• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

The Layers of the Vertebrate Gut, Their Function In Different Parts of the Gut and in Different Animals

Extracts from this document...

Introduction

The Layers of the Vertebrate Gut, Their Function In Different Parts of the Gut and in Different Animals For the purposes of the essay the gut is considered to start from the gastroesophageal junction and terminates at the anus. The gut layers are described and their functions in different parts of the gut discussed, beginning at the gastroesophageal junction and working downward through the gastrointestinal tract. Description and discussion of the human and mammalian gut predominates, as it is these animals that have been most studied, but variations in different groups of vertebrates have been included where possible. A cross-section through the gut reveals four separate main layers with each layer performing a functionally distinct role (Fig. 1). Some layers remain relatively unchanged throughout the entire length of the tract whilst other layers are adapted for different functions in different regions of the gut. The inner mucosa is the most variable layer and is sub-divided into three further layers (1) the innermost epithelial lining adjoining the lumen of the tract (2) the lamina propria, a layer of fibrous connective tissue usually containing abundant blood and lymphatic capillaries that enable efficient secretion and absorption at the mucosal surface. It may also contain glands, lymph nodules and diffuse smooth muscle fibres (3) the muscularis mucosae, a number of layers of smooth muscle fibres that improve contact between the epithelium and contents of the lumen for absorption by persistent agitation. ...read more.

Middle

Glandular secretions are squeezed out by the contraction of thin bands of muscularis mucosae running between the gastric glands. Preliminary digestion is enhanced by mechanical mixing of the stomach contents to produce semi-digested chyme. In humans mechanical mixing is achieved by three layers of muscle in the muscularis externa. Elsewhere in the human digestive tract (with the exception of the pyloric sphincter) there are only two layers of muscle in the muscularis externa, an inner circular layer and outer longitudinal layer. The muscularis externa of the stomach wall contains a third incomplete layer of muscle set obliquely to the other two muscle layers. This arrangement allows vigorous mixing of the stomach contents. Some other mammals possess this third oblique layer of muscle near the gastroesophageal junction. In a number of marsupials and herbivorous primates it is restricted to taeniae and is practically absent from the gizzard of birds. The ruminant forestomach has a very intricate arrangement of muscle layers. In humans the branched glands of the pyloric region consist mainly of mucus secreting cells with a scattering of acid secreting cells. The mucus lubricates the tract to ease the passage of chyme and also protects the entrance to the duodenum from attack by acid and pepsin produced in the stomach. The pits in the pylorus are an irregular shape and deeper than in the cardia and fundus extending at least halfway from the epithelial surface to the muscularis mucosae. ...read more.

Conclusion

The mammalian colonic mucosa consists of both absorptive and mucus-secreting cells, microvilli are also present. The glands have a tightly packed straight tubular arrangement in humans, increasing the surface area of the absorptive cells. The mucus secreting cells protect the colonic mucosa from abrasion and the regular contraction of the thick muscularis mucosae in the colon prevents the glands clogging and facilitates the expulsion of mucus. The colonic submucosa of humans does not contain any glands but large lymph nodes in the mucosa often reach the submucosa. The colonic muscularis externa of many mammals propels the solids by peristalsis for evacution via the anus. In some mammals, adult amphibians, reptiles and birds the digestive tract terminates in a cloaca. The cloaca is comprised of a coprodeum, urodeum and proctodeum. The proctodeum is the posterior section and terminates at the anus. The reptilian and avian coprodeum and urodeum are lined with absorptive mucosa whilst the proctodeum lining is of a stratified squamous arrangement. The vertebrate gut is remarkable in its complexity and adaptability. The gut layers have an extraordinary ability to perform a multitude of different functions depending on their position in the gastrointestinal tract and in different animals. This is due to the adaptability of their basic structure, particularly the mucosa. This is further illustrated by their function in animals living in radically different environments. The diets and lifestyles of these animals are as far ranging as the environments in which we find them, yet the gut layers are well adapted to what is required of them. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Anatomy & Physiology section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Anatomy & Physiology essays

  1. Body in Motion

    For example; the muscles became responsible for up to 85-90 per cent of the cardiac output whereas at rest the other tissues took on this role. Our circulatory and respiratory systems' working together is what enabled my performance in the beep test.

  2. A level Project, Personal Exercise Program on Netball.

    Static Stretching. Tricep Stretch Triceps Stand with your feet hip-width apart and your legs slightly bent. Raise one of your arms and place your hand over your back. Try to reach as far down the midline of your spine as possible.

  1. Free essay

    Body In Action

    Like muscle, bone is living tissue that responds to exercise by becoming stronger. Young women and men who exercise regularly generally achieve greater peak bone mass (maximum bone density and strength)

  2. The human bodys immune system

    with antibodies and complement proteins they will neutralize or partly neutralize the antigen. Next, they must elude a series of nonspecific defenses - cells and substances that attack all invaders regardless of the epitopes they carry. These include patrolling scavenger cells, complement, and various other enzymes and chemicals.

  1. Physiology Within Sport

    Neuromuscular * Increased pliability of muscles * Increased speed of neural transmissions. Energy * Aerobic ATP production. 16. DESCRIBE THE CARDIOVASCULAR RESPONSES TO STEADY-STATE EXERCISE The following responses occur to steady-state exercise: * Heart rate plateaux's * Venous return increase this is the amount of blood going back to the heart after being transported around the body.

  2. PE Coursework - Section 1

    Here are the results of my tests Test What it measures Score National average Good or Bad? Standing stork test Balance 14.3 secs * Excellent - above 49 secs * Good - 40 - 49 * Average - 26 - 39 * Fair - 11-25 * Poor - below 11

  1. Anatomy and Physiology.

    These form a matrix of cells called osteoid tissue. This is similar to bone except for a lack of minerals. As the woven bone grows thicker, calcium phosphate is left in the matrix. The now-calcified trabeculae forms permanent spongy bone.

  2. Nutrition and Digestion

    The main differences between the two groups are their chemical structures. Simple sugars are made up of single or double sugar units while complex carbohydrates are made up of numerous units of sugar and are called polysaccharides. In our body, the end product of both is glucose which is transferred into energy.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work