Chapter 31: The human Chapter 31: The human circulatory systemcirculatory system

Leaving Certificate BiologyLeaving Certificate Biology

Higher LevelHigher Level

The Circulatory SystemThe Circulatory System

• Organisational complexity of the human involves having multiple organs and tissues each with their own individual functions and an extensive network of tubes carrying oxygen and nutrients to every living cell of the human body and the efficient disposal of wastes produced by all the living cells of the human

The Circulatory SystemThe Circulatory System

• The circulatory system of the human is a closed system whereby blood continually flows around the body inside a network of blood vessels and oxygen, carbon dioxide, nutrients, and wastes diffuses into and out of these vessels– The closed system involves blood flowing through

structures in the following order: strong muscular heart, arteries, arterioles, capillaries, venules, veins and finally back to the heart

The Circulatory SystemThe Circulatory System

• Advantages of the closed circulatory system are:– Blood can be pumped around the body fast

for fast and efficient delivery of oxygen and nutrients and fast and efficient removal of wastes

– Blood can be directed to different areas of the body through constriction and dilation of the blood vessels where needed

Blood VesselsBlood Vessels

• Arteries: carry blood away from heart• Arterioles (small arteries): carry blood from the

arteries to the capillaries• Capillaries: carry a single-file of red blood cells

through their lumens delivering oxygen and nutrients and removing wastes from local cells and tissues

• Venules (small veins): carry blood from the capillaries to the veins

• Veins: carry blood towards the heart

Arteries and VeinsArteries and Veins

VALVE

ARTERY VEIN

Collagen

SmoothMuscle

(involuntary)

Elastictissue

Endothelialcells

Smalllumen,

Novalves

Largelumen,

withvalves

Thick wall Thin wall

Differences between arteries and Differences between arteries and veinsveins

Artery Vein

Carries blood away from heart

Carries blood toward heart

Blood under high pressure Blood under low pressure

Thick walls Thin walls

Pulse flow Smooth flow

Narrow lumen Large lumen

No valves Valves present

Blood rich in oxygen (except pulmonary artery)

Blood poor in oxygen (except pulmonary veins)

Smooth Muscle, Skeletal Muscle Smooth Muscle, Skeletal Muscle and Valvesand Valves

• Smooth muscle is involuntary (not under conscious control): surrounds arteries and veins and help to push blood along

• Skeletal muscles in the legs and arms help to push blood along veins back to the heart

• Valves present in veins help to prevent blood flowing backwards thus preventing pooling of blood in the extremities

The HeartThe Heart

• Located slightly to the left of the sternum between the lungs above the diaphragm

• Composed of cardiac muscle (doesn’t fatigue as easily as skeletal or smooth muscle)

• Size of clenched fist

INTERNAL INTERNAL STRUCTURE STRUCTURE OF THE OF THE HUMAN HUMAN HEARTHEART(Fig. 27.9(Fig. 27.9p 261)p 261)

Double CirculationDouble Circulation

• In the heart there is two separate pumps – one on the right and one on the left – separated by the septum

• Double circulation in the human is necessary in order to keep deoxygenated (right-side) blood separate from oxygenated blood (left-side)

• The two circuits are called:– Pulmonary circuit– Systemic circuit

Blood Flow Through the Blood Flow Through the Pulmonary CircuitPulmonary Circuit

• Deoxygenated blood enters right atrium from the superior and inferior vena cavae which have carried blood from the upper and lower bodies, respectively

• Right atrium contracts and blood flows through the tricuspid valve

• Blood then enters right ventricle which in turn contracts• Right ventricular contraction causes the tricuspid valve to

close and the semi-lunar valve to open and blood flows in the pulmonary artery

• The pulmonary artery carries blood to the lungs to become re-oxygenated as the blood flows through the capillaries that surround the alveoli

Blood Flow Through the Blood Flow Through the Systemic CircuitSystemic Circuit

• Oxygenated blood is carried from the lungs via the pulmonary veins to the left atrium

• Blood enters the left atrium and the left atrium contracts forcing blood through the bicuspid valve

• Blood then enters left ventricle which in turn contracts more strongly than the right ventricle but at the same time

• Left ventricular contraction causes the bicuspid valve to close and the semi-lunar valve to open and blood flows into the aorta

• The aorta carries the blood to the head, upper body, and lower body to deliver oxygen and nutrients

Coronary ArteryCoronary Artery

• Cardiac muscle itself needs oxygen and nutrients in order to continue pumping

• Therefore, the heart itself is supplied with blood via a small branch from the aorta

• The coronary arteries splits up into many arterioles and capillaries that perfuse through the heart muscle

• These capillaries then drain into venules and into the coronary veins which eventually drain back directly into the right atrium

The Hepatic Portal SystemThe Hepatic Portal System

• The hepatic portal system begins in the capillaries of the digestive system and ends in the portal vein – it does not connect directly to the heart

• Consequently, portal blood contains substances absorbed by the stomach and intestines

• Portal blood is passed through the hepatic lobules where nutrients are absorbed and toxins are excreted or detoxified

Detailed Study of the Heart BeatDetailed Study of the Heart Beat

• The heart beat is controlled entirely by the pacemaker – which is a bundle of specialised nervous tissue located in the top of the right atrium

• The pacemaker is also called the sino-atrial (SA) node

• Pacemaker sends out regular nervous impulses which travel along the axons of the nerve cells out through the walls of the atria – this causes the atria to contract

• Atrial contraction is also called atrial systole

Detailed Study of the Heart Beat Detailed Study of the Heart Beat (cont.)(cont.)

• The impulse from the SA node travels via axons to the atrio-ventricular (AV) node – located further down in the right atrium

• This sets up an impulse that travels from the AV node down nerve fibres through the ventricular muscle causing the ventricles to contract – also called ventricular systole

Detailed Study of the Heart Beat Detailed Study of the Heart Beat (cont.)(cont.)

• The rate at which the SA node fires can be controlled by various factors:– Exercise– Temperature– Emotion– Shock

Heart SoundsHeart Sounds

• Sound of the heart beat is caused by the opening and closing of the valves of the heart

• The “lub” sound is caused by the closing of the tricuspid and bicuspid valves closing and the semi-lunar valves opening as the ventricles contract

• The “dub” sound is caused by the semi-lunar valves closing as the ventricles relax

PulsePulse

• A pulse is the pressure the flowing blood exerts on the walls of an artery causing the walls of the artery to expand

• Pulse can be felt most easily on the wrist or on the neck

• Pulse rate (pulses/min) is an indicator of heart rate (heart beats/min)

• Average heart rate is 72 bpm in an adult

Blood PressureBlood Pressure

• Blood pressure is given as a large number over a usually smaller number, e.g. 120/80 mmHg would be a normal blood pressure reading for a healthy adult

• The larger number is the systolic pressure – which is the pressure the blood exerts on the walls of an artery the moment the blood passes through

• The smaller number is the diastolic pressure – which is the pressure the blood exerts on the walls of the artery the moment there is no movement of blood

• Blood pressure is measured using a sphygmomanometer

Blood Pressure (continued)Blood Pressure (continued)• Drugs that reduce blood pressure and hence

heart rate are:– Anti-hypertensives: stimulate vasodilation where the

smooth muscle surrounding all the blood vessels relax and the blood vessels widen thereby reducing blood pressure

– Diuretics: stimulate loss of water from the blood by closing the pores present in the collecting duct of nephrons – therefore water is NOT reabsorbed into the blood – if there is reduced blood volume this reduces blood pressure and also heart rate

– Beta-blockers: act on the pacemaker of the heart directly reducing its rate

Effects of Smoking, Diet, and Effects of Smoking, Diet, and Exercise on the Circulatory SystemExercise on the Circulatory System

• Smoking:– Nicotine, present in all cigarettes, is an extremely

addictive chemical that causes increased heart rate and blood pressure by causing arteries and arterioles to narrow (vasoconstriction)

• Diet:– Diet high in saturated fat and cholesterol causes

increased risk of blockages in the arteries and arterioles (caused by atherosclerosis [fatty deposits in blood vessels]) – the main cause of heart attacks and strokes

Effects of Smoking, Diet, and Effects of Smoking, Diet, and Exercise on the Circulatory System Exercise on the Circulatory System

(cont.)(cont.)• Exercise:

– Causes the heart to beat faster and stronger thereby causing the heart muscle to increase in size

– Improves circulation by stimulating formation of more capillaries – thereby indirectly reducing blood pressure

– Increases the body’s ability to use oxygen – therefore the heart does not have to work as hard at rest

– Reduces body weight – thereby reducing blood pressure as the heart does not have to work as hard to pump blood