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THE DIGESTIVE SYSTEM OF A GUINEA PIG
The entire digestive tract measures approximately 2.3 metres long from the Pharynx to the Anus.
Mouth-
Food enters through the mouth assisted by the tongue.
Teeth- Guinea pigs have a gap in the mouth
called a Diastema where carnivores would have canine teeth or premolars. This enables it to draw in its cheeks and close off
the rest of its mouth, so it does not swallow any material that may injure the mouth while knawing, such as bark. They have
20 teeth altogether, which are all uprooted and continuously growing (Hyspiodonic). The arrangement of teeth consists of two
upper and two lower incisors for gnawing. There are four upper and four lower cheek teeth with one molar and three premolars
on either side.
Saliva- They have four pairs of salivary glands. The Parotid, Mandibular, Sublingual,
and Molar. These ducts empty into the oral cavity, which is near to the molars. Saliva contains Amalaise, which breaks down
the food.
Pharynx- The pharynx is the next part, which is a chamber situated at the back of the animals
throat. The soft palate a partition between the cavity of the mouth below and that of the nose above (Blacks veterinary Dictionary
19th edition, 1998, page 377), raises the Epiglottis a leaf like piece of elastic cartilage covered with mucus membrane, which
stands upright between the back of the tongue and the entrance to the Glottis and the Larynx (Blacks Veterinary Dictionary
19th edition, 1998, page 167), stops to cover the Trachea (windpipe) and opens the Oesophagous.
Oesophagus-
The oesophagus is a long muscular tube where the food is transported down by peristalsis from the mouth to the stomach.
Stomach-
Food enters the stomach through the Cardiac Sphincter. This is a ring of muscle, which prevents regurgitation. Guinea pigs
are unable to vomit, as they dont have the part of the brain, which induces this reaction. If their stomach disagrees with
a food it will send it through and cause diarrhoea. The stomach lies in the left cranial portion of the abdomen and attaches
to the left part of the liver. It is split into four sections, the Cardia, Fundus, Body and Pylorus. The Cardia is a small
part, which surrounds the Oesophagus as it passes through the wall of the stomach. The Fundus is large, pouching to the left
and cranial to the Cardia. The Body of the stomach is situated to the right of the Fundus and leads towards the thick-walled
Pylorus, which connects the stomach to the small intestine.
Small Intestine- There are 3 sections
to the small intestine.
These are-
Duodenum, a U shaped, short area in which bile and pancreatic
ducts enter.
Jejunum, an area mainly for the digestion and absorption of food and nutrients.
Ileum,
the longest section of the digestive system and a major area for absorption to take place.
Small projections called Vilia,
which is where fatty and amino acids go into the stomach, and these 3 sections are covered in them.
The entire small intestine
is approximately 125cm in length.
Large Intestine- Consists of-
Ceacum,
the most characteristic feature of the digestive system of a guinea pig as it is large, thin-walled semicircular sac with
numerous lateral pouches. It breaks down cellulose and bacteria in herbivores.
Colon- an area where
water is absorbed into the system
Rectum- The holding place for the faeces before it is excreted
Anus- A sphincter where the faeces is excreted when passed
The Liver- It
is the largest organ in the body and is situated caudal to the diaphragm. Six liver lobes are usually identified in the guinea
pig; right lateral, right medial, left lateral, left medial, caudate and quadrate lobes.
Several processes take place
in the liver these are as follows: -
1. The regulation of blood sugar- where the liver is able to convert glucose,
amino acids and other substances into the insoluble carbohydrate Glycogen.
2. The formation of bile- where green and yellow
pigments are formed as red blood celled are broken down. These pigments are removed by the liver and excreted in the bile.
The liver also produces bile salts, which play an important part in the emulsification and absorption of fats. It is continuously
produced by liver cells, but is stored and concentrated in the gall bladder. Then it is discharged through the bile duct into
the Duodenum, when the Chyme arrives. Bile salts are reabsorbed with the fats that they emulsify and will eventually return
to the liver.
3. The storage of Iron- as the decomposition of red blood cells is completed in the liver and the iron released
from the haemoglobin is stored.
4. Deamination- excess amino acids cannot be stored into the body. These are then converted
into carbohydrates by the removal of their amino group. The residue can then be converted into glycogen. The nitrogen from
these amino groups is converted by the liver to urea and is then diluted by water into urine.
5. Manufacture of plasma
proteins- most of the proteins found in blood plasma have been made by the liver.
6. Use of fats- when fats stored by
the body are required for energy production they travel in the blood stream. Some are used directly and others are oxidised
by the liver to substances, which can be further oxidised by other tissues, this then produces energy.
7. Detoxification-
when poisonous toxins produced in the large intestine, by bacteria on amino acids they are converted by the liver into harmless
substances and then excreted.
8. Vitamin storage- the fat-soluble vitamins A, D, E & K are stored in the liver. It
also stores a product of vitamin B12, which is necessary for the production of bone marrow.
The Pancreas-
A large grey-pink gland which lies in the abdomen close to the stomach. Two types of tissue are present within the pancreas
which have very different functions. The Exocrine tissue, which produces digestive enzymes and the Endocrine tissue, which
produces hormones such as Insulin and Glucagon.
Insulin and Glucogen are found dispersed throughout the Secretory Glandular
tissue of the pancreas known as the Islets of Langerhans. Insulin is produced in the Beta cells of the Islets and stimulates
the function of glycogen in the muscle and the liver from blood glucose.
It also produces pancreatic juice, which consists
of: -
Mineral salts- Sodium Hydrogen Carbonate, which help neutralise acid chyme from the stomach.
Proteases- such as Tripsinogen. This is activated by Enterkinase from the intestinal walls and forms
the Endopeptindase; Trypsin which then hydrolyses proteins into Peptides.
Pancreatic Amylase- which
completes the hydrolysis of starch to Maltose.
Lipase- which converts fast to fatty acids and Monoglycerides
by hydrolysis. |
