Endocrine System and Adolescence
ICSE Class 8 · Biology · Chapter 5
What this chapter covers
- Two ways the body controls itself
- Exocrine and endocrine glands
- Hormones
- Major endocrine glands
- Adolescence: physical and emotional changes
- Personal hygiene
- Stress and its management
Key definitions
Meditation is the practice of sitting quietly and focusing the mind on one thing, such as your breathing, for a few minutes.
Time management is the planning of how you divide your time between different activities so that important work gets done without a last-minute rush.
Rational thinking is the habit of looking at a problem calmly and with facts instead of imagining the worst.
Key points
- Coordination in humans is brought about by the nervous system (fast, short-lived) and by the endocrine system (slower, long-lasting).
- Exocrine glands have ducts; endocrine glands are ductless and release hormones directly into the blood.
- A hormone is a chemical messenger carried by the blood to a target organ; tiny amounts have large effects.
- The pituitary, at the base of the brain, is the master gland; it makes growth hormone and controls other glands.
- The thyroid, in the neck, makes thyroxine and needs iodine; a lack of iodine causes goitre.
- The adrenal glands, on top of the kidneys, make adrenaline, which prepares the body for danger.
- The pancreas is a mixed gland; its insulin lowers blood sugar, and too little insulin leads to diabetes.
- Adolescence is the change from childhood to adulthood, directed by hormones from the pituitary, testes and ovaries.
- Adolescence brings physical changes (growth spurt, body hair, voice change, menstruation) and emotional changes (mood swings, wish for independence).
- Personal hygiene keeps the body clean, prevents infection and builds confidence.
- Stress can be managed by yoga, meditation, time management, sports, hobbies, rational thinking and talking to someone you trust.
Questions answered
Name the two systems that bring about coordination in the human body. Which one acts faster?
The nervous system and the endocrine (hormonal) system bring about coordination. The nervous system acts faster.
Give two differences between an exocrine gland and an endocrine gland.
An exocrine gland has a duct, but an endocrine gland has none. An exocrine gland sends its secretion through the duct to a nearby place, while an endocrine gland releases hormones directly into the blood.
Define a hormone.
A hormone is a chemical messenger made by an endocrine gland and carried by the blood to a target organ, where it changes the way that organ works.
Why is the pancreas called a mixed gland?
Most of the pancreas pours digestive juice through a duct into the small intestine, which makes it exocrine. Its islets release insulin and glucagon directly into the blood, which makes it endocrine as well.
Why is the pituitary called the master gland? Name one of its hormones.
The pituitary controls the working of several other endocrine glands, such as the thyroid, the adrenal glands, the testes and the ovaries. Growth hormone comes from the pituitary.
A family in a hilly village uses non-iodised salt for years. Which disease might they develop, and why?
They might develop goitre. Without iodine the thyroid cannot make enough thyroxine and becomes enlarged.
Which hormone prepares the body for an emergency? List three changes it causes.
Adrenaline, from the adrenal glands, prepares the body for an emergency. It makes the heart beat faster, increases the rate of breathing and sends more blood and sugar to the muscles.
State two physical changes seen in boys and two seen in girls during adolescence.
Boys: the voice deepens and facial hair grows. Girls: the hips widen and menstruation begins.