6.2 BLOOD SYSTEM Flashcards
Composition of blood
- Plasma
Mainly water
Dissolves or carries all other components of blood, nutrients, wastes - Erythrocytes (RBC)
Transports oxygen in haemoglobin molecules - Leukocytes (WBC)
Phagocytes engulf and digest pathogens and dead cells
Lymphocytes (B cells, T cells) for the immune response - produce antigens to recognise and target phagocytes - Platelets
Clotting of blood following damage to cells or erythrocytes
Blood vessels
Arteries
→ Carry blood away from the heart
→ Pressure is high
→ Narrow lumen
→ Thick wall
→ No valves
→ Muscle tissue contracrs to create a pulse to move the blood
→ Elastic fibres stretch to deal with increased flow of blood
Capillaries
→ Blood moves slowly for blood exchange
→ Low pressure
→ Extremely narrow lumen
→ thin wall (contains pores)
→ No valves
Veins
→ Carry blood back to the heart
→ Low pressure
→ Wide lumen
→ Thin & flexible wall
→ Contains valves to ensure blood flows in the correct direction
→ Elastic fibres to push blood
Double circulation
Blood passes through the heart twice
- Deoxygenated blood enters through the right atrium
- it is pumped from the right ventricle into the lungs where it becomes oxygenated
- Oxygenated blood enters the left atrium ands is pumped from the left ventricle to the body
Heart Beat
A region of myocytes called Sinoatrial node (SAN) acts as the primary pacemaker – controlling the rate at which the heart beats
- The sinoatrial node sends out an electrical impulse that stimulates contraction of the myocardium (heart muscle tissue)
- This impulse directly causes the atria to contract and stimulates another node at the junction between the atrium and ventricle
- This second node – the atrioventricular node (AV node) – sends signals down the septum via a nerve bundle (Bundle of His)
- The Bundle of His innervates nerve fibres (Purkinje fibres) in the ventricular wall, causing ventricular contraction
Nervous system controlling heart rate
Two nerves connected to the medulla regulate heart rate by either speeding it up or slowing it down:
- The sympathetic nerve releases the neurotransmitter noradrenaline (a.k.a. norepinephrine) to increase heart rate
- The parasympathetic nerve (vagus nerve) releases the neurotransmitter acetylcholine to decrease heart rate
Hormonal signalling
Heart rate can undergo a sustained increase in response to hormonal signalling in order to prepare for vigorous physical activity
Coronary Heart Disease
- Atheromas (fatty deposits) develop in the arteries and significantly reduce the diameter of the lumen
- The restricted blood flow increases pressure in the artery, leading to damage to the arterial wall
- The damaged region is repaired with fibrous tissue which significantly reduces the elasticity of the vessel wall
- As the smooth lining of the artery is progressively degraded, lesions form called atherosclerotic plaques
- If the plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow
- If the thrombus is dislodged it becomes an embolus and can cause a blockage in a smaller arteriole (heart attack)
systole (contracted)
- The atria contracts and blood passes down to the ventricles
- The atrio-ventricular valves open due to blood pressure
- 70% of the blood flows passively down to the ventricles
Ventricle systoles
- The atria relaxes
- The ventricles walls contract forcing the blood out
- The pressure of the blood forces the atrio-ventricular valves to shut (producing the heart sound ‘lub’)
- The pressure of blood opens the semi-lunar valves
- Blood pases into the aorta and pulmonary arteries
Diastole (relaxed)
- The ventricles relax
- Semi-lunar valves closes to prevent backflow (producing the secon heart sound ‘dub’)
- Blood from the venacava and pulmunary veins enter the atria
- The whole cycle starts again
