Histology of the Adrenal Gland PDF

25 Jeyad Alkhzouz Reem Ghnemat Dr. Ghadah Abu El-Ghanam Adrenal Gland (Read only) - The adrenal gland (or suprarenal) glands are paired organs lying near the superior poles of the kidneys, embedded in the pararenal adipose tissue and fascia. - They are flattened structures wit...

25 Jeyad Alkhzouz Reem Ghnemat Dr. Ghadah Abu El-Ghanam Adrenal Gland (Read only) - The adrenal gland (or suprarenal) glands are paired organs lying near the superior poles of the kidneys, embedded in the pararenal adipose tissue and fascia. - They are flattened structures with a half- moon shape - 4-6 cm long and 1-2 cm wide and 4-6 mm thick in adults - It’s a yellowish retroperitoneal organs that lie on the upper poles of the kidneys - Surrounded by renal fascia - Each is covered by a dense connective tissue capsule that sends thin trabeculae into the gland’s parenchyma. o It’s devoid of fat tissue covering. - The stroma consists mainly of reticular fibers supporting the secretory cells and microvasculature - Separated from the kidneys by the perirenal fat - It has: o A yellow cortex: arises from the mesoderm (modified glandular structure) o and a dark brown medulla: arises from the neural crest (modified nervous structure) - Lacks a hilum; where suprarenal arteries arising from larger abdominal arteries penetrate the capsule independently. Blood supply will just penetrate through different regions. So, we have two layers: The cortex: - Cells have characteristic feature of steroid-secreting cells:  o Acidophilic cytoplasm (ghost cells) rich in lipid droplets with central nuclei - Cytoplasm shows profuse smooth ER (SER) of interconnected tubules, which contain the enzymes for cholesterol synthesis and conversion of the steroid pregnenolone into specific active steroid hormones. - Mitochondria are often spherical with tubular rather than shelflike cristae. - The function of steroid-producing cells involves close collaboration between SER and mitochondria. - Steroids diffuse freely from cells through the plasma membrane. They’re not stored in granules nor undergo exocytosis. As small lipid- soluble molecules, steroids diffuse freely from cells through the plasma membrane. - The adrenal cortex has three concentric zones in which the cords of epithelial steroid-producing cells are arranged somewhat differently, and which synthesize different classes of Rounded cord of the cells of steroid hormones: the zona glomerulosa 1. Zona glomerulosa: immediately inside the capsule and comprising about 15% of the cortex. a. Consists of closely packed, rounded or arched cords of columnar or pyramidal cells with many capillaries b. They make mineralocorticoids; these affect uptake of Na+/K+ and water by cells of renal tubules, so they control fluid and electrolyte uptake i. The principal product that is a mineralocorticoids called aldosterone. c. Aldosterone secretion is stimulated by angiotensin 2 and also by an increase in plasma K+ concentration, but only weakly by ACTH. 2. Middle zona fasciculata (largest): occupies 65-80% of the cortex and consists of long cords of large Has white appearance due it being filled with lipid droplets. polyhedral cells, one or two thick cells Cell appears in rows lined side by side separated by fenestrated sinusoidal capillaries. a. The cells are filled with lipid droplets and appear vacuolated in routine histologic preparations. b. These cells secrete glucocorticoids, especially cortisol, which affect carbohydrate metabolism stimulating gluconeogenesis in many cells and glycogen synthesis in the liver (control metabolism of carbohydrates, fats and proteins). i. Cortisol also suppresses many immune functions and can induce fat mobilization and muscle proteolysis. ii. Secretion is controlled by ACTH (from anterior pituitary) with negative feedback proportional to concentration of circulating glucocorticoids. iii. Small amounts of weak androgens are also produced Much wider capillaries, and more of them here Cells have no specific shape as to how they’re arranged 3. Innermost zona reticularis (represents primitive cortex): comprises about 10% of the cortex and consists of smaller cells in a network of irregular cords interspersed with wide capillaries. a. Cells are more heavily stained (more eosinophilic) than in other zones because they contain fewer lipid droplets and more lipofuscin pigment. b. Cells of this zone produce Weak androgens (small amounts), main site of weak androgen production.  i. Weak androgens include dehydroepiandrosterone (DHEA) that is converted to testosterone in both men and women. c. These androgens probably play a role in the prepubertal development of the sex organs. d. Secretion by these cells is also stimulated by ACTH with regulatory feedback. - So, the cortex secretes three hormones: 1. Mineralocorticoids: which control fluid and electrolyte balance 2. Glucocorticoids: control metabolism of carbohydrates, fats, and proteins 3. Sex hormones (small amounts): probably play a role in the prepubertal development of the sex organ. Histology - So, the general histologic appearance of the adrenal gland is typical of an endocrine gland, in which the cells of both the cortex and medulla are grouped in cords along wide capillaries - Superior, middle, and inferior suprarenal arteries arising from larger abdominal arteries penetrate the capsule independently and branch immediately to form a subcapsular arterial plexus. o From this plexus, arterioles for the adrenal cortex and medulla emerge separately to form rich networks of fenestrated capillaries and sinusoids. o Cortical capillaries irrigate endocrine cells of the cortex and then drain into the microvasculature of the medulla o The adrenal medulla thus has a dual blood supply: ▪ Arterial blood from the medullary arterioles ▪ Venous blood from capillaries of the cortex - Venous drainage from the glands occurs via the suprarenal veins. Adrenal Medulla (modified nervous tissue; rounded cells with no axons or dendrites) The adrenal medulla is composed of large, pale-staining polyhedral cells arranged in cords or clumps and supported by a reticular fiber network - A profuse supply of sinusoidal capillaries intervenes between adjacent cords o A few parasympathetic ganglion cells also exist - Medullary parenchymal cells, known as chromaffin cells (modified postganglionic sympathetic neurons), arise from neural crest cells, as do the postganglionic neurons of sympathetic and parasympathetic ganglia - Chromaffin cells can be considered modified sympathetic postganglionic neurons, lacking axons and dendrites and specialized as secretory cells. o These cells contain many electron dense granules for storage and secretion of catecholamines (either epinephrine or norepinephrine). o The granules of epinephrine-secreting cells are less electron dense and generally smaller than those of norepinephrine- secreting cells o Both catecholamines, together with Ca2+ and ATP are bound in granular storage complexes called chromogranins. - The conversion of norepinephrine to epinephrine (adrenalin) occurs only in chromaffin cells of the adrenal medulla. - About 80% of the catecholamine secreted from the adrenal gland Is epinephrine. - Medullary chromaffin cells are innervated by preganglionic sympathetic neurons, which trigger the release of epinephrine and norepinephrine during stress and intense emotional reactions o Epinephrine increases Heart rate, dilates bronchioles, and dilates arteries of cardiac and skeletal muscles. o Norepinephrine constricts vessels of the digestive system and skin, increasing blood flow to the heart muscle and brain o Both hormones stimulate glycogen breakdown, elevating blood glucose levels. - During normal activity, the adrenal medulla continuously secretes small quantities of these hormones. Lab Medulla Cortex Zona Glomerulosa Outer two stain lightly Zona Fasciculata Zona Reticularis; stains darker Veins H&N staining, Brightfield light microscope.  Adipose tissue Capsule Rounded cords, pale with fat droplets Straight cords that are lightly stained More basophilic, and more innervated by capillary network Spongiocytes that produce the cortizol 1-2 thick polyhedral cell layers interspersed by sinusoids Chromaffin cells Bigger cell with prominent nucleus. It’s a parasympathetic ganglia. Sinusoidal capillaries Chromaffin cells Parasympathetic ganglia Capsule Zona Glomerulosa Zona Fasciculata Zona Reticularis Trichrome stain Chromaffin Cells Sinusoids Kahoot quiz questions: 1. Removal or loss of this tissue will lead to the following consequences (picture showing histological features of posterior pituitary): a. Absence of TSH b. Absence of the stimulation to thyrotropes c. Absence of TRH d. Negatively affect breastfeeding 2. What is not seen in this image (picture showing structures): a. Secretory cells b. Sinusoids c. Capsule d. Endothelial cells 3. Which of the following hormones is delivered via hypophyseal portal circulation? a. Oxytocin b. ADH c. TRH d. TSH  4. Which of the following cell subpopulation is the highest in the pituitary gland? a. Somatotrophs b. Lactotrophs c. Corticotropes d. Gonadotrophs Answer key: 1. ANS: D. Loss of the posterior pituitary tissue causes disturbance in release of Oxytocin and ADH. Oxytocin is an important hormone that has important roles in milk let down, uterine contractions during birth, and other functions. 2. ANS: C. 3. ANS: C. TRH is a stimulating/releasing hormone that is produced by the hypothalamus. It acts on the anterior pituitary gland, stimulating it to release another hormone called TSH which goes on to act on the thyroid gland. TRH gets delivered to the anterior pituitary through the hypothalamic-hypophyseal portal system 4. ANS: A. Somatotrophs are the most abundant cell type in the pituitary gland, producing growth hormone (GH), which plays a key role in stimulating growth, cell repair, and metabolism, with effects on various tissues throughout the body.