Introduction
In the International Baccalaureate (IB) Biology syllabus, Topic 6.6 covers the concepts of hormones, homeostasis, and reproduction. This study note will delve into the intricate details of these topics, breaking down complex ideas into manageable sections. We'll cover the roles of hormones, the mechanisms of homeostasis, and the processes involved in human reproduction.
6.6.1 Hormones
What are Hormones?
Hormones are chemical substances produced by endocrine glands and released into the bloodstream. They serve as messengers that transmit information from one part of the organism to another, thereby regulating various physiological processes.
Endocrine System
- Endocrine Glands: These glands secrete hormones directly into the bloodstream. Examples include the pancreas, thyroid, and adrenal glands.
- Target Cells: Hormones affect only those cells that have specific receptors for them, ensuring that the hormonal signal is received only by the intended cells.
Receptors must be complementary to hormones for any effect to occur.
Functions and Examples
- Insulin and Glucagon: Produced by the pancreas, these hormones regulate blood glucose levels. Insulin decreases blood glucose, while glucagon increases it.
- Thyroxine: Produced by the thyroid gland, this hormone regulates metabolism.
- Adrenaline: Produced by the adrenal glands, this hormone prepares the body for 'fight or flight' responses.
When blood glucose levels rise after a meal, insulin is released to help cells absorb glucose, thereby lowering blood glucose levels.
Mechanism of Hormone Action
- Secretion: Hormones are secreted by endocrine glands into the bloodstream.
- Transport: They travel through the blood to reach target cells.
- Binding: Hormones bind to specific receptors on or inside the target cells.
- Response: The binding triggers a response within the target cell, such as altering gene expression or enzyme activity.
6.6.2 Hormones Continued
Feedback Mechanisms
Hormone levels are regulated by feedback mechanisms, primarily negative feedback, to maintain homeostasis.
- Negative Feedback: A change in a physiological variable triggers a response that counteracts the initial change.
When blood glucose levels drop, glucagon is released to increase glucose levels, which then inhibits further glucagon release.
Hormonal Imbalances
Imbalances in hormone levels can lead to various disorders:
- Hyperthyroidism: Excessive thyroxine production leading to increased metabolism.
- Diabetes Mellitus: Insufficient insulin production or action leading to high blood glucose levels.
Assuming that all glands in the body are endocrine glands. Some glands, like sweat glands, are exocrine glands and secrete substances through ducts.
6.6.3 Reproduction: Background
Human Reproductive Systems
The human reproductive system is responsible for producing gametes (sperm in males and ova in females) and supporting the development of offspring.
- Male Reproductive System: Includes structures like the testes, vas deferens, and penis.
