Reproductive Development and Puberty

Hormone Pathways and Phenotype Development

  • Phenotype depends on fully functioning hormone pathways.
  • Major steroid hormone pathway starts with cholesterol, which is essential for hormone production.
  • Key hormones in the pathway:
    • Progesterone: important in the female reproductive cycle.
    • Corticosteroids: include aldosterone and cortisol.
      • Aldosterone: regulates blood pressure, signals to kidneys for salt retention.
      • Cortisol: affects stress, glucose levels, and immune response.
    • Testosterone.
    • Estrogens (estrone and estradiol).
      • The female phenotype is the bodies default pattern.

Androgen Insensitivity Syndrome (AIS)

  • XY chromosomes, but phenotypically female due to inability to respond to androgens.
  • Testes are formed and produce high levels of testosterone, but the body's cells do not respond to it.
  • Can be complete or partial.
  • Lack a uterus and cannot reproduce; have internal testes.
  • Female phenotype is the default pattern in the absence of androgen activity and receptivity.

Hormone Intermediaries and Their Roles

  • Hormone pathways have other hormones as intermediaries.
  • Testosterone and estrogens are of primary interest.

Androgens and Puberty

  • Androgens promote sexual differentiation at birth and puberty.
  • Induce and maintain secondary sexual characteristics (body hair, widening of hips, Adam's apple).
  • Have anabolic effects (muscle growth).

Steroid Use and Health

  • Artificial steroids can induce adverse effects.
    • In men: diabetes and heart problems.
    • In women: liver damage.

Cholesterol and Hormone Conversion

  • Cholesterol is converted to progesterone, which is crucial in the female reproductive system.
  • Progesterone follows different pathways to corticosteroids.
  • Testosterone and estrogen are produced in smaller amounts compared to corticosteroids.
  • The size of the arrows in the pathway diagrams indicates the relative amounts of hormone production.

Estrogens and Female Development

  • Estrogens stimulate secondary sexual characteristics in females.
  • Androgen insensitivity syndrome may not be detected until puberty due to lack of estrogen response.
  • Small amount of oestrogen produced until puberty.
  • Regulate the secretion of other hormones; both testosterone and estrogen are present in both sexes, but in different balances.

Interruption of Hormone Pathways

  • Interruptions in hormone pathways due to mutations can lead to less typical phenotypes.
  • Androgen insensitivity syndrome and other conditions can affect phenotype at birth.

Five Alpha Reductase Deficiency

  • Genetically male (XY chromosomes) but deficient in the enzyme that converts testosterone to dihydrotestosterone (DHT).
  • DHT is essential for the development of the internal genitalia, penis, and scrotum.
  • Without sufficient DHT, infants may appear as little girls.
  • At puberty, a surge of testosterone can lead to the emergence of male characteristics.
  • Common in some communities and is inherited (Dominican Republic and Papua New Guinea).

Congenital Adrenal Hyperplasia (CAH)

  • Deficiency in the enzyme needed to produce cortisol or corticosteroid from progesterone.
  • Excess progesterone is shunted into the androgen pathways.
  • XX genotype females may display masculinized genitals at birth.
  • Can cause problems with kidneys and sugar levels.

Introduction to Puberty

  • Activation of the hypothalamic-pituitary-gonadal axis is key (HPG axis).
  • Role of body weight specifically in females is a focus.
  • Early or precocious puberty and environmental influences are discussed.

The Three Main Axes

  • Hypothalamic-pituitary-thyroid axis.
  • Hypothalamic-pituitary-adrenal axis.
  • Hypothalamic-pituitary-gonadal axis (focus).

Hypothalamic-Pituitary-Gonadal Axis (HPG)

  • Hormones trigger signals to the pituitary gland.
  • Pituitary gland then signals to the ovaries or testes.
  • Key hormones: gonadotropin releasing hormone (GnRH), luteinizing hormone (LH), and follicle stimulating hormone (FSH).
  • Hypothalamus produces GnRH which signals to the anterior pituitary.
  • Anterior pituitary releases LH and FSH which signal to the testes or ovaries.
  • Testes produce testosterone; ovaries produce estrogen and progesterone.

Hormonal Changes During Puberty

  • Testosterone levels in males increase during puberty.
  • Tanner stages are used to describe the stages of puberty.
  • Females have more estrogen, and males have more testosterone.

Follicle Stimulating Hormone and Luteinizing Hormone.

  • Produced by all, but concentrations differ based on sex.

Luteinizing Hormone Concentration Levels

  • Pre-puberty; low levels, but level capacity.
  • Early to mid puberty: levels increase, with a spike.
  • Mid to late puberty: increases, with an erratic nature.

Age of Development

  • The symptoms you will have with puberty are (in females): a rapid height increase, breast development, and pubic hair.

Symptoms of going through Puberty.

  • Male symptoms: Testes and penis further develop, can grow pubic hair.

Menarche

  • Menarche, scientific for a girls first period, indicates sexually maturity.

Theories being why puberty is being hit quicker in life.

  • Increase in body fat is the most common.
  • Social factors may play a key role.
  • Environmental influences can kick it off.

Female requirements.

  • Bodies require a curtain weight level before starting puberty.
  • The older a female, the most fertile she is.

Relationship of Nutrition on Reproduction.

  • Humans should maintain adequate body fat both to start menstruating, but also to become very fertile.
  • If the body reaches a nutritious level for puberty, it is possible things will kick into gear.
  • Body mass indexes have shown how conceiving a child can vary among indexes.

How nutrition Affects Puberty

  • Gonadatropin releasing hormones releases both luteininzing and follicle stimulating hormones from the pituitary.
  • Testosterone production can happen as well given the stimulation of glands to produce.
  • When fat storages become large, other hormones like leptin start kicking in, and give signals to the brain how the body is doing.

Deficiencies in Nutrition

  • Same pathway as those getting proper nutrients, but not sexually mature, so puberty and production overall is stunted.
  • Leptin can decline due to fat levels dropping, so the brain thinks it's signalling female fertility.
  • Puberty and periods get delayed.

Delaying Puberty or the Onset of Puberty.

  • Exercise or extreme dieting.
  • Menstrual cycles can be stopped by strenuous activity.
  • Dancers can also suffer the same issue.

Body signals being shown through exercise

  • Growth and development will still occur, but storage decreases.
  • Food may become used faster to maintain sustenance.
  • Leptin gets impacted, losing food reserves.

Leptin hypothesis

  • Leptin comes at a certain maturity level, where periods can start to onset.

Leptin evidence with rhesus monkeys

  • Luteinizing hormones start getting produced around puberty time.
  • Normal levels of luteinizing hormones start tapering off after levels spike for a short time.

Obese mice experiments.

  • Leptin, which sends signals to the brain, that the body has it's conditions together, but sending levels from a fat fat mouse can produce different results for different subjects. Leptin deficiencies can be tested on others with this treatment, showing reactions.