Circulatory System

Circulatory System Overview

• Comprised of the Cardiovascular System and the Lymphatic System.

Functions of the Circulatory System

• Delivers metabolic requirements to body cells through:

  • Blood

  • Interstitial fluids

  • Lymph

• Contains:

  • Blood Vascular System

  • Lymph Vascular System

Circulatory System Types

• Single-Loop Circulatory System

  • Typically found in fish:

    • One ventricle

    • One atrium

    • Blood flows from gills to body and back.

• Double-Loop Circulatory System

  • Found in most reptiles, crocs, birds, and mammals:

    • Two atria (right and left)

    • Two ventricles (right and left)

    • Separate pulmonary (lungs) and systemic (body) circuits.

The Heart

• Located in the mediastinum between lungs

  • Bounded by:

    • Cranially: Thoracic inlet

    • Caudally: Diaphragm

    • Ventrally: Sternum

    • Dorsally: Spinal column

• Anatomy:

  • Base (rounded cranial end)

  • Apex (pointed caudal end)

Pericardium

• Fibrous pericardium: Tough outer layer

• Serous pericardium:

  • Parietal layer: Lines the pericardial sac

  • Visceral layer: Covers the heart surface

Layers of the Heart Wall

• Epicardium: Outermost layer

• Myocardium: Thick muscular middle layer

• Endocardium: Inner lining of heart chambers

Heart Chambers

• Four chambers:

  • Atria: Receiving blood

  • Ventricles: Pumping blood

  • Atria are above ventricles; walls of left ventricle form the apex.

Septa in the Heart

• Interatrial septum: Separates left and right atria

• Interventricular septum: Separates left and right ventricles

  • Visible as the interventricular groove externally.

Blood Flow Direction

• Right ventricle pumps blood to pulmonary artery.

• Left ventricle pumps blood into systemic circulation via aorta.

• Right ventricular wall is thinner; left ventricular wall is thicker for greater pumping force.

Heart Valves

• Atrioventricular (AV) valves:

  • Tricuspid valve (right AV valve)

  • Bicuspid/Mitral valve (left AV valve)

• Semilunar valves:

  • Pulmonary valve (right semilunar)

  • Aortic valve (left semilunar)

• Chordae tendinae prevent backward flow of blood.

Circulatory System Auscultation Points

• Left AV Valve: Left 5th ICS at olecranon level

• Pulmonic Valve: Left 3rd ICS at olecranon level

• Aortic Valve: Left 4th ICS at shoulder level

• Right AV Valve: Right 4th ICS at olecranon level

Reptilian Circulatory System

• Three or four distinguishable heart chambers depending on species:

  • Crocodilians are unique with four-chambered hearts; includes crocodiles, alligators, and caimans.

Fetal Blood Circulation

• Unique pathway:

  • Ductus arteriosus bypasses lungs in fetus.

  • Foramen ovale allows blood flow from right atrium to left atrium.

Aorta Structure

• Divided into three parts:

  • Ascending Aorta

  • Aortic Arch

  • Descending Aorta (thoracic and abdominal)

Coronary Arteries

• First branches from the aorta, supply heart with blood:

  • Right Coronary Artery

  • Left Coronary Artery

  • Includes branches like paraconal, circumflex, and subsinusal.

Species Differences in Coronary Arteries

• Dogs/Ruminants:

  • Left coronary artery gives rise to both paraconal and subsinuosal branches.

• Horses/Pigs:

  • Right coronary artery gives rise to subsinuosal branch.

• Cats:

  • Subsinuosal branch can arise from either coronary artery.

Aortic Arch

• Sends branches to head, neck, and forelimbs:

  • Brachiocephalic trunk: First branch from the arch, present in all species.

  • Common Carotid Arteries: Supply head and brain.

  • Subclavian Arteries: Supply thoracic limb and neck.

Differences in Subclavian Arteries

• Dogs: Arise separately

• Ungulates: Arise via common bicarotid trunk.

Descending Aorta

• Divided into thoracic and abdominal aorta by diaphragm.

Lymphatic System Overview

• Functions:

  • Removal of excess tissue fluid

  • Waste material transport

  • Filtration of lymph

  • Protein and enzyme transport

• Linked to immune response through lymph nodes and vessels.

Lymphatic System Components

• Cellular: Lymphatic tissues (fixed and mobile cells like lymphocytes)

• Vascular: Lymph vessels and ducts.

Lymph Nodes

• Sites for trapping and processing antigens and maturing lymphocytes.

• Arrangement includes:

  • Cortex: Contains nodules predominantly B cells, and some T cells and macrophages

  • Medulla: Lymphatic sinuses present

  • Located superficially and deep throughout the body.