Blood vessels & Blood Pressure

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Structure of blood vessels: Inner layer - Tunica initima	Endothelium Basement membrane
Structure of blood vessels: Middle layer - Tunica media	Elastic laminae/tissue Muscle
Structure of blood vessels: Outer layer - Tunica externa (adventitia)	Most complex region Collagen - secreted structural proteins to provide mechanical support Nerves Vaso vasorum - the blood vessels that supply blood to the larger vessels Lymphatics - help to drain away fluid
Capillary	Wall made of endothelial cells only that are in contact with blood Cells are attached to the basement membrane - same as intima in other vessels
Elastic Arteries (Aorta)	Elastic tissue in the media (rather than smooth muscle) Elastic to cope with peak ejection pressure (highest pressure changes) Stretches and recoils Windkessel effect
Muscular Arteries	Media is mostly muscle rather than mostly elastic tissues Reflects change in function -> pressure lower-> muscle to maintain pressure
Arteriosclerosis	Thickening/toughening of arterial walls Focal calcification: Ca2+ deposition post muscle degeneration Damage to cell -> Ca2+ -> precipitation of proteins High blood pressure
Atherosclerosis	Lipid and monocyte deposition in tunica media Associated with: Cholesterol Low ApoE High LDL's Restriction in lumen -> increase in blood pressure
Arterioles	Arterioles and venules commonly found next to each other Arterioles have smooth muscle Key target area for control Innervation -> causes them to constrict or dilate therefore are major targets for drugs
AG and ACE inhibitors	Angiotensin II -> cardiovascular - vasoconstriction (powerful) -> Hypothalamus - thirst and drinking -> kidney - salt and water retention => Elevated blood pressure ACE inhibitors reduce blood pressure Eg. Ramipril, Perindopril
Capillaries	Capillary beds are the place where O2/CO2 exchange, waste removal and hormones take place Simplest vessel Smaller diameter than RBC -> RBCs need to be flexible (problems - SCA) Variable structure - leaky (liver) or tight (brain - BBB) Fenestrations (pores) and gaps Formation of tissue fluid
Venules	Less muscular than arterioles More prone to collapse/being compressed
Veins	Less muscular and more distensible (opens up more when under pressure) than arteries Can "store" blood - not static About the distribution of total blood volume Greater amount of blood in venous circulation than arterial
Large Veins	More muscular than venules More elasticity Contain pocket valves -> prevent backflow of blood due to low pressure Varicose veins -> when valves stop working properly
Lymphatic system	Diffuse system Close association with the immune system Delivers excess tissue fluid to CVS Impaired flow (if this stops) -> oedema can occur
Lymphatics	Close association with the capillary beds Blind-ended, freely permeable Flap valves -> vessel wall can open "Pocket valves" in larger lymphatics -> larger lymphatics are vein-like
Lymphatic system: Immune role	Lymph nodes -> areas where specialised immune cells are Wuchereria bancrofti: Parasitic worms Disturbances in fluid flow Elephantiasis
Blood pressure	Blood volume (4-6L related to body size) is a continuous column contained in a flexible closed system It has pressure without the heart pumping
Blood pressure waves - The action of the heart	Ejects blood (roughly 70bpm @ 70ml, CO ~ 5L/min) Increases pressures from venous to arterial pressure Induces a waveform in the arterial pressure
System blood pressure diagram	Image: ch37_0_b.gif (image/gif)
Blood pressure waves	The wave has a maxima (systolic) and minima (diastolic) pressures Incisura and dicrotic notch
Blood pressures in the pulmonary circuit	Systolic - 25 mmHg Diastolic - 8 Capillary - 10 Left atrial ~1-2
Blood pressures in the systemic circuit	Systolic ~ 120 mmHg Diastolic ~ 75 Capillary ~ 15 Right atrial ~ few
Mean arterial pressures	MABP = diastolic + 1/3 PP Pulse pressure = systolic - diastolic BP Pulmonary ~ 16 mmHg Systemic ~ 90 mmHg
Measurement of arterial BP	Inflatable cuff, pressure meter, stethoscope Attach on arm at heart level Cuff inflated above expected systolic pressure -> squashes artery shut Pressure released Listen for sounds in brachial artery
Diagram of BP & Korotkoff sounds	Image: images (image/jpg)
Korotkoff sounds	First sound -> loud tapping = systolic pressure Muting Pounding Muffling (Diastolic UK) Silence (Diastolic US)
Systemic pressure is mainly affected by:	Ejection velocity (EV) - how fast Stroke volume (SV) - how much
Diastolic pressure is mainly affected by:	Total peripheral resistance (TPR) -> determined by diameter (and therefore resistance) of arterioles Blood flow from arterial to venous sides through capillary beds
Arterial BP is under short and long-term control	Short term by baroreceptors: Embedded in the chamber of heart and also in vessels Aortic arch, carotid artery - feed back into CNS Long term by control of blood volume: Involves hypothalamus and kidneys
Eg. of baroreceptor control Orthostasis when standing up	Reduced blood to the brain so the body has to compensate To raise the MABP the reflex: Increases sympathetic outflow to the heart (and decreases parasympathetic) -> Rate and force of contraction both increase -> CO increases Increased sympathetic flow to vessels = constriction = increased resistance As MAPB = CO x TPR => it increases
Drugs and BP: 1) Increase TPR by vasoconstricting	Angiotensin II Sympathetic agonists at alpha-1 receptors -> phenylephrine
Drugs and BP: 2) Increase CO by increasing HR or SV	Sympathetic agonists at beta-1 receptors Dobutamine (rate and volume) Digitalis Na+/K+ ATPase pump inhibitor Na+ builds up, Na+ is exchanged for Ca2+ Ca2+ builds up -> improves contractability of the muscle
Drugs and BP: 3) Decrease TPR by vasodilating	Sympathetic antagonists at beta-1 receptors eg. Prazosin
Drugs and BP: 4) Decrease CO by decreasing HR or SV	Sympathetic anatagonists at beta-1 receptors eg. Atenolol Reduce rate and volume Beta blockers are being phased out because side effects Ca2+ channel blockers: eg. Verapamil Reduces force of muscle contraction Reduces amount of blood being pumped out of heart
Exercise changes: Supply changes	As you exercise the cardiac output increases Brain always gets 70ml of blood per minute Coronary blood flow increases Major shift is the amount of blood going to the skeletal muscle Amount to skin increases to lose heat, but at higher levels of exercise decreases significantly -> body temperature is a major factor in how intense we can exercise
Exercise changes: Blood pressure changes	BP changes minor during light exercise Diastolic decreases as TPR decreases Systolic increases as SV and EV increases

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Blood vessels & Blood Pressure

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