Circulation — The Heart and
Blood Vessels
Chapter 9
Circulatory System
• Accepts oxygen, nutrients, and other
substances from the respiratory and
digestive systems and delivers them to
cells
• Accepts carbon dioxide and wastes from
cells and delivers them to respiratory and
urinary systems for disposal
Functional Connections
food, water intake
oxygen intake
DIGESTIVE
SYSTEM
nutrients,
water,
salts
RESPIRATORY
SYSTEM
oxygen
elimination
of carbon
dioxide
carbon
dioxide
CIRCULATORY
SYSTEM
URINARY
SYSTEM
water,
solutes
elimination
of food
residues
rapid transport
to and from all
living cells
elimination of
excess water,
salts, wastes
Cardiovascular
System
• Heart
• Blood vessels
– Arteries
– Arterioles
– Capillaries
– Venules
– Veins
Location of the Heart
• Heart is about size
of a fist
• Lies in thoracic
cavity between the
lungs
• Enclosed in the
pericardium
Layers of Heart Wall
• Inner layer of the pericardium is the
outer layer of the heart wall
• Beneath that is the myocardium, the
thick cardiac muscle tissue
• Thin endocardium lines the chambers of
the heart and blood vessels
Heart Structure
• Each side has two
chambers
– Upper atrium
– Lower ventricle
• Valves between
atria and ventricles
Heart Valves
three cusps
two cusps
left AV valve
(bicuspid or
mitral valve)
right AV
valve
(tricuspid)
left semilunar
valve
right
semilunar
valve
Heart from above with atria removed
Cardiac Cycle
• Contraction
phase is
systole
• Relaxation
phase is
diastole
Mid to late
diastole
.
Early
diastole
Ventricular
systole
Direction of Blood Flow
•
•
•
•
•
•
•
•
Superior and inferior vena cava
Right atrium
Right ventricle
Pulmonary artery
Pulmonary veins
Left atrium
Left ventricle
Aorta
Pulmonary Circuit
right pulmonary artery
Short loop
that
oxygenates
blood
capillary
bed of
right
lung
left pulmonary artery
capillary bed
of left lung
pulmonary
trunk
(to systemic circuit)
(from
systemic
circuit)
pulmonary
veins
heart
lungs
Systemic
Circuit
Longer loop that
carries blood to
and from body
tissues
capillary beds of head
and upper extremities
(to pulmonary
circuit)
aorta
(from
pulmonary
circuit)
heart
capillary beds of other
organs in thoracic cavity
capillary bed of liver
capillary beds of intestines
Hepatic Portal System
• Carries blood from capillaries in
digestive organs to capillaries in the
liver
• Enables liver to detoxify substances
from digestive tract before they are
carried to the body
Statins: Heart-Saving Drugs
• Interrupt the metabolic pathway in the
liver that creates cholesterol
• Increase receptor proteins that bind with
and remove LDL cholesterol
• Raise blood level of “good” cholesterol
(HDLs)
• Lower blood levels of triglycerides
Conduction and Contraction
SA node
• SA node in right atrium
is pacemaker
• Electrical signals
cause contraction of
atria
• Signal flows to AV
node and down
septum to ventricles
Nervous System
• Triggers the contraction of skeletal
muscle
• Can only adjust the rate and strength of
cardiac muscle contraction
• Centers for neural control of heart
functions are in the spinal cord and
parts of the brain
Blood Pressure
• Highest in arteries,
lowest in veins
• Systolic pressure is
peak pressure
(ventricular
contraction)
• Diastolic pressure is
the lowest
• Greatest pressure drop is
in arterioles
Arteries, Arterioles, Capillaries
• Arteries: main
transporters of
oxygenated blood
• Arterioles: diameter
is adjusted to
regulate blood flow
• Capillaries: diffusion
occurs across thin
walls
Venous System
• Blood flows from capillaries into venules,
then on to veins
• Veins are large-diameter vessels with some
smooth muscle in wall
• Valves in some veins prevent blood from
flowing backward
Controlling Blood Pressure
• Cardiac output adjusted by controls
over rate and strength of heartbeat
• Total resistance is controlled by
vasoconstriction of arterioles
• Baroreceptor response is main shortterm control of blood pressure
Velocity of Flow Varies
• Volume of blood flowing through vessels
always has to equal heart’s output
• Flow velocity is highest in large-diameter
transport vessels
• Flow velocity is slowest in capillary beds;
blood spreads out into many vessels with
greater total cross-sectional area
Diffusion Zone
• Capillary beds are the site of exchange
between blood and interstitial fluid
• Capillary is a single sheet of epithelial
cells
• Flow is slow; enables gases to diffuse
across membranes of blood cells and
across endothelium
Bulk Flow
• Movement of water and solutes in
response to fluid pressure
to venule
inward-directed
osmotic
movement
from
arteriole
outward-directed
bulk flow
cells of
tissue
Net Bulk Flow
• Normally, ultrafiltration only slightly
exceeds reabsorption
• Fluid enters interstitial fluid and eventually
returns to blood by way of lymphatic
system
• High blood pressure causes excessive
ultrafiltration and results in edema
Risk Factors for
Cardiovascular Disease
• Smoking
• Gender (maleness)
• Genetic factors
• Old age
• High cholesterol
• Obesity
• Lack of exercise
• Diabetes mellitus
Hypertension
• Blood pressure above 140/90
• Tends to be genetic
• May also be influenced by diet
• Contributes to atherosclerosis
• “Silent killer” - few outward signs
Atherosclerosis
• Arteries thicken,
lose elasticity,
and fill up with
cholesterol and
lipids
• High LDL level
increases risk
Arrhythmias
• Bradycardia - slow heart rate
• Tachycardia - 100+ beats/minute
• Atrial fibrillation - irregular heartbeat
• Ventricular fibrillation - uncontrolled
contraction of ventricles; quickly fatal
Lymphatic System
• The circulatory system is leaky
• Some fluid is forced out of the smallest
vessels and into the interstitial fluid
• Vessels of the lymphatic system pick up
this fluid, filter it, and return it to the
circulatory system
Lymph Vascular System
• Fluid enters lymph
capillaries
• Capillaries merge into
lymph vessels
• Lymph vessels converge
into ducts that funnel fluid
into veins in the lower
neck
Lymph Nodes
• Located at intervals
along lymph vessels
• Act as a filter for lymph
• Contain lymphocytes
that can recognize a
foreign invader
Lymphoid Organs
• Central to the
body’s defense
• Tonsils
• Spleen
• Thymus gland