THE ENDOCRINE SYSTEM

1. THE ENDOCRINE SYSTEM Kristina C. Erasmo, M.D.

2. ENDOCRINE SYSTEM • System of glands that involve the release of extracellular signaling molecules known as hormones • Do not possess any excretory ducts • Integration and control system of the body

3. Hormone • Substance that is carried by the blood to target organs/tissues whose cells have the appropriate receptors for the substance • Function as “chemical signals”

4. ENDOCRINE SYSTEM • Hypothalamus • Pituitary gland • Pineal gland • Thyroid gland • Parathyroid gland • Adrenal gland • Pancreas

5. HYPOTHALAMUS • At base of brain, behind the optic chiasm • Forms the floor and part of the wall of the 3rd ventricle • Part of the diencephalon

7. HYPOTHALAMUS • Functions: • Control numerous bodily functions • Thirst, hunger, satiety • Temperature • Sexual behavior • Circadian rhythms • Produces several hormones • Oxytocin • Antidiuretic hormone • Neurohormones

8. HYPOTHALAMUS • The cell bodies of the neurons form numerous aggregations (nuclei) • Supraoptic nucleus • Above and lateral to optic chiasm • Paraventricular nucleus • In the lateral wall of 3rd ventricle

10. HYPOTHALAMUS • Oxytocin • Stimulates contractions of the uterus and ejection of milk • Vasopressin (antidiuretic hormone/ADH) • Regulates water retention (kidneys) • ↑ urine osmolarity (↑ concentration), ↓ urine excretion • Neurohormones (hypophysiotropic hormones) – secretory neurons

11. PITUITARY GLAND • Ovoid body attached to inferior surface of hypothalamus • Lodged in the hypophysealfossa of the sellaturcica of the sphenoid bone

12. PITUITARY GLAND: PARTS • Neurohypophysis (posterior pituitary) • From neural ectoderm • Adenohypophysis (anterior pituitary) • From oral ectoderm

14. Neurohypophysis • Greater part is formed by the axons of the secretory neurons whose cell bodies are in the SVN and PVN of hypothalamus • Proximal portions of these axons form hypothalamo-hypophyseal tract • Distal portions form bulk of the posterior lobe of pituitary

16. Neurohypophysis • Not a gland • Stores and secretes oxytocin and ADH (“posterior pituitary hormones”) • 2 parts: • Pituitary stalk (infundibulum, infundibular stem, infundibular stalk, hypophyseal stalk) • Attached to the hypothalamus • Pars nervosa (posterior lobe, infundibular process) • Expanded inferior continuation of the pituitary stalk

18. Adenohypophysis • Produces “anterior pituitary hormones” • Somatotropin, prolactin, thyrotropin, corticotropin, FSH, LH • 3 parts: • Pars distalis(anterior lobe) • Pars tuberalis(pars infundibularis) • Pars intermedia(intermediate lobe)

20. Pars Tuberalis • Forms a sleeve around the pituitary stalk of neurohypophysis • Where vessels of hypophyseoportal system and arteries that supply anterior and posterior lobe run through

21. Pars Intermedia • Thin, poorly developed region of adenohypophysis • Contain secretory granules • Melanocyte-stimulating hormone (MSH) • β-endorphin

22. Pars Distalis • Comprises 70% of pituitary gland • Nearly all hormones produced by pituitary gland come from this lobe (“anterior pituitary hormones”)

23. Pars Distalis • Consists of anastomosing and irregularly arranged cords and clusters of secretory epithelial cells that surround fenestrated capillaries

24. Pars Distalis • 2 types of secretory cells: • Chromophils • Acidophils (alpha cells) • Basophils (beta cells) • Chromophobes

25. Chromophobes • 65 % of epithelial secretory cells in pars distalis • Consists of follicular cells and undifferentiated stem cells

26. Chromophils • 35 % of epithelial secretory cells of pars distalis • Acidophils • Somatotrophs • Mammotrophs • Basophils • Thyrotrophs • Corticotrophs • Gonadotrophs

27. Chromophils

28. Hypophysiotropic Hormones • Hypothalamic control over anterior gland of pituitary gland • Corticotropin-releasing hormone (CRH) • Thyrotropin-releasing hormone (TRH) • Growth hormone-releasing hormone (GRH) • Growth hormone-inhibiting hormone (GIH, somatostatin) • Gonadotropin-releasing hormone (GnRH) • Prolacting-inhibiting hormone (PIH)

31. PINEAL GLAND • Small, conical structure • Base is attached to posterior portion of the roof of the 3rd ventricle of the brain by two short stalks • Well-developed in children • Starts to involute at puberty

32. PINEAL GLAND • Enveloped by thin CT capsule derived from the pia mater • CT septa arise from the capsule and divide the organ into irregular lobules • Lobules contain cells arranged in short cords or clusters surrounded by fenestrated capillaries • CT septa contain blood vessels and unmyelinated nerve fibers

33. PINEAL GLAND • Cells: • Pinealocytes (95 %) • Modified neurons • Produce melatonin • Glial cells (Interstitial cells) • Brain sand (Psammoma bodies) • Calcified bodies with a concentric lamellar structure • Increase in number with age

36. THYROID GLAND • Largest endocrine gland • Unpaired gland that lies on the anterior aspect of the neck • Left and right lateral lobes • Isthmus – horizontal bridge of glandular tissue which connects both lobes

37. THYROID GLAND • Enclosed by two capsules • CT septa divide the organ into lobules • CT infiltrated with lymphocytes and some lymphoid nodules • Each lobule contains follicles

38. THYROID GLAND • Follicles • Irregular spherical, cystic structures • Lined by simple cuboidal epithelium • Cavity contains colloid (homogenous, gel-like material)

39. THYROID GLAND • Epithelial cells: • Follicular cells (principal cells) • Majority • Synthesizethyroglobulin • Parafollicular cells (C or clear cells) • 0.1 % • Synthesize calcitonin– inhibits bone resorption (directly suppressing osteoclasts), thus lowering blood calcium levels

41. PARATHYROID GLAND • Two pairs (superior and inferior), yellowish-brown, tiny ovoid bodies • Attached to the posterior surface of the lateral lobes of the thyroid gland

42. PARATHYROID GLAND

43. PARATHYROID GLAND • Chief cells (principal cells) • Majority • Secrete parathyroid hormone (PTH) • Oxyphil cells (acidophil cells) • Non-secretory • Unknown function

44. ADRENAL GLAND • Paired, flat, pyramidal organs • Rest on the upper pole of their correspondin kidneys

45. ADRENAL GLAND • Enveloped by thick CT capsule • Cortex • Outer layer • Completely surrounds medulla • Mesodermal origin • Medulla • Inner layer • Ectodermal origin

46. Adrenal Cortex • 80 – 90 % of the adrenal gland • Produce adrenocortical hormones (steroid hormones) • Zonaglomerulosa– aldosterone • Zonafasciculata– cortisol • Zonareticularis– androgens (DHEA and androstenedione)

48. Adrenal Medulla • Comprises 10-20 % of adrenal gland • Central part: medullary veins that drain the entire gland • Consists of parenchymal cells arranged in groups or cords surrounded by sinusoids and richly supplied with nerves (associated with pre-ganglionic sympathetic neurons)

49. Adrenal Medulla • Chromaffin cells: secrete cathecolamines • Epinephrine (adrenaline) • Norepinephrine (noradrenaline) • Dopamine

50. PANCREAS • Islets of Langerhans • Small aggregations of pale-staining cells scattered among the dark-staining cells of the exocrine portion of the pancreas • Each islet surrounded by thin layer of fine reticular fibers • Provided by rich supply of capillaries • Millions but only 2 % of volume of pancreas