6.2 The Blood System Flashcards
Relatively (to the wall) small lumen maintains
high blood pressure (BP)
Thick muscular wall and fibrous outer layer help…
the artery to withstand high BP
Muscle contracts to decrease the size of the lumen →
increase BP and therefore maintains high BP between heart beats.
Elastic fibres stretch to increase the lumen with each pulse of blood. After…
the pulse of blood passes the fibres recoil decreasing the lumen size to maintain high BP (vasoconstriction)
Tunica externa:
A tough outer layer of connective tissue.
Tunica media:
A thick layer of smooth muscle and elastic fibres made of the protein elastin.
Tunica intima:
A smooth endothelium forming the lining of the artery.
The walls of capillaries consist of…
a single layer of endothelial cells, coated by a filter like protein gel (lamina) with pores between the cells. This allows the capillary to be semi-permeable.
Because permeability is high, part of the plasma can leak out into tissues, allowing for…
the movement of O2, CO2, glucose and other substances into/out of tissues. Proteins and amino acids are not able to move through capillaries.
Massive number of capillaries —>
large surface area available for the exchange of substances
Veins
return blood to the heart for recirculation.
The large lumen means..
that the blood is under low BP.
Because there is less BP to resist,
the walls of the veins are thinner and less elastic than arteries. They also contain less muscle than the arteries.
purpose of valves
required to prevent backflow of the blood and therefore ensure that the blood moves towards to heart.
purpose of skeletal muscles
when surrounding skeletal muscle contracts, it squeezes the vein, pushing blood in one direction.
William Harvey discovery
Blood flow is unidirectional with valves to prevent backflow
Flow rate of blood too high for blood to be “consumed” – must be recycled
Heart pumps blood out in the arteries and it returns through the veins
Predicted presence of small blood vessels that connect arteries and veins
Double circulation
blood passes through the heart twice on one circuit of the body
Pulmonary circulation
to/from the lungs
Systemic circulation
to/from the rest of the body
Key components of double circulation is that…
the oxygenated and deoxygenated blood do not mix and that blood flows only in one direction
Atrium
receives blood from lungs/body
Ventricle
receives blood from an atrium and pumps it out of the heart through arteries
Atrioventricular (AV)
between atria and ventricles
Semi-lunar
between ventricles and arteries
Pulmonary Artery
carries blood from the heart to the lungs
Pulmonary Vein
receives blood back from the lungs
Aorta
carries blood out of the heart to the body
Coronary Artery
delivers blood to heart tissue
Vena Cava
receives blood from body
Pathway of blood
Deoxygenated blood (↓ [O2], ↑ [CO2]) from the body returns to the heart via the right atrium.
The right atrium contracts, pushing blood through the AV valve into the right ventricle
The right ventricle contracts and pushes blood past semilunar valve into pulmonary artery.
Pulmonary artery carries blood to the lungs where it becomes oxygenated (↑ [O2], ↓ [CO2])
Pulmonary vein receives freshly oxygenated blood from the lungs and carries it to the left atrium.
The left atrium contracts, which increases pressure. This pushes blood past the AV valve into the left ventricle.
The thick walls of the left ventricle contract, increasing the pressure. This pushes blood past the semilunar valve and it enters the aorta.
The blood leaves the aorta and travels to the body where it becomes deoxygenated again.
A heartbeat is initiated by a group of specialized cells called …
the sinoatrial (SA) node.
sinoatrial (SA) node located
in the right atrium and acts as the heart’s pacemaker.
The SA node is made of
muscle cells and initiates its own contractions without neurons (myogenic)
The cardiac cycle is controlled by ..
the contraction and relaxation of the atria and ventricles, initiated by a nerve impulse in the SA node.
In systole..
the chambers of the heart contract (both atria, followed by the ventricles)
In diastole…
the heart relaxes and the ventricles fill with blood.
When measuring BP..
both the systolic and diastolic pressures are taken into account
cardiac cycle steps
- SA node contracts and sends an electrical signal that spreads through the atria, causing them to contract (systole). AV valves are open.
- The atrioventricular (AV) node receives the signal and delays transmitting the signal for 0.1 s.
- Signal is then transmitted through the left and right bundle branches of the ventricles to the Purkinje fibers.
- Ventricles contract (systole) and cause the AV valves to snap shut. After the ventricles are emptied, the semilunar valves close.
- Ventricles begin to relax (diastole), AV valves open and the ventricles begin filling with blood.
- Finally, all four chambers are in diastole and filling. When the atria are filled and the ventricles are 70% filled, the cycle has ended.
BP measurements are quoted in..
“mmHg”, and a typical, or optimal blood pressure is “120 over 80”.
Blood pressure
Higher number is a measure of the pressure in the artery when the ventricle contracts (systolic pressure)
Lower number is a measure of the pressure in the artery when the ventricle is relaxed and filling with blood (diastolic pressure).
Blood pressure cuffs are used to constrict the arm above the elbow, and a stethoscope is used to listen to the changes in heart sounds (when sound is audible, this is systolic… slowly the cuff deflates, and when sound disappears, this is diastolic)
Heart rate can be controlled by …
the autonomic nervous system – the part of the nervous system that responds automatically to changes in body conditions – two nerves originating from the cardiovascular centre in the medulla of the brain send signals to the SA node
Where myocardial contraction maintains the beating of the heart…
we may need to speed up or slow down heart rate.
Cardiovascular centre in medulla receives input from ..
receptors that monitor BP, blood pH ([CO2]) and [O2]
Low BP, low [O2], low pH (high [CO2])
heart rate needs to increase
When exercising, more CO2 is present in the blood. This is detected by chemoreceptors in the brain’s medulla oblongata, resulting in a nerve signal being sent to the SA node to speed the heart rate.
High BP, high [O2], high pH (low [CO2])
heart rate needs to decrease
The hormone adrenalin (a.k.a. epinephrine) produced by …
adrenal glands is controlled by the brain.
effect of adrenalin
When in the bloodstream it causes a rapid increase in heart rate to prepare for physical activity or in fight-or-flight responses, preparing the body for action.
This effect can be mimicked by stimulant drugs.
Atherosclerosis
common health issue that occurs when fatty tissue called atheroma develops in the artery wall (made of LDL’s and cholesterol).
what happens in atherosclerosis
Phagocytes, responding to signals from the endothelium, attack and engulf the atheroma and this causes smooth muscle cells to migrate and form a tough cap overtop.
effect of atherosclerosis
effect of atherosclerosis
This reduces the size of the lumen and impedes blood flow.
Atherosclerosis can go unnoticed until a major artery becomes so blocked that the tissues it supplies becomes compromised.
cause of occlusion of the coronary arteries
If a plaque is damaged, proteins and platelets will create a clot. This leads to greater pressure against the artery wall which results in hypertension.
Can lead to:
Arteries becoming narrow and stiff (arteriosclerosis)
Aneurysm
Stroke
Kidney failure
effect of occlusion of the coronary arteries
This blockage can cause:
Heart pain
Increased heart rate
Acute heart problems if bulge ruptures
