Term
| The Hypothalamus-pituitary complex |
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Definition
The hypothalamus-pituitary complex secretes into the circulation eight major hormones that regulate:
growth, production and ejection of milk and growth of the mammary glands, water metabolism, and the functions and endocrine secretion of the thyroid gland, adrenal cortex, and gonads. |
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Term
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Definition
| Consists of groups of glandular epithelial cells that synthesize and secrete six major hormones into a network of capillaries that deliver these hormones into the blood circulation The cells of the anterior pituitary do this when they are told to do so by special hormones synthesized by groups of neurons located in specific nuclei in the hypothalamus. These hormones (there are at least seven of them) are called release and release-inhibiting hormones, because they either stimulate or inhibit the release of hormones from the cells of the anterior pituitary. |
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Term
| The hypothalamus releases 7 hormones |
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Definition
1) Corticotropin-releasing hormone (CRH)
2) Gonadotropin-releasing hormone (GnRH)
3) Somatostatin (growth hormone release-inhibiting hormone)
4)Growth hormone releasing hormone (GRH)
5) Prolactin release inhibiting facto (PIH - may be dopamine)
6) A possible prolactin releasing factor (PRH)
7) Thyrotropoin releasing hormone |
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Term
| Hormones Released by the anterior pituitary |
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Definition
1) Grown hormone (GH = somatropin)
2) Adrenocorticotropic hormone (ACTH)
3) Thyroid stimulating hormone (TSH)
4) Prolactin
5) Luteinizing hormone (LH) - 1 of 2 that goes to the gonads
6) Follicle-stimulating hormone (FSH) - second hormone |
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Definition
| goes to the Thyroid and makes thyroid hormone |
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Definition
| goes to the Adrenal cortex and makes cortisol |
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Definition
| goes to the gonads and makes the gonadal hormones |
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Definition
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Definition
| goes to tissue growth, and liver, makes somatomedin |
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Term
| Growth Hormone (GH= Somatotropin) |
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Definition
| Growth hormone, also known as somatotoropin is a 191-amino acid protein. After synthesis by the very numerous somatrophs of the anterior pituitary, the hormone is stored in large secretory granules. Unlike many of the anterior pituitary hormones, growth hormone has many different actions on many different cells and tissues of the body. Somatrotropin has achieved some publicity recently, because dairy farmers have found that bovine somatotropin (BST) increases milk yield in cattle by up to 25% |
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Definition
| many of the growth-stimulating action of growth hormone are really due to somatomedin (insulin-like growth factor [IGF]), which is secreted mainly by the liver under the influence of growth hormone. |
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Term
| Release of GH is stimulated by... |
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Definition
Growth-hormone-releasing-hormone (GHRH). GHRH is secreted by neurons of the hypothalamus. Many, many factors stimulate release of GH. They probably operate through the hypothalamus and GHRH. These numerous factors include:
low blood glucose, low blood free fatty acids, a high-protein meal, certain amino acids (e.g. arginine), acute starvation, stress, onset of deep sleep, puberty, and thyroid hormone. |
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Term
| Release of GH is inhibited by... |
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Definition
| Somatostatin. It is secreted by neurons of the hypothalamus (note that somatostin is found in other areas of the brain and in other places in the body, such as the pancreas, where it also plays an inhibitory role). GHRH and somatostatin therefore have antagonistic actions on the release of growth hormone. Factors that inhibit GH release and probably operate through the hypothalamus and somatostatin include high blood glucose, high blood free fatty acids, adequate nutrition, and old age. |
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Term
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Definition
| GH inhibits its own secretion by negative feedback control. Thus, GH stimulates the release of somatostatin from neurons in the hypothalamus. Somatostatin then inhibits the release of GH by cells of the anterior pituitary. Neurons of the hypothalamus also release somatostatin in response to somatomedin (insulin-like growth factor [IGF]). Somatomedin is secreted mainly by the liver in response to increased levels of growth hormone. This constitutes another negative feedback loop. |
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Definition
-Regulates the body’s glucose, protein and fat metabolin.
-Too much of it can cause Gigantism.
-Too little causes stunted growth or dwarfism. |
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Term
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Definition
| growth hormone stimulates the liver to produce somatomedin Most of the growth-stimulating action of GH are actually due to somatomedin, which is released from the liver by the action of GH. Somatomedin is one of a group of “growth factors” involved in growth. Somatomedin is released malignly by the liver in response to the stimulation of GH. An alternative name for somatomedin is insulin-like growth factor [IGF]. Somatomedin stimulates growth of bone and cartilage. As noted before, aomatomedin has negative feedback effects on the secretion of GH by the anterior pituitaty because it stimulates the hypothalamus to secrete somatostatin. Somatostatin inhibits the secretion of growth hormone by cells of the anterior pituitary. |
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Term
| Variation in amounts of GH through life |
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Definition
| GH secretion rises sharply during puberty, then drops backs down during adult life, and then drops again to quite low levels in the aged. |
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Term
| Variation in growth hormone secretion during the day |
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Definition
| the secretion of growth hormone pulses every two hours, and there is a regular peak at night, about 1 hour after the onset of deep sleep. |
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| Suspected abuse of GH by athletes |
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Definition
| Human growth hormone is not known to improve athletic performance, but according to federal enforcement officials, people who have been busted for anabolic steroid abuse have always been found to have high levels of GH in their circulation |
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Term
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Definition
| The CRH-ACTH-Cortisol Axis involves the hypothalamus (which secretes CRH), the anterior pituitary (which secretes ACTH in response to CRH), and the adrenal cortex (the main response to ACTH is to secrete cortisol). |
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Term
| Adrenocorticotropic hormone |
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Definition
| is a 39 amino acid peptide. Unlike GH, adrenocorticotropic hormone acts specifically on certain cells of the adrenal cortex, regulating their growth and causing release of the adrenal cortical hormones |
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Term
| Adrenal cortical hormones |
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Definition
| cortisol sex hormone precursors aldosterone |
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Term
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Definition
| Aldosterone is mainly uder the control of the renin-angiotensin system. Aldosterone belongs to the steroid hormones known as mineralocorticoids. |
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Definition
1) Release of ACTH is stimulated by a peptide hormone called corticotropin hormone releasing hormone (CRH) -Secreted by neurons of the hypothalamus
2) Negative feedback -ACTH may inhibit its own secretion by decreasing CRH release - this is “short-loop negatice feedback.” Cortisol also inhibits ACTH and CRH release, another example negative feedback. The system is referred to as the “CRH-ACTH-corticol axis.”
3) Variation in secretion throughout the day ACTH is released in pulses throughout the day and night, but there is a large is a large increase in total ACTH secretion about 2-4 hours before you wake up in the morning.
5) Effect of stress ACTH secretion is stimulated by stress (low blood glucose, trauma, infection) and anxiety and depression. In fact, CRH, ACTH and cortisol are all very important in the body’s reactions to stress |
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Term
| Melanocyte-stimulate hormorne (MSH) Addison disease |
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Definition
-found in animals, but very little in humans -make large amounts of melanin
-very similar to ACTH Addison’s disease, where the adrenal cortex fails to produce adrenocortical hormones, and so there is a loss of the negative feedback inhibition on secretion of ACTH by the pituitary gland. Therefore, ACTH is secreted in large quantities. Causes pigmentation of the skin. |
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Term
| TRH-TSH-THYROID Hormone axis |
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Definition
| The TRH-TSH-Thyroid Hormone axis involves the hypothalamus (which secretes TRH), the anterior pituitary (which secretes TSH in response to TRH), and the thyroid (which secretes thyroxine and triiodothyronine in response to TSH). |
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Term
| Thyroid-stimulating hormone (=thyrotropin) |
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Definition
| is a glycoprotein that regulates the growth and metabolism of the thyroid gland, and the secretion of its hormones thyroxine (T_4) and triiodothyronine (T_3). The other thyroid hormone, calcitonin, is not controlled by the anterior pituitary. |
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Term
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Definition
1) Synthesis and secretion of TSH is stimulated by thyrotropin-releasing hormone (TRH).
-Secreted by neurons of the hypothalamus.
2) Negative Feedback control.
-Negative feedback of TSH secretion is mainly via the action of thyroxine and triiodothyronine, which block the action of TRH on the cells of the anterior pituitary. The thyroid hormone seem to act on the hypothalamus as well, by reducing the synthesis of TRH. The system is referred to as the “TRH-TSH-thyroid hormone axis”
3) Exposure to cold -In new-born infants, acute exposure to cold increases plasma TSH, which increases the amount of thyroid hormones and therefore the metabolic rate. The effects is insignificant in adults.
4) Secretion throughout the day.
-Plasma TSH secretion rises in late afternoon or evening and peaks around mid night, preceding the onset of deep sleep. |
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Term
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Definition
| Prolactin is a 198 amino acid protein. In humans, its major function is the regulation of mild production, but it also plays a role in breast development (together with other hormones, such as estrogen). During pregnancy, the concentration of prolactin in the plasma may increase by as much as ten times. After the infant is born, the prolactin levells fall, but increases occur during each period of suckling in response to a special reflex initiated by stimulation of the nipple. |
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Term
| Prolactin negative feedback, Variation |
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Definition
| Prolactin inhibits its own synthesis through a negative feedback loop that utilizes dopamine. Prolactin increases during sleep, and peaks about 5-* hours after the onset of sleep. |
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Term
| Hypothalamic-Pituitary-Goadal axis |
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Definition
| involves the hypothalamus (which secretes gonadotropin-releasing hormone), the anterior pituitary (which secretes follicle-stimulating hormone and lutenizing hormone in response to gonadotropin-releasing hormone), and the gonads. The proper fuctioning of the “hypothalamic-pituitary-gonadal axis” is essential for gonadal decelopment, growth, puberty, reproductive processes, and sex steroid hormones by the gonads of males and females. |
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Term
| Luteinizing hormone and follicle-stimulating hormone |
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Definition
| LH and FSH are called gonadotropins. They are both glycoproteins that are secreted by the gonadotroph cells of the anterior pituitary. Interestingly, both LH and FSH have chemical structural similarities to TSH and human chronic gonadotropin, which are also glycoproteins. |
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Term
| pulsatile release of FSH and LH |
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Definition
| Starting at puberty and continuing throughout adulthood, both FSH and LH are released in pulses. In women, these pulses are repeated every 1 to 7 hours, depending on the phase of the menstrual cycle. Normal men show about 8 to 10 secretory bursts per day. These pulses are probably due to pulsatile secretion of GnRH. In women, but not in men, there is also a striking monthly periodicity in the amount of LH secreted |
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Term
| FHS LH Feedback inhibition |
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Definition
| There is feedback inhibtion of both LH and FSH by products of the gonads. Testosterone and estradiol inhibit the action of GnRh on the cells of the anterior pituitary, and also the secretion of GnRH by neurons of the hypothalamus. Additionally, feedback inhibition of FSH secretion is specifically carried out by the glycoprotein hormone inhibin, which is secreted by the ovaries and testes |
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Term
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Definition
| Although estradiol has negative feedback effects on the hypothalmic-pituitary-ganadal axis, at high levels it has a positive feedback effect. This is important during the monthly ovarian cycle, and we shall discuss it later. |
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Term
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Definition
| High levels of progestorone inhibit the hypothalmic-pituitary-gonadal axis. Inhibition occurs at high levels of progestorone, another major steroid product of the ovary that is secreted by a structure called corpus luteum after ovulation has occurred. |
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Term
| Action Antidiuretic Hormone (ADH), Also Known as Vasopressin on the kidney |
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Definition
| The major action of ADH is to cause the insertion of special water-selective channels into cells in the collecting ducts of the kidney. This increases the water permeability of the collecting ducts, and leads to the absorption of water from the fluid that is destined to become urine. This fluid is normally very dilute, and in the interests of water conservation our bodies need to absorb some of this water produre a more concentrated urine. An increase in the secretion of ADH would therefore decrease the volume of urine from the body, an effect called antidiuresis. REduction in the secretion of ADH would have the opposite effect - diuresis |
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Term
| Action of ADH on the cardiovascular system |
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Definition
| In addition to its antidiuretic action, ADH can have a very potent effect in constricting arterioles everywhere in the body, incresing the peripheral resistance and arterial pressure. THis is the reason for its alternate name, vasopressin. Release of ADH can become very important in cases of shock, such as hemorhage. |
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Term
| First stimulus of ADH secretion, |
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Definition
| One stimulus of ADH is an increase in the osmotic pressure of the plasma. When the body is deprived of water, the concentration of salts and proteins in the plasma increases, causing an increase in the plasma osmotic pressure. Special osmoceptor cells in in the hypothalamus sense this increase in osmotic pressure, and send excitatory signals to the hypothalamic neurons that secrete ADH causes the kidneys to conserve water and prevent further increase of osmotic pressure. |
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Term
| Second stimulus for ADH, blood |
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Definition
| A second stimulus for ADH secretion is a reduction in blood volume and a decrease in blood pressure. One group of sensory receptors for this response are the so-called “volume” receptors of the cardiovascular system. These are stretch receptors on the low pressure side, located in the atria, vanae cavae and pulmonary arteries and veins. A rise in pressure in the atria increases the firing of these receptors, which inhibits the secretion of ADH. Conversely, a drop in pressure in the atria (due to hemorrhage, for example) decreases the firing of these receptors and causes an increase in the secretion of ADH. |
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Term
| Alcohol’s effect on ADH secretion |
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Definition
| Alcohol is common inhibitor of ADH secretion. As little as 30-90 ml of liquor is sufficient to suppress ADH secretion. Consequently, a large volume of dilute urine is generated when you drink alcohol. Under these conditions, the body may actually become dehydrated. |
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Term
| Hypothalamic diabetes insipidus |
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Definition
| is usually caused by a deficiency of ADH caused by destruction or loss of function of neutons in the suprooptic nucleus and the paraventricular nucleus of the hypothalamus. Urine volumes in a patient with diabetes insipidus may be as high as 12 liters per day compared with normal 1-3 liters. The patient urinates frequently both day and night, must drink large amounts of fluid to replace the water lost. If the patient loses access to fluids, life-threatening dehydration may occur. |
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Term
| Action of oxytocin on the breasts |
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Definition
| Oxytocin causes contraction of special smooth muscle cells (myoepithelial cells), causing milk ejection. |
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Term
| Suckling is the major stimulus for oxytocin release |
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Definition
| Stimulation of sensory receptors in the nipple sends a train of nerve action potentials into the spinal cord up the spinothalamic tract. From relays in the midbrain, they reach the paraventricular nuclei of the hypothalamus and trigger oxytocin release. As suckling continues, there may be stimulation of oxytocin synthesis in the hypothalamic neurons. Note that suckling also stimulates prolactin release. |
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Term
| Oxytocin during pregnency |
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Definition
| oxytosin may cause contraction of the smooth muscle in the uterus in pregnancy. |
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Term
| Oxytocin and ADH during sex |
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Definition
| Both of these hormones are believed to activate certain brain regions in the plesure/reward circuit (such as the nucleus accubens). Recently, there has been particular interest in the role of vasopressin in social behavior. It is though that vasopressin, released into the brain during sexual activity, initiates and sustain patterns of activity that support pair-bond between the sexual partners; inparticular, vasopressin seems to induce the male to become more aggressive towards other males. |
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