Functions of folicle stimulating hormones


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Functions of folicle stimulating hormones

  1. 1. Functions OF FOLICLE STIMULATING HORMONES: Gonadotropins: Luteinizing and Follicle Stimulating Hormones Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are called gonadotropins because stimulate the gonads - in males, the testes, and in females, the ovaries. They are not necessary for life, but are essential for reproduction. These two hormones are secreted from cells in the anterior pituitary called gonadotrophs. Most gonadotrophs secrete only LH or FSH, but some appear to secrete both hormones. As describef for thyroid-simulating hormone, LH and FSH are large glycoproteins composed of alpha and beta subunits. The alpha subunit is identical in all three of these anterior pituitary hormones, while the beta subunit is unique and endows each hormone with the ability to bind its own receptor. PHYSIOLOGIC EFFECTS OF GONADOTROPINS Physiologic effects of the gonadotrophins are known only in the ovaries and testes. Together, then regulate many aspects of gonadal function in both males and female FOLLICLE STIMULATING HORMONE (FSH) FSH is a glycoprotein hormone, produced in the anterior pituitary and released into the blood in response to GnRH (GnRH is released from the hypothalamus).  Glycoprotein hormones are protein hormones with carbohydrate chains. This carbohydrate group protects the FSH molecule from rapid breakdown and metabolism. This shielding group adds to the hormone's half-life, which in most species is several hours.  The FSH is transported to the ovary, enters the developing follicle, and stimulates the granulosa cells to produce oestrogen. Granulosa cells are a type of cells lining the follicle  FSH is also responsible for growth of the follicle, involving both an increase in the number of granulosa cells and secretion of follicular fluid.
  2. 2.  Peak blood concentrations of FSH occur in mid-dioestrus approximately 10 days before ovulation. This stimulates initial follicular growth (not usually palpable within the ovaries). Low concentrations of FSH are found during oestrus.  As the follicle grows, the granulosa cells secrete a hormone called inhibin into the follicular fluid. This hormone is carried, through the vascular system, back to the anterior pituitary where it suppresses the secretion of FSH. LUTEINIZING HORMONE (LH) Similar to FSH, LH is produced in the anterior pituitary and is a glycoprotein hormone, although the carbohydrate group is different from FSH.  LH is released due to the influence of GnRH from the hypothalamus. The LH is transported to the ovary and stimulates the theca cells surrounding the follicle to produce testosterone.  Circulating concentrations of LH are low in the late luteal phase. Initial rise occurs in early oestrus and reaches peak values after ovulation. In the mare, this hormone stimulates major follicular growth, maturation and ovulation. Values decrease as progesterone concentrations (from the developing CL) rise.  Both FSH and LH have two modes of delivery. One mode is "tonic", which maintains low blood hormone levels.  The second mode is a "surge", which results in a sharp increase or peak in the level of the gonadotropin. Both of these delivery modes are required at various times throughout the estrous cycle. CONTROL OF GONADOTROPIN SECRETION The principle regulator of LH and FSH secretion is gonadotropin-releasing hormone(GnRH, also known as LH-releasing hormone). GnRH is a ten amino acid peptide that is synthesized and secreted from hypothalamic neurons and binds to receptors on gonadotrophs. As depicted in the figure to the right, GnRHstimultes secretion of LH, which in turn stimulates gonadal secretion of the sex steroids testosterone, estrogen and progesterone. In a classical negative feedback loop, sex steroids inhibit secretion
  3. 3. of GnRH and also appear to have direct negative effects on gonadotrophs. This regulatory loop leads to pulsatile secretion of LH and, to a much lesser extent, FSH. The number of pulses of GnRH and LH varies from a few per day to one or more per hour. In females, pulse frequency is clearly related to stage of the cycle. Numerous hormones influence GnRH secretion, and positive and negative control over GnRH and gonadotropin secretion is actually considerably more complex than depicted in the figure. For example, the gonads secrete at least two additional hormones - inhibin and activin - which selectively inhibit and activate FSH secretion from the pituitary. FUNCTIONS OF CORTISOLS: Cortisol is an important hormone in the body, secreted by the adrenal glands and involved in the following functions and more:  Proper glucose metabolism  Regulation of blood pressure  Insulin release for blood sugar maintanence  Immune function  Inflammatory response Normally, it’s present in the body at higher levels in the morning, and at its lowest at night. Although stress isn’t the only reason that cortisol is secreted into the bloodstream, it has been termed “the stress hormone” because it’s also secreted in higher levels during the body’s „fight or flight‟ response to stress, and is responsible for several stress-related changes in the body. Small increases of cortisol have some positive effects:  A quick burst of energy for survival reasons  Heightened memory functions  A burst of increased immunity  Lower sensitivity to pain
  4. 4.  Helps maintain homeostasis in the body While cortisol is an important and helpful part of the body’s response to stress, it’s important that the body’s relaxation response to be activated so the body’s functions can return to normal following a stressful event. Unfortunately, in our current high-stress culture, the body’s stress response is activated so often that the body doesn’t always have a chance to return to normal, resulting in a state of chronic stress. Higher and more prolonged levels of cortisol in the bloodstream (like those associated with chronic stress) have been shown to have negative effects, such as:  Impaired cognitive performance  Suppressed thyroid function  Blood sugar imbalances such as hyperglycemia  Decreased bone density  Decrease in muscle tissue  Higher blood pressure  Lowered immunity and inflammatory responses in the body, slowed wound healing, and other health consequences  Increased abdominal fat, which is associated with a greater amount of health problems than fat deposited in other areas of the body. Some of the health problems associated with increased stomach fat are heart attacks, strokes, the development of metabolic syndrome, higher levels of “bad” cholesterol (LDL) and lower levels of “good” cholesterol (HDL), which can lead to other health problems! To keep cortisol levels healthy and under control, the body’s relaxation response should be activated after the fight or flight response occurs. You can learn to relax your body with various stress management techniques, and you can make lifestyle changes in order to keep your body from reacting to stress in the first place. The following have been found by many to be very helpful in relaxing the body and mind, aiding the body in maintaining healthy cortisol levels: Cortisol secretion varies among individuals. People are biologically ‘wired’ to react differently to stress. One person may secrete higher levels of cortisol than another in the same situation. Studies have also shown that people who secrete higher levels of cortisol in response to stress also tend to eat more food, and food that is higher in carbohydrates than people who secrete less cortisol. If you’re more sensitive to stress, it’s especially important for you to learn stress management techniques and maintain a low-stress lifestyle.
  5. 5. (functions of cortisols animation)