The heart and the vascular system Flashcards
Describe the 3 layered structure of blood vessels -
- Tunica Intima
- Tunica media - smooth muscle and connective tissue , binding the inner and outer layers
- Tunica externa - connective tissue sheath and stabilizing system to create attachments
Describe the structure and function of Arteries -
- Muscular or elastic
- Muscle are more abundant
- Tunica interna - elastic
- Media - smooth muscle depending on whether is a muscular or elastic muscle
- Tunica externa - collagen and elastic fibres
- High pressure changes
- Propel blood onwards
- even out pressure changes
- ANS stimulation causing vasodilation and vasoconstriction
- Constriction during damage
- Conducting vessels
- Little resistance
Describe the structure and function of arterioles-
- Smallest branches of arteries
- lead into the capillaries
- resistance vessels - regulate arterial blood pressure and distribute blood
Describe the structure and function of Capillaries-
- Smallest vessels with thin walls
- Permeate all active tissues
- Exchange vessels
- materials diffuse between blood and interstitial system
- Don’t have the 3 layers , just the tunica interna
- Multiple capillaries working together - capillary networks
Describe the structure and function of Venules-
- Smallest branches of the veins
- Allows blood to return from the capillary bed to the venous system
- Have the same function as veins.
Describe the structure and function of veins-
- Regulate and return the blood back to the heart
- same 3 layers
- Much thinner walls
- Unable to withstand high pressures
- Requires skeletal muscle pump to assist venous return
- One-way valve prevent backflow and aid venous return
Outline Venous return-
- Low blood pressure
- To overcome gravity = Valves , muscle pump and respiratory pump
- Inhale = pressures drop , drawing blood up.
Give the factors contributing to blood pressure -
- Cardiac output
- Peripheral resistance
- Blood volume
- Hypotension - low pressure
- Hypertension - High pressure - greater than 140/90 , essential and secondary hypertension , risk factors - genetics, age and pathology , smocking , diet etc. = damage to the blood vessels
Give some pathologies of the arterial wall -
- Arteriosclerosis - Hardening and loss of elasticity of large and medium arteries
- Arteriolosclerosis - Hardening and loss of elasticity of arterioles.
- Atherosclerosis - Hardening of an artery due to the deposition of an Atherosclerotic plaque - LDL- cholesterol.
Outline the cause of an Aneurysm-
Excessive localised enlargement of an artery caused by weakness in the arterial wall .
Common Locations , Aortic aneurysm and cerebral aneurysm
Outline the cause of deep vein thrombosis-
- Thrombus formed in large veins
- Risk factors - Inability, family history , recent surgery and obesity
- Symptoms- Discolouration, Pain , swelling and Homans Test - dorsiflex the ankle= pain
Outline the cause of Varicose veins-
- Bulging of the Veins , valves being incompetent.
Chronic Venous Insufficiency
- Valves aren’t working
- Blood not moving , lack of oxygen= Narcosis
Both treated with exercise ^
Describe the structure of red blood cells (Erythrocytes)
1 - Red Blood cells
2- Disc shaped - thin in middle and thicker as edge
Lack nuclei , mitochondria and ribosomes
3- contain haemoglobin - Oxygen carrying
4- Programmed to die after 120 days
Describe the structure of white blood cells (Leucocytes)
1- Role in inflammation and the immune response
2-Have nuclei and other organelles
3-Small numbers in blood
4- Connective tissue proper and Lymphatic system organs
Name the Granulocytes- Nucleus present
Neutrophils - Phagocytosis of bacteria/pus formed
Eosinophils- Allergic reactions , defence against parasites , control inflammation.
Basophils- Allergic reactions inflammatory reactions.
Name the Agranulocytes- No nucleus
Lymphocytes - Immunity t and b cells
Monocytes- Phagocytosis of large particles pathogens - attract immune system cells
Describe the structure of Platelets ( Thrombocytes)
1-small colourless disc shaped cell fragment without a nucleus , found in large numbers in bloof
2-Release important clotting chemicals
3-Temporarily patch damaged vessel walls
4-Actively contract tissue after clot formation.
Outline Haemostasis -
3 phases
Vascular phase
S1 - Immediate vasospasm - blood vessels contract
S2- Endothelial cells become exposed and release chemicals , which leads to further muscle contraction , cell division of endothelial cells, smooth muscle cells and fibrocytes - repair process
S3- Endothelial cell membranes become sticky and may seal off blood flow
Platelet Phase
S1- Platelet adhesion , begins within 15 seconds
Sticking to endothelial surfaces , basal laminae and exposed collagen fibres
S2- Platelet Aggregation , everything begins to stick together
Coagulation Phase
S1 - Blood clotting , involves a series of steps , converts circulating fibrinogen into insoluble fibrin
Chain reactions of enzymes and proenzymes
Haemostasis - 3 Pathways
A - Extrinsic Pathway - Begins in the vessel wall and outside the blood stream
B- Intrinsic Pathway - Begins with circulating proenzymes , within the bloodstream
C- Common Pathway - clotting factor number 10 , Prothrombinase , prothrombin - thrombin - fibrinogen - fibrin - Fibrin threads making a mesh + blood cells and plasma - Blood clot
Common Pathology -
Anaemia
Anaemia - Deficiency in Haemoglobin due to too few RBCs or too little Haemoglobin in the cells.
Various Causes
- Blood loss
- Inadequate RBC production
- Excessive RBC destruction
-Tired , weakness ,pale, shortness of breath, irregular heartbeat , chest pain , dizziness , cold hands and feet and headache.
Common Pathology-
Leukocytosis and Leukopenia.
Leukocytosis and Leukopenia
Leukocytosis - Increase in white blood cells
- Infection from bacteria , sometimes viruses , fungi and parasites
- Inflammation or inflammatory conditions
- Allergic reactions
- Leukaemia - acute and chronic
Leukopenia - Low white cell count
- Bone marrow damage or disorder
- Lymphoma - Hodgkin’s etc.
- Autoimmune disorders
- Dietary deficiencies
The Heart - Structure
- 4 chambered organ
- Atria and Ventricles
- Located posterior to the sternum , level with 3rd costal cartilage to 5th costal space
- Mediastinum
- 7.5cm left of midline
- Surrounded by Pericardium - Visceral , Epicardial and Parietal , with 15-20ml of pericardial fluid in between
How the heart Beats -
- 4 chambered organ
- Atria and Ventricles
- Located posterior to the sternum , level with 3rd costal cartilage to 5th costal space
- Mediastinum
- 7.5cm left of midline
- Surrounded by Pericardium - Visceral , Epicardial and Parietal , with 15-20ml of pericardial fluid in between
Properties of cardiac muscle -
- Muscular pump
- Actin and Myosin
- Muscle cells are connectedby intercalated discs or gap junctions
- Autorhythmic fibres , inherent rythmical activity , self-excitable , heart beats continually
Contraction of cardiac muscle -
Depolarisation
- Resting potential (-90mV)
- Action potential in adjacent fibre passes via gap junction ( intercalated disc) and opens the Na+ channel - rapid inflow of Na+ - rapid depolarisation
- Cardiac muscle AP lasts approximately 0.3 sec
Plateau
- There is a plateau because as Na+ is being pumped put of cell Ca++ slowly enters cell balancing loss of Na+ - balancing membrane potential as 0mV
Repolarisation
- Repolarisation does eventually occur
- The Ca++ channels slowly close
- The K + channels open - K+ Leaves cell
- Resting potential restored
- The mechanism of contraction is the same in cardiac muscle as it is in skeletal muscle with the AP causing a mechanical response
Refractory Period
- Is the time interval before another contraction can take place
- It lasts longer than a contraction
- It means the fibres are in relaxation before the next contraction can occur
- It allows the pumping action of cardiac muscle
Explain the coordination of contraction-
- AP needs to be co-ordinated
- Contract in sequence
- Pacemaker and conduction pathways
- SA node is pacemaker with an inherent of 100 APs per minute
- However this slowed down to 70-75 by the vagus nerve
The cardiac cycle-
1 - Atrial systole - atrial contraction forces a small amount of additional blood into relaxed ventricles
2-Atrial systole ends , atrial diastole begins
3-Ventricular systole - Ventricular contraction exerts enough pressure on the blood to close AV valves but not enough to open semilunar valves
4- Ventricular systole - Ventricular pressure rises and exceeds pressure in the arteries, semilunar valves open and blood is ejected.
5- Ventricular diastole - Ventricles relax, pressure drops , blood flow back against semilunar valves causing them to close, blood flow into relaxed atria
4- All chambers are relaxed.
Components of cardiac output-
- Total blood volume passing through lungs and systemic circulation in one minute
- CO=SVxHR
- Stroke volume (SV)= volume of blood ejected during ventricular systole
- E.g. CO= 70 ml x 75 bpm = 5230 mls/min
- Close to your total blood volume
- what happens if the body requires more blood for working tissues
- Ans= increase CO
- Cardiac reserve is 4to5 times that at rest
Stroke volume - factors.
- Preload - stretch on heart prior to contraction
Frank-starling law - More the heart is filled in diastole , the greater the stretch and the greater the force of systole.
- Contractility
Strength of contraction due to preload
- Afterload - Pressue needed to overcome on contraction
Increased afterload results in reduced SV because more blood remains in ventricles at the end of systole.
