Overview of Digestive Functions
● Ingestion: the process of taking in food and liquids through the
mouth, which is the first step in digestion.
- Begins with the mouth where food is chewed and mixed with
saliva, initiating the digestive process.
● Secretion: various substances such as water, acids, and buffers are
secreted into the digestive tract to aid in digestion.
- Salivary glands secrete enzymes like amylase, which starts
starch digestion, gastric juices in the stomach further aid
digestion.
● Digestion: involves both mechanical (physical breakdown) and
chemical (enzymatic breakdown) processes to convert food into
absorbable units.
- Mechanical breakdown occurs through chewing, while
chemical digestion involves enzymes breaking down
macromolecules.
● Absorption: The process by which nutrients from digested food are
absorbed into the bloodstream for use by the body.
- Primarily occurs in the small intestine, where nutrients pass
through the intestinal wall into the bloodstream.
● Defecation: the elimination of waste products that aren’t used by the
body, completing the digestive process.
- Involves the rectum and anus, where indigestible substances
are expelled from the body.
- Defecation reflex- begins when the mass peristaltic movement
of the large intestine pushes fecal matter from the sigmoid
colon to the rectum. This triggers stretch reflectors. In the
defecation reflex, when the rectum in distended receptors send
sensory info to the sacral descending colon, sigmoid, rectum
and anus. The resulting contraction of muscle shortens the
rectum and increases pressure. The pressure with contractions
of the diaphragm and abdominals, open the internal anal
sphincter. Diarrhea is the inability to absorb sufficient water
while constipation is the absorption of too much water.
Major Organs of the Digestive System
Mouth & salivary glands
● Mouth: NOT ORGAN contains teeth that indicate dietary habits;
salivary glands (parotid, submandibular, sublingual) secrete saliva.
● Saliva: contains salivary amylase secreted by the parotid gland, the
first enzyme to act on food, initiating starch digestions.
, ● Tongue: a muscular organ that aids in tasting and moving bolus to
the pharynx; innervated by the hypoglossal cranial nerve.
● Mastication: the mechanical breakdown of food by teeth, followed by
the formation of a bolus for swallowing.
Esophagus & stomach
● Esophagus: a flexible tube that transports the bolus to the stomach
via peristalsis, regulated by the lower esophageal sphincter.
● Stomach structure; composed of four sections (cardia, fundus, body,
pylorus) with rugae that increase surface area for digestion.
● Cell types; parietal cells produce hydrochloric acid; chief cells
produce pepsinogen, essential for protein digestion.
● Chyme formation: after digestion, food is converted into chyme
before passing through the pyloric sphincter into the small intestine.
Small & large intestine
● Small intestine: divided into three sections (duodenum, jejunum,
ileum); primary function is nutrient absorption.
● Duodenum: completes the breakdown of food; receives bile and
pancreatic juices for digestion.
● Jejunum & ileum: focus on absorbing nutrients into the bloodstream;
have specialized structures for increased absorption.
● Large intestine: comprises the ascending, transverse, descending,
and sigmoid colon; main function is water and salt absorption.
Accessory Organs of the Digestive System
● Liver: produces bile, which emulsifies fats but does not digest them;
essential for fat digestion.
● Gallbladder: stores and concentrates bile until it is needed in the
duodenum for fat emulsification.
● Pancreas: functions as both an endocrine and exocrine gland;
produces zymogens for protein digestion and hormones for blood
sugar regulation.
Pancreatic function
● Exocrine function: produces inactive zymogens (trypsinogen,
chymotrypsinogen, procarboxypeptidase) that are activated in
the duodenum.
● Activation process: enterokinase activates trypsinogen to
trypsin, which then activates the other zymogens to digest
proteins into amino acids.
● Ingestion: the process of taking in food and liquids through the
mouth, which is the first step in digestion.
- Begins with the mouth where food is chewed and mixed with
saliva, initiating the digestive process.
● Secretion: various substances such as water, acids, and buffers are
secreted into the digestive tract to aid in digestion.
- Salivary glands secrete enzymes like amylase, which starts
starch digestion, gastric juices in the stomach further aid
digestion.
● Digestion: involves both mechanical (physical breakdown) and
chemical (enzymatic breakdown) processes to convert food into
absorbable units.
- Mechanical breakdown occurs through chewing, while
chemical digestion involves enzymes breaking down
macromolecules.
● Absorption: The process by which nutrients from digested food are
absorbed into the bloodstream for use by the body.
- Primarily occurs in the small intestine, where nutrients pass
through the intestinal wall into the bloodstream.
● Defecation: the elimination of waste products that aren’t used by the
body, completing the digestive process.
- Involves the rectum and anus, where indigestible substances
are expelled from the body.
- Defecation reflex- begins when the mass peristaltic movement
of the large intestine pushes fecal matter from the sigmoid
colon to the rectum. This triggers stretch reflectors. In the
defecation reflex, when the rectum in distended receptors send
sensory info to the sacral descending colon, sigmoid, rectum
and anus. The resulting contraction of muscle shortens the
rectum and increases pressure. The pressure with contractions
of the diaphragm and abdominals, open the internal anal
sphincter. Diarrhea is the inability to absorb sufficient water
while constipation is the absorption of too much water.
Major Organs of the Digestive System
Mouth & salivary glands
● Mouth: NOT ORGAN contains teeth that indicate dietary habits;
salivary glands (parotid, submandibular, sublingual) secrete saliva.
● Saliva: contains salivary amylase secreted by the parotid gland, the
first enzyme to act on food, initiating starch digestions.
, ● Tongue: a muscular organ that aids in tasting and moving bolus to
the pharynx; innervated by the hypoglossal cranial nerve.
● Mastication: the mechanical breakdown of food by teeth, followed by
the formation of a bolus for swallowing.
Esophagus & stomach
● Esophagus: a flexible tube that transports the bolus to the stomach
via peristalsis, regulated by the lower esophageal sphincter.
● Stomach structure; composed of four sections (cardia, fundus, body,
pylorus) with rugae that increase surface area for digestion.
● Cell types; parietal cells produce hydrochloric acid; chief cells
produce pepsinogen, essential for protein digestion.
● Chyme formation: after digestion, food is converted into chyme
before passing through the pyloric sphincter into the small intestine.
Small & large intestine
● Small intestine: divided into three sections (duodenum, jejunum,
ileum); primary function is nutrient absorption.
● Duodenum: completes the breakdown of food; receives bile and
pancreatic juices for digestion.
● Jejunum & ileum: focus on absorbing nutrients into the bloodstream;
have specialized structures for increased absorption.
● Large intestine: comprises the ascending, transverse, descending,
and sigmoid colon; main function is water and salt absorption.
Accessory Organs of the Digestive System
● Liver: produces bile, which emulsifies fats but does not digest them;
essential for fat digestion.
● Gallbladder: stores and concentrates bile until it is needed in the
duodenum for fat emulsification.
● Pancreas: functions as both an endocrine and exocrine gland;
produces zymogens for protein digestion and hormones for blood
sugar regulation.
Pancreatic function
● Exocrine function: produces inactive zymogens (trypsinogen,
chymotrypsinogen, procarboxypeptidase) that are activated in
the duodenum.
● Activation process: enterokinase activates trypsinogen to
trypsin, which then activates the other zymogens to digest
proteins into amino acids.
