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Male Reproductive System

• Composed of distinct parts, each with specific functions crucial for reproduction.
• Testes are primary male reproductive organs, responsible for producing sperm cells and testosterone.
• Testes are oval-shaped glands suspended in the scrotum.
• Scrotum maintains sperm at a temperature slightly lower than the body's core temperature.
• Sperm production occurs at about 2°C lower than the body's standard temperature.
• Epididymis is a coiled tube located on the outside of the testes within the scrotum.
• Epididymis is where sperm cells mature and are stored after production in the testes.
• Vas Deferens (Sperm Duct) is a muscular tube that transports sperm from the epididymis to the urethra.
• Urethra runs through the penis and expels semen (during ejaculation) and urine (during urination).
• Seminal Vesicles are glands attached to the vas deferens near the base of the bladder.
• Seminal Vesicles produce a nutrient-rich fluid that provides energy for sperm cells' mobility and survival.
• Prostate Gland produces an alkaline fluid that is part of semen.
• The alkalinity of the prostate fluid neutralizes the acidic environment of the vagina, protecting the sperm.
• Cowper’s Gland (Bulbourethral Gland) produces a mucus-like fluid released before ejaculation.
• The Cowper's Gland fluid lubricates the urethra and neutralizes traces of acidic urine.
• Penis is the external organ through which the urethra runs.
• The penis delivers sperm into the female reproductive tract during sexual intercourse.
• Testosterone, produced by the testes, plays crucial roles in the male reproductive system.
• Testosterone aids in the development of male secondary sexual characteristics.
• Secondary sexual characteristics include facial hair, deep voice, and muscle mass.
• Testosterone stimulates the maturation of sperm cells.
• A sperm cell's structure delivers the male's genetic material to the female's egg.
• The sperm cell head contains the nucleus with 23 chromosomes and is capped by the acrosome.
• The acrosome contains enzymes essential for penetrating the egg cell during fertilization.
• The sperm cell middle section houses mitochondria, providing energy required for movement.
• The sperm cell tail is used for swimming, propelling the sperm towards the egg for potential fertilization.

Female Reproductive System

• Ovaries found as a pair on either side of the uterus, surrounded by germinal epithelium.
• Ovaries produce egg cells and secrete the hormones progesterone and estrogen.
• Fallopian Tubes connect the ovaries to the uterus and are lined with ciliated columnar epithelium.
• The ciliated columnar epithelium helps move the egg cells.
• Fallopian Tubes transport egg cells from the ovary to the uterus.
• The Fallopian Tubes are also the site of fertilization.
• The Uterus is a hollow, pear-shaped organ.
• The Uterus houses and protects the embryo and fetus during pregnancy.
• The Endometrium is the inner lining of the uterus.
• The Endometrium is the site of implantation and where the placenta forms.
• The Cervix is the lower, narrow opening of the uterus.
• The Cervix stretches and opens to allow the baby through during childbirth.
• The Vagina is a muscular tube that runs from the cervix to the exterior.
• The Vagina receives the penis and semen during sexual intercourse.
• The vagina serves as the birth canal and the passage for menstrual blood.
• Vulva - The opening to the vagina is covered by two labia.
• The Vulva protects the entrance to the vagina.

Puberty

• Male puberty is primarily stimulated by the hormone testosterone.
• There is an increase in size and function of male sex organs.
• Initiation of sperm cell production marks sexual maturation.
• There is the emergence of pubic, facial, and body hair.
• Muscles develop more prominently, and the voice deepens.
• Female puberty is driven by the hormone oestrogen.
• There is growth in the female sex organs.
• The start of the menstrual cycle and the production of ova indicate fertility.
• Pubic hair begins to grow.
• There's noticeable growth and development of breasts.
• The widening of hips marks physical maturity.

Gametogenesis

• Spermatogenesis refers to the process of male gamete (sperm cell) production in the testes.
• Spermatogenesis takes place in the seminiferous tubules' germinal epithelium.
• Spermatogenesis is driven by testosterone.
• Diploid germinal epithelial cells (with 46 chromosomes) divide through meiosis.
• Haploid sperm cells contain 23 chromosomes each.
• Sperm cells may carry either an X or a Y chromosome, contributing to offspring's sex determination.
• Under testosterone's influence, diploid germinal epithelial cells undergo meiosis.
• The meiotic division results in four haploid spermatids.
• Spermatids mature into fully-fledged sperm cells.
• The sperm cell head consists of the nucleus, housing 22 autosomes and one sex chromosome (X or Y).
• The sperm cell head also contains the acrosome, filled with enzymes for penetrating the egg's outer layers.
• The middle portion of the sperm is packed with mitochondria, supplying the energy for motility.
• The tail enables the sperm to swim through fluid, propelling the cell forward for fertilization.
• Oogenesis produces female gametes (ova or egg cells) in the ovaries.
• It begins in the diploid germinal epithelium, which divides through mitosis to form multiple follicles.
• Events are cyclical and occur approximately every 28 days, regulated by FSH.
• Mitosis of diploid germinal epithelium cells produces numerous follicles.
• FSH stimulates one of these follicles each cycle, leading to the enlargement of one cell.
• This meiotic process results in four haploid cells, but only one survives to become a mature ovum; the remaining three degenerate.
• Follicle cells surround the egg, offering support and protection.
• A layer of jelly safeguards the egg, particularly during the early developmental stages post-fertilization.
• The cytoplasm provides essential nutrients for the developing egg.
• A haploid nucleus containing 22 autosomes and one X chromosome merges with a sperm's genetic material.

Menstrual Cycle

• It involves changes in the ovaries (ovarian cycle) and the uterus (uterine cycle).
• The average cycle is 28 days, though this can vary.
• Days 1–7 (Menstruation): New follicles in the ovaries develop and secrete oestrogen.
• The endometrium breaks down and is shed during menstruation.
• Days 8–13 (Follicular Phase): A mature Graafian follicle develops in the ovaries.
• The Graafian follicle moves to the edge of the ovary and secretes oestrogen.
• Oestrogen leads to the thickening of the endometrium and the development of more blood vessels and glands.
• Day 14 (Ovulation): The Graafian follicle bursts to release an egg cell.
• Days 15–22 (Luteal Phase): The ruptured Graafian follicle transforms into the corpus luteum.
• The corpus luteum secretes progesterone.
• Progesterone further stimulates the endometrium to thicken and develop more blood vessels and glands.
• Days 23–28: If fertilisation does not occur, the corpus luteum shrinks and stops producing progesterone.
• The breakdown of the endometrium occurs, causing menstruation.
• If fertilisation does occur, the corpus luteum remains active and continues to secrete progesterone.
• Progesterone prevents menstruation and supports pregnancy.
• FSH (Follicle-Stimulating Hormone) is produced by the pituitary gland.
• FSH stimulates the development of the follicle in the ovaries.
• LH (Luteinizing Hormone) is also produced by the pituitary gland.
• LH levels peak around day 14, triggering ovulation and the formation of the corpus luteum.
• Oestrogen levels increase as the follicle develops, leading to the thickening of the endometrium.
• After ovulation, oestrogen levels initially decrease as the Graafian follicle ceases functioning.
• Progesterone is produced by the corpus luteum post-ovulation.
• Progesterone levels increase to prepare the endometrium for pregnancy.
• If fertilisation does not occur, progesterone levels fall, leading to the shedding of the endometrial lining.

Fertilization and Development of Zygote to Blastocyst

• During copulation, the penis is inserted into the vagina, and sperm cells are released close to the cervix.
• Sperm swim through the cervix, into the uterus, and up through the fallopian tubes.
• If a haploid ovum (released during ovulation) is present in the fallopian tubes, one sperm cell may penetrate its jelly layer, leading to fertilization.
• The union results in a diploid zygote, where the nuclei of the ovum and sperm cell fuse.
• Post-fertilization, the zygote undergoes mitosis while moving down the fallopian tube toward the uterus.
• This continuous mitotic division forms a solid ball of cells known as the morula.
• As division continues, the morula develops into a hollow, fluid-filled ball of cells termed the blastocyst.
• The blastocyst typically occurs around five days after fertilization.
• The blastocyst travels from the fallopian tube to the uterus, where it embeds itself into the endometrium, a process known as implantation.
• The outer cells of the blastocyst secrete enzymes that soften a portion of the uterine wall, allowing the blastocyst to embed.
• Following implantation, the outer layers of the blastocyst develop into extra-embryonic membranes—the amnion and the chorion.
• The chorion forms the chorionic villi that extend into the endometrium and contribute to placenta formation, which in turn secretes progesterone.
• At this stage, the blastocyst is referred to as the embryo.
• The embryo will develop throughout the gestation period, lasting about 40 weeks or 280 days, until birth.
• After 12 weeks of gestation, the embryo is then referred to as a fetus.

Implantation, Gestation, and the Role of the Placenta

• Ovulation occurs usually on day 14 of the menstrual cycle.
• A mature Graafian follicle in the ovary bursts and releases an egg cell.
• Fertilization happens high up in the fallopian tube.
• The egg cell (23 chromosomes) and the sperm cell (23 chromosomes) fuse to form a zygote (46 chromosomes).
• After fertilization, the zygote divides by mitosis, forming first a morula, then a blastocyst, and finally an embryo.
• The embryo is as it moves down the fallopian tube towards the uterus.
• The embryo reaches the uterus in about 5 to 7 days and embeds itself into the endometrium, known as implantation.
• Post-implantation the embryo develops many finger-like structures called villi from its outer membrane, that grow into the uterine tissue to form the placenta.
• The placenta connects to the embryo via the umbilical cord.
• The umbilical cord contains two umbilical arteries carrying deoxygenated blood from the embryo to the placenta, and one umbilical vein that carries oxygenated blood from the placenta to the embryo.
• The embryo is encased in a fluid-filled sac called the amnion.
• The fluid inside the amnion is referred to as amniotic fluid.
• After approximately eight weeks, the embryo develops into a fetus.
• Structures such as limbs and all necessary body organs have formed.
• Gestation is the time from fertilization to birth, typically lasts for about 9 months or 39–40 weeks.