CGIER 4 - The Heart: Structure, Physiology, Cardiac Cycle, Arterial Blood Pressure. Flashcards
The heart is the organ responsible for the _____________ of the blood.
circulation
Found in the thorax in a cavity of its own called the…
pericardium
The pericardium is lined by a layer of simple squamous epithelium called ______________ - forming part of the pericardial membrane.
mesothelium
The outer covering of the heart, the _________________, is covered by a mesothelium
epicardium
Cardiac muscle is __________ but arranged into individual cells separated by areas of _______________.
striated, intercalated discs
What are intercalated discs?
These are special membranes with numerous gap junctions allowing a free diffusion of ions from cell to cell.
Heart rate is regulated by the…
cardiovascular/cardiac centre in the medulla oblongata which responds to pressure receptors in the walls of blood vessels and other stimuli.
The adult human heart normally contract at about…
72 beats/min
The SA node or pacemaker consists of…
a modified cardiac muscle mixed with nerve fibres of the autonomic nervous system (i.e. Sympathetic and Parasympathetic [Vagus nerve, cranial nerve X] nervous systems).
Contraction begins spontaneously in an area called the…
sino-atrial (SA) node, in the right atrial wall near the entry of the superior vena cava.
The heart-beat originates spontaneously at the _________ because of the _________ of cardiac muscle (-the SA node generates ‘100 beats per min’ )
SA node, myogenic nature
How is the heart beat made to slow down or speed up?
By the autonomic nervous system (ANS).
Sympathetic fibres…
normally discharge at a slow rate but can increase heart rate by up to 100%.
Parasympathetic fibres can…
reduce the heart rate by 30%.
The atria are separated from the ventricles by the connective tissue of the _______________ (cannot carry the action potential) so the contraction wave stops.
annulus fibrosus
Because of the annulus fibrosus there is…
a delay of 0.11 sec between atrial and ventricular contraction.
Impulses travelling to the base of the right atrial wall near the centre of the heart, stimulate another special region which is called the…
Atrio-Ventricular (AV) node.
The AV node transmits an impulse to the muscles of the ventricles, via the _____________________ which cause the muscles to _______.
His-Purkinje system’ of specialized fibres, contract simultaneously.
The His-Purkinje system consists of the following parts:
Bundle of His/atrioventricular bundle (the start of the system)
Right bundle branch
Left bundle branch
Purkinje fibres (the end of the system
What is the contraction of heart chambers know as?
Systole
What is the relaxation of heart chambers known as?
Diastole
The cardiac cycle starts with the contraction of the _________, the impulse originating in the __________, causing the blood to be pumped into the ventricles.
two atria, sino-atrial node
The period from the end of one contraction to the end of the next is called the…
cardiac cycle
The frequency of the cardiac cycle is described by the…
heart rate, which is typically expressed as beats per minute.
Blood normally flows continuously into the atria from the…
vena cavae and pulmonary vein.
70% of atrial blood flows directly into the…
ventricles
During ventricular diastole the chambers fill to a volume of…
120-130 ml blood in each.
The remaining volume in each ventricle is called the…
end-systolic volume, usually 50 – 60 ml.
The remaining 30% is pushed by…
atrial systole
At the start of ventricular systole the rise in pressure causes the atrioventricular valves to _____, followed 0.02 to 0.03 sec later by the sudden _____ of the semilunar valves.
close, opening
70 ml of blood is ejected from the ventricle which is called the …
stroke volume output
Cardiac output is defined as the…
volume of blood ejected into the aorta by the left ventricle in a time period of 1 minute, but normally it isalsothe amount of blood pumped into the pulmonary circulation by therightventricle.
Note that __________ increases cardiac output (HR x SV) and ___________ decreases it.
sympathetic stimulation, parasympathetic stimulation
The atria act as ___________ for the ventricles.
primer pumps
Cardiac output is measured as…
stroke volume x heart rate = 70 ml x 72/min = 5040 ml / minute ~ 5 litres / min.
Frank - Starling Law of the heart explains the…
the intrinsic ability of the heart to adapt to changing loads of inflowing blood;
“within physiological limits, the heart pumps all the blood that comes to it without allowing excessive damming of blood in the veins”
Stroke volume depends mainly on ______________
venous return to the atria.
The P in an ECG chart is the…
atrial depolarization, which triggers atrial contraction.
The QRS in an ECG chart is the…
depolarization of AV node and conduction of electrical impulses through the ventricles. Ventricular contraction begins at R.
The T in an ECG chart is the…
repolarization of ventricles.
The P to R interval in an ECG chart is the…
time required for impulses to travel from SA node to ventricles.
What are the two heart sound heard using a stethoscope?
Lub and Dub
Lub is the first sound due to the…
closing of the bicuspid and tricuspid valves between the left and right atria and ventricles respectively, during ventricular systole.
Dub is the second sound due to the…
closing of semilunar valves in the pulmonary artery and the aorta, at the beginning of ventricular diastole.
Arterial blood pressure is measured using a…
sphygmomanometer.
The blood pressure in a young healthy adult is about…
120 mmHg at systole dropping to 80 mmHg at diastole
Written as 120/80
Equation for calculating blood pressure is…
Mean Arterial Pressure = Diastolic + 1/3rd (Systolic – Diastolic)
Mean pressure in the aorta is…
100 mmHg
Pressure is about _______ at the start of the arterial capillary bed
25 mmHg
Resistance is greatest in the arterioles at start of the capillaries where pressure drops to…
30 mmHg.
The venous capillary pressure is _________ and it continues to drop in the venous system being almost exactly _________ in the vena cava at the right atrium.
10 mmHg, 0 mmHg
The pulse pressure curve of high systolic and low diastolic pressures becomes less as…
blood passes through the smaller arteries until it almost disappears in the capillaries (1mm Hg).
What is pulse pressure?
The difference between the systolic and diastolic pressure readings.
The maximal systolic pressure is terminated by a sharp drop or __________ at the ______________.
incisura, commencement of ventricular diastole
This sharp drop or incisura is explained by a…
falling intraventricular pressure causing a backflow of blood from the aorta into the ventricles which causes a drop in aortic pressure but rapidly the aortic semi-lunar valves snap closed which causes a brief rebound in aortic pressure.
