The digestive system Flashcards
Digestion
The breakdown of large, insoluble molecules into small, soluble molecules to be absorbed into the bloodstream
Mechanical digestion
Breakdown of large food pieces into smaller ones without changing them chemically. Examples: chewing in mouth, churning in stomach, peristalsis and emulsification of fats.
Chemical digestion
Breakdown of large food molecules to smaller ones by the action of enzymes that pass out of cells and onto gut contents (produced by tissues and glands in gut)
Alimentary canal
Muscular, long tube (7-8m) lined by an epithelium (made of epithelial and goblet cells) which foods travels through. Starts at mouth, then oesophagus, stomach, duodenum, ileum, colon, rectum and egestion at anus.
Accessory (associated) organs
Glands (salivary) close to gut that secrete juices (may contain enzymes) to aid digestion.
5 main processes of food in gut
- Ingestion: taking food in mouth
- Digestion
- Absorption: passing digested food to blood in ileum
- Assimilation: making use of absorbed food in body
- Egestion: removal of undigested waste from food from the anus
Peristalsis
Walls of intestine contain 2 circular and longitudinal layers that contract and relax to move food along the alimentary canal.
Inner circular muscle contract, causing bolus to move down. Then, circular muscles relax and longitudinal muscle contract, widening the passage and bolus moves further along.
Mouth
- teeth carry out mechanical digestion; cutting, tearing and chewing food; increase surface area
- tongue helps taste, mix food with saliva and swallowing
- salivary glands produce saliva that is secreted onto food and contains amylase breaking down starch to maltose
- bicarbonates: decrease acidity of mouth to prevent dental decay
- mucus: softens and lubricates food for easy chewing and swallowing
- food passes through pharynx then oesophagus
Oesophagus
Lies in chest cavity behind trachea
Tube that transports food from pharynx to stomach by peristalsis
Stomach (to be edited)
Contains digestive gastric juice that digests protein into peptides by enzyme pepsin.
Contains HCl at pH 1.5-2.0 to kill pathogens and activate pepsinogen to pepsin and increase efficiency.
Contains mucus to protect stomach walls from high acidity and reduces friction between food and walls.
Mix of HCl, gastric juice and food called chyme.
Duodenum - Bile
First part of small intestine.
Bile juice: yellow-green, delivered from gallbladder to duodenum by bile duct, produced in pancreas, no enzymes.
Bile juice contains bicarbonates to reduce acidity and slightly alkaline solution for optimum pH.
Bile salts emulsify fats into small globules of fat.
Emulsification increases the surface area of fats to allow insoluble lipids to be digested by lipase dissolved in water and digest lipids.
Duodenum - pancreatic juice
Made in pancreas and transported along pancreatic duct.
Juice contains amylase (starch–> maltose); trypsin (polypeptides–> peptides); lipase (lipids–> fatty acids+glycerol).
Contain bicarbonates that neutralise pH and create alkaline medium.
Upper ileum
Completion of digestion using intestinal juice, produced by ileum walls.
Contains sucrase (sucrose–> glucose + fructose); maltase (maltose–>glucose); lactase (lactose–> glucose + galactose); peptidase (peptides–> amino acids).
Lower ileum (to be edited)
Where small, simple and water-soluble digested nutrients are absorbed into the bloodstream across lining by diffusion or active transport.
Absorption: movement of digested food molecules through wall of intestine to blood.
Large intestine
Colon: absorption of remaining water and minerals from undigested waste, leaving faeces.
Rectum: stores semi-solid faeces
Anus: egestion of faeces (defecation)
