Human Reproduction and Male Reproductive System

Human Reproduction

• Humans begin life as a single cell formed by the fusion of an egg and sperm from parents.
• During adolescence, the sex organs change to produce sex cells, essential for creating new individuals.
• Sex cells (gametes) contain chromosomes with genetic information, carrying traits like hair and eye color.
• Sex cells have half the number of chromosomes as regular body cells (somatic cells).
• Sperm cells and egg cells are haploid (n), containing 23 chromosomes.
• Regular body cells are diploid (2n), containing 46 chromosomes.
• The fusion of an egg and sperm forms a zygote with 46 chromosomes.

Male Reproductive System

• The male reproductive system produces sperm and delivers them to the female reproductive system.
• The primary reproductive organs are the testes, located in the scrotum.
• The scrotum's location outside the body regulates temperature for correct sperm development (one to two degrees lower than internal body temperature).
• Sperm are produced in the seminiferous tubules of the testes.
• Meiosis is the process of sperm cell production within the seminiferous tubules.
• Two hormones, Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH), secreted by the anterior pituitary gland, regulate testis function by stimulating testosterone production.
• Testosterone is produced by Leydig cells and important for developing secondary sex characteristics.
• Sperm mature in the epididymis, a coiled tube where they gain the ability to swim and move.
• The epididymis stores sperm, which are then transported through the vas deferens to the urethra.
• During sexual arousal, blood rushes to the penis, causing it to become rigid (erect).
• Sperm are mixed with fluids from accessory glands (prostate, seminal vesicles, and bulbourethral glands) forming semen, which nourishes the sperm.
• Semen exits the body through the urethra during ejaculation.

Female Reproductive System

• The female reproductive system produces eggs and nourishes the fertilized egg until birth.
• The ovaries are the primary reproductive organs, producing eggs (ova).
• The ovaries release a mature egg roughly every 28 days.
• Estrogen- one of the female reproductive hormones - is essential for triggering secondary female characteristics and egg development.
• The onset of mature egg production is called menarche (the first menstrual period).
• Each month, a mature egg is released into the fallopian tube (oviduct).
• Hair-like structures called cilia sweep the egg into the fallopian tube.
• The fallopian tube leads to the uterus.
• The uterus prepares for possible fertilization (thickening of the uterine lining).
• If pregnancy doesn't occur, the endometrial lining is shed, marking the menstrual cycle.

Stages of Human Development Before Birth

• Fertilization: Sperm penetrates the egg, releasing enzymes to break down the jelly-like layer. The sperm's nucleus fuses with the egg's, forming a zygote.
• Cell Division: The zygote travels down the fallopian tube and divides repeatedly.
• Implantation: The developing embryo implants into the uterine wall. The uterine wall prepares for possible fertilization and thickens the lining.
• Embryo Development: The dividing zygote forms an embryo. (Weeks 1-8) , essential organs and structures develop.
• Placenta Function: The placenta forms, connecting the embryo to the mother's uterine wall, facilitating nutrient and oxygen transfer and waste removal.
• Embryo Development and Amniotic Fluid: The amniotic sac develops around the embryo, filling it with fluid which protects it. Waste is removed.
• Fetal Stage: After 8 weeks, the developing human enters the fetal stage. (Months 3-9) Major organ development completes. The fetus also grows and its bones harden.
• Birth: The contractions of labor and the dilation of the uterus eventually allow the baby to pass through the vagina.