Download THE IMPORTANCE OF CIRCULATORY SYSTEM

SBI3C
Ms Mak: THE CIRCULATORY SYSTEM
The circulatory system (CS) is the transport system of
the body.
- complex network of tissues and organs (see Fig 2 pg.
196)
- 96 000 km of blood vessels in your body to sustain you
100 trillion cells
It has 4 principal functions:
-
transportation of oxygen and carbon dioxide
distribution of nutrients and transport of wastes
maintenance of body temperature
circulation of hormones
Structure of Circulatory System
It consists of 3 components
- fluid in which materials are transported: blood
- system of blood vessels or spaces throughout the body
- pump: heart
Cardiovascular system: heart + blood vessels
Circulatory System has two major circuits:
1. Pulmonary circuit: carries blood between the heart
and the lungs (to and from lungs):
o pulmonary arteries: carry O2-poor blood to the
lungs
o pulmonary veins: carry O2-rich blood to the heart
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2. Systemic circuit: caries blood between the heart and
the rest of the body (to and from the body); includes 3
branches:
o coronary: supplies blood to the muscle of the heart.
o hepatic-portal: carries blood from the digestive
tract to the liver.
o renal: carries blood to & from the kidneys.
Blood from the systemic system enters the right atrium.
Blood from the pulmonary system enters the left atrium.
HEART
Function of Heart:
- acts as a pump; made of cardiac muscle
- right side: sends O2-poor blood to heart
- left side: sends O2-rich blood to body
- location: left of the middle of the chest cavity
Structure
- pericardium: covers and protects the heart
- Heart is divided into 4 chambers:
o atria (auricles): two upper, thin-walled
o ventricles: two lower, thick-walled
- right and left sides of the heart are separated by a wall
called septum:
o prevents mixing O2-poor blood (right side) with O2rich blood (left side).
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- 4 flaplike valves control the direction of the blood flow
inside the heart.
o two of these valves: atrioventricular or A-V valves:
prevent blood from flowing from ventricles into the
atria.
o the other two valves: the semilunar valves (S-L
valves): prevent blood from flowing from arteries
into the ventricles.
The Heart Rhythms, Sounds and Pressure
Heart has 2 bundles of nerves that control its beating
- Sinoatrial (SA) node: acts as a pacemaker and sets a
rhythm of about 72 beats per minute.
- Atrioventricular (AV) node: passes the nerve impulses
to the ventricles ( causes them to contract in unison)
2 main periods:
- Diastole: the period of relaxation (dilation); A-V
valves are open; blood flows from the atria into the
ventricles:
o atria relaxed; ventricles contracted.
- Systole: the period of contraction; blood is pushed out
of the heart
o atria contracted; ventricles relaxed.
- The lubb-dubb sound: caused by closing of the A-V
valves and the S-L valves:
o lubb: when increasing pressure forces the
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right and left A-V valves shut (systole).
o dubb: when decreasing pressure forces the right and
left S-L valves shut (diastole).
Blood Pressure
- is a force of blood on the walls of the arteries.
- measured by sphygmomanometer (mm Hg)
o systolic blood pressure (contraction of ventricles);
about 120 mm Hg
o diastolic blood pressure (relaxation of ventricles);
about 80 mm Hg
- elastic connective tissue and muscular walls of the
arteries help to maintain blood pressure
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