Hormones, Homeostasis and reproduction

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  • Hormones, homeostasis, reproduction
    • insulin and glucagon are secreted by alpha and beta cells in the pancreas to control blood glucose concentration
      • 5 mmol -1
      • alpha cells - gucagon if the blood level falls below the set point
        • stimulates the breakdown of glycogen into glucose
      • beta cells - insulin when blood glucose rises above the set point
        • uptake of glucose to glycogen
          • lowers the blood glucose concentration
    • thyroxin is secreted by the thyroid gland to regulate the metabolic rate and help contro the body temperature
      • iodine
    • leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite
    • melatonin is secreted by the pineal gland to control circadian rhythms
      • SCN
        • set a daily rhythm
    • a gene on the Y chromosome causes embryonic gonads to develop as testes and secrete testosterone
      • SRY codes for a DNA - binding protein called TDF
    • testosterone causes prenatal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty
    • estrogen and progesterone cause prenatal development of female reproductive organs and female secondary sexual characteristics during puberty
    • the menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones
      • follicular phase - creation of a egg ready to be fertilised
        • luteal phase - wall of the follicle that releases an egg becomes a body called the corpus luteum
      • FSH rises when menstrual cycle is ending - stmulates the development of follicles
        • Estrogen - end of follicular phase. stimulates the repair and thickening of endometrium. inhibits FSH and stimulates LH
          • LH - end of follicular phase, stimulates completion of meiosis and permits to the follice to release the egg (Ovulation) - progesterone
            • progesterone - luteal phase and thickens the endometrium. lowers production of FSH and LH

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