biology mass transport

What is a single circulatory system?

Fish have them

heart -> gills --> body --> heart

What is a double circulatory system?

Mammals have them

heart --> body --> heart--> lungs --> heart

One circuit goes to the lungs to pick up oxygen (pulmonary circulation)

The other circuit carries the oxygen and nutrients around the body (systematic circulation)

What are the features of a double closed circulatory system?

Blood is confined to vessel and passes twice though the heart twice of each complete circuit

When blood passes through the lungs - pressure is reduced

blood is returned to the heart to boost its pressure before being circulated to the rest of the tissues

As a result, substances are delivered to the rest of the body quickly - maintains a high temperature and metabolism

What is an open circulatory system?

E.g. molluscs, invertebrates

Blood not in vessels

Trachea delivers 02 directly from environment to tissues

Body cavity filled with haemocoel (fluid)

What is a closed circulatory system?

E.g. vertebrates, a few invertebrates

Blood remains in vessels

Blood pumps at higher pressure and delivered faster

Waste removed more quickly

Tissues bathed in tissue fluid

Where is the heart?

Between the two lungs

Enclosed by pericardium

Pericardial fluid is secreted between them to aid movement

Pericardium protects the heart over expansion

What is the heart made of?

The walls of the heart are made of cardiac muscle (myocardium)

Only found in the heart

Never tires but can't tolerate lack of 02

What does the heart look like?

Contains two halves - two ventricles and two atriums split by a septum

What are the pressure changes like in the heart?

Atrium has a lower max pressure as only pumps blood into the ventricle - ventricle pumps to the whole body

closure of the valves is a passive process - it depends on the relative pressures on either side of the valve

How do the valves respond to pressure changes?

The atrioventricular valves close when the pressure in the ventricles is higher than in the atrium

They open when the pressure is higher in the atrium than the ventricle

What is the pathway of blood on the right side?

body

vena cava

deoxygenated blood

atrium

tricuspid valve

right ventricle

pulmonary valve

pulmonary artery

lungs

pulmonary vein

What is the pathway of blood on the left side?

pulmonary vein

oxygenated blood

atrium

bicuspid valve

left ventricle

semi-lunar valve

aorta

body

What are the roles of the chambers in the heart?

Atrium - receives blood from veins

Ventricle - pumps blood into arteries

What do valves do?

Valves prevent backflow

When pressure in the ventricles exceeds that in the atrium in the bicuspid/tricuspid valves hut

This makes the first noise we hear with a stethoscope

tendinous chords attached to papillary muscles prevent valves turning inside out

Semi-lunar valves prevent backflow in the pulmonary artery and aorta

Closure of these makes the second noise of the heart beat (hence lub-dub)

How is oxygen linked to the cycle?

The heart requires a lot of oxygen and nutrients

Some oxygenated blood leaving the left ventricle goes directly to the heart through the coronary arteries

These branch many times to supply oxygen and nutrients throughout the cardiac muscle

When these get blocked a heart attack is likely and by-pass surgery required

What is systole?

Contraction of the heart

What happens in the atrial systole?

Atria contract, ventricles are relaxed

Blood moves from the atria into the ventricles along pressure gradient - AV valve open

Semi-lunar valves closed - to prevent backflow of blood into the ventricles (pressure lower in ventricles than arteries)

What happens in the ventricular systole?

Ventricle contracts, atria are relaxed

Blood is forced into arteries along pressure gradient - semi-lunar valves open

Bicuspid and tricuspid (AV) valves closed to prevent backflow of blood (pressure lower in atria than the ventricles)

What is diastole?

Relaxation of the heart

What happens during diastole?

Ventricles relax and atria are still relaxed

Atria fills with blood from the veins

Semi-lunar valves closed to prevent backflow of blood from the arteries (as pressure in the ventricles is lower)

What is cardiac output?

Stroke volume x heart rate

What is the need for a transport system?

Size

Metabolic activity

Surface area to volume ratio

Why does size affect the need for a transport system?

Larger organisms have body cells too far away from their surface to allow efficient exchange

A transport system allows for all body cells to be extremely close to a supply of nutrients for metabolic processes and to get rid of waste

Why does metabolic activity affect the need for a transport system?

Very active animals and those that maintain their body temperature (endotherms) require a good supply of glucose and oxygen for respiration (for muscle contraction and heat production) and to get rid of waste products like carbon dioxide

Why does surface area to volume ratio affect the need for a transport system?

The larger the organism the smaller the surface area to volume ratio

This means for each gram of body tissue in a larger organism, there is a smaller surface area for exchange compared to a smaller organism

What does an artery look like?

Lumen

Endothelium

Elastic fibres

Smooth muscle

Collagen fibres

How is the structure of an artery related to its function?

Narrow lumen to maintain high blood pressure

Thick layer of elastic tissue to allow artery to expand and recoil to maintain blood pressure

Thick layer of smooth muscle to allow blood vessel to constrict and dilate to maintain blood pressure

Thick layer of collagen and elastic fibres in outer wall to withstand the high pressure of the blood

Inner endothelial layer is folded - so that it can stretch when there is an increase in pressure

What does a vein look like?

Lumen

Endothelium

Elastic fibres

Smooth muscle

Collagen fibres

How is the structure of a vein related to its function?

Wider lumen to reduce resistance and allow the blood to flow easier

Thinner layer of elastic tissue as veins do not need to expand and recoil to maintain blood pressure

Thinner layer of smooth muscle as veins do not need to constrict and dilate to maintain blood pressure

Thinner layer of collagen and elastic fibres in outer wall as the blood is under very low pressure

Presence of valves to prevent backflow of blood

What does a capillary look like?

Red blood cell

Endothelium

Lumen

How is the structure of a capillary related to its function?

Very narrow lumen (7um) so red blood cells are squeezed through reducing the rate of flow and providing materials to move between the blood and tissue fluid

Capillary wall consists of single layer of flattened endothelial cells providing a short diffusion pathway

Gaps between the endothelial cells allow materials to enter and leave the blood (leaky)

What are the roles of arterioles?

Connect arteries to capillaries

Smooth muscle in their wall allows them to constrict and dilate - vasoconstriction and vasodilation

Vasoconstriction will reduce blood flow to the tissue e.g. reduced blood flow to the skin on a cold day to regulate temperature

Vasodilation will increase blood flow to the tissue e.g. increased blood flow to the muscles during exercise

What are the roles of the venules?

Connect capillaries to veins

Similar to veins they have walls consisting of a thin later of muscle, elastic and collagen

Wider lumen than arterioles to reduce resistance to blood flow

What are the factors aiding venous return?

venous blood pressure alone is too low to promote adequate blood return and is aided:

-respiratory pump - pressure changes created during breathing, sucks blood towards the heart by squeezing local veins -muscular pump contraction of skeletal muscles move the blood toward the heart

valves prevent backflow during venous return

What is the biconcave shape on the red blood cell for?

maximises surface area for gas exchange and allows the cells to be flexible enabling them to squeeze through narrow capillaries

What does the lack of nucleus do?

mature red blood cells don't have a nucleus, allowing more space for haemoglobin and increasing their oxygen-carrying capacity

What does the haemoglobin do?

this protein binds to oxygen in the lungs and releases it in the tissues

it makes up 95% of the dry mass of a red blood cell

what does the flexible membrane do?

it allows the cells to deform and pass through narrow blood vessels

what do the lack of organelles?

just like mitochondria and ribosomes there are no organelles

maximises space for haemoglobin

what's the tertiary structure of haemoglobin?

each polypeptide folded into a precise shape - important for its ability to carry oxygen

What's the quaternary structure of haemoglobin?

four polypeptide chains are linked to form an almost spherical molecule

each polypeptide has a haem group which contains a fe2+ ion, each ion can bind to a single oxygen molecule

4 oxygen per haemoglobin

What is loading/associating?

The process by which haemoglobin binds with oxygen is called loading or associating

in humans this takes place in the lungs

What is unloading/dissociating?

The process by which haemoglobin releases oxygen

In humans it takes place in the tissues

What is a high affinity?

Haemoglobin with this can take up oxygen more easily but release it less easily

What is a low affinity?

Haemoglobin with this can take up oxygen less easily but release it more easily

What's the affinity of haemoglobin for oxygen in a gas exchange surface?

high oxygen concentration

low carbon dioxide concentration

high affinity of haemoglobin for oxygen

results in oxygen being associated

What's the affinity of haemoglobin for oxygen in respiring tissues?

low oxygen concentration

high carbon dioxide concentration

low affinity of haemoglobin for oxygen

results in oxygen being dissociated

What is the partial pressure of o2?

a measure of oxygen concentration

high in the lungs

lower in body tissues such as the muscles

What does it mean that haemoglobins affinity for oxygen depend on the po2?

oxygen associates with haemoglobin to form oxyhaemoglobin where there's a high po2

oxygen dissociates from haemoglobin where there's a lower po2

What's the oxygen dissociation curve?

when haemoglobin is exposed to different partial pressures of oxygen, it does not bind in a linear fashion

the relationship between partial pressure of oxygen and percentage saturation is like a filament lamp

Why is the curve s shaped?

At lower pressures, there isn't a great deal of change in the saturation of the Hb

A small change in the po2 can result in a large change in the percentage saturation of the blood

At higher partial pressures there isn't a great deal of change in the saturation of the Hb

What are the molecules like, making it s shaped?

First molecule of 02 combines with an Hb and slightly distorts it, the joining of the first is usually quite slow

After the Hb has changed shape a little, it becomes easier and easier for the second and third 02 to join (positive cooperativity)

It flattens off at the top because joining the fourth 02 is more difficult due to probability

How does it have to do with the shape of haemoglobin?

It's a protein molecule with a specific shape - held together by those bonds in the tertiary structure

After oxygen binds it causes a slight shape change in haemoglobin as it distorts some of the bonds in the tertiary structure, allowing the second and third oxygen to bind easily - positive co-operativity

The 4th oxygen struggles to bind as a matter of probability (most binding sites are occupied now so it's less likely oxygen will collide with a binding site)

What does the capillary look like?

arteriole

lymphatic system

venule

body cells

capillary

blood flow through

What is the capillary bed?

Made up of a network of many branching capillaries, ensuring every body cell is extremely close to the blood for exchange of materials

What is the plasma?

Contains dissolved oxygen and nutrients, is forced through the capillary wall at the arteriole end of the capillary bed

What is the fluid formed called?

Tissue fluid

It bathes the cells so they can receive the nutrients required

What happens to the cells?

cells, platelets and large plasma proteins remain in the blood as they are too large to pass through the capillary wall

What happens at the venule end of the capillary bed?

Most of the tissue fluid is returned to the blood and contains the waste products from the cells

What happens to some of the tissue fluid?

It's removed by the lymphatic system and is eventually returned to the blood via a vein near the heart

What is tissue fluid?

A watery liquid that contains glucose, amino acids, salts and oxygen, supplying them all to the tissues

Tissue fluid formation aids the movement of nutrients from the capillaries to the tissues

Tissue fluid does not contain plasma proteins or any blood cells - these are too large to leave the capillary

What's the pressure like at the arteriole end?

Water and small molecules leave plasma due to high blood pressure or hydrostatic pressure

What's the pressure like at the venule end?

The hydrostatic pressure is lower than the osmotic effect of the plasma proteins in the capillary

The majority of the fluid is drawn back into the capillaries by osmosis

What is hydrostatic pressure?

The pressure created by a fluid pushing against the sides of its container/vessel

What is osmotic/oncotic pressure?

The pressure created by the osmotic effects f dissolved substances in a liquid (lowering of water potential)

What happens at the arteriole end of the capillary?

​The blood entering the capillary is under higher hydrostatic pressure than the surrounding tissue fluid (5.2kPa compared to 1.3kPa)​

Oncotic pressure created by solutes dissolved in both the blood and the tissue fluid (-2.9kPa compared to -1.2kPa)​

The hydrostatic pressure has a greater effect and net movement is out of the capillary​

Plasma and dissolved nutrients are forced out of the capillary

What is the hydrostatic pressure forcing small molecules out of the arteriole end opposed by?

hydrostatic pressure of tissue fluid outside of capillaries, preventing outward movement of liquids

Lower water potential of blood (due to plasma proteins), pulling water back into capillaries

BUT Hp is large enough inside that it overcomes these and has enough pressure to force small molecules out of capillaries, leaving cells and proteins behind (ultrafiltration)

What happens at the venule end of the capillary?

At the venule end of the capillary, the hydrostatic pressure of the blood is much lower and there is now less of a difference between the hydrostatic pressure of the blood and tissue fluid (1.8kPacompared to 1.3kPa)

​Oncotic pressure now has a greater effect and net movement is into the capillary from the tissues​

Tissue fluid returns to the capillary with dissolved waste from the cells, such as carbon dioxide, in it

What is the osmotic pressure pulling the fluid back in at the venule end opposed by?

Hydrostatic pressure of the fluid inside of the capillaries, preventing inward movement of liquids

BUT the hydrostatic pressure is GREATLY reduced by the time we reach the venule end

Therefore the osmotic pressure is greater and fluid can return to the venule

What is lymph formation?

Not all tissue fluid is reabsorbed back into the capillary network. However excess fluid does need to be moved away.​

This fluid enters small, blind ended, lymphatic vessels. ​

The lymph vessels form a network throughout the body and drain back into the bloodstream via 2 ducts that join veins close to the heart.

What is oedema?

accumulation of excess tissue fluid

a failure to return excess interstitial fluid is oedema

edema is the swelling of ankles and feet

What does the lymph system contain?

jugular trunk

right lymphatic duet

brachiocephalic vein

bronchomediastinal trunk

intercostal trunk

internal jugular vein

thoracic duet

subclavian trunk

thoracic duct

intestinal trunk

lumbar trunk

lymphatic vessels

What are the main locations for the lymphatic system?

The main locations for fluid return to blood - right lymphatic duct and thoracic duct on left subclavian vein

This is because blood pressure is lowest here

What is lymph movement like?

Action of skeletal muscles

Respiratory movements

Smooth muscle in larger lymphatic vessels

Valves in lymphatic vessels