Skip to main content Accessibility help
×
Hostname: page-component-78c5997874-s2hrs Total loading time: 0 Render date: 2024-11-09T19:51:56.714Z Has data issue: false hasContentIssue false
This chapter is part of a book that is no longer available to purchase from Cambridge Core

11 - Gastrointestinal physiology

from Section 2 - Physiology

Tim Smith
Affiliation:
Alexandra Hospital, Redditch
Colin Pinnock
Affiliation:
Alexandra Hospital, Redditch
Ted Lin
Affiliation:
University of Leicester, NHS Trust
Robert Jones
Affiliation:
Withybush Hospital, Haverfordwest
Get access

Summary

The primary functions of the gastrointestinal (GI) tract are the digestion of ingested food, the absorption of water, nutrients, electrolytes and vitamins, and the excretion of indigestible and waste products. The GI tract should not be thought of as a single organ, but a series of organs each with specialised functions. Each section of the GI tract has characteristic motor and secretory properties to accomplish a particular role in the overall function of the gut.

Gastrointestinal motility

Apart from the proximal part of the oesophagus, the GI tract has a remarkably uniform structure consisting of three layers of smooth muscle. These are arranged as an outer longitudinal layer, a middle circular layer and an inner submucosal layer (muscularis mucosa) (Figure GI1).

The basic contractile unit of the circular and longitudinal muscle layers is the smooth muscle cell. Across each cell membrane a transmembrane potential of between −40 and −70 mV (negative intracellular charge) is maintained by an ATP-dependent Na+K+ATPase pump. In most areas of the GI tract, the transmembrane potential of smooth muscle cells rhythmically depolarises and repolarises, which is called basic electrical rhythm, slow-wave activity or electrical control activity (ECA). Gap junctions between individual cells allow transmembrane ionic movements to be conducted from cell to cell. Slow-wave activity is conducted along lengths of bowel in a synchronised pattern due to this electrical continuity between cells. Segments of intestine with similar electrical activity, therefore, behave as a functional syncytium.

Type
Chapter
Information
Publisher: Cambridge University Press
Print publication year: 2009

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Save book to Kindle

To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.

Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

Available formats
×

Save book to Dropbox

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.

Available formats
×

Save book to Google Drive

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

Available formats
×