3.1.2 transport in animals Flashcards
arteries
transport blood away from the heart at high pressure to tissues
have a narrow lumen to maintain high blood pressure
pulse is present
arterioles
arteries branch into narrower blood vessels which transport blood into capillaries
veins
transport blood to the heart at low pressure
have a wider lumen
receive blood passed through capillary network
rate of blood flow is slower
contain valves to prevent backflow
no pulse
venules
narrower blood vessels transport blood from capillaries to the veins
the layers of blood vessel walls
tunica externa
tunica media
tunica intima
structure of arteries: tunica intima
endothelial layer, layer of connective tissue and a layer of elastic fibres
what does the endothelium layer do?
one cell thick
lines lumen of blood vessels
smooth and reduces friction for free blood flow
structure of arteries: tunica media
smooth muscle cells and thick layer of elastic tissue
has a thick tunica media
what does the layer of muscle cells do?
strengthens arteries to withstand high pressure
enables them to contract and narrow the lumen for reduced blood flow
what does the elastic tissue do?
helps to maintain blood pressure in arteries
stretches and recoils to even out fluctuations in pressure
structure of arteries: tunica externa
made up of collagen
what does collagen do?
strong proteins protects blood vessels from damage by over-stretching
structure of arterioles
muscular layer to contract and partially cut off blood flow to specific organs to regulate blood flow e.g. during exercise
lower proportion of elastic fibres
structure of veins
tunica media - much thinner - dont have to withstand high pressure
lumen - much larger - ensure blood returns to heart at an adequate speed, reduces friction between blood and endothelial layer
structure of venules
few to no elastic fibres
large lumen
low pressure - no need for muscular layer
capillaries
can form networks called capillary beds which are important exchange surfaces within the circulatory system
structure of capillaries
blood travels slow for diffusion to occur
branch of capillaries form so substances can diffuse across a short diffusion distance
single layer of endothelial cells - reduce diffusion distance
fenestrations - allow blood plasma to lead out and form tissue fluid
white blood cells can combat infection in
structure of capillaries
blood travels slow for diffusion to occur
branch of capillaries form so substances can diffuse across a short diffusion distance
single layer of endothelial cells - reduce diffusion distance
fenestrations - allow blood plasma to lead out and form tissue fluid
components of the blood
red blood cells - transport oxygen
white blood cells - role in immune system
platelets - blood clotting
blood plasma - glucose, amino acids, mineral ions etc, oxygen, albumin
formation of tissue fluid
plasma leaks out of the fenestrations of capillaries as blood passes through
proteins stay in blood as they are too large to fit through the gaps
hydrostatic pressure
the pressure exerted by a fluid e.g. blood pressure generated by the contraction of the heart muscle
oncotic pressure
osmotic pressure exerted by plasma proteins within a blood vessel
plasma proteins lower the water potential within the blood vessel, causing water to move into the blood vessel by osmosis
arteriole end
hydrostatic pressure > oncotic pressure
net movement of water, dissolved solutes, glucose and amino acids out of capillary through fenestrations
increased protein content in capillary creates a water potential gradient between capillary and tissue fluid
venule end
oncotic pressure > hydrostatic pressure
net movement of water in
pressure in capillary is reduced due to increased distance from heart
water potential gradient - water moves into capillary from tissue fluid
what happens if blood pressure is high (hypertension)?
pressure at arterial end is greater
pushes more fluid out of capillary and fluid begins to accumulate around tissue
called oedema
formation of lymph
some tissue fluid enters lymph vessels
have closed ends and large pores to allow molecules to pass through that cannot pass through the capillary wall
liquid moves along the larger vessels by compression caused by body movement
backflow prevented by valves
lymph reenters bloodstream through veins
lipids are transported from the intestines to bloodstream by lymph system
features of erythrocytes
biconcave shape - increased surface area available for diffusion
flexible - pass through narrow capillaries
no nucleus - more room for haemoglobin
last for 120 days in bloodstream
contain haemoglobin
features of haemoglobin
red pigment that carries oxygen
large globular conjugated protein made up of four peptide chains, each with iron-containing haem prosthetic group
each haemoglobin can bind to 4 oxygen molecules
haemoglobin + oxygen
forms oxyhaemoglobin
reversible reaction
haemoglobin binds
- oxygen levels are low in capillaries - creating a steep concentration gradient between the erythrocytes and alveoli
- oxygen moves into erythrocytes and binds with haemoglobin
- as one oxygen molecule binds to the haem group, molecule changes shape, making it easier for the next oxygen to bind - positive cooperativity
- oxygen concentration stays low - to ensure the steep diffusion gradient is maintained until all haemoglobin is saturated with oxygen
- process is reversed when blood reaches the body tissues
- concentration of oxygen in cytoplasm is lower than in erythrocytes - oxygen diffuses out
what does an oxygen dissociation curve show?
the affinity of haemoglobin for oxygen - small change in the partial pressure of oxygen makes a significant difference to the saturation of the haemoglobin with oxygen
= high partial pressure in lungs - red blood cells rapid load with oxygen
= low partial pressure - oxygen release rapidly from haemoglobin to diffuse into cells
effect of carbon dioxide - the Bohr effect
- partial pressure of carbon dioxide rises, haemoglobin gives up oxygen more easily - Bohr effect
- in active tissue with a high partial pressure of CO2, haemoglobin gives up its oxygen more readily
- in lungs where the proportion of CO2 is low, oxygen binds to haemoglobin easily
fetal haemoglobin
- oxygenated blood from the mother runs close to the deoxygenated fetal blood in placenta
- fetal haemoglobin has a higher affinity for oxygen than adult at each point along the dissociation curve so it removes oxygen from the maternal blood as they move past each other
- shifts dissociation curve to the left
transporting carbon dioxide
- About 5% is carried dissolved in the plasma.
- 10-20% is combined with the amino groups in the polypeptide chains of haemoglobin to form a compound called carbaminohaemoglobin.
- 75-85% is converted into hydrogen carbonate ions (HCO3-) in the cytoplasm of the red blood cells.
- Most of the carbon dioxide that diffuses into the blood from the cells is transported to the lungs in the form of hydrogen carbonate ions.
- Carbon dioxide react slowly with water to form carbonic acid (H2CO3-). The carbonic acid then dissociates to form hydrogen ions and hydrogen carbonate ions.
- In the blood plasma this reaction happens slowly. However, in the cytoplasm of the red blood cells there are high levels of the enzyme carbonic anhydrase.
