Coordinated responses and HR control Flashcards
What is the fight or flight response and what does it involve?
- instinctive reaction to perceived threats preparing the body to flee or confront danger
- involves complex interactions between the nervous and endocrine systems
What are the mechanisms of the fight or flight response?
1) ANS detects a threat and passes a signal to the hypothalamus
2) hypothalamus activates the SNS sending nerve signals to glands and muscles
3) SNS triggers the secretion of adrenaline and noradrenaline from the adrenal medulla causing physiological changes
4) hypothalamus also communicates with adrenal-cortical system stimulating the pituitary gland to release ACTH
5) ACTH travels via the bloodstream to the adrenal cortex stimulating it to release several other hormones to help deal with the threat
What are the physiological reactions triggered by the fight or flight response and what is there purpose?
- increased HR = circulate more oxygenated blood
- pupil dilation = improved vision
- rise in BG levels = increase cellular respiration
- relaxation of airway muscles = allow more O2 into the lungs
- digestion stops = priorities emergency bodily functions
What is the second messenger model?
Involves a hormone (1st messenger) triggering the formation of a second messenger (cAMP) inside the cell activating enzymes to carry out a function
What are the stages of the cell signaling pathway for adrenaline?
1) adrenaline binds to complementary receptors on the cell surface membrane
2) binding of adrenaline causes the protein to change shape activating a G protein
3) this activates the enzyme adenyl cyclase which converts ATP into cAMP
4) cAMP acts as a second messenger binding to and activating many protein kinases via phosphorylation amplifying the signal from adrenaline
5) protein kinases activate enzymes that catalyse the breakdown of glycogen into glucose
6) glucose moves out of the liver cells via facilitated diffusion and into the blood through channel proteins
7) this increases the blood glucose concentration so that more glucose can be delivered to body cells for respiration
What is the cascade effect?
process meaning one hormone molecule can generate multiple cAMP molecules (the effect amplifying at each stage)
The heart is myogenic what does this mean?
the heart itself initiates the contraction of the cardiac muscle with the basic rhythm being controlled by a wave of electrical excitation
State and describe the pathway through the heart of an electrical impulse?
1) SAN = initiates heartbeat by stimulating atria to contract
2) AVN = picks up electrical activity from the SAN and imposes a slight delay
3) Bundle of his = receives electrical activity from the AVN and conducts the wave of excitation
4) Purkyne fibers = branch off the bundle of his causing the RV and LV to contract from the bottom up
How does the brain control heart rate?
medulla oblongata in the brain stem acts as a control center receiving information from chemo and baro receptors
Explain how high blood pressure affects the firing rate of the SAN?
1) high BP detected by baroreceptors
2) impulse generated via the parasympathetic pathway
3) neurotransmitter acetylcholine released
4) decreases electrical activity of SAN
5) HR decreases
Explain how low blood pressure affects the firing rate of the SAN?
1) low BP detected by baroreceptors
2) impulse generated via the sympathetic pathway
3) neurotransmitter noradrenaline released
4) increased electrical activity of SAN
5) HR increases
Explain how high O2, low CO2 and high PH levels affect the firing rate of the SAN?
1) chemoreceptors detect the change (stimuli)
2) impulse generated via the parasympathetic pathway
3) neurotransmitter acetylcholine is released
4) decreased electrical activity of SAN
5) HR decrease
Explain low O2, high CO2 and low PH levels affect the firing rate of the SAN?
1) chemoreceptors detect the change (stimuli)
2) impulse generated via the sympathetic pathway
3) neurotransmitter noradrenaline is released
4) increased electrical activity of SAN
5) HR increase
How does the ANS respond during exercise?
1) blood has a higher CO2 concentration so lower PH
2) chemoreceptors in the carotid arteries and aorta detect this and increases the frequency of nervous impulses sent to the medulla oblongata
3) The medulla oblongata increases the rate of impulses to the SAN via the sympathetic nervous system
4) HR increases
5) This provides the extra O2 required for increased respiration in active muscles
6) The increased blood flow also helps remove excess CO2 via the lungs
7) CO2 concentration reduces
