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A DIGESTIVE JOURNEY:“A TRIP THROUGH THE DONUT
HOLE”
SOME IMPORTANT DEFINITIONS
INGESTION – the taking of nutrients.
DIGESTION – the breakdown of complex organic molecules into smaller components by enzymes.
ABSORPTION – the transport of digested nutrients to tissues of the body.
EGESTION – the removal of waste food materials from the body.
A SERIES OF “STATIONS” ALONG A SUBWAY
STATION #1 – “THE MOUTH”
- Teeth (mechanical)
- Tongue (mechanical)
- Saliva (chemical)
STATION #2 – THE ESOPHAGUS
muscular tube, 2 cm in diameter
connects pharynx to stomach
made up of two main muscle layers: I. circular layer
II. longitudinal layer
there is a flap located at the start of the esophagus called the epiglottis, which protects food from entering the windpipe (trachea).
at the endpoints of the esophagus there are sphincters (esophageal and cardiac sphincter, respectively)
STATION #2 – THE ESOPHAGUS
NOTE: the purpose of sphincters is to prevent food from going in the reverse direction (i.e. reflux from the stomach into the esophagus).
FUNCTIONS OF ESOPHAGUS Moves bolus through to the
stomach, through a series of rhythmic contractions called peristalsis (MECHANICAL BREAKDOWN)
The circular and longitudinal muscles contract and release
STATION #3 – THE STOMACH- J-shaped stretchable organ
- involves sphinctor muscles (pyloric and esophageal/cardiac) - holds about 2L of food and
water
- consists of thick layers of smooth muscle and numerous folds called Rugae. What’s the purpose of rugae?Enable the stomach to contract & expand.
STATION #3 – THE STOMACH
Function(s):- storage of bolus (1.5-2 L)- MECHANICAL digestion through “churning”- CHEMICAL digestion with acids and enzymes
to convert bolus to chyme- cardiac and pyloric sphinctors regulate movement of food through digestive tract keeps food going ONE way.
Gastric pits - secrete hormones and mucus(mucus forms protective layer)Enzyme Action:- Hydrochloric acid or HCl (secreted by parietal cells) softens food and activates pepsinogen to pepsin- pepsin breaks down PROTEIN into short chains of AA’s
Hormonal Action:- Gastrin induces secretion of more mucus
ACCESSORY ORGANS
1. Salivary Glands (previously discussed)
2. Pancreas3. Liver 4. Gallbladder
ACCESSORY ORGANS
1. THE PANCREAS
- lies behind stomach and extends laterally from the duodenum- finger shaped organ-15 cm in length
Function(s):- secretes digestive enzymes into the small intestines & hormones into the blood- bicarbonate ions NEUTRALIZE the HCl when entering duodenum - releases amylase into small intestine
Enzyme Action: (all released into the small intestine)1) lipase – digests fat
2) amylase – further breakdown of carbohydrates
3) trypsin – breaks down protein into short chains of amino acids
ACCESSORY ORGANS
2. THE LIVER- second largest organ / roughly 1.5 kg- two main parts: the right and left lobes
Functions:- produces bile (emulsifies FAT into little fatty globules)- extracts absorbed nutrients or toxins from blood- decomposes toxins (ie. Alcohol, drugs)- key role in regulating body metabolism (homeostasis)- manufactures many essential body proteins- regulates the balance of hormones- regulates body cholesterol
Enzyme Action:- high concentration of catalase enzymes that play key role in decomposing toxins (i.e. Alcohol).
ACCESSORY ORGANS
3. THE GALLBLADDER- “pear-shaped” muscular
sac located under the right lobe of the liver
- connected to liver via hepatic duct
Function(s):- collects and concentrates the bile that it receives from liver
- releases bile to duodenum
Hormonal Action:- gall bladder contracts in reaction to hormone cholecystokinin (CCK) to release bile into the duodenum.
STATION #4 – SMALL INTESTINE3 Parts Duodenum, Jejunum, Ileum
1) DUODENUM- one inch tube - connected to stomach & Ileum
Function(s)- digestion and ABSORPTION of most
nutrients- mixes and propels food forward
Enzyme Action:- see pancreas
Hormonal Action:- Secretin to reduce acidity from food coming from stomach
STATION #4 – SMALL INTESTINE
2) JEJUNUM & ILEUM
Enzyme Action:
1) peptidases - break down short chain of amino acids into individual amino acids
2) disaccharidases - breaks disaccharides into simple sugars
Hormonal Action:- synthesis of melatonin = skin pigment
STATION #5 – LARGE INTESTINE (COLON)
- about 1.5 m in length
- divided into 3 parts: I. ascending II. transverse III. descending
Function(s):- absorb water and some minerals
- vitamin K and some B-complex vitamins are produced by resident bacteria.
- hold and compact the unabsorbed material from small intestine.
STATION #6 – RECTUM & ANUS
- Rectum = 8 inch chamber connected to anus
- Anus - 2 inches long, consists of pelvic muscle and two sphincters, surrounded by sphincter muscles
- muscles relax to release stool (feces)
- muscles contract to keep stool in placeFunctions:
Rectum - STORAGE of stool
Anus – EXPELS WASTE from the body
REVIEWING – THE USE OF CUE CARDS
1) Take 10 cue cards (one for each “station” and accessory organ in the digestive system.
2) FRONT of the cue card will represent the structure. - write the name of the organ- draw/sketch or print then glue on a labelled diagram
3) BACK of the cue card will represent the functions.- types of physical & chemical digestion- specific functions- enzyme action- hormonal action
4) QUIZ YOURSELF by:- putting the cue cards in order- having someone read one side of the card and you indicate what is on the other side.
Station #2 – The Esophagus
FRONT - Structure
BACK - Function
Physical – peristalsisChemical – none
Functions- Moves bolus from pharynx to stomach- sphincters (esophageal & cardiac) prevent
food from moving backwards.
Enzyme action – none
Hormonal action – none