Download Origin and Location of Thyroid Gland - eCurriculum

Histology of the Endocrine
System II
Dr. Jack L. Haar
Department of Anatomy and
Neurobiology
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
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
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
Functions
A. Synthesizes thyroxine
(tetraiodothyronine T4) and
triiodothyronine (T3) for metabolic
regulation
B. Synthesizes calcitonin, lowers blood
calcium levels
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
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
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
Thyroglobulin is produced and secreted to follicle lumen
Cells have polarity
Organelles for protein synthesis
Resorptive and degradative features
Histophysiology of follicle cells
Synthesis, secretion
and storage of
thyroglobulin in follicle
Iodination of tyrosines
on thyroglobulin
Rearrangement of
tyrosines to form thyroid
hormones
Histophysiology of follicle cells
Re-uptake of iodinated
thyroglobulin, hydrolysis
and release of thyroid
hormone from follicle cells
Feature
Active Follicle
Inactive Follicle
Follicle Epithelial Cells
Cuboidal to Columnar
Squamous
Amount Colloid
(Thyroglobulin)
Mitoses
Reduced
Extensive
Present
Absent
Regulation of the Thyroid Gland
Diseases of the Thyroid Gland
Hyperthyroidism (Grave’s Disease)
Hypothyroidism
– Myxedema (adult)
– Cretinism (childhood)
Iodine Deficiency Goiter
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
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
Parenchyma
– Chief (principal) 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
How PTH Regulates Blood Ca++
Levels
High Ca++
Low Ca++
Decreased PTH, Ca++
Deposition
Increased PHT, Ca++
Mobilization and
Increased Absorption
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
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
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
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
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
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
Chromaffin cell of the Adrenal Medulla
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
Capsule composed of pia mater
CT septa penetrate gland
Sympathetic axons and blood
vessels enter with septa
Pinealocytes
– Major cell type
– Euchromatic with nucleolus
– Cytoplasmic processes end
at a capillaries
– Secrete melatonin
Interstitial cells
–
–
–
–
Similar to astrocytes in brain
Nucleus more heterochromatic
Contain intermediate filaments
Found throughout the gland
Corpora arenacea
(brain sand)
– Globular accumulations of
calcium phosphate and
carbonates in interstitial
space
– Used to determine midline
in radiographic and CT
scans
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
http://www.path.uiowa.edu/virtualslidebox/
Table of Contents
Endocrine System
Thyroid-parathyroid #92
Parathyroid #SP02
Adrenal gland #160
http://java.vcu.edu/som-histology/