A&P Heart & Blood Vessels

Chambers of Heart (4)

2 Atria (Atrium - singular)-R & L separated by interatrial septum Receiving chambers Thinner, muscular walls Auricles (ears)-extensions of atria Each atrium communicates with a ventricle

The Heart as a Pump

A. Cardiac cycle-all the events associated with the flow of blood in one complete heartbeat Systole-contraction, pushes blood Diasatole-relaxation, chambers fill **atrial systole and diastole, followed by ventricular systole and diastole

Functional Anatomy of Heart

A. Coronary circulation -4% of all blood of systemic circuit supplies myocardium Heart requires almost 10% of all O2 that goes to body tissues L ventricle → Aorta→Coronary arteries →Cor. capillaries→Cor. veins→Cor. sinus→right atrium -Anastosmoses- many interconnections that allow for constant pressure to myocardium Coronary by-pass surgery- due to coronary artery disease Myocardial Infarction-AKA MI or heart attack; infarct=area of dead tissue

Valves - one-way blood flow:

Atrioventricular valves - consist of connective tissue flaps with surface endothelium. Tricuspid - 3 "cusps" - prevents backflow from R. ventrical to R. atrium . Bicuspid (Mitral)- 2 "cusps" - prevents backflow from L. Ventricle to L. atrium. Chordae tendineae-"Heart strings", attached to cusps of AV valves & connected to... Papillary muscles-contract & prevent the AV valves from everting (prevents backflow of blood)

Pulmonary System (circuit)

Blood flow to & from capillaries of lungs R Ventricle→Pulmonary trunk →Pulm. arteries →Pulm. capillaries → Pulm. veins → L atrium -pulmonary veins are O2 rich and CO2 poor

Path of blood flow: Cont

Blood leaves Right Ventricle via Pulmonary Trunk (begins Pulmonary Circulation). The Pulmonary Semilunar Valve guards base of pulmonary trunk which splits into right and left Pulmonary Arteries (carrying deoxygenated or "blue" blood). Pulmonary arteries supply the lungs and branch into pulmonary capillaries. Respiratory capillaries drain into Left and Right Pulmonary Veins carrying oxygenated blood to the Left Atrium. Blood flows into the Left Ventricle through the Left Atrioventricular Valve (AKA Left AV Valve or Bicuspid or Mitral Valve).

Path of blood flow: Cont 2

Blood leaving the left ventricle passes through the Aortic Semilunar Valve into the Systemic Circuit via the Ascending Aorta which branches to arteries to arterioles to service capillaries which deliver oxygenated blood to the tissues.

pulmonary semilunar valve

The pulmonary semilunar valve prevents backflow from the pulmonary trunk into the right ventricle. The PSV is pushed open when right ventricular BP exceeds pulmonary trunk BP. When pulmonary trunk BP exceeds right ventricular BP, blood fills the leaflets of the PSV and closes the valve.

Circulatory System - like a figure 8 with the heart in the middle

like a figure 8 with the heart in the middle Arteries -efferent vessels, carry blood away from the heart Veins - afferent vessels, carry blood to the heart Capillaries -smallest vessels, connecting arteries & veins

Mitral valve prolapse-

mitral valve cusps do not close properly Heart murmur-sound of regurgitation (back flow) into LA (mitral)

Cardiodynamics

-movements and forces generated during cardiac contractions

Semilunar valves-

-separate the ventricles from their great vessels. Aortic valve - 3 leaflet valve; prevents backflow from the Aorta to the L. ventricle. Pulmonary valve - 3 leaflet valve; prevents backflow from the Pulmonary trunk to the R. ventricle.

C. Sensory Receptors

- Baroreceptors or pressoreceptors, (in carotid arteries, aortic arch, vena cava and RA) - respond to changes in systemic blood pressure - reflex control of heart rate - Chemoreceptors - respond to changes in dissolved O2 and CO2

Aortic semilunar valve

The aortic semilunar valve prevents backflow from the aorta into the left ventricle. The ASV is pushed open when left ventricular BP exceeds aortic BP. When aortic BP exceeds left ventricular BP, blood flows back towards the ventricles, fills the leaflets of the ASV and closes the valve.

B. Regulation of Stroke Volume

- heart pumps ~ 60% of the blood that enters its chambers - at beginning of cardiac cycle, before ventricular systole, left ventricle contains ~120ml blood = End Diastolic Volume (EDV) - after ventricular systole: End Systolic Volume ESV = 50ml blood (is blood left over)

B. Heart Sounds "lubb-dup"

Auscultation- listening to heart sounds Lubb- longer, beginning of ventricular systole, AV valves close and semilunars open Dup-beginning of ventricular diastole, semilunars close

B. Intrinsic Conduction System - "built in"

Automaticity or autorhythmicity- cardiac muscle tissue contracts on its own in absence of neural or hormonal stimulation 21 day old fetus Can depolarize entire heart

Blood flow and pressure changes cause the valves to open and close:

Blood enters the ventricle when atrial BP exceeds ventricular BP. Blood flows down its pressure gradient and pushes the AV valve open. Ventricles fill passively. Atria contract and "top off" the ventricles. When the ventricle contracts, ventricular BP will exceed atrial BP. Blood will attempt to flow back into the atria, however, blood pushes the valve flaps towards the atria and this closes the valves. The chordae tendineae tighten (papillary muscles contract) and prevent the AV valves from eversion or "flipping" back up into the atrium

Fluid pressure gradient-

Blood flows from an area of high pressure to an area of low pressure **pressure changes on right side of the heart is 1/5th that of the left side, but each ventricle pumps the same volume of blood.

Cardiac Muscle Fibers (cardiocytes)

Branched, uninucleate, striated Almost exclusively aerobic metabolism Myoglobin stores O2 Intercalated discs -contain desmosomes to connect adjacent cells together & prevent them from separating during contraction and gap junctions which allow for chemical & electrical communication cell to cell Functional syncytium (together) (cells)-cardiac muscle fibers act like a single muscle fiber; all cardiomyocytes contract as a unit or none do.

e.g. CO(ml/min)=SV(ml) X HR (bpm)

CO (ml/min) = 80ml X 70bpm CO = 5,600ml/min or 5.6 L/min Increasing both SV and HR can increase CO

Cardiac output

CO, amount of blood pumped each minute, indicates ventricular efficiency over time.

Heart Wall:

Epicardium - visceral pericardium Myocardium - cardiac muscle (CT, blood vessels & nerves) Endocardium - lines inner surface, covers valves & is continuous with endothelium (lining of vessels)

Coverings

Heart is surrounded by (lies within) pericardial cavity, which is lined by pericardium (serous membrane) 2 subdivisions: visceral pericardium -AKA epicardium (covering) parietal pericardium -inner surface of pericardial sac; mesothelium secretes pericardial fluid pericardial fluid prevents friction in pericardial cavity

Summary

Most of the time, when one set of valves is open, the other set is closed. When the heart is "filling" or Ventricular diastole, the AV valves are open and the semilunars are closed. Isovolumetric contraction phase - "split second" when both sets of valves are closed When the heart is "pumping" or Ventricular systole, the AV valves are closed and the semilunars are open.

Specialized cardiac muscle fibers (2 types):

Nodal cells-establish rate of cardiac contraction; cell membranes depolarize spontaneously & start action potential; are electrically coupled to... Conducting fibers-distribute stimulus to the general myocardium

Structure of the Heart

Size- of a fist Shape - cone-shaped Location - in thoracic cavity, in anterior portion of mediastinum posterior to sternum from 3rd costal cartilage to the 5th intercostal space distally tips slightly to left 2/3 of mass to left of midsternal line rotated, apex points posteriorly to left hip rests on diaphragm (diaphragmatic surface)

CO depends upon:

Stroke volume SV = amount of blood ejected by a ventricle in a single beat; varies beat to beat

Systemic circuit-

blood to & from tissues & the rest of the body L Ventricle→Aorta→Systemic arteries→Syst. capillaries→Syst. veins →Venae cavae →R. atrium - systemic circuit is longer and blood is under greater pressure -sytemic arteries are O2 rich and CO2 poor

where does heart get calcium from

extracellular fluid

Cardiac Muscle Tissue: 1. Fibrous skeleton of heart

network of connective tissue, collagen and elastin, wraps each muscle fiber and adjacent cells are tied together into sheets of muscle tissue. concentric layers of muscle tissue wrap around atria and spiral around ventricles; also enclose each of heart valves 3 functions: 1) strength and prevents overexpansion of heart 2) helps maintain heart's shape 3) physically isolates muscle fibers of atria from ventricles

C. Electrocardiogram ECG or EKG

-tracing of the electrical events or the heart -electrodes placed on the body surface (left and right wrists, lower left leg) P wave- depolarization of the atria (precedes atrial contraction) QRS complex-ventricular depolarization (atrial repolarization occurs here, but is masked) T wave-ventricular repolarization Cardiac arrhythmias-abnormal patterns of cardiac activity Fibrillations-extremely rapid impulses, with no coordinated contractions (defibrillator) Ventricular fibrillations-ventricles fibrillating, rapidly fatal

D. Chemical Regulation

1) Hormones - Epinephrine and NE (from adrenal medulla, SNS) - Thyroxine - in large quantities, slower response but longer lasting, ↑ heart rate, (enhances NE and E) 2) Ions - electrolytes: Hypocalcemia - too little calcium, weak contractions, may stop heart Hypercalcemia -too much calcium; extreme excitability; calcium rigor; fatal Hypernatremia -too much sodium, blocks calcium entry into cells, heart can't contract Hyperkalemia -  conc. K+ ;weak and irregular heart beat (potassium affects depolarization and repolarization) Hypokalemia -↓ conc. of K+ ;hyperpolarization, ↓ rate of contraction (both hyperkalemia and hypokalemia life threatening)

ESV(how much is left over) affected by:

1) Sympathetic stimulation - due to an increased force of contraction, decreases ESV and increases SV 2) Parasympathetic stimulation - opposite of sympathetic, reduces force of contraction, increases ESV and decreases SV

EDV affected by:

1) filling time - faster heart rate, shorter filling time 2) venous return - how fast blood enters ventricles during ventricular diastole (affected by exercise, peripheral circulation, etc.) 3) degree of stretch of cardiac muscle fibers: Starling's Law of Heart - greater stretch, greater force of contraction (more in, more out)

Cardiac Physiology: A. Cardiac Contractions

1. Cardiac muscle fibers - have long refractory period compared to skeletal muscle fibers - (refractory period -time during which further stimulation will not produce another contraction) -e.g. skeletal muscle = 10 m sec. -e.g. cardiac muscle = 300 m sec. -cardiac muscle fiber enters relaxation before refractory period ends, therefore not capable of a tetanic contraction (with repeated stimulation)

Contraction sequence-

1. SA node-sinoatrial node; "pacemaker" ; 70-80 action potentials/minute 2. AV node- atrioventricular; 40-60 action potentials/minute; can become the pacemaker if SA node is non-functional 3. AV bundle or bundle of His-in interventricular septum, divides into... 4. Right and Left bundle branches- radiate across R& L ventricles 5. Purkinje fibers-wrap around ventricles & carry impulses from apex to all contractile cells of ventricles Average heart rate-72 bpm Disorders: Bradycardia-slower than normal heart beat, < 50 bpm Tachycardia-faster than normal heart beat, >100 bpm

Autonomic tone-

AKA vagal tone Constant low level activity of both divisions, but predominantly parasympathetic

2 ventricles

R & L separated by interventricular septum Pumping chambers Thick muscle (myocardium) Left ventricle-thicker

A. Sympathetic Division

Regulated by cardioacceleratory center in medulla Stressors are stimuli NE is neurotransmitter, binds to beta receptors ↑ heart rate & FOC

B. Parasympathetic Division

Regulated by cardioinhibitory center in medulla ACh is neurotransmitter released by Vagus nerve ↓ heart rate (to normal) & ↓ FOC (to normal)

Path of Blood Flow:

Right Atrium receives deoxygenated blood from systemic circuit via 2 large veins, Superior Vena Cava (blood from head, neck, arms and chest) and Inferior Vena Cava, (blood from trunk, viscera, legs) Blood enters Right Ventricle through Right Atrioventricular Valve (AKA Right AV Valve or Tricuspid) which lies between right atrium and right ventricle.

VI. Control of Heart Rate

SA node determines basic heart rate Modified by ANS via cardiac plexus Innervation from both divisions (parasympathetic NS & sympathetic NS) at SA & AV nodes, atrial & ventricular fibers

SV = EDV - ESV

SV (what is pumped out) EDV (full ventricle) ESV (blood left over) SV = 120ml -50ml SV = 70ml

Requirements for contraction:

a. Action potential-depolarization followed by repolarization; excitation-contraction coupling (Ca++ binds to troponin →filaments slide) b. Ca++ ions-from extracellular space and SR; slow Ca++ channels in sarcolemma are opened during depolarization →SR to release Ca++; Ca++ surge prolongs depolarization; longer action potential allows for blood ejection from heart. c. Energy- glucose (glycogen) & fatty acids, constant supply of oxygen. (CM tissue can metabolize lactic acid) d. 1% of cells are specialized cardiac muscle cells (see Intrinsic Conduction System)

External surface of heart:

coronary sulcus (atrioventricular groove) - deep groove, border between atria & ventricles interventricular sulcus -boundary between L & R ventricles