JUAREZ AUTONOMOUS UNIVERSITY TABASCO

Academic Division of Health Sciences

Basic English

“The Digestive System”

Team 3-Miguel Leyva Sánchez-Berenice Molina Gerónimo-María del Carme Fuentes Córdova-Marcela Alvarado Jaime

Teacher: Oscar Domínguez Cruz

The Digestive System

The digestive system is responsible for breaking down nutrients from food and incorporate them later in the body's cells.

This process is called metabolism.

The purpose is to give the body the energy needed for daily activity, as well as materials for the construction of new cells and tissues.

After ingested, is transported to the circulatory and lymphatic systems, and finally to the body cells.

Another function is to digest proteins and other nutrients found in the animal's blood to form human blood proteins such as hemoglobin.

Classes of Nutrients

There are six general classes of nutrients: carbohydrates, fats, proteins, water, vitamins, and minerals. Carbohydrates, fats, and proteins are characterized as energy nutrients. These organic molecules are responsible for providing our bodies with the majority of the energy needed for daily metabolic reactions.

For nutritional analysis the term kilocalorie (1,000 calories) is frequently used

Classes of Nutrients

• In aerobic respiration, energy is produced in cells THROUGH the glycolysis, the Krebs cycle, and the electron transport chain (ETC).

• The Krebs cycle and ETC Occur in the mitochondria of the cell and use oxygen to regenerate a cellular energy molecule called adenosine triphosphate (ATP). In the Krebs cycle, the carbon-carbon bonds are broken and a small amount of ATP is generated.

• Water is used to break the bonds linking the monomers in a process called hydrolysis.

Energy Production

CarbohydratesAll carbohydrates possess carbon, hydrogen, and oxygen in a 1:2:1 ratio, respectively. For example, the molecular formula for glucose is C6H12O6.

The most common of these is glucose, with the other two being fructose and galactose.

The monosaccharides are linked together by chemical bonds in to form disaccharides. There are three different disaccharides: maltose, sucrose and lactose.Polysaccharides, are composed of long chains of glucose units. Different classes of polysaccharides vary the physical structure of chemical bonds that link the glucose units.

Starch has chemical bonds that are easily digested by the digestive system.

Fibers

The fibers are indigestible by human enzymes, which play an increasingly important role in humans digestion.

Helps food move through the system and provides resistance to the muscles of the gastrointestinal tract.

Fats and Lipids Are sources of long-term energy.

They are hydrophobic molecules. Chemical secretions such as bile, and specialized proteins called lipoproteins, help transform and transport of these important energy nutrients.

Proteins They have the structural

function, as in the muscles. Others like hormones. Enzymes are an Important component of the digestive system and are covered in the next section.

The monomer proteins are amino acids, are 20.

• Food remains in the small intestine for three to five hours on average, during which most nutrients are removed.

• The intestines receive over 10 quarts (9 liters) of water daily, of which almost 95 percent is recycled back into the body.

The processing of vitamins, minerals and water are broken down by the digestive system.

Vitamins, Minerals, and Water

VitaminsVitamins are organic molecules,

and serve as enzyme assistants, or coenzymes.

Antioxidants

These serve as protectors of the cellular machinery (vitamins C&E). For vision (vitamin A), or in the building of healthy bones (vitamins D&A).

Nutritionists divide the vitamins into two groups:

The water-soluble

vitamins

Vitamin C&B. These vitamins

are readily absorbed by the digestive system and, with a few exceptions, do

not require special

processing.

The fat-soluble vitamins

These are the vitamins A, D, E, and K, they are packaged into

specialized lipoproteins and transported by the lymphatic

system.

MineralsMinerals are inorganic nutrients, function as assistants to metabolic pathways,

help regulate body fluid levels, and some serve as structural components of bones. Are also the major electrolytes in the circulatory system.

Nutritionists divide minerals into two broad classes:

MAJOR MINERAL MINERAL FUNCTION TRACE

MINERAL MINERAL FUNCTION

Calcium Strong bones and teeth*, and muscle

contraction and relaxation**. CopperHelps turn food into energy*. Brain and

nerve functions.

MagnesiumTurn food into energy***, build

enzymes and antioxidants. Iodine Make certain hormones, the thyroid

gland. Growth, development, metabolism, and reproduction.

Phosphorous *, *** and to store extra energy.

IronCarries oxygen through the body and

helps build red blood cells. *

Potassium

Water balance****, muscle contraction, and nerve impulses. Works with Na to control blood

pressure.

Manganese * and healthy bones and cartilage

formation.

Sodium **** and **. Works with K to control blood pressure.

ZincA strong immune system and a good

sense of taste and smell.

WaterThe digestive system is a water-based system that uses water to move nutrients, deliver digestive enzymes, lubricate the length of the gastrointestinal tract, and facilitate the absorption of nutrients into the circulatory and lymphatic systems. The average human requires about 2.65 quarts (approximately 2.5 liters) of water per day to meet the metabolic requirements of the body. The majority of this comes from liquids and foods that are consumed throughout the day.

The digestive system must simultaneously retain enough water for its own operation and supply the body with the water it needs to function; involves the use of minerals such as potassium and sodium to establish concentration gradients to efficiently move water. The large intestine, or colon, is the

major digestive organ responsible for this process.

The human digestive system is actually a series of organs that form a long, enclosed tube. This organ system of the human body is specialized for breaking down incoming food into the needed nutrients for the body’s vast array of metabolic functions.

The organs of the GI tract are those that physically comprise the tube, also called the alimentary canal, these include the oral cavity, esophagus, stomach, small intestine, and large intestine.

The Gastrointestinal Tract: Oral Cavity,

Esophagus, and Stomach

Gastrointestinal Trac

The upper GI tract

The lower GI tract

Consists of the oral cavity,

esophagus, and stomach, as

well as associated valves and accessory organs.

Consists primarily of the small intestine

and colon.

The Oral Cavity

The human mouth, also called the oral cavity or buccal cavity, is the entry point into the human digestive system.

Also serves as the connecting point between the respiratory system and the outside environment, as well as the location of a significant amount of sensory input from chemical receptors, most notably taste

Salivary GlandsVital to the digestive

functions of the oral cavity.-Two pairs are located along the bottom of the oral cavity.-The sublingular glands are located just below the tongue, and the submandibular glands are positioned just beneath these, near the mandibula (jawbone). -A third set, called the parotid glands, are located just in front of, and slightly below, the ears.

The chemical secretion of the salivary glands

Saliva

Saliva is primarily water (99.5 percent), which serves to lubricate and moisten the digestive system. However, the remaining 0.5 percent contains important ions, such as potassium, chloride, sodium, and phosphates, which serve as pH buffers and activators of enzymatic activity.

Enzymes

Lysozyme: inhibits, the formation of bacterial colonies in the oral cavity.

Salivary Amylase: initiates the process of carbohydrate digestion.

Mechanical DigestionIn the oral cavity:

• First, the action of the teeth and tongue break the food into small portions so that it may be sent to the stomach via the esophagus.

• The action of chewing, or mastication, is the first stage of mechanical digestion.

The movement of the tongue is controlled by the extrinsic muscles that enable the movement of the tongue. These muscles move the food from the area of the teeth to the back of the mouth (pharynx), where it is formed into a small round mass of material called a bolus.

• Second stage in the mechanical processing of the food involves the action of the tongue.

The pharynx: serves as the junction between the respiratory system and digestive system.

Teeth

• Teeth are made from a calcified form of connective tissue called dentin, which is covered with a combination of calcium phosphate and calcium carbonate commonly called enamel. • Within the center of each tooth is an area called the pulp cavity, which contains nerves, blood vessels, and ducts of the lymphatic system.

The combination of different types of teeth in the mouth allows for the processing of a large variety of foods.

There are three major types of teeth, molars and premolars are classified as one type.

Papillae

The papillae are sometimes mistakenly referred to as the taste buds, but the taste buds are actually specialized receptors located at the base of certain types of papillae. There are three different forms of papillae, which differ in their appearance and location on the tongue.

By the action of the tongue, the food is lubricated with saliva to

facilitate swallowing .

Enzymatic Digestion•Enzymatic digestion is responsible for breaking organic material into smaller subunits that can be absorbed into the circulatory system.

•The salivary glands, primarily the submandibular and sublingual glands, secrete an enzyme called salivary amylase.

•The salivary amylase is mixed into the food by the action of thetongue and cheeks and continues to break down the starches in the food for about an hour until deactivated by the acidic pH of the stomach.

Enzymatic Digestion

The food was mixed in the oral cavity with salivaThe chemical digestion continues down the esophagus

The bolus passes through the gastroesophageal sphincter and enters the stomach

It comes in contact with the highly acidic hydrochloric acid.

Once mechanical digestion begins lower in the stomach, the salivary amylase is quickly inactivated.

Contains salivary amylase.

Swallowing Reflex 1. The tongue moves upward against the roof (hard palate) of

the mouth to prevent the food from reentering the oral cavity. 2. The uvula, an inverted-Y-shaped flap of skin at the rear of

the mouth, moves upward to block the nasal passages. 3. The vocal cords in the larynx tightly close over the opening

of the windpipe, or glottis. 4. As the bolus passes into the esophagus, it forces a flap of

cartilaginous tissue called the epiglottis downward over the glottis as an added precaution to protect against the food entering the respiratory system.

Layers of The Digestive System The serosa is the outermost

layer of the digestive tract and is comprised of connective tissue.

These two muscle layers are the inner circular muscle and the outer longitudinal muscle.

The next layer inward is a dense section of connective tissue called the submucosa.

Esophagus and Stomach The esophagus is not a major digestive organ, because the

only enzymes that are active here are the salivary amylase and lingual lipase from the oral cavity.

•The stomach is commonly recognized as a muscular sac that functions as a holding site for food before it enters into the small intestine, as well as the location where the food is mixed and partially digested by mechanical processes.

Composition of Gastric Juice The stomach produces

about 2.12 quarts (2 liters) of gastric juice per day.

The gastric pits of the stomach showing the location of chief and parietal cells.

The parietal cells are responsible for manufacturing hydrochloric acid.

Regulating stomach motility

The emptying of the stomach contents, also called motility, usually take between two four hours following completion of a meal and is dependent on a large number of factors. These factors either inhibit or stimulate the movement of the chyme.

For the most part, actions of the stomach increase motility into the duodenum, while feedback from the duodenum inhibits movement of chyme through the pyloric sphincter.

the cephalic phase refers to the interaction of the brain with the stomach.

There are three distinct phases to stomach motility:

The cephalic phase

Gastric phaseIntestinal

phaseAs its name implies, the gastric phase involves the activity of the stomach.

The duodenum of the small intestine may also regulate the activity of the stomach during the intestinal phase.

If chemical receptors detect the smell or taste of food, a signal is sent to the medulla oblongata in the brainstem, which relays a signal along the vagus nerves to the submucosal plexus in the stomach. The submucosal plexus then stimulates the activity of chief and parietal cell, thus preparing the stomach for incoming food.

The cephalic phase

Two factors influence its activity. First, the amount of distention, or stretching of the stomach lining, acts as an indicator of the fullness of the stomach. As the stomach fills, and the rug relax, stretch receptors in the lining stimulate the release of gastrin by G cell in the mucosal lining of the antrum.

Gastric phase

Since the small intestine represents the major organ of digestion and absorption in the body, the duodenum must be ready to receive the incoming chyme for processing. the duodenum primarily has inhibitory effect on stomach motility. Distention of the duodenum, due to the presence of a large volume of chyme, initiates a neural response called the enterogastric reflex, which through the action of the medulla oblongata decreases the strength of peristaltic the duodenum.

Intestinal phase

Absorption of nutrients

As mentioned previously, very few nutrients are absorbed through the lining of the stomach, primarily due to the presence of the mucus layer, which isolates the mucosa tissue from the hydrochloric acid. However, water and some ions are able to be absorbed directly into the circulatory system. In addition, both ethyl alcohol (the form found in alcoholic beverages) and acetylsalicylic acid (commonly known as aspirin) are able to penetrate the mucus layer and enter into the circulatory system.