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When food is swallowed the swallow reflex is activated and the larynx elevates and closes to avoid portions of the food bolus entering the trachea causing aspiration of strange material to the bronchi.

A variety of specialized cells and tissues appeared with extracellular digestion to provide enzymes and special structures for the breaking down of dietary macromolecules.

This phenomenon allowed other cells to be liberated for other tasks and differentiations while benefiting from nutrients distributed through the circulation.

Intracellular digestion is that in which the breaking down of macromolecules takes place within the cell. Extracellular digestion is that in which macromolecules are broken down in places outside the cell (in the extracellular space, in the surrounds, in the lumen of digestive tubes, etc.) 

The advent of extracellular digestion in evolution allowed organisms to benefit from a greater variety of food. The breaking down of larger molecules into smaller ones outside the cell permitted the use of other foods than those that, due the size of their molecules, could not be interiorized by diffusion, phagocytosis or pinocytosis.

Chemical digestion is the series of enzymatic reactions to break macromolecules into smaller ones.

Mechanical digestion is the fragmentation of food aided by specialized physical structures, such as teeth, previous to extracellullar digestion. The mechanical fragmentation of food helps digestive enzymatic reactions because it provides a larger total area for the contact between enzymes and their substrates.

In some molluscs, the mechanical fragmentation is done by the radula (a teeth-like structure). Some arthropods, like lobsters and dragonflies, have mouthparts that make mechanical digestion of food. In earthworms and birds, the mechanical digestion is made by an internal muscular organ. In mandibulate vertebrates there are mandibles and chewing muscles to triturate food previous to the chemical digestion.

Bile, an emulsifier liquid, is made by the liver and later stored within the gallbladder and released in the duodenum.

Bile is composed of bile salts, cholesterol and bile pigments. Bile salts are detergents, amphiphilic molecules, i.e., molecules with a polar watersoluble portion and a non-polar fatsoluble portion. This feature allows bile salts to enclose fats inside water-soluble micelles in a process called emulsification for them to be in contact with intestinal lipases, enzymes that break fats into simpler fatty acids and glycerol.

The fat level of the chyme detected in the duodenum stimulates the secretion of cholecystokin (CCK). CCK acts by stimulating the secretion of the pancreatic juice also, and the releasing of bile by the gallbladder. 

The esophagus is a predominantly muscular organ so the assertion is correct. The esophagus is a muscular tube formed in its superior third of striated muscle tissue, in its middle third of mixed muscle tissue (striated and smooth) and in its lower third of smooth muscle tissue. The peristalsis of the esophagus provides the movement of the food towards the stomach even without gravitational help.

The small intestine is divided into three portions: duodenum, jejunum and ileum.

Bile is concentrated and stored in the gallbladder.

When fat rich foods are ingested the gallbladder contracts to release bile inside the duodenum. (This is the reason why patients with gallstones must not ingest fatty food, the reactive contraction of the gallbladder may move some of the stones to the point of blocking the duct that drains bile into the duodenum, causing pain and possible severe complications.)

Most part of water, vitamins and mineral ions are absorbed by the small intestine. The large intestine, however, is responsible for the reabsorption of nearly 10% of the ingested water, an important amount that gives consistency to feces (colon diseases can cause diarrhea).

The complete digestive tube allows animals to continuously feed themselves without waiting for residuals to be eliminated before beginning the digestion of new foods. In this way the absorption of larger amount of nutrients is possible and therefore bigger and more complex species can develop. Digestive tubes with two openings also make digestion more efficient since they provide different sites with different physical and chemical conditions (mouth, stomach, bowels) for the action of different complementary digestive enzymatic systems.

Some types of plant fibers are not absorbed by the intestine but play an important role in the functioning of the organ. They retain water inside the bowels and thus contribute to the softening of the fecal bolus. A softer fecal bolus is easier to be eliminated during defecation. People that eat less dietary fiber may suffer from hard stools and constipation.

Besides making bile for release in the duodenum, the liver has other digestive functions.

The venous network that absorbs nutrients from the guts, called mesenteric circulation, drains its blood content almost entirely to the hepatic portal vein. This vein irrigates the liver with absorbed material from the digestion. So the liver has the functions of storing, processing and inactivating nutrients. 

Glucose is polymerized into glycogen in the liver; this organ also stores many vitamins and the iron absorbed in the intestine. Some important metabolic molecules, like albumin and clotting factors, are made in the liver from amino acids of the diet. In the liver ingested toxic substances, like alcohol and drugs, are inactivated too.

The other adnexal gland of the digestive system is the pancreas. This organ makes digestive enzymes that digest proteins (proteases), lipids (lipases) and carbohydrates (pancreatic amylases). Other digestive enzymes, like gelatinase, elastase, carboxipeptidase, ribonuclease and deoxyribonuclease are also secreted by the pancreas.

Monosaccharides, amino acids, mineral salts and water are absorbed by the intestinal epithelium and collected by capillary vessels of the intestinal villi. From the capillaries, nutrients go to the mesenteric circulation, a system of vessels that drains the intestinal loops. The blood of the mesenteric circulation is drained to the portal hepatic vein and some nutrients are processed by the liver. From the liver, nutrients are gathered by the hepatic veins that discharge its blood content into the inferior vena cava. Blood from the inferior vena cava then gains the right chambers of the heart and is pumped to the lungs for oxygenation. From the lungs the blood then returns to the heart where it is pumped to the tissues distributing nutrients and oxygen.

Lipoproteins are complexes made of lipids (triglycerides and cholesterol) and proteins. The lipoproteins present different densities according to the relationship between their protein and lipid quantities since lipids are less dense than proteins. Low-density lipoproteins (LDL) are those with a low protein/lipid relation; high-density lipoproteins (HDL) have a high protein/lipid relation; another group is the very low-density lipoproteins (VLDL) with very low protein/lipid relation.

LDL is known as “bad cholesterol” because it transports cholesterol from the liver to the tissues and so induces the formation of atheroma plaques inside blood vessels, a condition called atherosclerosis (do not confuse with arteriosclerosis) that can lead to severe circulatory obstructions like acute myocardial infarction, cerebrovascular accidents and thrombosis. HDL is known as “good cholesterol” since it transports cholesterol from the tissues to the liver (to be eliminated with the bile) and elevation of the HDL blood level reduces the risk of atherosclerosis. (VLDL transforms into LDL after losing triglycerides in the blood).

Secretin is made in the duodenum. The chyme acidity causes the duodenum to release this hormone that in its turn stimulates the secretion of the pancreatic juice.

Triglycerides emulsified by the bile within micelles suffer the action of lipases that break them into fatty acids and glycerol. Fatty acids, glycerol and cholesterol are absorbed by the intestinal mucosa. In the interior of the mucosal cells fatty acids and glycerol form again triglycerides that together with cholesterol and phospholipids are packed in small vesicles covered by proteins and called chylomicrons. The chylomicrons are released in minuscule lymphatic vessels not in blood vessels and they gain the lymphatic circulation. So the lymphatic system plays an important role in the absorption of lipids. 

The lymphatic circulation drains its content to the venous blood circulation. In that manner chylomicrons reach the liver where their lipid content is processed and released in the blood under the form of protein-containing complexes called lipoproteins, like HDL, VLDL and LDL.

The presence of food in the stomach stimulates the secretion of gastrin that in its turn triggers the releasing of the gastric juice.

The pancreas secretes trypsinogen that, undergoing action of the enzyme enterokinase secreted by the duodenum, is transformed into trypsin. Trypsin in its turn catalyzes the activation of pancreatic chymotrypsinogen into chymotrypsin. Trypsin and chymotrypsin are proteases that break proteins into smaller peptides. The smaller peptides are then broken into amino acids by the enzyme carboxipeptidase (also secreted by the pancreas in a zymogen form and activated by trypsin) helped by the enzyme aminopeptidase made in the intestinal mucous membrane.

The digestive tube of birds has special structures, in this sequential order: the crop, the proventriculus and the gizzard.

The crop has the function of temporary storage of ingested food and it is a more dilated area of the avian esophagus. The proventriculus is the chemical stomach of the birds where food is mixed with digestive enzymes. Thegizzard is a muscular pouch that serves as a mechanical stomach where the food is ground to increase the exposure area of the food particles for the digestive enzymes to act.

The partially digested and semifluid food bolus that leaves the stomach and enters the duodenum is called chyme.

Until reaching the duodenum the food enters the mouth, passes the pharynx, goes down the esophagus and passes the stomach.

The valve that separates the stomach from the duodenum is the pylorus. It has the function of keeping the food bolus within the gastric cavity for enough time to allow the gastric digestion to take place. It also has the function of preventing the intestinal content from going back into the stomach.

Bird feces are more liquid than mammal feces, i.e., less water is absorbed in the avian digestive system. The more frequent elimination of feces in birds due to their less solid feces is an adaptation to flight since their body weight is kept lower.

The normal pH of the gastric juice is around 2. So it is an acid pH.

It is necessary for the gastric pH to be kept acid for the activation of pepsinogen (a proenzyme secreted by the gastric chief cells) into pepsin, the digestive enzyme that acts only under low pH. This pH level is attained by the secretion of hydrochloric acid (HCl) by the parietal cells. 

Peristalsis is the process of synchronized contractions of the muscular wall of the digestive tube. Peristaltic movements may occur from the esophagus until and including the bowels.

The peristaltic movements are involuntary and they have the function of moving and mixing food along the digestive tube. Peristaltic movement deficiency, for example, in case of injuries of the innervation of the muscular wall of the digestive tube caused by Chagas’ disease, can lead to the interruption of the food traffic inside the bowels and to severe clinical consequences like megacolon (abnormal enlargement of the colon) and megaesophagus (enlargement of the esophagus).

The hormones that participate in the regulation of digestion are gastrin, secretin, cholecystokin and enterogastrone.

The enteric juice is secreted by the small intestine mucosa. The enzymes of the enteric juice and their respective functions are described as follows:

Enterokinase: enzyme that activates trypsinogen into trypsin. Saccharase: enzyme that breaks sucrose (saccharose) into glucose and fructose. Maltase: enzyme that breaks maltose into two glucose molecules. Lactase: enzyme that breaks lactose into glucose and galactose. Peptidases: enzymes that break oligopeptides into amino acids. Nucleotidases: Enzymes that break nucleotides into its components (nitrogen-containing bases, phosphates and pentoses).

The digestive system, also known as “systema digestorium”, or gastrointestinal system, is composed of the digestive tube organs plus the digestive adnexal glands. The digestive tube is composed of mouth, pharynx, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (caecum, colon, rectum) and anus.

Entering the duodenum the chyme meets the pancreatic juice under a pH of approximately 8.5. The neutralization of the chyme acidity is necessary to keep adequate pH level for the functioning of the digestive enzymes that act in the duodenum. Without the neutralization of the chyme acidity the mucous membrane of the intestine would be injured.

When stimulated by the chyme acidity the duodenum makes a hormone called secretin. Secretin stimulates the pancreas to release the pancreatic juice and also the gallbladder to expel bile in the duodenum. The pancreatic secretion, rich in bicarbonate ions, is released in the duodenum and neutralizes the chyme acidity; this acidity is also neutralized by the secretion of bile in the duodenal lumen.

The stomach and the pancreas make zymogens of the proteases pepsin, chymotrypsin and trypsin and these zymogens are released into the gastric or duodenal lumen for activation. This happens to prevent the digestion of these organs' (stomach and pancreas) own cells and tissues by the active form of the enzymes. So the production of zymogens is a protective strategy against the natural effects of the proteolytic enzymes. 

The human digestive secretions are: saliva, gastric juice, bile, pancreatic juice and enteric juice. Among these secretions only the bile does not contain digestive enzymes.

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Agricultural Entrepreneur /Technical Entrepreneur/Industrial Entrepreneur

Ability to continue to do something, even when it is difficult is called Perseverance

a. The yarns on one beam are held at regular tension and those on the other beam are held at slack tension. The yarns are wound onto the two warp beams ingroups of 10 to 16 for a narrow stripe. As the reed beats the weft yarn into place, the slack yarns crinkle or buckle to form a puckered stripe, adds the regular tensioned yarns form the flat stripe. The stripes are always in the warp direction 

b. slow weaving speed 

c. summer suiting like dresses, curtains and sportswear.

The ability to continue to do something, even when it is difficult is called perseverance.

Adaptability refers to the capacity to adjust one’s thoughts and behaviours in order to effectively respond to uncertainty, new information, or changed circumstances. In business, adaptability becomes a survival skill as the nature of businesses is dynamic

We know that,

R = R₀ [1 + \(\alpha\) (T - T₀)]

where,

R = conductor resistance at temperature T

R = conductor resistance at reference temperature T.

\(\alpha\) = temperature cofficient of resistance for conductor material.

The resistance change per degree of temperature change.

as all materials have a certain specific resistance (at 20°C) , they also change resistance according to temperature by certain amounts. For pure metals, this cofficient is a positive number, meaning that resistance increase with increasing temperature.

In the beginning of the poem the tree is calm & silent & in the ending it ends with motionless & empty level.

Charles Darwin is the author of the book “the origin of species”.

According to Goode and Hatt “Questionnaire as a device for securing answers to question using a form which the respondent fills in himself’.