The Circulatory The Circulatory SystemSystem

Chapter 42Chapter 42

Why have a circulatory Why have a circulatory system?system?

Diffusion is too slow a process to Diffusion is too slow a process to transport chemicals through the body of transport chemicals through the body of an animal.an animal.

The presence of a circulatory system The presence of a circulatory system reduces the distance a substance must reduces the distance a substance must diffuse to enter or leave a cell.diffuse to enter or leave a cell.

The circulatory system does more than The circulatory system does more than move gases, it is a critical component to move gases, it is a critical component to maintaining homeostasis of the body.maintaining homeostasis of the body.

Components of the Components of the cardiovascular systemcardiovascular system

HeartHeart– Four chambers in humansFour chambers in humans

ArteriesArteries– Carry blood away from heartCarry blood away from heart– Branch into smaller arteriolesBranch into smaller arterioles

VeinsVeins– Carry blood toward the heartCarry blood toward the heart

CapillariesCapillaries– The site of chemical exchange between blood The site of chemical exchange between blood

and interstitial fluidand interstitial fluid– Connect arteries to veinsConnect arteries to veins

Blood flow pattern in Blood flow pattern in humanshumans

‘‘Double-loop’ circulationDouble-loop’ circulation body body vena cava vena cava right atrium right atrium right right

ventricle ventricle pulmonary artery pulmonary artery lung lung pulmonary vein pulmonary vein left atrium left atrium left left ventricle ventricle aorta aorta arteries arteries arterioles arterioles capillaries capillaries venules venules veins veins vena vena cavacava

The blood that is low in oxygen is The blood that is low in oxygen is completely separated from the blood that completely separated from the blood that is rich in oxygen is rich in oxygen

The heartThe heart

Located beneath the sternumLocated beneath the sternum Cone-shaped and about the size of a clenched Cone-shaped and about the size of a clenched

fistfist Surrounded by a double layered sacSurrounded by a double layered sac Comprised mostly of cardiac muscle tissueComprised mostly of cardiac muscle tissue The 2 atria are thin-walled and collect bloodThe 2 atria are thin-walled and collect blood The ventricles are thick-walled and pump The ventricles are thick-walled and pump

bloodblood There are 4 valves which prevent backflow of There are 4 valves which prevent backflow of

blood during contractionblood during contraction

The heartbeatThe heartbeat A complete sequence of contraction and A complete sequence of contraction and

relaxation is the cardiac cyclerelaxation is the cardiac cycle Systole – the heart muscle contracts and Systole – the heart muscle contracts and

the chambers pump bloodthe chambers pump blood Diastole – the heart muscle relaxes and Diastole – the heart muscle relaxes and

the chambers fill with bloodthe chambers fill with blood The tempo of contraction is controlled by The tempo of contraction is controlled by

the sinoatrial (SA) node, sometimes called the sinoatrial (SA) node, sometimes called the pacemakerthe pacemaker

The SA node can be influenced by The SA node can be influenced by hormones, body temperature, exercisehormones, body temperature, exercise

Blood pressureBlood pressure The force that blood exerts against a vessel wallThe force that blood exerts against a vessel wall Pressure is greatest in arteries during ventricular Pressure is greatest in arteries during ventricular

systole – this is the main force propelling blood systole – this is the main force propelling blood from the heart through the vesselsfrom the heart through the vessels

Stress may trigger responses that cause the Stress may trigger responses that cause the smooth muscles of vessel walls to contract, smooth muscles of vessel walls to contract, increasing blood flow and pressureincreasing blood flow and pressure

Blood in the veins is under very little pressure – Blood in the veins is under very little pressure – it is aided in returning to the heart by skeletal it is aided in returning to the heart by skeletal musclesmuscles

Veins have valves that prevent backflow of Veins have valves that prevent backflow of bloodblood

Blood flow to different body Blood flow to different body parts is regulatedparts is regulated

All tissues and organs receive enough blood All tissues and organs receive enough blood even though only 5% - 10% of the capillaries are even though only 5% - 10% of the capillaries are carrying blood at any given timecarrying blood at any given time– The brain, heart, kidneys, and liver usually carry a full The brain, heart, kidneys, and liver usually carry a full

load of bloodload of blood Blood flow to capillaries in other areas is Blood flow to capillaries in other areas is

controlled by smooth muscles in the artery wallscontrolled by smooth muscles in the artery walls After a meal After a meal increased flow to digestive tract increased flow to digestive tract Exercise Exercise increased flow to skeletal muscles increased flow to skeletal muscles

Exchange of materialsExchange of materials

Occurs across the thin walls of the Occurs across the thin walls of the capillariescapillaries

The capillary wall is a single ‘leaky’ The capillary wall is a single ‘leaky’ layer of endothelial cellslayer of endothelial cells

About 85% of the fluid that leaves the About 85% of the fluid that leaves the blood at the arteriole end of the blood at the arteriole end of the capillary re-enters from the interstitial capillary re-enters from the interstitial fluid at the venous endfluid at the venous end

The remaining 15% of the fluid is The remaining 15% of the fluid is lymphlymph

The lymphatic systemThe lymphatic system

Lymph is similar in composition to Lymph is similar in composition to interstitial fluidinterstitial fluid

It enters the lymphatic system by It enters the lymphatic system by diffusing into lymph capillariesdiffusing into lymph capillaries

It then drains back into the circulatory It then drains back into the circulatory system at two locations near the system at two locations near the shouldersshoulders

Lymph nodes are specialized swellings Lymph nodes are specialized swellings along the system that filter the lymph along the system that filter the lymph and attack viruses and bacteriaand attack viruses and bacteria

BloodBlood Connective tissue – cells suspended in liquid plasmaConnective tissue – cells suspended in liquid plasma

– Average person has 4-6 L of whole bloodAverage person has 4-6 L of whole blood PlasmaPlasma

– 90% water90% water– Also contains electrolytes and plasma proteinsAlso contains electrolytes and plasma proteins

Erythrocytes (RBCs = red blood cells)Erythrocytes (RBCs = red blood cells)– Transport oxygenTransport oxygen– No nucleiNo nuclei– Contain hemoglobinContain hemoglobin

Leukocytes (white blood cells)Leukocytes (white blood cells)– Function in defense and immunityFunction in defense and immunity– Number will increase during times of infectionNumber will increase during times of infection

PlateletsPlatelets– Function in blood clottingFunction in blood clotting

Blood clottingBlood clotting

Platelets clump together and form a Platelets clump together and form a temporary plugtemporary plug

Clotting factors are released that Clotting factors are released that convert fibrinogen to fibrinconvert fibrinogen to fibrin

Fibrin forms threads to form the clotFibrin forms threads to form the clot Hemophilia – caused by a defect in Hemophilia – caused by a defect in

the genes that control this processthe genes that control this process

Cardiovascular diseaseCardiovascular disease

Accounts for more than 50% of all U.S. deathsAccounts for more than 50% of all U.S. deaths Heart attack – blockage of coronary arteries Heart attack – blockage of coronary arteries

which leads to cardiac muscle damagewhich leads to cardiac muscle damage Stroke – blockage of arteries in the brainStroke – blockage of arteries in the brain Atherosclerosis – artery walls develop plaques Atherosclerosis – artery walls develop plaques

which narrow the space and increase chance which narrow the space and increase chance of clot formation and heart attackof clot formation and heart attack

Hypertension – chronic high blood pressure Hypertension – chronic high blood pressure which can promote atherosclerosis which can promote atherosclerosis