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Summary Physiology Basic Concepts Cardiovascular function
- Instelling
- Universiteit Leiden (UL)
Summary of the course PBC, the cardiovascular part.
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Voorbeeld van de inhoud
Physiology Basic Concepts © Carlita VerhoefCardiovascular and Respiratory System
C02 Cardiac Anatomy
Cardiac muscles are organized in vesicles. These vesicles are
organized in: muscle fiber Myofibrils Sarcomere. Thick are
myofibrils and thin are the actin. The sarcomere is the functional unit of
a fiber. Large T-tubules are located at the level of the Z-disc; one T-
tubule per sarcomere. The T-tubule is important for the calcium in the
fiber. It contains large mitochondria that are densely packed between
myofibrils.
Skeletal muscle cells are characterized by:
⋄ Peripheral nucleus (immediately under plasma membrane)
⋄ Single multinucleated protoplasmic unit (fiber)
Cardiac muscle cells are characterized by:
⋄ Central Nucleus, single, sometimes bi-nuclear cells
⋄ Juxtanuclear cytoplasm ( = near the nucleus of a cell)
⋄ End-to-end aligment of cells; individual cells joined by complex
junctions form a functional unit (1 fiber formed by numerous cells)
⋄ Branching pattern of the muscle fibers (= vertakt patroon)
⋄ Intercalated disks (complex junctions)
Intercalated disks are important for communication. Cardiac muscle cells are mechanically,
chemically and electrically connected to one another: Functional Syncytium; stimulation of
an individual muscle cell results in the contraction of all muscle cells.
The intercalated disk has three components;
⋄ Fascia adherens
Transverse component of the ID; transverse boundary between muscle cells
⋄ Maculae adherens (desmosomes)
Transverse and lateral components of the ID; binds individual cells to one another
⋄ Gap junctions
Lateral component of ID; ionic continuity between adjacent cardiac muscle cells
1
,Gap junctions are important for initiating an Action Potential.
They consist of 2 connexons (or hemichannels), which are
hexamers of transmembrane protein subunits called
connexins; necessary for electrical and metabolic coupling
between cells.
Electrical activation of the heart is necessary for a Cardiac
Conduction System. The myocytes causes the contraction of
the heart; they have a lot of input of the nervous system.
Sino-Atrial node is on the lateral wall of the vena cava
superior. SA-node is the primary pacemaker system of the
heart (60-80 bpm); all the cells of the heart has a beating
rhythm. The P-wave is the activation (or contraction) of the atria (caused by the SA-node).
The AV-node is in the triangle of Koch, near opening coronary sinus. The
AV node is in the dorsal part of the right atrium. The AV-node contains slow
conducting tissue because the cells are badly coupled; the impulse will be
delayed in the AV node (<100 msec) causing time for the ventricles to fill.
The AV-node can also take over the pacemaker function (30-40 bpm).
There is no amplitude in this part because there is an electrical silence; flat
line in the ECG.
The autonomic nerve fibers (sympathetic and parasympathic) terminate in
the nodes. Both sympathetic and parasympathetic stimulations have different effects on the
Cardiovascular system;
Sympathetic activation: ACTION! Parasympathetic activation: REST
⋄ Heart rate ⋄ Heart rate
⋄ Impulse contraction ⋄ Impulse conduction
⋄ Force of contraction ⋄ Force of contraction
⋄ Blood flow coronary vessels ⋄ Blood flow coronary vessels
(by dilation of vascular smooth muscle) (by restriction of the coronary arteries)
His-bundle is the muscular connection between the
atria and the ventricles of the heart; ring of fibrous
tissue This is called the annulus fibrosis.
It runs through the fibrous skeleton, eventually on
top of the IVS. Fibrous skeleton of the heart His
bundle: normally only electrical connection site.
Purkinje fibers are subendocardial branches,
extending into the walls of the ventricles.
Why is electrical isolation so important?
⋄ Filling of the ventricles
⋄ Disturbed isolation: atrial fibrillation, chaotic atrial activity, irregular conductance to
ventricle
⋄ No electrical silence; delta wave on ECG. Danger; high heart rates during arrhythmia
Accessory pathway: impulse travels through accessory connection, no delay before
ventricular activation, no electrical silence delta wave, high heart rate during arrhythmia.
2
, The T-wave is caused by the repolarization of the ventricles.
Atrial fibrillation is a chaotic atrial activity; Irregular conductance to ventricle.
To sum up:
⋄ Cardiac muscle cells can be distinguished from skeletal muscle cells by the presence
of intercalated disks, that have gap junctions in their lateral parts
⋄ Cardiac muscle cells are mechanically, chemically and electrically connected to one
another, and thus form a functional syncytium
⋄ The cardiac conduction system consists of various components, that can each be
recognized by their specific anatomical location and morphological
/electrophysiological characteristics
⋄ The surface ECG is a representation of the cardiac electrical function, and is the sum
of the electrical activity of the individual components of the cardiac conduction system
⋄ In the normal heart, the His bundle is the only structure that can bypass the insulation
annulus fibrosus of the heart
Orientation of the heart in the thorax; surrounded by pericardium, resting on the diaphragm.
It has narrow relation with the oesophagus > useful for making echoes of the heart.
Surface of the heart:
⋄ Anterior surface is mainly formed by the RV
⋄ Diaphragmatic surface is mainly formed by LV and partly by RV
⋄ Right pulmonary surface is formed by the RA
⋄ Left pulmonary surface is formed by the LV
Right Atrium Left Atrium
⋄ Muscular wall (mm pectinati) ⋄ Smooth posterior wall
⋄ Crista terminalis = border between ⋄ Tubular left atrial appendage, narrow
muscular wall and smooth wall in the opening to LA
atrium (outside: sulcus terminalis)
⋄ Smooth walled sinus venosus
⋄ Blunt right atrial appendage, wide opening
to RA
⋄ Fossa ovalis in interatrial septum
Right Ventricle Left Ventricle
⋄ Tricuspid valve (three leaflets) ⋄ Continuity mitral valve and aortic valve;
⋄ Muscular infundibulum; is the entrance blood comes in through the mitral
from the right ventricle into the pulmonary valve, goes to aortic valve tissue
artery and pulmonary trunk ⋄ Smooth septal surface
⋄ Myocardium between the fibrous tissue of ⋄ Fine trabecularisation
the tricuspid valve and pulmonary valve ⋄ The fibrous tissue between the valves
⋄ Coarse apical trabecularisation are connected
Wall thickness of LV usually thicker than RV; intracardiac pressure! Is much higher on the
left side. This cannot be used as a characteristic because in certain situations the RV is
thicker; ventricular inversion; pulmonary senosis or pulmonary hypertension.
The right pulmonary arteria goes under the aortic bow.
3
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