Studied by 1 personwhat is the role of this system
to ingest food and mechanically and chemically break it down into simple molecules so it can be accessible to cells
what is digestion
the process of breaking down food into smaller molecules so that cells can absorb/use them for metabolism
what is mechanical digestion
physical break up of food into smaller pieces, increasing the surface area of the food particles for efficient enzyme activity
what does mechanical digestion involve
mastication, peristalsis, churning and emulsification
what is chemical digestion
breaking down of complex carbs into smaller molecules by enzyme action so they can be absorbed into blood or lymph
what are the roles of the digestive system
ingestion
mechanical digestion
chemical digestion
peristalsis
absoprtion of nutrients into blood
elimination of undigested food
excretion of bile pigments
what are the main components of this system
alimentary canal → tube from mouth to anus
accessory organs → e.g. teeth, liver etc
describe the strucutre and fucntion of the mouth
the mouth takes in food and begins chemical and mechanical digestion
it contains the accessory organs of the teeth and the tongue and salivary glands
describe the teeth
incisors → pointy spades, bitng and cutting of food
canines → concial points for tearing food
pre molars → broader crown
molars → very broad crown for grinding food
what is the teeth formula
2 1 2 3 (upper)
------- half of jaw x 2 + 32 teeth
2 1 2 3 (lower)
describe the tongue
mixes food with saliva to form bolus (soft round mass of food to be swallowed)
describe salivary glands
secrete saliva (liquid rich in salivary amylase and mucus)
mucus lubricates mouth
salivary amylase breaks down 50% of starch into shorter chains
describe the strucutre and function of the pharynx
common passage of food and air
stratified epithelium lining coated in mucosa
describe the structure and the function of the oesophagus
muscular tube (circular and longitudinal smooth muscle) which takes food to the stomach
stratified epithelium lining with mucosa
what is peristalsis, in reference to digestive system
wave of involuntary muscular contractions of the walls of tubular organs
in the digestive system it moves food along the alimentary canal
how does peristalsis work in oesophagus
the circular msucles contract behind bolus
long muscles contract, shortneing path
muscles in front of bolus remain relaxed
describe the structure and the function of the stomach
a muscular organ which acts as a widening in the alimentary canal
brings about mechanical digestion by churing
has 3 muscle layers and is lined with mucosa
contains gastric pits, into glands which release mucus, inactive enzyme pepsinogen and HCl
what do mucus, pepsinogen and HCl do
the mucus protects the stomach lining, muscles etc
the pepsinogen is activated into pepsin which starts digestion of proteins
HCl activates pepsin by supplying H+ ions and kills bacteria
what produces mucus in the stomach
goblet cells
what is the pyloric sphincter
a circular muscle at the end of the stomach which regulates the passage of chyme
describe the structure and function of the small intestine
6.5m long narrow tube
3 sections → duodenum, jejunum, ileum
site of majority of digestion
digests all food groups
site of majority of absoprtion
what adaptive features does the small intestine have
mucosa is long and permanently folded
2 layers of smooth muscles for peristalsis and segmentation
glands which secrete digestive enzymes
villi and microvilli increase surface area
rich blood supply
lacteal
carrier proteins
many mitochondria for energy for transport
what are the pancreatic juice enzymes and their role
pancreatic amylase → break starch into shorter polysaccharide chains
pancreatic protease (trypsin) → breaks polypeptides into dipeptides
pancreatic lipase → breaks lipids into fatty acids and glycerol
ribonuclease and deoxxyribonuclease → break DNA and RNA into nucletodies
where are pancreatic juices secreted into
duodenum
why are pancreatic juices basic
because presence of HCO3- ions provides optimum pH
what are the intestinal juice enzymes and their roles
intestinal protease → break dipeptides into amino acids
intestinal amylases: a) sucrase → break sucrose into fructose + glucose
b) maltase → break maltose into 2 glucose
c) lactase → break lactose into galacatose and glucose
intestinal lipase → break lipids into fatty acids and glycerol
how does mechanical digestion occur in the small intestine
segmentation (forward and backward motion of food)
peristalsis
emulsification of lipids and fat by bile
how does bile emulsify fats and lipids
it breaks large fat globules into smaller fat droplets with larger surface area
what is bile
a green brown secretion of the liver which contaisn bile pigments ( like bilirubin) and bile salts
it is concentrated and stored in gallbladder
how is bile pigments formed
the breaking down of red blood cells in the liver
describe absoprtion in the small intestine
water and water soluble vitmans diffuse simply and by osmosis
glucose and amino acids are carried by active transport
minerals diffuse
describe absoprtion of fatty acids and glycerol
they diffuse into villi epithelial cells where they are reassembled into lipids and covered in proteins, forming a chylomicron
chylomicrons are actively transported into lacteal in the villus
what is the lacteal
lymph vessel inside villus
describe the large intestine
large diameter
1.5m length
no digestive enzymes secreted
contains good bacteria and minerals and some vitamins (k)
what do the good bacteria do in the large intestine
finish digestion of organic molecules
produce vitamin K
what occurs in the large intestine
formation of faeces by removal of water
storage of faeces
elimination
defacation
describe elimination and defacation
elimination is the removal of undigested or indigestable matter
defacation is the passing of faeces via the anus into an external environment
name the parts of the large intestine in order of which matter moves through it
cecum, ascedning colon, transverse colon, descending colon, sigmoid colon
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