Question

Write short notes on: (i) Reflex action
(ii) Lymph

Hint:

Reflex actions are quick and automatic responses controlled by the spinal cord, essential for quick reactions to avoid injury.

Answer 1

(i) Reflex action
Definition:
Reflex action is an involuntary and automatic response to a stimulus that does not require conscious thought. It is controlled by the spinal cord and occurs quickly to protect the body from injury or harm.
Mechanism:
1. Stimulus: A sudden stimulus (such as touching a hot object) activates sensory receptors in the skin.
2. Sensory Neurons: The sensory neurons carry the signal to the spinal cord.
3. Spinal Cord: The spinal cord processes the information and sends an immediate response.
4. Motor Neurons: The motor neurons carry the response from the spinal cord to the muscles, causing an immediate action (like pulling the hand away).
This entire process occurs without the involvement of the brain, making reflex actions very rapid.
Examples of Reflex Actions:
- The knee-jerk reflex.
- Withdrawal reflex when you touch something hot.
(ii) Lymph
Definition:
Lymph is a colorless fluid that circulates throughout the lymphatic system. It plays a key role in the immune system by transporting white blood cells, proteins, and waste products from tissues to the bloodstream.
Composition:
Lymph contains:
1. Water
2. White blood cells (especially lymphocytes, which help fight infections)
3. Proteins (including antibodies)
4. Waste products (from tissue cells)
5. Fat molecules (absorbed from the digestive system, particularly chyle)
Formation and Circulation:
1. Lymph is formed from interstitial fluid, which is the fluid that bathes the cells of tissues. This fluid is pushed out of blood capillaries and collects in tissue spaces.
2. The excess fluid is absorbed by lymphatic capillaries, forming lymph.
3. The lymph flows through lymph nodes, where it is filtered and cleaned of pathogens. It then moves into larger lymphatic vessels and eventually returns to the bloodstream near the neck.
Functions:
1. Transport of immune cells: Lymph transports lymphocytes to fight infection.
2. Waste removal: It removes waste products from tissues and carries them to the bloodstream for excretion.
3. Absorption of fats: Lymph absorbs fat molecules (chyle) from the digestive system and transports them to the bloodstream.
Conclusion:
Lymph is an important component of the circulatory and immune systems, assisting in nutrient transport, waste removal, and the body's defense against diseases.