Department of medical physiology7th week and 8th week

Semester: winterStudy program: Dental medicineLecture: RNDr. Soňa Grešová, PhD.Department of medical physiologyFaculty 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

• 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 function

Cardiovascular system Heart Wall

• Three layers

– Epicardium (outer layer)

– Myocardium (middle)

– Endocardium (inner layer)

Cardiovascular system Heart Cells

• Myocardial cells(working cells)

– Contraction

• Electrical conductionsystem 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&ved=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 membranesfuse 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 semilunarvalves

– Provides firm support forvalves and separates atriafrom 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 primarypacemaker site of heart– Normal rate 70-80

times per minute

• Other cardiac cellslower in conductionpathway play a back-up 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 myocardialcells more negatively chargedin relationship to outside where it ismore positivelycharged

Copyright: https://epfellow.files.wordpress.com/2009/08/cardiac_aps-scaled1000.jpg

Depolarization

• Occurs whenpositively chargedions move insidecells causinginterior to becomepositively charged– Change in electrical

charge over time

referred to as cell’s

action potentialCopyright: 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

• Phases4 – 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-20-the-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

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Contractile CellsPlateau phase

Repolarization

• Follows depolarizationand 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-20-the-heart/deck/14886115

Key Properties of MyocardialCells

• 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.

• 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)

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 impulsethat arises from SA node

• Impulse travels throughatria (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 itpasses through AV nodefrom atria to ventricles(PR segment)

– Allows atria time to

finish filling ventricles

• Impulse then rapidlytravels through His-Purkinje system

– Seen as a flat line

following P waveCopyright: 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 ventricularwalls 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 representedon 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

- QTCopyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

Cardiac axis orientation

• Pregnant women, peopleolder than 40y, small fatpeople

(-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.