Physiology Unit 3

Intercalated Discs

interdigitating folds between cells; mechanical junction (desmosomes) + electrical junctions (gap junctions) = syncytium

gap junctions allow for low resistance 1/400 pathway for electrical signal to spread cell-to-cell

Specialized Cells

“leading”

low contractility, no stable RMP = reach TH sans neuronal stimulus

located in: SA node, internodal bundles, AV node, bundle of His, bundle branches + purkinje fibers

Contractile Cells

“following”

Capillaries

greatest total cross-sectional area (6000cm²) so blood flow velocity is slowest + most efficient

Veins

type of vessel where BP is lowest

Arterioles

vessel where BP will drop the most

Cardiac Output

HR x SV (mL/min)

proportional relationship to stroke volume and heart rate (SV + HR)

inverse relationship to total peripheral resistance (TPR)

Total Peripheral Resistance TPR

force the heart must overcome to push blood thru systemic circulation; main sources are vessel diameter, blood viscosity + vessel length

inversely proportional to cardiac output CO

Laminar Flow

blood cells in the center of a vessel flow faster; silent

Pulse Pressure

systolic - diastolic

Poiseuille’s Law

Fibrous Insulator

collagenous skeleton; rigid framework for dense regular connective tissue between atria and ventricles

gives delay + produces sequential events — allows time for electrical signal to spread thru atria for contraction, then for signal to spread thru ventricles for contraction

Sarcomeres

striated actin and myosin filaments

Pericardium

fibrous + serous sac surrounding heart, cushions / prevents friction b/c fluid

1. fibrous pericardium - outer, tough, dense connective tissue

   1. pericardial cavity filled w/ fluid

2. serous pericardium - inner, thin, double layer

Parietal Surface

lines inner surface of parietal pericardium; attached to diaphragm and base of heart

Visceral Surface

surrounds heart surface (epicardium)

External Epicardium

first heart wall layer, visceral pericardial layer

Myocardium

middle heart wall layer, cardiac muscle tissue

Endocardium

innermost heart wall layer; simple squamous epithelium, covers internal surfaces of the heart / external surface of heart valves

Chordae Tendineae

“heart strings", collagen fibers attached to lower surfaces of AV valve cusps; prevent valve cusps from flipping into atria during ventricular contraction

Papillary Muscles

muscular ridges anchoring chordae tendineae

Right Atria

auricle, smooth wall (posterior), pectinate muscles (ridges), crista terminalis (muscular ridge), fossa ovalis, coronary sinus, IVS, SVC openings, right AV valve

Left Atria

auricle, mostly smooth wall, pectinate muscle (anterior), left AV valve (chordae tendineae)

Lub

(S1) closing of AV valves

Dub

(S2) closing of semilunar valves

Fossa Ovalis

fetal = foramen ovale (small valve on left side closes d/t higher BP on left atrium side)

hole in atrial septum, most blood goes thru here; right → left shunt in systemic circuit

Ligamentum Venosum

fetal = ductus venosus (closes d/t increased pressure in portal vein forcing blood flow thru liver sinuses)

shunt: blood bypasses liver to heart

Ligamentum Arteriosum

fetal = ductus arteriosus (closes d/t oxygen change after umbilical cord removed, vessel constricts and closes)

pulmonary artery to aorta shunt; right → left shunt to systemic circuit

PDA Patent Ductus Arteriosus

ductus arteriosus fails to close after birth = blood repeatedly flows back to lungs

net CO decreases so blood volume increases to compensate (high EPO); L+R ventricular hypertrophy, murmur thru systole + diastole

cyanosis of left skull + upper limb

Tetralogy of Fallot

4 heart defects —

1. pulmonary valve stenosis = decreased outflow to lungs

2. R ventricular hypertrophy = pumping lotta blood

3. ventricular septal defect

4. aorta displaced over ventricular septum

septal defect d/t right → left shunt, most blood bypasses lungs = majority aortic blood is deoxygenated

AV Nodal Delay

Specialized Fibers

Contractile Fibers

SA SinoAtrial Node

first to depolarize, no stable RMP (never at rest)

leaky Na+ channels open as soon as depolarize → repolarize → open Na+ → rise to threshold

dont’t need voltage, strategically open sodium channels

70-80 depol/min → steepest potential (highest intrinsic rythym)

ANS innervation most dense

Purkinje Fibers

fast conduction d/t many gap junctions at intercalated discs

15-30 depol/minute → more gradual prepotentials

Prepotential

AKA pacemaker potential, unique to hear cells, generate own AP without stimulus

AV AtrioVentricular Node

delays depolarization b/c cells smaller in diameter, more resistance, slower movement of electrical signal to bundle branches

40-60 depol/min

Chronotropy

decreased by parasympathetic: Ca⁺⁺, Na⁺, K⁺

increased by sympathetic: Ca⁺⁺, Na⁺, K⁺

Inotropy

force / strength of contraction, muscle fiber tension development

sympathetic (NE) division affects in all fibers (specialized + contractile), parasympathetic has little affect

Baroreceptor Reflux

detect stretch in aorta + carotid body, too much =

high BP → high frequency AP down sensory neurons to medulla oblongata → integration center for cardioinhibotory center → vagus nerve to effector SA node of heart → mAChR

low BP → low frequency AP to cardioaccelatory center →parasympathetic nerve fibers → (nor)epinephrine increases rate of depolarization

Absolute Refractory Period

very long in heart cells to prevent summation + tetany; cardiac contractile cell begins relaxation

Latent Period

need Ca++ out of sarcoplasmic reticulum first, contraction happens after

very short in cardiac cell, allows muscle to start contracting during AP

SKELETAL MUSCLE Excitation Contraction Coupling

1. AP moves along T-tubule,

2. voltage change senses by Na+VCG,

3. signal communicated to VOCC, contraction occurs,

4. calcium pumped back into sarcoplasmic reticulum,

5. Ca++ binds to calsequestrin to facilitate storage,

6. contraction terminated

CONTRACTILE CARDIOCYTE Excitation Contraction Coupling

1. AP moves along large T-tubule

EDV

ESV

Preload

degree of muscle tension when it begins to contract

frank-starling principle: more in, more out

Afterload

contractile force needed for ejection; affected by peripheral vasculature

Contractility of Ventricle

availability of calcium, positive and negative intropoy (rare)

Diastis