The Cardiac Cycle

The Cardiac Cycle

• each heartbeat is called CARDIAC CYCLE

• when the heart beats, the 2 ATRIA simultaneously contract, pushing blood through the AV VALVES into their respective VENTRICLES.

• once the atria contract, all the CHAMBERS relax temporarily.

• then the ventricles are triggered to contract simultaneously.

-the right ventricle sends blood to the PULMONARY CIRCUIT

-the left ventricle sends blood to the SYSTEMIC CIRCUIT

• when our heart chambers are actively contracting (pumping), this is called systole.

• when our heart chambers are relaxing (refilling), this is called diastole

• the sound heard by a stethoscope of the cardiac cycle is described as LUB-DUB

• LUB = closing of AV VALVES

• DUB= closing of SEMILUNAR VALVES

• each cardiac cycle occurs 60-80 times per minute

Intrinsic Control of the Cardiac Cycle

• sinoatrial nodes (SA NODES)

• located in the upper portion of the right atrium

• known as the “PACEMAKER”

• its role is to initiate the heartbeat by sending EXCITATORY impulses every 0.85 seconds

• the impulse cause both atria to contract simultaneously

• the impulse continues to travel to the next node (ATRIOVENTRICULAR NODE)

ATRIOVENTRICULAR NODE (AV node)

• located in the lower quadrant of the right atrium

• when the impulse from the SA NODE reaches the AV NODE, there is a slight delay which allows the atria to complete their conractions

• the impulse from the AV NODE travels through the branches of nervous tissue known as BUNDLE OF HIS or the ATRIOVENTRICULAR BUNDLE. These branches are located in the septum

• the bundles eventually reach the R and L VENTRICLES and sends it to the PURKINJE FIBRES

• embedded in the R and L VENTRICLES are PURKINJE FIBRES which are specialized nervous tissue that will cause the ventricles to contract simultaneously

Extrinsic Control of the Cardiac Cycle

MEDULLA OBLONGATA

• located on the brain stem, superior to the spinal cord

• it contains the cardiac, respiratory, vasomotor, and digestive centers

• in terms of cardiac and respiratory functions, it establishes the breathing rate, heart rate, and blood pressure

• the medulla influences the AUTONOMIC NERVOUS SYSTEM

what are the 2 nervous systems?

1. sympathetic n.s.

2. parasympathetic n.s.

sympathetic N.S.

• increases heart rate

• involved in fight or flight response

• is always active in low levels to ensure a quick response

parasympathetic N.S.

• decreases heart rate

• involved in “feed or breed” or “rest and digest” response

• activities that occur during a resting state include SALIVATION, URINATION, DEFECATION, DIGESTION, and SEXUAL AROUSAL

what are the 3 types of formed elements that make up whole blood? What is the percentage?

1. erythrocytes

2. leukocytes

3. thombocytes

erythrocytes

• there are 3 types of formed elements that contain about 45% of whole blood

1. erythrocytes - known as red blood cells

• produced in the bone marrow

• most numerous blood cell because there are 4-6 million/mm³ of whole blood

• shape of a RBC is a biconcave disc

• RBC are ANUCLEATED which means they lack a nucleus

• the increase SURFACE AREA caused by anucleation increases the amount of hemoglobin on the surface of the RBC for O² carrying capacity

• the mineral in hemoglobin is IRON (fe) which makes blood red

• anemia is caused by low levels of iron or low levels of RBC and be caused by many factors

• RBC live approximately 120 days and cannot undergo MITOSIS due to anucleation

Leukocytes

• known as white blood cells (WBC)

• produced in bone marrow

• WBC are NUCLEATED (have nucleus)

• there are about 4000 - 11 000/mm³ of whole blood

• WBC role is to FIGHT INFECTIONS and provide IMMUNITY against PATHOGENS (disease)

there are 2 major groups of WBC:

1. GRANULOCYTES - 3 types

neutrophils - most numerous WBC that phagocytizes pathogens and dead cells

basophils - plays a role in allergic responses by releasing histamine to cause vasodilation

eosinophils - involved in allergic responses and release substances to combat parasites

2. ARGRANULOCYTES - 2 types

lymphocytes - B and T cells that play an important role in fighting pathogens at the third line of defence. NK cells are also lymphocytes that can kill cancer cells or other threats without previous exposure to the pathogen

monocytes - are large immature argranulocytes that will differentiate into macrophages and dendritic cells which are types of phagocytic cells

thrombocytes

• known as platelets

• they’re produced in the bone marrow

• there are 150 000 - 300 000 cells/ mm³ of whole blood

• their role is in blood clotting which prevents blood loss and maintains blood pressure

• they clot together in a process called coaggulation/aggulation to seal a wound and prevent blood loss

Plasma

• liquid portion of blood tissue (made up of cells)

• this liquid contains inorganic (salts/electrolytes) and organic (proteins, carbs, etc.) substances suspended in H2O

• plasma makes up about 55% of whole blood, and 91% of that 55% is H2O

plasma also contains many types of plasma proteins which are produced by the liver! which has a variety of functions:

• transport materials

• aid in blood clotting which prevents

• fight pathogens

• maintain blood volume