Homeostasis Flashcards
(38 cards)
What is the key integrator of homeostatic systems?
Hypothalamus
What are homeostatic systems not limited to?
Autonomic nervous system
What is the largest threat to thermoregulation and why?
Overheating
-We have no mechanism for cooling out body but we do have mechanisms to heat it up
How do we resist hypothermia?
Heat conservation & increased heat production (shivering)
What is the body’s set point?
37C (if it drops below or above we feel cold and hot)
How do we vasodilate (to avoid too high of temperature)?
- Local temperature sensors cause release of NO
- NO stimulates Guanylyl Cyclase (enzyme) which converts GTP to cGMP
- Then cGMP causes MLCK to relax =vasodilate
{cGMP–> activates protein kinase G which phosphorylates proteins and decreases intracellular calcium –> relaxing muscles}
What do core temperature sensors do when you’re hot?
Send signals to the CNS to activate sympathetic nerve outflow (both adrenergic & cholinergic). This increases skin blood flow and increases sweating.
What are two mechanisms the body uses to avoid too low of temperature?
- Cold stimulates skin receptors to release NE which constricts blood vessels.
- Core temp sensors stimulate CNS to increase sympathetic nervous system outflow –> causes decreased skin blood flow.
IMPORTANT: What causes a fever???
- Pyrogen (IL-1, IL-6, TNF-alpha) stimulates hypothalamus
2. Hypothalamus produces PGE2 in medial pre-optic area causing shivering and increased metabolic rate
What is important to remember about fevers?
- PGE2 change the set point
2. Hypothalamic temperature does NOT change, it receives input from sensors elsewhere
What causes hot flashes in nearly 80% of post-menopausal women?
An extremely narrow (unmeasurable) thermoregulatory zone
What is blood pressure determined by?
BP = (Cardiac output/Flow) X (Peripheral resistance) BP = (Heart rate) X (Stroke volume) X (Total peripheral resistance)
What do sympathetic nerves do in regulation of blood pressure?
- Interact with beta1 receptors to stimulate heart rate
- Interact with beta1 receptors to increase stoke volume
- Interact with alpha1 receptors to increase resistance
What type of system is the vagus nerve associated with in bp regulation? What does vagus nerve do to bp?
- Parasympathetic nerve
2. Releases ACh to interact with muscarinic receptors in the heart to slow heart rate
How to baroreceptors regulate blood pressure? (simple version)
- If bp is low, sensory fibers are less stimulated
- Sensory fibers stimulate inhibitiroy interneurons less
- Inhibitory interneurons do NOT inhibit rest of pathway
- Rest of pathway is stimulated which causes constriction of the muscle (stimulation of sympathetic nerve ending)
- Constriction of the muscle causes an increase in bp (vasoconstriction)
Where are stretch receptors located?
Carotid arteries & Aortic arch
Pathway from stretch receptors to Nucleus Tractus Solitarius (NTS)?
- Stretch receptors sense stretch (blood pressure) [High bp]
- As blood pressure increases, firing rate increases
- Impulses are carried by glossopharyngeal and vagus nerve to medulla
- Nerves terminate in NTS of medulla.
What is the pathway from the NTS to the change in bp?
- Neurons in the NTS suppress neurons in rostal ventrolateral medulla (sympathoexcitatory area)
- These neurons excite sympathetic preganglionic neurons in the interomediolateral column of the thoracic cord.
- Sympathetics usually increase heart rate (beta1), stroke volume (beta1) and resistance (alpha1) to raise bp.
- Since input from baroreceptors inhibits activation of sympathetic nerves (and release of NE to elevate heart rate, stroke volume, resistance) the net effect is lessened intensity of the increase in bp (decrease in bp)
What might causes orthostatic hypotension in people my age?
Dehydration (less blood volume = lower bp
What happens if the bp in the carotid and aorta drops?
- Less activation of glossopharyngeal & vagus nerve
- Less stimulation of NTS
- Less inhibition of rostral ventrolateral medulla
- Greater stimulation of preganglionic sympathetics in thoracic cord
- Increases heart rate, stroke volume and resistance
- Lessens drop in blood pressure
What is the pump that generates pressure differentials when we breathe?
Diaphragm and External Intercostals
What is our breathing pacemaker that initiates breathing?
Pre-Boetzinger area of ventrolateral medulla
How does the pacemaker (Pre-Boetzinger area) work?
Stimulates C3-C5 via the phrenic nerve to innervate the diaphragm
What type of nerve is the phrenic nerve that innervates the diaphragm?
Somatic, releases ACh onto nicotinic receptors on the diaphragm. (all somatic nerves coming off spinal cord release ACh onto nicotinic)
