The Blood and Circulation

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  • THE BLOOD AND CIRCULATION
    • Some organisms do not need a circulatory system.
      • They have a large surface area compared to their volume and they are surrounded by the water they live in.
        • Dissolved oxygen diffuses from this water into the cell by osmosis.
    • The blood is your main transport system.
      • It takes oxygen and nutrients, such as glucose and amino acids, to cells.
      • It collects and removes waste, such as carbon dioxide and urea, from cells.
      • Blood is a tissue.
      • Red blood cells, white blood cells and platelets are suspended in the fluid plasma.
    • Various artificial blood products are available, but none contain red or white blood cells or platelets.
      • Volume expanders are used in emergency situations.
        • If a patient has lost a lot of blood, but there is no real blood of the correct type to infuse, saline (salt) solution can be used.
        • Some volume expanders also contain sugars and proteins.
        • They can maintain normal blood pressure, and the remaining haemoglobin will carry enough oxygen to the body tissues to sustain the patient.
      • If you loose a lot of red blood cells, you need artificial blood that can carry oxygen.
        • Some types contain chemicals that can carry and release oxygen.
        • Other types contain encapsulated haemoglobin.
          • Haemoglobin cannot be free in the blood as it would be filtered out in the kidneys and would damage them.
    • Unlike real blood, artificial blood does not have to be matched to patients.
      • They could be useful in countries where blood transfusions may not be safe.
        • They could be useful to rapidly treat trauma patients.
          • They can be stored for three years at room temperature.
            • They immediately restore full oxygen-carrying capacity to recipients, whereas this takes 24 hours with real blood.
    • Humans and other mammals have a double circulatory system.
      • Blood passes from the heart to the body organs and tissues, back to the heart, to the lungs to remove carbon dioxide and then back to the heart.
      • Because the blood makes two circuits from the heart, it needs four chambers.
      • The heart is a double pump.
      • Blood in a double circulatory system is under high pressure, and so it transports substances more quickly around the body.
    • Your heart is an organ.
      • Its function is to pump blood around the body.
      • The wall of the heart is made of muscle.
        • Its a specialised type of muscle called cardiac muscle.
    • Blood enters the atria of the heart, from veins.
      • The atria contract and force the blood into the ventricles.
        • The ventricles contract and force the blood out of the heart, into arteries.
          • Blood flows from the heart, to the organs, in arteries.
            • Blood returns from the organs to the heart, in veins.
    • The valves in the heart prevent the back flow of blood.
      • Surgeons can replace diseased or damage heart valves.
        • The valves may be synthetic or may be taken from other animals such as cows or pigs.
          • There is no risk of rejection, as heart valves have no capillary blood supply. This means that white blood cells do not patrol these valves.
    • Every time your heart beats, your ventricles contract and force blood out of the heart into arteries.
      • There are two arteries leaving your heart; the aorta and pulmonary artery.
        • The aorta leaves your left ventricle, carries oxygenated blood to your body tissues and smaller arteries branch off from it to take blood to your head and brain.
        • The pulmoary artery leaves the right bentircle, and takes deoxygenated blood to the lungs.
    • Arteries
      • The walls of the arteries are thick, because the blood is under high pressure.
        • Large amounts of muscle allow the wall to withstand and maintain the pressure.
          • Large amounts of elastic fibres allow the artery to stretch and recoil as blood surges through.
            • Narrow cavity (lumen).
    • Capillaries
      • Walls or very thin, only one cell thick, so diffusion is quick.
        • A large number of capillaries gives a large surface area for diffusion.
          • Molecules needed by the cells (such as oxygen and glucose) pass out of the blood.
          • Blood pressure has been lost, and the blood flows slowly by the time the blood reaches the capillaries.
            • They are very narrow, just wide enough to allow one red blood cell through.
    • Veins
      • They have thinner walls than arteries, because the blood pressure is lower.
        • Little muscle or elastic fibres as there is no high pressure to withstand.
          • They contain valves to prevent the back flow of blood.
            • Large cavity (lumen).
    • Blood is the only liquid tissue in your body.
      • It is made in the red bone marrow of your long bones.
        • You have about five litres of blood in your body and this volume has to be maintained, otherwise it cannot circulate properly.
          • It is slightly alkaline and the temperature is slightly higher than your body temperature.
            • Transport
            • Protection
              • If you cut yourself, your blood clots a forms a scab over the wound.
                • This stops blood loss and prevents pathogens from entering.
              • If pathogens do enter the body, white blood cells deal with them.
            • Regulation
              • Your blood regulates body temperature by distributing heat from respiring muscles and liver cells to other organs and your skin.
                • Your blood regulates your pH in body tissues by some of the proteins acting as buffers, which means they restrict changes in pH.
    • There are many dissolved substances in the blood.
      • Glucose
        • Amino acids
          • Fatty acids
            • Vitamins
              • Hormones
                • Cholesterol
                  • Carbon dioxide
                    • Hydrogencarbonate ions
                      • Mineral ions
                        • Fibrous proteins
                          • Antibodies
                            • Glucose
                              • Amino acids
                                • Fatty acids
                                  • Vitamins
                                    • Hormones
                                      • Cholesterol
                                        • Carbon dioxide
                                          • Hydrogencarbonate ions
                                            • Mineral ions
                                              • Fibrous proteins
                                                • Antibodies
      • Every red blood cells is filled with haemoglobin.
        • When oxygen diffuses into the red blood cells, it combines with the haemoglobin to form oxyhaemoglobin.
          • At respiring tissues, oxyhaemoglobin splits into oxygen and haemoglobin.
            • The oxygen diffuses into the body's cells to be used for respiration.

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