Endocrine

1. Endocrine Department of Histology and Embryology Li jinxin No.0453

2. Key Points • The structure and function of thyroid, parathyroid, adrenal and pituitary gland.

3. Difficult Points • The relationship between hypothalamus（下丘脑）and neurohypophysis（神经垂体）. • The component and significance of pituitary portal system（垂体门脉系统）.

4. endocrine glands and diffuse endocrine cells Composing pituitary gland pineal body thyroid and parathyroid thymus pancreatic islets adrenal interstitial cells corpus luteum

5. The characteristic of endocrine glands • Endocrine glands are ductless. • Cells arranged in glomerulus, cords, reticulum or in follicles. • Rich in blood and lymphatic capillaries between cells. • Release hormones either into the vascular system (endocrine), or to their surroundings (paracrine), and bind to specific receptors of target cells.

6. Classification of Endocrine Cells Nitrogen-containing hormone-secreting cells（含氮激素分泌细胞） • Found in thyroid, parathyroids, adrenal medulla, pituitary and pineal glands, etc. • Contain RER, Golgi complex and membrane bound secretory granules. • Hormones are secreted by exocytosis（胞外分泌）.

7. Steroid hormone-secreting cells（类固醇激素分泌细胞） • Found only in adrenal cortex, interstitial cells, corpus luteum. • Contain abundant SER, mitochondria with tubular cristae and lipid droplets. • Hormones are secreted by diffusion.

8. 1. Thyroid 1.1 General structure • Capsule: loose connective tissue sends septa into parenchyma, dividing the gland into lobules. • follicles: which are functional units and varied in size. • Parafollicular cells: between follicles is rich in fenestrated capillaries and also contains parafollicular cells.

9. colloid follicle capillary parafollicular cell

10. 1.2  Thyroid follicles a. Composed of a simple follicular epithelium, follicular lumen filled with colloid. b. The follicular epithelium is composed of the follicular epithelial cells and the parafollicular cells. follicular epithelial cell parafollicular cell

11. Height of cells ranges from squamous to columnar, depending on the functional activity of follicles. The cytoplasm is weakly basophilic or acidophilic. follicular epithelial cells

12. Ultrastructure • Apical surface is covered by numerous microvilli. • Cytoplasm rich in RER in basal part, well-developed Golgi complex in supranuclear area, secretory granules , pinocytotic colloid vesicles in apical part and abundant lysosomes. • Cells are joined laterally by junctional complexes, preventing thyroglobulin（甲状腺球蛋白） leakage from follicles into surrounding stroma.

13. Function • synthesis and release of thyroid hormones (T3, T4) • T3 and T4 increase rate of metabolism and influence development of central nervous system during fetal and neonatal life.

14. Synthesis of thyroglobulin (TG) in RER and released into lumen of follicles. Iodination of TG. iodide taken up and oxidized. The iodinated TG is stored as colloid in the follicular cavity. Pinocytosis. follicular cells take up iodinated TG, forming pinocytotic vesicles. Release of thyroid hormones.iodinated TG is degraded, and forms thyroxine (T4) and triiodothyronine (T3), released into capillaries. The secretory process of follicular epithelial cell

15. compensatory thyroid hyperplasia

16. Low-secretory of thyroid hormones: neonatal→cretinism adult →mucous edema High-secretory of thyroid hormones: hyperthyroidism

17. Located between follicular epithelial cells or between follicles as isolated clusters. Large and pale stained with H & E, argyrophilic granules（嗜银颗粒）with silver staining. Under EM, many small secretory granules. Secrete calcitonin（降钙素）, which lowers blood calcium level . 1.3 Parafollicular cells or C cells

18. 1.4 Colloid • Homogeneous, acidophilic, gelatinous substance. • Chemical composition is iodinated thyroglobulin（碘化甲状腺球蛋白）. • Vacuoles（空泡）at the periphery may represent pinocytosis of colloid.

19. Consist of 2 types of cells: Chief cells are small, pale stained and contain secretory granules; oxyphil cells are large, acidophilic because of many mitochondria. Parathyroid hormone secreted by chief cells elevates blood calcium by increasing activity of osteoclasts. 2. Parathyroid gland

20. 3. Adrenal gland 3.1 General description • Covered by a capsule of dense connective tissue. • Parenchyma consists of an outer adrenal cortex , and an inner adrenal medulla. • The cortical cells are steroid-secreting, and the medullar cells are nitrogen hormone- secreting.

21. subdivided into three layers according to cell arrangement Zona glomerulosa(球状带） Zona fasciculata(束状带) Zona reticularis(网状带) 3.2 Adrenal cortex

22. Beneath the capsule, occupy 15% of total volume of the glands. Composed of round clusters of columnar cells surrounded by capillaries. Secrete mineralocorticoids(盐皮质激素), which maintain electrolyte and water balance by acting on distal renal tubules and stimulating resorption of sodium. 3.2.1 Zona glomerulosa

23. 3.2.2 Zona fasciculata • Most thick layer in middle account for 65% of total volume of glands. • Composed of straight cords of large, polyhedral cells with acidophilic, sponge cytoplasm. • Cells have typical ultrastructural characteristics of steroid-secreting cells. • Synthesize glucocorticoids (糖皮质激素), which regulate carbohydrate, protein and lipid metabolism, and also suppress immune responses.

24. Innermost layer of smaller cells arranged in anastomosing cords, 7% of total volume. Produce sex hormones, mainly androgens（男性激素）, and small amounts of cortisol. 3.2.3 Zona reticularis

25. Composed of polyhedral cells arranged in nests or short cords. Cells contain chromaffin granules (嗜铬颗粒), so called chromaffin cells. Weekly basophilic cytoplasm. 3.3 Adrenal medulla

26. Function • Synthesize and release epinephrine (肾上腺素)and norepinephrine (去甲肾上腺素)by two different groups of cells. • Epinephrine increases the heart rate. Norepinephrine increases the blood pressure and blood flow to the heart, brain and skeletal muscle.

27. 4.Pituitary Gland • Consists of two parts: adenohypophysis and neurohypophysis. • pars distalis and pars tuberalis make up anterior lobe. • Pars nervosa and pars intermedia make up posterior lobe. median eminence pars tuberalis infundibular stalk pars distalis pars nervosa pars intermedia

28. largest part containing three types of cells interspersed with sinusoids Acidophil cells Basophil cells Chromophobe cells 4.1Pars distalis

29. 40%. Round or ovoid, and numerous coarse acidophilic granules. Two types of acidophil cells. Somatotrophs synthesize and release growth hormone, which stimulates body growth, particularly growth of long bones. Mammotrophs secrete prolactin（催乳激素，PRL）, which initiates and maintains the milk secretion after pregnancy. 4.1.1 Acidophil cells

30. Lack of somatotropin →dwarf Plethora of somatotropin infancy→gigantism adult →acromegaly

31. Thyrotrophic cells secrete thyrotropin or thyroid stimulating hormone (TSH). Corticotrophic cells secrete adrenocorticotrophic hormone (ACTH). Gonadotrophic cells secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH). 10%. Slightly larger than acidophil cells, with basophilic granules . Three types of basophil cells. 4.1.2 Basophil cells

32. 50% , Clusters of small cells without distinct boundaries, and pale stained. Few secretory granules, indicating they are undifferentiated precursor cells or degranulated chromophils. 4.1.3 Chromophobe cells

33. Composed of chromophobes and basophil cells arranged either in cords or in colloid-containing follicles. Secretes melanocyte stimulating hormone (MSH) . 4.2 Pars intermedia

34. 4.3 Relationship between pars distalis and hypothalamus • Activities of the cells in the pars distalis are controlled by hypothalamic neuroendocrine neurons that produce peptide releasing hormones and inhibitory hormones, which are transported to the pars distalis through the hypophyseal portal system. • Hypophyseal portal system includes • superior hypophyseal artery → the primary plexus → hypophyseal portal veins → the secondary plexus

35. Hypophyseal portal system superior hypophyseal artery primary plexus hypophyseal portal veins secondary plexus inferior hypophyseal artery

36. FSH LH GH PRL TSH MSH ACTH

37. 4.4 Neurohypophysis median eminence infundibular stalk pars nervosa

38. Unmyelinated nerve fibers. They originate from neurons of hypothalamic supraoptic and paraventricular nuclei. Herring bodies. Pituicytes are glial cells with irregular shape and short processes contain lipid droplets and pigment granules in their cytoplasm. Sinusoids. 4.4.1 Structure of neurohypophysis

39. 4.4.2 Function • Stores and releases vasopressin (antidiuretic hormone, ADH) and oxytocin. • Vasopressin stimulates water resorption in kidneys and contraction of vascular smooth muscle. • Oxytocin promotes contraction of uterine smooth muscle during parturition and contraction of myoepithelial cells in mammary glands during lactation.

40. They are the entiaof structure and function. Hypothalamus secrete the hormones. Neurohypophysis transport, store and release hormones. 4.5 The Relationship Between Hypothalamus and Neurohypophysis

41. 4.6 Diffuse Neuroendocrine System (DNES) • APUD ( amine precursor uptake and decarboxylation cells，摄取胺前体脱羧细胞 ) and neuroendocrine cells （神经内分泌细胞）. • They secrete amine or peptides hormone. • It cooperates with APUD and then unify nervous system and endocrine system, called diffuse neuroendocrine system (DNES).

42. Endocrine System Exercises: • State briefly the structure and function of thyroid • gland? • 2. State briefly the structural and functional • characteristic of adrenal cortex. • What are the kind of cells in the Pars distalis of adenohypophysis? Describe their structure and function. • What is the functional significance of the hypophyseal portal system?