Chapter 8 The cardiovascular system

Circulatory system

Has many functions, provides a means of movement for a variety of substances through the body, including: >White blood cells to provide immunity to the entire body > Red blood cells to transport O2 > Platelets & clotting proteins for forming blood clots > Buffer chemicals to maintain the proper body pH > CO2 waste gas >Nutrients such as proteins & sugars > Electrolytes to provide normal electrical charges for cellular function, especially for muscle & nerve cells >H2O >Waste materials from cellular metabolism

What wo types of circulatory systems exist with the body

The CARDIOVASCULAR SYSTEM & LYMPHATIC SYSTEM. Blood & its associated & products are carried by the cardiovascular system, whereas the lymphatic system carries a fluid called LYMPH. It is composed of H2O, proteins, & certain white blood cells.

Cardiac conduction system

A network of modified cardiac muscle cells within the heart muscle. The Punkin fibers, which conduct electrical impulses within the cardiac muscle, are part of that system. A collection of cells within the right atrium is called the si no atrial (SA) node, &this is where the normal electrical impulses in the heart originate. At the junction between the atria & ventricles is another collection of cells known as the atrioventricular (AV) node, which functions as a gateway through which electrical impulses pass from the atria to the ventricles.

heart rate

DEF: How often the heart contracts, usually stated in beats per minute

aorta

DEF: Major artery of the systemic circulation that receives blood from the left ventricle

pericardium

DEF: Tissue that forms a sac around the heart to protect it & to control the movement of the heart within the thorax

Exact path of the blood takes through the heart

>The right atrium receives blood from the abdomen via a vein - CAUDAL VENA CAVA & from the head via vein _ CRANIAL VENA CAVA > Right atrium contracts, the blood is forced through the TRICUSPID VALVE & into the RIGHT VENTRICLE > The right ventricle contracts, forcing the blood through the PULMONARY ARTERY to the pulmonary circulation of the lungs, where it is oxygenated. > Blood exiting the pulmonary circulation returns to the heart through the PULMONARY VEIN, which empties into the LEFT ATRIUM >Contraction of the LEFT ATRIUM pushes blood through the MITRAL VALVE into the LEFT VENTRICLE, which contracts to pump blood through the AORTIC VALVE into the AORTA & thus into the systemic circulation

pathway of blood through the heart

>The right atrium receives blood from the abdomen via a vein called CAUDAL VENA CAVE & from the head via a vein called CRANIAL VENA CAVA. >When the right atrium contracts, the blood is forced through the tricuspid valve & into the right ventricle >The right ventricle contracts, forcing the blood through the pulmonary artery to the pulmonary circulation of the lungs where it is oxygenated > Blood exiting the pulmonary circulation returns to the heart through the pulmonary vein, which empties in to the left atrium > Contraction of the left atrium pushes blood through the mitral valve into the left ventricle, which contracts to pump blood through the aortic valve into the aorta & thus into the systemic circulation.

gross anatomy of the heart- blood flow out of the heart (wb)

>Two semilunar valves that control blood flow out of the heart. Pulmonary artery exits the right ventricle, & the valve control blood flow out of the heart. Pulmonary artery exits the right ventricle, & the valve controlling blood flow through this opening - PULMONARY VALVE. Exiting the left ventricle is the aorta: thus, the valve controlling blood flow through this opening - AORTIC VALVE. These valves are one-way- valves; in other words, blood flow only in one direction. If blood attempts to flow in the wrong direction, the flaps close over the opening. When certain diseases damage these valves, the valves don not close properly, allowing some blood to flow in the wrong direction. This condition can lead to congestion & increased pressure in certain chambers as well as some veins, a condition called HEART FAILURE, which is described as inadequate pumping action of the heart. Ruptured chordae tendineae can lead to both acute valve failure & acute heart failure

Blood vessel Structure

All blood vessels have the same general structure. The outer layer of a blood vessel is the TUNICA ADVENTITIA, which is composed of CT. in larger vessels, this layer contains small blood vessels that transport O2 & nutrients tot he cells of the blood vessel walls. This may seems odd because there's blood within the blood vessel, but in larger blood vessels the wall is too thick for the blood within the lumen to supply O2 & nutrients to all of the cells within the wall. > The middle layer of blood vessels, the TUNICA MEDIA, is composed of smooth muscle cells that control the blood vessel's diameter. The tunica media of some blood vessels also contains elastic CT. The muscle cells are arranged in a ring around the diameter of the vessel, so as the muscles contract, the diameter of the vessel decrease, which increases the resistance to blood flow & increases the blood pressure. Contractions of the tunica media muscles is under the control of certain nerves & hormones, especially adrenaline, which causes contraction of the muscles. > The final & innermost layer of the blood vessel ins the TUNICA INTIMA, composed of a thin layer of epithelial cells, called the ENDOTHELIUM, & underlying CT. Each type of blood vessel modifies this basic plan to better suit its purpose.

electrocardiogram

An instrument that detects electrical currents that used to measure the electrical activity of the heart is the ELECTROCARDIOGRAPH., which measures electrical current using metal electrodes attached to the skin to produce an ELECTROCARDIOGRAM (ECG or EKG). The ECG is printed on graph paper, which moves under a stylus. If the stylus does not move, a straight line is drawn as the paper unrolls beneath it. Electrical currents causes the stylus to move up or down as the paper unrolls beneath it, creating record of depolarization & polarization as waves in the line that may be measured for magnitude & rate using the boxes on the graph paper > When the SA node generates an electrical impulse, & the impulse spreads across the atria, the stylus is momentarily deflected from the resting position, creating a bump in the previously straight line. The bump in the graph paper associated with the depolarization of the atria is called the P WAVE. Other waves are created by ventricular depolarization (the QRS COMPLEX) & by repolarization of the ventricles (the T WAVE). By counting how often the wave occur on the graph paper, HR may be calculated. By measuring the height & width of various waves, heart abnormalities may be found. EX., If the QRS complex is longer (takes more time) than normal, it may be due to enlargement of the ventricles or poor conduction of the electrical impulse through the Purkinje fibers of the ventricles. If there are more P waves (atrial depolarization) than QRS waves (ventricular depolarization), it suggests that not every electrical impulse generated by the SA node is being successfully transmitted through the AV node to the ventricles (condition called HEART BLOCK)

Arteries & arterioles

Arteries carry blood from the heart to the cells of the body & are also responsible for establishing the blood pressure within the circulatory system. Two types of arteries exist : ELASTIC ARTERIES & MUSCULAR ARTIES. > ELASTIC arteries contain a larger proportion of elastic CT within the tunica media than other arteries most of the major arteries close to the heart are elastic arteries, including most of the pulmonary arteries, aorta, & carotid arteries. During systole, the pressure of the blood being pumped by the heart pushes against the artery's wall, stretching the elastic fibers in the wall. During diastole, the blood pressure against the arterial wall decreases, & the blood pressure against the arterial wall decreases, & the elastic fibers in the tunica media snap back to their original length, causing the diameter of the blood vessel to return to normal. The pressure generated by the recoil of the elastic fibers helps maintain the blood pressure in the circulatory system & keeps blood flowing while the heart is relaxing > MUSCULAR arteries are branches off the main elastic arteries that carry blood to various regions of the body. They have more muscle than elastic fibers in the tunica media. The larger proportion of muscle allows for finer control of blood vessel diameter, because the fibers in elastic fibers, resistance to blood flow &, along with the elastic fibers, the blood pressure. The change from the more elastic tunica media to the more muscular tunica media is gradual> ARTERIOLES - the smallest form of artery, carry blood from the muscular arteries to the capillaries. They lack significant elastic fibers & have a few layers of smooth muscle cells in the tunica media: the TUNICA ADVENTITA & TUNICA INTIMIA are extremely thin. arterioles gradually decrease in diameter until they reach the capillary bed

Describe the structures of arteries, capillaries, & veins

Arties carry blood away from the heart & veins bring it back. Blood going through systemic circulation is under higher pressure than blood in the pulmonary or coronary circulation. It takes more pressure to carry blood to the far distance to every extremity than it does to carry it through the shorter pulmonary & coronary routes, especially when the forces of gravity are considered. The blood in the systemic circulation also encounters more resistance to flow, & there is more blood in the systemic circulatory system at any given time than there is in the coronary or pulmonary systems. The layers of the artery wall are similar to the layers in the walls of the heart: there is a tough outer fibrous layer, a middle layer of smooth muscle & elastic CT, & a smooth inner lining called ENDOTHELIUM. In the aorta & pulmonary arties, which carry blood out of the heart, the middle layer of the wall contains more elastic fibers than muscle fibers. This allows them to stretch slightly as they receive the high-pressure blood from the ventricles. >CAPILLARIES -blood flows through small arterioles into tiny, thin -walled capillaries which unlike other blood vessels, do not have muscle in their walls. In the systemic & coronary circulation, the capillaries are where oxygen & nutrients in the blood are exchanged for carbon dioxide & other waste products that are taken back toward the heart. In the pulmonary circulation, the capillaries of the lungs are where oxygen-poor blood picks up oxygen & transports it back to the heart. in the systemic & coronary circulation, arties carry oxygen- rich blood & veins carry oxygen-poor blood ; in the pulmonary circulation, the opposite is true > VEINS - The blood is under much less pressure in veins than in arteries, & the veins have thinner walls. Valves in small-& medium-sized veins ensure that the blood travels only in the direction of the heart. As the veins carry blood back to the heart, they are usually located right next to an artery carrying blood in the other direction.

The two dorsal chambers the heart closer to the spine

Atria (sig., atrium),

myocardium

Beneath the epicardium is the muscle layer of the heart, which constitutes the heart's largest mass. Lining the myocardium on the inside is a layer of elastic epithelial tissue called ENDOCARDIUM. Cardiac muscle cells are called MYOCYTES. They are connected to each other with intercalated disks & DESMOSOMES. This allows cells to work together in conducting electrical impulses & allowing heart muscle cells to contract & relax together

Describe the structure & locations of the heart valves (LO) [internal structure of the heart]

Blood flows from the right atrium to the right ventricle through the RIGHT ATRIOVENTRICLAR VALVE aka RIGHT AV NODE or TRICUSPID VALVE. (tri means "three", -cusp means "flap:) The tricuspid valve has (3) flaps or leaflets. The flaps originate from the ANNULUS (little ring, fibrous) of the valve. The annulus is the opening and the (2) leaflets move within that opening. When the atrial muscles contract during SYSTOLE, the increased blood pressure in the atrium forces the flaps to open into the right ventricle. However, when the ventricle contracts & the atrium relaxes, the flaps of the valve are prevented from bending back into the atrium by the CHORDAE TENDINASE. They connect the free edges of the valvular flaps to the PAPILLARY MUSCLES, which attach inside the ventricle on the interventricular septum that separates the right & left ventricles. > In the right ventricle, there is a band of tissue that originates at the interventricular septum but does not attach to the flaps of the tricuspid valve; it is called the MODERATOR BAND & it connects to the outside wall of the right ventricle. It gives the wall of the right ventricle additional structural support. > PULMONARY VALVE aka PULMONIC VALVE prevents backward flow of the blood from the pulmonary arteries into the right ventricle when the right ventricle relaxes & the pressure inside the ventricle drops. Like the tricuspid valve; the pulmonary valve has three flaps attached at their outer edges to a fibrous annular ring. Because the right ventricle is wrapped around the left ventricle, the tricuspid valve & the pulmonary valve are on nearly opposite sides of the heart; the tricuspid valve is actually located more on the left side of the heart than on the right. The combined efforts of the one-way tricuspid valve & the one-way pulmonary valve ensure that the right ventricle is filled from the right atrium & ejects blood only into the pulmonary arteries >after circulating through the lungs to dump CO2 & pick up O2, blood returns to the heart at the left atrium, from which it travels through the left atrioventricular valve (MITRAL VALVE) to the left ventricle. Like the tricuspid valve, the mitral valve opens in only one direction, preventing backward flow of the blood from the ventricle to the atrium when ventricle contracts. The mitral valve has (2) leaflets (flaps). Just like the tricuspid valve the right side of the heart, the outer edges of the mitral valve flaps are attached to the fibrous annulus, & the inner edges are attached to chordae tendinae, which in turn attach to papillary muscles on the septal portion of the ventricle wall. The thick-walled left ventricle does NOT have a moderator band like the thinner-walled right ventricle. > The last valve through which oxygenated blood passes on its way to the systemic & coronary arties is the AORTIC VALVE. Like the pulmonary valve, it has three flaps attached to an annulus. It opens outward to the aorta, only allowing blood to pass through during systole. & preventing it from returning to the left ventricle during DIASTOLE, thus ensuring that the ventricle is filled by blood from the atrium. The aortic valve & pulmonary vales are both called SEMILUNDAR VALVES

Capillaries

Branching out from each arteriole is a multitude of capillaries, tiny vessels that form a network to supply blood to the body's tissues. They have very thin walls that lack a tunica adventitia or tunica media. Essentially, the capillary wall is composed only of a tunica intima of endothelial cells. Capillaries allow the exchange of gases, fluids, nutrients,& waste products between the blood & the cells of that tissue; hence the need for a thin wall to minimize the distance these substances must cross. many capillaries have a diameter equal to the width of one RBC (or smaller). Certain areas in the liver, bone marrow, & spleen have larger capillaries called SINUSOIDS, because there's a need for sluggish blood flow to allow these organs to perform their functions more effectively. >Eventually, the capillaries fuse together to join the venous side of the capillary bed. More extensive capillary beds are found in tissues such as muscle. Because these muscles have increased metabolic rates, they require more O2 & nutrients. Exchange of material across the walls of the capillaries is very similar to the exchange of gases that occur in the alveoli of the lungs. Passive diffusion of material occurs because concentration of material is higher on one side of the capillary wall than on the other side. Cells produce CO2 as a result of cellular metabolism & must get rid of this waste. > Cells also need O2 for cellular energy production. Blood entering the capillary bed is rich in O2 & poor in CO@. As blood travels through the capillary bed, CO2 from the cells diffuses across the capillary bed, CO2 from the cells diffuses across the wall into the cells. Nutrients pass from the blood into the cells, whereas waste materials leave the cells & enter the bloodstream. By the time the blood exits the capillary bed, the blood has less Co2, less O2, more waste products & less nutrients than when it entered the capillaries.

Examples of heart rate & cardiac output

CO (cardiac output) = SV (stroke volume X HR (heart rate) So, if we know that a dog's heart effects 2 milliliters )ml) of blood into the aorta with each systolic contraction, & its heart rate is 100 beats per minute, The animal's cardiac out put can be calculated using formula: CO =2ml/min (SV X 100 beats/min (HR) = 200 ml/min Cardiac output for the dog would be 200 ml of blood per minute. >This equation can help explain why cows & horses survive with much slower heart rates than cats & dogs. A horse or cow needs more cardiac output than a dog or cat because it has much greater tissue mass, yet it has a slower heart. and CO goes up but HR goes down. Equation would be: ^ CO = ?SV X vHR Stroke volume must be increased considerably: equation ^CO + ^^SV X vHR >Horses & cows have much bigger hearts than dogs& cats, this allows them to have such a large stroke volume that they can generate sufficient cardiac output, even with a lower heart rate than smaller animals. The HR for an individual animal is based in part on the rate at which the SA node spontaneously DEPOLARIZES, but many factors can increase or decrease the demand or cardiac output & alter the HR. EX., vigorous exercise increase the demand for O2 in tissues, so cardiac output must increase to meet demands. The heart begins to contract more forcefully ( increased CONTRACTILITY or positive INTROPY), which increases HR. What happens during exercise can be summarized using the equation: ^^ CO = ^SV x ^HR

List the factors that influence heart rate & cardiac output (LO)

Cardiac output the amount of blood that leaves the heart, is determined by two factors: (1) STROKE VOLUME, which is the amount of blood ejected with each cardiac contraction, & (2) HEART RATE, or how often the heart contracts. >Heart rate for an individual animal is based in part on the rate at which the SA node spontaneously DEPOLARIZES, but many factors can increase or decrease the demand or cardiac output & alter the HR. Factors can include vigorous exercise, changes in blood pressure, trauma, illness

List the chambers of the heart & describe the path of blood flow through the heart (LO)

Chambers of the heart are: right atrium, right ventricle, Left atrium, left ventricle. SCHEMATIC DEPLICTUM OF BLOOD FLOW > In a healthy heart, blood travels in only one direction: a series of valves prevents backward flow. Deoxygenated blood is received into the RIGHT ATRIUM from the SYSTEMIC & CORONARY CIRCULATION. Coronary circulation supplies the heart muscle with blood; in addition to all of the other tissues, the heart must supply blood to itself. The many veins that collect deoxygenated blood from the tissues combine into progressively larger vessels, until they form the CRANIAL VENA CAVA & the CAUDAL VENA CAVA. The venae cavae empty into the right atrium, which is located at the base of the heart >After collecting in the right atrium, blood passes through the RIGHT ATRIOVENTRICULAR (AV) VALVE (Tricuspid valve), into the RIGHT VENTRICLE of the heart. during SYSTOLE (cardiac contraction), The RIGHT VENTRICLE contracts, the TRICUSPID VALVE (right atrioventricular (AV) valve) "closes". (preventing blood flow back into the atrium), & blood is ejected from the RIGHT VENTRICLE through the PULMONARY VALVE & into the PULMONARY ARTERIES, blood passes through branching vessels to the PULMONARY CAPILLARIES of the ALVEOLI, where oxygen exchange takes place. > After oxygenated in the pulmonary capillaries, blood travels through vessels that merge together & increase in diameter, becoming the PULMONARY VEINS that deliver blood into the LEFT ATRIUM. Blood that has collected in the left atrium flows through the LEFT ATRIOVENTRICULAR VALVE (MITRAL VALVE), into the LEFT VENTRICLE. During systole (heart contraction), the mitral valve snaps shut (preventing backward flow from the ventricle to the atrium) as the left ventricle contracts & ejects the blood through the AORTIC VALVE into the coronary arties & the AORTA (the largest artery in the body). From the aorta the blood travels through the various arterial branches to the capillaries of the tissues, where oxygen & nutrient exchange take place, After passing through the tissue capillaries, deoxygenated blood travels back to the heart through progressively larger venules & veins, until it once again passes through the VENAE CAVAE, or CORNARY VEINS, into the RIGHT ATRIUM

Systole

DEF : muscle contraction; The part of the cardiac cycle associated with contraction of the ventricles & atria & ejection of blood into the arterial systems

cardiac tamponade

DEF: A condition in which the heart becomes unable to expand normally between contractions because of fluid in the pericardial space

Sinoatrial node -(SA) node

DEF: A group of specialized cardiac muscle cells in the wall of the right atrium of the heart that act as the heart's pacemaker. The impulse that starts each heartbeat is initiated in the SA node

Pulmonary artery

DEF: Artery arising from the right ventricle that delivers blood into the pulmonary circulation

chordae tendineae

DEF: Fine, threadlike cords that connect two artioventricular valves to the appropriate papillary muscles in the ventricles

papillary muscles

DEF: Muscular, nipple-like projections in the heart that anchor the chordae tendineae. When contracted, papillary muscles act to open the atrioventricular heart valves

Parietal

DEF: Pertaining to the wall of a organ cavity

Cardiac output

DEF: The amount of blood that leaves the heart

Mediastinum

DEF: The area of the thorax between the lungs. It contains the heart & most of the other thoracic structures, such as the trachea, esophagus, blood vessels, nerves, & lymphatic structures

contractility

DEF: The inherent ability of the heart to develop a force by contracting, which increases chamber pressure

Myocarium

DEF: The middle layer of the heart & the main muscle layer responsible for contraction during systole

reticulum

DEF: The most cranial part of the forestomach: it has a honeycomb appearance inside

interpleural space

DEF: The space between the pleural covering of the right lung & the pleural covering of the left lung

hardware disease

DEF: a disease in ruminant animals caused by irritation of the lining of the reticulum by swallowing metal objects

Aortic valve

DEF: a semilunar valve; it separates the left ventricle & the aorta during diastole.

Mitral valve

DEF: aka left atrioventricular valve; separates the left atrium & ventricle & protects the pulmonary venous system from the high pressures in the left ventricle during systole

Tricuspid valve

DEF: aka right ventricular (AV) valve; separates the right atrium & ventricle

septic pericarditis

DEF: infection, & resulting inflammation, of the pericardium of the heart in ruminant animals often caused by the penetration of sharp foreign objects that have been swallowed through the wall of the reticulum & diaphragm, & into the pericardium

Auscultation

DEF: listening, with the ear or with a stethoscope, to sounds produced within the body

Epicardium

DEF: outer layer of the heart

patent ductus arteriosu (PDA)

DEF: persistent fetal connection between the aorta & the pulmonary artery that can result in congestive heart failure if not corrected

Visceral

DEF: pertaining to the soft internal of organs

SULCUS

DEF: sing., Sulci, means groove, especially shallow grooves in the cerebral cortex

Pulmonary circulation

DEF: the part of the circulatory system that delivers unoxygenated blood to the lungs & oxygenated blood to the left side of the heart WB>The pulmonary circulation is the blood supply that goes to the lungs so the blood can be oxygenated & rid itself of CO2. Therefore, the lungs actually have two supplies of blood: blood rich in O2 that comes from the heart to supply the pulmonary cells & blood poor in O2 that goes to the alveoli to be oxygenated > The right side of the heart pumps blood to the pulmonary circulation

Defibrillation ( clinical application)

DEFIBRILATION - Electrical conduction system of the heart, sometimes a disease heart will develop one or more ECTOPIC PACEMAKERS. The word ectopic - out of place, 7 the ecoptic pacemaker is located outside the heart's normal pacemaker, which is the SA node in the right atrium. Despite the presence of any ectopic pacemakers, the SA node continues to fire, meaning that the cardiac muscle cells receive electrical currents from more than one direction. The synchronized contraction of the heart, which begins in the artia & flows through the ventricles, is lost. If there is enough ectopic pacemaker activity, a condition called VENTRICULAR FIBRILLATION may develop, in which heart muscle cells in different areas contract independently of one another. In ventricular fibrillation, all coordinated pumping activity of the ventricles is lost. The defibrillator sends a large electrical current of short duration through the heart, with the objective of repolarizing all of the cells at the same time. If defibrillation is successful, the SA node & the heart's normal conduction system will resume control over depolarization of the heart after the cells have been "reset" by defibrillation.

gross anatomy of the heart. (wb)

Dividing the Heart has a large muscular sac divided into four chambers. The two dorsal chambers the heart closer to the spine Atria (sig., atrium),The two more ventral chamber of the heart closer to the sternum - ventricles. In domestic animals, the heart sits slightly skewed so that the right ventricle & right atrium sits slightly cranial to the left ventricle & left atrium. > The atria are smaller & less muscular than the ventricles. The atria is a wall of muscle called INTERATRIAL SEPTUM. Between the two ventricles is a similar wall called the INTRAVENTRICULAR SEPTUM. Between the atrium & ventricle on either side is a ring of fibrous CT. Attached to these rings are two to three roughly triangular flaps ( or valves of elastic fibrous CT that can cover opening between the atrium & ventricle > CHORDAE TENDINEAE are cords of fibrous tissue that anchor the tips of the flaps to papillary muscles, which are finger-like muscular projections of the myocardium into the lumen (or interior) of the ventricle. This structure of the fibrous ring & its associated flaps is called an atrioventicular valve. The right atrioventricular valve usually has three flaps ( tricuspid valve). However in dogs & cats, there is only two major flaps. The left atrioventriculat valve usually has only two flaps -BICUSPID VALVE (mitral valve)

Patent Ductus Arterious (clinical application)

During gestion, the fetal circulation does not carry much blood through the lungs: instead, there is an opening between the left pulmonary artery & the aorta that allows much of the blood that leaves the right ventricle to bypass the lungs on the way to the aorta & systemic circulation. Because the fetus does not breathe air - oxygen is provided to the fetus from the blood of the dam - there is only enough pulmonary circulation to nourish the tissues of the growing lungs. Following the rupture of the umbilical cord at birth, the fetus must generate it own oxygenated blood, so circulation through the lungs must be increased to include all of the blood that leaves the right ventricle. Normally, the shortcut opening between the pulmonary artery & aorta known as the DUCTUS ARTERIOSUS closes soon after birth. Occasionally, the opening fails to close in a newborn, a condition called PATENT DUCTUS ARTERIOSUS (PDA). Young animals with PDA suffer from inadequate oxygenation of their blood; in the long term, the condition is incompatible with life. PDA may be treated with drug therapy to promote closure, or surgical closure of the ductus arteriosus may be an option.

Cardiac cycle

Each complete contraction & relaxation of the heart. There are two main parts to the cardiac cycle: systole & diastole. During systole, the heart muscle contracts & blood is ejected from the artia to the ventricles & then from the ventricles to the arteries. During diastole the heart relaxes & refills with blood to be ejected during the next systolic contraction.

Atrioventricular (AV ) bundle

Electrical impulses are slowed as they move through the AV node. This provides the time needed for the atria to empty for the atria to empty into the ventricles before the ventricles are signaled to contract. Just ventral to the AV node is the ATRIOVENTRICULAR BUNDLE (AV) bundle, which conducts the signal into the ventricles. After entering the ventricles, the AV bundle branches out into right & left ventricles. The signal is carried rapidly to the apex of the heart before the bundles branch out into the ventricular muscle. Initiating the ventricular contraction at the apex of the heart causes the ventricle to contract in the ventral-to-dorsal direction, squeezing the blood up to the base from the apex. This pushes the blood toward the appropriate artery exiting each ventricle. The conduction fibers allow for more rapid transmission of the electrical impulse through the heart & also help coordinate the contractions for more effective pumping

Cardiac pacemaker

Electrical signals in the heart begin in the right atrium to the sinoatrial (SA) node aka cardiac pacemaker. These cells have an inherent ability to generate an electrical current, a process called SELF EXCITATION. The cells of the sinoatrial (SA) node have different "channels" in the cell membrane that transport sodium, calicum & potassium in or out of the cell. Such movements change the difference in electrical charges across the cell membrane & are some what dependent on the levels of sodium, potassium & calicum in the body

List the events responsible for the heart sounds heard on auscultation (LO)

In all species the heart is auscultated through the chest wall, usually with a stethoscope. In usual cardiac rhythm is typically described as LUB-DUB; the LUB is properly call S1, while the DUB is S2. S1 is associated with simultaneous closure of the MITRAL & TRICUSPID VALVES at the beginning of the VENTRICULAR SYSTOLE. Due to the orientation of the heart in the chest, while the tricuspid valve is best heard on the right. The S2 heart sound is associated with the closure of the semi-lunar (AORTIC & PULMONIC) valves at the beginning of the VENTICULAR DIASTOLE. The aortic valve is easier to hear on the left side of the chest as it exits the left ventricle, the pulmonary valve that exits the right ventricle is also easiest to hear on the left! The heart can be auscultated by placing a stethoscope against the chest wall at the level of the heart. In cattle & horses, this commonly requires slipping the stethoscope under the elbow to place the scope further forward on the animal's chest; in small animals, the stethoscope is placed against the chest caudal to the elbow. Large animals are also different from small animals in that one may hear a third sound, S3, due to rapid ventricular filing & a fourth, S4, due to contraction of the artia. S3 & S4 are not usually heard in dogs & cats.

Location of the heart

In cats & dogs, the heart lies at a level between the 3rd & 7th ribs. In horses & ruminants, the heart lies at a level between the 2nd & 6th ribs. The heart is slightly heart shaped; the round base of the heart is where the major blood vessels enter & exit, & the apex at the other end is where the left ventricle comes to a point. >In all veterinary species, the heart lies in the MEDIASTINUM, which is the space between the (2) pleural cavities that contain the lungs. The trachea, esophagus, & some vascular structures are also located in the mediastinum. The mediastinum is also called the INTERPLEURAL SPACE, because it is the space between the pleural covering of the right lung & the pleural covering of the left lung > In a standing animal, the base of the heart is oriented in a dorso-cranial direction

hardware disease (clinical application)

In cattle, the RETICULUM (the cranial stomach compartment) rests directly behind the heart, & the two organs are separated by the muscular diaphragm. Cattle are not very selective when eating, & it is not uncommon for them to ingest wires, nails, & other foreign metallic objects along with their feed. These bits of hardware are ingested into the rumen, from which digestive contractions move them forward into the reticulum. Continued rumenal contractions, particularly when combined with factors that increase abdominal pressure, such as pregnancy & parturition, may push pieces of wire through the cranial wall of the reticulum. Puncture of the reticulum wall by a foreign object often results in traumatic RETICULOPERITONITIS, also card HARDWARE DISEASE, which is an inflammation & infection of the reticulum & abdominal cavity. More severe disease occurs when a wire is pushed even farther cranially, through the diaphragm & into the pericardium. This can result in SEPTIC PERICARDITIS, which is an infection of the pericardium that usually progresses to heart failure & death. > Hardware disease can be prevented by the oral administration of a magnet about the size of a 5 ml blood tube. The magnet stays in the rumen or reticulum, usually for the rest of the anima's life. Wire & other objects ingested by the animal sticks to the magnet instead of being pushed cranially through the wall of the reticulum & beyond

List the names & locations of veins commonly used for venipuncture in animals

In dogs & cats, the CEPHALIC VEIN of the thoracic limb is commonly used to gain venous access. The cephalic vein runs between the elbow & the carpus on the cranio-medial aspect of the forearm. The cephalic vein carries blood from the distal extremity to the jugular vein. > In the pelvic limb of dogs & cats, the FERMORAL VEIN may be used for venipuncture. The femoral vein, which is more commonly used in cats than dogs, runs along the medial aspect of the hind limb between the groin & the tarsal joint (hock) & carries blood proximally to the iliac vein, which travels to the vena cava. >The SAPHENOUS VEIN, which is more commonly used in dogs, run along the lateral aspect of the hind limb from the cranial aspect of the leg just above the hock (tarsus) to the caudal aspect just below the knee (stifle). The saphenous vein carries blood to the femoral vein > The JUGULAR VEIN is commonly used for venipuncture in nearly all veterinary species both large & small. Jugular veins travel along the ventral aspect of each side of the neck, from the mandible to the shoulder, in the muscular jugular groove. The jugular veins are located near the carotid arteries. In equine species n particular, care must be taken to avoid accidental injection into the carotid artery of substances that are meant to be injected into the jugular vein. The carotid artery carries blood very quickly to the brain; substances that act as sedatives when injected into the jugular vein may actually cause seizures if accidently injected into the carotid artery. > In lactating dairy cattle, the SUPERFICIAL CAUDAL EPIGASTRIC VEIN , commonly called the MILK VEIN, is easily seen as it travels along the ventral aspect of each side of the abdomen from the udder to about the level of the sternum. This vein is not to be used for routine venipuncture, because its thin-walled, superficial character makes it prone to excessive bleeding & hematoma formation, which may lead to the development of an abscess. > In ruminants & rodents, the COCCYGEAL VEIN may be used for venipuncture. The coccygeal vein carries blood from the tail to the vena cava. It runs along the ventral midline of the tail.

Congestive heart failure (clinical application)

In older dogs, congestive heart failure (CHT) is fairly common problem. CHF occurs when the pumping ability of the heart decreases, usually due to disease of the heart muscle or a valve malfunction that restricts the forward flow of blood through a valve or allows a backward flow. CHF may be predominantly right-sided or left-sided. When the right side of the heart begins to fail, blood returning from the systemic circulation is no longer able to move through the right heart as quickly. This causes increased blood pressure in the systemic circulation, which results in fluid accumulation in the form of ASCITIES ( fluid in the abdomen) & EDEMA (fluid in the tissues). When the left side of the heart fails, venous return from the lungs is decreased, resulting in pulmonary edema, which interferes with respiratory function. The decreases in cardiac output associated with heart failure may also reduce perfusion of important organs, such as kidneys, to dangerously low levels. Medications used to treat CHF include CARDIAC GLYCOSIDES to increase the strength of cardiac contractions, DIURETICS to promote elimination of extra fluid to relieve edema, & VASODILATORS to enhance blood flow to the organs & decrease vascular resistance to outflow from the heart. CHF in pets cannot be cured, but it can often be medically managed to improve the animal's quality of life.

External structures of the heart

In the heart the base is located at the top, where the ATRIA are found & where the blood vessels enter & exit the heart. The APEX of the heart points in a ventral & caudal direction, & the tip of the apex of the heart is also the tip of the LEFT VENTRICLE The largest & most visible parts of the atria are the AURICLES. The auricles can be identified by determining which ventricle they lie above. The left auricle lies over the left ventricle, which is long & narrow & terminates at the apex of the heart. The right auricle lies over the right ventricle, which has a broader surface area & wraps around the left ventricle. The borders of the ventricles can be seen on the surface of the heart: they are separated by interventricular SULCI. The interventricular sulci contain fat & blood vessels that are part of the coronary circulation of the heart. >The blood returning to the heart from the pulmonary, coronary, & systemic veins is under relatively low pressure, the walls of the atria (blood returns) do not have to be as thick & strong as the walls of the ventricles (blood is ejected into the arteries). The texture of the auricles is quite pliable when compared with the firmness of the external surfaces of the ventricles. >Cranial & caudal venae cavae that collect blood from the systemic circulation can be seen joining together with the coronary sinus, which collects blood from the coronary circulation & conveys it into the right atrium. A # of pulmonary veins can be found entering the left atrium. The veins that enter the artia carry venous blood under relatively low pressure, so they have much thinner walls than the arteries that exit the ventricles carrying blood under higher pressure. [The thick-walled left ventricle of the heart appears to be narrower than the right ventricle (exterior of the heart is examined), and lower portion of the left ventricle defines the apex of the heart. The broader thinner walled right ventricle does not extend to the apex. The vessels that emerge from the ventricles actually emerge from the base of the heart near the auricles & veins supplying blood to them, not from the apex or the bottom of the heart} > The PULMONARY ARTERY, supplies the lungs emerge from the right ventricle as the PULMONARY TRUNK & quickly divides into right & left pulmonary arties that travel to each lung. The pulmonary trunk is larger & more curved than the nearby venae cavae. >Aorta emerges from the left ventricle into the aortic arch, which reserves the direction of the aorta from a dorsocranial to a caudal direction. Several vessels that supply the cranial part of the body branch off the aorta just after it originates at the aortic valve; these vessels include: the BRACYCEPHALIC TRUNK & the LEFT SUBCLAVIAN ARTERY. The Aorta is NOT the largest artery in the body, it is also the site of the highest blood pressure found in any vessel.( walls are the thickest of any blood vessel). The aorta may be distinguished from the pulmonary artery by the thickness of its walls. The aortic arch travels next to the pulmonary trunk & arch travels next to the pulmonary artery after it branches off the pulmonary trunk.

How the heart fills & pumps: the cardiac cycle

Just as the atria begins systolic contractions before the ventricles, they also complete systole & enter the resting phase (diastole) while the ventricles are still contracting. When the ventricles are contracting but the atria are relaxed, the pressure in the ventricles is much higher than the pressure in the artia, so the AV valves snap shut . With the AV valves closed, the relaxed & expanding atria can fill with blood from the veins that supply them. At about the time the atria are becoming completely full, systole comes to an end in the ventricles, & they begin to relax. This results in the pressure in the ventricles dropping lower than the pressure in the arteries they supply, so the aortic & pulmonary valves snap shut. Pressure in the ventricles also falls below the pressure in the full artia, so the AV valves are pulled open. > After the AV valves open, the ventricles fill with blood from the artia. Most ventricular filling is generated by the negative pressure caused by ventricular relaxation pulling blood in from the atria. Just as the pressure in the atria & the ventricles begins to reach equality due to the movement of blood from one chamber to the other, the SA node, which repolarizes during atrial diastole, depolarizes again. This causes the atria to contract & forcibly push even more blood into the ventricles & the cardiac cycle gegins again.

How does your body regulate the beating of its heart?

Multiple influences can cause the heart rate to speed up, slow down, become irregular, & cause the strength of cardiac contractions to increase or decrease. >FIrst, electrolytes such as sodium, potassium, chloride, & calcium affect the ability of the cardiac cells--especially the SA & AV nodes - to initiate autonomous electrical difference across the cardiac cell membranes is altered so the cells don't fire rapidly. Drugs called CALICUM CHANNEL BLOCKERS decrease transmission of the electrical impulse through the AV node by slowing down the repolarization of the AV node cells. This repolarization is dependent on the flow of calcium through the cell membranes via calcium channels. >Second, several nerves can speed up or slow down the heart rate by stimulating the SA node to increase or decrease the pacemaker's rate of firing. 1. increasing or decreasing the rate of transmission of current through the AV node, these nerves can also increase or decrease the strength of the cardiac contractions. 2. Hormones can also alter the rate & strength of cardiac contractions.[ ex., Adrenaline, a hormone secreted by the adrenal glands under conditions of stress or exercise that increase the rate & strength of contractions] 3. The amount of blood within the heart helps determine the strength of contractions. As more * more blood fills the heart, the heart senses the stretching of its wall & increases the strength of contractions, up to a point. If the heart wall is stretched too far, the heart muscle begins to fail & the strength of contractions actually drops.

List & describe the layers of the heart wall (LO)

Pericardium, which has two layers: the outer fibrous pericardium & an inner serous pericardium; which has two layers: the inner visceral layer & the outer parietal layer. The myocardium & the endocardium The outer layer of the heart is called the PERICARDIUM, which consists of two layer: an OUTER FIBROUS PERICARDIUM & an INNER SEROUS PERICARDIUM. The fibrous pericardium is made of tough, fibrous CT that protects the heart & loosely attaches it to the diaphragm. The serous is actually made up of two layers: the INNER VISCERAL LAYER, also called EPICARDIUM, which is closely adhered to the underlying muscle, & the OUTER PARIETAL LAYER, which lies between the epicardium & the fibrous pericardium. > Between the two layers of the serous pericardium is a thin cavity filled with fluid that acts as a lubricant between the layers, allowing the heart to smoothly expand & contract as it fills & empties > Inside the sac formed by the pericardium is the thickest layer of the heart tissue, the MYOCARDIUM is cardiac muscle. Like skeletal muscle, cardiac muscle is STRIATED (striped). Between the myocardium & the chambers of the heart is a thin membranous lining called the ENDOCARDIUM

Describe the process of depolarization & repolarization of cardiac muscle cells (LO)

Positively charge atoms or CATIONS includes sodium (Na+), potassium (K+), and calcium (Ca++). Negatively charged atoms or ANIONS include chloride (CI-). The SA node generates an electrical current by the movement of cations across the outer membranes of its cells. Cations are pumped out of the cell in a process called POLARIZATION that results in the outside of the cell having a more positive charge than the inside of the cell. (more cations outside the cell than inside). When gates in the cell wall are opened, cations flow into the cell to equalize the charge on either side of the cell membrane. This process called DEPOLARIZATION, generates an electrical current, which causes the heart muscle to contract. Depolarization of heart cells create a current by movement of positively charged ions across a cell membrane in the SA node. The SA node automatically repolarizes itself, then depolarizes again. In this way, the heart automatically keeps going through the cardiac cycle of depolarization (systole- heart contraction & repolarization (diastole -relax - filling of the heart chambers)

Fetal shunting

Shunting occurs from the pulmonary artery to the aorta in the fetus because the collapsed lungs provide a large amount of resistance to blood flow, so the pulmonary circulation pressure is greater that the systemic circulation.. Various anomalies of the circulatory circulation occur during fetal development in some animals; some create no problems, but others can be potentially fatal. some abnormalities of subclavian arteries or the aorta can wrap around the esophagus, constricting it ^ preventing food from passing down the esophagus. PORTOSYSTEMIC SHUNTS Are abnormalities of the portal vein in which the portal vein does not deliver blood to the liver, but instead carries blood from the intestines to the caudal vena cava. The result is an inability of the liver to detoxify substance absorbed in the intestine, leading to damage to the nervous system that can cause dementia, seizures, & even death. The liver fails to develop normally in patients with a portosystemic shunt because the intestine produces substances that promote normal liver development in the newborn. If a shunt exists, the liver does not receive these substances, is smaller than normal, & does not function normally. In some cases, surgery can correct the shunt.

Conduction system of the heart

Specialized cardiac muscle cells in the wall of the heart rapidly conduct an electrical impulse throughout the myocardium. The signal is initiated by the SA node (pacemaker) & spreads to the rest of the atrial myocardium & to the AV node. The AV node then initiates a signal that is conducted through the ventricular myocardium by way of the AV bundle.

Differentiate between SYSTOLE & DIASTOLE (LO)

Systole is the part of the cardiac cycle associated with contraction of the ventricles & artia & ejection of the blood into arterial systems. Where as diastole is the part of the cardiac cycle associated with relaxation of the artia & ventricles & the filling of the chambers with blood.

list the major arties & veins that travel from the heart to the systemic circulation

The aorta is the largest artery in the body, with the largest diameter & thickest vessel walls. The layers of the artery wall are similar to the layers in the walls of the heart: there is a tough outer fibrous layer, a middle layer of smooth muscle & elastic CT, & a smooth inner lining called ENDOTHELIUM. In the aorta & pulmonary arties, which carry blood out of the heart, the middle layer of the wall contains more elastic fibers than muscle fibers. This allows them to stretch slightly as they receive the high-pressure blood from the ventricles. Where the aorta emerges from the heart, the right & left subclavian arteries branch off & travel toward the forelimbs (thoracic limbs). Depending on the species, branching off one or both subclavian arteries are the right & left carotid arties, (travel to neck & supply blood to head). The main trunk of the aorta arches dorsally then travels caudally just below the spine, with numerous branches emerging from it in the thoracic & lumbar area, to supply blood to abdominal organs & to structures that support & enclose them. At the hind limbs, the main trunk of the aorta splits into right & left ILLAC ARTERIS, which supply blood to the arteries of the rear (PELVIC) limbs. The vein in the foreleg merge into larger & larger vessels to form right & left BRACHYCEPHALIC VEINS, which carry blood to the to the cranial vena cava & back to the heart. The veins in the hind limbs merge into right & left ILIAC VEINS, which return blood to the caudal vena cava. The caudal vena cava travels right next to the aorta underneath the vertebrae & then to the right atrium of the heart. Blood is drained from the head by the left & right JUGULAR VEINS, which travel along the neck next to the carotid arteries. In equines species in particular, care must be taken to avoid accidental injection into the carotid artery of substances that are meant to be injected into the jugular vein,

gross anatomy of the heart- the base & ventricles

The base is defined as the area where the atria reside along the entrance & exit of the large blood vessels along with the entrance & exit of the large blood vessels connected to the heart. The APEX is the opposite end of the heart, where ventricles end, which lies near the sternum. The long axis of the heart is a line drawn from the apex to the base. > If you cut the ventricles of the heart in cross section in a plane perpendicular to the heart's long axis, you will notice a distinct difference in the left & right ventricles. The left ventricle looks very similar to a circle with very thick muscular walls. The right ventricle is crescent shaped, wraps partially around the left ventricle, & has much thinner wall. The structural difference of these two chambers is due to the difference in their functions. The left ventricle has to pump against more resistance & needs to generate more pressure than the right ventricle. Moreover, by wrapping around the left ventricle, the right ventricle is aided in its contraction by the pumping of the left ventricle. In other words, as the left ventricle contracts, it pulls the outer wall of the right ventricle against it, helping the muscles of the right ventricle generate more force. The difference in the right & left atria is not marked; both are relatively thin-walled compared with the ventricles.

Polarization /Internodal pathways

The changes in the electrical current, a process called POLARIZATION , across the SA no deal cell membranes generate an electrical current that's transmitted through the atrial muscle fibers, which is a relatively slow process. The process continues more quickly along fibers within the atrial wall called INTERNODAL PATHWAYS that carry this signal throughout the right & left atria. The atrial muscle fibers contract as the electrical impulse reaches them. The internodal athwart carry the signal to the atrioventricular (AV ) nodes, collection of conduction fibers located at the junction of the atria &ventricles

Systole / diastole (wb)

The contraction phase of the heartbeat that occurs as the currents travel around the heart.is called SYSTOLE. All cells that undergo polarization must undergo repolarization (where the electrolytes' differences across the cell membranes return to normal) before the next depolarization can occur. During repolarization, the cardiac muscle cells relax, & the chambers enlarge & fill with blood, a phase known as DIASTOLE. As a survival mechanism, the heart has backup systems when the primary system fails. The Av node & the Purkinje fibers, as well as atrial & ventricular muscle fibers, also have an inherent ability to initiate an electrical current. However, the signal generated is weaker & occurs at a if the SA node fails, some other cardiac tissue tales over as the pacemaker. It's the tissue that has the most rapid rhythm that takes over next. If several areas fail to generate the current, the heart rate progressively slows to dangerous low levels

Describe the pathway of the electrical impulse generated by the SA node (LO)

The electric current generated by the SA node travels by two routes on its way from the base to the apex of the heart. There is a speedy "highway" route through the specialized cardiac muscle cells of the SA node, AV node, & PINKINJE FIBERS & a slower "local" route through the rest of the cardiac fibers. When the electrical impulse passes through the cardiac muscle, the muscle contracts. Unlike other muscle fibers in the body, cardiac muscle can transmit an electrical impulse form one muscle cell to anther, so electrical impulses & muscle contraction spread across the heart muscle like waves in a pond after a stone is tossed in . (skeletal muscle, by contrast, only contracts when it receives an electrical message from nerve tissue; it does not receive electrical impulses form other skeletal muscle cells) > After the electrical impulse is generated in the SA node in the right atrium, it spreads in a wave across both artia, causing them to contract & push blood through the AV valves in to the ventricles, which are still relaxed. The impulse generated by the SA node also travels quickly down the "highway" of specialized, fast-conducting muscle fibers to the ARTIOVENTICULAR NODE (AV node). The impulse conduction highway does encounter a slight delay at the AV node, which is the only route of conduction of the electrical impulse from the artia to the ventricles. The delay permits the artia to complete their systolic contraction before ventricular systole begins. (If atrial & ventricular systole took place at the same time, the pressure in the contracting ventricles would be so high that the weaker, thin-muscled atia could not push blood into the ventricles). > After the delay at the AV node, the electrical impulse resumes its speedy journey, this time through specialized fibers in the ventricles called the BUNDLE OF His & the PURKINJE FIBERS. The bundle of His fibers travel down the intraventricular septum to the bottom (apical) end of the left & right ventricles, & the Purkinje fibers carry the impulses from the bundle of His up into the ventricular myocardium. Because the impulse is delivered to the apex more quickly than it can spread form cell to cell in the ventricular muscle, the ventricles actually contract & then spread to the base of the heart, even though the impulse was generated at the base. This apex -to-base direction of ventricular contraction facilitates ejection of blood into the aorta & pulmonary arteries, which are located at the base of the heart

Specific Anatomy of the Systemic Circulation

The general purpose is to take O2 & nutrient-rich blood from the heart to the cells of the body, then to carry O2-and nutrient-poor blood from the body's cells to the heart. (Major arteries & veins) >The major artery the heart is the AORTA (largest blood vessel in the body of domestic animals). The aorta briefly travels cranially from the left ventricle, turns to the left briefly, then turns caudally & travel through the diaphragm & into the abdomen, where it ends at the pelvis by branching into several pairs of arteries called ILIAC ARTERIES that supply the legs & tail. > The first artery to exit the aorta is the CORONARY ARTERY, which supplies blood to the heart muscle & is the artery that becomes clogged in people, leading to heart attacks. >The SUBCLAVIAN ARTERIES branch off the aorta & give rise to the *CAROTID ARTERIES, the major arteries supplying blood to the head & neck. (felt on each side of the trachea) >There are several major arteries branching off the aorta that supply blood to the abdominal organs, including the COELIAC ARTERY (aka CELIAC ARTERY), which supplies the stomach, spleen, & liver > The CAUDAL MESENTERIC ARTERIES, which supply the intestines >The RENEL ARTERIES, which supply the kidneys >Practical importance, the FEMORAL ARTERY, which branches off the iliac arteries & travels distally along the medial surface of the rear leg. (felt in the groin area) *The lingual artery on the ventral surface of the tongue can be used to monitor the pulse in an anesthetized animal SEVERAL MAJOR VEINS > The JUGULAR VEINS on each side of the neck carry blood from the head to the cranial vena cava, which empties into the right atrium. > The CAUDAL VENA CAVA carries blood from the organs in the abdomen to the right atrium > A unique feature of the intestinal supply is the MESENTERIC VEIN SYSTEM, in which multiple veins from the intestines collectively join together & form the PORTAL VEIN. The portal vein empties into the liver, where blood is filtered & detoxified. > Blood from the liver is drained by the HEPATIC VEIN, which empties into the caudal vena cava Some veins in the leg & neck area are useful for drawing blood for testing. These include: JUGULAR VEINS in the neck, CEPHALIC VEIN on the anterior surface of the front legs, LATERAL SAPHENOUS VEIN on the lateral surface of the rear legs just proximal to the tarsus, & the MEDIAL SAPHENOUS VEIN on the medial surface of the femur. Some of these veins are located where intravenous catheters maybe placed to administer medications & fluids. Cattle possess a COCCYGEAL VEIN on the ventral surface of the tail near the base that's often used for blood collection.

Pericardial effusion & cardiac tamponade (clinical application)

The heart is able to expand & contract in the chest thanks to the layer of fluid that provides lubrication between layers of the SEROUS PERICARDIUM. Normally, only a small amount of fluid is contained within the pericardial sac. A # of conditions such as infection, inflammation, or hemorrhage may cause excess fluid to accumulate in the pericardial sac. This condition is called PERICARDIAL EFFUSION. Sometimes pericardial effusion is idiopathic, (may occur spontaneously with no reason) > The outer layer of the heart, called the FIBROUS PERICARDIUM, is not elastic: so when the pericardial space is over filled with fluid, the heart becomes unable to expand normally between contractions. This condition is called CARDIAC TAMPONADE, leads to less complete cardiac filling, decreased stroke volume, & decreased cardiac output. Pericardial effusion, with or without cardiac tamponade, may be treated by inserting a needle into the pericardial sac (usually through the chest wall) & withdrawing the excess fluid

WB definitions blood transport systems

The heart is the force behind the circulatory system, but the arteries, arterioles, capillaries, venules, & veins carry out the actual transport function of the circulatory system. > ARTERIES - are defined as blood vessels that carry blood away from the heart toward the cell of the body > ARTERIOLES - are smaller branches off arteries that connect directly to capillaries > CAPILLARIES- are microscopic blood vessels that connect arteries to veins & allow the exchange of gases, nutrients, & waste materials between the blood & the body's cells. > VENULES- are slightly larger than capillaries; they carry blood from capillaries to veins > VEINS- are blood vessels that carry blood from the body's cells back toward the heart. These definitions hold true for both the systemic & pulmonary circulations

Systemic circulation

The heart receives deoxygenated blood from the tissues of the body, pumps it through the lungs where it picks up oxygen, then pumps the oxygenated blood back out through the systemic circulation to provide the tissues with oxygen > DEF: The part of the circulatory system that provides blood flow to & away from the body tissue WB> is the network of blood vessels supply all cells of the body. The left side of the heart pumps blood to the systemic circulation

structural differences in the heart chambers

The left ventricle looks similar to a circle with very thick muscular walls. The right ventricle is crescent-shaped, wraps partially around the left ventricle, & it has a much thinner wall.The structural difference of these two chambers is due to the difference in their function. The left ventricle has to pump against more resistance & needs to generate more pressure than the right ventricle. Moreover, by wrapping around the left ventricle, the right ventricle is aided in its contraction by the pumping of the left ventricle. In other words, as the left ventricle contracts, it pulls the outer wall of the right ventricle against it, helping the muscles of the right ventricle generate more fore. The differences in the right & left atria is not marked; both are relatively thin-walled compared with the ventricles

Specific anatomy of the pulmonary circulation (WB)

The pulmonary circulation differs from the systemic circulation because its purpose isn't to carry O2 & nutrients to cells & Co2 & waste products away from cells . Instead, the purpose is to carry CO2 to the lungs & to carry O2 away from the lungs. Compared with the systemic circulation, the pulmonary circulation's layout is relatively simple. The pulmonary artery carries O2-poor blood from the right ventricle to the lungs, where it divides into various branches that travel to each lung. Capillaries line the outer wall of alveoli & are the site where gas exchange between the blood & the alveolar air occurs. These capillaries then join together to form the pulmonary venous system, which eventually forms the pulmonary vein. This vein carries O2-rich blood to the heart's left atrium

Birds, reptiles, & amphibians

The structure of the avian heart is similar to that of mammals, but quite unique in reptiles & amphibians species. The location of the heart within the body cavity varies depending on the species. Snakes' hearts are not completely fixed in place, which serves to facilitate the ingestion of large prey items. Structurally, the hearts of reptiles & amphibians are quite different from those of mammals. Most reptiles & amphibians have a three-chambered heart with two atria & one common ventricle, which is sub-divided into three distinct regions.

Auricles

The word auricle means ear, it is used to describe structures of the ear in people & animals ,& the auricles, perched upon the base of the heart , do looks somewhat like floppy ears hanging over the smooth, muscular ventricles. DEF: Ear-shaped appendage of either atrium of the heart

Gross anatomy of the heart - systemic & coronary circulation (wb)

There are actually two separate circulatory systems to which the heart pumps blood - the systemic circulation & the pulmonary circulation. SYSTEMIC CIRULATION - is a network of blood vessels supplying all cells of the body PULMONARY CIRCULATION- is the blood supply that goes to the lungs so the blood can be oxygenated & rid itself of carbon dioxide. Therefore, the lungs actually have two supplies of blood: blood rich in O2 that comes from the heart to supply the pulmonary cells & blood poor in O2 that goes to the alveoli to be oxygenated. The heart deals with these two supplies somewhat separately. The right side of the heart pumps blood to the pulmonary circulation, whereas the left side pumps blood to the systemic circulation.

Two semilunar valves

They control blood flow out of the heart. The pulmonary artery exits the right ventricle, & the valve controlling blood flow through this opening is the PIULMONARY VALVE. Existing the left ventricle is the aorta, thus, the AORTIC VALVE. These valves are one way valves; blood can only flow in one direction. If blood attempts to flow in the wrong direction, the flaps close over the opening.

Veins & venules

They have the same basic structure as arteries & arterioles. However, the tunica media is generally thinner & the lumen of the vessel larger relative to the diameter of the vessel as compared with arteries. [This means the wall of the vein is more compliant than that of an artery. Therefore the venous system can hold more blood volume than the atrial system, although the pressure is lower than the arterial system]. Because the muscle layer is much less developed, veins can't generate any pressure on the blood to continue blood flow. Instead the pumping action of skeletal muscles throughout the body compresses the veins that course through them, which helps pump blood out of the veins. The inability to generate internal pressure in the vein has no way to pump blood in the forward direction as do the arteries. Instead, the veins posses valves, extensions of the venous wall that act as one-way flaps to close off the lumen & prevent blood from flowing in the wrong direction.

List & describe the unique anatomical features of the fetal circulatory system (LO)

Unique anatomical features of the fetal circulatory system are: the ductus venosus, the foramen ovale, & the ductus arteriosus. >The major distinction between a fetus & a newborn is that the newborn receives O2 through its own lungs, & a fetus receives O2 from the blood of the dam (mother). Because the lungs of the fetus are not used for O2 exchange, they need only enough blood to keep the growing lung tissues alive. Consequently, in the fetus there are bypasses that allow most of the blood in the fetal circulation to go around the PULMONARY CIRCULATION instead of through it. The fetus receives O2 exchange between the fetal & maternal circulation. The oxygenated blood from the placenta flows into the fetus through the umbilical vein (cord). The vessel that carries oxygenated blood to the fetus is called a VEIN because it flows toward the heart of the fetus. The oxygenated blood from the umbilical vein flows through the liver & the DUCTUS VENOSUS (which allows some blood to bypass the liver) into the caudal vena cava, where it mixes with deoxygenated blood from the fetal systemic circulation. Just as in the newborn animal, blood from the vena cava fills the right atrium. However, in the fetus two structures allow most of the fetal blood to bypass the lung tissue, since the blood in the right atrium has already been oxygenated from the maternal blood, & the lungs of the fetus do not perform O2 exchange. The first bypass is the FORMAN OVALE (foramen -means " opening" & ovale -means "oval"). Much of the blood from the right atrium flows directly through the tricuspid valve into the right ventricle & then into the pulmonary artery. Blood from the pulmonary artery may flow into the lungs or through another bypass, the DUCTUS ARTERIOSUS , directly into the aorta to the fetal systemic circulation, where it supplies O2 & collects waste products from the tissues. The deoxygenated blood is then sent back to the placenta through the umbilical arties (cord). > With the first breath after birth, the lungs inflate, & the newborn begins to oxygenate it owns blood. In normal neonate, the ductus venosus constricts so that the blood no longer bypasses the liver, & the foramen ovale & ductus arteriosuus close so the blood may no longer bypass the lungs. > The ductus arteriosus closes and becomes ligamentun arteriosus. The oval foramen closes and becomes the fossa ovalis

Heart failure

When certain diseases damage the heart valves, the valves do not close completely, allowing some blood to flow in the wrong direction. This condition can lead to congestion I increased pressure in certain chambers of the heart as well as some veins, A condition called heart failure

Fetal circulation

Which performs the same general functions as the postpartum circulation, but with a structurally different. The most important difference between fetal circulation & mature circulation is that the fetal lungs are shrunken, collapsed, & empty of air: therefore, they don't function. Because the lungs are incapable of gas exchange, the fetus relies on the PLACENTA, the membrane attaching the fetus to the mother's uterus, to act as the site of gas, nutrient, & waste exchange Blood is carried from the fetus by the UMBILICAL ARTERIES to the placenta, where the fetal blood gets rid of CO2 & wastes * picks up O2 & nutrients. Blood from the placenta is carried via the UMBILICAL VEINS through the liver & to the right atrIum. The vessels to & from the placenta lie within the UMBIILICAL CORD. The fetus does not pump a lot of blood to the lungs because they are not functional; therefore, there are two openings within the circulation that shunt blood away from the lungs. >he 1st opening is the FOREMAN OVALE, an opening in the interatrail septum that connects the right & left atrium. As the right atrium contracts, part of the blood is pumped into the left atrium, so it doe not have to travel through the right ventricle, & the lungs. >The 2nd opening is the DUCTUS ARTERIOSUS, an opening connecting the pulmonary artery & the aorta, so blood pumped from the right ventricle travels from the pulmonary artery into the aorta, again by passing the lungs Both the foramen ovale & the ductus arteriosus normally close shortly before or after birth, so the normal operation of the pulmonary circulation is quickly established. in some cases, the ductus arteriosus fail to close off after birth, a condition called PATENT DUCTUS ARTERIOSUS (PDA), in which blood is partially shunted away from the lungs, creating an audible murmur. Animals with PDA have excessive pressure within the right ventricle ( pressure in pulmonary circulation is lower than the systemic circulation after birth). This pressure causes blood to flow from the aorta into the pulmonary artery, increasing volume & therefore the pressure in the right ventricle (leads to heart failure). Surgery in which the PDA is tied off can be performed to correct this condition.

Vascular anatomy& physiology

Arties carry blood away from the heart & veins bring it back. Blood going through systemic circulation is under higher pressure than blood in the pulmonary or coronary circulation. It takes more pressure to carry blood to the far distance to every extremity than it does to carry it through the shorter pulmonary & coronary routes, especially when the forces of gravity are considered. The blood in the systemic circulation also encounters more resistance to flow , & there is more blood in the systemic circulatory system at any given time than there is in the coronary or pulmonary systems.The aorta is the largest artery in the body, with the largest diameter & thickest vessel walls. The layers of the artery wall are similar to the layers in the walls of the heart: there is a tough outer fibrous layer, a middle layer of smooth muscle & elastic CT, & a smooth inner lining called ENDOTHELIUM. In the aorta & pulmonary arties, which carry blood out of the heart, the middle layer of the wall contains more elastic fibers than muscle fibers. This allows them to stretch slightly as they receive the high-pressure blood from the ventricles. Where the aorta emerges from the heart, the right & left subclavian arteries branch off & travel toward the forelimbs (thoracic limbs). Depending on the species, branching off one or both subclavian arties are the right & left carotid arties, (travel to neck & supply blood to head). The main trunk of the aorta arches dorsally then travels caudally just below the spine, with numerous branches emerging from it in the thoracic & lumbar area, to supply blood to abdominal organs & to structures that support & enclose them. At the hind limbs, the main trunk of the aorta splits into right & left ILLAC ARTERIS, which supply blood to the arteries of the rear (PELVIC) limbs. The smaller arteries that branch off the aorta continue to split into smaller & smaller vessels so that all tissues may be supplied with blood. Ultimately, blood flows through small arterioles into tiny, thin -walled capillaries which unlike other blood vessels, do not have muscle in their walls. In the systemic & coronary circulation, the capillaries are where oxygen & nutrients in the blood are exchanged for carbon dioxide & other waste products that are taken back toward the heart. n the pulmonary circulation, the capillaries of the lungs are where oxygen-poor blood picks up oxygen & transports it back to the heart. in the systemic & coronary circulation, arties carry oxygen- rich blood & veins carry oxygen-poor blood ; in the pulmonary circulation, the opposite is true. > From the capillaries, the blood begins its journey back to the heart through small venules that merge to form veins. The blood is under much less pressure in veins than in arteries, & the veins have thinner walls. Valves in small-&medium-sized veins ensure that the blood travels only in the direction of the heart. As the veins carry blood back to the heart, they are usually located right next to an artery carrying blood in the other direction. The vein in the foreleg merge into larger & larger vessels to form right & left BRACHYCEPHALIC VEINS, which carry blood to the to the cranial vena cava & back to the heart. The veins in the hind limbs merge into right & left ILIAC VEINS, which return blood to the caudal vena cava. The caudal vena cava travels right next to the aorta underneath the vertebrae & then to the right atrium of the heart. Blood is drained from the head by the left & right JUGULAR VEINS, which travel along the neck next to the carotid arteries

Describe the relationship between cardiac output, heart rate, & stroke volume (LO)

The relationship between cardiac output, heart rate, & stroke volume is expressed in a simple equation: CO (cardiac output) = SV (stroke volume X HR (heart rate) The heart rate for an individual animal is based in part on the rate at which the SA node spontaneously depolarizes, but many factors can increase or decrease. EX., vigorous exercise increases the demand for oxygen in the tissues, so cardiac output must increase to meet that demand. The heart begins to contract more forcefully (called increased CONTRACTILLY or positive INOTROPY), which increases stroke volume. During a period of increased physical activity, the heart also contracts more often, which increases heart rate> Summary of what happens during exercise (equation) ^^ CO+ ^SV X ^HR > Other factors can also affect cardiac output by changing stroke volume, heart rate, or both. EX> STARLING"S LAW states that increased filling of the heart ( INCREASED PRELOAD) results in increased cardiac contraction; this means that a slight stretch of the ventricular muscles increases the force with which they contract. [ the ventricles fill during diastole mostly because the drop in pressure (ventricles relax) pulls the blood in from the atria. When systole starts in the atria (while atrium the ventricles are still relaxed, because depolarization begins at the SA node in the right atrium), the contraction of the atria pushes about 25% MORE blood in to the ventricles than was pulled in by the relaxation of the ventricles. By pushing just a little more blood in to the ventricles with atrial contraction, the heart takes advantage of Starling's law causing the ventricular walls to stretch slightly, which leads to a more forceful contraction & increased stroke volume] > changes in blood pressure may affect both the SV & HR. Ex., animals in shock tend to have rapid, weak pulses. Pulses are felt because of the pressure differences in blood vessels during systole (when blood ejected into the vasculature & the pressure in blood vessels increases in the blood vessels) & diastole (when the heart is filling & pressure in the vessels decrease). When an animal ( or person) suffers shock, the blood pressure drops substantially. In HYPOVOLEMIC SHOCK (blood loss). In ANAPHYLACTIC SHOCK,( severe allergic reaction ) or SEPTICEMICSHOCK (infection), the blood pressure drops because the small blood vessels of the organs & tissues all dilate at the same time. Because of the reduced blood pressure, there is less pressure to fill the heart & the ventricles don't fill as completely (decreased preload). Stroke volume decreases. Because less blood ejected with each cardiac contraction, the increases in arterial blood pressure during systole are lessened, making arterial pulses weaker. Demand for cardiac output either the same or increased during shock, & since stroke volume is decreased, heart rate increases to compensate. These changes result in the weak, rapid pulse found in a patient suffering from shock > The autonomic nervous system can also influence cardiac output in other situations. Ex., during fight-or-flight response to a perceived threat, the sympathetic nervous system releases epinephrine (ADRENALINE), which increases stroke volume (by increasing the strength of contractions) & heart rate to prepae the body for the increased cardiac output that will be needed to flee or fight the threat. > General anesthesia, on the other hand can stimulate the parasympathetic nervous system, which releases actylchlorine that decreases stroke volume, heart rate & consequently, cardiac output. Of course, decreased cardiac output during surgery can be dangerous, so medications that block the actions of the parasympathetic nervous system are commonly given prior to the induction of general anesthesia.

The two more ventral chamber of the heart closer to the sternum

Ventricles

pericardial fluid

a small amount of fluid within the pericardium, between the two layers (outer fibrous pericardium, which attaches the heart to the diaphragm & the inner serous pericardium, is made up of an inner visceral layer [epicardium] & outer pericardial layer). This fluid lubricates the heart & makes it pump more efficently