Week 4: Circulatory System Cardiovascular System

arteries

blood vessels that carry oxygen-rich blood away from the heart to the rest of the body

arterioles

smaller branches of arteries that lead to capillaries, regulate blood flow/pressure from the arteries into the capillaries

capillaries

tiny, thin-walled blood vessels that connect arterioles to venules

• no tunica media / externa

• basement membrane surrounding

venules

small blood vessels that collect deoxygenated blood from capillaries and carry it to veins

veins

blood vessels that carry deoxygenated blood back to the heart

arteriovenous anastomosis

low resistance pathways that can bypass the capillary bed, used for rapid control of blood volume (ex. temperature regulation)

metarteriole

a small blood vessel that bridges the gap between arterioles and capillaries in the microcirculation

precapillary sphincter

a band of smooth muscle cells that regulates blood flow into the capillaries

typical artery

• round, thick wall

• tunica intima: endothelium is rippled due to vessel constriction, elastic membrane

• tunica media: muscle and elastic fibres, elastic membrane

• tunica externa: collagen/elastic fibres

typical vein

• flattened, thin wall

• tunica intima: smooth endothelium

• tunica media: thin, smooth muscle and collagen fibres

• tunica externa: collagen/elastic fibres, smooth muscle

tunica intima

encompasses the endothelial lining and connective tissue layer, internal elastic membrane (arteries only)

tunica media

concentric sheets of smooth muscle in loose connective tissue

• elastic fibres for arteries

• collagen for veins

external elastic membrane (arteries only)

tunica externa

anchors vessels to adjacent tissues

• collagen / elastic fibres (also smooth muscle in veins)

vasa vasorum

vasa vasorum

small arteries and veins in walls of large arteries and veins, serve blood to cells of tunica media and externa

endothelium

innermost lining of blood vessels

• releases vasoactive substances which affect vascular tone and blood pressure

• maintains vascular homeostasis via:

  • vasodilators (nitric oxide)

  • vasoconstrictors (endothelin)

vasodilators

nitric oxide

vasoconstrictors

endothelin

continuous capillaries

in all tissues except epithelia and cartilage

• complete endothelial lining

• permit diffusion of water / lipid soluble materials (block blood cells and plasma)

• specialised capillaries in CNS and thymus (blood brain barrier)

fenestrated capillary

• pores in endothelial lining

• rapid exchange of water and larger solutes

• found in choroid plexus, endocrine organs, kidneys, intestines

sinusoid capillaries

• have gaps between adjacent endothelial cell

• permit free exchange of water and large plasma proteins

• found in liver, spleen, bone marrow, endocrine organs

• phagocytic cells monitor blood at sinusoids

venous valves

• folds of tunica intima

• prevent blood from flowing backwards

total capillary blood flow

equals cardiac output (how much blood has left the heart per minute) and is determined by Pressure (P) and resistance (R)

pressure (P)

generated by the heart to overcome resistance, absolute pressure is less important than pressure gradient

pressure gradient (∆P)

the difference in pressure from one end of a vessel to the other

• ∆P across systemic circuit is about 85 mm Hg

flow (F)

is proportional to the pressure gradient (∆P) divided by resistance (R)

circulatory pressure

must overcome total peripheral resistance which can be affected by:

• vascular resistance

• blood viscosity

• turbulence

vascular resistance

due to friction between blood and vessel walls, depends on vessel length and diameter

normal blood pressure

120/80

hypertension

abnormally high blood pressure (greater than 140/90)

hypotension

abnormally low blood pressure

systolic blood pressure

the higher of the two numbers in a blood pressure reading and represents the pressure in your arteries when your heart beats

diastolic blood pressure

the minimum pressure in your arteries when your heart rests between beats, refilling with blood

parasympathetic regulation of heart rate

• via vagus nerve

• slows HR by inhibiting SA and AV node

sympathetic nervous system

• via cardiac accelerator nerves

• increases HR by stimulating SA and AV node

changes in stroke volume (SV)

increased force of contraction = increased stroke volume

1. increased sympathetic nervous system activation

2. increased end diastolic volume, leading to increased stretch of sarcomeres

end diastolic volume (EDV)

the volume of blood in the ventricle at the end of diastole (right before the heart contracts), When the ventricle fills with more blood, the muscle fibers (sarcomeres) stretch more because the heart chamber is expanded

• the Frank-Starling Mechanism