digestion ! Flashcards
ingestion !
intake of food into our body via the mouth
digestion !
process whereby large, complex, indiffusible, insoluble food molecules are broken down into small, simple, diffusible, soluble molecules that can be absorbed into body cells
physical digestion
physical process of breaking up food into smaller molecules through chewing & peristalsis
chemical digestion
process of hydrolysing (breaking down) food into simpler, soluble, diffusible molecules via enzyme action
importance of digestion
food must be digested to break down the large, complex, insoluble, indiffusible into smaller, simple, soluble and diffusible molecules
- can pass through the walls of the small intestine & into the blood vessels
- blood plasma can then transport the simple food molecules (glucose, amino acids) to other parts of the body for use of various processes
digestive tract
mouth & buccal cavity pharynx oesphagus stomach small intestine large intestine anus
mouth !
site of ingestion
physical : teeth
- chewing action breaks up solid food into smaller pieces -> increases surface area to volume ratio for salivary amylase to act on it more efficiently
chemical : salivary glands
- secrete saliva containing salivary amylase into food
- moistens food + breakdown starch -> maltose
tongue
- rolls food particles into bolus
- easier for food particles to be swallowed via the pharynx into the oesophagus - mix food with saliva
pharynx !
connects buccal cavity to oesophagus & larynx
common passageway for air and food
epiglottis
swallowing : food prevented from entering trachea
- larynx : moves upwards
- epiglottis covers glottis
breathing : air passes into trachea
- larynx : moves downwards
- glottis is open
if food gets into trachea : person will cough to force the food out
oesophagus !
transports food from pharynx to stomach
- gravity + peristalsis
peristalsis in oesophagus pt 1 !
enables food to be mixed with digestive juices
caused by the actions of antagonistic muscles
- circular & longitudinal
peristalsis in oesophagus p2 !
circular contract - longitudinal relax
- wall of gut : contracts -> becomes narrower & longer -> food is pushed forward
circular relaxes - longitudinal contract
- wall of gut : dialtes -> becomes wider & shorter -> widens lumen for food to enter
stomach !
secretes gastric juice : contains hydrochloric acid, pepsin, renin
distensible muscular bag with thick & well developed muscular wall
- can expand
stomach wall : has numerous pits
- secretes gastric juice into stomach cavity
presence of food in stomach : stimulates gastric glands to secrete gastric juice into stomach cavity
pyloric sphincter
muscular valve found at the end of stomach
contracts : entrance to small intestine (duodenum) closes
relaxes : entrance to small intestine (duodenum) opens
peristalsis in stomach !
churns + breaks up food substances from big particles to small particles
- increases surface area to volume ratio for protease to act on
- mixes food substances well with gastric juice
hydrochloric acid in gastric juice / stomach’s acidic conditions !
stops action of salivary amylase by denaturaing it
changes inactive form of pepsinogen to active form pepsin
provides an acidic pH condition for gastric enzymes
kills potentially harmful microorganisms in food
renin
curdles milk proteins : converts soluble caseinogen in milk -> insoluble caesin
- requires Ca2+ : allows insoluble caesin to remain in the stomach long enough for digestion by pepsin
chyme
partly digested food that has been liquified
enters duodenum in small amounts when pyloric sphincter relaxes & opens
small intestine parts !
duodenum : (from stomach ) + digestion
jejunum : more digestion + assimilation
ileum : absorption + digestion complete
duodenum !
pancreatic juice
- inactive trypsinogen -> active trypsin by enterokinase
- pancreatic lipase
- pancreatic amylase : starch -> maltose
intestinal juice
- erepsin : hydrplyses polypeptides -> amino acids
proteins -> polypeptides by trypsin
polypeptides -> peptidases by erepsin -> amino acids
- intestinal lipase
fat digestion : bile
emulsifies fat into minute fat globules : increase surface area to volume ratio for digestion by lipase
jejunum !
lactose : lactose -> galactose + glucose
sucrose : sucrose -> glucose + fructose
absorption !
process whereby digested food substances are taken in by the body cells
- diffusion
- glucose + amino acids into blood capillaries of villi
- glycerol + fatty acids into epithelium -> combine to form minute fat globules -> enter lymphatic capillary - active transport
- glucose + amino acids : when there is a low conc of digested food substances in lumen of small intestine than blood capillaries
small intestine features !
inner walls : extensively folded
- provides a large surface area to volume ratio -> increased efficiency for absorption
bears numerous villi : providing a large surface area for absorption
long & coiled : provide sufficient time for absorption
villi features !
walls : one cell thick
- shorter diffusion distance -> faster rate of absorption
microvilli in epithelium of villi : increases surface area to volume ratio -> faster rate of absorption
lacteal / lymphatic capillary + rich network of blood capillaries
- help transport amino acids & glucose away quickly -> maintain diffusion gradient -> maintain high rate of absorption
hepatic portal vein !
transports blood rich in glucose & amino acids absorbed from small intestine -> liver
assimilation !
process whereby absorbed food substances are converted into new protoplasm or used to provide energy
assimilation : glucose !
used by cells in respiration to release energy
- most glucose : converted to glycogen for storage in liver
- some glucose : transported by hepatic vein to diff parts of body
assimilation : amino acids !
used by cells to make proteins, enzymes, hormones & new protoplasm
excess amino acids : converted to urea by deamination
- remains of deaminated amino acids : converted back to glucose
assimilation : fats !
used to build protoplasm
stored in adipose tissues : protect vital organs from shock
broken down : to release energy when there is a lack of glucose
used as an insulating material against heat loss
liver : carbohydrate metabolism !
regulates concentration of blood glucose
after meals : too much glucose in blood
- insulin secreted (pancreas)
- excess glucose -> glycogen for storage in liver
- blood glucose level decreases
fasting / in between meals : too little glucose in blood
- glucagon secreted (pancreas)
- glycogen -> glucose to replenish glucose used in respiration by cells
- blood glucose increases
liver : fat digestion !
produces bile : stored in gall bladder + discharged into duodenum by bile duct
- emulsification of fats…
liver : iron storage !
worn out RBC : destroyed in spleen
- haemoglobin from RBC : transported to liver to be broken down
- iron released from haemoglobin : stored in liver for synthesis of new RBC
liver : deamination of amino acids !
excess amino acids deaminated in liver : amino groups removed
converts amino groups -> urea
- removed from body as an excretory product
converts remains of amino acids -> glucose
- excess glucose -> glycogen
liver : detoxification !
converts toxins & harmful substances into harmless substances
- alcohol
- hydrogen peroxide
liver : heat production !
numerous metabolic activities take place in the liver : large amt of heat produced
- heat generated : distributed to rest of body -> maintain body temperature -> opt temp for enzymes
effects of alcohol !
slower reaction time
reduces self control
increases risk of liver failure, gastric ulcers, cirrhosis (formation of fibrous tissue in liver), haemorrhage (bleeding in liver) & death
