Puberty and Human Reproduction Lecture Notes

Research Skills and Syllabus Requirements

• Contraceptive Methods for Selection:

  • Condom

  • Femdom

  • Diaphragm (Dutch Cap)

  • IUD (Copper 'T' or Loop)

  • Rhythm method

  • Vasectomy

  • Tubal ligation

• Research Methodology: Research may be carried out using internet-based, book-based, and/or questionnaire-based research.

• Research Components: This research involves:

  • Accurate data collection.

  • Recording of data in an appropriate way.

  • Analysis and interpretation of data.

  • A report summarising findings and commenting on those findings.

• Essential Knowledge Competencies:

  • The structure and function of human male and female reproductive systems.

  • Male reproductive parts: testes, scrotum, germinal epithelium, seminiferous tubules, epididymis, sperm duct, penis, prostate gland, seminal vesicle, and foreskin.

  • Distinction between sperm and semen; distinction between erection and ejaculation.

  • Female reproductive parts: ovary (including follicles and corpus luteum), oviduct, uterus, endometrium, cervix, vagina, and clitoris.

  • Physiological changes occurring during puberty.

  • Production of sperm and egg cells in the germinal epithelium via meiosis (controlled by hormones).

  • Detailed structure of a sperm cell and the functions of its parts.

  • The menstrual cycle, specifically the roles of FSH, LH, oestrogen, and progesterone, including negative feedback mechanisms linked to the endocrine system.

  • Development from primary follicle to Graafian follicle, ovulation, subsequent hormonal changes, and implantation.

  • Fertilisation concepts: location of occurrence, and the progression of a zygote into an embryo and then a foetus via mitosis.

  • Structure and functions of the placenta, umbilical cord, amnion, and amniotic fluid.

  • Initiation of labour and birth via hormonal changes; role of the mammary gland.

  • Specific contraceptive methods and their features: condom, diaphragm, contraceptive pill, hormone injections, IUD, and rhythm methods.

• Societal and Medical Topics for Discussion:

  • Attitudes and beliefs of different cultures regarding contraceptive use.

  • Sexually transmitted diseases and the effect of multiple partners.

  • Issues related to the reproductive system: Foetal Alcohol Syndrome (FAS) and HIV.

  • Infertility treatments for males and females.

  • Surrogacy.

  • Circumcision: Health, cultural, and religious issues.

Puberty: Physical, Physiological, and Emotional Development

• Definition of Puberty: Puberty is the stage of development during which a child's body physically matures into an adult body capable of sexual reproduction. It is a period of growth where sex organs begin to develop and produce sex cells.

• Hormonal Control: These changes are entirely controlled by hormones.

• Timing and Onset:

  • Boys: Usually begins at $11-13\,years$.

  • Girls: Usually begins at $10-11\,years$.

  • Note: Timing varies from person to person, but generally starts earlier in females.

• Trigger Mechanism:

  • The hypothalamus in the brain triggers the release of gonadotropin-releasing hormone (GnRH).

  • GnRH stimulates the pituitary gland to secrete Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH).

• Hormonal Functions During Puberty:

  • FSH (Females): Stimulates follicle development in the ovary to start the menstrual cycle.

  • LH (Females): Triggers ovulation and the subsequent production of progesterone.

  • FSH (Males): Stimulates spermatogenesis (sperm production).

  • LH (Males): Stimulates testosterone secretion from the testes.

  • Growth Hormone (GH): Responsible for the increased growth rate during puberty.

• Physical Changes:

  • Height and Weight: Rapid growth spurts occur. Females grow up to $12\,cm$ a year; males grow up to $10\,cm$ a year.

  • Secondary Sex Characteristics (Females): Breast development (thelarche), pubic and armpit hair (pubarche), widening of hips, and the onset of menstruation (menarche).

  • Secondary Sex Characteristics (Males): Genital development (penis and testes increase in size), pubic and armpit hair growth, facial hair (moustache and beard), broadening of shoulders/chest, and deepening of the voice (occurring around $13-14\,years$).

  • Other Changes: Skin becomes oilier, which may lead to acne/pimples; increased underarm perspiration.

• Emotional and Social Changes: Significant adjustments including mood swings, changes in relationships with family and friends, and the development of a stronger sense of identity.

Anatomy of the Female Reproductive System

• Uterus (Womb):

  • A hollow, pear-shaped organ that responds to hormones.

  • Function: Site for embryo implantation and foetal development during pregnancy.

  • The Uterine Wall (3 Layers):

    1. Serous layer: The outer membranous layer.

    2. Myometrium: The middle layer consisting of smooth involuntary muscle.

    3. Endometrium: The inner mucous membrane; it thickens with blood vessels to prepare for pregnancy and sheds during menstruation if fertilisation does not occur.

• Fallopian Tube (Oviduct):

  • Extends from each ovary to the uterus.

  • Function: Transports the egg cell; it is the specific site where fertilisation occurs.

• Ovaries:

  • Primary female sex organs, almond-shaped, approximately $1.5\,cm$ to $3-5\,cm$ long.

  • Held in position by ligaments.

  • Function: These are gonads and endocrine glands that produce ova, oestrogen, and progesterone.

  • Structure: Surrounded by a layer of cuboidal germinal epithelial cells. The cortex contains follicles, each forming one ovum.

• Cervix:

  • The narrow entrance to the uterus that connects the vagina to the uterine cavity.

  • Function: Stretches during labour; allows menstrual blood flow; directs sperm into the uterus during intercourse.

• Vagina:

  • A passage with folded muscular walls between the uterus and the outside of the body.

  • Function: Serves as the birth canal.

• Clitoris:

  • A small, sensitive, erectile sexual organ located outside the body in front of the vaginal opening.

  • It is considered analogous to the male penis.

Ovarian Follicle Development and the Corpus Luteum

• Ovarian Follicles:

  • Small, fluid-filled sacs within the ovaries containing a single oocyte (immature ovum).

  • Women begin puberty with approximately $300,000$ to $400,000$ follicles.

  • Development: Under the influence of FSH, a primary follicle develops into a secondary follicle and then into a mature Graafian follicle.

• Graafian Follicle:

  • The mature follicle that contains the mature egg cell.

  • Function: Produces oestrogen and releases the egg during ovulation.

• Corpus Luteum:

  • The structure remains of the Graafian follicle after the egg is released (ovulation).

  • Function: Acts as a temporary endocrine gland, producing progesterone and oestrogen.

  • Progesterone Role: Makes the endometrium thick for implantation and sustains pregnancy until the placenta takes over (around $10\,weeks$ gestation).

  • Lifespan: Lasts $12-14\,days$ unless it receives HCG (human chorionic gonadotropin) from an embryo. If no fertilisation occurs, it dies, progesterone levels drop, and the lining is shed.

Hormonal Regulation and Negative Feedback Mechanisms

• General Principle: Negative feedback is a regulatory mechanism where a hormone's action leads to a decrease in its own production to maintain homeostasis.

• Hormones in Males:

  • LH: Stimulates Leydig cells to produce testosterone.

  • FSH: Stimulates Sertoli cells to produce androgen-binding protein (ABP) for spermatogenesis and inhibin.

  • Feedback: High testosterone inhibits the hypothalamus and pituitary (reducing FSH/LH). High sperm count triggers Sertoli cells to release inhibin, which specifically inhibits FSH to slow spermatogenesis.

  • Note on Doping: Steroid/testosterone use can cause infertility because it triggers the negative feedback loop that shuts down FSH production, thus stopping sperm production.

• Hormones in Females:

  • FSH: Secreted by the pituitary; stimulates maturation of the ovarian follicle (follicular phase). The follicle then produces oestradiol.

  • LH: A surge in oestrogen triggers a surge in LH mid-cycle (Day 14), which causes ovulation and turns the empty follicle into the corpus luteum.

  • Feedback: Progesterone (produced by the corpus luteum) inhibits the release of FSH and LH. If levels of oestrogen and progesterone drop, the inhibition is removed, and FSH is produced again to start a new cycle.

The Menstrual Cycle Timeline

• Day 1-5 (Menstruation): The uterine lining breaks away and is shed. All hormone levels are low.

• Day 5-9 (Follicular Phase): FSH increases; a new endometrium begins to grow; a follicle matures and starts producing oestrogen.

• Day 14 (Ovulation): High levels of LH and oestrogen trigger the release of the ovum. The endometrium continues to thicken.

• Day 15-28 (Luteal Phase): Progesterone levels are high (secreted by the corpus luteum).

  • If fertilisation does not occur: The ovum dies, the corpus luteum shrivels, progesterone production stops, and the cycle restarts on Day 1.

• Survival Rates:

  • Ovum survival: approximately $24\,hours$ post-ovulation.

  • Sperm survival: $2-3\,days$ inside the female body.

• Menopause: The stage (usually around $50\,years$ of age) when menstruation stops because the woman no longer ovulates.