1.1Unit 1: Lifestyle, Transport, Genes and Health
SNAB The Circulatory System — IAL Edexcel Linear Revision Notes & Topical Questions
10 min read 13 parts Lesson 2 of 29 1 quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
1.1 The Circulatory System — IAL EDEXCEL LINEAR notes: Explain why large organisms need a mass transport system and relate the structure of the heart and vessels to the cardiac cycle, atherosclerosis and blood clotting.Single-celled organisms — they gain oxygen and glucose direct…
- Mammals have a double circulation
- Water is a medium
- Hydrogen bonds
- Closed circulation
- Vessels into the heart
- Vessels out of the heart
Part 1 of 11The need for a circulatory system
The need for a circulatory system
Single-celled organisms
- Single-celled organisms they gain oxygen and glucose directly from their surroundings by diffusion over short distances.
Large organisms
- Large organisms many cell layers make diffusion distances too great and their high energy needs require fast delivery of reactants.
- Exchange surfaces such as the lungs and digestive system are therefore connected to a mass transport system.
Mass transport
Mass transport bulk movement of gases or liquids in one direction, usually through vessels and tubes.
- It brings substances quickly from one exchange site to another.
- It maintains diffusion gradients at exchange sites and between cells and their surroundings.
- It supplies reactants and removes waste products so cells work effectively.
Mammals have a double circulation
- Mammals have a double circulation blood travels in two separate circuits, pulmonary and systemic.
Part 2 of 11Water as a transport medium
Water is a medium
- Water is a medium all metabolic reactions occur in it and all substances are transported in it.
Dipole
Dipole uneven sharing of electrons in the O–H covalent bonds that gives oxygen a weak negative charge and hydrogen a weak positive charge.
- A molecule with one negative and one positive end is polar.
Hydrogen bonds
- Hydrogen bonds they form between the positive and negative regions of adjacent water molecules.
- Hydrogen bonds are weak and constantly break and reform, so water molecules flow past each other as a liquid.
Cohesion
Cohesion attraction of water molecules to each other.
- Adhesion is hydrogen bonding of water to other molecules and surfaces, so water flows easily and pulls other water molecules along.
Solvent
- Solvent polar water dissolves ions and polar covalent substances (glucose).
- (sodium, chloride)
- The positive parts of water surround negative particles and the negative parts surround positive particles, so the particles separate and dissolve.
- Dissolved solutes are more chemically reactive, so reactions occur in cells and metabolites are transported efficiently.
Part 3 of 11Structure of the mammalian heart
Structure of the mammalian heart
Closed circulation
- Closed circulation blood is always contained within vessels, unlike an open system where blood bathes the organs.
Double circulation
- Double circulation blood passes through the heart twice in one complete circuit.
- The right side pumps deoxygenated blood to the lungs (pulmonary circulation).
- The left side pumps oxygenated blood at high pressure around the body (systemic circulation).
Heart
- Heart a hollow muscular organ of about 300 g in the chest cavity, protected by the tough fibrous pericardium.
- It has two atria above and two ventricles below.
- The septum is a muscular wall that stops blood mixing between the two sides.
- Coronary arteries on the surface supply the heart muscle with blood.
Vessels into the heart
- Vessels into the heart the vena cava brings blood from the body and the pulmonary vein brings blood from the lungs.
Vessels out of the heart
- Vessels out of the heart the pulmonary artery takes blood to the lungs and the aorta takes blood to the body.
Part 4 of 11Heart valves
| Valve | Position |
|---|---|
| Tricuspid (atrioventricular) | Between right atrium and right ventricle |
| Bicuspid (atrioventricular) | Between left atrium and left ventricle |
| Pulmonary (semilunar) | Between right ventricle and pulmonary artery |
| Aortic (semilunar) | Between left ventricle and aorta |
Opening
- Opening a valve opens when the pressure of blood behind it is greater than the pressure in front.
Closing
- Closing a valve closes when the pressure in front is greater than the pressure behind, which prevents backflow.
Valve tendons (cords)
- Valve tendons (cords) they attach the valves to the heart wall and stop them turning inside out under high pressure.
Part 5 of 11Blood vessels
| Feature | Artery | Vein | Capillary |
|---|---|---|---|
| Function | Carries blood away from the heart at high pressure | Returns blood to the heart at low pressure | Exchanges substances with cells |
| Lumen | Narrow, which helps maintain high pressure | Wide, which reduces friction and returns blood at an adequate speed | Very narrow, so red cells pass in single file and diffusion has more time |
| Wall | Thick smooth muscle and elastic tissue; collagen outer layer | Thin muscle and elastic layer because pressure is low | One layer of endothelial cells, so the diffusion distance is short |
| Valves | None | Present, to prevent backflow | None |
| Pulse | Present, as walls stretch with each heartbeat | Absent | Absent |
Artery endothelium
- Artery endothelium it is smooth, folded and one cell thick so that it reduces friction and expands under pressure.
- Smooth muscle strengthens the wall and can constrict to narrow the lumen and divert blood flow, for example away from the gut during exercise.
- Elastic tissue stretches and recoils to even out pressure fluctuations.
- Collagen in the outer wall protects against over-stretching.
Arterioles and venules
- Arterioles and venules arterioles carry blood from arteries into capillaries and venules carry blood from capillaries into veins.
Capillary pores
- Capillary pores gaps between wall cells let plasma leak out to form tissue fluid and let white blood cells squeeze out to fight infection.
Part 6 of 11The cardiac cycle
1Cardiac cycle
Cardiac cycle the series of events in one heartbeat, with contraction (systole) and relaxation (diastole) in a continuous cycle.
2Volume and pressure
- Volume and pressure contraction decreases chamber volume and increases pressure, and relaxation does the opposite.
1Atrial systole
- Atrial systole atrial walls contract, atrial volume falls and pressure rises above ventricular pressure, forcing the AV valves open and blood into the ventricles.
2Ventricular systole
- Ventricular systole ventricular volume falls and pressure rises above atrial pressure, so the AV valves close.
3
Ventricular pressure then rises above aortic and pulmonary artery pressure, so the semilunar valves open and blood leaves the heart.
4Diastole
- Diastole ventricular pressure falls below arterial pressure so the semilunar valves close, and both chambers are relaxed.
5Filling
- Filling blood returns via the vena cava and pulmonary vein, atrial pressure exceeds ventricular pressure, the AV valves open and blood flows passively into the ventricles.
Part 7 of 11Interpreting the left-heart pressure graph
| Stage | Events |
|---|---|
| Atrial systole (A–B) | Atrial pressure rises and forces blood into the ventricle with the AV valve open |
| Start of ventricular systole (B) | Ventricular pressure exceeds atrial pressure so the AV valve shuts |
| Ventricular systole (C) | Ventricular pressure exceeds aortic pressure so the aortic valve opens and blood enters the aorta |
| Start of diastole (D) | The emptied ventricle relaxes, pressure falls below aortic pressure and the aortic valve closes |
| Early diastole (D–E) | Ventricular pressure keeps falling while blood from the pulmonary vein raises atrial pressure |
| Diastole (E) | Atrial pressure exceeds ventricular pressure so the AV valve opens |
| Late diastole | The ventricle expands and both chambers fill slowly, so pressure rises gradually |
Heart rate
- Heart rate it is calculated as 60 divided by the duration of one cardiac cycle in seconds.
Cardiac output
Cardiac output stroke volume × heart rate.
Part 8 of 11Investigating heart rate with Daphnia
1Factors affecting heart rate
- Factors affecting heart rate drugs, sex, weight, height, temperature, diet and dehydration.
- (caffeine, alcohol)
- Only the factor being tested varies and all other variables are controlled.
2Daphnia
- Daphnia a small aquatic invertebrate with a transparent body, so its heart is visible under a light microscope.
1
Prepare five caffeine solutions of different concentrations (serial dilution) and a distilled water control.
2
Place pond water and three drops of the solution in the well of a cavity slide.
3
Transfer a large Daphnia to the slide with a pipette and view it under low power.
4
Find the heart on the dorsal side above the gut and in front of the brood pouch.
5
Count heartbeats for 20 seconds and multiply by three to give beats per minute.
6
Return the Daphnia to the stock culture and repeat with at least five other individuals.
7
Repeat for each concentration and plot mean heart rate (y) against concentration (x).
Result
- Result heart rate shows a positive correlation with caffeine concentration.
Ethics
- Daphnia cannot consent or express pain, so harm is minimised.
- Handle animals gently and keep examination short.
- Return animals promptly to the holding tank.
- Avoid extreme temperatures or very strong solutions.
Part 9 of 11Atherosclerosis
- Atherosclerosis progressive hardening of arteries as atheroma plaques form beneath the endothelium.
1
The endothelium is damaged, for example by high blood pressure, certain cholesterol types, smoking, diabetes, obesity or age.
2
An inflammatory response occurs and macrophages accumulate in the damaged area.
3
Lipids and cholesterol clump with macrophages under the endothelium as fatty streaks, and platelets add to the deposit.
4
The collection forms a plaque called an atheroma, which narrows the lumen, restricts blood flow and raises blood pressure.
5
The plaque calcifies and hardens, which reduces elasticity of the artery wall and raises blood pressure further.
Part 10 of 11Blood clotting and cardiovascular disease
1
A damaged vessel releases the protein thromboplastin.
2
Thromboplastin and calcium ions from plasma trigger conversion of soluble prothrombin into the enzyme thrombin.
3
Thrombin catalyses conversion of soluble fibrinogen into insoluble fibrin.
4
Fibrin fibres mesh together, trapping platelets and red blood cells to form a clot.
Blood clotting and cardiovascular disease
Function of clotting
- Function of clotting it prevents blood loss and pathogen entry and forms a scab under which healing occurs.
Atheroma and clots
- Atheroma and clots a plaque can rupture through the endothelium, leaving a rough surface that triggers thrombosis.
- A clot can block the artery completely or dislodge and travel to other vessels.
Stroke
Stroke sudden loss of brain function when a clot blocks the arteries supplying the brain, so cells cannot respire to make ATP (ischaemic stroke).
Heart attack (myocardial infarction)
- Heart attack (myocardial infarction) a clot in a coronary artery stops oxygen reaching heart cells,
- so they cannot make ATP, cannot contract and may die.
- Symptoms include chest pain, shortness of breath and sweating.
Deep vein thrombosis
- Deep vein thrombosis a clot forms in a deep vein, most commonly in the legs, after prolonged inactivity, in old age or with some medications.
Part 11 of 11More on this topic
1Heart
- Heart it is a four-chambered double pump with the right side serving the lungs and the left side serving the body.
2Atherosclerosis
- Atherosclerosis endothelial damage, an inflammatory response, accumulation of macrophages, cholesterol and platelets,
- and plaque formation raise blood pressure.
3Consequences
- Consequences a thrombus can cause a heart attack, a stroke or deep vein thrombosis.
Key terms
| Term | Meaning |
|---|---|
| Mass transport | Bulk movement of gases or liquids in one direction through vessels. |
| Dipole | A molecule with an uneven distribution of charge, such as water. |
| Systole | Contraction phase of the cardiac cycle. |
| Diastole | Relaxation phase of the cardiac cycle. |
| Atheroma | Plaque of cholesterol, lipids, macrophages and platelets under the artery endothelium. |
| Thrombin | Enzyme that converts soluble fibrinogen into insoluble fibrin. |
| Cardiac output | Volume of blood pumped by a ventricle per minute, equal to stroke volume multiplied by heart rate. |
| Thrombosis | Formation of a blood clot. |
Avoid these mistakes
1
Saying capillaries have cell walls — their walls are a single layer of endothelial cells.
2
Saying the tricuspid valve is on the left — the tricuspid valve is on the right and the bicuspid on the left.
3
Saying valves open and close by themselves — they move passively because of pressure differences.
4
Confusing prothrombin and thrombin — prothrombin is the inactive protein and thrombin is the enzyme that converts fibrinogen into fibrin.
Marked practiceQuizzes for this lesson
Last updated:
\n