transport in humans

Why do multicellular organisms require transport systems

• high metabolic demands - diffusion distances not fast enough

• Small SA:V ratio - amount of surface available to absorb substances relatively small

• Hormones and enzymes needed in different region to where they’re made

• Food digested by small intestine needs to be transported to every cell for metabolic reactions

• Waste products need to be removed from cells and transported to excretory organs

Describe an open circulatory system

• few transport vessels

• Haemolymph instead of blood - doesn’t carry oxygen or carbon dioxide and comes into direct contact with cells

Describe a closed circulatory system

• blood enclosed in blood vessels

• Does not come into direct contact with cells of body

• Heart pumps blood through vessels under high pressure

• Substances leave and enter blood by diffusion

• Blood flow can be diverted

Describe the function and structure of the arteries

• three layers in their wall

• Tunica media contains thick, smooth muscle and elastic fibres to withstand high pressure

• Carries blood at high pressure from the ventricles of the heart to tissues of boduy

Describe structure and function of the veins

• three layers in walls

• Thin smooth muscle and elastic fibre walls allows them to be pressed flat by muscles to carry blood under low pressure

• Valves to prevent backflow of blood

• Wide lumen for slow flowing blood

• Carry blood at low pressure from the tissues of body to the atria of the heart

Describe the structure and function of the capillaries

• single layer of endothelium

• Very narrow lumen (one red blood cell wide)

• Permeable walls

• Carry blood through tissues

• Exchange of materials between cells in the tissue and the blood in the capillary

What is the role of elastic fibres

• composed of elastin

• Can stretch and recoil - make vessel walls flexible

What is the role of smooth muscle

Contracts and relaxes to change size of lumen

What is the role of collagen

Provides structural support for vessels, thick collagen layer in arteries helps withstand high blood pressures

Why do artery walls require elastic fibres

• withstand force of blood pumped out of the heart

• Stretch to take large volume of blood

• Recoil evens out surges of blood pumped from heart

Describe and explain how the wall of an artery is adapted to withstand pressure

• wall is thick and contains collagen which provides strength

• Endothelium is folded so no damage to it as it stretches

Describe and explain how the wall of an artery is adapted to maintain pressure

• thick layer of elastic fibres , cause recoil to return to original size

• Thick layer of smooth muscle, narrows lumen

Why is the lining of the arteries smooth

reduces friction so less resistance to flow

How are capillaries adapted to their function

• endothelial pores between cells of the wall allows passage of small molecules from blood to tissue fluid

• Walls are one endothelial cell thick so give a short diffusion pathway

• Narrow lumen, red blood cells/erythrocytes pass through one at a time Which slows blood down to give more time for exchange

How are veins adapted to their function

• valves prevent backflow of blood

• Run between muscles so contractions squeeze veins, forcing blood towards heart

• Smooth endothelial lining to allow blood to flow easily

Why do veins require valves

• blood under much lower pressure than arteries

• No pumping from heart and little elastic recoil in veins so blood might flow backwards as it moves towards heart against gravity

• Valves prevent backflow, open as blood flows towards heart and close if it flows in opposite direction

Describe the endothelial cells of the arteries and veins

Once cell thick, flattened with a smooth surface

What are the components of the blood

• Red blood cells - erythrocytes

• White blood cells - leukocytes

  • Monocytes and neutrophils (engulfs and destroys pathogens)

  • Lymphocytes (produce antibodies)

• Plasma

• Proteins - maintains osmotic pressure

• Platelets - blood clotting

Describe a monocyte

Largest white blood cell with a bi-lobed (C-shaped) nucleus

Describe a neutrophil

Faintly staining granules with a multi-lobed nucleus

Describe a lymphocyte

Large nucleus

What is tissue fluid and what is its role

• Fluid forced out of the blood into surrounding space around cells

• It delivers oxygen and removes carbon dioxide to respiring cells, delivers amino acids, glucose and hormones to cells

Which feature of capillaries allow tissue fluid to form

Small gaps between cells - fenestrations

Which components of the blood does not make it out of capillaries

• red blood cells

• Most white blood cells

• Plasma proteins

Explain how hydrostatic pressure and oncotic pressure affect the movement of fluids into and out of capillaries

• hydrostatic pressure (from heart beat) forces liquid out of capillaries and is higher than oncotic pressure at arterial end of capillary so water is forced out of capillary forming tissue fluid

• As blood moves along capillary more fluid moves out so hydrostatic pressure decreases and by venous end of capillaries hydrostatic pressure falls while oncotic pressure remains the same

• Plasma proteins are too large to leave capillary so water potential remains constant

• Water moves back into capillary by osmosis at venous end and most tissue fluid moves back into capillaries

What is lymph

The small amount of tissue fluid that does not make it back into capillaries

Describe the lymph system

• lymph vessels - blind ended tubules with valves to prevent backflow

• Lymph nodes containing lots of lymphocytes

Where does lymph return to the blood

Subclavian veins

label

Explain why the left ventricle wall is thicker than the right

• requires more muscle to create more force

• Needs to create higher pressure to pump blood further

• Right ventricle only pumping blood to lungs

• To produces a higher pressure to overcome the greater resistance to flow in the systemic circulation

explain why ventricles have thicker walls than atria

• atria receive blood with lower pressure as they only have a short distance to pump the blood into the ventricle

• Ventricles have to contract strongly to pump high pressure blood to lungs or rest of body

what is the role of the valves in the heart

prevents blood flowing backwards and valve tendons prevent inversion

how do coronary arteries maintain a regular heart rhythm

• supply blood carrying glucose and oxygen to heart

• Heart cardiac muscles require oxygen and glucose for respiration

• ATP from respiration needed to contract muscle with regular rhythm

Describe the structure of cardiac muscles

• myogenic - can contract automatically

• Coronary arteries to supply oxygen and nutrients to the heart

• Valves prevent the backflow of blood

• Interconnecting cells separated by intercalated discs which allows waves of electrical excitation to pass easily between them

describe the cardiac cycle

Atrial systole

• walls of atria contract

• Blood forced from atria into ventricles via atrioventricular valves

• Semilunar valves closed

Ventricular systole

• walls of ventricle contract

• Atrioventricular valves closed, semilunar valves open

• Blood empties into arteries

• Atria start to refill

Diastole

• Ventricles stop contracting, pressure falls

• Semilunar valves closed preventing backflow from the arteries

• When ventricular pressure drops below atrial pressure, atrioventricular valves open

• Blood entering atria flows into ventricles

Annotate this graph

What can a blocked coronary artery lead to

Myocardial infarction

Describe diastole

• Blood enters from pulmonary vein and vena cavae

• Blood fills atria, pressure forces open the atrioventricular valves allowing blood to flow into the ventricles

• Muscular walls of atrial and ventricles relaxed

• Pressure in arteries is greater than in the ventricles

• Therefore semi-lunar valves are closed

Explain atrial systole

• Atrial walls contract, increasing pressure, forcing remaining blood into the ventricles

• Atrioventricular valves are open

• Semi-lunar valves are closed

Explain ventricular systole

• walls of ventricles contract

• Increases pressure in ventricles, forcing atrioventricular valves to close

• Semi-lunar valves are forced open allowing blood to flow into aorta or pulmonary artery

Explain how pressure changes in the heart bring about the closure of the atrioventricular valve

• Ventricular systole raise ventricular pressure

• Ventricular pressure higher than atrial pressure

• Valve tendons prevent inversion with the help of papillary muscles

Why does the aortic pressure remain high throughout the cardiac cycle

Thick muscle and elastic fibres in the artery wall

Describe the pressure changes in the blood as it flows through the circulatory system from the aorta to the veins

• Pressure drops as distance from the heart increases

• Greatest pressure drop while blood is in the arteries

• Pressure constant in veins

• Amplitude of fluctuation decreases from aorta to arteries

• No fluctuations in capillaries and veins

Explain what causes the overall change in pressure as blood flows from the aorta to arteries to capillaries

• blood flows into larger bumber of vessels

• Total cross sectional area increases

What is the sinoatrial node (SAN)

• group of specialised muscle cells in right atrial wall

• Trigger impulses - myogenic

• Causes cardiac muscle to contract

• Acts as a pacemaker

How is a heartbeat initiated

• SAN sends out electrical impulse that stimulates contraction of atrial muscle

• Impulse stimulated atrioventricular node (AV node)

• AV node delays impulse, sends impulses down septum via Bundle of His

• Stimulates Purkyne fibres in ventricular wall, causing ventricular contraction from apex

Explain the role of the atrioventricular node in the cardiac cycle

• acts to relay impulses to ventricles via purkyne fibres

• Introduces delay to ventricular systole to prevent simultaneous contraction of atria and ventricles

Explain why the excitation wave is carried to the apex by the purkyne fibres

So ventricular contraction starts at the bottom (apex) and pushes blood upwards into the arteries

What are erythrocytes

Red blood cells

What is the role of erythrocytes

Transport oxygen around the body

What is haemoglobin

• a pigment in red blood cells

• Globular protein made of four polypeptide chains (2 α-alpha chains and 2 β- chains)

• Each chain has a haem prosthetic group contain iron

• Oxygen binds to haemoglobin to form oxyhemoglobin in a reversible reaction

What are the three ways which carbon dioxide is transported in the blood

• 5% dissolved in blood plasma

• 10-20% combines with haemoglobin to form carbaminohaemoglobin

• 75-85% converted into hydrogen carbonate ions (HCO3-) in the cytoplasm of erythrocytes

Which enzyme catalyses the production of hydrogen carbonate ions

Carbonic anhydrase

Describe how hydrogen carbonate ions are produced in erythrocytes

• carbon dioxide diffuses into erythrocytes

• Reacts with water, catalysed by carbonic anhydrase

• Forms carbonic acid (H2CO3)

• Carbonic acid dissociates to form hydrogen carbonate ions and hydrogen ions

Give the equation for the conversion of CO2 to HCO3-

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

What happens to hydrogen carbonate ions after they have been produced

• diffuse down concentration gradient

• Out of red blood cells and into plasma

What is the chloride shift

The movement of Cl- ions into erythrocytes to balance the electrical change due to the negative hydrogen carbonate ions leaving.

How does haemoglobin act as a buffer

Prevents changes in pH by accepting 3 H+ ions to form haemoglonobic acid

Define partial pressure

The contributing pressure of a single gas to the total pressure of a mixture of gases

What happens to hydrogen carbonate ions at the lungs

• low partial pressure of carbon dioxide (pCO2) at lungs

• HCO3- diffuses back to erythrocytes

• Reacts with H+ to form H2CO3

• Carbonic anhydrase catalyses conversion of H2CO3 back into water and CO2

• CO2 diffuses out of blood into lungs

• Cl- ions diffuse out of erythrocytes into plasma

Describe the movement of oxygen in the lungs

• high partial pressure of oxygen (pO2) in alveoli

• Lower partial pressure of oxygen in blood in capillaries

• Oxygen diffuses from alveoli to blood

Describe the movement of oxygen at respiring tissues

• high partial pressure of oxygen in blood

• Lower partial pressure of oxygen in respiring tissues

• Oxygen diffuses from blood to respiring cells

Describe the role of haemoglobin in transporting oxygen around the body

• Haemoglobin has a high affinity for oxygen so it binds to haemoglobin in lungs (high pO2) forming oxyhemoglobin.

• Oxygen is released in respiring tissues (low pO2)

By what process does oxygen bind to haemoglobin to produce the sigmoidal shape of the oxygen dissociation curve

Cooperative binding

Explain how the binding of one oxygen molecule to a haem group affects haemoglobin

• binding of first oxygen molecule causes conformational change altering tertiary structure of haemoglobin (slightly)

• Affinity for oxygen increases so further loading of oxygen molecules is easier

Explain how removal of the first oxygen at respiring tissues affects haemoglobin

• removal of first molecule causes conformational change

• Affinity for oxygen decreases (next molecule can leave more easily)

Explain the significance of the oxygen dissociation curve

• High pO2 in lungs so haemoglobin rapidly loaded with oxygen

• Relative small drop in pO2 at respiring tissues leads to rapid dissociation of oxygen so it is free to diffuse into cells.

Explain the oxygen dissociation curve for human haemoglobin

• Haemoglobin becomes saturated at very high pO2

• As pO2

Describe difference in oxygen affinity between fetal haemoglobin and adult haemoglobin

Fetal haemoglobin has a higher affinity for oxygen

Explain why fetal haemoglobin curve is to the left of the adult haemoglobin curve

• placenta has low pO2

• Adult haemoglobin will release O2 at the placenta

• Foetal haemoglobin has a higher affinity for oxygen at low pO2

• It is able to take up oxygen in the placenta

What effect does carbon dioxide have on haemoglobin

at higher pCO2, haemoglobin gives up oxygen more easily

What effect does higher pCO2 have on the oxygen dissociation curve

• shifts to the right

• Bohr shift

Why is the bohr effect important

• Actively respiring tissues have high pCO2, haemoglobin gives up oxygen more easily

• Lungs have lower pCO2, haemoglobin binds to oxygen more easily

Explain how an increase in CO2 in the blood leads to the release of more O2 from red blood cells

• more carbon dioxide diffuses in to red blood cells

• More carbonic acid is formed by carbonic anhydrase

• More hydrogen ions formed

• Haemoglobin has a high affinity for hydrogen ions

• Haemoglobin binds to hydrogen ions to form haemoglobinic acid (HHb)

• Formation of HHb decreases the affinity of haemoglobin for oxygen

• Carbon dioxide binds to -NH2 of polypeptides to form carbaminohaemoglobin

• Causes change in tertiary structure, releasing more oxygen

Outline the benefits of the bohr shift to actively respiring tissue

• Actively respiring tissue requires more oxygen for aerobic respiration

• Actively respiring tissue produces more CO2

• Haemoglobin involved in transport of CO2 so there’s less haemoglobin available to combine with O2

• Bohr shift causes more oxygen to be released

What effect does pH have on Hb’s affinity for oxygen?

• Affinity decreases as pH decreases (more H+ ions)

What is the SAN and its role?

sinoatrial node is the pacemaker, sends out waves of excitation

What route does the electrical impulse take?

AVN —> Bundle of his —> Purkyne fibres

where in the heart is the bundle of His?

septum

Where in the heart is the Purkyne TIssue?

apex

What is the role of the AVN?

Causes a 0.1s delay in the electrical impulse and allows atria to finish contracting and pump all the blood into the ventricles before the ventricular systole.

what happens at the arteriole end of the capillary?

At the arteriole end there is a high hydrostatic pressure which is greater than the pull from the water potential so the net movement is out

what happens at the venule end of the capillary?

There is a low hydrostatic pressure - water potential of blood is much lower than tissue fluid so water moves in

Describe how the structure of a capillary is adapted for the exchange of substances between the blood and the tissue fluid.

• squamous endothelium is one cell thick - short diffusion distance.

• walls contain fenestrations (pores) between the endothelial cells - allows for bulk flow of water and small solutes

Is the water potential greater in blood or tissue fluid?

in tissue fluid

what can pass through the endothelium in the capillary?

water , glucose , amino acids, ions , urea and oxygen

what cannot leave the capillary into the tissue fluid?

RBC’s , Plateleets and large plasma proteins (fibrinogen)

what does the Bohr shift do to the affinity of Hb for O2>

Decreased affinity for O2 at the same partial pressures, resulting in more o2 released to actively respiring tissue

formula for carbonic acid

H2co3

what causes the sigmoidal shape of the Oxygen dissociation curve?

co operative binding

Explain co-operative binding

• Haemoglobins 3D structure makes it difficult for the first O2 to bind to one of the four haem groups

• once one O2 molecule binds there is a conformational change of the haemoglobin protein and the shape opens up increasing the affinity for o2

• easier to bind next 2 o2 molecules

• plateaus at top due to high saturations

Describe the sequence of events that occurs inside a red blood cell to transport carbon dioxide as hydrogencarbonate ions, including the role of the chloride shift?

• co2 diffuses from respiring tissue into the RBC down concentration gradient

• co2 is added h20 and catalysed by carbonic anhydride to form carbonic acid

• carbonic aid breaks down to form HCO3- and H+

• HCO3- diffuses out of the RBC into the blood plasma to be transported into lungs

• CL- ions diffuse into RBC from plasma to replace lost ions

Difference between affinities of haemoglobin to O2 in fetus and adult

Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin at all partial pressures

Explain haemoglobins affinity for O2 in fetuses?

Haemoglobin has a higher affinity for O2 in fetus compared to adult, allowing fetus to load oxygen from mothers blood across placenta (mothers hamoeglobing releases O2 at placenta)

What is the product formed when hydrogen ions (H+) bind to haemoglobin?

Haemoglobinic acid

The Bohr effect results in a rightward shift of the oxygen dissociation curve. What is the physiological advantage of this?

oxygen is more readily released at respiring tissues