Cardiovascular System

Intrinsic conduction system

• group of noncontractile, auto-rhythmic cells that generate and distribute action potentials to myocardium

• cells distribute signals so the atria can contract as a unit so the ventricles can contract as a unit (but not at the same time)

components of intrinsic conduction system

1. sinoatrial nerve (SA) node: “pacemaker”, generates signal to contract 60-100X per min

2. atrioventricular (AV) node: “back-up pacemaker”, generates signal to contract 40-60X per min, located in inferior part of right atrium, briefly delays action potential to give time for atria to contract

3. bundle of His (atrioventricular bundle): located in interventricular septum, only pathway for signal to contract and travel between atria and ventricles

4. bundle branches: located in interventricular septum, transmit signal to contract apex of heart

5. purkinje fibers: located in walls of ventricles, transmit signal to contract papillary muscles and the individual cardiac muscle cells of the ventricles

How does the signal to contract spread to cells that are not directly stimulated?

signal to contract spreads through gap junctions to reach cardiac muscle cells

heart contraction

1. first the atria contracts then the ventricles

2. ventricular contraction begins at the apex and proceeds superior forcing the blood towards the sumilunar valves

cardiac cycle

systole = contraction of heart
diastole = relaxation of heart

normal cardiac values

1. HR = 60-100 BPM

2. tachycardia = HR > 100 BPM

3. brachycardia = HR < 60 BPM

4. BP = 90/60 mmHg - 140/90 mmHg

5. stroke volume (amt. blood pumped w 1 contraction) = 70ml

6. cardiac output (volume of blood pumped in a minute) = 5L (HR X stroke volume )

7. Blood volume = 4-6L

types of blood vessels

1. arteries (branch) = carry blood away from heart, thickest tunica media, aorta is largest

2. capillaries (microscopic) = gas, nutreint, and waste exchanges, walls made of only endothelium

3. veins (merge) = carry blood to to the heart, rely on inhalation to help return blood to right atrium, coronary and dural sinuses

structure of tissue layers

1. tunica interna (intima) = lining of blood vessels - simple squamous epithelium + basement membrane

2. tunica media = controls vessel diameter - smooth muscle and elastic fibers

3. tunica externa (adventitia) structural support - collagen fibers

arteries vs. veins

arteries have more smooth muscle and elastic tissue than veins

types of arteries

1. elastic (conducting) arteries

2. muscular (distributing) arteries

3. arterioles

elastic arteries

aorta + major branches, thick walls of large lumen, low resistance to blood flow

muscular (distributing) arteries

medium sized arteries that distribute blood to individual organs

arterioles

smallest arteries that control blood flow into capillary beds

types of veins

1. venules (smallest)

2. veins (thin walls w large lumens) = limb veins have valves

3. sinuses (specialized - endothelium only) =

   1. coronary sinus = drains myocardium

   2. dural sinus = drain brain tissue

venous return

1. vascular valves = prevent backflow of blood

2. skeletal muscle contraction = “pump”

3. negative intrathoracic pressure = inhalation creates pressure gradient between thorax and inferior regions

   • blood flows against gravity = moves from high pressure in abdomen + lower limbs to low pressure in thorax

pulse points

where arteries are close to surface (pulse can be palpated)

• common carotid artery = up neck/head into brain

• brachial artery = draws arterial blood

• radial artery = most common

• femoral artery = groin region

• dorsalis pedis artery = can feel pulse, there is adequate blood flow to lower limbs

circulatory shock

blood vessels are inadequately filled

BP drops = poor perfusion (blood flow)

blood characteristics

• connective tissue (only fluid tissue)

  • 45% formed elements (cells)

  • 55% plasma (fluid)

• pH = 7.35-7.45 (arterial blood)

blood plasma

• nonliving,

• 90% H20

• 8% proteins (albumin, fibrinogen, prothrombin) - clotting proteins

• 2% nutrients, respiratory gases, electrolytes, and wastes

• serum is plasma w clotting proteins removed

formed elements

1. erythrocytes (RBC’s) = sacs of hemoglobin w no nucleus or organelles

2. leukocytes (WBC’s) = fight infection, known as true cells

3. thrombocytes (platelets) = hemostasis, known as cell fragments, most important formed element

hematocrit

• % RBC’s in blood sample

• normal adult values:

  • males = 47 ± 5%

  • females 42 ± 5%

• males have more because testosterone causes more erythropoietin secretion by kidney

erythrocyte structure

• flexible, biconcave disc

• lack nucleus and organelles

• plasma membrane filled w hemoglobin

erythropoiesis

• production of RBC’s in the red bone marrow

• stimulus = hypoxia (low O2)

• stimulus causes kidneys to produce hormone called erythropoietin (EPO)

• EPO stimulates red bone marrow to produce more RBC’s

RBC development

• reticulocyte (young RBC): accumulates hemoglobin

• mature RBC: lacks nucleus and organelles (amitotic) - cannot undergo mitosis and only produce ATP by anerobic respiration)

• life span = 100-120 days

Leukocytes

1. neutrophils = phagocytosis of bacteria

2. eosinophils = destroy parasitic worms; levels elevated during allergic reactions

3. basophils = involved in inflammatory response

4. lymphocytes = destroy virus infected cells + tumor cells

5. monocytes = become macrophages; involved in chronic infections (TB)

thrombocytes

involved in hemostasis = mechanism for preventing blood loss when a vessel is injured

hemostasis

3-6 min and highly regulated. 3 phases

1. vascular spasms

2. platelet plug formation

3. coagulation (blood clotting)

vascular spasms

• starts spasming due to release of chemicals from injured cells

• helps minimize blood loss

platelet plug formation

1. platelets cling to exposed collagen fibers to seal of injury site

2. initiate chemotaxis = release of stored chemical messengers that recruited more platelets to injury site (positive feedback mechanism)

coagulation

• requires clotting factors and Ca+

• forms fibrin “net” that holds platelets together and traps other substances (RBC’s)

last 2 chemical reactions to coagulation

1. prothrombin (plasma protein) = thrombin

2. fibrinogen (plasma protein) = fibrin

chambers and septum

1. Right and Left Atria: receiving chambers.

2. Right and Left Ventricles: pumping chambers.

3. The septum divides heart into right and left sides. Displays a remnant of fetal circulation: fossa ovalis

atrioventricular valves

• tricuspid and bicuspid (mitral) valves

• almost always open to allow blood from atria to flow into the ventricles

• only time they are closed is when the ventricles are contracting.

semilunar valves

• pulmonary and aortic valves

• almost always closed to prevent blood in the pulmonary trunk and the aorta from flowing back down into the ventricles

• only time they are open is when they are forced open during ventricular contraction

endocardium

the smooth, slick inner lining of the heart; made of simple squamous epithelium

myocardium

made of cardiac muscle tissue; where contraction occurs

intercalated discs

interlocking surfaces on adjacent cardiac muscle cells that increase the surface area for contact

origin and insertion of cardiac muscle tissue

fibrous skeleton

thymus gland

produce hormones that are involved in process of T lymphocytes gaining immunocompetence

3 functions of hemoglobin

1. transport oxygen

2. transport CO2

3. buffer H+ ions