THE DIGESTIVE SYSTEM

Digestive System

- a series of connected organs whose purpose is to break down, or digest, the food we eat.

- the digestive system is one long, winding tube. The digestive system of a grown-up is 20 to 30 feet (6 to 9 meters) long.

Digestion – is the process of reducing food to smaller molecules that can be absorbed into the body

-  digestion in human takes 4 hours

The Main Functions of Digestion

1. to break up big pieces of food into tiny particles
2. to break the tiny particles of food into molecules that will dissolve in body fluids and pass through the cell walls to be used by the cells

The Digestive Process

1. Mechanical Digestion – the process by which food is acted upon physically or mechanically

- through which food undergoes physical change by tearing, grinding, and chewing

2. Chemical Digestion – the breaking down of food by the action of enzymes

- food is broken down into simpler molecules and absorbed by the body

- at this stage, digestive enzymes are needed to hydrolyze and break down starch into glucose molecules, proteins to amino acids, and fats into fatty acids and glycerol

The Digestive System

-  it is a long, coiled, muscular tube stretching from the mouth to the anus.

- the digestive tract or food tube consists of the following:

1.    mouth/ oral cavity

2.    esophagus

3.    stomach

4.    small intestine

5.    large intestine

6.    anus

- the accessory organs are the following:

1.    salivary glands

2.    pancreas

3.    liver

4.    gallbladder

 

 

Main Parts of the Digestive System

1. mouth or oral cavity – mechanical breakdown of food by the teeth

- where food is chewed mixed with saliva

- the saliva contains an enzyme called ptyalin that begins chemical digestion: forms the bolus

- bolus is a form of food that we swallow

- digestion begins at the mouth, where food is taken in and broken down into smaller particles by chewing. Salivary glands make saliva in the mouth. Saliva contains mucus and water, which moisten the food, and an enzyme called ptyalin that helps digest starch. Food is swallowed and travels down the pharynx (throat) and into a muscular tube, called the esophagus, to enter the stomach.

- the adult humans typically have 32 teeth—16 in the upper jaw and 16 in the lower jaw—that fit together and work in concert to chew food.

Oral Cavity

• the first chamber of the digestive tract of humans
• it is where the teeth are located
• during our lifetime, we develop two sets of teeth
• the first set, the temporary teeth, grows during childhood and later replaced by the second set, the permanent teeth
• the teeth are involved in the mechanical breakup of food by biting and chewing

Different Types of Human Teeth

1. Incisors

- are the chisel-shaped teeth found in front.

- there are four incisors in the upper jaw and four in the lower jaw

- are used for biting

2. Canines

- are found one on each side in each jaw

- they are pointed and specialized for tearing food

3. Premolars

- there are two premolars found behind each canine

- are used in grinding and crushing food

4. Molars

- there are three molars in adults

- have flat and ridged surface

- are used for grinding, pounding, and crushing food

2. esophagus – a long tube that connects the mouth to the stomach

- a muscular tube about 25 cm (10 in) long through which the food go to the stomach from the pharynx

·      Peristalsis – waves of muscular contraction push the food through the esophagus

·      Sphincter – a special ring of muscle between the esophagus and stomach that prevents the contents of the stomach

3. stomach – a large J-shaped organ found at the end of the esophagus

- for storage and digestion of food

- it can hold 2.5 liters of food

-the stomach is an expandable pouch in the abdomen that releases gastric juice containing pepsin, an enzyme that acts on proteins; hydrochloric acid, which kills microorganisms that may have been ingested with food; and mucin, a component of mucus that coats the stomach to protect it from the acidic effects of gastric juice. Some foods, including simple sugars and alcohol, can be absorbed directly through the stomach wall, but most foods pass undigested from the stomach into the small intestine.

·      Chyme – the semi fluid mass of partly digested food expelled by the stomach into the duodenum

·      Gastric glands – found in the lining of the stomach

- secrete gastric juice, which contains digestive enzymes and hydrochloric acid

4. small intestine -  narrow, twisting tube, about 2.5 cm (1 in) in diameter, fills most of the lower abdomen, extending about 6 m (20 ft) in length.

- for the absorption of nutrients and minerals

-after food leaves the stomach, it enters the small intestine. Food is broken down with the aid of enzymes from the pancreas and bile made in the liver and stored in the gallbladder. The wall of the small intestine has many small, fingerlike projections called villi. Capillaries in the villi absorb nutrients from digested food into the bloodstream

- the small intestine, which is coiled in the center of the abdominal cavity, is divided into three sections.

                                             a.     the duodenum is a horseshoe-shaped section

- the upper 20 cm long tube connected to the stomach

- a region where most digestion and absorption occurs

                                             b.     the middle part of the small intestine is called the jejunum

- it is about 2.5 m long

                                             c.     the terminal portion is the ileum, which leads into the side of the first part of the large intestine

·      digestion in the small intestine is aided by enzymes secreted from two principal sources: the pancreas and the intestinal glands (lactase, sucrase and maltase)

5. large intestine – is 1.5 to 1.8 m (5 to 6ft) long and about 6 cm (2.5 in) in diameter

- it absorbs water about 6 liters daily from the undigested food materials which then become feces

- formation of semisolid feces from undigested food residue

- food not absorbed into the bloodstream in the small intestine travels into the large intestine. The walls of the large intestine absorb water from the undigested food, leaving semisolid waste matter called feces. These waste products are excreted from the body through the rectum and anus.

6. anus or rectum - makes up the final 15 to 20 cm (6 to 8 in) of the alimentary canal.

- the rectum stores the feces—waste material that consists largely of undigested food, digestive juices, bacteria, and mucus—until elimination. Then, muscle contractions in the walls of the rectum push the feces toward the anus. When sphincters between the rectum and anus relax, the feces pass out of the body.

The Accessory Parts of the Digestive System

1. salivary glands – secretion of mucin (to lubricate food) and amylase (carbohydrate splitting enzyme)
2. pancreas – a large, tongue-shaped glandular organ located just below the stomach

- it secretes enzymes such as lipase (digestive fats), pepsin (splits protein into fragments), and pancreatic amylase (splits starch into sugar)

3. liver – it is dark red, dome-shaped

- the largest gland in the body

- production of bile (fat emulsifiers); metabolism of carbohydrates, fats, proteins; storage of vitamins and some minerals; removal of poisonous substances

- secretes a yellow-green liquid called bile, which is stored in the gallbladder

4. gallbladder – a pear-shaped muscular sac attached to the surface of the liver

- about 7.5 cm (about 3 in) long and 2.5 cm (1 in) in diameter at its thickest part

- it has a capacity varying from 1 to 5 fluid ounces

- storage of concentrated bile

Diseases/Disorders of the Digestive System

1. Tooth decay – the bacteria in the mouth that corrodes the teeth
2. Gingivitis – inflammation of gum
3. Periodontitis – loss of bone and loosening of the teeth
4. Ulcer – open sore in the wall of the stomach due to over secretion of gastric juice
5. Diarrhea – loose bowel movement caused by infection of the lower tract, nervous stimulation, and food poisoning
6. Constipation – feces are hard and dry caused by inhibiting defecation to the point that normal reflexes are ignored
7. Appendicitis – infection of the appendix in which fluid content rises to the point that it burst
8. Jaundice – yellowish tint of the skin due to an abnormally large amount of bilirubin in the food
9. Hepatitis – inflammation of the liver
10.  Cirrhosis – the liver becomes fatty and then replaced by inactive fibrous scar tissue
11. mumps virus, which often infects the salivary glands;
12. the bacterium Helicobacter pylori, which causes most stomach and duodenal ulcers;
13. viruses and bacteria that cause various forms of gastroenteritis, often called stomach flu or traveler’s diarrhea.
14. Appendicitis is an inflammation of the appendix, a tube-like pouch about 9 cm (3.5 in) long that branches off the large intestine. It occurs most commonly among children and young adults.
15. Diarrhea—frequent elimination of loose, watery feces—is a symptom of many disorders that occurs when the large intestine is irritated or inflamed. As a result, food residues move through it too quickly for it to absorb the excess water.
16. Constipation, occurs when the large intestine absorbs too much water because food residues are moving slowly. As a result, the feces become hard and dry, which may make elimination difficult.
17. Cancerous tumors may develop in any part of the digestive system, though they most commonly occur in the large intestine, rectum, and anus (Colorectal cancer).
18. Colitis, which has various causes, is a potentially life-threatening inflammation of the large intestine. Chronic conditions that cause at least intermittent distress include irritable bowel syndrome, caused by spasms of muscles in the lower intestine
19. Crohn’s disease, an inflammation of the intestines. Abnormal sensitivity to proteins called glutens can damage the lining of the small intestine and hinder absorption of nutrients, leading to malnutrition and other problems.
20. The eating disorders anorexia nervosa and bulimia disrupt the normal functioning of the digestive system and are potentially fatal.

Enzymes of the Digestive System

1. salivary amylase or ptyalin – converts starch to sugar (mouth and small intestine)
2. trypsin – changes peptones and proteoses to peptides (small intestine)
3. sucrase – changes sucrose to simple form (small intestine)
4. maltase – changes maltose to glucose (small intestine)
5. lipase – hydrolyzes neutral fat to glycerol and fatty acids (stomach and small intestine)
6. bile – emulsifies fats (stomach and small intestine)
7. hydrochloric acid – strong acid that destroys microorganisms (stomach)
8. pepsin – breaks down proteins into polypeptides (stomach)