How Do Tissues Combine to Form Organs?
- An organ isn't defined by size or shape, but by coordination between multiple tissues.
- Each tissue contributes a distinct role that supports the organ’s overall job.
- This structure–function link is important because if one tissue fails, the entire organ is affected.
Definition
Organ
A structure made of two or more tissues working together to perform a specific function.
Example
The heart pumps blood only because several tissues interact in a precise pattern.
What Tissues Make Up an Organ?
Definition
Tissue composition
The specific arrangement of tissues inside an organ that enables it to function.
- Most organs use a core set of tissue types arranged in predictable ways.
- The table below shows how different tissues contribute to organ function.
| Tissue Type | What It Contributes to an Organ |
|---|---|
| Muscle tissue | Movement, pumping, constriction |
| Nervous tissue | Control, coordination, communication |
| Epithelial tissue | Protection, lining surfaces, forming barriers |
| Connective tissue | Support, structure, binding, transport |
Common Mistake
- Students sometimes think organs are made of only one tissue because that tissue appears most clearly.
- In reality, all organs contain multiple tissues.
How Does Tissue Arrangement Create Organ Function?
- Tissues are arranged deliberately, not randomly.
- For example, in the stomach:
- Muscle tissue churns food
- Epithelial tissue protects the lining
- Nervous tissue coordinates contractions
- Connective tissue holds everything together
- This specific layout allows the stomach to digest food efficiently.
- If the tissue arrangement changed, the organ would lose function.
Tip
- When in doubt, always ask: What is the organ’s job, and which tissues are needed to achieve it?
- This will help you decode unfamiliar organs quickly.
Why Do Organs Have Specialised Shapes?
- By now it should be clear that form follows function is a recurring theme.
- Organs are no different, for example:
- The heart’s chambers optimise blood flow direction.
- The lungs’ branching structure maximises gas exchange surface area.
- The small intestine’s folds and villi increase absorption efficiency.
- These shapes develop during growth and are supported by connective tissues that give strength and flexibility.
How Do Organs Maintain Their Structure Over Time?
Definition
Structural integrity
The ability of an organ to hold its shape and continue functioning under stress.
- Organs face constant forces: pressure, movement, chemical exposure, stretching.
- They maintain structure using:
- Connective tissue (collagen for strength, elastin for flexibility)
- Continuous repair from stem cells
- Regulation by hormones and the nervous system
- Some organs, like the skin and intestine, repair quickly.
- Others, like the brain, have limited repair because of highly specialised cells.
Common Mistake
- Students often assume all organs regenerate at the same speed.
- Regeneration depends on cell type, blood supply, and role within the body.
Why Can Some Organs Be Transplanted and Others Cannot?
- Some organs tolerate transplantation because they can survive brief periods without blood supply and resume function when reconnected.
- The kidney, liver, and heart are all examples of this.
- Other organs, such as the brain, depend on extremely fragile neural connections that cannot be repaired once cut.
- Immune rejection also limits transplantability.
Tip
Organs with strong connective tissue frameworks or simpler functions tend to be more transplantable.
Self review
- What defines an organ?
- Why must organs contain more than one tissue type?
- How does tissue arrangement determine an organ’s function?
- Why is shape essential for organ performance?
- Which tissues help organs maintain long-term structural integrity?
- Why are some organs transplantable while others are not?
