The Cardiovascular System

EFE Veterinary Science

Anatomy and Physiology

The Heart: Overview

Schematic drawing of the systemic and pulmonary circulation. 1, Left ventricle; 2, aorta; 3, capillary bed of head, neck, and forelimb; 4, abdominal aorta; 5, liver; 6, capillary bed of intestines; 7, portal vein; 8, capillary bed of kidneys; 9, capillary bed of caudal part of the body; 10, caudal vena cava; 11, cranial vena cava; 12, right ventricle; 13, pulmonary trunk; 14, capillary bed of lungs; 15, pulmonary vein; 16, hepatic veins.

The Heart: Structure

Section of the heart exposing the four chambers. 1, Cranial vena cava; 2, terminal sulcus; 3, right atrium; 4, interatrial septum; 5, left atrium; 6, left atrioventricular valve; 7, right atrioventricular valve; 8, right ventricle; 9, interventricular septum; 10, left ventricle; 11, sinuatrial node; 12, atrioventricular node; 13, 14, right and left limbs of atrioventricular bundle.

The Heart

Left (A) views of the heart. A, 1, Left auricle; 2, pulmonary trunk; 3, right ventricle; 4, left ventricle; 5, left azygous vein.

The Heart: Structure

Right (B) views of the heart. B, 1, Right atrium; 2, caudal vena cava; 3, aorta; 4, right azygous vein (opening into the cranial vena cava).

Major Vessels

• Aorta (exits left ventricle)• Pulmonary Arteries (exit right

ventricle)• Pulmonary Veins (enter left atrium)• Vena Cava (enters right atrium)• Know location and oxygenated v

deoxygenated blood

Blood Flow

• Capillaries”drops off” O2 • Deoxygenated blood returns via the veins

to the Vena Cava• Vena CavaRight atrium• Right atriumright AV valveright

ventricle• Right VentriclePulmonic

valvePulmonary Arteries

Blood Flow, 2

• Pulmonary Arterieslungspulmonary capillaries in alveoli, pick up O2, release CO2

• Pulmonary veinsleft atrium• Left atrium through left AV valveLeft

ventricle• Left ventricle through Aortic valveAorta

Blood Flow 3

• Aortaarteries• Arteriescapillaries, drop off O2, pick up

Co2, repeat cycle.

• Oxygen and pressure higher in arteries• Pulmonary arteries are the only arteries in

the body that carry deoxygenated blood!

Electrical Activity

• Electrical Activity initiates the contraction of cardiac muscle.

• Electrical activity is what is measured by an ECG (aka EKG)

• A Pacemaker produces a small electrical pulse to cause regular contraction of the heart

Electrical Activity

Schematic drawing of the conducting system of the heart. The broken lines suggest the passage of the excitation wave through the atrial wall. 1, Sinuatrial node; 2, atrioventricular node; 3, atrioventricular bundle; 4, left limb; 5, right limb; 6, branch of right limb traversing the septomarginal band.

Sinoatrial Node (equine)

A, Sinuatrial node of the equine heart. 1, Nodal myofibers; 2, bundle of nerve fibers (I-HE) (279×).

The Electrocardiogram (ECG/EKG)

ECG

Heart Sounds

• 2-part sounds: Lub—Dub• First sound (lub) is physical closing of the

right and left AV valves• Second sound (dub) is physical closing of

the aortic and pulmonic valves• A murmur is caused by flow through a

narrow opening (leaky valve, congenital abnormality)

Heart Sounds

Arteries

Carry blood away from heartUnder high pressureCan feel pulsation

The components of the arterial wall. 1, 2, Tunica interna (1, endothelium; 2, inner elastic membrane); 3, tunica media; 4, tunica adventitia; 5, vasa vasorum.

Arteries

The branching of the arteries. Note that (1) the sum of the cross-sectional areas of the branches always exceeds that of the parent trunk; (2) large branches leave the trunk at more acute angles than smaller branches; and (3) the smallest branches leave erratically.

Capillaries

Single cell thick walls for transfer of O2 and CO2 between blood and tissueSchematic drawing of a capillary plexus. 1, Arteriole; 2, venule; 3, communicating (low-resistance) channel; 4, closed capillaries; 5, open capillaries; 6, precapillary sphincters.

VeinsSchematic representation of the venous system (dog). 1, Caudal vena cava; 2, cranial vena cava; 3, azygous v.; 4, vertebral v.; 5, internal jugular v.; 6, external jugular v.; 7, linguofacial v.; 8, facial v.; 8 , angularis oculi v.; ′9, maxillary v.; 10, superficial temporal v.; 11, dorsal sagittal sinus; 12, subclavian v.; 12 , ′axillobrachial v.; 12″, omobrachial v.; 13, cephalic v.; 13 , accessory cephalic v.; 14, ′brachial v.; 15, radial v.; 16, ulnar v.; 17, internal thoracic v.; 18, vertebral venous plexus; 19, intervertebral v.; 20, intercostal vv.; 21, hepatic vv.; 22, renal v.; 22 , testicular or ovarian v.; 23, ′deep circumflex iliac v.; 24, common iliac v.; 25, right internal iliac v.; 26, median sacral v.; 27, prostatic or vaginal v.; 28, lateral caudal v.; 29, caudal gluteal v.; 30, internal pudendal v; 31, right external iliac v.; 32, deep femoral v.; 33, pudendoepigastric trunk; 34, femoral v.; 35, medial saphenous v.; 36, cranial tibial v.; 37, lateral saphenous v.; 38, portal v.; 39, gastroduodenal v.; 40, splenic v.; 41, caudal mesenteric v.; 42, cranial mesenteric v.; 43, jejunal vv.

Veins

• Function: Return deoxygenated blood to the heart for gas exchange in the lungs• Structure: Thinner-walled than

arteries due to lower pressure than arteries

Veins

A branching vein opened to expose valves. The arrow indicates the direction of blood flow.

Baroreceptors and Chemoreceptors

Baroreceptors and chemoreceptors at the origin of the internal carotid artery. 1, Common carotid artery; 2, external carotid artery; 3, internal carotid artery; 4, carotid sinus branch of the glossopharyngeal nerve; 5, carotid sinus (baroreceptor); 6, carotid body (chemoreceptor).

Function: To sense blood pressure and chemical composition of blood for feedback to the circulatory and endocrine systems.

Fetal and Postnatal Circulation

Semischematic drawing of fetal circulation (calf). 1, Thymus; 2, pulmonary trunk; 3, aortic arch; 4, ductus arteriosus; 5, pulmonary artery; 6, foramen ovale; 7, wall of left ventricle; 8, caudal vena cava; 9, ductus venosus; 10, junction of umbilical and portal branches within the liver; 11, umbilical vein; 12, stump of portal vein; 13, left umbilical artery; 14, gallbladder; 15, descending colon.

Fetal and Postnatal Circulation

Diagrams of the fetal (A) and postnatal (B) circulatory systems. 1, Cranial vena cava; 2, caudal vena cava; 3, right atrium; 4, arrow entering oval foramen; 5, right ventricle; 6, pulmonary trunk; 7, pulmonary artery; 7 , ductus arteriosus (in ′ B, vestige); 8, left atrium; 9, left ventricle; 10, aortic arch; 10 , descending aorta; 11, umbilical artery; 12, ′umbilical vein; 12 , ductus venosus; 13, liver; 14, portal vein.′

Umbilical Cord and Placental Circulation

• Umbilical veinfetal livercaudal vena cavaright atrium OR foramen ovaleleft atrium; RA mixes with other venous returnpulm trunkductus arteriosusaortaumbilical arteryplacenta; LALVaortic archaortaumbilical arteryplacenta

Umbilical Cord and Placental Circulation

• Postnatal changes: Closure of umbilical artery and vein; closure of foramen ovale; closure of ductus arteriosus; closure of ductus venosus and adult-pattern liver circulation

Lymphatics

Generalized schema of the lymph nodes and lymphatic vessels (dorsal view). The top of the diagram represents the neck region. 1, External and internal jugular veins; 2, lymph from the head; 3, lymph from the shoulder and forelimb; 4, tracheal duct; 5, thoracic duct; 6, lymph from the thoracic organs; 7, cisterna chyli; 8, lymph from the abdominal organs; 9, lymph from the lumbar region and kidneys; 10, lymph nodes of the pelvis; 11, lymph from the hindlimb.

Lymphatics

Structure of a lymph node (A) in which the germinal centers (lymph nodules) occupy the cortical region. In the pig (B) the germinal centers lie centrally. The arrows indicate the direction of lymph flow. 1, Afferent lymphatics; 2, subcapsular sinus; 3, efferent lymphatics.

Lymph Nodes

Lymph node (dog) (28×). 1, Cortex with lymph nodules; 2, medulla; 3, afferent lymph vessels.

A, Lymph node (pig) (28×). 1, Loose lymphoreticular tissue; 2, lymph nodules in centrally located “cortex”; 3, efferent lymph vessels.

Lymph Nodes

Palpable lymph nodes of the dog. 1, Parotid; 2, mandibular; 3, lateral retropharyngeal (inconstant); 4, superficial cervical; 5, axillary; 6, accessory axillary (inconstant); 7, superficial inguinal; 8, popliteal; 9, femoral (inconstant).

Lymph Nodes

Palpable lymph nodes of the cat. 1, Mandibular; 2, lateral retropharyngeal; 3, dorsal superficial cervical; 4, axillary; 5, accessory axillary; 6, superficial inguinal; 7, caudal epigastric; 8, popliteal.

Lymph Nodes

Lymph nodes associated with trachea and lungs of the dog. 1, Cranial mediastinal nodes; 2, tracheobronchial nodes; 3, pulmonary nodes.

Lymphatic Vessels

• Very thin-walled• Very low-pressure system• Passive circulation: Lymph moved by the

motion of surrounding tissue• Pregnant women with swollen ankles• Horses stocking up

Spleen

Visceral surface of the spleens of horse (A), cattle (B), and dog (C) to show the distribution of the splenic arteries. Branches to other structures are shown in blue.

Spleen

• Structure: Capsule, cortex and medulla– Lymphatic nodules– Blood Storage and Filtration– Can contract to release blood during times of high

demand

• Prone to hematoma and hemangioma or hemangiosarcoma leading to splenectomy

Thymus

Thymus of calf (HE) (70×). 1, Thymic lobules; 2, capsule.

Thymus

• Thymic cortex is origin of T lymphocytes• Medulla has unknown function• Regresses in adults