The Cardiovascular System

Chapter 15

Heart is two pumps in one:

Right side – pulmonary circulation

Left side – systemic circulation

Heart→ Arteries → Arterioles → Capillaries → Venules→ Veins → Heart

Artery – any vessels that carries blood away from the heart.

Vein – any vessels that carries blood toward the heart

Parietal pericardium:

outer fibrous layer

inner serous layer

Pericardial cavity

Visceral pericardium (epicardium)

Pericarditis

Cardiac Tamponade

Heart Wall3 Layers:

Epicardium – serous membrane

Myocardium – muscle layer

Endocardium – continuous throughout circulatory system

Cardiac Muscle :

involuntary, striated

Intercalated discs:

gap junctions

functional syncytium

desmosomes – “spot welds”

Anastomoses – collateral circulation

Ischemia – reduced blood flow

Hypoxia – reduced oxygen supply

Angina pectoris – “strangled chest”

Myocardial infarction – death of an area of tissue due to interrupted blood flow

Cardiac cycle

One complete heart beat:

systole (contraction) and

diastole (relaxation) of both atria and systole and diastole of both ventricles

Heart Murmurs – abnormal sounds caused by the flow of blood.Mitral stenosisMitral valve prolapse

Conduction system of the heart

Sinoatrial (SA) node – “pacemaker’ →

Atrioventricular (AV) node →

Atrioventricular (AV) Bundle - Bundle of His→

Purkinje fibers – conduction myofibers

Ectopic pacemaker

Regulation of Heart Rate

• Sympathetic N.S. increases heart rate and force of contraction – secrete epinephrine –accelerator nerves

• Parasympathetic N.S. decrease heart rate and force of contraction through the vagus nerve. Sends continuous impulses. Secretes acetylcholine

Other factors that influence heart rate

• Temperature

• Ions – K+ and Ca++

• Hormones

• Hypoxia, acidosis and alkalosis slow heart

• Age

• gender

• Physical fitness

Anatomy of blood vessels

• Arteries carry blood away from the heart

• Hole is called the lumen

• Three layers or tunics:– Tunica interna (intima)– Tunica media– Tunica externa (adventitia)

Tunica interna

• Simple squamous epithelium called endothelium

• Secretes biochemicals that inhibit platelet aggregation

• Also substances that dilate or constrict vessels

Tunica media

• Bulk of vessel wall

• Smooth muscle fibers

• Innervated by the sympathetic N.S. – vasoconstriction; decreased impulses = vasodilation

• Thick layer of elastic connective tissue

Tunica externa

• Thin layer

• Connective tissue

• Attaches artery to surrounding tissue

• Contains tiny vessels – vasa vasorum that form capillaries and provide blood to external cells of the vessel

Arteries

• Large arteries are elastic (conducting) arteries – pressure reservoirs

• Medium arteries are muscular (distributing) arteries – more smooth muscle

Arterioles

• Have all three layers, but thin as they divide

• Branches called metarterioles join capillaries

• Arteriovenous shunts

Capillaries

• Only a single layer of endothelium and a basement membrane

• Connect arterioles and venules

• Microcirculation

• Functional part of system for exchange of gases, wastes and nutrients

• True capillaries begin at a precapillary sphincter

Types of capillaries

• Continuous - intercellular clefts, but otherwise uninterrupted

Types of capillaries

• Continuous - intercellular clefts, but otherwise uninterrupted

• Fenestrated capillaries – have “windows” or pores – act in filtration

• Sinusoids or discontinuous capillaries have spaces between cells, and basement membrane is incomplete or absent

• Tight junctions – form a barrier

Venules

• Small vessels that join capillaries and veins

• Add layers

Veins

• Have same three tunics as arteries, but have a thinner tunica media

• Contain valves

• Act as blood reservoirs

Hemodynamics: Physiology of Circulation

Velocity of blood flow is inversely related to the cross-sectional area of the blood vessels (total area). Slow flow through capillaries allows for exchange.

The circulation time – right atrium to foot and back – is about one minute in a resting person.

Blood pressure

• Pressure on walls of a vessel

• Arterial pressure rises and falls as the left ventricle contracts

• Highest during systole – Systolic pressure

• Lowest during diastole – Diastolic pressure

• Mean arterial pressure is about 93 mm Hg

Factors that influence arterial blood pressure

Cardiac Output:

SV (ml/beat) X HR (beats/min) = CO(ml/min.)

70 ml X 75 = 5250 ml or 5.25 liters

Within limits, the greater the stretching of the muscle fibers, the greater the force of contraction – Starling’s Law

Hormonal Regulation of B. P.

• Epinephrine and norepinephrine

• Renin-angiotensin system

• ADH – antidiuretic hormone - vasopressin

• ANP – atrial natriuretic peptide

• Others

Hepatic Portal Circulation

• Drains spleen, stomach, pancreas, gallbladder and small and large intestines

• 2nd capillary bed in liver

• Glucose is removed, and stored as glycogen

• Blood is detoxified

• Leaves through hepatic vein → inferior vena cava

Fetal Circulation

• Obtains oxygen and nutrients from maternal circulation

• Two arteries off internal iliac arteries run through umbilical cord

• Umbilical vein returns oxygenated blood

• Several shunts in fetal circulation:

•Ductus venosus – bypasses fetal liver and dumps blood from umbilical vein into inferior vena cava.

•Foramen ovale – hole in atrial septum, blood passes from right atrium to left atrium, bypassing the developing lungs

•Ductus arteriosus – connects pulmonary artery with aorta

•If does not close – patent ductus arteriosus – get mixing of venous and arterial blood.

Circle of Willis