Chapter "Endocrine System" (Class 8)
Control and Coordination
• Organ Systems Working Together: In living organisms, various organ systems work in
harmony and coordination to maintain homeostasis, which is the steady state of
physiological functions.
• Adjusting to External Stress: The internal environment adjusts itself to handle external
stress, ensuring the body functions properly.
• Two Controlling Mechanisms:
o Chemical Control: Brought about by hormones secreted by endocrine glands
(ductless glands).
o Neural Control: Brought about by nerve impulses through the nervous system.
• Coordination in Organisms:
o Multicellular Animals: Have both chemical and neural coordination.
o Plants: Only chemical coordination takes place; they do not have a nervous
system.
Endocrine System
• Definition: Consists of endocrine glands that secrete hormones directly into the
bloodstream.
• Ductless Glands: Endocrine glands are ductless, meaning they do not have ducts to carry
their secretions.
• Function: The endocrine system coordinates the functioning of different body organs by
producing hormones.
Exocrine and Endocrine Glands
• Exocrine Glands:
o Have ducts.
o Release their secretions either outside the body (e.g., sweat, mammary, or salivary
glands) or into the cavity of some organs (e.g., pancreas or liver).
o Examples: Sweat glands, salivary glands, pancreas (exocrine part).
• Endocrine Glands:
o Do not have ducts.
o Release their secretions (hormones) directly into the bloodstream.
, o Examples: Pituitary gland, thyroid gland, adrenal glands, pancreas (endocrine
part).
Hormones
• Definition: Chemical regulators or messengers produced by endocrine glands.
• Function: Circulate throughout the body but influence only specific organs called target
organs.
• Control: The functioning of endocrine glands and the amount of hormone produced is
controlled directly or indirectly by the nervous system.
• Pheromones:
o Certain hormones are secreted outside the body and are called pheromones or
ectohormones.
o Function in recognition of sex, mating behavior, and alarm reactions in insects
and other animals.
Characteristics of Hormones
1. Secreted by Endocrine Glands: Released directly into the bloodstream.
2. Target Specific Organs: Influence only specific target organs despite circulating
throughout the body.
3. Required in Small Amounts: Effective even in very small quantities.
4. Destroyed After Action: Hormones are broken down after their function is completed.
5. Disorders from Imbalance: Both excess (hypersecretion) and deficiency
(hyposecretion) of hormones can lead to disorders.
6. Chemical Nature: Hormones can be proteins, polypeptides, amino acid derivatives, or
steroids.
Endocrine Glands in the Human Body
• Main Endocrine Glands:
o Pituitary gland
o Thyroid gland
o Parathyroid glands
o Adrenal glands
o Pancreas
o Testes (in males)
o Ovaries (in females)
, Thyroid Gland
• Largest Endocrine Gland.
• Location: Neck region at the base of the larynx; has two lobes connected by a band
called the isthmus.
• Hormone Secreted: Thyroxine, which contains iodine.
• Functions of Thyroxine:
o Regulates general metabolism.
o Influences growth and development.
o Controlled by a hormone from the pituitary gland.
• Disorders:
o Hypersecretion:
▪ Increased metabolism.
▪ Faster heartbeat.
▪ Increased pulse rate.
▪ Restlessness and nervousness.
▪ Bulging eyes.
o Hyposecretion:
▪ In Children: Cretinism (retarded physical and mental growth).
▪ In Adults: Myxoedema (sluggish metabolism, swelling of face, hands, and
body).
▪ Simple Goitre: Enlargement of the thyroid gland causing neck swelling;
often due to iodine deficiency.
o Prevention: Use of iodized salt is recommended to prevent iodine deficiency
disorders.
Adrenal Glands
• Location: A pair located on top of each kidney, like a cap.
• Structure:
o Adrenal Cortex (Outer Part).
o Adrenal Medulla (Inner Part).
• Hormones Secreted:
o Adrenal Cortex:
▪ Cortical Hormones (Corticoids):
▪ Regulate metabolism of carbohydrates, proteins, and fats.
▪ Control salt-water balance.
▪ Influence the amount of urine formed.
▪ Act as sex hormones affecting secondary sexual characteristics.
o Adrenal Medulla:
▪ Adrenaline (Epinephrine):
▪ Known as the "emergency hormone."
▪ Prepares the body for "fight or flight" response during stress.
▪ Increases heartbeat, blood pressure, and blood glucose levels.
Control and Coordination
• Organ Systems Working Together: In living organisms, various organ systems work in
harmony and coordination to maintain homeostasis, which is the steady state of
physiological functions.
• Adjusting to External Stress: The internal environment adjusts itself to handle external
stress, ensuring the body functions properly.
• Two Controlling Mechanisms:
o Chemical Control: Brought about by hormones secreted by endocrine glands
(ductless glands).
o Neural Control: Brought about by nerve impulses through the nervous system.
• Coordination in Organisms:
o Multicellular Animals: Have both chemical and neural coordination.
o Plants: Only chemical coordination takes place; they do not have a nervous
system.
Endocrine System
• Definition: Consists of endocrine glands that secrete hormones directly into the
bloodstream.
• Ductless Glands: Endocrine glands are ductless, meaning they do not have ducts to carry
their secretions.
• Function: The endocrine system coordinates the functioning of different body organs by
producing hormones.
Exocrine and Endocrine Glands
• Exocrine Glands:
o Have ducts.
o Release their secretions either outside the body (e.g., sweat, mammary, or salivary
glands) or into the cavity of some organs (e.g., pancreas or liver).
o Examples: Sweat glands, salivary glands, pancreas (exocrine part).
• Endocrine Glands:
o Do not have ducts.
o Release their secretions (hormones) directly into the bloodstream.
, o Examples: Pituitary gland, thyroid gland, adrenal glands, pancreas (endocrine
part).
Hormones
• Definition: Chemical regulators or messengers produced by endocrine glands.
• Function: Circulate throughout the body but influence only specific organs called target
organs.
• Control: The functioning of endocrine glands and the amount of hormone produced is
controlled directly or indirectly by the nervous system.
• Pheromones:
o Certain hormones are secreted outside the body and are called pheromones or
ectohormones.
o Function in recognition of sex, mating behavior, and alarm reactions in insects
and other animals.
Characteristics of Hormones
1. Secreted by Endocrine Glands: Released directly into the bloodstream.
2. Target Specific Organs: Influence only specific target organs despite circulating
throughout the body.
3. Required in Small Amounts: Effective even in very small quantities.
4. Destroyed After Action: Hormones are broken down after their function is completed.
5. Disorders from Imbalance: Both excess (hypersecretion) and deficiency
(hyposecretion) of hormones can lead to disorders.
6. Chemical Nature: Hormones can be proteins, polypeptides, amino acid derivatives, or
steroids.
Endocrine Glands in the Human Body
• Main Endocrine Glands:
o Pituitary gland
o Thyroid gland
o Parathyroid glands
o Adrenal glands
o Pancreas
o Testes (in males)
o Ovaries (in females)
, Thyroid Gland
• Largest Endocrine Gland.
• Location: Neck region at the base of the larynx; has two lobes connected by a band
called the isthmus.
• Hormone Secreted: Thyroxine, which contains iodine.
• Functions of Thyroxine:
o Regulates general metabolism.
o Influences growth and development.
o Controlled by a hormone from the pituitary gland.
• Disorders:
o Hypersecretion:
▪ Increased metabolism.
▪ Faster heartbeat.
▪ Increased pulse rate.
▪ Restlessness and nervousness.
▪ Bulging eyes.
o Hyposecretion:
▪ In Children: Cretinism (retarded physical and mental growth).
▪ In Adults: Myxoedema (sluggish metabolism, swelling of face, hands, and
body).
▪ Simple Goitre: Enlargement of the thyroid gland causing neck swelling;
often due to iodine deficiency.
o Prevention: Use of iodized salt is recommended to prevent iodine deficiency
disorders.
Adrenal Glands
• Location: A pair located on top of each kidney, like a cap.
• Structure:
o Adrenal Cortex (Outer Part).
o Adrenal Medulla (Inner Part).
• Hormones Secreted:
o Adrenal Cortex:
▪ Cortical Hormones (Corticoids):
▪ Regulate metabolism of carbohydrates, proteins, and fats.
▪ Control salt-water balance.
▪ Influence the amount of urine formed.
▪ Act as sex hormones affecting secondary sexual characteristics.
o Adrenal Medulla:
▪ Adrenaline (Epinephrine):
▪ Known as the "emergency hormone."
▪ Prepares the body for "fight or flight" response during stress.
▪ Increases heartbeat, blood pressure, and blood glucose levels.
