Pineal Thyroid Parathyroid Histology

Question 1

What is the Gross Structure of the Pineal Gland?

Answer 1

Small pine cone-shaped body (5-8 mm in humans), Attached by stalk to roof of third ventricle, Pia mater capsule with septa (Divide pineal into incomplete lobules), Rich capillary plexus. Extremely small.

Question 2

When is the Pineal Gland largest?

Answer 2

Largest in first decade of life, does not grow throughout life.

Question 3

Where is the Pineal Gland located?

Answer 3

Below the Corpus Callosum. It’s the stalk on roof of the 3rd ventricle

Question 4

What are the two cell types in the Pineal Gland?

Answer 4

Pinealocytes, Glial cells

Question 5

What are Pinealocytes?

Answer 5

95 percent of cells. Produce melatonin at night.

Question 6

What are Glial cells?

Answer 6

Cannot identify using light microscopy. Astrocytes (supportive role)

Question 7

What accumulates within the Pineal Gland?

Answer 7

Brain sand (corpora arenacea)

Question 8

What is Brain sand?

Answer 8

Concretions of calcium and phosphate. Accumulation with age. No known function. Radiological marker for the pineal gland (displacement of pineal from midline is evidence of cerebral tumors)

Question 9

What is the nerve supply to the Pineal Gland?

Answer 9

Sympathetic Nerve Fibers

Question 10

What are the features of Sympathetic Nerve Fibers?

Answer 10

Post-ganglionic fibers from superior cervical ganglion. End on pinealocytes. Release epinephrine.

Question 11

What is the main function of the pineal gland?

Answer 11

Produces Melatonin.

Question 12

When is Melatonin produced?

Answer 12

During low light periods. Circadian signals from he eye are sent to the suprachiasmatic nucleus (SCN) and the superior cervical ganglia.

Question 13

What are the functions of Melatonin?

Answer 13

Suppresses gonadotropin (FSH and LH) secretion via hypothalamus inhibition. Retards gonadal growth and function (tumors that destroy pineal gland in children cause precocious puberty). Possibly altered emotional responses to reduced day length during winter months. (SAD - seasonal affective disorder)

Question 14

What is the adult structure of the Thyroid gland?

Answer 14

Two lateral lobes connected by isthmus. Connective tissue capsule (delicate capsule, indistinct lobes and lobules). Fenestrated capillaries surround follicles. Appearance varies with such things as: sex, nutrition, temperature, age, season, iodine content.

Question 15

What are the gross features and location of the thyroid?

Answer 15

Two lateral lobes joined by isthmus, covers top of larynx and trachea

Question 16

Where are the Parathyroid glands located?

Answer 16

On the back side of the Thyroid gland.

Question 17

What is the microscopic structure of the Thyroid gland?

Answer 17

Follicle, Colloid, 2 cell types (Follicular cells, Parafollicular cells (C-cells))

Question 18

What does colloid contain in the Thyroid gland?

Answer 18

Thyroglobulin

Question 19

What are Follicles?

Answer 19

Structural unit of thyroid. Simple epithelium (cuboidal, squamous, columnar), Colloid contains thyroglobulin.

Question 20

What is thyroglobulin?

Answer 20

Gel-like, sometimes rippled

Question 21

What are Follicular Cells?

Answer 21

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. Round nuclei. Synthesize thyroid hormones.

Question 22

What are Inactive Follicular Cells?

Answer 22

“Resting”. Producing basal levels of thyroglobulin. Low cuboidal to squamous. Few mitochondria, small Golgi. Some rough ER in base of cells.

Question 23

What secretes TSH?

Answer 23

Pituitary thyrotrope (Basophil) cells in pars distalis.

Question 24

What are Active Follicular Cells?

Answer 24

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

Question 25

What stimulates Active Follicular Cells?

Answer 25

TSH from pituitary

Question 26

What is a another name for Parafollicular Cells?

Answer 26

C-Cells

Question 27

What are Parafollicular Cells?

Answer 27

Occur singly or in small groups. Between follicular cells and basement membrane. Also within inter follicular connective tissue. Neuroendocrine cells. Synthesize calcitonin.

Question 28

What is the origin of Parafollicular Cells?

Answer 28

Pharyngeal Endoderm

Question 29

What is Calcitonin?

Answer 29

Lowers blood calcium by inhibiting bone resorption. Decreases osteoclast motility and numbers. Promotes excretion of calcium and phosphate from kidneys.

Question 30

What makes Calcitonin?

Answer 30

Parafollicular cells

Question 31

What is Colloid?

Answer 31

Only endocrine gland to store large quantitates of tis secretory product extracellularly (3 month supply in humans). It’s semi-fluid or gel-like. (Sometimes vacuolated adjacent to follicular epithelium. Vacuoles more frequent in active gland)

Question 32

What does Colloid contain?

Answer 32

Thyroglobulin (Made up of Glycoprotein: ~660,000 MW, 3 percent tyrosyl residues - 70 percent of these are available for iodination)

Question 33

What does Colloid uptake?

Answer 33

Iodide. (Basal potion of follicular cells has an active iodide transport pump). Concentrates iodide 10-100x over plasma iodide

Question 34

How is Iodine oxidized?

Answer 34

It is oxidized to iodine at the cell surface. Iodide becomes Iodine via Thyroid peroxidase (TPO).

Question 35

How does the Iodination of thyroglobulin work?

Answer 35

Tyrosine residues only. Occurs extracellularly. Catalyzed by enzymes on the follicular cell surface (thyroid peroxidase (TPO))

Question 36

How is T3 and T4 produced? (step 1)

Answer 36

TSH stimulation. TSH produced by basophils (thyrotropes) in pars distalis of pituitary. Follicle cell height increases. Gland hypertrophy. Accelerated follicular cell metabolism.

Question 37

How is T3 and T4 produced (step 2)?

Answer 37

Pinocytosis of thyroglobulin in colloid. Fusion with lysosomes. Thyroglobulin proteolysis. Eventual formation and release of T3 and T4 to cytoplasm and diffusion to capillaries. T3 and T4 is bound to carrier proteins.

Question 38

What glands are required for survival/essential for life?

Answer 38

Parathyroid Glands

Question 39

What is the Structure of the Parathyroid Gland?

Answer 39

Two pairs located on posterior surface of each lateral lobe of thyroid. Derived from pharyngeal endoderm. Connective tissue capsules separate parathyroids from thyroid.

Question 40

What is the Parenchymal arrangement of the Parathyroid gland?

Answer 40

Anastomosing cored and groups of cells. Poorly defined lobules with fine connective tissue. 3 Cell types.

Question 41

What are the three cell types of the Parathyroid Glands?

Answer 41

Chief (Principle) cells, Oxyphil cells, Fat cells

Question 42

What are Chief (Principle) Cells?

Answer 42

Small cells, most numerous. Vesicular appearing nucleus. Small eosinophilic cytoplasm. Two states. Parathyroid hormone (PTH) production (regulates circulating calcium)

Question 43

What are the two states of Chief (principle) cells?

Answer 43

Resting (little rough ER, small Golgi, few vesicles, much glycogen). Active (much rough ER, large Golgi, numerous vesicles, depleted glycogen)

Question 44

What is Parathyroid Hormone?

Answer 44

Peptide. Involved in regulation of calcium and phosphate levels. Increases blood calcium.

Question 45

How does PTH increase blood calcium?

Answer 45

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.

Question 46

What are Oxyphil Cells?

Answer 46

Larger than chief cells. Smaller and darker-staining nuclei. Large eosinophilic cytoplasm that is finely granular. Many mitochondria. Unknown functions. Derived from chief cells??