Nutrition in humans Flashcards
In humans, what does nutrition consist of?
- feeding
- digestion
- absorption
- assimilation
What are the parts in the human digestive system?
- Mouth
- buccal cavity (teeth, tongue)
- pharynx
- oesophagus
- stomach
- small intestine (duodenum, jejunum, ileum)
- large intestine/colon
- rectum
- anus
What are the associated glands in the human digestive system?
- salivary glands
- liver
- gall bladder
- pancreas
What does the teeth do?
- it performs mechanical digestion
- it breaks up food into smaller pieces (mastication)
- increases surface area to volume ratio for salivary amylase to work on
What does the tongue do?
- rolls food up into bolus for easier swallowing
What does the pharynx do?
- it is a common passageway for respiration and digestion
- food and air had to enter the pharynx to enter the oseophagus or trachea
What does the oseophagus do?
- it is a long muscular tube that transports food from the pharynx to the stomach through peristalsis
What does peristalsis do?
- wave-like contractions
- along the walls oesophagus
- circular and longitudinal muscles work antagonistically
- circular muscles contract, longitudinal muscles relax → oesophagus constricts, narrower and longer → food is pushed forward
- circular muscles relax, longitudinal muscles contract → oesophagus dilates, oesophagus widens and shortens → food is pushed through
What does the stomach do?
- gastric glands in the stomach are stimulated by the presence of food and secrete gastric juices into the stomach cavity
- peristalsis churns the food and mixes it well with gastric juices
- food remains in the stomach for 3 to 4 hrs
- the partly digested food is liquefied, forming chyme
- chyme passes in small amounts into the duodenum when the pyloric sphincter relaxes and opens
What does gastric juice contain?
- dilute solution of hydrochloric acid and pepsin
What does dilute hydrochloric acid do?
- stops the action of salivary amylase by denaturing it
- changes the inactive form of pepsinogen, in the gastric juice into active pepsin
- provides a slightly acidic medium suitable for the action of pepsin
- kills potentially harmful microorganisms in food
How to proteins get digested into polypeptides?
- protease (pepsin) digests it
What happens when chyme enters the small intestine?
- it stimulates the pancreas to secrete pancreatic juice
- it stimulates the gall bladder to release bile
- it stimulates the epithelial cells in the small intestine to produce maltase, peptidase and lipase
What does pancreatic juice contain?
- the enzymes pancreatic amylase, pancreatic protease (trypsin) and pancreatic lipase
How does the pancreatic juice enter the duodenum?
- pancreatic juice passes through the pancreatic duct into the duodenum
What does bile contain?
- bile does not contain enzymes
- bile salts
What do bile salts do?
- speeds up the digestion of fats
How does bile enter the duodenum?
- bile passes through the bile duct into the duodenum
What do pancreatic juice, intestinal juice and bile do to food?
- all three fluids are alkaline
- they neutralise acidic chyme
- provide a suitable alkaline medium for the action of pancreatic and intestinal enzymes
What is starch digested by?
- amylases
Where does starch digestion occur?
- mouth
- small intestine
(no starch digestion in the stomach)
How much starch is digested in the mouth?
- only a little as food does not remain in the mouth for long
What starch digestion occurs in the small intestine using what enzymes?
- starch is digested by pancreatic amylase to form maltose
- maltose is digested by maltase to form glucose
- lactose is digested by lactase to form glucose and galactose
- sucrose is digested by sucrase to form glucose and fructose
What happens after carbohydrate digestion?
- the end product is simple sugars
- they can be absorbed into the bloodstream
What are proteins digested by?
- proteases
Where does protein digestion take place?
- stomach
- small intestine
What is the process of protein digestion in the small intestine?
- undigested proteins which enter the small intestine are digested into polypeptides by trypsin
- polypeptides are digested by peptidases into amino acids
What is the end product of protein digestion?
- amino acids
What do bile salts do?
- emulsify fats
What does emulsifying fats do?
- lowers surface tension of fats (reduces attractive forces between fat molecules)
- fats break into tiny fat droplets suspended in water (only physical break up)
- this forms an emulsion
What does emulsification do to speed up digestion by lipases?
- increases the surface area to volume ratio of fats
What are the emulsified fats digested by?
- lipase (pancreatic and intestinal lipases)
What does lipase digest emulsified fats into?
- glycerol
- fatty acids
What are the end products of fat digestion?
- glycerol
- fatty acids
What is absorption?
- the process in which digested food substances are absorbed into body cells
What is the process of absorption?
- products of digestion (simple sugars, glycerol, fatty acids and amino acids) are absorbed throughout the small intestine (especially the ileum)
- absorbed nutrients pass from the small intestine into the bloodstream
- water and mineral salts are absorbed by the small intestine and colon
Other than nutrients, what else does the small intestine absorb?
- most of the water that enters the alimentary canal
Where is undigested and unabsorbed matter stored?
- in the rectum
- before it is discharged as faeces through the anus
What is the removal of undigested and unabsorbed matter from the body called?
- egestion/defecation
What is assimilation?
- assimilation is a process in which some of the absorbed food substances are converted into new protoplasm or used to provide energy
What happens to the blood in the villi after absorption?
- it is now rich in nutrients
What do blood capillaries do to transport nutrients to the liver?
- they unite to form a large vein
- known as the hepatic portal vein
What happens to the absorbed sugar in the liver?
- converted to glycogen and stored
How does glucose help in the vital activities of cells?
- glucose is assimilated and oxidised during tissue respiration
- release energy for the vital activities of cells
What happens to excess glucose?
- excess glucose is returned to the liver and stored as glycogen
- a hormone called insulin, produced by the islets of langerhans in the pancreas stimulates liver cells to convert excess glucose to glycogen
What does the liver do when the body needs energy?
- the liver converts stored glycogen back into glucose (using glucagon secreted by the islets of langerhans in the pancreas)
- which is then transported by the blood to the cells
What are amino acids used for?
- amino acids which enter the cells are converted to new protoplasm used for growth and repair of worn out parts of the body
- used to form enzymes and hormones
What happens to excess amino acids?
- deaminated in the liver
- converted to urea
What are fats absorbed into?
- lymphatic capillaries
How are fats discharged into the bloodstream?
- lymphatic capillaries join to form a larger lymphatic vessel
- they discharge fats into the bloodstream
In normal conditions, when there is a sufficient supply of glucose, what are fats used for?
- fats not broken down
- building protoplasm
What are fats used for when glucose is in short supply?
- fats are broken down
- this is to provide energy needed by the body
What does the liver secrete?
- bile
Where is the substance secreted by the liver stored?
- gall bladder
What does the liver do to haemoglobin in red blood cells?
- breaks them down
- stores the iron released
What is formed from the breakdown of haemoglobin?
- bile pigment
What does the liver synthesize?
- proteins found in blood plasma
- from amino acids in diet
What are some plasma proteins?
- prothrombin
- fibrinogen
What is detoxification?
- a process in which harmful substances are converted to harmless substances
Where is alcohol broken down?
- liver
What do liver cells contain that break alcohol down?
- alcohol dehydrogenase
What is alcohol broken down into?
- acetaldehyde
What can acetaldehyde be broken down into to do what?
- compounds
- that can be used in respiration to provide energy for cell activities
What are the harmful effects of excessive alcohol consumption on the digestive system?
- gastric ulcer (due to excess stomach acid being secreted due to the alcohol stimulating it)
- cirrhosis of the liver (in which liver cells are destroyed and replaced with fibrous tissue, causing the liver be less able to function)
- liver failure
- death
What are the harmful effects of alcohol on the nervous system?
- depressant
- reducing self-control
- increased reaction time
How is alcohol a depressant?
- it slows down brain function
- effects may vary person to person
How does alcohol reduce self-control?
- a person become carefree as alcohol takes away inhibitions
- they might have social/personal liberties which they may regret
How does alcohol increase reaction time?
- as a person drinks more alcohol
- observable effects of intoxification:
- slurred speech
- blurred vision and poor muscle coordination
- judgement deteriorates (underestimating speed)
- they may drive faster, with less caution
What are some social implications of excessive alcohol consumption?
- neglect work and family
- exhibits violent behaviour (especially towards family)
- commit more crimes (compared to sober people)
