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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1

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

2

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)

3

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

4

Veins (4)

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

5

Capillaries

• 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)

6

Blood

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

7

Blood and Transportation
(NACHO-UH!)

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

8

Blood Flow

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

9

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

10

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)

11

Valves

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

12

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

13

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

14

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

15

Cardiac Cycle

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

16

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

17

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

18

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

19

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)