THE HEART, BLOOD VESSELS,
THE CLOSED CIRCULATORY SYSTEM
Humans have a closed circulatory system,
typical of all vertebrates, in which blood is
confined to vessels and is distinct from the
•The heart pumps blood into large vessels
that branch into smaller ones leading into the organs.
•Materials are exchanged by diffusion between the
blood and the interstitial fluid bathing the cells.
WHAT IS THE CIRCULATORY SYSTEM?
The circulatory system carries blood and dissolved
substances to and from different places in the body.
The Heart has the job of pumping these things around
The Heart pumps blood and substances around the
body in tubes called blood vessels.
The Heart and blood vessels together make up the
THE CARDIOVASCULAR SYSTEM
Three Major Elements –
2. Blood Vessels
1. THE HEART
•highly interconnected cells
•cardiac muscle tissue
How does this system work?
head & arms
Our circulatory system is a double circulatory system.
This means it has two parts.
the right side of
the left side of
This is a vein. It brings
blood from the body,
except the lungs.
These are arteries.
They carry blood away
from the heart.
hearts own blood
The heart has four chambers
now lets look inside the heart
Artery to Lungs
Vein from Head and Body
Artery to Head and Body
Vein from Lungs
HOW DOES THE HEART WORK?
The heart beat begins when the
heart muscles relax and blood
flows into the atria.
HOW DOES THE HEART WORK?
The atria then contract and
the valves open to allow blood
into the ventricles.
HOW DOES THE HEART WORK?
The valves close to stop blood
The ventricles contract forcing
the blood to leave the heart.
At the same time, the atria are
relaxing and once again filling with
The cycle then repeats itself.
BLOOD FROM THE HEART GETS AROUND
THE BODY THROUGH BLOOD VESSELS
There are 3 types of blood vessels
2. BLOOD VESSELS
•Arteries arterioles move away from the heart
•Circular Smooth Muscle
•Capillaries – where gas exchange takes place.
•One cell thick
•Serves the Respiratory System
•Veins Venules moves towards the heart
•Skeletal Muscles contract to force blood back from legs
•One way values
•When they break - varicose veins form
Arteries carry blood away from the heart.
the elastic fibres allow the artery
to stretch under pressure
thick muscle and elastic
the thick muscle can contract
to push the blood along.
Veins carry blood towards from the heart.
veins have valves which act to
stop the blood from going in the
thin muscle and
body muscles surround the veins so that
when they contract to move the body, they also
squeeze the veins and push the blood along the
Capillaries link Arteries with Veins
they exchange materials
between the blood and other body
the wall of a capillary
is only one cell thick
The exchange of materials between
the blood and the body can only occur
A collection of capillaries is known as a capillary bed.
WHAT’S IN BLOOD?
red blood cells
white blood cells
3. THE BLOOD
- Liquid portion of the blood
- Contains clotting factors,
dissolved gases, nutrients
It also contains useful
• carbon dioxide
cells and the
• amino acids
• waste materials
B. Erythrocytes - Red
- Carry hemoglobin and
oxygen. Do not have a
nucleus and live only
about 120 days.
-Can not repair
Red Blood Cells
a biconcave disc that is round
and flat without a nucleus
contain haemoglobin, a
molecule specially designed
to hold oxygen and carry it to
cells that need it.
can change shape to an
amazing extent, without
breaking, as it squeezes single
file through the capillaries.
C. Leukocytes – White
- Fight infection and are
formed in the bone marrow
- Five types: neutrophils,
basophils, and monocytes.
White Blood Cells
there are many different types and all
contain a big nucleus.
the two main ones are the
lymphocytes and the macrophages.
macrophages ‘eat’ and digest microorganisms .
some lymphocytes fight disease by making antibodies to destroy
invaders by dissolving them.
other lymphocytes make antitoxins to break down poisons.
D. Thrombocytes –
- These are cell fragment
that are formed in the bone
- Clot blood by sticking
together – via protein fibers
Platelets are bits of cell
broken off larger cells.
Platelets produce tiny
fibrinogen fibres to
form a net. This net
traps other blood
cells to form a blood
white blood cell
FUNCTIONS OF THE HEART
Generating blood pressure
• Heart separates pulmonary and systemic
Ensuring one-way blood flow
• Heart valves ensure one-way flow
Regulating blood supply
• Changes in contraction rate and force match blood
delivery to changing metabolic needs
SIZE, SHAPE, LOCATION
OF THE HEART
Size of a closed fist
•Apex: Blunt rounded
point of cone
•Base: Flat part at
opposite of end of cone
Located in thoracic
cavity in mediastinum
HEART CROSS SECTION
Three layers of tissue
• Epicardium: This serous membrane of
smooth outer surface of heart
• Myocardium: Middle layer composed of
cardiac muscle cell and responsibility for
• Endocardium: Smooth inner surface of
•Superior vena cava
•Bicuspid or mitral
Prevent blood from
FUNCTION OF THE HEART VALVES
BLOOD FLOW THROUGH HEART
SYSTEMIC AND PULMONARY
Consists of plate of
tissue between atria and
Fibrous rings around
valves to support
Serves as electrical
insulation between atria
Provides site for muscle
Elongated, branching cells containing 1-2 centrally located nuclei
Contains actin and myosin myofilaments
Intercalated disks: Specialized cell-cell contacts
Desmosomes hold cells together and gap junctions allow action
Electrically, cardiac muscle behaves as single unit
CONDUCTING SYSTEM OF HEART
Tachycardia: Heart rate in excess of 100bpm
Bradycardia: Heart rate less than 60 bpm
Sinus arrhythmia: Heart rate varies 5% during
respiratory cycle and up to 30% during deep
Premature atrial contractions: Occasional
shortened intervals between one contraction
and succeeding, frequently occurs in healthy
Heart is two pumps that work together, right
and left half
Repetitive contraction (systole) and
relaxation (diastole) of heart chambers
Blood moves through circulatory system
from areas of higher to lower pressure.
• Contraction of heart produces the pressure
First heart sound or “lubb”
• Atrioventricular valves and surrounding fluid vibrations as
valves close at beginning of ventricular systole
Second heart sound or “dupp”
• Results from closure of aortic and pulmonary semilunar valves
at beginning of ventricular diastole, lasts longer
Third heart sound (occasional)
• Caused by turbulent blood flow into ventricles and detected
near end of first one-third of diastole
LOCATION OF HEART VALVES
REGULATION OF THE HEART
Intrinsic regulation: Results from normal functional
characteristics, not on neural or hormonal
• Starling’s law of the heart
Extrinsic regulation: Involves neural and hormonal
• Parasympathetic stimulation
• Supplied by vagus nerve, decreases heart rate, acetylcholine secreted
• Sympathetic stimulation
• Supplied by cardiac nerves, increases heart rate and force of
contraction, epinephrine and norepinephrine released
Effect of blood pressure
• Baroreceptors monitor blood pressure
Effect of pH, carbon dioxide, oxygen
• Chemoreceptors monitor
Effect of extracellular ion concentration
• Increase or decrease in extracellular K+ decreases heart rate
Effect of body temperature
• Heart rate increases when body temperature increases, heart
rate decreases when body temperature decreases
EFFECTS OF AGING ON THE
Gradual changes in heart function, minor
under resting condition, more significant
Hypertrophy of left ventricle
Maximum heart rate decreases
Increased tendency for valves to function
abnormally and arrhythmias to occur
Increased oxygen consumption required to
pump same amount of blood
DISORDERS OF THE CIRCULATORY SYSTEM
Anemia - lack of iron in the blood, low RBC count
Leukemia - white blood cells proliferate wildly, causing
Hemophilia - bleeder’s disease, due to lack of fibrinogen in
Heart Murmur - abnormal heart beat, caused by valve
Heart attack - blood vessels around the heart become
blocked with plaque, also called myocardial infarction