Introduction
- The respiratory and circulatory systems work together to provide cells with the Oxygen they need for cellular Respiration.
- Cells also need glucose for cellular respiration. Glucose is a simple sugar that comes from the food we eat.
- To get glucose from food, digestion must occur. This process is carried out by the digestive system.
Overview of the Digestive System
- The digestive system consists of organs that break down food and absorb nutrients such as glucose.
- Organs of the digestive system are shown in Figure below. Most of the organs make up the gastrointestinal tract. The rest of the organs are called accessory organs
The Gastrointestinal Tract
- The gastrointestinal (GI) tract is a long tube that connects the mouth with the anus. It is more than 9 meters (30 feet) long in adults and includes the esophagus, stomach, and small and large intestines.
- Food enters the mouth, passes through the other organs of the GI tract, and then leaves the body through the anus.
- The organs of the GI tract are lined with mucous membranes that secrete digestive ENZYMES and absorb nutrients.
- The organs are also covered by layers of muscle that enable peristalsis.
- Peristalsis is an involuntary muscle contraction that moves rapidly along an organ like a wave (see Figure below).
Accessory Organs of Digestion
- Other organs involved in digestion include the liver, gall bladder, and pancreas.
- They are called accessory organs because food does not pass through them. Instead, they secrete or store substances needed for digestion.
Functions of the Digestive System
- The digestive system has three main functions: digestion of food, absorption of nutrients, and elimination of solid food waste. Digestion is the process of breaking down food into components the body can absorb.
- It consists of two types of processes: mechanical digestion and chemical digestion.
- Mechanical digestion is the physical breakdown of chunks of food into smaller pieces. This type of digestion 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. This type of digestion begins in the mouth and stomach but occurs mainly in the small intestine.
- After food is digested, the resulting nutrients are absorbed. Absorption is the process in which substances pass into the bloodstream, where they can circulate throughout the body.
- Absorption of nutrients occurs mainly in the small intestine. Any remaining matter from food that cannot be digested and absorbed passes into the large intestine as waste. The waste later passes out of the body through the anus in the process of elimination.
The Start of Digestion: Mouth to Stomach
Mouth
- The mouth is the first digestive organ that food enters. The sight, smell, or taste of food stimulates the release of digestive enzymes by salivary glands inside the mouth.
- The major salivary enzyme is amylase. It begins the chemical digestion of Carbohydrates by breaking down starch into sugar.
- The mouth also begins the process of mechanical digestion. Sharp teeth in the front of the mouth cut or tear food when you bite into it. Broad teeth in the back of the mouth grind food when you chew.
- Food is easier to chew because it is moistened by saliva from the salivary glands. The tongue helps mix the food with saliva and also helps you swallow. After you swallow, the chewed food passes into the pharynx
Esophagus
- From the pharynx, the food moves into the esophagus. The esophagus is a long, narrow tube that passes food from the pharynx to the stomach by peristalsis.
- The esophagus has no other digestive functions. 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 food from passing back into the esophagus.
Stomach
- The stomach is a sac-like organ in which food is further digested both mechanically and chemically.
- Churning movements of the stomach’s thick, muscular walls complete the mechanical breakdown of food.
- The churning movements also mix food with digestive fluids secreted by the stomach. One of these fluids is hydrochloric acid.
- It kills bacteria in food and gives the stomach the low pH needed by digestive enzymes that work in the stomach. The main enzyme is pepsin, which chemically digests protein.
- The stomach stores the partly digested food until the small intestine is ready to receive it. When the small intestine is empty, a sphincter opens to allow the partially digested food to enter the small intestine.
Digestion and Absorption: The Small Intestine
- The small intestine is a narrow tube about 7 meters (23 feet) long in adults. It is the site of most chemical digestion and virtually all absorption.
- The small intestine consists of three parts: the duodenum, jejunum, and ileum
Digestion in the Small Intestine
- The duodenum is the first and shortest part of the small intestine.
- Most chemical digestion takes place here, and many digestive enzymes are active in the duodenum (see Table below). Some are produced by the duodenum itself.
- Others are produced by the pancreas and secreted into the duodenum.
| Enzyme | What It Digests | Where It Is Made |
| Amylase | Carbohydrates | pancreas |
| Trypsin | Proteins | pancreas |
| Lipase | Lipids | pancreas, duodenum |
| Maltase | Carbohydrates | duodenum |
| Peptidase | Proteins | duodenum |
- The liveris an organ of both digestion and Excretion. It produces a fluid called bile, which is secreted into the duodenum. Some bile also goes to the gall bladder, a sac-like organ that stores and concentrates bile and then secretes it into the small intestine.
- In the duodenum, bile breaks up large globules of lipids into smaller globules that are easier for enzymes to break down. Bile also reduces the acidity of food entering from the highly acidic stomach.
- This is important because digestive enzymes that work in the duodenum need a neutral Environment. The pancreas contributes to the neutral environment by secreting bicarbonate, a basic substance that neutralizes acid.
Absorption in the Small Intestine
- The jejunum is the second part of the small intestine, where most nutrients are absorbed into the blood. The mucous membrane lining the jejunum is covered with millions of microscopic, fingerlike projections called villi (singular, villus).
- Villi contain many capillaries, and nutrients pass from the villi into the bloodstream through the capillaries. Because there are so many villi, they greatly increase the surface area for absorption.
- The ileum is the third part of the small intestine. A few remaining nutrients are absorbed here. Like the jejunum, the inner surface of the ileum is covered with villi that increase the surface area for absorption.
The Large Intestine and Its Functions
- From the small intestine, any remaining food wastes pass into the large intestine.
- The large intestine is a relatively wide tube that connects the small intestine with the anus.
- Like the small intestine, the large intestine also consists of three parts: the cecum (or caecum), colon, and rectum.
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The human digestive system is a complex Network of organs that work together to break down food into nutrients that the body can use. The digestive process begins in the mouth, where food is chewed and mixed with saliva. Saliva contains enzymes that begin to break down carbohydrates. The food then travels down the esophagus to the stomach. The stomach is a muscular sac that churns and mixes the food with gastric juices. Gastric juices contain hydrochloric acid, which kills bacteria and helps to break down proteins. The food then travels to the small intestine, where most of the digestion and absorption of nutrients takes place. The small intestine is a long, coiled tube that is lined with millions of tiny finger-like projections called villi. The villi increase the surface area of the small intestine, which allows for more efficient absorption of nutrients. The nutrients that are absorbed from the small intestine are transported to the bloodstream and carried to all parts of the body. The undigested food then travels to the large intestine, where water is absorbed and the remaining waste products are formed into stool. The stool is stored in the rectum and then eliminated from the body through the anus.
The digestive system is a vital part of the body and it is important to keep it healthy. There are a number of things that you can do to keep your digestive system healthy, including:
- Eating a balanced diet that includes plenty of fruits, vegetables, and whole grains
- Drinking plenty of water
- Getting regular exercise
- Managing Stress
- Avoiding smoking and excessive alcohol consumption
If you have any concerns about your digestive Health, it is important to see a doctor.
Mouth
The mouth is the first part of the digestive system. It is where food is chewed and mixed with saliva. Saliva contains enzymes that begin to break down carbohydrates. The tongue helps to move food around in the mouth and push it down the throat.
Esophagus
The esophagus is a muscular tube that connects the mouth to the stomach. It is about 10 inches long in adults. The esophagus contracts and relaxes in a wave-like motion called peristalsis to move food down to the stomach.
Stomach
The stomach is a muscular sac that holds food while it is being digested. The stomach produces gastric juices, which contain hydrochloric acid and enzymes that break down proteins. The stomach also churns and mixes the food to help break it down further.
Small intestine
The small intestine is a long, coiled tube that is about 20 feet long in adults. It is where most of the digestion and absorption of nutrients takes place. The small intestine is lined with millions of tiny finger-like projections called villi. The villi increase the surface area of the small intestine, which allows for more efficient absorption of nutrients.
Large intestine
The large intestine is a shorter, wider tube that is about 5 feet long in adults. It is where water is absorbed from the undigested food and the remaining waste products are formed into stool. The large intestine is also called the colon.
Rectum
The rectum is the last part of the large intestine. It is about 6 inches long in adults. The rectum stores stool until it is time to defecate.
Anus
The anus is the opening at the end of the digestive system. It is where stool is eliminated from the body.
Digestive enzymes
Digestive enzymes are proteins that help to break down food into smaller molecules that can be absorbed by the body. There are many different types of digestive enzymes, each of which breaks down a specific type of food.
Bile
Bile is a fluid that is produced by the liver. Bile helps to break down fats. It is stored in the gallbladder and released into the small intestine when food is eaten.
Pancreas
The pancreas is a gland that is located behind the stomach. It produces digestive enzymes and HORMONES that help to regulate blood sugar levels.
Liver
The liver is a large organ that is located in the upper right abdomen. It has many important functions, including:
- Metabolizing nutrients
- Producing bile
- Regulating blood sugar levels
- Detoxifying the body
Gallbladder
The gallbladder is a small, pear-shaped organ that is located under the liver. It stores bile, which is released into the small intestine when food is eaten.
Peristalsis
Peristalsis is a wave-like motion that moves food through the digestive system. It is caused by the contraction and relaxation of muscles in the walls of the digestive tract.
Segmentation
Segmentation is a type of movement that occurs in the small intestine. It mixes the food with digestive juices and helps to absorb nutrients.
What is the digestive system?
The digestive system is a series of organs that work together to break down food into nutrients that the body can use.
What are the organs of the digestive system?
The organs of the digestive system are the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus.
What is the digestive process?
The digestive process is the process of breaking down food into nutrients that the body can use. The digestive process begins in the mouth, where food is chewed and mixed with saliva. Saliva contains enzymes that begin to break down carbohydrates. Food then travels down the esophagus to the stomach. The stomach produces acid and enzymes that further break down food. Food then travels to the small intestine, where most of the nutrients are absorbed. The small intestine is about 20 feet long and is lined with millions of tiny finger-like projections called villi. The villi increase the surface area of the small intestine, which allows for more nutrients to be absorbed. The undigested food then travels to the large intestine, where water is absorbed. The large intestine is about 5 feet long and is lined with mucus-producing cells. The mucus helps to protect the lining of the large intestine. The undigested food then travels to the rectum, where it is stored until it is eliminated from the body through the anus.
What are the functions of the digestive system?
The functions of the digestive system are to break down food into nutrients that the body can use, absorb nutrients, and eliminate waste products.
What are some common digestive problems?
Some common digestive problems include indigestion, heartburn, diarrhea, constipation, and irritable bowel syndrome.
What are some tips for preventing digestive problems?
Some tips for preventing digestive problems include eating a healthy diet, getting regular exercise, and managing stress.
What are some home remedies for digestive problems?
Some home remedies for digestive problems include drinking plenty of fluids, eating bland foods, and taking over-the-counter medications.
When should you see a doctor about a digestive problem?
You should see a doctor about a digestive problem if it is severe or if it does not improve with home treatment.
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The human digestive system is made up of the following organs:
(A) Mouth, esophagus, stomach, small intestine, large intestine, and rectum
(B) Mouth, esophagus, stomach, small intestine, large intestine, and anus
(C) Mouth, esophagus, stomach, small intestine, large intestine, and gallbladder
(D) Mouth, esophagus, stomach, small intestine, large intestine, and pancreas -
The main function of the digestive system is to:
(A) Break down food into smaller molecules that can be absorbed by the body
(B) Transport food through the digestive tract
(C) Secrete digestive juices
(D) All of the above -
The process of digestion begins in the mouth, where food is chewed and mixed with saliva. Saliva contains an enzyme called amylase, which begins to break down carbohydrates.
(A) True
(B) False -
The esophagus is a muscular tube that connects the mouth to the stomach. Peristalsis, a wave-like motion of the muscles in the esophagus, helps to move food down the esophagus.
(A) True
(B) False -
The stomach is a muscular sac that holds food while it is being digested. The stomach produces gastric juices, which contain hydrochloric acid and enzymes that break down proteins.
(A) True
(B) False -
The small intestine is a long, coiled tube that is about 20 feet long. The small intestine is where most of the digestion and absorption of nutrients takes place.
(A) True
(B) False -
The large intestine is a shorter, wider tube that is about 5 feet long. The large intestine absorbs water and electrolytes from food waste, and it stores food waste until it is eliminated from the body.
(A) True
(B) False -
The rectum is the last part of the large intestine. It stores food waste until it is eliminated from the body through the anus.
(A) True
(B) False -
The digestive system is a complex system that works together to break down food and absorb nutrients.
(A) True
(B) False -
Digestion is the process of breaking down food into smaller molecules that can be absorbed by the body.
(A) True
(B) False