Ch 18 & 19 Human A&P 2

Shape and location of the heart?

Cone-shaped; located in the mediastinum

Where does the apex of the heart point?

Toward the left hip

Where does the base point?

Toward the right shoulder

Epicardium:

Outer layer of heart wall (visceral pericardium)

Myocardium:

Middle layer of heart wall ; cardiac muscle; contracts

Endocardium:

Inner lining of heart wall ; smooth endothelium

Right atrium receives blood from?

Superior & inferior vena cava

Right ventricle sends blood to?

Pulmonary trunk → lungs

Left atrium receives blood from?

Pulmonary veins

Left ventricle sends blood to?

Aorta → body

Function of valves?

Prevent backflow

Atrioventricular (AV) valves:

Tricuspid (right), Mitral (left)

Semilunar valves:

Pulmonary, Aortic

What prevents AV valve prolapse?

Chordae tendineae + papillary muscles

Blood Flow Pathway (simplified):

(Oxygen Poor) Right Atrium → Tricuspid → Right Ventricle → Pulmonary valve → Pulmonary trunk → Lungs → (Oxygen Rich) Pulmonary veins → LA → Mitral → LV → Aortic valve → Aorta

Why is heart a “double pump”? The right side is a pulmonary circuit pump and the left side is a systemic circuit pump.

Which ventricle has a thicker wall? What is the functional significance of this feature?

The left ventricle. The left ventricle can generate much more pressure than the right ventricle and is a far more powerful pump.

What is the function of the coronary circulation?

Supply the myocardium of the heart with nutrient- and oxygen-rich blood.

The cardiac veins drain venous blood from the myocardium

​​Which vessel empties into the right atrium?

Coronary sinus

Key features of cardiac muscle?

Striated, Branching cells, Intercalated discs

Which muscle type is self-excitable?

Cardiac

Function of gap junctions?

Electrical communication

Function of desmosomes?

Prevent cells from pulling apart

Describe two important consequences of the long plateau phase in the action potential of contractile cardiac muscle cells.

(1) (Ensures that contraction lasts long enough to efficiently eject blood from the heart),

(2) (Ensures that the absolute refractory period is long enough to prevent tetanic contractions)

What is the role of the intrinsic conduction system of the heart?

Coordinates the activity of the heart, ensuring that the heart beats as a unit.

It also serves as the pacemaker, setting the basic heart rate.

It initiates and distributes a wave of depolarization throughout the heart, so that it depolarizes and contracts in an orderly, sequential manner.

What is the role of the extrinsic innervation of the heart?

Can increase or decrease the heart rate depending on the needs of the body.

Which of the two subdivisions of the autonomic nervous system acts as the “accelerator” for heart rate?

Sympathetic

Increased sympathetic impulses increase heart rate and the force of contraction.

Which of the two subdivisions of the autonomic nervous system acts as the “brake” for heart rate?

Parasympathetic division.

Increased parasympathetic impulses decrease heart rate.

Pacemaker of heart?

SA node. Located in right atrial wall.

Conduction pathway:

SA node → AV node → AV bundle → bundle branches → Purkinje fibers

Why is AV node delay important?

Allows atria to finish contracting before depolarization hits ventricles.

P wave:

Atrial depolarization triggering contraction of atria. Initial bump

QRS complex:

Ventricular depolarization triggering contraction of ventricles.

Spikes in middle.

Also coincides with atrial repolarization.

T wave:

Ventricular repolarization triggering relaxation of ventricles.

Bump at end

How would a nonfunctional S A node affect the appearance of the E C G?

The P wave would be absent

​​Cardiac cycle:

(Sequence of events during one heartbeat consisting of one complete contraction and relaxation of the atria and the ventricles of the heart)

Systole:

Period of the cardiac cycle when a pair of heart chambers (usually ventricles) are contracting

Diastole:

Period of the cardiac cycle when a pair of heart chambers (usually ventricles) are relaxing

Which valves ensure one-way flow of blood from the atria to the ventricles?

(Atrioventricular (A V) valves)

AV Valves open when:

ventricular pressure (drops below) the atrial pressure.

AV Valves close when:

ventricular pressure (exceeds) the atrial pressure.

“Lub” sound:

AV valves closing

“Dub” sound:

Semilunar valves closing

When are all valves closed?

Isovolumetric phases

Cardiac output (C O):

(The amount of blood pumped out by each ventricle in 1 minute)

Heart rate (H R):

(The number of heart beats per minute)

Stroke volume (S V):

(The volume of blood pumped out by one ventricle with each heartbeat)

Cardiac Output (CO) Formula:

HR × SV

Stroke Volume (SV) Formula:

EDV (end diastolic volume) − ESV (end systolic volume)

Increase SV:

↑ EDV, ↑ contractility, ↓ ESV, ↑ Body Movement, ↑ ventricular filling, ↑ Thyroxine in blood

Decrease SV:

↑ afterload due to hypertension, ↓ venous return

Which autonomic division dominates at rest?

Parasympathetic

What is the intrinsic heart rate (number of beats/minute in the absence of autonomic regulation)?

100 beats/minute.

How do the sympathetic and parasympathetic divisions of the autonomic nervous system influence the intrinsic heart rate?

Activation of the sympathetic division during stressful situations increases heart rate above the intrinsic rate. The force of contraction also increases. The parasympathetic division opposes sympathetic effects and decreases heart rate.

Three layers of vessels?

Tunica intima (inner), Tunica media (smooth muscle), Tunica externa (outer)

Which layer controls diameter?

Tunica media

Arteries:

Away from heart, Thick walls, High pressure

Veins:

Toward heart, Valves, Blood reservoirs

What do capillaries do?

Exchange gases, nutrients, wastes

Elastic arteries:

Pressure reservoirs (aorta),

called conducting arteries,

largest diameter arteries,

convey blood to medium sized arteries

Muscular arteries:

Distribute blood to specific body organs,

called distributing arteries, (brachial artery),

thickest tunica media proportionally

Arterioles:

Resistance vessels (control flow), smallest of the arteries,

Why are capillaries called exchange vessels?

(Capillaries are called exchange vessels because they function in the exchange of materials (e.g., gases, nutrients, hormones, wastes) between the blood and the interstitial fluid.)

How do the structure and location of capillaries make them ideally suited for their function?

(The thin walls facilitate their role in the exchange of materials between blood and interstitial fluid.

In addition, most tissues in the body have a rich supply of capillaries.)

Continuous Capillaries: least permeable, The most common type of capillaries, Often have associated pericytes, Abundant in skin, muscles, lungs, and the central nervous system

Fenestrated Capillaries: filtration, Feature large fenestrations that increase permeability, Found in areas of active filtration or absorption

Sinusoid Capillaries: most permeable, Found in the liver, bone marrow, spleen, and adrenal medulla, Have large intercellular clefts and fenestrations but fewer tight junctions

microcirculation)

the flow of blood through a capillary bed from an arteriole to a venule.

a (terminal) arteriole branches into 10 to 20

(capillaries) that form the capillary bed.

Microcirculation flow

Terminal Arteriole → capillaries → postcapillary venule

Blood flows through the capillary bed when arterioles are

(dilated)

no blood flows through the capillary bed when arterioles are

(constricted).

(Veins compensate for low venous pressure with structural features that include:)

(1) (large-diameter lumens, which offer relatively little resistance to blood flow, and)

(2) (valves that prevent backflow of blood in the veins. In addition, constriction of the smooth muscle in the tunica media of a vein pushes blood toward the heart.)

Where is most blood stored?

Systemic veins

Anastomoses Function?

Alternate blood routes when the main route when the main route is blocked

Blood flow:

volume of blood flowing through a vessel, an organ, or the entire circulation in a given period (m l/min).)

Blood pressure:

Force per unit area exerted on a vessel wall by the contained blood;

Expressed in millimeters of mercury (m m H g).)

Resistance:

Opposition to flow and is a measure of the amount of friction blood encounters as it passes through the vessels.)

Blood flows from:

High → low pressure

High → low pressure

3 factors of resistance:

Vessel diameter (MOST important), Blood viscosity, Vessel length

Blood flow (F) is directly proportional to

the difference in blood pressure ( ) between two points in the circulation.

Blood flow (F) is inversely proportional to

the total peripheral resistance (T P R) in the systemic circulation.

Systolic pressure:

Pressure exerted by blood on the blood vessel walls during ventricular systole (the period of contraction);

this pressure is approximately 120 m m H g in healthy adults.)

Diastolic pressure:

Pressure exerted by blood on the blood vessel walls during ventricular diastole (the period of relaxation);

this pressure is approximately 70 to 80 m m H g in healthy adults.)

Pulse pressure:

Difference between the systolic and diastolic pressures.)

Mean arterial pressure (M A P):

Pressure that propels the blood to the tissues;

weighted average of the arterial pressure calculated from the systolic and diastolic pressures.)

Pulse Pressure =

Systolic Pressure - Diastolic Pressure

Mean Arterial Pressure (MAP) =

Diastolic Pressure + Pulse Pressure / 3

Highest pressure location?

Aorta

Biggest pressure drop?

Arterioles

Pulse disappears at?

Capillaries

Normal BP:

<120 / <80

Which pressure point could be compressed to help stop the bleeding from a laceration to the thigh?

Femoral artery

Describe in detail how blood pressure is typically measured by the auscultatory method.

(1) (Wrap the blood pressure cuff around the person’s arm, just superior to the elbow.),

(2) (Inflate the cuff until the cuff pressure exceeds systolic pressure.),

(3) (Reduce the cuff pressure gradually and listen with a stethoscope for sounds in the brachial artery distal to the cuff.),

(4) (The systolic pressure is read when the first soft tapping sounds are heard.),

(5) (The diastolic pressure is read when the sounds can no longer be heard.)

Why is it desirable to have low capillary blood pressure?

To force solute-containing fluids (filtrate) out of the blood and into the interstitial space.

higher would rupture the fragile capillaries.)

(Three functional adaptations that are critical to venous return are:)

(1) (the muscular pump,), (2) (the respiratory pump, and), (3) (sympathetic venoconstriction.)

Why might swollen ankles result from prolonged periods of standing?

a lack of activity in the skeletal muscles that surround deep veins in the lower limbs reduces venous return.

Vital signs:

BP, Pulse, Respiration, Temperature

Mean Arterial Pressure (MAP) =

Cardiac Output (CO) × Total Peripheral Resistance (TPR)