BIOLOGY STUDY MATERIALS

TYPES OF CLOSED CIRCULATORY SYSTEM In all vertebrates, higher molluscas and annelids, the blood is circulated all over the body through a network of blood vessels. In this type of circulation, blood flows within the blood vessels and does not come in direct contact with cells and body tissues. Exchange of material between blood and body tissues is through an intermediate fluid celled lymph. Blood flows with high pressure and contains respiratory pigments like haemoglobin for transportation of respiratory gases. Close circulation is of two types- single and double circulation. Single circulation In single circulation, the blood passes through heart only once during each cycle. ex. Fishes Deoxygenated blood is pumped from heart towards gills, where it undergoes oxygenation. This oxygenated blood moves towards various body parts, gets deoxygenated and returns back to heart for next cycle. The heart of Fish carries only deoxygenated blood, it also called 'Venous Heart'. Double Circ...

  MECHANISM OF ACTION OF LYMPHOCYTES

The Human Heart  Introducation- The Heart is the main pumping organ of the circulatory system. It is reddish brown in colour, hollow and muscular organ. Its average weight is about 300gm in males and 250gm in female. It is conical in shape and lies in mediastenum i.e. the space between two lungs. It is broader at upper and conical at lower end (apex). Conical end is slightly tilted to left side and rests above the diaphragm. Heart is enclosed in a membranous sac called pericardium . Pericardium is formed form two main layers- outer fibrous pericardium and inner serous pericardium . Serous pericardium is soft, moist and elastic. It is formed of squamous epithelium and is further divisible into two layers as parietal and visceral layer. Parietal and visceral sublayers of serous pericardium are separated by a pericardial space. This space is filled with pericardial fluid which acts as a shock absorber and protects the heart from mechanical injuries. It also keeps the heart moist...