9: Circulation system Flashcards
3 layers of blood vessel walls?
Tunica intima- inner layer
Tunica media- middle layer
Tunica extrena- outer layer
Central space of vessel?
Lumen
Tunica intima structure
inner endothelium
Tunica media structure
- Smooth muscle
- Elastin (vaso constriction and dilation)
Tunica externa
- tough connective tissue
- Collagen fibres- strong and connective
3 types of arteries
Elastic (conducting vessels)
Muscular (distributing vessels)
arterioles (resistance vessels)
Elastic arteries aka…
Conducting vessels
Muscular arteries aka….
Distributing vessels
Arterioles aka…
resistance vessels
Elastic arteries
- thin-walled
- located near the heart
Elastin present in all lumen - conduct vessels away from the heart
- 1-2.5cm diameter
Muscular arteries
- distal to elastic arteries
- thick tunica media
- Distributing vessels that change diameter to control pressure and therefore flow
- 0.3-1cm diameter
Arterioles
- smallest arteries
- can easily chnage lumen size and therefor play a major role in blood pressure and flow
- 10um- 0.3 mm
Capillaries general properties
- 1mm long
- 8-10 um diameter
- composed of tunica intima
- exchange vessels for nutrients, wastes, gases, hormones etc.
three types of capillaries
Continuous capillaries
Fenestrated capillaries
Sinusoidal capillaries
Continuous capillaries components
- composed of tightly joined endothelial cells forming a smooth lining.
- Intercellular clefts allow limited fluids and small solutes to pass through.
Pinocytotic vesicles= ferry larger solutes across the capillary wall
Fenestrated capillaries
pores
Endothelial cells that contain pores aka fenestrations
- porse= increase permeability thus increasing exchange.
- found in area of active filtration (kidneys), absorption (small intestines) and endocrine glands
Sinusoidal capillaries
Leaky capillaries
- large endothelial cells (sinusoids) and fenestration
- when blood flow is low large molecules and cells can pass through
- found in liver, lymphoid organs, adrenal medulla
Capillary beds
the connection between terminal arterioles and postcapillary venules.
- flow is controlled by venules dimaterter
Capillary diameter is effected by
immediate environment (temp) Sympathetic control (muscle demands)
Terminal arterioles
Oxygenated blood carries in capillary beds
Postcapillary venules
carry deoxygenated blood away from capillary beds
Venules and veins structure anf function
- capillaries- venules- veins
- large lumen= easy blood flow
- Tunic intima folds into valves to prevent back flow
Capacitance vessels
thick tunica externa proves support for accommodating a large blood volume.
Blood flow
Volume of blood flow through a vessel at a given time period
- measured in ml/min
- varies with demand
flow is determined by blood pressure and resistance
Blood pressure
the force exerted on a vessel wall by the blood in that vessel
- measured in mmHg
- generated by the pumping action
Resistance
is a measure of the amount of friction blood encounters as it flows through vessel.
- opposition to blood flow
Primary sources of total peripheral resistance (TPR)
Blood viscosity
Total blood vessel length
Blood vessel diameter
Viscosity
thickness/stickiness of fluid
- caused by concentration of blood cells ad plasma proteins.
Haematocrit
proportion of RBC in blood
Vessel length
resistance increases as the vessel length increases
- relatively constant in adults but changes as children grow.
+1kg weight= 1km more blood vessels
Vessel diameter
amount of contact surfaces determines the amount of friction. more friction= more resistance= reduced blood flow
- think vasoconstriction (when cold to preserve energy) and vasodilation (when hot to exert heat)
- decreased diameter by plaque creates turbulence aka increased resistance as more blood hits the vessel walls
Flow=
Pressure/resistance
MAP/R
Systemic blood pressure
the pumping action of the heart generates pressure which drives blood flow to the systemic circuit.
Explain the systemic blood pressure gradient
Blood pressure is at it highest in the aorta and reduces the further away it gets from the heart.
Arteriole blood pressure determined by
- compliance- stretch of vessel
2. Stroke volume- volume of blood forced into vessel after ventricular contraction
Systolic pressure range
90-120 mmHg
average= 120
Systolic blood pressure
peak pressure generated in the large arteries when the ventricle contracts
- increases as compliance decreases (afterload)
Diastolic pressure range
60-80 mmHg
Diastolic blood pressure
pressure in the large arteries during ventricular relaxation
average= 80
Pulse pressure equation
pulse pressure= systolic pressure - diastolic pressure
- felt at superficial arteries at common carotid and radial
Mean arterial pressure definition
MAP= pressure that propels blood through the vessels
- declines with distance away from heart
MAP equation
MAP= diastolic pressure + (1/3 x pulse pressure)
Hypotension
systolic blood pressure of 90mmHg
- dizziness and fainting
Hypertension
transient elevation due to exercise, illness, emotions
chromic hypertension= sustained systolic blood pressure >140mmHg
Capillary pressure
ranges from 15-35 mmHg.
- cant be to great otherwise damage and excess excretion of fluid are risked
Venous blood pressure
aprox. 15mmHg
Venous return mechanisms
- valves- compartmentalise blood and stop backflow
- muscular pumps- skeletal muscles that push blood towards heart
- respiratory pump- pressure changes during breathing help squeeze abdominal veins
- pulsation- of near by arteries
- venoconstriction- tunica media under sympathetic control
3 factors the determine blood pressure (thus flow)
Cardiac output
Peripheral resistance
Blood volume
Describe the effect of cardiac output on blood flow/pressure
- rapid and short term
What effects cardiac output (8)
- EDV (preload)
- Blood volume
- Venous return
- ESV
- Contractility
- ANS
- Hormones
- Plasma electrolytes
Describe the effect of resistance on blood flow/pressure
- rapid and short term
- altered by changing
- arteriole diameter (vaso constriction/dilation)
Describe the effect of blood volume on blood flow/pressure
- slower, long term regulation of BP
- controlled by renal/endocrine mechanisms
- changes in blood volume alter venous return and therefore EDV and preload
4 blood pressure regulation levels
- Autoregulation
- Neural regulation
- renal mechanisms
- Endocrine regulation
What is autoregulation
the tissue regulates it own diameter to regulate flow and pressure.
What are the two types of autoregulation?
- metabolic control- when CO2 increases, o2 and pH decrease arterioles dilate to increase blood to lungs to get co2 respired out out
- myogenic (muscle) control - high systemic blood pressure makes arterioles stretch and reflex constriction which changes blood flow
What are the three types of neural regulation
- Cardioinhibitory centre
- Cardioacceleratory centre
- Vasomotor centre
How does the cardioinhibitory centre work as neural regulation to regulate blood flow/pressure?
parasympathetic input into SA and AV nodes slows heart rate
How does the cardioacceleratory centre work as neural regulation to regulate blood flow/pressure?
sympathetic input to SA and AV nodes increases heate rate and therfore CO, sympathetic input into to ventricular myocardio=um= more blood to muscle=harder pump=increased CO
How does the vasomotor centre work as neural regulation to regulate blood flow/pressure?
sympathetic vasomotor fibres to smooth muscles of arterioles increase vessel diameter and therefore flow and CO, hypothalamus input regualted blood flow for body temp (dilation and constriction) and fight/flight response
Explain barareceptors
- streach receptors
- detect changes in pressure
inform medullary cardiovascular centres
location: carotid arteries, aortic arch, walls of most large arteries in the neck and thorax - initiate the baroreceptor reflex.
Name the two baroreceptor reflexs and their function
- carotid baroreceptor sinus reflex- monitors BP to ensure flow to the brain
- Aortic baroreceptor reflex- monitors BP to maintain flow to systemic circuit
Barorecptor reflexs function rapidly to protect against short term changes in blood pressure, thus maintaining blood flow.
function: rapidly to protect against short term changes in blood pressure, thus maintaining blood flow.
Renal mechanisms
- Direct mechanism- BP directly effects urine production as more blood volume increases the demand for filtration.
- Indirect mechanism- involves hormones renin-angiotensin-aldosterone system (RAAS) the release
Endocrine regulation
hormones that increase BP include
Adrenalin and noradrenalin (increase CO and peripheral vasoconstriction)
Angiotensin 2-> vasoconstriction, thirst and promotes secretion of aldosterone (increases sodium ion and water absorption) and ADH (peripheral vasoconstriction and increase renal water reabsorbtion)
Endocrine regulation
hormones that decrease BP include
Atrial natriuretic peptide (ANP)
- produced by atriasl myocardium in fresponse to high blood pressure.
- opposes the action of angiotensin 2 and decreases BV and BP
Describe capillary blood flow
- slow
- intermittent
- controlled by arteriole diameter in response to local conditions (high CO2 or low O2)
Capillary exchange
- exchange of solutes (gases, nutrients and wastes)
- bulk of fluid flow
4 types of capillary exchnage
- Diffusion through endothelial membranes (lipid soluble substances e.g. o2, CO2)
- intercellular clefts (water soluble substances e.g. electrolytes, glucose, amino acids)
- Fenstrations (small, water-soluble substances e.g. electrolytes glucose, amino acids)
- Active transport via vessel endocytosis and exocytosis (large substances e.g. proteins)
Bulk flow refers to
movement of fluid across capillary walls
- it determines the relative fluid volumes of the blood and ISF
Bulk flow occurs through
Intercellular clefts: between endothelial cells in all capillaries
Fenestrations: pores within endothelial cells in some capillaries
Sinusoids: big gaps between endothelial cells in some capillaries
What two pressures determine direction and volume of fluid flow
Hydrostatic
Colloid osmotic
Hydrostatic pressure
force exerted by fluid pushing against a tissue wall
Capillary HPc- pushes fluid and solutes out of the capillaries through intercellular clefts/fenestration/sinusoids at arterial end of bed
Colloid osmotic pressure
force related to the tonicity (solute concentration) of a solution- pulling force
Capillary OPc- sue to solutes within the plasma that are unable to diffuse out of the capillary e.g. proteins
-unable to pull fluid back into the capillaries at the end of the bed.
Net filtration pressure=
colloid osmotic pressure push and difference between hydrostatic pressure pull
Oedema is
an abnormal increase of interstitial fluid
- caused due to increased push or decreased pull
- increase in capillary hydrostatic pressure
Inflammation increases capillary permeability
- decreased colloid osmotic pressure due to low levels of plasma proteins due to lover disease or mal nutrition
- Blockage of lymphatic vessels that prevent fluid drainage from tissues. Parasites, surgical removal
Common traits of arteries
deep
away from heart
less interconnected
run parallel with veins and nerves that share a similar name
Common traits of veins
deep or superficial
to heart
more interconnected
run parallel with veins and nerves that share similar name
two subdivisions of the circulatory system
Pulmonary circuit
- heart to lungs and back
- provides no metabolic needs of body tissue
Systemic circuit
- functional blood supply to body tissues.
- delivers nutrients, gases, hormones and removes waste
