body fluids

• The lymphatic system includes structures like lymph nodes, vessels, ducts, and tissue spaces.
• Blood coagulation or clotting is a mechanism to prevent excessive loss of blood from the body in response to an injury or trauma
• A dark reddish brown scum formed at the site of a cut or injury over time is a clot or coagulum mainly composed of a network of threads called fibrins, trapping dead and damaged formed elements of blood
• Fibrins are formed by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin
• Thrombins are formed from another inactive substance in the plasma called prothrombin
• An enzyme complex called thrombokinase is required for the conversion of fibrinogens to fibrins, and it is formed by a series of linked enzymic reactions involving factors present in the plasma in an inactive state (cascade process)
• Platelets in the blood are stimulated by an injury or trauma to release certain factors that activate the mechanism of coagulation
• Factors released by tissues at the site of injury can also initiate coagulation
• Calcium ions play a crucial role in the clotting process
• The entire heart is made of cardiac muscles
• The walls of ventricles are much thicker than that of the atria
• Specialised cardiac musculature called nodal tissue is distributed in the heart
• A patch of nodal tissue is present in the right upper corner of the right atrium called the sino-atrial node (SAN)
• Another mass of nodal tissue is seen in the lower left corner of the right atrium close to the atrio-ventricular septum called the atrio-ventricular node (AVN)
• A bundle of nodal fibres, atrioventricular bundle (AV bundle), continues from the AVN passing through the atrio-ventricular septa to emerge on the top of the interventricular septum and immediately divides into a right and left bundle
• These branches give rise to minute fibres throughout the ventricular musculature of the respective sides and are called purkinje fibres
• The nodal musculature has the ability to generate action potentials without any external stimuli, i.e., it is autoexcitable
• The SAN can generate the maximum number of action potentials, i.e., 70-75 min–1, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart
• The heart normally beats 70-75 times in a minute (average 72 beats min–1)