Transcript The anatomy of the digestive system images

THE ANATOMY OF THE DIGESTIVE SYSTEM IMAGES
Milk teeth
Teeth are calcified structures found within the jaw, used to break down food into smaller particles. The white part of the tooth is the enamel, made of a very hard mineral known as hydroxyapatite. Underneath is a substance
called dentine. Less brittle than enamel, it is used to add support to the tooth. The centre of the tooth comprises the pulp. This area is filled with soft tissue containing blood vessels and nerves. The cementum covers the root of
the tooth. Humans have four types of teeth: incisors, which are found at the front of the mouth and are designed for cutting food; canines, which grip and tear food; and premolars and molars, which chew and grind food. The
image above shows a child’s deciduous teeth, also known as baby or milk teeth. These fall out during childhood to be replaced by a single set of permanent teeth.
Credit: Wellcome Images
BIGPICTUREEDUCATION.COM
Anatomy of the tongue
The tongue is the primary organ of taste, and its upper surface is covered in taste buds. The structure of a taste bud can be seen in the top right of the image. The tongue is also used to move food
around the mouth during chewing. The tongue consists of eight muscles: four that act to change its shape and four that are used to change its position. The tongue has a rich network of nerves and
blood vessels and is known as a ‘muscular hydrostat’ – made mainly of muscle, with no skeletal support. Its shape is maintained by the water within its muscles.
Credit: Medical Art Service, Munich/Wellcome Images
Gustatory centre of the brain
Humans are able to distinguish between five different tastes: sweet, sour, bitter, salty and umami. These are detected by the different taste buds present on the tongue. Contrary to popular belief, there are not specific
areas of the tongue that detect different flavours. Some areas are more sensitive to particular tastes than others, however. The taste buds are structures known as papillae and contain taste cells. These cells detect the
presence of flavour molecules, which induces a nerve signal that alerts the brain to the flavour’s presence. The nerve signals are transported to the brain via three cranial nerves.
Credit: Medical Art Service, Munich/Wellcome Images
BIGPICTUREEDUCATION.COM
Fruit bat tongue
Scanning electron micrograph of the tongue of a fruit bat. This image shows the papillae, small bumps that cover the surface of the tongue,
which efficiently scoop up nectar and pollen.
Credit: Kevin MacKenzie, University of Aberdeen/Wellcome Images
BIGPICTUREEDUCATION.COM
Illustration of swallowing
The act of swallowing food is a complex process controlled by multiple nerves and muscles. It is divided into three phases: oral, pharyngeal and oesophageal. During the oral phase, food is moistened by saliva and broken down
by the teeth. This ball of food, known as the ‘bolus’, is moved by the tongue to the back of the mouth and into the oesophagus (foodpipe). At this time, the nasopharynx and larynx are closed to prevent food from entering the
trachea (windpipe). A wave of contractions in the smooth muscle behind the bolus moves the food down the oesophagus and prevents it from returning to the mouth. Food enters the stomach via the oesophageal sphincter.
Credit: Medical Art Service, Munich/Wellcome Images
BIGPICTUREEDUCATION.COM
Stomach
The stomach contains a variety of chemicals and molecules designed to break down food. It consists of four separate layers of muscle and connective tissue. The uppermost layer, or ‘epithelium’, has multiple folds, as can be
seen in the image above. Within these folds are numerous ducts that produce mucus. This mucus is essential to protect the stomach from its acidic contents. Food enters the stomach via the oesophageal sphincter and becomes
mixed with both stomach acid and digestive enzymes. The digestive enzymes in the stomach work optimally at an acidic pH. The stomach acid provides this environment and also kills many microorganisms. Pepsin is the main
digestive enzyme. It breaks down the proteins in food into smaller chains of amino acids, known as peptides. The partially digested food, known as chyme, leaves the stomach via the pyloric sphincter and enters the duodenum –
the first section of the small intestine. Here, more enzyme-based degradation occurs.
Credit: Medical Art Service, Munich/Wellcome Images
BIGPICTUREEDUCATION.COM
Liver, pancreas and gall bladder
The image above shows a cross-section of some organs that are important in the digestion of food. The large organ at the top is the liver. This is the largest internal organ and has a multitude of
functions, including the storage of glucose as glycogen, the breakdown of toxins and the production of bile, which is needed for the digestion of fats. The yellow organ in the centre of the image is the
pancreas. This organ secretes a number of important hormones into the bloodstream, including insulin. The pancreas also releases digestive enzymes into the small intestine to aid in the breakdown
of partially digested food. The small organ to the left of the pancreas is the gall bladder, which stores bile produced by the liver.
Credit: Medical Art Service, Munich/Wellcome Images
BIGPICTUREEDUCATION.COM
Structure of the jejunal wall
Once foods have left the first section of the small intestine they enter the middle section, known as the jejunum. A diagram showing the cross-section of this part of the intestine can be seen above. Partially digested food is
passed through the jejunum via a wave of muscular contractions, known as ‘peristalsis’. Muscles contracting behind the ball of food push it slowly though the intestines and prevent it from going backwards.
The inside of the small intestines are covered in finger-like projections called villi, which are themselves covered in microvilli. These projections drastically increase the surface area within the small intestine and are needed to
absorb nutrients released.
Credit: Medical Art Service, Munich/Wellcome Images
BIGPICTUREEDUCATION.COM
Villi in the small intestine
A scanning electron micrograph of villi within the small intestine. Food particles can be seen within the crevices between the villi.
This picture is 450 micrometres (0.45 millimetres) wide.
Credit: Professor Alan Boyde/Wellcome Images
BIGPICTUREEDUCATION.COM
Cross-section of villi in the small intestine
This image shows a cross-section of two intestinal villi. The rich network of blood vessels within each can be seen. Molecules such as amino acids or sugars pass
through the intestinal wall by diffusion. By having a large surface area, the intestine increases the likelihood of absorbing these molecules.
The blood vessels transport these nutrients away.
Credit: Medical Art Service, Munich/Wellcome Images
BIGPICTUREEDUCATION.COM
Goblet cell
Goblet cells are found within many parts of the human body, including the respiratory tract, the eyes and the small intestine.
The cells release mucous globules that provide lubrication and protection to the body’s surfaces. These globules can be seen in the image above, stained blue.
They are condensed within the goblet cell, but once released they absorb water, expanding in around 20 milliseconds.
Credit: University of Edinburgh/Wellcome Images
BIGPICTUREEDUCATION.COM
Bacteria in the intestines
The surface of the lower human digestive tract is covered by an enormous number of microorganisms. These are known as the ‘gut flora’. There are hundreds of different species present in the gut.
Although it is possible to live without gut flora, the microorganisms perform a variety of important functions, including carbohydrate digestion and preventing disease-causing bacteria from growing.
The image above shows pathogenic E. coli bacteria binding to the intestinal lining. The red staining shows the nuclei of the intestinal cells (large) and bacteria (small).
Credit: S Schuller/Wellcome Images
BIGPICTUREEDUCATION.COM
Colonic crypt
Once food has been digested within the small intestine, the remaining indigestible matter passes into the large intestine. This section of the digestive tract comprises the cecum, colon and rectum. Water and salts are absorbed
in the large intestine, in addition to vitamins that are produced by bacteria that live there. The image above shows a cross-section of a colonic crypt. Mucin cells (stained red) within the crypt produce mucous that passes into the
interior of the colon through crypt lumen, the area in the centre surrounded by blue. This mucus helps to ease the passage of faeces through the colon.
Credit: Michela Schaeppi/Wellcome Images
BIGPICTUREEDUCATION.COM
Rectum
The final portion of the large intestine is known as the rectum, which leads to the anus.
Faeces are stored temporarily in the rectum before defecation.
Credit: Medical Art Service, Munich/Wellcome Images
BIGPICTUREEDUCATION.COM
Reusing our images
Images and illustrations
• All images, unless otherwise indicated, are from Wellcome Images.
• Contemporary images are free to use for educational purposes (they have a Creative Commons
Attribution, Non-commercial, No derivatives licence). Please make sure you credit them as we have
done on the site; the format is ‘Creator’s name/Wellcome Images’.
• Historical images have a Creative Commons Attribution 4.0 licence: they’re free to use in any way as
long as they’re credited to ‘Wellcome Library, London’.
• Flickr images that we have used have a Creative Commons Attribution 4.0 licence, meaning we –
and you – are free to use in any way as long as the original owner is credited.
• Cartoon illustrations are © Glen McBeth. We commission Glen to produce these illustrations for
‘Big Picture’. He is happy for teachers and students to use his illustrations in a classroom setting, but
for other uses, permission must be sought.
• We source other images from photo libraries such as Science Photo Library, Corbis and iStock and
will acknowledge in an image’s credit if this is the case. We do not hold the rights to these images,
so if you would like to reproduce them, you will need to contact the photo library directly.
• If you’re unsure about whether you can use or republish a piece of content, just get in touch with
us at [email protected].