git lecture 1&2

8/13/2019 GIT Lecture 1&2

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Dr. Osama A. Shaikh Omar

Physiology of

Gastrointestinal Tract

2ndyear

www.uqu.sa/oashaikhomar

Lectures 1 & 2


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References:

Human Physiology - Rhoades & Pflanzer

Textbook of Medical Physiology - Guyton & Hall

Physiology, a regulatory systems approach - Strand


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GIT is also referred to as an Alimentary Canal,

the GIT is just like a tube extending from

the mouth down to the anal opening.

It can be divided in two parts:

1- Component parts of segments of the GIT.

2-The accessory organs located inside the GIT.

Anatomic considerations


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1- The component parts of segments of the GIT:

Mouth, oropharynx, oesophagus,stomach, small intestine (duodenum,

jejunum & ileum) large intestine ( cecum,

ascending, transverse, descending &sigmoid colon) rectum & anal canal.

2- The accessory organslocated inside the GIT:

Teeth, Tongue, Salivary glands (Parotid,

sublingual & submandibular). Pancreas,liver & gall bladder & the appendix.

Anatomic Considerations


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GI tract is about 30 feet long from

mouth to anus.

The Histological organization of the

4 major digestive layers: Mucosa

Submucosa

Muscularis (2 layers)

- Inner Circular

- Outer Longitudinal Serosa (fibrous).

Basic Structure of the GIT


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Histology of the GIT Wall

MucosaThe mucosa is the inner most layer of the gastrointestinal tract that is

surrounding the lumen. This layer comes in direct contact with the food

and is responsible for absorption and secretion.

SubmucosaThe submucosa consists of a dense irregular layer of connective tissue

with large blood vessels, lymphatics and nerves branching into themucosa and muscularis.

Muscularis (2 layers)- Inner Circular - Outer LongitudinalThe circular muscle layer prevents the food from going backwards and

the longitudinal layer shortens the tract (peristalsis). Between the two

muscle layers are the myenteric plexus. Serosa or adventitia

consists of several layers of connective tissue .


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1-Port of entrance = Ingestion of food (nutrients,i.e. protein, carbohydrate & fat. water, vitamins, &minerals).

It is an active process that includes decisionmaking, mastication & swallowing.

2- Digestion of food, which starts in the mouth &continues in the stomach & in the small intestine.This is aided by enzymes in the saliva, stomach,small intestine but mainly the pancreatic enzymes

are involved in digestion.

Digestion of fat also requires bile from the liver.

Functions of the GIT


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3- Absorption of digested food

products of food in form of monosaccharide , amino

acids , fatty acids ,etc.

Absorption is partial in the stomach but mainly in the

small intestine.

4- Formation of feces and excreted via the rectum.

5- Formation of

RBCs through secretion of intrinsic factor hydrochloric acid - in the gastric juice

some vitamins by the colonic bacterial flora.


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6- Endocrine functions

e.g. secretion of GIT hormones .

7- Regulation of:

water balance.

blood glucose level.

blood reactions.



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To achieve these different functions the

following mechanisms are involved:

section of digestive juices such as saliva,

gastric HCl , enzymes & bile.

GIT motility for mixing with digestive

juices & passage through the GIT.

Secretion of GIT hormones.



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Control of the GIT functions:

GIT secretion & motility are both generallycontrol by:

1. Neural control.

2. hormonal control.

Control of the GIT functions


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1) Neural control

This is mainly by the autonomic nervous system (ANS).

In addition to the sympathetic (noradrenergic) &parasympathetic divisions ( Cholinergic), in the gut theenteric nervous system (ENS) is considered to be the

third division of the ANS.

The sympathetic stimulation inhibits motility , constrictssphincters & causes vasoconstriction (secretion is notnecessarily inhibited)

The parasympathetic stimulation increases motility ,relaxes the sphincters & vasodilatation & stimulatessecretions.



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The enteric nervous system:

Consists of two nerve plexuses:

Myenteric plexus which is mainly concerned with

regulation of motility e.g. peristalsis. lies between Longitudinal & circular muscles layers.

Meissners or submucous plexus which is mainly

concerned with regulation of sensory functions e.g.

increased blood flow, exocrine & endocrine secretions in

response to stimulation of mechano & chemo-receptorsof the gut.

lies in the Submucosa.



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2) Hormonal controlis mainly via GIT hormones suchas secretin, Cholecystokinin (CCK), somatostatin,Gastrin, Gastric Inhibitory Peptide (GIP), VasoactiveIntestinal Peptide (VIP), . .etc. These GIT hormonesmay acting in one of the following fashions:

The GIT hormones are divided into two familiesaccording to structural & functional similarities:

Gastrin Family including Gastrin & CCK.

Secretin Family including secretin, glucagons, VIP &GIP.



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3) Motility- the progression of food, fluids and wastethrough the digestive tract.

4) The digestive JuicesThese are of five types :

- Saliva,

- Gastric Juice,

- Pancreatic Juice,

- Bile , &

- Intestinal Juice (Succus Intericus).



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Functions of Saliva

- Initiates digestion of carbohydrates.

- Lubricates food to facilitates swallowing.

- Neutralizes any gastric acid that refluxes

from stomach.

- Keeps mouth moist .

- Keeps mouth & teeth clean.

- Antibacterial action (Enzyme role).


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Salivary glands

Salivary Glands are the main source of thesecretion in the mouth.

Saliva is form from:

1) Parotid glands - secrete serous saliva(watery fluid) such as Digestive enzyme-

Amylase (breaking down starch and glycogen(polysaccharides) to disaccharides).

2) Submandibular glands - secrete mucoussaliva.

3) Sublingual glands secrete mixed type of saliva.

4) Minor Salivary Glands - They are 1-2mm in diameter and unlike

the other glands. Their secretion is mainly mucous.

5) Von Ebner's Glands - found in on the tongue and they secrete aserous fluid that begin lipid hydrolysis. They are an essential

component of taste.


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The Tongue

Tongue: the tongue is covered

with papillae (small projections ).

- Many of the papillae haveMechanical processing that

help the tongue grip food.

- Many of the papillae have sensory analysis bytouch, temperature, and taste receptors (Large taste

buds & Small taste buds).


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The Mouth

Salivary glands

Teeth

Tongue

Teeth:

according to the location and function,

they are divided into:

Incisors

Canine Premolars

Molars.


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Digestion in Mouth

Chewing and swallowing

Voluntary stage

The presence of food in the mouth initiates

reflex inhibition lead to drop the lower jaw

which stimulates muscle to contract.

1. Voluntary stage

2. Pharyngeal stage

3. Esophageal stage

Mastication (Chewing) - form ball of food

called bolus.

Pushing the bolus to the pharynx (swallowing) - It

is controlled by the swallowing centers located in

the medulla oblongata.


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Pharyngeal stage: The epiglottis lowers to cover the

airway so that the bolus does notenter the larynx.

The bolus is passed into the

pharynx. Contract pharyngeal muscles

swallowing.

Esophageal stage: Open the upper esophagus

sphincter (ES).Start peristalsis close the upper(ES) and open the lower (ES).

Digestion in Mouth


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Structure of the Esophagus:

The esophagus is a flexible tubewhich leads from the pharynx in theupper throat to the stomach.

It is about 10 inches long.

Its walls are made of muscle fiberswhich contract in waves (calledperistalsis) to push the bolus down tothe stomach.

Innervation is by the Vagus nerve.

It has two sphincters:- upper esophageal sphincters.

- lower esophageal sphincters.

The Esophagus


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Functions of the esophagus:

1- Conduit to move food from the pharynx tothe stomach.

2- Prevention of air from entering thestomach via the upper esophagealsphincter.

3- Prevention of reflux of gastric contents to

the esophagus via the lower theesophageal sphincter stomachmovement.

The Esophagus


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Esophageal Secretion:

Mucous cells secrete entirely mucoidsecretion to:

- Lubricate esophageal walls peristalsis.

- Protect esophageal walls from digestionby gastric juice reflux.

The Esophagus

git lecture 1&2

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