My document provides a comprehensive study guide on the "Endocrine System," detailing the functions, structures, and hormonal regulations within the human body. It covers key topics such as the roles of major endocrine glands like the pituitary, thyroid, adrenal, and reproductive organs (testes and...
• 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.
• 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.
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