David Sadava H. Craig Heller Gordon H. Orians
William K. Purves David M. Hillis
Biologia.blu
C – Il corpo umano
Circulatory System
and Blood
Circulatory System and Blood
• Why do humans need a circulatory
system?
• How have vertebrate circulatory systems
evolved?
• How does the mammalian heart function?
• What are the properties of blood and
blood vessels?
• How is the circulatory system controlled
and regulated?
Circulatory System and Blood - Why do humans need a circulatory system?
A circulatory system consists of:
• a muscular pump - the heart;
• a fluid - blood;
• a series of conduits - blood vessels.
Together these are called the
cardiovascular system.
Circulatory System and Blood - How have vertebrate circulatory systems evolved?
Two circulatory circuits have evolved:
• pulmonary circuit - blood is pumped
from the heart to the lungs and back
again;
• systemic circuit - blood travels from
the heart to the rest of the body and
back to the heart.
Circulatory System and Blood - How have vertebrate circulatory systems evolved?
The closed vascular system contains:
• arteries carry blood away from the
heart and branch into arterioles that
feed the capillary beds;
• capillaries are the site of exchange
between blood and tissue fluid;
• venules drain the capillary beds and
form veins, which deliver blood back
to the heart.
Circulatory System and Blood - How does the mammalian heart function?
The human heart has four chambers: two atria
and two ventricles.
The right heart pumps blood through the
pulmonary circuit.
The left heart pumps blood through the
systemic circuit.
Circulatory System and Blood - How does the mammalian heart function?
Valves prevent backflow of blood:
• atrioventricular valves between the atria
and ventricles and prevent backflow when
ventricles contract;
• the pulmonary valve and aortic valve lie
between the ventricles and the major arteries
and prevent backflow when ventricles relax.
Circulatory System and Blood - How does the mammalian heart function?
The human heart and circulation (part 1)
Circulatory System and Blood - How does the mammalian heart function?
The human heart and circulation (part 2)
Circulatory System and Blood - How does the mammalian heart function?
The right atrium receives
deoxygenated blood from the body
through large veins:
• superior vena cava - blood from
upper body;
• inferior vena cava - blood from
lower body.
Circulatory System and Blood - How does the mammalian heart function?
Blood passes from the right atrium through an AV
valve into the right ventricle.
The atrium contracts, then the ventricle—the AV
valve closes and blood is pumped through the
pulmonary artery to the lungs.
Oxygenated blood returns to the left atrium of the
heart through the pulmonary veins.
The ventricle fills as blood enters through AV
valve.
The left atrium contracts, then the ventricle—the
aortic valve opens and blood circulates through
the aorta.
Circulatory System and Blood - How does the mammalian heart function?
In the cardiac cycle both sides of the
heart contract at the same time: first
the two atria contract, then the two
ventricles.
Two phases:
• systole - when ventricles contract;
• diastole - when ventricles relax.
Circulatory System and Blood - How does the mammalian heart function?
The cardiac cycle
Circulatory System and Blood - How does the mammalian heart function?
Blood pressure changes are measured
with a sphygmomanometer and a
stethoscope.
• Systolic value: pressure needed to
compress an artery so blood does not
flow.
• Diastolic value: pressure needed to
allow intermittent flow though the
artery.
Circulatory System and Blood - How does the mammalian heart function?
Measuring blood pressure
Circulatory System and Blood - How does the mammalian heart function?
Cardiac muscle functions as a pump:
• cells are in electrical contact with
each other through gap junctions,
spread of action potentials stimulates
contraction in unison;
• some cells are pacemaker cells and
can initiate action potentials without
input from the nervous system.
Circulatory System and Blood - How does the mammalian heart function?
The heart beat (part 1)
Circulatory System and Blood - How does the mammalian heart function?
The heart beat (part 2)
Circulatory System and Blood - How does the mammalian heart function?
An electrocardiogram (ECG) uses
electrodes to record events in the
cardiac cycle.
Large action potentials in the heart
cause electrical current to flow
outward to all parts of the body.
Electrodes register the voltage
difference at different times.
Circulatory System and Blood - What are the properties of blood and blood vessels?
Arteries and arterioles are called
resistance vessels because their
resistance can vary:
• walls have elastin and collagen that
allow them to stretch and recoil;
• smooth muscle cells in the walls
allow them to dilate or constrict.
Circulatory System and Blood - What are the properties of blood and blood vessels?
When the diameter of an artery
changes so does its resistance—
blood flow changes as a result.
Neuronal and hormonal mechanisms
control the resistance by influencing
the smooth muscle cells.
Circulatory System and Blood - What are the properties of blood and blood vessels?
Anatomy of blood vessels
Circulatory System and Blood - What are the properties of blood and blood vessels?
Blood pressure and flow through large arteries
are high, and are lower through the capillaries.
Pressure is reduced in smaller vessels because:
• arterioles are highly branched;
• capillaries contribute an enormous surface
area.
Capillary walls are a single layer of endothelial
cells and have tiny holes called fenestrations.
Capillary beds are permeable to water, ions, and
small molecules, but not to large proteins.
Circulatory System and Blood - What are the properties of blood and blood vessels?
One-way flow
Circulatory System and Blood – How is the circulatory system controlled and regulated?
The cardiovascular control center in
the medulla controls heart rate and
vessel constriction.
In the carotid arteries and the aorta:
• baroreceptors (stretch receptors)
monitor blood pressure changes;
• chemoreceptors send information
about blood composition.
Circulatory System and Blood – How is the circulatory system controlled and regulated?
Regulating blood pressure
Circulatory System and Blood - What are the properties of blood and blood vessels?
Red blood cells are generated in the bone
marrow.
Erythropoietin, a hormone released in the
kidney in response to hypoxia, controls red
blood cell production.
Red and white blood cells originate from
pluripotent stem cells in the bone marrow.
These cells constantly divide and can
differentiate into a variety of blood cells.
Circulatory System and Blood - What are the properties of blood and blood vessels?
Blood cells (part 1)
Circulatory System and Blood - What are the properties of blood and blood vessels?
Blood cells (part 2)
Circulatory System and Blood - What are the properties of blood and blood vessels?
Blood cells (part 3)
Circulatory System and Blood - What are the properties of blood and blood vessels?
Immature red blood cells divide and
produce hemoglobin while in the
bone marrow.
When cells are 30 percent hemoglobin
the organelles break down and the
cells enter the circulation.
Cells circulate about 120 days before
rupturing as they pass through
narrow capillaries, as in the spleen.
Circulatory System and Blood - What are the properties of blood and blood vessels?
Bone marrow produces megakaryocytes that
break off cell fragments called platelets.
Platelets initiate blood clotting when
activated by collagen exposed in damaged
blood vessels.
They release chemical clotting factors
which activate other platelets.
Circulatory System and Blood - What are the properties of blood and blood vessels?
Steps in blood clotting:
• cell damage and platelet activation;
• inactive enzyme prothrombin
converts to active form, thrombin;
• thrombin cleaves fibrinogen and
forms fibrin;
• fibrin threads form mesh that clots
blood and seals vessel.
Circulatory System and Blood - What are the properties of blood and blood vessels?
Blood clotting
Circulatory System and Blood - What are the properties of blood and blood vessels?
Plasma contains:
• Gases
• Ions
• Nutrients
• Proteins
• Other molecules, hormones and
vitamins
Circulatory System and Blood - What are the properties of blood and blood vessels?
Atherosclerosis: “hardening of the
arteries”.
• The endothelial lining of arteries is
damaged by high blood pressure,
smoking, diet, or microorganisms.
• Plaque forms at sites of damage.
• Damaged cells attract migration of
smooth muscle cells.
Circulatory System and Blood - What are the properties of blood and blood vessels?
• Smooth muscle cells have
cholesterol deposits that make the
plaque fatty.
• Connective tissue and calcium
deposits make the artery wall less
elastic, or “hardened”.
A thrombus, or blood clot, may form if
platelets stick to the plaque.
Circulatory System and Blood - What are the properties of blood and blood vessels?
The coronary arteries supply blood to
the heart muscle.
Atherosclerosis in these arteries
reduces blood flow; marked by chest
pain and shortness of breath.
Coronary thrombosis: if a thrombus
forms in a coronary artery it can lead
to a heart attack, or myocardial
infarction.
Circulatory System and Blood - What are the properties of blood and blood vessels?
An embolus is a piece of a thrombus:
• it may cause an embolism if it
lodges in a blood vessel.
• if the embolism is in the brain the
cells fed by that artery will die - a
stroke.
Circulatory System and Blood - What are the properties of blood and blood vessels?
Causes of atherosclerosis:
• genetic predisposition;
• age;
• environmental risk factors (high-fat
diet, smoking, sedentary lifestyle);
• medical conditions (hypertension,
obesity, diabetes).
Circulatory System and Blood - What are the properties of blood and blood vessels?
Atherosclerotic plaque