[BIO] Chapter 16 - Reproduction in Humans

© Hee Xin Wei (Copyrighted) Topic 16: Reproduction in humans

Chapter Analysis FOCUS EXAM WEIGHTAGE •Constitute to around 6.5% in Paper 2 in the past 5 years •commonly tested in MCQ and structured questions •tested once in section B in the past 5 years •straightforward chapter •linked to homeostasis & hormones

male reproduction system female reproduction system Key Concept

Testes •Produces sperms (male gametes) •Produce male sex hormones e.g. testosterone. Male sex hormones are responsible for development and maintenance of secondary sexual characteristics. Epididymis Where sperms are stored Scrotum •Testes are held in the scrotum, which are pouch-like sac outside the body •This allows the scrotum to be at a lower temperature than body temperature, which is essential for sperm production. Sperm ducts / Vas deferens Transport sperm from the epididymis to the urethra. Prostate gland •Together with Seminal vesicle and Cowper’s gland/Bulbourethral gland, these 3 glands secrete fluid that is mixed with sperms to make semen •The fluids contain nutrients and enzymes which nourish and activate the sperm, allowing them to swim actively. Urethra •Urethra is a tube which passes from the bladder •passage for urine and semen to pass out of the body Penis •Penis is an erectile organ, containing erectile tissue, which allows the spaces within the tissue to be filled up with blood. •When filled with blood, the penis becomes erect and hard, allowing it to enter the vagina of a woman during sexual intercourse to deposit semen. male reproductive system

sperm cell Head •The head is about 2.5 μm wide. •It contains a large nucleus with small amounts of cytoplasm. The nucleus carries a haploid number of chromosomes. •Acrosome is a vesicle containing enzymes. The enzymes break down part of the egg membranes so that the sperm can penetrate the egg during fertilisation. Middle piece •The middle piece contains numerous mitochondria, which provides energy for the sperm to swim towards the egg. Tail (flagellum) •It carries out beating movement to swim towards the egg

female reproductive system Ovaries •Produces ova (S:ovum), female gamete •Produce female sex hormones e.g. estrogen and progesterone. Female sex hormones are responsible for development and maintenance of secondary sexual characteristics. Oviducts / Fallopian tubes •Narrow muscular tube where ovary releases the ovum into and leads to uterus •Cilia on the inner lining help move the ovum to the uterus. •Where fertilisation happens Uterus •The uterus is a thick muscular organ. •The uterus is lined by uterine lining or endometrium •The endometrium is richly supplied with blood vessels. -It is broken down every month and flows out of the body in the process called menstruation. -It is the site of implantation of the embryo post-fertilisation. •Uterus is where foetus develops during pregnancy Cervix •The cervix is a circular ring of muscle that opens into the vagina. •It enlarges during birth to allow the passage of the foetus. Vagina •Birth canal through which the baby is born. •Where sperm is deposited during sexual intercourse.

Ovum (Egg cell) •The egg is spherical and about 120 μm - 150 μm wide (almost 50 times larger than sperm) •Has a large nucleus containing haploid set of chromosomes. •Has abundant cytoplasm which may contain a small amount of yolk. •Surrounded by a plasma membrane and an outer membrane. Cell membrane Outer membrane

menstrual cycle fertilisation implantation Key Concept

menstrual cycle Primary follicle Graafian follicle Corpus luteum Day 1 - 5 Menstruation •The endometrium breaks down and flows out of the body through the vagina. Day 6 - 13•The ovaries secrete estrogen which stimulates repair and growth of the endometrium. It becomes thick and spongy with blood vessels. •Estrogen prevents maturation and development of more ova Day 14 Ovulation •a mature ovum is released from the one ovary to oviduct. •Estrogen level starts to fall and secretion of progesterone is stimulated. Day 15 - 28•The ovaries secrete progesterone, which maintains the endometrium by causing it to thicken further and preparing for implantation of zygote. •Progesterone inhibits ovulation Day 28 •Secretion of progesterone and estrogen decline sharply at the end of cycle •If there is no implantation, The endometrium is no longer maintained and disintegrates. •The cycle repeats.

Fertilisation FERTILE PERIOD •The fertile phase of the cycle is from day 11 to 17. •This is because sperms can survive for 2 to 3 days in the female reproductive system, thus sperms deposited in the vagina from day 11 onwards can fertilise the ovum which is released on day 14 from the ovaries •The ovum can survive for 1 to 2 days after ovulation; hence fertilisation is possible up till day 17. •Other days of the menstrual cycle are infertile phase. 1.During sexual intercourse, semen containing sperms is deposited into the vagina of a woman. 2.The sperms swim up the oviducts and encounter the ovum. 3.The acrosome of the sperms release enzymes to disperse the layer of cells surrounding the ovum and break down the outer membrane of the ovum. 4.The sperm nucleus fuses with the egg nucleus. This process is called fertilisation, forming zygote 5.The plasma membrane of the egg undergoes a change as soon as a single sperm has entered, preventing other sperms from entering. 6.The remaining sperms eventually die.