Chapter 14 Cardiovascular System Flashcards
ATP
AEROBIC respiration
* Glucose + Oxygen -> Water + Carbon Dioxide + 36 to 38
ATP
The Cardiovascular System – big picture
Pump – the heart
Pipes – blood vessels
What is pumped?
*Blood cells
* Nutrients
* O2, CO2, H2O
* Waste molecules
* Hormones, antibodies
The Cardiovascular System Physiology - big picture
Blood continuously flows around animal’s body through the heart
Propelled by the pumping heart
Blood vessels – 5 kinds
Heart Location
Located in middle of the thoracic cavity
*In the space between the 2 lungs = mediastinum
Apex shifted to left
Sits more ventrally
Heart Coverings
Pericardium = fibrous sac containing the heart
*Pericardial sac
*Serous pericardium
*Visceral layer
*Parietal layer
Pericardial space is filled with pericardial fluid
Heart Layers
3 layers in the wall:
Epicardium - outer
Myocardium - middle
Endocardium covers papillary muscles - inner
Heart – 2 Pumps
Right ventricle
* Thinner walled;
* Deoxygenated blood to lungs
Left ventricle
* Thicker walled;
– the left ventricle must create a lot of pressure to pump blood into the aorta and throughout systemic circulation
* Oxygenated blood to body
Heart External Physiology
Auricles – largest and most visible parts of atria
* Blind pouches that come off the atria
Left ventricle – long and narrow, thick-walled, terminates at apex of heart
Right ventricle –broader surface area; wraps around left ventricle
Borders of ventricles are separated by interventricular sulci
* Contain fat and blood vessels that are part of coronary circulation
* Formed by interatrial septum and interventricular septum
Base of the heart at rounded cranial end
Apex of heart at more pointed caudal end
Internal Parts of the Heart
4 Chambers
* 2 Atria
* 2 Ventricles
Septum
4 Valves
* 2 Atrioventricular valves
(A-V valves)
* Chordae tendinae & papillary muscles
* 2 Semilunar valves
Cardiac
Valves
4 one-way valves control blood flow through the heart
Chordae tendinae prevent valves from opening backwards
right atrioventricular valve
—usually has three flaps and is therefore known as the tricuspid valve - however in dogs and cats only has 2 flaps
— left atrioventricular valve- usually has only two flaps and is thus known as the bicuspid valve (or mitral valve).
—pulmonary valve- pulmonary artery exits the right ventricle
—aortic valve -blood exiting the left ventricle is the aorta
Blood Supply to the Heart
Coronary arteries
*Branch off aorta
Coronary veins
* Coronary sinus drains into right atrium
Nerve Supply to the Heart
Cardiac muscle creates its own contractions and relaxations
Nerve supply to heart
* Not essential
*Serves a purpose
*Example: external motor stimulation to accommodate increased oxygen demands to certain tissues
The Cardiac Cycle
One heartbeat is produced
One cycle of atrial and ventricular contraction followed by relaxation
*Systole = myocardium contracting, “working”
* Diastole = myocardium relaxing and repolarizing
Each chamber goes through systole and diastole
* not at the same time
Normal Heart Sounds
Produced by heart valves snapping shut
One cardiac cycle produces two distinct heart sounds
* “Lub” after atrial systole
* Tricuspid and mitral valves snap shut
*“Dub” after ventricular systole
*Pulmonary and aortic valves snap shut
(left and right 5th intercostal space) - dogs and cats
Between the second and sixth ribs - ruminants and horses
- heart sounds is closing of a valve, two beat: lub (AV valves close) dub - (semilunar valves close)
Abnormal Heart Sounds
Extra sounds heard when the 2 AV valves or 2 semilunar valves are not closing simultaneously
Valvular insufficiency
* One or more valves don’t close all the way
* Murmur
Valvular stenosis
* One or more valves won’t open all the way
* Murmur
Pulse
Rate of alternating stretching and recoiling of elastic fibers in an artery as blood passes through with each heartbeat
Auscultation is not a true pulse
– gotten from veins
Rate equal to heart rate in healthy animals
Most often felt on superficial arteries lying against firm surfaces (bones)
*Best felt on different arteries in different species
*Best felt over a medium artery
Generally large animals have slower pulses, and small animals have faster pulses
Electrical Conduction System of the Heart
Modified cardiac muscle, not nervous tissue
SA node
AV node
AV Bundle (Bundle of His)
Purkinje fibers (conduction myofibers)
Sinoatrial Node (SA node)
Pacemaker of the heart
Located in right atrium
Generates electrical impulses that trigger repeated beating of the heart
Cells of the SA node have different “channels” in the cell membrane that transport sodium, calcium, and potassium in or out of the cell
-Such movements change the difference in electrical charges across the cell membrane
–a process called polarization
SA Node -> AV Node
First part of nerve impulse through heart
Impulse generated at SA node travels from one muscle cell to the next
* Wave pattern
*Initially causes both atria to contract
*Blood pushed through AV valves into ventricles
Impulse also travels quickly down the muscle fibers to the atrioventricular node (AV node)
cells have an inherent ability to generate an electrical current, a process called self-excitation
AV Node -> AV Bundle -> Purkinje Fibers
Next part of nerve impulse through heart (after starting in SA node)
Electrical impulse then spreads through the AV
Bundle (Bundle of His (pronounced hiss))
* Fibers in the ventricles
* Travels down the interventricular septum to the
bottom of the ventricles
Purkinje fibers carry impulses from the Bundle of
His up into the ventricular myocardium.
Electrocardiograms (EKG’s, ECG’s)
Definition
*A technological view of electrical activity of the heart during the cardiac cycle
P wave
- Atria are stimulated to contract
– looks short, rounded and similar to T wave
– Atrial depolarization
R wave
– actually full cycle is QRS wave
—Ventricular depolarization
— Purkinje fibers
– Quick, peaked higher than P and T wave
T wave
– ventricular repolarization
– looks short, rounded and similar but longer than P wave
Reasons for ECG’s
To evaluate anatomic heart changes
* Chronic heart disease
*Sudden acute trauma
Preventive medicine – older patients
*“Geriatric screen”
*Pre-anesthesia exam
Evaluate cardiac therapy (digitalis drugs)
Evaluate prognosis of heart disease
Monitoring during anesthesia and surgery
Stroke Volume
Amount of blood ejected from the left ventricle during one contraction
Represents strength of the heartbeat
Determined by 2 factors
*Preload
*Afterload
Can also be affected by length of cardiac muscle cells
Heart Rate
Normal rate for each species is set internally
* Rate of spontaneous SA node depolarization
* Heart rate of large animals is slower
* Heart rate of small animals is faster
Outside control comes through autonomic nervous
system
Cardiac Output (CO)
Volume of blood that is ejected out of the left ventricle over a unit of time, usually a minute
Determined by:
*Stroke volume (SV) = systolic discharge
* Heart rate (HR)
calculation: CO = SV × HR (Know this)
Cardiac Output Examples
Influence of autonomic nervous system:
*“Fight or flight” response – sympathetic nervous system releases epinephrine; stroke volume and heart rate increase
* General anesthesia – parasympathetic nervous system releases acetylcholine; stroke volume and heart rate decrease
List Blood Vessels
ARTERIES
ARTERIOLES
CAPILLARIES
VENULES
VEINS
Arteries/Arterioles
transportation!
Carry blood away from the heart
* Deoxygenated blood to lungs for oxygenation
–Pulmonary circulation
* Oxygenated blood throughout the body
–Systemic circulation
Usually come in pairs
2 types
*Elastic
*Aorta is largest elastic artery -
—The major artery of the systemic circulation, it receives blood from the left ventricle.
* Muscular
*Arterioles are smallest branches of arterial tree
Capillaries
Exchange
Microscopic blood vessels from branching arterioles
- smallest
Occur in groups called capillary beds or networks
Walls are one endothelial cell thick
*Exchange of gases and nutrients occurs at this level
Veins/Venules
transportation!
Carry blood toward the heart
* Oxygenated blood from the lungs
—Pulmonary circulation
* Deoxygenated blood and waste materials from throughout the body
—Systemic circulation
Capillaries join together to form venules
*Venules join together to form veins
One-way valves and muscular movements
All systemic veins drain into vena cava
Comparing Veins and Arteries
Veins
* Carry blood toward the heart
* Major veins
* Vena cava
—Deoxygenated blood
* Pulmonary vein
—Oxygenated blood
Arteries
* Carry blood away from the heart
* Major arteries
* Aorta
—Oxygenated blood
* Pulmonary artery
—Deoxygenated blood
Physiology of Blood Vessels
Smooth muscle in walls of most blood vessels
Constriction and relaxation allows the vascular system to direct blood to different regions of the body under different circumstances
Blood Pressure
Measurement of the amount of pressure that flowing blood exerts on arterial walls
Dependent upon interactions with:
* Heart rate
*Stroke volume
* Diameter and elasticity of the artery
* Total blood volume
Varies during the cardiac cycle
*Systolic blood pressure = highest number - the force by which blood is ejected from the left ventricle during systole.
* Diastolic blood pressure = lowest number
* Mean arterial pressure (MAP) = average pressure during one cardiac cycle
Blood Circulation in the Fetus
Fetus receives oxygen from the blood of its mother
* Lungs not used for oxygen/carbon dioxide exchange
* Lungs need only enough blood to keep growing tissues alive
Oxygen received from mother’s placenta
* Through the umbilical vein
After first breath after birth
* Lungs inflate and newborn oxygenates its own blood
* Foramen ovale and ductus arteriosus close so that blood no longer bypasses the lungs
Venipuncture – Canine/Feline
Cephalic vein: cranio-medial aspect of forelimb
Femoral (medial saphenous) vein: medial aspect of hind limb
Saphenous: lateral aspect of hind limb
External Jugular Veins (All species)
*Ventral aspect of each side of the neck in the jugular groove
* Close to the carotid arteries
* Care must be taken to avoid accidental injection into the carotid artery
Heart Anatomy
Located in the thoracic cavity within the mediastinum.
-surrounded by a sac called the pericardium (two layers)
—outer fibrous pericardium
—– Attached to diaphragm
— inner serous pericardium
—- Visceral and parietal layer
— pericardial fluid- lubricates heart
-Myocardium is the muscle of the heart (most of heart’s mass)
—lining inside of myocardium is the endocardium
-Cardiac muscle cells are called myocytes.
—Myocytes are connected to each other with intercalated disks and desmosomes.
4 Chambers of heart
Two dorsal chambers closer to the spine - atria
Two ventral chambers closer to the sternum - ventricles
In most domestic animal
– heart sits slightly skewed so the right ventricle and right atrium sit slightly cranial to the left ventricle and left atrium.
– Chambers of animals’ hearts are given the same names as those in people. (left ventricle, right ventricle, left atria, right atria)
Atria
Receive blood from large veins
Force blood (by one way valves) into ventricles
Smaller and less muscular than the ventricles
Divided by interatrial septum
Identified by auricles
Ventricles
Force blood, through one-way valves, into arteries
- Right ventricle pumps blood into pulmonary circulation through the artery.
—- Rt ventricle wall is thinner
- Left ventricle pumps lood into systemic circulation through the aorta
Together form the atrioventricular septum
interventricular septum
auricles
Small pouches on atria that look like ear flaps
Chordae tendineae
cords of fibrous tissue that anchor the tips of the flaps to papillary muscles,
Skeleton of heart
The cardiac skeleton consists of four rings of dense connective tissue that surround the AV canals (mitral and tricuspid) and extend to the origins of the aorta and the pulmonary trunk, providing structure and support for the heart as well as electrical isolation between the atria and the ventricles.
Blood flow heart circulatory systems (big picture)
Two separate circulatory systems
-systemic circulation: all cells of the body
— Left side of heart
-pulmonary circulation: blood supply that goes to the lungs
— Right side of heart- systemic circulation. Blood to the body
Follow a drop of blood
- Right atrium
- Tricuspid valve
- Right ventricle – pumps deoxygenated blood up into the pulmonary arteries
- Pulmonary valve
- Pulmonary arteries bifurcate going to each lung with deoxygenated blood – they are the only arteries in the body carrying deoxygenated blood
- Pulmonary arterioles
- Capillaries of the lungs where blood becomes oxygenated – CO2 is given off to lungs and O2 brought into capillaries
- Venules
- Pulmonary veins - 2 from each lung – they are the only veins in the body carrying oxygenated blood. All four of these pulmonary veins empty into the left atrium
10.Left atrium
11.Mitral valve
12.Left ventricle (aka “work horse”) – it is a lot thicker than the right ventricle because it has to pump oxygenated blood to every cell in the body
13.Aortic valve – located between the left ventricle and aorta
14.Aorta – bifurcates; one part going to the anterior part of the body and one going to the posterior part of the body. The descending aorta bifurcates into many arteries with 120/80 blood pressure.
15.Arteries – which bifurcate into lots of arterioles
16.Arterioles
17.Tissue capillaries – this is where blood becomes deoxygenated because all of the oxygen leaves the capillaries to go into the cells of the animal’s body
18.Venules
19.Veins – veins come together until we have the caudal vena cava and cranial vena cava
20.Caudal and Cranial vena cava
21.Right atrium – starts again – go back to number 1
Systemic Circulation
Blood returns to heart through the pulmonary vein from lungs
- empties into the left atrium.
Contraction of the left atrium pushes blood
—through mitral valve into the left ventricle,
Left ventricle contracts
—- pumps blood through the aortic valve into the aorta
Blood moves into systemic circulation.
What can Affect Heart Regulation
*electrolytes such as sodium, potassium, chloride, and calcium affect the ability of the cardiac cells—especially the SA and AV nodes—to initiate autonomous electrical activity.
*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.
*Hormones can also alter the rate and strength of cardiac contractions.
Cardiac Conduction System Physiology
Electrical signals begin in the right atrium
-in the SA node
—-Channels of SA Node change electrical charges as they transport sodium, calcium, and potassium in or out of the cell.
—The changes in the electrical current generate an electrical current that’s then transmitted through atrial muscle fibers
—–a relatively slow process.
The process continues more quickly along, called internodal pathway
— this carries the signal throughout the right and left atria.
— atrial muscle fibers contract as the electrical impulse reaches them
—The internodal pathways carry the signal to the AV node.
Electrical impulses are slowed as they move through the AV node.
-the atria empty into the ventricles
ventricles are signaled to contract.
—the atrioventricular (AV) bundle conducts the signal into the ventricles. After entering the ventricles,
—AV bundle branches out into right and left Purkinje fibers traveling through the right and left ventricles.
The signal is carried rapidly to the apex of the heart
Purkinje fibers branch out into the ventricular muscle.
—ventricular contraction at the apex of the heart causes the ventricle to contract in the ventral-to-dorsal direction
— blood is squeezed up to the base from the apex.
— blood exits each ventricle through the appropriate artery
internodal pathway
fibers within the atrial wall
-connection between the sinoatrial node and the atrioventricular node in the right atrium of the heart.
systole
The contraction phase of the heartbeat that occurs as the current travels around the heart
diastole
All cells that undergo polarization must undergo repolarization (where the electrolytes’ differences across the cell membrane return to normal) before the next depolarization can occur. During repolarization, the cardiac muscle cells relax, and the chambers enlarge and fill with blood
Capillaries
tiny vessels that form a network to supply blood to the body’s tissues
Essentially, the capillary wall is composed only of endothelial cells.
Capillaries allow the exchange of gases, fluids, nutrients, and waste products between the blood and the cells of that tissue
Branch out from arterioles
Eventually, the capillaries fuse together to join the venous side of the capillary bed.
mesenteric vein system
in which multiple veins from the intestines collectively join together and form the portal vein. The portal vein empties into the liver, where the blood is filtered and detoxified. Blood from the liver is drained by the hepatic vein, which empties into the caudal vena cava.
Fetal circulation
The most important difference between fetal circulation and mature circulation is that the fetal lungs are shrunken, collapsed, and 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, for gas, nutrient, and waste product exchange.
Blood is carried from the fetus by the umbilical arteries to the placenta, where the fetal blood gets rid of carbon dioxide and wastes and picks up oxygen and nutrients. Blood from the placenta is carried via the umbilical vein through the liver and to the right atrium.
foramen ovale
A feature of fetal circulation
- a hole between the left and right atria of the heart. This hole exists before birth, but most often closes shortly after being born.
Ductus arteriosus
A feature of fetal circulation
- an opening connecting the pulmonary artery and the aorta, so blood pumped from the right ventricle travels from the pulmonary artery into the aorta, again bypassing the lungs.
coronary circulation
Coronary circulation is the circulation of blood in the arteries and veins that supply the heart muscle (myocardium). Coronary arteries supply oxygenated blood to the heart muscle. Cardiac veins then drain away the blood after it has been deoxygenated.
Purkinje fiber
conduct electrical impulses within cardiac muscle
AV
atrioventricular node
-Gateway through which electrical impulses pass
located between an atrium and a ventricle.
right AV valve is the tricuspid valve
left AV valve is the mitral valve.
SA Node
Sinoatrial Node
- where normal electrical impulses in the heart originate.
- also called cardiac pacemaker
-located upper wall of right atrium
Atrium
The heart chamber that receives blood from the large veins.
Right atrium receives blood from the vena cava
left atrium receives blood from the pulmonary vein.
Interatrial septum:
The “wall” of myocardium that separates the left and right atria of the heart.
Mediastinum
The space in the thorax between the lungs that contains the trachea, esophagus, heart, nerves, lymphatic vessels, and major blood vessels
Semilunar valves:
Another name (based on their halfmoon shapes) for the pulmonary and aortic valves.
Interventricular groove
The fat-filled groove on the outside of the heart that corresponds to the location of the interventricular septum.
carotid artery
Supplies blood to the head
The pulmonic and aortic valves close when pressure in the
ventricles drops lower than the pressure in the arteries they supply.
Preload
The preload is the amount of blood the ventricle receives from the atrium;
Afterload
**Physical resistance by artery the ventricle is ejecting blood into
Animal Pulse Points
Dog- Femoral artery
Cat- femoral artery
Cow- coccygeal artery or facial artery
Horse - mandibular artery or posterior digital artery
Sheep - femoral artery
Pig - coccygeal artery
Piglet - femoral artery
Ways to evaluate the heart
▪ Auscultation of the thorax to determine heart rate and rhythm, and to detect heart murmurs
▪ Periphery artery palpation to evaluate rate, regularity, and strength of pulse
▪ Measurement of arterial blood pressure to evaluate cardiac output
▪ Thoracic radiography to evaluate the size and position of the heart
▪ Electrocardiography to evaluate the electrical activity of the heart
