A D IGESTIVE J OURNEY : “ A TRIP THROUGH THE DONUT HOLE ”

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