Chapter 9

• What is homeostasis?


  Homeostasis is the maintenance of a constant internal environment.
• How does homeostasis help organisms?

  • It allows organisms to be independent of changes in the external environment.
• What is the role of enzymes in the body regarding temperature?

  Enzymes in the body can only work within a certain range of temperatures.
• What happens to enzymes below the optimum temperature?

  Below the optimum temperature, enzymes will be inactivated.
• What happens to enzymes beyond the optimum temperature?

  Beyond the optimum temperature, enzymes will be denatured.
• Why is high fever considered fatal in relation to enzymes?

  High fever can denature enzymes, disrupting vital biological processes.
• What must be maintained in blood plasma and tissue fluid for homeostasis?

  The composition of blood plasma and tissue fluid needs to be kept within narrow limits.
• How do changes in water potential affect body cells?

  Changes in water potential can cause cells to either crenate or burst.
• What is the normal blood glucose concentration range?

  The normal blood glucose concentration is 70 – 90 mg of glucose per 100 cm³ of blood.
• What happens to blood glucose levels after a sugary meal?

  Blood glucose levels rise after a sugary meal.
• What happens to blood glucose levels after vigorous activities?

  Blood glucose levels drop after vigorous activities.
• What is the negative feedback process in homeostasis?

  • Homeostatic control occurs when the body reacts to bring about an opposite effect to the changes detected.
  • This is known as the negative feedback process.
• What is required for negative feedback to take place?

  There must be a normal set point, a stimulus, receptors, and a corrective mechanism.
• What is a hormone?


  A hormone is a chemical substance produced in minute quantities by an endocrine gland, carried by the blood, which alters the activity of one or more specific target organs.
• How do hormones affect the body?

  Hormones help to control and coordinate body activities.
• What can happen if too much or too little hormones are produced?

  The organism can be adversely affected if too much or too little hormones are produced.
• What are the two types of glands in the body?

  The two types of glands are endocrine glands and exocrine glands.
• What is the function of endocrine glands?

  Endocrine glands are ductless glands that transport their secretions through the bloodstream.
• What is the role of the pituitary gland?

  The pituitary gland is referred to as the 'master gland' and secretes many hormones that control the secretion of other hormones.
• What does the hypothalamus do?

  The hypothalamus regulates the secretion of some hormones, including those secreted by the pituitary gland.
• What hormones do the ovaries secrete?

  The ovaries secrete oestrogen and progesterone.
• What hormones do the testes secrete?

  The testes secrete testosterone.
• What is the summary of endocrine glands and their hormonal secretions?

  • Pituitary gland: Secretes hormones that control other endocrine glands.
  • Hypothalamus: Regulates the secretion of some pituitary hormones.
  • Pancreas: Secretes insulin and glucagon.
  • Testes: Secrete testosterone.
  • Ovary: Secretes oestrogen and progesterone.
• What is osmoregulation?


  Osmoregulation is the process through which blood water potential is maintained.
• How do antidiuretic hormones (ADH) affect blood water potential?

  ADH acts on the kidneys to regulate blood water potential by affecting the reabsorption of water.
• What happens when blood water potential increases?

  • Stimulus: Water potential of blood increases.
  • Receptor: Hypothalamus detects the stimulus.
  • Corrective Mechanism: Pituitary gland releases less ADH.
  • Result: Less water is reabsorbed, more water is excreted, and larger volume of urine is produced.
• What happens when blood water potential decreases?

  • Stimulus: Water potential of blood decreases.
  • Receptor: Hypothalamus detects the stimulus.
  • Corrective Mechanism: Pituitary gland releases more ADH.
  • Result: More water is reabsorbed, less water is excreted, and smaller volume of urine is produced.
• What happens to insulin secretion when blood glucose concentration is high?


  The islets of Langerhans in the pancreas increase the secretion of insulin.
• How does insulin affect blood glucose concentration?

  Insulin decreases blood glucose concentration by stimulating glucose utilization by body cells.
• How does insulin decrease blood glucose concentration?

  • Stimulates liver and muscle cells to convert glucose into glycogen for storage.
  • Makes cell membranes more permeable to glucose to increase uptake.
  • Increases the use of glucose during tissue respiration.
• What are the effects of lack of insulin secretion?

  Lack of insulin secretion results in abnormally high blood glucose concentration and symptoms like weakness and weight loss.
• What are the effects of over-secretion of insulin?

  Over-secretion of insulin results in abnormally low blood glucose concentration and symptoms like hunger and irritability.
• What happens when blood glucose concentration is low?

  The islets of Langerhans in the pancreas increase the secretion of glucagon.
• How does glucagon increase blood glucose concentration?

  Glucagon increases blood glucose concentration by stimulating the liver to convert glycogen to glucose.
• What are the effects of glucagon on blood glucose concentration?

  • Stimulates the liver to convert glycogen to glucose.
  • Stimulates the liver to convert fats and amino acids to glucose.
• What happens when blood glucose concentration increases?

  • Stimulus: Glucose concentration of blood increases.
  • Receptor: Detected by the pancreas.
  • Corrective Mechanism: Pancreas releases insulin.
  • Result: Blood glucose concentration decreases.
• What are some symptoms of diabetes mellitus?

  Weak body, continual weight loss, and glucose present in urine
• What condition could result from the symptoms of weak body, continual weight loss, and glucose in urine?

  Diabetes mellitus
• What happens when there is an over-secretion of insulin?

  It results in abnormally low blood glucose concentration
• What are some symptoms of over-secretion of insulin?

  Hunger, rapid heartbeat, and irritability