1. Thromboplastin is widely distributed in the body and is held securely in the tissues and the platelets of the blood. It is the «trigger» mechanism which initiates the process of coagulation. In injury, thromboplastin is liberated from the tissues and the coagulation process begins promptly. Excessive bleeding due to a deficiency of thromboplastin is observed in patients with hemophilia.
2. Senile erythrocytes are phagocytosed and broken down in the reticular connective tissue of the bone marrow and the spleen. Iron from the hemoglobin is temporarily stored in the phagocytes of the reticular connective tissue as hemosiderin, which in turn is broken down to ferritin, a molecular combination of six atoms of iron. Ferritin is carried through the blood stream to the bone marrow. Here it is taken up by the reticular cells which eventually release it to the erythroblasts.
3. From the stomach, the chyme passes into the small intestine through the pyloric sphincter. Much material is still undigested. Proteins have not been completely broken down, starches are still being converted into simple sugars, and fats remain in large globules. In the small intestine the process of digestion is completed by the action of the bile, which is secreted by the liver and released by the gall bladder, and by the action of various enzymes.
4. The body is continuously exposed to damage by viruses, bacteria, toxins and chemicals, and foreign proteins of plant origin. These insults are received by the skin, the respiratory system, and the digestive system. The skin suffers far more injuries than the rest of the body. This organ is looked upon as an important means that protects the tissues against mechanical, chemical and bacterial injuries. For the protection against mechanical injury, the skin develops thickness, as on the sole of the foot, and on the palms of the hand.