trace the various step of digestion in the alimentary canal of man discuss the function of liver?
Answers
Answer:
The mouth is the beginning of the digestive system, and, in fact, digestion starts here before you even take the first bite of a meal. The smell of food triggers the salivary glands in your mouth to secrete saliva, causing your mouth to water. When you actually taste the food, saliva increases.
Once you start chewing and breaking the food down into pieces small enough to be digested, other mechanisms come into play. More saliva is produced. It contains substances including enzymes that begin the process of breaking down food into a form your body can absorb and use. Chew your food more -- it also helps with your digestion.
Stop 2: The Pharynx and Esophagus
Also called the throat, the pharynx is the portion of the digestive tract that receives the food from your mouth. Branching off the pharynx is the esophagus, which carries food to the stomach, and the trachea or windpipe, which carries air to the lungs.
The act of swallowing takes place in the pharynx partly as a reflex and partly under voluntary control. The tongue and soft palate -- the soft part of the roof of the mouth -- push food into the pharynx, which closes off the trachea. The food then enters the esophagus.
The esophagus is a muscular tube extending from the pharynx and behind the trachea to the stomach. Food is pushed through the esophagus and into the stomach by means of a series of contractions called peristalsis.
Just before the opening to the stomach is an important ring-shaped muscle called the lower esophageal sphincter (LES). This sphincter opens to let food pass into the stomach and closes to keep it there. If your LES doesn't work properly, you may suffer from a condition called GERD, or reflux, which causes heartburn and regurgitation (the feeling of food coming back up).
Stop 3: The Stomach and Small Intestine
The stomach is a sac-like organ with strong muscular walls. In addition to holding food, it serves as the mixer and grinder of food. The stomach secretes acid and powerful enzymes that continue the process of breaking the food down and changing it to a consistency of liquid or paste. From there, food moves to the small intestine. Between meals, the non-liquefiable remnants are released from the stomach and ushered through the rest of the intestines to be eliminated.
Made up of three segments -- the duodenum, jejunum, and ileum -- the small intestine also breaks down food using enzymes released by the pancreas and bile from the liver. The small intestine is the 'work horse' of digestion, as this is where most nutrients are absorbed. Peristalsis is also at work in this organ, moving food through and mixing it up with the digestive secretions from the pancreas and liver, including bile. The duodenum is largely responsible for the continuing breakdown process, with the jejunum and ileum being mainly responsible for absorption of nutrients into the bloodstream.
A more technical name for this part of the process is "motility," because it involves moving or emptying food particles from one part to the next. This process is highly dependent on the activity of a large network of nerves, hormones, and muscles. Problems with any of these components can cause a variety of conditions.
While food is in the small intestine, nutrients are absorbed through the walls and into the bloodstream. What's leftover (the waste) moves into the large intestine (large bowel or colon).
Everything above the large intestine is called the upper GI tract. Everything below is the lower GI trace. sorry bro more then 5000 words can write..........short information
Answer:
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Explanation:
The digestive system uses mechanical and chemical activities to break food down into absorbable substances during its journey through the digestive system. Table 1 provides an overview of the basic functions of the digestive organs.
Table 1. Functions of the Digestive Organs
Organ Major functions Other functions
Mouth
Ingests food
Chews and mixes food
Begins chemical breakdown of carbohydrates
Moves food into the pharynx
Begins breakdown of lipids via lingual lipase
Moistens and dissolves food, allowing you to taste it
Cleans and lubricates the teeth and oral cavity
Has some antimicrobial activity
Pharynx
Propels food from the oral cavity to the esophagus
Lubricates food and passageways
Esophagus
Propels food to the stomach
Lubricates food and passageways
Stomach
Mixes and churns food with gastric juices to form chyme
Begins chemical breakdown of proteins
Releases food into the duodenum as chyme
Absorbs some fat-soluble substances (for example, alcohol, aspirin)
Possesses antimicrobial functions
Stimulates protein-digesting enzymes
Secretes intrinsic factor required for vitamin B12 absorption in small intestine
Small intestine
Mixes chyme with digestive juices
Propels food at a rate slow enough for digestion and absorption
Absorbs breakdown products of carbohydrates, proteins, lipids, and nucleic acids, along with vitamins, minerals, and water
Performs physical digestion via segmentation
Provides optimal medium for enzymatic activity
Accessory organs
Liver: produces bile salts, which emulsify lipids, aiding their digestion and absorption
Gallbladder: stores, concentrates, and releases bile
Pancreas: produces digestive enzymes and bicarbonate
Bicarbonate-rich pancreatic juices help neutralize acidic chyme and provide optimal environment for enzymatic activity
Large intestine
Further breaks down food residues
Absorbs most residual water, electrolytes, and vitamins produced by enteric bacteria
Propels feces toward rectum
Eliminates feces
Food residue is concentrated and temporarily stored prior to defecation
Mucus eases passage of feces through colon
Digestive Processes
The processes of digestion include six activities: ingestion, propulsion, mechanical or physical digestion, chemical digestion, absorption, and defecation.
The first of these processes, ingestion, refers to the entry of food into the alimentary canal through the mouth. There, the food is chewed and mixed with saliva, which contains enzymes that begin breaking down the carbohydrates in the food plus some lipid digestion via lingual lipase. Chewing increases the surface area of the food and allows an appropriately sized bolus to be produced.
This image shows the peristaltic movement of food. In the left image, the food bolus is towards the top of the esophagus and arrows pointing downward show the direction of movement of the peristaltic wave. In the center image, the food bolus and the wave movement are closer to the center of the esophagus and in the right image, the bolus and the wave are close to the bottom end of the esophagus.
Figure 1. Peristalsis moves food through the digestive tract with alternating waves of muscle contraction and relaxation.
Food leaves the mouth when the tongue and pharyngeal muscles propel it into the esophagus. This act of swallowing, the last voluntary act until defecation, is an example of propulsion, which refers to the movement of food through the digestive tract. It includes both the voluntary process of swallowing and the involuntary process of peristalsis. Peristalsis consists of sequential, alternating waves of contraction and relaxation of alimentary wall smooth muscles, which act to propel food along (Figure 1). These waves also play a role in mixing food with digestive juices. Peristalsis is so powerful that foods and liquids you swallow enter your stomach even if you are standing on your head.
Digestion includes both mechanical and chemical processes. Mechanical digestion is a purely physical process that does not change the chemical nature of the food. Instead, it makes the food smaller to increase both surface area and mobility. It includes mastication, or chewing, as well as tongue movements that help break food into smaller bits and mix food with saliva. Although there may be a tendency to think that s it enters the bloodstream and its nutrients are put to work. This occurs through the process of absorption, which takes place primarily within the small intestine. There, most nutrients are absorbed from the lumen of the alimentary canal into the bloodstream through the epithelial cells that make up the mucosa. Lipids are absorbed into lacteals and are transported via the lymphatic vessels to the bloodstream (the subclavian veins near the heart). The details of these processes will be discussed later.
In defecation, the final step in digestion, undigested materials are removed from the body as feces.