Sexual reproduction in humans

• Parts of the female reproductive system and their functions

  • Ovaries = produce egg cells in follicles
  • Fallopian tubes = transports an egg cell from ovary to uterus
  • Uterus = where embryo develops
  • Cervix = separates uterus from vagina, protects fetus
  • Vagina = leads from the cervix to outside of the body
• Where does spermatogenesis take place?
• How does the human body produce gametes?
• Parts of the male reproductive system and their functions

  • Testes = production of sperm cells and testosterone
  • Vas deferens = carry sperm from testes to urethra
  • Prostate gland = secretes alkaline fluid to counteract vaginal acidity
  • Urethra = allows excretion of urine and semen from the body
  • Seminal vesicle = secretes fluid (proteins and fructose) to nourish sperm
  • Penis = penetrates vagina, releases sperm
  • Epididymis = stores sperm
  • Scrotum = holds and maintains an optimum temperature for testes
• Structures of the female reproductive system

  • Fallopian tube (oviduct)
  • Vagina
  • Ovary
  • Cervix
  • Uterus
  • Endometrium
• Types of gametogenesis

  • Spermatogenesis
  • Oogenesis
• Structures of the male reproductive system

  • Testis
  • Scrotum
  • Penis
  • Urethra
  • Epididymis
  • Prostate gland
  • Seminal vesicle
  • Vas deferens
• Spermatogenesis


  Primordial germ cells → Spermatogonia → Primary spermatocytes → Secondary spermatocytes → Spermatids → Four spermatozoa
• Name the three types of cells within testes
• The second meiotic division of oogenesis is completed if fertilisation takes place
• How primary oocytes form

  1. Primordial germline cells in the ovaries (and oviduct) divide by mitosis, forming oogonia

  2. Growth period of oogonia without further division forms primary oocytes

  3. Meiosis begins but pauses in prophase I until puberty
• Second meiotic division


  Secondary oocyte develops into a fertilised ovum and a second polar body
• Oogenesis takes place in the ovaries
• Oogenesis is gametogenesis in females that results in the production of secondary oocytes
• First meiotic division of oogenesis

  1. Primary oocyte divides in meiosis I to form secondary oocyte

  2. Polar body buds off and sticks to the oocyte
• Stages of oogenesis

  Primordial germ cell → oogonia → primary oocyte → secondary oocyte and polar body → ootid and polar bodies → ovum
• Structure of a secondary oocyte

  • Corona radiata - outer layer of follicle cells
  • Zona pellucida - coating above cytoplasm that prevents polyspermy and hardens when cortical granules release chemicals
  • Haploid nucleus - fertilisation restores diploid chromosome number
• Structure of a mature sperm cell

  • Acrosome contains digestive enzymes which break down the zona pellucida of the egg
  • Flagellum for propulsion
  • Many mitochondria for energy
• A polar body is a haploid cell produced during meiosis in females that does not have the ability to be fertilised
• A secondary follicle is a larger follicle that has developed from a primary follicle
• A Graafian follicle is a mature fluid-filled follicle in the ovary within which an egg cell develops
• Early embryo development

  Zygote → Blastocyst → Implantation
• During fertilisation, the spermatozoa move into fallopian tubes, acrosome binds to zona pellucida and releases hydrolase enzymes that digest the zona pellucida, membranes of sperm and secondary oocyte fuse allowing sperm nucleus to enter oocyte, nuclei fuse forming a diploid zygote, and cortical reaction causes zona pellucida to harden preventing polyspermy
• Sexual intercourse is the entry of the male reproductive organ and the deposition of sperm into the female reproductive tract
• A blastocyst forms through the stages of zygote → blastocyst → implantation
• A corpus luteum is a mass of cells that forms from the Graafian follicle after ovulation. It serves as a temporary endocrine structure during pregnancy, secreting progesterone
• Fertilisation

  1. Spermatozoa move into fallopian tubes

  2. Acrosome binds to zona pellucida and releases hydrolase enzymes that digest the zona pellucida

  3. Membranes of sperm and secondary oocyte fuse, allowing sperm nucleus to enter oocyte

  4. Nuclei fuse, forming a diploid zygote

  5. Cortical reaction causes zona pellucida to harden, preventing polyspermy
• A primary follicle is an immature ovarian follicle surrounded by two layers of follicular cells
• How a blastocyst forms


  Several mitotic divisions of zygote (cleavage) produce a ball of cells, the blastocyst
• Hormones involved in the menstrual cycle

  • Follicle stimulating hormone (FSH)
  • Luteinising hormone (LH)
  • Oestrogen
  • Progesterone
• Early embryo development stages

  Zygote → Blastocyst → Implantation
• HCG


  • Human chorionic gonadotropin
  • Hormone secreted by the developing embryo that maintains the corpus luteum during early pregnancy
• Changes in progesterone and oestrogen levels prior to birth

  • Oestrogen levels increase
  • Progesterone levels decrease
• Role of the placenta during pregnancy

  • Exchange of gases and nutrients
  • Barrier between fetal and maternal blood
  • Secretes progesterone and oestrogen
  • Protects the mother’s immune system
  • Protection from the difference between maternal and foetal blood pressure
• Consequences if implantation does not occur

  • Corpus luteum degenerates due to decreasing FSH and LH levels
  • Progesterone levels decrease
  • Endometrium breaks down
• Spaces between the chorionic villi that contain maternal blood
• Role of amniotic fluid during fetal development

  It protects the foetus and acts as a shock absorber
• Role of the umbilical artery

  Carries deoxygenated blood from the fetus to the placenta
• Role of prolactin


  Stimulates lactation during and after birth
• What is amniotic fluid?