1.4 Flashcards
Follicle cells secrete
Chemicals that activate the release of enzymes from sperm
6 Parts of an ovum
Nucleus Follicle cells Cytoplasm Lipid droplets Zona pellucida Lysosomes
(Ovum) Cytoplasm is very large so
The egg can divide immediately
(Ovum) lipid droplets are the
Source of energy for growth and division for the developing embryo until the placenta has formed
(Ovum) zona pellucida hardens once the sperm nucleus has
entered the ovum, this stops the entry of other sperms into the ovum (avoids polyspermy)
(Ovum) lysosomes release chemicals that
Cause zona pellucida to harden
5 Parts of the sperm:
Nucleus Head Mid piece Tail (flagellum) Acrosome
(sperm) head contains the
Nucleus and the lysosomes (Acrosome)
(sperm) mid piece contains…
Lots of mitochondria which makes ATP for the sperms to swim
(sperm) the flagellum is made from proteins and micro tubules, which
uses ATP to propel the sperm forwards
(sperm) the Acrosome is a specially modified lysosome in the sperm’s head
The Acrosome swells and bursts when the sperm comes in contact with the follicle cells and zona pellucida
The enzymes in the Acrosome digest
The follicle cells and zona pellucida to allow the cell membrane of the sperm and ovum to fuse
During copulation the spongy tissues in the penis become swollen with blood making it hard and erect this:
Makes it easier to enter the vagina
Semen is ejaculated from the penis and released at the end of the vagina close to the cervix and is:
Alkaline to neutralise the acidity of the vagina
The sperm use their flagella to swim through the mucus in the cervix and towards the oviduct, usually takes between 3-5 hours and
Contractions of the uterine muscles are thought to help the sperm reach the oviduct
Capacitation are the changes that occur in the sperm along the fertilising tract to
Enable them to fertilise the oocyte
Capacitation involves the
Removal of cholesterol and some glycoproteins from the membrane above the Acrosome
(CAPACITATION) the removal of cholesterol and glycoproteins makes the membrane
More fluid and more permeable to calcium ions
The Acrosome reaction must take place before the
Sperm can fertilise the oocyte
The Acrosome reaction involves the Acrosome releasing the enzymes that help the sperm to digest it’s way through the
Zona pellucida
Stage 1 AR) the sperm head binds to the jelly coat - this triggers the entry of
Calcium ions into the sperm head
Stage 2 of AR) the outer membrane of the sperm fuses with the membrane surrounding the Acrosome. This allows the Acrosome to
Release enzymes that digest a pathway through the zona pellucida
Stage 3 of the AR) the sperm membrane fuses with the plasma membrane of the oocyte - allowing the sperm nucleus to
Enter the oocyte
When the successful sperm digests it’s way through the jelly coat, the sperm membrane fuses with the oocyte membrane, allowing the
Nucleus of the sperm to enter the oocyte
As the sperm membrane fuses with the oocyte this causes vesicles in the oocyte called cortical granules to fuse with the oocyte membrane and release their contents into the space between the oocyte membrane and the jelly coat - known as the
Cortical reaction
The cortical reaction changes the zona pellucida which forms a
Fertilisation membrane that prevents the entry of more sperm
Stage 1 of fertilisation)
Acrosome reaction occurs
Stage 2 of fertilisation) the enzymes have enabled the sperm to penetrate the jelly coat. The sperm membrane fuses with the
Plasma membrane of the oocyte
Stage 3 of fertilisation) the sperm nucleus enters the oocyte and the cortical reaction occurs
Cortical granules are released by the oocyte that change the structure of the ZP
- no more sperm can enter the oocyte
- oocyte undergoes the second division of meiosis
Stage 4 of fertilisation) the male and female nuclei fuse, forming a
Diploid zygote
Stage 5 of fertilisation) a spindle forms and the zygote divides by
Mitosis
The fertilised egg becomes a
Zygote
-diploid cell
As the zygote travels along the oviduct it divides by
Mitosis
After 3-4 days it has formed a ball or cells known as a
Morula
About 5-6 days it has formed a
Blastocyst
-hollow ball of cells
Outer layer of blastocyst =
Trophoblast
Trophoblast will develop into
The membranes around the embryo and the beginnings of the placenta
The inner cell mass is the part of the blastocyst from which the
Embryo will develop
The blastocyst reaches the uterus about a week after fertilisation it takes a few days for it to
Implant into the endometrium
(Implantation) The zona pellucida surrounding the blastocyst break soon at the trophoblast cells at one end of the embryo form
Branched extensions called villi that secrete enzymes
(Implantation) these enzymes digest the outer layer of the endometrium,
Releasing nutrients for the developing embryo
