1. The Digestive System PHL 226 Dr/ Abdulaziz Saeedan Pharmacy College
1- Mouth to Esophagus
Physiology -II
PHL 226
Dr/ Abdulaziz Saeedan
Pharmacy College

2. General Structure & Functions of the Digestive System
I- Structure of the Digestive System :
Digestive system composed of 2 separate groups of organs:
a- Alimentary canal:
It is a continuous tube that extends from the mouth to the anus (about 9 –10 m).
It includes mouth, pharynx, esophagus, stomach, small intestine and large intestine.
b- Accessory organs:
These are organs that help the digestive system in digestion of food by:
1- Mechanical processes as teeth and tongue.
2- Secretion of digestive substances as salivary glands, liver, gall bladder and pancreas.

3. II- Functions of the Digestive System:
1- Breakdown food into simpler molecules.
2- Absorb the nutrients which are necessary to life.
3- Removal of waste products from the body.
NOTES:
Food that is in the GIT is not really inside the body. To enter the body, food must be broken down into simpler molecules then enter to blood stream.
Food is moved through the digestive tract by muscular contractions called peristalsis.
The peritoneum is a membrane that lines the abdominal organs. It produces a lubricating fluid that reduces friction between organs.

4. Digestive Process The digestive process involves 5 basic activities :
Ingestion – is the process of taking food into the mouth.
Propulsion - is the process of movement of food through the GIT. It includes: a) Swallowing b) Peristalsis
3. Digestion- is the breaking down of food into simple components.
The process of digestion includes:
a) Mechanical digestion b) Chemical digestion
4. Absorption – is the passage of digested food from the digestive tract to blood stream.
5. Defecation- is the elimination of indigestible substances (wastes) through anus in the form of feces

5. Mechanical and Chemical digestions
1- Mechanical digestion
Mechanical digestion is the breakdown of food into smaller particles.
It prepares food for chemical digestion.
It begins in the mouth and continues into the stomach.
Mechanical digestion includes:
Mastication (Chewing) of food by teeth.
Mixing food with saliva by tongue.
Churning food in the stomach.
NOTE:
Churning = muscular contraction and relaxation of stomach.

6. 2- Chemical digestion
Chemical digestion is the changes in the chemical composition of food with the aid of digestive enzymes.
It converts complex molecules such as carbohydrates, proteins and fats into simpler molecules that can be absorbed and used by cells.
It begins in the mouth and ends in small intestine.
Chemical digestion includes:
Conversion of carbohydrates into simple sugars.
Conversion of proteins into amino acids.
Conversion of fats into fatty acids and glycerol.
NOTES:
In mechanical digestion No change in the chemical structure of food
In chemical digestion There is a change in the chemical structure of food.

7. Oral Cavity (Mouth) It is the gate of the GIT.
The tongue and teeth are the first “organs” of the digestive tract.
The digestive process begins in the mouth by 2 ways:
1- Mechanical digestion
The teeth cuts and grinds food. This process is called mastication.
Tongue:
Mixes food with saliva to form a semisolid bolus that is easily swallowed.
Pushes the bolus toward the pharynx.

8. 2- Chemical digestion (by enzymes of saliva).
Salivary glands secretes saliva (contain amylase enz) into the oral cavity.
Salivary amylase begins to break down complex carbohydrates and starch found in foods such as bread, cereals, potatoes and pasta.
Salivary amylase breaks the bonds between the polysaccharides, converting them to simple sugars such as fructose, maltose, glucose which can be absorbed.
Salivary amylase hydrolyze dietary starch into disaccharides and trisaccharides which are converted by other enzymes to glucose to supply the body with energy.
NOTE:
Foods that contain large amounts of starch but little sugar, such as rice and potatoes, may acquire a slightly sweet taste as they are chewed because amylase digest some of their starch into sugar.
Function of mouth
1- Mechanical breakdown of food
2- Secretion of saliva (salivary amylase) which convert complex carbohydrates and starch into simple sugars
3- Tasting

9. Salivary Glands They are 3 pairs:
1- Parotid glands (beneath the cheeks)
2- Submandibular glands (below the jaw bone)
3- Sublingual glands (below the tongue)
They secrete saliva.

10. Saliva
Saliva is clear, tasteless, odorless, viscid fluid, secreted from the parotid, submandibular and sublingual salivary glands.
Volume of saliva secreted daily = L  Most is produced during mealtime
Composition of Saliva
I- Water (99%) : To dissolve food easily  so food can be tasted.
II- Solutes (1%):
1- Salivary amylase- an enzyme that helps break down complex carbohydrates and starch into simple sugars such as fructose, maltose, glucose.
2- Mucous- lubricates food for easy swallowing.
3- Lysozyme- inhibit bacterial growth in the oral cavity and protect the teeth from decay.
4- Electrolytes- including sodium, potassium, chloride, phosphate, and bicarbonate ions

11. Functions of Saliva 1- Preparation of food for swallowing
Saliva moistens the food so converts it into a semisolid bolus that is easily swallowed.
2- Digestive function
Amylase in saliva digest complex carbohydrates and starch into simple sugars such as fructose, maltose, glucose.
3- Antibacterial action
Lysozyme in saliva inhibit bacterial growth in the oral cavity.

12. Pharynx It is the passageway of both food (bolus) and air
Bolus passes through the oropharynx then laryngopharynx to reach the esophagus
Once a bolus of food reaches the pharynx, swallowing is involuntary
Swallowing
Regulated by swallowing center in the medulla oblongata.
Stages of Swallowing
1- Buccal (Oral) stage
It is a voluntary stage.
The tongue pushes the bolus into the oropharynx.

13. 2- Pharyngeal stage
It is involuntary stage.
It involves passage of bolus from pharynx to esophagus
3 actions blocks bolus and drink from re-entering the mouth, the nasopharynx or larynx
a- The root of the tongue blocks the oral cavity
b- The soft palate rises to blocks the nasopharynx
c- Epiglottis close the airway that leads to the trachea
3- Esophageal Stage
It involves passage of bolus from the esophagus to stomach

14. Esophagus - Oesophagus
Esophagus is a straight muscular tube  About cm long.
Function of Esophagus:
It transports bolus from the pharynx to the stomach by peristalsis in about 7 seconds.
Due to peristalsis, bolus can be swallowed in zero gravity, or even when the body is upside down.
Esophagus meets with the stomach at an opening called the Lower Esophageal Sphincter (LES) OR Cardiac Sphincter.
Physiologically, LES remains contracted in contrast to the middle and upper part of esophagus which normally remains completely relaxed.
Function of LES:
It prevents reflux of stomach contents into the esophagus

15. GERD LES located between the esophagus and stomach.
LES relaxes to allow bolus to enter the stomach but prevents reflux of stomach contents into the esophagus
If LES becomes weak, it fails to close completely, so the acidic juice in the stomach can flow back up or reflux into the esophagus.
The stomach is protected from this acidic juice by a layer of mucus, while the esophagus does not have a barrier of mucus to protect it from acid.
 As a result, reflux can cause inflammation and damage to the inner lining of the esophagus.
This condition is known as heartburn (burning sensation behind the breastbone)
Chronic condition of heartburn is known as gastroesophageal reflux disease, or GERD.