circulatory systems - animals

• Fick's law

  Rate of diffusion = Surface area x Concentration gradient / Diffusion distance
• Types of circulatory systems

  • Open
  • Closed
  • Single
  • Double
• Open circulatory system

  • Blood (haemolymph) leaves vessels to go into tissue spaces
  • Blood and tissue (interstitial) fluid are mixed
  • Blood is pumped by heart into open space (haemocoel) and returns via ostia
  • In some animals blood is pumped by muscular contractions
• Closed circulatory system

  • Blood remains in the vessels
  • Blood is pumped by the heart into vessels
• Single circulatory system


  • Blood flows once around the heart and body
  • No separation for oxygenated & deoxygenated blood
• Double circulatory system


  • Blood flows twice around the heart and body
  • Separation of pulmonary and systemic circulation
  • Allows differentiation in blood pressure
  • Allows higher oxygenation of blood
• Layers of blood vessels

  • Tunica intima
  • Tunica media
  • Tunica externa or adventitia
• the arterial wall - Tunica intima

  • Inner layer consists of epithelium and connective tissue
  • Contains internal elastic lamina
  • Contains pores/fenestrations
  • Contains squamous cell epithelium, endothelium
• the arterial wall - Tunica media

  • middle layer
  • Made of smooth muscle and connective tissue
  • Mainly circular muscle with some longitudinal on the outer surface
  • Contains elastic fibres
• arterial wall - Tunica externa/adventitia

  • outer layer
  • Made of collagenous fibres and some elastic fibres
  • Outer layers blend with surrounding connective tissue
• Arteries

  • Relatively small lumen to thickness of wall
  • Thick muscular and elastic tissue layer
• Veins

  • Much larger lumen
  • Thinner wall
  • Contain valves to allow slow blood flow and act as a repository of blood
• Capillaries

  • Perfusion vessels (all leaky), making up the microcirculation
  • Made up of the endothelium
  • Three types: continuous, fenestrated, sinusoid
• Capillaries

  • Continuous
  • Found throughout the body
  • Contain endothelial lining and tight junctions
  • Allow exchange of water and small molecules
• Fenestrated capillaries

  • Found in the brain, choroid plexus, small intestine, kidney, endocrine glands
  • Have pores and tight junctions
  • Allow movement of larger molecules
• Sinusoid capillaries

  • Found in the liver, spleen, lymph nodes, bone marrow
  • Have extensive intercellular gaps and incomplete basement membranes
  • Allow passage of large molecules like plasma proteins and cells
• Larger vessels are too big for diffusion, so there are blood vessels called vasa vasorum
• Nervi vasorum are sympathetic nerves that cause vasoconstriction and dilation
• Exchange between blood and tissue fluid

  1. Arterial end

  2. Capillary

  3. Venous end
• Plasma proteins

  Contribute to oncotic pressure which opposes hydrostatic pressure
• Increased friction increases the number of vessels, giving a larger surface area for blood flow
• The human heart

  • Situated in the thoracic cavity between the lungs
  • Surrounded by the pericardium
  • Consists of left and right atrium, left and right ventricle
• Membranes covering the heart

  • Outer fibrous pericardium
  • Inner serous pericardium (parietal and visceral layers)
  • Pericardial cavity filled with serous fluid
• The right atrium receives deoxygenated blood from the superior and inferior vena cava
• The right ventricle supplies blood to the pulmonary trunk
• The left atrium receives oxygenated blood from the left pulmonary veins
• The left ventricle supplies oxygenated blood to the aorta
• Describe the process of the heart pumping blood around the human body - pulmonary circuit

  • the right atrium receives deoxygenated blood from the superior and inferior vena cava
  • blood passes through the tricuspid valve (AV) into the right ventricle
  • blood is then pumped up through the pulmonary semilunar valve, through the pulmonary trunk into the left and right pulmonary arteries to the lungs where gas exchange occurs and blood becomes oxygenated (pulmonary circuit)

  
• describe the process of the heart pumping blood around the human body - systematic circuit

  • the left atrium then receives oxygenated blood from the left and right pulmonary veins
  • blood passes through the bicuspid value (AV) into the left ventricle
  • blood is then pumped up through the aortic semilunar valve, through the aorta to the(systematic circuit)

  
• Describe where the human heart is situated in the human body

  • situated in the thoracic cavity between the lungs in the mediastinum in the pericardial space
  • surrounded by the pericardial space

  
• Gross anatomy of the human heart

  • Right atrium
  • Right ventricle
  • Left atrium
  • Left ventricle
• Pericardium

  • Outer fibrous pericardium which is tough and protects the heart and holds it in place
  • Inner serous pericardium made up of the parietal pericardium which is fused to the pericardium
  • Epicardium which is fused to the heart, is part of the heart wall
  • Pericardial cavity filled with serous fluid
• Layers of the heart wall

  • Epicardium
  • Myocardium
  • Endocardium
• Septum

  Separates the heart into chambers and is made up of an interatrial and interventricular septum
• Intercalated disc

  Connects cardiac muscle cells
• Heart valves

  • Atrioventricular valves
  • Semilunar valves
• Chordae tendinae

  Join the atrioventricular valves to the papillary muscles in the ventricular walls to stop the valves from inverting
• Papillary muscles

  In the ventricular walls, join to the chordae tendinae to stop the atrioventricular valves from inverting
• Coronary circulation

  • Coronary arteries
  • Coronary veins
• Regulating the heart rate - structures involved

  1. Impulse initiated at SAN

  2. Spreads across atrial walls

  3. Picked up at AVN

  4. Delay at AVN allows atria to empty and ventricles to fill before contracting

  5. Impulse passes down Bundle of His to apex of heart then up across Purkinje fibres

  6. Causes ventricles to contract from the bottom-up

  7. Heart is regulated by medulla oblongata and cardiac centre