Topic 3 — B: More Exchange and Transport Systems Flashcards
What is digestion, and why is it essential?
breaks down large biological molecules (e.g., starch, proteins) into smaller molecules that can cross cell membranes, allowing nutrients to be absorbed from the gut into the bloodstream and transported around the body for cellular use.
What is a hydrolysis reaction?
break down polymers into monomers by adding water. For example, carbohydrates are broken into monosaccharides, fats into fatty acids and monoglycerides, and proteins into amino acids.
Which enzymes are involved in carbohydrate digestion, and where are they produced?
Amylase, produced by the salivary glands and pancreas, catalyzes starch breakdown into maltose. Membrane-bound disaccharidases, located on the ileum’s epithelial cells, break down disaccharides into monosaccharides
Describe the role of amylase in carbohydrate digestion.
Amylase catalyzes the hydrolysis of glycosidic bonds in starch, producing maltose. It’s secreted into the mouth (by salivary glands) and the small intestine (by the pancreas).
What are membrane-bound disaccharidases? Give an example.
These enzymes, attached to the cell membranes of ileum epithelial cells, break down disaccharides into monosaccharides. For example, sucrase breaks down sucrose into glucose and fructose.
Explain the digestion process of lipids
Lipase enzymes break down lipids into monoglycerides and fatty acids by hydrolyzing ester bonds. Lipases are mainly made in the pancreas and secreted into the small intestine
What role do bile salts play in lipid digestion?
Bile salts, produced by the liver, emulsify lipids, increasing the surface area for lipases to act by breaking lipids into smaller droplets, facilitating their breakdown.
What are micelles, and what is their function in lipid absorption?
Micelles are tiny lipid-bile salt structures that help deliver monoglycerides and fatty acids to the ileum epithelium for absorption. Micelles break up and reform, releasing their contents for absorption.
Describe the process of protein digestion.
Proteins are broken down by peptidases, which hydrolyze peptide bonds. Endopeptidases act within proteins, exopeptidases remove amino acids from protein ends, and dipeptidases work specifically on dipeptides.
Provide examples of endopeptidases and their locations.
Trypsin and chymotrypsin (from the pancreas, active in the small intestine) and pepsin (from the stomach lining, active in acidic stomach conditions).
What are dipeptidases, and where are they located?
membrane-bound exopeptidases that hydrolyze dipeptides into amino acids. They are located in the cell-surface membrane of the small intestine’s epithelial cells.
How is glucose absorbed in the ileum?
Glucose is absorbed by active transport with sodium ions via a co-transporter protein in the ileum epithelial cells.
How are monoglycerides and fatty acids absorbed?
they are lipid-soluble and diffuse directly across the epithelial cell membrane after being transported to the epithelium by micelles.
Explain amino acid absorption in the ileum.
Sodium ions are actively transported out of epithelial cells into the ileum and then diffuse back in, carrying amino acids with them through sodium-dependent transporter proteins.
What is the main role of haemoglobin in the circulatory system?
Haemoglobin in red blood cells carries oxygen throughout the body. It binds oxygen in the lungs and releases it to respiring tissues where oxygen concentration is low
Describe haemoglobin’s quaternary structure and its oxygen-binding capacity.
has four polypeptide chains, each with a haem group that contains an iron ion, which allows each haemoglobin molecule to carry up to four oxygen molecules.
What is the relationship between pO₂ and haemoglobin’s affinity for oxygen?
Haemoglobin’s affinity for oxygen increases with higher pO₂ (e.g., in the lungs) and decreases with lower pO₂ (e.g., in respiring tissues).
Explain the terms “loading” and “unloading” in relation to haemoglobin and oxygen.
Loading” (association) occurs when oxygen binds to haemoglobin, forming oxyhaemoglobin, typically in the lungs. “Unloading” (dissociation) occurs when oxygen is released to tissues.
What is the oxygen dissociation curve, and why is it S-shaped?
shows the percentage saturation of haemoglobin at different pO₂ levels. Its S-shape reflects cooperative binding, where binding the first O₂ molecule makes it easier for additional molecules to bind
Describe the Bohr effect and its importance in oxygen unloading.
occurs when high pCO₂ (from active respiration) shifts the dissociation curve to the right, lowering haemoglobin’s oxygen affinity and promoting oxygen release to tissues.
How does haemoglobin adaptation help animals in different environments?
Animals in low-oxygen environments (e.g., underground or high altitudes) have haemoglobin with a higher oxygen affinity, while highly active animals have haemoglobin with lower affinity for efficient oxygen unloading.
What is haemoglobin and its primary role?
Haemoglobin is a protein in red blood cells that binds to oxygen in the lungs and releases it at tissues for respiration.
How does haemoglobin’s affinity for oxygen change?
Its affinity changes based on oxygen concentration (partial pressure of oxygen), CO₂ concentration, and pH (Bohr effect).
Define partial pressure of oxygen (pO₂).
Partial pressure of oxygen is a measure of oxygen concentration; high in the lungs and low in respiring tissues.
Explain the oxygen dissociation curve.
It shows haemoglobin saturation with oxygen at different pO₂. The curve is sigmoidal due to cooperative binding.
What is cooperative binding in haemoglobin?
When one oxygen molecule binds to haemoglobin, it increases the affinity for more oxygen molecules to bind.
Describe the Bohr effect
At high levels of CO₂, haemoglobin’s affinity for oxygen decreases, facilitating oxygen release in tissues.
How do fetal haemoglobin and adult haemoglobin differ?
Fetal haemoglobin has a higher oxygen affinity to extract oxygen from the mother’s blood across the placenta.
What adaptations do animals in low oxygen environments have in their haemoglobin?
They have haemoglobin with higher oxygen affinity for efficient oxygen uptake in environments with low pO₂.
What is myoglobin and how does it differ from haemoglobin?
Myoglobin is a muscle protein with a higher oxygen affinity than haemoglobin, storing oxygen for muscle use.
What is the cardiac cycle?
The cardiac cycle consists of systole (contraction of the heart) and diastole (relaxation), which pump blood through the circulatory system.
Differentiate between arteries, veins, and capillaries.
Arteries: Thick walls, high pressure, carry blood away from the heart.
Veins: Thin walls, lower pressure, have valves to prevent backflow, carry blood to the heart.
Capillaries: Thin, one-cell-thick walls for efficient exchange of substances.
What is tissue fluid, and how is it formed?
Tissue fluid is formed from blood plasma at the capillary bed, carrying nutrients and oxygen to cells while removing waste products.
What causes the movement of tissue fluid in and out of capillaries?
Hydrostatic pressure and osmotic pressure gradients between blood plasma and tissue fluid
Explain the lymphatic system’s role in the circulatory system
The lymphatic system collects excess tissue fluid (lymph), filters it, and returns it to the bloodstream, helping maintain fluid balance.
Describe the structure of haemoglobin.
Haemoglobin is a quaternary protein made of four polypeptide chains, each containing a haem group that binds oxygen.
What are coronary arteries, and why are they important?
Coronary arteries supply oxygen-rich blood to the heart muscle itself. Blockage can lead to heart attacks.
What factors affect the oxygen dissociation curve of haemoglobin?
Factors include pO₂, pCO₂, pH, temperature, and 2,3-bisphosphoglycerate (BPG) levels.
How does oxygen transport differ in high-altitude animals?
Their haemoglobin has higher oxygen affinity to maximize oxygen uptake in low-pO₂ environments.
What is cardiovascular disease (CVD)?
CVD refers to diseases affecting the heart and blood vessels, such as coronary heart disease (CHD) and stroke.
What causes atherosclerosis?
Atherosclerosis is caused by the buildup of fatty deposits (atheroma) in arterial walls, reducing blood flow and increasing blood pressure.
How does a blood clot (thrombosis) form in an artery?
Atheroma ruptures the arterial wall, triggering clotting factors that form a thrombus (blood clot), potentially blocking blood flow.
What is an aneurysm, and how is it related to atherosclerosis?
An aneurysm is a weakened arterial wall that balloons out due to increased pressure from atherosclerosis, which may rupture.
List risk factors for cardiovascular disease.
high blood pressure, smoking, high cholesterol, poor diet, lack of exercise, obesity, and genetics.
How does smoking increase the risk of cardiovascular disease?
Smoking damages arterial walls, increases blood pressure, reduces oxygen transport due to carbon monoxide, and promotes clot formation.
What role does high cholesterol play in CVD?
High levels of low-density lipoproteins (LDLs) contribute to atheroma formation, narrowing arteries and increasing blood pressure
Describe how diet can influence cardiovascular health.
Diets high in saturated fats and salt increase LDL levels and blood pressure, while diets rich in fiber, fruit, and omega-3 reduce risk.
What is the function of high-density lipoproteins (HDLs)?
HDLs help transport cholesterol from tissues to the liver for excretion, reducing the risk of atherosclerosis.
How can regular exercise reduce the risk of CVD?
Exercise improves heart efficiency, reduces LDL cholesterol, raises HDL cholesterol, and helps manage weight and blood pressure.
How does hypertension contribute to cardiovascular disease?
Hypertension (high blood pressure) damages arterial walls, promoting atheroma formation and increasing the risk of heart attacks and strokes.
What is angina, and how is it related to coronary heart disease?
Angina is chest pain caused by reduced blood flow to the heart muscle, often due to narrowed coronary arteries in CHD.
How can a myocardial infarction (heart attack) occur?
A heart attack occurs when a coronary artery is completely blocked, cutting off oxygen supply to part of the heart muscle, leading to damage or death of the tissue.
Explain the difference between LDLs and HDLs in terms of cardiovascular health.
LDLs (Low-Density Lipoproteins): Deliver cholesterol to tissues, can lead to atheroma buildup, and increase CVD risk.
HDLs (High-Density Lipoproteins): Remove excess cholesterol to the liver for disposal, reducing CVD risk.
What are some lifestyle changes to prevent or manage cardiovascular disease?
Stop smoking, maintain a healthy diet, engage in regular physical activity, manage stress, and monitor blood pressure and cholesterol levels.
What medications are commonly used to treat or prevent cardiovascular disease?
Statins (lower cholesterol), beta-blockers (reduce blood pressure), and anticoagulants (prevent blood clots).
How does obesity increase the risk of cardiovascular disease?
Obesity leads to high cholesterol levels, hypertension, and increased strain on the heart, all of which elevate CVD risk.
What is the role of antioxidants in cardiovascular health?
Antioxidants reduce oxidative stress and prevent damage to blood vessel walls, which may help lower the risk of atherosclerosis.
How does diabetes influence the risk of developing cardiovascular disease?
Diabetes causes high blood glucose levels, which can damage blood vessels and accelerate atherosclerosis.
Why is it important to reduce salt intake for cardiovascular health?
High salt intake raises blood pressure, increasing the risk of hypertension and subsequent cardiovascular complications.
What is tissue fluid, and how is it formed?
Tissue fluid surrounds cells and is formed from small molecules (e.g., oxygen, water, nutrients) filtered out of blood plasma under high hydrostatic pressure in the capillaries.
What prevents large molecules like proteins from entering the tissue fluid?
Large molecules such as proteins cannot pass through capillary walls due to their size.
Describe the pressure filtration process in tissue fluid formation.
At the arteriole end of a capillary bed, hydrostatic pressure inside capillaries exceeds that in the tissue fluid, forcing plasma out.
At the venule end, lower hydrostatic pressure and higher plasma protein concentration lead to water reentering capillaries via osmosis
What happens to excess tissue fluid?
Excess tissue fluid is drained into lymph vessels, which transport it back into the circulatory system.
How are capillaries adapted for efficient exchange of substances?
Walls are one cell thick for short diffusion paths.
Capillaries are numerous, increasing surface area.
Located near cells to reduce diffusion distance.
What are capillary beds?
Capillary beds are networks of capillaries that facilitate the exchange of substances between blood and tissues
How does high blood pressure affect tissue fluid formation?
High blood pressure increases hydrostatic pressure, leading to more fluid being pushed out, potentially causing tissue swelling (edema).
formula for oxyhemoglobin:
haemoglobin (Hb) + oxygen (4O2) →← HbO8 (oxyhaemoglobin)
affinity for oxygen meaning:
the tendency a molecule has to bind with oxygen.
what does haemoglobin’s affinity for oxygen varies depend on?
one of the conditions that affects it is the partial pressure of oxygen (pO2).
what is pO2
measure of oxygen concentration.
The greater the concentration of dissolved oxygen in cells, the higher the partial pressure.
As pO2 increases….
haemoglobin’s affinity for oxygen also increases
where does oxygen load onto?
haemoglobin to form oxyhaemoglobin where
there’s a high pO2.
where does Oxyhaemoglobin unload its oxygen?
where there’s a lower pO2
where does oxygen enter the blood capillaries?
at the alveoli in the lungs
why does Alveoli have a high pO2?
so oxygen loads onto haemoglobin to form oxyhaemoglobin.
what is used when cells respire?
oxygen — this lowers the pO2.
what do Red blood cells do?
deliver oxyhaemoglobin to respiring tissues, where it unloads its oxygen.
The haemoglobin then returns to the lungs to pick up more oxygen.
alveoli in lungs:
- high oxygen concentration
- high pO2
- high affinity
- oxygen loads
respiring tissue:
- low oxygen concentration
- low pO2
- low affinity
- oxygen unloads
what does the oxygen dissociation curve show?
shows how saturated the haemoglobin is with oxygen at any given partial pressure.
The affinity of haemoglobin for oxygen affects how saturated the haemoglobin is
pO2 in oxygen dissociation curve:
Where pO2 is high (e.g. in the lungs), haemoglobin
has a high affinity for oxygen, so it has a high
saturation of oxygen.
Where pO2 is low (e.g. in respiring tissues), haemoglobin has a low affinity for oxygen, so it has a low saturation of oxygen.
saturation affecting affinity:
saturation of haemoglobin can also affect the affinity
this is why the graph is ‘S-shaped’ and not a straight line.
The S-shaped dissociation curve for haemoglobin:
When haemoglobin combines with
the first O2 molecule, its shape alters
in a way that makes it easier for other
O2 molecules to join too. But as the
haemoglobin starts to become saturated,
it gets harder for more oxygen molecules
to join. As a result, the curve has a
steep bit in the middle where it’s really
easy for oxygen molecules to join,
and shallow bits at each end where it’s
harder — see Figure 5. When the curve
is steep, a small change in pO2 causes
a big change in the amount of oxygen
carried by the haemoglobin.
what is partial pressure of carbon dioxide (pCO2)?
a measure of the concentration of CO2 in a cell.
how does pCO2 affect oxygen unloading?
Haemoglobin gives up its oxygen more readily at a
higher pCO2 to get way more O2 to cells during activity.
what do cells produce when they respire?
carbon dioxide, which raises the pCO2. This increases the rate of oxygen unloading (i.e. the rate at which oxyhaemoglobin dissociates to form haemoglobin and oxygen)
what is the Bohr effect?
shape). The saturation of blood with oxygen is lower for a given pO2, meaning that more oxygen is
being released
haemoglobin in different organisms:
Different organisms have different types of haemoglobin with different oxygen transporting capacities — it depends on things like where they live, how active they are and their size.
how does having a particular type of haemoglobin help organisms?
helps the organism to survive in a particular environment.
Low oxygen environments:
Organisms that live in environments with a low concentration of oxygen have haemoglobin with a higher affinity for oxygen than human haemoglobin
why do organisms have a haemglobin with a higher affinity?
there isn’t much oxygen available, so the haemoglobin has to
be very good at loading any available oxygen.
lungworm example of haemoglobin:
A lugworm lives in burrows beneath sand where there’s a low oxygen concentration. Its haemoglobin has to be able to pick up as much oxygen as possible — it has a high affinity for oxygen.
High activity levels:
Organisms that are very active and have a high oxygen demand have haemoglobin with a lower affinity for oxygen than human haemoglobin.
why do organisms have haemoglobin with a lower affinity?
they need their haemoglobin to easily unload oxygen, so that it’s available for them to use.
hawk (tuah) example:
A hawk has a high respiratory rate (as it is very active) and lives where there’s plenty of oxygen. Its haemoglobin has to be able to unload oxygen quickly in order to meet the high oxygen demand
— it has a low affinity for oxygen.
why do smaller mammals lose heat quickly?
tend to have a higher surface area to volume ratio than larger mammals.
- means they have a high oxygen demand.
haemoglobin in smaller mammals:
Mammals that are smaller than humans have haemoglobin with a lower affinity for oxygen than human haemoglobin, as they need haemoglobin to easily unload oxygen to meet their high oxygen demand.
Reading values from a dissociation curve:
- Find 6 kPa on the x-axis.
- Use a ruler to draw a line up to the curve for
animal A.
Make sure the line is parallel to the y-axis.
Then draw a line across to the y-axis.
Make sure this line is parallel to the x-axis.
Read off the value at this point on the axis — 84%.
Repeat for the curve for animal B — 60%.
Find the difference between them: 84 – 60 = 24%
what do arteries do?
carry blood from the heart to the rest of the body.
structure of arteries:
walls are thick and muscular and have elastic tissue to stretch and recoil as the heart beats, which helps maintain the high pressure.
The inner lining (called the endothelium) is folded, allowing the artery to stretch — this also helps it to maintain high pressure.
what type of blood is in arteries?
All arteries carry oxygenated blood except for the pulmonary arteries, which take deoxygenated blood to the lungs.
what do arteries divide into?
smaller vessels called arterioles.
what do arterioles form?
form a network throughout the body.
Blood is directed to different areas of demand in the
body by muscles inside the arterioles, which contract to restrict the blood flow or relax to allow full blood flow
what is the function of veins?
take blood back to the heart under low pressure.
size of lumen in veins:
- have a wider lumen than equivalent arteries, with very little elastic or muscle tissue.
why do veins contain valves?
to stop the blood flowing backwards
how does blood flow through the veins?
Blood flow through the veins is helped by contraction of the body muscles surrounding
them.
All veins carry deoxygenated blood (as oxygen has been used up by body cells), except for the pulmonary veins, which carry oxygenated blood to the heart from the lungs.
what do arterioles branch into?
capillaries, which are the smallest of the blood vessels.
what substances are exchanged between cells and
capillaries?
glucose and oxygen for efficient diffusion
position of capillaries:
- always found very near cells in exchange tissues (e.g. alveoli in the lungs), so there’s a short diffusion pathway.
walls of capillaries:
- one cell thick, which also shortens the diffusion
pathway.
why are there a large number of capillaries?
- to increase surface area for exchange.
what are capillary beds?
Networks of capillaries in tissue
what is tissue fluid?
fluid that surrounds cells in tissues.
- made from small molecules that leave the blood plasma, e.g. oxygen, water and nutrients.
why doesn’t tissue fluid contain red blood cells or big proteins?
Unlike blood, tissue fluid doesn’t contain red blood cells or big proteins, as they’re too large to be pushed out through the capillary walls.
how do cells use tissue fluid?
Cells take in oxygen and nutrients from the tissue fluid, and release metabolic waste into it.
what happens in the capillary bed?
substances move out of the capillaries, into the
tissue fluid, by pressure filtration.
hydrostatic pressure at the start of the capillary bed.
At the start of the capillary bed, nearest the arteries, the hydrostatic (liquid) pressure inside the capillaries is greater than the hydrostatic pressure
in the tissue fluid.
what is meant by the difference in hydrostatic pressure?
means an overall outward pressure forces fluid out of the capillaries and into the spaces around
the cells, forming tissue fluid.
why does the hydrostatic pressure reduces
in the capillaries?
- happens as fluid leaves so the hydrostatic pressure is much lower at the venule
end of the capillary bed (the end that’s nearest to the veins).
why is the water potential at the venule end of the capillary bed lower than the water potential in the tissue fluid?
- fluid loss, and an increasing concentration of plasma proteins (which don’t leave the capillaries)
where does water re-enter the capillaries?
from the tissue fluid at the venule end by osmosis
how is excess tissue fluid drained?
excess tissue fluid is drained into the lymphatic system (a network of tubes that acts a bit
like a drain), which transports this excess fluid from the tissues and passes it back into the circulatory system.
what is the mammalian system?
a mass transport system- it carries raw materials + waste product around the body
Function of the circulatory system:
Multicellular organisms, like mammals, have a low surface area to volume
ratio so need a specialised mass transport system to carry raw materials from specialised exchange organs to their body cells (circulatory system).
Structure of the circulatory system:
- made up of heart and blood vessels
what does the heart do?
pumps blood through blood vessels (arteries, arterioles, veins and capillaries)
to reach different parts of the body.
how does the pulmonary artery carry blood?
from heart to lungs
how does Pulmonary vein carry blood?
from lungs to heart
how does aorta carry blood?
from heart to body
how does vena cava carry blood?
from body to heart
how does renal artery carry blood?
from body to kidneys
how does renal vein carry blood?
from kidneys to vena cava
what does blood transport around the body?
- respiratory gases
- products of digestion
- metabolic wastes
- hormones
what do the loops of the circulatory system do?
- One circuit takes blood from
the heart to the lungs, then back to the
heart. - The other loop takes blood around
the rest of the body, so the blood has to
go through the heart twice to complete
one full circuit of the body.
where is the heart’s blood supply from?
the left and right coronary arteries
what type of blood does the vena cava carry?
deoxygenated blood to heart
what type of blood does the aorta carry?
oxygenated blood to the body
what type of blood does the pulmonary artery carry?
deoxygenated blood to lungs
where do arteries carry blood?
from the heart to the rest of the body.
structure of arteries:
- walls are thick and muscular and have elastic tissue to stretch + recoil as the heart beats, which helps maintain the high pressure. The inner
lining (called the endothelium) is folded,
allowing the artery to stretch + also
helps it to maintain high pressure.
which artery does not carry oxygenated blood.
all except for the pulmonary arteries, which take
deoxygenated blood to the lungs.
what do arteries divide into?
smaller vessels called arterioles.
what do arterioles form?
form a network throughout the body.
where is blood directed in arterioles?
Blood is directed to different areas of demand in the
body by muscles inside the arterioles, which contract to restrict the blood flow or relax to allow full blood flow.
where do veins take blood?
back to the heart under low pressure.
lumen of veins:
They have a wider lumen than equivalent arteries, with very little elastic or muscle tissue.
what prevents back flow of blood in veins?
- valves
what is blood flow through the veins is helped by?
contraction of the body muscles surrounding them.
what type of blood does veins carry?
deoxygenated blood
(as oxygen has been used up by body
cells)
which veins carry oxygenated blood?
pulmonary veins, which carry oxygenated blood to the heart from the lungs.
what do Arterioles branch into?
capillaries, which are the smallest of the blood vessels.
why is exchanged between cells and capillaries?
Substances (e.g. glucose and oxygen)
- so capillaries are adapted for efficient diffusion.
where are capillaries found?
always found very near cells in exchange tissues (e.g. alveoli in the lungs), so there’s
a short diffusion pathway.
walls of capillaries:
one cell thick which shortens diffusion pathway
why are there lots of capillaries?
large number of capillaries, to increase surface area for exchange. Networks of capillaries in tissue are called capillary beds.
what is an endothelium?
part of the capillary one cell thick which shortens
what is tissue fluid? s
fluid that surrounds cells in tissues. It’s made from small molecules that leave the blood plasma, e.g. oxygen, water and nutrients
why does tissue fluid only contain small molecules?
(Unlike blood, tissue fluid doesn’t contain red blood cells or big proteins as they’re too large to be pushed out through the capillary walls.)
what do cells take in?
take in oxygen and nutrients from the tissue fluid, and release metabolic waste into it.
how do substances move out of the capillaries, into the tissue fluid
pressure filtration.
hydrostatic pressure at the start of the capillary bed:
at the start of the capillary bed, nearest the arteries, the hydrostatic (liquid) pressure inside the capillaries is greater than the hydrostatic pressure
in the tissue fluid.
what does the difference in hydrostatic pressure mean?
an overall outward pressure forces fluid out of the capillaries and into the spaces around
the cells, forming tissue fluid.
what happens to hydrostatic pressure as fluid leaves?
hydrostatic pressure reduces in the capillaries — so the hydrostatic pressure is much lower at the venule
end of the capillary bed (the end that’s nearest to the veins).
why is the water potential at the venule end of the capillary bed is lower than the water potential in the tissue fluid?
Due to the fluid loss, and an increasing concentration of plasma proteins (which don’t leave the capillaries)
what happens when the water potential at the venule end of the capillary bed is lower than the water potential in the tissue fluid?
some water re‑enters the capillaries from the tissue fluid at the venule end by osmosis
what is the lymphatic system?
- where any excess tissue fluid is drained into
- is a network of tubes that acts a bit
like a drain which transports this excess fluid from the tissues and passes it back into the circulatory system.
what happens when there is higher hydrostatic pressure in the capillaries than tissue fluid?
fluid is forced out of the capillary
what happens when there is lower water potential in the capillaries than in tissue fluid?
some water re-enters by osmosis
what does the right side of the heart do?
pumps deoxygenated blood to the lungs
what does the left side of the heart do?
pumps oxygenated blood to the whole body.
parts of the heart:
- aorta
- pulmonary vein
- left atrium
- semi lunar valve
- left atrioventricular valve
- cords
- left ventricle
- right ventricle
- right atrioventricular valve
- semi lunar va,be
- inferior vena cava
- superior vena cava
- pulmonary artery
adaptation of the left ventricle:
thicker, more muscular walls than right ventricle — this allows it to contract more powerfully and pump
blood all the way around the body.
why is the right ventricle less muscular?
so its contractions are only powerful enough to pump blood to the nearby lungs.
why are ventricle walls thicker than atria?
pushes blood out of the heart, whereas the atria just need to push blood a short distance into the ventricles.
what do the atrioventricular (AV) valves do?
link the atria to the ventricles and stop
blood flowing back into the atria when the ventricles contract.
what do The semi-lunar (SL) valves do?
link the ventricles to the pulmonary artery
and aorta, and stop blood flowing back into the heart after the ventricles
contract.
what do the cords do?
attach the atrioventricular valves to the ventricles to stop them
being forced up into the atria when the ventricles contract.
what does the opening of the valves depend on?
valves only open one way — whether they’re open or closed depends on
the relative pressure of the heart chambers
when are valves forced open?
If there’s higher pressure behind a valve
when is the valve forced shut?
if pressure is higher in front of the valve
what is the direction of the blood flow in the valves?
unidirectional — it only flows in one direction.
heart dissection practical:
Make sure you are wearing a lab coat and lab gloves
because heart dissections can be messy.
3. Place the heart you are given on your dissecting tray.
Look at the outside of the heart and try to identify the four main
vessels attached to it. Feel inside the vessels to help you — remember
arteries are thick and rubbery, whereas veins are much thinner.
4. Identify the right and left atria, the right and left ventricles
and the coronary arteries. You might be asked to draw
a sketch of the outside of the heart and label it.
5. Using a clean scalpel, carefully cut along the lines shown on Figure 5
to look inside each ventricle. You could measure and record the
thickness of the ventricle walls and note any differences between them.
6. Next, cut open the atria and look inside them too. Note whether
the atria walls are thicker or thinner than the ventricle walls.
7. Then find the atrioventricular valves, followed by the semi‑lunar
valves. Look at the structure of the valves and see if you can see
how they only open one way. you could draw a sketch
to show the valves and the inside of the ventricles and atria.
8. Make sure you wash your hands and disinfect all work
surfaces once you’ve completed your dissection.
what is the cardiac cycle?
an ongoing sequence of contraction and relaxation of the atria and ventricles that keeps blood continuously circulating round the body.
when does the volume of the atria and ventricles change?
as they contract and relax
when do pressure changes occur?
due to the changes in chamber volume
(e.g. decreasing the volume of a chamber by contraction will increase the
pressure of a chamber)
stage 1 of cardiac cycle:
Ventricles relax,
atria contract
The ventricles are relaxed.
The atria contract, decreasing the
volume of the chambers and increasing
the pressure inside the chambers.
This pushes the blood into the
ventricles. There’s a slight increase
in ventricular pressure and chamber
volume as the ventricles receive the
ejected blood from the contracting atria.
step 2 of cardiac cycle:
Ventricles contract,
atria relax
The atria relax. The ventricles
contract (decreasing their volume),
increasing their pressure. The
pressure becomes higher in the
ventricles than the atria, which forces
the atrioventricular (AV) valves shut
to prevent back-flow. The pressure
in the ventricles is also higher than
in the aorta and pulmonary artery,
which forces open the semi-lunar (SL)
valves and blood is forced out into
these arteries.
step 3 of cardiac cycle:
Ventricles relax, atria relax
The ventricles and the atria both relax. The higher pressure in the pulmonary
artery and aorta closes the SL valves to prevent back-flow into the ventricles.
Blood returns to the heart and the
atria fill again due to the higher
pressure in the vena cava and
pulmonary vein. In turn this starts
to increase the pressure of the
atria. As the ventricles continue
to relax, their pressure falls below
the pressure of the atria and so
the AV valves open. This allows
blood to flow passively (without
being pushed by atrial contraction)
into the ventricles from the atria.
The atria contract, and the whole
process begins again.
Cardiac output meaning:
the volume of blood pumped by the heart per
minute (measured in cm3 min-1).
formula for cardiac output:
cardiac output = stroke volume × heart rate
what is cardiovascular disease?
general term used to describe diseases associated
with the heart and blood vessels
what does cardiovascular disease include?
include aneurysms, thrombosis and myocardial infarction
what does most cardiovascular disease start with?
atheroma formation
example of cardiovascular disease:
coronary heart disease (CHD)
when does CHD occur?
occurs when the coronary arteries have lots of atheromas in them, which restricts blood flow to the heart muscle. It can lead to myocardial infarction.
what is the wall of an artery is made up of ?
made up of several layers
- The endothelium (inner lining) is usually smooth and unbroken.
what happens if damage occurs to the endothelium (e.g. by high blood pressure)?
white blood cells (mostly macrophages) and lipids (fat) from the blood, clump together under the lining
to form fatty streaks
what happens to WBCs, lipids, connective tissue over time?
build up and harden to form a fibrous plaque called an atheroma
what does atheroma do?
partially blocks the lumen of the artery
and restricts blood flow, which causes blood pressure to increase.
what is cardiovascular diseases?
a general term to describe diseases associated
with the heart and blood vessels
e.g aneurysms, thrombosis and myocardial infarction
what do most cardiovascular diseases start with?
atheroma formation
what type of diseases is Coronary heart disease (CHD)?
a type of cardiovascular disease.
when does Coronary heart disease (CHD) occur?
when the coronary arteries have lots of atheromas in them + restricts blood flow to the heart muscle
what can Coronary heart disease (CHD) lead to?
myocardial infarction
what is the wall of an artery is made up of?
several layers
what is the endothelium?
the inner lining of the artery
- it is usually smooth and unbroken
what happens if damage occurs to the
endothelium?
(e.g. can be damaged by high blood pressure)
- white blood cells (mostly macrophages) and lipids (fat) from the blood, clump together under the lining
to form fatty streaks.
what is atheroma?
more white blood cells, lipids and connective tissue
build up and harden to form a fibrous plaque
what does atheroma do?
partially blocks the lumen of the artery and restricts blood flow, which causes blood pressure to increase
what happens to them lumen due to atheroma?
- lumen shrinks as artery walls swells so it is difficult for blood to pass through
what is an aneurysm?
a balloon-like swelling of the artery
how does aneurysm start?
starts with the formation of atheromas.
what do Atheroma plaques do?
damage and weaken arteries
- narrow arteries, increasing blood pressure
what happens when blood travels through a weakened artery at high pressure?
may push the inner layers of the artery through the outer elastic layer to form an aneurysm.
- aneurysm may burst, causing a haemorrhage (bleeding)
what thrombosis?
the formation of a blood clot
how does thrombosis start?
with the formation of atheromas.
what can an atheroma plaque do to the endothelium (inner lining) of an artery?
can rupture (burst through) the endothelium
- This damages the artery wall and leaves a rough
surface.
what helps with damage or the artery wall?
Platelets and fibrin (a protein) go to the site of damage and form a blood clot (a thrombus)
what can the blood clot of thrombosis form?
complete blockage of the artery, or it can become dislodged and block a blood vessel
elsewhere in the body.
what can Debris from the rupture of thrombosis cause?
can cause a blood clot to form further down the artery.
other word for heart attack:
Myocardial infarction
what do the coronary arteries do?
supplies blood to heart
what does oxygenated blood contain due to coronary arteries?
oxygen needed by heart muscle cells to
carry out respiration.
what happens if a coronary artery becomes completely blocked?
can be blocked by (e.g. by a blood clot)
- an area of the heart muscle will be totally cut off
from its blood supply, receiving no oxygen, causing myocardial infarction
what can a heart attack can cause? heart attack can cause?
damage and death of the heart muscle.
Symptoms of heart attack:
- pain in the chest and upper body
- shortness of breath and sweating.
how can complete heart failure happen?
- if large areas of the heart muscle are affected + often fatal.
Risk factors for cardiovascular disease:
High blood pressure, High blood cholesterol and poor diet, Cigarette smoking
how does High blood pressure increase risk of cardiovascular disease?
- damage to the artery walls.
Damaged walls have an increased risk of atheroma formation, causing a further increase in blood pressure.
what can Atheromas do?
cause blood clots to form
- blood clot could block flow of blood to the heart
muscle, possibly resulting in myocardial infarction
what does anything that increases blood pressure also increase?
risk of cardiovascular disease, e.g. being overweight, not exercising and excessive
alcohol consumption.
link between high blood pressure, atheroma, myocardial infarction:
Not exercising + overweight →high blood pressure → atheroma formation → blood clots → myocardial infarction
High blood cholesterol and poor diet:
If the blood cholesterol level is high (above 240 mg per 100 cm3) then the risk
of cardiovascular disease is increased as cholesterol is one of
the main constituents of the fatty deposits that form atheromas which can lead to increased blood pressure and blood clots causing a myocardial infarction.
what is a diet high in saturated fat is associated with?
- high blood cholesterol levels.
A diet high in salt also increases the risk of cardiovascular disease as it increases the risk of high blood pressure.
The link between a diet high in saturated fat or salt,
atheroma formation and myocardial infarction:
diet high in saturated fat → high blood cholesterol → atheroma formation → blood clots → myocardial infarction → diet high in salt → high blood pressure
how does cigarette smoke increase the
risk of cardiovascular disease and myocardial infarction?
- carbon monoxide and nicotine, found in cigarette smoke
amount of oxygen transported in the blood, and so reduces the amount
of oxygen available to tissues. If the heart muscle doesn’t receive enough
oxygen it can lead to a heart attack.
what does smoking decrease in the blood?
amount of antioxidants in the blood
- important for protecting cells from damage. Fewer antioxidants means cell damage in the coronary artery walls is more likely, and this can lead to atheroma formation.
Flow chart for smoking decreasing amount of antioxidants in blood
smoking → carbon monoxide → less oxygen in blood → less oxygen to tissues → myocardial infarction
smoking → fewer antioxidants → damage to coronary artery walls → atheroma formation
Risk factors of cardiovascular disease that are controlled + not controlled:
- Most of these factors are within our control e,g smoking, fatty foods
- However, some risk factors can’t be controlled e.g genetic predisposition to coronary heart disease, high blood pressure as a result of another condition, e.g. some forms of diabetes.
Reducing the risk of cardiovascular disease:
Even so, the risk of developing cardiovascular disease can be reduced by removing as many risk factors as you possibly can
study of cardiovascular disease:
Figure 4 shows the results of a study involving 27 939 American women.
The LDL cholesterol level was measured for each woman. These women were then followed for an average of 8 years and the occurrence of cardiovascular events (e.g. heart attack, surgery on coronary arteries) or death from cardiovascular diseases was recorded. The relative risk of a cardiovascular event, adjusted for other factors that can affect cardiovascular disease, was then calculated.
Describing data in cardiovascular disease example of study:
relative risk of a cardiovascular event
increases as the level of LDL cholesterol in the blood increases from … to ….
Drawing conclusions in cardiovascular disease example disease study example:
The graph shows a positive correlation between
the relative risk of a cardiovascular event and the level of LDL cholesterol in the blood.
Check any conclusions are valid in cardiovascular disease study example:
Make sure any conclusions match the data, e.g. This data only looked at women — no males were involved
Impact of a large sample in graphs:
- Data based on large samples is better than data based on small samples as more representative of the whole population
Conflicting evidence in cardiovascular disease example:
one study might conclude that a factor isn’t a health risk, whereas another study might conclude that the same factor is a health risk.
- If two studies have produced conflicting results, think about why that might be. Was it to do with study design? Was one study based on a small sample size? Did both studies take into account other risk factors (variables) that could have affected the results? Knowing whether both
studies used similar groups can be helpful, e.g. same age, gender, etc.
How to resolve conflicting evidence in cardiovascular disease example:
carry out more studies and collect more results. Results need to be reproduced by other scientists before they’re accepted.
What is the xylem?
tissue transports water and mineral ions in solution.
These substances move up the plant from the roots to the leaves.
What is a phloem?
tissue transports organic substances like sugars (also in solution) both up and down the plant
What type of systems are xylem and phloem?
mass transport systems
- move substances over large distances.
What are Xylem vessels?
part of the xylem tissue that actually transports the water and ions.
Structure of Xylem vessels:
- very long, tube‑like structures formed from dead
cells (vessel elements) joined end to end - There are no end walls on these cells, making an uninterrupted tube that allows water to pass up through the middle easily.
How does water move up a plant?
against the force of gravity, from roots to leaves.
What is transpiration?
- Water evaporates from the leaves at the ‘top’ of the xylem.
What does transpiration cause?
tension (suction), which pulls more water into the leaf.
Water molecules in xylem:
- Water molecules are cohesive (they stick together)
- This means the whole column of water in the xylem, from the leaves down to the roots, moves upwards.
How does water enter the stem?
through the roots.
What is Transpiration?
the evaporation of water from a plant’s surface, especially the leaves.
- Water evaporates from the moist cell walls and accumulates in the spaces between cells in the leaf.
What happens When the stomata open?
Water moves out of the leaf down the water potential gradient as there’s more water inside the leaf than in the air outside
Factors affecting transpiration rate:
- Light intensity
- Temperature
- Humidity
- Wind
How does Light intensity affect transpiration rate?
- lighter it is the faster the transpiration rate ( positive correlation between light intensity and transpiration rate)
- stomata open when it gets light to let in CO2 for
photosynthesis. When it’s dark the stomata are usually closed, so there’s little transpiration.
How does Temperature affect transpiration rate?
the higher the temperature the faster the transpiration rate.
- Warmer water molecules have more energy so they evaporate from the cells inside the leaf faster.
- increases the water potential gradient
between the inside and outside of the leaf, making water diffuse out of the leaf faster.
How does Humidity affect transpiration rate?
- the lower the humidity, the faster the transpiration rate (there’s a negative correlation between humidity and transpiration rate)
- If the air around the plant is dry, the water potential gradient between the
leaf and the air is increased, which increases transpiration rate.
How does Wind affect transpiration rate?
the windier it is, the faster the transpiration rate.
Lots of air movement blows away water molecules from around the stomata. This increases the water potential gradient, which increases the rate of
transpiration.
What is a potometer?
- piece of apparatus used to estimate transpiration
rates. It actually measures water uptake by a plant, but it’s assumed that water uptake by the plant is directly related to water loss by the leaves. You can use it to estimate how different factors affect the transpiration rate.
Cutting plant for transpiration rate apparatus:
- Cut a shoot underwater to prevent air from entering the xylem. Cut it at a slant to increase the surface area available for water uptake.
Assembling potometer in transpiration practical:
Assemble the potometer under the water and insert the shoot with the apparatus still under the water, so no air can enter.
Removing apparatus for transpiration practical:
- Remove the apparatus from the water but keep the end of the capillary tube submerged in a beaker of water.
- Check that the apparatus is watertight and airtight.
Drying leaves in transpiration practical:
- Dry the leaves, allow time for the shoot to acclimatise and then shut the tap.
Bubbles in transpiration practical:
- Remove the end of the capillary tube from the beaker of water until one air bubble has formed, then put the end of the tube back into the water.
- Record the starting position of the air bubble.
- Start a stopwatch and record the distance moved by the bubble per unit time, e.g. per hour. The rate of air bubble movement is an estimate of the transpiration rate.
- only change one variable (e.g. temperature) at a time. All other conditions (e.g. light intensity, humidity) must be kept constant
Looking at xylem and phloem:
- You can look at xylem or phloem in plant tissue (e.g. part of a plant stem) under a microscope, and then draw them.
preparing xylem and phloem tools:
- Use a scalpel to cut a cross‑section of the stem.
- Cut thinly for better viewing under a microscope. - Use tweezers to gently place the cut sections in water until you come to use them. This stops them
from drying out.
Preparing xylem and phloem water on slide:
- Add a drop of water to a microscope slide, add the plant section and carefully add one or two drops of a stain, e.g. toluidine blue O (TBO), and leave for about one minute.
Preparing xylem + phloem cover slip:
- Carefully apply a cover slip so you have created a temporary mount
Viewing xylem + phloem under microscope:
When you view the specimen under the microscope, if you’ve used TBO you should be able to see the xylem cells stained blue-green. The phloem cells and the rest of the tissue should appear pinkish purple.
arrangement of the xylem and the phloem in a cross-section of a stem:
- has xylem
- phloem
- vascular bundle
- cambium
What does the phloem transport?
dissolved substances around the plant
What are Solutes?
dissolved substances.
What does phloem transport?
organic solutes (mainly sugars like sucrose) round plants
Arrangement in phloem!
Like xylem, phloem is formed from cells arranged in tubes.
Sieve tube elements and companion cells are important cell types in phloem tissue
What are Sieve tube elements?
- living cells that form the tube for transporting
solutes. They have no nucleus and few organelles so companion cells help
What do companion cells do?
- there’s a companion cell for each sieve tube element. They carry out living functions for sieve cells, e.g. providing the energy needed for the active transport of solutes.
What is Translocation?
the movement of solutes (e.g. amino acids and sugars like sucrose) to where they’re needed in a plant
Other word for solutes:
assimilates - energy-requiring process that happens in the phloem.
What does translocation do?
Translocation moves solutes from ‘sources’ to ’sinks’.
What is the source?
where assimilates are produced (so they’re at a high concentration there)
What is the sink?
where assimilates are used up (so they’re at a lower concentration there).
Example of sucrose in sink:
The source for sucrose is usually the leaves (where it’s made), and the sinks are the other parts of the plant, especially the food storage organs and the
meristems (areas of growth) in the roots, stems and leaves.
Enzymes in sink:
maintain a concentration gradient from the source to the sink by changing the solutes at the sink (e.g. by breaking them down or making them into something else).
- so there’s always a lower concentration at the sink than at the source.
Potatoe sink:
In potatoes, sucrose is converted to starch in the sink areas, so there’s always a lower concentration of sucrose at the sink than inside phloem
- so there is a constant supply of new sucrose reaching sink from phloem
Source in mass flow hypothesis:
Active transport used to actively load the solutes (e.g. sucrose from photosynthesis) from companion cells into the sieve tubes of the phloem at the source (e.g. the leaves)
- lowers water pot inside sieve tubes, so water enters the tubes by osmosis from the xylem and companion cells. This creates a high pressure inside the sieve tubes at the source end of the phloem.
Sink in mass flow hypothesis:
At sink, solutes are removed from the phloem to be used up.
- increases the water potential inside the sieve tubes, so water also leaves the tubes by osmosis. This lowers the pressure inside the sieve tubes.
Flow in mass flow:
- lower pressure inside sieve tube causes pressure gradient from source to sink end
- gradient pushes solutes along the sieve tubes
towards sink - When they reach the sink the solutes will
be used (e.g. in respiration) or stored (e.g. as starch).
The higher the concentration of sucrose at the source…..
the higher the rate of translocation.
Mass flow evidence (high conc of sugars):
- If a ring of bark (which includes the phloem,
but not the xylem) is removed from a woody
stem, a bulge forms above the ring - fluid has a higher conc of sugars than fluid from below ring as sugars can’t move past the area where bark has been removed
- shows there can be a downward flow of sugars
Mass flow evidence (pressure inside sieve tube phloem):
Pressure in the phloem can be investigated using aphids (they pierce the phloem, then their bodies are removed leaving the mouthparts behind, which allows the sap to flow out).
- sap flows out quicker nearer the leaves than further down the stem showing there’s a pressure gradient.
Mass flow evidence (radioactive tracer):
- e.g radioactive carbon (14C) can track movement of organic substances in a plant
Mass flow evidence (metabolic inhibitor):
a metabolic inhibitor (which stops ATP production) is put into the phloem, then translocation stops — showing that active transport is involved.
Objections for mass transport theory:
- Sugar travels to many different sinks, not just to the one with the highest water potential, as the model would suggest.
- sieve plates would create a barrier to mass flow. A lot of pressure would be needed for the solutes to get through at a reasonable rate.
How can Translocation of solutes be modelled?
- in an experiment using radioactive tracers.
- done by supplying part of a plant (often a leaf) with an organic substance that has a radioactive label, then tracking its movement.
How is Carbon dioxide containing the radioactive isotope used?
- as a radioactive tracer.
- can be supplied to a single leaf by being pumped into a container which completely surrounds
the leaf. The radioactive carbon will then be incorporated into organic substances produced by the leaf (e.g. sugars produced by photosynthesis),
which are moved around the plant by translocation.
What is autoradiography?
Tracks movement of substances in translocation
What does autoradiography do?
Reveals where radioactive tracer has spread to in a
plant, the plant is killed (e.g. by freezing it using liquid nitrogen) and then the whole plant (or sections of it) is placed onto photographic film — wherever the film turns black, the radioactive substance is present
What do results of autoradiography show?
- translocation of substances from source to sink over time e.g autoradiographs of plants killed at different times show an overall movement of solutes (e.g. products of photosynthesis) from the leaves towards the roots.
Correlation example:
The results in the table above show a positive correlation — as the width of the bark strip remaining increased, the amount of carbohydrate transported to the lower part of the stem (i.e. below the ringing) also increased.
Keyword for conclusions:
- something CAUSED something else
