Pineal, Thyroid, and Parathyroid Histology Flashcards
What is the small pine cone-shaped body (5-8 mm in humans)
Attached by stalk to roof of third ventricle between 2 hemispheres?
It has a Rich capillary plexus
Not separated by blood-brain barrier
it is Largest in first decade of life, does not grow throughout life
Pineal Gland
What cell types make up the pineal gland?
Pinealocytes
(95% of cells)
Glial cells (Interstitial cells)
Cannot identify using light microscopy
Astrocytes (supportive role) – similar to pituicytes of posterior pituitary
Pinealocytes produce what hormone and when?
Produce melatonin at night
What are the concretions of calcium phosphate & carbonate on carrier proteins that accumulate with age?
No known function
Radiological marker for the pineal gland
(displacement of pineal from midline is evidence of cerebral tumors)
Brain sand (corpora arenacea)
What is the pineal gland nerve supply?
Sympathetic nerve fibers
Post-ganglionic fibers from superior cervical ganglion
End on pinealocytes and
Release what?
epinephrine
Give the series of events that produce Melatonin during low light periods
Light/dark signals (photoreceptors) from the eye
suprachiasmatic nucleus (SCN)
paraventricular nuclei (PVN)
spinal cord
superior cervical ganglia
pineal gland
Suppresses gonadotrophin (FSH & LH) secretion via hypothalamus inhibition
Other pineal gland functions
Retards gonadal growth and function
(Melatonin inhibits hypothalamic GnRH
Inhibits FSH & LH in anterior pituitary)
Possibly alters emotional responses to changes in day length
In thyroid development, what gestational week does the Pharyngeal endoderm thickens and forms the thyroglossal duct and the
Ducts descends toward trachea and divides to form 2 lobes
4th gestational week
In thyroid development, what gestational week do Epithelial cells of fourth branchial pouch, ultimobranchial bodies, migrate toward thyroid gland, differentiate to parafollicular cells and scatter in lobes
7th gestational week
In thyroid development, what gestational week do Endodermal cells differentiate to follicular cells
9th gestational week
In thyroid development, what gestational week do Well developed follicles contain colloid in lumen
14th gestational week
What gland is on the Anterior neck adjacent to larynx and upper trachea
Two lateral lobes connected by isthmus
Connective tissue capsule
Follicles are functional unit
Fenestrated capillaries surround follicles
Thyroid gland
What are the 2 types of cells found in the thyroid gland
Follicular cells (Principal cells) Parafollicular cells (C-Cells)
What are the Structural units of thyroid?
Simple epithelium
(cuboidal, squamous, columnar)
Colloid contains thyroglobulin
(Gel-like, sometimes rippled)
These thyroid cells ... Apical ends of cells adjacent to colloid have microvilli that extend into colloid Basal ends of cells rest on basement membrane Junctional complexes between cells Slightly basophilic cytoplasm Round nuclei, prominent nucleoli Synthesize thyroid hormones
Follicular Cells
These thyroid cells ... “Resting” Producing basal levels of thyroglobulin Low cuboidal to squamous Few mitochondria; small Golgi Some rough ER in base of cells
Inactive Follicular Cells
These Thyroid cells ... Stimulated by TSH from pituitary Columnar cells Numerous mitochondria; enlarged Golgi Increased rough ER Lipid droplets and PAS-positive (polysaccharide) Colloid resorption by endocytosis Apical lysosomes Release T3, T4 on basal surface
Active Follicular Cells
These thyroid cells …
Occur singly or in small groups
Between follicular cells and basement membrane (not on lumen)
Also within interfollicular connective tissue
Slightly stained in H&E stains
Neuroendocrine
Synthesize calcitonin
Parafollicular Cells (C-Cells)
What are the actions of Calcitonin?
Lowers blood calcium by inhibiting bone resorption
Decreases osteoclast motility & numbers
Promotes excretion of calcium and phosphate from kidneys
Colloid contains what?
thyroglobulin
Oxidation to iodine at cell surface convers Iodide Iodine via what enzyme?
thyroid peroxidase (TPO)
Iodination of thyroglobulin occurs extracellularly at the
Tyrosine residues only
This process is Catalyzed by what enzymes on the follicular cell surface?
thyroid peroxidase (TPO)
This process produces what hormone?
Pinocytosis of thyroglobulin in colloid –>
Fusion with lysosomes –>
Thyroglobulin proteolysis –>
Eventual formation and release of _________ to cytoplasm and diffusion to capillaries
T3 and T4
bound to carrier proteins
What gland consists of Two pairs located on posterior surface of each lateral lobe of thyroid
- Derived from pharyngeal endoderm
- Connective tissue capsules separate it from thyroid
Parathyroid gland
Parathyroid gland is made up of what 3 cell types?
Chief (Principal) cells
Oxyphil cells
Fat cells
What parathyroid cell is responsible for Parathyroid hormone (PTH) production
which Regulates circulating calcium and phosphate levels
Chief (Principal) Cells
What Peptide hormone is
Involved in regulation of calcium and phosphate levels
This Increases blood calcium
Parathyroid hormone
What hormone stimulates increase in osteoclast numbers indirectly by stimulating osteoblasts to produce osteoclast stimulating factor (RANKL)
(Osteoclasts do not have PTH receptor, Osteoblasts have PTH receptor)
(Bone resorption increases blood calcium)
Parathyroid hormone
These parathyroid cells …
Larger than chief cells Smaller and darker-staining nuclei Large eosinophilic cytoplasm that is finely granular Many mitochondria Unknown function(s)
Oxyphil Cells
