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Heart is situated in the thoracic cavity in between two lungs, slightly tilted to the left it has size of clenched fist. It is protected by a double walled membrane bag pericardium enclosing pericardial fluid outer- parietal pericardium and inner visceral pericardium. The heart is four chambered two chamber are relatively smaller called atria and two large lower chambers called ventricle . A thin muscular wall called inter atrial septum separates left and right atrium. A thick walled inter ventricular septum separates left and right ventricles. Atrium and ventricles are separated by thick fibrous tissue called atrio ventricular septum. opening of left and right ventricles into pulmonary artery and aorta respectively are provided with semilunar valves. The atrioventricular opening between left atrium and left ventricle is guarded by bicuspid valves (it has two flaps). The atrioventricular opening between right atrium and right ventricle is guarded by tricuspid valve (it has ...

Nasal Cavity - It is located at the back of nostrils just above the mouth cavity. It has specific nasal epithelium by which air is filtered (by hair) moistened (by mucus) warmed by capillary network. Mucus traps the dust and other fine particle olfactory region is also situated for different smell. Nasopharynx- It is located at the posterior part of pharynx. Air enters into nasopharynx through two internal opening. Larynx- Also called as voice box. It is a cartilaginous structure at the opening of trachea and has fibro elastic ligaments called vocal chords. Different sounds can be produced using tension caused in vocal chords. Glottis - It is the opening to larynx through which air passes into trachea. Epiglottis - It is a triangular flap of cartilage present at glottis Trachea - It runs through the neck in front of oesophagus and extends into the thoracic cavity. It has C shaped rings of cartilage that prevents the collapse of trachea during respiration. The open...