the heart and the blood

• arteries


  -carry blood (usually oxygenated) away from the heart

  -thick walls and narrow lumen

  -needed to create high pressure
• arterioles


  -smaller vessels which carry blood between arteries and capillaries

  -oxygenated
• capillaries


  -smallest blood vessel

  -walls 1 cell thick- gas exchange

  -oxygenated to deoxygenated
• venules


  -carries blood between capillaries and veins
• veins


  -carries blood (usually deoxygenated) back to the heart

  -thin walls and relatively large lumen

  -may contain valves
• tunica interva


  -endothelium lining

  -inner lining

  -squamous epithelial cells

  -1 cell thick
• tunica media


  -middle band of tissue

  -contains smooth muscle, elastic fibres and collagen
• tunic externa


  -outer lining containing collagen and elastic fibres
• semi lunar valves


  -made from their endothelium

  -means blood keeps flowing towards the heart

  -help to overcome problem of moving blood against the force of gravity under fairly low pressure
• arteries


  -very thick walls with smooth muscle to constrict lumen

  -lots of elastic fibres in the tunica media allowing artery walls to stretch and recoil as blood surges at high pressure

  -narrow lumen helps maintain high pressure

  -collagen in walls provides strength to withstand the high pressure
• veins


  -thin walls- high pressure isnt needed

  -wide lumen

  -much thinner tunica media than arteries with fewer elastic fibres and less collagen

  -semi- lunar valves to prevent backflow
• capillaries


  -small diameter- 7-8 micrometres wide

  -1 red blood cell can pass through in single file

  -walls- squamous epithelium- 1 cell thick- short diffusion pathway
• leaky capillaries 


  -some capillaries have pores called fenestrations

  -allow exchange of molecules between plasma and tissues
• capillary bed


  -network of capillaries in a tissue is called a capillary bed

  -as blood flows through a capillary bed, some molecules are forced out of the capillary via fenestrations

  -only molecules small enough pass into the tissue fluid- larger molecules remain in the capillaries
• hydrostatic pressure


  -molecules forced out of the capillaries via the fenestration by the hydrostatic pressure at the arteriole end being greater than at the venule end
• tissue fluid


  -contains water, dissolved oxygen and dissolved solutes, some hormones and proteins, very few white blood cells and no plasma proteins
• formation of tissue fluid

  -arteriole end- hydrostatic pressure is higher than osmotic pressure

  -osmosis draws water back into the blood

  -net flow out of the capillary
• formation of tissue fluid


  -venule end- hydrostatic pressure is lower than osmotic pressure

  -osmosis draws water back into the blood

  -net flow into the capillary
• lymph


  -90% of fluid that leaks from capillaries returns to them and remaining 10% is returned to blood vessels via lymph vessels

  -lymphatic network

  -lymph nodes filter lymph fluid and remove bacteria

  -lymphocytes engulf bacteria
• heart- cardiac muscle


  -needs to respire constantly to produce ATP needed for contraction

  -coronary arteries supply the heart with oxygen and glucose

  -blockage of coronary arteries- leads to myocardial infarction (heart attack)- heart muscle is so deprived of oxygen it dies.
• atrioventricular valves


  -after contraction, ventricles recoil and go back to their original shape

  -this decreases the pressure in the ventricles below pressure in the atria

  -AV valves open and blood flows into the ventricles

  -during contraction of ventricles, pressure increases above pressure in the atria

  -AV valves snap closed to prevent the back flow of blood into the atria
• semi- lunar valves

  -during ventricle contraction, SL valves open as pressure in ventricles becomes greater than pressure in aorta and pulmonary artery

  -when ventricles relax and recoil, pressure in the ventricles falls below that of arterial pressure

  -this pushes SL valves closed as blood starting to push backwards collects in pockets in valves

  -prevents blood from returning to ventricles
• systole


  contraction
• diastole 


  relaxation
• lub


  -louder

  -av valves snap shut
• dup


  -quieter

  -semi lunar valves close

  -pockets fill up slowly

  -after ventricular systole and diastole starting
• myogenic


  -can initiate its own contractions

  -doesnt require stimulation from nervous system like most muscles do

  -heart beat must be coordinated because the atria have a tendency to contract more than the ventricles
• sinoatrial node


  -pacemaker

  -generates electrical impulse (sometimes called a wave of excitation)

  -electrical impulse spreads across the wall of both atria

  -this causes atriol systole as the cardiac muscles contract
• atrioventricular node


  -at the base of the atria, a non-conducting disc of tissue prevents the impulse reaching the ventricles

  -atrioventricular node (AVN) in the septum is the only route through the disc

  -the impulse is delayed in the ANV to give enough time for the atria to finish contracting and fully empty and for ventricles to fill with blood
• bundle of His and purkyne tissue


  -impulse from the AVN travels down the bundle of His and the purkyne tissue in the centre of the septum

  -when it reaches the bottom of the septum the impulse spreads out over the ventricle walls causing ventricular systole
• ventricular systole


  -once impulse has spread out in the ventricular walls causing ventricular systole, it contracts from the base/apex upwards to push the blood up and out through the arteries
• electrocardio grams (ecg)


  -detects electrical activity- uses sensors attached to the skin

  -can detect and diagnose heart conditions
• ECG P


  -excitation of atria leading to atrial systole
• ECG QRS


  excitation of ventricles leading to ventricular systole
• ECG T


  diastole
• bradycardia


  -heartbeat too slow
• tachycardia


  heartbeat too fast
• ectopic heartbeats


  -some heartbeats are earlier than expected and a patient may describe it as if their heart has skipped a beat
• atrial ectopic


  premature atrial contractions
• ventricular ectopic


  premature ventricular contractions