Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

The Reproductive System
Sexual Reproduction in Animals
Reproduction - Ability to produce individuals (offspring) of the same species
Most animals reproduce sexually
...
Gametes are formed by
meiosis

Male gamete = sperm – produced in testes and deposited though intercourse
(mating) into female reproductive tract by male reproductive system

23

Female gamete – egg (ovum) – produced in ovaries – fuses with male sperm to
form a zygote (which develops into a baby) in the female reproductive tract

Food store

23

A human egg surrounded by sperm
- one of which will fertilise it

1

Each gamete contains half the number of parental chromosomes
...


Sexual reproduction is the fertilization of a female gamete by a male gamete
...
g, bacteria
2 Budding – e
...
yeast; hydra
3 Vegetative propagation – e
...
strawberry

2

Stages in Sexual Reproduction in Humans
1
...
This is called ovulation
...
The egg cell moves into the oviduct
...
Many sperm are deposited in the vagina during sexual intercourse
...

4
...

5
...
Fusion of the
sperm and egg nucleus results in a single cell termed the zygote (46 chromosomes)
6
...
The embryo embeds itself in the uterus
wall and divides further
...
The cells continue to divide and
become specialised into tissues, which then form organs
...
The foetus than develops into the baby
...
The baby is delivered into the outside world at birth after 9 months (gestation period), by the
process of parturition (or labour)
The offspring varies genetically and phenotypically (physically) from the parent

3

Male Reproductive
System
Carries urine
from bladder to
urethra

Adds fluid containing
fructose (for energy),
enzymes and proteins
to sperm

Storage of sperm
Site of sperm
maturation

Adds alkaline fluid
containing sugars to
sperm

Semen – 3 to 5ml ejaculated
300 million sperm

Carries sperm from
testes to penis by wavelike muscular
contractions
(peristalsis) – also
termed vas deferens

Sac containing testes –
outside the body
Maintains optimum
temperature (below
body temperature of
370C) for sperm
formation by raising or
lowering the testes
Sperm cannot survive
for long at 370C

Carries urine from bladder
during urination and sperm
during ejaculation

Produces sperm and the
hormone testosterone
(sex hormone)

Becomes erect when stimulated to enter female vagina,
in order to deposit semen (sperm + fluid)
...


Hormonal control of sperm formation
Seminiferous tubules – site of
sperm production

4

Spermatogenesis (Sperm Production)
The control centres are the pituitary gland and the hypothalamus in the brain
...
This is released into the
blood and stimulates the anterior lobe of the pituitary gland
...

ICSH: this stimulates the leydig cells that produce testosterone
...

FSH: this stimulates the seminiferous tubules, including the Sertoli cells
...


Sertoli cell – nourish sperm

5

Female Reproductive
System
Narrow tube carrying
eggs from the ovaries
to the uterus
Has ciliated cells
Site of fertilisarion

Collects eggs released
from the ovary and
directs them into the
oviduct

Produces and releases
eggs
Produces hormones –
oestrogen and
progesterone

Ring of muscle between
vagina and uterus
Allows sperm to pass
into uterus from vagina
and blood to pass out
during menstruation
and the baby during
birth

Before ovulation, the cervix
produces a special mucous
for about 3 to 9 days
...

When mucous is present, it
nourishes and protects
sperm allowing them to live
for 3 to 5 days
...
Takes place in the ovaries
...

At birth, each ovary in a female has hundreds of thousands of eggs, but they are immature and
remain dormant until her first menstrual cycle, which occurs during puberty (sexual maturity)
...
This
whole process takes about three minutes and is known as ovulation
...


Effects of Oestrogen
Repair of uterine lining after menstruation
Stimulates release of LH
Inhibits production of \FSH
Secondary sexual characteristics at puberty

The outer layer of the ovary (the germinal epithelium) produces
primary oocytes (immature eggs)
...


After puberty one of these develops each month to form a secondary
oocyte (mature egg)
...
Fluid collects inside the
structure to form a fluid-filled cavity - the structure is called a Graafian
follicle
...
The secondary oocyte with
some surrounding follicle cells enters one of the oviducts – to be
propelled towards the uterus by cilia lining the oviducts

The remains turn into the corpus luteum

7

Ovary – Production and Release of Egg

The Menstrual Cycle

If an egg is not fertilised
The cycle begins with the start of the bleeding or menses (day 1), during which the lining of the
uterus and he unfertilised egg is shed
...

The menstrual cycle has 4 stages to it
...
The lining of the uterus breaks down and the bleeding starts (day 1-4)
2
...

3
...

4
...


8





The different stages of the cycle are controlled by a set of four hormones – FSH &
LH from the pituitary; OES & PROG from the ovary

Releasing hormone from hypothalamus - stimulates anterior lobe of the pituitary
gland to release FSH
...
The follicle
cells secrete oestrogen





Oestrogen stimulates the repair of the uterus wall and also inhibits the further
release of FSH so no new follicles develop in case pregnancy results
...

The surge in oestrogen stimulates the release of LH from the pituitary
...
Levels of LH
and FSH decline after day 14



The corpus luteum secretes progesterone
...
During this time the fertilised egg
divides a number of times to form a ball of cells, termed the embryo
...




The CL continues to secrete progesterone to maintain the lining
...

hCG maintains the CL and the secretion of progesterone and oestrogen from the
ovaries



If the egg is not fertilised, the CL breaks down and stops making progesterone and
menstruation occurs
...
LH and FSH are produced in the pituitary
gland in the brain
...
It also stimulates the ovary (follicle cells)
to secrete oestrogen
...
It also helps to trigger
the release of the egg by stimulating the pituitary to release LH – LH causes ovulation
...

Progesterone maintains the uterus lining after the egg is released and Inhibits FSH production
...
When the level of progesterone falls the lining breaks down

10

The hypothalamus releases GnRH: this stimulates the anterior lobe of the pituitary gland
...

The follicle secretes oestrogen: this stimulates the repair of the uterus wall
...
It also inhibits
the release of LH from the pituitary gland until shortly before ovulation
...

A surge of LH: this causes ovulation and the development of the corpus luteum
...

The corpus luteum secretes progesterone: this stimulates the thickening and the
vascularisation of the uterus wall in preparation for pregnancy
...
The discharge of the wall is called menstruation
...

b) If pregnancy occurs: the corpus luteum persists due to a hormone (CG - chorionic
gonadotrophin) being released
...
This allows fertility treatment and contraception
...
This keeps the oestrogen levels high which stops further egg release
...
It works well although if you give too
much you can get multiple births
Gender - Is it a girl or a boy?
Of the 23 pairs of chromosomes in the human cell’s nucleus there is 1 pair that is called the “sex
chromosomes”
...
However men have one X chromosome and a smaller one, the Y chromosome
...
(The phenotypes are what the genes actually
produce, the external features)
...
But since
both of the woman’s sex chromosomes are X, each egg cell will contain an X
...


11

The baby will be a girl if the fertilising sperm is an X sperm
...
The Y chromosome carries instructions for the male reproductive organs in a
region termed the sex determining region (SRY)
...

Some of the cells of the embryo produce outgrowth called villi (chorionic villi) – these extend into
the uterus wall and eventually form the placenta
Enzymes are released by the embryo to break down arterial and venous blood vessels in the
mother’s endometrium
...

The placenta allows a very close meeting between the baby’s blood and the mother’s
...

The mother and foetus are genetically different and may have different blood groups
– this may cause incompatability (agglutination) and may cause the foetus to die or
abort
...

However, some viruses (e
...
HIV, rubella) can cross the placenta
As the embryo grows it becomes surrounded by a membrane (bag) called the amnion
...
Waste materials such as carbon dioxide are also removed
...

Nutrients are carried by the mother’s artery to the placenta
...
They are taken to the foetus by the umbilical vein – e
...

Antibodies - pass from mother to foetus to give the foetus passive immunity during the pregnancy
and for a few months after birth
...
They diffuse into the bloodfilled space and into the mother’s vein to be carried away
...

Oestrogen:

Stimulates growth of uterus
...

Stimulates the duct system of the breasts to develop
...

Increases the sensitivity of the uterus to the hormone oxytocin (this causes the
uterus wall to contract)
...

Inhibits myometrium contractions (therefore decreasing the possibility of
miscarriage)
...

Inhibits the release of prolactin
...


HPL:

HCG:

Stimulates the growth and development of breasts
...

Maintains the corpus luteum for about 3 months
...


13

Needs of the Mother and Foetus
Practical and emotional support - from partner, family, friends and society
...

High levels of progesterone during pregnancy inhibit the release of the hormone oxytocin from
the pituitary
...

This causes the release of oxytocin from the pituitary
...

The cervix gradually dilates
...

Strong contractions of the uterus continue to push baby – within 10-60 minutes the head
emerges from the birth canal – the rest of the body following within minutes – helped by a
midwife or an obstetrician
Once the baby starts to breathe and cries, the umbilical cord is clamped in two places and
cut between the clamps
Stage 3 (Afterbirth)
Muscular contractions of the uterus continue after delivery to expel the placenta and the
remaining umbilical cord
...

Due to the loss of the placenta, oestrogen and progesterone levels fall, prolactin is no longer
inhibited so the breasts can produce milk
...

Complications
Breech birth – feet or bottom appear first
...
Can
endanger the baby – forceps delivery (use of forceps to turn the baby around – may damage head)
or Caesarian section (baby removed through a cut in the abdominal wall and uterus) performed
...
Performed in cases of health risks or overdue
birth

15

Mutations
Most of the time, everything from fertilisation to birth goes well
...
There seem to be mistakes made in the development of cells
...

Mutations are the changes in the DNA sequence
...
The base sequences are messed up!
Sometimes as little as one base might be missing or it could be a few
...
It is also possible that during meiosis parts of
chromosomes get damaged
...
It might end up making an
enzyme the wrong shape so that it doesn’t work
...

Mutations are more likely with exposure to nuclear radiation including X rays and UV rays, ’ Others
include chemicals known to cause mutations (termed “mutagens”) - cigarette and tobacco smoke
contains many carcinogens, cancer-causing chemicals
...

Women must be careful what they consume or take while they are pregnant
...
This
could cause serious damage to the developing embryo
...

In developing embryos they cause abnormal development and may cause early death
...
These cells develop into tumours,
spread into other parts of the body and so become cancers
...
For example a bacterial cell might mutate into a
form that shows antibiotic resistance
...
Natural selection is thought to be brought about by these rare,
beneficial mutations
...


16

Cystic Fibrosis
Mutation in chromosome 7
Sticky mucus produced in airways, digestive and reproductive tract
...
Up to menopause,
menstruation may stop temporarily due to:

18

Pregnancy
Breast feeding
Drop in body mass (e
...
in anorexia nervosa)
Towards reaching adulthood, a person gets taller, heavier, and changes in shape
Head becomes larger but relatively smaller – smaller proportion of body compared to earlier
years
Lymphoid system (thymus, lymph nodes and tonsils) – increases to 12 – body needs to
develop immunity to a large number of infectious diseases
Reproductive system – increase in growth after 12
General body growth – increases to adulthood
Brain, head, and nervous system – rapid growth from birth to 1 year

Old Age (Senescence) and Death
Senescence – decrease in the ability of a person to function maximally due to getting older
...
g
...

Malignant tumours – cells from malignant tumours invade surrounding healthy tissues or
enter the blood system and are carried to other parts of the body where they form
secondary tumours which are themselves cancerous
...

Causes

Chemical carcinogens (cancer causing substances) – tar in cigarette smoke
(lung cancer), asbestos (lung cancer), distillation products of fossil fuels
(tumours in the bladder), ionising radiation (X rays, gamma rays) – cause
cancer of the bone marrow (leukaemia) and other organs, UV light (skin
tumours)

Treated by surgery, radiotherapy or chemotherapy

19

Richard Doll – investigated correlation between cancer and its cause – accumulated data
and demonstrated the link (correlation - not a proof) between cigarette smoking and cancer
...
It takes place in the ovaries and begins before birth
...
It also produces
follicle cells that congregate around the oocytes, forming a structure called the primary follicle
...

After puberty one of these develops each month
...
The follicle cells
around it proliferate to form a wall many cells thick called the theca
...

The whole structure is called a Graafian follicle
...
The secondary oocyte with some surrounding
follicle cells leaves the ovary and enters one of the oviducts
...


Sexual Reproduction in Humans - The Final Stages
Sexual intercourse and fertilisation
For pregnancy to occur a sperm must fertilise the egg
...

For sex to take place, the penis needs to be inserted into the woman’s vagina and thus it needs to
be erect
...
Sperm are swept along,
past the prostate gland and the seminal vesicles, which secrete fluid to maintain the sperm in a
viable state
...
The alkaline semen is deposited at the top of the acidic vagina
...
It is thinnest, and therefore easiest for the sperm to penetrate
at the beginning of the menstrual cycle
...

It takes several hours to reach the oviducts, but this is beneficial because, before sperm can
fertilise an egg they must undergo a process called capacitation
...

It is possible for a sperm to fuse with a secondary oocyte if there is one near the top of an oviduct
...


21

The process of fertilisation is shown below:

When the two plasma membranes fuse the cortical reaction takes place
...
They cause the zona
pellucida to thicken and harden
...
After fertilisation the diploid zygote divides by mitosis to form a solid ball of cells
...
The morula moves towards the uterus, developing
into a hollow ball of cells, called the blastocyst
...


The development of a baby
About a week after the sperm has fertilized the egg, the egg has become a multicelled blastocyst,
a pinhead-sized hollow ball with fluid inside, now present in the uterus
...
It is the Oestrogen that causes the
endometrium to thicken and become rich with blood, and progesterone, another hormone released
by the ovaries, keeps the thickness of the endometrium constant so that the blastocyst can attach
itself securely to the uterus and continue to absorb nutrients from it
...

The egg grows and develops inside the uterus (womb) over the next 40 weeks under the protection
of the newly developed placenta
...


The cloning process of 'Dolly the sheep'
22

Produces exact copies
Genes copied within same species

Egg
donor

Nucleus
donor
unfertilised
egg from
first frog
u/v light
destroys
nucleus

(a)
Cloned frog is identical to second frog
Nucleus comes from this frog;
DNA/genes/information in nucleus; this controls
development
pipette

nucleus
(extracted from
second frog cell)
cell from
second frog

(b)
Advantages of cloning
large number of identical offspring;
guaranteed desired features; quick; economic
(c)
Disadvantages of clonoing
may all succumb to unexpected disease/change
in conditions
cut adaptation/reduce gene pool/limits variation

pipette

cell
division
growth

nucleus extracted
from second frog cell
injected into cell from
first frog
cloned frog

Plants can be cloned artificially using cuttings

23

24

25



---