NCERT Notes Biology Class 11 Chapter 19 Chemical Coordination and Integration: The study of chemical coordination and Integration forms an important part of human physiology. Chemical coordination, integration, and regulations in the human body are carried out by special chemicals called hormones. Regulation, growth, and development of our organs, the endocrine glands, and cells are carried out by hormones.
Here, in Chapter 19 of Biology Class 11 NCERT Chemical Coordination and Integration, we will study the Human endocrine system, Hormones, and their mechanism of action.
Endocrine Glands and Hormones
An endocrine gland secrets hormones directly into the bloodstream, through which it is transported to the target cell or organ throughout the body. Examples of endocrine glands include the pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pancreas, gonads (ovaries and testes), and pineal gland.
Hormones are non-nutrient chemicals that act as intercellular messengers. They are produced in trace amounts either by the glands or specialized cells in the body. They regulate various physiological processes and bodily functions.
Human Endocrine System
The human Endocrine system consists of Endocrine glands and hormones-producing cells and tissues. It is composed of the hypothalamus, pituitary, thyroid, adrenal, pancreas, parathyroid, thymus, and gonads (testis and ovary). And some organs like the gastrointestinal tract, kidney, heart, etc., also produce hormones. Let us discuss the major endocrine glands and their functions in detail in the following section:
The Hypothalamus
Hypothalamus forms the basal part of the diencephalon( forebrain) that regulates various body functions. Nuclei, which are neurosecretory cells, also produce hormones. They regulate the synthesis and secretion of the Pituitary gland. Hypothalamus produces two types of hormones,
- Releasing Hormones (which stimulate secretion of pituitary hormones) Example- Gonadotropin hormone
- Inhibiting Hormones (which inhibit secretions of pituitary hormones). Example – Somatostatin hormone inhibits the release of growth hormone.
Hormones after being produced, pass through the axon and are released through the nerve endings. They regulate the function of the anterior pituitary Gland. The posterior pituitary is directly under the control of the Hypothalamus.
Pituitary Gland
The pituitary gland is located in sella turcica (a bony cavity) and is attached to the hypothalamus through a stalk. It is divided into two parts:
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(1) Adenohypophysis
- Pars distalis (Anterior Pituitary)
- Pars intermedia
- (2) Neurohypophysis (Posterior pituitary).
The hormone produced by them are:
- Pars distalis produces growth hormone (GH), prolactin (PRL), thyroid-stimulating hormone (TSH), adrenocorticotrophic hormone (ACTH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH).
- Pars intermedia produces Melanocyte stimulating hormone(MSH).
- Posterior pituitary produces oxytocin and vasopressin.
Functions of Pituitary Gland Hormones
|
Hormones |
Functions |
| Growth hormone |
Regulates the growth in humans.
|
| Prolactin |
Regulates the growth of the mammary glands and the formation of milk in them. |
| Thyroid-stimulating hormone (TSH) |
Stimulates the synthesis and secretion of thyroid hormones. |
| Adrenocorticotropic hormone(ACTH) |
Stimulates the synthesis and secretion of glucocorticoid from the adrenal cortex. |
| Luteinising hormone(LH) |
|
| Follicle-stimulating hormone (FSH) |
Stimulates growth and development of ovarian follicles in females.Regulates spermatogenesis in males. |
|
Melanocyte stimulating hormone |
Acts on melanocyte cells present in the skin and regulates pigmentation of the skin. |
| Oxytocin |
Regulates uterine contraction at the time of childbirth and milk ejection from the mammary gland. |
| Vasopressin ( Antidiuretic hormone) |
Stimulates resorption of water and electrolyte from the kidney, hence reducing water loss through urine(diuresis). |
Pineal Gland
The Pineal Gland Secrets Melatonin regulates 24 the hour rhythm of our body like the sleep-wake cycle, body temperature, etc. It also regulates metabolism, pigmentation, the menstrual cycle, and the defense capability of the body.
Thyroid Gland
The thyroid gland consists of two lobes that contacted each other through the isthmus. The thyroid gland is composed of follicles and stromal tissues. Follicles synthesize two hormones: Tetraiodothyronine or thyroxine (T4) and Triiodothyronine (T3). Iodine is essential for the normal functioning of the thyroid gland.
The functions of thyroid gland hormones are:
- Regulates the basal metabolic rate.
- Helps in the process of red blood cell formation.
- Regulates the metabolism of carbohydrates, proteins, and fats.
- Maintains the electrolyte balance.
- Thyrocalcitonin (TCT) secreted by it regulates blood calcium levels.
Hypothyroidism
Caused due to deficiency of iodine in the diet. It results in the enlargement of the thyroid gland which is called a Goitre in adults. In children, it is known as Cretinism, characterized by stunted growth, mental retardation, low intelligence quotient, abnormal skin, deaf-mutism, etc.
Hyperthyroidism
Caused due to an increased rate of synthesis and secretion of thyroid hormone. It results in exophthalmic goiter, characterized by enlargement of the thyroid gland, protrusion of the eyeballs, increased basal metabolic rate, and weight loss. It is also called Graves’ disease. It severely affects the body’s physiology.
Parathyroid Gland
The parathyroid gland which is situated at the back side of the thyroid gland, secrets peptide hormone known as parathyroid hormone. Its level in the body is regulated by the circulating level of calcium ions. PTH is a hypercalcemic hormone, that is, it increases the blood Ca2+ levels, by following processes: stimulating the process of bone resorption, stimulating reabsorption of Ca2+ by the renal tubules, and increasing Ca2+ absorption from the digested food. It plays an important role in maintaining calcium balance in the body.
Thymus
It secrets the peptide hormone, Thymosin. It plays an important role in the development of the immune system. It provides Cell-mediated immunity through the differentiation of T – lymphocytes and Humoral immunity, through the production of antibodies.
Adrenal Gland
The adrenal gland is composed of two types of tissues, the centrally located tissue is called the adrenal medulla, and outside this lies the adrenal cortex. The adrenal medulla secretes two hormones( catecholamine) called adrenaline or epinephrine and noradrenaline or norepinephrine. These are also known as emergency hormones or hormones of Fight.
The function of these hormones is as follows:
- Facilitates the breakdown of glycogen, which results in an increased concentration of glucose in the blood.
- Increases the heartbeat, rate of respiration, increase alertness, pupillary dilation, piloerection (raising of hairs), sweating, etc.
Structure of Adrenal Gland
The adrenal cortex can be divided into three layers, called zona reticularis (inner layer), zona fasciculata (middle layer), and zona glomerulosa (outer layer). The adrenal cortex secretes many hormones that are known as corticoids, they are explained as follows:
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Corticoids carrying out carbohydrates metabolism is known as Glucocorticoid. It stimulates gluconeogenesis, lipolysis, and proteolysis, and inhibits cellular uptake and utilization of amino acids. It also helps
in maintaining the cardiovascular system and as well as kidney function. It suppresses the immune response and produces an anti-inflammatory reaction. It also stimulates RBC production. Example Cortisol. - Corticoids that regulate the balance of water and electrolytes in our body are called mineralocorticoids. It acts mainly at the renal tubules and stimulates the reabsorption of Na+ and water and the excretion of K+ and phosphate ions. Thereby, helping in the maintenance of electrolytes balance, body fluid volume, osmotic pressure, and blood pressure. For example, Aldosterone.
- The adrenal cortex also produces a small amount of Androgenic steroids which play a role in the growth of axial hair, pubic hair, and facial hair during puberty.
Pancreas
Pancreas act as both the Exocrine and Endocrine glands. The Exocrine part consists of Islets of Langerhans which contain two types of cells, alpha cells, and beta cells. Alpha Cells secrets Glucagon and beta cells secrets Insulin.
- Glucagon( Hyperglycemia hormone) is a peptide hormone, that plays an important role in maintaining normal blood glucose levels. It stimulates gluconeogenesis and glycogenolysis, by acting on liver cells, thereby increasing blood glucose levels. It reduces cellular glucose uptake and its utilization. Hyperglycemia leads to Diabetes mellitus characterized by loss of glucose in urine and the formation of ketone bodies.
- Insulin(Hypoglycemic hormone) is a peptide hormone. It stimulates glycogenesis by acting on liver and adipose cells. It enhances cellular glucose uptake and its utilization.
Testis
Testis acts both as a sex organ and an endocrine gland. It consists of seminiferous tubules and stromal or interstitial tissue. Leydig cells produce a group of hormones called Androgen. For example, Testosterone.
Androgen stimulates spermatogenesis (formation of sperm), muscular growth, growth of facial and axillary hair, aggressiveness, and low pitch of voice. Facilitates maturation of the male accessory sex organs like epididymis, vas deferens, seminal vesicles, prostate gland, and urethra.
Ovary
The ovary which is the primary female sex organ, produces two groups of steroid hormones called Estrogen and Progesterone.
- Estrogen is synthesized and secreted by ovarian follicles, which produce a wide range of functions like, it facilitates the growth and development of female secondary sex organs, development, and maturation of ovarian follicles, the appearance of female secondary sex characteristics, and mammary gland development.
- Progesterone supports pregnancy, acts on the mammary glands and stimulates the formation of alveoli, and facilitates milk secretion.
Hormones of the Heart, Kidney, and Gastrointestinal tract
- The atrial wall of our heart secrets a peptide hormone, Atrial natriuretic factor (ANF), which decreases blood pressure through the dilation of blood vessels.
- The kidney produces a peptide hormone called Erythropoietin which stimulates erythropoiesis (formation of RBC).
- The gastrointestinal tract secretes four major peptide hormones, namely Gastrin: which stimulates the secretion of hydrochloric acid and pepsinogen.
- Secretin: stimulates the secretion of water and bicarbonate ions.
- Cholecystokinin (CCK): stimulates the secretion of pancreatic enzymes and bile juice.
- Gastric inhibitory peptide (GIP): inhibits Gastric secretion and mobility.
For more information read: Hormones of Heart, Kidney, and Gastrointestinal Tract
Mechanism of Hormone Action
Hormone receptors are the proteins present in the target tissue only. When they are present on the cell membrane of the target tissue, they are called membrane-bound receptors and the receptors present inside the target cell are called intracellular receptors. The mechanism of action of hormones is as follows:
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Hormones interacting with membrane-bound receptors: Binding of the hormone to its receptor leads to the formation of a hormone-receptor complex. After the formation of the complex, biochemical changes in the target tissue occur. On the basis of their chemical nature, hormones can be divided into groups:
- Peptide, polypeptide, protein hormones (e.g., insulin, glucagon, pituitary hormones, hypothalamic hormones, etc.)
- Steroids (e.g., cortisol, testosterone, estradiol and progesterone)
- Iodothyronines (thyroid hormones)
- Amino-acid derivatives (e.g., epinephrine).
- A secondary messenger is generated when hormones interact with the membrane-bound receptor.It can’t enter the target cell. This regulates cellular metabolism. For example, Cyclic AMP.
- Hormones interacting with intercellular receptors: Generally they regulate gene expression, or the hormone-receptor complex may interact with the genome through which chromosome functions. Example: Steroid hormone.
FAQs on Chemical Coordination and Integration
Q1: Define Hormones.
Answer:
Hormones are non-nutrient chemicals that act as intercellular messengers and are produced in trace amounts by the various glands present in the body.
Q2: Which Hormone aids in Cell-mediated Immunity?
Answer:
Thymosin hormone, through differentiation of T lymphocytes.
Q3: What is the Difference between Hypothyroidism and Hyperthyroidism?
Answer:
- Hypothyroidism is caused due to decreased secretion of Thyroxin hormone. It results in Goitre in adults and Cretinism in children.
- Hyperthyroidism is caused due increased secretion of the Thyroxin hormone. It results in exophthalmic goiter.
Q4: Define Erythropoiesis. Name the Hormone that triggers it.
Answer:
The process of formation of RBC is known as erythropoiesis. The juxtaglomerular cells of the kidney trigger erythropoiesis to produce the Erythropoietin hormone.