Glossary

All glossary words are highlighted BOLD in the blog entries.

Ancillary Organs --- Organs of salivary glands, liver and pancreas.

Hormones --- Hormones are chemicals released by cells that affect cells in other parts of the body.

Molecules --- Defined as a sufficiently stable, electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds.

Serrated --- To make serrations.

Buoyancy --- The upward force that keeps things afloat.

Protrude --- Tojut out from the surrounding surface or context.

Atrophied --- The partial or complete wasting away of a part of the body.

Honeycomb --- A mass of hexagonal wax cells built by honey bees in their nests to contain their larvae and stores of honey and pollen.

Protozoa --- Protozoas are microorganisms classified as unicellular eukaryotes.

Reflection

After three weeks of journal, I have indeed learnt quite a number of things. These things or knowledge cannot be found just anywhere: textbooks, encyclopedias or any research materials. In contrast to make a good research paper and a good biology journal, it takes more than just copying from a source. However it takes time an effort to complete the journal. Although we were given weeks to complete this project. I found it hard to keep on track/schedule.

Given our busy schedules, I still managed to complete the biology journal on time. This may be due to good time management or fast work efficiency. This is a good starting point for many of us who are sort of lazy and too bothered to do projects. This is one good time to allow us to experience the meaning of research. As said in Wikipedia,

"Research is defined as human activity based on intellectual application in the investigation of matter. The primary purpose for applied research is discovering, interpreting, and the development of methods and systems for the advancement of human knowledge on a wide variety of scientific matters of our world and the universe. Research can use the scientific method, but need not do so."

Therefore, research is not anymore the "copy and paste" type of projects which many of us are greatly familiar with. This time around the research has to be detailed and at the same time understand the meaning of the information. We have to read the information, digest it and rewrite the whole of the information out for ourselves. In this way I feel, it is so much better as we will be able to absorb more information and understand it deeper.

On another note, this time's biology journal made me smarter! In fact I have learnt much more things that the textbooks do not have. We therefore must be independent in our own learning and not rely on the teachers to spoon feed us with all the answers and information that we need.

The world out there is very huge! There are many things out there waiting for us to discover and learn at the same time. These things do not fly to us and therefore we ourselves have to search it on our own. The Internet is a very good example. There are many websites all over the world with billions of valuable information waiting for us to discover. Just a click of a mouse and we can easily find information. Using the search engines will be a popular choice. Hence, I have learnt how to search for information more effectively and learning how to sieve out false information from correct ones.

However we cannot just rely on the Internet. Books are indeed more reliable as they stated their facts down clearly in comparison to the Internet. Information on the Internet can easily be edited by some crooks and therefore making the information not reliable at all.

In addition, we need to have the right attitude towards learning. We cannot do things just for the sake of doing. We have to think of the brighter side and think of the valuable knowledge that we will be discovering. Doing this research with the wrong attitude will bring us nowhere. Thus we have to have the right kind of mindset and attitude to fully accomplish the research effectively.

To conclude, this time's biology journal is a great learning experience for me. I have learnt things outside the textbook be it Science or any other matters relating to the biology journal.

Conclusion

After researching on the different digestive systems in differnent types of animals, I can finally conclude something.

I can conclude that these animals have different digestive system due to their lifestyle, habits, diet and many other factors.

For example, a cow needs to have four chambers of stomach. It helps the cow to bring the boluses of food up back into the mouth where they rechew their food. Also to keep the feed mixing by strong contractions, and to provide a suitable environment for the bacteria and protozoa to live.

Another example of having a digestive system due to a diet will be the snake. The salivary glands found in snakes include the palatine, lingual, sublingual and labial gland. These glands help moisten the prey for swallowing.

An example of a digestive system adapting to its habitat would be that of a shark. The liver is the largest organ and serves as a hydrostatic organ, helping the shark in buoyancy. The vast amount of oil created and stored in the shark’s liver, decreasing the weight of the shark and increasing its flotation.

Although there are many types of animals out there in the entire world, it is quite impossible for me to study everyone one by one. But still this is a good experience for me to know that different animals have so much difference in their digestive systems.

Seventh Entry

Fish... Fish... Fish

Like all animals the fish's body is basically a long tube that is twisted up on itself a bit in the middle and has a layer of muscles and ancillary organs around it. This tube has the mouth at one end and the anus or cloaca at the other. Mostly we consider the mouth to be the entrance to the tube and the anus to be the exit, food items come in and faeces go out. Different things happen in different parts of the tube and for the sake of study and understanding we give the various parts names.

Mouth - Pharynx - Oesophagus - Gizzard - Stomach - Intestines - Rectum.

However not all fish have all these parts, some, like many of the Cyprinids and Cyprinidonts, lack a stomach, while a gizzard is only found in a relatively few species.

Mouth

Food is brought into the body via the mouth, and the jaws of modern teleost fish are a mechanical wonder, and the way the many bones work together is quite inspiring. However there is, as always a large variety in fish as a whole and the mouths of a Basking Shark, a Yellowfin Tuna and a Seahorse are quite different in both form and function. Lips are rare in fish, most species have a hard edge to their mouth. Some suction feeders that take in small prey items have small protractible lips that help give the mouth the form of a tube with a circular opening.

The teeth of most fish are the fore-runners of vertebrate teeth with an outer layer of enamel and an inner core of dentine. A fish may have teeth at the front of its mouth and along the jaws and in the pharynx as well as on its tongue.

The buccal cavity (the empty space in an empty mouth) secretes mucus to aid in the swallowing of food, but there are no special organs involved, no salivary glands, and this mucus is a lubricant only, it contains no digestive enzymes such as mammalian saliva does and is lined with squamous epithelium.

Pharynx

Immediately behind the mouth is the pharynx which is the continuation of the tube started at the mouth and in which the are found the gill clefts, through which water flows out of the alimentary canal and into the gills. It is short which leads to the oesophagus.

Oesophagus

It is constructed of two layers of non-striated muscle, one of which is longitudinal and the other circular, strangely in some species of fish the longitudinal muscle is the inner layer while in others the circular muscle is the inner layer. With so many species generalisations only apply to the majority, there are always exceptions.

The whole oesophagus contains many mucus cells, the mucus keeps the food lubricated and helps it to move along the tube.

Gizzard

The gizzard is really a highly muscular modification of the first part of the stomach. Its main purpose is to grind up coarse food items into smaller pieces thus facilitating their later digestion. In those fish which have a gizzard, such as Shad, it is the place where digestion begins because as well as its muscular activity the gizzard also secretes digestive enzymes into the food.

The Liver

Is a large organ that play various roles in the fishes body, it is the site of glycogen storage, it produces a variety of substances, including enzymes that help with the digestion and it is a major chemical factory producing various hormones as well as numerous other important molecules.

Links/Resources:

http://www.infovisual.info/02/033_en.html
http://www.aqualex.org/elearning/fish_feeding/english/digestion/structure.html
http://en.wikipedia.org/wiki/Fish

Sixth Entry

I wonder what goes on in the tiny body of a spider.

Therefore I decided to find out more and I clearly learned much more from this piece of research.

The mouth parts of the spider include the coxa of the pedipalps which have been modified as chewing mouth parts. They are often serrated as it is these the spider uses to bite a hole in the skin, or exoskeleton of its prey. The parts of the coxa that function as mouth parts are called maxillae. Apart from their cutting edge the maxillae also have a a filtering edge covered in fine hairs that prevents solid particles from entering the spiders mouth. This filtering system is so fine that only particles smaller than 1 micron (0.001 of a mm) can pass through.

The maxillae form the sides of the mouth. To the front of the mouth is a hinged and movable organ called the rostrum and to the back of the mouth is the labium. Behind the mouth is pharynx a short tube lined with microscopic teeth that also filter the incoming fluid. The pharynx leads into the oesophagus, another tube through the food reaches the sucking stomach. This sucking stomach is a muscularly driven pump that draws the spiders liquid food into its digestive system, there are valves at both the entrance and exit of the stomach that ensure the food only passes one way through the system.

The midgut, or intestine starts immediately behind the stomach and leads from the prosoma to the opisthosoma via a tube that passes through the pedicel. From the midgut two branches or diverticula extend out into the prosoma, in most species they even extend into the coxa of the walking legs. In the opisthosoma there are many of these diverticula branch off from the midgut and surround the other organs present there. At the end of the midgut is the stercoral pocket (cloacal chamber) this is a storage area for wastes which are eventually passed along the short hind gut and out of the body via the anus.

Creepy Video:



Links/Resources:

http://www.everythingabout.net/articles/biology/animals/arthropods/arachnids/spiders/ http://encarta.msn.com/encnet/refpages/RefArticle.aspx?refid=761566464&pn=3
http://en.wikipedia.org/wiki/Spider

Fifth Entry

Today I am going to talk about a shark's digestive system.

A smooth, shiny membrane called peritoneum can be seen lining the inside of the body wall. The visceral organs are suspended dorsally by a double membrane of peritoneum know as mesentery.

The liver is the largest organ lying within the body cavity. Its two main lobes, the right and left lobes, extend from the pectoral girdle posteriorly most of the length of the cavity. A third lobe much shorter lobe is located medially and contains the green gall bladder along its right edge.

The liver is rich in oil which stores energy for the shark. The oil's low specific gravity is also responsible for giving the shark a limited amount of buoyancy.

Esophagus

The esophagus is the cranial extension of the stomach and is short in length. It connects the pharynx and the stomach. The differentiation between the pharynx, the esophagus, and the stomach can be made by examining the mucosal surfaces of these organs.

Liver

The liver is divided into three lobes: the paired right and left lateral lobes and the singular median lobe. The lateral lobes extend caudally for the majority of the coelem’s largest of two fluid filled sacs. The liver is the largest organ and serves as a hydrostatic organ, helping the shark in buoyancy. The vast amount of oil created and stored in the shark’s liver, decreasing the weight of the shark and increasing its flotation.

Gall Bladder

The gall bladder is green in colour as it stores bile in its lumen. Bile is used to blend fats during digestion. The gall bladder is attached to the ventral surface of the median lobe of the liver. Bile is stored in the gall bladder until it is needed.

Bile Duct

Bile travels from the gall bladder to the first part of the intestine, the duodenal section, by means of the bile duct. It is light brown in colour and passes on the dorsal side of the duodenum for it goes through its wall.

Stomach

The shark’s stomach is J-shaped and is positioned ventral to the liver. The diameter of the stomach increases when traced distally. The part of the stomach between the esophagus and the sharp bend is known as the body. Following the bend, the stomach runs cranially for a short distance and is greatly reduced in diameter. When it bends again, it becomes parallel to the duodenal portion of the intestine.

Pancreas

The pancreas is divided into two lobes: the ventral lobe and the dorsal lobe. The ventral lobe is positioned on the ventral side of the duodenum and continues to the larger dorsal lobe of the pancreas, which is located dorsal to the stomach and duodenum. This exocrine gland is responsible for the bulk of the enzymes produced for digestion.

Spleen

Located at the bend of the stomach, the spleen is triangular in shape and dark in colour. It is connected to the stomach by the gastrosplenic ligament. The spleen’s function is the production, degradation, and storage of red blood cells and is integral to the shark’s immune system.

Small Intestine

Situated away from the duodenum, the intestine exhibits a large diameter. This section is called the spiral intestine and is so named because of its spiral fold. It makes up the majority of the intestine. Its many rungs are attached inside of the intestine and its spiral shape allows for an increase of internal surface area. With a greater surface area, the time food takes to digest is greatly reduced resulting in greater absorption of nutrients. The rungs of the intestine change direction near the middle of the intestine.

Rectum

The rectum is the part of the large intestine directly before the anus.

Papillae

The papillae are small projections located on the mucosal lining of the esophagus and contain the shark’s taste buds. The change between papillae of the esophagus and rugae of the stomach signifies the transition between these two organs.

Gastric Rugae

The gastric rugae line the stomach and function to increase the surface area of the stomach. When the stomach is empty, they protrude but when the stomach is full, they become flat.

Cloaca

The cloaca is where the digestive, urinary, and reproductive systems empty.

Rectal Gland

Also known as the digitiform gland and is a small cylindrical-shaped gland located dorsal to the colon. The Rectal Gland communicates with the colon via a small duct. The function of the rectal gland is to eliminate excess body salt by secreting it into the colon. Therefore, it plays an important role in osmoregulation.

Osmoregulation

Maintains control of the levels of water and mineral salts in the blood.This helps to maintain homeostasis, the maintenance of constant internal conditions, in the body.

Links/Resources:

http://www.pc.maricopa.edu/Biology/ppepe/BIO145/lab04_2.html
http://foggs.wikispaces.com/Shark+Digestion
http://en.wikipedia.org/wiki/Physical_characteristics_of_sharks
http://www.biology-online.org/articles/physical-characteristics-sharks/feeding-digestion.html

Fourth Entry

In today's biology journal entry I will be talking about a snake's digestive system.

All snakes are carnivorous, but they do not chew. They swallow their prey whole. They are specially designed with unique, flexible jaws that allow them to swallow prey larger in diameter than the snake itself. Since they consume such large meals, many snakes eat only occasionally.

Scientists studying the digestive systems of certain snakes, such as boa constrictors and pythons, have found some interesting design concepts. In these snakes the period of time between meals can be several weeks. It was found that during the long periods of fasting the lining, or mucosa, of the small intestine becomes atrophied, conserving the snake’s energy and resources.

The salivary glands found in snakes include the palatine, lingual, sublingual and labial gland. These glands help moisten the prey for swallowing. These glands lie on either side of the head and neck and lead to ducts in the modified maxillary teeth.

Directly inside the mouth of snakes is the buccal cavity. Then comes the long oesophagus which can cover more than half of the snake's body. Inside the oesophagus, are many folds which helps the food go down into the stomach by peristalsis.

The stomach is a j-shaped organ in which most of the digestion occurs in snakes. The cells of the stomach secrete digestive enzymes and gastric juices that breakdown proteins. The food then passes through the pyloric valve and into the small intestines.

The small intestines is similar to the human's intestine. It is also a long narrow coiled tube where absorbance of nutrients takes place. The small intestines is divided into three regions: the duodenum, the ileum, and jejunum. The liver produces bile, excretes digestive enzymes into the duodenum of the small intestines. Also, the pancreas, which produces insulin and glycogen as well, produces digestive enzymes such as lipases, proteases and carbohydrases and secretes them into the duodenum.

At the junction of the small intestines and large intestines is the caecum. The large intestines is the least muscular and most thin-walled structure of the snake digestive system. It passes into the cloacae chamber. This chamber is divided into a copradaeum for receiving feaces and a urodaeum for urine and products of the genital organs. The cloaca plays an important role in the reabsorption of water.

Links/Resources:

http://www.dandydesigns.org/id42.html

http://www.biologycorner.com/resources/anatomy_snake.jpg

http://campus.murraystate.edu/academic/faculty/terry.derting/cva_atlases/Stephsnake/snakepage3.htm

http://animal.discovery.com/guides/reptiles/snakes/anatomy_03.html

Third Entry

Today I will be talking about the cow's digestive system.

The cow's digestion body parts are slightly different from that of a human.

Firstly I would like to share a astonishing fact that I found on the internet:

"The dairy cow is a magnificent producer of food. In approximately 10 months, a good cow can produce 496 pounds of protein, 784 pounds of energy in the form of the sugar lactose, 560 pounds of fat, and 112 pounds of minerals all in 16,000 pounds of milk. This is enough protein to supply the needs of a man for nearly 10 years, enough energy for 5 years, and enough calcium for 30 years."

Amazing? I found it amazing though.

Reticulum

This fermentation vat is composed of two areas called the reticulum and the rumen. The reticulum has a distinctive "honeycomb" appearance. It aids to help bring boluses of food back up to the mouth for rechewing. It also serves as a receptacle for heavy foreign objects that she eats.

Rumen

The rumen is, by far, the largest compartment. Its purpose is to store large quantities of feed, keep the feed mixing by strong contractions, and to provide a suitable environment for the bacteria and protozoa to live. This environment is kept agreeable to the microorganisms by maintaining a relatively constant temperature and pH and by removing many of their waste products.

Most of the waste products are volatile fatty acids. These volatile fatty acids are the primary sources of energy for the cow. They are absorbed by thousands of "finger-like" projections lining the bottom and sides of the rumen wall. These can be 1/2 inch long and they increase the surface area of the rumen so as to increase her ability to absorb volatile fatty acids.

Omasun

Once the feed has been reduced in size by chewing and digestion by the bacteria and protozoa, it can pass into a third compartment called the omasum. It looks like an open book with three sides bound. The tissues within are likened to the pages of a book and are called leaves. Up to 100 leaves can be found in the omasum. These leaves have small papillae on them which absorb a large portion of the volatile fatty acids that were not absorbed through the rumen wall. Water and electrolytes such as potassium and sodium are likely absorbed here as well thus drying out the foodstuffs before they enter the next compartment.

Abomasun

This fourth and last compartment which make up the cow's stomach is the abomasum or "true" stomach as it is called because it functions in a very similar way to the stomach of a man or pig. As in the omasum, the abomasum contains many folds to increase its surface area. The pH of the digesta coming into the abomasum is around 6.0 but is quickly lowered to about 2.5 by the acid. This creates a proper environment for the enzymes to function. The chief digestive function of the abomasum is the partial breakdown of proteins.

Small and Large Intestine

The small and large intestine of a cow is similar to a human's. The intestine also has villi to help absorb the digested food into the bloodstream.

Links/Resources:

http://wiki.answers.com/Q/How_does_a_cows_digestive_system_work
http://msetdata.rst2.edu/portfolios/b/brewster_r/rumen/images/zepictures/cow4%20copy.jpg
http://edis.ifas.ufl.edu/DS061
http://www.ca.uky.edu/Agripedia/GLOSSARY/digecow.htm

Second Entry

For today's biology Journal, I will be talking about the human's digestive system in depth. For many of us if we remember, we have already got to know about the human's digestive system in primary school. However, I will be going further and more in depth.

The above picture shows the Human Digestive Tract.

OVERVIEW

The digestive system is made up of a series of hollow organs joined in a long, twisting tube from the mouth to the anus together with the other organs that help the body break down and absorb food (see figure).

Inside these hollow organs is a lining called the mucosa. The mucosa contains tiny glands that produce juices to help digest food. The digestive tract also contains a layer of smooth muscle that helps break down food and move it along the tract.

Two “solid” digestive organs, the liver and the pancreas, produce digestive juices that reach the intestine through small tubes called ducts. The gallbladder stores the liver’s digestive juices until they are needed in the intestine. Parts of the nervous and circulatory systems also play major roles in the digestive system.

PARTS AND FUNCTIONS IN THE DIGESTIVE SYSTEM

Mouth and Tongue

The mouth is the first portion of the alimentary canal that receives food and begins digestion by mechanically breaking up the solid food particles into smaller pieces and mixing them with saliva. During chewing, the tongue moves food about and manipulates it into a mass called a bolus. The bolus is pushed back into the throat and is forced through the opening to the oesophagus

Pharynx

Pharynx describes the part of the throat that begins from behind the nose to the beginning of the voice box and the oesophagus. The nasal airway and the food passage share the same pharyngeal passage to conduct air and food. After passing the pharynx, the airway goes into the lungs while food goes into the esophagus. It blocks food from entering the windpipe preventing us to choke.

Oesophagus

The oesophagus is a muscular tube in the chest that connects the mouth and throat to the stomach. Muscular contractions and relaxations will enable food to propel forward. When the food reaches the sphincter, the sphincter will open up and allow food to pass it and into the ctomach where further digestion take place.

Stomach

In most mammals, the stomach is a hollow, muscular organ of the digestive system, between the throat and the small intestine. It is involved in the second phase of digestion, following chewing. The stomach churns food before it moves on to the rest of the body.

The stomach is composed of five layers. Starting from the inside and working our way out, the innermost layer is called the mucosa. Stomach acid and digestive juices are made in the mucosa layer. The next layer is called the submucosa. The submucosa is surrounded by the muscularis, a layer of muscle that moves and mixes the stomach contents. The next two layers, the subserosa and the serosa are the wrapping for the stomach. The serosa is the outermost layer of the stomach.

Liver

The liver is an organ in the upper abdomen that aids in digestion and removes waste products and worn-out cells from the blood. The liver is the largest solid organ in the body. The liver has a multitude of important and complex functions. Some of these functions are to:

1. Metabolize and store carbohydrates, which are used as the source for the sugar (glucose) in blood that red blood cells and the brain use.

2. Synthesize, store, and process (metabolize) fats, including fatty acids (used for energy) and cholesterol.

3. Detoxify, by metabolizing and/or secreting, drugs, alcohol, and environmental toxins.

Pancreas

A fish-shaped spongy grayish-pink organ about 15 cm long that stretches across the back of the abdomen, behind the stomach. The head of the pancreas is on the right side of the abdomen and is connected to the duodenum (the first section of the small intestine). The narrow end of the pancreas, called the tail, extends to the left side of the body.

The pancreas makes pancreatic juices and hormones, including insulin. The pancreatic juices are enzymes that help digest food in the small intestine

As pancreatic juices are made, they flow into the main pancreatic duct. This duct joins the common bile duct, which connects the pancreas to the liver and the gallbladder.

Gallbladder

The function of the gallbladder is to store bile and concentrate. Bile is a digestive liquid continually secreted by the liver. The bile emulsifies fats and neutralizes acids in partly digested food. A muscular valve in the common bile duct opens, and the bile flows from the gallbladder into the cystic duct, along the common bile duct, and into the duodenum (part of the small intestine).

Duodenum

The duodenum is a short portion of the small intestine connecting the rest of the intestine to the stomach. Though the duodenum is such a tiny fraction of the small intestine, it is the site of most of the breakdown of the food passing through it. The duodenum is lined with Brunner's glands, which secrete an alkaline mucus that supports the intestinal enzymes and aids in the absorption of nutrients.

IIeum

The ileum is a very long part of the small intestine. After protein digestion in the stomach and starch digestion in the mouth, the ileum releases many enzymes to digest the remaining products of starch hydrolyis (which are sugars).

Jejunum

The jejunum is the second and largest section of the small intestine. The surface area of the lining of the jejunum is greatly increased by many small, finger-like outgrowths called villi. This makes it easier for digested material to be absorbed, which is the main function of the jejunum.

Large Intestines

The large intestine is about 1.5 m long and consists of the caecum, appendix, colon and rectum - which are distributed in the abdominal cavity.

The large intestine does the following:

1. reabsorbs water and maintains the fluid balance of the body

2. absorbs certain vitamins

3. processes undigested material (fibre)

4. stores waste before it is eliminated

Caecum

The caecum is the first part of the large intestine. Shaped like a small pouch and located in the right lower abdomen, it is the connection between the small intestine and the colon.

The caecum accepts and stores processed material from the small intestine and moves it towards the colon.

Appendix

The appendix is a small projection emerging from the caecum.

In human beings, the appendix has no known function and is thought to be a remnant from a previous time in human evolution.

Colon

Shaped like an inverted 'U', the colon is the longest part of the large intestine.

Within the colon, the mixture of fibre, small amounts of water, and vitamins, etc, mixes with mucus and with bacteria that live in the large intestine - and starts to form faeces.
As faeces travels through the colon, the lining of the colon absorbs most of the water and some vitamins and minerals.

Rectum

The rectum is the final part of the large intestine. It is where stool (faeces) is stored before being passed as a bowel motion.

Last but not least, here's a video clip for your enjoyment!

Links/Resources:

http://images.main.uab.edu/healthsys/ei_0132.gif
http://digestive.niddk.nih.gov/ddiseases/pubs/yrdd/
http://en.wikipedia.org/wiki/Mouth
http://weblogs.newsday.com/sports/watchdog/blog/mouth-diseases.jpg
http://www.sghhealth4u.com.sg/Health4U/otolaryngology/the_throat.htm
http://jeremyboelter.com/images/GERD3small.gif
http://en.wikipedia.org/wiki/Stomach
http://www.mamashealth.com/organs/stomach.asp
http://www.medterms.com/script/main/art.asp?articlekey=4179
http://www.mamashealth.com/organs/gallbladder.asp
http://www.wisegeek.com/what-is-the-duodenum.htm
http://wiki.answers.com/Q/What_is_the_function_of_the_iieum
http://www.daviddarling.info/encyclopedia/J/jejunum.html
http://www.gesa.org.au/digestive-system/large_intestine.cfm
http://www.youtube.com/watch?v=1nFwO-9iU5Y
Proteins, Enzymes, Genes The Interplay of Chemistry and Biology by Joseph S. Fruton

First Entry

This is my first official blog entry on the topic of Digestion.

My topic question is "How do the digestive systems in other animals work?"

Firstly we have to analyse the meaning and why the need of digestion.

Why is there a need for digestion?

The food we eat consists of large bulky molecules that cannot pass through the walls of the intestines into the blood vessels. Digestion is necessary to break down food into smaller, soluble and diffusible molecules that can be absorbed into our body. Digestion may be physical or chemical.

Physical breakdown of food into smaller pieces without any chemical change to the molecules of the food is called physical digestion.

Chemical digestion is the breakdown of large food molecules into smaller molecules. It involves the action of enzymes, which are special types of proteins produced by the body. The enzymes speed up specific chemical reactions in the body.

Most of the work of digestion requires the presence of enzymes. Enzymes are common proteins, but they are unique in that they can latch on to a specific molecule, such as another protein, and cut that molecule into smaller fragments.

Elsewhere in the body enzymes may do the opposite, namely build large molecules from smaller ones. But in the intestines, enzymes generally break apart molecules so that they can be more easily transported (absorbed) across the cells of the intestines and into the bloodstream. Thus, a meal that contains protein, triglycerides, and complex sugars (dissacharides) is degraded into amino acids, fatty acids, and simple sugars, respectively.

These smaller molecules are then absorbed and transported through the blood to places where they are needed.

In the second part of my entry I will be talking about the human's digestive system.

Links/Resources:

http://en.wikipedia.org/wiki/Digestion

The Stuff of Life by Eric P. Widmaier