Chemical Coordination And Integration Revision Notes, Key Concepts & Important Questions
Class 11 Biology’s Chemical Coordination and Integration is an important chapter that explains how chemical messengers regulate and coordinate different functions in the human body. The chapter focuses on the endocrine system, the role of hormones, and how different glands, such as the pituitary, thyroid, pancreas, adrenal, and gonads, control various physiological processes. It also covers hormone classification, mechanisms of hormone action, feedback regulation, and common hormonal disorders.
These revision notes on Chemical Coordination and Integration, prepared by ALLEN’s expert faculty, provide a clear overview of the endocrine glands, hormones, and their functions in the body. These notes are designed for quick and effective revision and they help students to understand key concepts, remember important hormone functions and disorders, and prepare confidently for board and competitive exams.
1.0Concept-Wise Important Revision Notes
1. What is chemical coordination and integration?
Chemical coordination refers to the regulation and control of physiological processes through chemical signals called hormones.
The body uses two systems for coordination:
Neural coordination
- Fast and precise
- Short-term effects
Chemical coordination
- Slower but long-lasting
- Acts over a wider range of cells
Since many body cells are not directly connected to nerve fibres, hormones provide continuous regulation of cellular functions.
2. What are endocrine glands and hormones?
- Endocrine glands are ductless glands that release chemical substances called hormones directly into the bloodstream.
- A hormone is a chemical substance that is produced by the endocrine glands, released into the blood and transported to a distant target organ where it produces specific effects.
3. What is the human endocrine system?
The endocrine system consists of endocrine glands and hormone-producing tissues distributed throughout the body.
Major endocrine glands include:
- Pituitary gland
- Pineal gland
- Thyroid gland
- Adrenal glands
- Pancreas
- Parathyroid glands
- Thymus
- Gonads (testes and ovaries)
Some organs such as the gastrointestinal tract, liver, kidneys, and heart also produce hormones.
4. What is the role of the hypothalamus?
The hypothalamus is located at the base of the diencephalon in the forebrain.
Functions:
- Contains neurosecretory cells (nuclei)
- Produces neurohormones
- Controls the production and release of pituitary hormones
Thus, it acts as an important link between the nervous system and endocrine system.
5. What are the structure and functions of the pituitary gland?
The pituitary gland is located in the sella turcica of the sphenoid bone and is connected to the hypothalamus by the infundibulum.
Based on structure, it has two parts:
- Adenohypophysis (anterior pituitary)
- Neurohypophysis (posterior pituitary)
The pituitary gland plays an important role in regulating several endocrine glands.
Growth hormone deficiency may lead to dwarfism, characterised by reduced growth and short stature.
6. Describe the structure of the thyroid gland.
The thyroid gland is the largest endocrine gland.
Structure:
- Located in the neck between the trachea and larynx
- Composed of two lobes
- Lobes are connected by a thin tissue called the isthmus
- Shape resembles the letter “H”
- Origin: Endodermal
7. What are the functions of thyroid hormones?
Thyroid hormones perform several important functions:
- Regulate basal metabolic rate (BMR)
- Support red blood cell formation (erythropoiesis)
- Control metabolism of carbohydrates, proteins and fats
- Maintain water and electrolyte balance
- Support physical, mental and sexual growth
- Help in development and myelination of nerve fibres
- Stimulate metamorphosis in tadpole larvae
8. What are the major thyroid disorders?
Cretinism
- Caused by hypothyroidism during pregnancy
- Leads to stunted growth, mental retardation, low IQ, abnormal skin and deaf-mutism
Multinodular Goitre
- Enlargement of the thyroid gland
- Characterised by multiple nodules
Exophthalmic Goitre (Graves’ disease)
- Autoimmune disorder affecting the thyroid gland.
9. What are the structure and functions of the parathyroid gland?
The parathyroid glands are located on the backside of the thyroid gland.
Characteristics:
- Four glands (one pair for each thyroid lobe)
- Origin: Endodermal
- Hormone secreted: Parathyroid hormone (PTH)
Functions of PTH:
- Increases blood calcium level (hypercalcemia)
- Decreases blood phosphate level (hypophosphatemia)
- Maintains calcium and phosphate balance in extracellular fluid (ECF)
10. What is the structure and control of adrenal glands?
The adrenal glands are also called suprarenal glands.
Characteristics:
- Present one above each kidney
- Known as glands of emergency
Structure:
- Adrenal cortex – outer region
- Adrenal medulla – inner region
Control of adrenal secretion:
- ACTH from anterior pituitary controls glucocorticoid secretion
- Renin from kidneys controls mineralocorticoids
- Nervous system regulates adrenal medullary hormones.
11. What are the thymus and pineal glands?
Thymus gland
- Origin: Endodermal
- Location: Between lungs behind sternum
- Structure: Bilobed gland
- Hormone secreted: Thymosin
- Nature: Proteinaceous
Pineal gland
- Origin: Ectodermal
- Location: Dorsal side of the forebrain
- Hormone secreted: Melatonin
Melatonin characteristics:
- Light reduces its production
- Maximum level occurs at midnight
- Minimum level occurs at noon
12. What is the pancreas and its endocrine role?
The pancreas is a heterocrine or mixed gland because it has both endocrine and exocrine functions.
Characteristics:
- Located between the limbs of the C-shaped duodenum
- Exocrine part secretes pancreatic juice with digestive enzymes
- Endocrine part secretes hormones:
13. What are gonads and their hormones?
Male Gonads (Testes)
- Present in the scrotal sac
- Act as primary sex organs and endocrine glands
- Composed of seminiferous tubules and interstitial tissue
Female Gonads (Ovaries)
- Located in the abdomen
- Produce one ovum per menstrual cycle
Hormones produced:
- Estrogen – secreted by developing ovarian follicles
- Progesterone – secreted by the corpus luteum after ovulation.
14. What is the mechanism of hormone action?
Hormones act on specific target tissues by binding to hormone receptors.
Types of hormones:
- Water-soluble hormones
- Lipid-soluble hormones
Types of receptors:
- Membrane-bound receptors – located on the cell surface
- Intracellular receptors – located inside the cell (often in the nucleus)
Mechanism:
- Hormone binds to its specific receptor
- A hormone-receptor complex is formed
- This complex triggers biochemical changes in the target cell
- These changes regulate metabolism and physiological functions
Each receptor is specific to a particular hormone, ensuring precise regulation.
15. What are the properties of hormones?
Hormones show several important properties:
a. Specificity: Each hormone acts on specific target cells.
b. Regulation: Hormone secretion is controlled by feedback mechanisms to maintain homeostasis.
c. Transport
- Hormones travel through the bloodstream.
- Water-soluble hormones circulate freely, while lipid-soluble hormones require carrier proteins.
d. Mode of action
- Direct action on target cells
- Indirect action by stimulating release of other substances.
e. Potency: Hormones act effectively even at very low concentrations.
f. Duration: Effects may be short-lived or long-lasting.
g. Secretion pattern: Hormones may be released continuously, in pulses, or in response to stimuli.
h. Excretion: Hormones are eventually broken down in the liver or kidneys to maintain balance.
2.0Memory Tricks
Major Endocrine Glands: “Happy People Take Pretty Good Tea Always”
H → Hypothalamus
P → Pituitary
T → Thyroid
P → Parathyroid
G → Gonads
T → Thymus
A → Adrenal
Functions of Thyroid Hormone: “BRAIN-MET”
B → Basal metabolic rate (BMR)
R → RBC formation (Erythropoiesis)
A → Amphibian metamorphosis
I → Ion balance (water & electrolytes)
N → Nervous system development
M → Metabolism of carbs, proteins, fats
E → Energy regulation
T → Tissue growth (physical & sexual growth)
Properties of Hormones: “SMART PED”
S → Specificity
M → Mechanism of action
A → Action (direct/indirect)
R → Regulation (feedback control)
T → Transport in blood
P → Potency (effective in small amounts)
E → Excretion
D → Duration of effect
Hormone Action Mechanism: “HRM”
H → Hormone binds receptor
R → Hormone–Receptor complex forms
M → Metabolic response in target cell
3.0Previous Year Questions on Chemical Coordination And Integration
Which hormone is known as the "fight or flight" hormone?
a. Insulin
b. Thyroxine
c. Adrenaline
d. Oxytocin
Answer: c. Adrenaline
The hormone that regulates the sleep-wake cycle is produced by the:
a. Pituitary gland
b. Pineal gland
c. Adrenal gland
d. Pancreas
Answer: b. Pineal gland
Which of the following hormones is involved in the regulation of calcium levels in the blood?
a. Thyroxine
b. Parathyroid hormone
c. Insulin
d. Glucagon
Answer: b. Parathyroid hormone
The posterior pituitary gland secretes:
a. Oxytocin and vasopressin
b. Prolactin and growth hormone
c. Thyroxine and calcitonin
d. Cortisol and aldosterone
Answer: a. Oxytocin and vasopressin