The digestive system
of leech
It consists
of a straight tube called alimentary canal and associated salivary glands.
Alimentary canal:
The alimentary canal of a leech starts with the mouth and ends with the anus. It is divisible into the following parts.
1. Fore gut or stomodaeum consisting of
pre-oral chamber, buccal cavity and pharynx. They are lined with cuticle.
2.Mid gut consists of oesophagus, crop, stomach, and intestine. All these have an endodermal lining.
3) Hindgut or proctodaeum consists of a rectum
lined with cuticle.
1) Pre oral chamber: The alimentary
canal begins with mouth. The mouth is a small triradiate aperture situated in
the centre of anterior sucker. It is guarded by velum made by three lips. The
hollow space of anterior sucker present in front of the mouth is termed as a preoral chamber.
2) Buccal cavity: The triradiate
mouth opens into the buccal cavity. Three crescent jaws are embedded in the
mucous membrane of buccal cavity. One jaw is mid-dorsal in position and the
other two are ventrolateral in position. Each jaw is laterally compressed
muscular structure. It is covered with a fine cuticle. It is thickened at the
free edges to form a ridge.
This ridge shows a row of minute teeth or denticles. Hence
the jaw is termed as monostichodont. The median jaw has 103 to 128 teeth, while the lateral
jaws bear 85 to 115 teeth on each jaw. On the
either side of the jaw 40-45 salivary papillae with many openings of salivary
glands are present.
3) Pharynx: The next chamber
is the pharynx present in the 5th to 7th segment. It is surrounded by salivary glands.
The ducts of salivary glands open through the salivary papillae present on
jaws.
Midgut or Mesenteron :
1) Oesophagus: The pharynx opens
into short narrow tube called oesophagus which opens into the crop.
2) Crop: It extends from the ninth to the eighteenth segments. It consists of ten segments. It consists of
ten chambers, one in each segment. Each chamber is produced into 2 lateral
diverticula. The diverticula of the last chamber are the biggest and reach
up to twenty-second segment. The crop acts as a blood storage organ of the leech.
3) Stomach: The crop enters
into a comparatively small stomach present in the nineteenth- segment. Then, the opening of the crop into the stomach is guarded by a sphincter.
4) Intestine: The intestine is a straight & narrow tube. It extends from the 20th segment to the 22nd segment.
Its mucous membrane shows longitudinal and transverse folds which increase the
absorptive surface. The intestine leads into the rectum.
Hindgut or Proctodaeum:
1) Rectum: It is broad and a short chamber lying in the 22nd segment to 26th segment.
2) Anus: Rectum opens out through anus. It is very small opening present on the dorsal side of the body near the posterior sucker.
Digestive Glands:
Leech shows 2 types of digestive
glands. 1) Salivary glands, 2) Gland cells in the gut.
1) Salivary glands: They are
unicellular glands present below the pharynx. Each gland gives small duct. They
open on the salivary papillae of the jaw.
The saliva contains a substance
called HIRUDIN. It prevents the clotting of the blood of the host
during sucking.
2) Gland cells in the gut: These are scattered in the epithelium of the crop, stomach, and intestine. They secrete mucous in the cop. Food of Leech:
It sucks the blood of vertebrate animals.
structurally leech is a sanguivorous animal.
Feeding:
Leech attaches to the host with the
posterior sucker. Then it applies the anterior sucker to the host body. The jaws
move and make an "A." shaped wound. The blood of the host is then sucked
up by pump like actions of the pharynx. The salivary glands secrete a substance
i.e. Hirudin, which prevents coagulation of blood. This enables the leech to
draw blood continuously. A leech can suck blood which is 3 to 6 times more than
its body weight. This is stored in the crop. When once leech drinks the blood,
it need not go for sucking the blood till 3 months to one year.
Digestion:
The globin of the blood is the food of
leech. The blood is digested in the stomach. The mechanism is not clear,
The digested food is absorbed in the
stomach and intestine.
No comments:
Post a Comment