viernes, 24 de diciembre de 2010
domingo, 19 de diciembre de 2010
absorption: The process in which nutrients pass into the blood stream, where they can circulate throughout the body; occurs mainly in the small intestine.
amylase : This enzyme helps break down complex starch molecules into simpler sugar molecules.
cecum: The first part of the large intestine, where waste enters from the small intestine.
celiac disease: An immune reaction to a food protein called gluten, which is found in grains.
chemical digestion: Digestion in which large food molecules are broken down into small nutrient molecules. It takes place mainly in the small intestine.
colon: The second part of the large intestine, where excess water is absorbed. After the excess water is absorbed, the remaining solid waste is called feces.
constipation: Having three or less bowel movements each week.
digestion: Process of breaking down food into nutrients.
digestive system: Body system that breaks down food, absorbs nutrients, and gets rid of solid food waste.
duodenum: The first part of the small intestine; site where most chemical digestion occurs.
enzyme: A substance, usually a protein, that speeds up chemical reactions in the body.
esophagus: The narrow tube that carries food from the pharynx to the stomach.
food intolerance: Occurs when the digestive system is unable to break down a certain type of food.
gall bladder: A small, pear-shaped structure below the liver; stores substances from the liver until they are needed by the small intestine.
gastritis: Inflammation of the lining of the stomach.
gastrointestinal (GI) tract: Organ of the digestive system; a long tube that connects the mouth with the anus.
ileum: The third part of the small intestine; covered with villi; the few remaining nutrients are absorbed in the ileum.
jejunum: The second part of the small intestine; where most nutrients are absorbed into the blood; lined with tiny “fingers” called villi.
large intestine: A relatively wide tube that connects the small intestine with the anus where excess water is absorbed from food waste. It consists of three parts: the cecum, colon, and rectum.
mechanical digestion: Digestion in which large chunks of food are broken down into small pieces. It takes place mainly in the mouth and stomach.
peristalsis: Involuntary muscle contractions which push food through the digestive system.
pharynx: Connects the mouth to the rest of the digestive tract; also connects the mouth and nose to the rest of the respiratory system.
rectum: The third part of the large intestine; where feces accumulates. As the rectum fills, the feces become compacted. The feces are stored in the rectum until they are eliminated from the body.
small intestine: The narrow tube between the stomach and large intestine where most chemical digestion and absorption of nutrients take place.
stomach: A saclike organ located between the end of the esophagus and the beginning of the small intestine. In the stomach, food is further digested both mechanically and chemically.
stomach ulcer: A sore in the lining of the stomach.
villi : Contain microscopic blood vessels; nutrients are absorbed into the blood through these tiny vessels; located on the jejunum and the ileum.
The large pouch-shaped cecum marks the beginning of the colon. Attached near the cecum bottom is the vermiform (worm-like) appendix. The appendix contains lymphoid tissue and intercepts pathogenic microorganisms that enter the digestive tract. Sometimes, fecal matter may become trapped in the appendix, resulting in appendicitis (infection and inflammation).
The three parts of the colon absorb water and minerals from the undigested food and compact the remaining material into feces.
Gut flora or intestinal flora consists of microorganisms that live in the intestine, mostly in the colon. The intestinal bacteria of the gut flora prevent the growth of harmful bacteria and synthesize some vitamins and other functions. The composition of the gut flora differs from person to person and depends on age, diet, environment and use of antibiotics.
Defecation is the digestive process final stage: feces (undigested waste products) are carried to the rectum through peristalsis and eliminated through the anus. It has internal and external sphincters.
A first review
A second review
I recommend you see them to improve your knowledge on the digestive system.(The parts that are above the level of this course, you can skip them or try to learn)
domingo, 12 de diciembre de 2010
As shown in Figure, the mucous membrane lining the small intestine is covered with very small, fingerlike projections called villi (singular: villus). Epithelial cells of each villus has thousands of microscopic projections called microvilli (singular: microvillus). Because there are millions of these tiny projections, they greatly increase the surface area for absorption. In fact, villi increase the absorptive surface of the small intestine to the size of a tennis court! This increases the amount of surface area available for the absorption of nutrients.
Each villus has a network of capillaries and fine lymphatic vessels called lacteals close to its surface. The epithelial cells of the villi transport nutrients from the lumen of the intestine into these capillaries (amino acids and carbohydrates) and lacteals (lipids). The absorbed substances are transported via the blood vessels to the liver and different organs of the body. The food that remains undigested and unabsorbed passes into the large intestine.
The small intestine finishes the process of digestion, absorbs the nutrients, and passes the residue on to the large intestine.
The small intestine is made up of three parts: the duodenum, jejunum, and ileum. Each part has different functions.
The duodenum is the first part of the small intestine. It is about 25 cm long. This is where most chemical digestion takes place. In this part the liver and gall bladder release bile and the pancreas secretes pancreatic juice.
The jejunum is the second part of the small intestine. This is where most nutrients are absorbed into the blood. The jejunum is lined with tiny “fingers” called villi. Each one is only about 1 mm long.
The ileum is the third part of the small intestine. Like the jejunum, the ileum is covered with villi. A few remaining nutrients are absorbed in the ileum. From the ileum, any remaining food waste passes into the large intestine.
Chyme emerging from the stomach into the duodenum is very acidic. The gall bladder release alkaline bile and the pancreas a large amount of sodium bicarbonate which neutralize the acidity of the chyme. This is important for digestion, because digestive enzymes in the duodenum require a neutral environment in order to work. The duodenum is protected from acid by a thick layer of mucus
Inside the duodenal tube, chyme is mixed with the bile and pancreatic juice. Bile breaks down fat particles into smaller droplets thus provide a largely increased surface area for the action of the enzyme pancreatic lipase that breaks down fats. Pancreatic juice conteins many enzymes ( lipase, protease,..) that finalize the food digestion process.
Do not worry about understanding every word. The important thing is to understand the overall process and improve your English comprehension .
There are three parts
Food moves through the esophagus due to peristalsis. At the end of the esophagus, a muscle called a sphincter controls the entrance to the stomach. The sphincter opens to let food into the stomach and then closes again to prevent the food from passing back into the esophagus.
The stomach is a saclike organ located between the end of the esophagus and the beginning of the small intestine. In the stomach, food is further digested both mechanically and chemically. Churning movements of the stomach’s thick muscular walls break down food mechanically. The churning movements also mix the food with gastric juice, a fluids secreted by the stomach. These fluids include hydrochloric acid, digestive enzymes and mucus.
• Hydrochloric acid is a strong acid (pH – 2) and gives the stomach a very acidic environment. This helps destroy any bacteria that have entered the stomach in foods or beverages. An acidic environment is also needed for the stomach’s digestive enzymes to work.
• The main digestive enzyme secreted in the stomach is pepsin that breaks down proteins into smaller molecules .
• Mucus secreted by the gastric glands helps protect the stomach lining from the action of gastric juice.
Small molecules like water, alcohol and salts can be absorbed through the lining of the stomach. Most other substances need further digestion in the small intestine before they can be absorbed. The stomach stores the food until the small intestine is ready to receive it. When the small intestine is empty, a sphincter (Pyloric sphincter) opens between the stomach and small intestine. This allows the partially digested food, now called chyme, to enter the small intestine.
sábado, 11 de diciembre de 2010
The salivary glands, inside the mouth, produce saliva that moistens the food and makes it easier to chew. The salivary enzyme is amylase that breaks down complex starch molecules into simpler sugar molecules (chemical digestion).The mouth also plays an important role in mechanical digestion. The teeth help to digest food mechanically by breaking it into smaller pieces.
There are different teeth types with different shapes and functions:
Incisors: These are your front teeth and are used for biting into your food. They are chisel or wedge-shaped. A human adult has 4 incisors in each jaw
Canines: These are pointed and are used for tearing. An adult human has 2 canines in each jaw.
Premolars and molars at the back of the mouth are larger and broader. They grind food into smaller pieces as you chew. An adult human has 4 pre-molars and 6 molars in each jaw. Third molars are often called wisdom teeth; (they developed thousands of years ago when human diets consisted of mostly raw and unprocessed foods that required the extra chewing and grinding power of a third set of molars. Today wisdom teeth are not needed for chewing and, because they can crowd other teeth, are often removed).
A human baby has 20 baby or milk teeth. These start to develop at about 6 months old and last until you are about 5 - 6 years old. A human adult has 32 teeth called permanent teeth. These start to grow when you are about 5 -6 years old. They replace your milk teeth.
Each tooth consists of a crown and one or more roots.
The crown is the functional part that is visible above the gum. The root is the unseen portion that supports and fastens the tooth in the jawbone. The clear outer layer of the crown is the Enamel, the hardest substance in the human body. The outer layer of the roor is cementum, a bonelike substance that anchors the tooth to the jawbone. Directly beneath the outer layer is dentin, a hard, mineral material that is similar to human bone, only stronger. Dentin surrounds and protects the pulp, or core of the tooth. Pulp contains blood vessels, which carry oxygen and nutrients to the tooth, and nerves, which transmit pain and temperature sensations to the brain.
The muscular tongue helps mix the food with saliva and the enzymes it contains.
When you swallow, the lump of chewed food, now called a bolus, passes into the pharynx.
The pharynx serves both the respiratory system and the digestive system. It connects the mouth to the rest of the digestive tract and, also connects the mouth and nose to the rest of the respiratory system. To prevent food or liquid from entering the trachea (windpipe), the epiglottis (a small flap of tissue) closes over the opening of the larynx (voice box) during swalowing (deglutition).
jueves, 9 de diciembre de 2010
In the digestive process we can consider four stages:
Stage 1: Ingestion.
The intake of food into the body trhough the mouth
Stage 2: Digestion .
The transformation of food into nutrients which the body can absorb. There are two types of digestion:
Mechanical digestion is the physical breakdown of chunks of food into smaller pieces. It takes place mainly in the mouth and stomach.
Chemical digestion: is the chemical breakdown of large, complex food molecules into smaller, simpler nutrient molecules that can be absorbed by the blood. It takes place mainly in the small intestine and trhough the action of enzymes.
Enzymes are substances that speed up chemical reactions. Digestive enzymes speed up the reactions of chemical digestion. Digestive enzymes are secreted by glands in the mucous membranes of salivary glands, stomach, small intestine, and pancreas.
The name of a digestive enzyme typically ends with the suffix -ase, which means “enzyme”. The rest of the name refers to the type of food molecules the enzyme helps digest. For example
proteases split proteins into their monomers, the amino acids
lipases split fat into three fatty acids and a glycerol molecule.
amylases split starch into sugars.
In this video you can learn a little more about enzymes It’s in english but you have in the same page the transcrip of the video.
Stage 3: Absorption:
Absorption is the process in which nutrients pass from the digestive system into the blood stream, where they can circulate throughout the body and carry the nutrients to the cells. Absorption occurs mainly in the small intestine
Stage 4: Egestion:
Egestion is the elimination of undigested food that cannot be absorbed and waste products from the digestive system. These products are transformed into faeces, and expelled from the organism through the anus.
It should not be confused with excretion, which is getting rid of waste formed from the chemical reaction of the body, such as in urine, sweat, etc.
miércoles, 8 de diciembre de 2010
Nutrients in the foods you eat are needed by the cells of your body, we eat foods to obtein nutrients. But:
What organs and processes break down the foofs into nutrients that the body can use for fuel?
What organs and processes let the nutrients enter your bloodstream so they can travel to the cells where they are needed?
The basic processes involved are digestion and absorption. The organs involved are the organs of the digestive system.
Organs that make up the digestive system are shown in figure. Most of the organs form the gastrointestinal tract. Other digestive organs are called accessory organs.
Organs of the digestive system.
1. Gastrointestinal Tract
The gastrointestinal (GI) tract is a long tube that connects the mouth with the anus. It is more than 9 meters long in adults. The upper GI tract includes the mouth, pharynx, esophagus, and stomach. The lower GI tract includes the small and large intestines. Food enters the mouth, passes through the upper and lower GI tracts, and then exits the body as feces through the anus.
The organs of the GI tract are covered by two layers of muscles that enable peristalsis. Peristalsis is a rapid, involuntary, wave-like contraction of muscles. It pushes food through the GI tract.
The inside of GI tract is lined with mucous membranes. Mucous membranes can secrete and absorb substances. The ability to secrete and absorb substances is necessary for the functions of the digestive system.
2. Accessory Organs of the Digestive System
They are additional organs that play important roles in digestion. Food does not pass through them, but they make substances needed for digestion. The accessory organs are the salivary glands, the liver and the pancreas.
- The salivary glands are found in and around your mouth and throat. We call the major salivary glands the parotid, submandibular, and sublingual glands.They all secrete saliva into your mouth .
- The liver is a large organ next to the stomach. It produces digestive substances that are carried by tubes,to the small intestine and gall bladder. The gall bladder is a small, pear-shaped structure below the liver. It stores substances (bile) from the liver until they are needed by the small intestine.
- The pancreas is a gland below the stomach. It produces digestive substances that are carried by a duct to the small intestine.