Category Zoology

Hormones are the chemical messengers that travel between the body’s organs and tissues. They can only instruct cells that have the right receptors to detect them, so many different hormones are involved in the chain of events of puberty.

The starting point

Puberty begin in the brain. Between the ages of about 9 and 12, an area of the brain called the hypothalamus sends messages to the pituitary gland to release hormones that start the process of puberty, by instructing other glands to produce hormones.

Growth hormone

The body grows very fast during puberty – and growth hormone ( ) is the driver of growth spurts. It is released by the pituitary gland, and affects all parts of the body, making muscles and organs larger, and bones longer.

Hormone cell

Growth hormone is made by cells in the pituitary gland. The brown spots in the outer part of the cell are storing newly made growth hormone.

Getting ready to reproduce

The chain of some of the hormones that turn children into adults, capable of having their own children. Luteinizing hormone (LH) and follicle – stimulating hormone (FSH) play a major role, stimulating different hormones in boys and girls that control the necessary changes.

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The human body goes through many changes from birth to old age. The glands and organs of the endocrine system produce the hormone that trigger different stages of development. The most important period of change is adolescence – the transition from a child to an adult. During this stage of rapid growth, called puberty, the body changes shape and the reproductive system develops. A hormone in the brain triggers puberty, while other hormones regulate functions, such as growth, mood, and sleep.

Once a hormone is secreted in the body, it travels through the bloodstream to target cells designed to receive its message. These target cells have receptors that only attach onto specific hormones, so that each hormone communicates only with specific target cells.

When the hormone reaches its target cell, it locks onto the cell’s specific receptors and these hormone-receptor combinations transmit chemical instructions to the inner parts of the cell. Important body mechanisms exist to maintain the appropriate level of hormone in the blood. Too much or too little of any hormone can be harmful to the body.

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Hormone factory

The main hormone-producing glands are in the brain, neck, abdomen, and groin. Other organs, such as the stomach, liver, and heart, release hormones, too. Hormones are released only when the gland receives the correct trigger – a change in blood, a nerve signal, or an instruction from another hormone.

Thymus

The thymus secretes hormones to boost the production of disease-fighting white blood cells. It is only active during childhood and early teenage years, and shrinks to be almost invisible in adults.

Pineal gland

The pineal body is located below the corpus callosum, in the middle of the brain. This gland makes melatonin, which affects sleep.

Hypothalamus

The hypothalamus is located at the base of the brain, near the optic chiasm ???where the optic nerves behind each eye cross and meet. This parts o the brain links the nervous and endocrine systems.

Pituitary gland

The pituitary gland is located below the brain. Usually no larger than a pea, the gland controls many functions of the other endocrine glands. Hormones that control other glands are produced here.

Thyroid gland

This gland releases thyroxine, which controls the body’s metabolic rate – the speed at which cells use up the oxygen that fuels them.

Parathyroid glands

These four small glands regulate levels of calcium, which is vital for healthy teeth and bones.

Heart

The heart releases hormones that control blood pressure.

Stomach

The walls of the stomach secrete gastrin, which triggers the release of digestive juices when we eat.

Adrenal glands

These glands produce hormones that control salt levels, as well as adernaline, which prepares the body to respond to danger. The adrenal glands make and release corticosteroid hormones and epinephrine that maintain blood pressure and regulate metabolism.

Pancreas

The pancreas is located across the back of the abdomen, behind the stomach. The pancreas plays a role in digestion, as well as hormone production. The pancreas makes insulin and glucagon, which control glucose levels in the blood.

Small intestine

This organ releases hormones that help with digestion.

Ovaries

A woman’s ovaries are located on both sides of the uterus, below the opening of the fallopian tubes (tubes that extend from the uterus to the ovaries). Ovaries produce the sex hormones pestrogen and progesterone, which control a woman’s reproductive cycle.

Testes

Also called testicles, these release the male sex hormone testosterone, which triggers the production of sperm.

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As well as sending high-speed signals along the nervous system, the body also uses chemicals called hormones to carry messages to specific parts. These hormones are produced and released into the bloodstream by the tissues and glands of the endocrine system.

There are about 50 different kinds of hormone, made by a dozen or so major glands as well as some organs. As it travels around the body, each hormone targets a particular cell or tissue to alter how it works. Hormones control growth, hunger, sleep, reproduction, and many other functions of the body.

Hormone levels that are too high or too low indicate a problem with the endocrine system. Hormone diseases also occur if your body does not respond to hormones in the appropriate ways. Stress, infection and changes in the blood’s fluid and electrolyte balance can also influence hormone levels, according to the National Institutes of Health.

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Every nerve is made up of neurons, and there are billions of them. If all the body’s neurons were put end to end they would stretch 60 km (37 miles).

Electrical signals pass from one neuron (coloured green) to another by moving down their long extensions, which are called axons (coloured blue). Signals cross a tiny space to the receiving parts of the next neuron, which are called dendrites (also blue). Messages travel at high speeds, going all the way from the brain to the feet in 0.01 seconds.

Ultimately, biological neuron models aim to explain the mechanisms underlying the operation of the nervous system for the purpose of restoring lost control capabilities such as perception (e.g. deafness or blindness), decision making, and continuous limb control. 

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Each neuron has thousands of fibres extending from its cell body. One large fibre, called an axon, carries outgoing electrical signals, while smaller branching fibres, called dendrites, carry incoming electrical signals. The neurons connect with each other at junctions called synapses. Signals cannot jump across these tiny gaps without the help of chemicals called neurotransmitters.

Axon

An axon is a large fibre that transmits an electrical signal to the next neuron. Individual axons are microscopic in diameter – typically about one micrometre across – but may extend to macroscopic lengths.

The longest axons in the human body, for example, are those of the sciatic nerve, which run from the base of the spine to the big toe of each foot.

Dendrite

These smaller fibres receive signals from nearby neurons. The functions of dendrites are to receive signals from other neurons, to process these signals, and to transfer the information to the soma of the neuron.

Synapse

This is the junction between the axon of one neuron and the dendrite of another. Most synapses are chemical; these synapses communicate using chemical messengers. Other synapses are electrical; in these synapses, ions flow directly between cells.

Nerve cell

Each neuron has a nucleus at the centre and fibres projecting from it. Nerve cells may be described as receivers and transmitters of information that allow an organism to respond appropriately. 

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