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Anatomy and Physiology 1111 > Module 16 > Flashcards

Module 16 Flashcards

1
Q

Position of the Heart

A

The heart is close to the midline-
- The center is slightly to the left of the midline
- At about the same level as the nipples
- About the size and shape of a closed fist.
The heart lies in the cavity called the mediastinum
- Mediastinum = thoracic cavity minus pleural cavity
- Mediastinum includes esophagus, thymus, great vessels of heart and heart.

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2
Q

Cross-Sectional Anatomy of the Heart

A

The Heart is within a “slippery bag.” This membrane is called the pericardium.
- The relationship of the esophagus and heart in the mediastinum makes transesophageal echocardiography (TEE) possible.

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3
Q

What are the 4 layers of the Heart wall?

A

Endocardium
- A thin layer of simple squamous epithelium lining the inside of the heart over a thin layer of connective tissue.

Myocardium
- The muscular wall of the heart. Makes up 95% of the heart and is responsible for the pumping action

Epicardium

  • The thin outermost layer, a delicate membrane of epithelial and connective tissue giving the heart a slippery covering.
  • This layer is synonymous with the visceral layer of the pericardial covering

Pericardium

  • Parietal layer of serous percardium
  • fibrous percardium
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4
Q

Endocardium Diseases

A

The endocardium can develop chronic infections. Patients at risk for endocarditis (e.g. transplanted heart valve), or who have history of infective endocarditis, should receive antibiotics prior to dental cleanings.

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5
Q

Pericardium

A

Surrounds and protects the heart. It consists of a deeper serous pericardium, and the outermost fibrous pericardium.

  • The serous pericardium has 2 layers, the deeper visceral layer covers the heart and is synonymous with the epicardium. The parietal layer is fused to the fibrous pericardium.
  • Pericardial fluid fills the pericardial cavity between the visceral and parietal layers of the serous pericardium.
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6
Q

Pericardial Effusion

A

An accumulation of excess fluid in the pericardial space. This may occur due to infections, trauma, or myocardial infarction. This fluid puts pressure on the heart. This pressure may become great enough to prevent the heart from pumping , a condition called cardiac tamponade that is life-threatening.

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7
Q

Cardiac Muscle Tissue

A

Cardiac muscle, like skeletal muscle, is striated. Unlike skeletal muscle, cardiac fibers are shorter, branch, and have one centrally located nucleus.

  • Have intercalated discs for structural strength and connect neighboring fibers.
  • The discs contain desmosomes which hold fibers together, and gap junctions which allow muscle action potentials to travel between fibers.
  • Cardiac muscle cells contain more and larger mitochondria than skeletal muscle.
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8
Q

What are the 4 chambers of the heart?

A

The atria are in the superior portion of the heart and are holding chambers for blood. The ventricles are in the inferior portion of the heart and pump blood to the lungs and body.

  • Right atrium
  • Left atrium
  • Right ventricle
  • Left ventricle
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9
Q

Right Atrium

A

This chamber receives deoxygenated blood from the body.

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10
Q

Left Atrium

A

This chamber receives oxygenated blood from the lungs

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11
Q

Right Ventricle

A

This chamber receives blood from the right atrium. It’s job is to pump deoxygenated blood out to the lungs.

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12
Q

Left Ventricle

A

This chamber receives oxygenated blood from the left atrium. It’s job is to pump oxygenated blood out to the body.

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13
Q

What are the 4 valves of the heart?

A

Tricuspid Valve
- Right Atrium to Right Ventricle

Pulmonary Valve
- Right Ventricle to Pulmonary Trunk

Mitral Valve (bicuspid valve)
- Left Atrium to Left Ventricle

Aortic Valve
- Left Ventricle to Aorta

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14
Q

What are the names of the valves and chambers that operate in pairs?

A
  • Atrioventricular Valves (AV): These valves control the flow of blood between the atria and the ventricles.
  • Semilunar (outflow) Valves: These valves control the flow of blood leaving the heart from the ventricles
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15
Q

Atrioventricular Valves (AV)

A

Control the flow of blood between the atria and the ventricles:

  • Right Atrioventricular Valve (AV) or tricuspid valve: Between the right atria and right ventricle
  • Left Atrioventricular Valve (AV), bicuspid valve, or mitral valve: Between the left atria and left ventricle.
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16
Q

Semilunar (outflow) Valves

A

Control the flow of blood leaving the heart from the ventricles:

  • Pulmonary Semilunar Valve: Regulates blood flow from the right ventricle to the pulmonary trunk (out to the pulmonary circulation)
  • Aortic Semilunar Valve: Regulates blood flow from the left ventricle to the aorta (out to the systemic circulation)
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17
Q

Functions of Atria

A

Atria function as reservoirs and filling chambers

  • thin walls, little muscle tone
  • right atrium: receives deoxygenated blood from body
  • left atrium: receives oxygenated blood from lungs
  • small amount of pumping action called atrial “kick
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18
Q

Functions of Ventricles

A

Ventricles function as pumps

  • Right Ventricle: Pumps to lungs
  • Left Ventricle: Pumps to body
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19
Q

Functions of the Chambers and the Valves

A

Valves regulate flow of blood between chambers and out of the heart. Valves do not actively open, rather, they are pushed open by increased pressure.

Atrioventricular (AV) valves between atrium and ventricle

  • Tricuspid valve between right atrium and right ventricle
  • Mitral (bicuspid) valve between left atrium and left ventricle

Outflow valves between ventricle and other organs

  • Pulmonary valve to pulmonary trunk (then to lungs)
  • Aortic valve to aorta (then to body)
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20
Q

Functions of the Chambers

A

Ventricals are pumping chambers

  • Right ventricle pumps short distance and against low pressure to lungs
  • Left ventricle pumps long distance and against large pressure to body
  • Therefore, left ventricle muscle wall very thick compared to right
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21
Q

What are the 4 Great Vessels?

A
  • Pulmonary Trunk
  • Pulmonary Vein
  • Aorta
  • Venae Cavae

The great vessels of the heart bring blood to and away from the heart. Veins carry blood towards the heart, arteries carry blood away from the heart.

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22
Q

Pulmonary Trunk

A

Carries deoxygenated blood to lungs

  • divides into pulmonary arteries (left and right)
  • named “arteries” because they lead away from the heart
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23
Q

Pulmonary Vein

A

Carries oxygenated blood from lungs

- Named “veins” because they lead back to the heart

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24
Q

Aorta

A

Takes blood away from left ventricle of heart to body

- ascending, arch, and descending portions

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25
Q

Venae Cavae

A

Carry deoxygenated blood from body back to right atrium of the heart

  • Inferior vena cava from body below heart
  • Superior vena cava from body above heart
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26
Q

Pattern of Blood Flow through Heart and Great Vessels 1-5

A
  1. Blood from superior and inferior venae cavae enters right atrium
  2. Blood flows from right atrium to right ventricle via tricuspid valve
  3. Blood pumped from right ventricle to pulmonary trunk via pulmonary valve.
  4. Blood oxygenated in pulmonary capillaries of lungs
  5. Blood returns to heart via pulmonary veins
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27
Q

Pattern of Blood Flow through Heart and Great Vessels 6-10

A
  1. Oxygenated blood from lungs returns to left atrium
  2. Blood flows through mitral (bicuspid) valve into left ventricle
  3. Blood is pumped through aortic valve into aorta
  4. Blood distributed to body through branches off aorta and other vessels into capillaries
  5. Blood returns to heart via systemic veins and venae cavae
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28
Q

Operations of Valves during Pattern of Blood Flow

A

Blood flow through the right and the left side of the heart simultaneously.

Tricuspid and mitral valves open as a pair:

  1. Blood flows from right atrium to right ventricle via tricuspid valve
  2. Blood flows through mitral (bicuspid) valve into left ventricle

Pulmonary and aortic valves open as a pair:

  1. Blood pumped from right ventricle to pulmonary trunk via pulmonary valve
  2. Blood is pumped through aortic valve into aorta
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29
Q

What are the 2 Abnormal Sounds due to Turbulent Flow?

A
  • Valvular Stenosis

- Valvular Incompetence

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30
Q

Valvular Stenosis

A

Valves that are narrowed and too “stiff” and don’t open properly

  • Mitral stenosis
  • Aortic stenosis
  • Pulmonary stenosis
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31
Q

Valvular Incompetence

A

Valves that are too “floppy” and leak. This commonly leads to valvular regurgitation: when ventricular pressure increases, blood leaks in the “wrong” direction out of “wrong” (closed) valve (i.e. from ventricle to atrium through tricuspid or mitral valve)

  • Mitral regurgitation
  • Aortic regurgitation
  • Tricuspid regurgitation

The turbulent blood also produces abnormal heart sounds. Turbulent blood is also more prone to clotting due to shear forces activating platelets.

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32
Q

Mitral Valve Prolapse

A

The most common valvular heart disease. The condition is often genetically inherited and is more common in women than men.

  • The mitral valve may also become leaky when muscle of left ventricle is damaged, usually due to myocardial infarction or hypoxia (lack of oxygen).
  • The left ventricle cannot pump blood sufficiently and become dilated (stretched out). This can lead to mitral regurgitation.
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33
Q

Doppler Ultrasounds for Dysfunctional Valves and Chambers

A

A Doppler ultrasound can be used to measure the velocity and direction of the blood.

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34
Q

Endocarditis

A

Blood flow through an incompetent valve is often turbulent instead of smooth. This can activate platelets which in turn can lead to the formation of blood Clots

Endocarditis may lead to bacterial growth (vegitations) on heart valves. This growth not only leads to incompetent valves but can also cause sepsis. Part of the vegetation may break free becoming emboli which may in turn lodge in vessels blocking blood flow.

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35
Q

Autorhythmic Cells

A

Special cardiac cells can fire an action potential without nervous stimulation. These cells are said to be autorhythmic. When a heart is used for transplant, the autorhythmic cells keep the heart beating, even outside of the body.

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36
Q

What are the 4 Pacemakers of the Heart?

A

Pacemakers of the Heart have Autorhythmicity. These fire action potentials at a regular rate even without outside stimulation or control.

  • Sinoatrial Node (SA Node)
  • Atrioventricular Node (AV Node)
  • Atrioventricular Bundle (Bundle of His)
  • Purkinje Fibers
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37
Q

Sinoatrial Node (SA Node)

A
  • These are the primary pacemakers (fire action potentials about 100 times per minute)
  • A cluster of specialized heart muscle cells (cardiomyocytes) at the base of the heart
  • Location near coronary sinus and right atrium
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38
Q

Atrioventricular Node (AV Node)

A
  • Location near junction of left atrium and right ventricle

- These only act as pacemakers if SA node cells are dead (ectopic pacemaker)

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39
Q

Atrioventricular Bundle (bundle of His)

A
  • This bundle of conductive muscle cells leads from the AV node and through the interventricular septum
  • AV bundle branches shortly after it begins into right and left bundle branches.
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40
Q

Purkinje Fibers

A
  • These large-caliber, non-contractile cells conduct the electrical impulses to the cardiac muscle cells of the right and left ventricles.
  • Because of gap junctions, all muscle cells of the ventricle contract at about the same time.
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41
Q

Autorhythmicity

A

99% of the heart’s cells are contractile and do the work of pumping. 1% are special autorhythmic cells. The action potential of a cardiac autorhythmic cell is different than a neuron and involves 3 ions: Na+, K+, and Ca++.

  1. Na+ Funny channels open causing the membrane to “drift” towards threshold. A special Na+ channel called a funny channel (only found in Autorhythmic cells) opens when the cell becomes more negative. At the same time, K+ channels close, decreasing K+ outflow.
  2. After the threshold is hit, Caa++ channels open causing depolarization of the cell membrane, making the membrane potential more and more positive. K+ leak channels close.
  3. K+ channels open causing repolarization of the cell membrane, when the membrane potential becomes more negative.
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42
Q

Effects of Blood Ion Concentrations on the Heart

A
  • Increase in K+ slows down the heart
  • Increase in Na+ blocks Ca++ from entering the cell slowing down the heart
  • Moderate increase in Ca++ speeds up and strengthens the heart
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43
Q

The Cardiovascular Center

A

The cardiovascular center is located in the medulla.

  • As blood leaves the heart through the aorta, it branches into the carotid arteries. Baroreceptors in the sinus of the carotid artery sense blood pressure
  • This info is sent to the medulla through the glossopharyngeal nerve (Cranial nerve IX).
  • If the pressure is too high, the parasympathetic nervous system responds to slow down the heart rate through the Vagus nerve (Cranial nerve X).
  • If the pressure is too low, the sympathetic nervous system responds to speed up the rate of the heart through the cardio accelerator spinal nerves.

The cardiovascular center also receives input from the limbic system and cerebral cortex and sends output based on this feedback

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44
Q

Neurotransmitters as Innervaters of the Heart

A

Sympathetic: Norepinephrine release binds to beta-1 and beta-2 adrenergic receptors on cardiac muscle fibers, speeding up the heart rate

Parasympathetic: Acetylcholine release binds to muscarinic receptors slowing down the heart rate. Note that acetylcholine is an excitatory neurotransmitter in skeletal muscle, but inhibitory in cardiac muscle.

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45
Q

What are the 3 phases of cardiac muscle action potential?

A

Cardiac muscle cells have different action potentials than other nerve or muscle cells. Instead of about 3msec, these last about 300 msec. Prolonged depolarization due to special Ca++ channels in these cells (voltage-gated slow Ca++ channels).

  1. Depolarization
  2. Plateau
  3. Repolarization
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46
Q

Depolarization

A

Contractile muscle cells have a resting potential of about -90 mv. When an action potential is triggered, voltage-gated fast Na+ channels open which quickly lead to depolarization of the cell.

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47
Q

Plateau

A

Contractile cells differ from neurons and skeletal muscle in that they sustain a prolonged depolarization phase called a plateau.

  • Voltage-gated slow Ca++ channels in the sarcolemma open. Ca++ flows into the cytosol triggering the further release of Ca++ from the sarcoplasmic reticulum.
  • As with skeletal muscle, Ca++ ions bind to troponin allowing actin and myosin to bind, sliding past each other and increasing tension causing contraction.
48
Q

Repolarization

A

Voltage-gated K channels open, causing K+ to rush out of the cell restoring the negative membrane potential. Ca++ channels close at the same time leading to repolarization.

49
Q

Refractory Period

A

This is the time during which a second action potential cannot be triggered. This period is longer than in skeletal muscle. This allows for the ventricles to relax while the atria contract, and for the ventricles to contract while the atria rest.

50
Q

Cardiac Muscle vs. Skeletal Muscle Action Potentials

A

Please Review the slide in Objective 13 now. : )

51
Q

Arrhythmias Treatment

A

Arrhythmias, disorders of the rhythm of the heart, are typically either excessively slow (bradyarrhythmias or bradycardias), or overly rapid (tachycardias). Drugs used to treat arrhythmias affect either ion channels or neurotransmitter receptors.

  • Beta blockers block norepinephine neurotransmitters or hormones that speed up the heart rate.
  • Calcium channel blockers slow the flow of calcium into and out of cells
  • Quinidine, lidocaine, and others block sodium channels
52
Q

ECG or EKG

A

An electrocardiogram is a recording of the electrical changes on the surface of the body resulting from the depolarization and repolarization of the myocardium.

  • By measuring the ECG we can quantify and correlate the electrical and mechanical activities of the heart
  • Abnormal ECGs show problems within the conduction pathways of the heart. It can show if the heart is enlarged, if certain regions of the heart are damaged, and the cause of chest pain.
53
Q

What are the 3 discernable waves in an ECG?

A
  • P Wave: Atrial depolarization
  • QRS complex (wave): Ventricular depolarization
  • T Wave: Ventricular repolarization

Atrial repolarization is hidden behind the large QRS complex. We can also measure the area between the waves:

  • P-Q Interval: Area between P and Q on the ECG. It measures the time it takes for the atria to depolarize.
  • S-T Segment: Time it takes to empty the ventricles before they repolarize (the T wave).
  • Q-T Interval: Area from the start of the QRS complex to the end of the T wave. Time from ventricular depolarization to the end of ventricular repolarization.
54
Q

What are the 4 types of Abnormal EKG Tracings?

A
  • Abnormal EKG: missing waves or abnormal wave shape, or abnormal time interval between waves
  • Atrial fibrillation (“A-fib”): most common acute EKG abnormality. Almost normal, but missing P
  • Ventricular tachycardia (“V-tach”): Ventricle depolarizes, but pumping action not effective. Can progress to…
  • Ventricular fibrillation (“V-fib”): Disorganized electrical activity that is life threatening.
55
Q

Comparing the Cardiac Muscle Action Potential and EKG

A

Note: cardiac action potential lasts about 300 msec (=0.3 sec). The EKG lasts about the same amount of time. These two events are correlated:

  • QRS is rapid depolarization as ventricular muscle cells open Na+ channels
  • QT interval is the time Ca++ channels are open
  • T is the repolarization from an influx of K+
56
Q

Systole

A

Contraction

57
Q

Diastole

A

Relaxation

58
Q

The Cardiac Cycle

A
  1. Diastole: entire heart relaxes, atria fill with blood
  2. Atrial systole: atria contract, atrial “kick”
  3. Ventricular systole: powerful ventricular contraction sends blood from R ventricle to lungs and L ventricle to body
59
Q

Individual Breakdown of the Cardiac Cycle

A

When the Heart rate is 75 beats/min, a cardiac cycle lasts 0.8 seconds.

  1. Action potential starts at the SA node causing depolarization of atrium producing P wave.
  2. Atria contract (atrial systole)
  3. Action potential pauses at AV node. It then spreads to the ventricles causing depolarization. (QRS wave)
  4. Contraction of ventricles. Begins shortly after QRS complex appears and continues during S-T segment
  5. Repolarization of ventricles (T wave)
  6. Ventricular diastole begins shortly after T wave begins

In the heart rate of 75 beats/min, atrial systole (contraction) lasts about 0.1 sec. This is followed by ventricular systole which lasts about 0.3 seconds. The heart rests during the remaining 0.4 seconds

60
Q

Explain how systole and diastole in the cardiac cycle are related to systole and diastole in arterial pressure

A
  • When ventricles pump, wave of pressure is sent into aorta, then into arteries.
  • This wave of pressure occurs because of ventricular systole and the pressure developed is systolic pressure
  • When ventricles relax (diastole), pressure drops (diastole pressure)
61
Q

Blood Pressure

A

When blood pressure is measured, the top number in the reading reflects the systolic pressure - the pressure of the left ventricle before and after systole. The bottom number reflects the diastolic pressure or the pressure when the left ventricle rests.

A blood pressure reading of 120/80 reflects a systolic pressure of 120 mmHG and a diastolic pressure of 88mmHG. Pumonary pressure is a result of right ventricular function which is not easily measured.

62
Q

Heart Sounds

A

During the cardiac cycle, all four of the heart valves have a chance to open and close. Listening to the sounds the heart makes is called auscultation
- Valve opening is usually silent. The “Lub Dup” we associate with heart auscultation is produced by valve closure.

63
Q

What are the two loudest sounds called?

A
  • S1: Lower pitched “lub.” This is the AV valves closing plus the semilunar valves opening
  • S2: Higher pitched “lub.” This is the semilunar valves closing plus the AV valves opening.
64
Q

Cardiac Function Measurements

A

With exercise, a normal heart can increase end-diastolic volume to 180 ml. It also pumps more strongly reducing end-systolic volume to 10 ml. This means stroke volume output can increase to 170 ml and ejection fraction to 94 % (170/180).

  • Heart Rate
  • End-diastolic volume
  • End-systolic volume
  • Stroke volume output
  • Ejection fraction
  • Cardiac output
65
Q

Heart Rate

A
  • Beats per minute (bpm)

- number of cardiac cycles per minute

66
Q

End-diastolic Volume

A
  • At diastole, ventricles fill to about 120 ml

- ventricular volume at diastole is the EDV

67
Q

End-systolic Volume

A
  • amount remaining in ventricles after contraction

- about 50 ml

68
Q

Stroke Volume Output

A
  • At systole, volume of ventricles decreases by amount pumped out.
  • End-diastolic volume - End -systolic volume = about 70 ml
  • This is stroke volume output
69
Q

Ejection Fraction

A
  • Stoke volume output divided by end-diastolic volume (i.e. percentage of ventricle emptied at systole)
  • Is usually about 60% (70ml/120ml)
  • Lower ejection fraction means blood is pooling in heart and may clot
  • Also, heart not effectively pumping (e.g. congestive heart failure)
70
Q

Cardiac Output

A
  • Quantity of blood pumped into aorta each minute.

Cardiac output is the heart rate times the stroke volume output. At rest, heart rate may be 72 beats per minute and the stoke volume output 70ml, so the cardiac output would be:

72 bpm x 70 ml per beat = 5 L

With extremely vigorous exercise in a 20 year old (maximum heart rate is about 220 minus age):

200 bpm x 170 ml per beat = 34 L

71
Q

Frank-Starling Mechanism

A

The more the ventricles fill, the more forcefully they contract. Thus, with exercise, muscle action increases venous pressure and more blood returns to right atrium; more is pushed into right ventricle; and the right ventricle contracts more strongly.

More blood enters the lungs and returns, oxygenated, from the lungs to the left atrium; more blood volume fills the left ventricle, and the ventricle pumps blood more forcefully into the aorta. In this way, the body adapts to increased demand.

72
Q

What are the 3 Basic “Tunics” or Layers that make up Blood Vessel Walls?

A

All blood vessels in the body have a lumen and share components of three basic “tunics” or layers:

  • Tunica Interna
  • Tunica Media
  • Tunica Externa
73
Q

Tunica Interna

A

Forms the innermost layer and consists of a simple layer of squamous epithelium (endothelium) connected to a basement membrane.
- Endothelium provides a very smooth, almost friction free surface for blood cells to “skate” on. Endothelial cells are active participants in a variety of vessel-related activities that influence blood clotting, blood flow, and capillary permability.

74
Q

Tunica Media

A

Is a muscular and connective tissue layer that displays the greatest variation among the different vessels.
- Vasoconstriction and vasodilation in arteries to control blood flow and blood pressure

75
Q

Tunica Externa

A

Is the outer covering of blood vessels made up of elastic and collagen fibers. This layer contains numerous sympathetic nerves which control the diameter of the vessel, and tiny blood vessels called the vasa vasorum, which are especially present in large vessels like the aorta.

76
Q

Blood Vessel Anatomy from the Center Out

A
  • Lumen
  • Endothelium
  • Elastic Tissue
  • Smooth Muscle
  • Elastic Connective Tissue
77
Q

Arteries Anatomy

A
  • Smooth muscle layer thickened

- Lumen diameter can change depending on muscle tone

78
Q

Vein Anatomy

A

Veins have thinner walls, less muscle and elastic tissue, and operate at much lower pressures.

  • Thin or absent smooth muscle layer
  • Lumen diameter does not change
  • Valves prevent backflow
79
Q

What are the 5 Types of Intermediate Vessels?

A
  • Elastic arteries: Large diameter and thin walls. Able to withstand high pressure
  • Muscular or distributing arteries: Medium size. Contain more smooth muscle and fewer elastic fibers.
  • Arterioles: Tiny arteries. Adjust rate of blood flow to the capillaries.
  • Capillaries: Site of nutrient and gas exchange
  • Venules: Small veins
80
Q

Varicose Veins

A

Sometimes valves become incompetent and floppy in veins. This causes a backflow and pooling of blood (venous stasis) leading to varicose veins. The pooling of blood increases the risk of clot formation.

81
Q

Capillaries

A

Capillaries join arterioles and venules.

  • Capillaries occur as capillary beds of interconnected vessels.
  • Capillaries are small enough that RBCs must fold to pass through
  • Precapillary sphincters are smooth muscle cuffs that regulate flow of blood through capillary bed.
82
Q

What are the 3 Types of Capillaries Found in the Body?

A
  • Continuous capillaries: Endothelial cells form a continuous tube, interrupted only by small intercellular clefts. Substances pass through by pinocytosis
  • Fenestrated capillaries: (fenestra: Latin for “window”) Are much more porous. They are found in the kidneys, villi of the small intestine, and endocrine glands. Holes + basement membrane allows for passage of substances
  • Sinusoid: These capillaries have open spaces between cells and the basement membrane to facilitate easy passage of substances. Sinusoids are found in the liver and the spleen.
83
Q

Capillary Exchange

A

Capillaries are specialized for exchange of materials.

  • Oxygen, glucose, and other nutrients must be delivered to cells (filtration)
  • Carbon dioxide, acid, uria, and other wastes must be carried away to be excreted (reabsorption)
84
Q

Starling’s Law of the Capillary

A

Delivery of nutrients to tissue depends on blood pressure at capillary (like water pressure in pipes: hydrostatic pressure)

  • This is opposed by the concentration force of water trying to dilute out higher concentrations of solutes in blood. (interstitial fluid osmotic pressure)
  • The balance between these forces is called the Starling forces and the equation which relates them is called Starling’s Law of the Capillary.
  • Interstitial fluid osmotic pressure is about the same throughout the capillary, but hydrostatic presssure drops. This means the capillary delivers nutrients on the arteriole side, and picks up wastes on the venule side.
85
Q

Capillary Exchange Process

A

At the arterial end of the capillary, forces favor filtration.

  • Blood hydrostatic pressure (pushing) generated by the pumping action of the heart. (Blood hydrostatic pressure decreases from 36 to 16 mmHg from the arterial to the venous end of the capillary).
  • Interstitial fluid osmotic pressure (pulling), which is constant at about 1 mmHg.

At the venous end, forces favor reaborption.

  • Blood colloid osmotic pressure (pulling) is due to the presence of plasma proteins to large to cross the capillary wall. (Average 36 mmHg throughout the capillary)
  • Interstitial fluid hydrostatic pressure (pushing) which is normally close to zero mmHg becomes a significant factor only in states of edema.

In a healthy individual, about 20 liters is filtered each day from the capillaries. About 17 liters per day is reaborbed and the remaining 3 liters is reabsorbed by the lypmhatic system.

86
Q

Autoregulation in Capillaries

A

The ability of capillaries to regulate blood flow is called autoregulation. Autoregulation is due to low oxygen in tissues. This increases the capillary blood flow:
- muscles undergoing metabolic demand
- brain in areas of greater neural activity
- skin autoregulates oxygen and nutrients; neural mechanisms control body temperature
- lungs operate in an opposite way:
low 02 leads to vasoconstriction
high 02 leads to vasodilation

87
Q

Precapillary Sphincters

A

Precapillary sphincters are collars of smooth muscle.

  • When these are relaxed, blood flows through capillary bed
  • When these are contracted, blood bypasses capillary bed and takes thoroughfare channel.
88
Q

What Neurotransmitters and Hormones are Vasoconstrictors in Blood Vessels?

A
  • Norepinephrine
  • Epinephrine
  • Antidiuretic Hormone (ADH)
  • Angotensin II
  • Endothelium-derived Factors (release in low blood flow)
89
Q

What Neurotransmitters and Hormones are Vasodilators in Blood Vessels?

A
  • atrial natriuretic peptide
  • nitric oxide
  • inflammatory mediators: histamine ( also increases capillary permeability), prostacylin, and kinins.
  • ethanol: inhibits ADH and vasomotor center
90
Q

Blood Flow

A

Blood flow is the volume of blood that flows through any tissue in a given time period.. Controlling the rate of blood flow is important. Blood that flows too slowly is prone to clots. It is also important for the body to control the rate of blood flow so that tissues, that are actively working, receive more oxygen, and inactive tissues receive less.

91
Q

Blood Flow According to Ohm’s Law

A 
Recall Ohm's Law:  V = I x R
- V is voltage, analogous to pressure
- I is current, analogous to flow rate
- R is resistance
Divide both sides by R:  I = V/R

Now in fluid:

  • V is the pressure difference between arteries and veins
  • Arterial pressure is PA
  • Venous pressure is Pv
  • Substitute these for V: I = PA-Pv / R = flow
92
Q

Resistance to Blood Flow According to Ohm’s Law

A

A related equation gives us the relationship between the radius of a vessel (r) and resistance to blood flow (R)

R = nL/r^4

n (with longer right side) is blood viscosity
L is length of all blood vessels in the body
both of these don’t change much
we can and do change r (the radius of a vessel)
- remember conductance = I/R, so conductance is related to the radius of the vessel to the fourth power: flow a r^4
- the symbol a (alpha) means “is proportional to”
- that is, flow = a constant times r^4

93
Q

Viscosity

A

R = nL/r^4

This equation tells us that blood viscosity (n) increases resistance. The thicker the blood, the more resistant blood flow will be, putting the patient at increased risk for clots.

94
Q

Length of Blood Vessels in the Body

A

The more fat we accumulate, the more blood vessels are needed to feed those fat cells. So obese individuals have greater resistance to flood flow which, in turn, increases blood pressure.

95
Q

Radius

A

r^4 stands for the radius of a vessel raised to the 4th power. As the radius or diameter of the vessel gets bigger, resistance decreases.

Ex. If a vessel vasodilates and the diameter doubles in size, if we plug 2 into the equation: 2^4 or 2x2x2x2
A blood vessel with a diameter that is twice as big has 16 times the flow rate! Thus, a small change in blood vessel diameter has a large effect on blood flow.

96
Q

Decreased Elasticity in Arteries

A

As our arteries age they lose elasticity. Plaque accumulation in the arteries also affects elasticity. This greatly affects the ability of the arteries to vasodilate or vasoconstrict and regulate blood flow. Consequently, blood pressure rises and we develop hypertension.
- Vessel diameter depends on the action of smooth muscle in arteries, arterioles and capillaries.

97
Q

Laminar Flow

A

Laminar flow describes the most efficient way liquids (such as blood) can flow.

  • Friction with walls of vessel reduces velocity at edges
  • In the center of the vessel, flow is fastest
  • Flow rate is similar in concentric shells (laminae) so flow is called laminar.
98
Q

Turbulent Flow

A

Turbulent flow occurs when laminar flow is disrupted. A car hitting a guardrail then hitting other cars is similar to what can happen in the blood. This causes fluid levels to mix which is called turbulent flow. Turbulent blood flow can activate platelets, causing blood clots.

Turbulent Flow = Platelet Shearing = Blood Clotting

99
Q

Blood Pressure

A

Is usually measured in the larger conducting arteries (e.g. the brachial artery) where the high and low pulsations of the heart can be detected.

  • Systolic BP: is the higher pressure measured during left ventricular systole when the aortic valve is open.
  • Diastolic BP: is the lower pressure measured during left ventricular diastole when the aortic valve is closed.

A normal BP is less than 120mmHg systolic and less than 80 mmHg diastolic. People who are in good physical condition may have even lower BPs.

100
Q

Measuring Blood Pressure

A

When blood pressure is measured, the sphygmomanometer (blood pressure cuff) is inflated to a pressure greater than the systolic pressure of the blood. Blood flow is stopped and no sounds are heart.

  • Slowly releasing air in the cuff drops the cuff pressure and blood begins to flow. The first sound heard is the systolic blood pressure, now greater than the pressure in the cuff
  • Air continues to be released and the diastolic pressure is measured when no blood sounds are heard. The cuff pressure is now less than the diastolic pressure.
101
Q

Arterial and Venous pressures

A

Blood pressure is highest in the aorta as it leaves the heart. As blood travels through systemic circulation, it gets further away from the pump and pressure drops. So differences between systolic and diastolic pressure is greatest at the aorta

  • As blood passes from arterioles into capillaries, pressure drops to about 35 mmHg. We can no longer discern the differences between the systolic and diastolic pressures.
  • This makes sense as we want the blood to move more slowly here so the exchange of gasses and nutrients can occur.
102
Q

Muscle’s part in Arterial and Venous Pressures

A

When blood gases get to the venous system, blood pressure is very low. The blood needs help to run uphill and get back to the heart. Muscles act a pumps to help venous blood return to the heart. The closing of valves in the veins prevents the blood from running back downhill. Changes in pressure during inhalation also draws venous blood back up towards the heart.

103
Q

Hypertension

A

Hypertension is an elevated systemic arterial blood pressure that is consistently elevated over time. Systolic blood pressures over 140 mmHG, and/or a diastolic pressure over 90 mmHg is considered hyertensive.

104
Q

Prehypertension

A

Is a category used to indicate an individual at risk of developing hypertension. Systolic pressures of 121-139, and diastolic pressures of 81-89 are classified as prehypertensive

105
Q

Hypotension

A

Hypotension or low blood pressure is blood pressure that is too low to adequately deliver oxygen and nutrients to vital organs. Hypotension is typically defined by signs and symptoms rather than by blood pressure numbers.

106
Q

Atherosclerosis

A

Atherosclerosis, the build up of fatty plaque in the arteries affects blood pressure in two ways:

  1. It causes a decrease in elasticity of arteries
  2. It causes a decrease in the diameter of arteries

If a vessel loses half of its diameter, blood flows 16 times slower. The heart has to work harder to overcome this resistance, and blood pressure goes up.

107
Q

Shock

A

Shock is a failure of the cardiovascular system to deliver enough oxygen and nutrients to meet cellular needs. The body utilizes a negative feedback loop to raise blood pressure. Homeostatic mechanisms can compensate for as much as 10% of total blood loss.

108
Q

Responses to Falling Blood Pressure

A

Baroreceptors in the kidneys and aorta sense falling blood pressure. Responses include:

  • Renin release initiates the renin-angiotensin-aldosterone system which acts to release aldosterone leading to conservation of salt and water in the kidneys and vasoconstriction of vessels.
  • ADH release which conserves water from the kidneys
  • Increased sympathetic response causing an increase in heart rate and contractility and vasoconstriction.

The net result is to raise blood pressure

109
Q

Baroreceptor Reflex

A

The baroreceptor reflexes are homeostatic loops that regulate blood pressure.
- Baroreceptors sensing pressure are located in the aorta, internal carotid arteries, and other large arteries in the chest and neck

110
Q

Response to an Increase in Blood Pressure

A

An increase in blood pressure is detected by stretching at the baroreceptors. Impulses are sent at a faster rate to the cardiovascular center in the medulla. The response is:

  1. Nerves from the medulla increase parasympathetic stimulation by the vagus nerve and decrease sympathetic stimulation.
  2. Rate of impulses on sympathetic neurons to the vessels slow, causing vasodilation. Blood pressure drops as a result.
111
Q

Response to a Decrease in Blood Pressure

A

When blood pressure is low, baroreceptors are stretched less and send impulses at a slower rate. The response is:

  1. The cardiovascular center decreases parasympathetic stimulation and increases sympathetic stimulation.
  2. Adrenal medulla increases secretion of epinephrine and norepinephrine
  3. Blood vessels constrict, and blood pressure increases as a result
112
Q

Chemoreceptor Reflex

A

Chemoreceptors sense the chemical composition of the blood. They are located close to the baroreceptors in the carotid bodies (where the carotid artery splits) and the aorta.

  • Chemoreceptors detect O2, CO2, and H+ levels.
  • Under conditions of hypoxia (low O2), acidosis (high H+ levels), or hypercapnia (hyper CO2), signals are sent to teh Cardio vascular center of the medulla. The response is an increase in sypathetic stimulation to arterioles and veins causing vasoconstriction and increasing blood pressure

Signals are also sent to the respiratory center to adjust the depth and rate of breathing.

113
Q

Sympathetic Control of Blood Pressure

A

Arteries have this layers of smooth muscle. This muscle is responsive to sympathetic stimulation (epinephrine and norepinephrine). There are 3 types of receptors:

  • alpha-1 adrenergic receptors: cause vasoconstriction
  • alpha-2 adrenergic receptors: cause vasoconstricion
  • beta-2 adrenergic receptors: cause vasodilation

Vasoconstriction increases blood pressure
Vasodilation decreases blood pressure

114
Q

Hormonal Control of Blood Pressure

A

Please review slide in Objective 29

115
Q

The Venous Reserve

A

About 60% of blood is in the venous system. If massive blood loss occurs, baroreceptors of carotid sinus signal emergency.

The nervous system can mobilize about 1 L blood from organs with venous reserves:

  • Spleen
  • Liver
  • Large abdominal veins
  • Venous plexi beneath skin
116
Q

Anastomosis

A

Arteries and veins often form anastomosis. (ana: backwards, stoma: mouth).

  • Mostly, arteries branch like a tree as they move away from the heart
  • At anastomoses, branches fuse often to provide a “backup plan” if one route of blood supply is blocked.

Ex. the cerebral arterial circle (Circle o Willis) is an example of an anastomosis (“backward mouth”).

117
Q

Upper Extremity Arteries

A

Blood supply to the head and upper extremity is different on the left and right:

  • Left: the left common carotid and left subclavian each arises as separate branch of the aortic arch.
  • Right: a single branch called the brachiocephalic trunk arises from the aortic arch and then divides into the right common carotid and right subclavian.
  • Brachial: the subclavian artery changes name as it crosses the clavical and becomes the axillary artery. As it crosses the plane of the shoulder joint, it changes name again to the brachial artery. The brachial branches further into the ulner and radial arteries.

Anatomy and Physiology 1111 (7 decks)

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