Histology of Endocrine system.

Endocrine System

Dr..Deepak N.KhedekarAsst professor

Dept of Anatomy

LTMMC & GH,MUMBAI2013.

The Endocrine System…

• This system is comprised of a variety of ductless glands. • Some exist as discrete organs, while others are associated with

exocrine glands and/or found within complex organs. • All endocrine glands secrete their products (hormones) into

the connective tissue surrounding the secretory elements; from there, those products enter the blood or lymph, in which they travel to their target organs.

• While protein and steroid hormones differ in mechanism, the effects of both are mediated by specific receptors in their target cells.

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Hormones …

– are “messenger molecules”– Circulate in the blood– Act on distant target cells– Target cells show receptors to respond to the hormones– The effects are dependent on the programmed response of

the target cells– Hormones are just molecular triggers

• Basic categories of hormones…

– Amino acid based: modified amino acids (or amines), peptides (short chains of amino acids), and proteins (long chains of amino acids)

– Steroids: lipid molecules derived from cholesterol

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Endocrine Organs

• Cells forming endocrine organs– Pituitary gland– Thyroid gland– Parathyroid glands– Adrenal: 2 glands Cortex

Medulla

-Pineal gland

• Endocrine cells in other organs– Pancreas– Thymus– Gonads– Hypothalamus

• Isolated endocrine cells-APUD cell system

Pituitory gland…

1.Hypophysis (Pituitary Gland)

• The hypophysis consists of glandular(Adenohypophysis) &

nervous portions(Neurohypophysis)

At low power, identify: • Adenohypophysis: Pars anterior (pars distalis; anterior pituitary). Pars intermedia( remnant of rathke pouch rudimentary in human

beings) . Pars tuberalis • Neurohypophysis: Pars nervosa ( posterior pituitary) consist of median eminence

and infundibulum.

Hypophysis cerebri…

Anterior Pituitary (Pars Distalis /Pars Anterior)• Cells can be divided into two classes on

the basis of their staining characteristics:• Chromophils ("color-loving"), and

chromophobes ("color-fearing"). • Chromophils are further classified as

acidophils and basophils.

• Each cell type produces only one type of hormone.

• parenchyma consists of secretory epithelial cells arranged in anastomosing cords and clusters.

• Abundant sinusoidal capillaries with fenestration

Anterior pituitory…Chromophil:

Acidophils ; strongly-staining, acidophilic

cytoplasm due to granules. cells are larger,most abundant

than chromophobes. well developed cell outline

Basophils- Cells are variable in sixe and

shape with basophilic cytoplasm.

secretory granules responsible for the staining characteristics of these cells are.

Anterior pituitory…

Chromophobe-

clear, faintly-staining, sparse cytoplasm.

Do not have granules Indistinct cell outline Represent chromophil

without granules or stem cells Sinusoidal Capillaries in

Anterior Pituitary Chromophil granules are

dense cored vesicles

Pars Intermedia…

• Intermediate portion of pituitary

• part of the adenohypophysis, • is non-neural. • composed of a thin layer of

epithelial cells, which enclose colloid-filled spaces.

• Identify colloid vesicles, and the surrounding low columnar cells .

Pars Nervosa…• is a downgrowth from the

hypothalamus • Exhibits characteristics of nervous

tissue.• Axon terminals within this area

originate from cells in the hypothalamus; those in the supraoptic nucleus produce ADH (vasopressin), while those in the paraventricular nuclei produce oxytocin.

• Cell bodies of these neurons are located in the hypothalamus,

• The pars nervosa contains no neuronal cell bodies.

Pars nervosa…

• Pituicytes : Glial cells, variable in cell size

and shape. barely visible having orange

stained cytoplasm.• Herring bodies: large unmyelinated axon

terminals, containing large numbers of neurosecretory granules.

Rich capillary network present in pars nervosa

Thyroid gland…

Thyroid Gland-General Structure

• It stores the inactive form of hormone extracellularly in follicles .

• General Structure. Identify … connective tissue capsule . connective tissue septa that

divide the bilobed gland into lobules .

follicles -of various sizes, filled with pink-stained colloid

and lined by cuboidal epithelial cells. These are the

functional units of the thyroid gland.

follicle size varies inversely with secretory activity.

Interfollicular regions – the presence of connective tissue,

sinusoidal capillaries into which hormone is released)

parafollicular cells

Thyroid Follicles• Follicular epithelium: vary from high cuboidal to low

cuboidal ; reflects the level of follicle secretory activity.

follicle cells (principal cells) have large, centrally- or basally-located nuclei,

cells active in protein secretion. Storage and release of thyroid

hormones involves the protein thyroglobulin .

Parafollicular Cells Found scattered singly or in

small groups present in periphery of the follicles ,

cells are responsible for production of calcitonin, a peptide hormone that is synthesized and secreted independently of thyroid hormone.

Also called C, clear, or light cells.

Parafollicular Cell…

can be distinguished from follicular cells because they are large oval have eccentrically-placed nuclei and extensive, but lightly-stained cytoplasm.

They are placed in periphery of follicles

Thyroid gland…

Parathyroid Glands…

General Structure : Thin C.T. capsule that

surrounds each gland and gives rise to internal septa.

glands are actually embedded in the capsule of the thyroid gland.

Parathyroid Glands-Parenchyma

present as a mass of crowded single cells, not arranged as follicles. It consist of 2 type of cells:

Chief cells (principal cells): Numerous ,small cells with

prominent nuclei, and the pale,scant cytoplasmic staining.

Parathyroid Glands…

Oxyphil cells: single or clumps of larger

cells with acidophilic (oxyphilic), cytoplasm with dark staining nucleus.

Number inrease with age. Oxyphil cells are not

always present in a section of parathyroid gland.

Adrenal gland…

Adrenal Glands…

Like the pituitary, they are composed of two distinctly different components, one of mesothelial origin and one of neural origin .

General Structure • outer cortex , and the inner medulla .

These zones are readily observed even in a fresh, unstained section.

• 3 histological zones of the cortex. • tough connective tissue capsule and

radial trabeculae that extend into the cortex.

• Prominent central vein in the medulla.

Adrenal Cortex…

• The cortex is divided into three layers:– Zona glomerulosa– Zona fasciculata– Zona reticularis

reticularis

medulla

capsule

Adrenal Cortex: Zona Glomerulosa

Identify…• outermost cortical layer , and

note the presence of columnar epithelial cells arranged in long cords that appear as ovoid clumps when cut in cross-section.

• cytoplasm is pink and relatively scant contain lipid droplets.

• capillary sinusoids are abundant.

Adrenal Cortex: Zona Fasciculata…

• Note that this is the broadest, lightest-staining of the three cortical zones, with epithelial cells that have large, abundant, poorly-stained cytoplasm.

• Cells are arranged in vertical columns of radial plates

• Identify capillary sinusoids between cords of secretory cells.

Adrenal Cortex: Zona Reticularis…

• Note that the epithelial cells of this innermost, prominently stained zone are arranged in irregular, anastomosing cords and clumps with wide capillary sinuses intervening.

• Note that the secretory cells are small, with relatively darkly stained cytoplasm that may contain yellow pigment.

Adrenal Medulla: Chromaffin Cells• Derived from neural crest, cells

of the medulla are functionally equivalent to postganglionic sympathetic neurons.

• Chromaffin cells. The secretory cells of the medulla contain catecholamines (norepinephrine and epinephrine) in cytoplasmic granules that are oxidized to a brown color by potassium bichromate (the chromaffin reaction).

Adrenal Medulla: Chromaffin Cells

Note that chromaffin cell cytoplasm is quite basophilic, compared to the acidophilia of the adjacent zona reticularis.

Note that the cells are arranged into tight clumps, with wide capillaries and venous channels intervening .

Adrenal Medulla: Blood Supply

• The medullary capillary network receives blood from a capsular plexus both indirectly, via cortical capillary sinusoids, and directly, via small arteries passing through the cortex from the capsule.

• Identify the extensive network of dilated capillaries in the medulla.

Pineal Gland-General Structure

• The pineal gland is an evagination of the diencephalon of the brain, and contains highly modified neurons called pinealocytes.

General structure • Under low power, identify trabeculae that

arise from pia mater. Trabeculae divide the pineal parenchyma into indistinct lobules.

Pineal Gland-Parenchyma

• The parenchyma contains two cell types, pinealocytes and neuroglia.

• The pinealocytes are modified neurons. • You will not need to distinguish these two cell

types.

Pineal Gland-Pineal Sand

• Basophilic, extracellular concretions . They are often calcified, which makes the pineal gland an excellent radiological marker, particularly of the midline.

Epiphysis (Pineal Gland)

• The pineal is innervated by unmyelinated axons of postganglionic sympathetic neurons. This is an unusual example of a central nervous system structure that receives sympathetic innervation.

• Presence of a rich vascular supply characteristic of all endocrine glands.

Endocrine Pancreas: Islets of Langerhans

• The pancreas is a mixed exocrine and endocrine gland.

General Structure • Note that islet cells are found as

clumps of small secretory cells with relatively lightly-stained cytoplasm present in connective tissue .

• Compare their appearance to that of the prolific protein-secreting cells of exocrine pancreatic acini .

• Identify the rich network of capillaries that characterize all endocrine organs.

Islet of Langerhans…

• Consist of 3 types of cells Alpha cells (30%) Stains pinks present

more on peripheral region

Beta cells (70%) Stains blue

More in the centre Delta cells

Least in no.

Clinical Histology1.Goiter (Multinodular)

• common cause of overactivity of the thyroid gland (hyperthyroidism).

• Increased TSH production results in the formation of characteristic large nodules .

• Rx- surgical removal of part of the thyroid, or by injection of radioactive iodine

2.Graves Disease (hyperthyroid)– Follicles are very small (little

colloid)– Colloid appears to have open

spaces along its edge scalloped edges (common to hyperthyroidism

3. Hashimoto's Thyroiditis:• Autoimmune condition in

which the immune system attacks the thyroid, causing a reduction in the number and size of follicles.

• Rx replacement/ admin. of thyroid hormone.

4.Adrenal Atrophy:– Hypoplasia (decrease in cells) usually in the cortex

but also gaps in the medulla– Proliferation of parenchymal cells

5.Adrenal Pheochromocytoma:– Benign condition where Medulla is enlarged and

represents the majority of the adrenal gland – Large, bizarre looking nuclei (large and dark-

staining)– Large vascular spaces

5.Hyperparathyroidism (bone):– Within the bone spicules, you can see osteoclasts

degrading the bone (more osteoclasts than usual)– osteoclasts are multinucleate

6.Parathyroid Oxyphil Adenoma:– Identify healthy parathyroid for its darkly staining

chief cells, pink oxyphil cells, and fat throughout– Tumor is made entirely of oxyphil cells – Monoclonal proliferation= tumor composed of 1 type

of cell)

7.Pituitary Acidophilic Adenoma:– Tumors tend to be in the anterior pituitary; monoclonal

proliferations of 1 of the 3 common anterior pituitary cells– In this case, it is an acidophilic adenoma so the

cytoplasms are predominantly pink-staining– Acidophils make hormones that serve non-endocrine

glands (ex. Mammary gland)

8.Type II Diabetes (pancreas):– Enlarged islets of Langerhans– Hyaline deposits in the islets (pinker than usual)

Thank u.