Cardiovascular system Flashcards
Why do we have a circulatory system?
Only unicellular organisms can meet their metabolic needs by simple diffusion and convection
Evolutionary consequence of increasing in size and complexity
Maintenance of steep concentration gradients to deliver nutrients and remove waste
What are the primary functions of the circulatory system?
Distribution of gases and other molecules for nutrition, growth and repair
What are secondary functions of the circulatory system?
Fast chemical signalling of hormones
Dissipation of heat
Mediates inflammatory and host defence responses to invading microbes
How is the heart a dual pump?
Pumps blood in two circuits:
The left heart pumps to the systemic circulation and the right right heart pumps to the pulmonary circulation
What are the functions of the arteries, veins and microcirculation?
Arteries- the distribution system
Veins- collection system (resevoir)
Microcirculation- diffusion and filtration systems
What are the 4 building blocks of blood vessels?
Endothelial cells
Elastic fibres
Collagen fibres
Smooth muscle cells
What are the 3 layers of blood vessel walls?
Tunica interna
Tunica media
Tunica externa
Elastic arteries
Large arteries
High compliance- walls stretch easily without tearing in response to pressure increases
Enables vessels to cope with peak ejection pressures
Recoil of elastic fibres forces blood to move through even when the ventricles are relaxed
Muscular arteries
Medium sized arteries
Smooth muscle cells are arranged circumferentially
Capable of greater vasoconstriction and vasodilation to adjust rate of blood flow
Vascular tone- state of partial contraction maintains vessel pressure and efficient flow
Arterioles
Smooth muscle to regulate rate of blood flow into capillary networks- regulated microcirculation
Terminal regions of arterioles are known as metarterioles
Precapillary sphincters monitor blood flow into capillaries
Venules
Postcapillary venules are porous as they act as exchange sites for nutrients and waste
Muscular venules have a thin smooth muscle layer, less muscular than arterioles
Thin walls allow expansion which makes them excellent reservoirs for blood
Veins
Less muscular and elastic but distensible enough to adapt to variations in volume and pressure of blood
Like venules veins can ‘store’ blood
Large veins
More muscular than venules and small veins
Possess valves to prevent backflow
Defective leaky valves allow backflow and can lead to varicose
Other than being a principle exchange site, what other additional needs do capillaries serve?
Glomerular filtrate
Skin temperature regulation
Hormone delivery
Platelet delivery
What are the three kinds of capillaries in order from least to most leaky?
Continous
Fenestrated
Discontinuous/sinusoidal
What is the function of the lymphatic system?
Drains excess interstitial fluid and maintains circulating volume of blood
Transport of dietary lipids
Lymph nodes/organs important for immunology
What is blood made up of?
Plasma- ECF that is rich in protein
Erythrocytes
Leukocytes
Platelets
What are the principle proteins of blood plasma?
Albumin
Fibrinogen
Globulin
Other coagulation factors
What are the 3 major functions of erythrocytes?
Carrying oxygen from the lungs to the systemic circuit
Carrying carbon dioxide from tissues to the lungs
Buffering of acids and bases
What is unique about the shape of erythrocytes? How is this maintained?
Non-nucleated bioconcave discs to maximise SA:V
Cytoskeleton anchored to the membrane by glycophorin and band 3 Cl-/HCO3 exchanger
What are the 3 types of granular white blood cells (granulocytes) and what are their specific functions?
Neutrophils- phagocytose bacteria
Eosinophils- combat paracites and viruses
Basophils- release IL-4, histamine, heparin and peroxidase
What are the 3 types of non-granular white blood cells and what are their specific functions?
Lymphocytes- mature into T cells and B cells (plasma cells)
Monocytes- macrophages and dendritic cells
Where do platelets come from?
Bud off from megakaryocytes in the bone marrow
What structures are found in platelets?
Mitochondria, lysosomes, peroxizomes, alpha granules and dense core granules
What is haematocrit? What relationship does it have with blood flow?
A test that determines the proportion of red blood cells in your blood
Blood flow decreases with increasing haematocrit
What is viscosity in terms of blood flow?
Viscosity measures resistance to sliding of shearing fluid layers
What is the viscosity of blood dependent on?
Haematocrit Fibrinogen plasma concentration Vessel radius Linear velocity Temperature
What is haemostasis? How is it usually maintained?
Prevention of haemorrhaging
Vasoconstriction- thromboxane A, serotonin, thrombin, endothelin-1
Increased tissue pressure which decreases transmural pressure
Platelet plugs which are small breaches in vascular endothelium
How is blood cotting usually prevented?
Homeostatic mechanisms prevent haemostasis
Endothelial cells maintain normal blood fluidity through paracrine fators and anticoagulant factors
What is a thrombus?
An intravascular clot
What are the two pathways for blood clotting?
Intrinsic- surface contact activation on membrane of activated platelets
Extrinsic- membrane bound tissue factor activation, activated when blood contacts material from damaged cell membranes
How can a thrombus form in pathological situations?
CV system- balance between pathological states of inadequate and overactive clotting
DVT risk factors- venous stasis, vascular injury and hypercoagubility
Arterial thrombosis can occur following erosion or rupture atherosclerotic plaque