Cardiovascular

Blood flow

• out of left side via arteries, returns to right side via veins

• atria = receiving chambers, ventricles = ejecting chambers

Cardiovascular functions

• delivery of oxygen, nutrients, humoral factors, & immune cells

• removal of CO2 & waste

• fluid & temperature homeostasis

• hemostasis

Lymph flow

• one way circuit, collects fluid from extracellular spaces to enter venous return

• low volume & low pressure

• immune function, filtration via lymph nodes

Vascular structure

• tunica intima, media, adventitia layers

• endothelium included in tunica intima

Tunica intima

• endothelial cells + basement membrane

• thin inner layer

Endothelial cell function

• important to regulating coagulation

  • anticoagulation at rest, procoagulation during injury

• modulate blood flow

• synthesis of collagen + proteoglycan, production of growth hormone, catecholamine degradation

• leukocyte adhesion, acute inflammation mediation, & antigen presentation

Tunica media

• middle layer of smooth muscle & extracellular matrix (elastin + ground substance)

• much thicker in arteries than veins

Elastin

• makes up internal & external elastic lamina in larger arteries (brackets the tunica media)

Tunica adventitia

• outer layer of connective tissue, may contain small vessels + nerves, adipose, & periocytes

Arterial morphology

• diameter gets smaller further from the heart

• tunica media gets thinner & contains less elastin further from the heart

Aorta

• high pressure, high volume + continuous pulsatile flow

• thick tunica media w/a lot of elastin

Muscular arteries

• large: internal + external elastic lamina but no elastin fibers throughout

• small: minimal elastin, mostly smooth muscle tunica media

Arteriole

• few layers of smooth muscle in tunica media

• sparse tunica adventitia

Capillaries

• extensive anastomosing network of small caliber vessels

• deoxygenation + nutrient transfer occur here

Continuous

• complete endothelium & basement membrane

• ex: brain, lung

Fenestrated

• holes in endothelium but complete basement membrane

• ex: glomeruli

Sinusoidal/discontinuous

• holes in endothelium & incomplete basement membrane

• for large molecule transport

• ex: liver, spleen

Venous morphology

• diameter is larger closer to the heart

• tunica proportions similar in veins of all sizes

  • slightly thicker tunica media in larger veins

• contain valves (protrusions of tunica intima) to prevent backflow of blood in low pressure system

Post-capillary venule

• responsible for leukocyte release into tissues

Vein

• broader tunica adventitia

• slightly thicker tunica media but still thinner than arteries

Chyle

• lymph fluid mixed with fat droplets (milky white to pink)

Lymph vessel

• thin/inapparent tunica media + adventitia, rudimentary basement membrane, & valves

• no periocytes

• not found in every organ system

Endocardium

• inner lining of heart

• thin layer of fibrous connective tissue lined by endothelium

Valves

• lined by endothelium on both sides

• stroma containing collagen, elastic fibers, proteoglycans, & interstitial fells

Myocardium

• bulk of the heart, thickest in left ventricle

• made up of cardiac myocytes/cardiomyocytes

• contain fibrous skeleton & conduction system

Ventricle v.s. atrium

• ventricle: denser myocardium, thicker walls

• atrium: looser arrangement of myocytes, thicker epicardium, more connective tissue/adipose

Cardiac muscle features

• branching cardiac myocytes w/intercalated disks

• prominent connective tissue

• central nuclei

• Purkinje fibers present (conduction system)

Intercalated disks

• junctions at z-lines that support synchronized contraction of cardiac myocytes

Conduction system

• pulse generated at sinoatrial node (crista terminalis), travels through AV node (cranial to septal cusp of R AV valve) & His bundle, exits at Purkinje fibers/AV bundles (interventricular wall, pass through trabecular septomarginalis)

• comprised primarily of modified cardiac myofibers

Sinoatrial node

• smaller cells w/less cytoplasm & more surrounding connective tissue

• located at crista terminalis of right auricle

Purkinje cells

• larger cells w/more cytoplasm (pale pink on histo)

Fibrous skeleton

• connective tissue around all 4 valves at heart base for muscle attachment

• purple on histo

Pericardium

• epicardium = visceral serous pericardium (overlies surface of heart)

• parietal pericardium = outer layer of pericardial sac

  • serous (mesothelium) + fibrous (collagenous stroma w/adipose, nerves, & small vessels)

  • pericardial mediastinal pleura adhered to fibrous layer

Pericardial cavity

• space between the fibrous pericardium and parietal serous pericardium

Pericardial ligaments

• phrenicopericardial ligament: fibrous pericardium to diaphragm

• sternopericardiac ligament: fibrous pericardium to sternum

Heart location

• middle mediastinum from ribs 3-6

• forms 45 degree angle with sternum

• slightly left of midline

Heart surface

• auricular (left) & atrial (right)

• interventricular grooves separate ventricles

  • left side = paraconal, right side = subsinuosal

• coronary groove separates atria from ventricles

• interatrial septum

Right atrium

• receives systemic venous blood (deoxygenated) from caudal & cranial vena cava, azygous v., coronary sinus, & small cardiac vv.

• divided into sinus venarum (atria proper) & auricle (blind cranial part)

• contains intervenous tubercle & fossa ovalis (caudal)

Intervenous tubercle

• ridge between cranial & caudal vena cava openings

• diverts blood to right ventricle

Right auricle

• pectinate muscle

• crista terminalis @ entrance of auricle (where pectinate muscles radiate from)

• location of SA node

Right ventricle

• receives blood from R atrium, ejects blood to lungs via pulmonary trunk (R + L pulmonary aa.)

Ventricular structures

• papillary muscles (3 projections) w/chordae tendineae attaching to AV valves

• trabeculae carneae (muscle of ventricular wall)

• trabeculae septomarginalis (moderator band, connects septal & parietal walls)

Left atrium

• receives blood from lungs via pulmonary veins (oxygenated)

• valve of foramen ovale (fold of tissue in cranial part of septal wall)

Left ventricle

• receives blood from L atrium, ejects blood to body via aorta

Heart valves

• 2 AV valves (L + R)

• 2 semilunar valves w/3 cusps + free nodules (aortic + pulmonary)

Right AV valve

• tricuspid valve (only 2 in dogs)

• septal + parietal cusps

Left AV valve

• bicuspid/mitral valve

• septal + parietal cusps

Puncta maxima

• optimal point for auscultation of heart valves

• pulmonary: L intercostal 3 (low)

• aortic: L intercostal 4 (high)

• mitral/L AV: L intercostal 5 (low)

• R AV: R intercostal 3-4 (low)

Heart sound

• lub: closure of L + R AV valves

• dub: closure of aortic + pulmonary valves