Question

1. Trace the parts of the digestive system in the pig (same as man) giving the sites of activity, secretions released, enzymes involved and substrates acted on.Be complete.

2. Describe the blood flow of the heart starting with the inferior and superior vena cava. Include blood vessels and valves involved.

Answer 1

Answer: (1)

The pig has a digestive system which is classified as monogastric or nonruminant. Humans also have this type of digestive system. They have one stomach (mono = one, gastric = stomach). The monogastric differs from that of a polygastric or ruminant digestive system found in cattle and sheep. These animals have one stomach broken into four compartments. Due to the differences in the digestive systems, cattle can utilize different types of feeds than pigs. Cattle and sheep can live on hay and pasture, while pigs must eat grains that can be digested more easily.

Digestion is the break-down of food occurring along the digestive tract. The digestive tract may be thought of as a long tube through which food passes. As food passes through the digestive tract, it is broken down into smaller and smaller units. These small units of food are absorbed as nutrients or pass out of the body as urine and faeces.

The digestive tract of the pig has five main parts: the mouth, oesophagus, stomach, and small and large intestines. The following discussion explains how each part digests nutrients.

1. Mouth: The mouth is where food enters the digestive tract and where mechanical breakdown of food begins. The teeth chew and grind food into smaller pieces. Saliva, produced in the mouth, acts to soften and moisten the small food particles. Saliva also contains an enzyme which starts the digestion of starch. The tongue helps by pushing the food toward the oesophagus.

2. Oesophagus: The oesophagus is a tube which carries the food from the mouth to the stomach. A series of muscle contractions push the food toward the stomach. Swallowing is the first of these contractions. At the end of the oesophagus is the cardiac valve, which prevents food from passing from the stomach back into the oesophagus.

3. Stomach: The stomach is the next part of the digestive tract. It is a reaction chamber where chemicals are added to the food. Certain cells along the stomach wall secrete hydrochloric acid and enzymes. These chemicals help break down food into small particles of carbohydrates, protein, and fats. Some particles are absorbed from the stomach into the bloodstream. Other particles that the stomach cannot absorb pass on to the small intestine through the pyloric valve.

4. Small intestine: The small intestine is a complex tube which lies in a spiral, allowing it to fit in a small space. Its wall has many tiny finger-like projections known as villi, which increase the absorptive area of the intestine. The cells along the small intestine’s wall produce enzymes that aid digestion and absorb digested foods.

At the first section of the small intestine (called the duodenum), secretions from the liver and pancreas are added. Secretions from the liver are stored in the gall bladder and pass into the intestine through the bile duct. These bile secretions aid in the digestion of fats.

Digestive juices from the pancreas pass through the pancreatic duct into the small intestine. These secretions contain enzymes that are vital to the digestion of fats, carbohydrates, and proteins.

Most food nutrients are absorbed in the second and third parts of the small intestine, called the jejunum and the ileum. Undigested nutrients and secretions pass on to the large intestine through the ileocaecal valve.

A “blind gut” or caecum is located at the beginning of the large intestine. In most animals, the caecum has little function. However in animals such as the horse and rabbit, the caecum is very important in the digestion of fibrous feeds.

5. Large intestine: The last major part of the digestive tract, the large intestine, is shorter, but larger in diameter than the small intestine. Its main function is the absorption of water. The large intestine is a reservoir for waste materials that make up the faeces. Some digestion takes place in the large intestine. Mucus is added to the remaining food in the large intestine, which acts as a lubricant to make passage easier. Muscle contractions push food through the intestines. The terminal portion of the large intestine is called the rectum.

The arse is an opening through which undigested food passes out of the body. Food that enters the mouth and is not digested or absorbed as it passes down the digestive tract is excreted through the arse as faeces.

This was a general discussion of the digestive tract of the pig. The tract acts to digest and absorb nutrients necessary for maintenance of cells and growth. Efficient absorption of nutrients depends on each segment of the digestive system functioning to its maximum capacity.

Answer: (2)

The circulatory system consists of the heart which is a four chamber suction and pressure pump that moves blood through two separate systems, one to and from the lungs and the other around the body. The blood returns to the heart from the body through a series of veins, which terminate in two large veins called the anterior and posterior vena cava. Blood returns from the lungs through the pulmonary veins.

The top two chambers or auricles receive the blood from the veins and pass it into the strong muscular bottom chambers called the ventricles. Oxygen depleted blood from the body enters the right auricle, where it is then pumped into the right ventricle leaving by two pulmonary arteries that deliver the still un-oxygenated blood to the lungs.

Oxygenated blood from the lungs is then returned through the pulmonary veins to the left auricle, where it is pumped to the left ventricle and finally out through the main artery, the aorta, to be transported around the body. If the lungs are damaged by disease such as pneumonia, they cannot oxygenate the blood efficiently, the tissues become starved of oxygen and cannot function properly.

When the pig walks or runs its skin may then become blue and it has difficulty breathing. Chronic pneumonia may also hold back the blood supply causing congestion and heart problems.

Arteries are the muscular tubes that carry the blood away from the heart. These branch off into smaller arteries like the branch of a tree eventually becoming very fine arterioles. The arterioles branch further into microscopic tubes called capillaries which exchange fluid through their walls.

This enables the cells of the body to receive both oxygen and nutrients and eliminate carbon dioxide. The capillaries then combine to form first small veins, which in turn lead to larger ones. The blood now contains carbon dioxide and reduced levels of oxygen and returns to the heart via the anterior and posterior vena cava to recommence its circulation around the lung.

The blood consists of two main parts, a fluid called plasma and cells. Nutrients such as proteins, sugars and fats are circulated throughout the body in the plasma and waste products are collected to be detoxified in the liver and excreted via the kidneys. The plasma also carries hormones which are produced in one part of the body and act on another. It also carries antibodies to combat infection.

The plasma also supports red blood cells (erythrocytes) which contain the substance haemoglobin whose main function is to transport oxygen around the body and bring back carbon dioxide to be expelled from the lungs. The next largest group in the plasma are the white cells (leucocytes) which are the first line of defence against infectious agents. The third type of cells are blood platelets. These are really small fragments of cells which are associated with the clotting mechanisms of blood. When blood clots the liquid that remains outside the clot is serum and this contains the antibodies. Serum may be used to inject into pigs to provide an immediate source of immunity.

Failure of blood to clot and subsequent loss of red cells into the tissues is not uncommon in pigs and occurs in thrombocytopaenic purpura - a clotting defect disease - and warfarin poisoning.