Biology topic 1 part 2- Lifestyle, health and risk

Why does the left ventricle have a thicker wall

because it pumps blood at a higher pressure and to the whole body, while the right side of the heart only has to pump a short distance to the lungs

Describe the path of blood through the heart

- Blood enters the right atrium through the vena cava (deoxygenated)

- Blood flows from the right atrium to the right ventricle. The AV valve prevents backflow

- When the right ventricle contracts, blood is forced through the pulmonary artery, which travels to the longs to pick up oxygen. Semi lunar valves prevent backflow.

- Oxygenated blood returns to the heart by the pulmonary vein, into the left atrium

- Blood flows to the left ventricle. Av valve prevents backflow

- The ventricle pumps oxygenated blood around the body via the aorta. Semi lunar valve prevents backflow

What is a double circulatory system

Blood is confined to vessels and passes twice through the heart for each complete circuit of the body

What is a closed circulatory system

Contains a pump, vessels and a medium to transport substances around the body

Why do multicellular organisms need transport systems

They have a low SA:V ratio, so cannot rely on diffusion to supply all their cells and tissues with they need or to remove waste substances, because the diffusion distance is too long

Order of blood vessels from aorta to vena cava

-Oxygenated blood exits the heart through the vena cava

- Arteries carry oxygenated blood

- Arteries branch into arterioles

- Arterioles branch into capillaries which form networks in tissues called capillary beds

- Deoxygenated blood flows through the capillaries into the venules

- These join to form veins

- Blood re enters the heart through the vena cava

What are the layers of blood vessels

Smooth muscle layer, Elastic layer and Endothelium

Smooth muscle layer

contracts to control flow of blood in arteries, arterioles and veins

Elastic layer

Allows the vessels to stretch and recoil in arteries, veins and arterioles

Endothelium

Thin inner lining which is smooth to reduce friction in all vessels.

Arteries

- Carry blood away from the heart

- Narrower lumen to maintain high pressure

- Thick muscular walls and elastic layer alows stretch and recoil with each ventricular contraction to maintain high pressure

- Endothelium is folded to allow stretching to maintain high pressure

Veins

- Carry blood towards the heart

- Wider lumen than arteries, as blood is at a lower pressure

- Thinner layers of muscle and elastic tissue

- Valves to ensure no backflow

- When skeletal muscles contract they compress veins, helping to increase the pressure and push blood along

Capillaries

- Smallest blood vessel, the diameter is the same as a red blood cell

- Site of substance exchange with cells

- Very close to cells, for a short diffusion pathway

- Walls are one cell thick for a short diffusion distance

- Gaps called fenestrations between endothelial cells allow substances to diffuse out between

- Large number of capillaries increase the surface area for gas exchange

What are the gaps between endothelial cells called

Fenestrations

Role of arterioles

Smaller than arteries and form a network throughout the body, they can contract to restrict blood flow and relax to increase blood flow. This allows blood to be directed into different areas according to demand.

What is meant by diastole

relaxation stage of the cardiac cycle when the atria and ventricles are relaxes

What is stroke volume

Volume of blood pumped out at each beat, measured in dm3

What is cardiac output

The volume of blood pumped out by one ventricle of the heart in one minute, measured in dm3 min-1

Cardiac muscle

Made up of cardiomyocytes, which contract without a nervous impulse to stimulate it.

Explain the stages of the cardiac cycle

1) Atrial systole- Ventricles are relaxed and atria contract, this decreases their volume so increases the pressure which forces AV valves open fully, and blood is pushed into the ventricles. Ventricular pressure increases slightly as they fill with blood

2) Ventricular systole- The atria relax, the ventricles contract which decreases their volume and increases the pressure forcing the AV valves closed. When pressure increases enough, the SL valves are forced open and blood is pumped out through the arteries

3) Diastole- Both atria and ventricles are relaxed. The pressure in the arteries is now higher than the ventricles, so SL valves shut. Blood starts to enter the atria through the veins. This starts to increase the pressure in the atria and eventually the pressure exceeds the ventricular pressure, and the AV valves open slightly, and blood begins to passively flow into the ventricles.

The cycle restarts

What is the blood clotting cascade

A series of enzyme controlled reactions in the blood, leading to the formation of a blood clot

Describe the process of the blood clotting cascade

1) Damaged vessel releases a protein called thromboplastin

2) Calcium ions from the plasma, along with thromboplastin, trigger the conversion of soluble prothrombin protein into the enzyme thrombin.

3) Thrombin catalyses the conversion of the soluble protein fibrogen into the insoluble protein fibrin.

4) Fibrin fibres mesh and tangle together, trapping platelets and red blood cells.

Is fibrogen soluble or insoluble

soluble

Is prothrombin soluble or insoluble

soluble

Is fibrin soluble or insoluble

insoluble

What is CVD

A general term used to describe any disease associated with the heart or blood vessels. Most are caused by atheroma formation in the blood vessels.

What is CHD

CHD is a type of CVD when the coronary arteries contain many atheromas which restrict blood flow to the heart muscle. This can lead to myocardial infarction.

What is an atheroma

Fibrous plaque that narrows lumen of arteries

How does an atheroma form

When the endothelium becomes damaged, usually due to high blood pressure, white blood cells and platelets arrive to repair the damage, and clump together with lipids in the blood to form fatty streaks under the lining. Over time, more and more build up and form a fibrous plaque.

How can an atheroma lead to more atheromas

The atheroma partially blocks the lumen of the artery and restricts blood flow, increasing blood pressure. This may lead to more damage of the endothelium.

What CVD is caused by atheromas

- Aneurysm

- Thrombosis

- Angina

What is an aneurysm

The build up of blood behind a blockage causing the artery walls to bulge and weaken, increasing the chance of the wall splitting and internal bleeding

What is thrombosis

The formation of a blood clot due to an atheroma bursting through the endothelium and causing a rough surface. This can cause a blood clot due to the accumulation of platelets

What is angina

The build up of plaque in the coronary arteries, reducing blood flow to certain areas of the heart muscle. This causes a person to anaerobically respire, which can cause pain.

Stroke

Caused by an interruption to the blood supply in the brain. This could be a bleed from a damaged blood vessel or blockage cutting off blood supply

Myocardial Infarction

Caused by blood clots due to atherosclerosis. The walls around a plaque are stiffened, making them more prone to crack. This damage is detected by platelets which trigger the clotting mechanism, which can lead to the blockage of the whole heart vessel. The heart muscle is starved of oxygen and nutrients, leading to a heart attack.

Why is hypertension a risk factor of CVD

Increased risk of damage to the artery walls due to increased friction, which increases the risk of atheromas forming

What is hypertension caused by

Obesity, limited exercise, and excessive alcohol consumption

How do you reduce the risk of hypertension

Reduce alcohol consumption, consume less saturated fat, exercise regularly and maintain a healthy weight

Why is high blood cholesterol a risk factor of CVD

Increases the risk of atheromas because cholesterol is one of the main contributors to the fatty deposits that cause them

How to reduce the risk of high blood cholesterol

Consume less saturated fat and salt, get regular exercise and maintain a healthy weight

How does smoking increase the risk of CVD

- CO binds to haemoglobin so less oxygen can be transported in the blood, as well as antioxidants that protect cells from damage, making the artery walls more susceptible to damage

- Nicotine narrows the artery walls which increases blood pressure. It also stimulates the production of adrenaline, which increases heart rate and blood pressure.

- Chemicals found in smoke can cause damage to the lining of the arteries, causing atherosclerosis

- Has been linked to the reduction of HDL levels

What does HDL cholesterol do

Removes cholesterol from tissues and transports it to the liver for excretion.

What does LDL cholesterol do

Transport cholesterol from the liver to the tissues, including the artery walls, leading to the development of an atheroma

How can stress increase the risk of CVD

Causes the release of adrenaline, increasing heart rate and constricting arteries

Why do the capillaries and arterioles have lower pressure than the arteries

They have a greater surface area , causing more peripheral resistance, slowing the blood down and reducing pressure

What is oedema

Fluid building up in tissues and causing swelling

How is tissue fluid formed

At the arterial end of the capillaries blood is under pressure, forcing fluid and small molecules found in the plasma out through the tiny gaps in the walls of the capillaries into the intercellular space

How is an oedema formed

At the arterial end of the capillaries blood is under pressure, forcing fluid and small molecules found in the plasma out through the tiny gaps in the walls of the capillaries into the intercellular space. The tissue fluid drains into a network of lymph capillaries which returns the fluid to the blood via a lymph vessel, which empties into the vena cava. If blood pressure rises above normal, more fluid may be forced out of the capillaries, causing oedema.

What is a calorie

the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius

How many joules is in one calorie

4.18

How can LDL cholesterol lead to atheroma formation

Triglycerides from our diet combine with cholesterol and proteins to form LDL's which transport cholesterol to body cells. LDL's circulate in the bloodstream and bind to receptor sites on cell membranes . Excess LDL's overload these cell receptor sites resulting in high blood cholesterol levels. This cholesterol may be deposited in artery walls, forming atheromas.

What are apolipoproteins

Protein components of lipoproteins, mostly found in the liver and small intestines.

APOA

Major protein in HDL. Mutations in this gene can lead to reduced HDL levels, increasing risk of CHD

APOB

Main protein in LDL. Mutations result in higher LDL levels and increase the chance of CVD

APOE

Main component of HDL's and VLDL's . Three variations of the gene. APOE4 slows the removal of cholesterol from the blood so may increase chance of CHD

How can antioxidants reduce the risk of CVD

Provide hydrogen atoms that can bind to free radicals in the body. Radicals are very reactive so can cause damage to body cells.

How can wine and fruit juice reduce risk of CVD

Contain useful antioxidants and help prevent platelets from sticking together

How does salt increase the risk of CVD

Causes the kidney to retain more water. More fluid in the blood results in higher blood pressure.

Three drugs used to treat high blood pressure

- ACE inhibitors

- Calcium channel blockers

- Diuretics

ACE inhibitors

Reduce the production of angiotensin II, which causes constriction of blood vessels. Can also reduce the chance of kidney failure in patients with kidney disease.

Calcium channel blockers

Block calcium channels in the muscle cells lining the arteries. Calcium must pass through these channels for muscles to contract, so this reduces constriction of the blood vessel, lowering blood pressure.

Diurectics

act on kidneys to increase excretion of water and sodium. Leads to a decrease in blood plasma volume and cardiac output, decreasing blood pressure

Statins

Inhibits an enzyme involved in LDL cholesterol production by the liver

When are anticoagulant and platelet inhibitory drugs used

When a person is at high risk of CVD

What do anticoagulant and platelet inhibitory drugs do

Reduce platelet aggregation and clotting

Aspirin

Reduces stickiness of platelets

Clopidogrel

Antiplatelet

Risks of aspirin and clopidogrel

Serious bleeding in the gastrointestinal tract