chapter 5 - digestion in humans Flashcards
nutrition
process by which organisms obtain food and energy for growth, repair and maintenance of the body
ingestion
food is taken into the digestive system
digestion
process where large, complex, insoluble molecules are broken down to small, simple, soluble molecules for absorption into body cells
describe the different forms of digestion
physical process : mechanical breakdown of food into smaller pieces through chewing
(eg. chewing, peristalsis, emulsification), which increases the food molecules’ surface area to volume ratio for faster chemical digestion
chemical process : mechanical break of bonds in molecules which involves enzymes
(eg. hydrolytic reaction)
absorption
digested food substances such as glucose and amino acids will be taken up by the body cells and absorbed into the bloodstream through the wall of the ileum of the small intestine by process like active transport and diffusion. the absorbed food substances in the bloodstream will then be diffused into the body cells for assimilation
assimilation
uptake of absorbed food substances into cells and tissues to be converted into protoplasm or used to release energy
egestion
removal of undigested material
describe the mouth and the processes happening in it
-the salivary gland in mouth secretes saliva, which is mixed with the food by the tongue
- the saliva contains mucin which softens the food
the chewing action of teeth breaks up larger pieces of food into smaller pieces to increase surface area to volume ratio
- the tongue rolls the food into small, slippery round masses (boli)
describe the pharynx, larynx and epiglottis
- pharynx connects buccal cavity to the oesophagus and larynx, and the trachea to the lungs
- the larynx has a slit-like opening known as glottis, which is covered by a flap-like tissue known as the epiglottis. during breathing, air passes into the trachea and into the lungs, the larynx moves downwards and the glottis is open. during swallowing, the larynx moves upwards and the epiglottis covers the glottis, preventing food particles from entering the trachea.
oesophagus
- made up of two antagonistic muscles : circular and longitudinal
- peristalsis in the walls of the oesophagus and the gravity pushes the bolus into the stomach
stomach
food in the stomach is digested by enzymes found in the gastric juice produced and secreted by the gastric glands. when the bolus enters the stomach, it stimulates the release of gastric juices by the gastric glands. peristalsis in the walls of the stomach mixes the food with the gastric juices
what is in the gastric juice secreted by the gastric glands in the stomach?
dilute solution of hydrochloric acid, mucus and pepsin
what does the hydrochloric acid in gastric juice do?
- denatures salivary amylase
- converts inactive pepsinogen into pepsin
- provides an acidic medium (pH 2) for the action of pepsin
- kills harmful microorganisms in food
small intestine
- consists of the duodenum, jejunum and ileum
- chyme enters the duodenum and stimulates release of pancreatic juice by pancreas, bile by gall bladder, and intestinal juice by the small intestine. the alkaline fluids neutralises the acidic chyme. the alkaline medium is needed for the action of intestinal and pancreatic enzymes.
what do the juices released at the small intestine consist of?
- pancreatic juice : secreted by pancreas, contains pancreatic amylase, pancreatic lipase, trypsin
- bile : secreted by gall bladder, passes through bile duct into duodenum
- intestinal juices : secreted by intestinal glands, contains maltase, sucrase, lactase, peptidase and intestinal lipase
liver
- 3 important blood vessels found at its lower surface : hepatic artery, hepatic vein and hepatic portal vein
- produces and releases bile
- regulate the blood glucose concentration in blood plasma
functions of liver
- produces bile involved in the emulsification of fats, which is the physical breakdown of large fat globules into smaller fat globules for faster chemical digestion of fat molecules into fatty acids and glycerol by lipase
- regulate blood glucose concentration by secreting insulin and glucagon
- uses amino acids to synthesise plasma proteins such as prothrombin and fibrinogen for clotting of blood
- after worn-out red blood cells are destroyed in the spleen, haemoglobin will be released and transported to liver
- haemoglobin broken down to produce iron and bile, iron stored in liver
- detoxification of harmful substances like alcohol, into less harmful substances
what is bile made up of?
- alkaline, greenish-yellow liquid
- made up of bile salts and pigments which aids in fat digestion by emulsification of fats
describe the role of bile in the digestion process
- physical digestion of fat molecules
- used for emulsification of large fat globules to smaller fat droplets
which increase the fat molecules’ SA2VR for faster chemical digestion by lipase into glycerol and fatty acids
describe the fate of amino acids in the liver
- used to synthesise plasma proteins in the liver
- excess amino acids undergoes deamination in the liver
- amino group will be removed and converted into urea, that will be excreted in the kidneys
- carbon residue converted into glucose, excess glucose converted and stored as glycogen in liver
gallbladder
- temporarily stores bile produced by the liver
- when gallbladder contracts, bile would flow through the bile duct and the duodenum
pancreas
- connected to the duodenum by the pancreatic duct and joins to the bile duct before it opens into the duodenum
- produces and secretes pancreatic juices that contains enzymes
- produces and secretes hormones like insulin and glucagon
peristalsis
rhythmic, wave like muscular contractions in the wall of the alimentary canals where the circular and longitudinal muscles contract and relax alternately
what does peristalsis do?
- helps to move food along the gut
- helps food to be mixed with digestive juices
- occurs in oesophagus, stomach, small/large intestine
antagonistic muscles
pair of muscles whose movements oppose each other eg. circular and longitudinal muscles in wall of gut
describe movement of antagonistic muscles
when the wall constricts, the circular muscles contract and the longitudinal muscles relax, pushing the food forward. when the wall dilates, the longitudinal muscles contract and the circular muscles relax, widening the lumen to allow food to enter.
enzymes in mouth
salivary amylase
starch to maltose
enzymes in stomach
gastric juice contains pepsin
protein to polypeptides
enzyme in duodenum
bile :
from the liver, from fats to fatty acids and glycerol
pancreatic juice :
contains pancreatic amylase, pancreatic lipase and trypsin
from starch to maltose, fats to fatty acids and glycerol and proteins to polypeptides respectively
intestinal juice:
enterokinase (trypsinogen → trypsin), maltase (maltose → glucose), lactase (lactose → glucose + galactose), sucrase (sucrose → glucose + fructose), erepsin (polpeptides → amino acids), lipase
(fats → fatty acids + glycerol)
describe the digestion and absorption processes of proteins in mammals
physical digestion of proteins begins at the mouth through chewing, to increase SA2VR. this is for faster chemical digestion of proteins in the stomach by pepsin
pepsin in the stomach chemically digests the proteins into short polypeptides. trypsin, produced by the pancreas, will chemically digest the short polypeptides into amino acids. the amino acids will the be absorbed into the villi and into the blood stream at the small intestine via active transport and diffusion
describe the digestion and absorption processes of starch in mammals
physical digestion of starch begins at the mouth via chewing to increase the SA2VR, for faster chemical digestion of starch in the mouth by salivary amylase
salivary amylase found in saliva secreted by salivary glands will chemically digest the starch into maltose. pancreatic amylase, produced by the pancreas, will chemically digest the remaining starch into maltose at the duodenum. maltase produced by the small intestine will chemically digest the maltose into glucose
the glucose will be absorbed into the villi and into the bloodstream by active transport and diffusion
adaptations of small intestine
- walls have numerous folds for a larger surface area for absorption of digested food substances.
- presence of villi to increase surface area to volume ratio for faster absorption of digested nutrients
- villi walls are one cell thick to decrease diffusion distance for faster absorption of digested food substances
- villi have microvilli to increase surface area to volume ratio for faster absorption of digested food substances
- each villus is richly supplied with blood capillaries and lymphatic capillaries to quickly carry away the absorbed food substances to maintain a steep concentration gradient (lacteals absorb and transport fats
blood capillaries absorb and transport glucose and amino acids away from the small intestine) - small intestine is long to provide sufficient time for more efficient absorption of digested food substances
adaptations of villus
- each villus has numerous microvilli to increase surface area to volume ratio for faster absorption of digested food
- villus wall is one cell thick to decrease diffusion distance for faster absorption of digested food into the blood capillaries and lacteals by diffusion and active transport
- continuous blood flow to maintain a steep concentration gradient for faster absorption of digested nutrients into blood capillaries by diffusion
- surrounded by large network of blood capillaries so that digested food substances can be transported away faster to maintain a steep diffusion gradient
- blood capillaries absorb and transport glucose and amino acids from small intestine to liver
lacteals absorb and transport fats
how are nutrients transported?
glucose and amino acids diffuse into the blood capillaries and glycerol and fatty acids diffuse into the epithelium, and recombine to form minute fat globules which enter the lymphatic capillary.
glucose and amino acid are transported by active transport
what happens to the nutrients absorbed in the liver?
glucose : excess glucose converted to glycogen and stored in muscles and tissues. it is transported by the hepatic vein to the different parts of the body
amino acids : excess AA are converted to urea by deamination. amino acids are converted into new cytoplasm that is used for growth and repair of worn out cells and used to form enzymes and hormones. they are transported by the hepatic vein to the different parts of the body.
fats : fats are absorbed into lymphatic capillaries, which join to form larger lymphatic vessels that discharge fats into bloodstreams. blood carries the fats to all parts of the body, especially to the liver. when there is enough glucose, fats are not broken and instead are used to build protoplasm like cell membranes. when glucose is in supply, fats are broken down to provide the energy needed for vital activities in the body. excess fat is stored in adipose tissues beneath the skin and around the heart and kidneys. adipose tissues protect organs by acting as shock absorbers.
function of liver
- regulates blood glucose concentration and keeps it constant by secreting insulin and glucagon when required
- produces bile that aids in fat digestion as it emulsifies fats into smaller fat globules to increase surface area to volume ratio for faster digestion of lipase into fatty acids and glycerol
- involved in deamination where the amino group are removed and converted to urea in the liver. the carbon residues of amino acids from deamination are converted to glucose in the liver
- alcohol is broken down in the liver as liver cells contain an enzymes which breaks down alcohol to compounds that used in respiration to provide energy for cell activities
short term effects of alcohol
- depressant and slows down brain functions
- reduced self-control
- longer reaction time and decreased reaction rate
- slurred speech, blurred vision and poor muscular coordination
- drive faster with less caution due to decreased reaction rate
long term effects of alcohol
- liver cirrhosis where liver cells are destroyed and replaced the fibrous tissue. alcoholic cirrhosis may lead to haemorrhage in the liver
- addiction with many withdrawal symptoms
- shrinkage of brain volume where the brain becomes smaller than normal, especially the regions associated with memory and reasoning
- wet brain : type of dementia caused by brain damage. alcohol interferes with the absorption of vitamin b1, part of enzyme needed to break down glucose to release energy for brain activities like conduction of nerve impulses
what happens when the bile duct is blocked?
lack of bile released from the gall bladder into the duodenum. there will not be emulsification of fats into smaller fat globules, lesser surface area for digestion of fats by lipase, hence, a slower rate of fat digestion. carbohydrate and protein digestion is not affected.
what happens when the pancreatic duct is blocked?
- pancreatic juice is unable to enter the duodenum from the pancreas → no digestion of proteins to polypeptides, no digestion of starch to maltose, no digestion of lipids to fatty acids and glycerol in the small intestine → reduced digestion of starch, lipids and proteins
- bile unable to enter the duodenum from the gallbladder → no bile to emulsify fats into smaller fat globules → smaller surface area to volume ratio for lipase to act on → slower digestion of fats by lipase
