Hormones and their mechanism Questions in English

(A) The term 'Hormone' is derived from the Greek word 'hormaein',which means 'to set in motion' or 'to excite'. Therefore,it is a Greek word.

(B) Peptide hormones are water-soluble and cannot cross the plasma membrane of the target cell.
They bind to specific receptors present on the surface of the plasma membrane.
This binding triggers the generation of second messengers,such as cyclic $AMP$ $(cAMP)$,$IP_3$,or $Ca^{2+}$,inside the cell.
These second messengers then regulate cellular metabolism and physiological responses.
Therefore,the action of peptide hormones is mediated by cyclic $AMP$.

(C) hormone is a chemical messenger produced by endocrine glands and secreted directly into the bloodstream to exert a specific effect on a distant part of the body.

(B) The term "hormone" is derived from the Greek word "hormaein", which means "to excite" or "to stir up".
It refers to a substance that arouses a specific organ or tissue to activity or sets a physiological process in motion.
Therefore, the correct meaning of the word "hormone" is "to excite".

(A) The rate of hormone synthesis and secretion is primarily regulated by the feedback control mechanism.
$(a)$ $A$ decrease or increase in the circulating level of a hormone has a direct effect on the rate at which it is secreted by the endocrine gland cells.
$(b)$ If hormone levels are low,the gland is stimulated to produce more; if levels are high,the gland is inhibited to reduce production.
$(c)$ This self-regulating system ensures that hormone concentrations in the blood remain within a physiological range,maintaining homeostasis.

(D) Hormones are chemical messengers that carry information to target cells. They are typically secreted in very low amounts and generally have a short half-life to ensure precise regulation. However,hormones are not exclusively proteinaceous in nature. They belong to diverse chemical groups,including peptides,proteins,amines,and steroids. Therefore,being proteinaceous is not a universal property of all hormones.

(B) Protein hormones,as well as peptide and amino acid derivative hormones,are generally water-soluble and cannot pass through the lipid bilayer of the plasma membrane.
Therefore,they bind to specific receptor molecules located on the cell surface (plasma membrane) of target cells.
This binding triggers the generation of second messengers (like $cAMP$ or $Ca^{2+}$) inside the cell to carry out the hormonal response.

(D) The term '$pheromone$' was proposed by $Peter$ $Karlson$ and $Martin$ $Lüscher$ in $1959$.
$Adolf$ $Butenandt$ was the scientist who first isolated and identified the structure of the first pheromone, '$bombykol$', from the silkworm $Bombyx$ $mori$.
Therefore, the term is attributed to $Karlson$ and $Lüscher$, but in the context of many biology textbooks, the credit for the discovery and naming is often associated with the work of $Karlson$ and $Butenandt$ regarding chemical signaling.

(D) Synergism is a phenomenon where two or more hormones interact to produce a combined effect that is greater than the sum of their individual effects.
In this process,multiple hormones work together to regulate a specific physiological process in the body.
Antagonism refers to the opposite effect,where one hormone opposes the action of another.
Feedback mechanism refers to the regulation of hormone secretion based on the levels of the hormone or its effect in the blood.

(C) Hormones exert their physiological effects by binding to specific receptor molecules located either on the cell membrane or within the cytoplasm/nucleus of target cells.
These receptor-hormone complexes initiate a cascade of biochemical reactions that lead to the specific response.
If the receptor molecules are removed from the target organs,the hormone cannot bind to the cells.
Without this binding,the signal transduction pathway is not activated,and therefore,the target organ will not respond to the hormone.

(B) Hormones are non-nutrient chemicals produced in trace amounts that act as intercellular messengers.
They are secreted by endocrine glands directly into the blood,which transports them to target organs located away from the site of their production.
Enzymes are typically secreted into ducts or act locally,while blood and lymph are the transport media themselves,not the substances being secreted to act on distant organs.

(C) The feedback control mechanism is a fundamental process in the endocrine system used to regulate the levels of hormones in the blood.
In this mechanism,the output of a system acts as an input to regulate the process,ensuring that hormone levels remain within a specific physiological range.
Negative feedback is the most common type,where an increase in the concentration of a hormone inhibits its further production,while positive feedback is less common.
Therefore,hormonal secretion is directly controlled by this mechanism to maintain homeostasis.

(B) The term 'second messenger' refers to molecules that relay signals received at receptors on the cell surface to target molecules in the cytosol and/or nucleus. Cyclic $AMP$ $(cAMP)$ and cyclic $GMP$ $(cGMP)$ are classic examples of second messengers that mediate the action of various hormones and neurotransmitters,thereby regulating cell metabolism.

(D) Hormones are chemically diverse molecules. Based on their chemical nature,they can be classified as:
$1$. Peptide,polypeptide,or protein hormones (e.g.,insulin,glucagon,pituitary hormones).
$2$. Steroids (e.g.,cortisol,testosterone,estradiol,progesterone).
$3$. Iodothyronines (thyroid hormones).
$4$. Amino acid derivatives (e.g.,epinephrine).
Therefore,all the given options are correct.

(A) Hormones are classified based on their chemical nature into peptide,protein,amino acid derivatives,and steroid hormones.
$A$. Hormones of the ovary (e.g.,estrogen and progesterone) are steroid hormones,not proteins or peptides.
$B$. Thyroid hormones (e.g.,thyroxine) are amino acid derivatives (iodinated tyrosine).
$C$. Parathyroid hormones (e.g.,$PTH$) are peptide hormones.
$D$. Pancreatic hormones (e.g.,insulin and glucagon) are peptide/protein hormones.
Therefore,the correct answer is the hormones of the ovary.

(D) Steroid hormones are lipid-soluble and can easily cross the plasma membrane of the target cell.
Once inside the cell,they bind to specific intracellular receptor proteins to form a hormone-receptor complex.
This hormone-receptor complex then enters the nucleus and binds to specific regulatory sequences of $DNA$ (hormone response elements).
This binding interaction directly influences the transcription of target genes,thereby regulating gene expression.

(A) Hormones are classified based on their chemical nature into peptide,protein,steroid,and amino acid derivatives.
$1$. $Growth \ hormone$ $(GH)$,$ACTH$ (Adrenocorticotropic hormone),and $FSH$ (Follicle-stimulating hormone) are all peptide or protein-based hormones.
$2$. $Testosterone$ is a steroid hormone derived from cholesterol.
Therefore,$Testosterone$ is not a protein hormone.

(B) Cyclic adenosine monophosphate $(cAMP)$ is a secondary messenger important in many biological processes. It was discovered by Earl $W$. Sutherland Jr. and his colleagues in $1958$ while studying the mechanism of action of hormones like epinephrine. For this discovery,Sutherland was awarded the Nobel Prize in Physiology or Medicine in $1971$.

(A) $E.W. Sutherland$ was awarded the Nobel Prize in Physiology or Medicine in $1971$ for his discoveries concerning the mechanisms of the action of hormones.
He specifically identified $cAMP$ (cyclic adenosine monophosphate) as a 'second messenger' in hormone signaling pathways,explaining how hormones exert their effects on cells.

(B) Chemically,hormones are diverse molecules. They can be classified into three main categories based on their chemical structure:
$1$. Peptide,polypeptide,and protein hormones (e.g.,insulin,glucagon,pituitary hormones).
$2$. Steroid hormones (e.g.,cortisol,testosterone,estrogen,progesterone).
$3$. Iodothyronines (thyroid hormones) and amino acid derivatives (e.g.,epinephrine,norepinephrine,which are biogenic amines).
Therefore,hormones are composed of proteins,steroids,and biogenic amines.

(D) In multicellular animals, the coordination and integration of various physiological activities are essential for survival. This is achieved through two primary systems:
$1$. The $\text{Nervous System}$: Provides rapid, point-to-point communication via electrical impulses and neurotransmitters.
$2$. The $\text{Endocrine System}$: Provides slower, long-lasting communication via chemical messengers known as hormones, which travel through the blood to target organs.
Together, these systems ensure that the body functions as a unified, coordinated unit.

(D) Hormones are chemical messengers that regulate various physiological processes in the body. Based on their chemical nature,hormones can be classified into several groups:
$1$. Peptide,polypeptide,and protein hormones (e.g.,insulin,glucagon,pituitary hormones).
$2$. Steroids (e.g.,cortisol,testosterone,estrogen,progesterone).
$3$. Iodothyronines (thyroid hormones).
$4$. Amino acid derivatives (e.g.,epinephrine).
Since hormones can belong to any of these chemical categories,the correct answer is 'All of the above'.

(C) Steroid hormones are lipid-soluble and can easily cross the plasma membrane of the target cell.
Once inside the cytoplasm,they bind to specific intracellular receptors (usually located in the cytoplasm or nucleus).
This hormone-receptor complex then moves into the nucleus and interacts with the genome $(DNA)$ to regulate gene expression and protein synthesis.
Therefore,they do not require secondary messengers like cAMP or $IP_3$ to exert their effects.

(C) Insulin is a peptide hormone composed of $51$ amino acids arranged in two polypeptide chains,referred to as chain $A$ and chain $B$.
$LH$ (Luteinizing Hormone) and $FSH$ (Follicle Stimulating Hormone) are glycoprotein hormones.
Thyroxine is an amino acid derivative (iodinated derivative of tyrosine).
Therefore,insulin is the correct answer as it is a polypeptide hormone.

(B) Hormones that do not enter the target cell,such as protein hormones,interact with specific receptors on the cell surface to generate secondary messengers.
These secondary messengers then regulate cellular metabolism.
Common examples of secondary messengers include cyclic $AMP$ $(cAMP)$,$IP_3$ (inositol triphosphate),and $Ca^{2+}$ ions.
Therefore,cyclic $AMP$ is a well-known secondary messenger.

(B) Hormones that do not enter the target cell interact with specific receptors on the cell surface to generate secondary messengers.
$cAMP$ (cyclic Adenosine Monophosphate),$IP_3$ (Inositol triphosphate),and $Ca^{2+}$ are common examples of secondary messengers.
These molecules regulate cellular metabolism by triggering biochemical responses within the cell.
Therefore,$cAMP$ acts as a secondary messenger.

(B) Hormones that do not enter the target cell interact with specific receptors on the cell surface to generate second messengers on the inner side of the plasma membrane.
Cyclic $AMP$ $(cAMP)$ is a well-known second messenger that regulates cellular metabolism by activating protein kinases.
Therefore,cyclic $AMP$ is termed as a second messenger.

(C) Hormones are classified based on their chemical nature into peptide/polypeptide/protein hormones,steroid hormones,iodothyronines,and amino-acid derivatives.
$1$. Insulin,Antidiuretic hormone $(ADH)$,and Oxytocin are peptide/polypeptide hormones.
$2$. Prostaglandins are lipid-derived compounds (specifically fatty acid derivatives),not polypeptides.
Therefore,the correct option is $C$.

(C) The term "hormone" was coined by the British physiologist $E.H. Starling$ in $1905$. He defined hormones as chemical messengers produced in one part of the body and transported to another part to regulate physiological processes.

(A) Hormones that do not enter the target cell (e.g.,protein hormones like insulin or epinephrine) interact with specific receptors on the cell membrane.
This interaction triggers the generation of a 'second messenger' inside the cell,which regulates cellular metabolism.
Common examples of second messengers include $cAMP$,$IP_3$ (inositol triphosphate),and $Ca^{2+}$ ions.
Among the given options,$cAMP$ is a well-known second messenger that facilitates the intracellular signaling pathway.

(D) Hormones are classified based on their chemical nature into peptide/protein hormones,steroid hormones,amino acid derivatives,and iodothyronines.
$1$. Relaxin is a peptide hormone.
$2$. $HCG$ (Human Chorionic Gonadotropin) is a glycoprotein hormone.
$3$. Placental lactogen is a protein hormone.
$4$. Estradiol is a steroid hormone derived from cholesterol.
Therefore,Estradiol is not a protein hormone.

(A) Prostaglandins are a group of lipid compounds having diverse hormone-like effects in animals. They are derived enzymatically from fatty acids. One of their primary physiological roles is the regulation of blood pressure. They act as vasodilators or vasoconstrictors depending on the specific type of prostaglandin and the target tissue,thereby influencing systemic blood pressure.

(B) Steroid hormones are lipophilic (lipid-soluble) in nature.
Due to their lipophilic nature,they can easily pass through the lipid bilayer of the cell membrane.
Once inside the cell,they typically bind to intracellular receptors located in the cytoplasm or the nucleus to form a hormone-receptor complex that regulates gene expression.
While they often have receptors in the nucleus,the defining characteristic that allows them to enter the cell is their lipophilic nature.
Therefore,option $B$ is the most accurate description.

(B) Hormones are classified based on their chemical nature and their mechanism of action.
$1$. Hormones that interact with membrane-bound receptors (e.g.,proteins,peptides,and amino acid derivatives like insulin,glucagon,and epinephrine) usually generate secondary messengers.
$2$. Hormones that interact with intracellular receptors (e.g.,steroid hormones like estradiol,progesterone,and thyroid hormones like $T_3$ and $T_4$) are lipid-soluble and can cross the plasma membrane to bind with receptors located inside the cell (cytoplasm or nucleus).
$3$. Therefore,thyroid hormones and estradiol belong to the group that interacts with intracellular receptors.

(B) Steroid hormones are lipid-soluble molecules that are synthesized from cholesterol. Examples include cortisol,testosterone,and estrogen. Unlike peptide hormones (which are proteins) or amine hormones (derived from amino acids),steroid hormones have a characteristic four-ring structure derived from the cholesterol backbone.

(D) Hormones are non-nutrient chemicals that act as intercellular messengers and are produced in trace amounts.
$1$. Hormones are not all proteins; they can be steroids,amino acid derivatives,or peptides.
$2$. They are secreted in very small quantities.
$3$. They regulate various metabolic processes in the body.
$4$. Hormones are $NOT$ catalysts. Catalysts (enzymes) speed up chemical reactions without being consumed,whereas hormones act as signaling molecules that regulate physiological functions by binding to specific receptors. Therefore,the statement that they act as catalysts is incorrect.

(D) Hormones exert their physiological effects by binding to specific receptor molecules located on or within the target cells.
These receptors are essential for the transduction of the hormonal signal into a cellular response.
If the receptor molecule is removed from the target organ,the hormone cannot bind to the cell,and consequently,the signal cannot be transmitted.
Therefore,the target organ will show no response to the hormone.

(A) In hormone action,secondary messengers are molecules that relay signals received at receptors on the cell surface to target molecules in the cytosol and/or nucleus.
Common secondary messengers include $cAMP$,$cGMP$,$IP_3$ (inositol triphosphate),$DAG$ (diacylglycerol),and $Ca^{2+}$ (calcium ions).
Sodium $(Na^+)$ ions do not function as secondary messengers in hormonal signaling pathways; instead,they are primarily involved in maintaining the ionic balance and membrane potential of the cell.
Therefore,the correct answer is Sodium.

(D) Hormones are chemical messengers secreted by endocrine glands. Their key characteristics are as follows:
$1$. Hormones are released into the blood and reach target organs.
$2$. They are metabolized in the liver or other tissues after performing their function,meaning they are destroyed after use.
$3$. Most hormones are non-antigenic,which means they do not stimulate an immune response.
Therefore,both options $A$ and $C$ are correct.

(D) Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.
They are often referred to as chemical messengers because they carry signals from endocrine glands to target organs.
They are also known as primary messengers because they initiate the physiological response by binding to specific receptors on or inside the target cells.
Therefore,both $B$ and $C$ are correct descriptions of hormones.

(A) When adrenaline binds to its receptor on the surface of heart muscle cells,it activates the enzyme adenylate cyclase via a $G$-protein.
This enzyme converts $ATP$ into cyclic $AMP$ $(cAMP)$.
$cAMP$ acts as a second messenger that triggers a cascade of intracellular events,leading to increased calcium ion influx and enhanced muscle contraction.
Therefore,$cAMP$ is the correct second messenger involved in this process.

(D) Protein hormones are water-soluble and cannot cross the lipid bilayer of the plasma membrane. Therefore,they interact with specific receptors located on the cell-surface (membrane-bound receptors) to initiate their physiological response. This interaction generates second messengers like $cAMP$ or $IP_3$ inside the cell,which then regulate cellular metabolism. In contrast,steroid hormones,which are lipid-soluble,have intracellular receptors located in the cytoplasm or nucleus.

(D) Sex hormones (such as estrogen,progesterone,and testosterone) are primarily regulated by the hypothalamic-pituitary-gonadal axis.
$1$. Gonadotropins ($LH$ and $FSH$) secreted by the anterior pituitary are essential for the production and release of sex hormones.
$2$. The placenta acts as an endocrine gland during pregnancy,secreting hormones like $hCG$,$hPL$,estrogen,and progesterone.
$3$. The pituitary gland is the master gland that controls the secretion of sex hormones via gonadotropins.
$4$. Insulin is a peptide hormone involved in glucose metabolism and does not play a direct regulatory role in the synthesis or function of sex hormones.
Therefore,sex hormones function independently of insulin.

(D) Hormones that are lipid-soluble (like steroid hormones and thyroid hormones) typically cross the cell membrane and bind to intracellular receptors.
Estrogen,Progesterone,and Thyroxine are lipid-soluble hormones that act directly on the nucleus or cytoplasm.
Prostaglandins are lipid-derived signaling molecules that often utilize $Ca^{++}$ or $IP_3$ (inositol triphosphate) as second messengers to mediate their physiological effects within the cell.
Therefore,among the given options,Prostaglandins are the ones that utilize $Ca^{++}$ as a second messenger.

(A) Locally acting hormones,often referred to as paracrine or autocrine signaling molecules,include a diverse group of compounds. Among the most well-known groups of locally acting hormones identified in biological systems are the prostaglandins. Prostaglandins are lipid compounds derived from fatty acids that have diverse hormone-like effects in animals,such as regulating inflammation,blood flow,and the formation of blood clots.

(A) Hormones that do not enter the target cell (e.g., protein hormones, amino acid derivatives) bind to specific receptors on the cell surface.
This binding triggers the generation of intracellular molecules known as "second messengers" that regulate cellular metabolism.
Cyclic $AMP$ $(cAMP)$, $IP_3$ (inositol triphosphate), and $Ca^{2+}$ are common examples of second messengers.
$ATP$, $ADP$, and $DNA$ do not function as second messengers in this context.

(A) Cortisone and progesterone are examples of steroid hormones.
Steroid hormones are derived from cholesterol,which is a sterol.
These hormones are lipid-soluble and act by binding to intracellular receptors.
Therefore,they are classified as sterol-type steroids.

(C) Hormones are classified based on their chemical structure.
$1$. Peptide hormones are chains of amino acids (e.g.,insulin).
$2$. Biogenic amines and catecholamines (e.g.,epinephrine) are derived from amino acids like tyrosine.
$3$. Steroid hormones are derived from cholesterol,which is a lipid. Therefore,steroid hormones are lipid derivatives.

(B) Hormones can be classified based on their chemical nature into peptide,steroid,iodothyronines,and amino-acid derivatives.
$1$. Peptide,polypeptide,and protein hormones include insulin,glucagon (secreted by the pancreas),pituitary hormones (like $GH$,$TSH$,$ACTH$,$LH$,$FSH$),and parathyroid hormone $(PTH)$.
$2$. Steroid hormones are secreted by gonads (testosterone,estrogen,progesterone) and the adrenal cortex (cortisol,aldosterone).
$3$. Therefore,the pancreas,pituitary,and parathyroid glands are the primary sources of peptide hormones.