Hormones of the adenohypophysis

The gonadotropins, follicle-stimulating hormone and luteinizing hormone, exert their effects on the gonads (ovaries in the female and testes in the male). Taken together, the gonadotropins stimulate the gonads to  

Prolactin (PRL), produced by the lactotrope cells of the adenohypophysis, is involved with the initiation and maintenance of lactation in females. Its function in males is uncertain. Lactation involves three processes  

The release of prolactin from the adenohypophysis is normally inhibited by prolactin-inhibiting hormone (PIH, dopamine) from the hypothalamus. Prolactin secretion is also controlled by prolactin-releasing factor (PRF). The release of PRF from the hypothalamus is mediated by reflexes elicited by suckling and breast stimulation. 

Growth hormone also has many metabolic actions in the body  

The net effects of these actions include enhanced growth due to protein synthesis enhanced availability of fatty acids for use by skeletal muscle as an energy source and glucose sparing for the brain, which can use only this nutrient molecule as a source of energy. 

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The answer is b. (Murray, pp 505-626. Scrivei, pp 5029-5250. Sack, pp 121-138. Wilson, pp 287-320.) Steroid hormones such as aldosterone are ultimate derivatives of cholesterol. The compound illustrated in the question is cholesterol, one of a large group of steroids. Cholesterol, which can be derived from the diet as well as synthesized de novo, is the precursor of all steroids involved in mammalian metabolism. These include the bile acids, the steroid hormones, and vitamin D. Cholesterol cannot be metabolized to carbon dioxide, and water in humans. It must be excreted as a component of bile. Adrenocorticotropin (ACTH) is a peptide hormone of the adenohypophysis that influences the secretion of corticosteroid hormones. Prostaglandins are eicosanoid derivatives that are also made up of... 

It is now firmly established that the synthesis and release of the hormones of the adenohypophysis are controlled by substances released from nerve endings in the hypothalamus and conveyed to the anterior pituitary gland via the portal vessels. The evidence which demonstrated the fundamental importance of the hypothalamus and the hypothalamo-hypophysial portal vessels came mainly from experiments which involved transection of the pituitary stalk, transplantation of the pituitary gland to a site remote from the sella turcica or electrical stimulation of the hypothalamus. 

It is well documented, that for example stress, general malnutrition and Zn-deficiency do modulate immune responses. Furthermore involvement of hormones of the adenohypophysis and adrenal glucocorticoids is reported. Since in some of the in vivo studies the Cd-dosing also induced effects like weight gain reduction, anemia and histo-pathological lesions in non-lymphoid tissues, it remains unclear whether immune effects result from a direct interaction. 

Explain how negative feedback mechanisms limit release of hormones from the adenohypophysis... 

The adenohypophysis does not have a direct anatomical connection with the hypothalamus therefore, regulation of hormone secretion by way of neuronal signals is not possible. Instead, these two structures are associated by a specialized circulatory system and the secretion of hormones from the adenohypophysis is regulated by hormonal signals from the hypothalamus (see Figure 10.2). Systemic arterial blood is directed first to the hypothalamus. The exchange of materials between the blood and the interstitial fluid of the hypothalamus takes place at the primary capillary plexus. The blood then flows to the adenohypophysis through the hypothalamic-hypophyseal portal veins. Portal veins are blood vessels that connect two capillary beds. The second capillary bed in this system is the secondary capillary plexus located in the adenohypophysis. 

Located in close proximity to the primary capillary plexus in the hypothalamus are specialized neurosecretory cells. In fact, the axons of these cells terminate on the capillaries. The neurosecretory cells synthesize two types of hormones releasing hormones and inhibiting hormones (see Table 10.2). Each of these hormones helps to regulate the release of a particular hormone from the adenohypophysis. For example, thyrotropin-releasing hormone produced by the neurosecretory cells of the hypothalamus stimulates secretion of thyrotropin from the thyrotrope cells of the adenohypophysis. The hypo-thalamic-releasing hormone is picked up by the primary capillary plexus travels through the hypothalamic-hypophyseal portal veins to the anterior pituitary leaves the blood by way of the secondary capillary plexus and exerts its effect on the appropriate cells of the adenohypophysis. The hypophyseal hormone, in this case, thyrotropin, is then picked up by the secondary capillary plexus, removed from the pituitary by the venous blood, and delivered to its target tissue. 

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. 

Arterial blood reaches the pituitary gland via the superior hypophyseal artery, a branch of the internal carotid artery. Venous blood is supplied through a venous portal system that originates in the median eminence of the hypothalamus and ends in sinusoidal capillaries of the pituitary gland. This venous system is known as the hypothalamic-hypophyseal portal system. This system carries neurosecretory hormones from the hypothalamus to the adenohypophysis. These hypothalamic factors stimulate or inhibit the release of hormones from the adenohypophysis. Retrograde flow from the adenohypophysis to the median eminence of the hypothalamus is also believed to occur. With upstream flow, pituitary hormones can reach the hypothalamus and influence hypothalamic function through a short feedback loop. 

Prolactin (PRL) is a hormone secreted by special cells of the adenohypophysis. It stimulates and sustains lactation in postpartum mammals, the mammary glands having been prepared by other hormones, including estrogens, progesterone, growth hormone, corticosteroids, and insulin. It also stimulates formation of milk in the crop sac of birds, such as pigeons and doves (an action formerly used for bioassay), is luteotropic m certain mammals, and has many other... 

Growth hormone (GH), somatotropin, somatotropic hormone, STH, a single-chain proteohormone (Mr 21.5 kDa) produced by somatotrophs of the adenohypophysis. GH is an anabolic hormone that regulates the metabolism of proteins, sugars, fats... 

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. 

The adenohypophysis is derived embryonically from glandular tissue, specifically, Rathke s pouch. This tissue originates from the oropharynx, or the roof of the mouth. It then migrates toward the embryonic nervous tissue destined to form the neurohypophysis. When these two tissues come into contact, Rathke s pouch loses its connection with the roof of the mouth and the pituitary gland is formed. Unlike the neurohypophysis, which releases hormones originally synthesized in the hypothalamus, the adenohypophysis synthesizes its own hormones in specialized groups of cells. Similar to the neurohypophysis, however, the release of these hormones into the blood is regulated by the hypothalamus. 

A noteworthy feature of this specialized circulation is that the regulatory hypothalamic hormones are delivered directly to the adenohypophysis by the portal system. Therefore, the concentration of these hormones remains very high because they are not diluted in the blood of the entire systemic circulation. 

In many cases, hormones released from the adenohypophysis are part of a three-hormone axis that includes the ... 

Cortisol is an important component of the body s response to physical and psychological stress. Nervous signals regarding stress are transmitted to the hypothalamus and the release of CRH is stimulated. The resulting increase in cortisol increases levels of glucose, free fatty acids, and amino acids in the blood, providing the metabolic fuels that enable the individual to cope with the stress. A potent inhibitor of this system is cortisol itself. This hormone exerts a negative-feedback effect on the hypothalamus and the adenohypophysis and inhibits the secretion of CRH and ACTH, respectively. 

Thyrotropin (thyroid-stimulating hormone, TSH) and the related hormones lutropin (luteinizing hormone, LH) and follitropin (follicle-stimulating hormone, FSH) originate in the adenohypophysis. They are all dimeric glycoproteins with masses of around 28 kDa. Thyrotropin stimulates the synthesis and secretion of thyroxin by the thyroid gland. 

Connected to the brain by a stalk (Fig. 30-1), the pituitary gland releases at least ten peptide or protein hormones that regulate the activity of other endocrine (hormone-producing) glands in distant parts of the body. The pituitary is composed of several distinct parts the anterior lobe (adenohypophysis), a thin intermediate portion (pars intermedia), and a posterior lobe (neurohypophysis). Each has its own characteristic endocrine functions. 

The adenohypophysis is the part of the gland in which the tropic hormones are secreted They include the adrenocorticotropic hormone lACTHl. die thyrotropic hormone (TSH). and. somatotropin, as well as three hormones with pronounced effects upon the gonads the hormone prolactin, the follicle-stimulating hormone tFSHl and the luteinizing or interstitial cell stimulating hormone tLH or ISCH)... 

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