Human Fertilization

Human fertilization is the union of a human egg and sperm, usually occurring in the ampulla of the uterine tube. It is also the initiation of prenatal development. Scientists discovered the dynamics of human fertilisation in the nineteenth century.^[1]

The process of fertilization involves a sperm fusing with an ovum—usually following ejaculation during sexual intercourse. It is possible, but less probable, for fertilization to occur without sexual intercourse, artificial insemination, or In vitro fertilisation.^[2][3][4]Upon encountering the ovum, the acrosome of the sperm produces enzymes which allow it to burrow through the outer jelly coat of the egg. The sperm plasma then fuses with the egg's plasma membrane, the sperm head disconnects from its flagellum and the egg travels down the Fallopian tube to reach the uterus.

Its the process of fertilization from where it begins. Before ovulation, mucus is secreted which is extremely stretchable. This is the highly fertile period for chancing conception. As it is the mucus that carries the sperm into the uterus. During intercourse the excitement dilates the arterioles that supplies the blood to the penis. The blood then is accumulated in three cylindrical soft sinuses that move through the penis lengthwise. They cause pressure that enables the penis toenlarge, get erect and penetrate the vagina.

Straddling increases the tension to end in ejaculation where the walls of the vas deferns contract and force the sperm out. On the way out seminal vesicles, Cowper's glands, and the prostate glands add some more fluids. These fluids are like a source of energy they provide a chemical environment for the sperm. When the sperm is mixes with these fluids it is called semen. It helps the mobility of the sperm into the urethra and to the vagina.

From the vagina the sperm moves on to the egg i.e. through the fallopian tubes to the egg (i.e. if the egg ispresent). The sperm swims for several centimetres every second but the muscular movement of the wall of the uterus and the tubes helps its mobility. Research also claims that the egg attracts the sperm through some chemical secretions. However, the sperm takes at least 15 minutes to reach the egg. At any ejaculation a hundred thousand sperms are flushed out. Out of these only a few reach the urethra and only one breaks the egg.

When the sperm reaches the egg, fertilisation begins. First the head of the sperm gets attached to the egg. As they merge the concerned membranes take in all the contents of the sperm into the egg. Immediately the egg releases the cytosol from the egg that makes it impenetrable for the other sperms that arrive.

Then the nucleus of male increases in size to form the male pronucleus and the egg enlarges to form the female pronucleus. These two nuclei then move to form a set of chromosomes, this them is the fertilized egg or zygote.
The zygote then gets settled in the womb and sends the message to the brain that fertilization has taken place. The body then gets ready to house a baby.

In vitro fertilisation (IVF) is a process by which egg cells are fertilized by sperm outside the womb, in vitro.

Oxygen Transport in Human Body

The important principle to remember is that oxygen is needed by the cell and that carbon dioxide is produced as a waste product of the cell. Carbon dioxide must be expelled from the cells and the body.

The lungs serve to exchange the two gases in the blood. Oxygen enters the blood from the lungs and carbon dioxide is expelled out of the blood into the lungs. The blood serves to transport both gases. Oxygen is carried to the cells. Carbon dioxide is carried away from the cells.

Respiration and Transport in Human Body

Respiratory System: Oxygen Delivery System

The primary function of the respiratory system is to supply the blood with oxygen in order for the blood to deliver oxygen to all parts of the body. The respiratory system does this through breathing. When we breathe, we inhale oxygen and exhale carbon dioxide. This exchange of gases is the respiratory system's means of getting oxygen to the blood.

Respiration is achieved through the mouth, nose, trachea, lungs, and diaphragm. Oxygen enters the respiratory system through the mouth and the nose. The oxygen then passes through the larynx (where speech sounds are produced) and the trachea which is a tube that enters the chest cavity. In the chest cavity, the trachea splits into two smaller tubes called the bronchi. Each bronchus then divides again forming the bronchial tubes. The bronchial tubes lead directly into the lungs where they divide into many smaller tubes which connect to tiny sacs called alveoli. The average adult's lungs contain about 600 million of these spongy, air-filled sacs that are surrounded by capillaries. The inhaled oxygen passes into the alveoli and then diffuses through the capillaries into the arterial blood. Meanwhile, the waste-rich blood from the veins releases its carbon dioxide into the alveoli. The carbon dioxide follows the same path out of the lungs when you exhale.

The diaphragm's job is to help pump the carbon dioxide out of the lungs and pull the oxygen into the lungs. The diaphragm is a sheet of muscles that lies across the bottom of the chest cavity. As the diaphragm contracts and relaxes, breathing takes place. When the diaphragm contracts, oxygen is pulled into the lungs. When the diaphragm relaxes, carbon dioxide is pumped out of the lungs.