Lecture Notes on Puberty and Male Reproductive System

Puberty Triggers and Timing

• Puberty is triggered by a combination of hormones leading to secondary sexual characteristics and sexual maturity.
• Tanner stages describe the physical development during puberty in both females and males.

Nutrition and Body Fat

• There's evidence suggesting a correlation between body size, body fat, nutrition and the onset of puberty. However, the exact trigger is still unknown.

Other Hypotheses for Early Puberty Onset

• Media Exposure: Increased exposure to images in popular media is theorized to potentially influence the timing of puberty, though there isn't enough data available.
• Family Stress: Some researchers suggest a possible correlation between family stress/structure (e.g., presence of father) and early puberty onset, but data remains limited and difficult to measure.
• Endocrine Disrupting Factors: Environmental factors that interfere with hormone balance may affect the timing of puberty.

Hormones in Meat

• The theory suggests the hormones in meat could be a trigger for earlier puberty.
• Cattle and beef have been treated with hormones in the Western world for over 50 years to promote muscle growth.
• Using hormones in animals changes the percentage of muscle and fat.

Myth about Chickens:

• The idea that chicken meat is full of hormones is a myth.
• Hormones have been banned from being put in chicken feed for many years worldwide.
• Chickens are dosed with antibodies and vaccinations, but not hormones.

Implications of Earlier Puberty

• Earlier onset of puberty can significantly impact a female's reproductive life.

Changes in Menstrual Cycles:

• Past (120+ years ago):
  • Reproductive years: 16-45
  • Approximately 29 years of reproductive lifetime.
  • $\approx$ 12 cycles/year
  • Total: 348 cycles
• Present:
  • Puberty onset at 12
  • Menopause around 50
  • Approximately 38 years of reproductive life
  • Total: 456 cycles
• Menopause has also been creeping later.
• Calculations assume no lactational anovulation.
• Lactational anovulation refers to the suppression of ovulation during breastfeeding.

Lifestyle and Pregnancy:

• Past:
  • Approximately six pregnancies and five lactations
  • Subtracting those months, $\approx$ 234 cycles per lifetime.
• Present:
  • Smaller families, on average two pregnancies and lactations
  • Shorter lactations
  • Approximately 426 cycles on average for a female’s lifetime.

Environmental Contaminants

• Endocrine disrupting chemicals can interfere with the hypothalamic-pituitary-gonadal axis.
• Chemicals can bind to hormone receptors, interfere with hormone degradation, and affect the body in minuscule quantities.
• Examples include DDT, PCBs, and dioxins.
• Precocious Puberty: Puberty occurring at an unexpectedly early age.

Examples of Environmental Impact

• American alligators exposed to PCBs on golf courses had lower plasma testosterone levels and were less aggressive.
• Some frog species exposed to herbicides developed hermaphroditism.
• Some evidence presents endocrine disruptors may adversely affect human males.

Male Reproductive System

Learning Objectives

• Understand the structure and function of the male reproductive organs.
• Learn about spermatogenesis and its stages.
• Understand the hormonal control of male reproduction (HPG axis).
• Learn about Leydig and Sertoli cells.

Male Reproductive Tract

• Major structures include: testes, epididymis, vas deferens, seminal vesicle, prostate gland, bulbo-urethral gland, penis, urethra.

Function of Male Reproductive Organs

• Production of sperm (spermatogenesis).
• Maturation of sperm (spermiogenesis).
• Production of sex steroid hormones (androgens).
• Delivery of sperm.

Testes Anatomy

• The testes are divided into two main compartments that produce sperm and androgens.
• Seminiferous tubules are the site of sperm production.
• Androgen-producing tissue is located between the tubules.
• The sperm are separated from the androgens through blood vessels to avoid degradation.

Key Terms:

• Seminiferous Tubules: Structures within the testes where sperm is produced.
• Sertoli Cells: Support cells within the seminiferous tubules that aid in sperm production.
• Leydig Cells: Cells located between the seminiferous tubules that produce androgens.

Spermatogenesis

• Spermatogenesis (sperm production) occurs within the seminiferous tubules.
• The cells are protected by sertoli cells or nourished cells, which facilitates what is needed from the cardiovascular system.

Three Main Steps of Spermatogenesis:

• Mitosis.
• Meiosis.
• Differentiation (cytodifferentiation).

Process:

• Mitosis produces germ cells.
• Germ cells undergo meiosis and move toward the lumen (center) of the seminiferous tubule.
• Cytodifferentiation transforms the cells into sperm.

Sperm Structure

• Sperm consists of a head (containing the acrosome, vital for fertilization), mid-piece (full of mitochondria for energy), and tail (for propulsion).
• The tail of the sperm moves in a spiral motion.

Hormonal Control in Males (Hypothalamic-Pituitary-Gonadal Axis)

• The HPG axis regulates sperm production and androgen levels.
• The hypothalamus releases gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary.
• The anterior pituitary releases luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

Roles of Hormones:

• LH: Promotes testosterone production by Leydig cells.
• FSH: Stimulates Sertoli cells to support spermatogenesis.
• Inhibin: A hormone that provides negative feedback to the hypothalamus and pituitary, regulating sperm production.
• Testosterone: Provides a feedback loop to stop signalling.

Process Overview:

1. Hypothalamus produces GnRH.
2. GnRH stimulates the anterior pituitary to release LH and FSH.
3. LH stimulates Leydig cells to produce testosterone.
4. FSH and testosterone stimulate Sertoli cells to promote spermatogenesis.
5. Inhibin and testosterone provide negative feedback to the hypothalamus and pituitary.
6. Sperm mature within the epididymis.
7. Sugars and glycoproteins are added, creating the tail and the acrosome.
8. The tails can move although they don't become fully capacitated until reaching the female's vagina, and are then are dribbled out.

Sperm Health

• Various factors can threaten sperm health, including heat, mumps, and autoimmune responses.
• The blood vessels are separated from the sperm.
• Mumps is dangerous because the swelling of the testes can be irreversible for the epididymis.

Temperature Regulation

• The position of the testes outside the body helps maintain optimal temperature for sperm production.
• The cremaster muscle contracts to pull the testes closer to the body for warmth or relaxes to lower them for cooling.

Semen Composition

• Semen protects and nourishes sperm.

Components:

• Fructose (energy).
• Prostaglandins (may cause vaginal contractions).
• Buffers (protect against the acidic vaginal environment).
• Reducing agents (prevent oxidation).

Sperm Count

• Each ejaculate contains approximately 280 million sperm or approximately this per sperm per mL.

Path of Sperm

1. Testes.
2. Epididymis.
3. Vas deferens.
4. Past seminal vesicles, prostate gland, and bulbourethral glands.
5. Urethra.
6. Penis.