The Endocrine System

1. The Endocrine System

2. Mechanisms of hormone release (a) Humoral: in response to changing levels of ions or nutrients in the blood (b) Neural: stimulation by nerves (c) Hormonal: stimulation received from other hormones

3. 1.Hypophysis (Pituitary Gland) • The hypophysis consists of glandular(Adenohypophysis) & nervous portions(Neurohypophysis) At low power, identify: • Adenohypophysis: • Pars anterior (pars distalis; anterior pituitary). • Pars intermedia( remnant of rathke pouch rudimentary in human beings) . • Pars tuberalis • Neurohypophysis: • Pars nervosa ( posterior pituitary) consist of median eminence and infundibulum.

4. Anterior Pituitary (Pars Distalis /Pars Anterior) • Cells can be divided into two classes on the basis of their staining characteristics: • Chromophils ("color-loving"), and chromophobes("color-fearing"). • Chromophils are further classified as acidophils and basophils. • Each cell type produces only one type of hormone. • parenchyma consists of secretory epithelial cells arranged in anastomosing cords and clusters. • Abundant sinusoidal capillaries with fenestration

5. Anterior pituitory… Chromophil: • Acidophils ; • strongly-staining, acidophiliccytoplasm due to granules. • cells are larger,most abundant than chromophobes. • well developed cell outline • Basophils- • Cells are variable in sixe and shape with basophilic cytoplasm. • secretory granules responsible for the staining characteristics of these cells are.

6. Anterior pituitory… Chromophobe- • clear, faintly-staining, sparse cytoplasm. • Do not have granules • Indistinct cell outline • Represent chromophil without granules or stem cells • Sinusoidal Capillaries in Anterior Pituitary • Chromophil granules are dense cored vesicles

7. Pars Intermedia… • Intermediate portion of pituitary • part of the adenohypophysis, • is non-neural. • composed of a thin layer of epithelial cells, which enclose colloid-filled spaces. • Identify colloid vesicles, and the surrounding low columnar cells .

8. Pars Nervosa… • is a downgrowth from the hypothalamus • Exhibits characteristics of nervous tissue. • Axon terminals within this area originate from cells in the hypothalamus; those in the supraoptic nucleus produce ADH (vasopressin), while those in the paraventricular nuclei produce oxytocin. • Cell bodies of these neurons are located in the hypothalamus, • The pars nervosa contains no neuronal cell bodies.

9. Pars nervosa… • Pituicytes : • Glial cells, variable in cell size and shape. • barely visible having orange stained cytoplasm. • Herring bodies: • large unmyelinated axon terminals, containing large numbers of neurosecretory granules. • Rich capillary network present in pars nervosa

10. Thyroid Gland-General Structure • It stores the inactive form of hormone extracellularly in follicles . • General Structure. Identify … • connective tissue capsule . • connective tissue septa that divide the bilobed gland into lobules .

11. follicles -of various sizes, • filled with pink-stained colloid and lined by cuboidal epithelial cells. These are the • functional units of the thyroid gland. • follicle size varies inversely with secretory activity. Interfollicular regions – • the presence of connective tissue, sinusoidal capillaries into which hormone is released) • parafollicular cells

12. Thyroid Follicles • Follicular epithelium: • vary from high cuboidal to low cuboidal ; reflects the level of follicle secretory activity. • follicle cells (principal cells) have large, centrally- or basally-located nuclei, • cells active in protein secretion. • Storage and release of thyroid hormones involves the protein thyroglobulin .

13. Parafollicular Cells • Found scattered singly or in small groups present in periphery of the follicles , • cells are responsible for production of calcitonin, a peptide hormone that is synthesized and secreted independently of thyroid hormone. • Also called C, clear, or light cells.

14. Parathyroid Glands-Parenchyma • present as a mass of crowded single cells, not arranged as follicles. It consist of 2 type of cells: Chief cells (principal cells): • Numerous ,small cells withprominent nuclei, and the pale,scant cytoplasmic staining.

15. Parathyroid Glands… Oxyphil cells: • single or clumps of larger cells with acidophilic (oxyphilic), cytoplasm with dark staining nucleus. • Number inrease with age. • Oxyphil cells are not always present in a section of parathyroid gland.

16. Adrenal Glands… Like the pituitary, they are composed of two distinctly different components, one of mesothelial origin and one of neural origin . General Structure • outer cortex , and the inner medulla . These zones are readily observed even in a fresh, unstained section. • 3 histological zones of the cortex. • tough connective tissue capsule and radial trabeculae that extend into the cortex. • Prominent central veinin the medulla.

17. Adrenal Cortex: Zona Glomerulosa Identify… • outermost cortical layer , and note the presence of columnar epithelial cells arranged in long cords that appear as ovoid clumps when cut in cross-section. • cytoplasm is pink and relatively scant contain lipid droplets. • capillary sinusoids are abundant.

18. Adrenal Cortex: Zona Fasciculata… • Note that this is the broadest, lightest-stainingof the three cortical zones, with epithelial cells that have large, abundant, poorly-stained cytoplasm. • Cells are arranged in vertical columns of radial plates • Identify capillary sinusoids between cords of secretory cells.

19. Adrenal Cortex: Zona Reticularis… • Note that the epithelial cells of this innermost, prominently stained zone are arranged in irregular, anastomosing cords and clumps with wide capillary sinuses intervening. • Note that the secretory cells are small, with relatively darkly stained cytoplasm that may contain yellow pigment.

20. Adrenal Medulla: Chromaffin Cells • Derived from neural crest, cells of the medulla are functionally equivalent to postganglionic sympathetic neurons. • Chromaffin cells. The secretory cells of the medulla contain catecholamines (norepinephrine and epinephrine) in cytoplasmic granules that are oxidized to a brown color by potassium bichromate (the chromaffin reaction).

21. Adrenal Medulla: Chromaffin Cells • Note that chromaffin cell cytoplasm is quite basophilic, compared to the acidophilia of the adjacent zona reticularis. • Note that the cells are arranged into tight clumps, with wide capillaries and venous channels intervening .

22. Pineal Gland-Pineal Sand • Basophilic, extracellular concretions . They are often calcified, which makes the pineal gland an excellent radiological marker, particularly of the midline.