The Cardiovascular System

ANS 215

Anatomy and Physiology of Domestic Animals

1. Structure and Function
1. Heart is a cone-shaped, hollow, muscular structure located in the thorax.



2. Large arteries and veins are continuous with the heart at its base.
1. Base is directed upward (dorsal) and forward (cranial).
2. Opposite end of the cone is known as the apex
3. Membrane around the heart is known as the pericardium
1. Membrane next to hear fuses with the heart muscle and is called the visceral pericardium or epicardium
2. Outer membrane is parietal pericardium
3. Apex is free
4. Inflammation of the pericardium is called pericarditis
1. increase in fluid in pericardium
2. traumatic pericarditis (hardware) disease in cattle





4. Mycardium
1. Muscular Part of the heart which forms the walls for the chambers.
2. Heart chambers (4) divided into left and right side of the heart

a. Each side has an atrium and ventricle and

each atrium has an extension known as the

auricle





3. Atria receive blood from veins and ventricles receive

blood from atria.

5. Heart Valves
1. Valves located between the atria and ventricles are known as the atrioventricular (A-V) valves.
1. valve on right side has 3 cusps (tricuspid)
2. vakve on left side has 2 cusps (bicuspid)
2. A-V valves prevent backflow of blood into atria when ventricle

Contracts

1. Eversion of valves into atrium is prevented by cords

(chordae tendineae) attached to free margin of cusps and to small muscles (papillary muscles) at heart wall

3. Semilunar valves prevent backflow of blood into ventricles

Following contraction.

1. Each have 3 cusps
2. Valve on right side is pulmonary semilunar
3. Valve on left side is aortic semilunar



6. Blood Flow Through the Heart
1. Blood that circulates to the tissues returns to the heart by the cranial vena cava(forward parts of body) and caudal vena cava (blood from rear parts of body).
2. Venous blood enters the right atrium during the atrial relaxation phase of the cardiac cycle and is then directed through the tricuspid valve to the right ventricle.
3. Ventricles then contract and the blood is pumped through the pulmonary semilunar valves to pulmonary arteries and lungs
4. After circulation through the lungs the blood enters the left atrium via the pulmonary veins.
5. Blood (now oxygenated) is directed to the left ventricle where it is pumped throughout the body through aorta.
7. Blood Vessels



1. Inner aspect of the pericardium is described as the outer cell layer of the heart and is known as epicardium
2. Middle layer of heart is cardiac muscle
3. Inner layer of heart is endocardium which is continuous with the endothelium of all blood vessels.
1. endothelial cells are single-layerd squamous epithelium
1. inflammation of endocardium is endocarditis
2. inflammation of heart valve is valvular endocarditis.
4. Blood vessels provide for a continuous route for blood leaving

The heart to return to the heart.

5. arteries, arterioles, capillaries, venules, veins
1. arteries more elastic
2. small arteries have some portion of elastic tissue replaced by smooth muscle-helps to regulate blood flow to capillary beds
3. Capillaries are merely endothelial tubes



4. Where endothelial cells border each other, a thin slit

(slit pore) or intracellular cleft is provided for diffusion of dissolved substances from plasma.

5. Pinocytotic vesicles are also present in the

Endothelial cells for nutrient transfer



6. Veins are thin-walled tubes reinforced by connective

Tissue. They also contain some smooth muscle fibers

7. Valves are present in the veins at irregular intervals

that are directed towards the heart – prevents backflow







2. Blood Circulatory Systems
1. Pulmonary
1. Circulates blood through the lungs
2. Pressure for this system originates in the right ventricle
3. Capillaries for this system lie in pulmonary alveoli



2. Systemic circulation
1. Carries blood that has returned from the lungs.
2. Pressure for this system orginates in the left ventricle
3. Blood traversing this system leaves the left ventricle through the aorta and is returned to the right atrium via the venae cavae.
1. First branches of aorta supply heart muscle through coronary arteries.

 

 



 

4. Within the systemic circulation are a few portal systems.
1. Vein heading to the heart rebranches to form a capillary bed which reunite to form veins.
2. Primary example is the hepatic portal system

 

1. Veins draining viscera all empty into the liver which reforms a capillary bed (liver sinusoids)
2. This portal system permits uptake of nutrients from digestive tract at the liver for metabolism and transport to other tissues.

 

3. Also permits cleansing of blood or the removal of harmful substances (detoxification).

 



 

 

 

 

 

 

3. Lymphatic System
1. Important adjunct to the circulatory system
2. Lymphatic vessels have blind beginnings in the interstitial spaces
3. Continuation vessels of the lymphatic system tend to parallel veins.
4. Lymph vessels join with each other and eventually form a few large lymph vessels that empty directly into large veins.



5. Fluid of lymph vessels is called lymph
1. Very close in composition to interstitial fluid
2. Protein in interstitial space can only return to plasma via lymph
1. 100% of plasma protein is turned over every 24 hours



6. Blind beginnings of lymph vessels are adapted for the intake of

` G. Lymph nodes are nodular structures of varying size located along the

course of lymph vessels.

1. Contain clusters of germ cells that divide to form

Lymphocytes.

2. Also contain fixed populations of macrophages
1. Attach and digest foreign substances

1. Spleen
1. Largest lymphoid organ of the body
2. Circulating fluid is blood instead of lymph
3. Only organ specialized to filter blood



4. Spleen outside covering is called the capsule
1. Contains connective tissue and smooth muscle
2. Smooth muscle is pronounced in carnivores
5. Trabeculae extend from the capsule
1. composed of elstic fibers, collagen and smooth muscle
2. Arteries, veins, lymph vessels and nerves are contained within the trabeculae.
6. Parenchyma of the spleen is comprised of red and white pulp

And is supported by trabeculae and blood vessels.



7. Most of the pulp is red because of the blood that is being

Filtered and contains fixed macrophages.

8. The white pulp is lymphoid tissue that is distributed

Throughout the spleen and which produces lymphocytes.

9. Spleen is site of red blood cell removal, reservoir of red cells

1. Cardiac Contractility
1. Origin of the heartbeat
1. All muscles have inherent rhythmicity of contraction
1. Frequency of contraction is greatest in cardiac muscle
2. Atria muscle cells have higher frequency of contraction than ventricular cells.
3. Small area (S-A- node) near junction of cranial vena cava and right atrium has higher frequency of contraction than atria.
1. This is location of origination of cardiac contraction.
2. Specialized muscle fibers send out impules which spread throughout the musculature of the atria.
3. Serves a pacemaker function.
2. Conduction of the Impulse
1. Muscles of the atria and those of the ventricles are arranged to form an atrial and ventricular syncytium.
1. syncytium is an arrangement of muscle fibers in which the fibers fuse to form an interconnected mass of fibers.



 

 

 

 

 

 

 

2. The atrial syncytium is separated from the ventricular

Syncytium by a fibrous ring that surrounds the A-V valves.

1. Fibrous ring acts as an insulator between the two

Syncytia

2. Impulse that spreads throughout the atria does not

Spread to the ventricles.

3. Permits independent contraction.

3. To facilitate conduction of the impulse from the S-A node and

Coordinate contraction the heart has a specilialized conduction tract.

1. Purkinje fibers join to form internodal pathways
2. transmission of impulses and subsequent depolarization is facilitated by intercalated discs interposed between muscle fibers.
3. Impulse conduction by internodal pathways is received by the A-V node which is located at a point between the atria and ventricles/
4. A-V node is continued throughout the A-V ring by the A-V bundle.
5. A-V bundle fibers are smaller in diameter than other Purkinjee fibers which slows impulse down and allows emptying of atria before contraction of ventricles.
6. Conduction fibers are continued from the A-V bundle in the wall dividing to form the right and left bundle branches to supply the right and left ventricles.
7. Cardiac muscle contracts more slowly than skeletal muscle and the refractory period is longer.
8. Both atria contract at the same time and both ventricles contract at the same time.
1. Contraction of muscle fibers within a syncytis is synchronized.
9. Defibrillation causes simultaneous depolarization of all

Cardiac muscle fibers. This permits initiation of a new cycle with impulses that begin at the S-A node.

3. Cardiac Cycle
1. Refers to the sequence of events that occurs during one complete heartbeat.
2. Events are continuous and the assigned periods are arbitrary for descriptive purposes
3. Diastole refers to relaxation of a heart chamber before and during filling of the chamber
4. Systole refers to contraction of a heart chamber in the process of emptying.



4. Electrocardiogram (ECG)
1. Record of voltage changes which occurs across the nerve and muscle membranes during waves of depolarization and repolarization.
2. Connection of the amplifier with wires (leads) to selected body parts (usually the limbs) and to a recorder proves a characteristic wave form.
1. Recording of electrical activity of the heart.
2. ECG is altered when heart muscle is damaged or ventricle walls are thickened.

 



3. P wave is associated with depolarization of atria, after

Depolarization, atrial contraction occurs

4. QRS complex represents both positive (upward) and

Negative (downward) deflections associated with ventricular depolarization; ventricular contraction begins after depolarization of fibers.

5. T wave represents ventricular repolarization
3. When viewing an electrocardiogram, it can be seen that

deflections of the waves whether positive or negative occur

occur from a common line known as the isoelectric line.

5. Heart Sounds
1. Listening to the heart (cardiac auscultation) permits identification of sounds that accompany contraction of heart muscle and closure of the heart valves.
1. Sounds are repeated for each cardiac cycle.
2. First sound is ventricular contraction and A-V valves
3. Second sound is ventricular relaxation and closure of semilunar valves.
4. Abnormal heart sounds are called murmurs and are usually associated with valve disorders
2. Heart Rate and Its Control
1. Heart rate refers to frequency of cardiac cycles
1. Usually measured as beats per minute
2. Generally, smaller animals have higher heart rates
1. Consequence of metabolic rate and oxygen consumption
2. Larger surface area to body mass ratio in smaller animals



3. Physical conditioning lowers heart rate as a result of cardiac

Hypertrophy.

4. Young animals have a higher heart rate than adult animals
1. higher metabolic rate
2. Tonic vagal inhibition is less developed in young animals.
3. Autonomic Nervous System regulates heart rate
1. Sympathetic innervation occurs via efferent fibers from the stellate ganglia of the sympathetic trunk.
1. Increases heart activities
2. Parasympathetic innervation is supplied by fibers from the vagus nerves.
1. Decreases heart activities
3. Heart activities include rate of contraction, force of

Contraction, rate of impulse conduction and amount of coronary blood flow.

4. Autoregulation of the heart rate also occurs
1. Based on volume of blood received in atria
2. Starling"s law of the heart
1. The more the heart is filled during diastole the greater the volume pumped out.
5. Reflexes
1. Several important reflexes within the cardiovascular system assist in its regulation.
1. In the arch of the aorta and where the carotid arteries branch to form the internal carotid thee are many receptors that respond to stretching of these vessels.
2. These are called Baroreceptors because they respond to blood pressure.
1. When the artery is stretched the receptors increase their firing rate.
2. The impulses from the aorta are transmitted to the medulla by the vagus nerves
3. The impulses from the carotids are transmitted to the medulla by the glossopharyngeal nerves
4. Response of the medulla center is to decrease the blood pressure through parasympathetic stimulation of the heart and inhibition of the vasomotor center (dilating blood vessels).
3. Bainbridge Reflex
1. Receptors in right atrium stimulated by stretch

To increase heart activities

 



 

3. Blood Pressure
1. Greatest pressure develops within the aorta when the left ventricle contracts.
1. High point of blood pressure is called systole.
1. At peak of left ventricular contraction
2. The lowest point is called diastole
1. Occurs during left ventricular relaxation
3. The term pulse pressure refers to the difference between the

Systolic and diastolic pressures.

4. Mean pressure is the diastolic pressure and 1/3 of systolic

Pressure.

1. Determines the average rate at which blood flows

Through the systemic circulation.



4. Cardiac Output
1. Defined as the amount of blood pumped by the heart in a unit period of time.
1. Usually measured in milliliters or liters per minute.
2. Divided among tissues according to need.
1. Accomplished by regulating arteriole constriction or relaxation altering blood flow to vascular beds.
5. Effect of Breathing
1. When animals inhale air (inspire) a vacuum develops in the intrapleural space that is also transferred to the mediastinal space
2. Thin-walled structures in mediastinal space can then expand
1. Venae cavae, lymph vessels, esophagus
2. Helpful for return of venous blood and lymph to the heart



6. Circulation Time
1. Time required for blood to return to the right atrium after it has been pumped from the left ventricle.
1. Variable but approximately 40-60 seconds.
7. Capillary dynamics



1. Refers to physical factors associated with the exchange of fluid between the blood and interstitial fluid at the level of the capillaries.
2. Two Types
1. Diffusion of water and dissolved substances accounts for the greatest degree of interchange between capillaries and interstitial fluid.
2. Bulk flow results from osmotic and hydrostatic pressure

differences between plasma and interstitial fluid.

1. Volume of bulk flow into the interstitial space from

Plasma is usually balanced by amount returning to the capillaries from interstitial space.

3. Mechanism of bulk flow
1. capillary pressure
1. hydrostatic pressure in capillary
2. plasma colloidal osmotic pressure
1. effective osmotic pressure of capillary
3. Interstitial fluid pressure
1. Hydrostatic pressure in the interstitial fluid
4. interstitial fluid colloidal osmotic pressure
1. effective osmotic pressure of the interstitial fluid



 

4. Capillary imbalances
1. imbalance of bulk flow due to
1. blockage of venous drainage
2. blockage of lymphatic drainage
3. loss of protein from capillary to interstitial space
4. depletion of blood protein through malnutrition
2. Leads to edema or swollen tissue due to excess fluid in