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-Ex. The hypothalamus releases a releasing hormone→ stimulates anterior pituitary to release thyroid stimulating hormone→ acts on cells of thyroid gland→ hormones produced by thyroid act on target cells causing biological response and feedback to pituitaryand hypothalamus and inhibit them (turning system off) -The Hypothalamic-pituitary-adrenal (HPA) axis is activated by stress. It fluctuates on circadian rhythm (turn system on right before you get up in the morning) -The menstrual cyclebegins with the hormone FSH (follicle stimulating hormone). This hormone is release to the ovary, which causes the maturation of the follicle. As the follicle matures, ovaries begin to secrete estrogen. Estrogen then feeds back to the anterior pituitary. This signals the pituitary to release more FSH and LH (luteinizing hormone), which triggers ovulation. What was the follicle then becomes the corpus luteum, which secretes progesterone. At this point, the fertilized egg either implants or does not. If it does, estrogen and progesterone remain high. If it does not, all hormones drop back off and you get a period. -Sex hormones share a common pathway of synthesis. Sex hormones all begin with a
cholesterol base. The pathway is as follows: cholesterol → progesterone→ testosterone. At this point, the testosterone can either become one of two things. -With the enzyme aromatase, testosterone becomes ESTRADIOL -With the enzyme 5-alpha reductase, testosterone become DHTSexual Development and Behavior-There are two different effects of sex hormones. -Developmental, or organization affects organize the body and brain in some particular way. These effects influence the development on anatomical, physiological, and behavioral characteristics that differentiate sexes. They occur during a critical period (prenatal) and are permanent. -Activationaleffects occur later in life (beginning in puberty), and trigger reproduction-related behavior in mature individuals. These effects are temporary. An example is menstrual cycle, in the sense that without the hormones, the menstrual cycle would cease. -Sex steroid hormones are released by the gonads and can be classified into three types. -Androgens, which are testosteroneand DHT. -Estrogens, which is estradiol-Progestins, which is progesterone-The sex hormone pathway is as follows: cholesterol → progesterone→ testosterone. At this point, the testosterone can either become one of two things. -With the enzyme aromatase, testosterone becomes ESTRADIOL -With the enzyme 5-alpha reductase, testosterone become DHT-In 6 weeks gestation, the primordial gonads identical in XX and XY, and it has the potential to develop into ovaries or testes. -In 8 weeks gestation, the XX develops into ovaries and the XY develops into testes.
-The SRY gene of the Y chromosome triggers the synthesis of SRY proteins: testes determining factor→ gonads develop as testes.