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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.

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some important definitions
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.

station 1 the mouth
Station #1 – “The Mouth”
  • Teeth (mechanical)
  • Tongue (mechanical)
  • Saliva (chemical)
station 2 the esophagus
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 (esophagealand cardiac sphincter, respectively)
station 2 the esophagus1
Station #2 – 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

NOTE: the purpose of sphincters is to prevent food from going in the reverse direction (i.e. reflux from the stomach into the esophagus).

station 3 the stomach
Station #3 – The Stomach
  • - J-shaped stretchable organ
  • - involves sphinctormuscles (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 stomach1
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
Accessory Organs
  • Salivary Glands (previously discussed)
  • Pancreas
  • Liver
  • Gallbladder
accessory organs1
Accessory Organs
  • THE PANCREAS
  • - lies behind stomach and extends laterally from the duodenum
  • - finger shaped organ
  • -15 cm in length
  • Function(s):
  • - secretes digestiveenzymes 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 organs2
Accessory Organs
  • 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 organs3
Accessory Organs
  • 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 intestine
Station #4 – Small Intestine

3 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 intestine1
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
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
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 place

Functions:

Rectum - STORAGE of stool

Anus – EXPELS WASTE from the body

reviewing the use of cue cards
Reviewing – The Use of Cue Cards

Take 10 cue cards (one for each “station” and accessory organ in the digestive system.

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

BACK of the cue card will represent the functions.

- types of physical & chemical digestion

- specific functions

- enzyme action

- hormonal action

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.

FRONT - Structure

Station #2 – The Esophagus

BACK - Function

  • Physical – peristalsis
  • Chemical – none
  • Functions
  • Moves bolus from pharynx to stomach
  • sphincters (esophageal & cardiac) prevent food from moving backwards.
  • Enzyme action – none
  • Hormonal action – none