Human reproduction

• Ovary

  • produces egg and female sex hormones (estrogen & progesterone)
• oviduct

  • narrow muscular tube with a funnel-like opening at the ovary
• Uterus (womb)

  • Location where the fetus develops;
  • Elastic muscular walls that enable contraction during birth to expel the fetus
• Uterine lining

  • Soft, smooth inner lining of the uterus rich in blood supply that is important for embryo implantation
• Cervix

  • Circular ring of muscle at the lower end of uterus
• Vagina

  • Location where semen is deposited during sexual intercourse; spans the area from the cervix to the vulva.
• Ovum

  made up of a:

  • large nucleus containing one haploid set of chromosomes,
  • large amount of cytoplasm which may contain a small amount of yolk, and
  • cell surface membrane that is surrounded by an outer membrane.
• Female gamete

  Structure

  • Spherical in shape
  • Haploid nucleus contains only X chromosome
  • Diameter 120μm to 150μm

  Motility

  • Non-motile

  Numbers

  • Number of eggs determined at birth
  • Usually only one matured egg is released per month
• Male gamete:

  Structure

  • Has a head, mid body and a flagellum
  • Haploid nucleus contains either X or Y chromosome
  • 60μm long

  Motility

  • Motile

  Numbers

  • Numerous sperms are produced throughout the life from puberty onwards
  • Large number of sperms released during each ejaculation
• During puberty :

  • Sex organs mature
  • Sex organs secrete sex hormones:
  • Testosterone (male)
  • Estrogen and progesterone (female)
  • Sex hormones cause secondary sexual characteristics to develop.
• Puberty refers to the stage of human growth and development in which a person’s body becomes capable of reproduction.
• Secondary sexual characteristics in males:

  • Hair starts to grow in the pubic region, at the armpits and on the face.
  • The penis and testicles increase in size
  • Larynx enlarges and voice deepens
  • Production of sperm begins
• Secondary characteristics in females:

  • Hair starts to grow in the pubic region and at the armpits.
  • Breast and uterus enlarge
  • Hips broaden
  • Menstruation and ovulation begin
• Testis

  • produces sperms and male sex hormones such as testosterone
• Epididymis

  • stores inactive sperms from the testis before they are released into the sperm ducts
• Spermatic cord

  • supplies blood to the testis
• Scrotum

  • pouch-like sacs located outside the body cavity to help maintain a lower temperature for the development of sperms
• Sperm duct

  • the pathway travelled by sperms after they are released from the testis
• Seminal vesicle

  • stores sperms temporarily before they are released through the urethra
• Seminal vesicle, prostate gland, and Cowper’s gland

  activate sperms by secreting a slippery fluid that contains nutrients and enzymes
• The mixture of this fluid and sperms is called semen.
• The reproductive system and the urinary system are interconnected through urethra and penis for delivery of semen during ejaculation and urine.
• Urethra

  • a tube that extends from the bladder, through the penis, to outside the body
  • Both urine and semen exit the body through the urethra, but never at the same time.
  • The sphincter muscles at the base of the urinary bladder prevent urine from exiting the body during ejaculation.
• Penis

  • erectile organ that becomes erect and hard during sexual intercourse in order to enter and deposit semen into the vagina
  • An erection occurs when the spongy tissue in the penis is filled with blood.
  • Sperms are ejaculated through the penis into the female passage during sexual intercourse
• Sperm

  
• Sperm

  Head contains :

  • a nucleus that carries one haploid set of chromosomes,
  • small amount of cytoplasm,
  • an acrosome that contains enzymes for breaking down part of the egg membrane for sperm penetration.

  Middle piece:

  • contains numerous mitochondria that release energy for sperm to swim to the egg.

  Tail:

  • Enable the sperm to swim towards the egg. The sperm is motile.
• Menstruation: The monthly discharge of blood from the uterus via the vagina
• average length of a menstrual cycle is 28 days.
• natural variation in the length of the menstrual cycle; ranging from 21 to 33 days.
• Ovarian cycle (in the ovaries)

  • Development of follicles
  • Release of sex hormones (estrogen and progesterone) in regulating uterine cycle
• Uterine cycle (in the uterus)

  • The repair/ growth / shedding of uterine lining
  • Regulated by sex hormones released by ovaries
• Menstrual flow stage (Day 1–5)

  • The first day of menstruation is the first day of the menstrual cycle.
  • The uterine lining breaks down and flows out of the body through the vagina.
  • The anterior pituitary gland secretes follicle-stimulating hormone (FSH) into the bloodstream.
  • Low levels of estrogen and progesterone
• Follicle stage (Day 6–13)

  FSH stimulates:

  • follicle development in the ovaries, and
  • estrogen secretions by the follicles
  • Level of estrogen is the highest a few days before ovulation
  • Estrogen causes the repair and growth of the uterine lining
• Ovulation (Day 14)

  • LH causes ovulation and the formation of the corpus luteum.
  • The corpus luteum secretes progesterone and some estrogen.
• Corpus luteum stage (Day 15–28)

  • High concentration of progesterone

  Progesterone prepares the uterine lining for the fertilised egg by:

  • causing it to thicken further, and
  • supplying it with blood capillaries.