Circulation And Blood

Question 1

Cnidarians eg jellyfish

Answer 1

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

Question 2

Platyhelminthes eg flatworms

Answer 2

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

Question 3

Nematodes

Answer 3

small (most < 2.5 mm long) and do not need a circulatory system

Question 4

Annelida worms

Answer 4

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.

Question 5

Blood vessel definition

Answer 5

A tubular structure carrying blood through the tissues and organs I.e. vein, artery or capillary

Question 6

Heart definition

Answer 6

A muscular organ in most animals, which pumps blood through the blood vessels of the circulatory system

Question 7

Blood definition

Answer 7

A body fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away

Question 8

Haemolymph definition

Answer 8

A body fluid that is a mixture of blood and interstitial fluid

Question 9

Annelida circulatory system

Answer 9

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

Question 10

Mollusca circulatory system

Answer 10

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

Question 11

Mollusca closed circulatory system

Answer 11

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.

Question 12

3 different hearts in cephalopods

Answer 12

One per gill (brachial hearts) x2
One systemic heart

Question 13

Molluscan circulation

Answer 13

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

Question 14

Arthropoda- insecta

Answer 14

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

Question 15

Arthropoda- insects

Answer 15

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

Question 16

Arthropoda - crustacea

Answer 16

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

Question 17

Cephalochordata- amphioxus

Answer 17

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

Question 18

Vertebrate hearts

Answer 18

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

Question 19

Teleost (bony fish) heart

Answer 19

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

Question 20

Conus arteriosus

Answer 20

Sharks
Contractile to maintain blood pressure

Question 21

Cardiac system in teleosts

Answer 21

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

Question 22

Limitations of the teleost heart

Answer 22

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

Question 23

Spongy myocardium

Answer 23

lots of vessels to supply blood but this limits the amount of muscle.

Question 24

Compact myocardium

Answer 24

coronary blood vessel mean that the myocardium can increase its muscle content and so generate more thrust during a contraction.

Question 25

Amphibian cardiac system

Answer 25

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.

Question 26

Crocodilians

Answer 26

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

Question 27

Crocodilians cardiac system

Answer 27

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

Question 28

Cardiac systems in birds and mammals

Answer 28

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

Question 29

Selective distribution

Answer 29

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

Question 30

Maintenance of different blood pressures in systemic and pulmonary circuits

Answer 30

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

Question 31

Redistribution of cardiac output

Answer 31

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

Question 32

Comparison between vertebrates

Answer 32

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

Question 33

Which group of organisms has a three-chambered heart?

Answer 33

Amphibians

Question 34

In annelids, which blood vessel carries blood towards the head?

Answer 34

Dorsal vessel

Question 35

How does blood enter the crustacean heart?

Answer 35

Haemolymph enters heart via several ostia

Question 36

In terms of their circulation, how do cephalopods differ from other molluscs?

Answer 36

Closed system rather than open system

Question 37

Which one of these is the odd one out, and why? Blackbirds, squirrels, or turtles

Answer 37

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

Question 38

The heart as a pump

Answer 38

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

Question 39

Why is blood forced out of the heart under pressure

Answer 39

Blood, being water-based, is resistant to compression and so is forced out of the heart under pressure.

Question 40

What does atrial and ventricular systole cause

Answer 40

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

Question 41

Myogenic

Answer 41

Rhythmic depolarisation originating in muscle

Question 42

Neurogenic

Answer 42

Depolarisation that originates in neurones

Question 43

Where is a neurogenic heart found

Answer 43

Lobsters Spiders

Question 44

Neurogenic heart

Answer 44

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

Question 45

Myogenic heart

Answer 45

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

Question 46

Where is the pacemaker located in a birds/mammals myogenic heart

Answer 46

Wall of right atrium

Question 47

Where is pacemaker of myogenic heart in fish/amphibians/non-avian reptiles

Answer 47

Sinus venosus or at its junction with the atrium

Question 48

Path of depolarisation in myogenic heart

Answer 48

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.

Question 49

Micro capillary beds

Answer 49

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

Question 50

Blood flow through vessels

Answer 50

Rates of blood flow depend on differences in pressure and vascular resistance Consider non-turbulent flow of water through a horizontal, rigid-walled tube

Question 51

Factors affecting the rate of blood flow

Answer 51

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

Question 52

Flow rate

Answer 52

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

Question 53

Vasoconstriction that reduces the lumen radius by ½ reduces blood flow by

Answer 53

1/16

Question 54

Vascular resistance

Answer 54

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

Question 55

Leaky capillary walls

Answer 55

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

Question 56

Starling-Landis hypothesis

Answer 56

there is a net loss of liquid as blood passes through a capillary bed

Question 57

How is plasma returned to the circulatory system

Answer 57

by the lymph system Body movement and muscular contractions move lymph through vessels

Question 58

Gravity and blood pressure

Answer 58

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

Question 59

Gravity, blood pressure and lower limbs

Answer 59

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

Question 60

Gravity, blood pressure and giraffe

Answer 60

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

Question 61

Heart rate and body size

Answer 61

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

Question 62

Control of heart rate

Answer 62

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

Question 63

Cardiac output

Answer 63

Cardiac output (mL/min) = heart rate (beats per min) x stroke volume (mL)

Question 64

Rate of O2 delivery

Answer 64

Rate of O2 delivery = cardiac output x (arterial [O2] – venous [O2])