The GI System

8/8/2019 The GI System

http://slidepdf.com/reader/full/the-gi-system 1/5

The GI System

The gastro-intestinal system is essentially a long tube running right through the body, witspecialized sections that are capable of digesting material put in at the top end and extracuseful components from it, then expelling the waste products at the bottom end. The whois under hormonal control, with the presence of food in the mouth triggering off a cascade

hormonal actions; when there is food in the stomach, different hormones activate acid sec

increased gut motility, enzyme release etc. etc.

Nutrients from the GI tract are not processed on-site; they are taken to the liver to be brofurther, stored, or distributed.



Parts of GI system Anatomy & Physiology

1. Esophagus Once food has been chewed and mixed with saliva in the mouth, it is swallowed and p

esophagus. The esophagus has a stratified squamous epithelial lining (SE) which protects thetrauma; the submucosa (SM) secretes mucus from mucous glands (MG) which aid the passa

the esophagus. The lumen of the esophagus is surrounded by layers of muscle (M)- voluntary

progressing to involuntary in the bottom third- and food is propelled into the stomac

peristalsis.



2. Stomach The stomach is a 'j'-shaped organ, with two openings- the esophageal and the duodenal- a

the cardia, fundus, body and pylorus. Each region performs different functions; the fundus c

gases, the body secretes pepsinogen and hydrochloric acid, and the pylorus is responsible foand pepsinogen secretion.

The stomach has five major functions;

y Temporary food storage

y Control the rate at which food enters the duodenum

y Acid secretion and antibacterial action

y Fluidization of stomach contents

y Preliminary digestion with pepsin, lipases etc.



3. Small

Intestine

The small intestine is the site where most of the chemical and mechanical digestion is carried

virtually all of the absorption of useful materials is carried out. The whole of the small intest

an absorptive mucosal type, with certain modifications for each section. The intestine alsmuscle wall with two layers of muscle; rhythmical contractions force products of digest

intestine ( peristalsis). There are three main sections to the small intestine;

y The duodenum forms a 'C' shape around the head of the pancreas. Its main functio

the acidic gastric contents (called 'chyme') and to initiate further digestion; Brunne

submucosa secrete an alkaline mucus which neutralizes the chyme and protects th

duodenum.

y The jejunum

y The ileum. The jejunum and the ileum are the greatly coiled parts of the smatogether are about 4-6 metres long; the junction between the two sections is not w

mucosa of these sections is highly folded (the folds are called plicae), increasing

available for absorption dramatically.

4. Pancreas The pancreas consists mainly of exocrine glands that secrete enzymes to aid in the digestio

small intestine. The main enzymes produced are lipases, peptidases and amylases for facarbohydrates respectively. These are released into the duodenum via the duodenal ampulla

that bile from the liver drains

Pancreatic exocrine secretion is hormonally regulated, and the same hormone that enco

(cholesystokinin) also encourages discharge of the gall bladder's store of bile. As bile

emulsifying agent, it makes fats water soluble and gives the pancreatic enzymes lots of surfa

on.

Structurally, the pancreas has four sections; head, neck, body and tail; the tail stretches bac

of the spleen.



5.Large

Intestine

By the time digestive products reach the large intestine, almost all of the nutritionally usefu

been removed. The large intestine removes water from the remainder, passing semi-soli

rectum to be expelled from the body through the anus. The mucosa (M) is arranged int

straight tubular glands (G) which consist of cells specialized for water absorption and mucus

cells to aid the passage of feces. The large intestine also contains areas of lymphoid tissue

found in the ileum too (called P eyer's patches), and they provide local immunological protec

weak-spots in the body's defences. As the gut is teeming with bacteria, reinforcement

surface defenses seems only sensible.

Source: http://www.le.ac.uk/pa/teach/va/anatomy/

Documents

The GI System