2.27-2.32 Digestive System

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Consuming/eating food to let it enter the digestive system.

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Muscles move contents of the alimentary canal forward.

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Mechanical and chemical decomposition of large, insoluble food molecules into smaller, water-soluble molecules that can be absorbed by the bloodstream.

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Chemical digestion

Chemical break-down of food, changing the chemical composition of food into smaller, simpler molecules.

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Mechanical digestion

Mechanical/physical break-down of food into smaller particles without changing chemical composition, e.g. chewing.

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Taking nutrients from the digestive system into the blood for use in the body by transporting them to cells.

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Digested food products move into cell for use, and are converted into the cell/tissue's fluids, organelles, or other solid parts.

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Absorption of water

Water/fluids are absorbed from the stool to solidify faeces.

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Removal of indigestible food (faeces) from the alimentary canal, occurs ONLY in animals.

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Removal of metabolic waste products, occurs in plants AND animals.

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Why is egestion NOT excretion?

Egestion simply removes faeces from the body, the faeces do NOT experience any chemical change or reaction and they are hence NOT a metabolic product.

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Digestive System

Organ system responsible for conducting digestion.

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Our digestive system is a combination of the __________________ with ____________.

alimentary canal, accessory organs.

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Alimentary canal

The passage/tract along which food passes through the body from the mouth to the anus during digestion.

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Accessory organs

Organs that aid digestion but are not part of the alimentary canal, food does NOT pass through accessory organs.

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Examples of digestive accessory organs

tongue, teeth, salivary glands, pancreas, liver, gallbladder.

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Proteins that act as biological catalysts to speed-up and aid digestion.

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Oral cavity through which animals ingest food and emit vocal sounds.

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The mouth aids ______ digestion, by ______ with the __________ and ________ to break down food into smaller particles.

mechanical, chewing, tongue, teeth

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Small, rounded mass of chewed food.

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Roof of mouth that separates the oral and nasal cavities to prevent food and other substances from entering the nasal passage when swallowing.

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Fleshy hanging ball at the back of your throat, prevents food and liquid from going up your nose when you swallow.

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Bones in the mouth that mechanically digest food and mix it with salivary enzymes to make it a bolus.

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Fleshy muscular organ in the mouth, moves food around mouth to aid chewing as well as swallowing.

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Organs that secret chemical substances for use in the body or for discharging into surroundings.

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Salivary glands

Glands that secret saliva, aid digestion, keep the mouth moist, and keep the teeth healthy.

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Watery liquid containing enzymes that aid digestion, secreted into the mouth by glands, provides lubrication for chewing and swallowing.

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Saliva contains the enzyme _______, it moistens the food and with the combined help from the teeth's _______, can turn it into a ______, which makes _________ easier.

amylase, chewing, bolus, swallowing.

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Parotid glands

Salivary glands in front of your ears, they secrete saliva into the mouth through small ducts near your upper molars.

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Submandibular glands

Salivary glands below the jaw, they secrete saliva into the mouth from underneath your tongue.

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Sublingual glands

Salivary glands below either side of your tongue, under your mouth's floor, they secrete saliva into the mouth from underneath your tongue.

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Part of throat behind the mouth and nasal cavity, carries air/fluids/food down the nose and mouth.

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Flap that covers the trachea during swallowing so food and fluids do not enter the trachea and go into the lungs.

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Larynx (voice box)

Hollow tube allowing air to pass from the throat to the trachea, it contains vocal cords. This organ is part of the respiratory system.

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Oesophagus (gullet)

Hollow, muscular tube that carries the bolus from your throat to your stomach by peristalsis.

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Lower esophageal sphincter

Ring-like muscle allowing the bolus to enter the stomach from the oesophagus when it relaxes.

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Ring-shaped muscles that relax to open a passage/opening in a body and contract to close passages/openings in the body.

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Produces bile, neutralizes the pH of stomach and fatty acids to provide alkaline conditions necessary for the small intestine. The liver processes nutrients absorbed from the small intestine.

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Alkaline digestive juice produced in the liver and stored in the gallbladder. It emulsifies fats and neutralizes the stomach and fatty acids' pH to create alkaline environment conditions for small intestine enzymes.

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Muscular sac attached to the liver, it stores bile, concentrates bile, and ejects bile into the small intestine's lumen when stimulated.

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Central cavity of a tubular or hollow structure in an organism.

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You ____ live without the gallbladder, because your liver produces _____ bile. However, bile will just _________________ into the digestive system ___________ the gallbladder.

can, enough, continually drip, without

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Common bile duct

Tube where ducts from the liver and gallbladder join and end at the small intestine. Carries bile from liver and gallbladder through the pancreas, into the small intestine.

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Organ behind the stomach, produces pancreatic juices containing enzymes and hormones. Its alkaline pancreatic juices neutralize the acidity of stomach and fatty acids.

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The pancreas produces the hormones ______ (which _______ blood sugar levels) and ______ (which _______ blood sugar levels).

insulin, decreases, glucagon, increases

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Pancreatic duct

Duct joining the pancreas with common bile duct, supplies pancreatic juices to small intestine to aid chemical digestion.

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Muscular organ that temporarily stores food. It secretes hydrochloric acid (pH1.5-2.0) that kills pathogens, activates pepsin (a protease), as well as breaks down protein & plant fibers.

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Stomach acid _________ an enzyme, it ________ pathogens, and provides _____ pH environments for ______.

is NOT, kills, low, pepsin.

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Stomach acid ______ the stomach lining, so cells produce _______ to prevent lining/membranous ______.

damages, mucous, damage.

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The stomach churns and mixes the food into a thick paste called _______


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Pyloric sphincter

Ring of muscle keeping chyme in the stomach whilst it contracts, and releasing chyme into the small intestine when it relaxes.

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Small intestine

6m-7m long organ where 90% of nutrients from food is absorbed into the bloodstream. It is made from the duodenum, jejunum, and ileum.

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First part of small intestine. It receives chyme from the stomach, digestive enzymes from the pancreas, bile from the liver, and mixes these together to further chemically digest food and absorb nutrients. It contains sodium hydrogen carbonate, which neutralizes acid from the stomach, producing a pH of 7-8.

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Middle part of small intestine. It absorbs sugars (glucose), fatty acids, glycerol, amino acids, vitamins, minerals, and water from the partially-digested food.

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Last part of small intestine, absorbs remaining nutrients that were not absorbed by the duodenum and jejunum, it's where most nutrient absorption occurs. It contains the ileocecal valve.

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Ileocecal valve

Sphincter controlling the entry or blockage of digested food from the ileum to the colon at their junction.

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The small intestine has many tiny, finger-like projections called ____ that maximize surface area for ____________________ and are the _______ walls of the small intestine.

villi, nutrient absorption, inner

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Large intestine

2m long organ that absorbs water and electrolytes, as well as is involved in the processing/propulsion of faeces. It contains the cecum, ascending colon, transverse colon, descending colon, and sigmoid colon.

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Digested food with nutrients partially absorbed from the small intestine that now enters the large intestine.

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First part of large intestine, it's a pouch connecting the small intestine to the large intestine, providing space for mixing bacteria with partially-digested food from the small intestine to form faeces. It absorbs fluids, salts, and lubricates stool with mucous.

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Ascending colon

Second part of large intestine, absorbs remaining water and key nutrients to solidify the stool, carries stool from cecum to transverse colon.

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Transverse colon

Third part of large intestine extending across the abdominal cavity, it absorbs water, salts, and minerals from the faeces whilst connecting the ascending and descending colon.

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Descending colon

Fourth part of the large intestine, stores the remains of the faeces before they pass through the rectum/anus by peristalsis. Connects transverse to sigmoid colon.

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Sigmoid colon

Last part of the large intestine, stores faeces and propulse them to the rectum/anus by peristalsis.

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Receives stool from the colon, and temporarily stores it there. It contains stretch receptors, which detect when the chamber is full to stimulate defecation urges.

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Last part of alimentary canal and digestive system. It contains sphincters that allow stool/faeces to be egested or to allow conscious delay of egestion (e.g. voluntarily holding your poo).

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Narrow, thin, finger-shaped pouch projecting out from the colon.

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Some say the appendix is a _______ remnant of our evolution, others believe it stores ________________ that is provided/released into the digestive tract after ________________.

useless, good bacteria, diarrheal illness.

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  1. ____________ & ______________ digestion happens in the mouth.

  2. ___________ is formed for easier swallowing.

  3. ______________ by ___________ propulsing food to the stomach.

  4. ______________________ relaxes to let __________ enter stomach.

  5. ____________ digestion (churning) happens in the stomach, turning the _______ into a thick, paste called _________.

  6. ___________ digestion at stomach by secreting the protease _________ to metabolize proteins and ________________ (pH1.5-2.0) to kill _________.

  7. ________________ relaxes to let ______ enter the _____________.

  8. ________ is propulsed throughout small intestine via ____________.

  9. _____________ neutralizes the stomach and fatty acids, providing ___________ conditions for ________ in the small intestine. _________ is mixed with _______________/enzymes, as well as __________, allowing chemical digestion to occur. Mechanical digestion occurs by the __________ of fat into smaller droplets by _______.

  10. The villi ___________ nutrients whilst ____________ the surface area across which this ___________ occurs.

  11. Nutrients are ____________ with/into cells.

  12. After the chyme passes through the ___________, ____________, and __________ of the small intestine, it is propulsed to the ________ of the large intestine via _________.

  13. The ________ mixes ________ with partially-digested __________ from the small intestine, to form ______. It also absorbs ______, salts, and __________ stool with _________ to allow easier passage through the _______________ canal.

  14. The _______ pass through the _______________ of the large intestine, where remaining ________ and key ________ are absorbed. It then passes through the __________________, where water, salts, and ____________ are absorbed from the faeces. The _________________ stores the remains of the ___________, it connects the ____________ and ________ colon. In the __________ colon, faeces are _________ and propulsed to the / using peristalsis for egestion.

  15. ____________ faeces are now stored in the _________. When the ________ is full, its ______________ stimulates the urge to _________.

  16. The _________ is the last part of the ________________, it contains ______________ that allow stool to be ___________ or voluntarily/consciously prevented from defecation (e.g. holding poo in). Resisting the urge to defecate for prolonged durations makes _________ harder later on as ________ are still absorbed from the faeces when they're stored in the _________, making them _______ and harder to defecate.

mechanical, chemical, bolus, peristalsis, oesophagus, lower oesophageal sphincter, bolus, mechanical, bolus, chyme, chemical, pepsin, hydrochloric acid, pathogens, pyloric sphincter, chyme, small intestine, chyme, peristalsis, bile, alkaline, enzymes, bile, pancreatic juices, chyme, emulsification, bile, absorbs, maximizing, absorption, assimilated, duodenum, jejunum, ileum, cecum, peristalsis, cecum, bacteria, chyme, faeces, fluids, lubricates, mucous, alimentary, faeces, ascending colon, water, nutrients, transverse colon, minerals, descending colon, faeces, transverse, sigmoid, sigmoid, stored, rectum, anus, indigestible, rectum, rectum, stretch receptors, defecate, anus, digestive system, sphincters, digested, digesting, fluids, rectum, drier.

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Involuntary, wave-like contractions and relaxations of the intestinal muscles or another part of the alimentary canal, which push contents of the digestive tract forward.

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Circular muscle layer

Smooth muscle layer of the intestine walls, it has fibre arranged in rings around the gut.

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Longitudinal muscle layer

Smooth muscle layer of the intestine walls, it has fibre running vertically along the length of the gut.

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When the gut lumen narrows, circular muscles _______ and longitudinal muscles ________. This _______ the bolus through the ________ tract.

contract, relax, pushes, digestive

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When the gut limen widens, circular muscles ________ and longitudinal muscles ________. This _________ the bolus to pass through the _______ tract.

relax, contract, allows, digestive

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Circular and longitudinal muscles work together to produce wave-like muscular ____________ that ______ the bolus through the ___________ tract.

contractions, push, digestive

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Enzymes _________ with the ________ of food whilst it passes through the digestive tract. Soluble __________ diffuse through intestinal walls to be transported around the body by __________ and blood vessels. The contents that continue to move through the gut by ___________ is mainly fibrous _________.

react, bolus, nutrients, capillaries, peristalsis, waste

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Dietary fibre contains _______, we ________ the enzyme to digest _________. This fibre/roughage _________ faecal volume, hence ___________ peristalsis and aiding ______ movement.

cellulose, lack, cellulose, increases, stimulating, bowel

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Enzymes' names usually end with which 3 letters?


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Enzymes that catabolize carbohydrates into maltose and/or glucose.

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Carbohydrases that catabolizes starch into maltose. Amylase enzymes working in the mouth are secreted by the salivary glands, amylase enzymes working in the small intestine are produced in the pancreas.

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Carbohydrates that catabolizes maltose into glucose, it works in the small intestine and is produced by the small intestine's walls.

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Enzymes that catabolize proteins into peptides and/or amino acids.

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Protease that catabolizes proteins into peptides, it works in the stomach and is produced by the stomach walls.

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Protease that catabolizes protein into peptides, it works in the small intestine and is produced by the pancreas.

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Protease that catabolizes peptides into amino acids, it works in the small intestine and is produced by the small intestine's walls.

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Enzyme that catabolizes lipids into glycerol and fatty acids, it works in the small intestine and is produced by the pancreas.

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Decomposition of fat globules into smaller droplets by bile, to create larger surface areas for the lipase enzyme to catabolize the lipids into fatty acids and glycerol.

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Emulsification is a _________ NOT _________ process as the ____________ composition of the lipids do not change, they are just broken down into ________ particles.

physical, chemical, chemical, smaller

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Bile ___________ fats, but it _________ an enzyme, as no _________ changes are produced.

emulsifies, is not, chemical

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  1. The small intestine is highly adapted for nutrient absorption. It ___________ diffusion rate, by __________ diffusion distance through having , 1-_ thick villi lining the intestinal walls.

  2. It is over _________ long to _______ surface area.

  3. It has a _______ lumen, which ___________ the ____________________ ratio. A narrower intestinal _____________ means __________ boluses can pass through at once, this makes the path that needs to be travelled through the intestine _________, allowing slower ___________ through the small intestine, which gives __________ time for the villi to ___________ nutrients.

  4. Has an _______________ blood supply, which allows for __________ of nutrients into the ___________.

  5. _____________ intestinal wall/villi lining -> Easy nutrient __________, however, only small, _________-soluble molecules can diffuse through the gut wall into the blood.

  6. Has ________ and _____________ -> Increased absorption _________________ and enables higher secretion of digestive _____________.

  7. Has ___________ in the villi to absorb ______________ and ___________ from digestion of ________ in the small intestine.

increases, decreasing, thin, cell, 6-7m, maximize, narrow, increases, surface:volume, lumen, smaller, longer, peristalsis, more, absorb, elaborate, diffusion, bloodstream, permeable, diffusion, water, villi, microvilli, surface area, enzymes, lacteals, glycerol, fatty acids, lipids.

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Villi (plural for villus)

Tiny, hair-like projections that line the inside of the small intestine. They contain blood vessels and help absorb nutrients. Villi are only 1-2mm long.

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Microvilli (plural for microvillus)

Minute, hair-like projections on each villus that further maximize the surface area.

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Hepatic portal vein

Transports absorbed nutrients from the small intestine to the liver.

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The intestine walls contain a ________ membrane lining, _________ layer that secretes and absorbs substances, circular and longitudinal muscles, as well as folded _______.

mucous, glandular, villi

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1-cell thick cell layer on surface of villi. They reduce diffusion distances by being so thin.

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Epithelium cells are involved in ____________________ so have many __________ for respiration to provide energy for the ____________, where molecules move ________ a concentration gradient from a region of ______ concentration to a region of _______ concentration. The epithelium is also ________.

active transport, mitochondria, active transport, against, low, high, moist.

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Lymphatic vessel in the center of the villi, conveys chyle (which contains fatty acids and glycerol from smaller or digested fat droplets) from the small intestine to the lymph, which eventually drains into the bloodstream.

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Milk fluid containing fat droplets, chyle drains from the lacteals of the small intestine into the lymphatic system during digestion.

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Colorless fluid that circulates throughout the lymphatic system, filters against pathogens and wastes. It carries lymphocytes throughout the body that fight infections.

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Capillaries __________ nutrients ______ from the ____________'s _______ into the ________.

transport, away, small intestine, villi, blood

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