6.2 The Blood System Flashcards
NOS: Harvey’s discovery of blood circulation
Before Harvey:
- arteries and veins were separate networks except for area connected by invisible pores
- veins pumped natural blood (produced by liver)
- arteries pumped heat (produced by heart) via lungs (for cooling)
Harvey’s discoveries:
- arteries and veins parts of a singular connected blood network
- arteries pumped blood from heart (to lungs and body tissues)
- veins pumped blood to heart (from lungs and body tissues)
- blood flow through vessels is unidirectional with valves to prevent backflow
- blood circulates around the body is recycled, not consumed
- predicted existence of small vessels connecting arteries and veins (ie. capillaries)
pulmonary and systemic circulation
pulmonary circulation:
transportation of deoxygenated blood from the right ventricle to the lungs via the pulmonary artery
systemic circulation:
transportation of oxygenated blood from left ventricle to all parts of the body (except lungs) via the aorta
- double circulation allows both circuits to have different blood pressures
arteries - structure and function [4]
function: convey blood at high pressure from left heart ventricle to tissues of the body
- thick wall: contains outer layer of collagen to prevent artery from rupturing under high pressure
- muscle and elastic fibers (elastin): found on inner arterial wall, maintains pulse flow (can contract and stretch)
- narrow lumen: (relative to wall thickness) maintains high blood pressure
how do muscle and elastic fibers maintains blood pressure between cycle pumps? [3]
muscle fibers:
- form rigid arterial wall that can withstand high blood pressure without rupturing
- contract to narrow the lumen => increases pressure between pumps => maintain bp throughout cardiac cycle
elastic fibers:
- allow arterial wall to stretch and expand upon the flow of a pulse through the lumen
* pressure exerted on arterial wall is returned to the blood when lumen returns to normal size (elastic recoil)
* elastic recoil helps to push the blood forward through the artery and maintain arterial pressure between pump cycles
capillaries - structure and function [5]
function: exchange materials between cells in tissues and blood travelling at low pressure
arteries -> arterioles -> capillaries (arterial pressure decrease as total vessel volume increases) => ensures blood moves slowly and all cells are close to a blood supply
after material exchange, capillaries -> venules -> veins
small diameter: only allows one RBC to pass through at a time (optimal exchange)
one cell thick wall: minimizes diffusion distance for permeable materials
basement membrane: surrounds capillary, only permeable to necessary materials
presence of pores: aids transport of materials between tissue fluid and blood
- capillary structure may vary depending on location in body and specific role
eg. in tissues specialized for absorption (eg. intestines, kidneys), capillaries may be fenestrated (contain pores)
capillaries may be sinusoidal (incomplete basement membrane) with large intercellular gaps => permeable to large molecules and cells
flow of blood in the capillaries [2]
high bp in the arteries is dissipated by extensive branching of vessels and narrowing of lumen => slow, low pressure of blood flow in the capillaries => maximal material exchange
higher hydrostatic pressure at the arteriole end of capillary forces material (needed for cell res: oxygen and nutrients) from bloodstream into the tissue fluid
lower hydrostatic pressure at venule end of capillary allows material (cell waste: urea, carbon dioxide) from tissue fluid to enter bloodstream
veins - structure and function [4]
function: collect blood at low pressure from tissues of the body and return it to the atria of the heart
wide lumen: (relative to wall thickness) maximize blood flow for more effective return
thin wall: less muscle and elastic fibers because blood flows at a very low pressure
valves: prevent backflow and stop blood from pooling at lowest extremeties
flow of blood in veins [2]
blood flow at very low pressure - difficult to move against downward force of gravity
=> valves maintain circulation of blood by preventing backflow
skeletal muscle groups: facilitate venous blood flow via periodic contractions
* veins usually pass through skeletal muscle groups
- skeletal muscles contract => squeezes vein => blood flows from site of compression
heart structure - valves and vessels [6]
atrioventricular valves (bwt atria and ventricles):
left - bicuspid
right - tricuspid
semilunar valves (bwt ventricles and arteries):
left - aortic
right - pulmonary
vena cave (superior - top; inferior - bottom):
feeds into the right atrium, returns deoxy blood from the body
pulmonary artery:
connects to right ventricle, sends deoxy blood to lungs
pulmonary vein:
feeds into left atrium, returns oxygenated blood from lungs
aorta:
extends from left ventricle, sends oxy blood around the body
heart beat
- heart contractions are myogenic - initiated by heart muscles (cardiomyocytes) instead of brain signals
- cardiomyocytes are found in the right atrium of the heart and are collectively know as the sinoatrial node (SA node)
- SA node = primary pacemaker (∼60-100 contractions/min = normal sinus rhythm)
- SA node fails, AV node maintains contractions (∼40-60 bpm)
- AV node fails, Bundle of His maintains contractions (∼30-40 bpm)
- interference of the pacemakers => irregular and uncoordinated contraction of heart muscle (fibrillation)
- normal sinus rhythm can be re-established by a controlled electric current (defibrillation)
electrical conduction of heartbeat [3]
- SA node sends out an electrical signal => spreads through walls of the atria which stimulate an atrial systole (both atria contract => blood forced into ventricles)
- atria contracts => stimulates AV node => sends signal down septum via Bundle of His after a time delay => ventricular systole
- delay bwt systoles allows ventricles to fill with blood following atrial contractions => maximize blood flow
regulation of heart rate by external signals [2]
nerve signaling:
pacemaker is under autonomic control from the brain, specifically the medulla oblongata (brain stem)
- two nerves connected to the medulla can regulate heart beat by speeding it up or slowing it down:
sympathetic nerve - releases neurotransmitter noradrenaline => increase heart rate
parasympathetic nerve (vagus nerve) - releases neurotransmitter acetylcholine => decrease heart rate
hormone signaling:
- hormone epinephrine (adrenaline) secreted by adrenal glands to prepare for vigorous physical activity
- secretion is controlled by the brain, adrenaline increases heart rate by stimulating SA node to emit electrical signals at a faster rate
cardiac cycle [3]
atrial systole (ventricle relaxed):
- walls of atria contract => pressure in atria > pressure in ventricles => blood is pushed from atria to ventricles through atrioventricular valves (open), semi-lunar valves (closed) => ventricles fill with blood
ventricular systole (atrium relaxed):
- walls of ventricle contract => pressure in ventricles > pressure in atria => atrioventricular valves close (prevent backflow), both valves closed => pressure builds rapidly in contracting ventricles (isovolumetric contraction) => pressure in ventricles > pressure in aortic valve => aortic valve (open), blood released into aorta
diastole (both relaxed):
- blood exits ventricle via aorta => pressure in ventricle drops => pressure in ventricle < aortic pressure => aortic valve closes (prevent backflow) => pressure in ventricles < pressure in atria => atrioventricular valve (open), blood flows from atria to ventricles
- throughout cycle aortic pressure remains high due to muscle and elastic fibers in arterial walls which maintain bp
heart disease - cause and consequence
blood pumped through heart is at high bp => cannot be used to supply heart muscle with oxygen and nutrients
- coronary arteries are vessels that surround the heart and nourish the cardiac tissue to keep the heart working
- when ca are occluded, region of the heart tissue nourished by the blocked artery will cease to function and die
cause:
atherosclerosis - hardening and narrowing of the arteries due to deposition of cholesterol
- fatty deposits develop in the arteries and significantly reduce the diameter of the lumen
- restricted blood flow => increase pressure in the artery => damage of arterial wall
- damage region repaired with fibrous tissue => significantly reduces elasticity of arterial wall
- smooth lining of artery is progressively degraded => lesions (atherosclerotic plaques)
- if plaque ruptures => blood clotting triggered => thrombus => restrict blood flow
- if thrombus dislodges it becomes an embolus => blockage in smaller arteriole
consequence:
atherosclerosis => blood clots - causes coronary heart disease when occurs in ca
myocardial tissue requires oxygen and nutrients transported via ca in order to function
- when ca are completely blocked => acute myocardial infarction (heart attack)
- blockages of ca are usually treated using by-pass surgery or creating a stent (eg. balloon angioplasty)
blood composition
55% - plasma
- mainly water, dissolves minerals => transport medium
- electrolytes => maintain fluid balance, blood pH
- proteins => maintain osmotic potential, transport lipids, clot blood
- transports nutrients and waste products
45% - RBCs
- bind with hemoglobin to transport oxygen around the body
- oxygen binds with hemoglobin in the lungs, released from RBCs at respiring cells
<1% - buffy coat
- WBCs (eliminate infections - immunity)
- platelets (clotting)
