1. Histology of the Endocrine System II
Dr. Jack L. Haar
Department of Anatomy and Neurobiology

2. Origin and Location of Thyroid Gland
Develops during the 4th week of gestation
Forms in the floor of the primitive pharynx
Thyroid diverticulum is the anlagen
Foramen cecum of the tongue is the site of its origin

3. Origin and Location of Thyroid Gland
Develops during the 4th week of gestation
Forms in the floor of the primitive pharynx
Thyroid diverticulum is the anlagen
Foramen cecum of the tongue is the site of its origin

4. Origin and Location of Thyroid Gland
Develops during the 4th week of gestation
Forms in the floor of the primitive pharynx
Thyroid diverticulum is the anlagen
Foramen cecum of the tongue is the site of its origin

5. Functions
A. Synthesizes thyroxine (tetraiodothyronine T4) and triiodothyronine (T3) for metabolic regulation
B. Synthesizes calcitonin, lowers blood calcium levels

6. Anatomy of the Thyroid Gland
Bilobed gland anterior to larynx
Lobes connected by an isthmus of tissue
Lobes lie lateral to trachea and extend from thyroid cartilage to fifth or sixth tracheal ring
Extensive vascularization

7. Composed of spherical follicles. Follicular or principal cells
Composed of spherical follicles Follicular or principal cells height varies from squamous to columnar
Center of follicle contains colloid proteinaceous, gelatin-like material, held in follicle: thyroglobulin, a glycoprotein ` thyroglobulin secreted by follicle cells Contains modified tyrosine (aa) in the primary sequence, a storage form of thyroid hormone.
Fenestrated Capillaries

8. Parafollicular cells (C Cells, Clear Cells). -Neural crest origin
Parafollicular cells (C Cells, Clear Cells) -Neural crest origin -Single or in clusters between follicles -High in protein synthetic machinery, non-polar -Secrete Calcitonin -Inhibits bone resorption, lowers blood Ca++ levels -Secretion stimulated by high blood Ca++ levels

9. Thyroglobulin is produced and secreted to follicle lumen
Cells have polarity
Organelles for protein synthesis
Resorptive and degradative features

10. Histophysiology of follicle cells
Synthesis, secretion and storage of thyroglobulin in follicle
Iodination of tyrosines on thyroglobulin
Rearrangement of tyrosines to form thyroid hormones

11. Histophysiology of follicle cells
Re-uptake of iodinated thyroglobulin, hydrolysis and release of thyroid hormone from follicle cells

16. Follicle Epithelial Cells
Feature
Active Follicle
Inactive Follicle
Follicle Epithelial Cells
Cuboidal to Columnar
Squamous
Amount Colloid
(Thyroglobulin)
Reduced
Extensive
Mitoses
Present
Absent

17. Regulation of the Thyroid Gland

18. Diseases of the Thyroid Gland
Hyperthyroidism (Grave’s Disease)
Hypothyroidism
Myxedema (adult)
Cretinism (childhood)
Iodine Deficiency Goiter

19. Histology of the Parathyroid Gland
Embryology
Derived from portions of 3rd and 4th pharyngeal pouches
Gross Anatomy
Two pairs (superior/inferior on posterior surface of thyroid
Embedded in CT capsule of Thyroid
Ellipsoid, 6x1x2mm, tan in color
Number and location may vary
Functions
Increase blood Ca++ via parathyroid hormone (PTH)
PTH acts on osteoclasts, renal tubule cells, intestinal epithelial cells

20. Microscopic Anatomy of the Parathyroid
Stroma
Thin CT capsule with septae (trabeculae) that divide gland into lobes
Adipose Tissue which may be up to 70% of the gland in aged individuals
Fenestrated capillaries

21. Parenchyma Chief (principal) cells Oxyphilic Cells
Major cell type; arranged in cords
Secrete PTH
Oxyphilic Cells
Large cells found singly or in clumps
Heterochromatic nucleus and intensely eosinophilic cytoplasm (high in mitochondria)
No secretory granules
Function not known

23. How PTH Regulates Blood Ca++ Levels
High Ca++
Low Ca++
Decreased PTH, Ca++ Deposition
Increased PHT, Ca++ Mobilization and Increased Absorption

24. Histology of the Adrenal Gland
Gross Anatomy: 4-6 cm x 4-6 cm
Cortex: derived from mesoderm
Medulla: derived from neural crest cells
Cortex: General Cell Characteristics
Large numbers of cytoplasmic lipid droplets
Large amount of SER
Mitochondria with tubular cristae
Secretion by diffusion, not stored products

25. Anatomical Zones of Adrenal Cortex
Zona Glomerulosa (15%): Just beneath CT capsule
Cells in round clusters
Secrete Mineralcorticoids (aldosterone)
Zona Fasiculata (80%); Middle and largest layer
Rows of cells perpendicular to capsule; alternating sinusoidal capillaries
Cells appear highly vacuolated (lipid droplets)
Secrete Glucocorticoids (corticosterone, cortisol, androgens and estrogens)
Zona Reticularis (5%): Deepest cortical layer
Cells in anastomosing chords
Secretions same as in fasiculata

30. Organization of Adrenal Medulla
Neural Crest Derivative; Sympathetic Ganglion
Cells Arranged in Cords or Clumps
Chromaffin Cells
Synthesize and release Epinephrine and Norepinephrine
Synthesize Products Stored in Dense Core Granules
Merocrine Secretion of Products
Innervated by Preganglionic Sympathetic Fibers

31. Organization of Adrenal Medulla
Neural Crest Derivative; Sympathetic Ganglion
Cells Arranged in Cords or Clumps
Chromaffin Cells
Synthesize and release Epinephrine and Norepinephrine
Synthesize Products Stored in Dense Core Granules
Merocrine Secretion of Products
Innervated by Preganglionic Sympathetic Fibers

32. Organization of Adrenal Medulla
Neural Crest Derivative; Sympathetic Ganglion
Cells Arranged in Cords or Clumps
Chromaffin Cells
Synthesize and release Epinephrine and Norepinephrine
Synthesize Products Stored in Dense Core Granules
Merocrine Secretion of Products
Innervated by Preganglionic Sympathetic Fibers

33. Organization of Adrenal Medulla
Neural Crest Derivative; Sympathetic Ganglion
Cells Arranged in Cords or Clumps
Chromaffin Cells
Synthesize and release Epinephrine and Norepinephrine
Synthesize Products Stored in Dense Core Granules
Merocrine Secretion of Products
Innervated by Preganglionic Sympathetic Fibers

35. Chromaffin cell of the Adrenal Medulla

37. Pineal Gland Regulates daily body rhythm
Develops from neuroectoderm of posterior roof of diencephalon
Located at posterior wall of 3rd ventricle
Pine cone-shaped, 5x3 mm

38. Capsule composed of pia mater
CT septa penetrate gland
Sympathetic axons and blood vessels enter with septa

39. Pinealocytes Major cell type Euchromatic with nucleolus
Cytoplasmic processes end at a capillaries
Secrete melatonin

40. Interstitial cells Similar to astrocytes in brain
Nucleus more heterochromatic
Contain intermediate filaments
Found throughout the gland

41. Corpora arenacea (brain sand)
Globular accumulations of calcium phosphate and carbonates in interstitial space
Used to determine midline in radiographic and CT scans

42. Function of Pineal gland
Timekeeper of the body regulating circadian rhythm
Retinal stimulation by light relayed to pineal via sympathetic innervation from superior cervical ganglion
Melatonin is released in the dark, inhibited by light
Melatonin affects neurons in the hypothalamus that produce Gonadotropin releasing factors, thus in animals it influences seasonal sexual activity.
Tumors that destroy the pineal lead to precocious (early onset) puberty

43. http://www. path. uiowa. edu/virtualslidebox/ Table of Contents
Table of Contents Endocrine System Thyroid-parathyroid #92
Parathyroid #SP02
Adrenal gland #160