digestive system role Flashcards
miscunsuption of the role of digestive system.
The major functions of the digestive tract are usually summarized in two words—digestion and absorption. However, many of its specific activities (such as smooth muscle activity) and certain regulatory events are not really covered by either term. To describe digestive system processes a little more accurately, we need to consider a few more functional terms. The essential activities of the GI tract include the following six processes (summarized in Figure 14.11).
the real functions of digestion
Ingestion. Food must be placed into the mouth before it can be acted on. This is an active, voluntary process called ingestion.
Propulsion. To be processed by more than one digestive organ, foods must be propelled from one organ to the next. Swallowing is one example of food movement that depends largely on the propulsive process called peristalsis. Peristalsis is involuntary and involves alternating waves of contraction and relaxation of the longitudinal muscles in the organ wall (Figure 14.12a). The net effect is to squeeze the food along the tract.
Food breakdown: Mechanical breakdown. Mechanical breakdown physically fragments food into smaller particles, increasing surface area and preparing food for further degradation by enzymes. Chewing and mixing of food in the mouth by the teeth and tongue, and churning of food in the stomach are examples of processes contributing to mechanical food breakdown. In addition, segmentation (Figure 14.12b) in the small intestine moves food back and forth across the internal wall of the organ, mixing it with the digestive juices. Although segmentation may also help to propel foodstuffs through the small intestine, it is more an example of mechanical digestion than of propulsion.
Food breakdown: Digestion. The sequence of steps in which large food molecules are chemically broken down to their building blocks by enzymes (protein molecules that act as catalysts) is called digestion.Absorption. Absorption is the transport of digestive end products from the lumen of the GI tract to the blood or lymph. For absorption to occur, the digested foods must first enter the mucosal cells by active or passive transport processes. The small intestine is the major absorptive site.
Defecation. Defecation is the elimination of indigestible residues and gut bacteria from the GI tract via the anus in the form of feces.
Because each of the major food groups has very different building blocks, let’s take a little time to review these organic molecules (which we first introduced in Chapter 2). The building blocks, or units, of carbohydrate foods are
monosaccharides (mon″o-sak′ah-rīdz), or simple sugars. We need to remember only three of these that are common in our diet—glucose, fructose, and galactose. Glucose is by far the most important, and when we talk about blood sugar level, we are referring to glucose. Fructose is the most abundant sugar in fruits, and galactose is found in milk.
The only carbohydrates that our digestive system digests, or breaks down to simple sugars, are
sucrose (table sugar), lactose (milk sugar), maltose (malt sugar), and starch.
Sucrose, maltose, and lactose are referred to as
to as disaccharides, or double sugars, because each consists of two simple sugars linked together. Starch is a polysaccharide (literally, “many sugars”) formed by linking hundreds of glucose units. Although we eat foods containing other polysaccharides, such as cellulose, we do not have enzymes capable of breaking them down. The indigestible polysaccharides do not provide us with any nutrients, but they help move the foodstuffs along the gastrointestinal tract by providing bulk, or fiber, in our diet.
protien needs to be broken down to be digested but how:
Protein: When you eat protein, it’s too large for your body to use directly.
Polypeptides: The first step in digestion is breaking the protein down into polypeptides (chains of amino acids). These are smaller than the whole protein but still too big to be absorbed by your body.
Amino Acids: The polypeptides are then broken down further into individual amino acids, which are the smallest form your body can absorb and use.
lipids(fats) breakdown
When lipids (fats) are digested, they yield two different types of building blocks—fatty acids and an alcohol called glycerol (glis′er-ol).
Digestion of Lipids (Fats):
Fats (Lipids): When you eat fats, they’re generally in the form of triglycerides, which are made up of one glycerol molecule and three fatty acid chains.
Breaking Down Fats:
In the stomach, fat digestion begins but only a small amount occurs. The primary digestion of fat happens in the small intestine.
The enzyme lipase, released by the pancreas, is responsible for breaking down the triglycerides into fatty acids and glycerol.
Monoglycerides and Fatty Acids:
The lipase enzyme splits triglycerides into monoglycerides (a glycerol molecule attached to a single fatty acid) and fatty acids.
In some cases, monoglycerides may remain unprocessed if digestion isn’t complete.
Absorption:
The fatty acids and monoglycerides are then absorbed into the cells of the small intestine, where they are reassembled into triglycerides and packaged into chylomicrons (lipid carriers) for transport through the lymphatic system into the bloodstream.
Key Points:
Fatty acids and glycerol are the main products of fat digestion.
If the digestion process isn’t fully completed, monoglycerides and fatty acids might still be present, which can be absorbed directly.
Just like with proteins and carbohydrates, the digestive system breaks down lipids into smaller components (fatty acids and glycerol) so they can be absorbed and used by the body for energy, storage, and other functions.
It sounds like you’re looking at a diagram or summary of digestion (like Figure 14.13). If you need more details on that or a specific part of digestion, let me know!
The number at the beginning refers to the number of fatty acid molecules attached to the glycerol molecule.
Here’s how it works:
Monoglyceride = 1 fatty acid + glycerol
Diglyceride = 2 fatty acids + glycerol
Triglyceride = 3 fatty acids + glycerol
So, the “mono”, “di”, and “tri” parts of the name always tell you how many fatty acids are attached to the glycerol backbone.
nucleous breakdown
Digestion of Nucleic Acids:
Nucleases:
Nucleases are enzymes produced by the pancreas that start the digestion of nucleic acids (DNA and RNA) in the small intestine. These enzymes break the long strands of nucleic acids into nucleotides, which are the basic building blocks of DNA and RNA.
Nucleotides:
Nucleotides consist of three components:
A nitrogen base (adenine, thymine, cytosine, guanine, or uracil for RNA)
A 5-carbon sugar (deoxyribose for DNA and ribose for RNA)
A phosphate group
Brush Border Enzymes:
The brush border is the tiny hair-like projections (microvilli) that line the walls of the small intestine. These cells produce nucleosidases and phosphatases, which further break down the nucleotides into their individual components:
Nitrogen bases
5-carbon sugars (ribose or deoxyribose)
Phosphate ions
Absorption:
Once the nucleotides are broken down into their components (bases, sugars, and phosphates), these components can be absorbed by the cells lining the small intestine and enter the bloodstream.
Key Points:
Nucleases break down nucleic acids into nucleotides.
Nucleosidases and phosphatases break down the nucleotides into their components: nitrogen bases, sugars, and phosphate ions.
These components are then absorbed and can be used by the body for various functions, including the synthesis of new nucleic acids.
This digestion process allows your body to break down nucleic acids from food into usable building blocks, which can be incorporated into your own DNA and RNA for various cellular processes!
the dgestive system is like a factory
Some of these processes are the job of a single organ. For example, only the mouth ingests, and only the large intestine defecates. But most digestive system activities occur bit by bit as food is moved along the tract. Thus, in one sense, the digestive tract can be viewed as a “disassembly line” in which food is carried from one stage of its processing to the next and its nutrients are made available to the cells in the body along the way.
digestive system conditions
While the body as a whole strives to maintain homeostasis—a stable internal environment—throughout its systems, the digestive system operates a bit differently. It creates an optimal environment(so diffrent ideal conditions for each digestive organ) specifically for digestion to occur efficiently, but this process takes place in the lumen of the alimentary canal, which, as you mentioned, is technically outside the body.
receptors of digestive system
Digestive activity is mostly controlled by reflexes via the parasympathetic division of the autonomic nervous system. (This division is the “rest-and-digest” arm. See Chapter 7.) The sensors (mechanoreceptors, chemoreceptors) involved in these reflexes are located in the walls of the alimentary canal organs and respond to a number of stimuli, the most important being stretch of the organ by food in its lumen, pH of the contents, and presence of certain breakdown products of digestion. When these receptors are activated, they trigger reflexes that activate or inhibit (1) the glands that secrete digestive juices into the lumen or hormones into the blood, and (2) the smooth muscles of the muscularis that mix and propel the food along the tract.
Now that we have summarized some points that apply to the function of the digestive organs as a group, we are ready to look at their special capabilities.
