Chemical Coordination and Integration mind map

Chemical Coordination and Integration: what the chapter covers

The main idea of each topic with its first key points. Open a branch above for everything, or read the full notes.

1. 1Chapter Overview

   Chemical coordination is the regulation of body activities through hormones secreted by endocrine glands. Unlike nervous coordination, which is fast and short-lived, endocrine coordination is slower but has long-lasting effects on growth, metabolism, reproduction, stress response, water balance, calcium balance and biological rhythms. This chapter explains endocrine glands, hormones, their chemical nature, mechanism of action, major glands such as hypothalamus, pituitary, thyroid, parathyroid, adrenal, pancreas, gonads, pineal and thymus, and important disorders caused by hormone deficiency or excess. For NEET, the most important areas are gland-hormone-target organ relationships, feedback regulation, peptide versus steroid hormone action, and disorder-based questions.

   • Chemical coordination integrates body functions along with the nervous system.
   • Hormones act only on target cells having specific receptors.
   • Endocrine glands include pituitary, pineal, thyroid, parathyroid, adrenal, pancreas, thymus and gonads.
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2. 2Endocrine Glands

   Endocrine glands are ductless glands that secrete hormones directly into the blood for transport to distant or nearby target organs. They form the endocrine system, which works with the nervous system to maintain homeostasis. Exocrine glands, in contrast, have ducts and release secretions such as saliva, sweat or digestive enzymes onto epithelial surfaces or into cavities. Major endocrine glands include pituitary, pineal, thyroid, parathyroid, adrenal, pancreas, thymus, testes and ovaries. Some organs like kidney, heart, gastrointestinal tract, liver and placenta also secrete hormones. Neuroendocrine integration is best shown by the hypothalamus, which receives neural inputs and controls pituitary hormone secretion.

   • The endocrine system regulates metabolism, growth, development, reproduction, sleep, stress and ionic balance.
   • Endocrine secretions act in very small quantities but produce powerful effects.
   • Endocrine glands are richly supplied with blood capillaries for rapid hormone entry.
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3. 3Hormones

   Hormones are non-nutrient chemical messengers produced in trace amounts by endocrine glands or endocrine tissues. They regulate physiological processes by binding to specific receptors on target cells. Based on chemical nature, hormones are commonly grouped into peptide/protein/glycoprotein hormones, steroid hormones and amino acid-derived hormones. Peptide hormones are usually water-soluble and include insulin, glucagon, growth hormone, prolactin, TSH, FSH and LH. Steroid hormones are lipid-soluble and include cortisol, aldosterone, testosterone, estrogen and progesterone. Amino acid-derived hormones include thyroid hormones, adrenaline, noradrenaline and melatonin. NEET frequently asks classification, source, target and function of hormones.

   • Target specificity depends on receptors, not simply on blood supply.
   • Peptide hormones usually cannot cross the plasma membrane.
   • Steroid hormones cross the lipid bilayer and affect transcription.
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4. 4Hormone Action

   Hormones produce effects only after binding to specific receptors present on target cells. Water-soluble hormones such as peptide hormones and catecholamines usually cannot cross the plasma membrane, so they bind to cell surface receptors and activate intracellular second messengers such as cAMP, IP3, DAG or calcium ions. These second messengers change enzyme activity and produce rapid responses. Lipid-soluble hormones such as steroid hormones and thyroid hormones cross the membrane and bind intracellular receptors. The hormone-receptor complex then regulates gene expression, producing slower but longer-lasting responses. Hormonal secretion is controlled mainly by feedback regulation, especially negative feedback, which maintains homeostasis.

   • Hormone specificity depends on receptor specificity.
   • Cell surface receptors convert extracellular hormone binding into intracellular signals.
   • Second messengers amplify the signal, so small hormone amounts can produce large effects.
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5. 5Human Endocrine System

   The human endocrine system consists of hypothalamus, pituitary, pineal, thyroid, parathyroid, adrenal glands, pancreas, gonads and thymus. The hypothalamus controls pituitary using releasing and inhibiting hormones. The pituitary secretes growth hormone, prolactin, TSH, ACTH, FSH, LH and also releases ADH and oxytocin from posterior pituitary. Pineal secretes melatonin, thyroid secretes T3, T4 and calcitonin, parathyroid secretes PTH, adrenal cortex secretes corticoids and adrenal medulla secretes catecholamines. Pancreatic islets secrete insulin and glucagon. Gonads secrete sex hormones, and thymus secretes thymosins for immune maturation. NEET heavily tests gland, hormone, target and function charts.

   • Pituitary is anatomically connected to hypothalamus and functionally regulated by it.
   • Growth hormone excess before epiphyseal closure may cause gigantism; in adults it causes acromegaly.
   • TSH stimulates thyroid, ACTH stimulates adrenal cortex, FSH and LH regulate gonads.
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6. 6Endocrine Disorders

   Endocrine disorders occur when hormones are secreted in deficient or excessive amounts, when receptors fail to respond, or when feedback regulation is disturbed. Diabetes mellitus is caused by insulin deficiency or insulin resistance and produces hyperglycemia, glycosuria and polyuria. Diabetes insipidus results from ADH deficiency or poor renal response, causing excessive dilute urine. Thyroid disorders include hypothyroidism, hyperthyroidism, goitre and cretinism. Growth hormone imbalance causes dwarfism, gigantism or acromegaly depending on age and secretion level. Adrenal cortex disorders include Addison's disease due to hyposecretion and Cushing's syndrome due to excess cortisol. NEET questions commonly ask cause, hormone involved and symptoms.

   • Always identify whether the disorder is due to hormone deficiency, hormone excess or receptor resistance.
   • Diabetes mellitus and diabetes insipidus both cause polyuria, but their hormones and urine composition differ.
   • Iodine deficiency reduces thyroxine synthesis and may increase TSH, causing thyroid enlargement.
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