15. OCR A Level Biology Homeostasis, Liver and Kidney

• What is homeostasis?

  Maintenance of a constant internal environment despite external changes around a set point
• What are some changes that need to be monitored?

  -Temperature -Glucose concentration-PH of blood-H2O potential of blood-Ions concentration of blood
• What does a Negative feedback system do? And give an example

  The negative feedback system works to reverse the initial stimulus. A small change in one direction is detected by sensory receptors, effectors work to reverse the change and restore conditions to the base level. Examples - temperature control, water balance
• What does a Positive feedback system do?

  a change in the internal environment of the body is detected by sensory receptors, and effectors are stimulated to reinforce that change and increase the response.
• Examples of Positive feedback

  Blood clotting cascade - blood vessel is damaged, platelets stick to the damaged region and they release factors that initiate clotting, continues until a clot is formed Childbirth - the head of of the baby presses against the cervix, stimulates the production of the hormone oxytocin, oxytocin stimulates the uterus to contract, pushing the head of the baby even harder against the cervix and triggers the release of more oxytocin
• What are ectotherms?


  Use their surroundings to warm their bodies. This includes all invertebrate animals, along with fish, amphibians, and reptiles.They cant control there body using their metabolism.
• How do fish maintain their temperature?

  The high heat capacity of the water means the temperature of their environment doesn't change.
• What are behavioral responses of Ectotherms to control there body temperature?

  - Basking in the sun- orientate their bodies to maximise SA exposured to sun- extend areas of their body to increase SA exposed to sun- absorb heat energy by conduction by pressing their bodies against the warm ground- Cool down by going into shade/water/mud or pressing body against cool surface
• What are physiological responses of Ectotherms to control there body temperature?

  - Dark colours more radiation- Vary their heart rate to increase or decrease the metabolic rate
• What are endotherms?

  They relay on their metabolic processes to warm up and they usually maintain a very stable core body temperature regardless of the environment. Their metabolic rate is 5 x higher than ectotherms
• How do endotherms detect temperature change?

  - Skin, detect changes in the surface temp.- Hypothalamus, receptors detect the temperature of blood combination of the two means body has can respond to actual change in the temp. of blood and can pre-empt possible problems
• How do endotherms cool down?

  - Vasodilation, arterioles dilate (get wider) increases blood flow to surface of skin, heat is lost by conduction-Increased sweating, sweat evaporates and heat is lost, cooling blood below the surface-Hairs or feathers muscles relax, so they lie flat, which aviods trapping an insulating layer of air
• How do endotherms warm up?


  - Vasoconstriction, arterioles constrict (get narrower) decreased blood flow to surface of skin. reducing heat loss by radiation- Decreased sweating, sweat production will stop- Hairs muscles erect, so they stand up, this traps an insulating layer of air - Shivering, rapid, involuntary contracting and relaxing of the large voluntary muscles in the body releasing heat energy
• What is excretion?


  The removal of metabolic waste from the body
• What are the 3 main metabolic waste products of the body?

  1. Carbon Dioxide2. Bile Pigments3. Urea
• What blood vessel brings oxygenated blood to the liver?

  Hepatic artery
• What does the hepatic portal vein do?

  Brings deoxygenated blood, rich in digested nutrients, from the small intestine to the liver
• What does the hepatic vein do?

  Takes deoxygenated blood away from the liver and joins the vena cava
• What is a lobule?

  Many vertical rows of hepatocytes arranged around a central vein
• Where in the body would you find a hepatocyte?

  The liver
• What are sinusoids?

  Capillaries which run along liver lobules
• Branches of which two vessels provide blood to the sinusoids?

  Hepatic artery and hepatic portal vein
• What are canaliculi?


  Fine ducts which carry bile from hepatocytes to the main bile duct
• In which direction do canaliculi run?

  The opposite direction to sinusoids
• Where are sinusoids and canaliculi found in lobules?


  Running in between columns of hepatocytes
• What do Kupffer cells in sinusoids do ?

  Phagocytose pathogens and old red blood cells
• What adaptations do sinusoids have?

  They are dilated and have discontinuous basement membranes, which not only allows for ready exchange of macromolecules but allows them to expand if necessary
• How many different metabolic functions are linked to the liver?

  500
• What adaptations do hepatocytes have?

  Lots of mitochondria and an enlarged Golgi apparatus, numerous microvilli in contact with sinusoids to maximise exchange
• Why do sinusoids and canaliculi run in opposite directions?

  To maximise exchange from hepatocytes
• What are the 9 basic functions of the liver?

  1. Gluconeogenesis2. Storage 3. Ornithine cycle4. Bile synthesis5. Production of plasma proteins6. Detoxification of poisons7. Synthesis of cholesterol from acetyl CoA8. Metabolism of amino acids, fats and carbohydrates9. Phagocytosis of old red blood cells
• How is bile formed?

  It is formed from haemoglobin, which is broken down after being taken from old red blood cells
• Where is bile formed?

  The liver
• Where is bile stored?

  The Gall Bladder
• How is excess blood glucose stored?

  Is converted to glycogen and stored in hepatocytes as granules
• How are blood glucose levels increased?

  The hormone glucagon (produced at alpha cells in the pancreas) causes hepatocytes to convert glycogen back into glucose, then release it into the blood
• What is transamination and where does it occur?

  The conversion of one amino acid into another. Occurs in the hepatocytes
• What is deamination?

  Where amine groups are removed from excess amino acids, forming ammonia and organic carboxylic acids
• What happens to the organic carboxylic acids produced during deamination?

  They can be respired to give ATP or converted to carbohydrates and stored as glycogen
• Why isn't ammonia excreted directly?

  It is too toxic