digestive system Flashcards
functions of digestive system
- ingestion of food and water
- mechanical digestion of food
- chemical digestion of food
- movement of food along the alimentary canal
- absorption of digested food and water into the blood and lymph
- elimination of material that is not absorbed
nutrients
- carbohydrates
- proteins
- lipids (fats)
- vitamins
- minerals
- water
carbohydrates
Carbohydrates break up into simple sugars, Amylase acts on carbohydrates (starch) resulting simple sugars (e.g. glucose)
function: source of energy and movement
lipids
Lipids (fats) break up into fatty acids and glycerol, Lipase acts on lipids resulting fatty acids
function: energy reserves and insulation
proteins
Proteins break up into amino acids, Protease acts on proteins resulting amino acids
function: repair and growth
what is digestion
The process in which carbohydrate, protein and fat molecules are broken down to products small enough to be absorbed into the blood and into the cells
mechanical digestion: definition and location
Mechanical digestion = physical breakdown of food particles
- The mouth – teeth cut, tear and grindfood
- The stomach – churning action in thestomach breaks the food down further
- The small intestine – The gall bladderreleases bile into the small intestine. Bile salts act as emulsifying agents, breakingfat down into smaller droplets
effect of mechanical digestion on surface area
Mechanical digestion increases surface areawhich allows more effective chemicaldigestion, as the chemicals can access more ofthe food
chemical digestion
chemicals break down large, complex molecules into smaller, simpler molecules. Molecules are then small enough to beabsorbed into the bloodstream, chemical digestion achieved by enzymes (catalysts which increase reaction rate)
alimentary canal
continuous tube that runs from mouth to anus, it is the lining of the alimentary canal that absorbs nutrients
- the alimentary canal and associated organs (pancreas & gall bladder) make up digestive system
mastication
process in which food is chewed
The action of the jaws & teeth begin mechanical digestion, mastication
bottom teeth + function
- Fourincisors(biting and cutting)
- Twocanines(tearing)
- Fourpremolars, two on each side of the jaw
- Sixmolars, threeon eachside of the jaw. Third molars = Wisdom teeth (crushing and grinding)
tongue function
shapes food into a bolus - to swallow, the tongue moves upwards & backwards,pushing the bolus to the pharynx which leads to theoesophagus
Salivary glands secrete salivary amylase which breaks down carbohydrates into disaccharides.
salivary glands
Three pairs of salivary glands secrete saliva (fluid) containing salivary amylase which lubricates the food and breaks down carbohydrates into disaccharides.
oesophagus
the oesophagus is a tube that is about 23-25 cm long, has a double layer of muscle (circular muscle and longitudinal muscle) like the rest of the canal apart from the stomach (has a oblique muscle)
peristalsis
The contraction of successive bands ofcircular muscle causes the constrictionto move in a wave-like motion called peristalsis, contractions and relaxations of the circular muscle move the bolus along canal
stomach: mechanical digestion
- contains three types of muscle: circular (prevents food from travelling backwards), longitudinal (propels everything forward), oblique
- Mechanical digestion is achieved by waves of muscular contraction whichchurnthe food, mixing it withstomach juices until it is concerted to a thick, soupy liquid calledchyme.
- The lining of the stomach (mucosa) are flat and smooth when full, but as it empties the layers formconspicuous longitudinal wrinkles calledgastricrugae
- Cardiac sphincter and pyloric (gastroduodenal) sphincter – thick ring of smooth muscle -(to prevent acid from leaving the stomach and regulate chyme into the duodenum)
gastric juice
stomach - chemical digestion
- The lining of the stomach, themucosa, is specialised for the secretionof gastric juice bygastric glands* located in narrow, tube-likestructures calledgastric pits
- Gastric juiceis a digestive juice containingHCl, mucus and digestiveenzymes(all secreted by different cells in the gastric pits)*
- Gastric juice is responsible for chemical digestion in the stomach,which is mainly the start of protein digestion
what cells secrete components of gastric juice?
- parietal cells secrete HCl which kills bacteria and activates pepsinogen forming pepsin which breaks down proteins into polypeptides
- chief cells secrete pepsinogen
- goblet cells secrete mucus which protects inner layer from self digestion
small intestine structure
6m, large surface area
small intestine: mechanical digestion
from bile secreted from the liver (emulsification and segmentation which is where the muscles break the bolus and mix it with juices and bile)
small intestine: chemical digestion
intestinal juice secreted by glands in the lining of the small intestine and pancreatic juices secreted from the pancreas into the duodenum
pancreatic juices
- pancreatic amylase: breaks down carbohydrates into disaccharides
- typsin (pancreatic protease): breaks down polypeptides into peptides
- pancreatic lipases: breaks down lipids into fatty acids and glycerol
intestinal juices
- amylases (maltase, lactase, sucrase): breaks down disaccharides (maltose, lactose, sucrose) into simple sugars
- peptidases: breaks down peptides into amino acids
- lipases: breaks down lipids into fatty acids and glycerol
absorption of nutrients
nutrients are absorbed through the internal surface of the small intestine into the blood, effective absorption requires surface area
duodenum
first part
- most of chemical digestion occurs here
- bile salts emulsifies fats (increasing surface area) (bile secreted from the liver into duodenum)
jejunum
middle section
- allows for effective absorption of carbohydrates and proteins
ileum
last part
- B12, bile salts and any remaining products of digestion and absorption
villus
- 1mm, covered by a single cell, for small intestines inside is a lacteal (lymph capillary) surrounded by a network of capillaries, Glucose, amino acids, water and minerals are absorbed into the blood capillaries, Fatty acids and glycerol are absorbed into the lacteals (forming chyle)
- Small Intestine and Stomach have villi but small intestine has lacteals.
functions of large intestine
- Further absorption of water and some salts
- Takes 18-24 hours to pass through → Semi-solid material calledfaeces→elimination
pathway for food
mouth + salivary glands → pharynx → esophagus → stomach → small intestine (bile from liver/gallbladder) → large intestine → anus
bile
- made in liver which aids in the digestion and absorption of fat
- stored in gall bladder and secreted into small intestine when needed
bacterial activity in digestive system
there are trillions of resident bacteria in the large intestine. They are believed to have several important roles in addition to digesting cellulose in plant foods and synthesising some vitamins (e.g. folic acid)
constipation
the movements of the large intestine are reduced and the contents remain there for a long period of time, the faeces become drier and harder than usual
diarrhoea
the frequent defecation of watery faeces, irritation of small intestine or large intestine leads contents of the intestines move through before there is adequate absorption of water
