Human DigestiveDigestive System - YouTube.flv System http://vimeo.com/76306734 Video link Human DigestiveDigestive System - YouTube.flv System Click digestive system to see video

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? Mouth Oesophagus Stomach Small intestine Large intestine Anus 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.

Digestion Mechanical / 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 maltose amylase

Starch (carbohydrate) digestion: in mouth and small intestine. Chemical digestion: Starch (carbohydrate) digestion: in mouth and small intestine. Protein digestion: in stomach and small intestine Fat 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 digestion Saliva (pH 7) moisten and soften food Starch maltose Tongue mixes food with saliva and rolls food into a bolus before swallowing Saliva - water, mucus, salivary amylase Salivary amylase

https://vimeo.com/76306735 Swallowing (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.htm

What Happens During Breathing and Swallowing? Normally, air passes into the trachea (windpipe) while food passes into the oesophagus. pharynx During breathing, the larynx is lowered and the glottis is open. air larynx (voice-box) Figure 6.4 page 92 oesophagus glottis trachea (windpipe)

What Happens During Breathing and Swallowing? During swallowing, the larynx is raised and the glottis is covered by the epiglottis. This prevents food particles from entering the trachea. pharynx food particles Figure 6.4 page 92 epiglottis oesophagus glottis larynx (voice-box) trachea (windpipe)

What Happens During Breathing and Swallowing? Occasionally, small particles of food or water may get into the larynx or trachea. food particles Figure 6.4 page 92 larynx (voice-box) trachea (windpipe)

What Happens During Breathing and Swallowing? This automatically induces violent coughing to force the food particles or water out and to prevent choking. food particles Figure 6.4 page 92 larynx (voice-box) trachea (windpipe)

Oesophagus Minimal digestion Carries food from mouth to stomach by peristalsis Oesophagus has circular and longitudinal muscles which are antagonistic. When circular muscles contract, longitudinal muscles relax and vice-versa.

Peristalsis Part of the gut wall 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. circular muscles Figure 6.6 page 93 longitudinal muscles

Direction of movement of food Circular muscles relax Wall here dilates Direction of movement of food Circular muscles relax Wall here constricts. Circular muslces contract; longitudinal muscles relax Longitudinal 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

Stomach Stores food temporarily Stomach 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 pepsin HCl is very acidic (pH2), thus it kills bacteria and other microorganisms, as well as stopping the action of salivary amylase Provides acidic medium for gastric enzymes to work Only 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. Compare the stomach wall n oesophagus wall? Which is thinker? Why? ( pro https://vimeo.com/76306734 Click stomach or video link to see video

Small Intestine Subdivided into duodenum, jejunum and ileum In the small intestine, chyme stimulates Pancreas to secrete pancreatic juice Gall bladder to secrete bile Intestinal glands to secrete intestinal juice All three juices secreted are alkaline, pH 8.5

Pancreatic and intestinal juice contain many digestive enzymes. 2 bile 1 bile duct pancreatic juice Pancreatic and intestinal juice contain many digestive enzymes. Bile does not contain enzymes. Bile emulsifies fats, increasing the surface area for lipase action pancreatic duct 3 intestinal juice

Villi – absorption by diffusion To liver From intestine To

Large Intestine (colon) Large inverted U shaped tube. No digestion takes place here Absorbs water and minerals salts Stores 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 faeces Anus – egests (= removal of undigested matter) faeces

Organs associated with the alimentary canal These organs do not digest food but aid in digestion Gall bladder Pancreas Liver

One cell thick epithelium – for efficient absorption of food particles Blood capillaries – transport sugars and amino acids away from the small intestine Lacteal – fatty acids and glycerol recombine in the epithelium to form fat which then enters the lacteal as fine fat droplets This continual transport of digested food substances maintains the concentration gradient for the absorption of digested food substances.

Gall bladder Temporarily 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

Pancreas Connects to small intestine by pancreatic duct Produces pancreatic juice Secretes hormones like insulin (controls blood glucose concentration) and glucagon (controls carbohydrate metabolism) Liver Produces bile, which is stored in the gall bladder

Absorption Adaptations of the small intestine Small 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 villi These 3 adaptations increase surface area for absorption

Assimilation After travelling through the blood stream to the rest of the body, cells can now make use of glucose as source of energy amino acids to build new cytoplasm and tissue cells fatty acids to build new cell membranes