Aimee Baish FSC group A
Assignment C
The digestive system
The digestive system (figure 1) is the organ system in the human body which is responsible for
breaking down food (digestion), absorbing nutrients and fats, flushing waste out of the body. The
digestive system is made up of hollow organs and solid organs (accessory organs) and the
gastrointestinal (GI) tract. Hollow organs are the organs which are critical in the digestion process
and are a part of the movement/path of food. Hollow organs usually consist endothelial tissue which
can stretch and compress and/or move however it needs to. Solid organs (accessory organs) are the
organs which don’t play a part in the transportation of food but still have a critical role in the
digestive system. Accessory organs normally don’t have linings that stretch, they normally are
almost always the same shape. Their shape doesn’t normally change. These solid organs tend to
produce and store enzymes and digestive juices.
Organs of the digestive system
The mouth is the cavity at the start of your digestive system which is made up of muscles and tissues
which help to mechanically digest food. The tongue, which is made up muscles, is covered in taste
buds which work with your soft palate to help you taste food. Your soft palate is the fold of tissue on
the roof of your mouth. Your jaws and facial muscles help with the movement of mastication. Your
jaws also help to hold your teeth in place, and your teeth rip, tear, break and crunch food to help
make the pieces smaller. Your salivary glands which are found under your chin and jaw and at the
back of your mouth, produce saliva to help keep your mouth and oesophagus lubricated which
prevents dry foods getting stuck to stop you choking. There are your Parotid glands, your
submandibular glands and your sublingual glands. Your sublingual glands are located at the front,
underneath your jaw behind your chin, they secrete viscous saliva. Your submandibular glands are
located behind and underneath your sublingual glands, under your jaw near your jawline, they
secrete viscous saliva as well. Your parotid glands are located at the back of your mouth, up the side
of your cheek, near your ear, these secrete watery saliva. The more viscous saliva is used to keep
your mouth and oesophagus lubricated and the waterier saliva is used to dissolve food. The saliva
has the enzyme amylase in it, which helps break down starch into glucose. Saliva also helps dissolve
and soften food, it protects your teeth from decaying, it also initiates digestion, and keeps your
mouth clean because it takes germs and pathogens away when you swallow. The flow of saliva is
started by the presence, smell or even sight of food. The epiglottis is a flap of tissue and muscle at
top of your throat which closes over the opening in the trachea to prevent food from getting into it.
The oesophagus is a tube which is made of muscles. Your oesophagus is around 25cm (10”) long and
leads from your throat to your stomach, it’s 4 layer wall helps to: a mucus membrane which secretes
mucus to make sure that food travels smoothly, a submucosa which helps to hold the mucus
membrane in place, a thick muscle layer which is made of circular and longitudinal smooth muscle
fibres, and an outer protective layer to prevent tears or holes in the oesophagus. By using peristalsis,
the two muscle layers contract and relax alternatively which makes the oesophagus push the food to
the stomach. However, aid can travel back from the stomach to the oesophagus which is called
heartburn, to help heartburn there are antacid tablets like Gaviscon, which help to neutralise the
acid and coat the oesophagus with a cooling film to prevent the acid burning your oesophagus.
,The stomach is a muscular bag which has a J-shape to it, it stores and breaks down the food that you
eat, it breaks it down to make the digestion process easier. The stomach contains acid to kill any
bacteria from the saliva or the food. The food that is mixed with enzymes and acid and found in the
stomach is called chyme. The stomach mixes food with digestive juices which contains enzymes to
break down proteins into amino acids and lipids into fatty acids and glycerol. Proteins are broken
down by protease which is the enzyme which breaks apart the peptide bonds to make amino acids.
Lipids are broken down by lipase which breaks triglycerides into diglycerides to make them easier to
digest. Foods normally are kept in the stomach for 2-3 hours to make sure they are properly broken
down and mixed with acids.
The small intestine is made up of 3 parts, the duodenum, the jejunum and the ileum. It is 7 meters
long in total. The duodenum is the part of the small intestine closest to the stomach, which uses bile
to neutralise acidic chyme when its needed. The jejunum is the middle part of your small intestine
that is the second longest part and connects your duodenum to your ileum. And the ileum is the
longest part and is the part that connects to your large intestine, this is where the waste begins to
form. The small intestine has little finger-like projections all over it, these are called villi and these
villi help to move food or waste around your intestines. These villi also help to increase the surface
area of the ileum, these villi are covered in microvilli. These help to increase surface area of
absorption. For example, these microvilli absorb vitamins and minerals, carbohydrates, lipids,
proteins, carbohydrates and 80% of ingested water. The nutrients from foods flow into the
bloodstream and through into the walls of the small intestine. The small intestine also secretes
digestive enzymes like protease, lipase, and amylase. The duodenum receives the pancreatic juices
and bile from the liver.
The large intestine is 5 feet long, it accepts and absorbs things that the small intestine didn’t. Its
functions are bacterial digestion so absorbing all the bacteria our gut needs, fermentation of
carbohydrates, and breaking down proteins. It also absorbs more water and concentrates waste to
make it solid enough to be excreted. The rectum stores the waste for a short period of time until it is
ready to be excreted. The large intestine dries up food and keeps it there until it is dry enough to
form faeces.
The anus is a muscular ring at the end of your GI tract which excretes waste. When faeces reach the
anal canal, the brain receives signals to open the external anal sphincter by voluntary decision.
However, the anus would then excrete the waste from the anal canal.
The liver is an accessory organ which produces bile, and filters out toxins and waste, like drugs and
alcohol out of your blood. Bile contains salts that help to emulsify fats by increasing their surface
area, hydrogen carbonate (HCO3-) ions which neutralise acidic chyme, and products of broken-down
red blood cells and cholesterol (bilirubin and biliverdin). However, bile doesn't contain enzymes. The
liver also transports bile to the gallbladder. The liver also stores glycogen, it helps regulate blood
sugar(glucose) levels, makes plasma proteins, stores fat soluble vitamins (vitamins A,D,E &K) and it
metabolises (chemically changes by reactions in cells) alcohol, drugs and other toxins. It also breaks
down excess amino acids to make them into urea which is removed by the kidneys.
The gall bladder is located underneath the liver, it stores bile and releases it into the small intestine.
However fatty diets can cause gallstones because the fatty acids and/or lipids can build up in the
gallbladder.
The pancreas produces enzymes to digest carbohydrates, fats and proteins (amylase, lipase and
trypsin). It also regulates blood sugar levels as it produces insulin, which helps to break down
glucose.
, The gastrointestinal tract (GIT/GI tract) is the tract that travels from your mouth to your anus, its
around 9 meters long. The GI tract is split into the Upper GI tract and the lower GI tract. The upper
GI tract consists of the mouth, pharynx, oesophagus and stomach. The lower GI tract consists of the
small intestine, large intestine rectum and your anus. Its function is to help food travel through the
digestive system. The GI tract can get infections which can be caused by viruses, bacteria or
parasites. These can cause inflammation of the GI tract which is called gastroenteritis. There are also
many different GI tract diseases, these include Constipation, Irritable bowel syndrome (IBS), Colon
cancer and Haemorrhoids. Constipation is when bowel movements are infrequent or incomplete,
this is normally due to a lack of fibre. IBS is a condition where the colon muscles contract more often
than in other people, it causes bloating, abdominal pain and cramps, and diarrhoea. This is normally
caused by a fibre deficiency. Colon cancer normally starts in the large intestine and normally affects
older people. It tends to begin as little, non-cancerous lumps, these lumps eventually transform into
cancer. It is treated by surgery, radiotherapy and radiotherapy. Haemorrhoids are swollen blood
vessels that surround the anus opening. These are normally due to excess pressure when bowel
movements are strained. (Byju’s, 2022, online)
Functions of the digestive system
The Digestive system has 3 functions. Absorption of fats and vitamins, breaking down food, and
excretion of waste (faeces).
The digestive system absorbs fats, vitamins and minerals by using the microvilli in the ileum. These
microvilli increase the surface area of absorption, which helps to increase the amount of fats,
vitamins and minerals absorbed. However smaller molecules like glucose may be absorbed in the
stomach instead. The process of nutrient absorption is as follows. Glucose and amino acids flow into
the capillaries inside the villus, then the fatty acids and glycerol pass into the lacteal. Glycerol and
fatty acids are fat soluble, so they diffuse through the cell surface membrane. Fatty acids and
glycerol are transformed into triglycerides and proteins transform into chylomicrons. However, the
chylomicrons (lipoproteins) pass into the lacteal. Sodium ions actively transport out of the epithelial
cell, the concentration of these sodium ions inside the cell drops. ATP changes into ADP and P1.
Then sodium ions pass through a protein channel and a glucose or fatty acid moves with it. The
absorption in the ileum can also happen by diffusion, facilitated diffusion or active transport.
Diffusion is the movement of particles from an area of high concentration to an area of low
concentration. This can be through a somewhat permeable membrane, but not always. It only uses
the kinetic energy of the molecules and not energy from ATP. Facilitated diffusion is diffusion that is
boosted by carries or channels made of protein, which will be found in the cell surface membrane.
Active transport is the movement of molecules in and out of cells against their concentration
gradient. It uses carrier proteins and energy from ATP.
The digestive system digests food using both chemical and mechanical digestion. Mechanical
digestion is the process of mastication (chewing) using the teeth, jaws and facial muscles. Larger
molecules like proteins, starch and lipids go through hydrolysis, which breaks them down into
smaller molecules. Hydrolysis is the process that breaks down large molecules into smaller
molecules using water. Chemical digestion is the hydrolysis of macromolecules into smaller ones.
These smaller molecules can then be absorbed through the gut wall and into the bloodstream. This
then means that they can be used in the body. Assimilation is where digested food molecules flow
into cells in the body to be used.
The elimination or excretion of waste is when the body takes products of digestion and forms them
into faeces. These faeces then move through the large intestine to the anal canal. After these faeces
reach the anal canal, the brain then receives signals to excrete these faeces. Through a voluntary
