Topic 6.2: The Blood System Flashcards Preview

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Flashcards in Topic 6.2: The Blood System Deck (19)
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The Circulatory System and William Harvey (4)

• The major blood vessels (arteries & veins) are connected by a single network
• Blood flow is unidirectional (due to the presence of one-way valves)
• The heart is a central pump (arteries = from heart ; veins = to heart)
• Blood flows continuously and is not consumed by the body


Further Discoveries of the Blood System

• Arteries and veins are connected by capillaries (via arterioles & venules)
• There is a separate circulation for the lungs (pulmonary versus systemic)


Arteries (4)

• Transport blood from the heart
• Blood at high pressure (80-120 mmHg)
• Walls are thick (muscle and elastin)
• Walls stretch or contract with pulse


Veins (4)

• Transport blood to the heart
• Blood at low pressure (<15 mmHg)
• Walls are thin (with wider lumen)
• Have valves to prevent pooling



• Facilitate material exchange
• Blood at low pressure (~10 mmHg)
• Walls made of single layer of cells
• Extremely narrow lumen (~10 μm)
Capillaries may be categorised as:
• Continuous (intact basement membrane)
• Fenestrated (have endothelial pores)
• Sinusoidal (discontinuous membrane)



Blood contains three main elements:
• Red blood cells (transport oxygen)
• White blood cells (fight infections)
• Platelets (responsible for clotting)


Blood and Transportation

• Nutrients (e.g. glucose)
• Antibodies
• Carbon dioxide
• Hormones
• Oxygen
• Urea
• Heat


Blood Flow

A heart pumps blood around the body via two distinct circulatory pathways


Right Side of Heart

• Deoxygenated blood (from tissues) enters right atrium via the vena cava
• Blood in the right ventricle is pumped to lungs via the pulmonary artery
• Gas exchange at the lungs (capillaries ⟷ alveoli) oxygenates the blood


Left Side of heart:

• Oxygenated blood (from lungs) enters left atrium via the pulmonary vein
• Blood in the left ventricle is pumped to the body tissues via the aorta
• Material exchange occurs at the respiring tissue (deoxygenates the blood)



Valves in veins ensure proper circulation by preventing backflow of blood
• Contraction of skeletal muscles may compress NACHO-UH! veins to aid blood flow


Heart Structure

- Superior Vena Cava
- Inferior Vena Cava
- Right Atrium
- Triscuspid valve
- Right Ventricle
- Pulmonary Valve
- Pulmonary Artery
- Pulmonary Vein
- Left Atrium
- Bicuspid Valve
- Left Ventricle
- Aortic valve
- Aorta


Mechanism of Heart Beat

A heart beat is myogenic (contraction initiated by the heart)
• Electrical signals are initiated by a sinoatrial (SA) node
• This pacemaker stimulates the atria to contract and also
relays signals to an atrioventricular (AV) node
• The AV node sends signals to ventricular Purkinje fibres
(via a Bundle of His within the wall of the septum)
• The Purkinje fibres cause the ventricular walls to contract


Regulators of Heart Beat

The SA node maintains a normal sinus rhythm (60-100 bpm)
• The pacemaker is regulated by the medulla oblongata
• Sympathetic nerves release noradrenaline (􂀐︎ heart rate)
• Parasympathetic nerves release acetylcholine (􂀑 heart rate)
• Heart rate may also be increased via hormonal action
(via the release of adrenaline / epinephrine)
• Adrenaline will cause a more sustained elevation in heart
rate than that achieved by the action of the brainstem


Cardiac Cycle

The cardiac cycle describes the events of a heart beat (Systole / Diastole)


Systole (contraction)

• As atria contract, atrial pressure exceeds ventricular
pressure (AV valves open → blood flows to ventricles)
• As ventricles contract, ventricular pressure exceeds
atrial pressure (AV valves close → 1st heart sound)
• Pressure builds (isovolumetric contraction) until the
ventricular pressure exceeds the arterial pressure
• Semilunar valves open and blood flows into arteries


Diastole (Relaxation)

• As blood flows into arteries, ventricular pressure drops
• Backflow closes semilunar valves → 2nd heart sound
• When ventricular pressure drops below atrial pressure,
the AV valves will open and cardiac cycle is repeated


Coronary Heart Disease

Coronary thrombosis is caused by clots within the coronary arteries
• Vessels are damaged by cholesterol deposition (atherosclerosis)
• The deposits reduce vessel diameter and increase blood pressure
• The stress damages arterial walls (and is repaired with fibrous tissue)
• The vessel wall loses elasticity and forms atherosclerotic plaques
• If a plaque ruptures, blood clotting is triggered, forming a thrombus
• If the thrombus blocks blood flow, a myocardial infarction results
• These events are collectively described as coronary heart disease


Risk Factors for CHD (GODDESS)

• Genetics (e.g. hypertension)
• Obesity (overweight = risk)
• Diseases (e.g. diabetes)
• Diet (e.g. High trans fats)
• Exercise (inactivity = risk)
• Smoking (High blood pressure)
• Sex (males = higher risk)