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Digestion Master Traithana ChaowanapreechaMaster Alfredo V. Garcia III
DefinitionDigestion – the process of breaking down food particles (macromolecules) into smaller, simple molecules that can be absorbed into cells or the bloodstream. EnzymesExamples: Enzymes Starch Glucose Protein Amino acids
The digestion of different organisms1. Intracellular digestion – food is taken into cells by phagocytosis forming a food vacuole, then lysosome fuses the vacuole and releases enzymes to digest food. Food molecules are absorbed to cytoplasm. Waste is expelled by exocytosis.Examples: Amoeba, paramecium, other
The digestion of different organisms2. Extracellular digestion – organisms secrete enzymes out of their cells. Food is digested and absorbed into cells.Examples: Bacteria, fungi, most animals including humans
The digestion of different organisms2 methods to digest:1. Mechanical digestion – Food is broken into smaller pieces by chewing, contracting muscles (peristalsis of intestines and a stomach). Food can bind to enzymes better.2. Chemical digestion – Macromolecules are broken down into smaller molecules
Human digestive systemDigestion in the oral cavityOral cavity includes upper jaws, lower jaws, teeth, gum, cheek lining, hard and soft palates.Mechanical digestionTeeth cut, tear, and grind food into small pieces, then a tongue mixes food with saliva secreted from 3 pairs of salivary glands (sublingual, submandibular, and parotid).
There are 2 sets of human teeth formed by ectoderm.- Deciduous teeth, D.T., are firstly formed at age 6 months and start to fall out at 6 years old. There are totally 20 D.T.- Permanent teeth, P.T., are completely formed at age 13. There are totally 32 P.T.
32 Human permanent teeth include:1. 4 upper incisors – cut food (well- developed in rodents) 4 lower incisors2. 2 upper canines – cut, tear, and separate food 2 lower canines (well-developed in carnivores)3. 4 upper premolars – cut and tear food 4 lower premolars (well-developed in carnivores)4. 6 upper molars – chew and grind food
Salivation is controlled by parasympathetic nervous system (cranial nerve pairs no.7 and 9)Stimuli: seeing food, smelling, tasting, toughts amylaseChemical digestion amylaseStarch + water dextrinDextrin + water maltose
How is food transferred from a mouth to a stomach?Food travels along esophagus to a stomach by peristalsis (muscle contractions: the waves of involuntary muscle contractions that transport food, waste matter, or other contents through a tube-shaped organ.)
Digestion in a stomach- Capacity when it’s empty = 50 – 100 mL- Capacity when it’s full = 1-2 LEpithelial cells line inner surface of the stomach and secrete about 2 liters of gastric juices per day. Gastric juice contains hydrochloric acid, pepsinogen, rennin, lipase, potassium chloride, and mucus; ingredients important in digestion.
Secretions are controlled by nervous (smells, thoughts, and caffeine) and endocrine signals.The stomach secretes hydrochloric acid and pepsin. Hydrochloric acid (HCl) lowers pH of the stomach so pepsin is activated. Pepsin is an enzyme that pepsin controls the hydrolysis of proteins into peptides. The stomach also mechanically churns the food.Protein short polypeptides
UlcersPeptic ulcers result when these protective mechanisms fail. Bleeding ulcers result when tissue damage is so severe that bleeding occurs into the stomach.Perforated ulcers are life-threatening situations where a hole has formed in the stomach wall. At least 90% of all peptic ulcers are caused by Helicobacter pylori. Other factors, including stress and aspirin, can also produce ulcers.
Functions of the stomach- Storing food- Producing intrinsic factor (IF) important in B12 absorption at the small intestine- Digesting protein- Controlling the proper amount of food leaving the stomach for the small intestine- Producing hormone gastrin helping in pepsin and HCl production (in the stomach) and bile production (in the liver)- Buffering the food condition if it’s too alkaline.
Digestion in the small intestine-Final digestion and absorption occur.-The small intestine is a coiled tube over 3 meters long. Coilsand folding plus villi give very large surface area.-Final digestion of proteins and carbohydrates must occur, andfats have not yet been digested.- Food has been broken down into particles small enough topass into the small intestine.-Sugars and amino acids go into the bloodstream viacapillaries in each villus. Glycerol and fatty acids go into thelymphatic system.-Absorption is an active transport, requiring cellular energy.
Digestion in the small intestine1. CarbohydratesPancreatic amylasePolysaccharides + water disaccharides Disaccharidases from intestineDisaccharides + water monosaccharides
Digestion in the small intestine2. Proteins Trypsin and chymotrypsinPolypeptides + water protein fragments Carboxypeptidase from pancreasFragments + water Aminopeptidase from intestine amino acidsFragments + water amino acids
Digestion in the small3. Lipids intestine Pancreatic lipase + bile (liver)Triglycerides + water fatty acids + monoglycerides Pancreatic lipase + bile (liver)What is the function of bile??????
4. Nucleic acids Pancreatic nucleaseDNA and RNA nucleotides Intestinal nucleaseNucleotides nucleotide bases + monosaccharides (ribose or deoxyribose)
Absorption- Alcohol and aspirin are absorbed through the stomach lining into the blood.
Most absorption occurs in the duodenum and jejeunum. The circular folds and villi covered with epithelial cells provide a large surface area for absorption. The epithelial cells are lined with microvilli that further increase the surface area; a 6 meter long tube has a surface area of 300 square meters.
Glucose, fructose, and galactose areabsorbed by the microvilli by activetransport, then leave the cell and enterthe capillary. Amino acids cross the epithelial cellmembranes by active transport, thenenter the capillary. Water, vitamins and minerals areabsorbed by diffusion without digestion. Absorbed food molecules will be
Absorption of lipids by cells in the small intestine.
Any activities happen in large intestine?- Water, vitamin, and mineral absorption happens.- Bacteria E. coli synthesizes vit. K.- Feces formation
AppendectomyAppendicitis is a painful inflammation of the appendix, a finger-sized tube attachedto the large intestine. To remove an inflamed appendix, surgeons perform a surgicalprocedure known as an appendectomy.The inflammation can be caused by undigested food particles and bacteria.Microsoft ® Encarta ® Reference Library 2003.