3.2- Transport in Animals (copy)

the need for transport systems in multicellular animals

larger organisms require mass transport systems due to:

• large transport distances between exchange sites→ diffusion not fast enough to meet metabolic requirements of cells

• SA:V ratio decreases as size of organism increases→ less SA for absorption and excretion, greater volume= longer diffusion distance

• high metabolic rate→ higher demand for oxygen and nutrients, more waste produced

what is mass flow

the bulk movement of materials between exchange sites

what is the purpose of mass transport systems

• move substances quickly between exchange site to another

• maintain diffusion gradient at exchange sites and between cells and extracellular fluid

• ensure effective cell activity by keeping immediate fluid environment within suitable metabolic range

single circulatory system

blood passes through heart once during one complete circuit of the body

single circulatory system in fish

• deoxygenated blood pumped from heart to gills

• oxygen and carbon dioxide exchanged at gills

• oxygenated blood flows from gills to rest of body→ travels through capillaries in organs delivering oxygen and nutrients

• blood returns to heart→ 1 atrium, 1 ventricle

double circulatory system

blood passes through heart twice during one complete circuit of the body

double circulatory system in mammals

• heart has left and right side separated by septum:

  • left side→ oxygenated blood

  • right side→ deoxygenated blood

• blood in right side leaves and travels to lungs

• returns to left side and is pumped around the rest of the body

• once body has passed through organs, it returns to right side of the heart again

advantages of double circulation

• higher blood pressure and avg speed of flow→ blood only passes through one capillary network before returning to the heart

• increased pressure and speed= steeper concentration gradient

open circulatory system

• blood not contained in blood vessels→ pumped directly into body cavities

• arthropods and molluscs have open circulatory systems

closed circulatory system

• blood pumped around body and is always contained in a network of blood vessel

• all vertebrates and invertebrates have closed circulatory systems

path of blood around the body

heart → arteries → arterioles → capillaries → venules → veins

insect circulatory systems

• have one main blood vessel→ dorsal vessel

• tubular heart in abdomen pumps haemolymph (insect blood) into dorsal vessel

• haemolymph delivered into haemocoel (body cavity)→ surrounds organs and re-enters the heart via ostia (one way valves)

• oxygen not transported in haemolymph→ tracheal system

arteries

transport blood away from heart

veins

transport blood to the heart

arterioles

narrower blood vessels that transport blood from arteries to capillaries

venules

narrower blood vessels that transport blood from capillaries to veins

structure of arteries

• consist of three layers:

  • tunica externa, tunica media, tunica intima

  • tunica externa→ made of collagen to provide rigidity and overprotection

  • tunica media→ layer of muscle cells strengthening arteries so they can withstand high pressure. elastic tissue maintains blood pressure

  • tunica intima→ endothelial layer- one cell thick

structure of arterioles

• have muscular layer→ can contract to partially cut off blood flow to specific organs

• lower proportion of elastic fibres and large number of muscle cells

structure of veins

• thinner tunica media due to lower blood pressure

• larger lumen than in artery→ ensures blood returns to heart at adequate speed

• have valves→ prevent backflow

structure of venules

• connect capillaries to veins

• few/ no elastic fibres and a large lumen

• no need for muscular layer→ blood is at low pressure

structure of capillaries

• very small lumen→ blood travels slower so more diffusion can occur

• large number of capillaries→ short diffusion distance

• wall of capillary is one cell thick→ reduced diffusion distance

• cells of walls have gaps→ allow blood plasma to leak out and form tissue fluid

what is tissue fluid

• a liquid that has substances dissolved in it→ similar to plasma but with fewer proteins

• exchange of substances between cells and blood occurs via tissue fluid→ surrounds all cells of the body not in circulatory system

hydrostatic pressure

• pressure exerted by a fluid e.g. blood

• e.g. blood pressure

oncotic pressure

• osmotic pressure exerted by plasma proteins within a blood vessel

• lower WP within blood vessel→ water moves into vessel by osmosis

tissue fluid formation

• at arterial end of capillary:

  • hydrostatic pressure forces fluid out of capillary

  • proteins remain in blood→ too large

  • WP gradient created due to increased protein content

  • hydrostatic pressure>oncotic pressure→ water moves out of capillaries into tissue fluid

• at venous end:

  • hydrostatic pressure reduced due to greater distance from heart

  • WP gradient stays same as at arterial end

  • osmotic pressure>HS pressure→ water flows back into capillary from tissue fluid

formation of lymph

• not all tissue fluid re-enters capillaries→ enters lymph vessels

• vessels separate to circulatory system

• larger molecules that can’t pass through capillary wall enter lymphatic system as lymph

• liquid moves along larger vessels in system by compression caused by body movement→ backflow prevented by valves

• lymph re-enters bloodstream through veins located close to the heart→ plasma proteins are returned to blood via lymph capillaries to maintain WP gradient

• lipids transported from intestines to bloodstream by lymph system

structure of the heart

• divided into 4 chambers

• left and right sides of the heart separated by septum

• atria and ventricles separated by valves

When are valves open/ closed?

What valves are found in the heart

• open when BP behind is greater than BP in front of them

• closed when BP in front of them is greater than BP behind them

• RA and RV separated by tricuspid valve

• RV and PA separated pulmonary valve

• LA and LV separated by bicuspid valve

• LV and aorta separated by aortic valve

blood vessels going into and coming from heart

• Pulmonary artery:

  • heart→ lungs

  • from right ventricle

• Pulmonary vein:

  • lungs→ heart

  • into left atrium

• Vena Cava:

  • body→ heart

  • to right atrium

• Aorta:

  • heart→ body

  • from left ventricle

coronary arteries

Arteries that provide blood to the heart for its own aerobic respiration for muscle contraction

stages of the cardiac cycle

• atrial systole

• ventricular systole

• diastole

atrial systole

1. atrial walls contract:

   • volume in atrium decreases, pressure increases

2. atrial pressure rises→ AV valves open

3. blood forced into ventricles

ventricular systole

1. walls of ventricles contract:

   • volume decreases, pressure increases

2. pressure in ventricles rises above atrial pressure:

   • AV valves forced close

3. pressure in ventricles rises above that in aorta and PA:

   • semilunar valves forces open→ blood forced into arteries

diastole

• atria and ventricles both relaxed

• pressure in ventricles drop below that in arteries→ SL valves forced close

• atria continue to fill with blood

• pressure in atria rises above that in ventricles→ AV valves forced open

• blood passively flows into ventricles

• cycle begins again

cardiac output

the volume of blood pumped by the heart per unit time

factors affecting cardiac output

• fitness→ fitter=higher cardiac output due to thicker ventricular muscles in the heart

• exercise→ cardiac output increases during exercise

heart rate

number of times a heart beats per minute

stroke volume

volume of blood pumped out of left ventricle in one cardiac cycle

calculating cardiac output

cardiac output= heart rate*stroke volume

myogenic

heart beats without external stimulus

sinoatrial node

• group of cells in right atrial wall

• initiates wave of depolarisation→ causes atrial contraction

myogenic contraction

1. SAN creates wave of depolarisation→ causes atrial contraction

2. Annulus Fibrosus→ non-conducting so prevents depolarisation spreading straight to ventricles

3. depolarisation carried to atrioventricular node (AVN)→ conducting tissue between atria and ventricles

4. After delay, AVN is stimulated→ stimulation passed along bundle of His (in septum):

   • delay= ventricles contract after atria

5. bundle of His divides into two conducting fibres→ Purkyne tissue- carries wave of excitation along them

6. Purkyne fibres spread around ventricles and initiate depolarisation of ventricles from bottom of heart→ causes ventricular contraction

ECG

• electrocardiogram

• electrodes that detect electrical signals are placed on skin→ produce electrocardiogram

• shows distinctive electrical waves produced by activity of heart

• used to detect heart problems

reading ECG traces

• P wave:

  • depolarisation of atria, resulting in atrial systole

• QRS complex:

  • depolarisation of ventricles, resulting in ventricular systole

  • largest→ ventricles have largest muscle mass

• T wave:

  • repolarisation of ventricles→ ventricular diastole

• U wave:

  • uncertainty→ repolarisation of Purkyne fibres?

tachycardia

• heart beat too fast

• peaks of ECG too close together

bradycardia

• heart beat too slow

• peaks of ECG too far apart

ectopic heartbeat

• early heartbeat followed by a pause

fibrillation

• irregular heartbeat→ rhythm is lost

role of haemoglobin

• allows for transport of oxygen around body

• each haemoglobin molecule contains 4 haem groups- each able to bond to one O₂ molecule

equation of fomation of oxyhaemoglobin

• Oxygen + Haemoglobin ⇌ Oxyhaemoglobin

• 4O₂ + Hb ⇌ Hb4O₂

cooperative binding

binding of first oxygen molecule results in conformational change in structure of haemoglobin molecule→ easier for each successive oxygen molecule to bind

How is carbon dioxide transported around the body

• dissolves directly in blood plasma

• binds to haemoglobin→ forms carbaminohaemoglobin

• most transported as hydrogen carbonate (HCO₃^-)

formation of HCO₃^- ions

1. CO₂ diffuses into RBC from plasma

2. In RBC, carbon dioxide combines with water to make carbonic acid:

   • CO₂ + H₂O  ⇌  H₂CO₃

   • carbonic anhydrase catalyses reaction

3. Carbonic acid readily dissociates into H⁺ and HCO₃^- ions:

   • H₂CO₃⇌  HCO₃^– + H⁺

4. H⁺ ions combine with haemoglobin→ forms haemoglobinic acid:

   • acts as a pH buffer

5. Hydrogen carbonate ions diffuse out of RBC into plasma

The chloride shift

• movement of chloride ions into RBC→ occurs when hydrogencarbonate ions are formed

• negatively charged hydrogencarbonate ions transported out of red blood cells

• negatively charged chloride ions transported into RBC via transport proteins→ prevents electrical imbalance

oxygen dissociation curves

shows rate at which oxygen associates and dissociates with haemoglobin at different partial pressures of oxygen

partial pressure of oxygen

• pressure exerted by oxygen within mixture of gases→ measure of oxygen concentration

affinity for oxygen

• ease with which haemoglobin binds and dissociates with oxygen

• high affinity→ binds easily and dissociates slowly

• low affinity→ binds slowly and dissociates easily

explanation of oxygen dissociation curve

• shallow gradient at start→ difficult for 1st oxygen molecule to bind

• after first O₂ molecule binds, protein changes shape→ easier for next oxygen molecule to bind ∴ steeper gradient in middle

• levels off at end→ less remaining binding sites so longer for 4th oxygen molecule to bind

interpretation of oxygen dissociation curves

• low pO₂:

  • oxygen binds slowly to haemoglobin

  • low affinity for oxygen at low pO₂

• medium pO₂:

  • oxygen binds more easily to haemoglobin

  • saturation increases quickly

  • small increase in pO₂=large increase in haemoglobin saturation

• high pO₂

  • oxygen binds easily to haemoglobin→ can pick up oxygen and become saturated as blood passes through lungs

  • high affinity for O₂ at high pO₂

foetal haemoglobin

• higher affinity for oxygen than adult haemoglobin

• allows foetus to obtain oxygen from mother’s blood:

  • foetal haemoglobin can bind at low pO₂

  • at low pO₂, mother’s haemoglobin is dissociating with oxygen

• after birth, baby produces adult haemoglobin→ gradually replaces foetal haemoglobin:

  • important for release of oxygen in respiring tissue

types of haemoglobin

• haem groups same

• globin chains can differ between species→ determine precise properties of haemoglobin

• can bind to oxygen in different conditions→ adaptations

effects of altitude on haemoglobin

• pO₂ is lower at higher altitudes

• haemoglobin adapted to conditions→ binds more readily