chapter 6 nutrition in humans Flashcards
what organs are part of the digestive system/alimentary canal?
mouth, oesophagus, stomach, small intestine, large intestine
what organs are associated with the digestive system but food does not pass through them?
pancreas, liver
how does peristalsis work to push food?
area of contraction (behind bolus): circular muscles contract while the longitudinal muscles relax = walls of the alimentary canal to constrict = lumen becomes narrower and longer = pushes the bolus forward
how does peristalsis work to accept pushed food?
area of relaxation (in front of bolus): circular muscles relax while the longitudinal muscles contract = the walls of the alimentary canal dilates = lumen becomes wider and shorter = bolus enters lumen.
What is digestion?
process whereby large food molecules are broken down into smaller, soluble molecules that can be absorbed into bloodstream
types of digestion
-> involves physical digestion: mechanical break-up of food into smaller particles = increases SAVR of ingested food - digestive enzymes act more efficiently
-> and chemical digestion: breaking down large molecules in the food (eg proteins, starch, fats) into smaller molecules that can be absorbed
Involves hydrolytic reactions catalysed by digestive enzymes
digestion in mouth
physical: teeth chews food ingested into smaller pieces = increases SAVR for enzymes to work on
physical: tongue mixes food with saliva
chemical: saliva contains salivary amylase - active in saliva (pH: neutral at 7) = digests starch into maltose
processes in stomach
- food stimulates gastric glands to secrete gastric juice - dilute solution of hydrochloric acid (pH 2), mucus, pepsin
chemical: pepsin digests proteins into polypeptides
physical: peristalsis in stomach = churns and breaks up food + mixes food well with gastric juices = forms chyme
function of gastric juice (functions of hydrochloric acid and mucus)
HCl:
1. denatures salivary amylase = stop digestion of starch
- Changes inactive form of enzyme pepsinogen into active form pepsin
- Provides slightly acidic medium for action of pepsin
4.Kills certain potentially harmful microorganisms in food
Mucus: prevents walls of stomach from being digested by pepsin - most cells are made of protein
what does chyme stimulate when it enters the small intestine
- Pancreas to secrete pancreatic juice: pancreatic amylase, trypsin and pancreatic lipase = passes through pancreatic duct into duodenum
- Gallbladder contracts to release bile - passes through bile duct into duodenum
- Epithelial cells in SI to produce intestinal juice: maltase, peptidases, lipase
processes in small intestine
chyme comes into contact with alkaline pancreatic juice, bile and intestinal juice
= neutralise acidic chyme = provide suitable medium (alkaline) for the enzymes in pancreatic and intestinal juices to work
carbohydrate digestion (mouth and small intestine)
- mouth: salivary amylase digests starch into maltose = starch is able to be digested - food does not stay long in mouth
- small intestine:
Pancreatic amylase digests starch into maltose
Maltase digests maltose into glucose
Lactase digests lactose into glucose + galactose
Sucrase digests sucrose into glucose + fructose
End products of carbohydrate digestion: simple sugars (fructose, galactose, glucose) = can be absorbed into bloodstream
Cellulose cannot be digested in humans
protein digestion (stomach and small intestine)
stomach: pepsin digests proteins into polypeptides
small intestine:
trypsin digests undigested proteins into polypeptides
peptidases digest polypeptides into amino acids
endproducts of protein digestion: amino acids = can be absorbed into bloodstream
fats digestion (small intestine)
small intestine:
lipase digests emulsified fats into fatty acids and glycerol - absorbed into bloodstream
how can liver help in fat digestion
liver produces bile which helps in emulsification:
- bile salts lower surface tension of fats = reduce attractive forces between fat molecules
- fats break up into small fat droplets suspended in water (emulsion) = increases SAVR of fats
- increase rate of digestion of fats by lipase into fatty acids and glycerol
emulsification is physical digestion
how is small intestine adapted for absorption? (structure + function)
- inner surface of SI is folded and bears numerous finger like projections called villi = epithelial cells of villi have numerous microvilli: increase SA = increase rate of absorption
- Villi have thin walls/membrane (epithelial is only 1 cell thick): take a shorter time to pass through a thinner membrane = increase rate of absorption
- Steep concentration gradient
One villus - contains a lacteal/lymphatic capillary surrounded by blood capillaries
Lacteals: transport fats
Blood capillaries: transport sugars and amino acids away from intestine
Continuous transport of digested food = maintains concentration gradient for absorption of digested food substances - SI is long = provides sufficient time for absorption
how does absorption take place in SI
- glucose and amino acids: absorbed by diffusion into blood capillaries of villi = transport to liver (right side)
- glucose and AA also absorbed by active transport when concentration of G and AA is lower in lumen of small intestine than in blood capillaries
- glycerol and fatty acids diffuse into epithelium = combine to form minute fat globules that enter lacteals
how are absorbed glucose/amino acids assimilated?
transportation: blood capillaries join to form larger blood vessels = form hepatic portal vein - transports glucose and amino acids absorbed in blood in villi to the liver
- some glucose and amino acid leave liver and transported around body by hepatic vein
Glucose: source of energy - assimilated and oxidised during tissue respiration = release energy for vital activities of cells
Amino acids:
converted into new protoplasm = growth and repair of worn out parts around the body - Forms enzymes and hormones
if excess glucose/amino acids in the liver:
Islets of Langerhans (in pancreas) produce insulin - stimulate liver cells - convert excess glucose to glycogen = stored in liver and muscles - Excess amino acids converted into urea by deamination
how are absorbed fats assimilated
transportation: lymphatic capillaries (lacteals) join to form larger lymphatic vessels - transport fats all around body
- Sufficient supply of glucose: fats not broken down - used to build protoplasm eg cell membrane
- Glucose in short supply: fats broken down = provide energy
- Excess fats: stored in adipose tissues (beneath skin, heart, kidneys) - absorbs shock = protect organs
functions of the liver (6)
- regulates blood glucose concentration (BGC)
Too much glucose in blood - insulin secreted = glucose converted into glycogen - stored in liver/muscles = BGC decreases
Too little glucose in blood - glucagon secreted = glycogen converted into glucose - released into bloodstream = BGC increases - produces bile (stored in gallbladder): makes fat digestion more efficient
- iron storage: red blood cells do not have enough nuclei - destroyed in spleen (gland near liver) - liver breaks down haemoglobin = iron from haemoglobin stored in liver
Haemoglobin broken down = produces bile pigment - synthesises proteins: amino acids synthesised into proteins - found in plasma
- deamination of amino acids: process whereby amino groups are removed from excess amino acids and converted into urea (removed in urine)- remains of deaminated amino acids: converted into glucose in liver - excess glucose produced converted into glycogen
- detoxification: converting harmful substances into harmless ones - alcohol is broken down in liver: liver cells contain alcohol dehydrogenase - break down alcohol into acetaldehyde - further broken down: used in respiration - provide energy for cell activities
effects of alcohol consumption (6)
digestive system:
1. Stimulates acid secretion in stomach - excess acid increases risk of stomach ulcers
2. causes liver cirrhosis: liver cells are destroyed and replaced with fibrous tissue - liver is less able to function
3. May lead to haemorrhaging/bleeding in liver
-> nervous system:
4. Depressant: slows down some brain functions
5. Reduced self control: alcohol takes away a person’s ability to decide = reduce self control - may take personal/social liberties
6. Reaction time is affected: increased reaction time/ slow reaction which results in reduced self-control = slurred speech, blurred vision, poor muscular coordination, unable to walk steadily
