B5 The Living Body

B5.1 Skeletons

Internal skeletons provide internal framework, grow with the body, they are flexible and they allow easy attatchment of muscles. Cartilage and bones contain living tissue which means they can become infected and they can also repair themselves. Long bones consist of a long, hollow shaft of bone marrow with blood vessel and the end is covered with cartilage. In the very early stages of human skeletons, the bones are cartilage then by the process of ossification (deposition of calcium and phosphorus). If cartilage remains between the head and shaft, the person is still growing. Bones can be broken easily with a sharp knock and if an elderly person lacks calcium or phosphorus their bones may fracture easily.

Synovial joints contain synovial fluid, a synovial membrane, ligament and cartilage e.g. ball and socket joint or hinge joint. Ball and socket joints have a wider range of movement than hinge. The forearm is raised and lowered by antagonistic muscles. To raise the forearm the biceps contract and the triceps relax. Synovial fluid acts as a cushion against shock and a lubricant for easy movement. A synovial membrane hold the fluid and cartilage protects the bone head. Raising and lowering the forearm is an example of a lever with the elbow as the fulcrum (pivot). The effect is multiplied resulting in greater force.

B5.2 Circulatory systems and cardiac cycle

Many animals need blood circulatory systems to get rid of waste products and recieve food and energy. In a single circulatory system (e.g. fish) there is a single blood circuit to the heart, gills and body. In a double circulatory system (e.g. mammals) has two circuits, one from the heart to the lungs then the other from the heart to the body. A double circulatory system requires a four chambered heart - two atria to recieve blood and two ventricles to distribute blood to the body. Its ensures high blood pressure for a fast and effective distribution of food and energy.A single circulatory system needs two chambers, one to recieve blood and one to send blood to the body.

The cardiac cycle is the sequence of blood entering and leaving the heart. The two atria contract together and the ventricles relax to recieve blood and the antrio-ventricular valves preveting backflow into atria. Muscles of the two ventricles contract together to force blood to lungs or around body and the semi-lunar valves prevent backflow into the atria. 

More muscular activity causes a greater demand for oxygen and food so heart rate increases. When heart rate increases, so does the presences of the hormone adrenaline to prepare the body for 'fight or flight'. Groups of cells in the heart form pacemakers which control the rate of heart beat by producing an electric current to stimulate the muscle contracting. An electrocardiogram (ECG) shows changes in electrical impulses in heart muscles and echocardiograms display videoes of the heart in action - both investigate an irregular heart beat. Two pacemakers, the sino-atrial node (SAN) and the atrio-ventricular…