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1 Human Human DigestiveDigest DigestiveDigest ive System - ive System - YouTube.flv YouTube.flv System System

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Human Digestive Digestive System - YouTube.flv System. http://vimeo.com/76306734 Video link. 5 Digestion Processes (IDAAE). Ingestion : taking in of food into the body. Digestion : breaking down of food into simpler substances - PowerPoint PPT Presentation

Text of Human Digestive Digestive System - YouTube.flv System

  • *Human DigestiveDigestive System - YouTube.flv System

  • *5 Digestion Processes (IDAAE)Ingestion: taking in of food into the body.

    Digestion: breaking down of food into simpler substances

    Absorption: diffusion of food from small intestine into the blood

    Assimilation: using digested nutrients to make new material

    Egestion: removal of undigested waste material

  • *Recall. . . What are the main organs of the alimentary canal?

    MouthOesophagusStomachSmall intestineLarge intestineAnus

    Although not part of the alimentary canal, the liver, gall bladder and pancreas are closely associated with it. They play an important role in digestion by secreting digestive enzymes.

  • *DigestionMechanical / physical digestion physically breaks down the food in the mouth (chewing). Smaller pieces of food increase surface area for digestion. It also takes place in the stomach (churning of food by the muscular stomach walls)Chemical digestion uses enzymes to chemically break down complex food substances into their simplest form. e.g. Starch maltoseamylase

  • *Chemical digestion:Starch (carbohydrate) digestion: in mouth and small intestine.Protein digestion: in stomach and small intestineFat digestion: only in small intestine

    Why must food be digested???Large molecules of food are unable to pass through cell membranes, thus must be broken down into small molecules so that they can diffuse through cell membranes into the blood stream

  • *Mouth (Ahhh....)Mouth ingests food Teeth masticates food into small pieces to increase surface area for digestionSaliva (pH 7) moisten and soften food

    Starch maltoseTongue mixes food with saliva and rolls food into a bolus before swallowingSaliva - water, mucus, salivary amylaseSalivary amylase

  • *

  • *Swallowinghttps://vimeo.com/76306735

  • *trachea (windpipe)glottisDuring breathing, the larynx is lowered and the glottis is open.

    pharynxoesophaguslarynx (voice-box)airWhat Happens During Breathing and Swallowing?Normally, air passes into the trachea (windpipe) while food passes into the oesophagus.

  • *During swallowing, the larynx is raised and the glottis is covered by the epiglottis. This prevents food particles from entering the trachea.

    pharynxtrachea (windpipe)oesophagusglottisepiglottisfood particleslarynx (voice-box)What Happens During Breathing and Swallowing?

  • *Occasionally, small particles of food or water may get into the larynx or trachea.trachea (windpipe)larynx (voice-box)food particlesWhat Happens During Breathing and Swallowing?

  • *What Happens During Breathing and Swallowing?This automatically induces violent coughing to force the food particles or water out and to prevent choking.trachea (windpipe)larynx (voice-box)food particles

  • *OesophagusMinimal digestionCarries food from mouth to stomach by peristalsisOesophagus has circular and longitudinal muscles which are antagonistic.When circular muscles contract, longitudinal muscles relax and vice-versa.

  • *The two layers of muscles cause rhythmic, wave-like contractions of the gut walls. Such movements are known as peristalsis.Peristalsis: enables food to be mixed with the digestive juices; and moves the food along the gut.

    Part of the gut wallPeristalsiscircular muscleslongitudinal muscles

  • *Wall here constricts. Circular muslces contract; longitudinal muscles relaxWall here dilatesDirection of movement of foodCircular muscles relaxLongitudinal muscles contract

  • *Peristalsis Move the food down!When circular muscles contract, longitudinal muscles relax. Gut wall constricts i.e. gut becomes narrower and longer. Food is squeezed or pushed forward.

    Gravity and slippery mucous lining helps push food down too.http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/basics/peristalsis.html

  • *StomachStores food temporarilyStomach muscles churns and mixes food (also by peristalsis) with gastric juice to form chyme.Gastric juice contains hydrochloric acid (HCl) and enzymes like rennin and pepsinHCl is very acidic (pH2), thus it kills bacteria and other microorganisms, as well as stopping the action of salivary amylaseProvides acidic medium for gastric enzymes to workOnly protein digestion here

  • *The stomach is guarded at the entrance and exit points by sphincter muscles which control the amount of food entering and leaving the stomach.https://vimeo.com/76306734

  • *Small IntestineSubdivided into duodenum, jejunum and ileumIn the small intestine, chyme stimulatesPancreas to secrete pancreatic juiceGall bladder to secrete bileIntestinal glands to secrete intestinal juice

    All three juices secreted are alkaline, pH 8.5

  • *bileintestinal juicepancreatic ductpancreatic juicebile duct132Pancreatic and intestinal juice contain many digestive enzymes.

    Bile does not containenzymes. Bile emulsifies fats, increasing thesurface area for lipase action

  • *

  • *Villi absorption by diffusionDiffusionFrom intestineTo To liver

  • *Large Intestine (colon)Large inverted U shaped tube.No digestion takes place hereAbsorbs water and minerals saltsStores the faeces (dead cells, mucus, germs, undigested food)

  • * Is the colon the main region for water absorption? No! About 94% of the total amount of water passing through the alimentary canal is absorbed by the small intestine! The large intestine absorbs most of the remaining 6% of water.

    Rectum temporarily stores faecesAnus egests (= removal of undigested matter) faeces

  • *Organs associated with the alimentary canal These organs do not digest food but aid in digestionGall bladderPancreas Liver

  • *Lacteal fatty acids and glycerol recombine in the epithelium toform fat which then enters the lacteal as fine fat dropletsBlood capillaries transport sugars and amino acids away from the small intestineOne cell thick epithelium for efficient absorption of food particlesThis continual transport of digested food substances maintains the concentration gradient for the absorption of digested food substances.

  • *Gall bladderTemporarily stores bile (smelly green substance) secreted by liver. Secretes bile in the presence of chyme.Bile breaks up large fat droplets into very small fat droplets to increase surface area for lipase action (Emulsification) Bile emulsifies fats*Bile is not an enzyme, so it is not affected by temperature

  • *PancreasConnects to small intestine by pancreatic ductProduces pancreatic juiceSecretes hormones like insulin (controls blood glucose concentration) and glucagon (controls carbohydrate metabolism)

    LiverProduces bile, which is stored in the gall bladder

  • *

  • *Absorption Adaptations of the small intestineSmall intestine is very long (~5 m)Internal surface of the small intestine has many folds.On these folds, there are many finger-like projections called villiThese 3 adaptations increase surface area for absorption

  • *AssimilationAfter travelling through the blood stream to the rest of the body, cells can now make use ofglucose as source of energyamino acids to build new cytoplasm and tissue cellsfatty acids to build new cell membranes

    (1)The initial stages of eating and swallowing are under voluntary control. (2)Once food enters the mouth the teeth break it down into smaller and smaller pieces. This has the dual function of making the food easier to swallow and increasing the surface area of food on which the saliva can act. The tongue, lips and cheeks assist the teeth in the process by allowing the food to be "rolled" around the oral cavity. The mechanical action described above produces a softened bolus of food which is now ready to be swallowed. The correct biological term for swallowing is deglutition. (3) shows the voluntary stage of deglutition. Here the bolus is pushed into the upper part of the pharynx (known as the oropharynx) by the action of the tongue. The pharyngeal stage of deglutiton is stimulated when the bolus enters the oropharynx. This stage of swallowing is mainly due to a reflex response. Various nerve receptors send messages to the deglutition centre of the brain stem. (see medulla and pons in your notes on the central nervous system). (4)This sets off muscular contractions in the pharynx. The soft palate closes off the nasopharynx. The vocal cords in the larynx are moved up and towards the front of the throat thus closing it off to the passage of food. This is extremely important in preventing food from entering the airway.I am sure we have all experienced the unpleasant feeling of food or drink going the "wrong way"!! Another effect of the process is to widen the opening of the oesophagus thus making the passage of the bolus along the alimentary canal easier. (5) As the bolus pushes it's way into the oesophagus it automatically pushes the epiglottis downwards further closing off the airway. (6) The bolus then enters the oesophagus and the final stage of swallowing begins. This final stage is known as the oesophageal stage of deglutiton.

    http://greenfield.fortunecity.com/rattler/46/upali4.htmFigure 6.4 page 92

    Figure 6.4 page 92

    Figure 6.4 page 92

    Figure 6.4 page 92

    Figure 6.6 page 93

    Compare the stomach wall n oesophagus wall? Which is thinker? Why? ( pro