Circulation Strategies Flashcards
Do all animals have circulatory systems?
no – some lack circulatory systems, but have mechanisms for propelling fluids around their bodies
Which animals lack circulatory systems?
- sponges and flatworms
- cnidarians
- echinoderms
- nematodes
How do sponges and flatworms propel fluids around their bodies without a circulatory system?
ciliated cells move water within body cavity
How do cnidarians propel fluids around their bodies without a circulatory system?
ciliated cells move water within body cavity
What type of circulatory system do insects have?
- open circulatory system
- tubular heart forces fluid in one direction into hemocoel, and ostia (holes) allow hemolymph to return to heart
What type of circulatory system do annelids have?
- polychaetes: open circulatory system
- oligochaetes: closed circulatory system
- circulate interstitial fluid with cilia or muscular contractions of body wall
What type of circulatory system do molluscs have?
- most have open systems
- only cephalopods have closed systems
Why do cephalopods have closed circulatory systems?
squids are highly active, therefore have closed systems to provide more O2 to tissues so they can be more metabolically active
How many hearts do cephalopods have?
three
- systemic heart: pumps blood to body tissues
- branchial hearts (2): pump blood through gills
What type of circulatory system do crustaceans (arthropods) have?
open circulatory system
- heart pumps fluid around, and ostia return fluid to heart
- have some control over distribution of blood flow in body*
Why do circulatory systems of crustaceans (arthropods) become more complex in larger animals?
have more tissues that need to be bathed
How much space does air or hemolymph take up in insects? Why is this a challenge?
70% of animal
- tracheal system takes up about 30% of body
- hemocoel takes up about 30-40% of body
- only takes up 5% in humans – much smaller volume, with more control
What type of circulatory system do urochordates (tunicates) have?
open system
- tubular heart at base of digestive tract
What type of circulatory system do cephalochordates (lancelets) have?
closed system with few open sinuses
- tubular heart at base of digestive tract and pulsatile blood vessels
What type of circulatory system do vertebrates (fish, amphibians, reptiles, birds, mammals) have?
closed system
How do nematodes propel fluids around their bodies without a circulatory system?
muscle contraction moves interstitial fluids
How do echinoderms propel fluids around their bodies without a circulatory system?
water vascular system used to move O2 and nutrients
What type of circulatory system circuit do water-breathing fish (jawed vertebrates) have?
single circuit
- some fish have accessory hearts in tail that helps pump blood back to heart
What type of circulatory system circuit do air-breathing tetrapods (jawed vertebrates) have?
double circuit
- pulmonary: right side of heart perfusing lung
- systemic: left side of heart perfusing other tissues
Single-Circuit, Closed Circulatory System – Water-Breather
Describe the single circuit of blood flow.
- cardiac output leaves heart
- cardiac output passes through respiratory (gills, branchial) capillaries for O2 uptake and CO2 excretion
- cardiac output travels to body
- cardiac output passes through systemic (peripheral; tissue) capillaries for tissue O2 delivery and CO2 removal
- cardiac output returns to heart
Single-Circuit, Closed Circulatory System – Water-Breather
Does each capillary bed have small or large resistance? How does this affect pressure in the circuit?
large resistance
- RBCs are forced through capillaries – need large pressure to pump them through
- leftover pressure needs to pump cells through the other capillary bed
- pressure drop for this circuit is large
Single-Circuit, Closed Circulatory System – Water-Breather
How does Ohm’s law apply to vessel resistance?
vessel resistance to blood flow in gills and tissues is additive
What are the 4 chambers of fish (teleost) hearts?
- sinus venosus
- atrium – contractile (cardiac muscle)
- ventricle – contractile (cardiac muscle)
- bulbus arteriosus (or conus arteriosus)
What are the two contractile chambers of fish (teleost) hearts? How do they function?
atrium and ventricle
- contract in sequence, and generate sufficient blood pressure to propel blood around entire body
- wall thickness is indicative of blood pressure it can generate – atrium thinner
What is the sinus venosus chamber of fish (teleost) hearts? What specialized region does it have?
- elastic chamber that collects venous blood
- sinoatrial region: site of cardiac pacemaker (electrical signal that drives heartbeat)
What is the bulbus arteriosus (conus arteriosus) chamber of fish (teleost) hearts?
- elastic chamber connected to aorta, which takes deoxygenated blood to gills
- expands and contracts with each pressure pulse, and dampens large pressure pulse created by ventricle to smooth out flow
Where are the two non-contractile chambers of fish (teleost) hearts located?
inside pericardial cavity
- sinus venosus
- bulbus arteriosus (or conus arteriosus)
What type of myocardium do fish (teleost) hearts have?
spongy myocardium in ventricles
- blood that moves through ventricle is moving through sponge-like tissue
- O2 is unloaded to sponge-like tissue to permit contraction
Double-Circuit, Closed Circulatory System – Mammals
Describe the double circuit of blood flow.
blood returns to the heart twice to complete a circuit of body – two functional pumps in one heart, each having atrium and ventricle
- right atrium and right ventricle pump deoxygenated blood into pulmonary circuit
- left atrium and left ventricle pump oxygenated blood into systemic circuit
Double-Circuit, Closed Circulatory System – Mammals
What is the benefit of two functional pumps (left and right)?
two functional pumps can work at different blood pressures, but their flow outputs must be identical
- high systemic blood pressure allows good control of blood delivery to tissues that need it (ie. high blood pressure and vasodilation generates lots of blood flow to tissue)
- low pulmonary blood pressure because too high pressure would cause catastrophic capillary blowout (blood comes out)
- lungs cannot deal with pressure according to Fick equation – for efficient gas exchange, need high surface area and low diffusion distance (thickness)
compare to fish that has one pump, that must create high enough pressure to drive blood through two in-series capillary beds
How many chambers do bird and mammal hearts have?
4
- two atria
- two ventricles
Describe the circuits of birds and mammals.
double circuit – systemic and pulmonary circuits are divided
- high pressure systemic
- low pressure pulmonary
oxygenated (from lung) and deoxygenated blood are completely separated
- right side of heart that pumps blood to lungs is low pressure and has less muscle, and therefore lower metabolic demand
- left side of heart that pumps blood to body needs lots of O2 and is receiving oxygenated blood
- compare to fish that only has deoxygenated blood coming back to heart
What type of myocardium do mammals have?
mostly compact
What type of myocardium do birds have?
mostly compact
What type of myocardium do fish have?
mostly spongy
What type of myocardium do amphibians have?
mostly spongy
What type of myocardium do active fish (ie. tuna) have?
more compact myocardium to generate more force for their activity
How is spongy myocardium arranged in fish and amphibians?
arranged as trabeculae that extend into chambers – creates more surface area for gas exchange with venous blood returning to heart
Describe the myocardium in fish.
- spongy myocardium allows for much greater surface area for gas exchange
- some compact myocardium on outside
Describe the myocardium in humans.
- humans have same internal volume as fish for pumping blood, but much more compact myocardium
- more muscle for same cross-sectional area that blood would be pumped through – can do lots more work, selected for in organisms with higher metabolic rate
- some spongy myocardium
In fish hearts, what is the main contractile chamber?
ventricle
- atrium has some contraction
Fish hearts have ventricles with spongy myocardium. What does this mean for fish?
- spongy myocardium lack coronary vessels
- when there are no coronary arteries, ventricle has to deal with low PO2
- heart needs to be able to extract O2 from that or it cannot work – main reason why fish reach some limitation for exercise capacity or hypoxia
What are the chambers of amphibian hearts?
3-chambered
- left atrium
- ventricle
- right atrium
Describe the path of blood flow in amphibian hearts.
- pulmonary vein leaves lung, and oxygenated blood enters heart through left atrium
- deoxygenated blood from body enters right atrium
- blood enters ventricle, which has trabeculae that helps prevent mixing of oxygenated (from lung) and deoxygenated (from body) blood
- spiral folds in conus arteriosus helps direct deoxygenated blood to pulmocutaneous circuit, and oxygenated blood to systemic circuit
beginning of partially divided system – partial separation of blood flow
Is there separation of blood flow (oxygenated and deoxygenated blood) in amphibian hearts?
partial separation
What are the chambers of reptile hearts?
- left atrium
- right atrium
three interconnected ventricular compartments:
- cavum venosum
- cavum pulmonale
- cavum arteriosum
Describe blood flow in reptile hearts.
- oxygenated blood from lung → pulmonary vein → left atrium → cavum arteriosum → left or right aorta (directed to systemic circulatory system)
- deoxygenated blood from body → right atrium → cavum venosum → cavum pulmonale → pulmonary artery → lung
Is there separation of blood flow (oxygenated and deoxygenated blood) in reptile hearts?
nearly complete separation
- there is approximately equal blood volume going to lung circuit and systemic circuit
- opens up opportunities for shunts and redirecting blood flow through heart
What are the chambers of bird hearts?
(same as mammals)
- two atria
- two ventricles – separated by intraventricular septum
Is there separation of blood flow (oxygenated and deoxygenated blood) in bird and mammal hearts?
complete separation
What are the valves in bird and mammal hearts?
atrioventricular (AV) valves: between atria and ventricles
- right AV valve: between right ventricle and right atrium
- left AV valve: between left ventricle and left atrium
semilunar valves: between ventricles and arteries
- pulmonary semilunar valve: between right ventricle and pulmonary artery
- aortic semilunar valve: between left ventricle and aorta
Describe the blood flow through the heart and circulatory system of amphibians.
- lots of cutaneous respiration
beginning of some separation of flow
- deoxygenated blood going to lung and skin – both act as gas exchangers
- oxygenated blood going to heart
- more oxygenated blood goes to aorta and then to tissues, where O2 is extracted and some mixing occurs
part of heart receives oxygenated blood from lungs
- part of heart receives mix of oxygenated blood from skin and deoxygenated blood from tissues
compare to fish heart, where everything is venous – the more O2 tissues extract, the larger the problem for the heart
What is shunting in reptile hearts?
can shunt blood to bypass pulmonary or systemic circuit
What does a right-to-left shunt in reptile hearts do?
deoxygenated blood entering right atrium normally goes to pulmonary circuit, but right-to-left shunt can direct blood into systemic circuit
- deoxygenated blood bypasses pulmonary circuit and enters systemic circuit during breath-holding
What does a left-to-right shunt in reptile hearts do?
oxygenated blood entering left atrium normally goes to systemic circuit, but left-to-right shunt can direct blood into pulmonary circuit
- oxygenated blood re-enters pulmonary circuit, aids O2 delivery to myocardium in right heart
Describe the blood flow through the heart and circulatory system of reptiles.
deoxygenated blood from body goes to lung and gets oxygenated
- blood goes back to heart and gets sent to systemic circuit where O2 is extracted by tissues
nice separation of oxygenated and deoxygenated blood
- optimizes taking up O2 at lung, and delivering them to tissues
Is there separation of blood flow (oxygenated and deoxygenated blood) in reptile hearts?
yes – nice separation, which optimizes taking up O2 at lung, and delivering them to tissues
Crocodile (reptile) hearts resemble more to what type of heart?
bird and mammal hearts
Describe the blood flow through the heart and circulatory system of reptiles.
- oxygenated blood from pulmonary vein → left atrium → left ventricle → right aorta → systemic circulatory system
- deoxygenated blood from body → right atrium → right ventricle → pulmonary artery → lung
What is the benefit of the circulatory systems of crocodiles (reptiles)?
potential to shunt blood
- can shut down pulmonary artery and blood flow to lung, and instead direct it to systemic circulatory system
How does shunting blood help with diving in crocodiles (reptile)?
can isolate lung from system and pump blood around systemic system
- there is something on pulmonary artery that can shut down blood flow to that artery, and blood would go to left aorta from right ventricle
Describe shunting in crocodile hearts (reptiles).
left aorta (systemic) is connected to right ventricle
- usually want to send deoxygenated blood that comes into right ventricle to lung to be oxygenated
- but can also send deoxygenated blood to left aorta and other parts of systemic circulatory system – potentially inefficient and problematic
left and right aorta are connected by vessel
- when left ventricle contracts, it pumps blood into right aorta, but pressure generated is higher in left ventricle than right ventricle
- recall do not want high pressure in lung, therefore there is low pressure in right ventricle pumping blood to lung
- blood that goes to right aorta also goes to left aorta through foramen of panizza – get good oxygenated blood flow from left ventricle to left aorta
there are times when right ventricle could be pumping blood to left aorta
- with completely divided circulatory system, each side has to pump same volume – if one side is pumping more than the other, at some point all blood will be on one side of the system
- if system is pumping more blood to left aorta and it starts to accumulate on left side, it can return to other side of circulatory system through anastomosis
strange that one of the systemic arteries is coming off right ventricle instead of left ventricle – not sure why
Why are highly divided circulatory systems (high pressure to systemic, low pressure to pulmonary) needed in birds and mammals?
because they are endotherms (regulate body temperature at higher level)
- their metabolic rate is 30x higher than ectotherm of similar size
- high metabolic rate requires high pressures to direct adequate blood flow to tissues
What are the chambers of crocodiles hearts?
4-chambered
- two atria
- two ventricles
Which organisms have no division of the ventricle into chambers?
- fish
- frogs
Which organisms have partial division of the ventricle into chambers?
- turtles and lizards (reptiles)
Which organisms have complete division of the ventricle into chambers?
- crocodiles (reptiles)
- birds
- mammals
Describe the fish cardiac cycle.
serial contractions of chambers
- sinus venosus contracts and forces blood into atrium
- atrium contracts and forces blood into ventricle, then into bulbus arteriosus
valves are passive
- opens and closes according to pressure differences
- assure unidirectional flow of blood
in teleosts, non-contractile bulbus arteriosus serves as volume and pressure reservoir
- has lots of connective tissue so it can expand and dampen pressure pulse, and even out pressure that is leaving heart
How does the mammalian cardiac cycle work?
atria and ventricles alternate systole and diastole:
- two atria contract simultaneously
- slight pause
- two ventricles contract simultaneously
- atria and ventricles relax while heart fills with blood – important for maximizing stroke volume
Describe the steps of the mammalian cardiac cycle.
- ventricular diastole
- pressure in atria exceeds ventricular pressure
- AV valves open and ventricles fill passively
- atrial systole
- atrial contraction forces some additional blood into ventricles – but majority of blood entering ventricles is driven by venous pressure (high in mammals, birds)
- ventricular systole – isovolumetric contraction
- ventricular contraction pushes AV valves closed and increases pressure inside ventricle
- volume does not change, but pressure does
- but force is not yet sufficient to move blood
- ventricular systole – ventricular ejection
- increased ventricular pressure forces semilunar valves open and blood is ejected
- ventricular diastole
- as ventricles relax, pressure in arteries excess ventricular pressure, closing semilunar valves
- ventricular diastole
- pressure in atria exceeds ventricular pressure
- AV valves open and ventricles fill passively
How does ventricular filling occur in birds and mammals?
- ventricles fill passively by venous pressure during diastole
- atrial contraction adds some blood to ventricles
How does ventricular filling occur in fish and some amphibians?
- ventricle filled by contraction of atrium
- requires atrial filling due to low venous pressure
- two capillary beds in parallel (gill first), therefore high pressure would blow out the gill
- low pressure system once blood goes through both capillary beds, therefore amount of ventricular filling is very small
Describe the different pressures in the mammalian heart.
- left ventricle contracts more forcefully and develops higher pressure to pump blood to body
- right ventricle contracts less forcefully and requires less pressure to pump blood through lungs
Why does the right ventricle of mammalian hearts require less pressure to pump blood through the lungs?
- low resistance in pulmonary circuit due to high capillary density in parallel (large cross-sectional area)
- low pressure protects delicate blood vessels of lung and prevents edema
Do the systemic and pulmonary circuits of the mammalian heart have the same total blood flow?
yes
Changes in Ventricular Pressure in the Right Side of the Heart
(similar pattern to left side, but much lower pressure)
- pressure in right atrium increases as it contracts
- once atrial pressure is same as ventricular pressure, blood is forced into ventricle
- ventricle contracts, but valve is closed therefore pressure in atrium falls
- ventricle contracts, which forces blood into aorta
- peak pressure occurs at same time as ventricle relaxes
- when ventricular pressure eventually drops below pressure in pulmonary artery, valve closes and pressure in pulmonary artery is maintained, which forces blood into lung circuit
Changes in Ventricular Pressure in the Left Side of the Heart
blood pressure in left ventricle: increases
- arterial blood pressure decreases until pressure in ventricle exceeds that of aorta, then blood is pumped into aorta
- isovolumetric contraction until pressure in ventricle exceeds that of the aorta
blood pressure in left atrium: increases during atrial filling
blood pressure in aorta: increases and matches ventricular pressure
- as ventricle relaxes and its blood pressure decreases, valve closes, and blood pressure progressively decreases as blood leaves heart
Where are pacemakers located in fish? What do they do?
- in sinus venosus
- sends wave of excitement through heart, and sequential contraction of chambers to force blood flow
Where are pacemakers located in tetrapods (amphibians, reptiles, birds, mammals)?
in right atrium at sino-atrial (SA) node
What are pacemaker cells?
- derived from cardiomyocytes
- small with few myofibrils, mitochondria, or other organelles
- do not contract
- have unstable resting membrane potential (pacemaker potential) that depolarizes until it reaches threshold and initiates AP
