Human Endocrine System: Hormones, Glands & Disorders Guide

1. Introduction to Chemical Coordination and Regulation
   o Importance of hormones in homeostasis
   o Chemical vs. neural coordination
2. What Are Endocrine Glands?
   o Difference between endocrine and exocrine glands
   o Hormone characteristics
3. Human Endocrine System Overview
   o Endocrine gland locations
   o Integration with the nervous system
4. Hypothalamus: The Master Coordinator
   o Hormones secreted by the hypothalamus
   o Role in linking the nervous and endocrine systems
5. Pituitary Gland: The Master Gland
   o Anterior and posterior lobes
   o Hormones and their functions
   o Disorders related to pituitary malfunction
6. Pineal Gland and Its Role
   o Melatonin and circadian rhythm
   o Disorders and dysfunctions
7. Thyroid Gland: Regulator of Metabolism
   o Structure and function
   o Hormones secreted and their roles
   o Disorders: Goitre, Cretinism, Myxedema
8. Parathyroid Glands: Calcium Homeostasis

o Parathyroid hormone (PTH)
o Hyperparathyroidism and hypoparathyroidism

9. Adrenal Glands: Stress Responders
   o Adrenal cortex and medulla
   o Hormones and their action
   o Disorders: Addison’s disease, Cushing’s syndrome
10. Pancreas: Dual Role Gland
    o Endocrine vs. exocrine functions
    o Insulin and glucagon
    o Diabetes types and symptoms
11. Gonads: Ovaries and Testes
    o Sex hormones
    o Functions and disorders
12. Mechanism of Hormone Action
    o Receptor binding
    o Second messengers and feedback loops
13. Hormones as Messengers and Regulators
    o Hormonal balance
    o Hormone action in growth and development
14. Disorders Due to Hormonal Imbalance
    o Hypo and hypersecretion
    o Common endocrine disorders explained
15. Previous Year Questions (PYQs) with Answers
    o NEET/CBSE-style questions from 2015–2024
16. FAQs
17. Introduction to Chemical Coordination and Regulation

Let’s face it—our body is like a well-synced orchestra. While the nervous system
sends lightning-fast signals to control muscles and reflexes, there’s another slower,
yet equally important player: the endocrine system. It uses hormones—tiny chemical
messengers—to manage everything from growth to metabolism, stress to sleep. This
process, called chemical coordination and regulation, is what keeps your internal
environment steady despite external changes.
Unlike nerve impulses that travel via neurons, hormones travel through the
bloodstream. This means they can reach every cell, influencing functions like heart
rate, digestion, reproductive cycles, and mood. Understanding this system is like
unlocking the command centre of your body—a necessity for every biology
enthusiast and medical aspirant.

2. What Are Endocrine Glands?
   Endocrine glands are ductless organs that pour hormones directly into the blood.
   They differ from exocrine glands, which release substances via ducts (like sweat or
   saliva). These glands are spread throughout your body and work silently but
   powerfully.
   Characteristics of Hormones:
    Act in minute quantities
    Are transported by blood
    Influence physiological functions
    Work through receptors
    Can trigger or stop a reaction
   Major Endocrine Glands Include:
    Hypothalamus
    Pituitary
    Pineal
    Thyroid
    Parathyroid
    Adrenal
    Pancreas
    Gonads (Ovaries/Testes)

Each of these glands plays a unique role, and together, they maintain balance and
harmony within the body.

3. Human Endocrine System Overview
   Picture the endocrine system as a complex network of stations where hormones are
   manufactured, released, and delivered. Each gland has a specialized function, but
   they don’t work in isolation. The nervous system, especially the brain, is closely
   linked with endocrine functions—making coordination essential.
   Here’s how they’re mapped:
    Brain Region: Hypothalamus, Pituitary, Pineal
    Neck: Thyroid, Parathyroid
    Above Kidneys: Adrenal glands
    Abdomen: Pancreas
    Pelvic Region: Gonads
   These glands secrete hormones that influence everything from your heartbeat to
   your bone growth.
4. Hypothalamus: The Master Coordinator
   Located deep within your brain, the hypothalamus is the real boss. It keeps
   monitoring the body’s internal environment and regulating hunger, thirst, temperature,
   and emotions. Most importantly, it controls the pituitary gland, earning its title as the
   “Master of the Master Gland.”
   Hormones Produced:
    Releasing Hormones (e.g., TRH, CRH, GnRH): Stimulate pituitary to release
   hormones
    Inhibitory Hormones (e.g., GHIH, PIH): Stop pituitary from releasing certain
   hormones
   Think of it as the Wi-Fi router of your endocrine system—it connects the nervous
   system to the endocrine world. When your body needs something, the hypothalamus
   sends a signal to the pituitary, which then tells other glands what to do.
5. Pituitary Gland: The Master Gland

The pituitary gland is a pea-sized gland hanging from the hypothalamus. Despite its
small size, its impact is enormous. It has two major parts: the anterior pituitary (front)
and the posterior pituitary (back), each releasing different hormones.
Anterior Pituitary Hormones:

1. Growth Hormone (GH) – Stimulates growth; its deficiency causes dwarfism,
   and excess leads to acromegaly.
2. Thyroid Stimulating Hormone (TSH) – Activates the thyroid gland.
3. Adrenocorticotropic Hormone (ACTH) – Stimulates the adrenal cortex.
4. Follicle-Stimulating Hormone (FSH) – Regulates gamete production.
5. Luteinizing Hormone (LH) – Triggers ovulation/testosterone production.
6. Prolactin (PRL) – Promotes milk production.
   Posterior Pituitary Hormones:
    Oxytocin – Stimulates childbirth contractions and milk ejection.
    Vasopressin (ADH) – Controls water balance in kidneys.
   Abnormal secretion of growth hormone can lead to gigantism or dwarfism. Too little
   ADH causes diabetes insipidus, where the body loses too much water.
7. Pineal Gland and Its Role
   The pineal gland may be tiny, but it’s crucial for maintaining your body’s biological
   rhythm. Located deep in the centre of the brain, this gland looks like a pine cone
   (hence the name). It’s often called the “third eye” due to its influence on circadian
   rhythms and sleep cycles.
   Main Hormone: Melatonin
    Melatonin is secreted in response to darkness and helps regulate the sleep-
   wake cycle.
    It influences mood, immune function, and even reproductive hormones in
   some species.
    Secretion is inhibited by light—so yes, those late-night screen times can mess
   up your melatonin levels.
   Disorders and Dysfunction:
    Disruption in melatonin secretion can lead to insomnia, seasonal affective
   disorder (SAD), and jet lag.

 Though not commonly associated with life-threatening diseases, chronic
disruption may affect overall health, mood, and hormonal balance.
This tiny gland acts like your internal clock. Treat it well—dim the lights at night and
avoid screens before bed for quality sleep!

7. Thyroid Gland: Regulator of Metabolism
   The thyroid gland, located in the front of your neck, is butterfly-shaped and governs
   the pace of nearly every process in your body. It’s your metabolic
   powerhouse—controlling how fast or slow your body uses energy.
   Hormones Produced:
    Thyroxine (T₄) and Triiodothyronine (T₃) – Control metabolism, body
   temperature, heart rate, and growth.
    Calcitonin – Regulates calcium levels by lowering blood calcium.
   Common Disorders:
8. Hypothyroidism:
   o Cretinism (in children): Leads to stunted growth and mental
   retardation.
   o Myxedema (in adults): Causes fatigue, weight gain, depression.
   o Caused by iodine deficiency or autoimmune diseases like Hashimoto’s
   thyroiditis.
9. Hyperthyroidism:
   o Graves’ disease: Causes exophthalmic goitre—a condition where
   eyes bulge out.
   o Symptoms: Weight loss, irritability, increased heartbeat, sweating.
10. Goitre:
    o Enlargement of thyroid due to iodine deficiency or hormonal imbalance.
    Managing thyroid function is key to staying energized and mentally sharp. A simple
    blood test for TSH, T3, and T4 levels can give valuable insight into your thyroid
    health.
11. Parathyroid Glands: Calcium Homeostasis

Behind the thyroid ,there are four rice-sized glands known as the parathyroid
glands. Though small, they play a huge role in keeping your bones strong and your
heart beating right—by regulating calcium and phosphate balance in the blood.
Main Hormone: Parathyroid Hormone (PTH)
 Increases blood calcium levels by:
o Stimulating bone resorption
o Enhancing calcium reabsorption in kidneys
o Promoting activation of Vitamin D (increases intestinal calcium
absorption)

Disorders:

1. Hypoparathyroidism:
   o Causes low calcium levels (hypocalcaemia)
   o Symptoms: Muscle cramps, spasms, convulsions
2. Hyperparathyroidism:
   o Causes high calcium levels (hypercalcaemia)
   o Leads to kidney stones, bone pain, fatigue

Together with calcitonin from the thyroid, PTH maintains a delicate calcium balance.
Even slight imbalances can affect nerves, muscles, and bones significantly.

9. Adrenal Glands: Stress Responders
   Adrenal glands are located above the kidneys, these are your body’s emergency
   responders. They help you deal with stress, both physical and emotional, and
   maintain vital functions.
   Two Parts of Adrenal Gland:
10. Adrenal Cortex (outer layer)
11. Adrenal Medulla (inner layer)
    Cortex Hormones:
     Glucocorticoids (Cortisol) – Controls metabolism, immune response, and
    stress adaptation.
     Mineralocorticoids (Aldosterone) – Regulates salt-water balance, blood
    pressure.

 Androgens – Sex hormones, more relevant in females.
Medulla Hormones:
 Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine) – Fight-or-
flight hormones; increase heart rate, blood flow, and energy.
Disorders:

1. Addison’s Disease:
   o Insufficient cortisol and aldosterone.
   o Symptoms: Fatigue, weight loss, low blood pressure,
   hyperpigmentation.
2. Cushing’s Syndrome:
   o Excess cortisol.
   o Symptoms: Weight gain, moon face, high blood sugar, muscle
   weakness.

Life’s stress won’t stop, but your adrenal glands ensure your body can
respond—sometimes too well, which is when trouble begins.

10. Pancreas: Dual Role Gland
    The pancreas is a mixed gland—it works both as an exocrine gland (releasing
    digestive enzymes) and an endocrine gland (releasing hormones). Located just
    behind the stomach, its endocrine function is carried out by clusters of cells called
    Islets of Langerhans.
    Major Hormones:
11. Insulin (from β-cells):
    o Lowers blood sugar by promoting glucose uptake and storage.
12. Glucagon (from α-cells):
    o Raises blood sugar by converting glycogen to glucose in the liver.

Common Disorders:

1. Diabetes Mellitus:
   o Type 1: Autoimmune destruction of β-cells → no insulin.
   o Type 2: Insulin resistance or insufficient insulin.

o Symptoms: Excessive urination, thirst, fatigue, weight loss.

2. Hypoglycaemia:
   o Excess insulin → very low blood sugar → confusion, shakiness,
   seizures.

Balancing blood sugar is like walking a tightrope—and your pancreas is the acrobat.
Keep it healthy through diet, exercise, and regular checkups.

11. Gonads: Ovaries and Testes
    The gonads—ovaries in females and testes in males—are essential not only for
    reproduction but also for the release of sex hormones that influence behaviour,
    development, and secondary sexual characteristics.
    In Females (Ovaries):
     Produce Estrogen and Progesterone
     Regulate menstrual cycle, pregnancy, and the development of female
    characteristics
    In Males (Testes):
     Produce Testosterone
     Regulates sperm production, muscle mass, voice deepening, and other male
    traits
    Disorders Related to Gonads:
12. Polycystic Ovary Syndrome (PCOS):
    o Hormonal imbalance causing irregular periods, acne, infertility
13. Hypogonadism:
    o Reduced hormone production leading to infertility or developmental
    issues

These hormones also affect bone health, mood, and even fat distribution—proving
that reproductive hormones are not just about reproduction.

12. Mechanism of Hormone Action

Ever wonder how these microscopic chemical messengers actually work? Hormones
are like keys that fit into specific locks—receptors—on target cells. Once the
hormone binds, it triggers a series of events inside the cell.
Two Major Mechanisms:

1. Peptide Hormones (e.g., insulin, adrenaline):
   o Bind to cell surface receptors
   o Use second messengers like cAMP to trigger a cascade of reactions
2. Steroid Hormones (e.g., testosterone, cortisol):
   o Pass through the cell membrane
   o Bind directly to DNA in the nucleus and alter gene expression

Feedback Mechanism:
 Most hormones work on a negative feedback loop.
 Example: High levels of T3 and T4 inhibit TSH secretion from the pituitary.

13. Hormones as Messengers and Regulators
    Hormones are more than chemical substances; they’re information carriers that
    keep the body functioning in harmony. They regulate:
     Growth and development
     Mood and emotions
     Metabolism
     Sexual function
     Immune responses
    They adapt the body to changes, maintain internal balance (homeostasis), and even
    help in emergencies (adrenaline rushes).
    Examples of Regulatory Roles:
     Insulin lowers blood sugar after meals.
     Aldosterone retains sodium to balance fluid levels.
     Estrogen prepares the uterus for pregnancy.
    Just a pinch too much or too little, and the balance is gone—causing diseases and
    disorders that can affect your entire system.
14. Disorders Due to Hormonal Imbalance
    Hormonal disorders occur when a gland secretes too much (hypersecretion) or
    too little (hyposecretion) of a hormone. Let’s look at some major conditions:
15. Dwarfism:
     Caused by GH deficiency in children
     Results in stunted growth
16. Acromegaly:
     Caused by GH excess in adults
     Enlarged hands, feet, and facial features
17. Cretinism:
     Severe hypothyroidism in infants
     Causes physical deformities and mental retardation
18. Goitre:
     Thyroid enlargement due to iodine deficiency
     Visible swelling in the neck
19. Exophthalmic Goitre (Graves’ Disease):
     Autoimmune hyperthyroidism
     Symptoms: Bulging eyes, weight loss, increased heartbeat
20. Diabetes Mellitus:
     Type 1: Autoimmune; pancreas fails to produce insulin
     Type 2: Insulin resistance
     Symptoms: Frequent urination, thirst, fatigue
21. Addison’s Disease:
     Cortisol and aldosterone deficiency
     Symptoms: Weakness, weight loss, low BP, skin darkening
    These disorders underline how critical even minute quantities of hormones are.
    Treatments may include hormone replacement, surgery, or lifelong medication,
    depending on the condition.
22. Previous Year Questions (PYQs) with Answers
    NEET 2024
    Q: Which of the following hormones does not require a second messenger for
    action?
    A: Testosterone
    Explanation: Steroid hormones like testosterone directly influence gene expression
    without second messengers.

CBSE 2023
Q: Name the gland that acts as a link between the nervous and endocrine system.
A: Hypothalamus

NEET 2022
Q: Identify the mismatch:

1. Insulin – Diabetes mellitus
2. Thyroxine – Goitre
3. Growth hormone – Acromegaly
4. Adrenaline – Addison’s disease
   A: 4. Adrenaline – Addison’s disease
   Explanation: Addison’s is caused by cortisol deficiency, not adrenaline.

CBSE 2021
Q: Which hormone is secreted by the posterior pituitary?
A: Oxytocin

NEET 2020
Q: A person is suffering from frequent urination and high blood sugar. What is the
likely diagnosis?
A: Diabetes Mellitus

16. FAQs

Q1: What is the main difference between endocrine and exocrine glands?
A: Endocrine glands are ductless and secrete hormones directly into the
bloodstream, while exocrine glands use ducts to transport their secretions to a
surface or cavity (e.g., sweat glands, salivary glands).

Q2: Why is the hypothalamus called the “master coordinator”?
A: The hypothalamus controls the pituitary gland, which in turn regulates other
endocrine glands. It bridges the nervous and endocrine systems, hence earning the
title “master coordinator.”

Q3: How does insulin help in lowering blood glucose levels?
A: Insulin promotes the uptake of glucose by body cells and stimulates the liver to
convert glucose into glycogen for storage, thereby reducing blood glucose levels.

Q4: What causes goitre, and how can it be prevented?
A: Goitre is usually caused by iodine deficiency, which impairs thyroid hormone
synthesis. It can be prevented by using iodized salt and ensuring a diet rich in iodine-
containing foods like seafood and dairy.

Q5: What’s the difference between Type 1 and Type 2 diabetes?
A: Type 1 diabetes is an autoimmune condition where the body destroys insulin-
producing cells, while Type 2 diabetes results from insulin resistance or insufficient
insulin production due to lifestyle or genetic factors.