CIRCULATORY SYSTEM

PRIMARY FUNCTIONS OF CIRCULATORY SYSTEM

  • Transport necessary materials to cells
  • Transport waste products away from cells to be released into environment

COMPOSITION OF BLOOD

  • plasma, RBC, WBC, platelets
  • contain dissolved nutrients, proteins, gases and other molecules

3 TYPES OF CIRCULATION
1. GASTROVASCULAR
2. OPEN CIRCULATORY - anthropods, mollusks
3. CLOSED CIRCULATORY

COMPONENTS OF CIRCULATORY SYSTMES

  1. fluid containing cells and solutes
  2. system of vessels, that're hallow tubes
  3. one or more muscular structures that pump fluid through vessels

OPEN CIRCULATORY SYSTEMS

  • contain fluid (hemolymph)
  • pumped by 1 or more hearts
  • through vessels that open into body cavity (hemocoel)
  • diffusion exchanges nutrients and wastes

CLOSED CIRCULATORY SYSTEMS

  • Blood and interstitial fluid are physically separated (components and composition)
    • blood under pressure by 1 or more contractile muscular hearts
    • blood remains within vessels
    • capacity to heal themselves when wounded (clots)

ADVANTAGES

  • animal can grow larger with more efficient supply
    • Blood flow selectively controlled

SINGLE CIRCULATION

  • single atrium collects blood from tissues
    • single ventricle pumps blood out of heart
    • arteries carry blood away from heart to gills
    • oxygen picked up and CO2 dropped off, then blood delivers oxygen and nutrients to cells and collects wastes
    • partially deoxygenised blood is returned to heart by veins
    • heart doesn't generate high pressure, limits rate oxygenated blood can be delivered

DOUBLE CIRCULATION

  • ocygenated and deoxygenated blood kept separate
    • heart has 2 sets of atria and ventricles with one way valves
    • pulmonary circuit ( to the lungs and heart)
    • systemic circuit (blood to the body and deoxygenated to the heart)
    • two different blood pressures (higher in arteries than veins)

MYOGENIC HEART

  • generates own action potential
  • MYOCYTES form interlocking networks with other myocytes to rapidly spread electrical current
  • nervous input can increase or decrease rate

EXCITATION OF VERTEBRATE HEART
1. ATRIAL PHASE

  • electrical signals generated at SA Node (pacemaker)
  • modified myocytes with unstable resting membrane potential
  • action potentials spread quickly through gap junctions
  • both atria contract together forcing blood through AV valves into ventricles

2. VENTRICULAR PHASE

  • Electrical impulses reach the AV Node
  • conducts impulse from atria to ventricles
  • both ventricles contract together

CARDIAC CYCLE

  • Two phases:

1. Diastole:

  • ventricles relaxed and fill with blood coming from atria
  • low blood pressure

2. Systole:

  • ventricles contract and blood is pushed through semi-lunar valves
  • high blood pressure

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BLOOD VESSELS

ELECTRO CARDIOGRAM (ECG/EKG):

  • Records electrical impulses generated during cardiac cycle
  • displays amplitude and direction of electrical signal
  • examine for frequency, strength, duration and direction of signals


  • monitors the electrical activity produced by SA node
  • P WAVE: begins when SA node generates action potentials
  • QRS COMPLEX: begins when branches from AV node excite ventricles
  • T WAVE: repolarisation of ventricles back to resting state

ARTERIES AND ARTERIOLES


ARTERIES

  • layers of smooth muscle and connective tissue around smooth endothelium
  • blood away from heart
  • walls contain elastin

ARTERIOLES

  • Formed as artery branches become narrower
  • can dilate/constrict to control blood distribution to tissues

CAPILLARIES

  • site of gas and nutrient/waste exchange
  • composition: endothelium resting on basal lamina
  • narrowest vessels

1. CONTINUOUS CAPILLARIES smooth walls and small number of tiny openings
2. FENESTRATED CAPILLARIES numerous larger holes

VEINS AND VENULES


VEINS

  • blood back to heart
  • thinner
  • less muscular
  • blood pressure lower
  • smooth muscle contractions propel blood
  • veins squeezed by skeletal muscles

VENULES

  • Small
  • thin extensions of capillaries

MOVEMENT OF WATER IN AND OUT OF CAPILLARIES


  1. blood enters capillary under pressure
  • pressure forces some water out through openings into interstitial fluid
  1. Most fluid leaves is recaptured and end of capillary
  • pressure decreases along cap
  • proteins in blood create osmotic force to draw fluid back into blood
  • if valves weren't present contractions of leg muscles would force blood in both directions

RELATIONSHIP WITH BLOOD PRESSURE, BLOOD FLOW AND RESISTANCE: - Blood pressure is responsible for blood flow - resistance is the tendency of blood vessels to slow down blood flow

MATHEMATICA; RELATIONSHIP - Poiseuille's law
Flow (F) = change in Pressure (P) divided by Resistance (R)

RESISTANCE TO FLOW

  • R is function of vessel radius, length and blood viscosity
    • change in arteriolar R is mechanism for controlling blood flow
    • radius is most important
    • vasodilation increases radius
    • vasoconstriction decreased radius

VASODILATORY FACTOR PRODUCED BY ENDOTHELIAL CELLS


  • ACh causes vasodilation by relaxing smooth muscle in anteriolar walls
  • ACh causes
  1. vasodilation in circular strips
  2. vasoconstriction in flat strips
  • vasodilatory factor is nitric oxide (NO)

SYSTEMIC BLOOD PRESSURE

  • CARDIAC OUTPUT (CO) is the amount of blood the heart pumps in litres per minute
  • Flow refers to CO
  • BP = CO x TPR
    (TPR is the total peripheral resistance)

CARDIAC OUTPUT

  • CO depends on heart size, BPM, and how much blood it ejects
    • stroke volume amount of blood heart ejects at each beat

TOTAL PERIPHERAL RESISTANCE

  • greater cardiac and resistance, higher blood pressure
    • arterial blood pressure is function of
    1. CO
    2. how constricted/dilated of various arterioles

ADAPTIVE FUNCTIONS OF CLOSED CIRCULATORY SYSTEMS

  • adapts to changing conditions (sleep, activity, emergencies)

EXERCISE

  • blood must be routed to different areas in proportion to their need for oxygen and nutrients
  • controlled by Vaso dilation/constriction

  • Cardiac output increases



    • EPINEPHRINE: hormones from adrenal gland increases cardiac output (increases stroke volume/ heart rate)

  • blood pressure increases a bit (blood vessels dilate, reducing resistance)

BARORECEPTORS

  • stretch receptors in certain arteries (aorta and carotid)
  • communicate with brain to signal when BP is outside normal range
  • brai/nerves can decrease/increase cardiac output/resistance as needed