Endocrine 1

• Hormones


  Substances secreted directly into the blood streams by glands. Chemical that regulates the function of a specific target organ. Hormones act only on the target tissues which bear the specific receptors (extracellular or intracellular) for them. Generally elicits a rapid response in a relatively short period of time when it binds to an extracellular receptor on the surface of a target
• Male Reproductive System Hormones

  • The hypothalamus (part of the brain) control the secretion of the pituitary gland. At puberty (for both male and female), an unknown stimuli trigger the hypothalamus to secrete gonadotropin releasing hormone (GnRH) which is secreted to the blood into the anterior lobe of the pituitary gland and activated the release of Luteinizing hormone (LH) and follicle-stimulating hormones (FSH). In males, LH promotes the cells of the testes and stimulates the secretion of testosterone, the hormone that stimulates the maturity of male reproductive system and development of secondary sexual characteristics: growth of body hair, Increased muscular development, broad shoulders and pelvis and deepening of voice
• Female Reproductive System Hormones

  • In females, the FSH stimulate the ovarian follicle to produce Estrogen. The hormone that stimulates the maturation of the female sex organs and the development of the female secondary sexual characteristics: development of the mammary gland, broad pelvis, growth of body hair, and increase of fat distribution (breast, thighs, and buttocks). After ovulation, the LH will stimulate the remainder of the ovarian follicle known as corpus luteum to secrete estrogen and progesterone. Progesterone – develops and maintain the uterine lining in pregnancy and it also prevents the uterine contractions and dilations of the cervix. It also prepares the mammary glands for milk production. Aside from FSH and LH, the pituitary gland secretes hormones for females whose ovum is fertilized, Prolactin (PRL), a hormone that maintains the production of milk of the mammary glands after giving birth. Oxytocin (OT) is also secreted by the pituitary gland to stimulates the contraction of uterus during childbirth and releases milk by the mammary gland.
• Negative Feedback


  A mechanism that maintains hormone levels in the blood stable
• Phases of Menstrual Cycle

  1. Follicular phase: Estrogen level decreases. The hypothalamus will send GnRH to pituitary gland to release FSH & LH, the hormones that cause a few follicles to develop to maturity. But only one of this follicles will continue to develop.

  2. Ovulation phase: The hypothalamus will send GnRH to release more LH as a positive feedback to the increasing amount of estrogen. The increase of FSH & LH will affect the follicle until it ruptures. The mature egg is released into fallopian tube.

  3. Luteal phase: Begins after the egg is released. As the egg moves from the ovary to the fallopian tube the follicles transforms into corpus luteum. It will continue the secretion of the estrogen and will also begin to secrete progesterone. At day 14 of the cycle the rising estrogen level develops the endometrium of the uterus. The progesterone stimulates the formation of blood vessels in the uterine lining. During the first 2 days of luteal phase, right after the ovulation, the egg has a high chance of being fertilized. High levels of progesterone will send negative feedback that inhibits the secretion of GnRH by the hypothalamus & FSH and LH by the pituitary gland.

  4. Menstrual phase: if the egg is not fertilized after 2 to 3 days, of ovulation, it passes through the uterus without implantation. The corpus luteum disintegrates causing the sudden drop of the estrogen and progesterone level. And this will trigger the breakdown of endometrium (lining of the uterus) The lining will detach itself from the uterine wall and will be discharged through the vagina together with the unfertilized egg and will lead to menstruation.
• If fertilization occurs


  The fertilized egg divides & become a zygote. It implants itself in the uterine lining & releases hormones to keep the corpus luteum functioning To nourish and protects the developing embryo.
• The hypothalamus controls the secretion of hormones from the anterior pituitary by releasing tropic hormones (TRH, GHRH, CRH)
• Thyroid-stimulating hormone (TSH): Stimulates thyroid gland to synthesize and secrete T3 and T4
• The anterior pituitary gland is also known as the adenohypophysis
• The posterior pituitary gland is also known as the neurohypophysis
• Tropic hormones are called TRH, GHRH, CRH
• Growth hormone (GH): Promotes cell division and protein synthesis; increases height and muscle mass; regulates metabolism
• Adrenocorticotropic hormone (ACTH): Stimulates adrenal cortex to secrete glucocorticoids such as cortisol
• Prolactin (PRL): Stimulates lactation in women