Circulatory System Flashcards
What does blood transport?
Oxygen, Nutrients, Antibodies, Hormones, Heat, Carbon dioxide, Urea
Function of Erythrocytes/Red Blood Cells?
Transports oxygen from lungs to respiring cell and carbon dioxide from respiring cells to the lungs
Function of Thrombocytes/Platelets?
Have a role in the blood clotting mechanism. Important for wound healing.
Function of Plasma?
A solvent which transports nutrients (from gut to liver), hormones, urea (from liver to kidney), dissolved proteins and antibodies, gases and waste.
Function of Leukocytes/White Blood Cells?
Have major roles in the immune system and have many different cells. Lymphocytes form antibodies. Other leukocytes (phagocytes) ingest bacteria or cell fragments.
Composition of the Blood Plasma
- Nutrients – needed by cells to make chemical energy (e.g. glucose)
- Antibodies – involved in pathogen identification and elimination
- Carbon dioxide – waste produced as a by-product of cell respiration
- Hormones – chemical messengers that move through the bloodstream
- Oxygen – required by body issues in order to respire aerobically
- Urea – compound that is excreted to remove nitrogen from the body
- Heat – not a molecule, but still an important component of blood plasma
Arteries vs Capillaries vs Veins
Arteries: Carry high pressure blood away from the
heart to issues that need it
Veins: Carry the low pressure blood back to the
heart using valves to ensure blood flows in the
correct direction.
Capillaries: are very small (< 10 μm diameter) and
therefore can penetrate virtually every tissue in the
body. Blood moves slowly through them under low
pressure providing opportunities for the exchange
of substances.
The structure of arteries
- Arteries carry blood away from the heart
- Relatively (to the wall) small lumen maintains high blood pressure
How does blood move through the arteries?
Muscle contracts to decrease the size of the lumen. This is called vasoconstriction. This causes an
increase blood pressure and therefore maintains high blood pressure between the pulses of high
pressure blood travelling from the heart. Vasodila;on occurs when the circular muscles relax and it
decreases blood pressure.
- Elastic fibres stretch to increase the lumen with each pulse of blood. After the pulse of blood
passes the fibers recoil decreasing the lumen size and therefore helping to maintain a high blood
pressure. - Flow of Blood: Blood is expelled from the heart upon ventricular contraction and flows through the
arteries in repeated surges called pulses. - This blood flows at a high pressure and the muscle and elastic fibres assist in maintaining
this pressure between pumps.
How does muscle and elastic fibres help to move blood through the arteries?
The muscle fibres help to form a rigid arterial wall that
is capable of withstanding the high blood pressure
without rupturing
o Muscle fibres can also contract to narrow the
lumen, which increases the pressure between
pumps and helps to maintain blood pressure
throughout the cardiac cycle.
The elastic fibres allow the arterial wall to stretch and
expand upon the flow of a pulse through the lumen
o The pressure exerted on the arterial wall is
returned to the blood when the artery returns
to its normal size (elas(c recoil)
o The elastic recoil helps to push the blood
forward through the artery as well as maintain
arterial pressure between pump cycles
Adaptions and structure of capillaries?
o Capillaries are the smallest blood vessels and are
adapted for the exchange of substances to and from
the blood. They are only once cell thick (~5 μm).
o This enables tissues to gain nutrients and molecules
such as oxygen and to rid themselves of waste
material.
o Arteries split into arterioles which in turn split into
capillaries, decreasing arterial pressure as total vessel
volume is increased
o The branching of arteries into capillaries therefore
ensures blood is moving slowly and all cells are
located near a blood supply
How does blood flow through the veins back to the heart?
- Veins return blood to the heart for recirculation
- The large lumen (compared to arteries and the thickness of the wall) means that the blood is under
low pressure - Because there is less pressure to resist
the walls of the veins are thinner and
less elas;c than arteries. They also
contain less muscle than the arteries. - Because of the low pressure one-way
valves are required to prevent back-flow
of the blood and therefore ensure that
the blood moves towards the heart.
How do skeletal muscles impact the flow of blood in the veins?
Blood is at very low pressure in the veins
which can make it difficult for the blood to move against the downward force of gravity.
- The veins contain numerous one-way valves in order
to maintain the circulation of blood by
preventing back flow
- Veins typically pass between skeletal muscle groups, which
facilitate venous blood flow via periodic contractions.
- When the skeletal muscles contract, they squeeze
the vein and cause the blood to flow from the site of
compression
- Veins typically run parallel to arteries, and a similar effect can be caused by the rhythmic arterial bulge created by a pulse
How to differentiate the structure of veins, arteries and capillaries?
- Arteries have thick walls composed of three distinct layers (tunica)
- Veins have thin walls but typically have wider lumen (lumen size may vary depending on
specific artery or vein) - Capillaries are very small and will not be easily detected under the same magnification as
arteries and veins
Pressure in the veins and arteries
- Blood leaving the heart and going into the arteries is under high pressure and travels in waves or pulses, following each heartbeat. By the time the blood has reached the capillaries, it is under much lower pressure, without a pulse. The pressure is almost 0 mm Hg by the time the blood is in the veins.
Systolic pressure: the pressure of the arteries when the ventricles are contracting
Diastolic pressure: the pressure in the arteries when the ventricles are relaxed
Speed and pulse in the veins and arteries
The blood travels very quickly through the arteries and reaches very low speed in the
capillaries. When the blood goes back into the veins the speed increases. This is because
the diameter of the blood vessels decreases in the capillary slowing down the pace.
Ventricular contractions of the heart force a wave of
blood through the arteries. The expansion of the
arteries can be felt as a pulse, particularly where the artery is near the skin surface and passes over a bone.
The wrist (radial artery) or neck (carotid artery) is typically used to take the pulse.
