Download Lecture 7 th ​, 8 th week

Department of medical physiology
7th week and 8th week
Semester: winter
Study program: Dental medicine
Lecture: RNDr. Soňa Grešová, PhD.
Department of medical physiology
Faculty of Medicine PJŠU
Cardiovascular system
1. The basic properties of the
myocardium
2. Excitation and conduction of the
heart impulse
3. Metabolism and energetics of
the heart
Cardiovascular system function
• Functional components of the cardiovascular system:
– Heart
– Blood Vessels
– Blood
• General functions these provide
– Transportation
• Everything transported by the blood
– Regulation
• Of the cardiovascular system
– Intrinsic v extrinsic
– Protection
• Against blood loss
– Production/Synthesis
Cardiovascular system
Heart Wall
• Three layers
– Epicardium (outer layer)
– Myocardium (middle)
– Endocardium (inner layer)
Cardiovascular system
Heart Cells
• Myocardial cells
(working cells)
– Contraction
• Electrical conduction
system cells
– Initiate and carry
electrical impulses
throughout heart
Copyright:
https://www.google.sk/search?q=heart+cells&biw=1745&bih=807&source=lnms&tbm=isch&sa=X&ve
d=0ahUKEwjf5Y6t2ZvQAhWHbhQKHcJXAQsQ_AUIBigB#imgrc=8t9wfe7Ll-r6gM%3A
Cardiovascular system
Working Cells
• Myocytes
– Enclosed in sarcolemma
– Composed of :
• Actin filaments (thin)
• Myosin filaments (thick)
Cardiovascular system
Myocardial Cells
• Intercalated discs
– the cell membranes
fuse with one another
(gap junctions)
– ions move with ease in
the intracellular fluid
along the longitudinal
axes
Cardiovascular system
Internal Heart
• Heart consists of four
chambers
– 2 atria collect blood and
deliver to ventricles
– 2 ventricles pump
blood to pulmonary and
systemic circulation
• Septum separates heart
into two functional units
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
Cardiovascular system
Heart Valves
• Function is to prevent backflow
- Mitral and bicuspid valve
(AV valve)
• Prevent backflow to the atria
• Prolapse is prevented by the
chordae tendineae
– Tensioned by the papillary muscles
- Tricuspid valve (AV valve)
- Aortic and pulmonic valves
(semilunar valves)
• Prevent backflow into ventricles
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and
Hall textbook of medical physiology. Philadelphia, PA:
Saunders Elsevier.
Cardiovascular system
Skeleton of Heart
• Fibrous tissue :
– Forms fibrous rings
around AV and semilunar
valves
– Provides firm support for
valves and separates atria
from ventricles
• Cardiac muscle
– Attached to fibrous
connective tissue
– Contract ventricles in a
wringing motion
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
Cardiovascular system
Heart’s Conduction System
• Consists of
“pacemaker” cells
and conduction
pathways
– Coordinate the
contraction of the
atria and ventricles
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
Cardiovascular system
Pacemaker Sites
• SA node is primary
pacemaker site of
heart
– Normal rate 70-80
times per minute
• Other cardiac cells
lower in conduction
pathway play a backup role
– AV node (rate 40-60
times per minute)
– Purkinje fibers (rate
15-40 times per
minute)
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
Resting membrane potential
• Inside of myocardial
cells more
negatively charged
in relationship to
outside where it is
more positively
charged
Copyright: https://epfellow.files.wordpress.com/2009/08/cardiac_aps-scaled1000.jpg
Depolarization
• Occurs when
positively charged
ions move inside
cells causing
interior to become
positively charged
– Change in electrical
charge over time
referred to as cell’s
action potential
Copyright: https://epfellow.files.wordpress.com/2009/08/cardiac_aps-scaled1000.jpg
Autorhythmic Cells
(Pacemaker Cells)
• Characteristics of Pacemaker Cells
Excitation and conduction of the heart
impulse
• Phases
4 – resting membrane potential -90mV
0 – depolarization
• Due to gap junctions or conduction fiber
action
• Voltage gated Na+ channels open… close
at 20mV
1 – temporary repolarization
• Open K+ channels allow some K+ to leave
the cell
2 – plateau phase
• Voltage gated Ca2+ channels are fully
open (started during initial
depolarization)
3 – repolarization
• Ca2+ channels close and K+ permeability
increases as slower activated K+ channels
open, causing a quick repolarization
Copyright: https://www.studyblue.com/notes/note/n/ch-20the-heart/deck/14886115
Excitation and conduction of the heart impulse
• Plateau phase prevents
summation due to the
elongated refractory
period
- absolute refractory period
- the relative refractory period
• No summation capacity =
no tetanus
Copyright:
http://163.178.103.176/Tema1G/Grupos1/GermanT1/GATP13/E7
.htm
Copyright: https://studydroid.com/printerFriendlyViewPack.php?packId=51109
Contractile Cells
Plateau phase
Repolarization
• Follows depolarization
and occurs when:
– Potassium leaves cell
causing positive charge
to lower
– Sodium and calcium
are removed by
special transport
systems
Copyright: https://www.studyblue.com/notes/note/n/ch-20the-heart/deck/14886115
Key Properties of Myocardial
Cells
• Automaticity (Chronotropic effect)
– Can produce electrical activity without
outside nerve stimulation
• Conductivity (Dromotropic effect)
– Ability to transmit an electrical stimulus
from cell to cell throughout myocardium
• Excitability (Batmotropic effect)
– Ability to respond to an electrical
stimulus
• Contractility (Inotropic effect)
– Ability of myocardial cells to contract when
stimulated by an electrical impulse
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
Electrocardiography (ECG or EKG)
• The EKG device detects and amplifies the tiny electrical changes on
the skin that are caused when the heart muscle depolarizes during
each heartbeat.
• During each heartbeat a healthy heart will have an orderly
progression of a wave of depolarisation that is triggered by the cells
in the sinoatrial node, spreads out through the atrium, passes
through "intrinsic conduction pathways" and then spreads all over
the ventricles.
• A 12-lead EKG is one in which 12 different electrical signals are
recorded at approximately the same time and will often be used as
a one-off recording of an EKG, traditionally printed out as a paper
copy.
Electrocardiography (ECG or EKG)
Copyright: Hall, J. E., & Guyton, A. C.
(2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA:
Saunders Elsevier.
Electrocardiography (ECG or EKG)
• Heartbeat initiated by
an electrical impulse
that arises from SA
node
• Impulse travels through
atria (P wave)
– generates a positive
waveform on ECG
and contraction of
atria
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
Electrocardiography (ECG or EKG)
• Impulse slows as it
passes through AV node
from atria to ventricles
(PR segment)
– Allows atria time to
finish filling ventricles
• Impulse then rapidly
travels through HisPurkinje system
– Seen as a flat line
following P wave
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
Electrocardiography (ECG or EKG)
• Depolarization of
septum and ventricular
walls generates QRS
complex and
contraction of ventricles
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
Electrocardiography (ECG or EKG)
• Repolarization of
ventricles is represented
on ECG by ST segment
(plateau phase) and T
wave
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
Electrocardiography (ECG or EKG)
• Waves
-P
- QRS
-T
• Segments
- PR
- ST
• Intervals
- PR
- QRS
- QT
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
Cardiac axis orientation
• Pregnant women, people
older than 40y, small fat
people
(-30° - +30° )
• People older than 30y,
(+30° - +60° )
• People younger than 30y,
(+60° - +90° )
• Children
(+90° - +120° )
Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of
medical physiology. Philadelphia, PA: Saunders Elsevier.
3. Metabolism and energetics of the
heart
•
•
•
•
Heart muscle is highly oxidative tissue.
Mitochondrial respiration produces more than 90% of energy
Mitochondria occupy 30% of cardiomyocyte space
>95% of ATP formation comes from oxidative phosphorylation
in mitochondria
• 60-70% of ATP hydrolysis is used for muscle contraction,
• 30 - 40% for the sarcoplasmatic reticulum (SR) Ca2+-ATPase
and other ion pumps.