Circulatory system

Question 1

Heart Location

Answer 1

• The heart is located in the mediastinum (prosteriorly extends
  from the sternum anteriorly to the vertebral column, and lies medially
  between the two lungs and the pleural membranes that
  cover them)

Question 2

Heart Angle

Answer 2

The base of the heart is
tipped up medially and
posteriorly, while the apex
projects inferiorly and
laterally.

Question 3

The Pericardium

Answer 3

• membrane that
  surrounds and
  protects the heart
• helps retains its
  position in the
  mediastinum,
  while allowing for
  some freedom of
  movement

Question 4

The Pericardium - structure

Answer 4

• The pericardium is composed of a tough
  outer fibrous layer lined by a delicate serous membrane.
• The fibrous pericardium is a very dense
  and non-flexible connective tissue that
  helps protect and anchor the heart.
• The inner serous pericardium is
  subdivided into a parietal layer which
  adheres to the outermost fibrous layer
  and a visceral layer which is also viewed
  as the outer surface of the heart wall.
• A thin pericardial fluid lubricates the
  space between the visceral and parietal
  pericardium.

Question 5

Layers of the Heart Wall

Answer 5

• The epicardium, the thin, transparent
  outer layer of the heart wall, is also called
  the visceral layer of the serous pericardium.
• The myocardium, the thick middle layer, is
  composed of cardiac muscle.
• The endocardium is a simple squamous
  epithelium that is known throughout the
  circulatory system as endothelium

Question 6

Chambers of the Heart

Answer 6

• The heart has 4 Chambers:
• The upper 2 are the right
  and left atria.
• The lower 2 are the right
  and left ventricles.

The right heart consists of the
right atrium and right
ventricle, taking venous blood
from the body and pumping it
to the lungs for oxygenation.

The left heart consists of the
left atrium and left ventricle,
taking freshly oxygenated
pulmonary
blood and pumping it
systemically to the body.

Question 12

Arteries

Answer 12

• always conduct blood
  away from the heart
  – mostly contain oxygenated blood.
• Mostly thick-walled
• exposed to high pressures
  and friction forces.

Question 13

Veins

Answer 13

• Veins are vessels that always bring blood back to the heart
• mostly contain deoxygenated blood.
• thin-walled
• exposed to low pressures
• minimal friction forces.

Question 14

major arteries attach to…

Answer 14

attach to the heart are the arch of the aorta ,the
pulmonary trunk and the coronary arteries

Question 15

major veins that attach to…

Answer 15

attach to the heart
are the superior and inferior vena cava,
the four pulmonary veins and the coronary sinus.

Question 16

Arterioles

Answer 16

• Have thin tunica interna with thin fenestrated
  internal elastic lamina.
• Tunica media consists of one or two layers of
  smooth muscle cells
• Tunica externa consists of connective tissue
  and sympathetic nerve supply that can vary
  rate of flow.

Question 17

Capillaries

Answer 17

• Smallest vessels that have narrow diameters, red blood cells pass single file through the lumen of
  vessel.
• Allow exchange of
  substances between the
  blood and interstitial
  fluid.
• Lack both tunica media
  and externa.
• Single layer of endothelial cells.

Question 18

Venules

Answer 18

• Post capillary venules have thin walls that do not readily maintain shape (exchange of nutrients & wastes, white blood cell emigration).
• Muscular venules one or two smooth muscle layers, no exchanges now possible.
• Drain capillary blood and begin return flow back toward the heart.

Question 19

Blood flow (2 circuits)

Answer 19

• The body’s blood flow can best be understood as two circuits arranged in series. The output of one becomes the input of the other:
• Systemic circuit ejects blood into the aorta, systemic arteries, and arterioles and is powered by the left side of the heart.
• Pulmonary circuit ejects blood into the pulmonary trunk and is powered by the right side of the heart.

Question 20

Coronary Circulation (info)

Answer 20

• Only the innermost tissues lining the chambers of the heart can derive oxygen from the blood flowing through those chambers.
• The myocardium and other tissues of the thick cardiac walls must get nutrients from blood flowing through the coronary circulation.
• Even then, only during the relaxation phase of ventricular diastole, will blood actually flow through the coronary circulation

Question 21

Coronary Circulation (route)

Answer 21

Starting at the aortic root, the
direction of blood flow is
from the aorta to the left and
right coronary arteries (LCA,
RCA):
* LCA to anterior
interventricular and
circumflex branches
* RCA to marginal and posterior
atrioventricular branches

• Coronary veins all
  collect into the coronary
  sinus on the back part of
  the heart:
• The coronary sinus empties into the right
  atrium where the deoxygenated coronary
  blood joins with oxygendepleted blood from the rest of the body.

Question 22

Name 2 coronary arteries:

Answer 22

left coronary artery & right coronary artery

Question 23

Cardiac Muscle Tissue

Answer 23

• Cardiac muscle, like skeletal muscle, is
  striated. Unlike skeletal muscle, its fibres are shorter, they branch, and they have only one centrally located nucleus.
• Cardiac muscle cells connect to and
  communicate with neighbouring cells
  through gap junctions in intercalated discs.

Question 24

Autorhythmicity

Answer 24

• The rhythmical electrical activity they produce is called autorhythmicity. Because heart muscle is autorhythmic, it does
  not rely on the central nervous system to sustain a lifelong heartbeat.
• Autorhythmic cells spontaneously depolarise at a given rate, some groups faster, some groups slower. Once a group of autorhythmic cells reaches threshold and starts an action potential (AP), all of the cells in that area of the heart also depolarise.

Question 25

Cardiac Conduction

Answer 25

- The self-excitable myocytes that ‘act like nerves’ have the 2 important roles of forming the conduction system of the heart and acting as pacemakers within that system. - Because it has the fastest rate of depolarisation, the normal pacemaker of the heart is the sinoatrial (SA) node, located in the right atrial wall just below where the superior vena cava enters the chamber. Spontaneous Depolarization of autorhythmic fibres in the SA node firing about once every 0.8 seconds, or 75 action potentials per minute - The action potential generated from the SA node reaches the next pacemaker by propagating throughout the wall of the atria to the AV node in the interatrial septum. - At the AV node, the signal is slowed, allowing the atrium a chance to mechanically move blood into the ventricles. - From the AV node, the signal passes through the AV bundle to the left and right bundle branches in the interventricular septum towards the apex of the heart. - Finally, the Purkinje fibres rapidly conduct the action potential throughout the ventricles (0.2 seconds after atrial contraction)

Question 26

Co-ordinating Contractions

Answer 26

- Although anatomically the heart consist of individual cells, the bands of muscle wind around the heart and work as a unit – forming a functional syncytium . - This allows the top and bottom parts to contract in their own unique way.

Question 27

Describe contraction of the heart

Question 28

what is stroke volume