Digestive system 2

Kok Jun Yi (12)Ong Sim Hao (17)

Trevor Tan Yi Shin (22)

Mouth Oesophagus (Gullet) Stomach Small Intestines Large Intestines Rectum Anus

The food that we eat are not in a form that the body can use as nourishment

Food and liquid need to be broken down (mechanically and chemically) into very small molecules of nutrients before they can be absorbed into the blood and carried to cells throughout the body.

Digestion is the process by which food and liquid are broken down into their simplest substances, a form that the body can use to build and nourish cells and organs to provide a source of energy

The collection and elimination of waste products are also important parts of digestion. Indigestible parts of foods (like fibre) and some water are eliminated from the body as faeces.

Thus, it is very important to maintain a healthy digestive system for our general health and well-being.

The mouth is normally moist, and is lined with a mucous membrane.

Digestion begins when we put food in our mouth and begin to chew.

Our teeth help to break the food into smaller pieces by chewing.

Saliva produced in the salivary glands and mixed with the food helps soften it for chewing, easy swallowing and digestion in the stomach.

The tongue rolls the food into small balls and pushes the food down the throat (pharynx)

This process is known as mastication. Fact: Chewing food takes from 5 to 30

seconds while swallowing takes about 10 seconds.

The oesophagus is an organ which consists of a muscular tube through which food passes from the pharynx to the stomach.

During swallowing, food passes from the mouth through the pharynx into the oesophagus and travels via peristalsis to the stomach.

Usually about 25-30cm long

Peristaltic movement is initiated by circular smooth muscles contracting behind the chewed material to prevent it from moving back into the mouth, followed by a contraction of longitudinal smooth muscles which pushes the digested food forward.

An animation…

Is located just below the heart and it makes digestive juices that help to break food down into a thick paste known as chyme.

The churning action of the stomach together with the gastric juices help to further break down food into simpler substances.

Food stays in the stomach for about 3 to 4 hours.

The stomach releases proteases (protein-digesting enzymes such as pepsin) and hydrochloric acid, which kills or inhibits bacteria and provides the acidic pH of two for the proteases to work.

The small intestine (also known as the small bowel) is the longest portion of the digestive tract - it is more than 6 meters long and is located within the middle of the abdomen.

Made up of 3 sections, duodenum, jejunum and ileum.

Small Intestine

Much of the small intestine is coiled and suspended in a thin layer of fat - which gives the intestine a lot of flexibility and mobility.

This is where the major part of digestion and the absorption of nutrients take place.

More digestive juices are added to break the chyme further down for absorption.

Located at the junction of the stomach and the small intestine, the duodenum is the first part of the small intestine. It is C-shaped and about 25 cm long.

The duodenum receives the thick liquid mixture of partly-digested food and acid from the stomach. This acid is quickly neutralised in the alkaline environment of the duodenum.

The duodenum also receives bile from the gallbladder, and other digestive enzymes from the pancreas. These enter the duodenum through small ducts or tubes.

Other glands produce mucus that coats the digestive mixture to help ease its passage.

The food mixes with bile, mucus, and pancreatic and other digestive enzymes.

The bulk of the digestion of proteins, fats and carbohydrates takes place in the duodenum before the material travels further into the small intestine

The jejunum is the 1-2 m long, coiled mid-section of the small intestine. The ileum is the final portion of the small intestine, which leads into the large intestine. The ileum measures 2-4 m in length.

The inner linings of the jejunum and ileum contain very small finger-like bumps called 'villi'.

The presence of these tiny bumps on the inside of the small intestine means that the surface area is much larger than if the lining were just a flat surface.

This increased surface area improves the small intestine's ability to absorb nutrients into the bloodstream.

The nutrient components found after digestion:◦ smaller molecules (e.g. glucose from

carbohydrates; amino acids from proteins; fatty acids and cholesterol from fats)

◦ vitamins◦ minerals◦ salts◦ water

Digestion ends here. All digested nutrients pass through the

intestinal walls into the bloodstream, where the circulatory system transports the nutrients to cells throughout the body to provide energy.

The large intestine (or large bowel) is the part of the digestive system where waste products from the food you eat are collected and processed into faeces.

The large intestine is about 1.5 m long and consists of the caecum, appendix, colon and rectum - which are distributed in the abdominal cavity.

The large intestine performs the following functions:◦ reabsorbs water and maintains the fluid balance

of the body◦ absorbs certain vitamins◦ processes undigested material (fibre)◦ stores waste before it is eliminated

The caecum is the first part of the large intestine. It is shaped like a small pouch and located in the right lower abdomen, it is the connection between the small intestine and the colon.

The caecum accepts and stores processed material from the small intestine and moves it towards the colon.

As the processed food approaches the end of the small intestine, a valve separating the small and large intestines opens, the caecum expands and the material enters.

At this stage, the mixture normally contains:◦ undigested food (fibre)◦ a little bit of water◦ some vitamins◦ some minerals or salts

The appendix is a small projection emerging from the caecum.

In human beings, the appendix has no known function and is thought to be a remnant from a previous time in human evolution.

In some people, the appendix becomes infected or inflamed (a condition known as 'appendicitis'), and the appendix needs to be removed (via surgery).

Shaped like an inverted 'U', the colon is the longest part of the large intestine.

The colon has four sections that are located in the abdominal cavity.◦ Ascending colon - starts at the caecum at the

bottom right hand side of the abdomen and ascends (i.e. goes upwards) towards the liver.

◦ Transverse colon - transverse means 'across'. This part of the colon extends across the abdomen from right to left.

◦ Descending colon - descends (goes downwards) on the left hand side of the abdomen.

◦ Sigmoid colon - it is the last part of the large intestine, and is located on the bottom left hand side of the abdomen. It is the S-shaped connection between the descending colon and the rectum.

Within the colon, the mixture of fibre, small amounts of water and vitamins etc. mixes with mucus and with bacteria that live in the large intestine - and starts to form faeces.

As faeces travels through the colon, the lining of the colon absorbs most of the water and some vitamins and minerals

The bacteria in the colon chemically break down some of the fibre to produce nutrients for their own survival and to nourish the cells lining the colon. Thus, the fibre in your diet is extremely important to maintain the long-term health of the colon.

Through muscular movements of the colon, faeces is pushed along until finally, the walls of the sigmoid colon contract, causing the faeces to move into the rectum.

The rectum is the final part of the large intestine. It is where stool (faeces) is stored.

It is usually 12cm long in humans. The faeces are passed out of the body in a

bowel motion via the anus as stools.