heart and blood vessels

Blood vessels:

delivery

system of dynamic

structures that begins and

ends at heart

Arteries:

carry blood away

from heart; oxygen-rich

except for pulmonary

circulation

Capillaries:

Veins:

carry blood toward

heart; oxygen-poor except

for pulmonary circulation

Pressure gradient

difference in

pressure between two regions

Blood flow:

volume of blood flowing

through vessel, organ, or entire circulation

in given period (mL/min)

• Resistance (peripheral resistance):

opposition to flow

• Flow decreases as resistance increases

total peripheral resistance (TPR)

Measurement of amount of friction blood encounters with vessel walls,

generally in peripheral (systemic) circulation

Blood viscosity

Resistance increases as viscosity increases

Total blood vessel length

Resistance increases as length increases

Blood vessel diameter

Resistance decreases as diameter increases

• Vasoconstriction vs. vasodilation

Vasoconstriction of arterioles

provides the greatest resistance

to blood flow and can redirect

flow to/from particular organs

autoregulation.

Used by some organs (brain and kidneys) to

promote constant blood flow when there is

fluctuation of blood pressure;

Myogenic control mechanisms:

Vascular

smooth muscle responds to changes in arterial

blood pressure.

Blood pressure (BP):

force per unit

area exerted on wall of blood vessel

by blood

pulsatile

Blood pressure near heart

Systolic pressure:

pressure exerted in aorta

during ventricular contraction

Diastolic pressure:

lowest level of aortic

pressure when heart is at rest

Pulse pressure

systolic pressure - diastolic

pressure

Mean arterial pressure (MAP):

pressure that

propels blood to tissues

Three main factors regulating blood

pressure:

• Cardiac output (CO)

• Total peripheral resistance (TPR)

• Blood volume

Baroreceptor reflex

activated by

changes in blood pressure detected

by baroreceptors (stretch

receptors) in carotid arteries and

aorta

Arteriolar vasodilation:

reduces

peripheral resistance, MAP falls

Decreased cardiac output:

impulses to cardiac centers

inhibit sympathetic activity and

stimulate parasympathetic

Flow = flow rate =

volume of blood that passes a given

point in the system per unit time

Velocity of flow

distance a fixed volume of blood

travels in a given period of time

Hydrostatic pressure (HP):

force exerted by

fluid pressing against wall

Capillary hydrostatic pressure (HPc):

capillary

blood pressure that tends to force fluids

through capillary walls

Interstitial fluid hydrostatic pressure (HPif):

pressure pushing fluid back into vessel; usually

zero because lymphatic vessels drain interstitial

fluid

Capillary colloid osmotic pressure (OPc):

“Sucking” pressure created by nondiffusible

plasma proteins pulling water back into

capillary

Lymphatic system

• Transports excess interstitial

fluid (lymph) from tissues to

the veins

• Lymph: fluid of the

lymphatic system that

originated from the blood

and returns to the blood

Edema:

abnormal increase in amount

of interstitial fluid

Cardiovascular system:

• Heart (pump)

• Blood (fluid)

• Blood vessels (tubes)

The cardiovascular system transports

materials throughout the body

• From external environment: nutrients, water,

and gases

• Materials between cells: hormones, immune

cells, antibodies

Waste eliminated by cells:

CO2, heat,

metabolic waste

Desmosomes:

hold cells together;

prevent cells from separating

during contraction

Gap junctions:

allow ions to pass

from cell to cell; electrically

couple adjacent cells

Contractile cells

• 99% of heart

• Striated fibers organized into sarcomeres

• Responsible for contraction

• Contracts when depolarized

Non-contractile / Autorhythmic cells (pacemakers)

• 1% of heart

• Autorhythmicity - spontaneously depolarize

• Initiate depolarization of entire heart

• Do not need nervous system stimulation

Stroke volume:

volume of blood pumped out by one ventricle with each beat

Preload:

degree to which cardiac

muscle cells are stretched just before

they contract

EDV is determined by venous

return

amount of blood

returning to heart from venous

circulation

Contractility

contractile strength at any

given fiber length

Afterload:

combined load of EDV and arterial resistance during ventricular

contraction