Histology study

Histological structure of Pancreas

1.     The section showed the following characters:

2.     Two distinct regions are observed: the exocrine pancreas and the endocrine

3.     The exocrine pancreas is composed of numerous acinus.

4.     The acinus is composed of small pyramidal cells, the acinar cells; whose nucleus is situated at the base of the cell.

5.     The acinar cells shows all the characteristic features of a protein secreting cells: presence of golgi bodies, ribosomes, RER,etc.

6.     The endocrine pancreas is a pale staining region also called as the islet of langerhans.

7.     Routine stains shows the presence of two types of cells

A.   the acidophil cells or the α cells and

B.   The basophilic cells or the β cells.

 8.     Using immunocytochemical techniques four types of cells are identified – the A, B, D and F cells.

9.     α cells have regular granules with a dense core surrounded by a clear region bounded by a membrane.

10.                        β cells have irregular granules with a core formed of irregular crystals of insulin.

11.                        Presence of a complex network of capillaries with fenestrated endothelium. 

THYROID GLAND

Introduction

1.     It’s the only endocrine gland that is situated superficially in the body, for this reason reachable for physical examination.

2.     It’s the only endocrine gland that depends on external environment for raw material, iodine, to synthesize its hormones.

3.     It’s the only endocrine gland, which doesn’t pour its hormones into blood immediately after formation but stores them and after that discharges them in blood to be used as and when needed.

4.     It’s one of the organs of the body having an extremely rich blood circulation.

 

Location

The thyroid gland lies in the lower part of the front and side of the neck reverse to Structure

Presence of numerous spherical follicles, the thyroid follicles.

• In each follicle, lie cuboidal or columnar follicular cells on the basement membrane.

• The follicles have a central dark staining nucleus.

• The basal part of the follicular cell is rich in RER.

• The apical pole has a discrete golgi complex and small secretory granules.

The thyroid gland contains 2 types of secretory cells:

1.     follicular

2.     parafollicular.

 

The follicular cells are cuboidal epithelial cells creating the wall of spherical thyroid follicles. They secrete 2 hormones: thyroxine and triiodothyronine.

Thyroglobulin is the storage form of thyroxine and is an iodinated glycoprotein.

• Another kind of cells, called the parafollicular cell is present either as a part of

Functions of thyroxin

1.     These hormones are necessary for normal growth and development, especially of the skeletal and nervous system.

 

 

Thyroid is a bilobed gland. The two lobes lie on either sides of larynx.The two lobes are connected by isthamus. They secrete a hormone called "Thyroxine". It is rich "iodinated hormone". It contains an aminoacid called "Thyroxine". Thyroxine increases the metabolic activities. Hence it maintains B.M.R [Basal metabolic Rate]. The thyroxine is essential for metamorphosis in frog. It is also essential for tissue differentiation

If the thyroid glands are removed in tadpole larva of frog it fails to undergo metamorphosis. When such thyroid free tadpole larva is fed with thyroid glands, it undergoes metamorphosis. If normal young tad poles are fed with thyroxine, they metamorphose into frogs prematurely [the normal period of metamorphosis is reduced].

 In human beings, failure of thyroid secretion in child hood leads to mental retardation. This disease is called "cretinism". Defeciency of thyroid secretion in adults produces "Myxedema". Hyper thyroidsm leads to "exophthalmic goiter" or Grave's disease. Less secretion in the aged persons leads to the swelling of lobes of thyroid. The disease is called simple goitre.

 

 

  T. S. of Pituitary Gland of a Mammal

 

T. S. of anterior lobe of  pituitary gland of a mammal shows the following

histological structures:

1.The pituitary gland is more or less rounded in  shape and occurs at the base of brain just beneath the diencephalon.

2. It composed of three lobes namely , anterior   lobe, intermediate lobe and posterior lobe.

3.The anterior lobe  forms the largest part of the   pituitary gland formed of three distinct kinds of cells differing in their staining reaction :

1.  basophil cells , 
2.  acidophil cells 
3. chromophobes.

4. Usually on the outside are the basophil cells which are stained by basic stains.

5.In the centre are found acidophil or Oxyphil cells   Which take acidic stains.

6.The chromophobe cells are indifferent to either  basic or acid stains. They are found scattered    throughout the anterior lobe.

7.Antrior lobe produces many hormones , namely   somatotrophic hormone , thyrotrophic   hormone, adrenocorticotropic hormone,   gonadotrophic hormone  and , thus , controls   growth , development of sex glands as well as the   activities of thyroid,   parathyroid and adrenal glands.

8.Intermediate lobe is composed of cell cords with  colloid filled  follicles. It produces an  intremedin  hormone.

9.postrior lobe is composed of neuroglial  cells  connective tissue fibres and blood vessels.    It produces Pituitrin, vasopressin, and oxytocin  Hormones.

10.The pituitary gland is an endocrine gland of  utmost importance to organisms. It is called  master gland.            

ADRENAL GLANDS

There are two adrenal or supra renal glands situated longitudinally on the ventral surface of kidneys. These are orange-colored glands. The outer part of each gland is called "cortex" and the inner part is called "medulla". 

The cortex of adrenal gland is stimulated by A.C.T.H. of the pituitary. But medulla is not stimulated by the pituitary gland. The cortex secretes gluco corticoids, mineral corticoids and sex corticoids.

Glucocorticoids:  These increase blood glucose level by the synthesis of glucose from proteins. It is called "gluconeogenesis". Blood glucose level is also increased by the convertion of glycogen to glucose. It is called "glycogenolysis".

Mineral corticoids:  These maintain water and salt balance.

 Sex corticoids: These stimulate the development of secondary sexual characters.

Excessive secretion of sex corticoids in women causes the development of male secondary sexual characters like "beard" and "moustaches". The disease is called "virilism". Defeciency of mineral corticoids leads to bronze pigmentation in skin. The disease is called "Addison's disease".

The central part or medulla of the adrenal gland secretes two amines, "epinephrine" [adrenaline] and "norepinephrine" [noradrenaline]. These regulate the blood pressure, heart beat, respiration, contractions and relaxations of smooth muscles. The epinephrine prepares the individual for meeting stress or emergency. Hence the adrenal medulla is considered as the gland for "fight, fright and flight".