Physiology of Cardiovascular System

The cardiac skeleton consists of 4 bands of

dense collagenous tissue - fibrous rings

central fibrous body/trigone - function

supports 4 valves + insulator that prevents contact bw myocardial cells and stops n impulses

layers of pericardium

fibrous (outermost) and serous (visceral and parietal)

pericarditis vs pericardial effusion

- inflammation of the pericardium, reducing pericardial fluid (friction)

- fluid accumulation, increased p, tamponade (wall collapse)

Myocytes arranged in

myofibrils - striated and branched

Myocytes in myocardium are connected by ________ that help them adhere to desmosomes

intercalated discs

Pores in myocardium that allow electric conductivity?

gap jxns of connexin proteins bw myocytes

layers of cells of endocardium

outer - n, v, purkinje fibers

middle - connective tissue

inner - endothelial cells

Which conducting tissue is normally suppressed instead of performing spontaneous action potentials

SA node

Electrophysiological cardiac cycle steps (3)

1. action potential in SA node

2. action potential thru atria then av bundle then ventricles (delay)

3. signal to bundle of His then Purkinje fibers to ventricular myocytes

How does action potential carry out

myocardium made of sarcomeres that contract if Ca+2 released from sarcoplasmic reticulum

What happens after action potential causes inward Ca+2 current?

triggers release more Ca2+ in sarcoplasmic reticulum, binds to troponin C, tropomyosin moves out and actin + myosin make cross-bridges

Relaxation of action potential occurs when

ca2+ reaccumulated in sarcoplasmic reticulum by Ca2+ ATPase

Ventricular diastole begins when

cardiac valves closed + ventricles relax

ventricular systole begins after

atrial systole, valves close

What happens in ventricular diastole

- ventricles relax + p falls

- valves open + blood flows from atria to ventricles

- v + p rises, atria contract (systole)

What happens in ventricular systole

- ventricular p rises, closing valves

- isovolumic contraction until aortic + pul valves open and blood ejected into circ

Stroke volume

The amount of blood ejected from the ventricle in one contraction

EJection fraction

the fraction of the end-diastolic volume ejected from the heart, measures ventricular efficiency/ contractility

cardiac output

the total volume of blood ejected from the ventricle per minute

Cardiac output depends on

stroke volume (v ejected on 1 beat) and heart rate (# beats/min)

Stressed volume

The volume of blood contained in the arteries

Smooth muscles in walls of arterioles are always

contracted (tonically active)

sympathetic adrenergic nerve fibers of arteriole's smooth muscle walls

a1 - in arterioles of vascular beds, vasoconstrictor

b2 - in arterioles of skeletal m, vasodilator

Lipid vs water-soluble substances thru capillary walls

lipid - cross by dissolving in and diffusing across

water - cross by clefts or pores of fenestrated caps

Blood flow thru vessel is determined by

pressure diff bw ends of vessel and resistance of vessel to blood flow

Total Peripheral Resistance (TPR)

the resistance to the flow of blood through the entire systemic circulation

Poiseuille's equation - resistance to flow is :

proportional to viscosity + length

inversely to r 4 of vessel

Series vs. Parallel resistance

series - total resistance equal to sum of individual resistances

parallel - resistance in parallel way less than individuals, no loss p in big a.

Korotkoff sounds

series of sounds that correspond to changes in blood flow through an artery as pressure is released (turbulent flow)

positive vs neg inotropy

pos - increase contractility, SV, CO

Pulse pressure

difference between systolic and diastolic pressure, reflects stroke volume

pulse pressure depends on

stroke volume and arterial compliance

Mean Arterial Pressure (MAP) (def + dependent on)

pressure forcing blood into tissues

- peripheral resistance and cardiac output

in the steady state, cardiac output from the heart equals

venous return to the heart

3 types of cardiac muscle + their levels of contractability

1. Atrial

2. Ventricular

3. Excitatory & conductive (low)

What do myocytes do with synaptic input from autonomic neurons?

use synapses to modulate (not initiate) electrical activity + contractile force of cardiac muscle

Myocytes are surrounded by __________ which delimits the __________

sarcolemma

sarcoplasm/cytoplasm

A vs I bands of myofibrils

dark regions (anisotropic)

light regions (isotropic)

I bands are divided in the middle by darker lines called

Z lines

Protein aggregates of sarcomere

contractile (actin and myosin), regulatory and structural proteins

structure of myosin

2 heavy chains in helix and 4 lights chains

2 types of myosin

a (higher atpase activity) and b (higher velocity contraction)

cross-bridges of myosin

protruding arms and heads, that bind to actin

3 isoenzymes of heavy chains

V1 - 2 a chains

V2 - a and b chains

V3 - 2 b chains

Which isoenzyme of heavy chains is dominant in atrial myocardium vs ventricular myocardium

V1 in atrial

all 3 in ventricular

2 types of actin (thin filaments)

globular (G, monomer) and fibrillar (F, in vivo)

Constitution of an actin molecule

2 G actins that make F actin - 2 F actins in helix

The main regulatory proteins of the sarcomere are represented by

tropomyosin and troponin (only in actin)

Where is tropomyosin bound when resting?

rest - active sites of actin (blocks interaction bw actin and myosin, no contraction)

protein subunits of troponin + roles

troponin C - binds Ca2+

troponin T - structural, binds troponin w/ tropomyosin

troponin I - inhibitory

What do the regulatory proteins do during contraction?

Ca+2 binds to troponin C, tropomyosin moves deeper into grooves bw actins, myosin sites uncovered

Function of titin

anchors thick myosin to Z line w/ its extensible part

power stroke

action of myosin pulling actin inward (toward the M line), when Ca2+ levels high

sliding filament mechanism

Myosin binds to actin when it breaks down atp (closer to backbone) . The myosin then alters its configuration, resulting in a "stroke" that pulls on the actin filament and causes it to slide across the myosin filament, sarcomere shortens

Sympathetic stimulation _________ activity of Ca+2 channels

increase

Activity of Ca2+ ATPase

energy from atp cleavage expels ca2+ from cell (against gradient), stimulated by calmodulin

Na+/Ca2+ exchanger

sarcolemmal protein w/ Transverse tubules that expulses ca2+

the passive release of Ca+2 from sarcoplasmic reticulum occurs thru

ryanodine-receptor channels in jxnal region of sarcoplasmic reticulum

What does Ca2+-dependent ATPase transport?

performs ca2+ reuptake into sarcoplasmic reticulum

phospholamban

regulatory protein in contractile myocardium that inhibits Ca2+ ATPase in the sarcoplasmic reticulum

Ca2+ storage in sarcoplasmic reticulum relies on binding to _________, a protein in jxnal region of SR

calsequestrin

____________ of myocyte plays a buffer role of intra/extracell Ca2+ concs

mitochondria

Action potential is caused by opening of 2 channels

- voltage-activated fast sodium channels (same as skeletal)

- L-type calcium channels (slow)

After the onset of action potential, what decreases in cardiac m membrane

permeability for K+ ions (less outflux)

At the end of plateau of cardiac action potential, what happens?

Ca+2 influx stops and they are pumped back out into SR and T tubule extracell space, sodium transported out

Phase 1: initial repolarization

-Na+ channels close

-K+ leave thru open K+ channels

Phase 2: plateau

Ca+2 channels open + influx, fast K+ channels close (efflux)

(+ brief repolarization)

Phase 3: Rapid Repolarization

Ca+2 channels close, slow K+ channels open

How is the T tubule system in cardiac muscle different from skeletal muscle?

T-tubules @ Z lines - part of extracell, helps in Ca+2 diffusion from extracell

Ca2+ induced Ca2+ release (CICR)

most important trigger for Ca+2 rise, increased Ca2+ in SR causes further release

Action potential is conducted via

T tubules in myocyte

_________ stimulation is the main physiological factor that modulates electro-mechanical coupling, related w/ β1-adrenergic receptors stimulation to induce ____________

sympathetic

phosphorylation (of channels, increase Ca2+)

absolute refractory period of heart

time during which normal cardiac impulse can't re-excite an already excite area, longer in ventricles