Anatomy and Physiology of the cardiovascular system Flashcards
What is the heart?
A hollow muscular organ that pumps blood through the cardiovascular system. The horse’s heart makes up approximately 0.94% of its bodyweight, weighing in at 3.5-7 kgs.
The heart rate can be anywhere between 35-40bpm at rest, although this is affected by age, stress and level of fitness, as well as their environment.
The heart is a myogenic organ, but 1% of its fibres are autorhythmic and can be innervated and controlled by ourselves.
What are the functions of the heart?
- it is the central pump of the cardiovascular system
- distributes oxygen and removes carbon dioxide
- transports blood and the nutrients within it
- transports metabolic waste products
- carries antibodies (WBC)
- controls the pH of body tissues
- water balance
- temperature regulation
Define PULMONARY CIRCULATION
Pulmonary circulation is the portion of the circulatory system which carries deoxygenated blood away from the right ventricle of the heart to the lungs and returns oxygenated blood to the left atrium and ventricle of the heart.
Define SYSTEMIC CIRCULATION
Systemic circulation is the portion of the circulatory system which carries oxygeated blood from the left ventricle through the arteries to the capillaries in the tissues of the body. It then returns to the right atrium of the heart.
What are the three types of blood vessel?
Arteries, capillaries and veins
What is the make up of cardiac muscle?
- involved in involuntary movement
- supplied by the vagus nerve
- interconnected network of fibres that are surrounded by tissue and cross bonded
- have a very rich bloody supply
- myogenic fibres can be innervated if necessary
Define the PERICARDIUM
The pericardium is the membrane that encloses the heart. It consists of an outer fibrous layer, and an inner double layer of serous membrane. It is tight, non-elastic and prevents over filling and over stretching.
What are the 4 chambers of the heart?
The left and right atrium
The left and right ventricle
What are the atrioventricular valves?
The bicuspid (left) and the tricuspid (right) valves
Define the BICUSPID VALVE
The bicuspid valve sits on the left side of the heart and permits blood to flow one way only, from the left atrium to the left ventricle
Define the TRICUSPID VALVE
The tricuspid valve is the first valve that blood encounters as it enters the heart. It permits blood to only flow one way, from the right atrium to the right ventricle.
What are chordae tendinae?
Heart strings. They retain tension in the heart.
Define the SEMILUNAR VALVES
Semilunar valves are found at the base of the aorta and the pulmonary artery, it consists of 3 flaps which prevent the back flow of blood into the heart.
What are the three layers of arteries?
The tunica externa, tunica interna and tunica media
Define the TUNICA EXTERNA
The tunica eterna is the outermost layer of a blood vessel. It is mainly composed of collagen.
Define the TUNICA MEDIA
The tunica media is made up of smooth muscle cells, elastic tissue and collagen. It is the middle layer of blood vessels.
Define the TUNICA INTERNA
The tunica interna is the innermost layer of blood vessels. It is made up of smooth muscle cells and epithelial tissue.
Describe arteries
These have thick walls and elastic fibres that allow stretch and a smooth coating of muscle.
Describe veins
These are bigger than and thicker than capillaries. They contain valves to prevent the backflow of blood. Lower pressure than arteries and as they get closer to the heart they get ticker. They are aided by skeletal muscles to ensure venous return.
Describe capillaries
These are the smallest vessels. They can reach individual cells and get to a wide range of tissues because they are between 3 and 100 micrometres in diameter. They have porous walls which allow the transport of nutrients through them.
Describe the process of pulmonary circulation
Right ventricle - pulmonary arteries - arterioles - capillary bed - alveolar gas exchange - capillary bed - venules - pulmonary veins - left atrium
Describe the process of systemic circulation
Left atrium - left ventricle - aorta - arteries - veins - venules - capillaries - artioles - vena cava - right atrium
Define ARTERIOLES
Arterioles are a small branch of an artery leading into capillaries.
Define VENULES
Venules are a very small vein, especially one collecting blood from the capillaries.
Define the CONDUCTION SYSTEM
The conduction system is a group of specialised cardiac muscle cells in the walls of the heart that send signals to the heart muscle causing it to contract. It is a process that is initiated 60-100 times per minute.
Define MYOGENIC
Myogenic means something originates in muscle tissue, rather than from nerve impulses.
Define the SA NODE
The sino atrial node. Part of the conduction system and the anatomical pacemaker of the body. A cluster of cells situated in the wall of the right atrium. Excitation originates here.
Define the AV NODE
The atrioventicular node. Controls the heart rate. Serves as a electrical relay station slowing the electrical current sent by the SA node before it is allowed down into the ventricles.
Define the BUNDLE OF HIS
The bundle of His is the bundle of cardiac muscle fibres that conduct the electrical impulses that regulate the heartbeat.
Define PURKINJE FIBRES
Purkinje fibres are any of the specialised cardiac muscle fibres forming a network in the ventricular walls that conduct electrical impulses responsible for contractions of the ventricles.
What are the phases of cardiac muscle contraction?
Phase 0: rapid depolarisation Phase 1: partial repolarisation Phase 2: plateau Phase 3: repolarisation Phase 4: pacemaker potential
Define DEPOLARISATION
Depolarisation is a change within a cell where the cell changes its electronic charge from negative to positive.
Define REPOLARISATION
Repolarisation is a change within a cell where the cell changes its electronic charge from positive to negative.
Define the REFRACTORY PERIOD
The refractory period is the period in which the cardiac cells cannot initiate another action potential after one has just been. It is 250ms in length.
Define an ECG
An ECG is a test used to show the heart’s rhythm and electrical activity. Sensors attached to the skin detect electrical messages every time it beats.
What are the stages of the cardiac cycle?
- relaxation period - all 4 chambers are in diastole (relaxed and filling with blood).
- ventricular filling - ventricles fill first rapidly and then more slowly
- ventricular systole - blood forces the AV valves shut. They are shut for about 50ms.
The the process restarts.
Define the CARDIAC OUTPUT
Cardiac output is the amount of blood ejected from the ventricle into the respective blood vessel per minute.
Define the STROKE VOLUME
Stroke volume is the volume of blood pumped by a ventricle per beat
Define the HEART RATE
Heart rate is the number of times a heart beats per minute.
What is special about the pulmonary vein?
It is the only vein that carries oxygenated blood (usually veins bring deoxygenated blood back).
