1. Reproductive system

3. Male Reproductive system
Function- to produce sperm in the testes and deliver it into the female’s body.
The process of producing sperm cells is called spermatogenesis, which occurs in the seminiferous tubules of the testes.
Diploid spermatogonia divide through meiosis to create 4 sperm cells with only 23 chromosomes each (half the number of necessary chromosomes).

5. The testes are held in place by a flap of skin called the scrotum.
The scrotum maintains an ideal temperature for sperm survival, which is slightly lower than normal body temperature.
Cremaster muscles control how near the testes are to the body based on external temperature.

6. Sperm cells have 3 main sections:
Other cells in the testes produce hormones or jelly- like semen, which nourish and help the sperm move.
Sperm cells have 3 main sections:
Head, midpiece, tail
The head contains the nucleus and has an acrosome on the front portion, which contains enzymes to break into the egg cell during fertilization.
The midpiece is surrounded by mitochondria, giving the sperm ample energy to swim.
The tail (flagellum) provides the movement.

8. Male reproductive system
After production in the testes, the sperm move to the epididymis to mature.
The epididymis is a long, tightly-coiled tube that leads to the vas deferens. The vas deferens carries sperm up and over the bladder, where it meets the urethra, then the sperm exits through the penis.
The urethral sphincter prevents urine entering the urethra during ejaculation.

9. Male reproductive system
During this journey, sperm also pass 3 structures:
Seminal vesicle- adds fluid to the semen
Prostate gland- adds alkaline fluid to semen to counteract the acidity of the male urethra and female vagina
Bulbourethral gland (Cowper’s gland)- adds more alkaline fluid to semen

11. Female Reproductive System
Fallopian tubes: site of fertilization, moves ova towards uterus
Uterus (womb): composed of smooth muscle that can expand during pregnancy
Ovaries: Site of oogenesis; contain follicles that produce ova after puberty
Cervix: ring of smooth muscle
Vagina: muscular tube that receives penis and delivers baby (“birth canal”)

12. The process of producing egg cells (ova) is called oogenesis, which occurs in the ovaries.
The ovaries contain about 400,000 follicles (clusters of cells surrounding an egg) at a female’s birth. Only about 400 of these follicles will mature and be released as eggs.
About every 28 days, one follicle matures into an egg and it released. This is called ovulation.
The ovaries alternate, with one producing an egg each cycle.

14. Female reproductive system
The mature ovum is carried through the oviducts (Fallopian tubes) towards the uterus.
If a sperm and ovum meet in the oviduct, fertilization usually occurs.
The fertilized egg will then continue toward the uterus, where it will continue development.
If the ovum is unfertilized, it will degenerate.

15. Uterine lining is shed through the vagina (called a period).
The corpus luteum (which is the portion of the follicle that remains after the release of the egg) secretes progesterone, which causes uterine lining to thicken.
If egg is unfertilized, estrogen and progesterone levels decrease, causing the uterine lining to stop thickening.
Uterine lining is shed through the vagina (called a period).
Pituitary gland secretes Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH).
This stimulates eggs to develop. FSH causes only the most mature egg to be released.
Egg is released by one ovary and enters fallopian tube.

16. Female reproductive cycles
Watch a video of the menstrual cycle here:

17. Human development & birth

18. Fertilization
When a sperm cell attaches to an ovum (egg), the acrosome on the tip of the sperm cell releases enzymes that break down the protective barrier around the ovum.
When one sperm penetrates the barrier, the ovum releases a material that coats the outside of the ovum, preventing other sperm from penetrating.
After fertilization, the chromosomes of the ovum and sperm unite, making a full diploid set. This fertilized egg is now called a zygote.

20. Fertilization
A fluid-filled cavity forms, which will eventually be the placenta, umbilical cord, and amniotic sac. This is the blastula stage. Implantation in the uterine wall follows. 3
Once there are 64 cells (3 days after fertilization), the embryo is known as a morula. 4 2
Cells begin to divide in a process called cleavage and the zygote is pushed along by cilia within the fallopian tube. 1
One sperm fertilizes the ovum within the fallopian tube and creates a zygote.

21. Early development
As the zygote moves down the oviduct (Fallopian tube), it goes through several mitotic cycles until it has 64 cells. The zygote is now called a morula.
The morula attaches itself to the uterine wall 6-7 days after fertilization.
This uterine wall will eventually become the placenta, which is the connection between the mother’s and baby’s body.
The morula begins to arrange into 3 germ layers and becomes hollow. It is now called a blastocyst. The 3 germ layers will give rise to different structures:
Ectoderm- hair, nails, nervous system
Mesoderm- muscles, blood, bones
Endoderm- lining of the digestive tract, respiratory tract, bladder, and urethra
Gradually, these layers develop the neural tube, which will become the spinal cord.
Watch this development in the following video:

22. Extraembryonic membranes develop to protect and nourish the embryo during growth.
Amnion- contains the amniotic fluid, which protects, maintains temperature, and provides flexible space for the embryo to move
Chorion- the baby’s portion of the placenta
Diffused substances (oxygen, waste, and even drugs) pass through the placenta from mother to child. The blood is not exchanged.
Allantois- many blood vessels that form the umbilical cord
Watch how twins form

23. Later development
After 8 weeks, the clearly recognizable human embryo is called a fetus.
Watch development here:
youtube.com/ watch?v=ysyG Ga5It9Q

24. Images:
By Chris 73 / Wikimedia Commons, CC BY-SA 3.0, rid=19707