HUMAN PHYS CARDIO & CA2+

What are the 3 principal components that make up the circulatory system?

1. the heart (the pump)

2. the blood vessels (the pipes)

3. the blood (the fluid to be moved)

The cardiovascular system function is impacted by what?

endocrine system, nervous system, and kidneys

What are the 2 “loops” in the cardiovascular system?

systemic and pulmonary

What does the pulmonary loop do?

carries oxygen-poor blood to the lungs and back to the heart

What does the systemic loop do?

carries blood from the heart to the rest of the body

What is the cardiovascular system considered?

a “closed system",” leaks are bad

What are the 2 major division of the circulatory system?

pulmonary and systemic circuit

What side of the heart is the pulmonary circuit apart of and what does it do?

right, carries blood to lungs for gas exchange and back to heart

What side of the heart is the systemic circuit apart of and what does it do?

left, supplies oxygenated blood to all tissues of the body and returns it to the heart

What does it mean that the heart is a dual pump?

the heart functions as a dual pump, meaning the right side pumps deoxygenated blood to the lungs (pulmonary circulation), while the left side pumps oxygenated blood to the rest of the body (systemic circulation)

Describe the 4 aspects of the pulmonary circuit

1. right side of the heart

2. carries blood to lungs for gas exchange and back to heart

3. oxygen-poor blood arrives from superior and inferior venae cavae (attached to right atrium) → right ventricle

4. blood sent to lungs via pulmonary trunk (right and left pulmonary arteries)

Describe the 4 aspects of the systemic circuit

1. left side of heart

2. supplies oxygenated blood to all tissues of the body and returns it to the heart

3. fully oxygenated blood arrives from lungs via pulmonary veins (attached to left atrium) → left ventricle

4. blood sent to all organs of the body via aorta

What 5 things can blood vessels be divided into?

1. arteries (muscular and conduit)

2. arterioles

3. capillaries

4. venules

5. veins

All arteries do what?

carry blood away from the heart

All veins do what?

carry blood to the heart

In general, arteries carry what and veins carry what?

arteries: carry oxygenated blood and veins: carry deoxygenated blood

What is the exception to arteries carrying oxygenated blood and veins carrying deoxygenated blood?

the exception to this is the pulmonary arteries carry deoxygenated blood to the lungs to get oxygenated and the pulmonary veins carry oxygenated blood to the heart to get sent to the rest of the body

What 2 terms are used to describe blood supply to a tissue?

flow and perfusion

Define blood flow

the amount of blood flowing through an organ, tissue, or blood vessel in a given time (mL/min)

Define perfusion

the flow per given volume or mass of tissue in a given time (mL/min/g)

At rest, what is total flow like?

total flow is quite constant, and is equal to the cardiac output (5.25 L/min)

Blood pressure, resistance, and blood flow are all important for what?

delivery of nutrients and oxygen, and removal of metabolic wastes

What is hemodynamics and how do pressure and resistance affect blood flow?

refers to the physical principles of blood flow based on pressure and resistance. Blood flow (F) is directly proportional to the pressure difference (ΔP) divided by resistance (R), expressed as F ∝ ΔP/R. the greater the pressure difference between two points, the greater the flow; the greater the resistance, the less the flow

How is blood pressure determined?

cardiac output, blood volume, and resistance to flow

How is blood volume mainly regulated?

kidneys

What is the formula for cardiac output?

heart rate x stroke volume

What are the 3 things that contribute to resistance?

1. blood viscosity (affected by water volume and # of RBC)

2. total blood vessel length (how much tubing is needed)

3. blood vessel diameter (relaxed vessels decrease resistance, constricted vessels increase resistance; this is the biggest contributor to minute-to-minute control of resistance in the vascular system)

What is peripheral resistance?

the opposition to blood flow encountered in the blood vessels, primarily in the arterioles, away from the heart

What are the arterioles in regards to peripheral resistance? How much of total peripheral resistance do they produce?

most significant point of control of peripheral resistance and flow, produce half of the total peripheral resistance

What are 4 aspects of the arterioles?

1. on proximal side of capillary beds and best positioned to regulate flow into the capillaries

2. outnumber any other type of artery, providing the most numerous control points

3. more muscular in proportion to their diameter

4. highly capable of changing radius

What is the equation for resistance in blood vessels and what do the variables represent?

Resistance (R) is calculated as:
R = (8 × L × η) / (π × r⁴)
Where:

a. L = length of the vessel

b. η (h) = fluid viscosity

c. r = radius of the vessel

d. 8/π = mathematical constant

Where is the heart located?

in the mediastinum, between the lungs

Define base in regards to the heart

wide, superior portion of heart, large vessels attach here

Define apex in regards to the heart

tapered inferior end, tilts to the left

In adults, what is the average size of the heart?

weighs 10 ounces, 3.5 in. wide at base, 5 in. from base to apex. at any age, heart is the size of a fist

Define epicardium

the most superficial (outer) layer. it is the visceral layer of the serous pericardium

Define myocardium

the middle layer of the heart muscle. it is composed of cardiac muscle and forms the bulk of the heart mass. this is the layer that contracts

Define endocardium

the inner layer of the heart. it is of endothelium which rests on the thin layer of connective tissue. it is continuous with the lining of the blood vessels entering and leaving the heart

What are the 4 chambers of the heart?

1. right and left atria

2. right and left ventricles

What are 3 aspects of the right and left atria?

1. two superior chambers

2. receive blood returning to heart

3. auricles (see on surface) enlarge chamber

What are the 2 aspects of the right and left ventricles?

1. two inferior chambers

2. pump blood into arteries

What do the valves ensure?

one-way flow of blood through heart

Define atrioventricular (AV) valves

control blood flow between atria and ventricles

How many cusps does the right AV valve have?

three cusps (tricuspid valve)

How many cusps does the left AV valve have?

two cusps (mitral valve, formerly “bicuspid”)

Define chordae tendineae

cords connect AV valves to papillary muscles on floor of ventricles

What do the chordae tendineae and papillary muscles prevent?

prevent AV valves from flipping or bulging into atria when ventricles contract

What do the papillary muscles specifically do?

each papillary muscle has 2-3 attachments to heart floor (like Eiffel tower) to distribute physical stress, coordinate timing of electrical conduction, and provide redundancy

Define semilunar valves

control flow into great arteries; open and close because of blood flow and pressure

Where is the pulmonary semilunar valve located?

in opening between right ventricle and pulmonary trunk

Where is the aortic semilunar valve located?

in opening between left ventricle and aorta

Describe the basic path of blood flow

pulmonary trunk → left atrium → left ventricle → aorta → arteries → capillaries → veins → vena cavae → right atrium → right ventricle → pulmonary valve

How are the cardiac muscle cells of the myocardium arranged?

arranged in layers bound together and completely encircle the blood-filled chambers

What happens when the walls of a chamber contract?

they come together like a squeezing fist and exert pressure on the blood they enclose

What is implied when it is said that every heart cell contracts with every beat of the heart?

the heart cells don’t get much rest

Why is it difficult for the heart to recover from a heart attack?

because the heart has a very limited ability to replace its muscle cells, only about 1% of myocytes are renewed each year, making recovery from heart attack–induced cell death very challenging

Define cardiomyocytes

straited, short, thick, branched cells, one central nucleus surrounded by light-staining mass of glycogen

The repair of damage of cardiac muscle is almost entirely by what?

fibrosis (scarring)

Define intercalated discs

join cardiomyocytes end to end with 3 features: interdigitating folds, mechanical junctions, and electrical junctions

Define interdigitating folds

folds interlock with each other, and increase surface area of contact

What do mechanical junctions do?

tightly join cardiomyocytes

Define fascia adherens

broad band in which actin of the thin myofilaments is anchored to the plasma membrane. each cell is linked to the next via transmembrane proteins. fascia adherens are anchoring junctions in intercalated discs that link cardiac muscle cells together using cadherin proteins, which connect to the actin cytoskeleton, transmitting mechanical force during contraction

Define desmosomes

mechanical linkages that prevent contracting cardiocytes from being pulled apart from each other

Define electrical junctions (gap functions)

allow ions to flow between cells; can stimulate neighbors. entire myocardium of either two atria or two ventricles act like single, unified cell

Cardiac muscle depends almost exclusively on what?

aerobic respiration to make ATP. rich in myoglobin and glycogen. huge mitochondria: fill 25% of cell

How is cardiac muscle adaptable to different organic fuels?

fatty acids (60%); glucose (35%); ketones, lactic acid, and amino acids (5%). more vulnerable to oxygen deficiency than lack of a specific fuel

How are cardiac muscles fatigue resistant?

they make little use of anaerobic fermentation or oxygen debt mechanisms. does not fatigue for a lifetime

What is ischemia and how can it lead to a myocardial infarction?

ischemia is reduced blood flow and oxygen delivery to tissue. In the heart, prolonged ischemia can cause myocardial infarction (heart attack) due to the death of cardiac muscle cells

Describe the 4 key aspects of cardiac communication

1. About 1% of cardiac cells are non-contractile but specialized for electrical conduction, forming the heart’s conducting system.

2. These conducting cells are not nerves, but modified muscle cells that are in electrical contact with contractile cardiac muscle cells via gap junctions in the intercalated discs.

3. The conducting system functions to initiate the heartbeat (e.g., SA node) and rapidly spread the electrical impulse through the heart to coordinate contraction.

4. Some specialized atrial cells also produce the hormone atrial natriuretic peptide (ANP), which plays a role in regulating the concentration of Na+ in the extracellular fluid

What are the 5 steps in the conduction system?

1. SA node fires

2. excitation spreads through atrial myocardium

3. AV node fires

4. excitation spreads down AV bundle

5. Purkinje fibers distribute excitation through ventricular myocardium

What does the conduction system do?

coordinates the heartbeat and generates and conducts rhythmic electrical signals

In the conduction system, describe what is composed in the coordinating of the heartbeat

composed of an internal pacemaker and nerve-like conduction pathways through myocardium

What is the role of the sinoatrial (SA) node in the cardiac conduction system?

the SA node, located in the right atrium near the base of the superior vena cava, is made of modified cardiomyocytes and acts as the pacemaker of the heart. It initiates each heartbeat, determines the heart rate, and spreads electrical signals throughout the atria via internodal pathways

What are the 3 aspects of the atrioventricular (AV) node?

1. located near the right AV at lower end of interatrial septum

2. electrical gateway to the ventricles

3. fibrous skeleton of the heart acts as an insulator preventing currents from getting to ventricles by any other route

What are the 2 aspects of the atrioventricular (AV) bundle (bundle of His)?

1. bundle forks into right and left bundle branches

2. branches pass along length of interventricular septum toward apex

What are the 2 aspects of the Purkinje fibers?

1. nerve-like processes spread throughout ventricular myocardium

2. cardiomyocytes then pass signal from cell to cell through gap functions

Where does the electrical signal for heart excitation originate, and at what rate?

the signal starts at the SA node, generating about 75 signals per minute under normal resting conditions

How does the depolarization wave travel from the SA node to the AV node?

the wave travels via gap junctions along the internodal pathway to reach the AV node

Why is there a delay at the AV node, and how long is it?

there is a 0.1-second delay at the AV node to allow the atria to contract and fully fill the ventricles before ventricular contraction begins

After the AV node, where does the depolarization wave travel?

it moves through the AV bundle (bundle of His) and then down to the Purkinje fibers

What is the path of the Purkinje fibers, and what do they stimulate first?

the Purkinje fibers travel to the apex of the ventricular septum and then turn upward. They also supply the papillary muscles, which contract before the ventricles to help prevent valve backflow

What does the cardiac action potential only include?

myocardium only; heart muscle cells

What is the stable resting potential of cardiocytes and when does it depolarize?

-90 mV, and depolarize only when stimulated

What are the 3 phases of cardiocyte action potential?

depolarization, plateau, repolarization

Describe the 3 aspects of the depolarization phase (very brief) of the cardiocyte action potential

1. stimulus opens voltage-gated Na+ gates (Na+ rushes in, positive feedback), membrane depolarizes rapidly

2. Na+ influx/ permeability transient because Na+ becomes inactive quickly

3. action potential peaks at +30 mV

Describe the 4 aspects of the plateau phase of a cardiocyte action potential

1. lasts 200 to 250 ms, sustains contraction for expulsion of blood from heart

2. voltage-gated slow Ca2+ channels (L-type channels) open admitting Ca2+ which triggers opening of Ca2+ channels on sarcoplasmic reticulum (SR)

3. Ca2+ (mostly from the SR) binds to troponin triggering contraction

4. Ca2+ entry in just balances K+ exit

Describe the 3 aspects of the repolarization phase of the cardiocyte action potential

1. eventual inactivation of L-type Ca2+ channels, voltage-gated K+ channels open, rapid diffusion of K+ out of cell returns it to resting potential (close via negative feedback in response to membrane being repolarized to negative values)

2. has a long absolute refractory period of 250 ms (compared to 1 to 2 ms in skeletal muscle)

3. prevents wave summation and tetanus which would stop the pumping action of the heart

What are the 5 basic steps of the electrical behavior of the myocardium?

1. Na+ channels open

2. rapid depolarization

3. Na+ gates inactivate

4. slow Ca2+ channels (L-type) open

5. Ca2+ gates inactivate, K+ channels open (repolarization)

What are node cells and what is their role in heart function?

are specialized cardiac cells with automaticity, meaning they can generate spontaneous electrical impulses. They are found in the SA node, AV node, AV bundle, bundle branches, and Purkinje fibers. In a healthy heart, the SA node acts as the pacemaker, initiating electrical signals that trigger contraction. Damage to the SA node or surrounding heart tissue can disrupt this conduction system and lead to rhythm problems

How is the SA node excited and what type of cells generate the pacemaker potential?

the SA node contains modified cardiomyocytes that do not contract but instead generate and conduct electrical signals. These cells produce a pacemaker potential through hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels, which are influenced by cAMP. This allows them to spontaneously depolarize and initiate each heartbeat

What are the 6 key steps involved in SA node pacemaker potential and action potential generation?

1. Unstable resting membrane potential: Begins at –60 mV and slowly depolarizes due to Na⁺ inflow via HCN (F-type) channels, also known as hyperpolarization-activated, cyclic nucleotide-gated channels.

2. Pacemaker potential: Slow depolarization caused by Na⁺ entry, influenced by cAMP.

3. T-type Ca²⁺ channels open: Provide a brief "boost" to help the membrane reach threshold (~–40 mV).

4. L-type Ca²⁺ channels open: Trigger rapid depolarization (action potential), peaking around 0 mV. This Ca²⁺ influx drives the action potential (unlike neurons, which use Na⁺).

5. K⁺ channels open: Repolarization occurs as K⁺ exits the cell.

6. Cycle restarts: After K⁺ channels close, the membrane potential returns to –60 mV and the next cycle begins.

The SA node fires spontaneously about every 0.8 seconds, setting the resting heart rate at ~75 bpm.

Why does the SA node fire first?

the SA node fires first because it has a high density of HCN (hyperpolarization-activated cyclic nucleotide-gated) channels, which allows for a faster depolarization due to the influx of Na⁺. This results in the pacemaker potential reaching threshold quicker than other parts of the heart, setting the heart rate

How does the impulse conduction work in the myocardium?

the signal from the SA node stimulates the atria to contract almost simultaneously and reaches the AV node in 50 ms. It then slows down through the AV node due to thin cardiocytes with fewer gap junctions, delaying the signal by 100 ms, allowing the ventricles time to fill before contracting

How does the impulse conduction progress through the ventricles?

signals travel quickly through the AV bundle of His, bundle branches, and Purkinje fibers, causing the entire ventricular myocardium to depolarize and contract nearly simultaneously

Why is the contraction of the ventricles coordinated?

ventricular systole progresses upward from the apex, with the spiral arrangement of the myocardium twisting the ventricles slightly, similar to wringing out a towel

Do the papillary muscles contract at the same time as the rest of the ventricles?

no, the signals reach the papillary muscles slightly later than the rest of the ventricular myocardium

What are the 6 steps heart innervation and by which neurotransmitters?

1. The heart is innervated by both sympathetic and parasympathetic nerve fibers.

2. The sympathetic nervous system (SNS) innervates the entire heart muscle and node cells, releasing norepinephrine (NE).

3. The parasympathetic nervous system (PSNS) primarily innervates the node cells and releases acetylcholine (ACh).

4. The receptors for NE on cardiac muscle are mainly beta-adrenergic receptors.

5. Epinephrine, released by the adrenal medulla, binds to the same beta-adrenergic receptors as NE and has the same effect on the heart.

6. The receptors for acetylcholine (ACh) are muscarinic receptors.

Where are muscarinic and beta-adrenergic receptors located in the heart, and what do they do?

1. Muscarinic receptors are primarily on SA and AV nodal cells in the atria and mediate parasympathetic effects (e.g., slowing heart rate).

2. Beta-adrenergic receptors are found on nodal and myocardial cells in both atria and ventricles, mediating sympathetic effects (e.g., increasing heart rate and contractility)

How do beta-adrenergic receptors influence cardiac cells?

1. Beta-adrenergic receptors are G protein-coupled receptors.

2. They bind norepinephrine (and epinephrine).

3. Activation leads to increased cAMP production via adenylyl cyclase.

4. cAMP acts as a second messenger to enhance the opening of HCN (funny) channels and L-type calcium channels, increasing heart rate and contractility.

How do muscarinic receptors affect the heart?

1. Acetylcholine (ACh) binds to muscarinic receptors on nodal cells.

2. These are G protein-coupled receptors (specifically Gi, inhibitory).

3. They inhibit adenylyl cyclase, decreasing cAMP levels.

4. This slows the opening of HCN channels, thereby lowering heart rate.