Anatomy: The circulatory system Flashcards
What is the circulatory system made up of?
The cardiovascular and lymphatic systems
What are the functions of the circulatory system ?
- distribution of gases and other molecules
- chemical signalling
- thermoregulation
- mediate inflammatory and host defence responses
What 3 components is the cardiovascular system comprised of?
arterial system, heart and venous system
Describe the flow of blood through the heart
Deoxygenated blood enter the heart via the superior vena cava (from the head) and the inferior vena cava (from the abdomen) > into the right atrium > right ventricle> pulmonary truck > left and right pulmonary arteries > lungs > pulmonary veins (x4)> left atrium > left ventricle > aorta > rest of the body
Describe the 3 layers of the heart.
Endocardium (internal) - is continuous with endothelium of blood vessels connecting with the heart.
Myocardium (middle) - is a cardiac muscle layer
Epicardium (external) - is visceral serous pericardium
Why is the myocardium thicker around the left ventricle than the right?
To allow the left ventricle to push high pressure blood out of the heart and to the body
What do cardiac valves do and where are they?
They ensure uni-directional blood flow
- tricuspid valve = between right atrium and ventricle
- pulmonary valve = between right ventricle and pulmonary trunk
- mitral (bicuspid) valve = between left artrium and left ventricle
- aortic valve = between left ventricle and the aorta
Describe the route of electrical conduction in the heart
Electrical impulse starts spontaneously at SA node causing both atria to contract > travels to AV node at atrioventricular septum > travels down right and left bundles in the interventricular septum > spreads out to myocardium through connecting fibres causing both ventricles to contract
What are the three layers of most blood vessels ?
Tunica intima (internal) - endothelium Tunica media (middle) - smooth muscles and elastic fibres Tunica adventitia (external) - connective tissue
What’s the difference between the lumen of arteries and veins?
Artistries have a round lumen Due to the high pressure blood whereas in veins the lumen is flatter
Describe the features of arteries
Often part of a neurovascular bundle
High pressure
Pulsatile
Carry oxygenated blood
Typically deeper than veins
They give rise to branches (bifurcation =divides into 2, trifurcation =divides into 3)
Terms “common” or “trunk” indicate that the artery will divide again
What does the smooth muscle in the walls of the arterioles do?
RELAXATION of the smooth muscle leads to widening of the lumen to increase blood flow = VASODILATION
CONTRACTION of smooth muscle reduces the size of the lumen and causes a reduction in blood flow = VASOCONSTRICTION
What is sympathetic tone?
A background, low level of contraction of the smooth muscles in arterioles. It is due to the tonic (continuous) conduction if action potentials to arterioles by sympathetic nerves.
What is an anastomosis ?
Where arteries connect with each other without an intervening capillary network > this provides alternative routes for blood to flow to supply cells distal to an arterial occlusion (blockage)
What is “collateral”?
An alternative route in any give anastomosis
What is a disadvantage of an anastomosis ?
Collaterals bleed from both sides of a cut so the haemorrhage can be worse
What is an end artery?
The only arterial bloody supply to a given area of the body (i.e there are no collaterals)
What is an infarction?
Irreversible cell death due to hypoxia caused by loss of arterial blood supply
What happens to the walls of the aorta under pressure?
The elastic walls expand and elastic recoil maintains peripheral flow when the heart relaxes.
What are the 4 parts of the aorta?
1- ascending aorta
2- arch of the aorta
3- thoracic aorta
4 - abdominal aorta
What are the branches of the arch of the aorta?
1 - brachiocephalic trunk
2- left common carotid artery
3- right subclavian artery
Where are u likely to find peripheral pulses?
Carotid pulse (at the bifurcation of the common carotid artery) Brachial artery pulse (elbow joint) Radial artery pulse (wrist) Femoral artery pulse (groin) Popliteal all artery pulse (knee joint) Dorsalis pedis artery pulse (foot)
Describe the features of veins
Often run a neurovascular bundle Carry deoxygenated blood Low pressure Non-pulsatile Drain blood away from a territory Thin walled which collapse when empty Have valves to stop back flow of blood
How is venous blood pumped back towards the heart?
- Venous valves ensure unidirectional flow
- skeletal muscle in the lower limb contracts to pump blood
- accompanying arteries pulsations push venous blood along the vein
What does the hepatic portal venous system do?
Drains venous blood from absorptive parts of the GI tract and associated organs to the LIVER for “cleaning”
What does the systematic venous system do?
Drains venous blood from all organs and tissues (apart from those associated with the GI tract) into the superior or inferior vena cava
Describe the features of capillaries
Forms an extensive vascular network
Lined with a single layer of endothelium
Has a narrow lumen only allowing one red blood cell through at a time
Allows for exchange of gases, metabolites and waste products.
Describe lymphatic circulation
Lymphatic capillaries collect tissue fluid which is then called lymph.
Lymphatics carry lymph through lymph nodes which contain white blood cells to filter and fight infection
The lymph eventually drains back into the venous system at the venous angles in the root of the neck. (Right lymphatic duct drains lymph into right venous angle) (thoracic duct drains lymph into the left venous angle)
