CY systems - circulatory Flashcards
Blood vascular system
Blood travels away from the heart in arteries
Returns to heart in veins
Arteries and veins connected by capillaries
What are the 2 parts to the blood vascular system?
Systemic circulation:
- delivers blood rich in oxygen from left side to most of body tissues
Returns blood low in oxygen to right side of the heart
High pressure system
Extensive network formed
Pulmonary circulation:
- delivers blood low in oxygen from right side of heart to the lungs
- returns blood rich in oxygen to left side of heart
Low pressure system
Name the 3 layers of blood vessels
Tunica intima (endothelium) Tunica media (muscle layer) Tunica externa/adventia (connective tissue
Name the vessels in the CV system
Arteries: - elastic - muscular - arterioles Microcirculaton: - capillaries (continuous and fenestrated ) - venules Veins
What do arteries have that veins do not?
Have a thicker wall Smaller lumen Maintains their shape More resilient Don't contain valves, veins contain many
Describe arteries
- Elastic
eg. aorta, brachiocephalic, common carotid
- withstand changes in pressure
- ensure continuous blood flow
- thick tunica media, many elastic fibres - Muscular
- most named arteries
- distribute blood to muscles and organs
- lots of smooth muscle in tunica media
- thick tunica externa - Arterioles
- vasoconstriction and vasodilation
Describe capillaries
Site of gas exchange/nutrient/waste exchange
- thin walled = endothelial and basement membrane layer
- types:
> continuous
> fenestrated (pores, found in kidneys)
> sinusoids (large gaps, found in liver)
Capillary beds:
- supplied by single met arteriole, contains 1000s of capillaries
- met arterioles connect arterioles and venules
- pre-capillary sphincters control blood flow to capillary beds
Arteriovenous anastomoses
Form direct communication between arteriole and venules
- dilated blood bypasses the capillary bed and flows directly to venous circulation eg. temperature control
Venules
Collect blood from capillary beds and deliver to small veins
Veins
Low pressure system
Thin walled
Easily distensible
Lymphatic system functions
Involved in the body’s defence mechanisms
Drainage of interstitial fluid
- At arteriole end, high pressure caused by contraction of the heart forces fluid to move out and into the interstitial space
- Lower pressure at the venous end causes fluid to be reabsorbed back into the capillary, however not all fluid is reabsorbed
- Interstitial fluid forms lymph, and enters the lymphatic system, where it is returned into the blood stream at the subclavian vein in the neck
pathway is:
lymph capillaries, lymph vessels, lymph nodes, lymph trunks, thoracic duct and drained to left subclavian veins, or right lymphatic duct and drained to right subclavian vein
+ if fluid stays in interstitial space = oedema +
Position of the heart
Protected by the ribs and body of the sternum 2/3 lie to the left of midline between 2nd and 5th ribs Apex projects anteriorly to the left The great vessels arise from the base
Pericardium
Consists of:
Fibrous pericardium
- inelastic sac of dense connective tissue that wraps around the heart
- prevents overfilling
Serous pericardium
- two layers - parietal and visceral - separated by pericardial cavity which contains serous fluid
- prevents friction
Describe the layers of the heart wall
3 layers
- Endocardium: inner layer - endothelium
- Myocardium: middle layer - cardiac muscle
- Epicardium: outer layer - visceral pericardium
Organisation of the heart
RIGHT SIDE - from systemic circulation so low in oxygen > Superior and inferior vena cava > Right atrium > Tricuspid valve > Right ventricle > Pulmonary semilunar valve > Pulmonary trunk and arteries TO THE LUNGS LEFT SIDE - from lungs so blood rich in oxygen > pulmonary veins > left atrium > bicuspid valve > left ventricle > aortic semilunar valve > aorta
Heart valves
AV Valves -
- opened by blood flowing from atria to ventricles
- anchored by chordae tendinae to papillary muscles, prevent eversion of valves during ventricular contraction
- prevent backflow of blood into atria
Semilunar valves -
- opened by blood being pushed out of ventricles
- no chordae tendinae
Coronary circulation
Blood delivered to myocardium during ventricular relaxation Left coronary artery - - anterior interventricular - circumflex Right coronary artery - - marginal artery - posterior interventricular Most cardiac veins drain into coronary sinus which empties into right atrium
What are the properties of the cardiac muscle?
- forms a branching network of cells
- cells are interconnected by intercalated discs which contain gap junctions
- gap junctions allow ion transport between cells which promotes coordinated contraction
- cardiac cells act as a functional syncitium
- cardiac muscle is autorhythmic
The conducting system
Coordinates heart contraction
Consists of non-contractile cells that initiate electrical impulses:
1. SA node spontaneously reaches threshold
2. Impulse spreads throughout the atria
3. Passes through remainder of heart via the cardiac conductive system
4. SA node sets rhythm – the pacemaker
5. Rate is modified by ANS
Describe an ECG
Records the spread of electrical activity through the heart muscle
P wave = depolarisation of atria
QRS complex = depolarisation of ventricles
T wave = repolarisation of ventricles
Describe the different between adult circulation and foetal circulation
Oxygen and nutrients received from placenta via umbilical vein need to bypass non-functional lungs
Foetal has 3 circulatory short cuts:
1. Ductus venosus connects umbilical vein to inferior vena cava
2. Foramen ovale connects right and left atria
3. Ductus arteriosus connects pulmonary artery to arch of aorta
Changes at birth
Lungs expand therefore resistance falls in pulmonary circuit = decreased pressure in pulmonary trunk
Ductus arteriosus closes = decreased pressure in pulmonary trunk
Umbilical vessels close = increased pressure in aorta
