hormones

Question 1

hormones

Answer 1

Hormones are chemical messengers secreted into blood by endocrine or ductless glands.
The term hormone was introduced by Satrling in 1905 and comes from the Greek word “Hormacin” meaning “excite” or “arouse”.
Hormones are substances synthesized in the body in small quantities but have a profound biochemical effect in the control and regulation of metabolic events and contribute in some cases to intercellular and intracellular communication.
A characteristic of hormones is that they are released, usually by specialized secretory cells in endocrine glands, and are carried by the circulation, to target cells where they have an effect.

Question 2

major hormone secreting glands are

Answer 2

The major hormone secreting glands are:
Pituitary
Thyroid & Parathyroid
Adrenal
Pancreas
Ovaries
Testes

Question 3

functions of hormones

Answer 3

Reproduction,
Growth and development,
Maintenance of internal environment, and
Energy production, utilization and storage.

Question 4

classification of hormones is based upon

Answer 4

Chemical Composition
Location of Receptors
Solubility Properties

Question 5

based on chemical composition

Answer 5

Hormones can be classified chemically into three major groups.
Steroids Hormones: These hormones are fat soluble compounds like adrenal cortical hormone and sex hormones (androgens and estrogens).
Amines: these hormones are small, water-soluble compounds containing amino groups like epinephrine, thyroxine and several derivatives of tyrosine.
Peptides/Protein Hormones: these are either large protein or small or medium size peptides e.g., insulin, glucagon and pituitary hormones.

Question 6

based on mechanism

Answer 6

Hormones that bind to Intracellular Receptors: These include androgens, calcitrol, estrogens, glucocorticoids, mineralocorticoids, progestins, reticnoic acid, and thyroid hormones (T3 and T4).
Hormones that bind to Cell Surface Receptors: These can be further classified on the basis of secondary messengers. It can be cAMP, cGMP, DAG, InsP3 and calcium ion.

Question 7

on basis of solubility

Answer 7

On the basis of solubility, hormones can be classified as:
Lipid-Soluble Hormones: The lipid soluble hormones include steroid and thyroid hormones.
Water-Soluble Hormones: The water soluble hormones include amines, peptide hormones, and the eicosanoid hormones.

Question 8

steroid

Answer 8

These include the sex hormones and the hormones from adrenal cortex.
These are synthesized in mammals by the ovary (or testis), adrenal cortex, corpus luteum and the placenta.

Question 9

sex hormones

Answer 9

Sex Hormones
Three types of sex hormones are recognized :
Estrogens (female or ovarian or follicular hormones)
Androgens (male or testicular hormones)
Progestins (corpus luteal hormones).

Question 10

Ovarian hormones

Answer 10

Mammalian ovary contains ovarian follicles and corpus lutea.
Hormones produced mainly in the follicles are known as estrogens.
Chemically, the estrogens are derivatives of a C18 hydrocarbon, estrane.

Question 11

chemistry of ovarian hormones

Answer 11

The three compounds of this group with hormonal activity are :
β-estradiol
Estriol
Estrone

All these are characterized by the absence of a CH3 group at carbon 10 and by the aromatic nature of ring A, making the OH group phenolic in character.
Of all these, β-estradiol is most potent physiologically, estrone less potent and estriol is least active.
Their relative potencies are 50 : 5 : 1 respectively.
Although ovary is the chief source of estrogens, they are in smaller amounts also produced by the testis and the adrenal cortex.

Question 12

testicular hormone

Answer 12

These hormones are secreted mainly by the testes, the male reproductive organs and are called as androgens.
Chemically, these are derivatives of a C19 hydrocarbon, androstane.
They have no side chain on the 17-carbon of steroid skeleton.

Question 13

hormones secreted from testes

Answer 13

There are many hormones secreted from testes with androgenic activity.
The three important ones are :
Testosterone
Androsterone
Dehydroepiandrosterone

Testosterone is most potent of all these and dehydroepiandrosterone is least active.
The relative potency ratio of these three forms is 20 : 7 : 1.
A few testicular hormones are also produced by the adrenal gland.

Question 14

corpus luteal hormones

Answer 14

The hormones secreted by the ovarian bed, corpus luteum are collectively called as gestagens or progestins.
The principal gestogen is progesterone.
Progesterone is a C21 steroid and is secreted by the corpus luteum during the second half of the menstrual cycle.
Chemically, progesterone is one of the pregnane derivatives.

Question 15

adrenal corticol hormones

Answer 15

Adrenal cortex secretes some 40-50 closely related C21 steroids, collectively called as corticosteroids.
The corticosteroids may be grouped under two categories :
Mineralocorticoids. — concerned primarily with the transport of electrolytes and the distribution of water in tissues, e.g., aldosterone and deoxycorticosterone.
Glucocorticoids. — concerned primarily with the metabolism of carbohydrates, proteins and fats, e.g., cortisone, cortisol and corticosterone.

Question 16

compoun of adrenal gland

Answer 16

The estimated 24-hour production of major compounds of human adrenal gland is :
Cortisol
8-24 mg
Corticosterone
1.5−4 mg
Aldosterone
0.04−0.2 mg

Aldosterone is 30 times more active than deoxycorticosterone.
Deoxycorticosterone, in its turn, is 4 times more potent than cortisone and cortisol in maintenance of life.
Corticosterone is least active in this regard.

Question 17

biosynthesis of androgens and estrogens

Answer 17

The androgens are synthesized from cholesterol by the gonadal tissues, chiefly from testes.
In the testes, cholesterol is converted to pregnenolone, progesterone and 17α-hydroxyprogesterone.
17α-hydroxyprogesterone is then converted to androstenedione, which is then converted to testosterone and androsterone.
Testosterone can be converted to estradiol by the action of aromatase.
Testosterone can also be converted to dihydrotestosterone by 5α-reductase.

Question 18

biosynthesis of progesterone

Answer 18

In the corpus luteum, placenta and adrenal cortex, progesterone is synthesized from pregnenolone by 3β-hydroxysteroid dehydrogenase.
Progesterone is an intermediate common to the biosynthesis of all steroid hormone from cholesterol.

Question 19

biosynthesis of glucorticoids

Answer 19

Biosynthesis of Glucocorticoids
Progesterone is converted to either 17α-hydroxyprogesterone by 17α-hydroxylase or to 11-deoxycorticosterone by 21α-hydroxylase.
17α-Hydroxyprogesterone is then converted to 11-deoxycortisol by 21α-hydroxylase.
11-deoxycortisol is then converted by 11β-hydroxylase to cortisol.
11-deoxycorticosterone is converted to corticosterone by 11β-hydroxylase.

Question 20

synthesis of mineralcorticoids

Answer 20

Synthesis of Mineralocorticoids
Corticosterone is converted to aldosterone by 18-hydroxylase.
This reaction is stimulated by angiotensin II, a hormone produced in angiotensin by angiotensin-converting enzyme.

Question 21

peptide hormones

Answer 21

Peptide hormones are most prevalent and consist of chains of amino acids.
Larger peptides are usually referred to as proteins, while complex protein hormones with carbohydrate side chains are called glycoprotein hormones

Question 22

peptide hormones are classified as

Answer 22

Peptide Hormones are classified as:
Hormones of the pancreas
Hormones of the Hypophysis
Hormones of the Parathyroid
Hormones of the Gastrointestinal Tract
Hormones of the Corpus Luteum

Question 23

hormones of the pancreas

Answer 23

Each pancreas has about 1,00,000 islets of Langerhans, which are clusters of various types of cells.
These islets in mammals contain at least 4 major types of cells:
α cells
β cells
δ cells
F cells
The β cells contain granules which manufacture a hormone insulin, store it and eventually release it directly into the bloodstream at the appropriate times.
The α cells contain granules which produce another hormone, glucagon.
The δ cells secrete a hormone, somatostatin.
The F cells secrete pancreatic polypeptide.
The α and β cells make up 20% and 75% of the total, respectively.

Question 24

insulin

Answer 24

Human insulin is a molecule of 5,734 Da which falls on the borderline between a large polypeptide and a small protein.
It is composed of two separate peptide chains, designated the A chain and the B chain.
These two chains are joined together by two disulfide bridges.
The human insulin A chain consists of 21 amino acid residues and the B chain of 30 amino acid residues.
A third disulfide exists in the A-chain between the cysteine 6 and 11.

Question 25

biosynthesis of insulin

Answer 25

Insulin is synthesized as a pre-prohormone, that is a pre-proinsulin.
The initial portion of 23 amino acids is called the leader sequence and directs the synthesis of pro-insulin. The leader sequence is cleaved off.
The pro-insulin which is synthesized has the conformation necessary for forming the proper disulphide bridges between A- and B-chains.
It undergoes a series of site-specific cleavages forming the mature insulin and an equimolecular amount of connecting peptide (C-peptide) of 31 amino acids.

Question 26

glucagon

Answer 26

Glucagon has a molecular weight of 3,485 Da and is comprised of a single amino acid chain of 29 amino acids that is devoid of disulfide linkages.
Histidine is the N-terminal amino acid and threonine, the C-terminal amino acid.
Glucagon’s N-terminal histidine at position #1 is essential for its biological activity.
The adjacent residues, #2 (serine) and #5 (threonine), are involved in implementing the adenylyl cyclase activity which is key to the initiation of glucagon-mediated biological responses.
Residues #19–#26 (blue color) have an equal potential to stabilize the structure either as β sheets, or as α-helices.
The C-terminal two residues, asparagine (#28) and threonine (#29), increase glucagon’s tight binding to its receptor.
Unlike insulin, it contains no cystine, proline or isoleucine, but possesses methionine and tryptophan in appreciable amounts.

Question 27

somatostatin

Answer 27

Somatostatin
Two forms of somatostatin exists; S14 and S28, which are single chain polypeptides of 14 and 28 amino acids, respectively.
Somatostatin-14 has one disulfide bond.
It is produced by the δ-cells of the endocrine pancreas and dispersed cells in the gastrointestinal tract.

Question 28

pancreatic polypeptide

Answer 28

Pancreatic Polypeptide (PP)
Pancreatic polypeptide (PP) is a 36-amino-acid peptide that is known to stimulate the gastric secretion of HCl and pepsin.
Most of the PP is expressed and then secreted by the F cells of the pancreas.
PP circulates in the plasma as a dimer with a half-life of 6–7 minutes.

Question 29

amylin

Answer 29

The pancreatic β-cell islets produce the peptide hormone amylin.
It has also been formerly known as islet amyloid polypeptide (IAPP).
Amylin is a 37-amino-acid peptide.
Amylin and insulin are co-secreted from the pancreatic beta cells at the time of food intake.

Question 30

hormones of hypophysis

Answer 30

2. Hormones of the Hypophysis or Pituitary Gland
   Hypophysis or pituitary gland consists of 3 lobes:
   An anterior lobe or adenohypophysis
   An intermediate lobe
   A posterior lobe or neurohypophysis
   All the three lobes secrete substances having hormonal activity.
   The secretion of pituitary hormones is controlled by the hormones (or factors) released from hypothalamus, a region of the brain immediately proximal to the pituitary.
   These hormones are called as hypothalamo-releasing hormones or hypothalamic factors.

Question 31

hormones of anterior pitiutary

Answer 31

Hormones of Anterior Pituitary (Adenohypophysis)
Anterior pituitary gland (Adenohypophysis) secrete a number of hormones of vital importance and all of them are protein in nature, and these nourish the secretory activities of other glands.
These hormones are called as tropins or trophic hormones.

Question 32

thyrotropin or thyroid stimulating hormone

Answer 32

A. Thyrotropin or Thyroid-Stimulating Hormone, TSH.
The molecule of TSH is a dimer made up of α and β subunits.
It is a glycoprotein with molecular weight about 30,000.
Each molecule has 8-9 cystine residues and the disulfide groups are present as intrachain linkages rather than interchain linkages.

Question 33

adrenalcorticotropic hormone

Answer 33

B. Corticotropin or Adrenocorticotrophic Hormone, ACTH.
Corticotropin is a straight chain polypeptide with a molecular weight of about 4,500 and consists of 39 amino acid residues.
The most potent segment of activity is from residue 15 to 18 (Lys.Lys.Arg. Arg).
The release of ACTH is controlled by CRH.

Question 34

gonadotropins

Answer 34

. Gonadotropins or Gonadotrophic Hormones, GTH.

Gonadotropins include:
Follicle Stimulating Hormone, FSH
Luteinizing hormone, LH
Prolactin, PRL
The gonadotropins, FSH and LH, are both regulated by the hypothalamic gonadotrophin releasing hormone, GnRH.

Question 35

follcile stimulating hormone

Answer 35

Follicle-stimulating hormone, FSH
It is a glycoprotein that contains galactose, mannose, galactosamine, glucosamine, sialic acid, fucose and uronic acid.
It has a molecular weight of about 30,000 in man.

Question 36

lutenizing hormone

Answer 36

Luteinizing hormone, LH
It is a peptide hormone with molecular weight of about 26,000 (in man).
It lacks tryptophan but has a high content of cystine and proline.
Each molecule contains 10 glucosamine and 3 galactosamine residues.

Question 37

Prolactin PRL, Luteotrophic Hormone, LTH

Answer 37

Prolactin PRL, Luteotrophic Hormone, LTH
This is also a peptide hormone with 198 amino acid residues and a molecular weight of about 23,500.
It has 3 disulfide bonds between cysteine residues at 4-11, 58-173 and 190-198.
It differs from FSH and LH in that it contains no carbohydrate.

Question 38

somatotropin

Answer 38

D. Somatotropin or Somatotrophic hormone, STH or Growth Hormone, GH.
Somatotropin obtained from human hypophysis is a protein with molecular weight 27,000.
It has 191 amino acids and consists of 2 disulfide bridges between adjacent cysteine residues.
The N-terminal and C-terminal residues are both phenylalanine.

Question 39

Hormones of Posterior Pituitary or Neurohypophysis

Answer 39

Two important hormones are secreted from the posterior pituitary in both males and females.
These are:
Oxytocin (OT)
Vasopressin (VP), the antidiuretic hormone,
The two hormones are structurally closely related nonapeptides that are derived from a common ancestral gene.

Question 40

oxytocin

Answer 40

Oxytocin
It is a nonapeptide amide.
A disulfide bond is present to link the two cysteine residues present in the molecule.

Question 41

vasopressin

Answer 41

t is also a cyclic nonapeptide amide and resembles oxytocin except that isoleucine is replaced by phenylalanine and leucine by arginine.

Question 42

hormones of the parathyroid

Answer 42

Parathyroids secrete a hormone called parathyroid hormone (parathormone, PTH) or Collip’s hormone.
It is a linear polypeptide consisting of 84 amino acids (molecular weight=9300) with no cysteine residues and hence no disulfide bridges.
A fragment of the intact hormone consisting of the first 34 amino acids at the N-terminal region of the molecule is sufficient for the peptide to exert its entire spectrum of characteristic biological effects.

Question 43

hormones of the gastrointestinal tract

Answer 43

4. Hormones of the Gastrointestinal Tract
   The gastrointestinal hormones are a family of polypeptides produced by specialized endocrine cells present in the stomach, intestine, and colon which function both as traditional hormonal messengers and as neurotransmitters.
   Of the many regulatory gastrointestinal peptides, following are well understood are considered to be the authentic hormones:
   Gastrin
   Secretin
   Cholecystokinin (CCK)

Question 44

gastrin

Answer 44

Gastrin
It is produced G cells in the pyloric mucosa, which is apparently stimulated by the proteins present in food or possibly by HCl.
The main form of gastrin obtained from G cells is a heptadecapeptide.
At the N-terminal end of the heptadecapeptide, there is a pyroglutamyl residue, and at the c-terminal end, there is a phenylalaninamide residue.
Two forms of heptadecapeptide exist:
One in which the tyrosyl residue at postion 12 is free (Gastrin 1)
The other in which it is sulphated.

Question 45

secretin

Answer 45

Secretin has only 27 amino acids with molecular weight of 3,056.
The entire molecule of 27 amino acids is required for full biological activity.
Secretin is localized to the upper duodenal and jejunal S cells.

Question 46

Cholycystokinin, CCK

Answer 46

It is also secreted by the upper part of the small intestine.
Cholecystokinin is a polypeptide with 33 amino acid residues and a molecular weight of 3,883.
It is, however, noteworthy that the last 5 amino acids towards the C-terminal in the gastrin and cholecystokinin are exactly the same.
It is in this terminal portion of these hormones that the principal activity resides.

Question 47

thyroid hormones

Answer 47

Thyroidal Hormones
The mammalian thyroid gland biosynthesizes, stores, and secretes two molecular species of thyroid hormone:
Thyroxine (T4; 3,5,3′,5′-tetraiodothyronine)
Triiodothyronine (T3; 3,5,3′-triiodothyronine)
Thyroid hormones are poorly soluble in water, and more than 99% of the T3 and T4 circulating in the blood is bound to a carrier proteins.
The principle carrier of thyroid hormones is thyroxin-binding globulin.

Question 48

calcitonin

Answer 48

[Calcitonin (CT) is a small polypeptide hormone secreted by the specialized C cells that are found primarily in the thyroid gland.
It consisting of a straight chain peptide of 32 amino acids, with a seven-membered disulfide ring at the N-terminus and a prolinamide residue at the C-terminus. ]

Question 49

hormones of adrenal medulla

Answer 49

Hormones of Adrenal Medulla
The adrenal medulla produces two hormones:
Epinephrine or Adrenaline
Norepinephrine or Noradrenaline
Chemically, these two hormones are catecholamines (dihydroxyphenylamines) and are closely related to tyrosine and phenylalanine.
Norepinephrine, however, differs from epinephrine structurally in having a hydrogen atom in place of the methyl group.