HUBS M4 Endocrine

• Homeostasis


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


  A variable for which there is a sensor and a system to ensure the variable is kept within a normal range, around a set-point
• Set-point


  The physiological value of any given variable, around which its normal range fluctuates

  
• Normal range


  The restricted set of values for a regulated variable, that permits optimal cell functioning
• Population reference range


  Tends to be wider than any given individual's normal range
• Most individuals (~95%) will have a set point that is within the population reference range
• Negative feedback control loop

  Keeps a regulated variable within its normal range, around its set-point
• Negative feedback control loop

  1. Sensors monitor the variable and detect changes

  2. Control centre compares variable's changed value to its set-point and sends signals to effectors if correction is required

  3. Effectors act to oppose the effect of the stimulus, thereby correcting the change and restoring the variable to its set-point
• Positive feedback control


  Drives a process to completion by amplifying the change to a regulated variable
• Positive feedback control loop


  1. Sensors monitor the variable and detect changes

  2. Control centre sends signals to effectors to amplify change

  3. Effectors' action amplifies the change, to drive a process to completion
• Differences between nervous and endocrine system control

  • Nervous system control: Homeostatic control, Sensory detection and interpretation, Control of muscle & movement, Higher functions
  • Endocrine system control: Homeostatic control, Cellular metabolism, Reproduction, Growth and development, Immunity and stress management
• Endocrine gland


  Cells that release hormones into the bloodstream
• Hormone


  Chemicals released by endocrine gland cells that travel through the blood and bind to receptors on target cells
• Receptor


  Binds to hormones on the target cell membrane or within the target cell
• Target cell


  Cell that responds to the hormone
• Differences between water-soluble and lipid-soluble hormones

  • Water-soluble hormones do not require carrier proteins to travel in the blood
  • Lipid-soluble hormones require carrier proteins to travel in the blood
  • Water-soluble hormones bind to receptors on the target cell membrane
  • Lipid-soluble hormones bind to intracellular receptors inside the target cell
  • Water-soluble hormones activate a second messenger system to produce a response
  • Lipid-soluble hormones stimulate creation of new proteins, often enzymes, to produce a response
• Hormones


  Chemicals released into the bloodstream by an endocrine gland/organ
• How hormones work


  1. Hormones bind to target cell receptors

  2. Hormones stimulate target cells to produce a response

  3. Hormone effects stop when hormones are removed
• Each hormone binds only to a receptor designed specifically to receive it
• Lipid-soluble hormones


  Slower-acting, longer-lasting hormones made from amines or cholesterol (e.g. thyroid or steroid hormones)
• Water-soluble hormones


  Faster-acting, short-lasting hormones made from amines, peptides or proteins (e.g. adrenaline, insulin, and most other hormones)
• Lipid-soluble hormone action mechanism


  1. Lipid-soluble hormone diffuses across plasma membrane

  2. Binds to receptor in cytosol OR in nucleus

  3. Causes gene activation, transcription and mRNA production and translation

  4. For protein (e.g. enzymes) synthesis

  5. The protein creates a cellular response
• Balance – homeostasis


  A relatively constant internal environment that supports cell functioning and life processes
• Water-soluble hormone action mechanism

  1. Water-soluble hormone binds to a membrane receptor on a target cell

  2. Activating the attached G-protein

  3. G-protein activates or inhibits 2nd messengers (e.g. cAMP or Ca2+)

  4. 2nd messengers affect actions of other proteins (e.g. enzymes or ion channels)
• Imbalance – loss of homeostasis


  As cells function they use up nutrients and produce biproducts
• A small amount of water-soluble hormone can cause a large response by activating 2nd messengers
• Hormones from these glands/organs are involved in

  • Homeostasis of plasma calcium and glucose concentrations
  • Growth and cell metabolism
  • Immunity and stress management
  • Endocrine disorders and disease
• Negative feedback control loops

  1. Keep a regulated variable within its normal range, around its set-point

  2. If the variable goes up, negative feedback brings it down

  3. If the variable goes down, negative feedback brings it up
• Homeostasis


  A relatively stable internal environment that supports cell function and body processes
• Regulated Variables


  • Core temperature
  • Plasma glucose concentration
  • Plasma calcium concentration
  • Basal metabolic rate
  • Many more...
• Hormones from these glands/organs are involved in homeostasis of plasma calcium and glucose concentration, growth and cell metabolism, immunity and stress management, and endocrine disorders and disease
• Normal range


  The restricted set of values for a regulated variable
• Plasma [Ca2+] Homeostasis


  • Why is plasma [Ca2+] regulated?
  • How does the body use Ca2+?
  • What are some dietary sources of Ca2+?
  • How does Ca2+ enter or exit the blood plasma?
  • Which glands/organs and hormones are involved in plasma [Ca2+] homeostasis?
  • How does the body correct hypocalcemia - low plasma [Ca2+]?
  • How does the body correct hypercalcemia - high plasma [Ca2+]?
• Set-point


  The physiological value around which the normal range fluctuates

  
• Population reference range


  The set of values for a regulated variable that are expected in a healthy population
• Negative feedback system


  The processes involved in reducing or correcting a change that has occurred to a regulated variable
• Why is plasma [Ca2+] regulated?

  There needs to be enough Ca2+ calcium in the blood for cells to use it when they need it
• Positive feedback system


  The processes involved in amplifying a change to a regulated variable, until an outcome is achieved
• Endocrine gland/organ


  A gland or organ that secretes hormones
• How the body uses Ca2+

  • Interacts with vesicles to facilitate release of neurotransmitter
  • Interacts with myofilaments in sarcomeres to facilitate cross-bridge formation
  • More than 99% of Ca2+ in the body is stored in bones (as hydroxyapatite)