The Heart and Blood Vessels

Describe the circulatory system of mammals

- Pulmonary circulation - right hand side of the heart transports blood from the body along the pulmonary artery to the lungs

- Systemic circulation - left hand side sends oxygenated blood from the lungs to the aorta to the rest of the body

Define oxygenated

- High oxygen conc

- Low carbon dioxide conc

Define deoxygenated

- Low oxygen conc

- High carbon dioxide conc

Why is it an advantage for the human heart to have 2 separate pumps rather than one?

- The right hand side generates more pressure to send blood to the lungs where pressure drops

- When returned to the left hand side of the heart, the left ventricle generates more pressure so the blood can travel around the body to generate a high metabolic rate

How is blood delivered to the heart muscles?

Coronary arteries

Why does the cardiac muscle need a rich supply of blood?

- Needs a good supply of blood for oxygen and glucose for high rates of aerobic respiration to produce lots of ATP for the hearts muscle contraction

What separates both sides of the heart?

Septum

Why are the walls of the left ventricle thicker than the right?

- The left ventricle needs to contract with greater force and generate a higher pressure so that it can pump blood all around the body rather than the lungs only

What is the function of the atrioventricular and semi lunar valves?

- Prevent backflow of blood

- Atrioventricular valves prevent backflow of blood from ventricle to atria

- Semi-lunar valves prevent backflow of blood from arteries to ventricles

What is a cardiac cycle?

One complete contraction and relaxation of the heart

Name and describe the processes in which the heart can produce

Atrial systole - atria contract

Ventricular systole - ventricles contract

Diastole - heart relaxes

Where does blood flow?

From a region of high pressure to a region of low pressure

What happens during diastole?

- The heart relaxes and the atria fill up with blood from the vena cava and the pulmonary vein

- The atrioventricular valves can open due to the increase in pressure in the atria

- Blood can flow from atria to ventricle - this is known as passive filling (no contraction takes place) as pressure in atria is greater than the ventricle

Why are the semi-lunar valves closed during diastole?

- Pressure higher in arteries than the ventricles

Describe atrial systole

- Blood fills the atria from the vena cava and the pulmonary vein

- The atrial muscles contract, further increasing the pressure above that of the ventricles

- This forces open the atrioventricular valves further and blood flows into the ventricles

Describe ventricular systole

- The ventricle muscles contract

- The volume of the ventricles decrease increasing the pressure

- This causes atrioventricular valves to close - ventricular pressure is greater than atrial

- Blood is pushed upwards, towards the arteries to the top of the heart

- This opens the semi-lunar valves and blood flows into the aorta and pulmonary artery

Why do the atrioventricular valves close during ventricular systole?

- Pressure higher in the ventricles than the atria

Why do the semi lunar valves open?

- Pressure higher in the ventricles than the arteries

Why do atria contract with lower force than ventricles?

- They generate a lower force

- The muscle in the atria are thinner than the ventricles so have less forceful contractions

Why do the atrioventricular valves open?

Pressure greater in the atria than the ventricles

Why do the atrioventricular valves close?

Pressure greater in the ventricles than the atria

Why do the semi-lunar valves open?

Pressure in the ventricles greater than the arteries

Why do semi lunar valves close?

Pressure in the arteries greater than the ventricles

What vessels carry blood to and away from the kidneys?

- Renal artery

- Renal vein

What vessels carry blood to and away from the liver?

- Hepatic artery

- Hepatic vein

What are arteries and veins?

They are organs as they are a collection of different tissues which work together for a particular function.

Describe arteries

- Thick walls

- Lots of elastic tissue and some muscle tissue

- Have a coat of single layer endothelium

- relatively small lumen

What is the advantage of the endothelium being smooth in arteries?

- Reduces friction between blood and blood vessel wall

What is the advantage of the elastic tissue in arteries?

- Stretch during systole

- Recoil during diastole

- Reduces fluctuations in pressure and smooths blood flow

Why do arteries closer to the heart have more elastic fibres in their walls than arteries further away from the heart

- Higher blood pressure closer to the heart with large fluctuations

- Pressure drops as blood moves further along due to friction

- Stretch and recoil of elastic tissue in large arteries reduces fluctuations and smooths out blood flow before blood reaches other arteries

Describe arterioles

- Branch from arteries

- Control blood flow to capillaries to different organs

- Lots of muscle tissue

- Thinner than arteries

- Single layer endothelium

Name and describe contraction and relaxation of blood vessels

Vasocontraction - narrow lumen diameter

Vasodilation - widen lumen diameter

Compare the proportions of elastic/ muscle tissue in artery and arteriole walls

- Arteries -> More elastic tissue

- Arterioles -> More muscle tissue

What do veins branch off from?

Venules

Describe veins

- Carry blood at low pressure

- Thin vein walls

- Valves stop backflow - semilunar

- Fewer muscle/ elastic tissue fibres than arteries

- Large lumen

How is blood transported in the veins in the legs?

When the leg muscles contract they push on the veins temporarily raising the pressure in them

Describe rate of blood flow in the capillaries

- Low which gives more time for material exchange

Describe capillaries

- Single layer squamous endothelium gives short diffusion pathway

- Small pores means capillaries are highly permeable

How do most muscles contract?

Impulse travels down nerve tissue

So are neurogenic

How does cardiac muscle contract?

It is myogenic as contractions arise from the cardiac muscle itself

Cardiac cycle 1-3

1 - wave of electrical impulse is sent out from the sinoatrial node

2 - this spreads out through both atria causing them to contract

3 - a band of non conductive tissue prevents the impulse passing directly into the ventricles

Cardiac cycle 4-6

4 - the electrical impulse reaches the atrioventricular node where it is delayed

5 - the delay allows the atria to fully empty the blood into the ventricles before the contract

6 - the atrioventricular node sends out electrical impulses

Cardiac cycle 7-9

7 - after the delay, impulses spread down the ventricles into the bundle of his

8 - the impulse is transmitted to the base (apex) of the ventricles where it is passes up the purkinje fibres

9 - the ventricles contract from the base upwards, blood is forced into the arteries

What is a pulse?

- stretch and recoil of the arteries

What is stroke volume?

volume of blood pumped out of one ventricle per contraction

What is cardiac output?

volume of blood pumped out of one ventricle per minute

How do you calculate cardiac output?

cardiac output (dm3min-1) = stroke volume (cm3) x heart rate (bpm)

How does a larger heart increase stroke volume?

- larger ventricles can fill with a greater volume

- more muscle means stronger contraction and pushes more blood per beat

Describe coronary heart disease

- Layers of fatty material (atheroma) build up inside coronary arteries that supply blood to the heart

- This narrows them and reduces blood flow through them resulting in a lack of O2 to the heart muscle cells

- The atheroma builds over time restricting blood flow causing thrombosis (blood clot formation)

- This can block the coronary artery completely causing myocardial infarction (heart attack)

What is a risk factor?

Something which increases the chance of developing a disease

Name some unavoidable risk factors

- Inheritance

- Gender

- Increasing age

Describe the risk factor smoking

Nicotine acts as a vasoconstrictor which increases blood pressure

Describe the risk factor high blood cholesterol

- Eating lots of saturated fats/ cholesterol leads to high levels of LDL cholesterol in the blood which leads to atheroma

- Statins are used to reduce blood cholesterol levels

- Stents keep open narrowed coronary arteries

Give an overview to blood

A tissue made from a fluid called plasma with suspended substances called red blood cells, white blood cells and platelets

What does blood plasma transport?

- Carbon dioxide from organs to lungs

- Soluble products of digestion from the small intestine to other organs

- Urea from liver to the kidneys

Describe white blood cells

- Fight against microorganisms

- Contain nuclei

- Eg lymphocytes and phagocytes

- antibodies are proteins

Describe platelets

helps blood clot at a wound

Describe red blood cells

- No nucleus

- Contain haemoglobin

- Carries oxygen to respiring tissues

Give the 3 ways in which a red blood cell is structured

- Biconcave shaped

- Vey small

- No organelles

Why are red blood cells very small?

- Every haemoglobin molecule is close to the cell's surface so has a short diffusion pathway for oxygen

- This provides a large SA: volume ratio

Why are red blood cells biconcave disc shaped?

- They have dents to provide a large SA: volume ration

- Oxygen can diffuse quickly in and out of the cell

Why do red blood cells not contain any organelles?

- No ER, nucleus or mitochondria

- Maximises carrying capacity for haemoglobin to carry maximum amount of oxygen

Can red blood cells carry out protein synthesis?

No

- No ER that contain ribosomes for synthesising proteins

- No nucleus that contains genetic code

- No mitochondria to produce ATP

Can red blood cells undergo cell division?

No

- No nucleus for DNA

- No mitochondria to provide ATP

Can red blood cells use active transport?

No

- No mitochondria for ATP production

Describe haemoglobin in detail

- High affinity for oxygen

- Oxygen loads on in high O2 concentrations

- Unloads oxygen in low O2 concentrations

Where does oxygen bind to on a haem group?

Fe2+

Define conjugated

non protein molecule attached to the structure (prosthetic group)

Haem group in haemoglobin

How many polypeptide chains are there in each haemoglobin molecule?

4

How many oxygen molecules can each haemoglobin molecule carry?

4

What is it called when oxygen binds to haemoglobin?

Oxyhaemoglobin

What is haemoglobin?

Protein with quaternary structure

What is cooperative binding?

- Each haemoglobin molecule can bind with 4 oxygen molecules in 4 reversible reactions

- The binding of the first haem group with oxygen changes the tertiary structure and shape of the haemoglobin molecule which uncovers the second haem group binding site, making it more accessible which increases the affinity

- This repeats for the third haem group and this is cooperative binding

- The curve has a sigmodal shape (S shaped)

Describe an oxygen dissociation curve

- partial pressure on the x axis (PO2)

- % saturation on the y axis

- sigmoidal shape

What can an oxygen dissociation curve be affected by for animals?

- Temperature

- pH

- CO2 concentration

this is usually during exercise

Describe the bohr shift on animals

- A temp increases, pH decreases and CO2 concentrations increase

- The curve is displaced to the right

- This facilitates delivery of oxygen to respiring tissues

- Lower affinity for oxygen

What is the importance of the bohr shift during exercise?

- During exercise, blood CO2 conc and temp increases as pH decreases due to the high rate of respiration so the bohr shift occurs

- This decreases the affinity for oxygen

- There is a higher demand for O2 at the respiring tissues to maintain the high rate of resp

- More O2 is released by the haemoglobin to respiring tissues

Lugworms have very high affinities for oxygen

Explain what this means

- Haemoglobin readily binds with O2 to form oxyhaemoglobin even at low PO2 values

- O2 isn't released until the PO2 value is very low

Describe and explain the oxygen dissociation curve of a shrew

- Large SA:vol loses heat very fast

- Very high metabolic rate which replaces lost heat by high rate of resp

- They need a low affinity for oxygen to release the oxygen to respiring tissues easily so the curve is shifted right

Describe the effect of size on the oxygen dissociation curve

- Smaller animals have a lower affinity for oxygen to deliver oxygen to the respiring tissues more easily

- The curve is shifted right

- Larger animals have a higher affinity for oxygen to load oxygen on more easily

-The curve is shifter left

Describe high affinity oxygen

- Usually found in areas of a lack of O2 eg altitude

- Oxygen needs to load onto the haemoglobin more easily

- The curve is shifted left

- Haemoglobin is more saturated at any given pO2 than humans haemoglobin

Describe low affinity oxygen

- Usually in animals with high metabolic rates

- Haemoglobin is released to the respiring tissues more easily

- Curve shifted right

- Haemoglobin is less saturated at any given pO2 than humans haemoglobin

Describe the benefit of cooperative binding

- Easier uptake of O2 in the lungs

- Easier release of O2 in the respiring tissues

What surrounds all body cells?

Tissue fluid

What does tissue fluid provide?

- Water

-Oxygen

- Glucose

- Solutes/ Other nutrients

Why is tissue fluid essential?

- Needed for material exchange between blood and blood cells

Where is tissue fluid formed and reabsorbed(water)?

- Formed at the arteriole end of the capillary

- Water reabsorbed at the venule end of the capillary

How are capillaries suited for their function in tissue fluid formation?

- Pores in walls increases permeability

- Small size + large number gives large SA:vol ratio

- Narrow diameter (1 rbc wide) slows blood flow which increases time for material exchange

Why does the arteriole end of the capillary have a high hydrostatic pressure?

Contraction of the ventricle (left) in ventricular systole

Name and describe the forces involved in formation and reabsorption of tissue fluid

- Hydrostatic pressure - high blood pressure forces solutes and water out of the capillaries

- Osmotic pull - soluble plasma proteins reduce water potential of the blood creating a water potential gradient exerting a pulling force of water back into the capillary

Why do plasma proteins not leave the capillary due to hydrostatic pressure?

Too large to fit through the pores

Describe the arteriole end of the capillary in tissue fluid formation

Hydrostatic pressure is greater than osmotic pull so water and solutes are forced out of the capillaries to form tissue fluid

Describe freshly formed tissue fluid

- High O2, glucose and mineral ion conc

- Substances diffuse into the cells

What happens to waste products of cells? Refer to tissue fluid

- Waste products eg CO2 diffuse out of the cells into the tissue fluid

- They diffuse back into the capillaries along with water at the venule end of the capilaries

What is tissue fluid the site of?

Metabolite exchange

What causes the drop in pressure at the venule end of the capillary?

- loss of fluid from the capillary to the tissue fluid

- friction as blood flows through narrow lumen of capillaries

Describe the venule end of the capillary for tissue fluid

- High osmotic pull due to higher water potential in tissue fluid than the capillary due to plasma proteins which causes a water potential gradient

- Osmotic pull is greater than hydrostatic pressure

- This means water is reabsorbed into the capillaries by osmosis

What happens to the water that isn't absorbed back into the capillaries? How does it get back into the circulatory system?

- Lymphatic system reabsorbs excess water

In 5 points summarise tissue fluid formation

- At the arteriole end of the capillary, the hydrostatic pressure is greater than the osmotic pull (caused by plasma proteins)

- Water, ions and solutes are forced out of the blood in the capillaries into the spaces between cells forming tissue fluid

- The loss of fluid lowers the hydrostatic pressure as the blood approaches the venule end of the capillary

- At the venule end of the capillary, the osmotic pull is greater than the hydrostatic pressure so water is reabsorbed into the capillary by osmosis down a water potential gradient

- Tissue fluid is drained away from cells by the lymph vessels and returned the the circulatory system