homeostatis

  • homestatis is how the body keeps itself in physiological limits
    • body temperature
    • blood glucose
    • amount of hydration
    • energy balance - eating, exercise and growth
  • it sounds like it happens automatically
    • but we contribute homeostasis with voluntary actions
  • classical homeostasis
    • study involving the hypothalamus
  • less classical view of homeostasis
    • thermoregulation
    • voiding
    • breathing
    • sleep-wake cycle

hypothalamic anatomy

  • diencephalon is the inner bulk of the brain
  • hypothalamus is below the thalamus, in the diencephalon
  • hypothalamus is above the pituitary gland
  • the thalamus and the hypothalamus are connected to the mid brain in the back

  • in the front is the nose

  • the hypothalamus controls the pituitary
    • the pituitary pumps out hormones
  • hypothalamic targets
    • skeletal muscles
    • cardiac muscles
    • smooth muscles
    • glands
    • telencephalon
  • hypothalamus is the chief controller
    • coordinates between different homeostatic functions

pituitary gland

  • hypothalamus controls the hormones secreted in the body
    • including the ones secreted by the pituitary gland

growth hormone

  • the growth hormones are secreted at night when sleeping
  • tumors in the pituitary’s hormone secreting cell types causes gigantism (children before puberty) and acromegaly (adults)
  • the treatment for these is not as simple as one hopes for it to be

mood disorders

  • hypothalamus is a pump
    • the pump can go awry
  • nuanced issue is a mood disorders
    • behavioral packages are controlled by hormonal changes
  • behavioral package of post-partum (post-baby-delivery)
    • sleep deprivation occurs
    • body changes
    • two main hormones
      • oxytocin and prolactin
    • oxytocin and prolactin work together in normal childbirth and post-partum.
  • common mood disorders are
    • anxiety
    • psychosis
    • depression
  • these mood disorders are in part due to a problem in release in oxytocin and prolactin

thermoregulation

  • balancing act between
    • heat production: metabolism and skeletal muscle contraction produces body heat
    • heat conservation: autonomic mechanisms, keeping heat by reducing body surface
    • heat loss: autonomic mechanisms, sweating, increasing surface area
    • no way to refrigerate ourselves
  • at room temperature
    • body temperature is at 37ºC (98.6ºF)
    • this happens completely through vaso-motion
  • vaso-motion
    • when hot, the blood is sent out to the skin (shell of the body)
      • lose heat
    • when cool, the blood is sent into the core of the body to reduce heat loss
      • retain and conserve heat
  • extreme cold - frost bite
    • skin freezes when abandoned to cold
    • to counter this vaso-dialation occurs to let more blood flow to the cold parts
  • extreme heat
    • cant lose heat to something hotter than body
    • sweating is the defense for extreme heat
    • the evaporating water takes heat away from the body
      • not effective in humid environments
    • air conditioner is a requirement during heat waves
      • as cooling cannot occur in hot and humid environments

hyperthermia

  • in response to a hot environment, there is nothing we can do to cool off
    • this is where modern technology comes to play
    • body temperature more than 105ºF causes death

fever

  • set point:
    • hypothalamus at 37ºC
    • the body defends this temperature
  • more than set point - hyperthermia

  • less than set point - hypothermia

  • during fever, the set point changes to ~40ºC
    • the temperature of the body will lag
    • this makes the body feel chills
  • when the set point of 40ºC is reached, the set point is set back to 37ºC
    • the body lags in cooling again
    • this causes the body to feel hot and chills
  • this fever cycle helps fight infections
    • by strengthening the immune system

hot flashes

  • vasomotor disorders
    • hot flashes
    • night sweats
  • there is a neutral zone around 37ºC where changes to body temperature is fine
    • does not elicit a metabolic response or sweating
    • the zone is about 1ºF or 0.5ºC
  • in women with hot flashes, the bandwidth is zero
    • they feel too hot or too cold easily

breathing

  • depends on changing pressure in the thoracic cavity
    • this is done by the diaphragm
  • when diaphragm becomes larger, the thoracic cavity becomes larger
    • lower pressure sucks air in
  • eupnia
    • when sitting quietly, at rest
  • during exercise generates metabolic waste like carbon-dioxide
    • is detected in the brain
    • there is an engagement of abdominal muscles
      • that push thoracic cavity in the other direction
      • they blow out air faster
    • depends on how much carbon-dioxide needs to be expelled
  • the medulla has a central pattern generator for eupnia
    • the motor neurons for the abdominal muscles and the diaphragm is controlled by this central pattern generator
  • carbon dioxide is detected in the mid brain
    • and sends signal to abdomen muscles for active exhalation

urination

  • urination depends on two muscles
    • the bladder
    • the external urethral sphincter (EUS)
  • the bladder is a smooth muscle
    • gets innervation from parasympathetic neural in the sacral cord
    • this is involuntary
  • the EUS is closed 99% of your life because it is spent in urine storage
    • to void, this has to relax
    • the relaxation is controlled voluntarily
    • so the control in the dorsal pons
  • when bladder is has a sufficient volume, it elicits a voluntary decision to void
    • this allows the parasympathetic motor neurons
    • and relaxes voluntarily along with the EUS
  • the trigger in the bladder is not volume, but pressure
    • a certain volume has to be filled before a pressure is felt
    • urge to intolerable pressure
  • the bladder walls are elastic and are controlled by sympathetic and parasympathetic nerves
    • this helps for instance, during sleep to keep pressure low until waking
      • even if the volume fills up
    • but when nervous, it might contract the bladder even if no pressure is racked up due to urine volume
  • pons is the boss in urination control
    • the control flows through the sacral cord

sleep

  • sleep is a state that is innate
    • low postural activity
    • low sensory reactivity
    • reversible i.e. can be woken up
  • sleep is consolidated into the night time
    • two different forms of sleep
    • SWS: Slow Wave Sleep
      • neocortex is offline
      • not much processing is happening
      • a person woken up might report a dream
    • REM: Rapid Eye Movement sleep
      • neocortex looks like it is awake
      • offline motor neurons prevent us from being awake
        • atonia - hard to fire motorneuron to move
      • higher chance of reporting a dream in REM sleep
        • more associated with dreaming
  • if motor neurons aren’t inhibited, then we would act out our dreams
    • REM sleep behavior disorder
      • afflicts men around ~60
      • dreams are invariably violent
    • part of a bigger nerve degenerative disorder
  • SWS wave depth increases as sleep progresses
    • the waves are interrupted by periods of REM sleep
  • REM sleep periods are short
    • they get longer as SWS progresses
    • they are the longest just before waking
    • this sleep structure is called sleep architecture

sleep mechanisms

  • sleep is produced in a push-pull cycle
  • sleep pressure increases as the day progresses
    • working against the sleep pressure is the circadian rhythm
    • circadian rhythm
      • “getup and go eat”
  • circadian rhythm is fed by light and dark
    • driven by light to the eye
    • info sent to hypothalamus
  • the circadian rhythm shift during daylight savings
    • jet lag is a problem arises from lagging circadian rhythms
  • sleep and wakefulness are both positively influenced by different parts of the hypothalamus
  • homeostatis helps anticipate changes so the rest of the organs
    • can manage error preventively