Growth and Reproduction (MYP Science)

What's a hormone?

The nervous system isn’t the only message-relaying system of the human body. The endocrine system also carries messages. The endocrine system is a system of glands that release chemical messenger molecules into the bloodstream. The messenger molecules are hormones. Hormones act slowly compared with the rapid transmission of electrical messages by the nervous system. They must travel through the bloodstream to the cells they affect, and this takes time. On the other hand, because endocrine hormones are released into the bloodstream, they travel throughout the body. As a result, endocrine hormones can affect many cells and have body-wide effects.

Glands of the Endocrine System

The major glands of the endocrine system are shown in the figure below. You can access a similar, animated endocrine system chart at the link below.http://www.abpischools.org.uk/page/modules/hormones/horm2.cfm

The glands of the endocrine system are the same in males and females except for the testes, which are found only in males, and ovaries, which are found only in females.

Hypothalamus

The hypothalamus is actually part of the brain, but it also secretes hormones. Some of its hormones “tell” the pituitary gland either to secrete or to stop secreting its hormones. Its other hormones include antidiuretic hormone (ADH) and oxytocin.

Antidiuretic hormone stimulates the kidneys to conserve water by producing more concentrated urine.

Oxytocin stimulates the contractions of childbirth, among other functions.

The hypothalamus and pituitary gland are located close together at the base of the brain.

Pituitary Gland

The pea-sized pituitary gland is attached to the hypothalamus by a thin stalk (see Figure above). Most pituitary hormones control other endocrine glands. That’s why the pituitary is often called the “master gland” of the endocrine system.

Other Endocrine Glands

The thyroid gland is a large gland in the neck. They control how quickly cells use energy and make proteins.

The pancreas is located near the stomach. Its hormones include insulin and glucagon. These two hormones work together to control the level of glucose in the blood. 

The two adrenal glands are located above the kidneys. The inner part of each adrenal gland, called the medulla, secretes fight-or-flight hormones such as adrenaline, which prepare the body to respond to emergencies. 

The male gonads are called testes. They secrete the male sex hormone testosterone. 

The female gonads are called ovaries. They secrete the female sex hormone estrogen. 

Sex hormones are involved in the changes of puberty. They also control the production of gametes by the gonads.

Study Guide (Final)

Criterion A 

Sex cells and chromosomes

Human body cells each contain 23 pairs of chromosomes. Parents pass on their genes to their offspring in their sex cells.

• female sex cells are called egg cells, or ova
• male sex cells are called sperm.

Collectively, eggs and sperm are called gametes or sex cells. When fertilisation occurs, an egg (ovum) and a sperm fuse (join) to form a zygote.

Process of fertilisation

Sex cells only contain one chromosome from each pair; meaning that the egg contains 23 chromosomes and the sperm contains 23 chromosomes.

When an egg cell and sperm cell join together, the fertilised egg cell contains 46 chromosomes or 23 pairs of chromosomes. One chromosome in each pair comes from the mother, the other from the father.

The female reproductive system

Ovaries

The two ovaries contain ova (eggs). Ova are the female gametes or sex cells. Women have these cells in their bodies from birth, whereas men produce new sperm continually.

Oviducts (Fallopian Tubes)
Each ovary is connected to the uterus by an oviduct (fallopian tube). The oviduct is lined with ciliated cells. Every month, an ovum (egg) develops and becomes mature, and is released from an ovary. The cilia waft the ovum along inside the oviduct and into the uterus.

Uterus and cervix
The uterus is a muscular bag with a soft lining. It is where a baby develops until its birth. The cervix is a ring of muscle at the lower end of the uterus. It keeps the baby in place while the woman is pregnant.

Vagina and urethra

The vagina is a muscular tube that leads from the cervix to the outside of the woman's body. A man's penis goes into the woman's vagina during sexual intercourse. The opening to the vagina has folds of skin called labia that meet to form a vulva.
The urethra also opens into the vulva, but it is separate from the vagina. It passes urine out of the body from the bladder.

The male reproductive system

Testes

The two testes (one is called a testis) are contained in a bag of skin called the scrotum. They have two functions:

• to produce sperm (the male gametes or sex cells)
• to make the hormone testosterone

Sperm duct and glands

The sperm pass through the sperm ducts, and mix with fluids produced by glands (seminal vesicles). The fluids provide the sperm cells with nutrients. This mixture is called semen.

Penis and urethra

The penis has two functions:

• to pass urine out of the body from the bladder
• to pass semen into the vagina of a woman during sexual intercourse

The urethra is the tube inside the penis that can carry urine or semen. A ring of muscle ensures that urine and semen do not get mixed up.

Fertilisation

During sexual intercourse the man's penis releases semen into the woman's vagina. Sperm cells travel from the sperm duct in semen to the penis and into the top of the vagina. They swim past through the cervix and enter the uterus towards the fallopian tube. If a sperm cell meets with an egg cell there, fertilisation can happen. Fertilisation happens when an egg cell meets with a sperm cell and joins with it.

The fertilised egg divides to form a ball of cells called an embryo. This attaches to the lining of the uterus and begins to develop into a foetus (pronounced "fee-tuss") and finally a baby.

Development of the foetus

The foetus relies upon its mother as it develops. These are some of the things it needs:

• protection
• oxygen
• nutrients (food and water).
• It also needs its waste substances to be removed.

The foetus is protected by the uterus and the amniotic fluid, a liquid contained in a bag called the amnion. 

The placenta is responsible for providing oxygen and nutrients, and removing waste substances. It grows into the wall of the uterus and is joined to the foetus by the umbilical cord. 

The mother's blood does not mix with the foetus's blood, but the placenta lets substances pass between the two blood supplies:

• oxygen and nutrients diffuse across the placenta from the mother to the foetus
• waste substances, such as carbon dioxide, diffuse across the placenta from the foetus to the mother.

This means that in the placenta there is a large surface area and a thin barrier between the two bloods (mother’s and baby’s) and so exchange of materials by diffusion is possible.

Birth
After nine months the baby is ready to be born. The cervix relaxes and muscles in the wall of the uterus contract, pushing the baby out of the mother's body.

Criterion B:

Hint: Designing an experiment to test the effects of a drug on a named disease (i.e. vitamin D; arthritis).

Criterion C:

Hint: Processing data related to in vitro fertilization