Flashcards in Circulation and respiration - Part 2 - 2 Deck (67):
What determines cardiac output?
What is heart rate?
How fast the heart beats
What is stroke volume?
How much blood leaved the heart with every beat
How can heart rate be changed?
Through autonomic or hormonal input
Describe the autonomic inputs to heart rate.
Adrenergic increases heart rate - epineprhine
Cholinergic decreases heart rate - acetylcholine
_______ events upregulate the adrenergic response
__________ works on the cholinergic system.
Describe how temperature affects cholinergic stimulation of heart rate.
In cold temperatures, initially, heart rate decreases due to increased cholinergic stimulation until acclimation occurs, whereby the HR gets more constant.
What are the daily regulators of heart rate?
adrenergic and cholinergic response
________ control is more a seasonal control of heart rate.
What are the three factors that control stroke volume?
1 - Afterload or arterial pressure
2 - Preload
3 - Ventricular strength
Which of the three factors that control stroke volume is the most important?
What is afterload? How does it affect SV?
Afterload or arterial pressure is the amount of blood in the bulbus (if sticking with teleosts) when the ventricle contracts.
If there is backlog, or blood remaining in the bulbus, this will decrease the amount of blood that can leave the ventricle.
When would afterload be an issue?
Doesnt happen that often in fish.
In a diseased state, bulbus is less elastic and reduces stroke volume
What is preload and how does it affect SV?
How much blood is in the heart at the start of contraction.
If there is more blood in the heart before the next beat, more of it can be put out
What can affect preload?
heart rate; if HR is too fast, not enough time to fill up and thus reduced SV
What is ventricular strength?
How strongly the ventricle contracts.
Describe Starling's law of the heart.
Cardiac myotomes have increased force of contraction as fiber length increases
Contractility of the heart is affected by what?
cholinergic and adrenergic stimulation
The ventrcile wall is full of muscle fibres called __________.
When the ventricles contract, the fibres pull against each other the generate _________.
What pulls the fibres apart in the heart?
What is the relationship between filling pressure and stroke volume?
As filling pressure increases, the fibres get pulled apart generating a larger stroke volume
Which fish doesnt really follow the Starling's law of the heart?
Essentially, their heart is always pumping as hard as possible, always at max SV
How does calcium affect ventricular strength?
More calcium to the muslces makes them contract more powerfully.
How does adrenergic stimulation affect ventricular strength?
Adrenergic --> increase ventricular strength
cholinergic --> decrease ventricular strength
How does acidosis affect ventricular strength?
Acidosis or acid buildup decreases contractility.
If the heart is working too hard, get buildup of acid; or
pH of water can affect fish heart ability to deliver blood to the tissues
What does the RAS react to?
Low blood pressure of hypotension
Describe the RAS.
Series of cells located at the glomerular junction that function to detect blood pressure going into the tubules.
When blood pressure is low, causes them to secrete renin.
Renin then converts angiotensin 1 to angiotensin 2.
Angiotensin 2 will act on arteries and capillaries throughout the body to constrict them and increase blood pressure.
Angiotensin 2 will also induce drinking behaviour (if saltwater fish)
Is RAS a short term or long term fix?
Short term/long term
What does renin do? Where is it secrete from?
Converts angiotensin 1 to angiotensin 2
Secreted from pressure detector cells in the glomerular capillaries.
What does angiotensin 2 do?
Cause vasoconstriction of arteries and capillaries throughout the body to increase blood pressure - short term fix
Also increases drinking behaviour in fish - this is shut off in freshwater fish since they aren't fluid deprived
What is the species different for RAS?
Freshwater fish will shut off the increased drinking behaviour pathway; saltwater fish will not
How does RAS work in sharks?
Not as sensitive, need a drastic decrease in blood pressure before this kicks in.
What are the two kinds of swimming?
Burst and sustained
What is burst swimming?
Swim fast for a short period of time.
What is sustained swimming?
Migrating somewhere or against the current, swimming fast for longer.
In burst swimming, overall CO ________; in sustained swimming, overall CO ________.
Why does overall cardiac output decrease in burst swimming?
In burst swimming, using anaerobic pathway.
Fast muscles, dont need more oxygen.
The thought is that this is protective, since as the fish bursts, trunk muscles bend and squeeze, if send quick burst out of the heart, thought is it would overwhelm the gill capillaries and cause damage.
Once it stops bursting, the output might increase to supply blood to the tissues.
Why does overall cardiac output increase in sustained swimming?
Need lots of blood in the tissue causing both HR and SV to increase.
Describe the differences between teleosts, sharks and icefish in sustained swimming cardiac output.
- both HR and SV will increase to increase CO
- most of the changes in CO will come from changes in SV since they dont have a good control of HR
-- increase contractility of ventricle to increase SV
- can only change HR since ice fishes are always working at maximum stroke volume
Why are icefish always working at maximum stroke volume?
Ice fish have no Hb, all oxygen dissolved in blood, always pump out maximum amount to get enough blood throughout the system
- can increase HR however, to move it along faster during sustained swimming
Heart rate and hypoxia is highly ______ dependent.
Hypoxia decreases output via _________ reflex in teleosts.
In eels, hypoxia causes shutdown of ______ pathway.
________ ______ can withstand five hours of hypoxia before downregulating output but _______ _____ can be unaffected after 5 days of complete hypoxia.
In general, for teleosts, how does heart rate change with hypoxia in the water?
In really hypoxic waters, get decreased CO through cholinergic reflex
i.e. less blood pumped out from the heart
Why do teleosts use the cholinergic reflex when in hypoxic waters?
If in hypoxic waters and send oxygen to the gills, the oxygen will diffuse out of the blood into the water.
So, it is better to send less blood out of the heart and keep it in the body for longer and get as much oxygen from it as possible.
Still needs to return to normoxic water, however.
Describe how eels handle hypoxic conditions.
Shut down gill pathway (i.e. blood flow to the gills) and breathe through their skin.
Describe how carp survive hypoxic waters.
Don't really regulate their heart rate.
Even if the system detects low oxygen in the water, they have trained their heart to ignore it since they can gulp air.
So, they override the cholinergic reflex.
(can still use reflex but, much more resistant to it)
__________ and _________ are concentrated in the branchial cavity.
Baroreceptors and chemoreceptors
Neural controls regulate HR, blood pressure and CO on a _______-________ cycle.
Where are baroreceptors located in fish?
Blood vessels, especially in the gills.
How do baroreceptors work?
Pressure detectors located on the walls of capillaries around the gills that detect stretch on the capillaries and thus, blood pressure
If the blood pressure is too high, how to baroreceptors lead to change in BP?
When they detect the blood pressure is too high, they communicate to the autonomic system and tell the cholinergic reflex to slow things down
What do chemoreceptors detect?
Gas concentrations in the blood at the gills.
Where do chemoreceptor feed back to?
the autonomic nervous system and may feedback to larger scale hormonal control (same with baroreceptors)
What is a more conserved response regarding blood pressure?
Response to hypertension.
Immediate response is to slow things down - bradycardia
___________ response is more variable, have RAS to deal with it.
What are chromaffin cells?
In your answer describe how they are unique to, what they are homologous to, where they are located and what they release.
unique to fish
probably homologous to the medulla of the kidneys, act like adrenal glands
these are special cells around the blood vessels (especially larger ones and the heart)
they release epineprhine into the body to control heart function
Describe, very briefly, the mechanism of action of chromaffin cells.
Detect changes in pressure and send out broad level hormone signals to the heart and blood vessels to increase contractility and constrict blood vessels.
Chromaffin cells are a ______-scale control of blood pressure and ______ ______ in respond to changes in pressure and, to some extent, can tie into __________ and look at blood composition.
Chromaffin cells probably led to the ______ ______ in mammals.
Chromaffin cells can be referred to as what?
Broad scale hormonal control of the heart and blood vessels.
____ _______ are a fine scale control of blood flow through the gills.
NT receptors tend to be a more ________ response