BIOL Lecture 14 - The Cardiovascular System

What are the 3 main components of the cardiovascular system?

• Heart (muscular pump), blood vessels (conduits for blood to flow such as arteries, veins, capillaries), and blood (circulating fluid for transport and cell communication)

• Blood is really important for communication between different organs, different tissues, different cells, as it carry things like chemical messengers, sometimes hormonal chemical messengers, neurotransmitters that allow for communication

What are some examples of affiliated organs/tissues?

• An important one to look at is the lymphatic system.

• The lymphatic system includes things like lymph nodes, lymphatic vessels, spleen, tonsils, thymus

What is the circulatory system?

• Cardiovascular system + lymphatic system for fluid balance and immune support

• Lymphatic system plays an important role in maintaining fluid balance, filtering out any harmful substances from the body.

• Supports the immune system by transporting white blood cells.

• Cardiovascular and lymphatic system are very closely linked as the cardiovascular system transports blood around the body

How does blood travel throughout the body?

• Blood vessels conduct blood in continuous loops

• Deoxygenated blood returns to right side of heart (enters right atrium) from venous circulation

• Atria receive blood

• Heart contracts, pumps blood to ventricles
  Right ventricle – to the lungs! To left atrium!

• Oxygenated blood leaves left ventricle via the aorta (enters the heart through the left side)

• Note the deoxygenated blood in the pulmonary artery and the oxygenated blood in the pulmonary vein

What happens in the pulmonary circuit?

• Important site of oxygen and CO2 exchange at the lungs

• As the blood moves from the pulmonary artery into those capillaries, or the capillary bed, we see the movement of oxygen into the blood from the lungs.

• The movement of CO2 from the blood to the lungs.

• Important for making deoxygenated blood become oxygenated.

• Notice colour change!

• In the pulmonary vein there is oxygenated blood, which then moves down into the left atrium on the left side of the heart.

What occurs in the systemic capillary beds?

• Oxygen will leave the blood and CO2 enters → Blood becomes deoxygenated again

• Blood moves through veins (which have a larger diameter)

• As they move from the veins, they go into venules (smaller diameter)

• Then into the capillaries, which have an even smaller diameter.

• Blood vessels branch out → diameter is smaller, but surface area has increased!

Describe the path of deoxygenated blood through the heart and lungs

Right atrium → right ventricle (via AV valve) → pulmonary artery → lungs (O2 in, CO2 out) → pulmonary vein → left atrium

 Describe the path of oxygenated blood through the heart and body

Left atrium → left ventricle (via AV valve) → aorta (via semilunar valve) → systemic capillaries (O2 out, CO2 in) → veins → right atrium

Where is blood held in the body?

Mostly in the systemic veins and venules (60%)

Describe Artery Characteristics

• Thick muscular walls (smooth muscle) designed to handle high pressures

• Largest diameter (along with veins)

• Blood flows faster than in capillaries (Larger diameter = faster blood flow)

Describe Arterioles Characteristics

• Bit less muscle (pressures are now dropping), but there is lots of innervation to control smooth muscle contraction/ i.e. vessel diameter

• **main site of BP regulation

• Highly Innervated → Helps to regulate blood flow and blood pressure, and maintain overall circulatory stability and homeostasis.

• Don't see a rapid rise in blood pressure or blood flow to downstream capillaries - arterioles smooth out and regulate local flow

Describe Capillary Characteristics

• No muscle - so, there’s no control over diameter, or connective tissue - no ability to withstand high pressures.

• But movement of fluid and solutes is maximized here (highly permeable)!!

• Blood flows more slowly

Describe Venule Characteristics

• Main site of lymphocytes (white blood cells) crossing from blood to lymph nodes

• There’s a small amount of smooth muscle but if we compare to our veins and arteries and even our arterioles we see that there’s comparatively less.

• This allows the venules to allow movement of fluid

• For example it is the key site where white blood cells exist, and the venules allow these white blood cells to cross from blood to lymph

Describe Vein Characteristics

Thin walled, fairly muscular, for easy expansion and recoiling

We see on the slide the movement of blood from the vena cava to veins, then venules (deoxygenated blood), then reaching the capillaries which again is a key site of O2 and CO2 exchange. The blood now becomes oxygenated and moves through arterioles, arteries and the aorta. You can also see visually on this slide how diameter changes from veins to venules to capillaries etc.  You can see as the blood moves through these different blood vessels, there are changes in both surface area and velocity. In the capillaries surface area is large, whereas velocity is low. This is the ideal state for nutrient, waste, and fluid exchange

Why do capillaries have slow blood velocity and high surface area?

• Larger Blood Vessels → Higher Velocity

• Capillaries have lower velocity but higher surface area (more branched)

• Lot of surface area + Slow moving blood = Ideal site for nutrient exchange!

• Increases time and area for nutrient/O2 exchange between blood and tissues

Organ Specific (Capillary Bed-Specific Control of Blood Flow)

• Different blood flow due to the various metabolic demands, and functions of different organs and tissues in the body

• Some organs/tissue require more blood to carry out their functions

• Will change depending on the state of the human body

• When exercising → cardiac output increases

• The cardiac output is the amount of blood pumped by the heart per minute. It is a product of heart rate x stroke volume

• Blood flow to skeletal muscles increases while working out

• Cardiac output ↑; more blood to skeletal muscle, less proportionally to kidneys/GI/brain

Lecture Question

D is the correct answer

Lecture Question #2

Answer is E

How do Veins Carry Blood to the Heart?

• Blood is moved against gravity toward the heart by:

• Pressure gradient between left and right side of heart

• Facilitated by:

  • Expansion of the thoracic cavity during breathing (helps to keep blood moving against gravity, in the way that it's supposed to)

  • Contracting skeletal muscles (as they relax and contract, that can help move blood flow against gravity)

  • Valves (prevent blood flowing backwards)

What causes varicose veins?

• One-way valves malfunction

• Allow backwards flow of blood and pooling

• Generally, occurs in superficial veins in thigh and calf (saphenous vein – longest vein in the body)

• Common in legs/older adults

The Heart as a Muscular Pump

• The heart is made of cardiac muscle tissue called myocardium

• Muscle tissue is different from skeletal muscle → it contracts and relaxes involuntarily (automatic/autonomic)

• Gap junctions → Help the heart to beat properly, and beat very quickly, contracting as a full unit

• Metabolism → Very high oxidative capacity

• 35% compared to 5% in skeletal muscles  

• Fatigue-resistant → The heart will beat about 3 billion times over a lifetime 

• Skeletal muscles less fatigue resistant (can only run so far until the muscles give out, can’t lift as much weight as before etc)

What causes the "lub-dub" heart sounds?

• Lub: AV valves (tricuspid/mitral) closing.

• Located between each atrium and ventricle

• Dub: semilunar valves (pulmonary/aortic) closing

• Located between each atrium and its artery

• Dub sound is louder than Lub sound

Name 5 common cardiovascular diseases/conditions.

• Coronary artery disease → Blood vessels that supply oxygen and nutrients to the heart become narrowed or blocked (Stenosis)

• Stroke → Interruption of blood flow to the brain (Blocked artery/brain bleed)

• Myocardial infarction (heart attack) → Part of the blood that's flowing to the heart becomes blocked (blood clot)

• Heart failure → Not pumping blood as effectively as it should

• Hypertension/Diabetes → High blood sugar makes blood viscous ("syrupy"), damaging vessels, causing blockages, peripheral neuropathy, heart disease

What is dyslipidemia, and how does high LDL cause atherosclerosis?

• Lipid levels, cholesterol levels are out of whack, so they're outside of that normal, healthy reference range.

• Common type is elevated LDL cholesterol

• LDL is lousy (bad) cholesterol and contributes to plaque buildup in arteries narrowing/blocking them

What does the Framingham Risk Score (FRS) assess?

• Age

• HDL cholesterol (healthy)

• Total cholesterol

• Systolic blood pressure

• Smoking status

• Diabetes diagnoses

• It will assess these factors and assign you a “heart age”

• Ex. 25 years old, but you don't have great blood lipid levels, you're a smoker, you have high blood pressure, then your heart could actually be older than what your actual age is.

• Note: at the same FRS, risk in males is greater than risk in females

Case Study

1. 14 points

2. Within the next 10 years, there is a 18.4% chance of this patient developing a cardiovascular disease (moderate risk)

3. Heart Age is 68 

4. Being a smoker would add 4 points, bringing the score up to 18 which puts him in the high risk catergory