IGCSE - Biology
Homeostasis (Part 1)
Shervin Koohi
Definition
 Sef-regulating process of the body aimed at keeping the internal environment of the body
constant by adjusting to conditions that are optimal for survival.
 Why?
 To help the cells work as efficiently as possible.
Examples
 Controlling blood glucose concentration
 Controlling body temprature
 Removal of urea, toxins, excess water and ions by the kidneys
Controlling blood glucose concentration
 Importance of glucose:
 Cells need a steady supply of glucose to allow them to respire
 No glucose -> No energy! -> cell death
Controlling blood glucose concentration
 Problems with too much glucose
 It can create an osmotic gradient -> water moves out of the cells and into the blood -> cells shrink
and will not have enough water to carry on their normal metabolic process
Controlling blood glucose concentration
 How is blood glucose controlled
 Hormones (Insulin + Glucagon)
 Secreted by pancreas
 Role of insulin -> REDUCE glucose contentration in the blood
 Role of Glucagon -> INCREASE glucose concentration in the blood
https://www.youtube.com/watch?v=OHrX3X3LGzI
Controlling blood glucose concentration
 Pancreas
 Two glands in one
 1. Ordinary gland cells (MOST of pancreas)-> makes pancreatic juice -> flows along the pancreatic duct
into the duodenum
 2. Islet cells -> Make hormones (Insulin + Glucagon) -> secreted into Liver
 Glucagon -> causes liver to break down glycogen into glucose -> glucose released to blood -> increase of
concentration and normal glucose levels
Controlling blood glucose concentration
 Insulin & glucagon work by a system of Negative Feedback
 3 components of negative feedback:
 Set point (range of normal values)
 Normal blood glucose concentration: 0.8 – 1.1 mg/cm3
 We have 5 dm3 of blood -> 4g of circulating glucose
 Pancreas & liver work together to keep the values within the set points
 Receptors (measuring device) -> to keep track of the level
 If the level goes outside of the set point -> events get triggered to bring it back
Controlling blood glucose concentration
 Insulin
 -> causes liver to absorb glucose from the blood
 -> some is used for respiration -> by breaking it down to carbon dioxide & water
 -> some is converted into glycogen (insoluble polysaccharide) -> to be stored in the liver
 Goal -> blood glucose falls back to normal
Controlling blood glucose concentration
 Glucagon
 -> causes liver to break down glycogen into glucose -> glucose released to blood
 Goal -> increase of concentration and normal glucose levels
Controlling blood glucose concentration
Controlling blood glucose concentration
 What can push the concentration beyond / below the set points?
Controlling blood glucose concentration
Diabetes
https://www.youtube.com/watch?v=bFnO8Uc9gjQ
Definition
 Diabetes is a chronic disease that occurs either when the pancreas does not produce
enough insulin or when the body cannot effectively use the insulin it produces. (WHO)
Type I Diabetes
 The Islet cells that produce insulin die
 Why?
 Autoimmune -> body’s own immune system attacks and destroys the cells
 Usually appears at a young age
Type I Diabetes
 What if a patient with Type I Diabetes eats too much carbohydrates?
 Normally, this would trigger an increase in the secretion of insulin, but in these patients it cannot
happen
 This causes the glucose concentration to stay above the set point and remain high
 Symptoms: Dry mouth – Blurred vision – feeling thirsty – increase in heart rate & breathing rate
Type I Diabetes
 What if a patient with Type I diabetes does not eat carbohydrates for a long time?
 In these patients, there is no built up stores of glycogen (because there is no insulin secreted
previously to trigger liver to turn the extra glucose into glycogen)
 This means that they do not have glucose to compensate for the low blood sugar -> blood sugar
levels drop and remain below the set point -> cells will not have enough energy
 Symptoms: feeling tired – confusion - irrational behaviour – eventually loss of consciousness
 What should they do when this happens? Eat something sweet!
Type I Diabetes
 Treatment:
 The patient should the blood sugar levels frequently
 The patient should be educated on how much carbohydrates to eat, and should balance his
intake / day
 Most patients, will need an insulin injcetion
 Rapid acting insulin -> before/after eating a meal
 Long-acting insulin -> for a ‘background dose’ of insulin. To be taken daily at the same time
Type I Diabetes
Type I Diabetes