CHEMICAL COORDINATION AND INTEGRATION

INTRO

The glands are secretory organs and are of two main types, viz. (i) exocrine glands and (ii) endocrine or ductless glands.  Endocrine glands secrete active substances called Hormones.  Hormones are informational molecules.  They are secreted in response to changes in the environment inside or outside the body.  They are secreted into the blood, which distributes it all over the body, especially to their target organs and tissues.

Hormones are the chemical substances produced from an endocrine or a ductless gland.  They may be defined as, “substances which are produced in one part of an organism and transferred to some other part where their physiological effects are observed”.  Chemically they may be polypeptides, steroids and biogenic amines (non-protein compounds containing amino group).

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Internal Environment of animal body is maintained in a steady state by

1. Autonomic Nervous System
2.  Endocrine System

What are glands?

They are secretory organs.

Types of glands:

Exocrine glands – Duct glands - Enzymes

Endocrine glands – Ductless glands – Hormones

What are Hormones?

Chemical regulators / messengers / information molecules 

Chemical nature of Hormones

Organic substances of varying complexity fall into two major classes;

1. Steroid Hormone

2. Amino acid Hormone

Characteristics of Hormone:

•Target organs / tissues

•Specific in their action 

•Trace amount

Functions of Hormones

•Metabolic activities

•Homeostasis

•Morphogenic activities

•Mental activities

•Growth, maturation and regeneration

•Secondary sexual characters and reproductive activities

•Control of other endocrine glands

Endocrine glands in man

•Pituitary glands – In head

•Thyroid glands – In neck

•Parathyroid – embedded on thyroid gland

•Adrenals – upper end of kidney

•Thymus – on either side of trachea

•Gonads – In or below pelvic cavity

•Gastric – In the wall of stomach & intestine

•Pineal gland – dorsal side of brain

•The hypothalamus is a region of the brain that controls an immense number of bodily functions.

•The pituitary gland, also known as the hypophysis, is a roundish organ that lies immediately beneath   

   the hypothalamus

• It composed of two distinctive parts:

  The anterior pituitary (adenohypophysis) & the posterior pituitary (neurohypophysis).

Characteristics of hormones:



·         Hormones have more or less a specific role.  The spectrum of action varies with the hormone.  Some are highly selective, while others are more generalized.

·         Hormones are produced from a tissue or an organ, and then they act on different tissues or organs i.e., they have a target organ to act or their activity is at a remote rate.

·         Hormones can be easily transported via blood.  They are poured into venous blood.

·         They are active in minute concentrations, only a few picograms (10-12 g) or a few microgram (10-6 g).  The number of hormone molecules per unit target tissue is definite.

·         A hormone in its “primary action” affects one or a limited number of reactions and does not influence directly all other metabolic activities of the cell.


Differentiate hormones and enzymes:

Mammalian endocrine system:

The mammalian endocrine system consists of the following organs and tissues : Hypothalamus pituitary, thyroid, four parathyroids, two adrenals, two testes (male) or two ovaries (female), thymus, pineal, islet tissue of pancreas, and hormonal tissues on gastrointestinal tract. The hypothalamus is a nervous system of the brain, which is also integrated with the endocrine system and secretes hormones.



Hypothalamo-pituitary Axis:



Hypothalamus as an endocrine gland:

Hypothalamus is a part of the brain and consists of several masses of grey matter called hypothalamic nuclei.  In fact, it forms the floor of the third cerebral ventricle of the brain.  Neurons of the hypothalamic nuclei control the activity of pituitary gland.  The hypothalamus is connected to the anterior lobe of pituitary by hypophyseal portal vessels.  The hypothalamic nuclei or neurosecretory cells secrete several hormones called neurohormones that reach the anterior pituitary by hypophyseal portal vessels.  These neurohormones control the secretions of the hormones from the anterior pituitary.  These neurohormones are given below:

Pituitary as an endocrine gland :

Pituitary is a small body, about the size of a gram located on the ventral side of the diencephalon region of the brain.  The pituitary hangs below the hypothalamus by a stalk called as infundibulum.  The pituitary has three different parts viz. anterior lobe or adenohypophysis, intermediate lobe and posterior lobe or neurohypophysis.  The adenohypophysis is compact and highly vascular.  It is connected to the hypothalamus by hypophyseal portal vessels.  The neurohypophysis is connected to the hypothalamus by nerve fibres.  The anterior lobe of pituitary releases six hormones (all protein in nature) that control the activities of various other endocrine glands also.  They are given below:

1.      Growth hormone or Somatotrophic hormone (GH or STH).  It is secreted by the Somatotrophic cells of anterior pituitary and regulates general body growth; increases the length of bones; control carbohydrate, protein, and fat metabolism; muscles and viscera growth; may counteract insulin to raise blood glucose levels etc.  Its deficiency causes dwarfism in youngs, and acromicria (rarely) in adults – hypoactivity; while its excessive secretion – hyperactivity causes gigantism in youngs, and acromegaly in adults.

2.      Adrenocortico-trophic hormone (ACTH).  It is secreted by the Corticotrophic cells of anterior pituitary and controls the growth and secretion of adrenal cortex to release glucocorticoids – cortisol, cortisone etc.  However, the secretion of mineralocorticoids by adrenal medulla is stimulated to a much less degree.

3.      Thyroid stimulating hormone (TSH) or Thyrotrophic hormone or Thyrotropin.  It is secreted by the Thyrotrophic cells of anterior pituitary and controls the growth and activity of the thyroid gland.  It acts on thyroid to release its hormone – thyroxine.

4.      Follicle stimulating hormone (FSH).  It is also secreted by Gonadotrophic cells of anterior pituitary and increases the number and size (maturation) of graffian follicles in the ovaries in females; and stimulates spermatogenesis in males. 

5.      Luteinising hormone (LH) or interestitial cell stimulating hormone (ICSH).  It is also secreted by Gonadotrophic cells.  In females: (i) it completes the development of graffian follicles to its secretory stage and brings about ovulation along with FSH; (ii) it causes appearance, growth and maintenance of corpus luteum; (iii)  it stimulates the secretion of progesterone from the ovaries.  In males:  it stimulates the development and functional activity of interestitial cells to produce testosterone.

6.      Prolactin or Lactogenic hormone or Luteotrophic hormone (LTH).  It helps in the growth of mammary glands during pregnancy and initiates the secretion of milk after child birth.

            The posterior lobe of pituitary releases the following two peptide hormones.  Both these hormones are synthesized in the hypothalamus and are carried to the posterior pituitary along with nerve fibres where they are stored.  From posterior pituitary, they are released into the blood.

1.      Vasopressin or Pitressin or Antidiuretic hormone (ADH).  It is released from posterior pituitary in response to stress and dehydration.  It increases the reabsorption of water in the distal convoluted tubules and the collecting tubules of kidney.  So its deficiency in the body increases the urine flow causing diabetes insipidus.  It also raises blood pressure by constricting the peripheral blood vessels.









Deficiency of ADH

Hypothalamic ("central") diabetes insipidus results from a deficiency in secretion of antidiuretic hormone from the posterior pituitary.

Nephrogenic diabetes insipidus occurs when the kidney is unable to respond to antidiuretic hormone

The major sign of either type of diabetes insipidus is excessive urine production.

2.      Oxytocin or Pitocin.  It is an important uterus-contracting hormone at the time of child birth.  It also acts on mammary glands and helps in the expulsion of milk at the time of suckling.  It is, therefore, also known as `milk-ejection hormone’ and `birth hormone’.  It decreases the blood pressure by dilating the peripheral blood vessels (opposite to that of vasopressin).



Feed back inhibition of hormones:



Hypothalamus produces thyrotropin releasing factor (TRF) that acts on anterior pituitary to release thyroid stimulating hormone (TSH).  This TSH then acts on thyroid to release its hormone – thyroxine.  Now if the level of thyroxine in the blood is more, it will inhibit the hypothalamus to produce TRF, hence less of TSH and thyroxine.  And if thyroxine is less, more of TRF is produced.  Hypothalamus may also be inhibited or activated by the levels of TSH.  This is known as feed back inhibition.



Thyroid Gland:



Thyroid hormones are derivatives of the amino acid tyrosine bound covalently to iodine.

The two principal thyroid hormones are: thyroxine (known affectionately as T4 or L-3,5, 3',5'-tetraiodothyronine) triiodotyronine (T3 or L-3,5,3'-triiodothyronine).

Thyroid epithelial cells - the cells responsible for synthesis of thyroid hormones – are arranged in spheres called thyroid follicles. Follicles are filled with colloid, a proteinaceous depot of thyroid hormone precursor.

Thyroid is found on the ventral side in the neck region of the body.  At the base of larynx, it has two lateral lobes one on either side of trachea. Cells lining the thyroid follicles secrete two thyroid hormones, thyroxine and triiodothyronine. Both are iodinated forms of an amino-acid called thyronine and stored in the form of semifluid material (colloid) in the lumen of follicles.  Whenever necessary, the hormones are released from the colloid to the blood.





Functions:

·         Thyroid hormones increase the metabolic rate of the body, enhance heat production and maintain BMR.

·         They also promote growth of body tissues-both physical growth and development of mental faculties are stimulated.

·         They stimulate tissue differentiation; hence promote metamorphosis of tadpoles into adult frogs.







Disorders due to thyroid hormone imbalances:



·         Excessive secretion of thyroid hormone (hyperthyroidism) results in exophthalmic goitre or Grave’s disease.  It is accompanied by the bulging of the eye ball.  It is associated with high metabolic rate, heart beat and blood pressure rises, restlessness, tremors, nervousness, rise in body temperature, etc.

·         Less secretion of thyroid hormone (hypothyroidism) results in Myxedema in adult and cretinism (feeble mindedness) in children.  The patient of myxedema suffers from low metabolic rate, slow heart rate, low body temperature and reproductive failure.  Adminsitration of thyroid hormones cures the symptoms.

·         For the synthesis of thyroid hormone (thyroxine), an important inorganic ion called iodine is needed in the body.  Hence the dietary deficiency of iodine causes goitre in which thyroid gland enlarges in an effort to produce more thyroxine.

·         Failure of thyroid hormone secretion in children slows body growth and mental development and reduces metabolic rate.  The child becomes stunted and mentally retarded.  The body temperature, heart rate and blood pressure are lower than normal.  The patient is pot-bellied and pigeon chested and has a protruding tongue.  This disease is known as cretinism.

Thyroid gland – Disorders

Hypothyroidism:

Reasons:

•Failure of thyroid gland

•Hyposecretion of TRH, TSH or Both

•Inadequate dietary iodine

Symptoms:

•Low metabolic activity

•Poor tolerance of cold

Hypothyroidism

Cretinism (in children):

Poor skeleton growth – dwarfism – mentally retarded – dry skin – thick tongue – lethargy – respiratory problems – constipation – neonatal jaundice.

Myxoedema (in adult):

Edema – facial tissues to swell and look fluffy.





Hyperthyroidism

Grave’s disease (exophthalmic goitre):

•An immune disease in which autoantibodies bind to and activate the thyroid-stimulating hormone receptor, leading to continual stimulation of thyroid hormone synthesis – edema behind eyes (exophthalmos) with – more often in females.



Parathyroids:

They are four pea-sized organs, clinging to the rear surface of thyroid, but are independent of thyroid structurally and functionally.  This gland secretes parathormone (PTH) whose functions are as follows:

a)      It regulates the calcium and phosphate balance between blood and other tissues.

b)      It inhibits synthesis of collagen by osteoblasts and bone resorption by osteoclasts.

c)      It helps in absorption of calcium from the intestine and reabsorption by kidneys.

Disorders:

a)      Hypoparathyroidism:

It leads to deficiency of plasma calcium. Nerve and muscle action potentials rise leading to muscle twitches, spasm, etc., and the condition is called hypocalcemia or parathyroid tetany.

b)      Hyperparathyroidism:

It causes demineralization of bones leading to their easy fracture and deformation.  It may lead to osteitis fibrosa cystica.

Adrenals or Suprarenals:



There are two adrenal glands, one on the top of each kidney.  Adrenal gland has an outer portion called adrenal cortex, and an inner portion called adrenal medulla.  Both these parts differ in the nature of hormone produced and also with respect to their functions. 



Adrenal cortex:



This part of adrenal gland is very important for the animal and its removal or destruction will kill the animal.  It produces mainly three groups of steroid hormones viz., (i) glucocorticoids; (ii) mineralocorticoids; and (iii) sex corticoids.

(i)                 Glucocorticoids regulate the metabolism of carbohydrates, proteins and fats; they also increase the blood glucose level e.g., cortisone, cortisol and corticosterone.  The secretion of glucocorticoid hormones is regulated by ACTH from anterior pituitary.

(ii)               Mineralocorticoids are produced from the outermost cellular layer of the adrenal cortex.  The main hormone in mammals and birds is aldosterone that reduces the sodium loss from the body in urine, sweat, saliva etc. by its active reabsorption from those fluids.  It also increases the excretion of potassium, in an exchange with the absorption of sodium; retain water in the body along with sodium.  Thus it regulates the ionic and water balance of the body.  The secretion of aldosterone is stimulated by three factors : (a) a fall in the sodium ions in the plasma of blood; (b)  a rise in the potassium ions in the plasma of blood ; (c) a fall in the volume of blood itself.

(iii)             Gonadocorticoids: They stimulate the development of secondary sexual characters in males







Adrenal medulla:



            It helps the body to prepare for stress or any emergency conditions.  This part of adrenal, unlike cortex, is not so vital for the survival of the organism and so its removal will not cause death.

            It produces two hormones called as adrenaline or epinephrine and nor-adrenaline or nor-epinephrine.  Both these hormones act on tissues and organs that are supplied by sympathetic fibres and produce similar effects.  Thus adrenal medulla and sympathetic system function as a closed integrated unit and is known as sympathetico-adrenal system. 



Pancreas :



The pancreas comprises both exocrine and endocrine parts.  The endocrine part of pancreas forms the islets of langerhans.  They are small patches of cells present in the pancreas.  They produce the following two hormones:



•The endocrine portion of the pancreas takes the form of many small clusters of cells called islets of Langerhans

•Pancreatic islets house three major cell types, each of which produces a different endocrine product:

•Alpha cells (A cells) secrete the hormone glucagon.

•Beta cells (B cells) produce insulin

•Delta cells (D cells) secrete the hormone somatostatin.

1.      Insulin.  It is protein hormone produced by Beta-cells of islets of langerhans.  It regulates the amount of glucose in the blood by converting excess of glucose into glycogen (glycogenesis) which can be stored in the liver and muscles.  Lack of insulin, therefore, results in excess glucose in blood (hyperglycemia) and it starts appearing in urine.  This disease is known as diabetes mellitus.

Functions of  Insulin:



·         It increases the utilization of glucose in the tissues and facilitates the storage of glucose as glycogen in the liver and muscles.  As a consequence, insulin lowers the blood glucose level in the body.

·         It increases the synthesis of fats in the adipose tissues from fatty acids and also from glucose.

·         It reduces the break down and oxidation of fats.

·         It promotes protein synthesis from amino acids in the body tissues.

·         It also reduces the breakdown of proteins in the body.  Thus, insulin can be regarded as an anabolic hormone.

2.      Glucagon.  It is also protein hormone produced by Alpha-cells of islets of langerhans.  It also regulates the amount of glucose in the blood by converting glycogen back to glucose whenever required.  Thus its effect is opposite to that of insulin.

3.      Somatostatin:  It inhibits the secretion of glucagons and insulin.









Insulin Disorders

Hyperglycaemia:

High blood Glucose level – Breakdown of muscle tissue – loss of weight – tiredness.

Hypoglycaemia:

Low blood Glucose level – Hunger – Sweating – Irritability – Double vision.

Pineal Gland

The pineal gland or epiphysis synthesizes and secretes melatonin, a structurally simple hormone that communicates information about environmental lighting to various parts of the body.  It is attached to the roof of third ventricle in the rear part of brain.  It functions as a biological clock and a neurosensory transducer, converting the neural information. 

Thymus:



It secretes thymosin, thymic factor and thymopoietin.  It stimulates the entire immune system and hence is called as ‘throne of immunity’.  It stimulates the spleen and other organs, which have stopped functioning to function again.  Its secretion decreases with advancing age and entirely ceases by about 50 years.

Endocrine functions of Gonads:



The male gonad is testes and female gonad is ovary.  Gonads produce reproductive cells and secrete hormones, which control reproductive organs.  These hormones are called as sex hormones.  They start to secrete from the age of puberty or sexual maturity.

In female:



a)      Ovarian follicle – Estrogen – Development of female sexual characteristics and regulate the menstrual cycle.

b)      Corpus luteum – Progesterone and Estrogen – help in implantation and maintaining pregnancy, lactation.

      Relaxin – relaxes pubic symphysis to dilate uterine cervix

      Inhibin / Actin – Inhibition / activation of FSH and GnRH production.



Placenta: 



a)      Human Chorionic Gonadotropin – Stimulates progesterone release from the corpus luteum and maintains it.

b)      Human placental lactogen – stimulates mammary growth.

In Male :



a)      Testes – Testosterone – Development of male sexual characteristics and stimulation of spermatogenesis.

b)      Inhibin / actin – activation / inhibition of LH and FSH production.

Gonads – Disorders

In Male: Hyposecretion:

Eunuchoidism : Prostate, seminal vesicles and penis remain small – infertility – no secondary sexual characters.

Gynaecomastia: Development of breast tissues in males – due to increased estrogen during pregnancy & puberty.

In Females : Infertility – poor development of secondary sexual characters.

Pineal Gland

The pineal gland or epiphysis synthesizes and secretes melatonin, a structurally simple hormone that communicates information about environmental lighting to various parts of the body

Hormone from Heart:

The atrial wall of our heart secretes atrial natriuretic factor (ANF), when the blood volume and pressure in the atria increase.

Horomone from Kidney:

The cells of juxtaglomerular apparatus produce a peptide hormone called erythropoietin; it stimulates the formation of erythrocytes (RBC).

Hormones from Gastro-intestinal Tract:

a)      Gastrin: It is secreted by the mucosa of pyloric stomach and duodenum.  It controls the secretion of gastric juice by the gastric glands.

b)      Secretin: It acts on the exocrine region of pancreas and stimulates the secretion of water and bicarbonate ions.

c)       Cholecystokinin (CCK): It is secreted by the intestinal mucosa. It acts on pancreas to secrete pancreatic enzymes.  It also acts on gall bladder to release bile juice into duodenum.

d)      Gastric Inhibitory Peptide (GIP): It is secreted by the mucosa of duodenum.  It inhibits gastric secretion and mobility.

Molecular action of Hormone action

a)  Steroid Hormones:

                The lipid soluble hormones can enter the cell through the bilayer of phospholipids and interact with intra cellular receptors to regulate gene expression.



b)  Peptide Hormones:

                The water soluble hormones interact with a surface receptor.  For example, insulin hormone has a surface receptor, which is a hetero-tetrameric protein, consisting of four subunits.  Of these two alpha subunits protrude from the surface of the cell and bind insulin and two beta subunits span the membrane and protrude into the cytoplasm.  The following are the five steps in the hormone action:

a)      Binding to the receptor

b)      Use of second messengers, the mediators

c)       Amplification of signal

d)      Antagonistic effect

e)      Synergistic effect

सामान्य विज्ञान के अति महत्वपूर्ण प्रश्न जो 100 % आते है ।

1.मधुमक्खियों का प्रजनन एवं प्रबंधन कहलाता है?
उत्तर : एपीकल्चर
2. रक्त के थक्का बनने में सहायक विटामिन है ?
उत्तर : K
3. कैल्शियम एल्युमिनेट तथा कैल्सयम सिलिकेट का मिश्रण कहलाता है उत्तर : सीमेंट
4. खट्टे फलों में होता है
उत्तर : साइट्रिक अम्ल
5. कार्य की इकाई है
उत्तर : जूल
6. क्लोरो-फ्लोरो कार्बन को किस नाम से जाना जाता है ?
उत्तर : फ्रेआॅन
7. एक मात्र अम्ल जो स्वर्ण को घोलता है
उत्तर : एक्वा रेजिया
8. आधुनिक परमाणु सिद्धांत का प्रणेता माना जाता है
उत्तर : जॅान डॅाल्टन को
9. सेब को दाँतों से काटने के लिए किस प्रकार के दाँतों का उपयोग होता है
उत्तर : कृन्तक
10. कौन-से दो रंगों को मिश्रित करने से हरा रंग तैयार होता है
उत्तर : नारंगी और बैंगनी
11. RNA का अभिप्राय है
उत्तर : Ribo Nucleic Acid
12. लोलक का संचलन क्या कहलाता है?
उत्तर : दोलन गति
13. वायुमंडल में उपस्थित कुल गैसों का कितना प्रतिशत नाइट्रोजन होता है ?
उत्तर : 78%
14. किसका प्रयोग चिकित्सक रोगियों की जांच में करते है
उत्तर : स्टेथोस्कोप
15. मलेरिया संबंधित है
उत्तर : ज्वर से
16. रक्त शर्करा स्तर को नियंत्रित करने वाला हार्मोन है
उत्तर : इन्सुलिन
17. कैल्शियम हाइड्रॅाक्साइड का प्रयोग करके मोर्टार के प्लास्टर का निर्माण किया जाता इसे किस नाम से जाना जाता है ?
उत्तर : चूना जल
18. प्रकाश संश्लेषण में सहायक, पत्तियों के हरे पदार्थ को क्या कहते है ?
उत्तर : क्लोरोफिल
19. पीतल हवा में किस गैस की उपस्थिति के कारण बदरंग हो जाता है ?
उत्तर : ऑक्सीजन
20. ‘बार’ किसकी इकाई है
उत्तर : वायुमंडलीय दाब
21. ठोस से सीधे वाष्प अवस्था में पदार्थ के रूपांतरण को कहा जाता है
उत्तर : उदात्तीकरण
22. किसकी परत बनने के कारण चाँदी बदरंग हो जाता है
उत्तर : सल्फाइड परत
23. चेचक होने की वजह है
उत्तर : वायरस
24. प्रतिरोध की SI इकाई है
उत्तर : ओम
25. सबसे व्यस्त मानव अंग है
उत्तर : दिल
26. बेकरी में साधारण तथा उपयोग किये जाने वाला बेकिंग सोडा वास्तव में है
उत्तर : सोडियम बाइकार्बोनेट
27. आनुवंशिकता की इकाई है
उत्तर : जीन
28. आनुवंशिकता के नियम की खोज की
उत्तर : ग्रेगरी मेंडल
29. कोशिका झिल्ली पाई जाती है
उत्तर : पादप एवं पशु कोशिका दोनों में
30. पानी की स्थायी कठोरता दूर की जा सकती है
उत्तर : पोटैशियम परमैग्नेट को डालकर
31. पानी का अधिकतम घनत्व होता है
उत्तर : 4°C पर
32. निकट दृष्टि दोष दूर करने के लिए किसका उपयोग किया जाता है
उत्तर : अवतल लेंस
33. मानव शरीर में सबसे बड़ी धमनी है
उत्तर : महाधमनी
34. सौर प्रणाली में सबसे बड़ा प्राकृतिक उपग्रह है
उत्तर : गैनीमीड
35. शरीर के किस अंग में आयोडीन संचित रहता है
उत्तर : थायरॅायड ग्रंथि
36. समतल दर्पण की नाभिक कितनी होती है
उत्तर : अनन्त
37. ध्वनि की प्रबलता किस पर निर्भर करती है ?
उत्तर : आयाम
38. चाय में कौन-सा उत्तेजक विद्यमान रहता है
उत्तर : कैफीन
39. फाइलेरिया रोग किसके कारण होता है
उत्तर : कृमि
40. मानव मूत्र होता है
उत्तर : अम्लीय
41. विटामिन-A का रासायनिक नाम है
उत्तर : रेटिनॅाल
42. क्रायोजेनिक इंजनों का अनुप्रयोग कहाँ किया जाता है ?
उत्तर : रॅाकेट टेक्नोलॉजी
43. पलको के किनारे कौन-सी ग्रंथियाँ पाई जाती है
उत्तर : मीबोमियन
44. मनुष्य की आहार नाल के किस भाग में कोई एंजाइम नहीं पाया जाता है
उत्तर : ग्रसिका
45. आमाशय की दीवार से कौन-सा एंजाइम निकलता है
उत्तर : गैस्ट्रिन
46. रूधिर किस प्रकार का एक उत्तक है
उत्तर : संयोजी उत्तक
47. साइटोकाइनेसिस में किसका विभाजन होता है ?
उत्तर : कोशिका द्रव्य
48. साँप का जहर है
उत्तर : प्रोटीन
49. किस संघ की जातियों की संख्या सबसे अधिक है
उत्तर : आर्थोपोडा
50. मानव शरीर में सबसे अधिक मात्रा में पाया जाने वाला तत्व है
उत्तर : ऑक्सीजन
51. मनुष्य के रक्त चाप को किस धमनी से मापा जाता है
उत्तर : ब्रैंकियल धमनी
52. हास्य गैस का रासायनिक नाम है
उत्तर : नाइट्रस ऑक्साइड
53. कैल्कुलस के आविष्कारक है
उत्तर : आइजेक न्यूटन
53. शकरकंद किसका रूपांतरण है
उत्तर : जड़
54. एड्स के विषाणु किसे नष्ट कर देते है ?
उत्तर : लिम्फोसाइट
55. उंगली के नाखून में विद्यमान प्रोटीन है
उत्तर : ग्लोबिन
56. पक्षियों को उड़ने की प्रक्रिया कहलाती है
उत्तर : ब्रेलिंग
57. एन्जाइम के प्रोटीन भाग को क्या कहते है
उत्तर : एपोएन्जाइम
58. किस हार्मोन को ‘आपातकालिक हार्मोन’ कहते है
उत्तर : ऐड्रिनलीन
59. बुद्धि का केंद्र स्थित है
उत्तर : प्रमस्तिष्क मे

Gregor Mendel

Gregor Mendel was an Austrian monk who discovered the basic principles of heredity through experiments in his garden. Mendel's observations became the foundation of modern genetics and the study of heredity, and he is widely considered a pioneer in the field of genetics.

Synopsis

Gregor Mendel, known as the "father of modern genetics," was born in Austria in 1822. A monk, Mendel discovered the basic principles of heredity through experiments in his monastery's garden. His experiments showed that the inheritance of certain traits in pea plants follows particular patterns, subsequently becoming the foundation of modern genetics and leading to the study of heredity.

Early Life

Gregor Johann Mendel was born Johann Mendel on July 22, 1822, to Anton and Rosine Mendel, on his family’s farm, in what was then Heinzendorf, Austria. He spent his early youth in that rural setting, until age 11, when a local schoolmaster who was impressed with his aptitude for learning recommended that he be sent to secondary school in Troppau to continue his education. The move was a financial strain on his family, and often a difficult experience for Mendel, but he excelled in his studies, and in 1840, he graduated from the school with honors.

Following his graduation, Mendel enrolled in a two-year program at the Philosophical Institute of the University of Olmütz. There, he again distinguished himself academically, particularly in the subjects of physics and math, and tutored in his spare time to make ends meet. Despite suffering from deep bouts of depression that, more than once, caused him to temporarily abandon his studies, Mendel graduated from the program in 1843.

That same year, against the wishes of his father, who expected him to take over the family farm, Mendel began studying to be a monk: He joined the Augustinian order at the St. Thomas Monastery in Brno, and was given the name Gregor. At that time, the monastery was a cultural center for the region, and Mendel was immediately exposed to the research and teaching of its members, and also gained access to the monastery’s extensive library and experimental facilities.

In 1849, when his work in the community in Brno exhausted him to the point of illness, Mendel was sent to fill a temporary teaching position in Znaim. However, he failed a teaching-certification exam the following year, and in 1851, he was sent to the University of Vienna, at the monastery’s expense, to continue his studies in the sciences. While there, Mendel studied mathematics and physics under Christian Doppler, after whom the Doppler effect of wave frequency is named; he studied botany under Franz Unger, who had begun using a microscope in his studies, and who was a proponent of a pre-Darwinian version of evolutionary theory.

In 1853, upon completing his studies at the University of Vienna, Mendel returned to the monastery in Brno and was given a teaching position at a secondary school, where he would stay for more than a decade. It was during this time that he began the experiments for which he is best known.

Experiments and Theories

Around 1854, Mendel began to research the transmission of hereditary traits in plant hybrids. At the time of Mendel’s studies, it was a generally accepted fact that the hereditary traits of the offspring of any species were merely the diluted blending of whatever traits were present in the “parents.” It was also commonly accepted that, over generations, a hybrid would revert to its original form, the implication of which suggested that a hybrid could not create new forms. However, the results of such studies were often skewed by the relatively short period of time during which the experiments were conducted, whereas Mendel’s research continued over as many as eight years (between 1856 and 1863), and involved tens of thousands of individual plants.

Mendel chose to use peas for his experiments due to their many distinct varieties, and because offspring could be quickly and easily produced. He cross-fertilized pea plants that had clearly opposite characteristics—tall with short, smooth with wrinkled, those containing green seeds with those containing yellow seeds, etc.—and, after analyzing his results, reached two of his most important conclusions: the Law of Segregation, which established that there are dominant and recessive traits passed on randomly from parents to offspring (and provided an alternative to blending inheritance, the dominant theory of the time), and the Law of Independent Assortment, which established that traits were passed on independently of other traits from parent to offspring. He also proposed that this heredity followed basic statistical laws. Though Mendel’s experiments had been conducted with pea plants, he put forth the theory that all living things had such traits.

In 1865, Mendel delivered two lectures on his findings to the Natural Science Society in Brno, who published the results of his studies in their journal the following year, under the title Experiments on Plant Hybrids. Mendel did little to promote his work, however, and the few references to his work from that time period indicated that much of it had been misunderstood. It was generally thought that Mendel had shown only what was already commonly known at the time—that hybrids eventually revert to their original form. The importance of variability and its evolutionary implications were largely overlooked. Furthermore, Mendel's findings were not viewed as being generally applicable, even by Mendel himself, who surmised that they only applied to certain species or types of traits. Of course, his system eventually proved to be of general application and is one of the foundational principles of biology.

Later Life and Legacy

In 1868, Mendel was elected abbot of the school where he had been teaching for the previous 14 years, and both his resulting administrative duties and his gradually failing eyesight kept him from continuing any extensive scientific work. He traveled little during this time, and was further isolated from his contemporaries as the result of his public opposition to an 1874 taxation law that increased the tax on the monasteries to cover Church expenses.

Gregor Mendel died on January 6, 1884, at the age of 61. He was laid to rest in the monastery’s burial plot and his funeral was well attended. His work, however, was still largely unknown.

It was not until decades later, when Mendel’s research informed the work of several noted geneticists, botanists and biologists conducting research on heredity, that its significance was more fully appreciated, and his studies began to be referred to as Mendel’s Laws. Hugo de Vries, Carl Correns and Erich von Tschermak-Seysenegg each independently duplicated Mendel's experiments and results in 1900, finding out after the fact, allegedly, that both the data and the general theory had been published in 1866 by Mendel. Questions arose about the validity of the claims that the trio of botanists were not aware of Mendel's previous results, but they soon did credit Mendel with priority. Even then, however, his work was often marginalized by Darwinians, who claimed that his findings were irrelevant to a theory of evolution. As genetic theory continued to develop, the relevance of Mendel’s work fell in and out of favor, but his research and theories are considered fundamental to any understanding of the field, and he is thus considered the "father of modern genetics."

Gregor Mendel experiments

Gregor Mendel was an Austrian monk who developed the principles of inheritance by performing experiments on pea plants

• First, he crossed different varieties of purebred pea plants, then collected and grew the seeds to determine their characteristics
• Next, he crossed the offspring with each other (self-fertilization) and grew their seeds to similarly determine their characteristics
• These crosses were performed many times to establish reliable data trends (over 5,000 crosses were performed)

As a result of these experiments, Mendel discovered the following things:

1. When he crossed two different purebred varieties together the results were not a blend – only one feature would be expressed
   • E.g. When purebred tall and short pea plants were crossed, all offspring developed into tall growing plants
2. When Mendel self-fertilised the offspring, the resulting progeny expressed the two different traits in a ratio of ~ 3:1
   • E.g. When the tall growing progeny were crossed, tall and short pea plants were produced in a ratio of ~ 3:1 

From these findings, Mendel drew the following conclusions:

• Organisms have discrete factors that determine its features (these ‘factors’ are now recognised as genes)
• Furthermore, organisms possess two versions of each factor (these ‘versions’ are now recognised as alleles)
• Each gamete contains only one version of each factor (sex cells are now recognised to be haploid)
• Parents contribute equally to the inheritance of offspring as a result of the fusion between randomly selected egg and sperm
• For each factor, one version is dominant over another and will be completely expressed if present
  

While there are caveats to Mendel’s conclusions, certain rules can be established:

1. Law of Segregation: When gametes form, alleles are separated so that each gamete carries only one allele for each gene
2. Law of Independent Assortment: The segregation of alleles for one gene occurs independently to that of any other gene*
3. Principle of Dominance: Recessive alleles will be masked by dominant alleles^†

*  The law of independent assortment does not hold true for genes located on the same chromosome (i.e. linked genes)
^†  Not all genes show a complete dominance hierarchy – some genes show co-dominance or incomplete dominance

Mendel’s Garden Pea Plant Experiment

GENETICS

Heredity is the transfer of character from parents to their offsprings. These hereditary characters are present on the chromosomes in the form of genes.  These gene combinations express characters which may be more similar to one of its two parents.

The differences in characters of offspring mainly depend upon unique process of crossing over that occurs during meiosis.  This is one of the main reasons of producing recombinations.

Gregor Johann Mendel was born in 1822 in Heinzendorf, which was a part of Czechoslovakia.  He began his genetic experiments on garden pea in 1856 in the garden at the monastery.

Selection of pea plant:  The main reasons for adopting garden pea (Pisum sativum) for experiments by Mendel were – 

Pea has many distinct contrasting characters.

Life span of pea plant is short.

Flowers show self pollination, reproductive whorls being enclosed by corolla.

It is easy to artificially cross pollinate the pea flowers.  The hybrids thus produced were fertile.

Working method:  Mendel’s success was also due to his meticulous planning and method of work – 

He studied only one character at a time.

He used all available techniques to avoid cross pollination by undesirable pollen grains.

He applied mathematics and statistics to analyse the results obtained by him.

Mendel’s work and results:
The results obtained by Mendel were studied and on their basis he proposed certain laws known as “Laws of heredity”.  These laws are discussed below:

1)  Law of dominance:
This law states that when two contrasting genes for a character come together in an organism, only one is expressed externally and shows visible effect.  It is called dominant and the other gene of the pair which does not express and remains hidden is called recessive.
2)  Law of segregation or Purity of gametes:
This law states that both parental alleles (recessive and dominant) separate and are expressed phenotypically in F2 generation.  When F2 generation was produced by allowing F1 hybrid to self pollinate, to find out segregation or separation it was observed that both dominant and recessive plants appeared in 3:1 ratio. 

3)  Law of Independent assortment:
The law of independent assortment states that when inheritance of two or more genes occur at one time, their distribution in the gametes and in the progeny of subsequent generations is independent of each other.  To prove this, he did a dihybrid cross.  He crossed homozygous dominant smooth and yellow seeded (YYRR) with homozygous recessive wrinkled and green seeded (yyrr) plants. The F1 hybrid was self pollinated and F2 generation was obtained with the phenotypic ratio of 9:3:3:1 and genotypic ratio of 1:2:1:2:4:2:1:2:1.

Test Cross:
A cross between F1 hybrid (Aa) and its homozygous recessive parent (aa) is called Test Cross. This cross is called test cross because it helps to find out whether the given dominant phenotype is homozygous or heterozygous.

Incomplete dominance:
When neither of the alleles of a character is completely dominant over the other and the F1 hybrid is intermediate between the two parents, the phenomenon is called incomplete dominance.

The most common example of incomplete dominance is that of flower colour in 4’O clock plant.  Homozygous red (RR) flowered variety was crossed with white (rr) flowered variety.  F1 offspring had pink flowers (Rr).  This is called incomplete dominance.  Incomplete dominance is also known to occur in snapdragon.  The phenotypic ratio and genotypic ratio in F2 generation in case of incomplete dominance is 1:2:1.

Multiple Allelism / Codominance:
When a gene exists in more than two allelic forms, it shows the phenomenon of multiple allelism.  A well known example is the inheritance of A, B and O blood groups in human being.  The gene for blood group occurs in three allelic forms  IA, IB and i.  A person carries any two of these alleles.  The gene IA produces glycoprotein (sugar) A and the blood group is A.  The gene IB produces glycoprotein B and the blood group is B.  The gene ‘i’ is unable to produce any glycoprotein and so the person homozygous for it , has O group blood. The genes IA and  IB are dominant over ‘i’.   When IA and  IB are present together, both are equally dominant and produce glycoproteins A and B and the blood group is AB.  They are called codominant alleles. 

 Phenotypic (Blood group)                        Genotype
 A                                                               IAIA  /  IA IO
 B                                                               IBIB  /  IB IO
 AB                                                             IAIB
 O                                                               IOIO  (ii)

Chromosome theory of Inheritance:
Chromosome theory of inheritance was proposed by Sutton and Boveri independently in 1902.  The two workers found a close similarity between the transmission of hereditary characters and behaviour of chromosomes while passing from the one generation to the next through agency of gametes. 

Salient features of chromosome theory:

Both chromosomes as well as genes occur in pairs in the somatic or diploid cells.

A gamete contains only one chromosome of a type and only one of the two alleles of a character.

The paired condition of both chromosomes as well as Mendelian factors is restored during fertilization.

Parallelism of behaviour between chromosomes and Mendelian factors:

Both the chromosomes as well as Mendelian factors (whether dominant or recessive) are transmitted from generation to generation in an unaltered form.

A trait is represented by only one Mendelian factor inside a gamete.  A gamete similarly contains a single chromosome out of a pair of homologous chromosomes due to meiosis that occurs before the formation of gametes.

An offspring contains two chromosomes of each type, which are derived from the two parents through their gametes that are involved in fusion and formation of zygote.  It also contains two Mendelian factors for each character.  The factors come from two different parents through their gametes.

Linkage and Recombination:
Linkage is the phenomenon, where two or more linked genes are always inherited together and their recombination frequency in a test cross progeny is less than 50%.

A pair of genes may be identified as linked, if their recombination frequency in a test cross progeny is lower than 50 percent.  All the genes present on one chromosome form a linkage group and an organism possesses as many linkage groups as its haploid number of chromosomes.  If the two genes are fully linked, their recombination frequency will be 0%.

Sex Determination by chromosomes:
Those chromosomes which are involved in the determination of sex of an individual are called sex chromosomes while the other chromosomes are called autosomes.

1) XX – XY type:  In most insects including fruit fly Drosophila and mammals including human beings the females possess two homomorphic sex chromosomes, named XX.  The males contain two heteromorphic sex chromosomes, i.e., XY. Hence the males produce two types of gametes / sperms, either with X-chromosome or with Y-chromosome, so they are called Heterogamety.

2) ZZ – ZW type:  In birds and some reptiles, the males are represented as ZZ (homogamety) and females are ZW (heterogamety).

3)  XX – XO type:  In round worms and some insects, the females have two sex chromosomes, XX, while the males have only one sex chromosomes X. There is no second sex chromosome. Therefore, the males are designated as XO.  The females are homogametic because they produce only one type of eggs.  The males are heterogametic with half the male gametes carrying X-chromosome while the other half being devoid of it.

Sex determination in Humans:
Human beings have 22 pairs of autosomes and one pair of sex chromosomes.  All the ova formed by female are similar in their chromosome type (22+X).  Therefore, females are homogametic.  The male gametes or sperms produced by human males are of two types, (22+X) and (22+Y).  Human males are therefore, heterogametic. The two sexes produced in the progeny is 50:50 ratio.

Mutation:
It is a phenomenon which results in alteration of DNA sequences and consequently results in changes in the genotype and phenotype of an organism. 

Gene / Point mutation:
Due to change in a single base pair of DNA. Ex. Sickle cell anemia (GAGàGUG).

Chromosomal mutation:
Due to change in structure or number of chromosomes. Ex. Down’s syndrome.

Mutagens: 
The chemical and physical factors that induce mutations are known as Mutagens. Ex. UV rays.

Genetic Disorders:
Pedigree analysis:  It is a system to analyse the distribution and movement of characters in the family tree.

Mendelian Disorders: 
These are mainly determined by alteration or mutation in the single gene.  These disorders are transmitted to the offspring on the same line as the principle of inheritance.
Examples : Haemophilia, Cystic fibrosis, Sickle cell anemia, Colour blindness, Phenylketonuria, Thalesemia, etc.

Haemophilia: 
It is a sex linked recessive disease, which shows its transmission from unaffected carrier mother to some of the male progeny.  Haemophilia is a disorder in which a vital factor for clotting of blood is lacking.  So clotting of blood is abnormally delayed and it can be fatal.  Bleeding can be checked by transfusion of the entire volume of blood or the clotting factor in concentrated form.

Sickle cell anemia: 
It is an autosome linked recessive trait.  It is due to a mutant allele on chromosome 11 (autosome), that causes change of glutamine (GAG) to valine (GUG) at the sixth position of  β-chain of haemoglobin.  The disease is controlled by a single pair of allele, HbA HbA (normal) ; HbA HbS (carrier)  and HbS HbS (diseased). The patient has sickle shaped RBCs with defective haemoglobin.  They are destroyed more rapidly than normal RBCs.

Phenylketonuria: 
It is due to a recessive mutant allele on chromosome 12 (autosome).  The affected individual lacks an enzyme (phenylalanine hydroxylase) that converts the amino acid phenylalanine into tyrosine.  As a result, this phenylalanine and its derivatives accumulate in the cerebrospinal fluid leading to mental degeneration (retardation) and are excreted in the urine due to its poor absorption by kidney.

Chromosomal Disorders: Due to absence or excess or abnormal arrangement of one or more chromosomes. 
A change in the number of chromosomes in an organism arises due to non-disjunction of chromosomes, during gamete formation.

Aneuploidy:  This arises due to loss or gain of one or more chromosomes during gamete formation. Example: Down’s syndrome (47) and Turner’s syndrome (45).

Polyploidy:  In this, the number of chromosomes is the multiple of the number of chromosomes in a single set (haploid).  Accordingly, these may be haploid, diploid and polyploid.

Down’s Syndrome:  It was first described by Langdon Down (1866). It is due to trisomy of 21st chromosome, arising from non-disjunction of chromosomes during gamete formation.  As the maternal age increases, the instances of non-disjuction increase.  When such an ovum containing two 21st chromosomes (24) is fertilized by a normal sperm (23), the zygote (47) comes to possess three copies of 21st chromosome.

Symptoms:  Short statured with small round mouth, palm is broad with characteristic palm crease, physical, psychomotor and mental development is retarded.

Klinefelter’s syndrome:  It arises due to non-disjunction of X-chromosomes during ova formation.  When an ovum containing two X-chromosomes is fertilized by a Y-carrying sperm, XXY individual (47) appears.

Symptoms:  A male with underdeveloped breasts (gynaecomastia), sparse body hair, mentally retarded and sterile.

Turner’s Syndrome:  It arises due to non-disjunction of X-chromosomes during ova formation. When an ovum carrying no X-chromosome is fertilized by a sperm carrying X- chromosome, a zygote with XO appears.

Symptoms: A female with rudimentary ovaries, short stature, lack of secondary sexual characters, they are sterile.

IMPORTANT TERMS:

Heredity: - It can be defined as the transmission of characters from one generation to successive generations of living organisms.

Alleles: - The various forms of a gene are called alleles.

Phenotype: - The external / observable characteristics of an organism constitute its phenotype.

Genotype: - The genetic constitution of an organism is its genotype.

Homozygote: - It is an individual organism in which the members of a pair of alleles for a character are similar.

Heterozygote: - It is an individual organism in which the members of a pair of alleles of a character are different.

Dominant character: - The form of the character which is expressed in the F1 hybrid is called dominant character.

Recessive character: - The form of the character which is suppressed in the presence of the dominant character in a hybrid is called recessive character.

Monohybrid cross: - It is a cross between individuals of the same species, in which the inheritance of contrasting pairs of a single trait is considered.

Dihybrid cross: - It is a cross between two individuals of the same species, in which the inheritance of contrasting pairs of two traits is considered.