Homeostatic Control

• Homeostasis


  A relatively constant internal environment which supports optimal cell functioning and life processes
• Regulated variable


  A variable for which there is a sensor and a system to ensure that the variable is kept within a normal range, around an individual's set point
• Normal range


  The restricted set of values for a regulated variable which permits optimal cell functioning
• Regulated variables move outside of the normal range


  May lead to illness, disease or symptoms of disorder
• Set point


  The physiological value of any given variable which is considered normal and/or healthy
• Population reference range


  The set of values for a regulated variable which are considered normal and/or healthy
• The population reference range is wider than the individual normal ranges
• Negative feedback loop


  A control loop which keeps a regulated variable within its normal range, around the set point
• Function of a negative feedback loop

  To maintain homeostasis
• Components of a negative feedback loop

  • Sensor
  • Control center
  • Effector
• Positive feedback loop


  A control loop which drives a process to completion by amplifying a change to achieve a desired outcome
• Components of a positive feedback loop

  • Sensor
  • Control center
  • Effector
• Main functions of the endocrine system


  • Cellular metabolism
  • Reproduction
  • Growth and development
  • Immunity and stress management
• Hormones


  Chemicals which are released into the bloodstream
• Main endocrine glands


  • Hypothalamus
  • Pituitary gland
  • Thyroid gland
  • Parathyroid gland
  • Adrenal glands
  • Pancreas
• Lipid soluble hormones


  Hormones which require proteins in order to travel through the blood, can easily diffuse across membranes, bind to intracellular receptors, made as required and stimulate the creation of new proteins
• Water soluble hormones


  Hormones which can travel freely through the blood, cannot cross membranes so bind to receptors on the membranes of target cells and activate a 2nd messenger. All water soluble hormones are pre made and stored
• Why is plasma calcium regulated


  so there is enough calcium in the blood for cells when they need to use it
• How calcium is used in the body


  • Activates or inhibits 2nd messengers
  • Interacts with vesicles to release neurotransmitters
  • Interacts with myofilaments to facilitate cross bridge formation
  • Makes bones hard
• How calcium enters the plasma


  1. Being eaten, entering the digestive tract and then being absorbed into the plasma

  2. Being released into the plasma from osteoclasts breaking down bone

  3. Being reabsorbed back into the plasma from the kidneys
• How calcium exits the plasma


  1. Being removed from the plasma by osteoblasts to make bone

  2. Being filtered out of the plasma by the kidneys
• Glands/organs involved in calcium regulation

  • Thyroid gland
  • Parathyroid glands
  • Kidneys
  • Bones
  • Digestive system
• Hypocalcemia


  Low plasma calcium concentration
• Sensor and control center for hypocalcemia

  Parathyroid glands
• Hormone released by parathyroid glands in response to hypocalcemia

  Parathyroid hormone (PTH)
• Cells with PTH receptors responding to hypocalcemia

  • Bone
  • Kidneys
• What does PTH signals for in the bones in response to hypocalcemia

  More calcium reabsorption by osteoclasts
• What does PTH signals for in the kidneys in response to hypocalcemia

  1. More calcium reabsorption from the pre-urine filter

  2. More vitamin D to be converted into calcitriol, extracting more calcium from the digestive tract
• Hypercalcemia


  High plasma calcium concentration
• Sensor and control center for hypercalcemia

  Parathyroid glands
• Hormone released by parathyroid glands in response to hypercalcemia

  Parathyroid hormone (PTH)
• Cells with PTH receptors responding to hypercalcemia

  • Bones
  • Kidneys
• What does parathyroid hormone (PTH) signal for in the bones in response to hypercalcemia

  Less calcium reabsorption by osteoclasts
• What does parathyroid hormone (PTH) signal for in the kidneys in response to hypercalcemia

  1. Less calcium reabsorption from the pre-urine filter

  2. Less vitamin D to be converted to calcitriol, extracting less calcium from the digestive tract
• Why is plasma glucose regulated


  so there is enough glucose in the plasma for cells when they need to use it
• How glucose is used in the body


  • Make ATP
  • Makes glycoproteins
  • Stored as glycogen
• How glucose enters the plasma


  1. Being eaten, entering the digestive tract and then being absorbed into the plasma

  2. Being released into the plasma from the liver
• How glucose exits the plasma


  1. Used by all body cells

  2. Stored in the liver and skeletal muscles as glycogen

  3. Stored in adipose as fat
• Organs involved in plasma glucose regulation

  • Pancreas
  • Liver
• Hormones released by the pancreas

  • Glucagon
  • Insulin