digestive system Flashcards
digestion
the process by which foods are broken down into smaller molecules or nutrients
absorption
the uptake of these nutrients and how the body utilises these nutrients to perform a wide range of bodily functions
excretion
the way in which the body removes unwanted, unnecessary or harmful substances from the body once it has extracted what it needs
fibrous foods
- cannot be digested or absorbed
- provide bulk and roughage
- facilitate the movement of through the digestive tract
- diets that lack this bulky constituent, increase the risk of constipation and is linked with higher risk of serious things like bowel cancer
mechanical digestion
- first stage of digestive process
- begins as soon as food enters mouth
- physical process of chewing = primer for chemical digestion
mechanical digestion relies on the effective action of the following teeth
- incisors = teeth at front of the mouth and are required for biting, scraping and cutting food. healthy human teeth = 8 incisors
- canines = longest and most stable teeth. more important for piercing and tearing foods
found in carnivorous animals. healthy human = 4 canines - molars = located at back of mouth and are needed to grind larger particles of food into smaller before swallowing
healthy adults = 12 molars
peristalsis
- a process involved in mechanical digestion
- accomplished by the action of the smooth muscle tissue found throughout digestive system
- involuntary action of the smooth muscle tissue that occurs through progressive, wave-like contractions
peristaltic waves
occur in oesophagus, stomach and intestines and are essential to ensure the ingested food continues to move through digestive tract
chemical digestion
- initiated by the action of enzymes and starts as soon as food enters the mouth
enzymes in chemical digestion
- enzymes are protein molecules that are produced within the body and are used as catalysts for chemical reactions
- enzymes accelerate the rate at which reactions
primary enzymes active within the digestive tract
- amylase = responsible for breakdown of carbs
largely present in saliva but also released in pancreas into small intestine to digest more complex carbs - pepsin =
degrades proteins
produced by stomach
trypsin also secreted into pancreas to help this process - lipase = breakdowns fats into fatty acids entering the intestines
water soluble enzyme that is produced in the pancreas but also in smaller quantities in mouth and stomach
the digestive tract
- also called alimentary tract, alimentary canal or gastrointestinal tract
- describes the internal passage through which ingested food passes from the moment it enters mouth to point it is excreted via anus
- average human tract is 9 metres long
- comprised of a series of hollow organs that are joined together by a long, twisting-like tube
- each of the structures and organs perform a specific digestive role
transit time
- the time it takes for food to pass through the digestive tract
- in a healthy adult the average transit time is between 24 and 72 hours
3 functions of saliva
1) moistens food so tongue can roll it into manageable sized balls in prep for swallowing = bolus
2) starts carb digestion (contains amylase)
3) mixes antibodies into the foods to kill bacteria that may be present in the food consumed
the tongue
- responsible for churning and mixing food in mouth
- this actions stimulates the release of saliva and chemical breakdown of foods
- has taste buds at back of tongue
time food takes in mouth
each mouthful takes about 30-60 seconds to chew and swallow depending on the type of food and the speed it is chewed
pharynx
- throat
- has both respiratory and digestive functions
- forms the passageway connecting the mouth and nose to the oesophagus and larynx
- consists of 3 different muscles
- primary structure for swallowing
- swallowing action = reflex ~ lasts 1-3 seconds
oesophagus
- about 10 inches long
- connects throat to stomach
- runs parallel to trachea
- protected at the top by a small flap of cartilage called ‘epiglottis’
- food moves down oesophagus into stomach using peristalsis to prevent any reflux in mouth
- with a medium sized bolus, it takes 5-8 seconds to deliver food to stomach
stomach
- J shaped organ
- can expand up to 8 times its size after food
- located just left to the centre of the chest area, immediately below sternum
- internal structure has 3 different layers of tissue that are arranged into deep muscular folds
- these folds enable the stomach to blend and churn the ingested food
- food is digested both mechanically and chemically here
chyme
a thick liquid created by the peristaltic action of the stomach’s lining mixing gastric juices into the food
hydrochloric acid
- contained in the gastric juices
- helps to kill bacteria
- so potent it can dissolve metal so the stomach is lined with thick layer of mucus to stop it from digesting itseld
pepsin (enzyme)
- contained in gastric juices
- breaks down any protein in food
- can only work in very acidic conditions
alcohol and the stomach
- alcohol is absorbed in the stomach
- which is why it enters bloodstream very quickly
- it is the only substance that is directly absorbed in the stomach
emptying of stomach
- takes about 3-4 hours depending on types of foods consumed, hydration status and physical activity levels
pancreas
- long flattened gland
- located deep in the abdomen
- adjacent to stomach and small intestine
functions of the pancreas
- producing and releasing enzymes responsible for digestion ~ e.g. trypsin and lipase
- create and release blood regulating hormones
- produces large quantities of bicarbonate which neutralises high acidic contents of stomach
gall bladder
- 4 inch pear shaped organ
- located below the liver in upper-right section of abdomen
- stores the bile produced by the liver
- delivers bile to the small intestine via bile ducts
bile
- largely made from acids, salts, cholesterol and water
- emulsifies and disperses fats as they move from stomach to small intestine ~ this allows fat-soluble vitamins and other nutrients to be easily absorbed into bloodstream
liver
- largest glandular organ
- located to the right of the abdominal cavity and just beneath diaphragm
- weighs about 3lbs
- not directly involved in digestion of specific nutrients
- first organ to be nourished and replenished with nutrients, but also means any toxins like alcohol/drugs, the liver has to detoxify to prevent cellular damage
functions of the liver
- storage of carbs in form of glycogen
- hormone production
- blending and emulsification of fats
- excretion of old blood cells
- production of bile for storage in the gall bladder
- production of cholesterol
- filters and neutralisers toxins
- storage of some vitamins and iron
small intestine
- longest of the intestinal tracts
- about 5-6 metres
- sometimes called small bowel
- takes about 3-4 hours for food to pass through
small intestine can be divided into 3 sections
- duodenum
- jejunum
- ileum
duodenum
- first section of small intestine
- about 10 inches long
- adjacent to pancreas
- here the pancreas secretes enzyme trypsin to further digest protein
jejunum
- second and longest section of the small intestine
- between 2-3 metres in length
- where most of the absorption of nutrients takes place
- the internal structure is a series of hair like structures called cilia
cilia
- provide a large surface area that enables absorption to occur at a much greater rate
- nourished with a rich blood supply from capillaries, and from lymphatic structures called lacteals
lacteals vs capillaries
lacteals are more permeable than capillaries so they enable larger molecules, particularly fats to pass through their walls = facilitates absorption of fats in jejunum
ileum
- final stage of small intestine
- about 3-4 cm
- here any remaining nutrients are absorbed, particularly bile salts and vitamins
large intestine
- final stage of digestive journey
- where waste is excreted
- about 1.5 metres
functions of large intestine
- reabsorb water from remaining matter
- manufacture vitamins B and K and start the process of excretion
the 3 sections of the large intestine
- caecum
- colon
- rectum
caecum
- first stage of large intestine
- receives chyme from ileum of small intestine
- ascends from lower right hip region where it joins colon
- primary function is to absorb fluid and salts from remaining matter and to help solidify it before excretion
appendix
- immediately below the caecum
- hollow, sac-like structure
- connected to lower portion of the caecum
- exact function is unclear
- called the redundant organ
colon
- largest section of the large intestine
- has 3 sections which are named according to the direction they carry waste = ascending colon, transverse colon, descending colon
- primary function is to reabsorb water and to store the waste before it is excreted
rectum
- final section of large intestine
- about 8 inches
- serves as a place for storing waste before excreted as faeces
- also compresses waste into solid form
- when faecal matter starts to accumulate, the rectum wall is stretched and initiates the sensation of needing to go to the toilet
- waste is passed through the anus
- residence time for waste in colon ranges from 4-72 hours - av. time being 36 hours before it is excreted
summarised journey of digestive tract
1) mouth
2) oesophagus
3) stomach
4) duodenum
5) jejunum
6) ileum
7) colon
8) rectum
9) anus
