2.7.2Additional lessons
Identifying Blood Vessels — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 35 of 142
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.
Part 1 of 5Structure and Function
Each vessel has a wall structure that suits the pressure of the blood it carries.
Artery
- Artery Thick wall with muscle and elastic fibres and a narrow lumen;
- it carries blood away from the heart at high pressure.
Vein
- Vein Thin wall with little muscle and a wide lumen;
- it returns blood to the heart at low pressure and contains valves.
Capillary
- Capillary Wall of a single endothelial cell and a lumen just wide enough for one red blood cell;
- this is where exchange happens.
Elastic fibres
- Elastic fibres Artery walls stretch with each heartbeat and recoil afterwards, which smooths and maintains the flow of blood.
Valves
- Valves Pocket-shaped flaps in veins close if blood tries to flow backwards, so flow towards the heart is one-way.
| Feature | Artery | Vein | Capillary |
|---|---|---|---|
| Wall thickness | Thick | Thin | One cell thick |
| Lumen | Narrow | Wide | Very narrow |
| Pressure | High | Low | Falls along length |
| Valves | Absent | Present | Absent |
| Direction | Away from heart | To heart | Between arteries and veins |
Part 2 of 5Identifying Vessels in Sections
1
Look first at the wall: a thick wall with a clear layer of muscle and elastic tissue points to an artery.
2
Check the lumen shape: arteries keep a rounded lumen, whereas the thin wall of a vein often collapses to an irregular shape.
3
Compare the size of the lumen with the thickness of the wall; a small lumen inside a thick wall is an artery.
4
If the wall is only one cell thick and a red blood cell fills the lumen, the vessel is a capillary.
5
Remember that arteries and veins usually lie side by side, so the thicker one is the artery.
Part 3 of 5Measuring and Magnifying
Measuring and Magnifying
Magnification
- Magnification Magnification equals the image size divided by the actual size, measured in the same units.
Scale bar
- Scale bar A scale bar on a micrograph lets you calculate the real size of a structure by proportion.
Drawing
- Drawing Draw clear, unshaded lines and label the lumen, wall and any layers you can see.
Pulmonary vessels
- Pulmonary vessels The pulmonary artery carries deoxygenated blood, so an artery is not always oxygenated blood.
Part 4 of 5Worked Example
Question
- A micrograph shows an artery with a diameter of 45 mm.
- The real diameter is 3 mm.
- Calculate the magnification, and the real width of a wall that measures 12 mm on the image.
- Magnification = image size ÷ actual size = 45 mm ÷ 3 mm = 15.
- Actual size = image size ÷ magnification = 12 mm ÷ 15 = 0.8 mm.
Answer
- Magnification ×15;
- real wall thickness 0.8 mm.
Part 5 of 5Exam Checklist & Tips
2.7.2 – Key Points for the Exam
- Lumen The central space inside a blood vessel through which blood flows.
- Endothelium The single inner layer of flat cells lining all blood vessels.
- Elastic fibres Fibres in artery walls that stretch and recoil to maintain blood pressure.
- Capillary bed A network of capillaries where exchange with tissue fluid occurs.
Common Mistakes
- Stating that all arteries carry oxygenated blood; the pulmonary artery carries deoxygenated blood.
- Describing a vein as having a narrow lumen; veins have a wide lumen compared with arteries.
- Writing that capillaries have valves or muscle; they have neither.
- Forgetting units when calculating magnification, which should cancel to give a ratio.
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