Fasciola hepatica part -2nd
Digestive system
Respiration in fasciola
Excretory system -
Flame cell
Nervous system of fasciola
Digestive System of Fasciola Hepatica:
(i) Alimentary Canal:
The oral sucker encloses a ventral mouth which leads into a funnel-
shaped mouth cavity, followed by a round muscular pharynx with thick
walls, and a small lumen. The pharynx has pharyngeal glands. F. indica has
a short muscular pharynx from which arises an oral pouch which is about
half the size of the pharynx. There is a short narrow oesophagus leading
into an intestine which divides into two branches or Intestinal caeca or
crura each running on one side to the posterior end, and ending blindly.
The Intestinal caeca give out a number of branching diverticula in order to
carry food to all parts of the body since there is no circulatory system. The
median diverticula are short and lateral ones are long and branching.
There is no anus. The interior part of the alimentary canal up to the
oesophagus is lined with cuticle and serves as a suctorial fore gut; the
intestine is lined with endodermal columnar epithelial cells. The caceal
epithelium has secretory gland cells.
(ii) Food, Feeding and Digestion:
It feeds on bile, blood, lymph and cell debris. The oral sucker and pharynx
together constitute an effective suctorial apparatus. Digestion is
extracellular, occurs in intestine. The digested food material is distributed by
branching diverticula of intestine to all parts of the body as the
circulatory system is not found in this animal. Thus, the digestive system
functions as a gastro vascular system. In fact, the digested nutrients are
passed into the parenchyma through intestinal diverticula; from parenchyma
they are diffused into the various organs of the body.
Reserve food, mostly in the form of glycogen and fats is stored in the
parenchyma. However, monosaccharide sugars like glucose, fructose, etc.,
are directly diffused into the body of the fluke through general body surface
from the surrounding fluid of the host. The indigestible remains of the food,
if any, are probably said to be ejected through the mouth.
Respiration of Fasciola Hepatica:
Mode of respiration is anaerobic or anoxybiotic. In fact, glycogen is
metabolised to carbon dioxide and fatty acids releasing energy in the form
of heat. The process is completed in following steps:
(i) The glycogen undergoes anaerobic glycolysis to form pyruvic acid,
(ii) The pyruvic acid is decarboxylated to form carbon dioxide and an acetyl
group,
(iii) The acetyl group then combines with coenzyme A to form acetyl
coenzyme A, and
(iv) The acetyl coenzyme A is then finally condensed and reduces to form
fatty acids.
The carbon dioxide, thus, produced is diffused out through general body
surface and the fatty acids are excreted through the excretory system.
Excretory System of Fasciola Hepatica:
The excretory system of Fasciola hepatica is concerned with excretion as
well as osmoregulation. It consists of a large number of flame cells or flame
bulbs or protonephridia connected with a system of excretory ducts.
(i) Flame Cells:
The flame cells, supposed to be modified mesenchymal cells, are numerous,
irregular in shape bulb-like bodies found distributed in the mesenchyma
throughout the body of Fasciola. The distribution pattern of flame cells
follows a specific pattern referred to as ‘the flame cell pattern’ (Faust, 1919).
The flame cells are characteristic, each has a thin elastic wall with
pseudopodia-like processes, a nucleus and an intracellular cavity having
many long cilia arising from basal granules. In living condition, the cilia
vibrate like a flickering flame, hence, the name flame cell.
(ii) Excretory Ducts:
There is an excretory pore at the posterior end from which arises a longitudinal excretory canal,
from this arise four main branches, two dorsal and two ventral, which subdivide into numerous
small capillaries which anastomose; the capillaries are continued into the intracellular cavity of
flame cells. The longitudinal excretory canal is non-ciliated but the capillaries are lined with
cilia.
Nervous System of Fasciola Hepatica:
A nerve ring surrounds the oesophagus, it has a pair of cerebral ganglia dorsolaterally, and a
ventral ganglion below the oesophagus. Small nerves are given out anteriorly from the ganglia.
Posteriorly three pairs of longitudinal nerve cords arise from the ganglia, a dorsal, a lateral, and
a ventral pair of nerve cords.
The lateral nerve cords are best developed and they run to the posterior end. Nerve cords are
connected by transverse commissures and they give out many small branches, some of which
form plexuses. The nerve cells are mostly bipolar. Due to parasitic life, sense organs are lost in
adult Fasciola.
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