Mammalian digestion In heterotrophic organisms the digestive system provides the means by which nutrients are taken in and broken down. Large insoluble food molecules are converted into small soluble ones that can be absorbed and made available to the body cells.
Obtaining nutrients • There are 5 steps involved in heterotrophs obtaining nutrients: • Ingestion: the intake of food • Digestion: the breakdown of food into smaller, soluble chunks that can be easily absorbed. The end products of digestion are amino acids (from proteins), simple sugars (from carbohydrates) and fatty acids (from lipids).
3. Absorption: basic units of food are absorbed across the digestive tract wall, into the bloodstream and into cells. 4. Assimilation: the end products of digestion are built into useful substances as either biological material or as an energy source 5. Egestion: the removal of undigested food as waste.
Describe the role of teeth in increasing the surface area of complex foods for exposure to digestive chemicals The function of teeth is to physically break down food into smaller pieces. Chewing food increases the surface area thereby increasing the rate of reaction with digestive enzymes (chemical breakdown).
Humans have four types of teeth: incisors, canines, premolars and molars. • Incisors: used to grasp, hold and bite food • Canines: used for ripping and tearing food • Premolars: used for chewing and cutting flesh • Molars: used for grinding and chewing
Diets • Herbivores Have front teeth (incisors) adapted to tear off vegetation and back teeth (molars) to chew on plant material. The molars are specially designed to help break open the cellulose walls of plant cells. Cellulose is extremely hard to break down physically and chemically.
Herbivores cont. • Herbivores need to chew for a long period of time because: • To break down the cellulose • Large quantities of vegetation is needed to provide sufficient energy for the animal • To further increase the surface area
Carnivores They have powerful jaws and well developed canine teeth designed to hold and kill prey and tear off meat. The meat is then chewed by the molars to increase the surface area before swallowing it.
Explain the relationship between the length and overall complexity of digestive systems of a vertebrate herbivore and a vertebrate carnivore with respect to: • the chemical composition of their diet • the functions of the systems involved Herbivores Eat plant material that is high in fibre and starch and depending on the plant may include sugars, proteins, oils and other nutrients. Herbivores have adaptations of their digestive tract to enable them to digest cellulose.
Herbivores cont. • Large herbivores have microbes living in their gut who produce an enzyme to break down cellulose and release energy. This is called microbial fermentation. • The gut is complex and extremely long providing space to hold the large quantity of food that must be eaten. It also gives maximum opportunity for the microbes to digest cellulose and the nutrients to be absorbed.
Herbivores cont. • Small herbivores eat plant material with less cellulose and their diet is predominately nectar. • The gut is usually simple and small because their diet is easier to digest as it has little or no fibre and is high in sugar.
Carnivores • Eat animal matter which is more easily digested. • Their diet is high in protein, low in fibre and has more energy than plant material. This means that carnivores need to consume lesser quantities of food than herbivores. • Due to the ease at which food can be digested, the gut is relatively short. Little undigested material is egested due to low fibre diet.
Herbivore Adaptations • The microbes living in the gut of animals need to be protected from being lost with the passage of food. The microbes are present either in the: • Stomach (fore-gut fermenters) • Caecum (hindgut fermenters)
Fore-gut Fermentation • Microbes in the eastern grey kangaroo use majority of the dietary glucose and protein but release fatty acids as energy for the host animal. Some microbes are digested by the host and a source of amino acids.
Cattle: • They regurgitate the contents of the first part of their stomach and re-chew the food to further break it down. • Ruminant fore-gut fermenters meaning they have four stomachs: two for microbial fermentation, one for storage and one which acts as a true stomach. • Food remains in the two fermentation chambers for a long period of time so that the microbes have enough time to break down the cellulose
Hindgut Fermenters • Takes place in the caecum (large intestine) • The main difference is that the microbes cannot be digested by the host animal as a source of amino acids. This is because protein digestion has already occurred before the large intestine and the amino acids are therefore egested. • This is why rabbits eat their faecal pellets to digest the nutrient-rich microbes
Carnivore Adaptations • They have a simple stomach and a short intestine relative to their body size. The caecum may be absent, of if it is present is greatly reduced in size.