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Transport in Humans (and other Mammals)

The Circulatory System

Cardiovascular SystemConsists of Heart, Lungs and Vessels

Double Circulatory System

BODY HEART LUNGSSystemic

circulationPulmonary circulation

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The Heart• Weighs approx 300g

• Thick muscular layer (myocardium) made of Cardiac muscle

• Has it’s own blood supply– covered in capillaries which get blood from coronary

arteries

• Myogenic- self exciting– Continuous rhythm (can be altered)

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• Two upper thin walled chambers – atria

• Two lower thick walled chambers – ventricles

• Atria collect blood from the body – attached to veins

• Ventricles send blood to the body – attached to arteries

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The Heart• Right side – deoxygenated• Left side – oxygenated• Separated by a thick walled septum• Right atrium and ventricle connected by

tricuspid valve• Left atrium and ventricle connected by bicuspid

(mitral) valve• Cuspid valves held shut by Chordae Tendinae• Left ventricle is thicker than the right

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Vessels of the Heart

• Pulmonary artery*• Pulmonary vein• Superior and Inferior Vena cava• Aorta*

• *Semi-lunar valves

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Diagram of the Heart

pg 13

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Blood Flow Through the Heart

1. Vena Cava – Superior/Inferior2. Right Atrium3. Tricuspid Valve4. Right ventricle5. Pulmonary Artery

LUNGS

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Blood Flow Through the Heart

6. Pulmonary veins7. Left Atrium8. Bicuspid/Mitral/Atrioventricular valve9. Left Ventricle10.Aorta

MAJOR ORGANS

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Control of the Heart

• Myogenic-Initiated from inside the heart as opposed to nervous stimulus outside

• Initial Stimulus originates in the Sinoatrial node (SA node)

• A pacemaker that determines heart rate• Wave of excitation across both atria

causes them to contract

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Control of the Heart• Atrioventricular node (AV node)

• Sends waves of excitation along Purkinje Fibres which collectively make up the Bundle of His. Along septum, radiate upwards

• Causes ventricles to contract

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Cardiac cycle• Systole -contraction of heart• Diastole -Relaxation/filling of the heart

• Both atria contract at the same time – Called ………………….

• Both ventricles contract at same time– Called ………………….

• Relaxation of atria and ventricles– Called ……………………….

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Cardiac cycle

• Remind me…. What is it?

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Vessels of the Cardiovascular System

Artery

Arteriole

Capillary

Vein

Venuole

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Vessels of the Cardiovascular System

• Arteries – Arterioles – Capillaries - Venuoles - Veins

• Different structures and functions

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Arteries

• Carry blood away from the heart• Blood in arteries is under high pressure• Their structure is related to their function• Round in structure with relatively thick

walls composed of three layers

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Arteries

A. Tunica Intima – Single layer of endothelial cells

B. Tunica Media – A thick layer containing elastic fibres and muscle tissues. Closer to heart more elastic fibres those further away have more muscle fibre

C. Tunica Externa – Contains collagen fibres for strength

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Diagram of an Artery… volunteer?

Blood vessels – the arteries

TUNICA EXTERNA

TUNICA MEDIA

TUNICA INTIMA (LUMEN

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Veins• Carry blood back to the heart (generally

deoxygenated)• Blood now flowing slowly, smoothly and under

low pressure (structure related to this function)• Walls are relatively thin compared with arteries• Still same three layers but the tunica media

differs in size – relatively narrow with few muscle fibres and elastic fibres

• Semi Lunar valves present along length

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Diagram of Veins

Blood vessels – the veins

TUNICA EXTERNA

TUNICA MEDIATUNICA INTIMA

LUMEN

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Capillaries• Link the arterial and venous blood supplies• Blood flow is slow, blood pressure is falling and

is non-pulsatile• Capillaries form vast networks in all tissues and

organs• Composed of only the Tunica Intima, only a

single layer of endothelial cells, no elastic fibres and no muscle tissue

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Capillaries

• Exchange of materials between the blood and the body takes place in the capillary bed

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Diagram of a Capillary

Blood vessels – the capillaries

LUMEN

ONE CELL THICK

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Time for an exam questionpage 13

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Components of Blood

• Blood is made up of:– Variety of cells– Suspended in fluid – Plasma

• All blood cells develop from stem cells in bone marrow

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Plasma• Transports everything.• Blood cells.• Digested foods

(glucose).• Waste.• Hormones

• 90% water, 10% solutes• 3 Proteins:

– Globulins, Albumins and Fibrinogen

clottingimmune

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Red Blood cells• Erythrocytes• Red Blood cells carry

oxygen around the body in haemoglobin.

• They have no nucleus thus leaving more space for oxygen

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White blood cells • Leucocytes• Fight against disease.• Destroys bacteria by

using antibodies.• Fights toxins by using

antitoxins.• Kills foreign microbes

by consuming them.

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White blood cells cont.• WBC’s divided into 2 groups:

– GRANULOCYTES– AGRANULOCYTES

• Granulocytes have granules in cytoplasm & multilobed nucleus. 3 types:– Neutrophils– Eosinophils– Basophils

• Agranuloycytes are NOT granular or lobed– Monocytes– lymphocytes

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Platelets

• Thrombocytes• Platelets are tiny

fragments in the body that help blood clot at wounds.

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Transport of gases

• Oxygen combines with Haemoglobin:Haemoglobin + oxygen oxyhaemoglobin

• Reversible so O2 is available to body tissues.

• Each g of haemoglobin can combine with 1.34cm3 of oxygen.

• See WJEC (oxygen dissociation)

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Oxygen Dissociation Curves

• Concentration of gases are measured in partial pressures

• As haemoglobin is exposed toincreasing ppO2, haemoglobintakes it up until saturated

• Each haemoglobin can take up___ molecules O2

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Oxygen Dissociation Curves• Curve shape depends on number

of factors:– pp CO2– Temp– pH

• Increasing ppCO2 shifts curve right, Bohr Effectdue to decrease in affinity of haemoglobin to O2

• Means oxyhaemoglobin releases more O2 as CO2 rises ie when cells are respiring more

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Fetal Haemoglobin

• Haemoglobin F has a higher affinity for oxygen than adult haemoglobin

• Means it is able to gain oxygen from mothers haemoglobin

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Myoglobin• Myoglobin is a pigment found in muscle and

hearts of mammals

• Combines reversibly with Oxygen

• Takes up oxygen more readily than haemoglobin

• Blood reaching muscle transfers O2 to myoglobin acting as a temp store

• Myoglobin gives up its O2 when ppO2 drops to very low value, eg after exercise

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CO2

• See WJEC (transport of gases)• CO2 produced in respiration diffuses into blood

and into RBCs

• In RBCs the CO2 combines with H2O to form carbonic acid (H2CO3) – enzyme carbonic anhydrase

• Carbonic acid then dissociates to hydrogencarbonate ions

CO2 + H2O H2CO3 H+ + HCO3-

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CO2

• Hydrogencarbonate ions diffuse into plasma in exchange for Cl- ions

• CO2 reacts with haemoglobin and other proteins to form carbamino compounds

• CO2 can be transported in blood 3 ways:– Hydrogencarbonate ions– Carbamino compounds– Simple solution, dissolved in plasma

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Tissue Fluid• Fluid that leaks out of

capillaries is called tissue fluid

• It fills spaces between body cells

• It contains:– Water Glucose– Amino acids Fatty acids– Glycerol mineral

ions– vitamins– Dissolved gases

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• Blood pressure at arteriole end of capillaries (5.3kPa) forces water out

• • This hydrostatic pressure must be greater than the osmotic

pressure drawing water in.

• Plasma Proteins stay in capillaries (so low ψ) and the hydrostatic pressure keeps dropping as the blood passes through the capillary beds.

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• At venular end, pressure has dropped to less than that of the osmotic effect of the proteins (1.3kPa)

• Water drawn back in to capillaries (99% of it anyway)

• Excess fluid and some waste products like urea enter lymph system and are returned via that pathway.