Physiology - Cardiovascular System 1, Lecture 24

What is stroke volume (SV)?

How much blood comes out of your heart when it contracts. At rest your SV is about 70mL (60mL-80mL).

When does your blood move fastest?

When it leaves the heart. Nutrient exchange occurs in your capillaries - at the point of nutrient exchange your blood velocity is at its slowest. This is important because velocity needs to be relatively slow to give time for the nutrients to exchange.

What are the 3 principle components that make up the circulatory system?

1. Heart 2. Blood Vessels 3. Blood The CVS function is impacted by the endocrine system, nervous system and kidneys.

What is heart rate (HR)?

At rest the heart rate beats 50-80 times per minute.

What type of flow is observed in the pulmonary and systemic circuits? List the benefits of having parallel flow?

Blood flows sequentially through these circuits, which are arranged in series. Within both circulations we have massive amounts of parallel flow. That's because it can choose where to go (liver, lungs, arms etc.), this is important because if it were to flow in series the whole way the region of the body that would receive the blood at the end of the circuit would be receiving blood with lower amounts of nutrients, oxygen etc. With parallel flow, everything gets a fresh supply of blood coming from the heart. Parallel flow can also determine flow rate at different parts of the body - this is important because some tissues need more blood than others. (exercise requires more blood to be pumped to the muscles).

What is cardiac output (CO)?

CO is the amount of blood pumped by each side of the heart each minute. CO = HR x SV = ~4900mL (5L). 5L is close to your total blood volume so your heart circulates almost all the blood in your body every minute. CO depends on body size, a smaller person will have a proportionally smaller SV and CO.

Capillaries:

Endothelial cells - exchange vessels. Cannot cope with pulsatile flow.

Aorta & large arteries:

High pressure reservoir/conduit arteries - job is to get the blood away from the heart as fast as possible. They have a thick wall with many layers of smooth muscle that can cope with the high pressure.

Which side of the heart pumps the cardiac output through the body via the systemic circulation?

Left side.

The size of the vessel is really important for function. What is the name and sequence of vessels in the systemic and pulmonary circuits?

Left ventricle, aorta, arteries, arterioles, capillaries (one RBC can move through), venules, veins and vena cava (this puts blood back into the right side of your heart. Right side of heart, arterioles and arteries, capillaries, venules and veins and left side of heart.

Poiseuille's law tells us that 3 factors govern resistance, what are the 3 things:

Length, radius and viscosity of the blood. Length of blood vessels shouldn't change once you've reached adulthood, viscosity of blood shouldn't change - you'd have to be massively dehydrated for this to happen. The radius of the blood vessels DO change. This is what controls our resistance. Poiseuille's law tells us that the resistance is equal to 8 times the viscosity of blood times the length of the tube, divided by pi multiplied by the radius to the power of 4 (do not need to remember this equation).

Blood is made up of what 3 formed elements?

Plasma (55%), liquid part of blood that carries everything else. Plasma carries a lot of your blood cells, proteins, nutrients, metabolic wastes, sugars etc. Erythrocytes (45%) are your RBCs, small portion of blood is leukocytes and platelets which are crucial in blood clotting.

Circulation plays a crucial role in homeostasis. What is bulk flow?

Rapid flow of blood throughout the body is produced by the pressure created by the pumping action of the heart. Bulk flow allows you to distribute a lot of important things (heat, ions, water, co2, hormones) which essentially regulates a lot of processes.

Smaller arteries & arterioles:

Resistance vessels that can control their diameter to control the volume of flow through the circulation.

Veins & venules:

Return conduits, primary reservoir or capacitance of the vasculature.

Which side of the heart pumps the cardiac output through the lungs via the pulmonary circulation?

Right side.

Whats the difference between series and parallel?

Series is to say one thing is going from one to the other to the other etc. Parallel is to say something will come along and it will choose which pathway to go in and they can all go along next to each other. Your circulation has both types of flow.

Summarize the jobs of both sides of the heart:

So the right side of the heart is responsible for pulmonary circulation and the left side of the heart is responsible for systemic circulation. The two sides of the heart do not cross over in adulthood. The systemic circulation is high pressure and the pulmonary is low pressure because it doesn't need to go as far.

How does the body determine and regulate the amount of blood going to each organ? What are hemodynamics?

To start or maintain blood flow, energy must be put into the system - this is done via the beating of the heart. Blood will flow from a region of high pressure to a region of low pressure. Energy is lost from flowing blood through friction. Friction is responsible for the resistance to blood flow. Energy put into the system by the heart raises the pressure of the blood. Blood flow = drop in blood pressure/resistance to flow. Flow is directly proportional to change in blood pressure. Flow is inversely proportional to resistance, meaning an increase in flow would result in a decrease in resistance and vice versa. Also change in pressure is directly proportional to resistance.

Our circulation is a double circulation, what does this mean?

We have 2 circulation 'loops'. One is called your pulmonary circulation and it goes TO and FROM your lungs. The other loop is your systemic circulation and it goes from the left side of your heart to the right.