Unit 8: Physiology of Human Body Systems
C: Explore the physiology of the digestive system and the use of corrective treatments for dietary related diseases
Nutrition and health
This report will outline the anatomy and physiology of the digestive system, sources and uses of various important
nutrients and associated symptoms of nutrient deficiency linked to the treatments for dietary related diseases.
Structure of the digestive system
Figure 1 - Labelled diagram of digestive system
Functions of digestive organs
Mouth
In the mouth, mechanical digestion is the first thing that takes place. This is when the teeth grind food and mix it
with saliva to form a bolus [1]. During the mixing, an enzyme called salivary amylase starts breaking down
carbohydrates [1]. This is known as chemical digestion [1]. Once the food is soft and relatively flexible, the tongue
pushes it to the back of your mouth and into the oesophagus [1].
Salivary glands
The salivary glands make saliva which aids in digestion, keeps your mouth moist and supports healthy teeth [2].
Saliva contains enzymes that aid in the digestion of carbohydrates, such as amylase. Amylase is an enzyme that
converts starches (complex carbohydrates) into sugars that your body can easily absorb [3]. Saliva also contains
lingual lipase, an enzyme that breaks down lipids [3].
,Unit 8: Physiology of Human Body Systems
C: Explore the physiology of the digestive system and the use of corrective treatments for dietary related diseases
Oesophagus
The main function of the oesophagus is to transport food and liquid from your mouth to your stomach [4]. When
you swallow, food and drink travel from your mouth to your throat (pharynx) [4]. A small muscular flap called the
epiglottis closes to prevent food and liquid from going down the trachea [4]. Another little flap called the uvula
prevents liquid from travelling upward into the nasal cavity [4]. The oesophagus does not produce any digestive
enzymes but it produces mucus for lubrication [5].
Stomach
The stomach receives food from your oesophagus and sends it to your small intestine [1]. Food is mixed with
enzymes and acid until it becomes a liquid called chyme [1]. It produces pepsin for protein digestion and
hydrochloric acid to aid in the destruction of bacteria as well as other dangerous organisms [6].
Liver
Bile is constantly produced by the liver. This is a chemical that aids in the conversion of fats into energy that your
body can use. Albumin is also produced by the liver. This is a blood protein that aids in the transport of hormones,
medicines, and fatty acids throughout the body. The liver also produces the majority of the chemicals that aid in
blood clotting following damage [7].
Gallbladder
The gallbladder stores and concentrates bile from the liver [8]. Bile is then released into the duodenum, where it
helps the body to break down and absorb fats from food [8]. Cholic acid and chenodeoxycholic acid are produced in
the gallbladder. These are two primary bile acids which undergo dehydroxylation by bacteria in the small intestine,
forming the secondary bile acids deoxycholic acid and lithocholic acid [9]. Both primary and secondary bile acids are
conjugated by the liver with an amino acid, either glycine or taurine [9]. Conjugated bile acids are known as bile salts
[9].
Pancreas
The pancreas helps the small intestine by secreting pancreatic juice, a liquid rich in enzymes and sodium bicarbonate
that can inhibit pepsin digestion [1]. It also secretes insulin, which aids in blood sugar regulation [1].
Small intestine
The small intestine consists of three parts: duodenum, jejunum and ileum [10]. In the duodenum, the food is mixed
with bile from the gallbladder and digestive juices from the pancreas [10]. Vitamins, minerals and other nutrients
are then absorbed [10]. The jejunum is responsible for fat absorption and the ileum absorbs vitamin B12, bile salts
and all digestive products that were not absorbed in the duodenum and jejunum [11]. Water and electrolytes are
absorbed by the duodenum, jejunum and ileum [11].
Large intestine
The large intestine consists of three parts: caecum, appendix and colon [12]. The caecum receives undigested food
material from the small intestine [12]. The appendix stores good bacteria [13], this bacteria can help promote good
digestion and support the immune system [14].
Rectum and anus
The rectum's main function is to store excrement until it is time to expel it [15]. The rectum relaxes and stretches to
accept waste as it passes through your colon [15]. While retaining the excrement, the rectum absorbs the leftover
, Unit 8: Physiology of Human Body Systems
C: Explore the physiology of the digestive system and the use of corrective treatments for dietary related diseases
water and electrolytes, solidifying the waste further. It secretes mucus to assist in passage. When it is full, nerves
trigger the need to defecate [15].
The anus aids in bowel movements. Nerves and muscles around the anus work together to warn you when you need
to defecate, while also allowing you to keep it in until you can go to a toilet [16]. When you're ready, your nerves
and muscles will work together to push excrement out of your body [16]. The mucus lining of your anus secretes
mucus to lubricate the canal and help the excrement pass through smoothly [16].
Key nutrients needed for a balanced diet
Protein
Protein is needed in the body for building and repairing bones, muscles, cartilage, skin and tissues [17]. It is also
important for providing oxygen throughout the body [17]. Red blood cells contain haemoglobin, which is a protein
compound that carries oxygen throughout the body [17]. This helps supply your entire body with the nutrients it
needs [17]. Proteins can be used to make enzymes, these enzymes help to break down food during digestion, make
new cells and make new body chemicals [17]. Hormones can also be regulated with the aid of proteins, especially
during the transformation and development of cells during puberty [17]. The average adult needs a minimum of 0.8
grams of protein per kilogram of body weight per day [18]. Sources of protein include: eggs, milk, yoghurt, chicken,
fish and tofu [19].
Hydrochloric acid and a group of enzymes called proteases break down protein sources in the stomach into smaller
chains of amino acids [20]. Proteases are enzymes that break down amino acids into peptides. These shorter amino
acid chains travel from the stomach to the small intestine [20].
Carbohydrates
One of the main benefits of carbohydrates in one’s diet is that they provide energy to the body [21]. This is done by
breaking them down into glucose, which is the primary energy source for the brain and muscles [21]. Some other
reasons as to why carbohydrates are important in maintaining a balanced diet include: they improve sleep, uplifts
one’s mood, provides fibre to the body, helps to prevent diseases, prevents blood clots and reduces the risk of
cancer [21].
It is generally suggested that adults consume 45-65% of their total calories per day in the form of carbohydrates
[22]. However, carbohydrate requirements are determined by a variety of factors, including body size, activity level
and blood sugar regulation [22]. The Food and Drug Administration (FDA) recommends that people should consume
275 g of carbohydrate each day in a 2,000 calorie diet [22]. This includes dietary fibre, total sugars and added sugars,
all of which are indicated on food labels [22]. Sources of carbohydrates include: fruits and vegetables as well as
whole grain products like bread, potatoes, cereals and rice [23].
Lipids
Lipids are fatty, waxy, or oily molecules that are necessary for many bodily activities and serve as the foundation for
all living cells [24]. Lipids have a range of functions, such as supporting cells and aiding in essential functions,
protecting nerve cells, helping the body absorb certain vitamins and helping to produce hormones including
oestrogen, testosterone and cortisol [24].
The initial phase of lipid digestion occurs in the mouth, when lipids come into contact with saliva [25]. The physical
process of chewing, along with the activity of emulsifiers, then allows the digestive enzymes to become activated
[25]. The digestive process is started by the enzyme lingual lipase and a small amount of phospholipid is used as an
