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.