Hormone Receptors: Examples, Notes, Receptors And Mechanism

What Are Hormone Receptors?

Hormone receptors are specific proteins either on the surface or inside the target cells. They bind to specific hormones and bring about a series of cellular events that lead to a physiological response. Each receptor is specific to any particular hormone, providing for targeted and effective action of the hormones.

Examples of Hormone Receptors

Examples of hormone receptors are:

Insulin Receptors

These receptors are located on the surface of cells and bind to insulin to facilitate glucose uptake.

Estrogen Receptors

Found in the nucleus and associated with estrogen for transcriptional regulation of genes related to reproductive functions and secondary sexual characteristics.

Adrenergic Receptors

These are cell surface receptors that associate with adrenaline or epinephrine and execute the fight-or-flight response.

Classification of Hormone Receptors

Hormone receptors are classified according to their location and the type of hormone they associate with. This includes:

Cell Surface Receptors

Location: Integrated into the plasma membrane of target cells.

Function: To interact with water-soluble hormones such as peptide hormones and amino acid-derived hormones.

Mechanism: The binding of a hormone brings about a signal transduction pathway via second messengers, leading to cellular responses.

Intracellular Receptors

Location: Found within the cytoplasm or the nucleus of target cells.

Function: Bind to lipid-soluble hormones such as steroid and thyroid hormones.

Mechanism: The hormones diffuse across the cell membrane and find some intracellular receptors that, in turn, affect gene transcription and protein synthesis.

Mechanism of Hormones Action

Hormones themselves do not exert their effects on target cells but trigger all of their effects via receptor mediated mechanisms:

Cell Surface Receptor Mechanism

1. The hormone binds to the receptor on the cell surface.

2. Binding activates the signal transduction pathway via second messengers.

3. This initiates a cascade of events to produce the cellular response.

Intracellular Receptor Mechanism

1. Lipid soluble hormones diffuse through the plasma membrane.

2. Hormones bind to receptors within the cytosol or nucleus.

3. The hormone receptor complex acts on DNA

4. This initiates gene transcription and synthesis of proteins.

5. The newly synthesized proteins mediate physiological responses.

Control and Regulation of Hormone Receptors

The number and affinity of hormone receptors can be controlled under various conditions.

Receptor Sensitivity

The cells through positive/negative feedback modulate the sensitivity of receptors to these circulating hormones, thereby altering the strength of the response.

Receptor Density

The number of receptors may increase or decrease, thus changing the cell's sensitivity to the hormone.

Desensitization

When a hormone is continuously present, the receptor becomes desensitized to the presence of the hormone, and a decreased cellular response ensues.

Dynamics Of Hormone Receptor Interaction

The dynamics of hormone receptor interactions are mentioned below:

Receptor Binding Affinity

It is the strength with which a hormone binds to its receptor.

Impact: The strength of binding has a huge effect; high-affinity binding results in more effective signalling, while low-affinity binding may lead to weak responses.

Receptor Agonists And Antagonists:

Agonist: Molecule which binds to the receptor to produce an effect similar to that of the hormone.

Antagonist: Molecule that binds to the receptor but may block or dampen the effect of the hormone.

Receptor Internalization and Downregulation

The receptor internalization and downregulation is discussed belwo:

Internalization

The hormone receptor complex is internalized into the cell. This process generally leads to the cessation of signalling. This mechanism controls the duration and amplitude of the hormonal response.

Downregulation

It occurs in response to continuous exposure to a hormone by reducing the quantity of the receptors or by decreasing their sensitivity, thus diminishing cellular responsiveness and preventing overstimulation of the cells.

Mutations Of Hormone Receptors

Genetic mutations may alter hormone binding or signalling of the respective receptors, leading to a panoply of endocrine disorders.

Examples: Insulin receptors have mutations that confer insulin resistance; those in thyroid hormone receptors disturb thyroid function.

Clinical Implications

Clinical implications are discussed below:

Diagnosis

The identification of receptor mutations helps diagnose certain endocrine disorders.

Treatment

Targeted therapies may have to be instituted to address receptor mutations and to reconstitute normal function.

Crosstalk Between Receptor Pathways

The crosstalk between receptor pathways includes:

Pathway Interactions

The interaction of different signalling pathways that may modify the activity of hormone receptors.

Examples: Crosstalk between insulin signalling and growth factor pathways can impact metabolic and growth responses, respectively.

Functional Implications

Synergistic Effects: Augmented or changed physiological responses because of pathway interactions

Antagonistic Effects: The effect of one pathway is inhibited by another.

Hormone Receptors NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Hormone receptors and their location

• Mechanism of hormone action

Practice Questions for NEET

Q1. Which ONE of the following statements is TRUE concerning the human ovary?

1. Estrogen is secreted by Graafian follicles and progesterone by the corpus luteum.

2. Estrogen is secreted by the corpus luteum and progesterone by Graafian follicles.

3. Both estrogen and progesterone are secreted by the corpus luteum.

4. Both estrogen and progesterone are secreted by Graafian follicles.

Correct answer: 1) Estrogen is secreted by Graafian follicles and progesterone by the corpus luteum.

Explanation:

Graafian follicle – a fluid-filled structure in the mammalian ovary within which an ovum develops before ovulation. A corpus luteum refers to the composition of the cells that produce the hormone progesterone. The corpus luteum forms into the ovary after the discharge of an ovum. However, it degenerates after some days as its roles depend on fertilization.

Hence, the correct answer is option 1) Estrogen is secreted by Graafian follicles and progesterone by corpus luteum.

Q2. _____ Regulates sex characters, mammary gland development, development of growing ovarian follicles etc

1. Estrogen

2. Relaxin

3. Prolactin

4. Progesterone

Correct answer: 1) Estrogen

Explanation:

Estrogens produce wide-ranging actions such as stimulation of growth and activities of female secondary sex organs, development of growing ovarian follicles, the appearance of female secondary sex characters (e.g., the high pitch of voice, etc.), and mammary gland development. Estrogens also regulate female sexual behaviour

Hence, the correct answer is option 1) Estrogen.

Q3. Name a peptide hormone which acts mainly on hepatocytes, and adipocytes and enhances cellular glucose uptake and utilization.

1. Insulin

2. Glucagon

3. Secretin

4. Gastrin

Correct answer: 1) Insulin

Explanation:

Insulin - Insulin is a peptide hormone, which plays a major role in the regulation of glucose homeostasis. Insulin acts mainly on hepatocytes and adipocytes (cells of adipose tissue) and enhances cellular glucose uptake and utilization

Hence, the correct answer is option 1) Insulin.

Also Read-

• MCQs on Mechanism of Hormone Action

• Pituitary Gland

• Adrenal Gland

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