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| Transportation in Earthworm |
To make it easier to understand, let’s break
down the general structure and function of this system.
Overview of the Circulatory System
An earthworm has:
- Longitudinal blood vessels
(running along the body length)
- Transverse vessels (connecting
different parts)
- 4 to 5 pairs of hearts (aortic arches)
- Several smaller vessels for circulation
Together, these components maintain a steady
flow of blood and ensure that nutrients and oxygen reach every part of the
body.
Main Blood Vessels
in Earthworm
1. Dorsal Blood
Vessel
The dorsal vessel runs along the top
(mid-dorsal line) of the body, just above the digestive canal.
Key features:
- Thick and muscular walls
- Contracts rhythmically from back to front (peristaltic
movement)
- Contains valves that prevent backward flow of blood
- Acts mainly as a collecting vessel
It collects blood from:
- Intestine
- Body wall
- Excretory organs (nephridia)
In the first 14 segments, it also acts as a distributing
vessel, sending blood to the front part of the body and to the hearts.
2. Ventral Blood
Vessel
The ventral vessel lies below the
digestive tract and runs along the entire body length.
Key features:
- Functions as a distributing vessel only
- Blood flows from front to back
- Does not contain valves
- Gives off small branches to supply blood to each body segment
It delivers blood to:
- Body wall
- Septa (dividing walls between segments)
- Nephridia
3. Sub-Neural Blood
Vessel
The sub-neural vessel is located below
the nerve cord and extends from the 14th segment to the rear end.
Key features:
- Collects blood from the nerve cord and lower body wall
- Blood flows backward
- Connects with the dorsal vessel through commissural vessels
At the 14th segment, it splits into two lateral
oesophageal vessels.
4. Supra-Oesophageal
Blood Vessel
This vessel is found between the dorsal
vessel and the oesophagus, extending from the 9th to the 13th segment.
Key features:
- Connects with the ventral vessel through special hearts
(latero-oesophageal hearts)
- Plays a role in maintaining blood circulation in the anterior
region
Hearts (Aortic
Arches)
Earthworms have 4 to 5 pairs of hearts,
depending on the species.
Location: Between the 7th and
13th segments
Function:
- Pump blood from the dorsal vessel to the ventral vessel
- Ensure continuous circulation
Special valves at the junctions prevent the
backward flow of blood, keeping circulation efficient.
Role of Valves in
Blood Flow
Valves are essential for controlling the
direction of blood flow.
They are present in:
- Dorsal vessel
- Hearts (aortic arches)
- Junctions of major blood vessels
These valves ensure that blood moves in one
direction and does not flow backward.
Earthworm blood has some unique features:
- Bright red color due to
dissolved hemoglobin in plasma
- Contains colorless, nucleated blood cells (corpuscles)
Unlike humans, hemoglobin is not inside
cells—it is freely dissolved in the plasma.
How Nutrients Are
Distributed
After digestion, nutrients such as:
- Glucose
- Amino acids
are absorbed into tiny blood vessels
(capillaries) in the intestinal wall.
Process:
- Nutrients enter capillaries in the digestive tract
- Capillaries connect to the dorsal vessel
- Blood carries nutrients throughout the body
This system ensures that every cell receives
the energy it needs.
Key Points to
Remember
- Earthworm has a closed circulatory system with
continuous blood flow
- The dorsal vessel collects blood, while the ventral
vessel distributes it
- Hearts (aortic arches) pump blood and
maintain circulation
- Valves play a crucial role in preventing backward flow
- Blood contains dissolved hemoglobin, giving it a red
color
- Nutrients from digestion are quickly transported to all
body parts
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