Hypophysis posterior

Pituitary Hormones. The hormones of the hypophysis (pituitary gland) are quite numerous, being secreted variously in three parts of the gland — the ncurohypophysis (posterior lobel. the adenohypophysis (anterior lithe), and the pars intermedia, which connects the other two. 

Posterior Lobe. The posterior pituitary, or neuro-hypophysis, secretes two hormones antidiuretic hormone (ADH) and oxytocin.2 12 ADH exerts its effect... 

Vasopressin Hypophysis Isolated posterior lobe (rat P2Y) Sperlagh et al. 1999... 

The result of this anatomical characteristic of endothelial cells in the CNS is an increased resistance to water-soluble and ionized drugs entering the brain, and cerebrospinal fluid (CSF), from capillary blood. However, in a few areas of the brain the barrier is absent. These areas include the lateral nuclei of the hypothalamus, the area postrema of the fourth ventricle, the pineal body, and the posterior lobe of the hypophysis. Highly lipophilic compounds can cross the barrier. Tranquilizers such as diazepam and its analogs are known to gain access rapidly to the CSF with a half-life (tm) entry time of less than 1 minute. 

The posterior pituitary gland is the source of circulating oxytocin and vasopressin (iantidiuretic hormone, ADH). These hormones are actually produced in specific nerve cells in the hypothalamus and travel down the axons into the neuro-hypophysis. The structures of oxytocin and vasopressin are shown in Chapter 4. It may be seen that both are nanopeptides with disulfide bonds and that they differ by two amino acids only. Both hormones originate from larger proteins vasopressin from prepressophysin and oxytocin from pro-oxyphysin. These are converted to pressophysin and oxyphysin, respectively (collectively,... 

The pituitary gland (hypophysis) is located at the base of the skull (Figure 50-1) in a bone cavity called the sella turcica (Turkish saddle). The gland is small—1 cm or less in height and width and weighs approximately 500 mg. As discussed previously, the gland is anatomically divided into the anterior (adenohypophysis) and the posterior (neurohypoph-ysis) lobes. A third lobe (the intermediate lobe) is present in most vertebrates and in the human fetus this lobe is rudimentary in the adult human. 

The hypothalamus is a small region of the brain in the ventral aspect of the diencephalon. In the adult human, it is about 2.5 cm in length and weighs about 4 g. Ventromedi-ally, it surrounds the third ventricle and is continuous with the infundibular stalk of the pituitary (hypophysis). This cone-shaped region of the hypothalamus, the median eminence, consists mainly of axonal fibers from hypothalamic neurons, which either terminate in the median eminence or continue down into the posterior lobe of the pituitary, and it is perfused by a capillary network (primary plexus) derived from the carotid arteries. Blood from the primary plexus is transported by portal vessels (hypophyseal portal vessels) to another capillary network (secondary plexus) in the anterior lobe of the pituitary (adenohypophysis) (Figure 31-1). 

The pituitary gland, also referred to as the hypophysis, is located at the base of the brain in a cavity of the sphenoid bone known as the sella turcica. The pituitary is separated from the brain by an extension of the dura mater known as the diaphragma sella. The pituitary is a very small gland, weighing between 0.4 and 1 g in adults. It is divided into two distinct regions, the anterior lobe, or adenohypophysis, and the posterior lobe, or the neurohypophysis (see Fig. 75-1). 

Pituitary, Posterior, Pituamin Di-Sipidin Pitni-trin. Desiccated hypophysis. The cleaned, dried, and powdered posterior lobe of pituitary body of domesticated animals used for food by man. Contains both oxytocin and vasopressin, q.q.v. 

Although the adenohypophysis receives few, if any, nerve fibres, it is linked to the median eminence area of the hypothalamus by a highly specialized portal vascular system from which it receives its entire blood supply. The hypothalamus is supplied with blood by a branch of the internal carotid artery which forms a capillary plexus, the primary plexus, within the median eminence. Hie blood flows into the hypothalamodiypophysial portal vessels which pass down the infundibulum to the adenohypophysis where they break into sinusoidal vessels. The nervous and vascular supplies of the neurohypophysis differ markedly from those of the adenohypophysis. The neurohypophysis is well supplied with nerve fibres, being connected to 2 prominent groups of cells in the hypothalamus, the supraoptic and paraventricular nuclei, by the well-defined supraoptico-hypo-physial tract. There is no vascular link between the hypothalamus and the neurohypophysis but the latter is supplied directly by a pair of posterior hypophysial arteries which originate from the internal carotid arteries. 

The hypophysis is a small, bean-shaped organ (0.6-0.65 g) located in the sella turcica at the base of the skull. On close examination of the gland, an anterior yellowish and a posterior more fibrous and whitish part can be distinguished. The two parts are separated by a pars intermedia, a lamellar structure, grayish and fibrous in appearance. The gland is attached to the floor of the third ventricle by a hollow pedicle, the stalk of the hypophysis. 

The antidiuretic hormone is secreted according to a first-order neuroendocrine mechanism. A central nervous system neuron secretes the active polypeptide, which is transported in the blood to the target organ. This assumption is based on the experiments of Horsley and Clarke, who destroyed the hypothalamic nuclei without affecting the hypophysis itself by approaching the thalamus from above. These experiments demonstrated that destruction of the supraoptic nuclei or of the fiber tracts that lead from these nuclei to the posterior lobe was consistently associated with diabetes insipidus. In contrast, total hypophysectomy does not necessarily induce diabetes insipidus. 

The details of the mechanism triggering the secretion of the neurohypophyseal hormones have not been elucidated, but it is assumed that the release of the posterior lobe hormone depends upon neurostimulation of the axon of the pituitary stalk. Two observations supporting these assumptions are (1) the injection of hypertonic solution into the common carotid artery generates an action potential in the neuron of the paraventricular and supraoptic nuclei and (2) the electrostimulation of the neurohypophyseal track, the median eminence, and the posterior lobe of the hypophysis stimulates ADH release. 

Normal individuals possess a regulatory mechanism that maintains the osmotic pressure of the body fluid at a relatively constant level. This mechanism prevents cells from shrinking or swelling in response to changes in the osmolarity of the body fluid. The water balance is partly regulated by excreting urine of varying tonicities. The urine is diluted in overhydration (decreased osmotic pressure) and is concentrated in dehydration (increased osmotic pressure). Urinary tonicity is controlled by the antidiuretic hormones of the posterior hypophysis. 

Whenever a pathological condition bilaterally destroys the tracks that connect a supraoptic nuclei to the hypophysis, a lack of antidiuretic hormone follows with the excretion of large amounts of water. Many injuries of the posterior lobe of the hypophysis lead to insufficient secretion of posterior lobe hormones. The major manifestation of this disturbance is diabetes insipidus. 

May be responsible for pituitary dwarfism III. Tumors of the posterior lobe of the hypophysis... 

Control of ACTH Secretion. While the neurohypophysis is technically part of the brain, the anterior lobe of the hypophysis is disconnected from the central nervous system except for the existence of a common circulatory system, the portal system of the hypophysis. These differences between the anatomical structures of the anterior and posterior lobes are at the origin of the differences between the mechanisms controlling ACTH secretion. The secretion of ACTH is probably not triggered by any neurosecretory mechanism, like that triggering vasopressin secretion. 

The peptide type of structure is frequently employed for the chemical transmission of messages by means of hormones. An example is provided by the two hormones of the posterior hypophysis of vertebrates, oxytocin and vasopressin. These two polypeptides have been extracted from the gland itself, by rather a drastic treatment such that it still remains debatable... 

The pituitary body, or hypophysis, is double in origin and multiple in functions. From the stomodceal pouch of Rathke is developed the anterior lobe and the -pars intermedia from the floor of the third ventricle are formed the pars nervosa of the posterior lobe, the infundibulum and the tuber cinereum. The pituitary autacoids are of two types secretions acting directly on other tissues, and hormo-kinetic secretions acting indirectly by stimulating other endocrine glands. 

The hypophysis (pituitary gland) is an accessory gland of the brain. It consists of two anatomically distinct organs, the anterior lobe and the posterior lobe, and each lobe elaborates several different hormones. A middle lobe (pars intermedia developed to different extents in different animals), produces another hormone. The second part of Table XVIII (Section 1) lists all the different hypophyseal hormones. Many hormones of the anterior lobe are master hormones (Section 1). 

Neurosecretion. The posterior lobe of the hypophysis contains two hormones, ocytocin and vasopressin, but both are formed actually in the hypothalamus and not in the posterior lobe. It has been demonstrated that the two hormones are synthesized in neurosecretory cells and transported through the axon of the connecting nemon. The whole process is termed neurosecretion. The transported prod-... 

Corticotropin-Releasing Factor. A hormone-like factor found recently in the midbrain affects the adenohypophysis. This factor, like the hormones of the hypophyseal posterior lobe, is a neurosecretion. Progress has been made in its enrichment it may be related to the hormones of the neurohypophysis. It is not yet clear whether this factor is a link in the chain of the self-regulation of the hypophysis-adrenal cortex system, or whether it merely releases the stress reaction. 

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