Respiratory & Nervous Systems: Earthworm | Additional Study Material for NEET PDF Download

RESPIRATION

"Cutaneous respiration"

Skin :- Well adapted for cutaneous respiration, it is thin moist, highly vascular. A dense network of capillaries is present.

Normally - Aerobic respiration . But can also live without oxygen for 30 hrs.

Blood Vascular System [B.V.S.]

Closed - Vascular system

True blood vessels present.

Blood - Red colour (haemoglobin present) Hb - dissolved in plasma

R.B.C. - absent (nonchordata) this Hb is knwon as "erythrocruorin" or "inter cellular" Hb.

Dorsal Vessel - "Main blood vessel. from the 3rd to last segment at dorsal side of alimentary canal and it can be seen externally.

Wall of dorsal vessel is muscular and lumen have valves. flow of blood from posterior to anterior side.

Dorsal Vessel :- This function as "Collecting Vessel" from last segment to 14th segment.

- In each segment two pairs of vessels arise from alimentary canal. They are "dorso intestinal vessels". these collect blood from alimentary canal and take blood to dorsal vessel.

- dorsal vessel in anterior part - "distributing vessel"

- 3rd Segment - It gets branched into three branches. They supply blood to the wall of alimentary canal of first
three segments.

- In 3, 4, 5, 6, 8th segment dorsal vessel gives out a pair of vessels. These supply blood to the wall of alimentary canal.

(2) Ventral - vessel - from second to last segment present on the ventral side of alimentary canal.

Wall - non muscular

Valve - absent

Blood flows from - anterior to posterior side

Ventral Vessel - Is a "distributing vessel" in its whole length.

- V.V. in each segment gives out one pair "ventro integumental vessel". These (VIV) supply blood to body wall and related structures.

- septa, nephridia, gonads, etc. get the blood supply.

- After 13th segment V.I.V. supplies blood to the posterior segments.

- After 13th segment a small branch originates from the VIV. This is "septo nephridial" Vessel

This supplies blood to "Septal nephridia" and Inter Seg. septa.

- After 13th segment in each segment one "ventro - intestinal vessel" comes out from V.V. which then supplies blood to alimentary canal.

- V.V. receives blood from dorsal vessel

- the blood comes from dorsal vessel to ventral vessle by 4 pairs of "lateral Hearts".

Hearts :

- 7, 9, 12, 13. lateral hearts (4 pair)

- 12, 13 - "Lateral oesophageal heart"

The hearts are muscular and has valves.

(3) Subneural vessel-

- This is from last segment to 14th segment

- Ventral side of nerve chord

- In 14th segments it branches into two parts

- These are "lateral oesophageal vessel"

Both the branches are situated upto the 2nd segment in the lateral side of alimentary canal.

- S.N.V. and L.O.V. do not have muscular wall.

- They are without valves and blood flows from forward to backwards.

- They act as "collecting vessel" along whole length of animal.

- L.O.V. - Collects blood from walls of alimentary canal and body wall.

- S.N.V. - collects blood only from body wall

- S.N.V. - one pair of commisural vessel comes out from each segment. This supplies blood to "dorsal vessel".

Commisural vessel - Collects blood from "Septa" and Septal nephridia.
From each commisural vessel comes out one "Septo - intestinal vessel". They supply blood to alimentary canal.

Commisural Vessel :- is present at posterior face of septa (intersegmental plates)

(4) "Supra Oesophageal Vessel":-

- In 9-13th segment, on dorsal surface of alimentary canal i.e. on stomach

- collects blood from "gizzard wall". and "Stomach wall".

- In 10th and 11th segment are situated 2 pair of "anterior loops"

- They takes blood from L.O.V. to S.O.V.

- Blood also reaches from L.O.V. to S.O.V. by a dozen loop like ring vessels.

- Blood collected in S.O.V. reach the lateral - oesophageal heart.

From L.O.H. the blood reaches to ventral vessel.

Blood glands :- 3 Pairs of blood glands

- situated on dorsal part of alimentary canal in 4, 5 and 6, segments. They form Hb, blood cell (W.B.C.)

- Leucocytes Hb, blood cell

- Secreted in dorsal vessel.

Lymph glands :-
- On dorsal part of alimentary canal
- from 26th segment to last segment
- 1 (one) pair in each segment
- They form phagocytes and pour them into body cavity.

NERVOUS SYSTEM
Central nervous system :-
(1) Brain ring (2) Nerve cord

(1) Brain ring - This is present around pharynx supra-pharyngeal ganglion in 3rd segment at dorsal surface of pharynx.

- In 4th segment is "sub-pharyngeal ganglion" below the pharynx.

- Nervous strip joins both the two ganglia known as "circum pharyngeal connective"

- A ventral nerve cord comes out from sub-pharyngeal-ganglia. ventral nerve cord extends upto last segment on ventralside of alimentary canal.

- Nerve cord in each segment has one segmental ganglion .

- Ventral nerve cord of Pheretima - double but appears to be single because, it has only one common integument around it.

- 4 giant cells on dorsal surface of nerve cords. these giant cell starts from 4-segment and lasts upto last segment. they are known as "neuro-cords"

This is unique character of Pheretima.

- Pheretima gives rapid - response because of neuro cords.

- All ganglia of Pheretima - formed by fusion of '2 ganglion' in embryonic stage.

Peripheral - nervous system :-
- Supra-pharyngeal ganglia gives out 8-10 pairs of nerves.
- Circum pharyngeal connective - 2 pairs of nerve
- Sub. pharyngeal - 3 pairs of nerves
- Nerve cords - 3 pair nerves in each segment, that arises as:
2 pairs from ganglia and 1 pair directly from nerve cord
- "All nerves" - mixed types of nerves (Sensory + Motor + Adjustor)

Receptor - 3 types.
(1) Epidermal receptors - in epidermis. - tangoreceptors
(2) Buccal receptors - in buccual cavity. - chemoreceptors - ("Olfactory + gustatory)
(3) Photoreceptors- or "ocelli" or"little eyes"

- Maximum in prostomium and peristomium on dorsal side. Each photoreceptor has a large optic cell. Inside optic cell there is a "L" shaped. lens or phaosome.
- A network of nerve fibers is associated to lens. This network is known as "retinella"
- Nerve fibers - combine to form an optic nerve. they take sensory impulse to supra pharyngeal ganglia