Question

Find the total no. of hormones from the following which binds to intracellular receptors. Cortisol, Testosterone, \(T 3\), Glucagon, Oxytocin, FSH, Progesterone, ICSH, Oestrogen, \(G H\) (a) 4 (b) 5 (c) 6 (d) 7

Short answer

5

Step-by-step solution

Identifying Intracellular Hormones

Identify the hormones that bind to intracellular receptors. These include Cortisol, Testosterone, \(T 3\), Progesterone, and Oestrogen. They are steroidal or thyroid hormones that pass through the cell membrane and bind to intracellular receptors.

Count the Intracellular Hormones

Count the total number of hormones identified in the previous steps which bind to intracellular receptors.

Key concepts

Hormone Receptor Types

Hormones in the body exert their effects by binding to specific receptors, which can be located in different parts of the cell. The main types of hormone receptors are intracellular receptors and cell surface receptors.

• **Intracellular Receptors:** These receptors are located inside the cell, either in the cytoplasm or the nucleus. Hormones that bind to these receptors are usually small, lipophilic molecules, meaning they can easily cross the cell membrane.
• **Cell Surface Receptors:** These are embedded in the cell membrane and typically bind to larger or polar molecules that cannot easily pass through the lipid bilayer of the cell. They often trigger signal transduction pathways that lead to cellular responses.

Understanding where each hormone binds helps in determining its mechanism of action and potential impact on the target cell.

Steroid Hormones

Steroid hormones are a class of hormones that can pass through the cell membrane due to their lipophilic nature. Derived from cholesterol, these hormones include corticosterone, aldosterone, and sexual hormones such as testosterone, estradiol, and progesterone.

• **Characteristics:** Steroid hormones are soluble in lipids and can diffuse freely through the cell membrane to reach their intracellular receptors.
• **Mechanism of Action:** Once inside the cell, they bind to specific intracellular receptors forming a hormone-receptor complex, which then moves to the nucleus and influences gene expression by acting on DNA directly.
• **Examples in the human body:** Testosterone and estrogen are examples of steroid hormones that play pivotal roles in development and metabolic functions. These properties of steroid hormones make them powerful regulators of various physiological processes by directly modifying the expression of specific genes inside the cell nucleus.

Thyroid Hormones

Thyroid hormones are another group of intracellular hormones that adjust the body's metabolism and energy regulation. These hormones include thyroxine ( abl{}ft 4 eft), triiodothyronine ( abl{}ft 3 eft), and they are unique because even though they are not steroids, they act in a similar way by entering the cell and the nucleus to exert their effects. Thyroid hormones:

• **Importance in Metabolism:** They are essential in regulating metabolic processes, heart rate, and body temperature.
• **Mode of Action:** Like steroid hormones, they pass through the cell membrane owing to their small size and use specific transporters to reach their intracellular receptors in the nucleus. Here, they alter the transcription of genes to increase or decrease the production of specific proteins related to metabolism.

By understanding how thyroid hormones function, we appreciate their critical role in maintaining normal physiological functions and how their imbalance can lead to disorders like hyperthyroidism or hypothyroidism.

Cell Membrane Permeability

The cell membrane, made of a lipid bilayer, poses a selective barrier to the movement of substances into and out of the cell. This selectivity considerably impacts how hormones operate.

• **Structure:** The cell membrane is composed primarily of phospholipids, forming a bilayer with proteins and cholesterol interspersed, providing fluidity and mechanical stability.
• **Selective Permeability:** Due to the lipid structure, the membrane allows lipophilic molecules, such as steroid hormones and thyroid hormones, to pass through easily, while polar molecules, charged ions, and larger molecules require transport mechanisms.
• **Transport Mechanisms:** Channels and carriers are proteins that allow non-lipophilic or larger molecules to cross the membrane, ensuring cells receive necessary nutrients and ions and can dispose of waste materials.

Understanding cell membrane permeability helps us comprehend how different hormones reach their receptors and how the cell maintains homeostasis with its environment.