Anatomy and Physiology of the cardiovascular system

Question 1

What is the heart?

Answer 1

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.

Question 2

What are the functions of the heart?

Answer 2

• 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

Question 3

Define PULMONARY CIRCULATION

Answer 3

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.

Question 4

Define SYSTEMIC CIRCULATION

Answer 4

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.

Question 5

What are the three types of blood vessel?

Answer 5

Arteries, capillaries and veins

Question 6

What is the make up of cardiac muscle?

Answer 6

• 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

Question 7

Define the PERICARDIUM

Answer 7

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.

Question 8

What are the 4 chambers of the heart?

Answer 8

The left and right atrium

The left and right ventricle

Question 9

What are the atrioventricular valves?

Answer 9

The bicuspid (left) and the tricuspid (right) valves

Question 10

Define the BICUSPID VALVE

Answer 10

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

Question 11

Define the TRICUSPID VALVE

Answer 11

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.

Question 12

What are chordae tendinae?

Answer 12

Heart strings. They retain tension in the heart.

Question 13

Define the SEMILUNAR VALVES

Answer 13

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.

Question 14

What are the three layers of arteries?

Answer 14

The tunica externa, tunica interna and tunica media

Question 15

Define the TUNICA EXTERNA

Answer 15

The tunica eterna is the outermost layer of a blood vessel. It is mainly composed of collagen.

Question 16

Define the TUNICA MEDIA

Answer 16

The tunica media is made up of smooth muscle cells, elastic tissue and collagen. It is the middle layer of blood vessels.

Question 17

Define the TUNICA INTERNA

Answer 17

The tunica interna is the innermost layer of blood vessels. It is made up of smooth muscle cells and epithelial tissue.

Question 18

Describe arteries

Answer 18

These have thick walls and elastic fibres that allow stretch and a smooth coating of muscle.

Question 19

Describe veins

Answer 19

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.

Question 20

Describe capillaries

Answer 20

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.

Question 21

Describe the process of pulmonary circulation

Answer 21

Right ventricle - pulmonary arteries - arterioles - capillary bed - alveolar gas exchange - capillary bed - venules - pulmonary veins - left atrium

Question 22

Describe the process of systemic circulation

Answer 22

Left atrium - left ventricle - aorta - arteries - veins - venules - capillaries - artioles - vena cava - right atrium

Question 23

Define ARTERIOLES

Answer 23

Arterioles are a small branch of an artery leading into capillaries.

Question 24

Define VENULES

Answer 24

Venules are a very small vein, especially one collecting blood from the capillaries.

Question 25

Define the CONDUCTION SYSTEM

Answer 25

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.

Question 26

Define MYOGENIC

Answer 26

Myogenic means something originates in muscle tissue, rather than from nerve impulses.

Question 27

Define the SA NODE

Answer 27

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.

Question 28

Define the AV NODE

Answer 28

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.

Question 29

Define the BUNDLE OF HIS

Answer 29

The bundle of His is the bundle of cardiac muscle fibres that conduct the electrical impulses that regulate the heartbeat.

Question 30

Define PURKINJE FIBRES

Answer 30

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.

Question 31

What are the phases of cardiac muscle contraction?

Answer 31

Phase 0: rapid depolarisation
Phase 1: partial repolarisation 
Phase 2: plateau
Phase 3: repolarisation
Phase 4: pacemaker potential

Question 32

Define DEPOLARISATION

Answer 32

Depolarisation is a change within a cell where the cell changes its electronic charge from negative to positive.

Question 33

Define REPOLARISATION

Answer 33

Repolarisation is a change within a cell where the cell changes its electronic charge from positive to negative.

Question 34

Define the REFRACTORY PERIOD

Answer 34

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.

Question 35

Define an ECG

Answer 35

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.

Question 36

What are the stages of the cardiac cycle?

Answer 36

• 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.

Question 37

Define the CARDIAC OUTPUT

Answer 37

Cardiac output is the amount of blood ejected from the ventricle into the respective blood vessel per minute.

Question 38

Define the STROKE VOLUME

Answer 38

Stroke volume is the volume of blood pumped by a ventricle per beat

Question 39

Define the HEART RATE

Answer 39

Heart rate is the number of times a heart beats per minute.

Question 40

What is special about the pulmonary vein?

Answer 40

It is the only vein that carries oxygenated blood (usually veins bring deoxygenated blood back).