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Rachel Parlour

Sexual reproduction in humans
Zygote- the diploid cell resulting from the fusion of two gametes
Embryo- structure developed from zygote; repeated mitosis forms cells that differentiate into tissues
and organs
Fetus- the embryo after developing main features of adult form (humans after 2/3 months)
Functions of parts of the female urinogenital system
Part
Ovary
Endometrium
Oviducts
Uterus
Cervix
Vagina
Vulva
Clitoris
Ureter
Urethra

Function
Female gonads where female gametes are made (eggs/ova)
Contains glands and many blood vessels, the lining of the uterus
Tubes that carry eggs from ovaries to the uterus
Where fertilisation takes place (womb)
Narrow entrance to the uterus from the vagina, normally blocked by a plug of
mucus and a ring of muscle can close it
A muscular tube with walls with elastic tissue
...

Protects the opening to the female body
A small structure equivalent to the male penis and can become erect
Tube carrying urine from the kidney to the bladder
Tube through which urine exits the body

Function of parts of the male urinogenital system
Part
Testis
Seminiferous tubules
Epididymis
Scrotum
Vas Deferens
Cowper’s gland
Prostate gland
Seminal vesicle
Penis

Function
Male gonads
Site of spermatogenesis
There are leydig cells around the tubules that produce testosterone
Sperm storage and maturation- where they develop the ability to swim
Keeps testis at 2-3C below body temperature- optimum for sperm
production
A tube that carries the sperm to the urethra
Secrete alkaline fluid to
neutralise the acidity of To activate the sperm
any urine remaining
Secretes fructose as an energy source for the
sperm (respiratory substrate)
Contains erectile tissue so that the penis can enter the vagina during
sexual intercourse

Gametogenesis
The formation of gametes involves three main stages:




Multiplication- diploid cells in the embryo, destined to become gametes, divide repeatedly
by mitosis
Growth- daughter cells resulting from mitotic division grow in size
Maturation- the product of the growth phase divides by meiosis and the haploid daughter
cells differentiate into the appropriate gametes

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Spermatogenesis
The process by which spermatozoa are produced in the germinal epithelium of the seminiferous
tubule
 Diploid germinal epithelial cells undergo mitosis forming diploid spermatogenia
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 Primary spermatocytes undergo meiosis I forming haploid secondary spermatocytes
 Haploid secondary spermatocytes complete meiosis II forming spermatids
 Spermatids mature forming sperm/ spermatozoa
...
They secrete fluid to nourish the spermatids and
protect them from the male’s immune system
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The spermatozoa produced are motile
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The middle
piece is packed with mitochondria to provide ATP for movement of the tail
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At puberty, once a month;
 Hormones stimulate the follicles to develop further
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 The primary oocyte completes the first mitotic division, forming the haploid secondary
oocyte and a small non-functioning polar body
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After fertilisation;
 The secondary oocyte completes meiosis II, forming a large ovum and a second polar body
 The nucleus of the sperm fuses with the nucleus of the ovum, forming a zygote
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This produces hormones
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The sperm’s function is to convey genetic information from male to
female
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The tail is therefore a modified flagellum
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In the middle piece the microtubules are surrounded by mitochondria arranged in spirals to
provide energy for making the tail wave
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It contains enough nutrients, in the cytoplasm, and metabolites to sustain itself through the
early stages of development
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1mm diameter (100µm)- sperm’s head is 2
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Capacitation- essential changes to sperm surface
2
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Fusion between sperm head and plasma membrane of secondary oocyte
4
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Secondary oocyte stimulated to complete meiosis II- two haploid nuclei fuse, zygote forms
In the testes, seminiferous tubules are grouped together (of approx
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From each bundle one
tube emerges to connect the bundle to the epididymis
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Chemical changes activate the sperm to become motile
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They’re now able to fertilise an egg but fluid is
added from the seminal vesicles, prostate gland and cowper’s gland forming semen, increasing
fertility
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Male sexual excitement (psychological or
physical) causes erection of the penis by dilation of arteries entering the penis and the flow of

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arterial blood into the spongy tissue
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Sexual stimulation climaxes with an orgasm (explosive wave of
intense pleasure for a few seconds) and muscles of prostate gland, seminal vesicles, vas deferens
and urethra contract causing ejaculation of semen- 3cubic cm, about 40 million sperm cells
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Fluid from
blood seeps through the vaginal epithelium, lubricating the action of the penis
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At orgasm, muscles of the vagina and uterus contract, they can be centred on the clitoris or vagina
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Alkaline semen protects sperm from
pH5
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Most sperm leak from the vagina without penetrating the cervix, which is
normally blocked by mucus
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Sperm movement to the oviducts
depends on their swimming and action of cilia lining the uterus and oviducts
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Capacitation
This involves changes in the membrane covering the acrosome- thin cap over the sperm’s nucleus
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7 hours
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Glycoprotein is added by the epididymis, and plasma proteins come from seminal fluid- removed by
enzymes in the uterus
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It occurs in the oviduct, triggered by chemicals secreted by follicle cells or
the egg’s zona pellucida
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The enzymes soften the zona pellucida’s glycoprotein at the contact point to
allow sperm passage
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g
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After the sperm has penetrated the egg membrane, the head and middle piece are drawn through
the cytoplasm towards the nucleus
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The diploid chromosome number is restored and zygote (fertilised egg) is ready for the
first mitotic division
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The sperm has a surface protein which binds to a
specific protein binding site on the surface of the zona pellucida
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The embryo reaches the
uterus 4 days after ovulation and attaches to the uterus wall- implantation
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Chorionic gonadotrophin (embryo produced hormone) prevents degeneration
of the corpus luteum and signals to the ovary the woman is pregnant
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It takes
3 days to reach the uterus then 3-4 days to implant in the uterus lining
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The chorion develops
villi to absorb nutrients and form part of the placenta
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Pregnancy test
Pregnant women secrete the hormone human chorionic gonadotrophin in their urine
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Human pregnancy
tests use immobilised antibodies on a urine dipstick to detect rates
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Clones of cells producing one antibody type, produced by lymphocytes which can’t divide, are used
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On a test
there is the first band of immobilised antibodies
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Antibody-hormone complexes diffuse up the dipstick with the urine
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Mobile antibodies marked with coloured latex move up the
stick, not carrying the hormone, by capillary action, and bind with the upper band of immobilised
antibodies
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If pregnant, both lines are blue
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- In-fertility is the inability to conceive (very rare)
Causes:
- Failure to ovulate due to an absence of or irregular menstrual cycle- 95% treatable with
clomiphene drug
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A couple are
infertile if they fail to conceive after 12 months
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The oocytes are collected using a tube through the belly button to the oviducts,
guided by ultrasound
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Each oocyte is placed in a separate dish and 100,000 sperm are added to each
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Oocytes are examined every 2-3days to see those fertilised
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They are inserted into the uterus via a tube

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