The digestive system breaks down food into simple nutrients such as carbohydrates, fats, and proteins. These can then be absorbed into your blood so your body can use them for energy, growth, and repair. Anything that isn't used is waste and leaves the body as feces

Blood consists of:

• Red blood cells – to carry oxygen

• White blood cells – that make up part of the immune system

• Platelets – needed for clotting

• Plasma – blood cells, nutrients, and wastes float in this liquid.

  
  

  The heart pumps blood around the body. It sits inside the chest, in front of the lungs, and slightly to the left side. The heart is actually a double pump made up of four chambers, with the flow of blood going in one direction due to the presence of the heart valves. The contractions of the chambers make the sound of heartbeats.

  Blood vessels have a range of different sizes and structures, depending on their role in the body.

The main organ of the respiratory system is the lungs. Other respiratory organs include the nose, the trachea, and the breathing muscles (the diaphragm and the intercostal muscles).

Breathing in through the nose warms and humidifies the air that is breathed in. Nose hairs help to trap any particles of dust. The warmed air enters the lungs through the windpipe or trachea. The trachea is a hollow tube bolstered by rings of cartilage to prevent it from collapsing.

The lungs are inside the chest, protected by the ribcage, and wrapped in a membrane called the pleura. The lungs look like giant sponges. They are filled with thousands of tubes, branching smaller and smaller. The smallest components of all are the air sacs, called alveoli. Each one has a fine mesh of capillaries. This is where the exchange of oxygen and carbon dioxide takes place.

Three major glands of the endocrine system are the hypothalamus, pituitary, and thyroid. The hypothalamus The hypothalamus is in the lower central part of the brain. It links the endocrine system and nervous system. Nerve cells in the hypothalamus make chemicals that control the release of hormones secreted from the pituitary gland. The hypothalamus gathers information sensed by the brain (such as the surrounding temperature, light exposure, and feelings) and sends it to the pituitary. This information influences the hormones that the pituitary makes and releases.

The pituitary gland is at the base of the brain and is no bigger than a pea. Despite its small size, the pituitary is often called the "master gland." The hormones it makes control many other endocrine glands. The pituitary also secretes endorphins, chemicals that act on the nervous system and reduce feelings of pain. The pituitary also secretes hormones that signal the reproductive organs to make sex hormones.

The thyroid is in the front part of the lower neck. It's shaped like a bow tie or butterfly. It makes the thyroid hormones thyroxine and triiodothyronine. These hormones control the rate at which cells burn fuels from food to make energy. The more thyroid hormone there is in the bloodstream, the faster chemical reactions happen in the body.

Thyroid hormones are important because they help kids' and teens' bones grow and develop, and they also play a role in the development of the brain and nervous system.

• Bones: Bones are your body’s main form of structural support. Adults have between 206 and 213 bones in their bodies.

• Muscles: Muscles are made of tightly woven, stretchy fibers. You have more than 600 muscles in your body that help you do everything from walking, running and jumping to breathing and digesting food.

• Cartilage: Cartilage is strong, flexible tissue that acts like a shock absorber in joints throughout your body.

• The central nervous system is made up of the brain and spinal cord.

• The peripheral nervous system is made up of nerves that branch off from the spinal cord and extend to all parts of the body.

The nervous system transmits signals between the brain and the rest of the body, including internal organs. In this way, the nervous system’s activity controls the ability to move, breathe, see, think, and more.¹

The basic unit of the nervous system is a nerve cell, or neuron. The human brain contains about 100 billion neurons. A neuron has a cell body, which includes the cell nucleus, and special extensions called axons (pronounced AK-sonz) and dendrites (pronounced DEN-drahytz). Bundles of axons, called nerves, are found throughout the body. Axons and dendrites allow neurons to communicate, even across long distances.

• white blood cells

• antibodies

• complement system

  White blood cells are the key players in your immune system. They are made in your bone marrow and are part of the lymphatic system.

  White blood cells move through blood and tissue throughout your body, looking for foreign invaders (microbes) such as bacteria, viruses, parasites, and fungi. When they find them, they launch an immune attack.

  White blood cells include lymphocytes (such as B-cells, T-cells, and natural killer cells) and many other types of immune cells.

  Antibodies help the body to fight microbes or the toxins (poisons) they produce. They do this by recognizing substances called antigens on the microbe's surface or in the chemicals they produce, which mark the microbe or toxin as foreign. The antibodies then mark these antigens for destruction. There are many cells, proteins, and chemicals involved in this attack.

  The complement system is made up of proteins whose actions complement the work done by antibodies.

• Vagina – a muscular canal around 7.5 cm long that extends from the neck of the womb to the genitals, or vulva.

• Uterus (womb) – a muscular organ, shaped like an upside down pear. Its lining is called the endometrium. The neck or entrance to the womb is the cervix, which has a small hole in its center.

• Fallopian (uterine) tubes – these tubes extend from the womb, one on each side. They both open near an ovary. These tubes carry the egg (ovum) from the ovary to the womb.

• Ovaries – two small almond-shaped glands that contain ova. Sex hormones are also made by the ovaries.

The menstrual cycle

Hormones secreted by the ovaries and a small gland in the brain called the pituitary gland control the menstrual cycle. The average menstrual cycle is around 28 days.

After a period, rising levels of the hormone estrogen help to thicken the lining of the womb (the endometrium). At mid-cycle, an egg is released from one of the ovaries (ovulation). If the egg is fertilized on its journey down the fallopian tube, it lodges in the womb lining.

If the egg is unfertilized, falling levels of the hormone progesterone make the womb lining come away. This is called a period, or menstruation. The cycle then repeats.

When you want to have a baby you can improve your chance of getting pregnant if you know about ovulation and the ‘fertile window’ in the menstrual cycle. Read more on ovulation and the fertility window.

The egg (ovum)

A woman’s entire egg supply is developed when she is still an unborn baby. At the start of puberty, the eggs are ripened inside the ovary and one is released every month.

Each egg contains genetic material. At menopause, the ovaries stop making hormones and eggs are no longer ripened or released.

Female reproductive system problems

Some reproductive health conditions women may experience include:

• endometriosis – the presence and growth of functioning endometrial tissue in places other than the uterus

• polycystic ovarian syndrome (PCOS)

• fibroids – non-malignant tumors of the womb

• infertility – inability to become pregnant

• painful periods

• premenstrual tension

• sexually transmissible infections (STIs) – bacterial or viral infections acquired through sexual contact, some of which can cause cancer or infertility.

The male reproductive system

The male reproductive organs are the penis, the testicles, the epididymis, the vas deferens and the prostate gland:

• Penis – contains tissue that fills with blood during sexual arousal, making the penis erect (or ‘hard’). Semen is a mixture of sperm and fluid from the male reproductive organs. It exits the penis, through the urethra, during ejaculation.

• Testicles (testes) – oval sex glands located in a skin sack called the scrotum. Sperm and sex hormones are made by the testicles. Keeping the testicles outside of the body means they have a lower temperature than the rest of the body, which is important for sperm production.

• Epididymis – a series of small tubes attached to the back of each testicle. The epididymis collects and stores sperm.

• Vas deferens – the epididymis eventually becomes the vas deferens, a larger tube that transports sperm to the urethra (the urinary passage from the bladder).

• Accessory sex glands – including the prostate gland, seminal vesicles and the bulbourethral glands. These glands contribute nourishing fluid to the sperm.

https://www.betterhealth.vic.gov