Download Mechanical digestion

*
* Produces
various chemicals to break
down the food
* Filters out harmful substances
* Gets rid of solid wastes
*
* Mouth
* Pharynx
* Oesophagus
* Stomach
* Small and large intestines
*
* Changes the physical form of food:
* Chew
* Tear
* Grind
* Mash
* Mix
*
* Changes the chemical composition of food
* With the aid of digestive enzymes:
* Carbs
* Protein
* Lipid
* Digestive enzymes are special proteins
* Help break up large molecules of food into very
tiny molecules
* So that they can be absorbed
* Used by cells in the form of nutrition
*
* Ingestion
* Movement
* Digestion
* Absorption
* Further digestion
*
*
* Alimentary canal and the accessory digestive organs.
* Alimentary canal (also called the gastrointestinal tract/GI) is
the continuous, muscular digestive tube that winds through
the body.
* It digests food and absorbs the digested fragments through its
lining into the blood.
* These organs help breakdown the food, either mechanically
or chemically.
* Teeth
* Tongue
* Gall bladder
* A number of large digestive glands –salivary glands
* Liver
* Pancreas
*
*A long muscular tube
*Many sections & areas
*Begins with the mouth
*End with the anus
*
* PARTS OF DIGESTIVE TRACK:
* Mouth
* Pharynx
* Esophagus
* Stomach
* Small intestine
* Large intestine
*
* Organs that are not in the digestive tract, but helps
in the digestion:
* Teeth
* Tongue
* Salivary glands
* Liver
* Gall bladder
* pancreas
*
* Function:
* Food enter mouth
* Tasting
* Mechanical breakdown of food
* Secretion of salivary glands
*
* Structures in the mouth that helps with digestion:
* Teeth – cut, tear, crush and grind food
* Salivary
glands – produce & secrete saliva in oral
cavity:
* Beneath the teeth
* Below the jaw bone
* Below tongue
* Saliva moistens food
* Contains enzymes – ptyalin & salivary amylase
*Mixes
& roll food into tiny mashed up
bits
*Bolus
*Pushes the bolus towards the pharynx
*Into the esophagus when swallowing
*
* It is a coordinated activity of the
* Tongue
* Soft palate
* Pharynx
* Esophagus
* Phases:
* Food is pushed into the pharynx – by tongue
* Tongue blocks the mouth
* Soft palate closes off the nose
* Larynx(adam’s apple) rises
* Epiglottis(a flap of tissue) – closes the opening of
the trachea
*
* A straight muscular tube
* 25cm long
* Connect the mouth with the stomach
* Food takes about 4-8 seconds as it passes through the
stomach
* Walls contain smooth muscle
* It contracts in a wavy motion – peristalsis
* Peristalsis – move food & liquid slowly down the
esophagus into stomach
* Cardiac Sphincter (ring like valve) relaxes to allow
food into the stomach
*
* J shaped muscular sac
* Has inner folds – that increase the surface area of the
stomach
* Churns & grinds together the bolus into smaller pieces
* Food is mixed with gastric juices
* Secreted by the stomach walls
*
* Pepsin:
* Major enzyme
* Converts proteins into peptides
* Mucus:
* Lubricates food
* Protects the gastric lining form strong digestive juices
* Converts the bolus into a liquid( chyme)
* 4 hours of mechanical & chemical digestions
* Chyem passes through the pyloric sphincter into:
* Small intestine
* Long coiled tube beneath stomach
* About 7 meters long
* Has 3 parts:
* Duodenum:
* Upper part
* 23-28 cm
* Connected to stomach
* Where the digestive juices form pancreas & liver
combine with chyme
* Making it thin & watery
* Jejunum –
* Ileum -
*
* The processing of food by the digestive system
involves six essential activities:
* The
digestive tract can be viewed as a
disassembly line
* Food
becomes less complex at each step of
processing
* Nutrients become available to the body.
*
* Ingestion
* The taking of food into the digestive tract via the mouth.
* Propulsion
* Movement of food through the alimentary canal.
* It includes swallowing, which is initiated voluntarily, and peristalsis, an
involuntary process.
* Peristalsis, the major means of population, involves alternate waves of
contraction and relaxation of muscles of the organ walls.
* Its main effect is to squeeze food from one organ to the next, but some mixing
occurs as well.
* Peristaltic waves are so powerful that, once swallowed, food and fluids will move
to your stomach even if you stand on your head.
Mechanical digestion
* Physically prepares food for chemical digestion by enzymes.
* Mechanical processes include chewing, mixing of food and
saliva by the tongue, mixing of food in the stomach, and by
rhythmic local contractions of the intestine.
* Segmentation mixes food with digestive juices and increase
the efficiently of absorption by repeatedly moving different
parts of food mass over the intestinal wall.
Chemical digestion
* Is a series of catabolic steps in which complex food molecules
are broken down to their chemical building blocks.
* It is accomplished by enzymes secreted by various glands into
the lumen of the alimentary canal.
* The enzymatic breakdown of foodstuffs begins in the mouth,
and is essentially complete in the small intestine.
Absorption
* The passage of digested end products from the lumen
of the GI tract into the blood or lymph.
* For absorption to occur, these substances must first
enter the mucosal cells by active or passive transport
processes.
* The small intestine is the major absorptive site.
Defecation
* Eliminates indigestible substances from the body via
the anus in the form of faeces.