Chpt. 27: Heart and Blood Vessels

(The Circulatory System)

Circulatory Systems

Circulatory system : provides cells in organisms with all the materials they require.

• Unicellular organisms have no need for a circulatory system. In these diffusion is sufficient for transport of materials.

• Two types of circulatory system:- Open circulatory system: blood is not always

enclosed in blood vessels e.g. Crayfish- Closed circulatory system: blood remains

enclosed in blood vessels e.g. Humans

Circulatory Systems

Closed Circulatory System

More efficient than an open system because:

1. There is a faster transport of O2 and nutrients.

1. It maintains sufficient blood pressure for larger organs.

Circulatory Systems

Components of the closed circulatory system of humans:

1. Blood

3. The Heart

2. Blood Vessels

Blood Vessels

Arteries

VeinsCapillaries

Blood Vessels

• Arteries: carry blood Away from the heart.

- divide into smaller vessels called arterioles.

• Veins: carry blood to the heart.

- small veins are called venules.

• Capillaries: are tiny vessels that link arteries and veins.

Arteries and Veins

Arteries and veins have three similar walls in their layers:

- outer layer of rough – inelastic protein (collagen)

- middle layer of muscle and elastic fibres.

- Endothelium – inner single layer of living cells.

Arteries and Veins

Arteries

• blood is under high pressure

• have thick walls and a small lumen

• have no valves

• carry mostly oxygenated blood

• blood flows in pulses

Veins

• blood is under low pressure

• have thin walls and large lumens

• have valves to prevent back flow of blood

• carry mostly deoxygenated blood

• blood flows smoothly i.e. no pulse

Veins

Capillaries• thin walled blood vessels

• allow exchange of materials between blood and body tissue

• have no valves

• carry oxygenated and deoxygenated blood

• allow diffusion of dissolved substances e.g. Gases, wastes etc.

• have no pulse

Capillaries

V. Slow flowSlower flowFast flow

No valvesValvesNo valves

Link arteries to veins

To heartAway from heart

Low PressureLow PressureHigh Pressure

One cell thickThin wallsThick walls

CapillariesVeinsArteries

Differences in Blood Vessels

The Heart

The Heart

• the heart is located between the two lungs and just above the diaphragm

• it is under involuntary control

• made of cardiac muscle

• surrounded by a membrane called the pericardium which prevents friction with nearby organs

Structure of the Heart

• divided into two sides by a wall called the septum

• four chambers:two upper chambers - atria

two lower chambers - ventricles

Left atrium

Right Atrium

Left Ventricle Right Ventricle

Pumps blood to the lungs

Pumps blood to the head and body

Structure of the heart• Valves

- prevent the backflow of blood- held in place by tendons- tendons held to walls of heart via papillary

muscles

- Tricuspid valve – has three flaps located on right hand side of heart

- Bicuspid valve – has two flaps located on left hand side of heart

- Semilunar valves – allow blood to flow out of heart into two main arteries

Aort

a

Pulmonary

Vein

Pulm

onar

yAr

tery

Vena Cava

The heart has four major blood vessels

Blood flow through the heart

• Deoxygenated Blood enters right atrium from the superior vena cava and the inferior vena cava

• Right atrium contracts forcing blood down through the tricuspid valves into the right ventricle

• Right ventricle contracts forcing blood out of the heart to the lungs through the semilunar valve in the pulmonary artery.

Blood flow through the heart

• Oxygentated Blood returning to the heart from the lungs enters the left atrium via the pulmonary veins

• It is pumped through the bicuspid valves to the left ventricle

• The left ventricle contracts pumping blood out to the body through the semilunar valve in the aorta.

LORD: Left Oxygenated Right Deoxygenated

Double Circulation

Double Circulation: refers to the fact that the blood passes through the heart at least twice before reaching the same point.

Double circulation humans:• Two sides of the heart are separated by the septum.• Septum necessary to separate deoxygenated and oxygenated blood• This separation is an important part of the two – circuit circulatory system in humans:

- pulmonary circuit- systemic circuit

Double Circulation

Pulmonary Circuit:• right ventricle pumps blood around the pulmonary circuit.

• in pulmonary circuit blood is pumped from heart to lungs back to heart.

•blood is oxygenated and loses carbon dioxide in the lungs.

Double Circulation

Systemic Circuit:• left ventricle pumps blood around the systemic circuit.

• in systemic circuit oxygenated blood is pumped to the head, arms, trunk and legs.

Double Vs Single Circulation

Double Circulation: - allows oxygen-rich and oxygen-poor blood to be kept separate. - ensures blood pressure is high enough to reach all parts of the body.

Single Circulation:-Blood is pumped from the heart around the body and back to the heart again in a single circuit e.g. Earthworms, fish.- can only produce low blood pressure around most of the body.

Portal System

Portal System: is a blood pathway that begins and ends in capillaries.

• Vessels in portal system do not connect directly to the heart.

• Example of a portal system:Hepatic Portal Vein: connects the stomach and

intestines to the liver.

Blood Supply to the Heart

• Coronary (cardiac) arteries: supply blood to the muscle of the heart.

• Coronary (cardiac) veins: drain blood from the muscle of the heart.

Blockage of the coronary arteries is a cause of heart attacks and warning chest pains prior to this are commonly known as angina.

Control of Heartbeat(Higher Level Only)

• Heartbeat can occur independently of the brain.

• Pacemaker (Sino-atrial node/SA) - is a small bundle of specialised tissue

responsible for controlling heartbeat- located in the wall at the top of right atrium- pacemaker sends out regular electrical impulses causing atria to contract and subsequently ventricles

• Brain can control the frequency of these impulses

(brain - nerves and hormones)

Control of Heartbeat – Detail:1.Atrial Systole – pacemaker pulses causing atria to contract.

1.Electrical impulse from pacemaker stimulates the atrio-ventricular (AV) node.

(AV node similar to pacemaker located further down in right atrium)

3.AV node sends impulse down special muscle fibres located in septum.

4.Ventricular Systole – this impulse is passed out to the walls of the ventricles by thin fibres. The impulses from these fibres cause the ventricles to contract.

Some important points:

• Electrocardiogram (ECG) – uses electrodes placed on the chest to measure electrical activity of the heart.

• Factors that increase the rate of heartbeat:- exercise- temperature- emotions- shock

• Factors that decrease the rate of heartbeat:- relaxation- sleep- alcohol

Stages of Heartbeat – Cardiac Cycle

(Higher Level only)

• Stages of heartbeat refer to the events which occur during one heartbeat.

• *Diastole – is when heart chambers relax

• *Systole – is when heart chambers contract

Stages of Heartbeat – Cardiac Cycle

Stage 1 - Atrial Diastole: - diastole – the atria and ventricles are both relaxed- all valves are closed as blood enters atria

Stage 2 – Atrial Systole:- systole – electrical impulses from pacemaker cause atria to contract- this causes blood to be pumped to ventricles- Tricuspid & bicuspid valves open, venae cavae & pulmonary veins close, semi – lunar valves remain closed.

Stage 3 – Ventricular Systole:- Ventricular Systole – atria relax and electrical impulses from AV node cause ventricles to contract- this forces blood out of heart into pulmonary artery and aorta- the pressure forces open semi lunar valves and closes tricuspid and bicuspid valves – ‘lub’ sound- ventricles relax again, semi lunar valves close preventing backflow and causing ‘dub’ sound- venae cavae and pulmonary veins open and cycle starts again

Sounds of Heartbeat• The double sound (‘lub-dub’ sound) of the heartbeat is caused by valves being forced shut.

• ‘Lub’ – low pitched, quieter, long lasting, due to the bicuspid and tricuspid valves being forced shut when the ventricles contract.

• ‘Dub’ – higher pitched, louder, shorter, due to the semilunar valves snapping shut.

Heart Murmur: is any abnormal sound associated with heartbeat and may indicate damage to one or more valves.

Pulse and Blood Pressure

The Pulse: is a wave of vibrations through the arteries following the expansion of the aorta.

• Pulse can be felt easily in the wrist and neck.

• Pulse rate indicates the rate of heartbeat.

• Average adult pulse rate is 72 beats per minute.

Pulse and Blood PressureBlood pressure: is the force exerted by the blood against the walls of the blood vessels (mainly the arteries).

• blood pressure is recorded by measuring the pressure needed to stop the flow of blood in the arteries of the upper arm.

• normal blood pressure – 120/80 mm mercury.

• Upper value – Systolic Pressure Lower value – Diastolic Pressure

• High blood pressure occurs when lower value is over 95 mm of mercury. It indicates the heart has to pump harder to get enough blood around the body which can lead to heart attacks if not treated.

Lifestyle and the HeartEffects of Smoking:• Nicotine increases the heart rate and raises blood pressure.• Carbon Monoxide reduces the ability of the blood to carry oxygen.• chemicals in smoke increase the risk of blood clots.

Effects of Diet:Diet may affect the heart in three ways:1. A fat rich diet increases the chance of the arteries becoming blocked - heart attacks, strokes.2.Too much salt raises blood pressure.3.Being severely overweight increases blood pressure and results in heart attacks.

Lifestyle and the Heart

Effects of Exercise:• enlarges and strengthens the heart.• improves blood circulation.• causes loss of weight.

What else effects Heart Rate?

•Caffeine

•Cigarettes

•Drugs

•Stress

•Fever / illness

Steps to a Healthy Heart

•Avoid fatty foods/ cholesterol

•Watch your blood pressure

•Avoid Stress

•Reduce Salt Intake

•Do 30 minutes exercise