Rabbit Anatomy - Digestive System
As total herbivores, rabbits have an
extremely long digestive tract in order to process their food in the most efficient way.
The
whole of a rabbit anatomy has evolved to survive on a very poor diet,
the digestive tract especially. A special feature of the process, known
as caecotrophy, is a remarkable way the rabbit 'recycles' waste faecal
matter in order to extract any nutrients that may have been missed on
the first, second or even third time round in the digestion system. (See below for more on this).
The whole digestive system of the rabbit is huge and may account for between 10-20 per cent of its total body weight.
The whole digestive system of the rabbit is huge and may account for between 10-20 per cent of its total body weight.
Let's follow the process through the rabbit's anatomy...
Stomach
In an adult rabbit the total length of the alimentary canal is 4.5 to 5 m. After a short oesophagus there is a simple stomach which stores about 60-80 g of a rather pasty mixture of feedstuffs.
In an adult rabbit the total length of the alimentary canal is 4.5 to 5 m. After a short oesophagus there is a simple stomach which stores about 60-80 g of a rather pasty mixture of feedstuffs.
Food eaten by the rabbit quickly reaches the stomach where it remains for a few
hours, and although in an acid environment it has little chemical change.
Liver & Pancreas
Two major glands secrete into the small intestine: the liver and the pancreas.
Two major glands secrete into the small intestine: the liver and the pancreas.
Bile from the liver contains bile salts and
many organic substances but no enzymes. Bile aids digestion
catalytically.
The reverse is true of pancreatic juice which
contains a sizable quantity of digestive enzymes allowing the
breakdown of proteins (trypsin, chymotrypsin), starch (amylase)
and fats (lipase).
Small Intestine
If the small intestine of a rabbit was laid out it would be more than 10 times the length of the rabbit.
If the small intestine of a rabbit was laid out it would be more than 10 times the length of the rabbit.
The contents of
the stomach are gradually 'injected' into the small
intestine in short bursts, by strong stomach contractions.
The small intestine is about 3 m long and nearly 1
cm in diameter. The contents are liquid, especially in the upper
part. Normally there are small tracts, about 12 cm long, which
are empty. The small intestine ends at the base of the caecum.
This second storage area is about 40-45 cm long with an average
diameter of 3-4 cm. It contains 100-120 g of a uniform pasty mix
with a dry matter content of about 20 percent.
As the
contents enter the small intestine they are diluted by the flow
of bile, the first intestinal secretions and finally the
pancreatic juice.
After enzymatic action from these last two secretions the
elements that can easily be broken down are freed and pass
through the intestinal wall to be carried by the blood to the
cells.
Large Intestine
The large intestine is made up of the caecum and colon. The caecum is very large, (about 10 times the volume of the stomach, and about 40 per cent of the total volume of the gastrointestinal tract).
The large intestine is made up of the caecum and colon. The caecum is very large, (about 10 times the volume of the stomach, and about 40 per cent of the total volume of the gastrointestinal tract).
The colon separates the large and small
fibre particles. The large particles of indigestible fibre are moved
straight through the colon to form the hard droppings. the smaller fibre
particles and other small incomplete digested food particles are moved
backwards (by special muscles in the colon called haustrae).
This 'slurry' enters the caecum where it is broken down and fermented.
Caecum
The particles that are not broken down in the small intestine enter the caecum after less than 2 hours. There they have to stay for about 2 to 12 hours, while they are attacked by bacterial enzymes.
The particles that are not broken down in the small intestine enter the caecum after less than 2 hours. There they have to stay for about 2 to 12 hours, while they are attacked by bacterial enzymes.
Elements which can
be broken down by this new attack (mainly volatile fatty acids)
are freed and in turn pass through the wall of the digestive
tract and into the bloodstream.
Very near the end of the small intestine, at the entrance to
the caecum, begins the exit to the colon. The caecum has a blind pouch branching off from the small intestine-colon
axis. Physiological studies show that this blind
pouch-reservoir forms part of the digestive tract: the contents
circulate from the base to the tip passing through the centre of
the caecum, then return towards the base, along the wall.
The content of the caecum is then evacuated into the colon.
Approximately half consists of both large and small food
particles not already broken down, while the other half consists
of bacteria that have developed in the caecum, fed on matter from
the small intestine.
Colon
The colon is about 1.5 m and follows on from the caecum, it is creased and dented for about 50 cm (proximal colon) and smooth in the terminal section (distal colon).
The colon is about 1.5 m and follows on from the caecum, it is creased and dented for about 50 cm (proximal colon) and smooth in the terminal section (distal colon).
The rabbit's digestive tract is
virtually the same as that of other monogastric animals, however in the
rabbit anatomy, the digestive tract has a uniqueness that lies in the
dual function of the proximal colon.
If
the caecum content enters the colon in the early part of the
morning it undergoes few biochemical changes.
If the caecal content enters the colon at another
time of day the reaction of the proximal colon is entirely
different.
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