Digestive systems
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones.
In mammals, food enters the mouth, being chewed by teeth, with chemical processing beginning with chemicals in the saliva from the salivary glands. This is called mastication.
Then it travels down the oesophagus into the stomach, where hydrochloric acid kills most contaminating microorganisms and begins mechanical breakdown of some food (e.g., denaturation of protein), and chemical alteration of some.
The hydrochloric acid also has a low pH, which allows enzymes to work more efficiently. After some time (typically an hour or two in humans, 4–6 hours in dogs, somewhat shorter duration in house cats, ...), the resulting thick liquid is called chyme.
Chyme will go through the small intestine, where 95% of absorption of nutrients occurs, through the large intestine with waste material eventually being eliminated during defecation
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones.
In mammals, food enters the mouth, being chewed by teeth, with chemical processing beginning with chemicals in the saliva from the salivary glands. This is called mastication.
Then it travels down the oesophagus into the stomach, where hydrochloric acid kills most contaminating microorganisms and begins mechanical breakdown of some food (e.g., denaturation of protein), and chemical alteration of some.
The hydrochloric acid also has a low pH, which allows enzymes to work more efficiently. After some time (typically an hour or two in humans, 4–6 hours in dogs, somewhat shorter duration in house cats, ...), the resulting thick liquid is called chyme.
Chyme will go through the small intestine, where 95% of absorption of nutrients occurs, through the large intestine with waste material eventually being eliminated during defecation
Digestive systems
Digestive systems take many, many forms. There is a fundamental distinction between internal and external digestion.
External digestion was the first to evolve, and most fungi still rely on it. In this process, enzymes are secreted into the environment surrounding the organism, where they break down an organic material, and some of the products diffuse back to the organism.
Later, animals evolved by rolling into a tube and acquiring internal digestion, which is more efficient because more of the broken down products can be captured, and the chemical environment can be more efficiently controlled.
Some organisms, including nearly all spiders, simply secrete biotoxins and digestive chemicals (e.g., enzymes) into the extracellular environment prior to ingestion of the consequent "soup".
In others, once potential nutrients or food is inside the organism, digestion can be conducted to a vesicle or a sac-like structure, through a tube, or through several specialized organs aimed at making the absorption of nutrients more efficient.
External digestion was the first to evolve, and most fungi still rely on it. In this process, enzymes are secreted into the environment surrounding the organism, where they break down an organic material, and some of the products diffuse back to the organism.
Later, animals evolved by rolling into a tube and acquiring internal digestion, which is more efficient because more of the broken down products can be captured, and the chemical environment can be more efficiently controlled.
Some organisms, including nearly all spiders, simply secrete biotoxins and digestive chemicals (e.g., enzymes) into the extracellular environment prior to ingestion of the consequent "soup".
In others, once potential nutrients or food is inside the organism, digestion can be conducted to a vesicle or a sac-like structure, through a tube, or through several specialized organs aimed at making the absorption of nutrients more efficient.
Secretion systems
Secretion systems: Bacteria use several systems to obtain nutrients from other organisms in the environments.
Digestion is the breaking down of food in the body, into a form that can be absorbed and used or excreted. It is also the process by which the body breaks down food into smaller components that can be absorbed by the blood stream.
Digestion is the breaking down of food in the body, into a form that can be absorbed and used or excreted. It is also the process by which the body breaks down food into smaller components that can be absorbed by the blood stream.
Mechanical and chemical digestion begin in the mouth where food is chewed, and mixed with saliva to break down starches. The stomach continues to break food down mechanically and chemically through the churning of the stomach and mixing with enzymes. Absorption occurs in the stomach and gastrointestinal tract, and the process finishes with excretion.
Digestion is usually divided into mechanical processing to reduce the size of food particles and chemical action to further reduce the size of particles and prepare them for absorption
Ingestion:
placing food into the mouth.
Mechanical digestion & chemical digestion: mastication to tear and crush food, and churning of the stomach. Addition of chemicals (acid, bile, enzymes, and water) to break down complex molecules into simple structures.
Absorption:
movement of nutrients from the digestive system to the circulatory and lymphatic capillaries through osmosis, active transport, and diffusion.
Digestion:
Removal of undigested materials from the digestive tract through defecation.
The Stages of Digestion:
1/Cephalic phase - This phase occurs before food enters the stomach and involves preparation of the body for eating and digestion. Sight and thought stimulate the cerebral cortex. Taste and smell stimulus is sent to the hypothalamus and medulla oblongata. After this it is routed through the vagus nerve and release of acetylcholine.
2/ Digestion begin in the oral cavity where food is chewed. Saliva is secreted in large amounts by three pairs of exocrine salivary glands (parotid, submandibular, and sublingual) in the oral cavity, and is mixed with the chewed food by the tongue.
The Esophagus, a narrow, muscular tube about 30 centimeters (12 inches) long, starts at the pharynx, passes through the larynx and diaphragm, and ends at the cardiac orifice of the stomach. The wall of the Esophagus is made up of two layers of smooth muscles, which form a continuous layer from the Esophagus to the often and contract slowly, over long periods of time.
3/The food enters the stomach after passing through the cardiac orifice. In the stomach, food is further broken apart, and thoroughly mixed with a gastric acid and digestive enzymes that break down proteins. The acid itself does not break down food molecules, rather, the acid provides an optimum pH for the reaction of the enzyme pepsin.
4/After being processed in the stomach, food is passed to the small intestine via the Pyloric sphincter. The majority of digestion and absorption that occurs here as chyme enters the duodenum. Here it is further mixed with three different liquids:
a)bile, which emulsifies fats to allow absorption, neutralizes the chyme, and is used to excrete waste products such as bilin and bile acids (which has other uses as well). It is not an enzyme, however. The bile juice is stored in a small organ called the gall bladder.
b)pancreatic juice made by the pancreas.
c)intestinal enzymes of the alkaline mucosal membranes. The enzymes include: maltase, lactase and sucrase, to process sugars; trypsin and chymotrypsin are also added in the small intestine.
Most nutrient absorption takes place in the small intestine.
5/After the food has been passed through the small intestine, the food enters the large intestine. The large intestine is roughly 1.5 meters long, with three parts: the cecum at the junction with the small intestine, the colon, and the rectum. The colon itself has four parts: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon.
Digestion is the breaking down of food in the body, into a form that can be absorbed and used or excreted. It is also the process by which the body breaks down food into smaller components that can be absorbed by the blood stream.
Digestion is the breaking down of food in the body, into a form that can be absorbed and used or excreted. It is also the process by which the body breaks down food into smaller components that can be absorbed by the blood stream.
Mechanical and chemical digestion begin in the mouth where food is chewed, and mixed with saliva to break down starches. The stomach continues to break food down mechanically and chemically through the churning of the stomach and mixing with enzymes. Absorption occurs in the stomach and gastrointestinal tract, and the process finishes with excretion.
Digestion is usually divided into mechanical processing to reduce the size of food particles and chemical action to further reduce the size of particles and prepare them for absorption
Ingestion:
placing food into the mouth.
Mechanical digestion & chemical digestion: mastication to tear and crush food, and churning of the stomach. Addition of chemicals (acid, bile, enzymes, and water) to break down complex molecules into simple structures.
Absorption:
movement of nutrients from the digestive system to the circulatory and lymphatic capillaries through osmosis, active transport, and diffusion.
Digestion:
Removal of undigested materials from the digestive tract through defecation.
The Stages of Digestion:
1/Cephalic phase - This phase occurs before food enters the stomach and involves preparation of the body for eating and digestion. Sight and thought stimulate the cerebral cortex. Taste and smell stimulus is sent to the hypothalamus and medulla oblongata. After this it is routed through the vagus nerve and release of acetylcholine.
2/ Digestion begin in the oral cavity where food is chewed. Saliva is secreted in large amounts by three pairs of exocrine salivary glands (parotid, submandibular, and sublingual) in the oral cavity, and is mixed with the chewed food by the tongue.
The Esophagus, a narrow, muscular tube about 30 centimeters (12 inches) long, starts at the pharynx, passes through the larynx and diaphragm, and ends at the cardiac orifice of the stomach. The wall of the Esophagus is made up of two layers of smooth muscles, which form a continuous layer from the Esophagus to the often and contract slowly, over long periods of time.
3/The food enters the stomach after passing through the cardiac orifice. In the stomach, food is further broken apart, and thoroughly mixed with a gastric acid and digestive enzymes that break down proteins. The acid itself does not break down food molecules, rather, the acid provides an optimum pH for the reaction of the enzyme pepsin.
4/After being processed in the stomach, food is passed to the small intestine via the Pyloric sphincter. The majority of digestion and absorption that occurs here as chyme enters the duodenum. Here it is further mixed with three different liquids:
a)bile, which emulsifies fats to allow absorption, neutralizes the chyme, and is used to excrete waste products such as bilin and bile acids (which has other uses as well). It is not an enzyme, however. The bile juice is stored in a small organ called the gall bladder.
b)pancreatic juice made by the pancreas.
c)intestinal enzymes of the alkaline mucosal membranes. The enzymes include: maltase, lactase and sucrase, to process sugars; trypsin and chymotrypsin are also added in the small intestine.
Most nutrient absorption takes place in the small intestine.
5/After the food has been passed through the small intestine, the food enters the large intestine. The large intestine is roughly 1.5 meters long, with three parts: the cecum at the junction with the small intestine, the colon, and the rectum. The colon itself has four parts: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon.