Blood - 9.4

• Plasma- liquid part of blood, formed from special cells in the bone marrow.

  Red blood cells- biconcave blood cells with no nucleus which transport oxygen.

  White blood cells- blood cells with a nucleus that helps to defend against pathogens.

  Platelets- tiny cell fragments present in blood that help with clotting.
• RBCs contain haemoglobin which is a protein, contains iron and carries oxygen. The iron combines w oxygen when capillaries take blood close to the alveoli. Haemoglobin combined w oxygen is called Oxyhaemoglobin. Oxyhaemoglobin releases its oxygen when blood passes thru capillaries near the body cells which are respiring, and use the oxygen.
• RBCs don't have a nucleus or mitochondria. No nucleus means more space for more heamoglobin.
• RBCs are biconcave discs (like they've been pinched in from both sides) and are small in size. Both of these give them a relatively large surface area to volume ratio which allows oxygen to diffuse in and out easily.
• RBCs small size allows them to fit thru even the smallest of capillaries so oxygen can get close to every cell in the body.
• Haemoglobin- red pigment in RBCs, can combine reversibly w oxygen and is a protein.
• White blood cells have a large nucleus. Their function is to fight pathogens and clear up any dead body cells. 2 types of WBCs, phagocytes and lymphocytes.
• Phagocytes engulf the pathogen (into the cytoplasm) and digest it in a process called phagocytosis.
• The phagocyte goes to a group of bacteria and flows around them. The cell membrane fuses and encloses the bacteria in a vacuole. Enzymes get secreted in the vacuole which digests the bacteria. Soluble substances from the vacuole diffuse into the phagocyte's cytoplasm.
• Phagocytosis- taking bacteria or other small structures into a cell's cytoplasm, and digesting them with enzymes.
• Platelets are involved in blood clotting, which prevents excess blood loss from the body and also stops pathogens entering the body thru breaks in the skin.
• Blood plasma contains a soluble protein called fibrinogen. When a blood vessel breaks, platelets release a substance that turns this fibrinogen into an insoluble protein called fibrin, which forms fibers that layer on top of each other to create a mesh-like structure that traps RBCs and helps to seal the wound. The platelets stick together to form clumps. The fibers, trapped RBCs and platelet clumps form a blood clot.
• Blood plasma is made up of mostly water and many substances are dissolved in it. It transports many substances like water, various proteins, lipids, carbohydrates, excretory substances, mineral ions, hormones, and dissolved gases.
• Water- absorbed in the small intestine and colon, goes to all cells, and kidneys remove excess.

  Various proteins (including fibrinogen and antibodies)- Fibrinogen is made in liver and antibodies are made by lymphocytes, which remain in the blood, fibrinogen helps in blood clotting and antibodies fight against pathogens.
• Lipids (including fatty acids and cholesterol)- absorbed in the ileum and derived from fat reserves in the body, go to the liver for breakdown, to adipose tissue for storage, and to respiring cells as an energy source, breakdown of fats releases energy, which is very imp for the heart but too much cholesterol causes CHD.
• Carbohydrates (esp glucose)- absorbed in the ileum and produced by the breakdown of glycogen in the liver, goes to all cells for energy release by respiration, excess glucose is converted to glycogen and stored in the liver.
• Excretory substances (urea)- produced by amino acid deamination in the liver, go to the kidneys for excretion, kidneys excrete most, mixed w water to form urine.

  Mineral ions (Na, Cl)- absorbed in the colon and ileum, goes to all cells, excess ions are excreted by the kidneys.
• Hormones- secreted into the blood by endocrine glands, go to all parts of the body, hormones only affect their target cells and are broken down by the liver, and their remains are excreted by the kidneys.

  Dissolved gases (carbon dioxide)- CO2 is released by all body cells as a waste product of respiration, goes to the lungs for excretion and most CO2 is carried as hydrogencarbonate ions in the blood plasma.