(a) What is lymphatic system? What are its function?
(b) What is blood pressure? What are the two factors used to express the blood pressure of a person?
(c) Name the main nitrogenous waste in the human blood. How is it removed from the blood?

(a) Lymphatic system is a network of organs, lymph nodes, lymph ducts and lymph vessels in the human body that make and move the lymph from tissues to the bloodstream.

Following are the functions of lymphatic system:

• It collects and transports tissue fluid from the intercellular spaces in all the tissues, back to the veins in the blood stream.
• Lymph nodes play an important role in the defence mechanism of the body by killing the germs with the help of lymphocytes present in the lymph nodes and by making antibodies.
• They transport larger compounds like enzymes and hormones from their manufactured sites to the blood stream.

(b) Blood pressure is the pressure at which the blood is pumped around the body by the heart. It is always expressed in the form of two factors that are called systolic pressure and diastolic pressure.

• Systolic pressure is the pressure at which the blood leaves the heart through the aorta during the contraction phase.
• Diastolic pressure is the minimum pressure in the arteries during the relaxation phase of the heart.

(c) The main nitrogenous waste in the human blood is urea. The kidneys remove the urea from the blood and excrete them in the form of a dilute solution called urine.
Kidneys are the main excretory organ of the human body. There are millions of nephrons in each kidney. Each nephron contains a renal corpuscle and a renal tubule. The renal corpuscle consists of capillaries called the glomerulus, enclosed by a capsule called Bowman's capsule. The blood is filtered in the glomerulus and the filtrate travels through the renal tubules. Here, the materials needed by the body are reabsorbed, while the wastes (like urea) are collected and excreted in the urine.