transport in animals

• Why do large multicellular organisms need transport systems?

  - smaller SA:V ratio

  - big (larger) = more nutrients needed in shorter time

  - longer diffusion distance (takes longer for oxygen to diffuse into the required cells in the multicellular organism and to prevent CO2 from building up)

  - higher metabolic rate/ demands = more active than a single called organism so needs more oxygen and glucose for respiration (muscle contraction)
• Mass transport system

  A system (e.g. the circulatory system) that carries substances in bulk transport to and from individual cells.

  - bring substances from one place to another rapidly

  - effective cell activity

  - maintain diffusion gradient by keeping immediate fluid environment of cell within a suitable metabolic range
• Double circulatory system

  Blood passes through the heart twice in one complete circuit of the body e.g. in a human

  
• Single circulatory system

  Blood passes through the heart once only in a complete circuit of the body e.g. in a fish

  
• Fish circulatory system

  2 chambers heart

  - 1 atrium 1 ventricle

  single loop

  blood flows from heart to gills to rest of body back to heart

  
• Why is a double circulatory system more efficient than a single circulatory system?

  When blood enters network of capillaries, pressure and speed of blood flow decreases

  - In double circulatory system, blood only passes through one network of capillaries

  - In single circulatory system, blood passes through 2 capillary networks

  
  

  Blood in DCS maintains high pressure and speed of flow

  - steep diffusion gradient for efficient exchange
• Open circulatory system

  A circulatory system that allows the blood to flow out of the blood vessels and into various body cavities so that the cells are in direct contact with the blood
• Closed circulatory system

  A circulatory system in which blood is confined in network of blood vessels and is kept separate from the interstitial fluid.

  
• Insect open circulatory system

  - Tubular heart pumps haemolymph (blood) into dorsal vessel

  - Dorsal vessel carries and transports blood into haemocoel (body cavity)

  - Haemolymph surrounds organs and goes back to the heart via one way valve ostia

  - Able to survive with less efficient CS because as haemolymph not directed towards specific organs as oxygen is delivered directly from the environment via tracheae

  
• Pulmonary circulatory system

  The right side of the heart pumps deoxygenated blood to the lungs for gas exchange
• Systemic circulatory system

  Blood returns to the left side of the heart so oxygenated blood can be pumped efficiently around the body at high pressure
• Arteries

  - Carry blood away from the heart at high pressure

  - Narrow lumen = maintain ↑ B.P

  - Pulse present

  3 layers:

  - Tunica adventitia/externa = outer layer, consists of collagen

  Collagen is a very strong fibrous protein and prevents damage and protects arterial walls due to over stretching

  - Tunica media = layer of smooth muscle and elastic tissue. Smooth muscle allows withstanding ↑ B.P, can contract and narrow lumen to reduce blood flow

  Elastic tissue allows maintaining ↑ B.P, can stretch and recoil to even out fluctuations in blood flow

  - Tunica intima = endothelial layer, layer of connective tissue and layer of elastic fibres. Endothelium is one cell thick, lines lumen, smooth so reduces friction for free blood flow
• Arterioles

  - Narrower arteries that branch off of main arteries and carry blood to the capillaries

  - Large proportion of muscle cells and lower proportion of elastic tissue

  - Muscular layer allows them to contract and narrow lumen and cut off blood flow to certain organs i.e reduce blood flow in stomach when exercising to direct more oxygenated blood towards muscles for aerobic respiration
• Veins

  - Blood vessels that carry blood back to the heart

  - Receive blood that has passed through a capillary network so blood pressure is very low

  tunica media is much thinner as as there is no need for thick muscular layer as they don't need to withstand high pressure

  Larger lumen than artery

  -blood returns to heart at an adequate speed

  - Contain valves to prevent backflow of blood and ensure blood is returning back to the heart. no pulse
• Venules

  - Small blood vessels that gather blood from the capillaries into the veins

  - Large lumen

  - Few to no elastic fibres as pressure of blood flow is low after passing through capillary network
• Capillaries

  - smallest blood vessels

  - leaky walls = allow substances to leave the blood and to reach body tissues easily and efficiently

  - form networks called capillary beds = important exchanging surfaces in circulatory system

  - walls consist of single endothelial layer (one cell thick) = short diffusion distance for exchanging substances

  - large number of them branch between cells = short diffusion distance

  - pores on wall to allow tissue fluid to leak out of capillary
• Tissue fluid

  - Plasma is a straw coloured liquid mainly composed of water (substances dissolve in water as it is a solvent to be transported)

  - When blood goes through capillaries, plasma leaks out due to pores on walls of capillaries

  - This is known as tissue fluid

  - Tissue fluid bathes most cells

  - Exchange of substances between blood and cells occur via tissue fluid (dissolving in it and then being transported)

  - role of tissue fluid is to transport nutrients from the blood to the cells, and to carry CO2 and other wastes back to the blood.
• Hydrostatic pressure

  Pressure exerted by the fluid (blood) against walls aka blood pressure generated by involuntary contraction of heart
• Oncotic pressure

  The osmotic pressure in the blood vessels exerted by plasma proteins causing water to rush back into capillaries.
• Formation of tissue

  At arterial end:

  1. Higher hydrostatic pressure forcing blood to push fluid from plasma out of capillary

  2. Plasma proteins remain in capillary as they are too large to go through the gaps/fenestrations of the capillary wall

  3. This creates a water potential gradient between the tissue fluid (↑ψ) and capillary (↓ψ)

  4. This is oncotic pressure: osmotic pressure exerted by plasma proteins as they lower the ψ inside capillary

  5. BUT, at arterial end, hydrostatic pressure > oncotic pressure

  - net movement of water is out of capillary into tissue fluid

  
  

  At venous end:

  1. Hydrostatic pressure ↓ as pressure and speed of flow of blood is ↓ by going through capillaries (small diameter/lumen)

  2. Water potential gradient between tissue fluid and capillary remains the same as at the arterial end

  3. At venous end, oncotic pressure > hydrostatic pressure

  - net movement of water is inside capillary out of tissue fluid

  
  

  90% of fluid lost at arterial end is reabsorbed at venous end

  10% remains as tissue fluid and is collected by lymph vessels and returned to circulatory system

  
• Hypertension

  When blood pressure is too high, more fluid is forced out of capillary at arterial end and fluid begins to accumulate around tissues causing oedema
• Tissue fluid vs plasma

  In plasma:

  ↑ conc of glucose

  ↑ conc of glycerol and fatty acids

  ↑ conc of AAs

  ↑ conc of plasma proteins

  ↑ conc of oxygen

  
  

  ↓ conc of CO2

  ↓ water potential

  
  

  In tissue fluid:

  ↑ conc of substance secreted by cells i.e insulin

  ↑ water potential
• Formation of lymph

  - Lymph vessels separate from circulatory system: closed end and large pores to allow larger molecules to pass through

  - Larger molecules that could not pass through capillary wall enter lymphatic system as lymph

  - Small valves in the vessel walls are entry point to the lymphatic system

  - The liquid moves along larger vessels of this system by compression caused by body movement

  - Backflow prevented by valves

  i.e people who have been sedentary on planes experience swollen lower limbs

  - Lymph reenters bloodstream through veins closer to the heart

  - plasma proteins escaped from blood return via lymph capillaries (if not they could lower water potential of tissue fluid and prevent reabsorption)

  - lipids transported bloodstream after digestion via lymphatic system
• External and internal structure of the mammalian heart

  4 chambers:

  - Two atria

  - Two ventricles

  
  

  Left and right side separated by wall of muscular tissue = septum

  - Interatrial septum

  - Interventricular septum

  - Ensures deoxy and oxy blood dont mix

  
  

  Valves:

  - open when pressure of blood behind them is greater than pressure of blood if front of them

  - close when pressure of blood in front of them are greater than pressure of blood behind them

  - imp for keeping blood flowing forward in right direction and maintain correct pressure

  - Right = tricuspid and pulmonary

  - Left - bicuspid and aortic

  
  

  Left (red) = pulmonary vein → left atrium → atrioventricular (bicuspid) valve → left ventricle → semilunar (aortic) valve → aorta

  Right (blue) = vena cava → right atrium → atrioventricular (tricuspid) valve → right ventricle → semi lunar (pulmonary) valve → pulmonary artery

  
• Angina or heart attack (myocardial infarction)


  If plaque present in coronary arteries through which heart receives blood

  
• Systole

  Contraction of the heart
• Diastole

  Relaxation of the heart
• Cardiac cycle

  Sequence of events that make up a single heartbeat

  1. Blood flows into atria (vena cava and pulmonary vein)

  2. Pressure in atria ↑

  3. Pressure in atria > pressure in ventricles (left and right) so atrioventricular (bicuspid and tricuspid) valves open

  5. Blood flows from atria into ventricles

  6. Atrial systole = atria contract to force remaining blood into ventricles

  7. Atrial diastole = atria relax

  8. Pressure in ventricles ↑

  9. Pressure in ventricles > pressure in atria so AV valves close

  10. Pressure in ventricles > pressure in aorta and pulmonary artery so semi lunar (pulmonary and aortic) valve open

  11. Ventricular systole = ventricles contract and blood flows from ventricles into aorta and pulmonary artery

  12. Ventricular diastole = ventricles relax when empty

  13. Pressure in aorta and pulmonary artery > ventricles so SV close

  14. Pressure in aorta and pulmonary artery ↓ as blood out of heart (right = lungs, left = rest of body)

  15. Pressure continues to ↓ in ventricles until atrial pressure > ventricular pressure (more blood flowed in) so AV open

  
• Cardiac output

  CO = volume of blood pumped by the heart per unit time

  - 4.7l for average adult at rest

  - higher for those who exercise

  - blood pumped needs to match metabolic demands of cell

  Heart rate (bpm) = number of cardiac cycles per minute (1 in 1 second so 60bpm)

  Stroke volume (dm^3) = volume of blood pumped out of left ventricle in one cardiac cycle

  
  

  CO (dm^3) = HR x SV

  
• Myogenic

  heart muscle generates its own contractions without any external stimulus
• Heart initiation and coordination

  1) Sino-atrial node (SAN) at wall of right atrium is depolarised (fires action potentials without stimulation from nervous system bc its myogenic) and sends a wave of excitation which spread across the atria

  2) Atria contract (simultaneously/ synchronised) = atrial systole

  3) This wave of excitation in unable to spread straight to the ventricles as non- conducting tissue Annulus fibrosus separates the atrium and ventricle

  4) Wave of excitation detected by atrio-ventricular node (AVN) in between the atria

  - AVN connected to conducting tissue Bundle of His (in septum) which branch into two conducting fibres Purkyne tissue which go down the apex and up the ventricular walls

  5) After a slight delay, AVN is stimulated and passes this stimulation down to the Bundle of His and Purkyne tissue.

  - delay to ensure ventricles contract AFTER atria have contracted

  6) Purkyne tissue initiate depolarisation of ventricles = ventricles contract (ventricular systole) from bottom of the apex upwards

  - maximises volume of blood pumped out of ventricles to the aorta and pulmonary artery

  
• Electrocardiogram (ECG) traces

  Monitor electrical activity of the heart

  P wave = depolarisation of atria: atrial systole

  QRS complex = depolarisation of ventricles = ventricular systole (largest wave because they have largest muscle mass)

  T wave = repolarisation of ventricles (relaxing) = ventricular diastole

  U wave = repolarisation of Purkyne fibres

  
• Tachycardia

  Heartbeat too fast (>100bpm) at rest

  
• Bradycardia

  Heartbeat too slow (<60bpm) at rest

  (many athletes have slower heart rates)

  
• Fibrillation

  Irregular heartbeat

  Disrupts rhythm of heart

  
• Ectopic heartbeat

  An extra beat or an early heartbeat followed by pause

  
• Structure of haemoglobin

  In erythrocytes

  
  

  4 polypeptide chains

  - 2 alpha

  - 2 beta

  each chain has a haem group which contains a ferrous Fe2+ ion.

  
  

  Can carry 4 O2 molecules

  
• Oxygen + haemoglobin

  Oxyhaemoglobin

  
  

  4O 2 + Hb ⇌ Hb(O 2)4
• Conformational change

  - The binding of the 1st oxygen molecule results in a conformational change in the tertiary structure of haemoglobin molecule (alteration)

  - easier for each successive oxygen molecule to bind

  
  

  = cooperative binding
• Carbon dioxide transport

  1) Waste CO2 produced from respiration diffuses from tissues into blood

  - 5% CO2 can be dissolved directly into blood plasma and be transported

  - 10% Bind to haemoglobin (carbaminohaemoglobin)

  - 85% transported to form hydrogen carbonate ions (HCO 3-)