WEEK THREE - Anatomy of Blood vessels Flashcards
Describe the general structure and function of arteries and veins
tunica interna [INNER layer]
- Simple squamous endothelium
- repels blood cells and platelets
tunica media [MIDDLE layer]
Usually THICKEST; smooth muscle, collagen, some elastic
Smooth muscle for vasomotion
tunica externa [OUTER layer]
Loose CT w/ VASA VASORUM
Describe the structure and function of the different types of arteries
Elastic/conducting arteries
= largest arteries eg pulmonary a, aorta and common carotid a
- Expand during systole, recoil during diastole, lessens fluctuations in BP
Tunica media = perforated sheets of elastic tissue alternating w/ thin layers of smooth muscle, collagen + elastic fibres
Muscular arteries –> Distributed blood to specific organs [femoral and splenic]
tunica media = thick with more smooth muscle
Arterioles [SMALLEST arteries → lead to capillary beds]
- Control flow into capillary beds via vasodilation and constriction
- Under sympathetic modulation
Describe the structure and function of the 3 different types of capillaries
Continuous Capillaries [abundant in skin and muscles]
- Endothelial cells provide uninterrupted lining
Adjacent cells = connected w/ tight junctions –> intercellular clefts allow passage of fluids
Fenestrated Capillaries [porous]
- Found wherever active capillary absorption of filtrates occurs [eg small intestines, endocrine gland and kidneys]
= Greater permeability than continuous capillaries
Sinusoids Capillaries [holey]
- Highly modified, leaky fenestrated capillaries w/ large lumens [central space]
Found in liver, bone marrow, spleen, and some endocrine organs
–> Allow large molecules [proteins and bloods cells] to pass
Describe a capillary bed and explain how they regulate blood flow
Microcirculation of interwoven networks of capillaries with:
Vascular shunts/metarteriole - thoroughfare channel connecting an arteriole directly with postcapillary venule
- if precapillary sphincter is closed [like bypass]
Precapillary sphincter - cuff of smooth muscle that surrounds each true capillary
–> Regulates blood flow into the capillary
Describe the general route taken by blood in the circulation and exceptions to this route via portal systems and anastomoses
Most common route
Heart → arteries → arterioles → capillaries → venules → veins
exceptions
Portal system
Blood flows through two consecutive capillary networks before returning to heart
Hypothalamus - anterior pituitary
Found in kidneys
Between intestines - liver
Anastomosis
Arteriovenous anastomosis [shunt] = Artery flows directly into vein bypassing capillary bed
Venous anastomosis = One vein drains into another
Arterial anastomosis
Collateral circulation
Common around joints
Describe how blood pressure is expressed and measured
Force that exerts against a vessel wall
[normal value in young adult : 120/80 mm Hg]
Measured at brachial artery with a sphygmomanometer [inflated cuff to around 170mm Hg]
SBP
BP during ventricular systole [contraction/ejection of blood]
DBP
BP during ventricular diastole [relaxation/filling of blood]
Detail how pulse pressure and mean arterial pressure are calculated
Pulse pressure : systolic BP - diastolic BP
MAP = [2DBP + SBP]/3
Name and describe 3 factors that determine a person’s peripheral resistance to blood flow
peripheral resistance = opposition to flow in vessels away from heart
- blood viscosity [by RBCs and albumin]
- decrease with anemia, hypoproteinemia
- increase w/ dehydration, polycythemia - vessel length
- Pressure + flow DECREASES with distance [friction] - vessel radius [controls resistance quickly]
- Vasomotion = change in vessel radius
- Vasoconstriction = DECREASE in vessel radius
- Vasodilation = INCREASE in vessel radius
Laminar flow = flows in layers → faster in centre [blood flows slower near the vessel wall and also slower in smaller vessels as a larger proportion of the blood is in contact with the vessel wall = FRICTION
Blood flow proportional to the fourth power of the radius (r)
-eg If r = 3mm → F = (34) = 80mm/sec
Exemplify how vasomotion can be controlled by local mechanisms
vascular smooth muscle can regulate own flow
- increased metabolism in skeletal muscle = vasodilation
- vasodilatory substances [eg CO2, nitric oxide, K+] form w/ increased metabolism and decreased O2 = vasodilation
- arteriole relax = vasodilation
- [reactive hyperaemia] if tissue blood supply is cut off then restored - the flow is 4-7x normal = vasodilation
- arteriole stretch = vasoconstriction
Exemplify how vasomotion can be controlled by neural mechanisms
Vasomotor centre of medulla oblongata
= Sympathetic control stimulates most vessels to constrict, but dilates vessels in skeletal and cardiac muscle
- THREE autonomic reflexes
- baroreflexes
- changes in BP detected by baroreceptors in = arteries above heart eg aortic arch and sinus
- send afferent signals to brainstem
- inhibits vasomotor centre
- decreases sympathetic tone
- –> vasodilation and BP decreases - chemoreflexes
- located in aortic arch, subclavian arteries and external carotid arteries
- response to changes in blood chemistry eg pH, O2, CO2
- primary role = adjust respiration
- secondary role = vasomotion - medullary ischemic reflex
- when inadequate perfusion of the brainstem occurs –> cardiac and vasomotor centres send sympathetic signals to the heart and blood vessels
- increases CO = vasoconstriction
Exemplify how vasomotion can be controlled by hormonal mechanisms
Decreased BP stimulates renin enzyme [released from kidneys]
- renin + angiotensinogen = angiotensin I
- angiotensin I converted to angiotensin II in lungs
- angiotensin II stimulates adrenal cortex to release aldosterone
= increases Na+ and water retention = INCREASES BP
epinephrine + norepinephrine
- binds to ALPHA adrenergic receptors : vasoconstriction
- binds to BETA adrenergic receptors = vasodilation
Describe differences in the routing of blood during rest & exercise
during REST
- blood mainly routed to gut, kidneys and brain
during EXERCISE
- redistribution of blood from the gut, kidneys and brain at rest to the working muscles during exercise.
- increased perfusion of myocardium, skin and skeletal muscle
- decreased perfusion of kidneys and digestive tract
List & describe 4 different routes across a capillary wall for different types of molecules
- diffusion - through lipid bilayer of plas mem. [lipid soluble substances , O2 Co2 steroid hormones]
- intercellular clefts [small water solutes eg electrolytes, AA and glucose]
- fenestrations [small water solutes eg electrolytes, AA and glucose]
- vesicular transport [larger molecules eg proteins- albumin insulin ] [facilitated transport across membrane via vesicles]
Discuss the forces involved that govern fluid exchange across capillary walls
OPPOSING FORCES
- HYDROSTATIC PRESSURE
physical force exerted against a surface by liquid → drives fluid OUT of capillary
HIGH on arterial end of capillary // LOW on venous end - COLLOID OSMOTIC ORESSURE [COD]
draws fluid INTO capillary
results from more plasma proteins in the blood.
Describe the causes and consequences of edema
causes
Right ventricle failure = systemic edema
Left ventricle failure = pulmonary edema
Lack of activity = poor venous return
Presence of Histamines = capillaries more permeable
Decreased capillary reabsorption
Obstructed lymphatic drainage or removal of lymph nodes
consequences
- tissue necrosis - lack of blood supply + waste removal
- Pulmonary edema = suffocation as air in lungs = replaced by fluid
- cerebral edema = headaches, seizures, coma
- Circulatory shock - excess fluid in tissue spaced = decreased O2 perfusion
