Blood System
Order:
Heart
Arteries
Tissues (capillaries)
Veins
Back to heart
Detailed Order:
Heart
Large Artery
Medium Artery
Small Artery
Arteriole
Capillary
Venule
Small Vein
Medium Vein
Large Vein
Back to Heart
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Arteries
Arteries are blood vessels that take blood away from the heart
As arteries become more distant from the heart, their diameter decreases
Thinnest artery:
Arteriole
Branches off into a capillary bed
(a net of capillaries)
Is is the level of capillaries that all exchanges of nutrients and waste between the blood and body cells occur
The capillary bed then merges into venules
(thinnest veins)
Which merge into thicker and thicker veins until they reach the heart
Veins
Are blood vessels that bring blood into the heart
Take blood at high pressure away from the heart to the tissues of the body
Their walls are thick with elastic and muscle tissue that work with the heart to facilitate and controle blood flow
The elastic fibers stretch and recoil
helping propel the blood down the artery
The contraction of smooth muscle in the walls of arteries determines the diameter of the lumen and the rigidity of arteries
The aorta and the pulmonary artery take blood from the left and right ventricles, respectively
Bring blood at low pressure back to the heart
Their walls are thin with little elastic and muscle tissue
Veins have internal valves that close when blood start flowing backwards, preventing this back flow
The pulmonary vein and the vena cava bring blood to the left and right atria, respectively
The Human Heart
Capillaries
Allow exchanges between body tissues and blood to occur
Their walls are one cell thick only
with no elastic and muscle tissue
Cells that form the wall of capillaries are called endothelial cells
In most capillaries, there are pores between the endothelial cells
which allows some plasma to leak from the bloodstream into tissues
The permeability of capillaries varies among organ to organ
The diameter of capillaries is of about 10 um.
The net of capillaries in a tissue is often referred to as a capillary bed
Cartilages, the cornea and the eye lens do not have capillaries
Blood Vessels
Pulmonary Circulation
Takes blood from the heart (right side) to the lungs and back
Systemic Circulation
Takes blood from the heart (left side) to the body, except for the lungs
Coronary arteries:
Supply the heart muscle with oxygen and nutrients
Control of heart Rate:
Cardiac muscle cells are able to contract without nervous stimulation
(myogenic)
But their contraction must be synchronized
in order for the heart muscle to pump blood effectively
This synchronization is achieved through the activity of a natural pacemaker
the sinoatrial node (SA node)
its cells are the first to depolarize. It sends out an electrical signal that stimulates contraction of both atria
it also sends a signal to the atrioventricular node (AV node) to make it send its signal
AV node: sends electrical signals to trigger the contraction of both ventricles
Nervous and Endocrine Stimulation
The heart is able to contract autonomously
but it receives stimulation from the central nervous system (CNS)
either directly (through nerves) or indirectly (through hormones) to pump blood according to the body's needs
Receptors in blood vessels send information to the CNS about blood pressure, pH, and oxygen concentration
Low blood pressure, oxygen, and pH causes an increase in the heart rate
High blood pressure, oxygen and ph cause the heart rate to slow down
Epinephrine (Adrenaline)
Hormone that increases the heart rate
released in situations of stress to prepare the animal for a fight-or-flight response
Cardiac Cycle
Sequence of events that repeat every heartbeat
Divided into
systole (contraction)
diastole (relaxation)
1.
Starts with signal generation in the SA node
a) atria contract --> increase in pressure inside atria
2.
AV node sends signals to the ventricles
a) ventricles contract (ventricular systole)
- increase in pressure inside venricles
- atrioventricular valves close (1st heart sound)
- Rapid increase in pressure inside ventricles
b) semilunar valves open
- increase of pressure inside aorta
(equals pressure inside ventricles)
c) semilunar valves close (2nd heart sound)
- end of systole/beginning of diastole
d) atrioventricular valves open
- pressure inside atria drops as blood flows to ventricles