A&P II Exam 2

What are the three primary types of blood vessels and their functions?

Arteries – carry blood AWAY from the heart.

Capillaries – site of gas/nutrient exchange between blood and body cells.

Veins – carry blood TOWARD the heart.

Which of the following artery types functions in expanding and recoiling as blood pressure increases after heart contraction?

elastic artery

A patient is losing large amounts of blood (i.e., hemorrhage), which event will occur to compensate the drop in blood pressure?

The cardioacceleratory center will increase cardiac output.

All of the following blood vessels are inaccurately paired with their blood flow function EXCEPT:

capillaries --> site of exchange between the blood and tissues (cells)

Which of the following pathological terms describes a bulging in the blood vessel wall?

aneurysm

Blood vessels are made of tunics___. The tunica ___ the tunica comes into contact with blood, while the tunica___ contains the vasa vasorum.

media:intima:externa

Veins have a thicker Tunica Media than arteries.

False, Veins have a thicker Tunica Media than arteries.

Cardiac output equals the:

Heart rate multiplied by stroke volume.

All the following are dangerous consequences associated with an irregular conduction system EXCEPT:

autorhymicity

The PQ and ST segments of an ECG are associated with which electrical events of the cardiac myocytes?

atrial and ventricular plateau

All of the following structures are matched to their function accurately EXCEPT?

superior vena cava: returns blood to the left atrium

What is the direct effect of:

Both COand BP increase

Which valve prevents the backflow of blood into the left ventricle when the ventricles relax?

Aortic semilunar valve

During late ventricular systole:

The semilunar valves are open and the AV are valves closed.

The epicardium is another name for the:

Visceral layer of the serous pericardium.

The opening and subsequent closing of ALL heart valves is caused by:

pressure changes caused by the contraction and relaxation of heart chambers during the cardiac cycle.

Which vessel does NOT enter the atria of the heart?

Pulmonary artery

The pacemaker of the heart is considered to be the:

Sinoatrial node

False,A heart murmur is a normal sound that occurs when the AV valves are functional properly.

A heart murmur is a normal sound that occurs when the AV valves are functional properly.

Patient's blood pressure is: 155/98 What is the patient's MAP?

117 mmHG

Which chambers of the heart transport oxygenated blood?

Left atrium and ventricle

What does the T wave represent on an ECG?

Repolarization of both ventricles

Which of the following statements about the cardiac muscle is ACCURATE?

I. Cardiac muscle is striated.

Il. Cardiac muscle is innervated by the autonomic nervous system.

IlI. Cardiac muscle is composed of branching cells that form the myocardium.

V. Cardiac muscle cells are held together by microtubules.

I, II, III

A physician cuts open the heart as it lies in the thoracic cavity. The correct order of layers/spaces she would cut through would be:

• parietal pericardium, pericardial cavity, visceral pericardium, myocardium, endocardium

The hormone Epinephrine and NE is responsible for controlling which of the following events in the heart:

l. increase in heart rate

Il. decrease in stroke volume

Ill. increase in CO

IV. decrease in myocardium contraction

V. increase in myocardium contraction

I , III, and V

Bradycardia is defined as a condition in which the heart rate is faster than normal.

False, Bradycardia is defined as a condition in which the heart rate is faster than normal.

All of the following valves are inaccurately matched with their location within the heart, EXCEPT?

I. Pulmonary semilunar valve located between the Left Ventricle and Right Ventricle.

Il. Tricuspid valve located between the Right Atrium and Right Ventricle Ill. Bicuspid valve located between the Right Ventricle and Pulmonary Trunk IV. Aortic semilunar valve located between the Left Ventricle and Aorta

II and IV

A person has the following BP: 136/65. What is the Pulse Pressure?

71

Based on a pulse pressure of 30mm Hg, systolic pressure of 120mm Hg and a diastolic pressure of 90mm Hg, what is the Mean Arterial Pressure (MAP) of your patient? (MAP = diastolic pressure + (pulse pressure/3)

100 mmHg

Which of the following capillaries allows the free exchange of water, solutes, formed elements, and plasma proteins between the blood and interstitial fluid?

sinusoids

Blood colloid osmotic pressure is largely due to ______ and promotes ______

The proteins in the blood: reabsorption.

Scott was in a car accident and suffered a severe hemorrhage. In order for his body to restore homeostasis of blood pressure, his compensatory response did which of the following:

increased sympathetic stimulation to the heart and blood vessels

Which statement is true about blood vessels in the human body?

I. Capillaries are the site of gas and nutrient exchange.

II. Arteries always carry oxygenated blood.

III. Veins always carry deoxygenated blood.

IV. Arteries carry blood away from the heart.

V. Veins carry blood toward the heart.

I, IV٫ V

All of the following statements are false EXCEPT?

Sinusoid capillaries allow all components in blood to be exchanged between blood vessels and tissues.

The veins are known as the blood reservoir because, compared to arteries, they store a small amount of blood in the human body.

False, The veins are known as the blood reservoir because, compared to arteries, they store a small amount of blood in the human body.

Which of the following capillaries allows rapid exchange of water and large solutes via pinocytotic vesicles between blood and interstitial fluid?

continuous

To keep blood flowing out of the heart and to the body, the left ventricle must generate enough:

pressure to overcome afterload.

One of the functions of capillary exchange is to regulate fluid levels in the body. If too much fluid escapes from the capillary bed, enters the tissues, and is not returned to the cardiovascular system, blood volume and blood pressure will:

Decrease

Select the accurate description concerning the relationship of vessels and blood pressure.

As the size of the lumen decreases, resistance increases and blood pressure increases

Which of the following pathologies is caused by the collapse of a valve in the blood vessel?

varicose veins

Which of the following statements is accurate about the function of precapillary sphincters?

1. they control blood flow into the true capillaries.

2. they cause blood to flow directly from the metarteriole into the postcapillary venule.

3. they contract when the tissues needs have been met

4. All of the following are correct.

What is the general function of the cardiovascular system?

Transport blood throughout the body; allow gas exchange of substances between blood and body cells. Includes the heart and blood vessels.

What is the difference between oxygenated and deoxygenated blood?

Oxygenated blood: high in O2, low in CO2 (in systemic arteries and pulmonary veins).

Deoxygenated blood: high in CO2, low in O2 (in systemic veins and pulmonary arteries).

Define pulmonary circulation and systemic circulation.

Pulmonary: Right side of heart → lungs (gas exchange) → left side of heart.

Systemic: Left side of heart → body cells (cellular respiration) → right side of heart. Equal amounts of blood are pumped through both simultaneously.

What is edema and what causes it in the heart?

Edema is the accumulation of excess fluid in intercellular spaces. Cardiac edema results when the two ventricles pump unequal amounts of blood, causing fluid to back up into tissues.

Where is the heart located and how is it oriented?

Located in the mediastinum (middle compartment of the thoracic cavity), between the lungs. Slightly rotated so the right side is more anterior. Has an inferior apex and a superior base.

Name and describe the three layers of the pericardium.

1. Fibrous pericardium – outermost; dense irregular connective tissue; anchors heart, prevents overfilling.

2. Parietal layer of serous pericardium – lines inside of fibrous pericardium; simple squamous epithelium + areolar CT.

3. Visceral layer of serous pericardium (epicardium) – adheres to heart surface; same composition.

What is the pericardial cavity and what is its function?

Space between the parietal and visceral layers of serous pericardium, filled with serous fluid. The fluid lubricates the membranes to reduce friction as the heart moves.

Name the three layers of the heart wall from outside to inside.

1. Epicardium (= visceral layer of serous pericardium) – outermost.

2. Myocardium – middle; cardiac muscle; generates force to pump blood.

3. Endocardium – innermost; simple squamous epithelium + areolar CT; continuous with vessel lining.

Why is the left ventricular wall thicker than the right?

The left ventricle must generate high pressure to force blood through the entire systemic circulation. The right ventricle only pumps blood the short distance to the nearby lungs.

What are the three sulci (grooves) of the heart and what do they mark?

1. Coronary sulcus (atrioventricular) – separates atria from ventricles; encircles the heart.

2. Anterior interventricular sulcus – separates right and left ventricles on anterior surface.

3. Posterior interventricular sulcus – separates ventricles on posterior surface. All grooves contain coronary vessels.

Describe the internal features of the right atrium.

• Pectinate muscles on internal wall and auricle

• Fossa ovalis – oval depression on interatrial septum (remnant of fetal foramen ovale)

• Receives blood from SVC, IVC, and coronary sinus

• Blood exits through the Right AV (Tricuspid) valve into the right ventricle

Describe the internal features of the right ventricle.

Trabeculae carneae – irregular ridges on internal wall

• Papillary muscles – cone-shaped projections that anchor chordae tendineae

• Chordae tendineae – collagen fibers connecting papillary muscles to tricuspid valve cusps

• Blood exits through the pulmonary semilunar valve into the pulmonary trunk

Describe the internal features of the left ventricle.

• Trabeculae carneae on internal wall

• Papillary muscles anchor chordae tendineae to bicuspid/mitral valve

• Thickest walls of all four chambers

• Blood exits through the aortic semilunar valve into the aorta

What are the two types of heart valves? Describe each.

• AV (Atrioventricular) Valves – between atria and ventricles; close during ventricular contraction; held by chordae tendineae/papillary muscles.

• Tricuspid (right AV): 3 cusps, between right atrium and right ventricle

• Mitral/Bicuspid (left AV): 2 cusps, between left atrium and left ventricle

• Semilunar (SL) Valves – between ventricles and great arteries; 3 cusps; NO chordae tendineae.

• Pulmonary valve: right ventricle → pulmonary trunk

• Aortic valve: left ventricle → aorta

What are the heart sounds S1 and S2?

S1 ('lubb') – closing of AV valves at the beginning of ventricular systole.

S2 ('dupp') – closing of semilunar valves at the beginning of ventricular diastole.

Heart murmurs result from turbulent blood flow through a valve (valvular insufficiency = leaky; valvular stenosis = narrowed/scarred).

What are the functions of the fibrous skeleton of the heart?

1. Provides structural support between atria and ventricles

2. Forms rings that anchor the four heart valves

3. Provides framework for cardiac muscle cell attachment

4. Acts as an electrical insulator, preventing atria and ventricles from contracting simultaneously

Name the great vessels of the heart and each one's function.

• Superior Vena Cava (SVC) – drains upper body into right atrium

• Inferior Vena Cava (IVC) – drains lower body into right atrium

• Coronary Sinus – drains heart wall into right atrium

• Pulmonary Trunk – right ventricle → lungs

• Pulmonary Arteries (R and L) – pulmonary trunk → lung capillaries

• Pulmonary Veins (4) – lungs → left atrium

• Aorta – left ventricle → body cells

Trace blood flow through the entire heart in order.

Body → SVC/IVC → Right Atrium → Tricuspid Valve → Right Ventricle → Pulmonary Valve → Pulmonary Trunk → Pulmonary Arteries → Lungs (gas exchange) → Pulmonary Veins → Left Atrium → Bicuspid/Mitral Valve → Left Ventricle → Aortic Valve → Aorta → Body cells → back to SVC/IVC

Name the coronary arteries and the areas they supply.

Left Coronary Artery (LCA) branches:

• Anterior Interventricular (LAD/'widow maker') – anterior surface of both ventricles

• Circumflex artery – left atrium and left ventricle

Right Coronary Artery (RCA) branches:

• Right Marginal artery – right heart border

• Posterior Interventricular artery – posterior side of both ventricles

What are the coronary veins and where do they drain?

Great Cardiac Vein – runs alongside major coronary artery; drains to coronary sinus

• Middle Cardiac Vein – runs alongside major coronary artery; drains to coronary sinus

• Small Cardiac Vein – drains to coronary sinus

• Coronary Sinus – collects all venous blood and drains into the right atrium

What is the significance of coronary arteries being functional end arteries?

Although structural anastomoses exist, the connections are not sufficient to provide adequate collateral blood flow if one coronary artery is blocked. Therefore blockage leads to ischemia (oxygen deprivation) and possible myocardial infarction (heart attack). Coronary flow occurs during diastole (relaxation); during systole (contraction), vessels are compressed and flow stops.

What is a myocardial infarction?

A heart attack caused by sudden, complete occlusion of a coronary artery. The myocardium is deprived of oxygen, leading to potential cell death. Symptoms include excruciating chest pain radiating down the left arm, weakness, shortness of breath, nausea, anxiety, and sweating.

Describe the microscopic structure of cardiac muscle cells.

Short, branched cells with 1–2 nuclei

• Sarcolemma invaginates to form T-tubules (interact with sarcoplasmic reticulum)

• Myofilaments (thick and thin) give striated appearance

• Intercalated discs linking adjacent cells contain:

– Desmosomes: mechanical junctions preventing cells from pulling apart

– Gap junctions: protein pores allowing electrical connection (ion flow) between cells → functional syncytium

What is a functional syncytium and why is it important?

When gap junctions electrically connect cardiac muscle cells, the entire chamber functions as a single unit ('functional syncytium'). This allows synchronized, simultaneous contraction of all cells in a chamber, ensuring effective pumping.

How does cardiac muscle meet its energy needs?

•  Extensive blood supply and numerous mitochondria

• Uses multiple fuel sources: fatty acids, glucose, lactic acid, amino acids, ketone bodies

• Relies primarily on aerobic cellular respiration

• Contains myoglobin (O■ storage) and creatine phosphate (immediate energy)

• Highly susceptible to ischemia – loss of blood flow quickly causes cell death

Name all components of the cardiac conduction system in order.

1. SA Node (sinoatrial) – in right atrium wall; natural pacemaker; initiates heartbeat

2. AV Node (atrioventricular) – floor of right atrium; delays impulse 0.1 sec

3. AV Bundle (Bundle of His) – extends from AV node into interventricular septum

4. Bundle Branches (R and L) – travel down interventricular septum

5. Purkinje Fibers – spread through ventricular myocardium from apex upward

Why is there a delay at the AV node?

AV nodal cells have small diameter and fewer gap junctions, slowing conduction. The 0.1-second delay allows the atria to complete contraction and fill the ventricles with blood before the ventricles contract.

Compare sympathetic vs. parasympathetic innervation of the heart.

Sympathetic (Cardioacceleratory center – Medulla):

• Innervates SA node, AV node, myocardium, coronary arteries

• ↑ heart rate, ↑ force of contraction, coronary vessel dilation

• Neurotransmitters: Epinephrine and Norepinephrine

Parasympathetic (Cardioinhibitory center – Medulla):

• Travels via Vagus nerve to SA node and AV node only

• ↓ heart rate (vagal tone), ↑ AV node delay

• Neurotransmitter: Acetylcholine (ACh)

What is autorhythmicity and how do SA nodal cells achieve it?

Autorhythmicity = ability to spontaneously depolarize and fire action potentials without external stimulation. SA

nodal cells have an unstable resting membrane potential (RMP = -60 mV) called a 'pacemaker potential.'

3 events:

1. Voltage-gated cation channels open → Na■ enters → RMP rises from -60 to -40 mV (threshold)

2. Voltage-gated Ca²■ channels open → Ca²■ enters → depolarization (membrane goes positive)

3. Ca²■ channels close, K■ channels open → K■ exits → repolarization back to -60 mV

Cycle ~0.8s = ~75 bpm

How do nodal cells differ from neurons?

• Neurons require stimulation (neurotransmitters) to reach threshold; nodal cells spontaneously reach threshold

(pacemaker potential).

• Neurons depolarize due to Na■ entry; nodal cells depolarize due to Ca²■ entry.

Describe the action potential at the sarcolemma of cardiac muscle cells (3 phases).

Resting: RMP = -90 mV; maintained by Na■/K■ pumps, Na■ and K■ leak channels.

1. Depolarization: Voltage-gated Na■ channels open → Na■ rushes in → membrane becomes positive

2. Plateau: Voltage-gated Ca²■ channels open → Ca²■ enters → membrane stays depolarized (prolongs AP;

unique to cardiac muscle)

3. Repolarization: Ca²■ channels close; K■ channels open → K■ exits → returns to -90 mV

Key difference from skeletal muscle: the PLATEAU phase prolongs the action potential and extends the refractory

period.

What is the significance of the plateau phase in cardiac muscle?

The plateau (due to Ca²■ influx) prolongs the absolute refractory period. This prevents cardiac muscle from being re-stimulated before it fully relaxes, making tetanic (sustained) contraction impossible. This is essential so the heart can fill with blood between beats.

What are the components of a normal ECG and what does each represent?

• P wave – atrial depolarization (atria contract)

• QRS complex – ventricular depolarization (ventricles contract); atrial repolarization is hidden within QRS

• T wave – ventricular repolarization (ventricles relax)

• P-R interval – time from atrial depolarization to start of ventricular depolarization (includes AV delay)

• S-T segment – time ventricles are depolarized (between depolarization and repolarization)

• Q-T interval – total time of ventricular activity

List the 5 phases of the cardiac cycle in order.

1. Late diastole (filling) – all chambers relaxed; AV valves open; blood fills ventricles passively

2. Atrial systole – atria contract; AV valves open; ventricles finish filling (add ~20%)

3. Isovolumetric ventricular contraction – ventricles contract; ALL valves closed; pressure builds

4. Ventricular ejection – SL valves open; blood ejected into arteries

5. Isovolumetric ventricular relaxation – ventricles relax; ALL valves closed; pressure drops (Cycle then repeats from step 1)

What is ventricular balance and why is it important?

Both ventricles must eject exactly the same stroke volume each beat. If one pumps more than the other, blood accumulates in the pulmonary or systemic circuit, leading to pulmonary or systemic edema.

Define cardiac output and state its formula.

Cardiac Output (CO) = the volume of blood pumped by one ventricle per minute.

CO = Heart Rate (HR) × Stroke Volume (SV)

Normal resting CO ≈ 5.25 L/min (HR ~75 bpm × SV ~70 mL)

What is cardiac reserve?

The difference between resting cardiac output and maximal cardiac output. It represents the heart's ability to increase output during increased physical demand (exercise). Well-trained athletes have greater cardiac reserve.

What are chronotropic agents? Give examples.

Chronotropic agents alter heart RATE.

• Positive chronotropes increase HR: sympathetic NTs (epinephrine, norepinephrine), thyroid hormone, exercise,

fever, caffeine.

• Negative chronotropes decrease HR: parasympathetic NT (acetylcholine), certain drugs (beta-blockers). Bradycardia = HR < 60 bpm; Tachycardia = HR > 100 bpm.

What are the three variables that influence stroke volume?

1. Venous return (preload) – volume of blood returning to ventricle before contraction; ↑ venous return → ventricle stretches more → stronger contraction (Frank-Starling Law)

2. Inotropic effect (contractility) – force of contraction independent of preload; positive inotropes ↑ force (e.g., epinephrine, norepinephrine); negative inotropes ↓ force (e.g., ACh, calcium blockers)

3. Afterload – pressure the ventricle must overcome to eject blood; ↑ afterload → ↓ stroke volume (e.g., hypertension increases afterload)

State Frank-Starling's Law of the Heart.

The greater the stretch of the cardiac muscle (due to greater filling/venous return), the greater the force of contraction and the greater the stroke volume ejected. Within limits, the heart pumps whatever volume it receives.

Name and describe the three tunics (layers) of blood vessel walls.

1. Tunica Intima – innermost; endothelium (simple squamous); contacts blood; releases chemicals that regulate smooth muscle.

2. Tunica Media – middle; circularly arranged smooth muscle + elastic fibers; controls vasoconstriction/vasodilation.

3. Tunica Externa (Adventitia) – outermost; areolar CT, elastic and collagen fibers; anchors vessel to surrounding tissue; contains vasa vasorum in large vessels.

Compare arteries vs. veins structurally.

Arteries: narrower lumen, thicker tunica media, more elastic/collagen fibers, no valves, higher BP.

Veins: wider lumen, thicker tunica externa, less elastic fibers (collapses when empty), have valves, lower BP, contain ~65% of blood volume (capacitance vessels).

Compare the three types of arteries.

Elastic arteries: largest (aorta, pulmonary trunk); huge elastic fiber abundance → stretch during systole and recoil during diastole to propel blood; conducting arteries.

Muscular arteries: medium-sized; internal + external elastic laminae; more smooth muscle → greatervasoconstriction/dilation; distributing arteries (most named arteries).

Arterioles: smallest arteries; vasomotor tone; regulate systemic BP and local blood flow; resistance vessels.

Compare the three types of capillaries.

Continuous: complete lining with intercellular clefts; allows small molecules through; in muscle, skin, lungs, CNS.

Fenestrated: continuous + pores (fenestrations); allows larger molecules; in intestines, kidneys, endocrine glands.

Sinusoids: incomplete lining and basement membrane with large gaps; allows formed elements and large proteins; in bone marrow, liver, spleen.

Describe the components of a capillary bed.

• Metarteriole – vessel branch of arteriole feeding the capillary bed

• Thoroughfare channel – connects metarteriole to postcapillary venule; no smooth muscle; always open

• True capillaries – branch from metarteriole; bulk of capillary bed; controlled by precapillary sphincters

• Precapillary sphincter – smooth muscle ring controlling blood flow into true capillaries

• Postcapillary venule – drains the capillary bed

• Vasomotion – rhythmic cycle of sphincter contraction/relaxation; only 1/4 of capillary beds are open at any time

What is the relationship between cross-sectional area and velocity of blood flow?

As cross-sectional area increases, velocity decreases. Capillaries have the GREATEST total cross-sectional area, so blood moves SLOWEST through them. This is physiologically important: slow flow allows maximum time for gas and nutrient exchange.

What are the three mechanisms of capillary exchange?

As cross-sectional area increases, velocity decreases. Capillaries have the GREATEST total cross-sectional area, so blood moves SLOWEST through them. This is physiologically important: slow flow allows maximum time for gas and nutrient exchange.

What are the three mechanisms of capillary exchange?

1. Diffusion – most common; gases (O■, CO■), glucose, electrolytes, wastes move down concentration gradients.

2. Vesicular transport – pinocytosis and exocytosis; used for certain hormones and fatty acids.

3. Bulk flow – movement of large fluid volumes down a pressure gradient:

– Filtration: fluid moves OUT of capillary on arterial end (HP > COP)

– Reabsorption: fluid moves INTO capillary on venous end (COP > HP)

Define and contrast the pressures involved in bulk flow / net filtration pressure (NFP).

Blood Hydrostatic Pressure (HPb): force of blood against capillary wall → pushes fluid OUT (promotes filtration)

Interstitial Fluid Hydrostatic Pressure (HPif): ≈ 0 mmHg; opposes filtration

Blood Colloid Osmotic Pressure (COPb): plasma proteins pull fluid INTO blood (promotes reabsorption)

Interstitial Fluid COP (COPif): ≈ 5 mmHg; pulls fluid into interstitial space

NFP = (HPb − HPif) − (COPb − COPif)

Arterial end: (35−0)−(26−5) = +14 mmHg → FILTRATION

Venous end: (16−0)−(26−5) = −5 mmHg → REABSORPTION

Lymphatics pick up the ~15% of fluid not reabsorbed.

What factors regulate local blood flow?

1. Degree of vascularization (angiogenesis over weeks/months increases capillary density)

2. Myogenic response – if pressure ↑, smooth muscle contracts (vasoconstriction) to maintain flow; if pressure ↓,

muscle relaxes (vasodilation)

3. Local paracrine factors – metabolites (↑CO■, ↑lactic acid, ↑H■, ↓O■) cause vasodilation (autoregulation);

histamine, bradykinin, nitric oxide → vasodilation; leukotrienes, thromboxanes → vasoconstriction

4. Total blood flow (cardiac output) sets the maximum available

What is autoregulation of local blood flow?

The process by which a tissue controls its own local blood flow based on metabolic needs. When metabolic activity increases, O■/nutrients decline and CO■/lactic acid/H■/K■ increase — these act as vasodilators, increasing flow to the tissue. This is a negative feedback system.

Define systolic, diastolic, pulse pressure, and MAP. Give formulas.

Systolic pressure – arterial pressure when ventricles CONTRACT (e.g., 120 mmHg)

Diastolic pressure – arterial pressure when ventricles RELAX (e.g., 80 mmHg)

Pulse pressure = Systolic − Diastolic (e.g., 120−80 = 40 mmHg); reflects vessel elasticity

MAP (Mean Arterial Pressure) = Diastolic + (1/3 × Pulse Pressure)

Example: 80 + (1/3 × 40) = 93 mmHg

Normal MAP = 70–110 mmHg; below 60 is dangerous.

What mechanisms help venous blood return to the heart against low pressure?

1. Skeletal muscle pump – contracting muscles squeeze veins, propelling blood toward heart; valves prevent

backflow.

2. Respiratory pump – inspiration: diaphragm contracts → ↑ abdominal pressure, ↓ thoracic pressure → blood

driven from abdomen toward chest; expiration reverses this. Increased breathing rate ↑ venous return.

3. Venous valves – prevent backflow

4. Venoconstriction (sympathetic tone)

How does resistance affect blood flow? What three factors influence resistance?

Resistance opposes blood flow. As resistance increases, blood flow decreases (inverse relationship). Blood pressure must increase to maintain flow against higher resistance.

3 factors:

1. Blood viscosity – ↑ viscosity (e.g., dehydration, blood doping) → ↑ resistance; ↓ viscosity (anemia) → ↓

resistance

2. Vessel length – ↑ length (e.g., weight gain) → ↑ resistance

3. Vessel radius – MOST IMPORTANT; ↓ radius (vasoconstriction) → ↑ resistance; ↑ radius (vasodilation) → ↓

resistance (Poiseuille's Law: R ∝ 1/r■)

Describe the short-term (neural) regulation of blood pressure.

Cardiovascular Center in the Medulla Oblongata has two components:

Cardiac Center:

• Cardioacceleratory (sympathetic) → ↑ HR, ↑ force, ↑ CO → ↑ BP (via epinephrine/NE)

• Cardioinhibitory (parasympathetic via vagus) → ↓ HR → ↓ CO → ↓ BP (via ACh)

Vasomotor Center (sympathetic):

• Vasoconstriction → ↑ peripheral resistance → ↑ BP

• Also moves blood from venous reservoir into circulation

Sensory input via baroreceptors (in carotid sinus and aortic arch) detects stretch from pressure changes and

provides negative feedback to the cardiovascular center.

Describe the baroreceptor reflex for both a decrease and increase in blood pressure.

DECREASE in BP:

↓BP → ↓vessel stretch → ↓baroreceptor firing → Cardioacceleratory activated, Vasomotor activated,

Cardioinhibitory inhibited → ↑CO + ↑R → ↑BP

INCREASE in BP:

↑BP → ↑vessel stretch → ↑baroreceptor firing → Cardioinhibitory activated, Cardioacceleratory inhibited,

Vasomotor inhibited → ↓CO + ↓R → ↓BP

Describe the role of chemoreceptors in blood pressure regulation.

Peripheral chemoreceptors in the aortic bodies (vagus nerve) and carotid bodies (glossopharyngeal nerve) detect ↑CO■, ↓pH (↑H■), and very low O■.

They stimulate the vasomotor center → vasoconstriction → ↑BP and shift blood to the lungs for CO■ removal and pH correction.

Describe hormonal regulation of blood pressure (4 hormones).

1. Angiotensin II (most powerful) – from RAAS; vasoconstriction, stimulates thirst, ↓urine output, triggers

aldosterone and ADH → ↑BP

2. Aldosterone – from adrenal cortex; ↑Na■ and water reabsorption in kidneys → ↑blood volume → ↑BP

3. ADH (vasopressin) – from posterior pituitary; ↑water reabsorption, stimulates thirst, vasoconstriction → ↑BP

4. Atrial Natriuretic Peptide (ANP) – from atria when walls are stretched (↑blood volume); vasodilation + ↑urine output → ↓BP (the only one that DECREASES BP)