Task 2: As the surface area per volume ratio of an organism increases, so would it’s need for oxygen and other components, and it would be harder to effectively distrubute these components. Which is why multi-cellular organisms have to adapt and develop a specialised exchange surface, one of these being a good blood supply which is is part of the circulatory system I will be talking about below. The circulatory system is a closed system which passes through the heart twice during a complete circuit. It has 2 circuits which are : Pulmonary ( pumps blood to lungs for oxygenation ) and Systemic ( pumps oxygenated blood to head and body . Three main agents important in the circulatory system are: the arteries( they have thick, muscular and elastic walls to whistand the pressure and to exert force which is what gives you your pulse, and they serve to take blood away from the heart at high pressure); the capillaries( which allow exchange of materials between the tissues and the blood with they permeable walls) and veins (they have a large diameter to offer least flow resistance and valves to prevent back flow, they returns low pressure oxygenated blood to heart). The main component of the circulatory system is “blood”, it is a connective tissue which plays three main important functions which are: Transportation, regulation and protection. Transportation: The human body requires: oxygen and carbon dioxide to be exchanged for respiration, nutrients for energy, waste to be removed from the body so that we do not become intoxicated, and an even transport of hormones. For the transport of gases, we have red blood cells which are specialised cells (formed from stem cells in the bone marrow) that circulate around the body delivering oxygen to other cells while also removing carbon dioxide from the latter. It does not have a nucleus, mitochondria or ribosomes which means there is a larger surface area for the rapid diffusion of oxygen and carbo dioxide, it also has hemoglobin which is a molecule made of iron that gives red blood cells its red color. Waste and nutrients are also effectively transported by the blood . As it flows through the capillaries and into the lungs, the hemoglobin contained in the red blood cell releases carbon dioxide which is in turn removed from the lungs when we breathe out. Waste is also removed from our body tissues and organs and removed from the blood in a filter like system as it goes through the kidneys. The waste material will then exit the body in the form of urine. Blood also flows through the intestine’s capillaries and picks up nutrients( glucose, vitamins and minerals) which are then delivered to the rest of the body and cells that need it by blood flow. Hormones are chemical messengers produced by different glands which affect distant organs, such an example is the hormone insulin which is produced in the pancreas and affects the sugar levels in the blood. Our blood also transports hormones made by endocrine systems to organs and tissues. The circulatory system also delivers hormones such as peptides hormones which are secreted by the heart atrial cells to help regulate blood volumes and pressures. Estrogen is also transported here to promote vascular health in women and men. Regulation: Heat is absorbed and exchanged throughout the body by the blood which moves farther and closer from the skin in every areas of the body. This heat is produced by the tissues when they break down nutrients for energy, releasing waste and repairing themselves. As the body temperature rises, the blood vessels closer to the skin will increase in size, so that heat can be loss through the skin. If body temperature falls, the blood vessels closer to the skin will become smaller so that they can retain heat. It also distrubute heat generated by muscular contractions. Th circulatory system regulates blood volume and pressure by regulating fluid loss in the form of urine, and transports gonadotropic hormones which regulates reproductive functions. Protection: The circulatory system is very important when it comes to fighting diseases, it makes up most of the immune system and contains cells known as ” white blood cells”, which patrol the body in search of foreign bodies. As soon as a foreign body is detected, chemical signals are sent through the bloodstream, this then alerts the white blood cells of the situation which then are transported to the site of infection where they will engulf ( phagocytizing) or release chemicals at the bacteria or body responsible for the infection. Also during tissue damage or injury, messenger chemicals are released which starts the activation of platelets or attract platelets to the site. The platelets in the blood will then stick together to form a plug which will then cover the wound and coagulate to stop further blood loss and bacteria to enter the bloodstream through the wound. The circulatory system transports and makes tissue fluid not been abled to be reabsorbed by the vascular capillaries back to the lympathic system for processing.