Homeostasis: Blood glucose control

• What is homeostasis?


  - the maintenance of a constant internal environment despite changes in the external environment

  
  

  -The internal environment of mammals is the blood and tissue fluid that bathes all the cells of the body
• What is the pH of blood tightly regulated to be by homeostasis ?

  7.35-7.45
• What happens if blood pH is too high (alkaline) or too low (acidic)

  - enzymes become denatured

  
  

  - H bonds that hold tertiary structure broken

  
  

  - changing shape of active site so enzyme substrate complexes can't be formed

  
  

  - enzyme no longer works as catalyst so metabolic reaction less efficient
• what happens if body temperature is too low

  - rate of enzyme activity reduced

  
  

  - slowing metabolic rate

  
  

  - cells can't respire fast enough to produce enough ATP

  
  

  below 35 (symptoms of hypothermia)
• What happens if core temp too high ?

  -hydrogen bonds break

  
  

  - tertiary structure changes

  
  

  - the active site changes shape and the substrate no longer fits

  
  

  -enzyme substrate complexes can no longer form

  
  

  -the higher the temperature the more enzyme molecules will denature
• Explain why high blood glucose concentration (hyperglycaemia) is potentially dangerous.

  • Water potential of blood decreases

  
  

  • Water enters the blood from cells & tissues by osmosis •

  
  

  Organs, e.g. the brain, may become dehydrated - important metabolic reactions may not occur optimally

  
  

  • Blood pressure will increase, potentially leading to cardiovascular disease.
• Explain why low blood glucose concentration (hypoglycaemia ) is potentially dangerous

  • Cells may not have enough glucose to maintain respiration rates

  
  

  . Water potential of blood increases

  
  

  • Water leaves the blood and enters cells & tissues by osmosis

  
  

  • Organs, e.g. the brain, may swell up resulting in damage

  
  

  • Blood pressure will decrease, causing fainting
• What is negative feedback?

  Homeostatic systems (control of body temperature) detect and respond to changes by a control mechanism

  
  

  · A change from a set point is detected and this brings about physiological mechanisms to return to the set point, resulting in negative feedback loops

  
  

  · This maintains core body temperature at around 37oC
• What is positive feedback ?


  -any change away from the norm creates more change

  
  

  Eg. When core temp drops below 35oC a positive feedback mechanism develops that makes temperatures fall even further

  
  

  As body temp falls, the brain does not work properly, shivering stops and

  core temperature falls even lower, resulting in hypothermia.
• What is the role of the islets of langerhans?

  -Receptors in the Islets of Langerhans in the pancreas detect changes in blood glucose concentrations.
• What happens if blood glucose levels increase?


  .Receptors on β cells (beta cells) in the Islets of Langerhans detect the

  increase

  
  

  · β cells secrete insulin into the bloodstream

  
  

  · Insulin binds to specific protein receptors on the membrane of its target cells

  (mainly liver and muscle cells).
• How does this cause a reduction in blood glucose conc

  - glucose enters cells by facilitated diffusion through specific channel protein

  
  

  - insulin causes more of these channel proteins to be inserted into cell membrane

  
  

  - increases permeability of the membrane for glucose
• What is glycogenesis ?

  -Insulin activates enzymes which convert glucose to glycogen in the liver and muscle cells

  
  

  Glycogen can be stored.
• what else does insulin activate?

  enzymes which convert glucose to fats for storage in adipose tissue
• What happens if blood glucose levels decrease (after exercise)

  -Receptors on α cells (alpha cells) in the Islets of Langerhans detect the decrease

  
  

  - α cells release glucagon into the bloodstream

  
  

  -Glucagon binds to specific protein receptors on the membranes of its target cells
• How does this cause an increase in blood glucose conc ?

  Glycogenolysis :

  
  

  Glucagon activates enzymes which catalyse conversion of glycogen to glucose

  
  

  Gluconeogenesis:

  
  

  Glucagon activates enzymes which stimulate conversion of amino acids and glycerol to glucose
• General hormon action


  - produced by endocrine glands

  
  

  - transported in blood to target cells in other organs of the body

  
  

  - target cells have specific receptor proteins in plasma membrane or in cytoplasm
• Explain what makes a protein receptor specific ?

  -Each will have a specific tertiary structure which only a hormone with a complementary shape will be able to bind to (receptor has a specific binding site)
• What is the role of adrenaline?


  - secreted from adrenal glands when blood glucose conc is low (exercise)

  
  

  - binds to receptors on cell membrane of liver cells
• How does adrenaline lead to increases blood glucose conc

  - activates an enzyme that causes conversion of glycogen to glucose

  
  

  
  

  - INACTIVATING an enzyme that synthesises glycogen from glucose

  
  

  glucose then passes out of cells into blood raising blood glucose conc
• Second messenger model of hormone action ADRENALINE.

  - adrenaline approaches receptor site in liver cell

  
  

  -adrenaline attaches to receptor site so activates adenylate cyclase inside membrane

  
  

  - activated adenylate cyclase converts ATP to cyclic AMP (cAMP) acts as second messenger

  
  

  - activates protein kinase A

  
  

  - Protein kinase A activates chain of reactions that breaks down glycogen to glucose
• What is the cause of type 1 diabetes

  (insulin dependent )


  · β cells do not produce insulin

  
  

  · Maybe due to an autoimmune response where the body's immune system destroys the β cells

  
  

  · Usually appears in childhood.
• what are the effects of type 1 diabetes?

  -Hyperglycaemia - blood glucose concentrations rise and stay high for a long period of time after eating. This can be fatal

  
  

  
  

  · Kidneys cannot reabsorb all the glucose so some is excreted in the urine.
• What is the treatment of blood glucose concentrations

  -Blood glucose concentrations must be monitored regularly.

  
  

  
  

  -This can be done using a glucose biosensor

  
  

  · Insulin injections - the amount must match glucose intake

  
  

  · Management of diet and exercise to avoid hypoglycaemia (where glucose concentrations drop too low).
• Q. Why can insulin not be given orally in tablet form?

  It is a protein and so will be hydrolysed in the stomach and small intestine by proteases / denatured by low pH of stomach
• What is the cause of type II diabetes

  · gradual loss in the responsiveness of target cells to insulin due to receptor abnormalities

  
  

  · This type is more common (70% of cases in UK) and usually occurs later in life

  
  

  · Often linked with obesity. Other risk factors include age, lack of exercise and poor diet
• What is the treatment of type II diabetes?

  -careful regulation of diet, (especially sugar intake) and exercise

  
  

  
  

  · Losing weight may be advised

  
  

  · Eventually insulin injections may be necessary to control blood glucose concentration.
• Diagnostic features of type II diabetes

  · High blood glucose levels

  
  

  · Kidney is unable to reabsorb all the glucose

  so some appears in the urine

  
  

  · Persistent thirst

  
  

  · Frequent urination

  
  

  · Craving for sweet foods
• What are the health impacts of type II diabetes

  Increased risk of cardiovascular

  disease, blindness, amputation, kidney

  disease and depression
• Economic impacts of type II diabetes

  2018

  Cost to NHS for treatment, intervention and complications - £14 billion /year

  
  

  Cost of absenteeism from work - £8.4 billion

  
  

  
  

  Early retirement costs - £6.9 billion
• Q. What recommendations might heath advisors make to the public to reduce the incidence of type II diabetes?

  Eat a diet low in fat and sugar to lower calorie intake and so reduce risk of obesity;

  
  

  Take regular exercise to increase energy expenditure to reduce risk of obesity;

  
  

  Lose weight if necessary/ reach healthy BMI;
• Q. How might food and drink manufacturers attempt to make their products healthier?

  Reduce portion size to reduce calorie intake and reduce risk of obesity;

  
  

  Use low calorie sweeteners to reduce mass/calories of sugars in products;

  
  

  Reduce sugar salt and fat content of foods to lower calorie intake and reduce risk of obesity/hypertension;
• Q. Why might food and drink manufacturers be reluctant to make their products healthier?

  -Changing the formulation of their products may alter the taste, and so customers may not like the new taste and not buy the product any more this would decrease profits;

  
  

  
  

  Many customers know what they are eating and do not want to be forced to take healthy options (autonomy)