Chemical Coordination and Integration: Biology NCERT Textbook PDF

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Chemical Coordination and Integration NCERT Textbook With Solutions PDF Free Download

Chemical Coordination and Integration

Chapter 22: Excretory Products and their Elimination

You have already learned that the neural system provides point-to-point rapid coordination among organs. The neural coordination is fast but short-lived.

As the nerve fibers do not innervate all cells of the body and the cellular functions need to be continuously regulated; a special kind of coordination and integration has to be provided.

This function is carried out by hormones. The neural system and the endocrine system jointly coordinate and regulate the physiological functions in the body.

22.1 ENDOCRINE GLANDS AND HORMONES

Endocrine glands lack ducts and are hence, called ductless glands. Their secretions are called hormones.

The classical definition of the hormone is a chemical produced by endocrine glands and released into the blood and transported to a distantly located target organ has a current scientific definition as follows: Hormones are non-nutrient chemicals that act as intercellular messengers and are produced in trace amounts.

The new definition covers a number of new molecules in addition to the hormones secreted by the organized endocrine glands.

Invertebrates possess very simple endocrine systems with few hormones whereas a large number of chemicals act as hormones and provide coordination in the vertebrates. The human endocrine system is described here.

22.2 HUMAN ENDOCRINE SYSTEM

The endocrine glands and hormone-producing diffused tissues/cells located in different parts of our body constitute the endocrine system.

The pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus, and gonads (testis in males and ovary in females) are the organized endocrine bodies in our body (Figure 22.1).

In addition to these, some other organs, e.g., the gastrointestinal tract, liver, kidney, and heart also produce hormones.

A brief account of the structure and functions of all major endocrine glands and hypothalamus of the human body is given in the following sections.

22.2.1 The Hypothalamus

As you know, the hypothalamus is the basal part of the diencephalon, and forebrain (Figure 22.1) and it regulates a wide spectrum of body functions.

It contains several groups of neurosecretory cells called nuclei that produce hormones.

These hormones regulate the synthesis and secretion of pituitary hormones. However, the hormones produced by the hypothalamus are of two types, the releasing hormones (which stimulate secretion of pituitary hormones) and the inhibiting hormones (which inhibit secretions of pituitary hormones).

For example, a hypothalamic hormone called Gonadotrophin-releasing hormone (GnRH) stimulates the pituitary synthesis and release of gonadotropins.

On the other hand, somatostatin from the hypothalamus inhibits the release of growth hormones from the pituitary.

These hormones originating in the hypothalamic neurons, pass through axons and are released from their nerve endings.

These hormones reach the pituitary gland through a portal circulatory system and regulate the functions of the anterior pituitary. The posterior pituitary is under the direct neural regulation of the hypothalamus (Figure 22.2).

AuthorNCERT
Language English
No. of Pages16
PDF Size1808 KB
CategoryBiology
Source/Creditsncert.nic.in

NCERT Solutions Class 11 Biology Chapter 22 Chemical Coordination and Integration

1. Define the following:

(a) Exocrine gland

(b) Endocrine gland

(c) Hormone

Solution:

1. Exocrine gland – These glands liberate their secretions into ducts conveying either on the surface of the body or to particular organs of the body

2. Endocrine gland – These ductless glands liberate their secretions into the bloodstream, conveying it to target organs located at a distance

3. Hormone – It is a non-nutrient chemical that serves as an intercellular messenger and is secreted in trace amounts

3. List the hormones secreted by the following:

(a) Hypothalamus

(b) Pituitary

(c) Thyroid

(d) Parathyroid

(e) Adrenal

(f) Pancreas

(g) Testis

(h) Ovary

(i) Thymus

(j) Atrium

(k) Kidney

(l) G-I Tract

Solution:

The hormones secreted by the following structures are as follows:

Name of the structureHormone secreted
HypothalamusReleasing hormoneInhibiting hormone
Adrenocorticotropin-releasing hormone (ARH)Thyrotropin-releasing hormone (TRH)Luteinising hormone-releasing hormone (LH-RH)Follicle-stimulating hormone-releasing hormone (FSH – RH)Prolactin-releasing hormone (PRH)Growth hormone-releasing hormoneMelanocyte stimulating hormone-releasing hormoneGrowth inhibiting hormone prolactin inhibiting hormoneMelanocyte stimulating hormone – inhibiting hormone
PituitaryNeurohyophysis –OxytocinAnti-diuretic hormone (Vasopressin)Adenohypophysis –Follicle-stimulating hormone (FSH)Growth hormone (GH)Leutinising hormone (LH)Thyroid-stimulating hormone (TSH)Adrenocorticotropin hormone (ACTH)Intermediate lobe –Melanocyte-stimulating hormone (MSH)
ThyroidCalcitoninTri-iodothyronine(T3)Tetraiodothyronine/Thyroxine(T4)
ParathyroidParathormone (PTH)
AdrenalAdrenal cortex – Mineralocorticoids, GlucocorticoidsAdrenal medulla – Adrenaline, Noradrenaline
PancreasGlucagon, Insulin, Somatostatin
TestisTestosterone, Androsterone
OvaryRelaxin, Oestrogen, Progesterone,
ThymusThymosin
AtriumAtrial natriuretic factor (ANF)
KidneyErythropoietin
G-I TractStomach – GastrinIntestine – Secretin, Enterogastrone, Cholecystokinin, Enterocrinin, DuocrininLiver – Angiotensinogen

NCERT Class 11 Biology Textbook Chapter 22 Chemical Coordination and Integration With Answer PDF Free Download

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