transport in animals

• Unicellular organisms


  Transport of materials occurs through simple diffusion because they have a large surface area to hence called intracellular transport
• In multicellular organisms diffusion is not sufficient because:
• Circulatory system


  Vessels, transporting medium/fluid (blood) and a pumping organ
• Types of circulatory system

  • Open circulatory system
  • Closed circulatory system
• Open circulatory system


  • Blood flows in general body cavities called coelom/haemocoel
  • The fluid involved in the transport is called haemolymph and in direct contact with the body tissues
  • Haemolymph consists of white blood cells
  • Found in Arthropods e.g. insects which have one heart and main blood vessel called dorsal vessel/aorta
  • The aorta empties the haemolymph into sinuses in the head
  • Blood flows from the heart to the haemocoel and back to the heart through the openings called ostia (sing. Ostium)
  • The heart has valves that prevent back flow of haemolymph

  
• Closed circulatory system


  • Consists of blood vessels and muscular heart
  • The heart pumps blood into blood vessels which carry blood to the body tissues and back to the heart
  • Found in vertebrates

  
• Differences between open and closed circulatory system

  • Transport fluid is in contact with the tissues (open)
  • Transport fluid is not in direct contact with tissues/are found in blood vessels (closed)
  • Pressure is low (open)
  • Pressure is high (closed)
  • Transport fluid flows slowly (open)
  • Transport fluid flows faster (closed)
  • Facilitates slow rate of activity in the organism (open)
  • Facilitates higher rate of activity in organisms (closed)
  • Transport fluid has no pigment since it is not involved in the transport of oxygen and carbon (IV) oxide (open)
  • Transport fluid has a red pigment called haemoglobin for transportation of oxygen and carbon (IV) oxide (closed)
• Types of closed circulatory system/circulation

  • Single circulatory system/circulation
  • Double circulatory system/circulation
• Single circulatory system/circulation


  • Blood flows to the heart once for every complete circulation e.g. in fish

  
• Double circulatory system/circulation


  • Blood flows through the heart twice in every complete circulation e.g. in mammals and birds
• Advantages of double circulation over single circulatory system

  • Blood flows at a higher pressure since it is pumped twice
  • Oxygenated blood does not mix with deoxygenated blood
• Types of double circulation/circulatory system

  • Pulmonary circulatory system/circulation
  • Systemic circulatory system/circulation
• Pulmonary circulatory system/circulation


  • Blood is pumped to the lungs through pulmonary artery and back to the heart through pulmonary vein
  • It helps in oxygenation of blood

  
• Systemic circulatory system/ circulation

  • Blood flows from the heart to the rest of the body parts through the Aorta and back to the heart through Venacava
  • It helps to supply oxygen and nutrients to the body cells and also remove waste metabolic materials and carbon (IV) oxide

  
• Components of mammalian circulatory system

  • Heart (muscular pump)
  • Blood
  • Blood vessels

  
• Main blood vessels


  • Arteries
  • Veins
  • Capillaries

  
• Blood flow through blood vessels

  1. Arteries divide into smaller vessels called Arterioles which divide to form much smaller vessels called capillaries which spread out in a network fashion in the tissues

  2. The capillaries eventually re-unite to form venules which in turn form veins

  3. The veins take blood back to the heart

  
• Mammalian heart


  • Located between the lungs in the chest cavity
  • Covered by a membrane called pericardium

  
• Functions of pericardium membrane


  • Secretes a fluid (pericardial fluid) which lubricates the heart when it is working/ absorbs shock
  • Keeps the heart in position preventing over dilation/over relaxation during pumping

  
• On the outside of the pericardium there is a fat layer that acts as a shock absorber
• Cardiac muscle


  • Contracts continuously hence the heart pumps blood continuously throughout the life time/without fatigue and is myogenic (contract without nervous stimulation)
  • Has a coronary artery (which branches from the Aorta) which supplies blood containing nutrients and oxygen to the heart
  • Has a coronary vein to remove blood containing nitrogenous waste products and carbon (IV) oxide from the heart cells

  
• The heart consists of the muscle called cardiac muscle which brings about the pumping action of the heart
• Internal structure of the heart

  • Left and right sides separated by a thick muscular wall called septum which prevents mixing of deoxygenated and oxygenated blood
  • Consists of 4 chambers: Right auricle/atrium, Left auricle/atrium, Right ventricle, Left ventricle
  • Auricles/atria are thin walled and receive blood into the heart
  • Right atrium/auricle receives deoxygenated blood from the rest of the body parts except the lungs through the venacava
  • Left atrium/auricle receives oxygenated blood from the lungs through the pulmonary vein
  • Ventricles are thick walled and pump blood out of the heart
  • Left ventricle is thicker walled than the right ventricle to generate high pressure pump blood to distant parts of the body
  • Right ventricle is thinner walled to pump blood to a short distance to the lungs for oxygenation
  • Between the ventricles and atria/auricles there are atrioventricular/ cuspid valves which prevent the back flow of blood into the atria when ventricles contract
  • On the left side (between the left atrium and left ventricle) the valve is called bicuspid valve (it has 2 flaps)
  • On the right side (between the right auricle and right ventricle) it is called tricuspid valve (it has 3 flaps)
  • The valves are joined to the wall of the heart by structures called tendons which prevents the atrio-ventricular valves from turning inside out when under pressure when the ventricles contract
  • At the base of aorta and pulmonary artery there are valves called semi-lunar valves which prevent the back flow of blood into the ventricles when the ventricles relax

  
• Blood circulation


  1. Deoxygenated blood from the body tissues enters the right auricle/atrium through the vena cava

  2. The right atrium/auricle contracts pumping blood to the right ventricle through tricuspid valve which prevents backflow of blood

  3. When the right ventricle contracts, blood from the right ventricle is forced/ pumped into the lungs through the pulmonary artery through the semi-lunar valve for oxygenation

  4. Oxygenated blood from the lungs flows to the left auricle/atrium through the pulmonary vein

  5. The left atrium/auricle pumps blood into the left ventricle through the bicuspid valve which prevents the back flow of blood into the auricle

  6. The left ventricle contracts pumping blood through the semilunar valve and aorta to all parts of the body

  
• Blood vessels carrying blood to different body parts

  • Hepatic artery carries oxygenated blood the liver
  • Hepatic vein carries deoxygenated blood from the liver to the heart
  • Hepatic portal vein carries blood from the intestines and stomach to the liver
  • Mesenteric artery carries oxygenated blood from the heart to the intestines and stomach
  • Renal artery carries oxygenated blood into the kidney
  • Renal vein carries deoxygenated blood from the kidney

  
• Blood has to flow into the liver from the stomach/intestines before getting into the heart then into body parts/general circulation for excess glucose to be converted into glycogen and excess amino acids to be deaminated
• Pumping mechanism of the heart

  1. Diastole: Ventricles and auricles/ atria relax, increasing their volume and decreasing pressure, cuspid valves open while the semi-lunar valves close, oxygenated blood flows from the right auricle/atrium to the right ventricle, deoxygenated blood flows from the left auricle/ atrium to the left ventricle

  2. Systole: Atrial systole - atria/ auricles contract while ventricles remain relaxed, high pressure causes the cuspid valves to open and blood flows to the ventricles, Ventricular systole - ventricles contract, their volume decreases while pressure increases, the semi-lunar valves open while the cuspid valves close preventing blood from flowing back into the auricles, blood flows out of the heart to the lungs through the pulmonary artery or to all parts of the body through the aorta

  
• Working of the heart

  1. When the ventricular muscles contract, the cuspid valves close preventing back flow of blood into auricles, increased pressure in the ventricles forces the semi lunar valves to open and blood flows out of the heart to the lungs through pulmonary artery and to all parts of the body through Aorta

  2. When the ventricular muscle relax, the pressure inside decreases, the cuspid valves open to allow blood flow from the atria into ventricles, the semi-lunar valves close preventing back flow of blood into the ventricles, slight contraction of the atria forces blood into ventricles

  
• Heart beat


  • Contraction and relaxation of heart/cardiac muscles
  • The cardiac muscle contracts and relaxes without fatigue
  • The cardiac muscle is myogenic i.e. contraction and relaxation arises from the heart muscles without nervous stimulation
  • The heart beats about 72 times per minute and is felt at the hand wrist
  • The heart beat is initiated by a group of cells called sino atrial node (SAN)/ pacemaker located at the wall of the right atrium located near the vena cava
  • The heart has atrioventricular node (AVN) located between the atria and ventricles which relays contraction waves from sino atrial node (SAN) to the purkinje tissue
  • The purkinje tissue/fibres relay waves from the atrioventricular node (AVN) to the ventricular myocardium causing the ventricles to contract
  • Heart beat is controlled by the part of the brain called hypothalamus
  • The rate of heart beat is controlled by the vagus nerve (which slows down the rate) and the sympathetic nerve (which speeds up the rate)

  
• Significance/ importance of heart beat in blood circulation

  It generates high pressure that drives blood out of the heart to all parts of the body

  
• Factors affecting the heart rate

  • Age - higher in children than adults
  • Physical activity of the body - faster during exercise
  • Emotions - increased due to adrenalin
• If the nerve supply to the heart of a mammal is cut/ severed, the rhythmic movements of the heart will still on the heart continues to beat
• The rhythmic contraction of the heart arises from within the heart muscle and it is said to be myogenic

  
• Nerves that control the heart beat

  • Vagus nerve
  • Sympathetic nerve

  
• Importance of heart beat in blood circulation

  It generates high pressure that drives blood out of the heart to all parts of the body

  
• Blood vessels


  • Arteries
  • Veins
  • Capillaries

  
• Arteries


  • Originate from the heart and carry blood away from the heart
  • Deep seated in the muscles
  • Carry oxygenated blood from the heart to all parts of the body except pulmonary artery which carries deoxygenated blood to the lungs
  • Have thick elastic muscular wall to resist high blood pressure due to pumping action of the heart
  • The elastic muscle fibres contract and relax adjusting the diameter of the lumen during pumping hence blood flows in pulses
  • Have thin lumen to ensure that blood flows under high pressure
  • Do not have valves except at the bases of pulmonary artery and aorta
  • Blood is under high pressure and flows fast due to the pumping action of the heart
  • The innermost layer is called endothelium which provides a smooth lining providing least frictional resistance to blood flow
  • Branch to form arterioles, the arterioles further branch to form blood capillaries

  
• Veins


  • Carry deoxygenated blood into the heart except the pulmonary vein which carries oxygenated blood from the lungs into the heart
  • Lie close to the body surface and have thin and less elastic walls
  • Because the muscles are less elastic the walls cannot contract hence there is no pulse in the veins
  • Have a wider lumen, providing minimum resistance to blood flow
  • Blood is under low pressure because of resistance to the flow at the capillaries
  • Have valves throughout their length to prevent the back flow of blood and ensure that blood flows only towards the heart
  • Forward flow of blood is also maintained through contraction of skeletal muscles because large veins in legs and arms are located between the skeletal muscles
  • Blood contained in veins contain high levels of metabolic wastes and low level of nutrients except renal vein which has low level of nitrogenous wastes and hepatic portal vein which contains high amount of nutrients that have been absorbed in the gut

  
• Capillaries


  • Branch from the arterioles and branch to form venules
  • Numerous and very close to the body tissue and each cell is near the blood capillary
  • Exchange of substances take place between the blood and the cells/ tissues across the capillary wall
  • Wall of capillary is made up of endothelium which is thin/ one cell thick which reduces the distance hence faster diffusion of substances
• Adaptations of capillaries


  • Numerous to increase the surface area for diffusion of substances
  • Thin/ one cell thick/ have single celled endothelium for faster diffusion of substances
  • Selectively permeable for passage of materials
  • Narrow lumen to maintain pressure