Cardiovascular System Flashcards
What is the function of the cardiovascular system?
Transport essential nutrients and pass on the products of metabolism.
What does the cardiovascular system consist of?
Heart
Blood
Blood vessels
Outline the structure of the heart
Epicardium outer layer- outer layer. Pericardium (inner and outer) mostly structural and stability, connective tissue
Myocardium- middle layer. Composed of cardiac muscle. Thickest layer
Endocardium- inner layer, thin layer that lines the heart and valves
describe the chambers of the heart
Two atria Two ventricles Atria to ventricles split by valves Ventricles at apex, atria at base Split by sulci
What is the purpose of the valves and how do they work?
Prevent the back flow of blood
Work on a pressure gradient, filling of one chamber shuts previous chamber
Tricuspid, mitral, semilunar valves
describe the movement of blood through the heart
Deoxygenated blood enters the right atrium through the vena cava and is then passed to the right ventricle. Here it goes into the pulmonary arteries to the lungs. Oxygenated blood from the lungs travels through the pulmonary vein to the left atrium, to the left ventricle and then leaves the heart through the aorta.
How does the heart pump?
Myoepithelial muscle, generates own contractions through nodes.
Rhythmical contractility determines which sections of heart pump first.
What is the sinoatrial node?
Collection of myogenic muscular cells in the wall for the right atrium below the superior vena cava
Pacemaker
60-100 pulses a minute
What is the atrioventricular node?
Impulse from the SAN received by this
Situated at the septum between the atria and ventricles
Impulse passes to bundle of his and the to purkinje fibres at the apex, here the ventricles contract
What is systolic and diastolic?
Systolic- contraction
Diastolic - relaxation
Outline the cardiac cycle
Relaxation- completion of the cycle the heart is at a state of relaxation. Semilunar valves are shut due to the pressure gradient. Blood flows into atria.
Ventricular filling - tricuspid and mitral valves open due to high pressure in atria, blood flows into ventricle. Impulse from SAN assists flow
Ventricular contraction- impulse arrives at the purkinje fibres initiating contraction of ventricles
Entire cycle lasts 0.8 seconds
What is cardiac output?
The amount of blood ejected from the heart each minute
Average is 5L/min in adults
Discuss nervous control of the brain
Initiated by cardiovascular centre in the medulla of brain.
Recieves signals when the body exercises
Chemoreceptors on heart respond to chemicals in blood
Outline hormonal regulation of cardiac output
Involved adrenal glands
Exercise stimulates them to release adrenaline which increases heart rate and stroke volume
Describe the blood supply to the heart
Left and right coronary arteries branch off aorta soon after leaving the left ventricle
Describe arteries
Large vessels, substantial walls
Presence of muscle and elastic fibres allow the muscle to be elastic and to contract
Elasticity allows vasodilation
Contractility allows vasoconstriction
Describe arterioles
Connect the arterial network to the capillary network
Same as arteries in structure just smaller
Describe veins
Much thinner walls
Still able to contract and be elastic
Contains valves to prevent backward flow under lower pressure
Venous sinuses in heart and brain, contain no muscle cells
Describe venules
Structure similar to arterioles
Describe varicose veins and why they occur in pregnancy
Action of progesterone on smooth muscle of veins
Women with high blood pressure at greater risk
Pool of blood in veins
Can lead to thrombophlebitis
Can occur near anal sphincter causing haemorrhoids
What are capillaries? Function?
Supply almost every cell in body with.
Thin wall allows efficient diffusion of nutrients and gases
Describe the movement of blood through vessels
Blood moves as a result of the pressure created by the contraction of the heart, this means blood pressure in arteries is high and decreases in arterioles, capillaries, venules and veins.
What is blood pressure?
The pressure exerted on the interior walls of blood vessels 120/70 is average
Outline physical factors that affect blood pressure
Blood volume: increase in volume = increase in blood pressure
Blood viscosity: specialised cells in plasma, number of proteins in plasma affects viscosity , more viscosity means higher blood pressure
Elasticity of vessel walls: if the structure of vessel walls change it may be difficult for them to stretch and accommodate more blood. This increases pressure due to less room
Length of blood vessels: blood pressure decreases the longer you go along a vessel away from the heart.
Diameter of vessel: smaller diameter means higher pressure
Outline physiological factors that affect blood pressure
Alteration of cardiac output
Sympathetic nervous system: arterioles alter their diameter due to this
Hormonal regulation: adrenaline, noradrenaline effect cardiac output, ADH when there is great blood loss
Auto regulation: many organs are able to control blood pressure locally to meet the need of cells
Discuss hypertensive disorders of pregnancy
Hypertension occurs in 6-8% of pregnancies
Can lead to pre eclampsia or PIH
What are erythrocytes?
Red blood cells Make up 99% of blood cells Transport oxygen from lungs to the body Circular biconcave discs 120 day life span Contains haemoglobin- globular protein
What is iron deficiency anaemia?
A deficiency in the quality or quantity of red blood cells is the body leading to a decrease in the amount of oxygen available for cells.
Insufficient haemoglobin is formed
Causes in pregnancy:
Poor iron diet
Loss of iron due to vomiting
Excessive demand eg. Previous PPH
What are the four blood groups?
A
B
AB
O
What is the Rhesus factor?
There are several Rhesus factors but the most common is antigen d
80% has the antigen, problems arise for those without it
If someone rh neg recieves a transfusion with rh pos blood their body will produce antibodies to destroy the positive antibodies and cause a severe reaction
What is Rhesus incompatibility
A mother who is Rhesus negative may develop Rhesus antibodies if the fetus is Rhesus positive and their blood cells leak into the maternal blood stream during pregnancy
Anti D immunoglobulin is given which destroys the fetal cells in maternal blood stream before a response can be initiated by the body
What are leucocytes
White blood cells
Neutrophils, responsible for protecting the body form foreign cells. Release lysosomes which are digestive enzymes that ingest a pathogen or foreign cell.
What are thrombocytes?
Aka platelets, small fragments of cellular material, essential for clotting
When thrombocytes come into contact with damaged blood vessels they release seretonin which causes local vasoconstriction
Formation of a plug as platelets clump together
Coagulates blood
How does pregnancy effect the cardiovascular system?
Cardiac output risks by 40%, stroke volume and heart rate contribute to this, gradual increase over first and second trimester
Blood vessels increase in number and length to supply the placenta
This usually causes a decrease in blood pressure
Plasma volume increases by 50% and erythrocytes by 18%
These changes compensate for the apparent loss of blood volume
Slight increase in leucocytes
Increase in clotting agents
Supine hypotension- pressure of gravid uterus due to inferior vena cava
Haemodilution causing physiological anaemia
How does labour affect the cardiovascular system?
Caridiac input increases by 2L/min to meet increased metabolic demands
Increased clotting factors reading for third stage
How does the postnatal period effect the cardiovascular system?
Gradually returns to normal aided by diuresis (increased urine production) during first 48hrs post delivery
Mobility post delivery is important due to increSed numbers of clotting factors and that being potential risk for dvt
How does the cardiovascular system effect the neonate?
Fetal haemoglobin has higher affinity for oxygen than maternal haemoglobin to attract more oxygen across the placenta
