Absorption and Metabolism - Oral Cavity and Alimentary Canal


Absorption, Metabolism and Excretion

The hepatobiliary system, kidneys, skin and lungs are important for metabolism and excretion. After absorption of any substance (nutrients, drugs or toxins); be it through the digestive tract, skin, lungs, the eye, mammary gland or uterus, it is distributed via the bloodstream to reactive sites. By metabolism, the body process absorbed substances. In some cases, detoxification can produce substances more toxic than the initial compound. The liver receives the portal circulation, and is most commonly involved in detoxification. The kidneys are responsible for excreting metabolites not used by the body. Knowledge of these processes and the ways it can vary is important to evaluate treatment of patients.

Digestive system

The purpose of this topic is to practically illustrate the structures, organs and glands of the gastro-intestinal tract. The secretory units which were covered with glandular epithelia, should be reviewed for the salivary glands.

The digestive system can be divided into several parts:

Upper Digestive Tract (oral cavity, oesophagus and stomach).
Histology of the structures found in and around the mouth, the oesophagus and stomach.
Lower Digestive Tract (duodenum to anus).
Most digestion and absorption takes place from the duodenum to the ileum. The colon and lower is involved with water balance and excretion.
Accessory organs.
Those organs whose primary function related to the digestive system. These include the liver, gall bladder and pancreas.

You should be able to:

Digestive system in general

  • Describe the generic components, organisation and functions common to most of the digestive tract.
  • Describe how the basic organisation of the digestive tract is modified along its course.
  • Relate the structure to the function of each section of the digestive tract.
  • Describe the morphology and histology of each component of the digestive tract.
  • Describe functional variations related to differing functions.
  • Relate the morphology with the function of each component of the digestive tract.
  • Describe the appearance, organisation and functions of the epithelial cells throughout the digestive system.
  • Discuss the distribution of lymphoid tissue in the digestive system.
  • Identify and describe the cells found in the various areas of the digestive tract.
  • Describe the specialised functions of cells found in the various areas of the digestive tract.
  • Identify and describe the intrinsic glands of the digestive tract.
  • Describe the surface topology of the mucosa of the digestive tract.
  • Identify the layers of the digestive tract and compare cross and longitudinal appearance.
  • Define the cellular composition of the mucosal layers and their function.
  • Describe changes in layers in the transitional areas of the digestive tract.

Upper digestive tract

  • Describe the characteristics of the lip.
  • Name and identify the papillae on the tongue.
  • Name, identify and compare the salivary glands.
  • Identify and describe the structure and function of the salivary glands.
  • Describe and identify the histological structures of teeth.
  • Identify and describe the oesophagus.
  • Identify the regions of the stomach.
  • Identify the different types of secreting cells in gastric glands., and the function of each.

Lower digestive tract

  • Identify the neural tissue in the intestines and the coats in which they are found.
  • Distinguish between the various sections of the small and large intestine.

Accessory organs

  • Describe the organisation of liver tissue.
  • Recognise and describe the histological structure and function of liver lobules.
  • Explain how blood and bile pass through the liver lobules and relate this to liver function and pathologies.
  • Identify and describe the structure of the gall bladder and bile duct.
  • Identify and describe the structure and function of the exocrine and endocrine pancreas.

Slides for this week

For each slide, complete the work as listed below. Completing the whole slide will assist you in understanding and retention. For each slide, allocate an A3 spread in your workbook. Remember to add the slide and its page number to the index in the front of the book.
  1. Oral Cavity and Related Structures
  2. Transport Passages
  3. Digestive Tract
  4. Glands


Metabolism and Excretion

  1. Describe the process of metabolism and how individual patient differences can affect drug selection.
  2. Make a list of ingested substances and their toxic effects on the liver.

Digestive system

  1. Name and discuss the three types of papillae.
  2. What cells are responsible for the secretion of dentine?
  3. Name the 3 main salivary glands and their secretions.
  4. Tabulate the differences in the layers of the oesophagus, stomach, small intestine and colon.
  5. Name 7 functions of the liver.
  6. Name and discuss the functional structures of the liver.
  7. What classifies liver cirrhosis?
  8. What layer is absent in the mucosal layer of the gall bladder?
  9. What is the capsule of the pancreas composed of?
  10. How is ingestion, propulsion, mechanical digestion, chemical digestion, absorption, and defecation controlled?
  11. Name the six fundamental activities of the digestive system, giving an example of each.
  12. Why does the stomach not digest itself?
  13. Describe the mechanical and chemical digestion of food entering the stomach.
  14. What are the adaptations of the small intestine wall that increase its absorptive capacity
  15. What features are unique to the wall of the large intestine?
  16. Describe the contributions of the unique features of the large intestine to its function.
  17. What roles does bacterial flora play in functioning of the digestive system?
  18. Identify three main features of liver histology that are critical to its function.
  19. What is the function of the oesophagus?
  20. Explain and relate the histology of the oesophagus to the function of the oesophagus.
  21. What is the function of the stomach?
  22. Explain and relate the histology of the stomach to the function of the stomach.
  23. What stimulate secretions by the salivary glands?
  24. Secretory nerve fibres (efferent) to the salivary glands are derived from two sources. What are the two sources of efferent nerve supply to the salivary glands?
  25. What are the role or functions of the nerve supply to the salivary glands?
  26. The buccal mucosa of the mouth contains numerous small glands. What does these glands consist of?
  27. Some research suggest that serous demilunes as seen in mixed acini are artefacts of traditional fixation methods. Explain.

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