5/21/2021

1

Bio 1102 Lecture 5 Chapter 8: Heart & Blood Vessels

• Functions of Circulatory System:

– To carry oxygen from lungs to all cells, tissues, and organs of body

– To carry nutrients from digestive system to all cells, tissues and organs of body

• The heart is the organ that pumps blood through the body

• Heart is located between the lungs

• Three layers of the heart: – Pericardium: thin outer layer; protects & anchors

– Myocardium: thick middle layer; cardiac muscles

– Endocardium: thin inner layer; endothelial lining

• 2 Circuits of Blood Flow:

– Pulmonary Circuit: blood pumped to and from the lungs

– Systemic Circuit: blood pumped to and from the rest of the body

• Blood that has been circulated through body in the Systemic Circuit has lost its oxygen and picked up carbon dioxide

• Heart pumps this blood to lungs (via the Pulmonary Circuit) where carbon dioxide is expelled and oxygen is replenished

• 4 chambers of the heart – 2 on the left: pumps

oxygenated blood from the lungs through the systemic circuit

– 2 on the right: pumps deoxygenated blood from the body through the pulmonary circuit

– Note: “left” and “right” not as you read the diagram, but in relation to the organ

• Blood returning from systemic circuit enters heart via two large veins (superior and inferior vena cava)

– Superior, from upper part of body (head, neck, and arms)

– Inferior, from lower part of body

• Blood enters the right atrium (upper chamber), is pumped into right ventricle, and then through the pulmonary arteries to the lungs

5/21/2021

2

• Blood is oxygenated in lungs

• Blood returns to left atrium of heart via pulmonary veins

– Systemic System begins

• Blood enters left ventricle

– Thicker-walled than right ventricle

– Pumps blood to rest of body, via the aorta • Largest artery in body

• Heart valves

– 4 valves in heart control direction of blood flow

– Valves between atria and ventricles = atrioventricular valves • Anchored to walls of ventricles by chordae tendineae

• Right atrioventricular valve = tricuspid valve

• Left atrioventricular valve = bicuspid valve (aka mitral valve)

– Valves between ventricles and arteries are two more valves (semilunar valves) • Left side: between left ventricle and aorta = aortic

valve

• Right side: between right ventricle and pulmonary artery = pulmonary valve

• Heart Sounds

– The sound of the valves closing

– Incomplete closing of valves can be heard as a “heart murmur”

• Rheumatic fever

– Heart murmurs can also result from holes in the “septum” between the ventricles, or other heart defects

– When blood doesn’t flow efficiently through chambers of heart, the heart has to work harder

• Video of normal heart sounds: – https://www.youtube.com/watch?v=dDg7GDpR1RE&l

ist=PLD9731E70DD5BB801&index=1

• Video of heart murmur, due to mitral valve not closing fully – https://www.youtube.com/watch?v=vL0s_nEkC8Q&lis

t=PLD9731E70DD5BB801&index=7

• Video of heart murmur, due to aortic valve (left semilunar valve) stenosis – May result from congenital heart defect, from calcium

build up on the valve, or from damage due to infection such as rheumatic fever

– https://www.youtube.com/watch?v=MJg257pyt4I&list=PLD9731E70DD5BB801&index=4

• Control of Heart Rate – Heart beats at different speeds

depending on your activity level

– Has an internal “pacemaker” called the sinoatrial node • Inside wall of right atrium

• Cluster of cells that produce electrical impulses

• Impulses spread throughout heart (first to atria, then to ventricles)

• Synchronizes the contractions of atria

5/21/2021

3

– Signal then travels to another cluster of special cells, the atrioventricular node • Signal then is distributed to the

ventricles by the atrioventricular bundles (in the septum) and then the Purkinje bundles (see figure 8.13)

– Without some regulation, SA node would cause heart to beat 100 times per minute at rest – too fast

– Heart control center of brain (medulla oblongata) slows down the SA node

• On average, impulses from brain slow heart rate to about 70 beats per minute (at rest)

• When active, impulses from brain are reduced, so heart rate speeds up

• Other nerves and hormones (e.g. adrenaline) can also work to increase heart rate (up to about 180 beats per minute)

• Heart beat rate is regulated to meet the needs of the body’s cells for oxygen – Maximum heart beat rate = 220-your age – Generally don’t want to exceed 85% of your maximum

during strenuous exercise – Tachycardia = when your heart beats too fast

• Heart Attacks

– Most common type: myocardial infarction • Caused by blood clots in

arteries supplying blood to the heart

• Often associated with arteries narrowed by plaque

• Lack of flow to heart starves muscles of oxygen and nutrients, killing cells

– The damaged area is called an infarct

• What causes plaque formation?

– Poor diet

– Smoking

– Lack of exercise

– Heredity

– Stress

• Severity of the heart attack depends on how much of the heart muscle is damaged

• Warnings of Heart Attack

– May occur without warning

– Chest pain (angina) may precede heart attack for several weeks • Caused by reduced blood flow to heart

• Pain in center of chest, spreading to throat, jaw, back, and arms

• Occurs when person is active, under stress, or exposed to carbon monoxide

• Taking an aspirin during a heart attack can reduce damage

– Aspirin reduces clotting

• Other causes of heart attack

– Loss of control of heart muscle by sinoatrial (SA) node

• Heart muscles thus beat independently, reducing flow of blood through heart (= fibrillation)

• Heart stops beating = cardiac arrest

• Heart beat may be restored by applying strong electrical current to chest (defibrillation), or by cardiopulmonary resuscitation (CPR) – Applying pressure to breastbone, massaging the heart

5/21/2021

4

– High School senior Logan Stiner of LaGrange, Ohio, died in 2014 due to overdose of caffeine powder

– The medical examiner said the cause of death was “cardiac arrhythmia and seizure, due to acute caffeine toxicity due to excessive caffeine ingestion.”

– A teaspoon of caffeine powder = 16 to 25 cups of coffee!

• Treatments

– Balloon angioplasty

• A catheter with a tiny balloon attached is inserted into the artery

• Chemicals are injected to dissolve the clot

• Balloon is then inflated – Opens artery

– Flattens plaque against artery wall

– Stents may be inserted after balloon angioplasty

• Holds artery open after balloon is removed

– Coronary bypass surgery

• Used when coronary arteries are completely blocked by plaque

• Transplant small pieces of vein from other locations (usually the leg) into the heart

• These veins are connected so as to bypass the clog

• Atherosclerosis – Thickening of artery walls due to build up of

plaque

– Too much cholesterol in blood forms deposits in lining of arteries

– Can narrow blood vessels, increasing risk of a blockage • Can result in heart attack

• If occurs in vessels leading to or in brain, can cause stroke

• Can cause increase in blood pressure – This, in turn, can damage organs such as the kidneys

• Aneurysm

– Weakening and rupture of artery walls

– Caused by some diseases, atherosclerosis, and high blood pressure

– “Ballooning” of the artery in weakened areas

– If rupture occurs, blood lost rapidly

• Often results in death

– Prevention involves the usual steps: stop smoking, reduce stress, lower blood pressure, exercise and lose weight, etc.

– Omega-3 fatty acids may also be helpful

• Increase good cholesterol (HDL), which removes cholesterol from artery walls

• Found in oily fish (like salmon, trout, and sardines), the eggs of some chickens (free-ranging), milk and cheese from grass-fed cows, and vegetable sources such as flax seed and walnuts

5/21/2021

5

Blood Vessels

• 3 Types of Blood Vessels

– Arteries: carry blood away from heart

– Veins: carry blood to heart; have valves

– Capillaries: fine, branching network of vessels in tissues

Structure of Blood Vessels

• Inside of vessel = lumen • Innermost layer of vessel = endothelium

– A continuation of the lining of heart – Flattened squamous epithelial cells very smooth; minimize

friction

• Middle layer = smooth muscle with elastic fibers

• Outer layer = connective tissue (mostly collagen)

– Anchors vessels in place

– Protects vessels

• Arteries carry blood away from heart, toward capillary beds in tissues

– Branch into networks of the smaller and smaller arteries

– Smallest arteries, which lead directly to capillaries, are called arterioles

– Pressure in vessels declines as it reaches the arterioles

• Therefore, they lack the outer layer of connective tissue

• Also, have thinner layer of smooth muscle

– Arterioles can regulate amount of blood flow to each capillary by either dilating (allowing more blood to flow) or constricting (reducing blood flow)

5/21/2021

6

• Precapillary Sphincter – A band of smooth muscle at junction of an arteriole

and a capillary – Can open or close to adjust blood flow to capillaries

• Vasoconstriction: when the arteriole and/or precapillary sphincter constricts to reduce blood flow to a capillary bed

• Vasodilation: when the arteriole and/or precapillary sphincter relaxes to increase blood flow to a capillary bed

• Vasodilation and vasoconstriction regulated by hormones, nerve signals, and the local conditions surrounding the vessels

• Blood pressure

– Force of blood against walls of blood vessels generated by pumping of heart

– Highest in arteries; lowest in veins and capillaries

– Blood pressure can increase with:

• Stress/anger

• Age

• Plaque in arteries – High blood pressure can be a symptom of cardiovascular

disease

– “Top” number (higher number) is systolic pressure

• The highest pressure of blood against artery walls

• Occurs when heart ventricles contract and blood is pumped into the arteries

– “Bottom” number (lower number) is diastolic pressure

• The lowest pressure of blood against artery walls

• Occurs when the heart relaxes and re-fills with blood

– Normal blood pressure is defined as 120/80 or less

– Pre-hypertension is defined as 121-139 over 81-89

– Hypertension

• “a prolonged elevation in blood pressure”

• 140/90 or greater

• Can lead to heart attack

• New (2017) American Heart Association guidelines lower the definition of high blood pressure to 130/80, to allow earlier interventions for some people

• Means about half of Americans have “high blood pressure”

• Capillaries – Where nutrients, gases,

water, and hormones are delivered to cells, and wastes are carried away from cells

– Walls consist of single layer of squamous epithelial cells

– Microscopic pores in these cells; slits between the cells

– Materials move across the thin walls of capillaries by diffusion

5/21/2021

7

• At beginning of capillary bed, fluid filtered out of blood includes nutrients and oxygen

• At end of capillary blood, fluid returned to blood includes carbon dioxide and waste materials such as urea

• Veins – Once needed nutrients and gases are removed

from blood in capillary beds of systemic circuit, blood enters veins

– This blood contains waste materials (in systemic circuit)

– Blood pressure lower in veins, and veins have thin walls • Obstructions can cause bulges (varicose veins)

– Eventually, veins of systemic circuit empty this blood into the superior or inferior vena cava, and the blood enters the right atrium

• Veins have three layers, like arteries, but

– Outer two layers are much thinner

• Don’t need thick outer layer when blood pressure is low

– Also, a larger lumen

• Helps them hold a large amount of blood

• Veins serve as a blood volume reservoir – 2/3 of blood is located in your veins

• Veins contain one-way valves

– Prevents backward flow of blood

• How is blood returned to heart through veins? – Contraction of skeletal muscles

• Veins pass between skeletal muscles

• When they contract/relax, they push on the veins

• Pushes blood toward heart

– One-way valves • Blood cannot flow backwards due to these valves

– Movements associated with breathing • Inhaling puts pressure on veins in abdomen

• At same time, pressure in chest (thoracic) cavity decreases, dilating the veins there

• This results in blood being pushed from veins in abdomen toward veins in chest

• Lymphatic System – A system of vessels and glands

– Tissue fluid bathes cells of the body • Interstitial Fluid

• Materials diffuse through this fluid between capillaries and cells

– Fluid comes from capillaries; more water leaves capillaries than enters

– Excess water is picked up by lymph capillaries and ultimately returns to fluid to the circulatory system • Drain into veins at base of neck

– Lymph moves through vessels using gravity or muscle contractions

– Lymphoid organs (such as the spleen, thymus, and lymph nodes) involved in immune response (to be discussed later)

Activity Quiz #5

• Log on to Carmen Canvas and complete Activity Quiz #5