Main Components of the Digestive System
The
digestive system consists of the gastrointestinal (GI) tract and
accessory organs.
Gastrointestinal Tract (GI Tract)
This is
the continuous tube from the mouth to the anus, approximately 30 feet (9
meters) long in adults.
- Mouth:
a. Role: The starting point of
digestion.
b. Processes:
i. Food is
chewed (mechanical digestion) by teeth.
ii. Saliva
from salivary glands contains amylase, an enzyme that starts breaking
down carbohydrates (chemical digestion).
c. Tongue
helps in mixing food and forming the bolus (soft mass of chewed food).
- Pharynx and Esophagus:
a) Pharynx: A shared passage for food and
air.
b) Esophagus: A muscular tube that transports
the bolus to the stomach through peristalsis (wave-like muscle
contractions).
- Stomach:
a. Role: Stores and breaks down food
into a semi-liquid form called chyme.
b. Processes:
i. Gastric
glands secrete hydrochloric acid (HCl) and enzymes like pepsin
(breaks down proteins).
ii. Mucus
protects the stomach lining from acid.
c. Food
remains in the stomach for 2-6 hours.
- Small Intestine:
a. Role: Primary site of digestion and
nutrient absorption.
b. Sections:
i. Duodenum: Receives bile (from the liver)
and pancreatic enzymes (from the pancreas) for digestion.
ii. Jejunum: Absorbs most nutrients.
iii. Ileum: Absorbs vitamins like B12 and
bile salts.
c. Villi and
Microvilli:
Finger-like projections increase the surface area for absorption.
- Large Intestine (Colon):
a. Role: Absorbs water and electrolytes;
forms and stores feces.
b. Sections:
i. Cecum: Receives material from the
small intestine.
ii. Ascending,
Transverse, Descending, Sigmoid Colon: Process and compact waste.
iii. Rectum: Stores feces.
c. Houses gut
microbiota, which help ferment undigested food.
- Anus:
a) Role: Excretes feces from the body
through defecation.
b) Controlled
by internal (involuntary) and external (voluntary) anal sphincters.
Accessory Digestive Organs
These
organs assist digestion but are not part of the GI tract.
- Salivary Glands:
a) Produce
saliva, which contains enzymes and lubricates food.
- Liver:
a) Largest
internal organ.
b) Produces bile,
which emulsifies fats, making them easier to digest.
c) Processes
nutrients absorbed in the small intestine.
- Gallbladder:
a) Stores
and concentrates bile.
b) Releases
bile into the duodenum via the bile duct.
- Pancreas:
a) Produces
digestive enzymes (amylase, lipase, proteases) and bicarbonate to
neutralize stomach acid in the duodenum.
b) Also an
endocrine organ, releasing insulin and glucagon to regulate blood sugar.
Processes of Digestion
- Ingestion:
- Intake of food through the mouth.
- Propulsion: Movement of food through
the digestive tract (e.g., swallowing and peristalsis).
- Mechanical Digestion:
a) Chewing
in the mouth.
b) Churning
in the stomach.
c) Segmentation
in the intestines.
- Chemical Digestion:
a) Enzymatic
breakdown of macronutrients (carbohydrates, proteins, and fats).
b) Begins in
the mouth and continues through the stomach and small intestine.
- Absorption:
a) Nutrients
are absorbed into the bloodstream or lymph through the walls of the small
intestine.
b) Water and
electrolytes are absorbed in the large intestine.
- Elimination (Defecation):
a) Removal
of indigestible substances and waste products as feces.
Major Digestive Enzymes
|
Enzyme |
Source |
Function |
|
Amylase |
Saliva,
Pancreas |
Breaks
down carbohydrates into sugars. |
|
Pepsin |
Stomach |
Breaks
down proteins into peptides. |
|
Lipase |
Pancreas |
Breaks
down fats into fatty acids/glycerol. |
|
Trypsin |
Pancreas |
Continues
protein digestion in the small intestine. |
|
Maltase,
Lactase |
Small
Intestine |
Break
down disaccharides into monosaccharides. |
Common Disorders
- Acid Reflux (GERD): Stomach acid flows back
into the esophagus.
- Irritable Bowel Syndrome
(IBS):
Chronic inflammation of the colon.
- Ulcers: Open sores in the stomach
or duodenum caused by H. pylori or NSAIDs.
- Lactose Intolerance: Inability to digest
lactose due to lack of lactase enzyme.
- Celiac Disease: Immune reaction to gluten
damaging the small intestine.
- Constipation/Diarrhea: Problems with stool
consistency and frequency.
Fun Facts
- The stomach produces 2-3 litters
of gastric juice daily.
- The small intestine is about
20 feet long but folds to fit inside the abdomen.
- Your liver performs over 500
functions, including detoxification and metabolism.
Would you
like a deeper dive into any specific aspect, like disorders or dietary tips?