Circulatory System Flashcards
What type of organisms require circulatory systems?
large, complex organisms in which diffusion would be far too slow and inefficient = require bulk flow of nutrients
What type of organisms do not require circulatory systems? what do they use instead?
small, unicellular organisms
or simple organisms
What 5 phyla of animals do not require circulatory systems?
Porifera (sponges)
Cnidaria
Echinodermata
Platyhelminthes (flatworms)
Nematoda
What are the major functions of a CS?
to transport O2 to cells
to remove CO2 and other waste
to transport nutrients
to regulate salts and water
to regulate temperature
to transport signaling molecules (ex. hormones)
for immune responses
What are the 3 major components of a CS?
a pump or propulsive structure
a system of tubes, channels or spaces
a circulatory fluid
What is the function of a pump or propeller?
it generates a pressure gradient to move circulatory fluid around the body
What direction does circulatory flow around the body? why?
unidirectionally because of one way valves in the pump
What are the 3 types of pumps?
chambered hearts
skeletal muscles
pulsating blood vessels
Describe chambered hearts as pumps
hearts have contractile chambers which generate pressure to move fluid into and out of the body
How do skeletal muscles act as pumps?
muscle contraction can squeeze vessels to create pressure and move fluid
how can pulsating blood vessels act as pumps?
peristaltic (rhythmic) contractions of vessel walls move fluid
What are the 2 types fo circulatory fluid?
blood (closed)
hemolymph (open)
What are 3 types of tubes/channels that are used in the CS?
arteries to carry fluid away from heart which branch into arterioles which branch into capillaries
capillaries connect to venules which connect to veins which bring fluid back to the heart
What are capillaries for?
they are very fine, delicate and narrow channels where materials are exchanged between CS fluid and tissues
How does CS fluid flow around the body?
through the vascular system along/down the pressure gradient generated by the pump
what is peristalsis?
rhythmic wave-like contractions of vessel walls
Describe a closed CS (fluid, pumps, vessels, mixing with interstitial fluid, contact with tissues, organism types)
fluid: blood
pump: heart
vessels: blood vessels
no mixing with interstitial fluid
no direct contact with tissues
vertebrates
How are materials exchanged between CS fluid and tissues in closed systems?
through diffusion or transporters in vessels (ex. capillaries)
Describe an open CS (fluid, pumps, vessels, mixing with interstitial fluid, contact with tissues, organism types)
fluid: hemolymph
pump: can be heart
vessels:
sinuses
mixing with interstitial fluid and direct contact with tissues for exchange
invertebrates
What are sinuses? what type of CS are they used in?
they are spaces in the body cavity where CS fluid enters and mixes with interstitial fluid
in open systems
What is interstitial fluid? what type of CS is this in?
the extracellular fluid that surrounds tissues
in both open and closed
What are the 3 major components of blood and their proportion in human blood?
plasma (55%)
erythrocytes (45%)
white blood cells and blood clotting cells (< 1%)
Describe blood plasma
it’s the liquid component of blood
it’s mostly water, but contains some dissolved ions, organic solutes (HCO3) and proteins
What is serum?
blood plasma without the clotting factors
What are the proteins in blood plasma?
clotting factors (ex. thrombin, fibrinogen)
carrier proteins (ex. albumin, globulin)
What is HCO3 for in blood plasma?
it’s the form of CO2 that is carried through the blood = buffers blood
Describe erythrocytes
red blood cells
function in storing and transporting O2 in blood
What are the most abundant cell types in vertebrate blood?
red blood cells
What is the hematocrit?
the proportion of blood composed of red blood cells
in humans it’s ~45%
What makes red blood cells/erythrocytes so efficient at storing and transporting O2?
RBC have high concentrations of hemoglobin (respiratory pigments) which can each bind 4 O2 molecules
a single red blood cells has extremely high capacity to bind O2
What respiratory pigment is involved in binding O2 in red blood cells? how many O2 molecules can one bind?
hemoglobin can bind 4 O2 molecules at a time
What are examples of white blood cells and clotting cells in blood?
leukocytes and thrombocytes (platelets)
What is the open circulatory fluid?
hemolymph
What is lymph?
fluid in the vertebral lymphatic system involved in immune responses
which phyla have open circulatory systems?
urochordata
cephalochordata
annelids (tube worms only)
arthropods
molluscs (only bivalves and gastropods)
Which phyla have closed circulatory systems?
vertebrates
molluscs (cephalopods)
annelids (earth worms)
How do Porifera obtain nutrients?
ciliated cells lining their body cavity move water for diffusion
How do Cnidarian obtain nutrients?
muscle contractions of body wall move water for diffusion
How do flat worms obtain nutrients?
pharynx contractions bring water into body cavity for diffusion
What type of circulatory systems do Annelids have?
both
Polychaete (tube worms) = open
Oligochaete (earth worms) = closed
what are the pumps in annelids?
heart(s)
What system of tubes, channels, or spaces do Annelids use?
tubeworms = hemolymph vessels and sinuses
earthworms = blood vessels
What type of circulatory systems do Molluscs have?
both
bivalves + gastropods = open
cephalopods = closed
what type of pumps are used in molluscs?
hearts
what type of vascular system is used in molluscs?
vessels
What type of circulatory systems do Arthropods have?
open
How does the CS of crustaceans differ from insects?
they’re both open, but insects do not use their CS to transport O2, they have a separate tracheal system
What are ostia?
pores in the heart(s) of open CS animals that allow hemolymph to enter body cavity
What is unique to the insect CS?
CS is used only for delivering nutrients and immune cells, not for O2
Tracheal system used for O2
Describe the basic pathway of blood movement in vertebrates
aorta pumps blood out of heart
arteries carry blood away from heart and branch into smaller
arterioles which branch into smaller
capillaries which conduct material exchange between blood and tissues and coalesce into
venules which coalesce into
veins which carry blood toward the
ventricle of the heart
What are the 4 major layers of the walls of vertebrate blood vessels?
outermost:
tunica externa
tunica media
tunica intima
endothelium
What does the wall of vertebrate blood vessels surround?
a lumen (space) where blood flows
Describe the tunica externa
the outermost layer of the blood vessel wall
composed of collagen and some elastic fibers, but mostly very rigid
Describe the tunica media
the middle layer of blood vessel wall
composed of smooth muscle cells and elastic connective tissue
Describe the tunica intima
the internal lining of the blood vessel wall
made of smooth endothelial cells
How does the thickness of the blood vessel wall layers differ in veins compared to arteries?
veins have much thinner layers compared to arteries which have very thick tunica externa and tunica media (and thicker intima)
How does the lumen differ in size between major veins and arteries?
the lumen is much larger in veins than arteries
What layers of blood vessel walls do venules have? how does this affect the structure?
only tunica externa and endothelium lining
venules are very rigid
What layers of blood vessel walls do arterioles have? how does this affect the structure?
only tunica media and endothelium lining
more elastic
What layers of blood vessel walls do capillaries have? how does this affect the structure?
only has endothelial cells
capillaries are VERY fine and delicate
Which blood vessel types have one way valves? which do not?
only veins do
arteries and capillaries do not
What are the 3 types of capillaries?
Continuous
fenestrated
sinusoidal
Which capillary type is most abundant?
continuous
Describe continuous capillaries (tissues they’re found in, type of communication, etc)
most abundant type
found in skin and muscle tissues
found in the CNS-blood brain barrier
endothelial cells connected by tight junctions
Describe fenestrated capillaries (tissues they’re found in, type of communication, etc)
endothelial cells have pores (fenestrae)
found in kidneys, endocrine organs, intestine
very efficient in exchange
Describe sinusoidal capillaries (tissues they’re found in, type of communication, etc)
very few tight junctions, much more gaps
found in liver and bone marrow
very porous = key for large protein exchange
T or F: all capillary endothelial cells are linked by tight junctions
true
T or F: all capillaries leak very little fluid because of tight junctions
false, only continuous capillaries
fenestrated and sinusoidal capillaries have pores for exchanging more
order capillary types from least to most porous/good at exchanging
least: continuous (tight junctions only)
mid: fenestrated (pores)
most: sinusoidal (large gaps and fenestrae)
which vertebrates have single circuit CS?
water-breathing fish
which vertebrates have double circuit CS?
air-breathing tetrapods (amphibians, birds, reptiles, mammals)
What does it mean for the structure of the heart if there’s only one CS circuit?
only 2 chambers = 1 atrium, 1 ventricle
Describe the single circuit in water-breathing fish
heart pumps out deoxygenated blood via arteries over the gills which have capillaries to exchange O2 in water to oxygenate blood
oxygenated blood is carried through venules and veins throughout the body to exchange O2 with tissues
deoxygenated blood is carried back through veins to the heart
continue
What are the 2 circuits in double CS systems?
pulmonary circuit
systemic circuit
Why do water-breathing fish only have one circuit?
because they have a low metabolic rate = low O2 consumption, they do not require blood to be pumped out of the heart at super fast speed/high pressure
systolic pressure = 3045 mm Hg
Why do mammals require double circuits?
higher metabolic rate and O2 consumption requires heart to pump out blood faster and at higher pressures to move further distances quicker
need a mechanism to decrease pressure coming out of heart to avoid exploding blood vessels = 2 systems
systolic pressure = 120-180 mmHg
How does the systolic pressure of mammals compare to water breathing fish?
mammals = 120-180 mmHg
fish = 30-45 mm Hg
What side of the heart is the pulmonary circuit controlled by?
the right side
What is the function of the pulmonary circuit?
the right side of the heart pumps deoxygenated blood to the capillaries at respiratory tissues to pick up O2 and brings oxygenated blood back to the heart
What side of the heart is the systemic circuit controlled by?
the left side of the heart
What is the function of the systemic circuit?
the left side of the heart pumps oxygenated blood from the pulmonary system into the rest of the body
the veins bring back deoxygenated blood into the right side of the heart to enter the pulmonary system
Does the pulmonary system have high or low systolic pressure?
low
Does the systemic system have high or low pressure?
high
How many chambers do amphibian and non-bird reptilian hearts have? how is it divided?
only partially
into 2 atria and 1 ventricle
frogs have 3 chambered hearts
non-crocodilian lizards have 5 chambered hearts
How many chambers do frog hearts have?
3
How many chambers do non-crocodilian reptiles have?
5
Describe the pattern of blood flow in frog hearts
both atria pump blood into the ventricle and the ventricle pumps blood into pulmonary and systemic circuits
ventricle pumps deoxygenated blood into pulmonary circuit for lungs and skin capillaries
oxygenated blood returns to the heart
ventricle pumps oxygenated blood into systemic circuit to tissues in body and deoxygenated blood returns to heart
the return of deoxygenated blood to the heart from the systemic system and the oxygenated blood entering from the pulmonary system is where deox and ox blood mix
In amphibians and non-crocodilian reptiles, explain how the heart is only partially divided
oxygenated and deoxygenated blood are mostly separate but can mix and blood can be diverted between pulmonary and systemic circuits
Describe fluid flow in the decapod crustacean (arthropod) heart
open CS - fluid is hemolymph
heart pumps hemolymph out through arteries
hemolymph returns to heart via ostia during diastole (relaxation of heart)
What regulates the flow of hemolymph in crustacean hearts?
the opening and closing of ostia during systole and diastole (contraction and relaxation of the heart)
closed during systole
open during diastole
Where do signals for the crustacean heart to contract originate from (ie., neuro or myogenic)?
neurogenic
How is the crustacean heart situated within the body?
its suspended by ligaments
Describe the cardiac cycle steps in arthropods
spontaneous rhythmic depolarization of cardiac ganglia neurons causes
cardiomyocetes (cardiac muscles) to contract which
decreases volume of heart to increase pressure
increase in pressure closes ostia
hemolymph is pushed out of heart via arteries
ligaments suspending heart stretch - expanding walls of the heart
heart volume increases to decrease pressure
ostia open
hemolymph is sucked into the heart
(just follow pressure gradient - increased pressure in heart will push hemolymph out, decreased pressure in heart will pull hemolymph in)
What are the 4 layers of vertebrate heart walls?
pericardium
epicardium
myocardium
endocardium
What is the pericardium in vertebrate heart walls?
the outermost tissue composed of connective tissues that surround the heart
it includes the epicardium because the pericardium has 2 parts the parietal and visceral layers and the epicardium is the visceral pericardium
between the parietal and visceral layers there’s the pericardial fluid for protection
What is the epicardium in vertebrate heart walls?
aka the visceral pericardium - the inner layer of the pericardium
it is continuous with connective tissue on the heart and contains the nerves that mediate heart and coronary arteries
What is the myocardium in vertebrate heart walls?
more internal than the pericardium
the layer of heart muscle cells (cardiomyocetes) - usually the thickest layer
What is the endocardium?
the innermost layer
thin layer of connective tissue surrounded by epithelial cells
What are 2 types of myocardium?
the muscle cell layer in heart walls can either be compact or spongy
Which animal types have compact myocardium?
mammals
birds
reptiles
Which animal types have spongy myocardium?
fish
amphibians
Describe compact myocardium
cardiomyocetes are tightly packed together and arranged in a regular pattern
describe spongy myocardium
loosely connected cardiomyocetes that have spaces between them and are not regularly organized
In fish and amphibians, how are spongy myocardium arranged?
as trabeculae (extensions) that project into heart chambers
How many chambers do fish hearts have?
2 chambers (1 atrium and 1 ventricle) but they also have 2 other compartments in series (sinus venosus and bulbus arteriosus)
What are the 4 components of fish hearts? In what order (single circuit)?
blood enters from body through sinus venosus compartment
blood travels into single atrium
atrium pumps blood through ventricle
ventricle pumps blood into bulbus arteriosus which expands and recoils to move blood into body
Which components of a fish heart are contractile?
atrium, ventricle and sinus venosus is weakly contractile
bulbous arterious is not contractile
Describe the valves in a fish heart
passive (no muscles = no contractions)
they open and close depending on pressure gradient to allow blood to flow through unidirectionally
What is the functions of bulbous arteriosus?
maintains pressure and volume
How many chambers do amphibian hearts have?
3: 2 atria + 1 ventricle
What feature of spongy myocardium is present in amphibian ventricles? what function does it serve?
trabeculae in ventricle to prevent mixing of oxygenated and deoxygenated blood
How does the amphibian heart direct blood to the pulmonary circuit or the systemic circuit?
the conus arteriosus has a spiral fold that directs deoxygenated blood to the pulmonary circuit for the skin and oxygenated blood to the systemic circuit
How many chambers does a non-crocodilian reptile heart have? what are they?
5
2 atria
3 interconnected (not completely separated) ventricular compartments
- cavum venosum
- cavum pulmonale
- cavum arteriosum
are oxygenated and deoxygenated blood separate in non-crocodilian hearts?
not completely, but close
there’s a muscular ridge between atria side and ventricular side that is not a complete septum, so blood can flow over top
What are the 3 interconnected ventricular compartments of the non-crocodilian reptile heart?
cavum venosum
cavum pulmonale
cavum arteriosum
describe the flow of blood in non-crocodilian reptile hearts
oxygenated blood enters left atrium from pulmonary vein and pumped into cavum arteriosum
cavum arteriosum leads to cavum venosum
from the cavum venosum, oxygenated blood can be pumped out of the heart through the left or right aorta into the systemic system
deoxygenated blood enters the right atrium and is pumped into the cavum venosum
deoxygenated blood in the cavum venosum flows over the muscular ridge into the cavum pulmonale and out of the pulmonary artery
How do reptilian hearts direct flow of blood between pulmonary and systemic circuits?
blood can be shunted to skip one of the 2 circuits
What is right-to-left shunting? why might this occur?
in reptilian hearts, deoxygenated blood skips the pulmonary circuit and enters directly into the systemic circuit
occurs during periods of breath-holding - there’s no purpose in wasting energy sending blood through pulmonary system if there’s no oxygen in the respiratory organs
What is left-to-right shunting? why might this occur?
in reptilian hearts, oxygenated blood skips the systemic circuit and enters directly into the pulmonary circuit to increase O2 delivery to myocardium of heart
How many heart chambers do birds and mammals have? what are they?
4
2 atria
2 ventricles
In mammals and birds, are deoxygenated and oxygenated blood separate?
yes completely separated heart chambers
Are atria walls thick or thin in birds and mammals?
thin
Are ventricle walls thick or thin in birds and mammals?
thick, but left is thicker than right
What separates the 2 ventricles in the mammal and bird heart?
intraventricular septum (a complete septum unlike in non-crocodilian reptiles)
What are the 4 major valves in birds and mammal hearts?
tricuspid atrioventricular (AV) - right atria to right ventricle
bicuspid/mitral atrioventricular (AV) - left atria to left ventricle
pulmonary semilunar - right ventricle to pulmonary artery
aortic semilunar - left ventricle to aorta
T or F: valves in birds and mammal hearts (AV and semilunar) are contractile
false, they are not muscles
Where is the tricuspid AV valve?
between the right atria and right ventricle of bird and mammal hearts
Where is the bicuspid/mitral AV valve?
between the left atria and left ventricle of bird and mammal hearts
Where is the aortic semilunar valve?
between the left ventricle and aorta in bird and mammal hearts
Where is the pulmonary semilunar valve?
between the right ventricle and pulmonary artery in bird and mammal hearts
Describe blood flow in bird and mammal hearts
deoxygenated blood enters right atrium from systemic vein
right atrium pumps deox blood through tricuspid AV valve into the right ventricle
right ventricle pumps deox blood through pulmonary semilunar valve into pulmonary artery to enter pulmonary system
oxygenated blood returns through pulmonary veins into left atrium
left atrium pumps ox blood through bicuspid AV valve into left ventricle
left ventricle pumps blood through aortic semilunar valve into aorta
aorta carries oxygenated blood into systemic circuit
What prevents the mixing of deoxygenated and oxygenated blood in bird and mammal hearts?
a fully developed septum between right and left compartments of the heart
What are the 2 phases of the cardiac cycle?
systole - contraction that causes blood to enter circulation
diastole - relaxation that causes blood to flow into the heart
Describe the phases of the mammalian cardiac cycle
atria and ventricles alternate between systole and diastole
both atria contract simultaneously
pause
both ventricles contract simultaneously
atria and ventricle simultaneously relax to allow the heart to refill with blood
Describe the steps of the mammalian cardiac cycle
ventricles are both in diastole = pressure greater in atria = AV valves open so that blood flows passively into the ventricles
atria contract to force the rest of the blood into the ventricles
ventricles contract which causes the AV valves to close (no backflow) = ventricle pressure increases
increased pressure in the ventricles causes semilunar valves to open and blood to flow out of heart through arteries
ventricles relax and pressure builds in the atria, semilunar valves close (no backflow) and atria pressure will surpass ventricular to continue this flow
How do atrial systole/diastole overlap or not with ventricular systole/diastole in mammals?
ventricular diastole overlaps with atrial systole
followed by atrial diastole overlap with ventricular systole
followed by ventricular diastole overlap with atrial diastole until atrial systole happens again
why is the left ventricle thicker than the right in mammals?
the left ventricle pushes blood out to the systemic circuit which is the rest of the body so blood needs to travel further and maintain a fast velocity so the left ventricle generates a lot more contraction force - needs to have more muscles working
is resistance in the pulmonary circuit of mammals high or low? why?
low because there’s a very high density of capillaries (larger cross-sectional area of capillaries)
Is there high or low pressure required to pump blood through the pulmonary circuit in mammals? why?
low - because the lungs are not that far from the heart, less force is needed because less distance to travel
also because the capillaries on the lungs are extremely delicate and high blood pressure would cause them to burst
the right side of the mammalian heart is involved in sending blood out into which circuit?
the pulmonary circuit via the pulmonary artery
the left side of the mammalian heart is involved in sending blood out into which circuit?
the systemic circuit via the aorta
how does ventricular pressure vary between the left and right ventricles of mammalian hearts?
the right ventricle produces significantly less pressure and causes low pressure blood flow into the pulmonary artery
the left ventricle produces significantly higher pressure and causes much higher pressure blood flow into the aorta
how does the blood pressure in the left atrium compare to the right atrium in mammalian hearts?
they’re comparable, both quite low
but left is slightly higher than right
How does blood pressure in the vessels change as blood moves further from the heart (closer to the veins)? why?
blood pressure decreases and also variation (between systole and diastole of heart) decreases
blood pressure and the variation in blood pressure between contractions and relaxations of the heart decrease over distance because the blood is farther from the pump and is less affected by the pump
Which part of the circulatory system (ex. atria, ventricles, arteries, venules, etc.) has blood pressure changes most affected by the systole and diastole of the heart?
the blood pressure in the left ventricle varies the most due to systole and diastole of the heart (significantly more than the rest)
What explains the pressure and pulse decrease in arterioles in mammalian hearts?
arterioles have increased cross-sectional surface area = reduced pressure, reduced response to systole and diastole
Which component of the circulatory system (ex. ventricle, atria, arterioles, venules, veins, etc) has highest blood velocity? why?
arteries
because blood is leaving the heart through the arteries, it is being pushed out directly by the contractile force of the heart
Which component of the circulatory system (ex. ventricle, atria, arterioles, venules, veins, etc) has lowest blood velocity? why?
capillaries
blood flow needs to be slow in the capillaries in order for gas and nutrient exchange to occur
if blood is flowing too fast, O2 can’t be diffused into or out of the capillaries/tissues
Which component of the circulatory system (ex. ventricle, atria, arterioles, venules, veins, etc) has intermediate blood velocity?
veins
How is the blood pressure in the aorta measured?
MAP
Mean Arterial Pressure = the average arterial pressure in aorta over a period of time
How is MAP calculated (ie., how does it include diastolic and systolic pressure)?
MAP = 2/3 diastolic pressure + 1/3 systolic pressure
How is blood velocity (distance/unit time) measured?
blood velocity = Q/A
where
Q = blood flow - the fluid volume transported per unit of time
A = cross-sectional area of the vessel
How is the velocity of flow related to the cross-sectional area of the vessel? give an example of this
velocity is inversely related to the cross-sectional area of the vessel
Velocity = Q/A
capillaries: high cross-sectional area but low velocity = allows for more diffusion of O2
How does cross-sectional area affect the blood velocity?
if cross-sectional area of vessel is small, the velocity will be high (faster)
if A is large, the velocity will be slower
What is the law of bulk flow?
blood flow = pressure change divided by resistance of blood vessels
Q = delta P / R
where R is proportional to the length of the vessel and length of the vessel is inverse to the radius^4 of the vessel
also where R is proportional to the viscosity of the fluid
How is the resistance of a blood vessel influenced by the viscosity of the blood, the length of the vessel, and the radius of the vessel? how does this all effect blood flow?
increased viscosity = increased R
increased length of vessel = increased R
R and length of vessel are inverse of radius^4 of the vessel = a slight change to the radius of the vessel has a huge impact on R and blood flow (ex., if radius slightly decreased = huge increase of R = huge decrease of blood flow)
increased R = decreased blood flow (Q)
What does Poiseuille’s equation represent?
it’s the equation that determines how a change in pressure, the radius and length of a vessel, and the viscosity of blood affects the flow of blood through a particular vessel
it states that pressure is the primary force that regulates blood flow
What is the primary force moving blood throughout the body?
pressure
What do vasoconstriction and vasodilation mean? how do these processes affect blood flow?
they refer to the small changes in the radius of blood vessels
because R is inverse to the radius ^4 and blood flow depends on R, minor changes to the radius of blood vessels cause massive changes to resistance and blood flow
What does Fick’s Law of diffusion represent?
the diffusion rate across capillaries depends on the concentration gradient, surface area, diffusion coefficient, and the distance of diffusion
Where do substances diffused across capillaries come from?
red blood cells in the blood vessels (remember that it’s red blood cells that have hemoglobin which can bind O2)
How thick are capillary walls?
very very very thin
< 1 um
What makes blood velocity so slow in capillaries?
capillaries have diameters of 7 um, but red blood cells have diameters of 8 um so RBCs have to move through capillaries in single file
Why do capillaries have such high rates of diffusion?
maximized concentration gradient of O2 in RBC
minimized distance of diffusion (cap wall is <1 um thick)
maximized surface area of diffusion = contact between RBC and cap is huge because the diameter of RBC is bigger than capillaries
also, movement of RBCs along capillaries is very slow
Where do signals for vertebrate heart contractions originate from (neuro or myogenic)?
myogenic
cardiomyocetes undergo spontaneous rhythmic depolarizations without nerve signals
What produces coordinated contractions between cardiomyocetes so that the heart functions/contracts as a whole unit?
gap junctions between cardiomyocetes electrically couples the cells to pass APs directly from cell to cell
What are pacemaker cells?
cells derived from cardiomyocytes that produce electrical excitatory signal for muscle contraction
Where are pacemaker cells located in fish? in other vertebrates?
fish: in sinus venosus
other: in the sinoatrial (SA) node of the right atrium
Do pacemaker cells have contractile properties like other muscle cells?
no
Describe characteristics of pacemaker cells
very small
few myofibrils
mitochondria and other organelles present
What is the pacemaker potential?
the unstable membrane potential of pacemaker cells that allow APs to initiate
How does pacemaker potential initiate APs in pacemaker cells?
the unstable resting potential in pacemaker cells increases due to opening or closing of ion channels until it reaches threshold to produce an AP
What are the steps involved in initiating an AP in pacemaker cells
pacemaker potential increases because K channels are open and K+ leaves cell
opening of either If (funny current) or Ih current influx of Na+ generates the AP
T-type and/or L-type Ca2+ channels open and Ca2+ influxes while rapid depolarization
K+ fluxes back into cell as repolarization
T or F; there are, like other APs, Na+ sodium gated channels involved in the pacemaker APs
false
only K+, If and Ih currents, and T-type and L-type Ca2+ channels
What is the If or Ih current?
the ‘funny’ current
nonselective cation channels in pacemaker cells which allow the influx of Na+ ions into the cell and cause gradual depolarization of MP
How does AP initiation differ in vertebrates where pacemaker cells are in the SA node (not fish)?
it’s the same but the HCN channel (cyclic nucleotide gated) encodes the If or Ih currentT
T or F: APs in pacemaker cells do not rely on voltage-gated channels like other cells
true, they have no voltage gated cells
What branch of the nervous system regulates heart rate?
Sympathetic (increase) and parasympathetic (decrease) branches of the autonomic NS
Which neurotransmitter is involved in increasing heart rate?
sympathetic neurons either release norepinephrine to receptors on the pacemaker cells
or send a signal to the adrenal medulla to release epinephrine for the receptors on the pacemaker cells
What class of receptors are on pacemaker cells to receive neurotransmitters from nerves?
Gs-coupled Beta receptors
Describe the signal transduction steps involved in increasing heart rate
norepinephrine is released from sympathetic neurons or epinephrine is released from the adrenal medulla and binds to the Beta receptor on pacemaker membranes
binding to receptor causes conformational change which causes Gs to activate cAMP
cAMP activates PKA
PKA activates the funny channel and T-type Ca2+ channels to allow influx of Na+ and Ca2+ into cell causing depolarization of membrane and increased heart rate
What part of the nervous system is involved in controlling decreased heart rate?
parasympathetic autonomic NS
Which neurotransmitter is involved in decreasing the heart rate?
acetylcholine
describe the steps involved in decreasing heart rate
parasympathetic neurons (vagal nerve) releases acetylcholine at the synapse to the pacemaker cells of the heart
muscarinic ACh receptors on pacemaker cells bind ACh which causes conformational change in its Gi subunits
Gi activates GIRK (Kir3) K+ channels = outflux of K+ from cell causing hyperpolarization
Gi inhibits:
- T-type and L-type Ca2+ channels and prevents influx of Ca2+
- If channels = no influx of Na+
this adds to hyperpolarization
more hyperpolarization means it takes longer for depolarization and frequency of AP decreases = decreased heart rate
Which parasympathetic nerve is directly involved in decreasing heart rate?
vagus nerve
What receptor is on the pacemaker cells that is involved in slowing heart rate?
Gi coupled - muscarinic ACh receptors
Which G subunit is involved in slowing heart rate?
Gi
What does Gi do when activated? how does this contribute to reducing heart rate?
Gi activates GIRK K+ channel = outflux of K+ = hyperpolarization
Gi inhibits T-type and L-type Ca2+ channels = no influx of Ca2+ = hyperpolarization
Gi inhibits funny channel (If) = no influx of Na+ = hyperpolarization
all of this increases the time it takes to depolarize to the AP threshold = slower heart rate
less Cav and Kv channel activity
What type of receptor is GIRK? what is it involved in?
it’s a G-protein coupled receptor on pacemaker cell membranes involved in reducing heart rate when activated by Gi to allow outflux of K+ out of cell
What can explain the plateau peak phase of the APs in cardiomyocetes?
depolarization is extended because the refractory period is longer = length of contraction
this is because Ca2+ influxes through L-type channels and K+ channels are slow
What is the purpose of extended APs in cardiomyocetes?
to prevent tetanus and temporal summation
need one AP at a time
describe how APs are propagated along muscle sarcolemma
AP causes Na+ channels to open - Na+ influxes = depolarization
depolarization causes L-type voltage gated Ca2+ channels to open - Ca2+ influxes = more depolarization
Na+ channels inactivate = repolarization
K+ channels open = K+ outfluxes = repolarization
Na+/K+ ATPase and Ca2+ ATPases reestablish ion gradients
What can cause the heart to contract more forcefully and with more blood?
Sympathetic nervous system releasing norepinephrine (or epinephrine) and endocrine system
How does cAMP (and PKA) (activated by the binding of norepinephrine to beta adrenergic Gs-coupled receptor on cardiomyocetes) function to increase force of contraction and flow of blood from heart?
cAMP activates PKA
PKA phosphorylates L-type Ca2+ channels = influx of Ca2+ into cell = contraction via actino-myosin activity
PKA also phosphorylates Ca2+ channels (RyR) on SR to increase sarcoplasmic [Ca2+] = increase actino-myosin activity = contraction
PKA phosphorylates myosin = increased contraction
PKA also phosphorylates SR Ca2+ ATPase (SERCA) = reduces time for Ca2+ to be removed from cytoplasm during relaxation, decreasing relaxation time = increasing heart rate
What are the two types of voltage-gated Ca2+ channels?
L-type - long-lasting (need strong depolarization)
T-type - transient
What are modified cardiomyocytes? what do they look like, what do they do?
elongated cells that appear pale in colour
not contractile but spread AP rapidly through myocardium
can experience rhythmic depolarizations
these cells conduct electrical currents throughout the heart
How is electrical current conducted in the mammalian heart?
pacemaker cells in the sinoatrial (SA) node initiate an AP
depolarization is carried through the internodal pathway to the AV node
the AV node slowly transmits the signal through the atria via gap junctions = atria contracts
His and Purkinje fibers carry the depolarization from the AV node toward the ventricles
depolarization moves up the ventricles = ventricles contract pushing blood toward the arteries
What functions do His and Purjinke fibers have in mammalian hearts?
they conduct depolarization
bundles of His fibers carry depolarization from the AV nodes into the ventricles
Purjinke fibers carry depolarization up the ventricles
How is the depolarization signal spread throughout the myocardium of mammal hearts?
through gap junctions
What is ECG or EKG?
electrocardiogram
used to assess and diagnose conduction problems in the heart (arrhythmias)
What does an ECG/EKG measure?
composite APs in cardiac muscle
P wave
QRS complex
T wave
What does the P wave show in an ECG?
depolarization of the atria caused by the wave of depolarization from the SA node
What does the QRS complex show in an ECG? what does the segment between S and the following T wave correspond to?
ventricular depolarization
S-T = plateau phase of ventricular AP
What does the T wave show in an ECG?
ventricular repolarization
What is the series of signals shown in an ECG of a normal cardiac muscle?
small, short P wave followed by
Q
rapid increase for R
rapid decrease to S
followed by plateau then increase to T
decrease from T to a plateau until next atrial depolarization
What is ventricular fibrillation?
an arrhythmia that initiates in the ventricles
What does an ECG scan look like in a heart with ventricular fibrillation?
the peaks and waves are all over the place and there is no rest/relaxation between signals
What does cardiac output mean?
the volume of blood pumped per unit of time
How is cardiac output calculated?
CO = HR * SV
where HR = rate of contraction (bpm)
SV = stroke volume (volume of blood pumped per beat)
How is stroke volume calculated?
volume of blood at the end of diastole minus the volume of blood at the end of systole
How does the resting heart rate of a human compare to that of a blue whale? to a mouse? to a reptile?
blue whale = 6 bpm
human = 70 bpm
mouse = 580 bpm
lizard = 50 bpm
How can cardiac output be modified?
by regulating heart rate and/or stroke volume
What regulates heart rate?
autonomic nerves of the sympathetic (increase) and parasympathetic (decrease) systems and the adrenal medulla (increase)
What is bradycardia?
decreased heart rate
What is tachycardia?
increased heart rate
What regulates stroke volume of heart?
nervous system
hormones
physical factors
What is the Frank-Starling effect?
If end-diastolic volume is increased = contraction force is increased and stroke volume is increased
the effect: the heart automatically compensates for increased volume of blood returning to heart by shifting the cardiac muscle length-tension relationship
what type of curve does the Frank-starling effect produce?
an increasing curve between stroke volume and end-diastolic volume (position of muscle length-tension relationship)
How does increased sympathetic activity affect the frank-starling effect?
the FS curve (position of muscle length-tension relationship) is raised
= higher end-diastolic volume = higher stroke volume
How does decreased sympathetic activity affect the frank-starling effect?
the curve (position of muscle length-tension relationship) is lowered
= lower end-diastolic volume = lower stroke volume
What is it called when the heart automatically compensates for the increased volume of blood returning to the heart when there’s increased end-diastolic volume? (related to FS effect)
autoregulation
How can cardiac output be used to calculate Mean Arterial Pressure?
MAP = CO * TPR
TPR = total peripheral resistance
How is MAP maintained within a set range?
the body regulates cardiac output and total peripheral resistance to keep MAP within a specific range
How is blood flow regulated (what controls blood distribution)?
arterioles
they are arranged in parallel so they can change the blood flow to different organs by vasoconstricting or vasodilating (altering resistance of flow)
What processes do arterioles use to regulate blood flow? what factor of blood flow do these influence?
arterioles can use vasoconstriction or vasodilation to change their resistance to blood flow to either increase or decrease flow to certain organs
What 3 ways are vasoconstriction and vasodilation in arterioles controlled?
autoregulation - directly controlled by the smooth muscle of arterioles
intrinsic factors (ex. the metabolic state of the tissue)
extrinsic factors (ex. nervous and endocrine systems)
What is myogenic autoregulation? what kind of a feedback loop is it? what is the main function?
When blood pressure increases in arterioles, their smooth muscle cells are stretched which triggers them to contract
negative feedback loop
functions to prevent excess blood flow into tissues
How does metabolic activity of tissues regulate blood flow? what kind of feedback loop?
muscle cells in arterioles detect extracellular fluid conditions
vasoconstrict/dilate depending on concentration of metabolites = blood flow matches metabolic needs
negative feedback loop
Describe what happens to blood flow during exercise relating to metabolic activities of tissues
When tissue metabolic rate is increased (ex. from exercise)
tissues decrease in O2, increase in CO2 (more respiration)
these conditions trigger arteriole smooth muscles to vasodilate > decreased resistance = increased blood flow
increased blood flow allows for increased delivery of O2, removal of CO2 and waste
What is another example of how arteriole smooth muscle cells are sensitive to extracellular fluid?
if paracrine release of nitric oxide = vasodilation of arterioles = increased blood flow?
How does the nervous system influence arteriole regulation of blood flow?
release of norepinephrine from sympathetic neurons causes arterioles in:
- cardiac and skeletal muscles to vasodilate = increased blood flow
- other muscles to vasoconstrict
does the PNS play a role in vasodilation of arterioles?
no, vasodilation occurs in arterioles either as a result of NE release or when sympathetic tone is reduced
What other hormones can effect the blood flow regulated by arteriole smooth muscles?
vasopressin (ADH) = generalized vasoconstriction
angiotensin II = generalized vasoconstriction
Atrial natriuretic peptide (ANP) = generalized vasodilation
what factors influence total peripheral resistance in vasculature?
hormones like vasopressin, angiotensin II, ANP
Sympathetic NS + epinephrine or norepinephrine
metabolites and paracrines
^^ effect arteriole diameter ^^
number of red blood cells effects blood viscosity
What factors influence cardiac output?
Parasympathetic NS reduces heart rate
sympathetic NS (+ ENE and NE) increase heart rate and stroke volume
kidneys (salt/water balance and balance of interstitial fluids/blood) affect blood volume
respiratory pump
skeletal muscle pump
all increase the venous return
the venous return increases the EDV (Frank-Starling effect)
the EDV increases the stroke volume
what are baroreceptors? where are they?
stretch-sensitive mechanoreceptors in major blood vessel walls (especially carotid arteries and aorta)
what do baroreceptors do?
detect stretching of blood vessel walls and send signal to medulla oblongata (cardiovascular control center) to regulate MAP
What is the cardiovascular control center?
the medulla oblongata
What type of feedback loop is the baroreceptor reflex?
negative
increased MAP causes reduced MAP which causes increase in MAP
Where does the baroreceptor reflex occur?
in carotid arteries and aorta
