nutrition in humans Flashcards
name the processes of nutrition in humans
1) ingestion: food is taken into the body
2) digestion: large food molecules are broken down into smaller, more soluble molecules that can be absorbed into the body cells
3) absorption: nutrients move from the small intestine into the bloodstream
4) assimilation: nutrients are used by cells to provide energy to make new ectoplasm for growth
5) egestion: ingestion matter is removed from the body
describe the function of the mouth & the buccal cavity
- food enters through the mouth which leads into the buccal cavity (interior of the mouth)
- teeth breaks don food for more surface area so that enzymes can act on it more efficiently
- salivary glands secreted saliva into mouth
tongue mixes the food with saliva & moves food into back of mouth during swallowing
describe the functions of the pharynx and oesophagus
> the pharynx is a part of the AC that connects the buccal cavity to the oesophagus & larynx (voice box) leads to windpipe
oesophagus is a narrow muscular tube that joins mouth to stomach
wall of oesophagus contains 2 layers of muscles (longitudinal muscles on the outer side, circular muscles on inner side)
produces long, slow contractions of gut wall
describe the functions of the pharynx and oesophagus
> the pharynx is a part of the AC that connects the buccal cavity to the oesophagus & larynx (voice box) leads to windpipe
oesophagus is a narrow muscular tube that joins mouth to stomach
wall of oesophagus contains 2 layers of muscles (longitudinal muscles on the outer side, circular muscles on inner side)
produces long, slow contractions of gut wall
define peristalsis and state its function
definition: the rhythmic, wave-like muscular contractions in alimentary canal wall
function: enables food to be mixed with digestive juices pushes food long gut
peristalsis and its movement
1) when circular muscles contract, longitudinal muscles relax (when gut wall contract, it becomes narrower & longer)
- hence, food mass is squeezed & pushed forward
2) when longitudinal muscles contract, circular muscles relax (gut dilates, becoming wider & shorter, widening lumen for food to enter)
peristalsis in stomach
> dispensable musical bag with thick & well-developed muscular walls
inner surface of stomach wall has numerous pits, walls of which are lined with gastric glands
- glands secrete gastric juice which plays an important role in digestion
small intestine (parts)
- U-shaped duodenum (first part of intestine)
- very coiled ileum
- lining of walls contains glands that secrete digestive enzymes
> with these enzymes + enzymes from pancreas, food is digested - water & nutrients from food are absorbed in small intestine
organs & glands (gut)
1) the liver is dark red in colour & its upper surface touches the diaphragm & lower surface is in contact with stomach & small intestine
> blood vessels: hepatic portal vein, hepatic vein, hepatic artery
2) bile: liver cells produce & secrete bile (alkaline greenish-yellow liquid containing bile salts) - does not contain enzymes so it cannot chemically digest food but aids in physical digestion of fats
- bile is stored temporarily in gallbladder (greenish yellow bag attached to the liver)
- when it contracts, bile flows into duodenum via the bile duct
3) pancreas
- gland lying the loop of duodenum (connected to it by pancreatic duct)
- bile duct joins the pancreatic duct just before it opens into the duodenum
- produces pancreatic juice which contains digestive enzymes (amylase, lipase, protease)
- also secretes the hormones insulin & glucagon (control of blood sugar level)
define digestion, physical digestion (function + definition) & chemical digestion
digestion: process whereby large food molecules are broken down into smaller, more soluble molecules that can be absorbed into the body cells
physical digestion: mechanical break-up of food into small particles:
> in mouth, action of chewing is done by teeth/tongue
> in stomach, where contractions & relaxations of muscles in there stomach wall causes a churning action (breaking up food particles & mixes them with digestive enzymes)
> in small intestine, fats are broken up into small fat molecules by bile salts
- physical digestion (function): increases surface-area-to-volume-ratio of ingested food so that digestive enzymes can act on food more efficiently
chemical digestion: breaking down of large molecules in food, such as proteins, starch and fats, into smaller soluble molecules that can be absorbed
processes that take place in mouth (step by step)
1) food in mouth stimulates salivary glands to secrete saliva
2) saliva is mixed with food to soften it
3) salvia contains an enzyme called salivary amylase which digests starch to maltose
4) optimum pH for salivary amylase is at pH 7 (enzymes is most active)
5) chewing breaks food up into smaller pieces, increasing the surface-area-to-volume ratio for salivary amylase to work on
6) tongue rolls food into small, slippery, round masses or boli (singular: bolus)
7) the boli are swallowed & passed down into the oesophagus via the pharynx
8) peristalsis in the walls of oesophagus pushes each bolus of food down into the stomach
processes that take place in mouth (step by step)
1) food in mouth stimulates salivary glands to secrete saliva
2) saliva is mixed with food to soften it
3) salvia contains an enzyme called salivary amylase which digests starch to maltose
4) optimum pH for salivary amylase is at pH 7 (enzymes is most active)
5) chewing breaks food up into smaller pieces, increasing the surface-area-to-volume ratio for salivary amylase to work on
6) tongue rolls food into small, slippery, round masses or boli (singular: bolus)
7) the boli are swallowed & passed down into the oesophagus via the pharynx
8) peristalsis in the walls of oesophagus pushes each bolus of food down into the stomach
processes that take place in the stomach
- presence of food in stomach stimulates gastric glands to secrete gastric juice into stomach cavity
- peristalsis sin the stomach wall churns & breaks up food (also mixes the food well with gastric juice)
- gastric juice (stomach) contains hydrochloric acid (about pH 2), muscles & enzymes pepsin, which is a protease
> dilute hydrochloride acid (function)
1) it stops the action of salivary amylase by denaturing it
2) provides a low ph environment within the stomach, about pH 2, which is the optimum pH for enzymes protease to digest proteins (protease digests protein to polypeptides) - mucus layer protects the stomach wall against being digested by enzymes it produces & also moistens food to allow easy movement within stomach
- food normally remains in stomach for about 3-4h & partially digested food becomes liquified, becoming chyme
- chyme passes in small amounts into the duodenum when the pyloric sphincter relaxes & opens
> food stays in stomach for a few hours, peristalsis in stomach helps to churn the food, which is brown down both chemically & physically
processes that take place in small intestine
> chyme enters duodenum to stimulate:
- pancreases secreting pancreatic juice (juice passes through pancreatic duct into duodenum & contains the enzymes pancreatic amylase, protest and lipase)
- gallbladder to release bile (it passes through the bile duct into duodenum, but since it does not obtain enzymes, it cannot chemically digest food, but bile salts speed up the digestion of fats)
when food comes into contact with pancreatic juice, bile and intestinal juice, all 3 fluids are alkaline (function):
- neutralise the acidic chyme & provide a suitable alkaline edict (pH 8) for the action of pancreatic & intestinal enzymes
digestion of carbohydrates
- eg. starch, sucrose & cellulose (they are digested by carbohydrates such as amylase & maltose)
> carbohydrate digestion begins begins in mouth: salivary amylase in mouth digests starch into maltose, but only a little bit of starch can be digested because food does not remain long in the mouth
> no digestion of carbohydrates occurs in teh stomach (no carbohydrates)
when carbohydrates enter the small intestine, they are fully digested into simple sugars (eg. starch is digested by pancreatic amylase into maltose) which is then further digested by maltose into glucose - end products of carbohydrates digestion are simple sugars which can be absorbed into the bloodstream (ie. cellulose is not digested at all)
digestion of protein
- proteins are digested by proteases
> some protein digestion begins in stomach, where stomach protease differs proteins into polypeptides
> undigested proteins that enter the small intestine are digested by intestinal protease to polypeptides
> polypeptides produced are further digested to amino acids by intestinal protease - end products of protein digestion are amino acids, which can be absorbed
digestion of fats
> bile (produced by liver & stored in gallbladder) is released into duodenum
- in small intestine, bile salts emulsify fats (they lower the surface tension of the fats, meaning they reduce the attractive forces between the fat molecules)
- causes fats to breakup into tiny fat droplets suspended in water, forming an emulsion
physical break up, no chemical digestion of fat molecules has occured (emulsification increases the surface-area-to-volume ratio of fats, speeding up their digestion by lipase)
- emulsification (definition): breaking up of fats into tiny fat droplets
- emulsified fats are digested by lipases (pancreatic lipases & intestinal lipases) to fatty acids
define and explain the function of absorption
> definition: process whereby digested food substances are absorbed into the body cells
- products of digestion (simple sugars, amino acids, fatty acids & glycerol) are absorbed throughout small intestine (especially ileum) - absorbed nutrients diffuse from cells of small intestine into bloodstream
small intestine adaptations (for absorption)
- inner surface of ileum is folded extensively & has numerous minute finger-like projections called villi (singular: villus) which increases surface area for absorption
- epithelium or wall of the villus is only one cell thick which provides a short diffusion distance for nutrients to pass through
> epithelium cells have many microvilli which further increases the surface area of small intestine
> epithelium cells contain many mitochondria which provides energy for active transport of nutrients into villi - each villus has many blood capillaries that allow blood to transport the absorbed glucose & amino acids to maintain a diffusion gradient
absorption (in small intestine)
- glucose & amino acids are absorbed by diffusion into blood capillaries of villi
- glucose & amino acids are also absorbed by active transport (when there is a lower concentration of these digested food substances in lumen of the small intestine than in blood capillaries)
- glycerol & fatty acids diffuse into epithelium: where they combine to form minute fat globules that enter the lacteals
undigested & unabsorbed food:
> they are stored temporarily in the rectum before it is discharged as faeces through the anus (thus removal of undigested matter from the body is called egestion)
functions of liver
1) production of bile
- bile plays an important role in the digestion of fat
- the liver secretes bile (stored temporarily in gallbladder before use)
2) deamination of amino acids
- excess amino acids are transported to liver: there, their amino groups are removed & converted into urea (deamination)
> urea is removed & converted into urine: remains of deaminated amino acids are converted into glucose in liver (excess glucose formed this way are converted into glycogen)
3) regulation of blood glucose concentration
- key role in carbohydrate metabolism by keeping the amount of glucose in blood constant (eg. especially after a heavy amount of glucose intake or during fasting)
- pancreas contains special groups of cells known as islets of Langerhans which secrete hormones insulin & glucagon into bloodstream
- both insulin & glucagon help to regulate the level of glucose in blood
4) breakdown of hormones : hormones are broken down in liver after they have served their purpose
5) detoxification
- harmful substances may be absorbed into blood from gut (these substances are made harmless by liver cells - process of converting harmful substances into harmless ones is known as detoxification)
- example of a toxin: alcohol (it is broken down by the liver as alcohol can cause damage to digestive system & slow down brain functions) - liver cells contain an enzyme which breaks down toxins
define assimilation
assimilation: process whereby some of the absorbed nutrients are converted to cytoplasm or used to provide energy
describe the transportation of glucose & amino acids after absorption
- after absorption, blood in the villi is now nutrient rich
- blood capillaries unite to form larger blood vessels, which then unite again to form a large vein called the hepatic portal vein
> hepatic portal vein: transport nutrients from the small intestine to the liver - in the liver, most of the absorbed sugars are converted into glycogen & stored (some glucose is transported by blood leaving living & distributed around the body)
utilisation of nutrients
> glucose
- all cells use glucose as a source of energy (glucose is assimilated & then broken down during tissue respiration to release energy for vital activities of cells)
- excess glucose is returned to liver & stored as glycogen
a hormone called insulin (produced by the islets of Langerhans in the pancreas) stimulates liver cells to convert excess glucose into glycogen
when the body needs energy, liver converts stored glycogen back into glucose & it is then transported by blood to the cells to provide energy
utilisation of nutrients (glucose)
> glucose
- all cells use glucose as a source of energy (glucose is assimilated & then broken down during tissue respiration to release energy for vital activities of cells)
- excess glucose is returned to liver & stored as glycogen
a hormone called insulin (produced by the islets of Langerhans in the pancreas) stimulates liver cells to convert excess glucose into glycogen
when the body needs energy, liver converts stored glycogen back into glucose & it is then transported by blood to the cells to provide energy
