Human Reproduction and Development

Human Reproductive cells Sperm is the smallest cell in a human’s body and is the only flagellated cell found in humans Produced in the testes Eggs are the largest cells found in a human’s body and can be seen with the naked eye Produced in the ovaries

Male reproductive anatomy

Male reproductive anatomy Testes Testes are the organs that are responsible for producing sperm and release sex hormones including testosterone Testosterone The hormone that promotes the development of male reproductive tissues such as testes and prostate Promotes secondary sexual characteristics such as increasing muscle and bone mass, growth of body hair, deepening of voice, and broadening of shoulders relative to the hips

Male reproductive anatomy Sperm Production Sperm is immobile at body temperature, so the testes are located outside the body to regulate the temperature of the sperm The scrotum suspends the testes outside the body at about 2 degrees Celsius less than body temperature to produce viable sperm Sperm is produced in seminiferous tubules that are coiled in the testes Once the sperm have been produced, they move to the epididymis where they continue to mature

Male reproductive anatomy Vas Deferens (“Carrying-Away Vessel”) The tube that carries mature sperm from the epididymis to the urethra Bulbourethral (Cowper’s) Gland Secretes an alkaline mucus that neutralizes the acidity of the reproductive tract prior to ejaculation Seminal Vesicles Secrete a fluid that partly composes semen (approximately 60%) Prostate Gland Secretes a slightly alkaline fluid to help sperm move more easily and composes about 30% of the volume of semen

Spermatogenesis Stage 1: Spermatogonium divides mitotically to produce two spermatogonium sub-types one will restart the cycle, the other differentiates into a primary spermatocyte Stage 2: The primary spermatocyte divides meiotically (meiosis I) to produce two secondary spermatocytes Stage 3: Each secondary spermatocyte undergoes meiosis II and divides into two haploid spermatids Stage 4: The spermatids undergo a maturation process where they become motile

Spermatogenesis

Sperm Anatomy Head Middle Tail The head of the sperm cell contains the nucleus (containing 23 chromosomes) and the acrosome which contains digestive enzymes to break down the walls of the eggs cell Middle The middle contains the mitochondria that provides the cell with energy to propel itself Tail The flagellum that whips back and forth to propel the sperm cell

Sperm anatomy

Female Reproductive Anatomy

Female Reproductive Anatomy Ovaries Ovaries are the organs that are responsible for producing eggs and release sex hormones including estrogen Estrogen The hormone that is responsible for the development and regulation of the female reproductive system Promotes secondary sexual characteristics such as enlargement of breasts, growth of body hair, and broadening of hip relative to the waist

Female Reproductive Anatomy Egg Production The ovaries are the reproductive organs responsible for producing eggs Within each ovary are follicles – a group of cells, each with the potential to release an oocyte for fertilization A females is born with all the follicles, each containing one oocyte (immature egg) she will ever produce (more than one million) When the oocyte is mature, luteinizing hormone is secreted to begin ovulation, where the follicle ruptures and releases oocyte The follicle remains functional but reorganizes as a Corpus luteum, releases progesterone to prepare the uterus for the implantation of the embryo (thickening of the uterine lining)

Female Reproductive Anatomy The oocyte is released by the ruptured follicle, it enters the fallopian tube and gradually moves towards the uterus Approximately 1-2% of ovulations release more than one oocyte and the fertilization of more than one oocyte would result in fraternal twins Fertilization of the oocyte occurs in the fallopian tube The oocyte enters the uterus, a think-walled muscular organ that provides mechanical protection and nutritional support to the developing embryo/fetus

Oogenesis During the 6th to 8th week of embryonic development, oogonia differentiate from germ cells and divide mitotically during the 9th to 22nd week More the 7 million oogonia are created but only around 1-2 million will remain when she is born Before puberty, about 11 thousand oocytes dies every month She will have just 300000-400000 remaining when she hits puberty Each month after puberty, about 1000 oocytes die each month

Oogenesis Stage 1: Takes place when the female embryo is still in her mother’s uterus during development Through mitosis, oogonia proliferate during embryonic development creating millions of primary oocytes Stage 2: Primary oocytes begin meiosis I but are halted at Prophase I until puberty when menstruation begins and only a few do so every menstrual cycle Divides asymmetrically into one secondary oocyte that receives most cytoplasm and the first polar body that eliminates a set of chromosomes

Oogenesis Stage 3: The secondary oocyte begins meiosis II immediately after meiosis I has completed but is again halted at metaphase II until fertilization occurs and if it does, the oocyte completes meiosis II resulting in an ootid and another polar body Stage 4: The polar bodies disintegrate, leaving only the ootid, which then undergoes a maturation phase into a mature ovum (egg cell)

Menstrual Cycle In many cultures, in particular, Native American cultures, menstruation (or moon time) is a sacred time of inner purification by ridding a woman negative energy Women are life-givers and are the bearers of future generations Indigenous cultures say that women are more closely connected to the spirit world and Mother Earth because of their common ability to bear life and are more powerful and sacred

Menstrual Cycle