Endocrine

• What is homeostasis?


  a constant internal environment that supports cell functioning and life processes
• What is a regulated variable?

  A variable for which there is a sensor and a system to ensure the variable is kept with a normal range, around a set point
• What is the normal range?

  The restricted set of values for a regulated variable that permits optimal cell functioning
• What is the set point?

  the physiological value of any given variable, around which its normal range fluctuates (can only go to a certain value safely). Each person has a unique set point for every variable
• What’s the difference between a population reference range and an individuals normal range?

  Population reference range: Range of values for a specific test that includes 95% of the healthy population. Individual's normal range: Range of values specific to an individual based on their own health history and baseline levels.

  An individuals normal range can be different to the population reference range and if someone is outside of their normal range it can lead to illness, disease or symptoms of a disorder, even if they are in the population reference range
• How do negative feedback loops maintain homeostasis?

  if a variable goes up, negative feedback brings it back down and vice versa to keep it within its normal range, around its set point.
• What are the 3 characteristics of a negative feedback loop?

  • sensors - monitor stimulus and variable to detect changes.
  • control centre - compare variables changed value to its set point and send signals to effectors when change is needed (action potential and hormones)
  • Effectors - take action by opposing the stimulus and correct change, bringing variable back to its set point
• What is positive feedback control?

  • not for homeostasis
  • drives a process to completion by amplifying the change to a regulated variable (keeps making variable change till it reaches the desired point)
  • if the variable goes up, it makes it go up more and vice versa
• What are the characteristics of a positive feedback loop?

  • sensors - monitor variable and stimulus and detect changes
  • control centre - send signals to effector to amplify change
  • effectors - action that amplifies the change, to drive a process to completion
• Nervous system and endocrine system communication control systems

  • Both use homeostatic control
  • Nervous system controls sensory detection, interpretation, and muscle control/movement
  • Endocrine system controls cellular metabolism, reproduction, and growth and development
  • Nervous system manages brain functions
  • Endocrine system manages immunity and stress
• Nervous system

  Uses neurons, action potentials and neurotransmitters
• Endocrine system

  Releases hormones into the blood
• Neurotransmitters

  Bind to chemically gated ion channels on post-synaptic cells, so it is fast
• Hormones


  Bind to the membrane or intercellular receptors of target cells, so it is slower but longer lasting
• What are the endocrine glands?

  • hypothalamus
  • parathyroid gland
  • pituitary gland
  • thyroid gland
  • adrenal glands
  • Pancreas
• What are hormones?

  chemicals make from amino acids or cholesterol, released by endocrine gland cells that travel through the blood and bind to receptors on the target cell membrane or within the target cell
• What do lipid soluble hormones require to travel through the blood?

  Carrier proteins
• How do lipid soluble hormones work?

  Diffuse into cells across plasma membranes and bind to intracellular receptors inside the targets cells cytosol or nucleus. Each hormone will only bind to a receptor designed to receive it. It will then stimulate creation of new proteins (enzymes) to produce a response. The effects of the hormone will only stop when it unbinds from the receptor. The excess hormone will get broken down, recycled and excreted in sweat, urine or feces.
• How do water soluble hormones work?

  bind to receptors on the membrane of a target cell because they cannot cross it. They will only bind to a receptor that is designed to receive it. They will activate a second messenger system to produce a response (eg activate enzyme to make heart rate increase). The effect will stop when the hormone unbinds from the receptor. The excess will get broken down, recycled and excreted in sweat, urine or feces
• What are the 6 characteristic differences between lipid and water soluble hormones?

  lipids: amines (thyroid hormones - steroids), thyroid hormones are pre-made and stored but steroids are made as required. Binds to carrier protein. Uses intracellular receptor. Stimulates transcription to make new proteins. Slow response

  water: amines (catecholamines - peptides and proteins), all are pre-made and stored. doesn’t bind to carrier protein. uses plasma membrane receptors. Activates second messenger for an amplified response. Fast response (because of being premade)
• what are some examples for lipid and water soluble hormones?

  lipid: cortisol and thyroid hormones

  water: adrenaline and most other hormones
• What do the thyroid and parathyroid glands control the homeostasis of?

  plasma calcium concentration
• Why is plasma regulated?

  so there is a satisfactory amount of Ca2+ in the blood for cells to be able to use it
• How does the body use Ca2+?

  • as the second messenger for water soluble hormones
  • interact with vesicles to release neurotransmitters
  • interact with myofilaments to facilitate cross bridge formation and to make the bones strong
• How does Ca2+ enter/exit the blood plasma?

  • absorbed into blood from digestive tract, broken down bone (by osteoclasts) or kidneys
  • Removed by osteoblasts for bone remodeling/growth and filtered out by kidneys
• What hormones are involved in plasma homeostasis?

  parathyroid hormone (PTH) and calcitriol
• What glands are involved in plasma homeostasis?

  • parathyroid glands (posterior of thyroid glands)
  • kidneys
  • thyroid gland (around trachea / windpipe)
  • bones ( parathyroid, calcitriol and calcitonin affect release/removal of Ca2+ from bone)
  • digestive system (under the influence of calcitriol)
• How does the body correct hypocalcemia?

  A parathyroid glands detect the decrease and compares it to the set point, then releases more parathyroid hormone (PTH). The osteoclasts will break more bone down to increase Ca2+ in plasma. The kidneys will filter more Ca2+ from the urine into the plasma and convert more vitamin D to calcitriol to trigger the digestive tract to absorb more Ca2+ from food. When the plasma increase it will negatively feedback to the parathyroid glands and reduce parathyroid hormone (PTH) release.
• How does the body correct hypercalcemia?

  A parathyroid glands detect the increase of Ca2+ and compares it to the set point, then releases less parathyroid hormone (PTH). The osteoclasts will break less bone down to decrease Ca2+ in plasma. The kidneys will filter less Ca2+ from the urine into the plasma and convert less vitamin D to calcitriol to notify the digestive tract to absorb less Ca2+ from food. When the plasma decerases it will negatively feedback to the parathyroid glands and increase parathyroid hormone (PTH) release.
• What does the pancreas control the homeostasis of?

  glucose concentration
• Why is the plasma glucose concentration regulated?

  because there needs to be enough glucose in the blood for cells to use it when they need it
• How does the body use glucose?

  as the main substrate for making ATP, and also to make other essential substances like glycoproteins
• How is glucose obtained and stored?

  taken from our food / diet and stored as glycogen or fat
• How does glucose enter/exit the blood plasma?

  absorbed into blood from the digestive tract or released by liver (new or from glycogen)

  can be removed by all body cells, and stored as glycogen in liver, skeletal muscle and adipose (fat)
• When do cells use more glucose?

  during periods of growth, stress and exercise (higher metabolism)
• Which organs and hormones are involved in plasma homeostasis?

  pancreas - secretes glucagon from alpha islet and insulin from beta islet (secreted by pancreatic islet cells)
• What does glucagon do?

  signals liver to release glucose into the plasma by creating new glucose and breaking down glycogen into glucose
• What does insulin do?

  signals all body cells to use the glucose to make ATP (for energy), they can only do this if insulin tells them they can.
• What is the difference between the fasting and fed metabolic states?

  The glucose levels are much higher in a fed metabolic state
• How does the body correct hypoglycaemia?

  fasting state: alpha inset cells of the pancreas detect low glucose, compare it to the set point and release glucagon (receptors for this hormone are on the liver cells). This stimulates the liver to use gluconeogenesis, glycogenelysis and ketone synthesis to release glucose and ketones into the blood. When the plasma concentration increases it will negatively feedback to the alpha islet cells to reduce glucagon release