CBSE Class 11 Biology Chapter 22 Revision Notes

Chapter 22: Chemical Coordination and Integration

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Multiple Choice Questions

1. Which of the following organs does not produce hormones? ________
2. Hypothalamus is a part of ________.
3. _________ is released by neurohypophysis.
4. The thin flap of connective tissue that connects the two lobes of thyroid is known as ___________.
5. Which of the following is the main glucocorticoid in our body? ________
6. The hormones adrenaline or epinephrine and nor-adrenaline or nor-epinephrine are commonly known as ______________.
7. Hypothalamus directly regulates which of the following endocrine glands? _________________
8. Identify the incorrect statement about the pituitary gland. __________
9. Which of the following hormones regulates the growth of the mammary glands and formation of milk? _________________
10. Which of the following hormones of anterior pituitary are together called gonadotropins? ____________
11. Thymosins promote production of antibodies. ___________
12. Which of the following is NOT an effect of adrenaline / noradrenaline? ______________
13. Identify the incorrect statement on glucocorticoid. ______________
14. Assertion: Failure of secretion of somatotropin from an early age causes dwarfism.Reason: Somatotropin hormone stimulates the body growth and elongation of long bones. _________________________
15. Assertion: Melatonin influences the menstrual cycle, pigmentation and defense capability.Reason: It plays an important role in the regulation of diurnal rhythm of our body. _________________________

Hormones and Glands

• In the human body, there are specific substances that operate as hormones and offer chemical coordination, chemical integration, and chemical control.
• Endocrine glands and hormone-producing tissues/cells can be found throughout the body.
• Hormones are produced in minute amounts by the gastrointestinal tract, kidney, liver, and heart to govern and coordinate the operation of their respective organs.

 

Endocrine glands

• Ductless glands are endocrine glands. They secrete directly into the bloodstream, subsequently delivered to specific target organs to trigger a metabolic shift. 
• Hormones are substances secreted by the endocrine glands. 
• Hormones are non-nutrient molecules generated in tiny amounts that operate as intracellular messengers.

 

Sources: Endocrine glands

Hypothalamus

• The hypothalamus contains nuclei, groupings of neurosecretory cells that create hormones.
• Hypothalamic hormones control the synthesis and production of pituitary hormones. 
• The hormones generated by the hypothalamus go through the portal circulatory system to the anterior pituitary, where they control its activity. 
• The hypothalamus has direct control over the posterior pituitary. 
• Gonadotrophin releasing hormone (GnRH) – a hypothalamic hormone, stimulates the pituitary to synthesize and release gonadotrophins.
• Another hypothalamic hormone, Somatostatin, inhibits release of growth hormone from the pituitary.

Pituitary

• Pituitary gland is located in a bony cavity called sella tursica and is attached to the hypothalamus by a stalk.
• Adenohypophysis section of the pituitary is made up of 2 parts, pars distalis and pars intermedia.
• Pars intermedia secretes only one hormone called melanocyte stimulating hormone (MSH).
• The posterior part of the pituitary is called pars nervosa or neurohypophysis.
• Neurohypophysis stores and releases oxytocin and vasopressin.
• Excess Growth Hormone secretion promotes excessive bodily growth, resulting in gigantism, while inadequate secretion causes stunted growth, resulting in dwarfism. 
• Gonadotrophins released by the pituitary are LH and FSH.
• LH increases androgen hormone production and secretion from the testis in males.
• Prolactin promotes mammary gland development and milk production. 
• Oxytocin aids in uterine contraction and milk ejection from the mammary glands during childbirth.  
• Vasopressin promotes water and electrolyte absorption in the kidney. 
• MSH modulates skin pigmentation by acting on melanocytes.

 

Sources: Pituitary gland

Pineal gland

• Melatonin is a hormone that controls the body’s daily rhythms, such as sleep, wakefulness, and temperature.

 

Thyroid gland

• The isthmus connects two lobes on either side of the trachea. 
• Iodine is required for thyroid hormone synthesis.
• Hypothyroidism is caused by an iodine deficiency (Goitre).
• Hypothyroidism during pregnancy might result in a baby’s development being delayed and mental impairment. 
• Thyroid hormones regulate the basal metabolic rate (BMR).
• They assist in the production of red blood cells.
• They regulate glucose, protein, and fat metabolism.
• Thyrocalcitonin hormone controls calcium levels in the blood.

 

Parathyroid hormones

• Humans have 4 parathyroid glands.
• PTH regulates the calcium ion concentration in the blood.
• It also aids calcium absorption from the renal tubules and the gastrointestinal system.

 

Thymus

• This gland is present on the dorsal side of the heart and aorta.
• Thymosin, a peptide hormone released by this gland, aids in developing T-lymphocytes for cell-mediated immunity.
• It also encourages the generation of antibodies that aids in humoral immunity.

 

Adrenal gland

• The central adrenal medulla and the outer adrenal cortex are types of tissue that make up the adrenal gland, and it is positioned on the front region of each kidney.  
• Adrenaline and noradrenaline hormones, sometimes known as catecholamines, are secreted by the adrenal medulla.
• Emergency hormones are another name for these hormones.
• Alertness, pupil dilation, sweating, heart rate, rate of respiration, and glycogenolysis are all increased by these hormones. 
• The adrenal cortex is divided into 1 layers, zona reticularis (inner layer), zona fasciculata (middle layer) and zona glomerulosa (outer layer).
• The adrenal cortex produces glucocorticoids and mineralocorticoids.
• Gluconeogenesis is aided by glucocorticoids. Cortisol is the main glucocorticoid.
• Mineralocorticoids are hormones that control the body’s water and electrolyte levels. Aldosterone is the main mineralocorticoid.

Pancreas

• It has endocrine and exocrine functions.
• The “Islets of Langerhans”, which contain α-cells and β-cells, make up the endocrine pancreas.
• The hormone glucagon is secreted by α-cells, whereas insulin is secreted by β-cells. Both hormones have a role in keeping blood sugar levels in check. 
• Glucagon is a peptide hormone that increases blood sugar by stimulating glycogenolysis (hyperglycemia). 
• Insulin is a peptide hormone that regulates glucose homeostasis in the body.
• It causes glucose to flow quickly from the bloodstream to hepatocytes and adipocytes, resulting in lower blood glucose levels (hypoglycemia).

 

Testes

• Androgens, primarily testosterone, are produced by Leydig cells or interstitial cells, which govern the maturation of primary sex organs and spermatogenesis. 
• Androgen hormones produce anabolic effects on protein and carbohydrate metabolism.

Ovaries

• Estrogen and progesterone are two types of steroid hormones produced by the female reproductive system.  
• Growing ovarian follicles produce and release estrogen.  
• The ruptured ovum, called the corpus luteum, secretes progesterone after ovulation.  
• Estrogen has a wide range of effects, including the development of female secondary sex organs, the formation of ovarian follicles, and the regulation of female sexual behavior. 
• Progesterone is a hormone that controls pregnancy.

 

Hormones released by heart, kidney, and gastrointestinal tract

1. The peptide hormone atrial natriuretic factor (ANF) is secreted by the atrial wall of the heart and lowers blood pressure. 
2. The kidney’s juxtaglomerular cells generate the hormone erythropoietin, which stimulates erythropoiesis.

 

Four main peptide hormones are secreted by the gastrointestinal tract

1. Gastrin promotes hydrochloric acid and pepsinogen secretion. 
2. Secretin increases the production of water and bicarbonate ions by the exocrine pancreas. 
3. Cholecystokinin (CCK) promotes pancreatic enzymes and bile juice secretion. 
4. GIP (gastric inhibitory peptide) is a peptide that reduces stomach secretion and motility.

 

Based on their chemical nature, hormones can be divided into 4 groups

(i) peptide, polypeptide, protein hormones (e.g., insulin, glucagon, pituitary hormones, hypothalamic hormones, etc.)

(ii) steroids (e.g., cortisol, testosterone, estradiol and progesterone)

(iii) iodothyronines (thyroid hormones)

(iv) amino-acid derivatives (e.g., epinephrine)

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