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The mammalian circulatory system is a vast network of blood-filledvessels that delivers blood to every cell of the organism

The circulatory system is a mass flow system, moving bloodon mass from one part of an organism to another

The circulatory system is essential for ensuring that materials are transported between the various exchange surfaces of the organism

The capillaries of the blood system are the sites forexchange of materials between the blood and the tissues

The capillary networks surrounding the alveoli ofthe lungs are the sites at which gas exchange takes place

The capillary networks within the villi of the small intestinereceive and transport the digested food materials needed

by the cells of the organism

The circulatory systemis linked with exchange

surfaces

The Mammalian Circulatory SystemThe Mammalian Circulatory System

The heart, togetherwith the blood vessels and theblood that they contain forms

THE CIRCULATORY SYSTEM

R A L A

R V LV

C A P IL L A R IE SIN L U N G S

C A P IL L A R IE SA R O U N D

B O D Y T IS S U E S

The human heart,except during fetallife, is completelydivided into right

and left sidesThe heart has fourchambers with anupper and a lower chamber on each

sideThe upper chambers

are the right and left atria

(RA and LA), andthe lower chambers

are the ventricles(RV and LV)

Blood always entersthe heart along

veins, which deliverblood to the atria

Blood is pumpedaway from the

heart along arteries,which originate in

the ventricles

The LEFT SIDEof the heart

receivesOXYGENATED

BLOODfrom the lungs

and then deliversit to the body

tissues

The RIGHT SIDEof the heart

receivesDEOXYGENATED

BLOODfrom the body

tissues and then delivers it to the

lungs

LORD

The Human Circulatory System is a Double CirculationThe Human Circulatory System is a Double Circulation

Left side of the heart receives

Oxygenated blood and deliversit to the body tissues

Deoxygenated blood and delivers it to the lungs

Right side of the heart receives

R A L A

R V LV

C A P IL L A R IE SIN L U N G S

C A P IL L A R IE SA R O U N D

B O D Y T IS S U E S

The human circulation is a double circulation as there are two distinctcircuits along which blood flows

The heart pumpsoxygenated blood

TO the body tissuesand receives

deoxygenated bloodFROM the body

tissues

This circuit in whichblood flows from theheart TO the bodysystems and back

to the heart is calledTHE

SYSTEMICCIRCULATION

The heart pumpsdeoxygenated blood

TO the lungsand receives

oxygenated bloodFROM the lungs

This circuit in whichblood flows from theheart TO the lungs

and back to the heart is called

THEPULMONARY

CIRCULATION

The Human Circulatory System is a Double CirculationThe Human Circulatory System is a Double Circulation

lungs

head

liver

gut

kidneys

other bodyorgans

THE PULMONARY VEINdelivers oxygenated blood

from the lungs to the LEFTATRIUM of the heart

Smaller arteries branchfrom the AORTA in orderto deliver this oxygenated

blood into the various organs

The oxygenated blood enters the LEFT VENTRICLE,which pumps the blood

along the AORTA towardsthe body organs

The CORONARY ARTERIESdeliver oxygenated blood to

the heart muscle

The HEPATIC ARTERYdelivers oxygenated blood to

the liver

The RENAL ARTERIESdeliver oxygenated blood

to the kidneys

The CAROTID ARTERY delivers oxygenated blood

to the neck, head and brain

Veins carry deoxygenated bloodaway from the body organs. Theveins join to form two large veins

called the VENAE CAVAEThe VENAE CAVAE deliver

deoxygenated blood to the RIGHT ATRIUM

of the heart HEPATICVEIN

RENALVEIN

Deoxygenated bloodenters the right

ventricle from where it is pumped to the

lungs along the PULMONARY ARTERY

HEPATICPORTAL

VEIN

The liver receives bloodfrom BOTH the hepatic

artery AND theHEPATIC PORTAL

VEIN

The hepatic portal vein carries blood, rich in the products of digestion, from the gut to the liver

Naming The Blood VesselsNaming The Blood Vessels

The walls of the capillaries are only one cellthick and composed of flattened or squamous

epithelium called the endothelium

The endothelium rests on a basement membrane

Capillaries are referred to as the exchange vessels,since all the exchange of materials between the blood

and living cells takes place through their walls

The lumen of the capillary is just large enough forred cells to move along in single file

The human body contains about 40,000 kilometresof capillaries which is enough to circumscribe the

earth at the equator

Capillaries are so extensive that they permeate between and around all body cells

At the capillaries, metabolites such as oxygen and nutrients diffuse from the blood into the respiring

tissues. Metabolites such as carbon dioxide and other waste materials diffuse from the tissues into the blood

As blood in the capillaries is always moving, then steep concentration gradients for oxygen, carbon dioxide and nutrients will persist across the capillary walls

Capillaries and Metabolic ExchangeCapillaries and Metabolic Exchange

Most materials enter and leave the blood by diffusion

According to Fick’s Law...

Rate of diffusion =surface area x difference in concentration

thickness of exchange surface

The efficient rates of diffusion between the blood andbody cells occur as a result of:

• the large surface area presented by the capillaries

• the large differences in concentration of metabolites between the blood and the cells

• the thinness of the capillary walls

Capillaries and Metabolic ExchangeCapillaries and Metabolic Exchange

Capillary Cross Section

This cross-section of a capillary shows two endothelial cells formingthe wall around the lumen

Endothelial cells

LUMEN

The nucleus of one ofthe endothelial cells

(coloured red) is visiblewhilst the nucleusof the other cell is

located in a differentplane and hencenot visible withinthis thin section

The two epithelial cellsare separated fromone another by very

narrow gaps or capillary pores

through which mostsmall moleculescross the wall by

diffusionCapillary pore

Some larger moleculespass through the

endothelial cells by pinocytosis

The wall of thecapillary rests upon

a basement membrane

Capillaries and Metabolic ExchangeCapillaries and Metabolic Exchange

The cells of the body are bathed in a fluid called tissue fluid

Tissue fluid is essential for the efficient exchange of materials between the blood and the cells

Tissue fluid is formed at the arteriole end of the capillaries

CAPILLARY

TISSUE FLUID

Arteriole endof capillary

Venule endof capillary

BODYCELLS

Capillaries and Tissue Fluid FormationCapillaries and Tissue Fluid Formation

At the venule end of the capillary, the inward osmotic pull now exceedsthe outward hydrostatic pressure and some of the water re-enters the

capillary by osmosis

At the arteriole end of the capillary, the outward hydrostatic pressure isGREATER than the inward osmotic pull

Water, ions and small molecules are filtered out of the blood into the spaces between the cells - this is tissue fluid

The loss of fluid from the blood leads to a fall in hydrostatic pressure asthe blood approaches the venule end of the capillary

Tissue fluid is drained away from the cells by the lymphatic system and returnedto the circulation near the heart

CAPILLARY

TISSUE FLUID

Arteriole endof capillary

Venule endof capillary

BODYCELLS

Hydrostaticpressure

(kPa)

1.6

1.8

4.3

1.8

Summary of Tissue Fluid FormationSummary of Tissue Fluid Formation

small artery small veinlymphatic

cells

arteriole venule

capillaries tissue fluid

Tissue fluid is:• constantly being formed at the arteriole end of capillary beds• essential for the efficient exchange of materials between the blood and the cells• is constantly being drained away from the cells by lymph vessels

Acknowledgements

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