UNIT 8: Digestive system
What is the digestive system?
In order for the body to absorb and utilise
food for energy, development, and repair,
food must first be broken down into smaller
molecules by the digestive system, a
combination of organs and structures. The
mouth, oesophagus, stomach, small
intestine, large intestine, rectum, and anus
are all parts of the digestive system. As food
is eaten and combined with saliva in the
mouth, the digestive process starts. The
meal is further broken down by stomach
acid and enzymes as it passes down the
oesophagus and into the stomach. The
partially digested food leaves the stomach
and enters the small intestine where it is
combined with bile from the liver and
pancreatic digestive enzymes. Via the small
intestine's lining, nutrients from meals are
absorbed into the circulation and
transported to the body's cells. In the large
intestine, where water is absorbed and the
residual waste components are converted
into faeces, the waste moves. Until they are
passed via the anus during a bowel
movement, the faeces are held in the
rectum. A vital and intricate system that is
crucial to sustaining overall health and wellbeing is the digestive system.
Processes of the digestive system:
● Assimilation
The process by which nutrients are taken up from food and transferred into the circulation for
usage by the body's cells is referred to as assimilation in the digestive system. The nutrients
produced by food digestion are absorbed through the small intestine's walls and reach the
circulation after the meal has been broken down by digestive enzymes in the stomach and
small intestine. Carbohydrates, proteins, lipids, vitamins, and minerals are among the
vitamins and minerals that are absorbed. These nutrients may be delivered to the body's
cells and utilised there for energy, growth, and repair once they have entered the circulation.
Assimilation is essential for preserving the body's general health and wellbeing.
● Diffusion
Molecules migrate by a process called diffusion from a region of higher concentration to one
of lower concentration. Diffusion is crucial to the absorption of nutrients in the digestive tract.
Nutrients are first available in high quantities before they are broken down and delivered into
the small intestine. The cells lining the small intestine are able to absorb these nutrients
,through a process known as assisted diffusion. Transport proteins located in the cell
membrane enable nutrients to move from the small intestine lumen into the cells lining the
small intestine during facilitated diffusion. The initial high concentration of nutrients in the
small intestine's lumen established a concentration gradient that is essential to this process.
Nutrients can be delivered to the circulation and used by the body's cells after being
absorbed into the cells lining the small intestine. Since it enables the body to selectively
absorb nutrients as needed while limiting the absorption of hazardous substances or
excessive levels of nutrients, diffusion plays a crucial function in the absorption of nutrients.
● Hydrolysis
Large molecules including carbs, proteins, and lipids are broken down into more
manageable pieces by a chemical process known as hydrolysis during digestion. The
process by which water molecules are employed in the digestive system to dissolve the links
between the food molecules is known as hydrolysis. The hydrolysis reaction is catalysed by
digestive enzymes, which are released by numerous digestive system organs. For instance,
hydrolysis converts complex sugars like glucose into simpler sugars like starch and
glycogen. Amino acids are formed when proteins are broken down, and glycerol and fatty
acids are formed when lipids are broken down. Once in the circulation, these smaller
molecules are absorbed through the small intestinal walls and used by the body. Since it
enables the body to get nutrients from food that it would otherwise be unable to utilise,
hydrolysis is a crucial step in the digestive process.
Main functions of the digestive system
1. Ingestion: The act of ingesting involves consuming food and drinks through the
mouth. The selection of food based on elements like flavour and texture and the
experience of hunger and thirst are the first steps. During intake, mechanical
digestion, such as chewing, also occurs.
2. Mechanical digestion: This is the process by which food is physically broken down
into more readily digestible portions. Once food is chewed and combined with saliva,
which includes enzymes that aid in the breakdown of carbohydrates, mechanical
digestion begins in the mouth.
3. Chemical digestion: This is the method used to break down huge food molecules
into smaller ones that the body can absorb. The process of chemical digestion starts
in the mouth with the release of enzymes that break down carbohydrates and
continues in the stomach and small intestine with the breakdown of proteins, lipids,
and other nutrients by enzymes and acids.
4. Motility: The term "motility" describes how food moves through the digestive tract.
This comprises the peristaltic muscle contractions that transport food through the
small and large intestines as well as the rhythmic muscular contractions that force
food down the oesophagus and into the stomach.
5. Secretion: Different enzymes, acids, and other chemicals that are essential for
digestion are secreted by the digestive system. They include gastric juice, which
includes hydrochloric acid and enzymes that break down proteins, and saliva, which
has enzymes that break down carbs.
, 6. Absorption: The nutrients are absorbed into the circulation and sent to the body's
cells once food has been broken down into its component elements. The majority of
absorption takes place in the small intestine, where the surface area for absorption is
increased by the lining of the walls with tiny finger-like projections known as villi and
microvilli.
7. Elimination: Defecation is the last step in the digestive system's removal of waste
from the body. Via the rectum and anus, the body's waste materials, which also
include germs, undigested food, and other things, are expelled as faeces.
Mouth
Function and location
● The mouth is situated at the point where the respiratory and digestive processes
converge. It usually resides in the area known as the oral cavity, which is on the head
or face. The mouth's primary role is to absorb food, start the digestive process by
physically breaking it down with the teeth, and combine saliva—which includes
enzymes that start breaking down carbohydrates—into the mixture. The mouth has a
crucial role in communication, allowing us to communicate and show our feelings via
our facial expressions in addition to its role in digestion. Air enters and leaves the
body through the mouth during specific actions like yawning or panting, hence it also
affects breathing.
Oesophagus
Function and location
● A muscular tube that joins the neck and the stomach is the oesophagus. Its main job
is to move food and liquids from the mouth to the stomach so that they may be
digested. In a process known as peristalsis, the muscles in the oesophagus walls
contract and relax in a coordinated manner to force the food into the stomach. The
oesophagus runs from the throat to the stomach and is situated in front of the spine
and behind the trachea. It exits through a diaphragm aperture and terminates at the
lower esophageal sphincter.
Stomach
Function and location
● A muscular organ, the stomach is situated in the upper left portion of the abdomen,
slightly below the ribs. Its main job is to break down food into tiny pieces and
combine it with digestive fluids to start the digestive process. Before releasing food
into the small intestine for further processing and absorption, the stomach also
momentarily stores it. Several layers of muscles in the stomach contract and relax to
aid in the breakdown of meals. A coating of mucus covers the inside lining of the
stomach, shielding it from the digestive enzymes and stomach acid. Hydrochloric
acid, which is also produced by the stomach, aids in the destruction of germs and
other microbes in the meal. The majority of nutritional absorption occurs in the small
intestine, where the stomach releases the partially digested food in little quantities.
More mucus is produced by the stomach lining to ward off the acidity of the digestive
fluids after the meal has passed through the stomach.
, Small intestine
Function and location
● The large intestine and the small intestine are connected by a long, narrow tube-like
organ called the small intestine, which is situated in the belly. Its main job is to take
nutrients from meals and transfer them into the circulation so that the body may use
them. The duodenum, jejunum, and ileum are the three sections that make up the
small intestine. The first section of the small intestine, the duodenum, is in charge of
combining partially digested food from the stomach with fluids from the pancreas and
liver as well as digestive enzymes. Nutrients including carbs, proteins, lipids, and
vitamins are absorbed from the digested meal via the jejunum and ileum. Villi, which
increases the surface area of the gut and aids in nutritional absorption, covers the
inner lining of the small intestine. The absorbed nutrients are subsequently
transferred to the liver for digestion and delivery to other bodily regions via the
circulation.
Large intestine
Function and location
● A tube-shaped organ, the big intestine is joined to the small intestine at one end and
to the anus at the other. It is found in the bottom region of the abdomen. Its major job
is to absorb vitamins, electrolytes, and any residual food particles that haven't been
completely digested after passing through the small intestine. Faces are stored and
expelled from the body through the big intestine. The cecum, ascending colon,
transverse colon, descending colon, sigmoid colon, and rectum are among the
sections that make up the large intestine. The big intestine's cecum connects to the
small intestine as its first segment. The middle portion of the large intestine is made
up of the ascending colon, transverse colon, and descending colon, while the
sigmoid colon and rectum make up the lower portion. Millions of bacteria, collectively
known as the gut microbiota, live in the large intestine and are crucial to the body's
digestive functions. Undigested food particles are broken down by these bacteria,
which also generate vitamins like biotin and vitamin K and inhibit the growth of
dangerous bacteria.
Rectum
Function and location
● The rectum is a muscle organ that resembles a tube and is situated in the pelvic
region. It connects the colon to the anus. Its main purpose is to hold faeces until they
are ready to exit the body during a bowel movement. The internal and external anal
sphincters are the two primary muscle groups in the rectum. Whereas the external
anal sphincter is composed of skeletal muscle and is controlled voluntarily, the
internal anal sphincter is composed of smooth muscle and is controlled involuntarily.
The internal and external anal sphincters cooperate to release the faeces via the
anus and out of the body when faeces reach the rectum, which causes the need to
urinate. Moreover, the rectum possesses a layer of mucus-secreting cells that
lubricate faeces' transit and shield the rectal wall from harm brought on by faeces'
passage.
Anus
Function and location
