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THE CIRCULATORY
SYSTEM
THE HEART, BLOOD VESSELS,
AND BLOOD
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
interstitial fluid.
•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 body.

The Heart pumps blood and substances around the
body in tubes called blood vessels.

The Heart and blood vessels together make up the
Circulatory System.
THE CARDIOVASCULAR SYSTEM
Three Major Elements –
1. Heart
2. Blood Vessels
3. Blood
1. THE HEART
The Heart
•highly interconnected cells
•cardiac muscle tissue
•four chambers
•Right atrium
•Right ventricle
•Left atrium
•Left ventricle
How does this system work?
pulmonary
vein
pulmonary
artery
lungs
head & arms
aorta
main vein
Right
Left
liver
digestive system
kidneys
legs
Circulatory System
Our circulatory system is a double circulatory system.
This means it has two parts.
Lungs
the right side of
the left side of
the system
the system
deals with
deals with
deoxygenated
oxygenated
blood.
blood.
Body cells
THE HEART
This is a vein. It brings
blood from the body,
except the lungs.
These are arteries.
They carry blood away
from the heart.
2 atria
Coronary
arteries, the
hearts own blood
supply
2 ventricles
The heart has four chambers
now lets look inside the heart
The Heart
Artery to Lungs
Vein from Head and Body
Right Atrium
valve
Right Ventricle
Artery to Head and Body
Vein from Lungs
Left Atrium
valve
Left Ventricle
HOW DOES THE HEART WORK?
STEP ONE
blood from
the body
blood from
the lungs
The heart beat begins when the
heart muscles relax and blood
flows into the atria.
HOW DOES THE HEART WORK?
STEP TWO
The atria then contract and
the valves open to allow blood
into the ventricles.
HOW DOES THE HEART WORK?
STEP THREE
The valves close to stop blood
flowing backwards.
The ventricles contract forcing
the blood to leave the heart.
At the same time, the atria are
relaxing and once again filling with
blood.
The cycle then repeats itself.
BLOOD FROM THE HEART GETS AROUND
THE BODY THROUGH BLOOD VESSELS
There are 3 types of blood vessels
a.
ARTERY
b. CAPILLARY
c. VEIN
2. BLOOD VESSELS
•Arteries  arterioles move away from the heart
•Elastic Fibers
•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
The ARTERY
Arteries carry blood away from the heart.
the elastic fibres allow the artery
to stretch under pressure
thick muscle and elastic
fibres
the thick muscle can contract
to push the blood along.
The VEIN
Veins carry blood towards from the heart.
veins have valves which act to
stop the blood from going in the
wrong direction.
thin muscle and
elastic fibres
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
vessel.
The CAPILLARY
Capillaries link Arteries with Veins
they exchange materials
between the blood and other body
cells.
the wall of a capillary
is only one cell thick
The exchange of materials between
the blood and the body can only occur
through capillaries.
The CAPILLARY
A collection of capillaries is known as a capillary bed.
artery
vein
capillaries
body cell
WHAT’S IN BLOOD?
digested food
red blood cells
white blood cells
oxygen
waste (urea)
platelets
carbon dioxide
plasma
hormones
3. THE BLOOD
A. Plasma
- Liquid portion of the blood
- Contains clotting factors,
hormones, antibodies,
dissolved gases, nutrients
and waste
Plasma
It also contains useful
things like;
• carbon dioxide
A strawcoloured
liquid that
carries the
cells and the
platelets
which help
blood clot.
• glucose
• amino acids
• proteins
• minerals
• vitamins
• hormones
• waste materials
like urea.
B. Erythrocytes - Red
Blood Cells
- Carry hemoglobin and
oxygen. Do not have a
nucleus and live only
about 120 days.
-Can not repair
themselves.
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
Blood cells
- Fight infection and are
formed in the bone marrow
- Five types: neutrophils,
lymphocytes, eosinophils,
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 –
Platelets
- These are cell fragment
that are formed in the bone
marrow from
megakaryocytes.
- Clot blood by sticking
together – via protein fibers
called fibrin.
Platelets
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
clot.
THE BLOOD
red blood
cell
platelets
white blood cell
plasma
FUNCTIONS OF THE HEART
Generating blood pressure
Routing blood
• Heart separates pulmonary and systemic
circulations
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
Shape
•Apex: Blunt rounded
point of cone
•Base: Flat part at
opposite of end of cone
Located in thoracic
cavity in mediastinum
HEART CROSS SECTION
PERICARDIUM
HEART WALL
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
heart contracting
• Endocardium: Smooth inner surface of
heart chambers
HEART WALL
EXTERNAL ANATOMY
Four chambers
•2 atria
•2 ventricles
Auricles
Major veins
•Superior vena cava
•Pulmonary veins
Major arteries
•Aorta
•Pulmonary trunk
CORONARY CIRCULATION
HEART VALVES
Atrioventricular
•Tricuspid
•Bicuspid or mitral
Semilunar
•Aortic
•Pulmonary
Prevent blood from
flowing back
HEART VALVES
FUNCTION OF THE HEART VALVES
BLOOD FLOW THROUGH HEART
SYSTEMIC AND PULMONARY
CIRCULATION
HEART SKELETON
Consists of plate of
fibrous connective
tissue between atria and
ventricles
Fibrous rings around
valves to support
Serves as electrical
insulation between atria
and ventricles
Provides site for muscle
attachment
CARDIAC 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
potentials
Electrically, cardiac muscle behaves as single unit
CONDUCTING SYSTEM OF HEART
CARDIAC ARRHYTHMIAS
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
respiration
Premature atrial contractions: Occasional
shortened intervals between one contraction
and succeeding, frequently occurs in healthy
people
ALTERATIONS IN
ELECTROCARDIOGRAM
CARDIAC CYCLE
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
CARDIAC CYCLE
HEART SOUNDS
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
regulation
• Starling’s law of the heart
Extrinsic regulation: Involves neural and hormonal
control
• 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
HEART HOMEOSTASIS
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
BARORECEPTOR AND
CHEMORECEPTOR REFLEXES
BARORECEPTOR REFLEX
CHEMORECEPTOR REFLEX-PH
EFFECTS OF AGING ON THE
HEART
Gradual changes in heart function, minor
under resting condition, more significant
during exercise
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
anemia
Hemophilia - bleeder’s disease, due to lack of fibrinogen in
thrombocytes
Heart Murmur - abnormal heart beat, caused by valve
problems
Heart attack - blood vessels around the heart become
blocked with plaque, also called myocardial infarction