By the end of this lesson
- List substances carried in plasma.
- Trace substances between source and destination.
- Explain heat distribution by blood flow.
BIG QUESTION
How does plasma connect lungs, gut, liver, kidneys, glands and every tissue?
Dissolved and dispersed substances travel in the bulk flow of plasma.
Plasma carries materials between organs
Digested glucose and amino acids travel from the small intestine to the liver and body cells. ureaA nitrogen-containing waste product made in the liver from excess amino acids and removed by the kidneys in urine. travels from the liver to kidneys for excretion.
hormoneA chemical messenger made by an endocrine gland and carried in the blood plasma to target organs, where it causes a response. move from endocrine glands to target organs.
Carbon dioxide travels mainly in solution as ions
Most carbon dioxide entering blood is converted to hydrogencarbonate ions and carried in plasma; smaller amounts are dissolved or bound to haemoglobin.
At the lungs, these forms are converted back so carbon dioxide can diffuse into alveoli.
Moving blood redistributes heat
Metabolically active tissues release heat. Blood transfers thermal energy around the body and toward skin, where loss can be adjusted by blood flow.
Plasma also carries ions, antibodies and many proteins beyond the minimum specification list.
Plasma cargo routes
A complete answer can state source and destination.
| Substance | Important source | Destination/role |
|---|---|---|
| Carbon dioxide | Respiring tissues. | Lungs for exhalation. |
| Glucose/amino acids | Small intestine. | Liver and body cells. |
| Urea | Liver. | Kidneys. |
| Hormones | Endocrine glands. | Target organs. |
| Heat energy | Active tissues. | Other tissues/skin. |
Language that earns precision
- urea
- Nitrogenous waste made in the liver from excess amino acids.
- hormone
- Chemical messenger carried in blood to target cells.
- hydrogencarbonate ion
- Main form in which carbon dioxide is transported in plasma.
Common misconceptions
Claim: Plasma transports only nutrients.
Correction: It also carries wastes, hormones, carbon dioxide and heat.
Claim: All carbon dioxide is carried by red blood cells.
Correction: Most is transported in plasma as hydrogencarbonate ions.
Claim: Urea is made in kidneys.
Correction: It is made in the liver and excreted by kidneys.
Match the answer to the command word
Match each named substance to source or destination.
Do not say heat is a molecule dissolved in blood; thermal energy is transferred.
Recall, apply, then justify
Describe how plasma transports five named materials.
Hint
Use CO₂, food, urea, hormones and heat.
Suggested marking points
- Carries carbon dioxide from tissues to lungs.
- Carries digested food from intestine to cells/liver.
- Carries urea from liver to kidneys.
- Carries hormones from glands to targets.
- Distributes heat energy from active tissues.
Explain why urea concentration may be higher in blood entering a kidney than leaving it.
Hint
The kidney removes a waste.
Suggested marking points
- Urea is carried in plasma into the kidney.
- Kidney filtration/excretion removes some urea into urine.
Explain why reduced plasma flow can disrupt several organ systems at once.
Planning hint
One medium carries many substances.
What a strong design includes
- Nutrient delivery to cells decreases.
- Carbon-dioxide and urea removal decreases.
- Hormone delivery to targets slows.
- Heat distribution changes.
- Lower flow can reduce concentration gradients at exchange tissues.
- Multiple organs depend on the same circulating medium.