Circulation And Blood Flashcards
Cnidarians eg jellyfish
multi-cellular and relatively complex but rely on diffusion for gas exchange and flagella circulate digestion products around the coelenteric fluid to allow cells to directly phagocytose food particles
Platyhelminthes eg flatworms
Flat so short diffusion distances so can rely on diffusion
In large turbellaria diffusion distances are increased so they have gut ceca in which cilia move digestion products nearer the edges of the body
Nematodes
small (most < 2.5 mm long) and do not need a circulatory system
Annelida worms
Large and segmented
Require a circulatory system
Each segment has a coelom filled with fluid which is circulated by cilia on the internal walls and by muscular contractions
developed a haemal system where there are blood vessels and hearts that allow fluid transport around the body.
Blood vessel definition
A tubular structure carrying blood through the tissues and organs I.e. vein, artery or capillary
Heart definition
A muscular organ in most animals, which pumps blood through the blood vessels of the circulatory system
Blood definition
A body fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away
Haemolymph definition
A body fluid that is a mixture of blood and interstitial fluid
Annelida circulatory system
Dorsal and ventral blood vessels located in mesentery
Blood (containing haemoglobin) flows anteriorly in the dorsal vessel and posteriorly in the ventral vessel
In each segment blood moves from the ventral vessel to the dorsal vessel via a capillary plexus in the body wall and vice versa through vessels around the gut wall – ‘closed’ system
Walls of blood vessels (esp. dorsal) are contractile and pump blood via peristalsis
Mollusca circulatory system
Open system Increased size and body plan complexity mean that molluscs have a well developed circulatory system
Heart with pairs of atria and a medial ventricle
Dorsal aorta
Blood vessels
Haemolymph (blood)
Haemocoel – body cavity filled with haemolymph
Heart has one or more pairs of atria – receive oxygenated blood from gills
Empty into medial ventricle, which is continuous with aorta, which branches to smaller vessels to deliver blood to haemocoelic sinuses in the head, foot and bathe the visceral mass
Blood passes over the nephridia and returns to heart by afferent branchial vessels
Mollusca closed circulatory system
Cephalopods (octopus, squid, cuttlefish) are advanced invertebrates in a variety of ways. Their circulation is characterized by being a ‘closed’ system where blood is kept within vessels and there are hearts either side of the gills. Blood from the two gills flows to the systemic heart which pumps it around the body. After perfusing the systemic tissues the de-oxygenated blood is returned to two branchial hearts – one per gill. These hearts force the blood through the gills and beyond.
This system shows that blood can be pumped around in different states of oxygenation. Oxygen rich is forced from the gills by the branchial hearts pumping blood into the gill capillaries. The systemic heart then pumps this oxygenated blood to the rest of the body, where the tissues use the oxygen. Deoxygenated blood is then moving to the branchial hearts as the systemic heart beats. In effect, there is a pumping system to the respiratory organs and one for the rest of the body.
3 different hearts in cephalopods
One per gill (brachial hearts) x2
One systemic heart
Molluscan circulation
Molluscs have simple hearts that can only produce low differential pressure
One heart wouldn’t be enough to distribute blood through both the tissues and gills capillaries network so secondary hearts improve efficiency
Arthropoda- insecta
Insects have one dorsal blood vessel (‘heart’) that pumps haemolymph from the posterior to the anterior into the aorta
Haemolymph empties directly into haemocoel and returns to the heart directly via holes, ‘ostia’, in the vessel walls
Very simple system but only transports nutrients and waste products, NOT respiratory gases
Arthropoda- insects
Insects have one dorsal blood vessel (‘heart’) that pumps haemolymph from the posterior to the anterior into the aorta
Haemolymph empties directly into haemocoel and returns to the heart directly via holes, ‘ostia’, in the vessel walls
Very simple system but only transports nutrients and waste products, NOT respiratory gases
Arthropoda - crustacea
Crustaceans respire via gills and large species need more complex circulatory systems to transport respiratory gases
Blood pumped into haemocoel but infrabranchial sinus collects blood and haemolymph and delivers it to gills
An infrabranchial sinus collects haemolymph and the pumping action of the heart draws haemolymph through the gills and the branchio-pericardial ‘veins’ deliver it to the pericardial sinus.
Collecting vessels from gills deliver haemolymph into a pericardial sinus
Haemolymph enters heart via several ostia and is pumped out via arteries
Cephalochordata- amphioxus
Well developed haemal system but no compact heart
Ventral sinus venosus and aorta are contractile
Contractions push blood through gill capillaries to paired dorsal aorta
Colourless blood
Vertebrate hearts
Blood flows through tubular vessels
2nd Law of Thermodynamics predicts that fluid moving along a vessel will stop unless energy is expended
Circulatory systems require a pump, very often a heart, to keep blood moving
Need to an efficient heart increases as animals increase in size
Blood vessels are defined in terms of their relationship to the heart
Arteries carry blood away from a heart
Veins carry blood to a heart
Teleost (bony fish) heart
Heart has four sequential chambers
Blood delivered by the great veins enter the sinous venosus and then the atrium
Ventricle is the main propulsive chamber
Bulbus arteriosus has elastic properties to help maintain blood pressure
In sharks, it is contractile and is called the conus arteriosus
Passive valves between the chambers ensure that blood flows in the one direction
Conus arteriosus
Sharks
Contractile to maintain blood pressure
Cardiac system in teleosts
Heart receives deoxygenated blood from systemic tissue which is pumped to the gills via the ventral aorta
Dorsal aorta distributes oxygenated blood to the tissues via the dorsal aorta
Limitations of the teleost heart
Vertebrate circulation has two parts
Respiratory circulation
Systemic circulation
Single cycle circuit – blood goes to respiratory system first
Heart virtually empty after each systole (contraction phase)
Blood goes through capillaries in the gills and loses pressure
Systemic circulation is under low blood pressure
Heart receives de-oxygenated blood from the systemic tissues
Pumping is energy intensive so requires a lot of oxygen
In many fish blood perfusing the spongy myocardium, which comprises the ventricle, has a limited oxygen supply
Some species have some compact myocardium, which has its own coronary blood supply that delivers oxygenated blood
Spongy myocardium
lots of vessels to supply blood but this limits the amount of muscle.
Compact myocardium
coronary blood vessel mean that the myocardium can increase its muscle content and so generate more thrust during a contraction.
Amphibian cardiac system
Three-chambered heart and double cycle circuit
Separate atria – left receives oxygenated blood and right de-oxygenated blood
Single ventricle receives output from both atria (lacks septum)
Cardiac output from the ventricle can go to the lungs and/or skin- partially oxygenated blood——in practice differential contraction of the two sides of the ventricle wall, in conjunction with the septa, mean that the vast majority of the oxygenated blood goes to the body and deoxygenated blood goes to the lungs.
Crocodilians
Ventricle is completely divided into two chambers by a septum allows for differential pressure between ventricles
Two systemic arteries – one from each ventricle
Left and right aortas connected shortly after leaving heart - Foramen of Panizza
Also there is a anastomsis further away from heart
Crocodilians cardiac system
Air-breathing – blood can leave right ventricle easily and go the lungs.
Systolic pressure is low and does not open the flap into the systemic aorta
Diving – blood flow is restricted when leaving right ventricle so systolic pressure is increased and opens the flap into the systemic aorta
Cardiac systems in birds and mammals
Complete separation of the two ventricles
Double cycle circuit – completely independent systemic (high pressure) and pulmonary (low pressure) circuits
Improved respiratory gas exchange = higher metabolism and more active life style
Selective distribution
Generally deoxygenated blood sent to the lungs and oxygenated blood sent to the systemic tissues using anatomical features that physically block the mixing of blood
In amphibians and non-Archosaurs an effective double cycle circuit can be established despite anatomy suggesting otherwise – unclear how this is achieved
Crocodilians exhibit the variability in the system
Maintenance of different blood pressures in systemic and pulmonary circuits
Systemic circuits are longer and more complex so drops in blood pressure are likely – need high pressures be maintained to produce high flow rates
Such high pressures in the lung capillaries would induce ultrafiltration of plasma through vessel wall and the lungs would fill with fluid
Pulmonary circuits require lower blood pressures
Redistribution of cardiac output
Being able to adjust the flow of blood to the lungs can be advantageous if you have a low metabolism and breathe intermittently
A turtle during a dive will not be breathing air so having an incomplete septum in the ventricle means that blood can be diverted around the systemic system rather than go to the oxygen-depleted lungs
Amphibians – lungs get blood by having lower pressure in blood vessels— path of least resistance
Comparison between vertebrates
Metabolic rates vary between vertebrates with endo thermic species having higher metabolic rates
Trend towards increased heart mass with fish having the smallest hearts relative to body mass
Which group of organisms has a three-chambered heart?
Amphibians
In annelids, which blood vessel carries blood towards the head?
Dorsal vessel
How does blood enter the crustacean heart?
Haemolymph enters heart via several ostia
In terms of their circulation, how do cephalopods differ from other molluscs?
Closed system rather than open system
Which one of these is the odd one out, and why? Blackbirds, squirrels, or turtles
Turtle - has a ventricle chamber that has three parts that allows some mixing of oxygenated and deoxygenated blood. two atria but one ventricle that is incompletely divided into three chambers by horizontal and vertical septa
Blackbird/squirrel- 2 atria and 2 ventricles
The heart as a pump
Heart creates circulation by causing a pressure difference
A periodic muscle contraction increases pressure inside the heart and forces blood out of the lumen
Contraction phase = systole
Relaxation phase = diastole
Why is blood forced out of the heart under pressure
Blood, being water-based, is resistant to compression and so is forced out of the heart under pressure.
What does atrial and ventricular systole cause
Increase in blood pressure in the atrium lumen
Reduction in lumen volume causing blood to flow out under pressure into the ventricle
Back flow is prevented by valves in the veins delivering blood or in the heart
Myogenic
Rhythmic depolarisation originating in muscle
Neurogenic
Depolarisation that originates in neurones
Where is a neurogenic heart found
Lobsters
Spiders
Neurogenic heart
rhythmic depolarisation originates in neurones, e.g. lobster (Homarus), other crustacean and arachnids
Each muscle cell in heart is innervated and only contracts when stimulated by nerve impulses
Heart has cardiac ganglion – nine neuronal processes have direct nervous connection with each muscle cell
One posterior neuron assumes role of pacemaker – spontaneous periodic train of action potentials that stimulate other neurones and in turn muscle cells
Myogenic heart
Adjacent muscle cells are electrically coupled so depolarisation of one cell rapidly leads to direct depolarisation of adjacent cells
Cells will spontaneously contract but not in unison
Requires pacemaker
Fish, amphibians and non-avian reptiles – located in sinus venosus or at its junction with the atrium
Birds and mammals – located in wall of right atrium
Modified muscle cells with reduced contractile apparatus but first to spontaneously depolarise
Depolarisation spreads across myocardium via conduction
Where is the pacemaker located in a birds/mammals myogenic heart
Wall of right atrium
Where is pacemaker of myogenic heart in fish/amphibians/non-avian reptiles
Sinus venosus or at its junction with the atrium
Path of depolarisation in myogenic heart
depolarization starts in the S-A node in the right atrium wall. And spreads across the atrium wall causing the atrial systole (contraction). However, the tissue between the atria and ventricles is fibrous and not conductive. The two parts of the heart are connected by the Purkinje fibres that are in the atrioventricular bundle that allow the depolarization to cross the non-conductive barrier. The atrial depolarization causes depolarization of the A-V node, which depolarizes the Purkinje fibres which then depolarize the muscle cells in the ventricle wall. This system means that blood in the atria are pushed into the ventricular chambers before the ventricles contract.
Micro capillary beds
Arterial blood delivered via arterioles
Capillary walls consist only of vascular endothelial cells so wall is <1μm thick
1 cm³ of skeletal muscle can have 10-20 metres of capillaries
Blood leaves via venules
Leads to reduction blood pressure
Blood flow through vessels
Rates of blood flow depend on differences in pressure and vascular resistance
Consider non-turbulent flow of water through a horizontal, rigid-walled tube
Factors affecting the rate of blood flow
Pressure at the entry to the tube and pressure at the exit
Radius of the lumen
Tube length
Viscosity of the liquid
Hagen-Poiseuille equation describes the inter-relationships between these variables
Flow rate
Increasing the pressure difference increases the rate of the flow
Increasing viscosity reduces flow rate
Flow rate is a function of r4/l so it is very sensitive to changes in radius of the lumen
Friction between the liquid and the wall of the tube slows the rate of flow
Energy ‘lost’ as heat
Liquid in the middle of the tube flows faster
Vasoconstriction that reduces the lumen radius by ½ reduces blood flow by
1/16
Vascular resistance
Flow rate = ΔP/R, where ΔP = difference in blood pressure at start and end of vessel
Flow rate will increase if ΔP increases but will decrease if R increases
Blood vessels are not uniform in radius and although total cross-sectional area increases in a capillary bed, the radius of each vessel is very much reduced
Increased R in capillaries leads to slower rates of blood flow
Vascular resistance is proportional to the fourth power of the radius of the vessel lumen
When blood moves into a capillary bed its volume remains the same but lumen radius decreases slowing flow rate and increasing vascular pressure
Leaky capillary walls
Capillary walls are leaky – gaps between cells and aquaporin protein channels
As blood enters a capillary plasma is forced out
Some is reabsorbed by osmosis as blood leaves the capillary
Starling-Landis hypothesis
there is a net loss of liquid as blood passes through a capillary bed
How is plasma returned to the circulatory system
by the lymph system
Body movement and muscular contractions move lymph through vessels
Gravity and blood pressure
A liquid in a tube exhibits differences in pressure according to height because gravity is pulling the liquid down
Above a heart arterial pressure drops and vice versa
Human heart can only generate enough pressure (12.7 kPa) to pump blood 1.2 m above itself
Gravity, blood pressure and lower limbs
Blood has a mass and in the venous system blood pressure is low
Gravity could lead to blood pooling in parts of the body below the heart
Contractions of skeletal musculature help force blood through veins, which contain valves that prevent blood from going back down the vessel
Gravity, blood pressure and giraffe
Selective vasodilation / vasoconstriction helps distribute blood to parts of the body where needed most and relieve pressure on heart
Vasoconstriction in lower limbs redirects blood to the head
Large left ventricle and high aortic pressure (29 kPa vs. 13 kPa in other mammals)
Vasodilation in lower limbs redirects blood to the legs
Heart rate and body size
Heart rate (beats per minute) in mammals exhibit a negative relationship with body mass – small mammals have fast heart rates and big mammals have slow heart rates
Control of heart rate
Hormonal – epinephrine and norepinephrine increase heart rate and volume
Neural – all hearts have regulatory neurones that stimulate or inhibit the heart rate
Intrinsic controls – Frank-Starling mechanism suggest that stretching of the cardiac muscle tends to increase the force of contraction
Balances venous return with cardiac output
Cardiac output
Cardiac output (mL/min) = heart rate (beats per min) x stroke volume (mL)
Rate of O2 delivery
Rate of O2 delivery = cardiac output x (arterial [O2] – venous [O2])
