Circulation

• Blood


  Blood is a special type of tissue consisting of millions of cells in a fluid
• Blood roles


  1. Transport substance round the body e.g. O2 to cells, CO2 away

  2. Distributes heat around the body
• Plasma


  The liquid part of blood and consists of 90% water. It is a pale yellow colour

  The remaining 10% consists of a mixture of substance that are either dissolved or suspended in it (e.g. hormones)
• Composition of Blood


  1. Red blood cells (erythrocytes)

  2. White blood cells (lymphocytes)

  3. Plasma

  4. Platelets
• Function


  1. Plasma transports soluble substances around the body, e.g. minerals, vitamins digested food such as glucose, chemical waste products like CO2 and Urea

  2. Carries chemical messengers (hormones) and helps redistribute heat energy around the body
• Red blood cells


  - made in the red bone marrow, live for about four months and then are destroyed by the liver or spleen

  - most numerous type of cell in the blood
• RBC structure


  - Contain a red pigment called Haemoglobin

  - Do not contain a nucleus so that more haemoglobin fits in the red blood cell (more O2)

  - Biconcave disk, gives a greater surface area for the uptake of oxygen
• Haemoglobin

  A special protein which contains iron that enables it to carry oxygen- important for food to have source of iron (dark green veg and red meat)

  It combines readily with O2 to form oxyhaemoglobin allowing it to be transported around our body
• Haemoglobin equation


  Haemoglobin + oxygen (deep red/ purple) <—-> Oxyhaemoglobin (scarlet)
• carbon monoxide poisoning


  - Haemoglobin has a greater affinity for the gas carbon monoxide (CO) than it does for oxygen

  - CO is present in motor vehicle exhaust fumes an din cigarette smoke

  -when breathed in, less oxygen can combine with haemoglobin so that the tissues are starved of oxygen, possibly leading to death
• Platelets


  Small fragments of cells with no nucleus. They are made in the bone marrow and are involved in blood clotting. There are much less than red blood cells.
• Pathogens


  Skin provides effective barrier stopping pathogens entering blood, but if skin is cut they are able to get in. It is very important that the blood clots to prevent this from happening and to stop too much blood loss.
• blood clotting


  Clotting closes the wound to prevent blood loss, and prevent pathogens entering
• Formation of Blood Clot


  Blood vessels have smooth walls. If cut the platelets bump into the rough edges and react causing them to release a chemical that causes the formation of a blood clot. The chemical causes a soluble plasma Protein called fibrinogen to turn into an insoluble protein Fibrin.
• fibrin


  Soluble fibrinogen turns into insoluble protein Fibrin. Fibrin creates a mesh across the wound and red blood cells and platelets get trapped in the mesh, forming the clot.
• Flow diagram of Blood clotting

  1. Injury- the blood vessel is cut

  2. Platelets release a chemical

  3. Chemical changes the soluble protein (fibrinogen) into an insoluble protein (fibrin)

  4. Fibrin fibres form a mesh and RBC and platelets get trapped

  5. These cells dry out, and this forms a scab

  6. New layer of skin grows under the scab
• Micro-organisms


  Tiny living things that can only be seen using a microscope e.g bacteria and fungi
• diseases


  Microorganisms such as bacteria and viruses that cause diseases are known as pathogens
• Structure of Bacteria


  Prokaryote- cells with no proper nucleus (Bacteria)

  
• Structure of Virus

  Viruses are not living- they do not carry out MRS C GREN

  
• White blood cells


  Larger than RBC, contain a nucleus and there are fewer of them in the blood
• WBC function


  - Defending the body against disease causing microorganisms, known as pathogens
• Pathogens function


  Damage the body, or poison it by excreting toxins
• Skin


  Acts as a physical barrier to prevent microorganisms from entering the body. All openings secrete defensive chemicals e.g. mucus in the airways, and HCl in the stomach
• What happens if primary defences fail

  the WBC take over
• Two types of WBC

  phagocytes and lymphocytes
• Phagocytes


  Made in the red bone marrow and only live few days (only made when infections). Larger the RBC and are an irregular shape. They have multi-lobed nucleus and granular cytoplasm (digested pathogens).

  
• phagocyte function


  Destroy foreign substances such as bacteria by engulfing and digesting them by a process called phagocytosis
• Lymphocytes


  Made in the lymphatic system and may live for several years. They are spherical in shape and have a very large nucleus and a small amount of non-granular cytoplasm

  
• Lymphocytes function


  - Produce proteins called antibodies which target microorganisms, which get into the blood stream

  - Antibodies are produced in response to proteins found on the surface of bacteria and viruses
• Antigen


  Protein that causes an immune response
• Antigen + antibodies


  Antibodies from one lymphocyte only target one specific antigen. When this antigen enters the body on the surface of a microorganism it causes the lymphocyte to produce large quantities of the correct antibody.
• Antibodies response to pathogens

  - Cause the bacteria/ viruses to clump together

  - Promote Phagocytosis

  - Prevent the microorganism from invading host cells

  - Some bacteria/ viruses do their damage by releasing toxins
• Immune


  When somebody has had a disease, the body is then protected from getting it again
• Immunity


  - Virus enters the body, lymphocytes produce antibodies which eventually defeat the virus

  - Some lymphocytes become memory cells ( they can recognise the virus if person is re-infected)

  - Memory cells will produce antibodies quicker and in larger quantity than before

  - This is called secondary immune response

  - Virus is then defeated before person gets ill again

  - they are immune
• Vaccination


  - Person is infected with a weakened or dead pathogen

  - Will not cause disease but makes the lymphocytes recognise the weakened pathogen as foreign and make antibodies agains them

  - Memory cells then form which are capable of recognise the normal pathogen when infected + start producing antibodies quickly and in large concentrations (secondary immune response

  - Destroys pathogen before unwell, thus immune
• How can you treat bacterial infections?

  - Bacterial infections can be treated with antibiotics chemicals that kill the pathogen

  - Overuse of these drugs mean that bacteria can become resistant to them.

  - Viruses are not affected by antibiotics (treated with drugs that prevent them from replicating or entering host cells).

  - Other microorganisms can cause disease
• Other disease + cause

  Athletes foot —> caused by fungi

  malaria —> caused by Protoctist
• Pathogen definition


  A microorganism that can cause a disease is know as a pathogen. The most common types are bacteria and viruses.
• circulation


  - Transport system of the human body is the circulatory system

  - Consists of fluid tissue (blood) which circulates around the body in a series if tubes called blood vessels

  - The heart acts as central pump, which keeps the blood moving around

  - Blood consists of plasma containing blood cells