Chapter 19: Chemical Coordination and Integration Short Questions | biology Class 11 CBSE

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Chapter 19: Chemical Coordination and Integration Short Questions | biology Class 11 CBSE | ByteNotes.in

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Question 1

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Why are endocrine glands called ductless glands, and how do their secretions reach target organs?

Endocrine glands lack ducts, which is why they are called ductless glands.
Their secretions, called hormones, are released directly into the bloodstream.
The blood transports hormones to distantly located target organs where they exert their effects.

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Question 2

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State the modern scientific definition of hormones and explain why it differs from the classical definition.

Modern definition: Hormones are non-nutrient chemicals that act as intercellular messengers and are produced in trace amounts.
The classical definition restricted hormones to chemicals produced by organised endocrine glands and transported via blood to distant target organs.
The modern definition is broader as it includes signalling molecules from non-glandular tissues such as the heart, kidney, and gastrointestinal tract.

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Question 3

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What are releasing hormones and inhibiting hormones? Give one example of each.

Releasing hormones are produced by the hypothalamus and stimulate the secretion of pituitary hormones; example: Gonadotrophin Releasing Hormone (GnRH).
Inhibiting hormones are produced by the hypothalamus and inhibit the secretion of pituitary hormones; example: Somatostatin, which inhibits growth hormone release.
Both types of hypothalamic hormones travel through the portal circulatory system to regulate the anterior pituitary.

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Question 4

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Distinguish between adenohypophysis and neurohypophysis.

Adenohypophysis consists of pars distalis and pars intermedia; it secretes GH, PRL, TSH, ACTH, LH, FSH, and MSH.
Neurohypophysis (pars nervosa) is the posterior pituitary; it stores and releases oxytocin and vasopressin, which are actually synthesised by the hypothalamus.
Adenohypophysis is regulated by hypothalamic hormones via portal circulation, while neurohypophysis is under direct neural regulation of the hypothalamus.

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Question 5

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What is acromegaly? How does it differ from gigantism?

Acromegaly results from excess secretion of growth hormone in adults, especially in middle age, causing severe disfigurement particularly of the face.
Gigantism is caused by over-secretion of GH during childhood/developmental stages, leading to abnormal overall body growth.
Acromegaly is difficult to diagnose early and can lead to serious complications and premature death if unchecked.

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Question 6

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How does vasopressin (ADH) regulate water balance in the body? What happens when ADH secretion is impaired?

Vasopressin (ADH) acts on the kidneys and stimulates resorption of water and electrolytes by the distal tubules, reducing water loss through urine.
When ADH synthesis or release is impaired, the kidney loses its ability to conserve water, leading to excessive water loss and dehydration.
This condition is called Diabetes Insipidus.

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Question 7

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State the role of melatonin secreted by the pineal gland.

Melatonin regulates the 24-hour (diurnal) rhythm of the body, including the sleep-wake cycle and body temperature.
It also influences metabolism, pigmentation, and the menstrual cycle.
Melatonin also plays a role in enhancing the body's defense (immune) capability.

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Question 8

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How does iodine deficiency affect the thyroid gland? Name the resulting conditions.

Iodine is essential for the normal rate of thyroid hormone synthesis; its deficiency leads to hypothyroidism.
Hypothyroidism causes enlargement of the thyroid gland, a condition commonly called goitre.
Hypothyroidism during pregnancy leads to cretinism in the baby, characterised by stunted growth, mental retardation, low IQ, abnormal skin, and deaf-mutism.

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Question 9

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What is Graves' disease? Name the class of thyroid disorder it belongs to.

Graves' disease, also called exophthalmic goitre, is a form of hyperthyroidism where thyroid hormones are secreted at abnormally high levels.
It is characterised by enlargement of the thyroid gland, protrusion of the eyeballs, increased basal metabolic rate, and weight loss.
It belongs to hyperthyroidism, which can result from thyroid cancer or development of nodules in the thyroid gland.

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Question 10

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What is thyrocalcitonin (TCT) and what is its physiological role?

Thyrocalcitonin (TCT) is a protein hormone secreted by the thyroid gland.
It regulates blood calcium levels by lowering them (hypocalcaemic effect).
TCT works in opposition to PTH and together they maintain calcium homeostasis in the body.

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Question 11

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How does parathyroid hormone (PTH) increase blood calcium levels? Mention three mechanisms.

PTH acts on bones and stimulates bone resorption (dissolution/demineralisation), releasing Ca2+ into the blood.
PTH stimulates reabsorption of Ca2+ by the renal tubules, reducing calcium loss through urine.
PTH increases Ca2+ absorption from digested food in the gastrointestinal tract.

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Question 12

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Explain the role of thymosins in immunity.

Thymosins are peptide hormones secreted by the thymus gland that play a major role in the differentiation of T-lymphocytes, providing cell-mediated immunity.
Thymosins also promote production of antibodies to provide humoral immunity.
In old age, the thymus degenerates, reducing thymosin production and thereby weakening immune responses.

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Question 13

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Why are adrenaline and noradrenaline called 'fight or flight' hormones or emergency hormones?

Adrenaline and noradrenaline (catecholamines) are rapidly secreted by the adrenal medulla in response to stress of any kind and during emergency situations.
They increase alertness, heart beat, strength of heart contraction, rate of respiration, and cause pupilary dilation, piloerection, and sweating—all preparing the body for immediate action.
They also stimulate glycogenolysis, lipolysis, and proteolysis to provide energy during the emergency.

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Chapter 19: Chemical Coordination and Integration | Short Questions

Why are endocrine glands called ductless glands, and how do their secretions reach target organs?

State the modern scientific definition of hormones and explain why it differs from the classical definition.

What are releasing hormones and inhibiting hormones? Give one example of each.

Distinguish between adenohypophysis and neurohypophysis.

What is acromegaly? How does it differ from gigantism?

How does vasopressin (ADH) regulate water balance in the body? What happens when ADH secretion is impaired?

State the role of melatonin secreted by the pineal gland.

How does iodine deficiency affect the thyroid gland? Name the resulting conditions.

What is Graves' disease? Name the class of thyroid disorder it belongs to.

What is thyrocalcitonin (TCT) and what is its physiological role?

How does parathyroid hormone (PTH) increase blood calcium levels? Mention three mechanisms.

Explain the role of thymosins in immunity.

Why are adrenaline and noradrenaline called 'fight or flight' hormones or emergency hormones?

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