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Chemical Coordination and Integration - Role of hormones as messengers and regulators

Grade 11CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Hormones are defined as non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.

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Endocrine glands are ductless glands that secrete hormones directly into the blood stream to reach a specific target organ.

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Hormones are classified chemically into: Peptide/Protein hormones (e.g., Insulin, Glucagon), Steroids (e.g., Cortisol, Testosterone), Iodothyronines (Thyroid hormones like T3T_3 and T4T_4), and Amino-acid derivatives (e.g., Epinephrine).

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Hormones produce their effects by binding to specific proteins called hormone receptors located in the target tissues.

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Water-soluble hormones (e.g., Peptides) bind to membrane-bound receptors and do not enter the target cell but generate second messengers such as cyclic AMPAMP (cAMPcAMP), IP3IP_3, or Ca2+Ca^{2+}.

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Lipid-soluble hormones (e.g., Steroids, Iodothyronines) cross the cell membrane and bind to intracellular receptors (mostly nuclear receptors) to regulate gene expression or chromosome function by the interaction of hormone-receptor complex with the genome.

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The endocrine system maintains homeostasis through feedback mechanisms, most commonly negative feedback, where the product of a process inhibits its own further production.

📐Formulae

Hormone+Receptor→[Hormone-Receptor Complex]→Biochemical Responses\text{Hormone} + \text{Receptor} \rightarrow [\text{Hormone-Receptor Complex}] \rightarrow \text{Biochemical Responses}

ATP→Adenylate CyclasecAMP+PPi\text{ATP} \xrightarrow{\text{Adenylate Cyclase}} cAMP + PP_i

Glycogen→GlucagonGlucose (Hyperglycemia)\text{Glycogen} \xrightarrow{\text{Glucagon}} \text{Glucose (Hyperglycemia)}

Glucose→InsulinGlycogen (Hypoglycemia)\text{Glucose} \xrightarrow{\text{Insulin}} \text{Glycogen (Hypoglycemia)}

💡Examples

Problem 1:

Explain the mechanism of action of a peptide hormone like Follicle Stimulating Hormone (FSHFSH) on an ovarian cell.

Solution:

FSHFSH binds to a specific membrane-bound receptor on the ovarian cell surface. This interaction leads to the generation of a second messenger like cAMPcAMP.

Explanation:

Because FSHFSH is a peptide hormone, it is water-soluble and cannot cross the lipid bilayer of the plasma membrane. It triggers a cascade of biochemical responses via cAMPcAMP or Ca2+Ca^{2+}, which eventually leads to physiological responses like ovarian growth.

Problem 2:

How do steroid hormones like Estrogen differ from peptide hormones in their mode of action?

Solution:

Estrogen enters the cell and binds to an intracellular receptor, forming a complex that interacts with the DNADNA.

Explanation:

Steroid hormones are lipid-soluble. They diffuse through the cell membrane and bind to receptors in the cytoplasm or nucleus. The hormone-receptor complex acts as a transcription factor, binding to specific DNADNA sequences to regulate the synthesis of mRNAmRNA and proteins, leading to tissue growth and differentiation.

Problem 3:

Identify the antagonistic pair of hormones involved in calcium homeostasis and their roles.

Solution:

Parathyroid Hormone (PTHPTH) and Thyrocalcitonin (TCTTCT).

Explanation:

PTHPTH increases blood Ca2+Ca^{2+} levels (hypercalcemic) by acting on bones and reabsorption in kidneys, while TCTTCT decreases blood Ca2+Ca^{2+} levels (hypocalcemic) by inhibiting bone resorption.

Role of hormones as messengers and regulators Revision - Class 11 Biology CBSE