Biology 3 Part 3

Biology 3 Part 3

B3.3
1. Homeostatis
  1. This is the maintenance if a constant internal body environment. It usually involves a negative feedback mechanism.
  2. Osmoregulation
    1. The kidneys
      1. Urea is carried in the blood to the kidneys. It is here that unwanted substances in the blood are removed.
        There are two kidneys, one on each side of the body on the back side of the abdomen. Each kidney receives blood from a renal artery that branches odd from the aorta. In the kidney there are many renal tubules called nephrons in which the blood is filtered and cleaned. The blood then leaves the kidney in a renal vein.
        The waste, such as urea, and extra urine, not passes down a ureter to the bladder. When it is full, the bladder wall contracts and the urine passes to the outside through the urethra.
      2. Each kidney is divided into an outer cortex and an inner medulla. When blood enters the kindey, tiny blood vessels carry it it to the nephron. Each nephron begins in the cortex with a Bowman's Capsule. When the urine has been formed, it enters a collecting duct that carries it through the medulla to the kidney pelvis. Here is drains into a ureter to be carried to the bladder.
      3. The Nephron
        The afferent arterole is wider than the efferent one so the pressure in the glomerulus goes up. All the blood, except for plasma, protein and cells is forced into the Bowman's Capsule. This is FILTRATION. In the first coiled tube all the glucose and 80% of the salt and water is reabsorbed into the blood. The loop of Henle concentrated salt in the medulla. The second coiled tube reabsorbs some more salt and then drains into a collecting duct. This passes through the medulla to the pelvis. AS it does so, 19% of the remaining 20% of water is reabsorbed by osmosis.
      4. Control of Kidney Functions
        When the blood is too salty, the Hypothalamus increases the pituitary release of Anti-Diuretic hormone (ADH). This causes more water to be reabsorbed in the kidney, which results in less urine.
        When the blood is too watery, the Hypothalamus decreases the pituitary release of Anti-Diuretic hormone (ADH). This means less water is reabsorbed and more urine is produced.
      5. Dialysis
        In kidney failure there is no filtration of blood into the Bowman's Capsule. Therefore no urine is made and the waste products build up to dangerous levels in the blood.
        To clean the blood a sufferer will have to go on a dialysis machine for 4 to 5 hours, 2 to 3 times a week.
        The blood is taken out from the body and passed through a pump (to increase blood pressure and to keep the blood flowing) before entering the machine. The machine has dialysis fluid separated from the bloody by a thin membrane. The clean blood from the machine passes through a bubble trap (to stop air embolisms from occurring) before being returned to the body.
        The dialysis fluid contains the same substances that the blood wants to keep. The dialysis fluid does not contain the substances that the blood wants to lose. Therefore the unwanted substances pass from the blood into the fluid to be removed while the useful substances do not.
      6. Kidney Transplants
        Each person has 2 kidneys but can survive with 1. Therefore a large number of kidney transplants come from close relatives of the sufferer. The kidney is attached to the circulation in a different part of the body. It is not without risk because it is a full surgical operation, which puts the body under strain. This is not bad for the donor, but the recipient must not already be too weak due to the diseased kidneys. There is also a possibility that the kidney could be rejected.
        Our immune system is geared up to recoginse the foreign cells or pathogens. However, it will respond in the same way to any foreign cells in the body. Foreign antigens on the cells may be recognised as such and cause the lympohcytes to produce atnibodies against the transplanted organ. The kidney will be rejected.
        There are certain antigens that causes the most severe immune system response. It is vital that as many of these antigens on the recipient's cell match those on the donor's cells. This match is called TISSUE TYPING.
        Even when the match is very close the patient will have to take immunosuppressant drugs for the rest of his or her life. This means that the immune system is dampened down and the patient is at risk of catching other pathogens.
    2. Water and salt control
  3. Thermoregulation
    1. Temperate control
    2. Ectotherms are 'cold blooded' animals. They depend in the environment and behaviour to control body temperature.
      1. Endotherms are 'warm blooded' animals. They generate their own heat energy to maintain a constant core body temperature, 37C in a human.
    3. Temperature Perception
      1. Thermorecepter cells in the skin respond to changes in environmental temperature and send impulses, via nerves, to the thermoregulation centre in the Hypothalamus. However the more important trigger is the temperature of the blood flowing close the the Hypothalamus because it is a direct effect of body temperature.
    4. Responses to Changes in Temperature
      1. If the core body temperature exceeds 37C, the thermoregulation centre sends out nerve impulses that have the following effects
        Sweat Glands- secrete sweat onto the skin surface. This leads to heat loss and cooling of the skin by evaporation.
        Erector Muscles- in the skin relax and the hairs lie flat. This increases the affect of air movements for heat lose by convection and radiation.
        The Arterioles- leading to capilleries in the skin vasodilate (get wider) to allow much more warm blood through the adipose (fat) layer to get close to the skin surface.
      2. If the core body temperature falls below 37C
        Sweat Production- is stopped
        Erector Muscles- contract and hairs stand up to trap an insulating layer of air next to the skin.
        The Arterioles- to the skin vasoconstrict (get narrower) and most blood stays within the body, separated from the skin surface by the insulating adipose (fat) layer.
        The Thyroid Glands- gets more active, the body's metabolic rate increases and more heat energy is released.
        Voluntary Skeletal Muscles- start to contract and relax involuntarily. This shivering releases more metabolic heat and generates heat from friction.
  4. Glucoregulation
    1. Blood glucose control
    2. Starch is digested into glucose and absorbed into the blood. There is more than the body needs so the excess must be stored for later. The glucose level in the blood stimulates hormones from the Isles of Langhhans in the pancreas.
    3. If the blood glucose levels are too high, the pancreas is stimulated and insulin is released. The liver then absorbs glucose and forms GLYCOGEN and the blood glucose levels decrease.
    4. If the blood glucose levels are too low, the pancreas is stimulated and glycogon is released. The liver converts this into glucose and this enters the blood. This causes the blood glucose levels to return to normal.
    5. Diabetes
      1. If there is little or no insulin, the excess glucose is not stored in the liver; it stays in the blood to produce a sugary filtrate. The sugar in it makes it hold onto the water by osmosis. A large volume of sugary urine is formed.
        Symptoms- thirst, lack of energy, kidney damage, damage to blood vessels in the eyes, coma, death
      2. Treatment
        Injection of insulin directly into the blood. It cannot be taken in tablet form because insulin is a protein and would be digested.
        The insulin used in human insulin from genetically modified bacteria. It is a mixture of insulin for an immediate effect and proinsulin for a longer lasting effect. Some patients have an insulin pump under the skin to provide a more regular dose than injections.
        Multiple Insulin Injections
        Advantages- discreet: injection syringe or pen can be carried around in a bag and used in privacy, equipment is cheap
        Disadvantages- greater chance of extreme high or low blood glucose concentration, uses more insulin each day
        Insulin Pump
        Advantages- Better control of blood glucose concentration, uses less insulin per day
        Disadvantages- must be warn almost all the time, equipment more expensive
      3. Diagnosis
        The Glucose Tolerent Test
        Type 1 diabetes is an autoimmune responses against the pancreas cells that make the insulin.

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