7 - INTRODUCTION TO THE CARDIOVASCULAR SYSTEM AND BLOOD TYPING Flashcards
LOCATION OF THE HEART
- In the mediastinum with the lungs
- Level of the 2nd rib
- Roughly central, but with the base pointing towards the right and the apex towards the left
HEART COVERINGS: PERICARDIUM
The heart sits in a “bag”: pericardium • Lubrication • Mechanical protections = protects it and allows it to move smoothly Pericardium has 3 main layers: • Fibrous pericardium • Serous pericardium • Epicardium
Pericarditis
problems with the pericardium, which impact the movement and function of the heart.
pericardium formation
heart wall
3 muscular layers to provide the contractile properties of the heart
Epicardium
Myocardium (muscle layer)
Endocardium (lines the inside)
4 CHAMBERS AND 4 VALVES
left atrium right atrium Left Ventricle Right ventricle Pulmonary valve Aortic valve Bicuspid valce Tricuspid valve
HEART VALVES: ATRIOVENTRICULAR VALVES
Valves open and close in response to pressure changes as the heart relaxes and contracts.
Atrioventricular valves: prevent back flow from Ventricles to Aorta
Chordae tendinae stop valves acting like a swing door
Tricuspid on R, bicuspid on L (Mitral)
Semilunar valves
base of arteries: prevent back flow from arteries to ventricles
Aortic and pulmonic valves
• Release of contraction closes valves = Prevents blood running back to refill the ventricles
• Tricuspid
Problems with the valves
Incompetent valves - Valves (leaflets) do not fully close so there is regurgitant flow
• Valvular stenosis - stiffened valves caused by repeated infection, congenital disease or calcium deposits. Opening is narrowed so insufficient blood gets through.
STRUCTURE: ARTERIES AND VEINS
Same basic structure in both types of vessel, but the proportion may vary.
3 layers-
• Tunica adventitia/externa: supportive outer.
Nerves and blood vessels
• Tunica media: muscular middle, affects resistance to blood flow (ie involved in control of blood pressure)
• Tunica intima: endothelial, inner, layer creates a smooth surface and involved in communication
TUNICA MEDIA
Smooth muscle, helps move blood along the arteries
• Vasoconstriction of smooth muscle decreases lumen size
Vasodilation of smooth muscle increases lumen size
Importance of lumen size?
Lumen size affects blood flow rate and hence blood pressure.
Changes in radius affect resistance of the blood vessel inversely by 4. ie increase radius by ¼ gives a 16 fold decrease in resistance.
Affects single vessel, not whole system.
Small lumen size = increased blood pressure
ARTERIAL SYSTEM, elastic to absorb large eflux of blood from heart, even distribution of blood
Large arteries, small arteries, arterioles, capillaries
Large arteries
More muscular walls push blood along to organs.
Distribution role.
Renal, carotid, mesenteric.
Don’t affect BP.
Elastic to absorb high volume and pressure from heart
Small arteries
Distribution and resistance. Highly innervated. Regulate arterial Pressures. Receptors for circulating hormones and locally produced signals ie K+ and NO
Arterioles
smaller
when constricted, blood flow to organs can be bypassed.
Resistance vessels.
Same as small arteries
Capillaries
small and thin to allow for exchange of materials.
Exchange vessels.
No smooth muscle.
High exchange
• Blood flow in capillaries= Blood flow entering aorta.
• Velocity is 0.05 cms/s compared to 50cms in aorta
TYPES OF CAPILLARIES
Continuous Capillaries
Fenestrated Capillaries
Sinusoid Capillaries
Continuous Capillaries
Most common
• Continuous. Gaps only between endothelial cells (tight junctions)
• CNS, lungs, muscle tissue, skin
Fenestrated Capillaries
- Pores of 70-100nm in the capillary wall, transport of large substances
- Choroid plexus, kidneys, endocrine glands, villi and ciliary processes of the eye
Sinusoid Capillaries
- Wider gaps in the vessel walls (Lets blood cells through)
* Bone marrow, endocrine glands, placenta
VENOUS SYSTEM
Veins + venules
Veins
- Under less pressure
- Less smooth muscle (less resistance)
- Stretchy (high capacitance vessels)
- Larger veins have valves to prevent blood flowing backwards.
Venules
- 8-100µm in diameter, more porous than arterioles.
- Capillaries drain into venules
- Continued loss of BP, almost 0 by the time it gets to the vena cava
WHICH VESSELS CARRY BLOOD IN A BODY AT REST?
his differs between the upright and supne position
UPRIGHT Blood distribution at rest
- Vein = 65%
- Arteries = 13%
- Arterioles = 2%
- Capillaries = 5%
- Central blood volume = 15%
SUPINE blood distribution at rest
• Vein = 54% • Arteries = 10% Arterioles = 1% • Capillaries = 5% • Central volume = 30% * 12% in heart * 18% in lung In the supine position there is : 1. Less blood in peripheral veins 2. More blood in central volume
CIRCULATION AND THE HEART
Blood flows through and around the heart .
When it exits it can be split into three distribution systems:
1. Pulmonary Circulation (RHS)
2. Systemic Circulation (LHS)
3. Coronary Circulation (from aorta)
RHS: PULMONARY CIRCULATION
- Positioned towards back of the heart.
- Crescent shaped
- Blood in through Venae cavae
- Back out through pulmonary artery
LHS: SYSTEMIC CIRCULATION
- At front and apex
- More circular (thicker walls)
- In through pulmonary veins
- Out through Aorta to aortic arch
CORONARY CIRCULATION
- L and R Coronary arteries from the base of the aorta. Shut during contraction
- Coronary arteries branch to supply the heart
- Arteries supply the capillaries for gas and nutrient transfer before draining into the veins
BLOOD GROUPS
43 blood groups
• Most common are the ABO group and the Rhesus +/-groups
• The ABO group gives us 4 key groups; A, AB, B and O. Adding Rhesus status to this gives 8 main groups.
• Two antigens and two antibodies are responsible for the ABO types
• Discovered by Karl Landsteiner in 1901 (University of Vienna) who tried to understand why blood transfusions sometimes caused death but at other times saved a patient
ABO BLOOD TYPES: ANTIGENS AND ANTIBODIES
Red Blood Cells have different surface molecules (Antigens). The A/B antigens are sugars.
Blood plasma will have Antibodies to the surface molecules that your RBCs do not have.
When a blood transfusion occurs with the wrong blood type, the antibodies bind to the RBCs expressing the different antigen.
This causes clumping of the RBCs and antibodies (agglutination) and causes severe problems (thrombosis).
Blood transfusions
- Knowing blood type before transfusion avoids problems.
- Agglutination reactions are performed to determine blood type
- Type A: will agglutinate Blood type B so cannot receive blood from Type or type AB
UNIVERSAL DONORS AND RECEIVERS
Individuals with type O blood do not have A or B antigens = universal donor (will not agglutinate)
• Make antibodies to A and B, cannot receive blood from any other blood type
Individuals with type AB blood have A and B antigens = universal
receivers for transfusions
• do not make any A or B antibodies, their blood can only be given to AB
recipients
BLOOD GROUP INHERITANCE
- 3 alleles for human blood type: IA, IB, and I
- Both A and B alleles are dominant over O
- People who are type O have OO genotypes - they inherited a recessive O allele from both parents
- A and B alleles are codominant, so if A is inherited from one parent and B from the other, the phenotype is AB
ABO INCOMPATIBILITY IN BABIES
Common and generally mild condition in babies
• Can occur during pregnancy if mother and baby’s blood types are
incompatible
• RBCs are broken down causing jaundice, anaemia, and death if severe
• Mother’s antibodies linger after birth and destroy RBC of baby, causing an increase in bilirubin.
• Babies with high levels of bilirubin may need phototherapy (oxidises
bilirubin and facilitates its removal by the liver) or a blood transfusion
• More severe outcome with Rhesus incompatibility (haemolytic disease)
