Human Development: Puberty and Hormonal Changes

Puberty and Reproductive Development

• By weeks 7-8, in males, early gonadal tissue differentiates into primitive testes, leading to testosterone production.
• Testosterone stimulates the development of the male reproductive organs through the mesonephric duct while the paramesonephric duct regresses.
• If testosterone is absent by week 10, the gonadal tissue becomes ovaries and the paramesonephric duct develops into female reproductive organs.
• Puberty marks the onset of secondary sex changes, initiated by the hypothalamus releasing gonadotropin-releasing hormone (GnRH).
• GnRH triggers the anterior pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH), leading to the production of androgens and estrogens.

Hormonal Influence on Development

• Androgenic hormones are crucial for muscular development, physical growth, and increased sebaceous gland activity, causing typical acne.
• In males, androgens are produced by the adrenal cortex and testes; in females, by the adrenal cortex and ovaries.

Anatomy of the Female Reproductive System

• The uterus is a hollow, muscular organ located in the lower pelvis, positioned behind the bladder and in front of the rectum.
• During childhood, the uterus is around the size of an olive; it reaches adult size around 17 years, typically measuring 5-7 cm in length and 5 cm in width.
• The uterus weighs approximately 60 grams when not pregnant, and ectopic pregnancy refers to implantation outside the uterus.
• The endometrium has two layers: stratum functionalis (sheds during menstruation) and stratum basalis (permanent layer).

Female Reproductive Structures

• The vagina serves as a passage for sperm and menstrual flow, is a receptacle for the penis during intercourse, and can stretch considerably.
• The cervical mucosa consists of nonkeratinized stratified squamous epithelium, producing mucus that aids sperm survival and creates a less hospitable environment for pathogens.
• Cervical secretions can vary from 20-60 ml per day, contributing to lubrication and protection of sperm.

Menstrual Cycle

• The menstrual cycle begins on the first day of bleeding and lasts until the next cycle starts; cycles in teens can be long (up to 42 days).
• The average menstrual period lasts about 5 days, with blood loss ranging from 30 to 80 ml.
• Ovarian cycle phases include the Follicular Phase (Days 1-13), Ovulation (Day 14), and the Luteal Phase (Days 14-28), with hormonal changes driving the maturation of eggs.

Signs of Ovulation

• Mittelschmerz refers to abdominal tenderness related to ovulation, caused by irritation from peritoneal blood.
• Signs include changes in vaginal mucus, breast tenderness, and mood fluctuations; clear, transparent mucus indicates high fertility.

Sperm Transport Dynamics

• Sperm travel is optimized near ovulation due to the reduction in cervical mucus viscosity and facilitated by uterine contractions and undulatory movements of the fallopian tube cilia.
• Upon deposition in the vagina, spermatozoa can reach the cervix in about 90 seconds and the outer end of the fallopian tube within 5 minutes.