Digestive System

Question 1

What is the whole digestive system known as?

Answer 1

The alimentary canal, which runs from the mouth to the anus.

Question 2

How is the digestive system divided up?

Answer 2

Into three sections, by sphincters or valves.

Question 3

What is the role of the digestive system?

Answer 3

To digest food, which is made into substances that can be used by the body for its various functions.

Question 4

What does the muzzle do?

Answer 4

The mobile part of the upper lip, which feels for and separates food.

Question 5

What do the lips do?

Answer 5

Gather food into the mouth.

Question 6

What do the incisor teeth do?

Answer 6

Bite the food. In the adult horse there are 12 incisors: 6 at the front of each jaw.

Question 7

What does the tongue do?

Answer 7

Passes the food to the molars. The tongue is a muscular organ which acts as a primary organ for the sense of taste.

Question 8

What do the molars do?

Answer 8

Grind/masticate the food.

Question 9

What happens when the horse swallows?

Answer 9

• The bolus is pushed against the soft palate, which rises to block off the nasal passages. This allows the bolus to pass into the oropharynx, the muscular compartment created when the soft palate rises.
• At the same time the epiglottis (thin flap of cartilage) closes like a lid to over the upper respiratory tract. This prevents food passing down the trachea into the lungs.

Question 10

What is the role of the salivary glands?

Answer 10

They release saliva into the mouth. Saliva moistens the food to stop the horse from choking. It also contains enzymes which helps break the food down. Food is formed into a ball called the bolus.

Question 11

What is the oesophagus?

Answer 11

It’s a muscular tube starting at the back of throat, about 1.5m long and passes through the neck to the stomach. As the horses eat with their heads down, the food therefore travels up to the stomach by muscular contractions called peristalsis.

Question 12

What is the cardiac sphincter?

Answer 12

A ring of muscle which acts as a one way valve into the stomach, which is why horses colic as they can’t regurgitate their food, except in extreme circumstances (A sphincter is a ring of muscle at the opening of a hollow organ, which contracts to close it.)

Question 13

What is the stomach?

Answer 13

• Roughly the size of a rugby ball, it holds from 18-27 litres which is small for a large animal and it’s rarely more than two thirds full.
• Gastric juices are secreted, which include hydrochloric acid and three enzymes, pepsin, rennin and lipase, which begins the breakdown of proteins and lipids.
• Muscular contractions of the stomach mix the juices with food until it’s a soft mash called chime. Food stays in the stomach for about 30 minutes to 3 hours depending on the food.

Question 14

What is the pyloric sphincter?

Answer 14

A muscular valve into the small intestine which food passes though after an hour in the stomach.

Question 15

Describe the structure of the small intestine.

Answer 15

It has three parts where fluids from the liver and pancreas are secreted to help breakdown food and nutrients are absorbed. These are called the duodenum, jejunum and ileum.

Question 16

What is the duodenum?

Answer 16

• The first part of the small intestine - it is about 1 metre in length, where the food is broken down into basic nutrients by pancreatic enzymes and where bile enters from the liver via ducts. Enzymes are also introduced from intestinal glands.
• The bile emulsifies the fats and oils into smaller droplets to aid digestion. As the horse in its natural state feeds almost constantly, bile is produced and secreted continuously, so there is no need for a gall bladder.

Question 17

What is the jejunum?

Answer 17

• It’s the more folded section of the small intestine and about 20 metres in length. Digestive juices continue to be secreted and mixed with food.
• Absorption of amino acids, glucose, vitamins and minerals happens here. Nutrients pass into the blood stream, via absorption through the intestinal wall. Villi allow for greater absorption by creating a larger surface area.

Question 18

What is the ileum?

Answer 18

The last part of the small intestine. It continues the absorption of nutrients and controls the passage of partially digested food called ingesta (which now containing fibre and water) through another valve the ileocaecal valve into the large intestine. It is about 2 metres in length.

Question 19

What is the large intestine?

Answer 19

It is approx. 10 metres and consists of the caecum, large colon, small colon, rectum and the anus also known as the ‘Hind Gut’.

Question 20

What is the caecum?

Answer 20

– Nutrients and a high percentage of water are absorbed in the caecum.
- Cellulose in grass is broken down by bacteria called Gut Flora which live in the caecum. Gut flora is divided into many types and each one deals with a specific food. Any changes in food affects the type of bacteria which is why feed should be changed slowly, to allow new development within the bacteria populations.

Question 21

What is the role of the large colon?

Answer 21

• Water and nutrients are extracted and absorbed, bacteria continues to break down foods.
• This part of intestine folds over on itself causing sharp bends. The food matter contained here is bulky and a particular bend (the pelvic flexure) the intestine narrows creating an area prone to blockage which can result to a problem known as an impacted colic.
• Approx. length 4 metres and average capacity 90 litres.

Question 22

What is the role of the small colon?

Answer 22

Electrolytes (various kinds of salt) and water are extracted and absorbed. Approx. length 4 metres and average capacity 16 litres.

Question 23

What is the role of the rectum and anus?

Answer 23

• Rectum: waste matter passes from the small colon and forms into balls of faeces which are stored here until ready to be evacuated.
• Anus: a muscular valve or sphincter which regulates the evacuation of faeces.

Question 24

What are the three accessory organs which can be considered to be part of the digestive system?

Answer 24

The liver, pancreas and kidneys.

Question 25

What is the role of the liver in the digestive system?

Answer 25

• It is a gland which secretes bile and lipases, which help breakdown the digestion of fat and aids in fatty acid absorption. It is situated between the diaphragm and the stomach.
• It also filters blood coming from the digestive tract before it passes through rest of the body, via the portal vein.

Question 26

What is the role of the pancreas in the digestive system?

Answer 26

• It makes enzymes to help digest food. The enzymes within the pancreatic juices (alkaline fluid) help aid the digestion of proteins, carbohydrates and fats, and are secreted into the duodenum.
• It also produces hormone insulin that controls the level of glucose in the blood.

Question 27

What is the role of the kidneys in the digestive system?

Answer 27

They are situated just behind the back of saddle in the lumbar region, one either side of the spine. They act like a filter to remove waste from the blood, which runs through the ureter to the bladder and is excreted as urine. -

Question 28

How long does the digestive process usually ask?

Answer 28

The digestive process generally lasts about 40 hours therefore digesta can be present in the caecum and large colon for a couple of days or more, which causes the large colon to be bulky and grass fed horses to have a large distended belly.