Chapter 1: Digestive System
Section 1: Digestive system
What is the digestive system?
The digestive system includes a combination of functions and adaptations of the digestive organs which
helps conduct the process of digestion. Digestion therefore helps the body break down large complex
dietary molecules into smaller absorbable forms. The process usually includes where carbohydrates are
hydrolyzed to monosaccharides, proteins to be converted to amino acids and lipids into glycerol and fatty
acids (Li and Somerset, 2014).
Organs that function in the digestive system:
• Mouth
Structure
The mouth is structured to play a role in digestion, this includes the placement of teeth in the mouth. The
teeth located in the mouth allow large molecules of food to be grinded into small pieces which are broken
down by biological molecules called enzymes which are biological catalysts. The placement of the tongue
in an organism's mouth also aids digestion as it helps mix the food and segregates the mouth from the
cavity (mouth |Definition, Anatomy, & Function, 2022). In addition, the production of amylase in the
salivary glands allows the production of amylase in the mouth, this helps with the breakdown of complex
starch carbohydrates into sugars, which can be easily absorbed by the body. The mouth is therefore
responsible for mechanical and chemical digestion (Your Digestive System & How it Works | NIDDK, 2022).
• Pharynx
, Pharynx is situated at the back of the throat, it features the tongue that helps chew food into a ball and
pushes the substances at the top of the mouth, this then helps the mouth swallow food as a cranial reflex.
The muscles that are situated at the pharynx allow the tongue to rise against the mouth enabling the
epiglottis to close over the glottis allowing the airways to be closed (Khatri, 2022) (Hartley et al., 2016).
• Oesophagus
The oesophagus is a large muscular tube located from the mouth to the stomach. This allows food to
travel shown the body to be broken down too many extents allowing nutrients secreted within the food
to be absorbed in the blood. The oesophagus is adapted structurally and in terms of its function to aid in
digestion. The tube is formed by 4 layers of walls, mucous membrane, submucosa, thick layer of muscle
and outer protecting layer. The mucous membrane is used to secrete mucus which will help the
oesophagus provide a smooth passage for food. The submucosa allows the esophagus to hold the mucous
membrane. The thick layer of muscles allows the tube to perform peristalsis, which is a form of mechanical
digestion. The oesophagus ends with a sphincter which segregates the stomach and the tube. This controls
the movement of food from the tube to stomach (Hartley et al., 2016).
• Stomach
The stomach's main purpose is to digest food chemically and mechanically with plenty structural and
functional adaptations. This hollow shaped organ acts as a container that holds the food while it is being
mixed with stomach enzymes. (Digestive System: Function, Organs & Anatomy, 2022). The stomach
mechanically digests food by allowing the muscles to squeeze and churn the food, this also goes ahead
with the chemical digestion in the stomach. The stomach contains many digestive enzymes that aid in
chemical digestion in the stomach. This includes pepsin which breaks down proteins and gastric lipase
that breaks down triglycerides
• Small Intestine (Duodenum, Jejunum, Ileum)
The small intestine's main role in the digestive system is breaking down nutrients till its final stage so they
can be easily absorbed. The small intestine is made up of 3 tubular structures that aid in digestion. These
include the duodenum, jejunum and ileum. The first part of the small intestine is the duodenum, it is
connected to the stomach so therefore absorbs nutrients and water from foods so they can be used in
our body. The jejunum sits in the middle of the small intestine it is characterized to have similar functions.
With similar characteristics the ileum also further digests food coming from the stomach but plays a big
role in transferring food to the colon (Your Digestive System & How it Works | NIDDK, 2022).
• Large Intestine
The large intestine is composed of a 5 feet long tubular structure that plays a large role in bowel
movements and post-absorption of nutrients from foods. After most nutrients are absorbed from the
indigestible matter it is processed by the large intestine. The organ itself is composed of 4 parts that all
play individual roles in aiding digestion. Originally the large organelle absorbs water and electrolytes,
produces, and absorbs vitamins and prepares the feces towards the rectum. The ascending colon absorbs
the remaining water and nutrients that haven't been absorbed by the small intestines, leaving the
Section 1: Digestive system
What is the digestive system?
The digestive system includes a combination of functions and adaptations of the digestive organs which
helps conduct the process of digestion. Digestion therefore helps the body break down large complex
dietary molecules into smaller absorbable forms. The process usually includes where carbohydrates are
hydrolyzed to monosaccharides, proteins to be converted to amino acids and lipids into glycerol and fatty
acids (Li and Somerset, 2014).
Organs that function in the digestive system:
• Mouth
Structure
The mouth is structured to play a role in digestion, this includes the placement of teeth in the mouth. The
teeth located in the mouth allow large molecules of food to be grinded into small pieces which are broken
down by biological molecules called enzymes which are biological catalysts. The placement of the tongue
in an organism's mouth also aids digestion as it helps mix the food and segregates the mouth from the
cavity (mouth |Definition, Anatomy, & Function, 2022). In addition, the production of amylase in the
salivary glands allows the production of amylase in the mouth, this helps with the breakdown of complex
starch carbohydrates into sugars, which can be easily absorbed by the body. The mouth is therefore
responsible for mechanical and chemical digestion (Your Digestive System & How it Works | NIDDK, 2022).
• Pharynx
, Pharynx is situated at the back of the throat, it features the tongue that helps chew food into a ball and
pushes the substances at the top of the mouth, this then helps the mouth swallow food as a cranial reflex.
The muscles that are situated at the pharynx allow the tongue to rise against the mouth enabling the
epiglottis to close over the glottis allowing the airways to be closed (Khatri, 2022) (Hartley et al., 2016).
• Oesophagus
The oesophagus is a large muscular tube located from the mouth to the stomach. This allows food to
travel shown the body to be broken down too many extents allowing nutrients secreted within the food
to be absorbed in the blood. The oesophagus is adapted structurally and in terms of its function to aid in
digestion. The tube is formed by 4 layers of walls, mucous membrane, submucosa, thick layer of muscle
and outer protecting layer. The mucous membrane is used to secrete mucus which will help the
oesophagus provide a smooth passage for food. The submucosa allows the esophagus to hold the mucous
membrane. The thick layer of muscles allows the tube to perform peristalsis, which is a form of mechanical
digestion. The oesophagus ends with a sphincter which segregates the stomach and the tube. This controls
the movement of food from the tube to stomach (Hartley et al., 2016).
• Stomach
The stomach's main purpose is to digest food chemically and mechanically with plenty structural and
functional adaptations. This hollow shaped organ acts as a container that holds the food while it is being
mixed with stomach enzymes. (Digestive System: Function, Organs & Anatomy, 2022). The stomach
mechanically digests food by allowing the muscles to squeeze and churn the food, this also goes ahead
with the chemical digestion in the stomach. The stomach contains many digestive enzymes that aid in
chemical digestion in the stomach. This includes pepsin which breaks down proteins and gastric lipase
that breaks down triglycerides
• Small Intestine (Duodenum, Jejunum, Ileum)
The small intestine's main role in the digestive system is breaking down nutrients till its final stage so they
can be easily absorbed. The small intestine is made up of 3 tubular structures that aid in digestion. These
include the duodenum, jejunum and ileum. The first part of the small intestine is the duodenum, it is
connected to the stomach so therefore absorbs nutrients and water from foods so they can be used in
our body. The jejunum sits in the middle of the small intestine it is characterized to have similar functions.
With similar characteristics the ileum also further digests food coming from the stomach but plays a big
role in transferring food to the colon (Your Digestive System & How it Works | NIDDK, 2022).
• Large Intestine
The large intestine is composed of a 5 feet long tubular structure that plays a large role in bowel
movements and post-absorption of nutrients from foods. After most nutrients are absorbed from the
indigestible matter it is processed by the large intestine. The organ itself is composed of 4 parts that all
play individual roles in aiding digestion. Originally the large organelle absorbs water and electrolytes,
produces, and absorbs vitamins and prepares the feces towards the rectum. The ascending colon absorbs
the remaining water and nutrients that haven't been absorbed by the small intestines, leaving the
