8 · Transport in Mammals
Cambridge A Level Biology — Full F-drive source: 8 · Transport in Mammals — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions
5 min read 8 parts Lesson 21 of 21 Unit quiz
Lesson summary
8.0 Overview: Transport in Mammals (Part 1) Plasma, Tissue Fluid and Lymph — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe plasma, how tissue fluid forms and returns, and the role of the lymphatic system.Appearance — a straw-coloured liquid forming about 55…
- Arterial end
- What stays
- Venous end
- Proportion returned
- Factors that alter formation
- Lymph capillaries
Part 1 of 6Plasma and its composition
Appearance
- Appearance a straw-coloured liquid forming about 55 per cent of blood.
Water
- Water it is 95 per cent water, a good solvent that dissolves and transports substances.
Solutes
- Solutes glucose, amino acids, ions, urea, hormones, carbon dioxide as hydrogencarbonate, and plasma proteins such as albumin and fibrinogen.
Part 2 of 6Formation of tissue fluid
Leakage
- Leakage as blood passes through capillaries, some plasma leaks out through gaps in the walls to surround body cells.
Arterial end
- Arterial end hydrostatic pressure is high (about 4.8 kPa) because of the heart's pumping, which forces water and small solutes out.
What stays
- What stays large proteins and red cells stay in the blood.
- Water potential in the capillary is therefore lower than in the tissue fluid.
Part 3 of 6Return of fluid
1Venous end
- Venous end the volume of fluid is lower and the blood is further from the heart, so hydrostatic pressure is reduced.
2Osmosis
- Osmosis the solute concentration gradient stays the same, so water flows back into the capillary by osmosis.
3Proportion returned
- Proportion returned about 90 per cent returns;
- the rest drains into lymph capillaries and goes back to veins near the heart.
4Factors that alter formation
- Factors that alter formation blood pressure, plasma protein concentration and lymph drainage.
- Low plasma protein causes oedema.
Part 4 of 6Role of tissue fluid
- Exchange
- cells exchange nutrients and wastes with blood via tissue fluid.
- Oxygen and glucose diffuse in.
- Carbon dioxide and urea diffuse out.
Part 5 of 6Lymphatic system and pressure values
Lymphatic system and pressure values
Lymph capillaries
- Lymph capillaries they are blind-ended and have valves so lymph flows in one direction.
Movement
- Movement pressure from nearby muscles and breathing movements move the lymph.
Immune role
- Immune role lymph nodes contain lymphocytes that respond to pathogens.
Typical pressures
- Typical pressures hydrostatic pressure falls from about 4.8 kPa (arterial end) to about 1.5 kPa (venous end).
- The osmotic pull of plasma proteins is roughly 3.3 kPa.
- Net outward pressure at the start is positive and net inward pressure at the end is negative.
Oedema
- Oedema fluid that fails to return, as with low plasma protein, accumulates in the tissues.
Part 6 of 6More from the specification
More from the specification
Artery wall histological structures
- Artery wall histological structures arterial blood vessels possess thick muscular walls composed of elastic fibers and collagen surrounding a narrow lumen.
Smooth muscle in vascular regulation
- Smooth muscle in vascular regulation layers of vascular smooth muscle fibers contract or relax to control lumen diameter and regulate regional blood flow.
Double circulatory pulmonary circuit
- Double circulatory pulmonary circuit mammalian cardiovascular systems separate pulmonary circulation to the lungs from systemic circuits supplying oxygenated blood across peripheral organs.
Functional structures of blood vessels
- The circulatory system comprises specialized blood vessels: arteries, arterioles, capillaries, venules,
- and veins, each composed of tailored tunica layers to withstand or regulate hydrodynamic pressure.
Artery wall adaptations
- Arteries carry blood away from the heart under high systolic pressure;
- their walls possess a relatively narrow lumen, a thick layer of smooth muscle to regulate flow, elastic fibres for recoil,
- and an outer tunica externa of tough collagen fibres.
Vein characteristics and low pressure
- Veins have a relatively large lumen, thinner smooth muscle and elastic layers,
- and internal semilunar valves to maintain unidirectional venous return towards the heart.
Pulmonary and systemic circulation
- Pulmonary blood vessels transport deoxygenated blood from the heart to the lungs and return oxygenated blood to the left atrium, operating at lower hydrostatic pressures than systemic vessels.
Circulatory system
- Blood vessels, a pump and valves transporting blood around the body.
Smooth muscle
- Involuntary muscle that narrows or widens airways.
Tunica media
- The middle layer of the wall of a blood vessel containing muscle and elastic fibres.
Vessel
- A long tube formed from dead xylem cells.
Collagen
- A protein in skin, gums and bones that needs vitamin C to form.
Artery
- Vessel carrying blood away from the heart at high pressure.
Key terms
| Term | Meaning |
|---|---|
| Plasma | The liquid part of the blood, about 95 per cent water. |
| Tissue fluid | Fluid that surrounds cells, formed from plasma leaking out of capillaries. |
| Hydrostatic pressure | Pressure of blood that forces fluid out of capillaries. |
| Lymph | Tissue fluid drained into lymph capillaries. |
| Lymph node | A structure containing lymphocytes that filters lymph. |
| Oedema | Accumulation of excess tissue fluid. |
Avoid these mistakes
1
Saying tissue fluid contains red blood cells or large proteins — they stay in the blood.
2
Saying all tissue fluid returns directly to the capillary — about 10 per cent goes into lymph.
3
Saying oedema is caused by high plasma protein — low plasma protein causes it.
4
Saying the solute gradient changes along the capillary — it stays the same; hydrostatic pressure falls.
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