HYPOPHYSIS CEREBRI-Anatomy.pptx

ANATOMY OF PITUITARY GLAND

1. HYPOPHYSIS CEREBRI WITH ITS MICROSTRUCTURE DR.SRUTHY.K DEPARTMENT OF ORAL PATHOLOGY AND MICROBIOLOGY

2. Hypophysis cerebri (pituitary gland)

3. Pituitary gland The hypophysis cerebri or pituitary gland is an ovoid neuroglandular body suspended from the floor of the third ventricle by a stalk known as the infundibulum. It regulates the secretory activity of many other endocrine glands and tissues; hence the pituitary is sometimes called “the master gland”.

4. COMPONENTS OF HYPOPHYSIS CEREBRI (A)ADENOHYPOPHYSIS CEREBRI:         1- Pars Distalis (pars anterior )         2- Pars Tuberalis         3- Pars Intermedia ( B) NEUROHYPOPHYSIS CEREBRI:          1- Median eminence         2- Infundibulum: Neural ( Infundibular ) Stalk          3- Pars Nervosa

5. SITUATION OF THE PITUITARY GLAND Measurements: Breadth (Transverse) — 12 mm. Length (Antero-posterior) — 8 mm. Weight — 500 mg. Situation: The gland is lodged in the hypo­physeal fossa of sella turcica of the body of sphenoid bone. The fossa is roofed by the diaphragma sellae , which is a fold derived from the meningeal layer of Dura mater and extends from the tuberculum sellae and middle clinoid processes in front to the upper margin of the dorsum sellae and posterior clinoid precesses behind. The diaphragma sellae is pierced in the middle by the infundibulum (pituitary stalk), and is continuous on each side with the roof of the cavernous sinus. The capsule of the gland is adherent to the meninges of the fossa; hence the gland is not surrounded by a film of cerbro -spinal fluid.

6. PRESENTING PARTS The gland consists of an anterior lobe or adeno-hypophysis and a posterior lobe or neuro-hypophysis . In develop­ment, structure and functions these two parts are distinct from each other.

7. GROSS ANATOMY OF ANTERIOR LOBE Anterior lobe: It is highly cellular and occasionally presents an intra-glandular cleft. The part of the gland behind the cleft is known as pars intermedia which is rudimentary in man and embraces the front and side of the posterior lobe. The part extending upward along the infundibular stem is known as pars tuberalis . The rest of the gland in front of the cleft is called pars anterior (pars distalis ). Therefore the adeno-hypophysis consists of three parts—pars anterior, pars tuberalis and pars intermedia .

8. Posterior lobe: It is continuous above with the infundibulum which extends downward and forward from the floor of third ventricle and enters the hypophyseal fossa through an aperture in diaphragma sellae . The neuro-hypophysis consists of three parts— median eminence of tuber cinerium , infundibular stem and pars nervosa. The infundi-bular stem possesses an anterior covering of pars tuberalis and rest belongs to the neuro-hypophysis .

9. MICROANATOMY OF ANTERIOR LOBE: Anterior lobe: The parenchyma of the anterior lobe consists of irregular clusters of epithelial cells supported by reticular fibres and permeated by sinusoids and fenestrated capillary plexuses. The cells consist mainly of two types— chromophobes and chromophils . Chromophobes include 50% of the cells presen­ting agranular cytoplasm. Chromophils belong to the remaining 50% of cells. According to the staining of the cytoplasmic granules, the chromophils are subdivided into acidophil (alpha) and basophil (beta) cells.

10. (a) Acidophils comprise about 40% of paren­chymal cells.. They secrete growth hormone and prolactin, both of which are simple polypeptides. Orangeophil cells secrete growth hormone (GH or STH); hence they are called the soma­totrophs . ( b) The basophil cells secrete most of trophic hormones which are glycoproteins. These include thyroid stimulating hormone (TSH), follicle stimulating hormone (FSH), leutinizing hormone (LH) in female or interstitial cells stimulating hormone (ICSH) in male.

11. Blue arrow: acidophils Red arrow: basophils Yellow arrow: chromophobes

12. Posterior lobe: It consists of unmyelinated nerve fibres, fenestrated plexus of blood capillaries and some special types of neuroglial cells known as pituicytes . The nerve fibres present knob-like terminals, the Herring bodies, which contain membrane-bound secretory vesicles and abut on the surface, of capillaries. The posterior lobe is devoid of blood-brain barrier.

13. POSTERIOR LOBE HISTOLOGY

14. Hypothalamic control on anterior lobe functions HORMONES RELEASED BY ANTERIOR PITUITARY 1 . Thyrotropin releasing hormone (TRH) is a tripeptide and secreted by the dorso -medial nucleus. 2.Luteinising releasing hormone (LHRH) is a decapeptide and is synthesized in the preoptic area and anterior hypothalamus. It stimulates the secretion of LH as well as FSH. 3. Corticotropin releasing hormone (CRH) is produced by the cells in the supra-optic and paraventricular nuclei. 4 . Growth releasing hormone (GRH) is secreted by the ventro -medial nucleus.

15. 5. Growth inhibiting hormone (GIH) also known as somatostatin is secreted by the periventricular nucleus and is a tetra- decapeptide . 6. Prolactin releasing hormone (PRH) the location of secreting neurons is not yet known . 7. Prolactin inhibiting hormone (PIH) is synthesized by the arcuate nucleus which is dopaminergic. Dopamine inhibits prolactin release by means of axo-axonic synapses.

16. HYPOTHALAMIC CONTROL ON POSTERIOR LOBE HORMONES RELEASED BY POSTERIOR LOBE: 1.OXYTOCIN 2.ANTI DIURETIC HORMONE

17. BLOOD SUPPLY OF HYPOPHYSIS CEREBRI: The anterior lobe is supplied by the superior hypo­physeal artery, a branch of internal carotid, which enters the pars tuberalis and breaks up into tufts of capillaries in the median eminence and infundibular stems.

18. Nerve supply of pituitary gland There is definite control of nervous control to anterior lobe but only few fibres from hypothalamo hypophyseal tract of nerve fibres or carotid plexus of cervical sympathatic has been traced.

19. The posterior lobe is supplied by the hypothalamo-hypophyseal tract, which consists of a bundle of about 100,000 unmyelinated nerve fibres derived from the supra­optic and para -ventricular nuclei of the hypo­thalamus. The fibres of the tract reach the neurohypophysis through the infundibular stem and divide into a series of distended Herring bodies containing neuro -secretory vesicles of the hypothalamus. .

20. Applied anatomy • Adenoma • Craniopharyngeoma . •Pharyngeal hypophysis .

21. Pituitary adenoma A pituitary adenoma is a neoplasm of the pituitary gland. These tumours are usually benign and can be divided into two categories:  non-functional tumours  and  hormone secreting tumours . As the tumour increases in size, it can compress surrounding structures, such as the  optic chiasm . A lesion of the optic chiasm characteristically produces a visual defect known as a  bitemporal hemianopia. A pituitary tumour can also cause excessive hormone production, or insufficient hormone production (by destroying the normal glandular tissue ). Definitive treatment of a pituitary adenoma is via  trans- sphenoidal surgery . This technique involves gaining access to the gland via the nasal cavity and sphenoid sinus (which is located immediately inferiorly to the gland)

22. craniopharyngioma Craniopharyngiomas are benign brain tumors arising near the pituitary gland & may cause loss of pituitary hormonal function, visual loss  & headaches. The initial optimal treatment for craniopharyngiomas is maximal safe surgical removal. Fortunately for most patients, craniopharyngiomas can be removed through a keyhole route via the nose using an   endoscopic endonasal approach  or an  eyebrow craniotomy ..

23. Pharyngeal hypophysis

24. references 1.B D Chaurasias dental anatomy 2.Hormones : Definition, Properties and Chemical Natures of Hormones 3.Useful Notes on the Structure of Bone Marrow | General Anatomy 4.Article July  24, 1909 THE HYPOPHYSIS CEREBRI CLINICAL ASPECTS OF HYPERPITUITARISM AND OF HYPOPITUITARISM HARVEY CUSHING, M.D.

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