1、Bile juice A complex green fluid produced by the liver, stored in the gall bladder, It contains no chemical enzymes but two important substances for digestion: 1. Sodium hydrogen carbonate- help to neutralize the acid chyme from the stomach and so create a more neutral pH for the enzymes of the smal
2、l intestine 2. Bile salts - They emulsify fats into minute droplets - This is a physical digestion which increases the surface area for pancreatic lipase to act on,Pancreatic juice for digestion and hormone (insulin) secretion 1 Mineral salts (NaHCO3)- helps to neutralize the acid chyme from the sto
3、mach and to provide an optimum pH for the pancreatic enzymes to function,Intralobular duct,Acinar cells,Cellular structure of pancreas showing intralobular ducts,2. Proteasestrypsinogen trypsin,enterokinase (from intestine),Proteins peptides,trypsin,Chemotrypsinogen chemotrypsin,trypsin,Proteins pep
4、tides,chemotrypsin,Small peptides amino acids,carboxypeptidase,3. Pancreatic amylase -completes the digestion of starch into maltose 4. Lipase -hydrolyses fats into fatty acids and glycerol 5. Nuclease -changes nucleic acids into nucleotides,Intestinal juice Brunners glands secrete mucus and sodium
5、hydrogen carbonate Enzymes are produced by the breakdown of cells at the tips of the villi 1. Mucus lubricate and prevent autolysis 2. Mineral salts (NaHCO3) - produced by the Brunners glands to neutralize the acid chyme and provide a suitable pH for intestinal enzymes,3. Proteases (erepsin) - conve
6、rt peptides into smaller peptides and amino acids 4. Enterokinase - activates trypsinogen into trypsin 5. Nucleotidase - converts nucleotides into pentose sugars, phosphoric acid and organic bases 6. Carbohydrases - consisting of amylase, maltase, lactase, and sucrase, etc., to complete the digestio
7、n of sugars into simple sugars,Lining of ileum,TS of ileum showing villi,15.4.5 Absorption and assimilation Absorption by diffusion and active transport Other factors: glucose Ca+ absorption requires vitamin D,A large surface area is achieved by: 1. It is very long, e.g. 6 m in man, 45 m in cattle 2
8、. Its walls are folded to provide large internal projections 3. It has many finger-like villi 4. The epithelial cells possess microvilli (brush-border) In addition, the epithelium is only one cell thick which provides a very short distance for diffusion and active transport,Glucose, amino acids, vit
9、amins, minerals & water are small enough to enter the capillaries Fatty acids, glycerol & small droplets of oil are too big and they enter the lacteal,Absorption of digested substances,Simple sugars and amino acids go into blood capillaries which join to the hepatic portal vein going into the liver
10、for regulation.,Assimilation: Simple sugars & amino acids go to the liver via the hepatic portal vein Fatty acids & glycerol recombine to form very tiny oils before going into lacteal, then through lymphatic vessels, fats enter the blood vessels for transport throughout the body,Liver hepatic vein h
11、eart blood circulation,On reaching the liver, excess glucose will be converted into glycogen and stored in liver excess cannot be stored but deaminated in the liver,Functions of the liver Stores glycogen, converting back to glucose when necessary to maintain a constant blood glucose level:glucose gl
12、ycogen,2. Deamination of excess amino acids 3. Secretes bile for emulsifying fats;Provides an alkaline medium for enzymes in the small intestine,4. Stores fat soluble vitamins: A, D & EStores Fe from break down of haemoglobin & form new red blood cells 5. Synthesizes of plasma proteins,15.4.6 Water
13、reabsorption in the large intestine Most of the water drunk by man is absorbed by the small intestine Water from the digestive secretions (about 10 litres) is absorbed mainly in the ileum while the large intestine is responsible for reabsorbing the remainder,Bacteria in the large intestine synthesiz
14、e vitamin K and is absorbed by the large intestine together with water & some minerals Excess calcium and iron salts are actively transported from the blood into the large intestine for removal with the faeces,15.4.7 Elimination (Egestion) Faeces consist of indigestible food, residual material from
15、bile, bacteria, cells sloughed off the intestinal wall and some water Mucus is secreted by the rectum for lubrication & binding faeces together Defaecation through the anus is a reflex action in baby but voluntary as baby gets older Faeces: mostly egested materials except cholesterol & bile pigments
16、 which are excretory products,Adaptations to particular diets Herbivorous adaptations of mammals, e.g. deer A horny pad replaces the upper incisors & canines Diastema - a gap to separate newly nibbled food from those chewing at the back,Skull of deer,Dental formula of a sheep : 00333123 3. Cheek tee
17、th with ridged surfaces because of differential wearing of enamel and dentine,4. Jaws can move vertically & laterally - for more efficient grinding by teeth 5. Teeth have open roots - teeth grow continuously throughout life to replace wearing by constant grinding activity 6. Stomach is divided into
18、a number of chambers with micro-organisms to secreted cellulase for the digestion of cellulose (ruminants).Regurgitation of food from stomach to mouth before passing into the remaining stomach compartments 7. The alimentary canal is relatively long becausethe digestion of plant material is difficult
19、,Digestion of cellulose by microorganisms Micro-organisms must be kept separate from the gut so as to avoid the action of digestive enzymes, to provide long enough time for the break down of cellulose and a suitable pH for these micro-organisms In ruminants, e.g. cattle, sheep & deer four chambers:
20、rumen, reticulum, omasum, abomasum food first enters the first two chambers (rumen & reticulum) to carry out extracellular digestion of cellulose by cellulase secreted by microorganisms,Products of digestion are either absorbed by walls of the rumen & reticulum or micro-organisms which are later dig
21、ested A symbiotic relationship: mammal gets the products of cellulose break down Microorganisms get food supply & a warm, sheltered environment After some hours, the ruminant regurgitates the food into the mouth and thoroughly chews it (chewing the cud),When re-swallowed, food enters the omasum & ab
22、omasum ( true stomach) where the usual process of protein digestion in acid condition takes place - In rabbits and horse, the caecum & appendix are much enlarged and accommodate micro-organisms Absorption of digested food takes place through the walls of the caecum The yield is improved by re-swallo
23、wing of the faeces (coprophagy or refection),Carnivorous adaptations of mammals Food is chiefly meat which is a more nutritional than plant food. Adaptations concern modifications to the jaw & its dentition: Incisors are sharp and are used for nipping & biting,2. Canines are long used for killing pr
24、ey and tearing flesh from body 3. Carnassial teeth are particularly large for crushing bones 4. Teeth of upper jaw tend to overlap those of the lower jaw for slicing meat like two blades of a pair of scissors,5. Jaw muscles are well developed & powerful to grip prey firmly & crushing bones 6. No lat
25、eral jaw movement which might lead to dislocation of the jaw 7. Vertical movement of the jaw is large to allow a wide gap for capturing & killing prey 8. The alimentary canal is short, i.e. meat is relatively easy to be digested,Comparison of herbivorous and carnivorous adaptations in mammals,Compar
26、ison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adap
27、tations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivo
28、rous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mamm
29、als,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carniv
30、orous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison
31、of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,Comparison of herbivorous and carnivorous adaptations in mammals,TABLE 15.5. SUMMARY OF DIGESTION - see p.297 of text book 15.5 Nervous and hormonal control of secretions - not requ
32、ired in syllabus,Carnivorous plants All carnivorous plants are autotrophic but live in soils which are deficient in nitrogen, in cold places with slow decomposition of humus, or in places where leaching is common. Parasites Endoparasites: parasites live inside hosts body Ectoparasites: parasites liv
33、e outside hosts body,Parasites show some or all of the following features:,They 1 have agents for penetration of the host 2 have a means of attachment to the host 3 have protection against the hosts immune responses 4 show degeneration of unnecessary organs 5 produce many eggs, seeds or spores 6 hav
34、e a vector or intermediate host 7 produce resistant stages to overcome the period away from host,rostellum,Tapeworm,1. Structure of a tapeworm flat, long, ribbon like, with many (1000) segments head with hooks Secondary host - pig, for dispersal & infection,3. Adaptation of tapeworm to the parasitic
35、 mode of life in the ileum hooks bisexual for self-fertilization numerous eggs are produced to increase the chances of survival of the species,no digestive system is needed; absorption of digested food by diffusion through the body surface which is long & flattened to increase the surface area for a
36、bsorption of digested food can undergo anaerobic (no O2) respiration in the intestine body is covered by a thick cuticle and secretes anti-enzymes to protect itself against the digestive juice of host,4. Effect on host host loses weight pork should be thoroughly cooked before eating good sewage syst
37、em so that pigs do not get in contact with human faeces,Saprophytes saprophytes obtain food from dead organic matter, e.g. bacteria and fungi Mucor is a bread mould (fungus)which depends on bread for food;hyphae: filamentsmycelium: colony of filaments,Nutrition - hyphae go into bread; produce digest
38、ive enzymes to break down complex organic substances in bread into simple soluble compounds for absorption Extracellular digestion: digestion outside the cell Importance of saprophytism: dead organisms are broken down to recycle materials,Symbionts Examples of symbiosis: 1. Lichen - an association b
39、etween an alga and a fungus Alga receives protection, anchorage, water and minerals from the fungus Fungus receives food made by the alga through photosynthesis,Hydra-Chlorella symbiosisChlorella (unicellular green algae) in endoderm of hydra. They photosynthesize and make maltose for hydra. Endosym
40、biosis: inside the cells of the partner,3. Mycorrhizas - an association between roots of higher plants with fungi Fungus receives carbohydrates from plant Higher plant receives inorganic nutrients from fungus,Gut symbionts Protozoans and bacteria living in the gut receive food and protection. They s
41、ynthesize their own vitamins, especially vitamins K & B, and any excess is made available to the host animal.,In termites, protozoans producing cellulase which is essential for the digestion of wood. Many herbivorous mammals have an enlarged caecum and appendix to hold large masses of plant tissue w
42、hich is digested by the cellulase secreted by these symbionts. In ruminants, the rumen houses a great variety of symbionts than the caecum and they can achieve a more complete breakdown of cellulose. Further more, these symbionts provide a source of protein when they die and pass into the gut.,Symbiosis and the nitrogen cycle Nitrogen fixation by leguminous plants in their root nodules provides about 100 million tonnes of nitrogen per year. This association provides bacteria with carbon source and plants with nitrate.,
