Download Lecture`22`–`Heart`Anatomy` ` The Heart • muscular pump • circulates

Lecture'22'–'Heart'Anatomy'
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The Heart
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muscular pump
circulates blood throughout the body
left side pumps oxygenated blood
right side receives deoxygenated blood and pumps it to lungs
located in the middle of the thoracic cavity (mediastinum)
enclosed in the pericardium
o two layers (fibrous and serous)
o have cavity containing pericardial fluid
o surrounds and stabilises heart
o reduces friction between heart and lungs
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visceral layer makes up the outer layer of the heart wall
Layers of the heart wall
3 layers
• epicardium (connective)
• myocardium (muscle)
• endocardium (epithelial)
• lines chambers and valves
• continuous with blood vessels
Chambers of the heart
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2 atria
2 ventricles
Pressure
• need a pressure gradient for blood to flow from one area to another
• pressure increases during contraction
Valves of the heart
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4 valves in the heart
right AV valve (tricuspid)
left AV valve (bicuspid)
o try before you buy
pulmonary valve (semilunar)
aortic valve (semilunar)
heart string tendons prevent valves from flipping inside out
The Vessels
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arteries ALWAYS leave the heart
veins ALWAYS enter the heart
Flow of blood
• Vena cava > RA > tricuspid valve > RV > pulmonary valve > pulmonary artery
> lungs > pulmonary vein > LA > biscuspid valve > LV > aortic valve > aorta >
body
Systemic circulation
• takes blood from heart to tissues and back to heart
• LV to RA
Pulmonary circulation
• brings blood to lungs and back
• RV to LA
Hepatic Portal
• from small intestine to liver
• differs from all other veins as they do not return blood to the heart
Coronary circulation
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brings blood to the actual heart muscle
coronary arteries and coronary veins supply heart muscle with O2 and nutrients
if these arteries are obstructed the heart muscle can die
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Lecture'23'–'Heart'Physiology'
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Cardiac muscle
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need electrical stimulus to make it work
heart has its own stimulator
o so that it can beat even if the outer systems fail
adjusted by the nervous system
The conducting system
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SA node
o the pacemaker
o in the wall of the right atrium
o send APs through both the atria to depolarise them
o left and right atria then contract at the same time
AV node
o in the junction between atria and ventricles
o aims to depolarise ventricles
o splits into left and right AV bundle branches
o purkinje fibres distribute the signal around the rest of the ventricle
o AV node only fires once the atria have depolarised because we don’t
want the atria and ventricles contracting at the same time
ECG
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measures electrical activity that accompanies each heart beat
electrical signals recorded on graph
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QRS complex represents the signal spreading through the ventricles (and hides
atrial depolarisation)
Cardiac cycle
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period between start of one heartbeat and the beginning of the next
includes both contraction and relaxation
at rest
o all four chambers relaxed (diastole)
o passive refilling of atria
atrial systole
o electrical signal from SA node
o atrial depolarisation
o atria contract
o once they’ve contracted, they relax again (repolarisation)
ventricular systole
o electrical signal from AV node
o ventricular depolarisation
o ventricles contract
o AV valves snap shut, preventing backflow (first heart sound)
o when pressure in ventricle > artery, blood flows into artery
o ventricles repolarise
o SL valve snaps shut (second heart sound)
at rest, one cardiac cycle lasts about 0.8 seconds
o 0.4 relaxation
o 0.4 contraction
as heart rate goes up, relaxation time shortens, not contraction
if this is an ongoing issue, the heart will not have enough time to regenerate and
heal itself
Lecture'24'–'Blood'Vessels'/'Flow'
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Blood Flow
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Right side- deoxygenated blood
Left side- oxygenated blood
Fluid flow in the body
• blood vessels
• the vasculature
• lymphatic vessels
Classes of blood vessels
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arteries
o carry blood away from the heart
o elastic and muscular
arterioles
o smallest branches of arteries
o smooth muscle
o can vary diameter easily and quickly to increase or decrease blood flow
to a tissue
o redirect blood flow
capillaries
o smallest blood vessels
o thin epithelial layer
o location of exchange between blood and interstitial fluid
venules
o collect blood from capillaries
veins
o return blood to the heart
o have valves
! if the valves stop working you get a collection of fluid (varicose
veins)
o thin walls - little muscle
o bigger lumen - can hold a lot of blood
Blood vessels
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largest of the blood vessels
o attach to heart
o superior and inferior vena cavae
o pulmonary vessels (arteries and veins)
o aorta
smallest blood vessels
o capillaries
o within tissues of the body
o have small diameter and thin walls
o chemicals and gasses diffuse across walls
o mainly epithelial tissue with a bit of connective tissue
Structure of vessel walls
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three layers surrounding lumen
tunica intima
o epithelial for secretion and absorption
tunica media
o muscle for elasticity and adjustment
tunica externa
o connective for anchoring, protecting, strength
structure determines function
Blood flow
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volume of blood flowing through vessel within a given time period
determined by:
o pressure difference
! blood flows from higher pressure to lower pressure
resistance to flow
o blood flow decreases as resistance increases
depends on vessel length, diameter and viscosity of blood
Capillary pressures
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hydrostatic pressure - the pressure exerted by a fluid against the wall of a vessel
o capillary or interstitial hydrostatic pressure
oncotic (osmotic) pressure - pressure exerted by plasma proteins
o capillary or interstitial oncotic pressure
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Lecture'25'–'BP/HR'Regulation'
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Cardiac Output
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amount of blood ejected by the heart each minute
beats per minute (HR)
blood per beat (SV)
CO = HR x SV
cardiac output varies with amount of oxygen needed
EDV
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end diastolic volume
how much blood you have in your ventricle which can be ejected into your artery
bigger EDV = bigger SV
ESV
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end systolic volume
the amount of blood left in the ventricle after it has contracted
bigger ESV = smaller SV
SV = EDV - ESV
ejection fraction is the proportion of blood being ejected
Cardiac Reserve
• difference between resting output and maximum possible
Regulation of stroke volume
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healthy heart pumps all blood out
more blood in, more blood out
right and left side pump equal volumes
1. Preload
• stretch in muscle fibres to accommodate blood
• more stretch in a muscle: the more strongly it can contract
• the more blood in during diastole, the stronger the contraction
2. Contractility
• strength of contraction
• the more calcium, the bigger contraction you can get
• sympathetic - increased contractility
• parasympathetic - decreased contractility
3. Afterload
• the pressure against which the heart must work to eject blood during systole
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lower afterload - more blood ejected
arteriosclerosis makes it harder to eject blood
Regulation of heart rate
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SA node sets pace of 90-100bpm
body (parasympathetic or sympathetic) modifies this according to need
Autonomic regulation
• medulla oblongata
• control sympathetic and parasympathetic neurons
Chemical regulation
• hormones
• adrenaline and noradrenaline
Effects of exercise
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at rest
o less stretch
o EDV is low
o SV is low
during exercise
o more stretch
o EDV increases
o SV increases
o more oxygen to tissues
Blood pressure
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in arteries
systolic pressure
o pressure during systole
diastolic pressure
o pressure during diastole
pulse pressure
o systolic - diastolic pressure
MAP
o = diastolic pressure + 1/3 pulse pressure
Factors determining MAP
• cardiac output
• TPR
Baroreceptor reflex
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blood pressure homeostasis
in carotid and aortic sinuses
receptors respond to stretch
more stretch = more firing of signals to medulla oblongata
vasodilation occurs to lower pressure
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