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Leaving Cert Biology Revision: The Endocrine System

The Endocrine System

Body Coordination

Body coordination is regulated by the nervous and endocrine systems.

 The endocrine system:

1. Operates slowly.

2. Relies on hormones.

3. Transmits signals slowly throughout the body.

4. Generates long-lasting, widespread effects.

In essence, the nervous system is the antithesis of the endocrine system.


- Hormones are released by exocrine glands through ducts.

- Hormones are released by endocrine glands into bodily tissues and subsequently into the bloodstream.

- Hormones are chemical messengers that are created by endocrine glands and are delivered to particular body areas via the bloodstream.

- Although some are steroid-based, the majority of hormones are protein-based.

- Hormones are long-acting after they are produced.

The body contains ten primary endocrine glands.

But the stomach, kidneys, heart, and brain aren't the only organs that produce hormones.

Role of Main Glands

Pituitary Gland

Often referred to as the master gland, the pituitary secretes hormones that control the function of all other glands in the body.

  - Hormones such as growth hormone (GH), LH, and FSH are examples of those that are generated. These hormones encourage the body to absorb more amino acids, which in turn promotes growth.

  - Insufficient GH production causes dwarfism, whereas excessive GH production causes gigantism.


The hypothalamus serves as a link between the endocrine and neurological systems. controls the activity of the pituitary gland in response to signals from the brain and other hormones.

It generates two kinds of hormones: hormones that are released to stimulate the pituitary gland's production of hormones and hormones that are inhibited to repress the gland's production of hormones.

Pineal Gland

Numerous hormones, including melatonin, are produced by a small gland in the brain.

This hormone affects patterns of sexual maturity, ovulation, sleep, and activity.

Jet lag could also be influenced by it.


- The thyroid gland is located at the back of the neck and looks like the letter "H."

- The thyroid gland secretes the hormone thyroidine, which controls a person's metabolism.

- When the thyroid gland is underactive: - Insufficient production causes cretinism, which is stunted growth in early children.

  - This disorder, known as myxoedema or goitre, affects adults and manifests as weariness, poor energy, decreased mental and physical agility, and weight gain.


Swelling of the thyroid gland results in goitre. It typically indicates insufficient thyroxine production in the body. This frequently happens as a result of insufficient dietary iodine, which is present in seafood and iodized salt. 

Treating this kind of goitre can be aided by increasing iodine-rich dietary intake.

Overactive thyroid gland

The body's metabolism can be accelerated by as much as 60% when thyroxine is produced in excess. This may result in symptoms including swollen eyes, constant hunger, weight loss, excessive heat, and heightened anxiety or irritability. It's known as Graves' illness. Treatment options include surgically removing a portion of the thyroid gland or partially killing the gland with radioactive iodine.


The thyroid gland contains the four parathyroid glands. They generate a hormone known as parathormone, which instructs the body to release calcium into the bloodstream from the bones. This keeps the blood's calcium levels stable, but it also implies that people must continue consuming enough calcium to keep their bones healthy.


It is situated in the upper chest, behind the breastbone.

White blood cells mature and become active when the hormone thymosin, which is produced by the thymus gland, is released. The thymus stops functioning in middle age and breaks down throughout puberty.

The Adrenal glands

Above the kidneys are the two adrenal glands. They generate hormones that aid the body in handling stress, such as adrenalin.

The Adrenaline Effects

• It improves blood flow to the brain, heart, and muscles.

• It causes the skin's blood flow to be reduced, giving the appearance of pale skin.

• It increases blood glucose levels by converting glycogen to glucose and opening bronchioles to let more oxygen into the lungs.

• The heart rate goes up.

• Strengthening of muscular contractions; • Enhanced mental awareness.


The pancreas is classified as an endocrine and exocrine gland. Insulin, its primary hormone, reduces blood sugar levels. Blood glucose is absorbed by muscle and fat cells. It is converted to glycogen, which is then kept in the muscles and liver.

Hormone Supplements


Diabetes is a condition caused by low insulin production or a cell's incapacity to absorb insulin. It typically results in a lifelong inability to manufacture insulin in young individuals.

Diabetes causes symptoms such as high blood and urine glucose concentrations, excessive urine production, extreme thirst, weight loss, and fatigue.

Regular injections—one to four per day—are used to manage diabetes.

In addition, the consumption of carbs is limited, physical activity levels are raised, and a healthy weight is maintained.

Anabolic Steroids

These medications, which resemble the male hormone testosterone, aid with muscular growth. They increase muscular mass, strength, and post-exercise recovery rate.

They do, however, have a number of adverse effects, including as harm to the adrenal glands and liver, erectile problems in men, and the development of masculine traits in women.

Animals can also be given steroids to gain more muscle mass and produce leaner meat, but the European Union forbids this practice because of worries that the hormones will find their way into the human food chain.

Control of Thyroxine levels

This mechanism is similar to that of a central heating system. We call it unfavorable feedback. Normal thyroxine levels inhibit the pituitary gland's release of thyroid-stimulating hormone, which stops the gland from producing additional thyroxine. 

However, the pituitary gland produces thyroid-stimulating hormone if thyroxine levels go too low. This causes the thyroid gland to generate more thyroxine until its concentration recovers to normal.

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