L2: Physiology (Homeostasis)

• What is the concept of homeostasis?

  Control of internal environment in metazoans
• What are conformers in the context of homeostasis?

  Primitive organisms restricted to constant environments
• How do regulators differ from conformers?

  Regulators control their internal environment
• What percentage of total body weight is body water?

  60%
• What is the composition of the internal environment in terms of body water?

  33% extracellular fluid, 67% intracellular fluid
• Why is extracellular fluid (ECF) more important than intracellular fluid (ICF)?

  ECF is changeable with the outside world
• What can lead to illness in relation to homeostasis?

  Changes to internal environment from regulatory failure
• How does a block of blood supply affect the body?

  Reduces oxygen and glucose, leading to cell death
• How do microorganisms cause infections related to homeostasis?

  By disturbing the internal environment
• What does cholera toxin do in the intestine?

  Stimulates chlorine ion secretion into the lumen
• What is the result of cholera toxin's action?

  Causes watery defecation leading to dehydration
• What is the function of haemoglobin in homeostasis?

  Buffers oxygen levels by releasing it when low
• Why are low oxygen levels harmful?

  They can lead to cell death
• What is the product of aerobic respiration?

  Water and carbon dioxide
• What is the enthalpy change of combustion represented by?

  $\Delta H_c$
• How is carbon dioxide controlled in the body?

  Through the respiratory system
• What happens during hyperventilation?

  Decreases plasma carbon dioxide levels
• What happens during hypoventilation?

  Increases plasma carbon dioxide levels
• What are electrolytes?

  Ionic compounds dissolved in water
• What is the role of electrolytes in the body?

  Control body fluids and conduct electricity
• How is blood sugar regulated?

  Through the digestive system
• What system regulates acid-base balance?

  Renal system
• What system regulates blood pressure?

  Cardiovascular system
• What part of the brain acts as the body's thermostat?

  Hypothalamus
• What initiates thermoregulatory responses?

  Afferent inputs from thermoreceptors
• What is the role of negative feedback mechanisms?

  Maintain a variable within a given range
• What are the components of negative feedback mechanisms?

  • Set point
  • Sensor
  • Comparator
  • Effector
• What is the role of the comparator in negative feedback?

  Detect any error between sensor and set point
• What is the effector's role in negative feedback?

  Bring compensatory change
• How does insulin regulate blood sugar?

  Allows glucose to enter tissues from blood
• What does glucagon do in blood sugar regulation?

  Causes glucose to enter blood from tissues
• What is positive feedback mechanism?

  • Effector system reinforces the initiating stimuli
  • Examples:

  1. Blood clot formation
  2. Oxytocin stimulation during labor
• What initiates the positive feedback during childbirth?

  Stretching of the cervix
• What does oxytocin do during labor?

  Stimulates uterine contractions
• What happens to the positive feedback loop at birth?

  Stretching of cervix lessens, feedback is broken
• What is the water content in fat and muscle tissues?

  Fat = 20%, Muscle = 65%
• Why must fluid intake and output be balanced?

  To maintain homeostasis in the body
• What is the permeability of capillary walls?

  Freely permeable to small molecules
• What regulates the transport of substances across the plasma membrane?

  Selectively permeable barrier
• How does water enter the body?

  Through drinking or eating