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The digestive system is made up of the digestive tract (the gut) and other organs like the liver, pancreas, and gall bladder. It is where your body breaks down food and absorbs nutrients. The digestive system is a long, twisting tube that starts at the mouth and goes through the esophagus, stomach, small intestine, and large intestine, and ends at the anus.

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

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All cells in the body need to have oxygen and nutrients, and they need their wastes removed. These are the main roles of the circulatory system. The heart, blood, and blood vessels work together to service the cells of the body. Using the arteries, veins, and capillaries network, blood carries carbon dioxide to the lungs (for exhalation) and picks up oxygen. The blood gathers food nutrients from the small intestine and delivers them to every cell.

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.

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Our cells need oxygen to survive. One of the waste products produced by cells is another gas called carbon dioxide. The respiratory system takes oxygen from the air we breathe and expels the unwanted carbon dioxide.

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.

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The endocrine system is made up of glands that make hormones. Hormones are the body's chemical messengers. They carry information and instructions from one set of cells to another. The endocrine system influences almost every cell, organ, and function of our bodies.

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.

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The skeleton (which includes bones, ligaments, tendons, and cartilage) and muscles that are attached to it make up the musculoskeletal system. It gives the body its basic structure, posture, and the ability to move. In addition to the basic structural role , the larger bones in the body contain bone marrow, where blood cells are formed. Also, all bones are major storage sites for calcium and phosphorus. Muscles contract to help operate the respiratory system and maintain body temperature. Three main features of the musculoskeletal 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.

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The nervous system has two main parts:

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.

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The immune system is made up of a complex network of organs, cells, and proteins that fight infection (microbes). The three main parts of the immune system are:

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.

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The female reproductive organs are the vagina, womb (uterus), fallopian tubes and ovaries:

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.

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Table of Contents

human reproductive system, organ system by which humans reproduce and bear live offspring. Provided all organs are present, normally constructed, and functioning properly, the essential features of human reproduction are (1) liberation of an ovum, or egg, at a specific time in the reproductive cycle, (2) internal fertilization of the ovum by spermatozoa, or sperm cells, (3) transport of the fertilized ovum to the uterus, or womb, (4) implantation of the blastocyst, the early embryo developed from the fertilized ovum, in the wall of the uterus, (5) formation of a placenta and maintenance of the unborn child during the entire period of gestation, (6) birth of the child and expulsion of the placenta, and (7) suckling and care of the child, with an eventual return of the maternal organs to virtually their original state.

For this biological process to be carried out, certain organs and structures are required in both the male and the female. The source of the ova (the female germ cells) is the female ovary; that of spermatozoa (the male germ cells) is the testis. In females, the two ovaries are situated in the pelvic cavity; in males, the two testes are enveloped in a sac of skin, the scrotum, lying below and outside the abdomen. Besides producing the germ cells, or gametes, the ovaries and testes are the source of hormones that cause full development of secondary sexual characteristics and also the proper functioning of the reproductive tracts. These tracts comprise the fallopian tubes, the uterus, the vagina, and associated structures in females and the penis, the sperm channels (epididymis, ductus deferens, and ejaculatory ducts), and other related structures and glands in males. The function of the fallopian tube is to convey an ovum, which is fertilized in the tube, to the uterus, where gestation (development before birth) takes place. The function of the male ducts is to convey spermatozoa from the testis, to store them, and, when ejaculation occurs, to eject them with secretions from the male glands through the penis.

At copulation, or sexual intercourse, the erect penis is inserted into the vagina, and spermatozoa contained in the seminal fluid ( semen) are ejaculated into the female genital tract. Spermatozoa then pass from the vagina through the uterus to the fallopian tube to fertilize the ovum in the outer part of the tube. Females exhibit a periodicity in the activity of their ovaries and uterus, which starts at puberty and ends at the menopause. The periodicity is manifested by menstruation at intervals of about 28 days; important changes occur in the ovaries and uterus during each reproductive, or menstrual, cycle. Periodicity, and subsequently menstruation, is suppressed during pregnancy and lactation.

This articles describes the organs, both male and female, that are involved in human reproduction. The reproductive process itself is covered in other articles. For a detailed discussion of the series of changes that occur in a woman's body as her fetus develops, see pregnancy. For a description of the stages of labour and delivery, see parturition. For the development of the unborn child during gestation, see human embryology. For coverage of the many diseases and disorders that can affect the reproductive organs, see reproductive system disease.

Development of the reproductive organs

The sex of a child is determined at the time of fertilization of the ovum by the spermatozoon. The differences between a male and a female are genetically determined by the chromosomes that each possesses in the nuclei of the cells. Once the genetic sex has been determined, there normally follows a succession of changes that will result, finally, in the development of an adult male or female. There is, however, no external indication of the sex of an embryo during the first eight weeks of its life within the uterus. This is a neutral or indifferent stage during which the sex of an embryo can be ascertained only by examination of the chromosomes in its cells.

The next phase, one of differentiation, begins first in gonads that are to become testes and a week or so later in those destined to be ovaries. Embryos of the two sexes are initially alike in possessing similar duct systems linking the undifferentiated gonads with the exterior and in having similar external genitalia, represented by three simple protuberances. The embryos each have four ducts, the subsequent fate of which is of great significance in the eventual anatomical differences between men and women. Two ducts closely related to the developing urinary system are called mesonephric, or wolffian, ducts. In males each mesonephric duct becomes differentiated into four related structures: a duct of the epididymis, a ductus deferens, an ejaculatory duct, and a seminal vesicle. In females the mesonephric ducts are largely suppressed. The other two ducts, called the paramesonephric or müllerian ducts, persist, in females, to develop into the fallopian tubes, the uterus, and part of the vagina; in males they are largely suppressed. Differentiation also occurs in the primitive external genitalia, which in males become the penis and scrotum and in females the vulva (the clitoris, labia, and vestibule of the vagina).

At birth the organs appropriate to each sex have developed and are in their adult positions but are not functioning. Various abnormalities can occur during development of sex organs in embryos, leading to hermaphroditism, pseudohermaphroditism, and other chromosomally induced conditions. During childhood until puberty there is steady growth in all reproductive organs and a gradual development of activity. Puberty marks the onset of increased activity in the sex glands and the steady development of secondary sexual characteristics.

In males at puberty the testes enlarge and become active, the external genitalia enlarge, and the capacity to ejaculate develops. Marked changes in height and weight occur as hormonal secretion from the testes increases. The larynx, or voice box, enlarges, with resultant deepening of the voice. Certain features in the skeleton, as seen in the pelvic bones and skull, become accentuated. The hair in the armpits and the pubic hair becomes abundant and thicker. Facial hair develops, as well as hair on the chest, abdomen, and limbs. Hair at the temples recedes. Skin glands become more active, especially apocrine glands (a type of sweat gland that is found in the armpits and groin and around the anus).

In females at puberty, the external genitalia enlarge and the uterus commences its periodic activity with menstruation. The breasts develop, and there is a deposition of body fat in accordance with the usual contours of the mature female. Growth of axillary (armpit) and pubic hair is more abundant, and the hair becomes thicker.

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Human reproductive system | Definition, Diagram & Facts

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Human reproductive system, organ system by which humans reproduce and bear live offspring.

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https://www.britannica.com/science/human-reproductive-system

https://www.betterhealth.vic.gov