Circulation Flashcards
Circulatory system components
pumps, vessels, and circulatory fluid
Circulatory system functions
- maintenance of homeostasis
- mass transport of solutes and cells
- transport of heat
- transmission of force
Mammalian circulation; two circuits (double circulation)
- separate pulmonary and systemic circuits
- pressure differences possible
Systole
heart muscle contracts and chambers pump blood
Diastole
heart muscle is relaxed and chamber fills with blood
cardiac cycle
inherent activity of the heart and can be modified by outside influences
Arteries
carry blood away from the heart towards capillaries
- Arterioles (small branches of arteries, that convey blood to capillaries)
Capillaries
- microscopic vessels that penetrate the tissues
- consist of single layer of cells that allow exchange between the blood and interstitial fluid
Veins
return blood to heart from capillaries
- Venules (convey blood between a capillary bed and a vein)
Blood pressure and blood flow
velocity varies inversely with total cross - sectional area of vessels
systolic pressure
ventricles contracting
diastolic pressure
ventricle relaxing
Blood pressure
force of the heartbeat falls almost to zero in veins, venules
- returns to heart due to contraction of skeletal muscles
- one way valves in veins ensure direction of blood flow towards heart
Measurement of blood pressure
- record as two numbers; the first is systolic pressure and the second is diastolic pressure
- in healthy resting human; 120mm Hg at systole and 70mm Hg at diastole
Regulation of blood flow
- blood volume < systemic capacity
- blood flow is directed to active tissue
- relaxing/ contracting of precapillary sphincters (control mechanism)
- constriction/ dilation of arterioles (control mechanism)
Lymphatic system functions
- fluid balance, net leakage of fluid and proteins from blood capillaries, lymph capillaries collect lost fluid and return blood circulation
- defense; lymph nodes have defense cells
- lymph capillaries pick up fats absorbed by the small intestines, transfer it to blood
Lymphatic system Movement
- one way valves, contraction of skeletal muscles
- lymph does not circulate in a closed circuit
Lymphatic system thymus
the site of maturation of T lymphocytes (of the immune system)
Lymphatic system tonsils
handle infections in the mouth
Lymphatic system spleen function
- defense
- red blood cell destruction
- blood reservoir
Blood composition
- cellular elements
- plasma; blood minus the cells
Blood volume
heart rate (70 beats/min at rest) X stroke volume (75ml) = 5.25L/ min
Blood Hematocrit
- packed cell volume
- normal value (45%) is regulated
- departures are either adaptive or pathological
Leukocytes
- 5000-10 000 / mm3
- defense and immunity
Erythrocytes
- 5 -6 million / mm3
- O2 and CO2 transport
Platelets
- 250 000 - 400 000/ mm3
- blood clotting
Erythrocytes - shape
-biconcave disc (oval in camels)
-small size (mammals 5-10um)
= large surface area
Erythrocytes- Contents
- hemoglobin
- spectrin; predominant component of the membrane skeleton
- glycolytic enzymes; active carbohydrates metabolism (anaerobic)
- carbonic anhydrase; catalyze CO2 - bicarbonate
- no organelles or ribosomes
- mammals; no nucleus = more space for hemoglobin
Formation of Erythrocytes- erythropoiesis Process
- takes 4 days from stem cell to erythrocytes
- begins in bone marrow, completed in circulating blood
- initiated when not enough O2 reaches tissues
Formation of Erythrocytes- erythropoiesis Rate
- 100 million cells per minute
- normally balanced with erythrocytes destruction
- can exceed destruction under conditions of tissue oxygen deficiency
Destruction of Erythrocytes
- break apart in capillaries due to mechanical stress
- eaten by macrophages (defensive phagocytes) in spleen and liver
Human red blood cells
- responsible for transport of O2 around body
- 5-6 million
- bioconcave shape
- lack nucleus
- lack mitochondria
- life time of 120 days
- manufactured in red marrow of certain bones
- age or damaged cells phagocytosed by white blood cells in spleen and liver
Severe blood loss
- v blood pressure- v blood flow from damaged area
- constriction of blood vessel- v blood flow
- coagulation
Blood loss can be halted by
- platelet plugs (from early)
- fibrin clots (from later)
Platelets
- small, short lived fragments of cells
- 2 - 3 um (150 000 - 300 000mm)
- Do not respond to undamaged endothelial wall
Platelets are activated by
- exposed collagen fibres in damaged tissue of vessel walls
- foreign surfaces
- thrombin
Platelets upon activation …
- form of platelet plug
- release of clotting factor
- change shape
Platelets contain
- actin and myosin (help them contract)
- chemicals that help coagulation process to begin
- chemicals that attract other platelets
- chemicals that stimulate blood vessel repair
- chemicals that stabilize a blood clot
Blood clot formation
-takes place via an activation cascade; cascades amplify signals
Blood clot steps -1
- tissue damage (endothelium); exposed to foregin substance= exposure to collagen
- clotting factors; release from platelets and injured tissue, plasma protein synthesized liver, circulate in inactive form
Blood clot steps -2
- thrombin; enzyme, absent from circulating blood
- prothrombin circulates in plasma
- activation of blood factor= prothrombin= thrombin
- thrombin=fibrinogen= fibrin
Blood clot steps -3
- platelets; release substance that cause contraction of blood vessels
- sticky platelets form plug
- initiate formation of fibrin clot
- clot seals wound until vessel wall heals
Clotting dynamics
- opposing clotting; anticlotting agents (heparin)
- favouring clotting; activated platelets, activated blood factors, thrombin, fibrin
Clotting dissolution
- fibrinolysis
- dissolution of fibrin and thrombus
Plasmin
- main enzyme in fibrinolysis
- cleaves fibrin in multiple locations
- acts to dissolve a firbin clot
- produced in inactive form (plasminogen) in the liver
Plasminogen
- cannot cleave fibrin, but has an affinity for it
- incorporated into the clot when it is formed
Clot lysis
complex process involving proteolytic enzymes, activators and inhibitors of plasmin and other proteases
