Advanced Nutrition and Dietetics in Gastroenterology

Miranda Lomer

• Publisher: Wiley-Blackwell
• Year: 2014
• Print ISBN: 9780470671320
• eBook ISBN: 9781118872895
• Edition: 1
• Topic: Medicine
• Subtopic: Nutrition, Dietics & Bariatrics

Advanced Nutrition and Dietetics in Gastroenterology provides informative and broad-ranging coverage of the relation between nutrition and diet and the gastrointestinal tract. It explores dietary factors involved in causation of a variety of gastrointestinal disorders, as well as the effects on diet and the treatments available. It also provides an overview of anatomy and physiology, measurement and assessment of function, and dietary components relevant to gastrointestinal health.  

ABOUT THE SERIES

Dietary recommendations need to be based on solid evidence, but where can you find this information? The British Dietetic Association and the publishers of the Manual of Dietetic Practice present an essential and authoritative reference series on the evidence base relating to advanced aspects of nutrition and diet in selected clinical specialties. Each book provides a comprehensive and critical review of key literature in its subject.  Each covers established areas of understanding, current controversies and areas of future development and investigation, and is oriented around six key themes:

•Disease processes, including metabolism, physiology, and genetics
•Disease consequences, including morbidity, mortality, nutritional epidemiology and patient perspectives
•Nutritional consequences of diseases
•Nutritional assessment, drawing on anthropometric, biochemical, clinical, dietary, economic and social approaches
•Clinical investigation and management
•Nutritional and dietary management
•Trustworthy, international in scope, and accessible, Advanced Nutrition and Dietetics is a vital resource for a range of practitioners, researchers and educators in nutrition and dietetics, including dietitians, nutritionists, doctors and specialist nurses.

SECTION 1
Physiology and function of the gastrointestinal and hepatobiliary tract

Chapter 1.1
Physiology and function of the mouth

Michael P. Escudier

King’s College London and Guy’s and St Thomas’ NHS Foundation Trust London, UK

1.1.1 Physiology

The mouth is an important organ as it is the entry point into the gastrointestinal (GI) tract and damage and disease can compromise dietary intake. Even very minor disorders can have a profound impact on nutritional status.

Anatomy

The oral cavity consists of a number of structures.

The lips surround the mouth and comprise skin externally and a mucous membrane (which has many minor salivary glands) internally, which together with saliva ensure adequate lubrication for the purposes of speech and mastication.

The cheeks make up the sides of the mouth and are similar in structure to the lips with which they are continuous but differ in containing a fat pad in the subcutaneous tissue. On the inner surface of each cheek, opposite the upper second molar tooth, is an elevation that denotes the opening of the parotid duct which leads back to the parotid gland located in front of the ear.

The palate (roof of the mouth) is concave and formed by the hard and soft palate. The hard palate is formed by the horizontal portions of the two palatine bones and the palatine portions of the maxillae (upper jaws). The hard palate is covered by thick mucous membrane that is continuous with that of the gingivae. The soft palate is continuous with the hard palate anteriorly and with the mucous membrane covering the floor of the nasal cavity posteriorly. The soft palate is made up of a fibrous sheet together with the glossopalatine and pharyngopalatine muscles and the uvula hangs freely from its posterior border.

The floor of the mouth can only be seen when the tongue is raised and is formed by the mucosa overlying the mylohyoid muscle. In the midline is the lingual frenum (a fold of mucous membrane), on either side of which is the opening of the submandibular duct from the associated submandibular gland.

The gingivae form a collar around the neck of the teeth and consist of mucous membranes connected by thick fibrous tissue to the periosteum surrounding the bones of the jaw. The gingivae are highly vascular and well innervated.

The teeth are important in mastication and in humans, who are omnivores, they enable both plant and animal tissue to be chewed effectively. Each tooth consists of a crown, which varies in shape dependent on the position in the mouth, and one or more roots. There are eight permanent teeth in each quadrant, consisting of two incisors, a canine, two premolars and three molars, resulting in a total of 32 permanent teeth.

The tongue is a highly mobile, muscular organ in the floor of the mouth which is important in speech, chewing and swallowing. In conjunction with the cheeks, it guides food between the upper and lower teeth until mastication is complete. The taste buds situated on the tongue are responsible for the sensation of taste (salt, bitter, sweet and sour).

Function

The main role of the mouth is to prepare food for swallowing via the oesophagus and its subsequent passage to the stomach. The first phase of this process is mastication (chewing) which requires activity in the muscles of mastication (masseter, temporalis, medial and lateral pterygoids and buccinator). Chewing helps digestion by reducing food to small particles and mixing it with the saliva secreted by the salivary glands. The saliva lubricates and moistens dry food whilst the movement of the tongue against the hard palate produces a rounded mass (bolus) of food which can be swallowed.

The saliva required for this process is produced by the three paired major salivary glands (parotid, submandibular and sublingual), together with the many minor salivary glands throughout the oropharynx. The total daily production of saliva is around 500 mL, with the rate of production around 0.35 mL/min at rest which increases to 2.0 mL/min during eating and falls to 0.1 mL/min during sleep. The contribution of the various glands varies at rest and during eating (Table 1.1.1).

Table 1.1.1 Contribution of groups of salivary glands to overall saliva production at rest and during eating

	Resting %	Stimulated %
Parotid	20	50
Submandibular	65	49
Sublingual	8
Minor	7	1

In addition to its role in digestion and taste, saliva produces a film which coats the teeth and mucosa and helps to cleanse and lubricate the oral cavity. It also prevents dessication of the oral mucosa and acts as a barrier to oral microbiota [1], both physically and through its antimicrobial activity. The buffers within it also help to maintain optimal pH for the action of the salivary amylase and maintain the structure of the teeth.

Role in digestion

Very little digestion of food occurs in the oral cavity. However, saliva does contain the enzyme amylase which begins the chemical process of digestion by catalysing the breakdown of starch into sugars.

1.1.2 Measurement and assessment of function

Salivary function is the most commonly assessed measure of oral function and can be achieved clinically by using the Challacombe dry mouth scale (Box 1.1.1).

Box 1.1.1 Challacombe dry mouth scale

One point for each feature to a maximum of 10

• Mirror sticks to one buccal mucosa
• Mirror sticks to both buccal mucosa
• Mirror sticks to tongue
• Saliva frothy
• No saliva pooling in floor of mouth
• Tongue shows loss of papillae
• Altered (smooth) gingival architecture
• Glassy appearance to oral mucosa
• Cervical caries (more than two teeth)
• Tongue highly fissured
• Tongue lobulated
• Debris on palate

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A reasonable indication of salivary function may be obtained by measuring the resting (unstimulated) salivary flow over a period of 10 min. In health, the rate will normally be around 0.35 mL/min with a range of 0.2–0.5 mL/min. However, this will be reduced in the presence of xerostomic medications or underlying conditions such as Sjögren’s syndrome and a value below 0.2 mL/min requires further investigation and below 0.1 mL/min is indicative of an underlying condition or disease process. Whilst the stimulated parotid flow rate may also be determined, neither is particularly reliable and hence both should only be viewed as indicative rather than diagnostic.

1.1.3 Dental disease

The oral cavity is home to around 500 different microbial species. These bacteria together with saliva and other particles constantly form a sticky, colourless ‘plaque' on the surface of teeth. Brushing and flossing help to remove this layer which is intimately involved in the development of dental caries and gingivitis. Plaque that is not removed can harden and form calculus which requires professional cleaning by a dentist or dental hygienist to prevent the development of periodontal disease which can lead to the destruction of the dental support structures and eventually loss of the affected tooth or teeth.

Whilst both dental caries and periodontal disease have been common for many years, non-carious tooth surface loss, particularly in the form of erosion, is a more recent development and is associated with modern lifestyle and dietary intake.

Dental caries

Dental caries can occur at any stage throughout life and is one of the most common preventable diseases in childhood [2]. In developed countries there has been a fall in the lifetime experience of ...

Table of contents

• Cover
• Title page
• Copyright page
• Series page
• Preface
• Foreword
• Editor biographies
• Contributors
• SECTION 1: Physiology and function of the gastrointestinal and hepatobiliary tract
• SECTION 2: Dietary components relevant to gastrointestinal health
• SECTION 3: Gastrointestinal disorders
• SECTION 4: Hepatobiliary disorders
• Index
• End User License Agreement