Lymph and Circulatory System | Biology Class 11 - NEET PDF Download

What is lymph?

Lymph is a clear, colorless fluid that circulates through the lymphatic system. It is derived from interstitial fluid that has entered the lymphatic vessels

• When blood travels through tiny vessels in tissues, some water and small, water-soluble substances leak out into the spaces between cells, forming what's called interstitial fluid or tissue fluid. 
• This fluid, which has the same mineral content as blood plasma, serves as a medium for exchanging nutrients, gases, and other substances between blood and cells. The lymphatic system, made up of a network of vessels, collects this fluid and returns it to the main veins.
• The fluid in the lymphatic system is called lymph. Lymph is clear and contains special white blood cells called lymphocytes, which play a key role in the body's immune responses. It also carries nutrients, hormones, and fats absorbed from the intestines through structures called lacteals in the intestinal villi.

What is Circulatory System?

An expanded pipeline system is present in the human body. It is called the closed circulatory system. 

A continuous chemical exchange of materials between the animal body and environment among different tissues of the body is done through this system. In this way, digested nutrients from the digestive system, oxygen from respiratory organs, hormones from endocrine glands are distributed to all the cells of the body. Also, the transport of CO₂ from body cells to respiratory organs, NH₃, urea etc. excretory substances to excretory organs are the function of the circulatory system. The whole circulatory system is formed by the mesoderm of the embryo. Except the inner lining of blood vessels and heart which are of endodermal origin.Human Heart

Types of Circulatory System on basis of Complexity and Evolution

Types of Circulatory System on the basis of Circulating Fluid

In human beings (on the basis of circulating fluid) two types of circulatory system are observed.

• Blood circulatory system: It consists of Blood, Blood vessels, Heart.
• Lymphatic system: It consists of lymph, lymph capillaries, lymph vessels, lymph nodes, lymphoid tissues/organs.

The study of blood vascular system or circulatory system is called Angiology.

William Harvey is known as the father of angiology. He called the heart the "Pumping station of the body".

Path of Blood in Double Circuit (Man) 

It was first discovered by "William Harvey".

 Path of Blood in Double Circuit

Circulation of Blood

1. Single Circuit

Example: Fishes

2. Double Circuit

Example: Man, Rabbit

3. Transitional Type Circuit

Two circuits are not completely separate 

Example: FROG 

Blood mixes in ventricles Evolutionary sequence is present in vertebrates.

• Fishes have a tubular "Venous-Heart" In their heart, deoxygenated blood enters from one side and from the other side enters inside the gills for purification. This is called the "Single Heart Circuit".
• In amphibians (like Frog) and Reptiles, the auricles are divided into right and left. The right auricle gets impure and the left auricle gets pure blood from the body. But only 1 ventricle is present or is incompletely divided so after coming here the pure and impure blood mix up.
• In some reptiles (Crocodile, Gavialis and Alligator) and in all birds and mammals the heart is divided into 2 auricles and 2 ventricles so while circulating inside the heart the pure and impure blood remain separated. The right portion of the heart collects impure blood from the body and sends it to the lungs for purification, while the left portion takes pure blood from the lungs and distributes it to the whole body.

The right portion of the heart is called the "Pulmonary-Heart" and the left portion is termed as the "Systemic-heart". This is termed as "Double Circulation of Heart".because the blood has to pass through the heart twice before being delivered to systemic organs. Types of heart on the basis of type of blood which it receives:

• Venous/Brachial (fishes)
• Arterial (prawn)
• Arteriovenous (lung fishes, tetrapods)