Sunday, September 4, 2011

Respiratory structures and function in Arthropoda


  • Write a note on book lung of Buthus.

Book lungs are the aerial gas exchange structures of Buthus.
No. & location:-
Buthus  possesses 4 pairs of book lungs situated on the ventro lateral sides in the 3rd, 4th, 5th & 6th mesosomal segments.
Structure:-
Each book lungs consists of 2 parts
  1. Atrial chamber:-
The proximal or ventral part is called the atrial chamber. It is a small compressed air cavity.
 The roof of the atrial chamber bears many slit like openings, set parallel with each other. The chamber communicates with the interlamellar spaces of pulmonary chamber through these openings.
The atrial chamber communicates with the exterior through a slit, called stigma.
  1. Pulmonary chamber:-
The larger, distal or dorsal part is called the pulmonary chamber.
It contains  about 150 vertical folds or lamellae. The lamellae are lying parallel & are arranged like the pages of a book.
Each  lamella is a hollow structure made of 2 thin layers of membrane united at their end.
The outer sides of the lamellae bear ridges & bristles which keeps the adjacent lamellae apart & an inter-lamellar space is left between them for the for the flow of air.

Blood supply:-
The deoxygenated blood from the ventral sinus is sent to each book lung by a diverticulum.
        Then it enters the lamellae at their bases & is oxygenated.
The oxygenated blood from the lamellae is collected into a pulmonary vein which opens into the pericardium.

Mechanism of respiration:-
Dorso-ventral & atrial muscles control the inflow & outflow of air into the atrial chamber.
On contraction of these muscles air flows out through stigmata.
On relaxation of these muscles fresh air enters into the atrial chamber as well as interlamellar spaces.
Exchange of gases takes place through the highly vascularised walls of the lamellae.

  • Write a note on book gills of Limulus.
In xiphosuran, Limulus, the respiratory organs are book-gills.
Location:-
They occur on the posterior wall of the plate like appendages of 5 posterior segments of mesosoma.

Structure:-
They become modified as gills. On each appendage are found some 1500 thin walled lamellae formed by folding of posterior integument.
The lamellae project from the surface & since they lie parallel to each other resembling the pages of a book, they are characteristically known as book gills.

Mechanism of functioning:-
The beating of the appendages causes  a current of water to pass over the book gills.
The blood within the lamellae is separated from the surrounding sea water by only a thin wall. Blood contain respiratory pigment haemocyanin.
 A major ventral blood vessel gives rise to a series of afferent branchial vessels to supply blood to the book gills. After the gas exchange between the water & blood efferent vessels carry oxygenated blood to a large branchio-pericardial vessels leading back towards the heart.

No comments:

Post a Comment