HEART

        HEART

1.      INTRODUCTION:

   The heart is the roughly hollow muscular organ.

2.      SITUATION:

Ø  The heart lies in the thoracic cavity in the mediastinum between the lungs.

Ø  It lies obliquely a little more to the left than the right and presents a base above & an apex below.

3.      MEASURMENTS:

Ø  SHAPE              -   CONE SHAPE

Ø  LENGTH           -    10 cm long

Ø  SIZE                    - 225 gm in women.

                               More than 225 gm in Men.

4.      ORGANS  ASSOCIATED WITH THE HEART:

Ø  Inferiorly – the apex rests on the central trends f the diaphragm.

Ø  Superiorly- Blood venal that is the aorla, SVC, Pulmonary artery & Pulmonary veins.

Ø  Portiorly - The Oesophagus, trachea, left & right broumnchues, m Desceneling aorla, IVC & thoracic vertebrae.

Ø  Laterally -    The lungs the left lung overlaps the left side of the heart.

Ø  Anterior -    The sterum, Ribs & Intercostals muscles.

5.      STRUCTURE:

    The heart is composed of 3 layers

Ø  Pericardium

Ø  Myocardium

Ø  Endocardium

PERICARDIUM:

It is the outer conversing layer of the heart, made up of 2 sacs.

Ø   Other sac -  commits fibrous tissue

Ø  Inner sac   - Double layer of Serous membrane.

             The outer fibrous sac is continuous. With the tunica adventitia of the great blood vessels above and is adherent to the diaphragm below.

Ø     It’s elastic , fibrous nature.

Ø  The outer layer of the serous membrane, the parietal pericardium, lines the fibrous sac.

Ø  The Inner layer, the visceral pericardium or epicardium, which is continuous with the parietal pericardium, is adherents to the heart muscle.

Ø  Serous membrane consists of flattened epithelial cells.

Ø  It secretes serous third into the space between the visceral &parietal layers which allows smooth movement between them when the heart beats.

Ø  The between the parietal & visceral pericardium is only a potential space.   

MYOCARDIUM:

       The Myocardium is composed of specialized cardiac muscle found only in the heart.

Ø   It is not under voluntary control but like skeletal muscle, cross stripes are seen on microscopic examinations.

Ø  Each fiber has nuclei and one or more branches.

Ø  Microscopically these Joints or Intercalated discs can be seen as thicker,darker lines than the ordinary cross stripes.

Ø  When an impulse is initiated. It spreads from cell to cell via the branches and intercalated discs over the whole sheet of muscle, causing contraction.

Ø  The sheet arrangement of the myocardium enables the atria & ventricles to contract in a coordinated & efficient manner.

Ø  The myocardium is thickest at the Apex & thins out towards the base.

Ø  This reflects the amount of work each chamber contributes to the pumping of blood.

Ø  It is thickest in the left ventricle.

Ø  The Atria & the ventricles are separated by a ring of fibrous tissue that doesn’t conduct electrical impulses.

                    ENDOCARDIUM: -

It forms the lining of the myocardium and the heart values.

Ø  It is a thin, smooth, glistening membrane which permits smooth flow of blood inside the heart.

Ø  It consists of flattened epithelial cells, continuous with the endothelium that lines the blood verses.

INTERIOR OF THE HEART:

The heart is divided into a right & left side by the septum, a partition consisting of myocardium covered by endocardium.

Ø  After birth blood can’t cross the septum from one side to the other.

Ø  Each side is divided by an Atrioventricular value into an upper chamber, the Atrium and a lower chamber the ventricle.

Ø  The Atrioventricular values are formed by double folds of endocardium strengthened by a little fibrous tissue.

Ø  The Retro ventricular value [Tricuspid value] has 3 flaps or cusps & the it atrioventricular value or Bicuspid has two cusps.

Ø  The values between the atria & ventricles open & close passively according to change in pressure in the chambers.

Ø  They open when the pressure in the Atria is greater than that in the ventricles.

Ø  During ventricular systole (contraction) the pressure in the ventricles reissues above that in the Artia & the values snap that preventing backward flow of blood.

Ø  The values are prevented from opening upwards into the atria by tendinous cords called ‘ Chordate lendineae’  which expends from the inferior surface of the cusps to little projections of myocardium covered with endothelium called ‘papillary muscles’.

6.      BLOOD SUPPLY

ARTERIAL SUPPLY

       

                      The right & left coronary oratories which branches from the aorta immediately distal to the aortic value.

VENOUS DRAINAGE:

The venous blood is collected into several small veins that join to from the coronary sinus which opens into the right Atrium.

7.      NERVE SUPPLY:

PARASYMPHATHETIC N S:

The Vegas nerves supply mainly the SA &  AV nodes and aerial muscles

Ø  It reduces the Impulses & Decreases the heart rate

      SYMPATHETIC N S:

      It supplies the SA & AV nodes & the myocardium of Atria & Ventricles.

Ø  Sympatyhic stimulation increase the rate & force of the heart beat.

8.      FACTORS AFFECTING HEART RATE:

1.      AUTOMATIC NERVOUS SYSTEM:

The rate at which the heart beat is a balance of sympathetic & parasympathetic activity.

2.      CIRCULATING CHEMICALS:

   The hormones Adrenaline & nor adrenaline secreted by the adrenal medulla, it increase the heartrate.

3.      POSITION:

When the person is upright the heart rate is usually faster than when lying down.

4.      EXERCISE:

Active muscles med more blood than resting muscles &this is achieved by an increased heart rate & selective vasodilatation.

5.      EMOTIONAL STRESS:

            During excitement fear or anxiety the heart rate is increased.

6.      GENDER:

The heart rate is faster in women than men.

7.      AGE:

    In a babies & small children the heart rate is more rapid than in older children & adults.

8.      TEMPERATURE:

   The heart rate increases & decreases with body temperature.

9.      BARORECEPTOR REFLEX:

These are nerve endings sensitive to pressure changes ( stretch) within the vessel situated in the Arch of  the aorta & in the carotid sinuses.