and storage phase in the follicular cells, which also produce thyroid peroxidase. Follicular cells take in iodine, and thyroid peroxidase oxidizes it to combine with thyroglobulin in the colloid. Thyroid hormones are released through endocytosis, proteolysis, and secretion along the basal border of the follicular cells.

Parafollicular cells, or C cells, are arranged between follicular cells and the basement membrane and produce calcitonin in response to high calcium levels.

Parathormone is produced in response to low calcium levels and increases calcium levels by increasing its reabsorption from bone tissue, decreasing its excretion at the renal level, and stimulating its absorption at the intestinal level.

The adrenal glands are located near the kidneys and produce hormones such as cortisol, adrenaline, and aldosterone.

In some species, parathyroid glands also contain oxyphil cells, the function of which is unclear.

The thyroid gland is composed of morphological units called thyroid follicles, which contain a gelatinous substance called colloid. Colloid is iodized thyroglobulin, the storage form of thyroid hormones T3 and T4.

Thyroid hormones are released through endocytosis, proteolysis, and secretion along the basal border of the follicular cells.

Thyroid follicles have varying sizes and morphologies depending on their functional status.

Follicular cells take in iodine, and thyroid peroxidase oxidizes it to combine with thyroglobulin in the colloid.

Thyroid hormones are produced through synthesis and storage phase in the follicular cells.

Aldosterone is responsible for regulating the balance of water and electrolytes in the body and plays a key role in maintaining blood pressure.

Parafollicular cells, or C cells, are arranged between follicular cells and the basement membrane and produce calcitonin in response to high calcium levels.

The three main groups of hormones produced by the adrenal gland are mineralocorticoids (e.g., aldosterone), glucocorticoids (e.g., cortisol), and sex hormones (e.g., androgens, estrogens, and progesterone). Mineralocorticoids help regulate blood volume and electrolyte balance, glucocorticoids regulate metabolism and have anti-inflammatory and anti-allergic effects, and sex hormones play a role in the development and function of the reproductive system.

The glomerular zone, the outermost layer of the adrenal cortex, is composed of irregular cords of cells interspersed with capillaries, which are oriented in a glomerular pattern. These cells are responsible for producing mineralocorticoids, particularly aldosterone, and play a key role in regulating electrolyte balance and blood volume in the body.

The fascicular zone, the middle layer of the adrenal cortex, is composed of single-layer cords of cuboidal or slightly columnar cells that have a spongy appearance due to their high vacuolization. These cells produce glucocorticoids, such as cortisol, and androgens, estrogens, and progesterone, contributing to the regulation of metabolism and the function of the reproductive system.

The reticular zone, the innermost layer of the adrenal cortex, is made up of anastomosed cords of smaller, less vacuolized polyhedral cells with a more pyknotic nucleus. These cells produce small amounts of corticosteroids and are the source of sex hormones in both males and females, playing a crucial role in the development and function of the reproductive system.

The adrenal medulla is located centrally in the adrenal gland and is responsible for producing catecholamines, including epinephrine and norepinephrine, which are involved in the body's response to stress and play a role in regulating the body's physiological responses to various stimuli.

The adrenal cortex is of mesodermal origin and is brownish-reddish in color, whereas the adrenal medulla is of neuroectodermal origin and is greyish in color.

The stroma, a thin layer of dense connective tissue, surrounds the adrenal gland and occasionally forms fine trabeculae that penetrate the cortex but not the medulla. It provides structural support to the gland and separates the cortex from the medulla.

The medulla contains both glandular (chromaffin) cells and ganglion cells. The glandular cells produce and store catecholamines, while the ganglion cells function as neurosecretory cells and release neurotransmitters, particularly catecholamines such as epinephrine and norepinephrine.

The adrenal gland is essential for life and plays a critical role in producing hormones that regulate various physiological processes, including blood volume and electrolyte balance, metabolism, stress response, and reproductive system function.

Mineralocorticoids, such as aldosterone, help regulate blood volume and electrolyte balance by increasing sodium reabsorption in the kidney, which impacts the overall fluid balance and blood pressure regulation in the body.

Glucocorticoids, such as cortisol, regulate metabolism, have anti-inflammatory and anti-allergic effects, and play a crucial role in responding to stress and maintaining the body's homeostasis under various physiological conditions.

Sex hormones, such as androgens, estrogens, and progesterone, produced by the adrenal gland, play a crucial role in the development and function of the reproductive system, including the maturation of reproductive organs and the regulation of secondary sexual characteristics.