BSI 2 Lecture 16-17: Circulation Flashcards
Briefly describe circulation from arteries to veins.
Arteries carry oxygenated blood which enters the capillaries, via arterioles, in order to carry out gas and nutrient exchange. It then passes through venules and into the veins which carry the deoxygenated blood back to the heart.
What are the three layers of arteries?
Tunica interna, tunica media, and tunica externa
What is the tunica interna composed of?
It contains simple squamous epithelium, basement membrane, and a layer of elastic tissue
What is the tunica media composed of?
Elastic fibers and smooth muscle that extend around the lumen
What is the tunica externa composed of?
Elastic fibers and collagen
Which layer of the arteries is the thickest?
The tunica media
What separates the tunica externa from the tunica media in muscular arteries?
an external elastic lamina
Which arteries have a larger diameter? Muscular or elastic arteries?
Elastic
What does the tunica media, in elastic arteries, contain?
large amounts of elastic fibers
Why are muscular arteries capable of greater vasoconstriction and vasodilation than elastic arteries?
Because they have more smooth muscle that is innervated by the SNS
Do capillaries have smooth muscle?
No, they have thin walls of endothelium and basement membrane for gas exchange. They cannot vasoconstrict or vasodilate
What are the three layers of a vein?
Same as an artery. Tunica interna, tunica media, and tunica externa
What is the difference between the layers of an artery and vein?
The vein has a thinner tunica interna and tunica media, but a thicker tunica externa.
Which one is more compliant? Veins or arteries?
Veins are about 24 times more compliant than arteries
What do veins contain to prevent backflow?
valves
What three factors relate when it comes to blood flow?
cardiac output, mean arterial pressure, and total peripheral resistance (CO = MAP/TPR or MAP = CO x TPR)
What is blood pressure?
The force the blood is exerting on the walls of the blood vessel
What is the formula for MAP?
MAP = DBP + 1/3(SBP-DBP)
What causes blood to flow through the body?
A pressure gradient
What is a normal blood pressure reading?
Systolic: 120
Diastolic: 80
What is a normal mean arterial pressure reading?
93 mmHg
What is the normal mean pressure of the capillaries?
17 mmHg
Explain blood flow, briefly, using the normal values of pressure?
The pressure of the arteries is normally 93 mmHg, and the normal pressure of the capillaries is 17 mmHg. The pressure of the veins and right atrium are 0 mmHg. Blood will flow from high pressure to low pressure; therefore, this is how blood flows from the arteries to the capillaries, and then to the veins and right atrium.
What is the formula for pulse pressure?
SBP - DBP
What happens to pulse pressure when stroke volume increases?
Pulse pressure increases because a greater stroke volume results in greater pressure rise with each heartbeat
How does compliance affect pulse pressure?
A lower compliance will increase pressure with every beat which increases pulse pressure
What is TPR?
The resistance to blood flow through all of the vasculature. It’s mainly due to arterial pressure because veins are so compliant.
What happens to TPR during vasoconstriction?
TPR increases
What happens to TPR during vasodilation?
TPR decreases
What is venous pump?
The contraction and relaxation of skeletal muscle force blood back towards the heart, which increases venous return.
What is respiratory pump?
While breathing in, abdominal pressure increases and thoracic pressure decreases. This pressure gradient causes blood to flow back to the heart.
What is venous tone?
Venoconstriction increases venous tone which increases venous return. Vasodilation decreases venous tone, which decreases venous return.
How does RAAS increase blood volume?
When blood pressure is low, the kidneys release renin which converts angiotensinogen into angiotensin 1. ACE turns angiotensin 1 into angiotensin 2. Angiotensin 2 increases the release of NE and Epi, increases aldosterone, increases ADH, increases sodium and water retention, and causes vasoconstriction
Where is ADH released from?
The posterior pituitary gland
What is another name for ADH?
Vasopressin
What is ADH responsible for?
Causing vasoconstriction and promoting reabsorption of water
What does ANP (also called ANF) do?
It is released from the atria (caused by increased stretch) and lowers blood pressure by causing vasodilation and promoting loss of salt and water in urine
What does ANP suppress?
ADH, renin, and aldosterone
What innervates most vessels, except capillaries, precapillary sphincters, and metarterioles?
the SNS
What do beta-1 receptors control?
Heart rate and contractility
What do alpha-1 receptors control?
vasoconstriction
What do alpha-2 receptors control?
vasodilation
What do beta-2 receptors control?
vasodilation mainly in the lungs due to relaxation of smooth muscle
Are blood vessels innervated by the PNS?
Not the majority. The PNS is directly involved in decreasing heart rate and contractility.
What do chemoreceptors do?
They sense changes in oxygen content in the blood. If blood pressure decreases then blood flow decreases through the chemoreceptors. This stimulates the receptors to excite the vasomotor center and increase blood pressure
