nutrition in humans Flashcards
what is nutrition
it is the process by which organisms obtain food and evergy for growth, repair and maintenance of the body
what are the processed involved in nutrition
ingestion->digestion->absoption->assimilation->egestion
what is ingestion
it is the intake of food into our body via the mouth
what is digestion
it is the process whereby large food molecules are broken down into small, simpler, soluble, diffusible molecules that can be absorbed into the body
why must food be digested
the food we ingest are made up of large food molecules that cannot pass through the partially permeable cell membrane of the walls of the intestine and into the blood vessels. Food must then be digested to break down the large food molecules into smaller, simpler, soluble, and diffusible molecules that can pass thorugh the walls of the intestine and into the blood vessel. Blood can then transport the simple food molecule to other parts of the body to be used for various processes
whats the difference between physical digestion and chemical digestion
physical digestion is the process of breaking up food into smaller pieces (chewing and peristalsis). However, chemical digestion is the hydrolysing/ breaking down of food into simpler molecules via enzyme action
what organs make up the digestive system
alimentary canal: mouth, oesophagus, stomach, small intestine, large intestine, anus
organ associated with it: gall bladder, pancreas, liver
what is the function of the teeth
it grinds and break up solid food into smaller pieces by mastication to provide a larger surface area for enzyme action (mechenical digestion)
where does digestion begin
digestion begins in the mouth by the teeth, salivary glands, tongue
the mouth carry out both, chemical and physical digestion
teeth breaks food molecules into smaller pieces + saliva which contain amylase= maltose
what is the function of the salivary glands
(chemical digestion) it secretes saliva which contain:
- mucin: dilutes and moistens the food
- bicarbonate ions: buffer the saliva and maintain pH 6.5-7.5
- salivary amylase: digest starch to maltose
what is the function of the tongue
rolls food particles into boli which are swallowed via the pharynx into the oesophagus
what is the structure and function of the pharynx
- it is a common passage way for air and food.
- during swallowing, food is prevented from entering the trachea by the epiglotties
- the epiglotties is a flap like cartilage just above the larynx (voice box)
- when food gets into the trachea, the person will cough the food out
- during breathing, air passes into the trachea, the larynx moves downwards and the glottis is open
- during swallowing, the larynx moves upwards and the epiglotties overs the glotties, preventing the food particles to enter the trachea
what is the structure of the oesophagus
- narrow, muscular tube
- continues from the pharynx to the stomach
- the wall consist of four layers: serous coat, smooth muscles, submucous coat, mucose coat
what is the function of the oesophagus
the oesophagus transport food from the pharynx to the stomach via: gravity, peristalsis
what is peristalsis
- peristalsis is the rhythmic, wave-like muscular contractions in the wall of the alimentary canal
- it helps the movement of food along the gut
- it enables food to be mixed with digestive juices
- peristalsis is caused by the actions of the circular and longtitudinal mucsles (antagonistic mucsles)
what is the structure of a stomach
- distensible muscular bag
- at the end of the stomach, there is a muscular valve called pyloric sphincter:
contracts: food cannot enter the stomach
relaxes: food enters small intestine - muscous coat of the stomach walls bears many pits called gastric pits which secretes gasric juice
what are the functions of the stomach
- protein digestion begins in the stomach
- protein digestionin the stomach requires the gastric juice
- food in the stomach stimulates the gastric glands to secrete gastric juice
- gastric juice is the dilute solution of: hydrochloric acid, pepsin, rennin
- the stomach also serve to store food tempoarily (3-4 hours)
- peristalsis in the stomach help to mix and churn food in the stomach
- partly digested food becomes liquified to form chyme
- chyme enters the duodenum (in small amounts) when the phyloric sphincter relaxes
what is the function of dilute hydrochloric acid
-stops the action of salivary amylase cause of the different pH values
- converts inactive form of gastric enzymes to the active form:
pepsinogen (inactive) —– HCI———> pepsin (active)
prorennin (inactive) ——-HCI———-> rennin (active)
- provides a sligtly acidic medium for the action of the gastric enzymes
- kills germs and certani potential parasites
what is the function of pepsin
- pepsin is a protease which digest proteins to polypeptides
pepsinogen ——-HCI——> pepsin
proteins ——-pepsin—–> polypeptides
pepsin does not digest proteins to amino acids!!
what is the function of rennin
- rennin curdles milk proteins
- converts the soluble caeseinogen found in milk into insoluble caeseinogen:
caeseinogen (soluble)———-> caesin (insoluble) - this allows the insouble caesin to remain in the stomach long enough for digestion by pepsin
what is the structure of the small intestine
- long and coiled
- consists of 3 parts: duodenum, jejunum, ileum
- mucous coat conains glands that secrete digestive intestinal enzymes (maltase, sucrase, lactase, erepsin, intestinal lipase) these enzmes digest food molecules
function of the gall bladder
- stores bile temporarily
- contracts: releases bile into the duodenum via the bile duct
what is the function of a pancreas
- the pancreas secretes pancreatic juice (which contains digestive enzymes-> pancreatic amylase, pancreatic lipase, trypsin) which helps digest food
- the pancrease is connected to the duodenum via the pancreatic duct
what are the functions of the liver
- the cells of the liver secrete bile
- hepatic portal vein-> transport blood from the small intestine to the liver
- regulation of blood sugar
- deamination
- detoxification
- the liver keeps the blood glucose concentration constant (70-90mg)
- after meal:
- > excess glucose, the liver removes it from the blood and stores it as glycogen (stimulated by insulin)
- in between meals/ fasting:
- > glucose is used up by cells for respiration, glucose concentration in blood falls, liver converts some of its stored gllycogen into glucose (stimulated by glucagon), released into the blood stream
what is the function of the small intestine
2 major functions: digestion ( fats, proteins, carbohydrates), absroption
how does fat digestion happen in the small intestine
- bile:
- > emulsifies fat into minute fat globules
- > increases surface area for digestion by lipase
- > bile is not an enzyme and emulsification is not digestion!!!
- pancreatic and intestinal lipase:
-> digests emusifies fats into fatty acids and glycerol
fats — pancreatic lipase and intestinal lipase—-> fatty acids and glycerol
how does protein digestion happen in the small intestine
- trypsin:
-> synthesized as inactive trypsinogen
-> converted by enterokinase to active form
trypsinogen —- enterokinase—> trysin
-> digests proteins to polypeptides
proteins —trypsin—> polypeptides - erepsin:
-> hydrolyses polypeptides to amino acids
polypeptides —erepsin—> amino acids
how does carbohydrate digestion happen in the small intestine
- pancreatic amylase:
- > digests starch to maltose
- maltase:
->digests maltose into glucose
starch —pancreatic amylase–> matose — maltase—-> glucose
-lactase:
-> digests lactose to glucose and galactose
lactose—- lactase—> galactose + glucose
-sucrase:
-> digests sucrose to glucose and fructose
sucrose—sucrase—-> fructose+ glucose
what is absorption
the process whereby digested food materials are taken into the bloodstream
how is the rate of absorbtion influenced
the rate of absorption depends on:
- surface area
- thickness of seperating membrane
- concentration gradient
how are small intestine adapted for absorbtion
- inner walls are extensively folded: to provide a larger surface area for absorption
- bears numerous villi: provides a larger surface area for absorption
- long and coiled: the length of the small intestine increases the time for absorption
- the surface area is increased by the numerous folds in it inner wall, villi in its inner walls increase surface area
how are villi adapted for abdorption
- thin walls of the villi make it eady for nutrients to pass through to the bloodstream. Epithelium is only one cell thick, microvilli in the epithelium of villi increase surface area
- lacteal/lympahtic capillary helps to transport fats to the body (middle yellow part)
- richly supplied with blood capillaries that help to transport amino acids and glucose away quickly (red and blue part)
how are nutrients absorbed inthe small intestine
- by diffusion:
- > glucose and amino acids diffuse into the blood capillaries.
- > glycerol and fatty acids diffuse into the epithelium, and combine to form minute fa globules which enter the lymphatic capillary
- by active transport:
- > glucose and amino acids are absorbed by active transport
what is the function of the hepatic portal vein
- the blood capillaries that supply the small intestine unite to form the hepatic portal vein
- the herpatic portal vein transports sugars and amino acids to the liver
how are glucose and amino acids in the small intestine absorbed
simple sugars and amino acids are absorbed directly into the blood capillaries found in the villi-> the capillaries join up to form veins-> veins unite to form 1 large vein: herpatic portal vein-> herpatic portal vein carries nutrients in the blood to liver
what is the structure of the large intestine
- consists of:
- > caecum and appendix
- > asending colon
- > horizontal transverse colon
- > descending colon
- > rectum
what is the function of the large intestine
absorption of water and mineral salts
what is the function of the rectum and anus
- undigested and unabsorbed matter is stored temporarily in the rectum
- removed from the bodyo through the anus
- egestion: removal of undigested matter from body
what is assiiliation
the process whereby some of the absorbed food materials are converted into new protoplasm or used to provide energy
what happens to the absorbed sugar
- the hepatic portal vein carries the absorbed sugars to the liver
- in the liver:
- > most of the sugars are converted to glycogen and stored, requires the hormone calle insulin
- > some glucose leaves the liver by the herpatic vein to be distributed aroung the body
- > glucose is used by all living cells to release energy during respiration
- > when the body needs more glucose, the liver converts the stored glycogen back to glucose
what happens to the absorbed amino acids
- in the liver:
- > excess amino acid are converted to urea by deamination
- > the remains of the deaminated amino acid is then converted back to glucose
- > access glucose is converted to glycogen
- > amino acids are transported by the hepatic vein to the different parts of the body to be utilised like: formation of new protoplasm, growth and repair of worn out parts of the body, formation of enzymes and hormones
the assimilation of fats
- converted to forms that can be oxidised or stored
- under normal conditions:
- > fats are not oxidised
- > used to buid protoplasm
- > excess fats stored in special tissues called adipose tissues
- insufficient glucose:
- > fats are oxidised to provide energy
how do insulin and glucagon control carbohydrate metabolism
too much glucose in blood – insulin–> live converts glucose into glycogen—-> blood glucose level decrease
too little glucose in blood —glucagon—> liver converts glycogen into glucose—> blood glucose level increases
why is it important to maintain a constant blood sugar level
cells nedd glucose for respiration, excess gluose can lead to diabetes
what is deamination
- excess amino acids are deaminated
- deamination:
- > amino part ( ammonia) is removed, then converted to urea, and excreted by the kidneys
- the remains of the amino acids are converted to glucose and converted to gylcogen if in excess
what is detoxificaion
- detoxification i a process of converting toxic and harmful substances into harmless substances
- enzyme alcoho ldehydrogenas converts alcohol into acetaldehyde. Acetalgehyde is used as a source of energy in cells
alcohol — alcohol dehydrodenase—> acetaldehyde
why is it that high consumption of alcohol can lead to liver failure
overloads the liver to detoxify alcohol, thus, liver breaks down
what are some harmful effects of excessive alcohol consumption
- increase risk of gastric uclers
- cause liver cirrhosis
- slow down some brain functions
- reduce self-control
- cause symptoms of ‘drunkness’
- frequent intake may lead to addiction
