Leaving Certificate Agricultural Science Food and The Digestive System

The Functions of Food Food supplies the animal with energy for all animal activities. To provide the materials for growth and repair of cells To provide materials for production of hormones and enzymes. To provide raw materials for milk, egg and wool production etc.

Food Elements The six most common elements found in food are Carbon (C), Hydrogen (H), Nitrogen (N) Oxygen (O), Phosphorous (P) and Sulphur (S). The elements found in dissolved salts include Sodium (Na), Magnesium (Mg), Chlorine (Cl), Potassium (K) and Calcium (Ca). Trace elements are required in our body in very small amounts and include Iron (Fe), Copper (Cu) and Zinc (Zn). These elements, when combined in different ratios form larger units called biomolecules.

The Major Food Groups (Bio-molecules) There are five main food groups: Carbohydrates Lipids (Fats and Oils) Protein Vitamins Minerals Water is often considered the sixth food group, due to the huge importance it plays in our bodies.

Carbohydrates The main sources of carbohydrates in our diet are starches and sugars. Carbohydrates are made up of Carbon, Hydrogen and Oxygen molecules with the common formula Cx (H2O)x Carbohydrates are made up of Monosaccharides (1 sugar unit, e.g. glucose) Disaccharides (2 sugar units, e.g. sucrose) Polysaccharides (many sugar units, e.g. starch and cellulose). When carbohydrates are digested they break up into monosaccharides, i.e. glucose.

Lipids Contain the elements Carbon, Hydrogen and Oxygen but not in any given ratio unlike Carbohydrates. A unit of fat (called a triglyceride) is made up of one molecule of Glycerol with three fatty acids chemically attached. When lipids are digested they are broken down into glycerol and fatty acids. Saturated fats are animal fats Unsaturated fats are plant oils

Proteins Contain the elements Carbon, Hydrogen, Oxygen and Nitrogen (sometimes Sulphur) Proteins are made up of units called amino acids. There are over 80 known amino acids, but only 26 occur in proteins. When proteins are digested they break up into amino acids Proteins are used for growth and repair of cells

The Digestive System The alimentary canal is a long tube going from the mouth to the anus. Along the tube are glands where substances called enzymes are produced. The intake of food has five steps: Ingestion Digestion Absorption Assimilation Egestion

Five Stages of Nutrition Ingestion is the in take of food. Digestion is the physical or chemical breakdown of food, so that it can be absorbed into the blood stream. Absorption is the release of digested food into the blood stream. Assimilation is the use of digested food in the organisms cells. Egestion is the removal of indigestible waste materials from the body.

Types of digestion 2 types of digestion Mechanical/Physical digestion which involves physically breaking up the food using teeth, stomach and intestinal walls Chemical digestion which breaks up food using enzymes An enzyme is a biological catalyst that speeds up chemical reactions without being used up in the reaction E.g. amylase breaks up starch into maltose

The Human Digestive System Digestion in the human occurs in distinct areas: Mouth (Physical and Chemical) Stomach (Physical and Chemical) Duodenum (Chemical) Ileum (Chemical) Large Intestine (Chemical)

Digestive system in Farm Animals Monogastric: these animals have a simple digestive system with a single compartment in the stomach, e.g. the pig. This is similar to humans Polygastric: these animals have a more complex digestive system with several compartments in the stomach, e.g. cattle, sheep, goats, and are called Ruminants

The Mouth Food is mechanically broken down by the teeth, increasing the surface area for the enzyme to work. Saliva, containing the enzyme Salivary Amylase, breaks down Starch into Maltose. Food is brought down to the stomach, in a structure called a bolus through the oesophagus by peristalsis.

Functions of Teeth Incisors: cutting and biting Canines: tearing and gripping food Premolars: grinding and crushing food Molars: grinding and crushing food

Dental formula of Pig The Mouth and Teeth: 2 x 3 1 4 3 = 44 3 1 4 3 the pig has incisors, canines pre-molars and molars like humans Dental formula of adult pig is i c pm m 2 x 3 1 4 3 = 44 3 1 4 3 The remaining digestion is similar to humans

Pig’s skull

Dental formula for Sheep/Cow I C PM M 0 0 3 3 X 2 = 32 in total 3 1 3 3 No canines or incisors on upper jaw Has a dental pad that meets lower incisors and canines to allow them to crop grass Gap between front teeth and premolars called the diastema. This can store ingested material while animal is chewing

Feeding in the Cow The cow wraps her tongue around the grass and tears it from the ground Her tongue is long and rough for gripping grass She uses her tongue and lips to eat concentrates The diastema (gap between canines and premolars) allows the cow’s tongue to manipulate the bolus of food (cud), moving it repeatedly over the grinding surface

Continued The cow produces a large amount of saliva each day. It contains mainly mucous to lubricate the movement of food, up and down and up the oesophagus. It does not contain amylase. Ruminants swallow the grazed grass with the minimum of chewing (mastication) and it passes down the oesophagus to the rumen and reticulum. The food in the rumen can be regurgitated, to be chewed at the animal’s leisure (chewing the cud or rumination)

Digestion in the Ruminant Herbivores own digestive enzymes do not break down the large cellulose molecules in the plant cell walls and so require microorganisms/protozoans to do the job for them These m/o’s are housed in a special compartment in the stomach called the rumen.

The Four Ruminant Stomach Chamber Function The Rumen (the paunch) When grass is swallowed after grazing it enters here where anaerobic bacteria begin the breakdown of cellulose Reticulum (honeycomb) The grass is returned to the mouth for re-chewing through this chamber (chewing the cud) Omasum (the book) When the cow re-swallows the cud it enters here where water is reabsorbed Abomasum (the true stomach) Digestion through enzymes in completed here

Calf’s Rumen A calf’s rumen and reticulum aren’t fully developed at birth. Milk enters the abomasum and rennin causes the milk to curdle which slows down the passage of food to allow time for digestion The calf starts to eat concentrates and hay to develop the flora in the rumen By feeding hay, the farmer is introducing bacteria to the rumen and this is called the Scratch factor

The Stomach in Monogastric animals The stomach contains Hydrochloric Acid giving it a pH of 1 – 2 . Hydrochloric acid loosens food, kills bacteria, triggers stomach enzymes and turns off amylase. Inactive Pepsinogen is activated by the low pH turning it into Pepsin (Proteinase). Proteinase breaks down proteins into peptides. Peptides are short chains of Amino Acids. Young pigs also produce an enzyme called Rennin which converts casein in milk to caseinogen

The Stomach 2 The stomach churns the food for a number of hours until the food is a thick soupy liquid called Chyme. Sphincter muscles relax and the chyme enters the duodenum. Physical digestion by the churning process, chemical digestion by the action of enzymes.

The Duodenum Lots of enzymes are secreted from the wall of the duodenum, the pancreas and the Gall bladder. Enzymes including lipase, proteinase (trypsin), amylase, maltase, sucrase, lactase, are found there. Bile is also secreted from Gall Bladder. Bile emulsifies fat, so that it can be digested. Bile also neutralises the stomach acids.

The Ileum (Small Intestine) Intestinal juice secreted from the walls of the small intestine contains the same enzymes as the duodenum. Most food is digested here, as it is 5.5 metres long. The wall of the intestine contains millions of finger like projections called villi (villus in singular) so the surface area is increased. Sugars, Amino acids, vitamins, minerals and water are absorbed into the blood stream. This material travels to the liver via the Hepatic Portal Vein and then onto the heart. Fatty acids and glycerol are transported by the lymph vessels within the villus itself.

The Large Intestine Here water is reabsorbed and the remaining waste passes to the rectum as faeces. Bacteria in the colon manufacture vitamin K. which is absorbed by the body.

Functions of Liver Produces bile which emulsifies fats Regulates amount of glucose in the blood. If there is too much glucose, it converts it to glycogen as an energy reserve Detoxifies harmful substances, e.g. drugs and poisons Regulates body temp at 37oC Deamination takes place in liver which breaks down amino acids into urea

Digestion in Poultry Poultry have no teeth, so the food is swallowed whole, passing down the oesophagus into the crop The food is stored temporarily in the crop before passing into the proventriculus where it is acted on by enzymes It is ground to a paste in the gizzard, with the aid of grit and enzymes Digestion is completed in the ileum and digested products are absorbed

Parts of Digestive system of poultry Crop: stores food for later consumption Gizzard: grit or sand grinds down the food Proventriculus: secretes enzymes to break down food

Digestion in Horses The horse’s mouth, oesophagus, stomach and ileum are normal in function The large intestine (hind-gut) is very large and consists of two parts, the caecum and the colon Partially digested, the food enters the caecum where it is acted on by anaerobic bacteria. Here the cellulose and hemi-cellulose from forage foods are digested(similar to ruminants) After fermentation, the food enters the colon for further digestion and absorption Thus, microbial fermentation occurs in the hind-gut whereas in ruminants it occurs in fore-gut