Human
Reproduction
Scope
Adapted from DBE revision guidelines
Human reproduction
Male reproductive system
Notes
consists of:
• the main male sex organ – a pair of testes in the
scrotum
• various ducts and tubules – seminiferous tubules,
epididymis, vas deferens
and the urethra
• accessory glands – prostate gland, Cowper’s gland
and seminal vesicles
• the external genitalia – penis
Seminiferous tubules
The testes contain seminiferous tubules which
are lined by germinal epithelium cells which
produce sperm cells.
Some of the cells develop into Sertoli cells
which provide nutrients for the spermatids to
become mature sperm cells. The seminiferous
tubules are surrounded by connective tissue
that contain the Cells of Leydig which produce
testosterone.
Male sex hormone
Testosterone has the following functions:
• development of the male secondary Sperm cell
sexual characteristics
• stimulating the maturation of sperm cells
Gametogenesis
Formation of gametes
in males it is called spermatogenesis • The head contains the nucleus which
Under the influence of testosterone, the diploid contains 23 chromosomes.
germinal epithelial cells (2n) lining the seminiferous • The acrosome (in the head) contains
tubules go through meiosis enzymes that dissolve the outer layer of
Each cell that goes through meiosis produces 4 haploid the egg allowing fertilisation to occur.
spermatids (n) • The middle portion contains
Each spermatid matures to form a haploid sperm cell mitochondria which provides energy for
the movement of the sperm cell.
• The long tail allows the sperm cell
to swim faster through fluid.
Human reproduction
Female reproductive system
Notes
consists of:
•the main female sex organ – the ovaries
• the ducts – fallopian tubes
• the accessory organs – the uterus and the vagina
• the external genitalia – the vulva
The ovum
Female sex hormones
Oestrogen has the following functions:
• development of the female secondary
sexual characteristics
• thickens endometrium
Progesterone has the following function:
• Maintain the thickness of the endometrium
Gametogenesis
Formation of gametes
• The nucleus contains 22 autosomes and
in Females it is called oogenesis
one sex chromosome (X)
The diploid germinal epithelium cells (2n) of the ovaries
• The cytoplasm nourishes the egg
go through the process of mitosis to form many follicles
• The jelly layer provides protection for
Every 28 days, the follicle stimulating hormone (FSH)
the early developmental stages of the
stimulates one follicle. Only one cell inside of that
fertilised egg
follicle enlarges and goes through the process of
meiosis
Out of the 4 (four) haploid cells produced through
meiosis, only one cell will survive to form a mature ovum
The other three cells from meiosis will degenerate
Human reproduction
Notes
Puberty in males and females
Puberty is the period during which males and females reach sexual maturity. Puberty
usually begins between the ages of 11 to 15, though it may occur much earlier or later
depending on the individual. During puberty the sex hormones are produced which
stimulate gametogenesis and sexual maturity. At the same time secondary sexual
characteristics develop.
Human reproduction
The menstrual cycle
Notes
28 day cycle that Consist of two cycles:
• Ovarian cycle
Ovarian cycle
Changes in the ovary
• Uterine cycle
Uterine cycle
Changes in the uterus
FSH stimulates a primary follicle to become a
Graafian follicle which contains a mature ovum
Graafian follicle produces the hormone oestrogen,
increasing the oestrogen levels in the blood.
The endometrium breaks down and is released On day 14, mature ovum is released (ovulation)
(menstruation) for about 4-7 days. stimulated by the Luteinising Hormone (LH) which
The endometrium is stimulated by oestrogen to is released by the pituitary gland.
become thicker, vascular and glandular. LH converts ruptured Graafian follicle to the
Progesterone stimulates the endometrium to corpus luteum. The corpus luteum secretes the
become even thicker and develop more blood hormone progesterone increasing the levels of
vessels and glands in preparation for possible progesterone in the blood.
implantation of the fertilised ovum.
If fertilisation doesn’t take place, menstruation If fertilisation took place the corpus luteum
begins again. remains large. If fertilisation did not take place,
the corpus luteum degenerates.
Hormonal control
Negative feedback
If the ovum is fertilised, the corpus luteum
remains active and continues secreting
progesterone. Increased levels of progesterone
in the blood inhibit the secretion of the follicle
stimulating hormone. As a result, no further
development of the follicle occurs.
If the ovum is not fertilised, the corpus luteum
degenerates. Progesterone in the blood will
drop, FSH secretion will no longer be inhibited.
A new follicle develops.
Human reproduction
Fertilisation
Notes
During copulation the penis is inserted into the
vagina, sperm cells are released into the vagina
when the male ejaculates. If the ovum is present in
the fallopian tube, the haploid sperm fuses into the
haploid ovum to form a diploid zygote.
formation of Blastula
The zygote divides by mitosis to forom a morula,
the morula further divides by mitosis to form a
blastula/blastocyst. Implantation
The blastula moves from the fallopian tube into the
uterus. It secretes enzymes that make the uterus
sof and embeds itself into the endometrium.
The blastula forms extra-embryonic membranes
(amnion & chorion).
The chorion extends into chorionic villi (finger-like
outgrowths) and form a placenta (Secretes
progesterone).
The blastula is now an embryo.
Functions of parts The placenta has the following functions:
• It is the point of attachment of the
foetus to the mother
Amnion with amniotic fluid
• It allows for diffusion of nutrients from
• Protects the foetus against mechanical injury
the mother to the foetus
(shock-absorber)
• It allows for the diffusion of oxygen
• Prevents dehydration
from the mother to the foetus and for the
• Maintains the temperature of the foetus
diffusion of carbon dioxide from the
• Allows for free-movement of the foetus as it
foetus to the mother (gas exchange)
grows and develops
• It allows for the diffusion of waste
Umbilical cord Consist of products from the foetus to the mother
• two umbilical arteries which carry deoxygenated • After 12 weeks, the placenta secretes
blood and waste products from the foetus to the progesterone to maintain the pregnancy
placenta.
• One umbilical vein which carries oxygenated Gestation last for 40 weeks or 280 days
blood, nutrients, water and other substances from
the placenta to the foetus.
Human reproduction
Terminology
