NCERT Notes for Class 11 Biology Chapter 19: Chemical Coordination and Integration (original) (raw)

Last Updated : 23 Jul, 2025

Chemical coordination and integration play an important role in human physiology. These processes are regulated by special chemicals known as hormones. Hormones are responsible for regulating various functions in the human body, including the growth and development of organs, cells, and endocrine glands.

In Chapter 19 of _Chemical Coordination and Integration, we will explore the human endocrine system, the hormones it produces, and the mechanisms by which they exert their effects on the body.

Human Endocrine System

The human Endocrine system consists of Endocrine glands and hormones-producing cells and tissues. It is composed of ​the hypothalamus, pituitary, thyroid, adrenal, pancreas, parathyroid, thymus, and gonads (testis and ​ovary).

And some organs like the gastrointestinal tract, kidney, heart, etc., also produce hormones. Let us discuss the major endocrine glands and their functions in detail in the following section:

The Hypothalamus

Hypothalamus forms the basal part of the diencephalon( forebrain) that regulates various body functions. ​Nuclei, which are neurosecretory cells, also produce hormones. They regulate the synthesis and secretion of the Pituitary gland. Hypothalamus produces two types of hormones,

• ​**Releasing Hormones (which stimulate secretion of pituitary hormones) Example- Gonadotropin hormone ​
• **​Inhibiting Hormones (which inhibit secretions of pituitary hormones). Example - Somatostatin hormone inhibits the release of growth hormone.

Hormones after being produced, pass through the axon and are released through the nerve endings. They regulate the function of the anterior pituitary Gland. The posterior pituitary is directly under the control of the Hypothalamus.

Thymus

The thymus is a small, irregularly shaped gland located in the upper part of the chest, just beneath the breastbone and between the lungs. It is a specialized organ that produces and releases substances, such as hormones, to carry out various functions in the body.

The thymus plays a key role in the immune system, particularly in the development and maturation of T-cells, which are important for immune response. As we age, the thymus gradually becomes smaller and less active, but it remains important in early life for immune function.

Pineal Gland

The Pineal Gland Secrets Melatonin regulates 24 the hour​ rhythm of our body like the sleep-wake cycle, body temperature, etc. It also regulates metabolism, ​pigmentation, the menstrual cycle, and the defense capability of the body.

Melatonin production is influenced by light, increasing in darkness and decreasing with exposure to light. This gland plays a important role in maintaining the body's internal biological clock and overall hormonal balance.

Parathyroid Gland

The parathyroid gland, located behind the thyroid, releases a hormone called parathyroid hormone (PTH). The level of PTH in the body is controlled by the amount of calcium in the blood.

PTH raises blood calcium levels by: promoting the breakdown of bone, increasing calcium reabsorption in the kidneys, and enhancing calcium absorption from food. It helps maintain the body's calcium balance.

Pituitary Gland

The pituitary gland is a tiny, pea-sized gland located at the base of the brain, just beneath the hypothalamus. It produces various key hormones and regulates the activity of many other glands in the endocrine system.

Often referred to as the ****"master gland,"** it controls functions such as growth, metabolism, and reproduction. It has two main parts: the anterior pituitary, which releases hormones that affect other glands, and the posterior pituitary, which stores hormones produced by the hypothalamus.

**Functions of Pituitary Gland Hormones:

Thyroid Gland

The thyroid gland consists of two lobes that contacted each other through the isthmus. The thyroid gland is composed of follicles and stromal tissues. Follicles synthesize two hormones: Tetraiodothyronine or thyroxine (T4) and ​Triiodothyronine (T3). Iodine is essential for the normal functioning of the thyroid gland.

Adrenal Gland

The adrenal gland is composed of two types of tissues, the​ centrally located tissue is called the **adrenal medulla, and outside this lies the **adrenal cortex. The adrenal medulla secretes two hormones( catecholamine) called **adrenaline or epinephrine and noradrenaline or norepinephrine. These ​are also known as emergency ​hormones ​or hormones of Fight.

The function of these hormones is as follows:

• Facilitates the breakdown of glycogen, which results in an increased concentration of glucose in the blood.
• Increases the heartbeat, rate of respiration, increase alertness, pupillary dilation, piloerection (raising of hairs), sweating, etc.

Pancreas

The pancreas acts as both an exocrine and endocrine gland. The endocrine part contains clusters of cells called Islets of Langerhans, which have two types of cells: alpha cells and beta cells. Alpha cells release glucagon, and beta cells release insulin.

Glucagon, a hormone that raises blood sugar levels, plays a key role in keeping glucose levels normal. It helps release glucose by acting on liver cells, encouraging the breakdown of stored glycogen and the production of new glucose.

It also reduces how much glucose cells take in and use. High glucagon levels can lead to diabetes, which causes glucose to be lost in urine and the creation of ketone bodies.

Insulin, on the other hand, lowers blood sugar levels. It helps store glucose as glycogen in the liver and fat cells, and it encourages cells to absorb and use glucose.

Testes

The testes serves both as a sex organ and an endocrine gland. It contains seminiferous tubules and interstitial tissue. Leydig cells within the testis produce androgens, such as testosterone.

Testosterone stimulates sperm production, muscle growth, and the development of facial and body hair. It also increases aggression and lowers the pitch of the voice. and testosterone helps mature male reproductive organs like the epididymis, vas deferens, seminal vesicles, prostate gland, and urethra.

Ovary

The ovary which is the primary female sex organ, produces two groups of steroid hormones called Estrogen and Progesterone.

• **Estrogen is synthesized and secreted by ovarian follicles, which produce a wide range of functions like, it facilitates the growth and development of female secondary sex organs, development, and maturation of ovarian follicles, the appearance of female secondary sex characteristics, and mammary gland development.
• **Progesterone supports pregnancy, acts on the ​mammary glands and stimulates the formation of alveoli, and facilitates milk secretion.

Do You Know?

• Unlike most organ systems, the endocrine glands are not clustered together but are dispersed throughout the body, such as the pancreas, adrenal glands, and thyroid, making chemical coordination complex and wide-ranging.
• Some hormones, like thyroid hormones, have long-lasting effects on metabolism and growth.

Properties of Horomones

• Hormones are secreted directly into the blood by endocrine glands and travel through the circulatory system to reach their target organs or tissues.
• Most hormones have a short lifespan in the bloodstream and are quickly broken down or excreted from the body after completing their function.
• They help regulate and coordinate various physiological activities, such as metabolism, growth, reproduction, and mood regulation, ensuring proper body function.
• Hormones are effective in very low concentrations, yet they can have significant effects on the body.
• Some hormones, like adrenaline, act quickly to produce immediate responses, while others may take longer to have an effect.
• Some hormones, like proinsulin, are secreted in an inactive form and require conversion into their active form before they can exert their effects.
• Hormones are highly specific, and only cells with the corresponding receptors for a particular hormone can respond to it, ensuring that the right organ or tissue is targeted.
• Hormones can be peptide-based (protein or amino acid-derived) or steroid-based (derived from cholesterol), influencing how they interact with receptors on or inside target cells.
• Hormone secretion is often regulated through feedback loops, mainly negative feedback, to maintain homeostasis and prevent overproduction or underproduction.
• Hormones are transported through the bloodstream; water-soluble hormones travel freely in the blood, while fat-soluble hormones require carrier proteins to travel effectively.
• Hormones enable communication between different cells, tissues, and organs, allowing for the coordination of complex processes like metabolism, stress responses, and growth.
• They help regulate metabolic processes, influencing how the body uses energy, stores fat, and metabolizes nutrients like glucose.
• Hormone levels can be affected by environmental factors such as stress, diet, sleep, and exposure to toxins.
• An imbalance in hormone levels can lead to various disorders, including thyroid issues, diabetes, and adrenal problems, depending on which hormone is affected.
• As we age, the production and regulation of certain hormones, like estrogen, testosterone, and growth hormone, change, leading to age-related physical changes.

Functions of Horomones

• Hormones control how the body processes and uses energy, influencing the metabolism of carbohydrates, fats, and proteins.
• They are involved in physical growth, tissue repair, and the development of organs and systems, especially during childhood and puberty.
• Hormones regulate the reproductive system, controlling processes like menstruation, pregnancy, and sperm production.
• They influence emotional states, stress responses, and mood regulation, with examples including cortisol (stress hormone) and serotonin (mood regulator).
• Hormones maintain internal balance by regulating processes like body temperature, water balance, and pH levels.
• Some hormones, such as cortisol, help modulate the immune system, affecting inflammation and immune responses.
• Hormones like aldosterone regulate the balance of sodium and potassium in the body, helping maintain fluid and electrolyte homeostasis.
• Insulin and glucagon work together to control blood sugar levels, ensuring that cells have enough energy for metabolism.
• Parathyroid hormone and calcitonin help regulate calcium levels in the blood and bones, critical for bone health and muscle function.
• Hormones like adrenaline and cortisol trigger the fight-or-flight response, helping the body react to stress or danger.
• Hormones such as melatonin regulate sleep patterns and circadian rhythms, contributing to restful sleep.
• Hormones like ghrelin and leptin help regulate hunger, satiety, and energy balance.
• Hormones like renin, aldosterone, and vasopressin play key roles in maintaining blood pressure by controlling blood volume and vessel constriction.
• Sex hormones like estrogen, progesterone, and testosterone influence sexual development, libido, and fertility.
• Some hormones, like estrogen, affect brain function, memory, and cognitive abilities.

Conclusion

Chemical coordination and integration involve the regulation of various bodily functions by hormones secreted by endocrine glands, ensuring proper growth, development, and maintenance of homeostasis. This system works alongside the nervous system to help maintain overall balance in the body.

****"You may also read;** NCERT Solutions for Class 11th Biology Chapter 19