3.3.1.3. The Pineal Gland and Gonads

pineal gland et on earthFigure_43_04_01 Figure_43_04_02f Figure_43_04_04The pineal body, also called the pineal gland, is located in the middle of the brain. It secretes melatonin, a hormone that may help regulate the wake-sleep cycle.

The gonads are the main source of sex hormones. In males, they are located in the scrotum. Male gonads, or testes, secrete hormones called androgens, the most important of which is testosterone. These hormones regulate body changes associated with sexual development, including enlargement of the penis, the growth spurt that occurs during puberty, and the appearance of other male secondary sex characteristics such as deepening of the voice, growth of facial and pubic hair, and the increase in muscle growth and strength. Working with hormones from the pituitary gland, testosterone also supports the production of sperm by the testes.

The female gonads, the ovaries, are located in the pelvis. They produce eggs and secrete the female hormones estrogen and progesterone. Estrogen is involved in the development of female sexual features such as breast growth, the accumulation of body fat around the hips and thighs, and the growth spurt that occurs during puberty. Both estrogen and progesterone are also involved in pregnancy and the regulation of the menstrual cycle.

Pineal body (epiphysis)

Secreted hormone From cells Effect
Melatonin Pinealocytes Antioxidant
Monitors the circadian rhythm including inducement of drowsiness and lowering of the core body temperature

Testes

Secreted hormone From cells Effect
Androgens (chiefly testosterone) Leydig cells Anabolic: growth of muscle mass and strength, increased bone density, growth and strength,Virilizing: maturation of sex organs, formation of scrotum, deepening of voice, growth of beard and axillary hair.
Estradiol Sertoli cells Prevent apoptosis of germ cells[5]
Inhibin Sertoli cells Inhibit production of FSH

Ovary

Secreted hormone From cells Effect
Progesterone Granulosa cells, theca cells Support pregnancy:[6]

  • Convert endometrium to secretory stage
  • Make cervical mucus thick and impenetrable to sperm.
  • Inhibit immune response, e.g., towards the human embryo
  • Decrease uterine smooth muscle contractility[6]
  • Inhibit lactation
  • Inhibit onset of labor.

Other:

  • Raise epidermal growth factor-1 levels
  • Increase core temperature during ovulation[7]
  • Reduce spasm and relax smooth muscle (widen bronchi and regulate mucus)

Anti-inflammatory

  • Reduce gall-bladder activity[8]
  • Normalize blood clotting and vascular tone, zinc and copper levels, cell oxygen levels, and use of fat stores for energy
  • Assist in thyroid function and bone growth by osteoblasts
  • Increase resilience in bone, teeth, gums, joint, tendon, ligament, and skin
  • Promote healing by regulating collagen
  • Provide nerve function and healing by regulating myelin
  • Prevent endometrial cancer by regulating effects of estrogen
Androstenedione Theca cells Substrate for estrogen
Estrogens (mainly estradiol) Granulosa cells Structural:

  • Promote formation of female secondary sex characteristics
  • Accelerate height growth
  • Accelerate metabolism (burn fat)
  • Reduce muscle mass
  • Stimulate endometrial growth
  • Increase uterine growth
  • Maintain blood vessels and skin
  • Reduce bone resorption, increase bone formation

Protein synthesis:

  • Increase hepatic production of binding proteins

Coagulation:

  • Increase circulating level of factors 2, 7, 9, 10, antithrombin III, plasminogen
  • Increase platelet adhesiveness
  • Increase HDL, triglyceride, height growth
  • Decrease LDL, fat deposition

Fluid balance:

  • Regulate salt (sodium) and water retention
  • Increase growth hormone
  • Increase cortisol, SHBG

Gastrointestinal tract:

  • Reduce bowel motility
  • Increase cholesterol in bile

Melanin:

  • Increase pheomelanin, reduce eumelanin

Cancer:

  • Support hormone-sensitive breast cancers[9] (Suppression of production in the body of estrogen is a treatment for these cancers.)

Lung function:

  • Promote lung function by supporting alveoli.[10]
Inhibin Granulosa cells Inhibit production of FSH from anterior pituitary

Placenta (when pregnant)

Secreted hormone Abbreviation From cells Effect
Progesterone (Primarily) Support pregnancy:[6]

  • Inhibit immune response, towards the fetus.
  • Decrease uterine smooth muscle contractility[6]
  • Inhibit lactation
  • Inhibit onset of labor.
  • Support fetal production of adrenal mineralo- and glucosteroids.

Other effects on mother similar to ovarian follicle-progesterone

Estrogens (mainly Estriol) (Also Primarily) Effects on mother similar to ovarian follicle estrogen
Human chorionic gonadotropin HCG Syncytiotrophoblast Promote maintenance of corpus luteum during beginning of pregnancyInhibit immune response, towards the human embryo.
Human placental lactogen HPL Syncytiotrophoblast Increase production of insulin and IGF-1Increase insulin resistance and carbohydrate intolerance
Inhibin Fetal Trophoblasts Suppress FSH

Uterus (when pregnant)

Secreted hormone Abbreviation From cells Effect
Prolactin PRL Decidual cells milk production in mammary glands
Relaxin Decidual cells Unclear in humans and animals
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