Homeostasis

• What is homeostasis?

  The maintenance of a stable internal environment in the body despite fluctuations in internal and external conditions
• Why is homeostasis important?

  To ensure optimum conditions for enzymes and cellular processes in the body
• State three conditions within the body that must be controlled by homeostasis

  • Temperature

  • Blood glucose concentration

  • Water levels
• What is vasoconstriction?


  • Constriction of blood vessels near skin surface

  • Less blood flows close to the skin surface

  • Less heat lost to the surroundings
• Which organ is responsible for the maintenance of blood glucose concentrations?

  Pancreas
• How are blood glucose concentrations controlled?

  Controlled by the hormones insulin and glucagon which are secreted by the pancreas
• Insulin and glucagon are antagonistic hormones. What does this mean?

  They have opposite effects which counteract one another
• Describe the role of insulin in the regulation of blood sugar levels

  • Causes liver and muscle cells to increase their uptake of glucose from the blood

  • Glucose is converted into glycogen, a storage molecule
• Describe the role of glucagon in the regulation of blood sugar levels

  • Causes the breakdown of glycogen to glucose in the liver

  • Glucose is released into the blood
• What is the control of blood glucose concentration an example of?

  Negative feedback
• Describe what happens when blood glucose concentration becomes too high

  • Blood glucose concentration increases above a set point

  • Pancreas secretes insulin and stops producing glucagon

  • Liver and muscle cells increase uptake of glucose

  • Glucose is converted to glycogen and stored

  • Some glucose may be stored as lipid in tissues

  • Blood glucose concentration decreases, returning to normal level
• Describe what happens when blood glucose concentrations become too low

  • Blood glucose concentration decreases below a set point

  • Pancreas secretes glucagon and stops producing insulin

  • Liver cells convert glycogen into glucose which is released into the blood

  • Blood glucose concentration increases, returning to normal level
• What is diabetes?


  A condition where the homeostatic control of blood glucose levels stops working
• What is the cause of type 1 diabetes?

  Pancreas does not produce enough insulin
• How is type 1 diabetes treated?

  • Daily insulin injections at meal times

  • Limiting intake of refined sugars

  • Regular exercise
• What is the cause of type 2 diabetes?

  Person develops insulin resistance or doesn’t produce enough insulin (often due to obesity)
• How is type 2 diabetes treated?

  • Balanced diet (eating fewer simple sugars and replacing them with more complex carbohydrates)

  • Exercise

  • Medication or insulin injections (however these are less effective)
• How does exercise help to control diabetes?

  • Exercise increases respiration in muscle cells

  • Excess glucose is removed from the blood to produce energy in the form of ATP
• Why are type 2 diabetics advised to replace simple carbohydrates with more complex carbohydrates?


  • Simple carbohydrates are broken down quickly so can raise blood glucose levels rapidly

  • Complex carbohydrates take longer to break down so have a reduced effect on blood glucose levels
• What is the Body Mass Index?

  A value based on height and mass used to categorise an individual as underweight, normal weight, overweight or obese
• How is BMI calculated?

  Mass (kg) / height^2 (m)
• What BMI values indicate obesity and an increased risk of type 2 diabetes?

  30 or higher
• How is an individual’s waist-to-hip ratio calculated?

  Waist circumference (cm) / hip circumference (cm)
• What does a waist-to-hip ratio higher than 1.0 in males or 0.85 in females indicate?

  • Abdominal obesity

  • Increased risk of developing type 2 diabetes
• What is osmoregulation?

  The maintenance of constant water levels in the body fluids of an organism
• How is the concentration and volume of urine controlled?

  Controlled by the secretion of anti-diuretic hormone (ADH)
• What produces ADH?

  Pituitary gland
• Describe how ADH affects the reabsorption of water from the kidney tubules

  ADH increases the permeability of the collecting ducts, enabling more water to be reabsorbed into the blood
• What is required to maintain the ideal water content of blood?

  A negative feedback system involving :

  • Receptors in the hypothalamus

  • Hypothalamus

  • Effector i.e. pituitary gland
• Describe the negative feedback loop which occurs when low blood water concentration is detected

  • Receptors detect low blood water content and send information to the hypothalamus. This coordinates the information and sends instructions to the pituitary gland

  • Pituitary gland increases ADH secretion. ADH increases collecting duct permeability so more water is reabsorbed

  • Blood water content increases. More concentrated urine is produced
• Describe the negative feedback loop which occurs when high blood water concentration is detected

  • Receptors detect high blood water content and send information to the hypothalamus. This coordinates the information and sends instructions to the pituitary gland

  • Pituitary gland secretes less ADH. Collecting duct becomes less permeable so less water is reabsorbed

  • Blood water content decreases. More dilute urine is produced