Title Body Fluids and Circulation.pdf ✅

• Found in arthropods and mollusks. • Blood from the heart pumped into the open spaces in the body cavity called sinuses. • The body cavity remained filled with blood (haemolymph) called haemocoel. Closed circulatory system : • Found in annelids, echinoderms and all chordates. • Blood from the heart pumped into definite blood vessels. • Blood circulated in a wide network of blood vessel throughout the body. • Blood circulated in a regulated manner. Heart and circulation in vertebrates : • Fishes: have 2 chambered hearts with one atrium and one ventricle. • Amphibian and reptilian (except crocodile) has three chambered heart with two atria and one ventricle. • Crocodiles, birds and mammals possesses a 4-chambered heart with two atria and two ventricles • In fishes the two chambered heart pumped deoxygenated blood to the gills for oxygenation and then circulated to the body. (singlecirculation) • In amphibians and reptilians the left atrium receives oxygenated blood from the lungs and right atrium receives deoxygenated blood from the body. Blood from the atria pumped into the ventricle from which the mixed blood pumped into the body. (Incomplete double circulation). • In birds and mammals oxygenated and deoxygenated blood received by left and right atria respectively passed into ventricle of their side. The ventricles pump it out without any mixing up. (double circulation) HUMAN CIRCULATORY SYSTEM : Heart : • Originated from embryonic mesoderm. • Situated in the thoracic cavity, in between two lungs, slightly tilted towards left. • It has the size of the clenched fist. • Heart is covered by a double walled bag, pericardium. • Our heat is four chambered, two relatively smaller upper chamber called atria and two lower larger chamber calledventricles. • Two atria are separated by thin muscular wall called inter-atrial septum. • A thick walled inter-ventricular septum separates two ventricles. • Atrium and ventricle of same side is separated by a thick fibrous tissue called the atrio-ventricular septum. • Each of atrio-ventricular septa is provided with an opening through which the atrium and ventricle of same side are connected, called atrio-ventricular opening. • Right atrio-ventricular opening is guarded by tricuspid valve. • Left atrio-ventricular opening is guarded by bicuspid or mitral valve. • The right ventricle opens into systemic aorta and left ventricle opens into pulmonary aorta. • Both the aorta is guarded by semilunar valves. • The valves in the heart allow unidirectional flow of blood i.e. from atria to ventricles and from ventricles to their respective aorta. Conducting system of human heart : • The entire heart is made of cardiac muscles. • The wall of the ventricle is much thicker than the atria. • A patch of nodal tissue is present in the right upper corner of the right atrium called the Sino-atrial node(S A Node). • Another nodal tissue present in the posterior to the inter-ventricular septum called A V Node (Atrio-ventricular node). 96 Free Downlod This