Cardiovascular System in Horses

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Questions and Answers

What anatomical structure is the heart situated within?

Mediastinum (correct)

Thoracic cavity

Pericardial space

Pleural cavity

Which layer is directly on the heart?

Myocardium

Endocardium

Epicardium (correct)

Parietal pericardium

Which of the following best describes the shape of the heart?

Prismatic

Flask-shaped

Spherical

Inverted cone (correct)

What is contained within the pericardial space?

Pericardial fluid Signup and view all the answers

What is a common cause of pericardial effusion?

Heart tumor Signup and view all the answers

What are cardiac muscle cells connected by?

Intercalated discs Signup and view all the answers

What anatomical feature helps divide the chest into left and right halves?

Mediastinum Signup and view all the answers

What condition may require draining the pericardial effusion?

Hemangiosarcoma Signup and view all the answers

Which layer of the heart is composed of simple squamous epithelium?

Endocardium Signup and view all the answers

In which type of animal is the heart usually found between ribs 2-6?

Horses Signup and view all the answers

Which nervous system is responsible for increasing heart rate?

Sympathetic nervous system Signup and view all the answers

What is the primary function of baroreceptors?

Sense blood pressure Signup and view all the answers

What type of cells make up the walls of capillaries?

Simple squamous epithelial cells Signup and view all the answers

Which factor does NOT directly affect blood pressure?

Bone density Signup and view all the answers

What type of arteries are located closest to the heart?

Elastic arteries Signup and view all the answers

Which structure in the heart is primarily responsible for initiating the heartbeat?

Sinoatrial node Signup and view all the answers

What do chemoreceptors primarily monitor?

Carbon dioxide levels and pH Signup and view all the answers

Which component of blood vessels enables them to maintain shape and elasticity?

Dense irregular connective tissue Signup and view all the answers

What structure serves as a bypass for pulmonary circulation in a fetus?

Ductus arteriosus Signup and view all the answers

What is the role of valves in veins?

Prevent backflow of blood Signup and view all the answers

What condition occurs when blood flows backwards due to a valve not closing properly?

Mitral valve insufficiency Signup and view all the answers

Which part of the heart is responsible for generating action potentials that initiate the heartbeat?

Sinoatrial node Signup and view all the answers

Which electrical event on the ECG corresponds to the contraction of the ventricles?

QRS complex Signup and view all the answers

What happens to the heart's electrical signal as it travels from the sinoatrial node to the atrioventricular node?

Is delayed in the AV node Signup and view all the answers

What can cause the hearts of migrating birds to hypertrophy?

Increased physical demand during migration Signup and view all the answers

What is the role of the Purkinje fibers in the heart's electrical conduction system?

Spread electrical signals to the ventricles Signup and view all the answers

In what order do electrical impulses travel through the heart?

SA node, AV node, atria, ventricles Signup and view all the answers

What effect does the malfunction of the sinoatrial node have on the heart's rhythm?

Erratic heart rhythms Signup and view all the answers

What is a characteristic feature of a mitral valve stenosis condition?

Blood cannot flow forward through the valve Signup and view all the answers

Which of the following correctly describes the relationship between heart size and bird size?

Inversely proportional Signup and view all the answers

What is one of the primary functions of the cardiac skeleton?

To anchor valves and provide structure Signup and view all the answers

Which valves prevent backflow into the atria?

AV valves Signup and view all the answers

What sound is associated with the closure of AV valves?

Lub Signup and view all the answers

What prevents the AV valves from opening in the wrong direction?

Fibrous cords connected to papillary muscles Signup and view all the answers

During which phase do the semilunar valves close, producing the second heart sound?

When the ventricles relax Signup and view all the answers

What is the role of papillary muscles in heart function?

Support valve closure to prevent backflow Signup and view all the answers

What type of valves separate the ventricles from major outflow vessels?

Semilunar valves Signup and view all the answers

What condition is indicated by turbulent blood flow?

Valvular insufficiency Signup and view all the answers

What structure separates the right atrium from the left atrium?

Interatrial septum Signup and view all the answers

What is the primary purpose of heart valves?

To ensure one-way blood flow Signup and view all the answers

Study Notes

The Cardiovascular System

The cardiovascular system in a horse, as shown in the diagram, is a complex network of arteries, veins, and the heart.
The heart is located in the chest, dorsally to the olecranon, with its apex resting on the sternum, generally between ribs 3-6 (or 2-6 for horses). The base of the heart is tilted cranially (about 40°).
Veins and arteries such as the jugular vein, carotid artery, pulmonary artery, pulmonary vein, subclavian artery, and subclavian vein are vital components of this system, carrying blood throughout the body.
Structures like the aorta, posterior vena cava, femoral vein, and pedis artery and vein are key parts of the circulatory system.

Heart Location

The heart is situated within the chest cavity's mediastinum, a space between tissue layers separating the left and right halves.
This mediastinum contains crucial structures such as the trachea, esophagus, nerves, lymph nodes (including the thymus in young animals), and major blood vessels (like the aorta).

Heart Coverings

The pericardium is a fibrous sac encasing the heart. It consists of a parietal layer, fused with the fibrous tissue, and a visceral layer that directly adheres to the heart.
The space between these two layers is the pericardial space.
Pericardial fluid within the space facilitates smooth heart movements.

Heart Layers

The heart wall possesses three layers:
- Endocardium – a simple squamous epithelium.
- Myocardium – the heart muscle layer.
- Epicardium – also known as the visceral pericardium.
The parietal pericardium is the outer layer, fused with a fibrous tissue layer.
Pericardial space comprises the cavity between layers.

Pericardial Effusion

Bleeding from a heart tumor is often a reason for this condition.
In other cases, pericardial effusion may stem from idiopathic causes.
Physicians can sometimes drain the abnormal fluid collected around the heart using ultrasound-guided needles.

Hemangiosarcoma

A type of cancer originating from the blood vessels.
In some cases this cancer can spread into the pericardial sac. This causes issues with the heart's normal operation because the pericardial sac is compressed.

Thoracoscopic Surgery

A minimally invasive surgical procedure. In some cases, this procedure is used to extract fluid or abnormal structures from the pericardial space.

Hardware Disease in Cows

A condition associated with pericarditis in cows.
Symptoms often relate to inflammation or infection.

Cardiac Muscle Cell Characteristics

Cardiac muscle cells are joined by intercalated discs.
They exhibit striations.
Specialized junctions connect the cardiac muscle cells.
Cardiac cells have autorhythmicity.

Heart Layout

The heart (in dogs) has a right atrium (RA), a left atrium (LA), a right ventricle (RV), and a left ventricle (LV). These structures of the heart are divided by septa, the interatrial septum and the interventricular septum.

Inside the Heart

The heart's skeletal structure consists of four rings (ossified in cows).
- These rings help separate atria from ventricles.
- They also help secure valves.
- They provide support for the myocardium.

Blood Flow Diagram

The diagram shows blood flow from the lungs, through the heart, and subsequently to the body.
Blood flows through different chambers: right atrium, right ventricle, left atrium, left ventricle.

Valves Between Atria and Ventricles

The heart has valves governing the flow between atria and ventricles.
- The right AV (atrioventricular) valve is also known as the tricuspid valve.
- The left AV valve is known as the bicuspid or mitral valve.

AV Valves Function

Fibrous cords within the heart prevent valves from reversing their direction of opening.
The fibrous cords are attached to papillary muscles.

Semilunar Valves

These valves (pulmonary and aortic) prevent a backflow of blood within the heart. These valves are located between each ventricle and the major vessels that leave them.

Heart Sounds

Heart sounds result from the closure of heart valves.
- The "lub" sound corresponds to AV valve closure, and prevents blood from flowing back into the atria.
- The "dub" sound arises from the closure of semilunar valves, preventing blood from flowing back into the ventricles.
Abnormal heart sounds/murmurs may suggest problems with the heart's valves.

Murmur Types

Murmurs are caused by turbulent blood flow.
- Cases of valvular stenosis indicate a narrowing in a valve opening.
- Cases of valvular insufficiency happen when blood leaks back through the valve because it does not close properly.

Avian Hearts

Bird hearts are smaller relative to their size compared to other species.
Migratory birds' hearts show hypertrophy beforehand.
The structure may show a different number of cusps on their AV valves compared to mammals.

Heart Blood Supply

Details regarding the various arteries and veins supplying the heart are provided on diagrams. The details of coronary arteries are key to the blood supply.

Electrical Conduction in the Heart

The SA (sinoatrial) node acts as the heart's pacemaker.
Specialized muscle cells in the right atrium generate electrical impulses that control the heartbeat.
These impulses trigger contraction of atria and ventricles.
The electrical signals travel from the SA node through the heart through specialized conduction pathways.
Different parts of the pathway are associated with different electrical signal delays and conduction time.

Pathway of Electrical Signals

Electrical signals begin in the sinoatrial (SA) node; and proceed across the atria to cause them to contract. They then travel through the atrioventricular (AV) node, to the bundle of His; through the bundle branches and Purkinje fibres to cause the contraction of the ventricles.

Measuring Electrical Conduction

ECG (electrocardiogram) measures electrical conduction in the heart.
Different waves on the ECG represent different phases, such as atrial contraction, ventricular contraction, and ventricular relaxation.

Control of Heart Rate

Different parts of the heart are associated with controlling heart rate.

Heart Rate Control Mechanisms

The medulla oblongata (brainstem) has cardiovascular centres controlling sympathetic and parasympathetic nervous system activities that regulate the heart rate.
- Sympathetic neurons, releasing norepinephrine, trigger increased heart rates.
- Parasympathetic neurons, using acetylcholine (ACh), slow down heart rate.
Sensory receptors, such as baroreceptors (responding to pressure) and chemoreceptors (responding to blood chemistry), send information to the brain for controlling heart rate.

Blood Vessels

Blood vessels have three layers:
- Innermost endothelium: a simple squamous epithelium.
- Middle layer of smooth muscle (and/or elastic fibers).
- Outer tissue layer of connective tissue: dense irregular connective tissue.
The structure of a blood vessel depends if it's an artery, vein, or capillary.

Arteries, Veins and Capillaries

Arteries are high-pressure vessels, with thick walls (and smooth muscle and elastic tissue).
Veins are low-pressure vessels, with thin walls (and less smooth muscle and elastic tissue), that contain valves that prevent the backflow of blood.
Capillaries are single-layered vessels facilitating exchange of substances between the blood and surrounding tissues.

Capillaries

Capillaries are thin-walled vessels allowing for the exchange of vital substances between the blood and tissues.
They're organized into networks or beds.

Blood Pressure

Blood pressure is the force exerted by blood against the vessel walls.
Factors impacting blood pressure include heart rate, stroke volume, blood volume, blood vessel diameter, and vessel elasticity.

Arteries: Elastic vs. Muscular

Elastic arteries near the heart, like the aorta, are more compliant.
Muscular arteries farther from the heart have thicker smooth muscle layers, for regulating blood flow.
Arteries lack valves.

Feeling the Pressure Wave

Various animals, like cats, dogs, sheep, goats, piglets, horses, cows, and pigs, exhibit distinct pulse characteristics.
Palpating the pulse is a way of feeling the heart's beat against tissues and arteries/veins.

Veins: One-Way Valves

Veins contain valves, preventing blood from flowing backward because of low pressure inside the venous system.
Veins take blood from small vessels called venules through the tissues to larger vessels like veins. Blood then enters the vena cava, before entering the heart to be re-oxygenated.

Veins and Blood Samples

Specific veins in animals, including dogs, cats, horses, cows, sheep, and goats, are commonly used for blood collection.

Fetal Circulation

The fetus's circulatory system differs from that of a newborn.
- Foramen ovale and ductus arteriosus in the fetus are circulatory bypasses for pulmonary circulation.
- These structures are important pathways for bypassing pulmonary circulation.
- The closure of these pathways occurs in the transition to newborn function.

Veins Coming Back to the Heart

Diagrams illustrate specific veins returning blood to the heart in various species (e.g., dogs, cats, etc.). The details of the venous circulation are shown on diagrams.

Major Arteries and Veins

Diagrams illustrate major arterial and venous pathways, including pulmonary arteries, brachiocephalic trunks, subclavian arteries, and vena cava. These structures are vital parts of the cardiovascular system.

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Description

Explore the intricate cardiovascular system of horses, focusing on the structure and function of the heart, arteries, and veins. This quiz covers the anatomy, including the location of the heart and key components like the aorta and vena cava. Test your knowledge about equine circulatory physiology!