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Superior- a) Diapragma sellae b) Optic chiasma c) Tubercinerium d) Infundibular recess of 3rd ventricle Inferior- a) Irregular venous channels Between two Layers Of Dura Mater b) Hypophyseal fossa c) Sphenoidal Air sinuses
On Each Side- Cavernous sinus & Structures passing through it
Presenting parts The pituitary has two major parts Anterior Lobe / Adenohypophysis Posterior Lobe / Neurohypophysis Differ in their Origin, Structure & Function
Anterior Lobe / Adenohypophysis Ectodermal derivative of the stomatodeum. Highly cellular. Pars Anterior (Pars Distalis Or Glandularis). Pars Intermedia. Pars Tuberalis.
Histology Clusters of epithelial cells surrounded by reticular fibers Sinusoids & Fenestrated capillaries Glandular cells are arranged in irregular clumps or cords between a network of capillaries Types of cellschromophobe cellschromophil (acidophil and basophil ) cells.
chromophobe cells 50% of population Inactive precursor or degranulated after release of their most of hormonal content EM shows few granules inside.
Chromophil cells 50 % population Contains cytoplasmic granules The contents of the secretory vesicles are responsible for the staining characteristics of the chromophil cells.A. Acidophil cells (or acidophils)B. Basophil cells (or basophils)
A) Acidophil cells (or acidophils) 40 % of parenchyma Stains with Eosin, Acid Fuschin, Orange G of Azan, azocarmine frequent subtype of acidophils are the somatotrophs (stained with the dye orange G). Somatotrophs produce growth hormone (GH or somatotropin), which e.g. stimulates liver cells to produce polypeptide growth factors which stimulate growth (e.g. somatomedin which stimulates epiphyseal cartilage ) overproduction of this hormone may result in gigantism or acromegaly
Mammotrophs (or lactotrophs) , the second group of acidophils, secrete prolactin. Their number increases significantly in late pregnancy and the early months of lactation
B) Basophil cells (or basophils) 10 % of Parenchyma Stains poorly with Haematoxylin PAS staining Secrete Trophic hormonesThyrotrophs produce thyroid stimulating hormone (TSH or thyrotropin).Gonadotrophs produce follicle stimulating hormone (FSH), which stimulates the seminiferous epithelium in males in addition to early follicular growth in females. Gonadotrophs also produce luteinizing hormone (LH), which stimulates production of testosterone by Leydig cells in males in addition to late follicular maturation, oestrogen secretion and formation of corpus luteum in females.
Corticotrophs (or adrenocorticolipotrophs) secrete adrenocorticotropic hormone (ACTH or corticotropin) and lipotropin (LPH, no known function in humans). Corticotropes are the most frequent cell type in the pars intermedia. In the pars intermedia, the precursor of ACTH and LPH undergoes further hydrolysis into melanocyte stimulating hormone (MSH, increased pigmentation in patients with Addisons disease) and a number of other peptides (among them endogenous opioids e.g endorphin ).
Posterior Lobe / Neurohypophysis Neurohypophysis is a diencephalic downgrowth connected with the hypothalamus Neural Lobe Or Pars Posterior Median Eminence Infundibular Stem
consists of unmyelinated nerve fibers derived from neurosecretory cells of the supraoptic & paraventricular hypothalamic nuclei and pituicytes.(Near the posterior lobe, astrocytes are replaced by pituicytes ) oval or round nuclei of the pituicytes are visible Hypothalamic nerve fibers typically terminate close to capillaries Herring bodies - Scattered, large, and bluish-violet (in PAS/Orange G stained sections) masses represent dilations of these nerve fibers . Contain neurosecretory products of the hypothalamic cells.
In early fetal life the neurohypophysis contains a cavity continuous with the third ventricle Axons arising from groups of hypothalamic neurones (e.g. the magnocellular neurones of the supraoptic and paraventricular nuclei) terminate in the neurohypophysis. The long magnocellular axons pass to the main mass of the neurohypophysis They form neurosecretory hypothalamohypophyseal tract and terminate near the sinusoids of the posterior lobe.
Some smaller parvocellular neurones in the periventricular zone have shorter axons, and end in the median eminence and infundibular stem among the superior capillary beds of the venous portal circulation. These small neurones produce releasing and inhibitory hormones, which control the secretory activities of the adenohypophysis via its portal blood supply.
The neurohormones stored in the main part of the neurohypophysis are vasopressin (antidiuretic hormone; ADH), which controls reabsorption of water by renal tubules , and oxytocin, which promotes the contraction of uterine smooth muscle in childbirth and the ejection of milk from the breast during lactation. Storage granules containing active hormone polypeptides bound to a transport glycoprotein, neurophysin, pass down axons from their site of synthesis in the neuronal somata. The granules are seen as swellings along the axons and at their terminals, which can reach the size of erythrocytes
Development Prior to neurulation cell populations which give rise to these two portions of the pituitary gland are found next to each other within the rostral portion of the floor of the neural plate and the contiguous midline neural fold. Asneurulation proceeds the future neurohypophysis remains within the floor of the prosencephalon. The cells of the future adenohypophysis are displaced into the surface ectoderm, where they form hypophyseal placode in close apposition and adherent to the overlying prosencephalon.
development of the adenohypophysis progresses by the ingrowth of a mesenchymal stroma. Differentiation of epithelial cells into stem cells and three differentiating types is said to be apparent during the early months of fetal development. It has been suggested that different types of cells arise in succession, and that they may be derived in differing proportions from different parts of the hypophyseal recess. A craniopharyngeal canal, which sometimes runs from the anterior part of the hypophyseal fossa of the sphenoid to the exterior of the skull, is often said to mark the original position of the hypophyseal recess. Traces of the stomodeal end of the recess are usually present at the junction of the septum of the nose with the palate.
Just caudal to, but in contact with, the adenohypophyseal recess, a hollow diverticulum elongates towards the stomodeum from the floor of the neural plate just caudal to the hypothalamus this region of neural outgrowth is the neurohypophysis.
3rd week- hypophyseal diverticulum 5th week – diverticulum elongates & lower end constricted 6th week- connection with oral cavity cut off. At birth the hypophysis is about one-sixth the weight of the adult gland about one-half the weight of the adult gland at 7 years, attains adult weight at puberty. Throughout postnatal life the gland appears larger in females, in both size and weight.
Hypothalamic control Hypophysiotropic area of hypothalamus Cresentic band- from preoptic area to arcuate nucleus Axons of neurons from this area conveys releasing or inhibitory hormones to fenestreated upper radicals of portal vessels in median eminance & infundibular stem
TRH- secreated by dorsomedial nucleus LHRH- Preoptic area & anterior hypothalamus CRH- supra-optic & paraventricular nucli GRH- Ventero-medial nucleus GIH(Growth Inhibiting Hormone)- periventricular nucleus PRH-location is nt yet known PIH- Arcuate nucleus, dopaminargic. Dopamine inhibits Prolactin release
Pharyngeal hypophysis A small collection of adenohypophyseal tissue lies in the mucoperiosteum of the human nasopharyngeal roof By 28 weeks in utero it is well vascularized and capable of secretion, receiving blood from the systemic vessels of the nasopharyngeal roof. covered posteriorly by fibrous tissue This is replaced in the second half of fetal life by venous sinuses, and a transsphenoidal portal venous system develops The peripheral vascularity of pharyngeal hypophysis persists until about the fifth year Though it does not change in size after birth in males, in females it becomes smaller, returning to natal volume during the fifth decade
Reserve of potential adenohypophyseal tissue may be stimulated, particularly in females, to synthesize and secrete adenohypophyseal hormones in middle age, when intracranial adenohypophyseal tissue is beginning to fail.
Applied AnatomyEffect of pressure1. Sella turcica enlarged- headache due to stretching of dura2. Nasal discharge if sphenoidal sinus involved3. Upward spread- pressure on optic chiasma- bitemporal hemianopia4. Obesity- Frohlich’s Syndrome ( involvement of satiety centre in hypothalamus)5. Raised CSF Pressure6. Exopthalmos & Opthalmoplegia
Disturbance of endocrine function1. Adenoma of acidophils- giagantism in childrens , acromegaly in adults2. Basophil adenoma – cushing syndrome ( excess ACTH)3. Chromophobe adenoma – hypopituitarism4. Post. Lobe – diabetes insipidus