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ICSE Class X Notes 2026 : Biology (Lokhandwala Foundation School (LFS), Kandivali East, Mumbai)

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Bharati Gulajkar
Lokhandwala Foundation School (LFS), Kandivali East, Mumbai
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THE ENDOCRINE SYSTEM Q1. Define the following terms a) Endocrine glands- are the ductless glands which secrete chemicals called hormones which are poured directly into the blood. b) Hormones are the secretions of the endocrine glands, which are transported by the blood to the target cells. c) Homeostasis is a state of equilibrium produced by a balance of functions and of chemical composition within the body of an organism. Q2. Why hormones are often referred to as chemical messengers? Hormones are produced in the body in response to changes in the environment within or outside the body and thus help maintain homeostasis in the body of the individual. Q3. List out the characteristics and functions of hormones Hormones are secretions of the endocrine glands which are poured directly into the blood. They are produced in very small amounts. Chemically, hormones may be proteins, polypeptides, amino acid derivatives or steroids. Their action occurs in another part of the body far away from the source of production. They are specific in their action certain organs respond only to certain hormones. Hormones help adjust and restore homeostatic balance. They help the body cope with infections, stress, trauma, starvation and extreme temperatures. Q4. Differentiate between exocrine and endocrine glands. Hormones Secretions of endocrine glands Enzymes Secretions of exocrine glands. Chemically maybe steroids, proteins or Chemically always proteins amino acid derivatives Transported by ducts. Transported by blood Reaction occurs close to the site of Reaction occurs away from the site of secretion secretion in target cells or organs. Always accelerate chemical reactions They may accelerate or inhibit specific Their action is always quick. activity. Their action may be slow or quick 1 Q6. Differentiate between nervous control and endocrine control Nervous control Works by the conduction of nerve Endocrine control Works by release of hormones. impulses. Works slowly. Works rapidly. Hormones travel via the blood. Nerve impulse is conducted thorough It has a prolonged effect. nerve fibres. It brings about specific chemical Effects of nerve impulses are short-lived changes and regulates metabolism. Does not influence chemical changes and Affects growth cannot regulate metabolism. Does not affect growth. 2 Adrenal glands Shape: is divided into outer adrenal cortex and an inner adrenal medulla. Location- fits like a cap above each kidney or is found superior to each kidney. FUNCTION Adrenal cortex secretes 4 hormones 1. Mineralocorticoids 2. Glucocorticoids 3. Cortisone 4. Sex steroids Mineralocorticoids Regulates metabolism of K+ and Na+ ions. Stimulates kidneys to retain Na+ and excrete K + ions Glucocorticoids Regulates carbohydrate and protein metabolism Cortisone Suppresses the inflammation Sex steroids Proper functioning of sex organs & development of sex character. Androgens and oestrogens. Adrenal medulla Secretes a hormone called Adrenalin or Epinephrine ROLE OF ADRENALIN 1. Stimulates the breakdown of glycogen in muscles and hence increases glucose level in the blood. 2. Increases the contractility of muscles. 3. Helps body to adapt to various situations such as stress, trauma, fasting, starvation, etc. 4. Is often called the emergency hormone or the flight and fight hormone . HYPOSECRETION ADDISON S DISEASE Skin pigmentation Hypoglycaemia Low energy levels Nausea 3 HYPERSECRETION HYPERSECRETION CUSHING S SYNDROME Moon face Buffalo hump Spindly legs Hyperglycaemia ADRENAL VIRILISM In mature women, Develops certain male characteristics such as Beard, moustaches and deep male voice of adrenalin puts an individual through a prolonged version of fight or flight response which in the long run wears out the body In mature men Develops certain Female characteristics such as Enlargement of breasts. In general, the cortical hormone Increase blood glucose concentration Influence fat and protein metabolism Regulate salt and water balance in body Adapt the body to stress such as extreme heat or cold, burns, infection. Question 7: What is Adrenal virilism ? Androgens are male sex hormones produced in the testes and in the adrenal cortex. It regulates secondary sexual characteristics in the male. Appearance of some male characters in the female is called virilism. Excess secretion of adrenal androgen in female produces male secondary sexual characteristics such as appearance of beard, low pitched voice and under developed breasts PITUITARY GLAND LOCATION attached to the hypothalamus or below the hypothalamus. STRUCTURE Pea sized gland. Divided into a larger anterior lobe and a smaller posterior lobe. In between is an intermediate lobe which is more developed in animals It is called master gland as its control all other endocrine glands. 4 ANTERIOR LOBE POSTERIOR LOBE 1. Growth Hormone or Somatotropin 1. Oxytocin (GH)- stimulates the contraction of regulates normal body growth the uterine muscles at child birth Hypo secretion in the growing years Helps in production of results in dwarfism. Prolactin, which stimulates the Hypersecretion in growing years milk secretion in mammary causes gigantism. gland In an adult, it results in Acromegaly disproportionate growth of bones in the face, hand and feet. The person develops a large nose and thick nose 2. Tropic hormones 2. Vasopressin or ADH-Anti stimulate other endocrine glands to Diuretic Hormone- secrete their hormones regulates the reabsorption of They are following types: water in kidney tubules Contraction in blood vessels TSH- thyroid stimulating causing rise in blood pressure hormone- stimulates thyroid gland to Hypo secretion of Vasopressin produce thyroxin Causes Diabetes insipidus or ACTH-Adreno corticotropic excessive urine formation which hormone stimulates the adrenal leads to dehydration and extreme cortex to produce its hormone thirst. FSH -follicle stimulating hormone stimulates testes to produce sperms and ovaries to produce ova LH- Luteinizing hormone stimulates the testes to produce testosterone and the ovaries to produce progesterone and oestrogen Prolactin stimulates the breasts to produce milk at child birth 5 PANCREATIC GLAND EXOCRINE GLAND these cells produce pancreatic juice which is transported by the pancreatic duct to the duodenum (target organ) ENDOCRINE GLAND- these cells called the Islets of Langerhans produce hormones which are transported by the blood to the target cells LOCATION below the stomach, at the loop of the duodenum STRUCTURE Flattened leaf like. Three types of cells are differentiated in the Islets of Langerhans. They are the alpha, beta and the delta cells FUNCTION ALPHA CELLS: Secrete Glucagon. It converts the glycogen stored in the liver into glucose. It thus increases the glucose level in the blood. Secretion of glucagon is stimulated whenever there is a low level of glucose in the blood and while exercising. BETA CELLS: Secrete Insulin. It converts the glucose in the blood into glycogen to be stored in the liver and muscles. It thus checks the level of glucose in the blood. Raises sugar level in the blood. HYPOSECRETION- of insulin Causes diabetes mellitus. 6 In this disease the liver and muscle cells are unable to convert the glucose to glycogen, hence level of glucose in blood rises. This condition is also called Hyperglycaemia. Symptoms- increased thirst, frequent urination, with presence of glucose in the urine (sweet or honey like) HYPERSECRETION- of insulin Causes hypoglycaemia or decreased levels of glucose in the blood. If the glucose level falls too low, a person may enter into a coma state or may become unconscious this condition is called insulin shock. An excess intake can also cause this. Symptoms weakness, tremor Question - Insulin is administered to individuals suffering from diabetes mellitus in the form of injection and not in the form of tablets. Answer- Insulin is proteinaceous in nature and hence undergoes digestion, if taken orally as a tablet. When injected, it is directly transported by the blood to the target cells. Insulin enables cells to absorb glucose and use it or convert it in to glycogen. THYROID GLAND LOCATION situated on the lateral and ventral sides of the trachea, just below the larynx STRUCTURE- Butterfly shaped bi-lobed structure. The two lobes are joined by a narrow piece of tissue called isthmus. FUNCTION It secretes two hormone thyroxin and calcitonin. Iodine is an important constituent of thyroxin. Main functions of thyroxin are This regulates the basal metabolism, (BMR) which is the rate of cellular oxidation resulting in heat production and energy formation when the body is at rest. 7 It regulates general physical and mental growth and development esp. in children. It controls body weight. HYPERSECRETION EXOPHTHALMIC GOITRE- symptoms Protrusion of the eyeballs due to fluid retention behind the eyes. Metabolic rate becomes high, High body temp. Sweating, high blood pressure. Rapid heartbeat. HYPOSECRETION 1. CRETINISMCaused due to under secretion of thyroxin in the growth years. Symptoms This is characterized by low metabolic rate, retarded physical, mental and sexual development. Dwarfism. 2. MYXOEDEMACaused due to the under secretion of thyroxin in an adult. Symptoms Include puffiness and swelling of facial muscles and hands due to fluid retention. Low metabolic rate, low body temp. General lethargy. 3. SIMPLE GOITRE Caused due to iodine deficiency in one s diet Symptoms It leads to an enlargement of the thyroid gland to step up production of thyroxin. swelling in the neck Common in people in hilly area as soil is iodine deficient. In ageing thyroid, body activities slow down and heat production reduced. So, old tend to feel cold faster 8

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