Chapter 19 of Class 11 Biology is Chemical Coordination and Integration, the final chapter of the syllabus. It covers the human endocrine system, hormones, and their regulatory mechanisms. These Class 11 Biology Chapter 19 solutions are also useful as quick revision notes before exams.
Endocrine Glands and Hormones
Endocrine glands are ductless glands that secrete hormones directly into the bloodstream. Hormones are chemical messengers that act on distant target cells/organs possessing specific receptors.
Major Endocrine Glands
Hypothalamus: controls the pituitary (“master gland”). Pituitary: secretes growth hormone (GH), and hormones controlling other glands. Thyroid: secretes thyroxine (T3, T4, regulates metabolic rate) and calcitonin. Parathyroid: parathyroid hormone (PTH, regulates blood Ca²⁺). Adrenal: cortex (cortisol, aldosterone) and medulla (adrenaline/epinephrine — “fight or flight”). Pancreas: insulin (lowers blood glucose) and glucagon (raises blood glucose). Gonads: testes (testosterone), ovaries (estrogen, progesterone).
Mechanism of Hormone Action
Hormones bind specific receptors on/in target cells: peptide hormones (like insulin) typically bind cell-surface receptors, triggering intracellular second messenger cascades (e.g. cAMP). Steroid hormones (like cortisol, estrogen) are lipophilic and can cross the cell membrane, binding intracellular/nuclear receptors, directly influencing gene expression.
Feedback Regulation
Hormone secretion is tightly regulated, most commonly by negative feedback: rising hormone/product levels inhibit further secretion (e.g. thyroxine feeds back to suppress pituitary TSH release), maintaining homeostasis.
Hormonal Disorders
Diabetes mellitus (insulin deficiency/resistance, high blood glucose), goitre (enlarged thyroid, often from iodine deficiency), dwarfism/gigantism (growth hormone deficiency/excess).
Class 11 Biology Chapter 19 – Notes and Extra Questions
Along with these NCERT Solutions, students can also use the Class 11 Biology Chapter 19 Extra Questions and Class 11 Biology Chapter 19 Revision Notes for quick revision and extra practice.
