#09 Heart III/Circulation

Question 1

Why Do Contractile Myocytes Contract Moe Forcefully?

Answer 1

• Contractile myocytes are contracting more forcefully so we have increased strength and speed.

Question 2

When Referring To Increase In Heart Rate, We Refer To….

Answer 2

• When talking about an increase in heart rate, or in contractility, talking about sympathetic stimulation, the cardiac nerve, things like adrenaline, and increases in cAMP (comes from stimulations in beta-adrenergic receptors).

Question 3

Protein Kinase A

Answer 3

• Important steps in EC coupling are modified by phosphorylation by protein kinase A, which is activated by cAMP.

Question 4

What receptor does the parasympathetic nervous system target in the heart?

Answer 4

• When talking about parasympathetic control, acetylcholine only hits the muscarinic receptors in the heart. The vagus nerve ejects acetylcholine to this receptor which ultimately reduces the heart rate.

Question 5

What channel does parasympathetic NS activate in heart?

Answer 5

• The vagus nerve activates a specific type of muscarinic channel called M2. It is a POTASSIUM channel. To reduce heart rate, you need a more negative electrical potential to prevent an action potential through preventing depolarization. By opening up this channel when cell is supposed to depolarize, it’s allowing positive charge to leave the cell. So while sodium/calcium is entering the cell, potassium is flowing out, thus slowing down the cell. Increased potassium current must be overcome.

Question 6

How does PNS affect cAMP?

Answer 6

• Parasympathetic system can decrease the amount of cAMP to reduce heart rate.

Question 7

Acetylcholine, Norepinephrine, and Epinephrine Affects In Heart

Answer 7

• So speaking in terms of hormones, acetylcholine increases potassium conductance, and norepinephrine and epinephrine increases sodium and calcium conductance.

Question 8

At Heart Rest: PNS or SNS?

Answer 8

• At heart rest, the parasympathetic system overcomes sympathetic system. So if you want to increase heart rate, you have to turn off the parasympathetic system essentially so sympathetic can take over.

Question 9

Adrenal Medulla & Heart

Answer 9

• Adrenal Medulla can also secrete norepinephrine and epinephrine to the heart. Hormones will still bind to beta 1-adrenergic receptors to increase cAMP. Since these hormones are secreted directly into bloodstream, can also have effects on vasculature. So they also activate the alpha 1-adrenergic receptors, which is found on smooth muscle cells in the blood vessels.

Question 10

Thyroid Gland & Heart

Answer 10

• Thyroid gland can also secrete thyroid hormone to the heart. The hormone usually causes change in gene transcription, and one of them can be in the beta 1-adrenergic receptor. Having thyroid hormone will increase amount of them on cell surface and increase amount of channels that can activated to increase heart rate.

Question 11

Artery Function

Answer 11

• Arteries main function is to distribute blood to all of the body. Bringing that blood to the tissue.

Question 12

Vein Function

Answer 12

• Veins are returning blood to the heart. Main function is to bring blood back to the heart, usually deoxygenated except for pulmonary vein.

Question 13

Capllaries Function

Answer 13

• Capillaries are sites of exchange. They connect arterioles and venules.

Question 14

Artery vs. Vein: Walls

Answer 14

• Arteries have a very rounded structure and their walls are very thick. The thick walls are important for constricting the vessel. Veins meanwhile don’t really have a defined structure until blood is filled into them, otherwise they’re collapsed. Much thinner and weaker wall.

Question 15

Why Do We Draw Blood From The Veins?

Answer 15

○ We draw blood from the vein due to their weaker wall. It’s easier to draw blood from them then from arteries. They’re also closer to the surface.

Question 16

How Blood Flow Works

Answer 16

• Blood flow will always want to go from a high pressure system to a low pressure system. The function of the pump is to give us this concentration gradient. Arterial pressure is much larger than the venule pressure.

Question 17

Resistance

Answer 17

• Resistance is opposition to flow caused by friction between blood and walls of blood vessels. It is affected by blood vessel diameter, blood vessel length, and blood viscosity.

Question 18

Resistance: Hematocrit

Answer 18

○ If you increase the hematocrit, adding more formed element, making the blood more viscous, thickening the blood. More friction would form because of viscosity. Would not normally happen since it is regulated pretty strictly.

Question 19

Resistance: Vessel Length

Answer 19

○ The longer the vessel, the more time blood has to contact a vessel, thus more friction. Can’t really control length of blood vessel so not a major mechanism.

Question 20

Resistance: Vessel Diameter

Answer 20

○ Can change the blood vessel radius. This is how we regulate flow of blood. Resistance is inversely proportional to radius of vessel. Very small radius, very high resistance. Resistance = 1/r^4. Very small change in radius of vessel means a huge impact on the resistance.

Question 21

Poiseulle’s Law

Answer 21

§ Poiseulle’s Law quantifies the relationship between blood flow and the characteristics of blood and blood vessels. Says flow is proportional to the radius. Bigger radius of vessel more flow you can have through vessel.

Question 22

Radius Length From Arteries to Capillaries

Answer 22

§ Radius is smaller as you go from aorta to capillaries, because you want everything you need to be exchanged, to be exchanged. Go too fast and some items may not be exchanged.

Question 23

Law of La Place

Answer 23

§ Law of La Place says as you increase the radius, you also increase the tension on walls of vessel. More volume of blood in vessel puts more stress on the wall of the vessel. Means if you have a small vessel, it is much more prone to collapse than a large vessel due to this relationship.

Question 24

Blood Vessel Layers

Answer 24

Tunica intima, media, and externa.

Question 25

Tunica Intima

Answer 25

○ Tunica Intima is the innermost layer. It is composed of an endothelium (a simple squamous epithelium) and a subendothelial layer made up of a thin layer of areolar connective tissue.

Question 26

Tunica Media

Answer 26

○ Tunica Media is middle layer. It is composed of mainly smooth muscle cells. Sympathetic innervation causes smooth muscle to contract, resulting in vasoconstriction. When fibers relax, vasodilation results.

Question 27

Tunica Externa

Answer 27

○ Tunica Externa is the outermost layer of blood vessel wall. Composed of areolar connective tissue that contains elastic and collagen fibers. Collagen is what stimulates platelet plug formation in the intrinsic pathway.

Question 28

Arteries vs. Veins: Wall Layers

Answer 28

○ The arteries have a thicker tunica media, more muscular. You can better control diameter of artery. Arteries have an extra elastic layer that gives them a better stretch quality.

Question 29

Artery Diameter Differences

Answer 29

• Artery Diameter: Aorta (Elastic) > Arteries (Muscular) > Arterioles

Question 30

Arteries as a Pressure Reservoir

Answer 30

• Arteries are a pressure reservoir. Heart is going to push blood to arteries and stretch them all out. So they’ll recoil as a result, and put pressure into the system. Happens primarily in elastic arteries.

Question 31

Why Are Arterioles Important?

Answer 31

• Arterioles are going to constrict blood the most. It’ll reduce the flow, and is thus a control mechanism.

Question 32

Example of Arterioles Regulating Blood Flow

Answer 32

○ They’re very good at controlling local blood flow. For example, when we’re in a fight or flight response, we need to increase blood flow to skeletal muscle. Arterioles are the main mechanism of changing blood distribution. Capillaries throughout the whole body are connected and go through gas exchange at the same time. So arterioles adjust their diameter to increase blood flow to skeletal muscle and decrease it to all the other parts of the body. Vasodilate around skeletal muscle, vasoconstrict everywhere else.

Question 33

Regulating Arteriole Diameter: Locally

Answer 33

§ This can be regulated locally by the tissue and muscle in specific area we’re interested in. It is a very quick response.
□ If tissue is running out of oxygen, the smooth muscle in that area is as well, so the muscle will vasodilate and more blood will flow to that spot. Various signals like low oxygen, high carbon dioxide, and low pH are valid signals.
□ If vessels want to constrict, perhaps due to damage, tissue can release thromboxane (TxA2) from the endothelial cells.
□ Blood pressure in organ can also stimulate arterioles to act in accordance.

Question 34

Regulating Arteriole Diameter: Neural Reflex

Answer 34

§ Nervous system can increase sympathetic signals to induce vasocontriction or decrease sympathetic to induce vasodilation. Not a lot of parasympathetic control when it comes to blood vessels.

Question 35

Baroreflex

Answer 35

□ Baroreflex senses pressure. Have a sudden change in blood pressure nervous system responds. So when blood pressure rises, baroreceptor will send signal up to brain, and the brain will want to slow down heart. So brain can inhibit cardioaccelerator center, or activate parasympathetic control. Drop in pressure will inhibit cardioinhibitor center, or decrease parasympathetic control.

Question 36

Chemoreceptor

Answer 36

□ Chemoreceptor where oxygen or carbon dioxide levels are sensed. So a sudden drop in oxygen levels will make the tissue want more oxygen, so more will be brought to the tissue.
® The reason you don’t know you’re being poisoned by carbon monoxide is you have no chemoreceptor for it. Only for oxygen and carbon dioxide.

Question 37

Epinephrine Effect on Arteriole Diameter

Answer 37

□ Epinephrine can bind to alpha 1-adrenergic receptors to constrict the arterioles. They increase calcium and thus increase muscle constriction. There’s also beta 2-adrenergic receptors which increase cAMP. cAMP though is actually INHIBITORY in smooth muscle, so it’ll have a vasodilater effect.

Question 38

Antiotensin II Effect on Arteriole Diameter

Answer 38

□ Antiotensin II is a strong vasoconstrictor.

Question 39

Nitric Oxide Effect on Arteriole Diameter

Answer 39

□ Nitric Oxide is a strong vasodilator.

Question 40

Atrial Natriuretic Peptide

Answer 40

□ Atrial Natriuretic Peptide (ANP) is a homeostasis mechanism. Atrial cells have an endocrine function. As atria fills and stretches muscle, atria releases ANP which has effect of dilating the tissue.