Nutrition

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How unicellular organisms digest food
Holozoic nutrition / endocytosis
What is a sac gut
Prey is digested and the products are absorbed , the indigestible remains are egested through the mouth .
What is a tube gut
Digestive tube with two openings ( anterior and posterior)
food is ingested through the mouth and indigestible waste is egested at the anus.
Why must food be digested
food molecules that is too large and insoluble cannot be absorbed into the blood stream so the polymers must be converted into monomers so they can be absorbed and rebuilt into molecules needed by the body
What is ingestion 
Taking food into the body through the mouth
What is digestion  
Breakdown of large insoluble molecules into soluble molecules that are then small enough to be absorbed
what is Mechanical digestion
Cutting and crushing by teeth and muscle contractions of the gut wall , it increases the surface area for enzymes to act
What is chemical digestion
Larger insoluble molecules to small soluble molecules using digestive enzymes .
Bile and stomach acid also contribute
What is absorption 
The passage of small soluble molecules and ions though the gut wall
what is egestion 
The elimination of indigestible waste
Where does digestion and absorption occur
In the gut
What is the gut  
A long, hollow, muscular tube which allows the movement of the contents in one direction . The food is propelled along by peristalsis
What is peristalsis  
A wave of muscular contractions and relaxations of the gut wall which propell the contents along the whole length if the gut
Dietary fibre aids peristalsis in the intenstines
Human digestive system
The digestive systemn
mouth
oesophagus
stomach
illeum
duodenum
colon
rectum
anus
Function of the mouth
Ingestion
mechanical digestion of food( crushing action if the teeth )
chemical digestion of starch (by salivary amylase)
Function of the oesophagus 
Carriage of foods to the stomach by peristalsis
Function of the stomach
Contraction of stomach muscles to churn up the food (mechanical digestion). Secretion of hydrochloric acid (chemical digestion of proteins by enzymes )
Function of the Ileum 
Receives pancreatic juice from the pancreas and the bile from the gall bladder. Chemical digestion of carbohydrates, fats and protiens by enzymes
Function of the duodenum
Chemical digestion of carbohydrates, fats and proteins by enzymes
absorption of digestion food
function of the colon
Absorption of water
Function of the rectum
Storage of faeces
Function of the anus 
Site of egestion
structures of the mammalian gut wall
Serosa ,muscularis ( inner circular and outer longitudinal) ,sub-mucosa , mucosa, lumen
What is the serosa
Outermost layer which contains tough connective tissues which protects the gut wall. Reduces friction with other abdominal organs during peristalsis
What is the muscularis
Composed of two layers - inner circular muscles and outer longitudinal muscles.
Causes coordinated waves of contraction (peristalsis) which pushes bolus of food along the alimentary canal
What is the Submucosa
Connective tissues containing blood and lymph vessels which removes the absorbed products of digestion. Also contains the nerves which coordinate peristalsis
What is the mucosa
It lines the gut wall and is the inner most layer. The epithelium secretes mucus which lubricates and protects the mucosa.
in some regions it secretes digestive juices and in others it absorbs digestive food
Structure of the mammalian gut
Carbohydrate digestion
Protein digestion
Fats digestion
How does the buccaneer cavity work
Mechanical digestion occurs in the mouth , food is mixed with salvia by the tongue and chewed with the teeth which increases surface area for enzymes to work
What is salvia 
A watery secretion , containing amylase ( enzyme for starch to maltose) , bicarbonate ions for the optimum pH for amylase and mucus to lubricate the food
how does the oesophagus work
It connects the buccal cavity to the stomach
How does the stomach work
Bolus of food enters the stomach and is kept there by the contraction of sphincter muscles. It can remain there for several hours, the stomach wall muscles contract rhythmically to churn the food with gastric juice secreted from gastric gland in the mucosa of the stomach wall
What does gastric juice contain
Mucus -protective lining which protects the stomach wall from digestive enzymes and hydrochloric acid. It also helps to lubricate the food
Hydrochloric acid -lower pH of stomach contents to pH2 for the optimum environment for enzyme action
Pepsin -(secreted as inactive pepsinogen) enzyme for proteins which works optimum in acidic environment
Two regions in the small intestine
Duodenum and ileum
How is food moved into the small intestine
Relaxation of the sphincter muscles at the base of the stomach slowly release partially digested food into the duodenum
What is the function of the duodenum  
It is the first section of the small intestine and receives secretions from the liver and the pancreas. Food from the stomach is lubricated by mucus and hydrochloric acid is neutralised by alkaline secretions from the submucosa