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Cardiovascular (Heart & CV system anatomy & function (Heart …
Cardiovascular
Heart & CV system anatomy & function
Components of CV system
Heart
Establishes pressure gradient needed for blood to flow to tissues
Blood vessels
Passageway for blood
Blood
Materials dissolved or suspended and transported
Heart
Size of large fist
280-340g in men
Located thoracic cavity
Pericardium
Thin sac enclosing the heart
Holds heart in position whilst allowing movement for contraction
Fibrous pericardium
Prevents over stretching
Tough, inelastic
Attaches to diaphragm
Top fused to connective tissue of blood vessels entering and leaving the heart
Serous pericardium
Reduces friction between layers of serous pericardium as the heart moves
Thinner, more delicate membrane
Forms double layer around heart
Outer layer fixed to fibrous layer
Inner layer fixed to heart surface
Pericardial fluid in the middle
Chamber of the heart
Atria
Ventricles
Auricles - Wrinkled pouch-like structures, slightly increases the capacity of the atrium
Sulcus - Grooves which hold blood vessels and fat
Blood flow through the heart
Blood enters right atrium from superior and inferior vena cava
Blood flows from right atrium through tricuspid valve to right ventricle
Contraction of right ventricle causes pulmonary valve to open
Blood flows though pulmonary valve to pulmonary artery
Blood flows to lungs, unloads CO2 and take up O2
Blood returns to heart via pulmonary vein and enters left atrium
flows from left atrium though bicuspid valve to left ventricle
Contraction of left ventricle causes aortic valve to open
Flows though aortic valve to aorta and to the body organs and tissues
Unloads O2 and takes up CO2
Deoxygenated blood returns to heart via superior and inferior vena cava
Cardiac Output
Volume of blood ejected from a ventricle every minute
Calculated by
Stroke volume (SV)
(volume of blood expelled with each beat)
multiplied
by
heart rate
(number of beats)
e.g
Heart beat 72bpm
Stroke volume 70ml
72 x 70 = 5040ml/min
5040 / 1000
= 5.04L/min
How the heart ages
Heart shrinks
Decreased contraction strength
Valves become less flexible
Cardiac output decreases
Abnormal rhythms
Blood pressure regulation
Decreased blood pressure and volume
Endocrine mechanism
ADH, angiotensin II, aldosterone, EPO released
Increases blood volume
Neural mechanism
Baroreceptors, chemoreceptors stimulated
Cardiovascular centres stimulated
General sympathetic activation, release norepinephrine and epinephrine
Cardiac output increases
Peripheral vasoconstriction increases blood pressure
Decreases venous reserve
Nervous system controlling blood pressure
Regulates blood pressure via negative feedback loops
Baroreceptor reflex
Responds to stretch of artery wall
Feed info to the brainstem cardiovascular centre
Baroreflex
Drop in blood pressure
Drop in blood pressure detected by baroreceptor
Decrease parasympathetic activity to sinoatrial (SA) node
Increases heart rate = increased stroke volume = increased blood pressure
Increase in blood pressure
Increase in blood pressure detected by baroreceptor
Increased parasympathetic activity to SA node
Decreases heart rate = Decreased stroke volume = Decreased blood pressure
Limitation of baroreflex
Can responds to increase/decrease of atrial pressure, but most important role is responding to reductions/increases in arterial pressure
Long term regulation of arterial pressure requires activation of other mechanisms (hormonal and renal) to maintain normal blood pressure because baroreceptors adapt to sustained changes in arterial pressure
Hormonal regulation of blood pressure
Renin-angiotensin-aldosterone (RAA) system
Controls blood pressure by regulating the volume of blood in the body
Renin is an enzyme that hydrolyses angiotensinogen (liver) into angiotensin I
Angiotensin-converting enzyme converts angiotensin I into angiotensin II (a vasoconstrictor, elevates blood pressure)
Elevation of renin causes blood pressure increase
High blood pressure
Diagnosing Hypertension
Blood pressure measure in clinical setting
Stage 1 - 140/90 mmHg +
Stage 2 - 160/100 mmHg +
Severe hypertension - Systolic 160 mmHg or diastolic 110 mmHg
Long term consequences of hypertension
Stroke
Blood vessel damage (arteriosclerosis)
Heart attack or failure
Kidney failure
Blood vessels structure & function
Major blood vessels
Aorta
Largest artery in the body
Leaves heart at left ventricle
Carries oxygenated blood to the body
Vena cava
Major vein, returns deoxygenated blood from the body to the right auricle
Pulmonary artery
Carries deoxygenated blood from right ventricle to the lungs for oxygenation
Pulmonary vein
Carries oxygenated blood from lungs to left atrium
3 kinds of blood vessels
Arteries
Carries blood away from heart
Thick strong walls
Narrow lumen, varies with heartbeat
Capillaries
Gradually join up to form veins
Thin, one cell thick
Very narrow lumen
Veins
Carries blood towards the heart
Thin walls
Valves to prevent back flow
Transmission of an electrical impulse
Cardiac conduction system
Group of specialised cardiac muscle cells in the walls of the heart that send signals to the heart muscle causing it to contract
Sinoatrial node (SA) is natural pacemaker, starts the sequence by causing the atrial muscles to contract
Signal travels to the atrioventricular (AV) node, down through purkinje fibres, causing ventricles to contract
The signal creates an electrical current that can be seen on a graph called an electrocardiogram (ECG)
ECG electrical activity
P-wave
Activation of the atria
QRS complex
Activation of ventricles
T-wave
Recovery wave
Electrical activity of myocardium
P wave
SA nodes fire, atria depolarise and contract, atrial systole begins 100 milliseconds after SA signal
QRS complex
Ventricular depolarisation complex shape of spike due to different thickness and shape of the two ventricals
ST segment
Ventricular systole plateau in myocardial action potential
T wave
Ventricular repolarisation and relaxation
Mechanisms of action & control
Heart beat regulation
Autonomic nervous system
Hormonal control
Autonomic regulation of heart rate
Medulla oblongata contains the cardiovascular centre
2 Nerves link the cardiovascular centre in the medulla oblongata to the SA nodes of the heart
Accelerator nerve (Sympathetic NS)
When stimulated releases neurotransmitter at the SA node to increase heart rate
Vagus nerve (parasympathetic NS)
When stimulated releases neurotransmitter at the SA node to decrease heart rate
Cardiovascular centre receives input from 4 main receptor groups
Pressure receptors in heart (baroreceptors)
Found in carotid arteries and arch of the aorta
Chemoreceptors in heart (detects CO2 and O2 levels, and changes in pH)
Found in carotid arteries and arch of the aorta
Thermo receptors in muscles
Stretch receptors in muscles
Sympathetic NS activity increases heart rate
Parasympathetic NS decreases heart rate
Hormonal control
Adrenal medulla produces adrenaline (and noradrenaline)
Secreted from adrenal glands
Increases heart rate by increasing frequency of impulses released from the SA node
Increases force of contraction
Thyroid hormone (thyroxine) increases heart rate
Hyperthyroidism give tachycardia (heart rate exceeding normal)(heart rate over 100)
Cations controlling heart rate
K+, Ca2+ and Na+ have a big effect of cardiac function
Elevated blood K+ and Na+ decrease heart rate and contraction
Excess Na+ blocks Ca2+ inflow during cardiac action potentials, decreasing the force of contraction, excess K+ blocks generation of action potentials
A moderate increase in intestinal Ca2+ levels speeds heart rate and strengthens the heart beat
If you have low potassium levels you may have a heart problem e.g irregular heart beat
High potassium levels, heart muscle activity may be reduced
Ions need ions for action potential, imbalance of ions can therefore alter effectiveness of the heart
Elevated K+ and Na+ blood levels decrease heart rate and contractibility
Cardiovascular system & exercise
Exercise makes the heart work harder and increases cardiac output
Proprioceptors
(sensory receptors)
In muscles, tendons, joints inform cardiovascular centre that movement has increased
Chemoreceptors
Located in aorta and carotid arteries detect decrease in blood pH due to increase of lactic acid and CO2
Baroreceptors
Detect low blood pressure because of vasodilation in skeletal muscles