Class 11 Biology Chapter 19 Chemical Coordination and Integration Notes
These Chemical Coordination and Integration Class 11 Notes explain how hormones regulate growth, metabolism, reproduction and other body functions. Revise the major endocrine glands, their hormones, how hormones act on cells and important hormonal disorders.
Table of Contents
What is chemical coordination?
The nervous system sends rapid signals through neurons. The endocrine system coordinates body functions through chemical messengers called hormones. Endocrine glands have no ducts; they release hormones into the surrounding fluid and blood.
Hormones act in small amounts. A hormone produces an effect only in a target cell with the appropriate receptor.
Major endocrine glands and hormones
| Gland or organ | Important hormones | Main role |
|---|---|---|
| Hypothalamus | Releasing and inhibiting hormones | Regulates the pituitary gland |
| Pituitary | GH, TSH, ACTH, FSH, LH, prolactin; releases oxytocin and ADH | Growth, control of other glands, reproduction and water balance |
| Pineal | Melatonin | Helps regulate daily sleep–wake rhythms |
| Thyroid | T₃, T₄ and calcitonin | Metabolism, development and calcium balance |
| Parathyroid | Parathyroid hormone (PTH) | Raises blood calcium level |
| Adrenal glands | Adrenaline, noradrenaline, cortisol and aldosterone | Stress responses, metabolism and salt–water balance |
| Pancreas | Insulin and glucagon | Regulates blood glucose |
| Testes | Androgens, mainly testosterone | Male reproductive development and functions |
| Ovaries | Estrogens and progesterone | Female reproductive development and pregnancy |
The thymus also secretes thymosins, which support the development of immune cells.
Hypothalamus and pituitary gland
The hypothalamus links neural and hormonal control. Its releasing hormones stimulate the secretion of certain pituitary hormones, while inhibiting hormones reduce their secretion.
The pituitary has an anterior and a posterior part:
- The anterior pituitary produces hormones including growth hormone (GH), prolactin, TSH, ACTH, FSH and LH.
- The posterior pituitary stores and releases oxytocin and antidiuretic hormone (ADH), which are produced in the hypothalamus.
Growth hormone supports body growth. TSH stimulates the thyroid, while ACTH stimulates the adrenal cortex. FSH and LH regulate activities of the gonads. Prolactin supports milk production.
Oxytocin stimulates uterine contractions during childbirth and milk ejection. ADH, also called vasopressin, helps the kidneys conserve water.
Thyroid, parathyroid and pineal glands
The thyroid gland produces the thyroid hormones T₃ and T₄, which help regulate metabolism and support normal growth and development. Iodine is needed to make these hormones. The thyroid also secretes calcitonin, which helps lower blood calcium.
The parathyroid glands secrete PTH, which raises blood calcium. PTH and calcitonin therefore have different roles in calcium balance.
The pineal gland secretes melatonin, which helps regulate the body’s daily rhythms, including the sleep–wake cycle.
Adrenal glands and the pancreas
Each adrenal gland sits above a kidney. Its inner region, the adrenal medulla, secretes adrenaline and noradrenaline. These prepare the body to respond to a stressful or emergency situation by increasing alertness, heart rate and breathing rate.
The outer adrenal cortex secretes hormones including:
- Cortisol: Helps regulate metabolism and the body’s response to stress.
- Aldosterone: Helps regulate sodium, potassium and water balance.
The endocrine part of the pancreas contains clusters of cells called islets of Langerhans:
- Beta cells secrete insulin, which helps lower blood glucose.
- Alpha cells secrete glucagon, which helps raise blood glucose.
Together, insulin and glucagon help maintain blood glucose balance.
Gonads and other hormone-producing organs
The testes produce androgens, mainly testosterone. These support male reproductive functions and the development of secondary sexual characteristics.
The ovaries produce estrogens and progesterone. Estrogens support female reproductive development, while progesterone helps support pregnancy.
Hormones also come from organs other than the major endocrine glands. For example, the heart produces atrial natriuretic factor (ANF), which helps lower blood pressure, and the kidneys produce erythropoietin, which stimulates red blood cell formation.
How do hormones act?
A hormone binds to a specific receptor in or on its target cell. This binding starts changes inside the cell that produce the hormone’s effect.
At this level, remember two broad patterns:
- Some hormones bind to receptors on the cell membrane and use signals inside the cell to produce an effect.
- Others bind to receptors inside the cell and can influence gene activity.
A cell responds to a hormone because it has the appropriate receptor, even though the hormone may travel throughout the body.
Important hormonal disorders
| Disorder | Association to remember |
|---|---|
| Pituitary dwarfism | Too little growth hormone during childhood |
| Acromegaly | Excess growth hormone in adults |
| Goitre | Enlargement of the thyroid gland; iodine deficiency is one possible cause |
| Cretinism | Term used in the syllabus for impaired development associated with inadequate thyroid hormone during early development |
| Exophthalmic goitre | A form of hyperthyroidism associated with protruding eyes |
| Diabetes mellitus | Persistently high blood glucose associated with problems in insulin production or action |
| Addison’s disease | Inadequate production of hormones by the adrenal cortex |
Do not confuse: Diabetes mellitus concerns blood glucose regulation. Diabetes insipidus concerns the body’s ability to conserve water and is associated with inadequate ADH action.
Quick revision
- Endocrine glands are ductless and release hormones.
- Hormones act on cells with matching receptors.
- The hypothalamus regulates pituitary activity.
- Insulin lowers blood glucose; glucagon raises it.
- PTH raises blood calcium; calcitonin helps lower it.
- The adrenal medulla produces adrenaline and noradrenaline.
- ADH helps the kidneys conserve water.
Check your understanding
1. Why are endocrine glands called ductless glands?
They release hormones without using ducts.
2. Which gland secretes melatonin?
The pineal gland.
3. Which pancreatic cells secrete insulin?
Beta cells of the islets of Langerhans.
4. Which hormone helps raise blood calcium?
Parathyroid hormone (PTH).
5. What is the difference between insulin and glucagon?
Insulin helps lower blood glucose, while glucagon helps raise it.
Find the complete chapter list in the CBSE Class 11 Biology Complete Study Guide.
Frequently Asked Questions
What is an endocrine gland?
It is a ductless gland that releases hormones into surrounding fluid and blood.
What is a hormone?
It is a chemical messenger that helps regulate the activity of cells with suitable receptors.
How does the hypothalamus influence the pituitary?
It produces releasing and inhibiting hormones and regulates posterior pituitary release through neural connections.
Which hormone promotes body growth?
Growth hormone from the anterior pituitary supports body growth.
What is pituitary dwarfism?
It is stunted growth associated with too little growth hormone during childhood.
What is acromegaly?
It is a condition associated with excess growth hormone in adults.
What does the pineal gland secrete?
It secretes melatonin, which helps regulate daily rhythms.
Why is iodine needed by the thyroid?
Iodine is required for synthesis of thyroid hormones T₃ and T₄.
What is goitre?
It is enlargement of the thyroid gland; iodine deficiency is one possible cause.
What is exophthalmic goitre?
It is a form of hyperthyroidism associated with thyroid enlargement and prominent eyes.
What does parathyroid hormone do?
PTH raises the calcium level in blood.
What do insulin and glucagon do?
Insulin helps lower blood glucose; glucagon helps raise it.
What is Addison’s disease associated with?
It is associated with inadequate production of hormones by the adrenal cortex.
How do hormones affect target cells?
They bind specific receptors on or in target cells and trigger changes in cell activity.
How does diabetes insipidus differ from diabetes mellitus?
Diabetes insipidus involves impaired water conservation linked to ADH action; diabetes mellitus involves prolonged high blood glucose.