2.7.1Additional lessons
Blood Vessels — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 34 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 5Types of Blood Vessel
Arteries
- Arteries Carry blood away from the heart at high pressure, with thick walls and a narrow lumen.
Arterioles
- Arterioles Small branches of arteries whose muscle controls how much blood reaches the capillary beds.
Capillaries
- Capillaries Tiny vessels with walls one cell thick that form the exchange surface between blood and tissues.
Venules
- Venules Small vessels that collect blood from capillaries and join into veins.
Veins
- Veins Carry blood towards the heart at low pressure, with thinner walls, a wide lumen and valves.
| Feature | Artery | Capillary | Vein |
|---|---|---|---|
| Wall thickness | Thick | One cell thick | Thin |
| Lumen | Narrow | Very narrow | Wide |
| Valves | No | No | Yes |
| Blood pressure | High | Falling | Low |
Part 2 of 5Adaptations
Adaptations
Artery wall
- Artery wall Thick layers of elastic fibres and muscle withstand high pressure and recoil to keep blood flowing between heartbeats.
Capillary wall
- Capillary wall A single layer of endothelium gives a short diffusion distance, and gaps in some capillaries let plasma leak out as tissue fluid.
Capillary lumen
- Capillary lumen A lumen so narrow that red blood cells pass in single file slows flow and increases contact time for exchange.
Vein valves
- Vein valves Valves prevent backflow of blood, while skeletal muscle contraction squeezes veins to push blood toward the heart.
Part 3 of 5Identifying Vessels and Pulse
1
In a micrograph, the thick wall and small lumen show an artery, whereas a thin wall and large lumen show a vein.
2
Arteries often appear round because their walls are strong, while veins often look collapsed or irregular.
3
The pulse is the stretch and recoil of arteries caused by each contraction of the left ventricle.
4
It is measured at the radial artery in the wrist or the carotid artery in the neck.
5
Counting pulses for 60 seconds, or for 30 seconds and doubling, gives the heart rate in beats per minute.
Part 4 of 5Worked Example
Question
- A student counts 38 pulses in 30 seconds at the radial artery.
- Calculate the pulse rate in beats per minute.
- The count was taken over 30 seconds, which is half a minute.
- Multiply the count by 2 to scale it to 60 seconds.
- 38 × 2 = 76.
Answer The pulse rate is 76 beats per minute.
Part 5 of 5Exam Checklist & Tips
2.7.1 – Key Points for the Exam
- Artery A vessel that carries blood away from the heart.
- Vein A vessel that carries blood towards the heart.
- Capillary A very small vessel where exchange between blood and tissues occurs.
- Lumen The central space inside a blood vessel.
- Tissue fluid Fluid that leaks from capillaries and surrounds the cells, enabling exchange.
Common Mistakes
- Assuming arteries always carry oxygenated blood; the pulmonary artery carries deoxygenated blood.
- Saying veins have thick muscular walls; their walls are thin.
- Forgetting that valves occur in veins and not in arteries.
- Saying capillaries have valves or thick walls, when their walls are a single cell thick.
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