Chemical Coordination and Integration – Complete Notes for NEET & Class 11 Biology
Master Class 11 Biology’s Chapter – Chemical Coordination and Integration with our complete NEET-ready notes. Understand endocrine glands, hormones, their types, functions, and mechanisms of hormone action. Aligned with NCERT, perfect for NEET 2025 aspirants and school exams.
1. Hormonal Coordination in Human Body – Role of Endocrine and Neural Systems
In the human body, hormonal coordination plays a very important role in maintaining internal balance. The neural system provides a quick and direct connection between different body parts. It sends messages rapidly through nerve signals, allowing fast reactions. However, this kind of coordination is usually short-lived. Additionally, the nerves don’t reach every single cell in the body. All body cells need to be constantly regulated, especially for growth, metabolism, and long-term changes.
Understanding the roles of endocrine glands and hormones is crucial for grasping how our body maintains balance.
The interaction between endocrine glands and hormones plays a vital role in regulating various physiological processes.
That’s where hormones come in. These are chemical messengers that travel through the blood and reach all parts of the body. They ensure smooth and continuous control over various functions. This long-term coordination and regulation is possible because of the endocrine system, which works alongside the nervous system. Together, they manage and coordinate major physiological activities like digestion, reproduction, metabolism, and more.
In short, for proper body functioning, both fast neural control and slow but steady hormonal control are needed. This dual system ensures that the body reacts quickly when needed and also maintains balance over time.
By releasing endocrine glands and hormones directly into the bloodstream, these glands ensure that important signals reach all parts of the body.
2. Endocrine Glands and Hormones – Functions, Structure, and Coordination
The endocrine glands and hormones form one of the most important control systems in the human body. These glands are ductless, meaning they do not have tubes or pipes to carry their secretions. That’s why they are called ductless glands. Instead of using ducts, they release their chemicals, called hormones, directly into the bloodstream.
Various endocrine glands and hormones work together to coordinate body functions such as metabolism and growth.
The endocrine glands and hormones interact closely with the nervous system to maintain homeostasis.
In the beginning, scientists defined a hormone as a chemical substance made by endocrine glands, which travels through the blood to a specific organ far away in the body. But today, science has given a broader and more accurate definition. Now we understand that hormones are non-nutrient chemical messengers. This means they do not give energy or build body parts like nutrients do, but they act as signals that help cells communicate with each other. They are made in very small (trace) amounts, but even this tiny quantity can cause important effects in the body.
Each of the endocrine glands and hormones has a distinct function that contributes to the body’s overall health.
Studying the endocrine glands and hormones enhances our understanding of medical and biological sciences.
It is important to explore how endocrine glands and hormones are affected by lifestyle factors.
This modern definition also includes many other similar chemicals that may not come from major endocrine glands but still work like hormones. These include signaling molecules from tissues and organs outside traditional glands.
The effects of endocrine glands and hormones on emotions and behavior are also significant in psychological studies.
In invertebrates (animals without a backbone), the endocrine system is very simple and has only a few hormones. But in vertebrates, especially in humans, the system is complex and includes many different hormones that help coordinate activities like growth, metabolism, reproduction, and more.
This paragraph leads us into learning about the human endocrine system, which includes important glands like the pituitary, thyroid, adrenal, pancreas, and others. Each gland has a specific role in maintaining the body’s internal balance.
Recognizing the impact of endocrine glands and hormones on contemporary health issues is crucial for modern medicine.
3. Human Endocrine System – List of Glands and Hormone-Producing Organs
The human endocrine system is a powerful internal communication network made up of special glands and hormone-producing tissues that are spread throughout our body. These glands do not use ducts to transport their secretions, but instead release hormones directly into the blood, allowing them to travel to various organs and regulate body functions.
The endocrine glands form one of the most important control systems in the human body. These glands are ductless and release their chemicals, called hormones, directly into the bloodstream. Various endocrine glands and hormones work together to coordinate body functions such as metabolism and growth.
Apart from these main glands, there are also some non-endocrine organs that have hormone-secreting cells or tissues. These include the gastrointestinal (GI) tract, liver, kidneys, and heart. Though their primary role is not hormone production, they still secrete important chemicals that act like hormones and help in regulating specific body functions.
In the upcoming sections, we will learn briefly about the structure and function of each major gland, along with a very important part of the brain called the hypothalamus, which plays a key role in controlling the entire endocrine system.
3.1 Hypothalamus – Structure, Hormones, and Role in Pituitary Regulation
The hypothalamus is a small but powerful part of the brain that controls a wide range of body functions. It is located at the base of the diencephalon in the forebrain and plays a central role in regulating the endocrine system. Inside the hypothalamus are special nerve cells called neurosecretory cells, grouped into small clusters known as nuclei. These cells produce hormones that directly affect the functioning of the pituitary gland.
There are two main types of hormones produced by the hypothalamus:
🔹 Releasing hormones – These stimulate the pituitary gland to release its hormones.
🔹 Inhibiting hormones – These suppress or block the secretion of hormones from the pituitary.
For example:
The endocrine glands and hormones classification illustrates the diversity within the endocrine system.
- The Gonadotrophin Releasing Hormone (GnRH) from the hypothalamus stimulates the pituitary to release gonadotrophins, which control reproductive functions.
- In contrast, Somatostatin is an inhibiting hormone that blocks the release of growth hormone (GH) from the pituitary.
The hormones made in the hypothalamic neurons travel along their axons and are released at the nerve endings. From there, these hormones enter a special portal circulatory system (a network of blood vessels) that carries them to the anterior pituitary gland, where they control hormone production.
The posterior pituitary, however, is not controlled by these hormones. Instead, it is directly regulated by nerve signals from the hypothalamus — a process known as neural regulation.
Thus, the hypothalamus acts like the master controller, connecting the nervous system and the endocrine system, and making sure that hormone levels remain balanced for proper body function.
3.2 Pituitary Gland – Hormones, Functions, Disorders, and Regulation
The pituitary gland, also known as the master gland, plays a major role in controlling the endocrine system. It is located in a small bony cavity called the sella turcica inside the skull and is connected to the hypothalamus through a stalk-like structure. The pituitary is divided into two major parts: the adenohypophysis (anterior pituitary) and the neurohypophysis (posterior pituitary).
The adenohypophysis has two regions:
🔹 Pars distalis (anterior pituitary) – Secretes six major hormones:
- Growth Hormone (GH) – Controls body growth
- Prolactin (PRL) – Stimulates milk production in mammary glands
- Thyroid Stimulating Hormone (TSH) – Stimulates thyroid hormone production
- Adrenocorticotropic Hormone (ACTH) – Stimulates adrenal cortex to produce glucocorticoids
- Luteinizing Hormone (LH) – Triggers ovulation in females and androgen release in males
- Follicle Stimulating Hormone (FSH) – Helps in formation of sperm in males and ovarian follicles in females
🔹 Pars intermedia – Secretes Melanocyte Stimulating Hormone (MSH), which regulates skin pigmentation by acting on melanocytes. In humans, this part is almost merged with the anterior pituitary.
The neurohypophysis (posterior pituitary) does not produce its own hormones but stores and releases two hormones made by the hypothalamus:
- Oxytocin – Stimulates strong uterine contractions during childbirth and milk ejection during breastfeeding.
- Vasopressin (also called Antidiuretic Hormone or ADH) – Acts on the kidneys to reduce water loss by reabsorbing water, helping prevent dehydration.
If GH is secreted in excess during childhood, it causes gigantism. If secreted in low amounts, it leads to pituitary dwarfism. In adults, excess GH can lead to a disfiguring condition called acromegaly, especially affecting the face and bones, and may lead to serious health problems if untreated.
LH and FSH are together called gonadotrophins as they control gonadal functions.
- In males, LH promotes androgen secretion from testes, and FSH along with androgens regulates sperm production.
- In females, LH helps in ovulation and supports the corpus luteum, while FSH promotes follicle development in ovaries.
MSH controls skin color by acting on pigment-containing cells.
ADH deficiency causes a disorder called Diabetes Insipidus, where kidneys fail to conserve water, leading to excessive urination and dehydration.
3.3 Thyroid Gland – Structure, Hormones, Functions & Related Disorders
The thyroid gland is one of the most vital endocrine glands in the human body. It is made up of two lobes, situated on either side of the trachea (windpipe), and these lobes are joined in the middle by a thin bridge of connective tissue called the isthmus. Inside the thyroid gland are many follicles made up of follicular cells that surround a central cavity. These cells produce two important hormones:
🔹 Tetraiodothyronine (T4 or thyroxine)
🔹 Triiodothyronine (T3)
Both these hormones are iodine-dependent, which means the body must have enough iodine in the diet to make them. If iodine is lacking, it leads to hypothyroidism — a condition where the gland underperforms. One of the most visible effects of this is the swelling of the thyroid gland, called goitre.
In pregnant women, hypothyroidism can cause stunted physical and mental development in the baby — a condition known as cretinism, marked by low IQ, abnormal skin, deaf-mutism, and delayed growth. In adult women, hypothyroidism may cause irregular menstrual cycles.
On the other hand, when the thyroid becomes overactive — either due to cancer or thyroid nodules — it produces hormones in excess, leading to hyperthyroidism. This condition disrupts body balance and increases metabolism abnormally. A classic example is exophthalmic goitre (or Graves’ disease), which shows symptoms like bulging eyes, rapid weight loss, enlarged thyroid, and increased basal metabolic rate.
Thyroid hormones are essential for regulating the basal metabolic rate (BMR) — the speed at which your body uses energy at rest. These hormones also:
✔ Support red blood cell formation
✔ Help in metabolism of carbohydrates, proteins, and fats
✔ Maintain water and electrolyte balance in the body
Apart from T3 and T4, the thyroid gland also produces another hormone called thyrocalcitonin (TCT), which helps in lowering blood calcium levels, thus playing a role in calcium regulation.
3.4 Thymus Gland: Powerful Role in Immunity
The thymus gland plays a vital role in the immune system, especially during childhood and adolescence. This gland releases thymosins, which are crucial for the development and functioning of the body’s immune defense. One of the main functions of thymosins is to help immature T-lymphocytes mature properly, providing cell-mediated immunity. They also assist in enhancing humoral immunity by supporting antibody production. However, as a person grows older, the thymus gland gradually shrinks, leading to a decrease in thymosin production and a weaker immune response.
3.5 Pineal Gland: Natural Regulator of Sleep and Body Rhythms
The pineal gland is a small, pea-shaped structure situated on the dorsal side of the forebrain. Despite its small size, it performs a powerful function by producing a hormone called melatonin, which acts as the body’s internal clock. Melatonin is mainly responsible for maintaining the 24-hour (diurnal) biological rhythm, which includes essential daily patterns like the sleep-wake cycle and body temperature regulation. This means that the pineal gland helps signal the body when it’s time to sleep or stay awake, based on the amount of light received through the eyes. In addition to controlling sleep, melatonin also affects several other bodily functions. It plays a role in regulating metabolism, skin pigmentation, and even the menstrual cycle in females. Furthermore, melatonin is also believed to support the body’s defense system, making it important for immunity. Thus, the pineal gland is not just a sleep regulator — it’s a multi-functional hormone gland that impacts various aspects of physical and mental health. Understanding how the pineal gland works can help you maintain a healthier lifestyle and better sleep patterns.
3.6 Parathyroid Gland: Key Hormone Regulating Calcium Levels in Body
The parathyroid glands are four tiny but crucial endocrine glands located on the back side of the thyroid gland, with one pair embedded in each lobe of the thyroid. These glands secrete a vital peptide hormone known as parathyroid hormone (PTH), which plays a major role in maintaining calcium balance in the body. The release of PTH is automatically regulated by the amount of calcium (Ca²⁺) circulating in the blood. When calcium levels drop, the parathyroid gland responds by releasing more PTH to restore balance. This hormone acts in multiple ways — it stimulates bone resorption, a process where calcium is released from bones into the bloodstream, increasing blood calcium levels. It also enhances calcium reabsorption by the renal tubules in the kidneys and boosts calcium absorption from the digested food in the intestines. This makes PTH a hypercalcemic hormone, meaning it raises calcium concentration in the blood. Alongside another hormone called TCT (Thyrocalcitonin), PTH plays a critical role in calcium homeostasis, ensuring that the body has just the right amount of calcium for bone strength, nerve function, and muscle activity. Clearly, the parathyroid gland is a small gland with a big impact on your health.
3.8 Pancreas: Dual Role in Digestion and Blood Sugar Regulation Explained
The adrenal glands are a pair of small, triangular-shaped endocrine glands located just above each kidney. Each adrenal gland is made up of two distinct regions — the adrenal medulla at the center and the adrenal cortex surrounding it. These regions function differently but together they play a vital role in maintaining overall body balance. The adrenal cortex is responsible for producing important steroid hormones called corticoids, which include glucocorticoids, mineralocorticoids, and androgenic steroids. The glucocorticoids, mainly cortisol, help manage carbohydrate metabolism by promoting gluconeogenesis, lipolysis, and proteolysis — which means they help generate glucose from fats and proteins. Cortisol also reduces inflammation, supports kidney and cardiovascular function, boosts RBC production, and suppresses the immune response when necessary. The mineralocorticoids, especially aldosterone, regulate the balance of electrolytes and body fluids. Aldosterone acts on the renal tubules to reabsorb sodium and water, and excrete potassium and phosphate, thereby helping maintain blood pressure, osmotic balance, and fluid volume. The adrenal cortex also releases androgenic steroids in small amounts, which promote the development of axial hair, pubic hair, and facial hair during puberty. Structurally, the adrenal cortex has three layers — the zona glomerulosa (outer), zona fasciculata (middle), and zona reticularis (inner), each contributing to hormone production. On the other hand, if the adrenal cortex fails to produce sufficient hormones, it can lead to Addison’s disease, a condition marked by severe fatigue, weakness, and disturbed metabolism. Hence, the adrenal gland is much more than just a stress responder — it’s a multi-tasking hormonal hub essential for energy, immunity, fluid balance, and puberty-related changes.
3.8 Pancreas: Dual Role in Digestion and Blood Sugar Regulation Explained
The pancreas is a composite gland that functions as both an exocrine and an endocrine gland. The endocrine part of the pancreas consists of clusters of specialized cells called the Islets of Langerhans, which form only 1 to 2% of its total mass. The α-cells secrete glucagon, helping to increase blood sugar levels, while the β-cells produce insulin, crucial for glucose homeostasis. Together, they maintain the delicate balance of glucose in the bloodstream.
3.9 Ovary: Powerful Female Gland Controlling Reproduction and Hormones
The ovary is the primary female sex organ, and every female has a pair of ovaries located in the abdominal region. These small yet powerful glands perform two major functions — they produce ova (eggs) and secrete female sex hormones. During each menstrual cycle, the ovary releases one ovum, which is essential for reproduction. Structurally, the ovary is made up of ovarian follicles and stromal tissues. The growing ovarian follicles are mainly responsible for the production of estrogen, a steroid hormone that influences multiple aspects of a female’s reproductive system and physical characteristics. After ovulation, when the follicle ruptures, it transforms into a temporary gland-like structure known as the corpus luteum, which starts secreting another key hormone — progesterone. The estrogen hormone is involved in stimulating the growth and functions of female secondary sex organs, helps in the development of ovarian follicles, and leads to the appearance of secondary sexual characters such as the high-pitched voice and breast development. Estrogen also plays a role in regulating female sexual behavior. On the other hand, progesterone is crucial for maintaining pregnancy. It acts on the mammary glands, stimulating the development of alveoli — the milk-storing sacs, and also enhances milk secretion. Together, estrogen and progesterone regulate various reproductive and hormonal activities in the female body, making the ovary a central organ in female health and fertility.
Knowledge about endocrine glands and hormones is essential for anyone studying health and human biology.
Research on endocrine glands and hormones continues to evolve, revealing new insights into their effects on health.
Testis: Dual Role in Male Reproduction and Hormonal Regulation
The testis is a vital organ in the male reproductive system, and every male has a pair of testes located in the scrotal sac, which hangs outside the abdominal cavity. The testis performs a dual role — acting both as a primary sex organ and an endocrine gland. Structurally, each testis is made up of seminiferous tubules and interstitial (stromal) tissues. The spaces between the seminiferous tubules contain specialized cells called Leydig cells or interstitial cells, which are responsible for producing a group of male sex hormones known as androgens, the most important being testosterone. These androgens control the development, maturation, and proper functioning of male accessory sex organs, including the epididymis, vas deferens, seminal vesicles, prostate gland, and urethra. In addition, testosterone is responsible for promoting muscular growth, the development of facial and axillary hair, a deep or low-pitched voice, and male aggressiveness. It plays a crucial role in spermatogenesis, the process by which sperm cells are formed inside the seminiferous tubules. The testis hormones also act on the central nervous system, influencing male sexual behavior (libido). Furthermore, androgens have anabolic effects, meaning they stimulate the synthesis of proteins and regulate carbohydrate metabolism, which contributes to muscle building and energy use. Thus, the testis is not only essential for reproduction but also for defining and maintaining male characteristics, fertility, and overall hormonal balance.
4 Hormones of Heart, Kidney, and Gastrointestinal Tract: Secret Roles in Body Functions
Besides the well-known endocrine glands, certain non-endocrine organs and tissues in the human body also secrete crucial hormones that support a variety of physiological processes. Among these, the heart, kidney, and gastrointestinal (GI) tract produce some highly specialized hormones. The heart, specifically the atrial wall, secretes a peptide hormone called Atrial Natriuretic Factor (ANF). This hormone plays a key role in reducing blood pressure. When blood pressure rises, ANF is released, causing dilation of blood vessels, which leads to a drop in blood pressure, helping maintain cardiovascular balance. Moving to the kidneys, specialized juxtaglomerular cells produce erythropoietin, another peptide hormone that stimulates erythropoiesis — the formation of red blood cells (RBCs) in the bone marrow, which is essential for oxygen transport in the body. The gastrointestinal tract also contains endocrine cells that secrete important digestive hormones like gastrin, secretin, cholecystokinin (CCK), and gastric inhibitory peptide (GIP). Gastrin stimulates the gastric glands to secrete hydrochloric acid and pepsinogen, aiding in digestion. Secretin acts on the exocrine pancreas and promotes the release of water and bicarbonate ions, which neutralize stomach acid. CCK targets the pancreas and gallbladder, helping in the release of pancreatic enzymes and bile juice for food digestion. Meanwhile, GIP works by inhibiting gastric secretions and reducing stomach motility, balancing digestion. Additionally, many other non-endocrine tissues produce growth factors, which are vital for normal tissue growth, repair, and regeneration. These hormones and factors, though secreted outside typical endocrine glands, are essential for body regulation and internal harmony.
5. How Hormones Work: Their Mode of Action on Target Cells
Hormones show their effect on specific organs or tissues, known as target tissues. Each target tissue contains specialized proteins called hormone receptors, which bind only to a specific hormone—just like a key fits into a particular lock.
These hormone receptors are of two main types based on their location:
- Membrane-bound receptors – Present on the surface (cell membrane) of target cells.
- Intracellular receptors – Present inside the target cell, usually within the nucleus (also known as nuclear receptors).
When a hormone binds to its specific receptor, it forms a hormone-receptor complex, which triggers biochemical changes inside the cell. These changes regulate various body functions like metabolism, growth, reproduction, etc.
🧪 Types of Hormones Based on Chemical Nature:
Hormones are chemically classified into four groups:
- Peptide, polypeptide, and protein hormones – Example: Insulin, Glucagon, Pituitary hormones, Hypothalamic hormones.
- Steroid hormones – Example: Cortisol, Testosterone, Estradiol, Progesterone.
- Iodothyronines (Thyroid hormones) – Example: Thyroxine (T4), Triiodothyronine (T3).
- Amino acid derivatives – Example: Epinephrine (Adrenaline).
⚙️ How Hormones Act:
1. Hormones with Membrane-Bound Receptors:
- These hormones do not enter the target cell.
- Instead, they bind to receptors on the cell membrane and produce second messengers inside the cell like:
- cAMP (cyclic AMP)
- IP₃ (Inositol triphosphate)
- Ca²⁺ (Calcium ions)
- These second messengers activate internal enzymes or proteins that bring about the required effect.
✅ Example: Insulin works through this method.
2. Hormones with Intracellular Receptors:
- These hormones are lipid-soluble and can enter the cell membrane.
- Inside the cell, they bind to nuclear receptors and directly affect gene expression or DNA function.
- This can result in long-term effects like cell growth, protein synthesis, and development.
✅ Example: Steroid hormones and thyroid hormones use this mechanism.
🔁 Final Outcome:
Regardless of the mechanism, the final result of hormone action is to:
- Control metabolism
- Regulate physiological processes
- Maintain homeostasis
- Influence development and reproduction
6. SUMMARY: Hormonal Regulation in Human Body
The human body uses hormones for chemical coordination, integration, and regulation. These hormones are secreted by specialized glands or cells and affect various functions like metabolism, growth, development, and reproduction.
🧠 Main Endocrine Glands and Their Hormones
1. Hypothalamus
- Controls the pituitary gland.
- Produces releasing and inhibiting hormones.
2. Pituitary Gland (Master gland)
- Has 3 parts:
- Pars distalis (Anterior) – secretes 6 major hormones.
- Pars intermedia – secretes MSH (Melanocyte Stimulating Hormone).
- Pars nervosa (Posterior) – secretes oxytocin and vasopressin.
- Controls other endocrine glands and body growth.
3. Pineal Gland
- Secretes melatonin, which controls sleep-wake cycle and body temperature.
4. Thyroid Gland
- Produces:
- Thyroxine (T4) and Triiodothyronine (T3) – regulate BMR, brain development, and metabolism.
- Calcitonin – lowers blood calcium levels.
5. Parathyroid Glands
- Secretes parathyroid hormone (PTH) – raises blood calcium level; balances calcium with calcitonin.
6. Thymus Gland
- Secretes thymosins – help in T-cell maturation and antibody production for immunity.
- Shrinks with age.
7. Adrenal Glands
- Adrenal Medulla:
- Secretes epinephrine and norepinephrine – increase alertness, heart rate, sweating, etc.
- Adrenal Cortex:
- Glucocorticoids (e.g. cortisol) – regulate glucose, reduce inflammation, increase RBCs.
- Mineralocorticoids (e.g. aldosterone) – control Na⁺/K⁺ balance and BP.
- Small amounts of androgens also secreted.
8. Pancreas (Islets of Langerhans)
- α-cells: Secrete glucagon – increases blood sugar.
- β-cells: Secrete insulin – lowers blood sugar.
- Imbalance leads to diabetes mellitus.
9. Testis (in males)
- Secretes androgens (mainly testosterone):
- Develop male sex organs & characters
- Promote sperm production, protein synthesis, RBC formation, and sex drive.
10. Ovary (in females)
- Secretes:
- Estrogen – develops female sex organs, secondary sex characters.
- Progesterone – maintains pregnancy, supports mammary glands for milk production.
🫀 Other Hormone-Secreting Organs (Non-Endocrine Tissues)
1. Heart
- Secretes Atrial Natriuretic Factor (ANF) – lowers blood pressure.
2. Kidneys
- Secrete Erythropoietin – stimulates RBC formation.
3. Gastrointestinal (GI) Tract
- Secretes:
- Gastrin – increases HCl and pepsinogen.
- Secretin – increases bicarbonate.
- CCK – releases bile and pancreatic enzymes.
- GIP – slows down gastric functions.
⚙️ Mechanism of Hormone Action
- Hormones bind to specific receptors:
- Membrane-bound receptors: Use second messengers (like cAMP, Ca²⁺).
- Intracellular receptors: Enter cells and directly affect gene expression (e.g., steroids, thyroid hormones).
- Each hormone works only with its matching receptor.
✅ Key Roles of Hormones:
Understanding the roles of endocrine glands and hormones is vital for grasping how our body maintains balance.
- Regulate growth, metabolism, immune system, blood pressure, digestion, reproduction, and homeostasis.
The study of endocrine glands and hormones offers a window into our biological processes.
