Digestive System Flashcards
Weeks 3-5
Ingestion
Taking food into the mouth
Digestion
Breaking down of the food into smaller chunks
Mechanical
-chewing, cutting, grinding food - mouth and stomach
Chemical
-digestive enzymes and acids (mouth (saliva), stomach (gastric juices) and small intestine)
Absorption
Taking nutrients into the cells of the body
occurs in small intestine thanks to Villi (folds to increase the surface area of the small intestine to increase absorption of nutrients into the bloodstream)
Elimination
Waste products and undigested remains expelled from the body
- urinary system (urine)
- digestive system (faeces)
- respiratory system (gasses)
- integumentary system (perspiration)
Secretion
Glands produce chemicals like enzymes and hormones to aid in digestion among other things
Mouth
Chewing
- Mastication (cutting-carnivores vs grinding-herbivores)
- increase surface area
Saliva (secreted by glands in the mouth)
- Salivary Amylase
- the enzyme that breaks starch down into glucose
- mucin
- slippery glycoprotein protects soft lining and lubricates
Tongue
- manipulates food into a ball (bolus)
- pushes food to the back of the throat
Swallowing
- forceful movement of a ‘bolus’ (ball of masticated food)
- drives a wave of muscle action pushing it down the oesophagus into the stomach
Teeth
Unique among vertebrates
Parts:
Enamel coating -for crushing, chewing, piercing
Above gum: cusp, enamel, dentin
Bellow gum: cementum, dentin, root, pulp
Types:
Polyphyodont - teeth continuously replaced
Diphyodont - two sets of teeth (baby + adult)
- Deciduous Dentition (baby/milk teeth)
- Permanent Dentition (adult teeth)
specialised teeth - unique formation
- Elephants tusks (defence, digging, gathering food)
- Tuatara (two rows on top, one row on bottom)
- Sabre-tooth Cats (fangs to stab deep and strong bleed)
- Rodents (incisors grow continuously, must grind)
Sabre-Tooth Cats
TEETH
Evolved independently on 4 separate occasions
fangs long and curved, sharp in inside
- to cut deep into animal and cause arterial bleed
weak jaw but could open wide (don’t need to hold onto an animal for long due to rapid blood loss)
- not overly quick, reliant on slow prey
- energy conservation evolution (for both points)
hunted to extinction by humans
- slow and huge, easy to capture
- didn’t have time to evolve to escape humans
Snakes
SWALLOWING
flexible jaw to surround prey whole
a wave of contractions force bolus down the throat
windpipe peaks out of throat and mouth so when the mouth is stretched tight around prey snake can still breathe
Vocal Chords and Syrinx
-
Syrinx in birds
- much more complicated
- bands of muscle and cartilage
- evolved due to sexual selection of mates
- some birds can imitate other birds mating calls to disrupt their mating abilities
Pharynx and Oesophagus
pharynx = throat
- Epiglottis
- cartilage flap that blocks glottis (opening of windpipe) when food is going down
Oesophagus
- connects pharynx and stomach
- muscles at top of oesophagus are under voluntary control
- Peristalsis: waves of muscle contractions through rest of oesophagus are involuntary (bolus)
Stomach
elastic wall
Rugae - accordian-like folds of musclein wall that can stretch and contract
gastric juice - digestive fluid excreted by stomach (HCl -breaks down most things and kills bacteria, Pepsin -breaks down proteins into amino acids)
chruns food and gastric juice up together
forms acid chyme
- backflow of stomach chyme = heartburn
- overflow of stomach chyme = diarrhea
Self-digestion: 3 defences
- pepsin is activated by HCl in lumen of stomach meaning it doesn’t digest itself earlier
- coating of mucus that protects stomach lining
- epithelium constantly erroded, is replaced every 3 days
Pyloric Sphincter
regulates how much stomach chyme gets into small intestine and when it gets in there
diarrhea
- body doesn’t care about getting nutrients, just wants to get the bad food out.
- pushes all chyme out of body as fast as possible
Small Intestine
Duodenum
