Ch. 12 – The Circulatory
System
•  Heart
•  Blood vessels
Blood vessels…and you!
Blood is conducted in a
continuous loop
•  Arteries
–  carry blood away from
the heart
–  arterioles
•  Veins
–  carry blood towards the
heart
–  Venules
•  Separated by capillaries
–  Site of exchange
1
Types of blood vessels
Arteries
•  carry blood away from the heart
•  Higher pressure vessels
•  Walls have lots of elastin (an elastic protein) to
withstand pressure
•  Pulse stretch/recoil of arteries with each heartbeat
•  Thick wall compared to lumen size
–  Walls have lots of smooth muscle to direct blood flow
•  vasoconstrict (↓ vessel diameter)
•  vasodilate (↑ vessel diameter)
•  Arterioles really small arteries
Capillaries
•
exchange between blood and
interstitial fluid
–
–
–
–
•
Gases: oxygen and carbon dioxide
nutrients
wastes,
etc.
Microscopic, extremely thinwalled, leaky
2
Capillary fluid exchange
•  Slightly more fluid leaves the capillaries for the tissues than
re-enters the capillaries from the tissues
–  The excess is returned to the circulation by the lymphatic system
Blood flow through
capillary beds
•  Precapillary sphincters
may contract
(vasoconstrict) or relax
(vasodilate) to adjust
blood flow in response
to metabolic needs of
different tissues/organs
Velocity of blood flow
•  Flow slows
down as
blood
spreads
throughout
capillary
beds
–  So more
time for
exchange
3
Veins
•  carry blood towards
the heart
•  Lower pressure
vessels
•  Blood flow
–  Pressure from heart
–  skeletal muscle
contraction
–  one-way valves
•  Thin wall
•  Venules: really small
veins
The heart
•  muscular pump
•  ~ 100,000
heartbeats/day!
•  ~ 9000 liters of
blood/day!!
Heart wall
•  Surrounded by
pericardium
•  Lined by thin, smooth
endocardium
•  Middle, thickest layer
is myocardium
(cardiac muscle
tissue)
–  Thicker on
left side…
why?
(Intercalated disc)
● Intercalated
discs are
specialized junctions that
electrically connect cells, allow
rhythmic contraction
4
Some cardiac anatomy
Papillary muscles
The heart is a
double pump
•  Right heart:
–  Pumps into
pulmonary circuit
–  to and from lungs
–  Receives blood
from systemic
circuit
•  Left heart:
–  Pumps into
systemic circuit
–  to and from rest of
body
–  Receives blood
from pulmonary
circuit
Heart valves
•  One-way valves; prevent backflow
–  Closing of valves creates heart sounds ( lub-dup )
•  Papillary muscles contract and tense chordae tendineae to prevent AV
valves from opening the wrong way (back into atria) when ventricles
contract
5
Coronary
circulation
•  Feeds blood to the
myocardium of the
heart
Cardiac cycle
Diastole relaxation
the events of one
heartbeat
Systole contraction
Cardiac conduction system
•
•
•
•
SA node
AV node
Bundle branches
Purkinje fibers
•  Electrical impulses spread
cell to cell via intercalated
discs, causing cardiac
muscle to contract
rhythmically
6
Generation of heartbeat
•  Sinoatrial (SA) node ( pacemaker )
spontaneously generates electrical
impulses – sets basic heart rate
–  No nervous or hormonal input
–  autonomic nervous input and/or
hormonal input needed to change
heart rate ↑ or ↓
down septum
Electrocardiogram
(ECG or EKG)
•
graphical recording of electrical activity
•  ECG waves – record electrical changes
from baseline
–  P wave electrical impulse
through atria
–  QRS complex electrical
impulse spreads through
ventricles
spreads
•  (Return of atria to resting
electrical state is hidden)
–  T wave ventricles return to
resting electrical state
Blood
pressure (BP)
•
the force exerted by
blood against the
wall of a vessel
•  Systolic pressure
maximum BP generated
during ventricular
contraction
•  Diastolic pressure
minimum BP at end of
ventricular relaxation
•  BP typically reported as:
systolic pressure ≈ 120 mm Hg
diastolic pressure 80 mm Hg
7
A BV
problem
Atherosclerosis
Some solutions?
Balloon angioplasty
Coronary
bypass
surgery
Lymph
•  Slightly more fluid leaves the
capillaries than re-enters
•  excess is returned to the circulation by
the lymphatic system
Lymphatic system
Components:
•  Lymph
•  Lymphatic vessels
•  Lymphoid tissues and organs
8
Lymphatic system
Functions:
•  Lymph
–  excess interstitial fluid that gets
absorbed and transported by…
•  Lymphatic vessels
–  low pressure tubes that ultimately
return lymph to bloodstream
•  Lymphoid tissues and organs
–  contain lymphocytes and other
supporting cells
General functions:
•  Return excess interstitial fluid to
bloodstream
•  Transport products of fat
digestion from small intestine to
bloodstream
•  Help defend against pathogens
( disease-causing organisms) –
more detail in Ch. 13
Lymphatic capillaries
•  tiny, low pressure tubes
that drain excess interstitial
fluid
•  Larger and more
permeable than blood
capillaries
•  Flaplike minivalves help
ensure one-way flow
•  Drain into larger
lymphatic vessels
Flow of lymph
•  Lymphatic vessels
ultimately return lymph
to cardiovascular system
at subclavian veins
•  No pump, so lymph moves
slowly, in same ways that
venous blood moves
(skeletal muscle contraction,
one-way valves, breathing)
•  Lymph passes through
lymph nodes on the way
(see next slide)
9
Some lymphoid
tissues and organs
Peyer s patches
•
Keep bacteria from breaching
the intestinal wall
10