Download Cardiovascular System: Heart Valves, Blood Flow, and Circulation and more Lecture notes Anatomy in PDF only on Docsity!
Cardiovascular System
ANS 215
Physiology and Anatomy of Domesticated Animals
I. Structure and Function A. Heart is a cone-shaped, hollow, muscular structure located in the thorax.
B. Larger arteries and veins are continuous with the heart as its base.
- Base is directed upward (dorsal) and forward (cranial).
- Opposite end of the cone is known as the apex C. Membrane around the heart is known as the pericardium
- Membrane next to hear fuses with the heart muscle and is called the visceral pericardium or epicardium
- outer membrane is parietal pericardium
- apex is free
- Inflammation of the pericardium is called pericarditis. a. increase in fluid in pericardium b. traumatic pericarditis (hardware) disease in cattle
Left view of bovine thorax and abdomen showing location of the heart relative to the stomach. Foreign objects (nails, wire), sometimes ingested by cattle, accumulate in the reticulum ( one of the bovine forestomachs). Contraction of the reticulum can force pointed objects through the reticulum wall and the diaphragm, causing final penetration of the pericardium and subsequent inflammation (pericarditis).
A sagittal section of the heart. The right and left chambers are shown with separation of the atria and ventricles by atrioventricular valves. The auricles (not pictured here) are extensions of the atria. The aorta is seen to be arising from the left ventricle. The pulmonary trunk arises from the right ventricle and divides into right and left pulmonary arteries just beyond the pulmonary semilunar valve. The cranial/superior vena cava and caudal/inferior vena cava deliver venous (unoxygenated) blood into the right atrium. (Note: recall that super/inferior would be used in reference to bipeds while cranial/caudal would be used for quadrupeds)
E. Heart valves
- Valves located between the atria and ventricles are known as the atrioventricular (AV) valves. a. valve on right side has 3 cusps (tricuspid) b. valve on left side has 2 cusps (bicuspid)
- AV valves prevent backflow of blood into atria when ventricle contracts a. eversion of valves into atrium is prevented by chords (chordae tendinea) attached to free margin of cusps and to small muscles (papillary muscles) at heart wall
- Semilunar valves prevent backflow of blood into ventricles flowing contraction. a. each have 3 cusps b. valve on right side is pulmonary semilunar c. valve on left side is aortic semilunar
F. Blood flow through the heart
- Blood that circulates to the tissues returns to the heart by the cranial vena cava (forward parts of body) and caudal vena cava (blood from rear parts of body).
- Venous blood enters the right atrium during the atrial relaxation phase of the cardiac cycle and is then directed through the tricuspid valve to the right ventricle.
- Ventricles then contract and the blood is pumped through the pulmonary semilunar valves to pulmonary arteries and the lungs.
- After circulation through the lungs, the blood enters the left atrium via the pulmonary veins.
- Blood (now oxygenated) is directed to the left ventricle where it is pumped throughout the body through the aorta.
G. Blood vessels
c. capillaries are merely endothelial tubes
d. Where endothelial cells border each other, a thin slit (slit pore) or intracellular cleft is provided for diffusion of dissolved substances from plasma. e. Pinocytotic vesicles are also present in the endothelial cells for nutrient transfer.
f. Veins are thin-walled tubes reinforced by connective tissue. They also contain some smooth muscle fibers.
General scheme of mammalian circulation showing the pulmonary system, which serves the lungs, and the systemic system which serves the remainder of the body. The pulmonary circulation is shown in black.
II. Blood Circulatory Systems A. Pulmonary
- circulates blood through the lungs
- Pressure for this system originates in the right ventricle.
- Capillaries for this system lien in pulmonary alveoli
Schematic representation of the lungs and the pulmonary circulation. The circled inset represents a functional unit of the lung, the alveolus. Mixed venous blood leaves the right ventricle through the pulmonary trunk and is oxygenated at the level of the alveoli. Oxygenated blood returns to the left atrium through the pulmonary veins.
B. Systemic circulation
- carries blood that has returned from the lungs
- Pressure for this system originates in the left ventricle.
- Blood traversing this system leaves the left ventricle through the aorta and is returned to the right atrium via the vena cava. a. first branches of the aorta supply the heart through coronary arteries
The mammalian hepatic portal system. Blood in the portal vein from the stomach, spleen, pancrease, and intestines goes to the liver, where it flows through the sinusoids and is reformed by the central vein of each lobule. It finally enters the caudal vena cava through the hepatic veins.
III. Lymphatic System A. Important adjunct to the circulatory system B. Lymphatic vessels have blind beginnings in the interstitial spaces. C. Continuation vessels of the lymphatic system tend to parallel veins. D. Lymph vessels join with each other and eventually form a few large lymph vessels that empty directly into large veins.
Schematic representation of lymph drainage. Interstitial fluid gains access to the blind beginnings of lymph capillaries and proceeds centrally through lymph vessels of increasing size. Lymph nodes are located along the course of lymph vessels. Lymph is returned to blood by drainage into veins.
E. Fluid of lymph vessels is called lymph
- very close composition to interstitial fluid
- protein in interstitial space can only return to plasma via lymph a. 100% of plasma protein is turned over every 24 hours
H. Spleen
- largest lymphoid organ of the body
- circulating fluid is blood instead of lymph
- only organ specialized to filter blood
Projection of viscera on the left body of the female dog showing the location of the spleen relative to other body organs. Except for the dorsal tip, the dog spleen is somewhat variable in position, and its long axis can be almost longitudinal.
- The spleen’s outer covering is called the capsule. a. contains connective tissue and smooth muscle b. smooth muscle is pronounced in carnivores
- trabeculae extend from the capsule a. composed of elastic fibers, collagen, and smooth muscle b. arteries, veins, lymph vessels, and nerves all contained within the trabeculae
- The parenchyma of the spleen is comprised of red and white pulp and is supported by the trabeculae and blood vessels.
Schematic representation of the pig spleen. Multiple branches of the splenic artery enter the capsule and extend into the trabeculae. The lymphatic nodules and periarterial sheaths comprise the white pulp that produces lymphocytes. The red pulp is the reticular fiber mesh that acts as a filter because of its fixed macrophages. Smooth muscle cells are present in the capsule and in the trabeculae. The venous sinuses collect filtered blood and drain into venules and finally trabecular veins (not shown).
- Most of the pulp is red because of the blood that is being filtered and contains fixed macrophages.
- The white pulp is lymphoid tissue that is distributed throughout the spleen and which produces lymphocytes.
- The spleen is the site of red blood cell removal, reservoir of red cells lymphocytes.
IV. Cardiac Contractility A. Origin of the heartbeat
- All muscles have an inherent rhythmicity of contraction. a. frequency of contraction is greatest in cardiac muscle b. Atria muscle cells have higher frequency of contraction than ventricular cells. c. Small area (SA node) near junction of cranial vena cava and right atrium has higher frequency of contraction than atria. i. This is the location of origination of cardiac contraction. ii. Specialized muscle fibers send out impulses, which spread throughout the musculature of the atria.
it from the right and left bundle branches to supply the right and left ventricles
- Cardiac muscle contracts more slowly than skeletal muscle and the refractory period is longer.
- Both atria contract at the same time and both ventricles contract at the same time. a. contraction of muscle fibers within a syncytis is synchronized.
- Defibrillation causes simultaneous depolarization of all cardiac muscle fibers. This permits initiation of a new cycle with impulses that begin at the SA node. D. Cardiac Cycle
- Refers to the sequence of events that occurs during one complete heartbeat.
- Events are continuous and the assigned periods are arbitrary for descriptive purposes.
- Diastole refers to relaxation of a heart chamber before and during filling of the chamber.
- Systole refers to contraction of a heart chamber in the process of emptying.
The cardiac cycle of the mammalian heart. Which valves must be open and which ones must be closed for proper function during each stage of the cycle?
E. Electrocardiogram (ECG)
- Record of voltage changes, which occurs across the nerve and muscle membranes during waves of depolarization and repolarization.
- Connection of the amplifier with the wires (leads) to selected body parts (usually limbs) and to a recorder proves a characteristic wave form. a. recording of electrical activity of the heart b. ECG is altered when heart muscle is damaged or ventricle walls are thickened
c. P wave is associated with depolarization of atria, after depolarization, atrial contraction occurs d. QRS complex represents both positive (upward) and negative (downward) deflections associated with ventricular depolarization; ventricular contraction begins after depolarization of fibers e. T wave represents ventricular repolarization
- When viewing an electrocardiogram, it can bee seen that deflections of the waves whether positive or negative, occur from a common line known as the isoelectric line. F. Heart Sounds
- Listening to the heart (cardiac auscultation) permits identification of sounds that accompany contraction of heart muscle and closure of the heart valves. a. sounds are repeated for each cardiac cycle b. first sound is ventricular contraction and AV valves c. second sound is ventricular relaxation and closure of semilunar valves d. abnormal heart sounds are called murmurs and are usually associated with valve disorders
V. Heart Rate and its Control A. Heart rate refers to the frequency of cardiac cycles.
- usually measured in beats per minute (bpm) B. Generally, smaller animals have higher heart rates
- consequence of metabolic rate and oxygen consumption
- larger surface area to body mass ratio in smaller animals
Heart Rates in Adult, Resting Animals
