Digestion

What is digestion? • Before our bodies can use the (Biomolecules)food that we eat it must first be digested. How does it work? • Along the pathway through our body our food is broken down into very small molecules by digestive juices and enzymes

Can you label the main parts of your digestive system? Beginning (mechanical and chemical)

The chewing, softening and breaking up food is called mechanical digestion. Which makes it have a larger surface area, then and enzyme in your saliva called amylase starts breaking the carbohydrate into sugar. Salivary amylase begins the chemical digestion of starch into maltose. Once chewed the food is now called a bolus

The bolus then moves through the pharynx and into esophagus and then pushed down the oesophagus to the stomach by PERISTALSIS.

What is peristalsis?

Peristalsis is the contraction and relaxation of the circular muscles in the wall of the gut.

When the muscle relaxes the food drops down and

when it contracts at the top the food at the bottom is pushed down

Purpose of the muscular stomach: to temporarily store ingested food, partially digest, and kill bacteria.

The food is then in the stomach, the food is churned around by more waves of peristalsis to make it into mush, and it mixes with gastric juice.

In the stomach gastric juices contain an enzyme called pepsin which breaks down, yup you guessed it, protein, into smaller peptides (amino acids). pH2 It also contains hydrochloric acid which kill bacteria and makes the optimum PH for this enzyme, meaning it will work at its best at a lower PH. HCL also kills bacteria. The partially digested food, now called, chyme is ready to enter the small intestine through the pyloric sphincter. About 23 feet for the ave. person.

The pancreas secretes a number of enzymes into the small intestine: trypsin, chymotrypsin, pancreatic lipase, and pancreatic amylase via the pancreatic duct. What do each of these enzymes do? Bile is another enzyme secreted into the small intestine, it is not a digestive enzyme but an emulsifier: it mechanically breaks up fats into smaller fat droplets. Bile is made in the liver and stored in the gall bladder

These enzymes complete the digestion of fats to fatty acids, glycerol, (carbohydrate) to simple sugars and protein to amino acids. Oh I see, what then?

The ileum is specially adapted for absorption, passing digested food into the blood. It is very long to allow time for digestion

It has a very large surface area due to the presence of villi (finger like projections) and microvilli This allows rapid diffusion of the products of digestion. Aren’t villi walls only one cell thick?

Yes, this helps speed up the diffusion. Within each villus there are lymph vessels, called lacteals that absorb fatty acids.

Hormones involved in digestion: Gastrin: which stimulates stomach cells to produce gastric juice. Secretin: stimulates pancreas to produce bicarbonate and digestive enzymes. Cholecystokinin: stimulates the secretion of pancreatic enzymes and release bile.

The food will then move to the large intestine and reabsorb water and salt. It harbours harmless bacteria that break down undigested food and in the process provide essential vitamins, Vitamin K. The left over undigested food, called feces, then moves out into the rectum.

Review • • • •

Molars (tear food apart-break plastic bag). Saliva (use spray bottle to squirt on food). Pancreatic juices (spray on food). Small intestines (absorb food, find plastic bags of candy and pass to blood). • Blood (transports food, distribute the food to every cell/participant). • Large intestine (reabsorbs moisture, sponge up water on the floor). • Rectum (puts the waste papers in the trash can).

How much did you remember? What enzyme is in saliva?

What does that help break down? What type of food is broken down in the stomach?

What happens to food that can’t be digested? What is the function of bile?

Well here’s what I got! 1)Amylase 2) That starts to break down carbohydrates

3) Proteins, by an enzyme called protease 4) It is passed out of the body through the anus 5) It neutralises the acid that was added in the stomach. This helps the small intestine work more effectively. Well done 5/5!

Each part of your digestive system has a special job! http://dsc.discovery.com/tv-shows/othershows/videos/assignment-discovery-shorts06-07-07-08-human-digestion.htm

• Lets put it all together! – Digestion animation – http://www.medtropolis.com/VBody.asp

Why does your stomach growl? •

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The digestive system is, in essence, a long tube that starts at the mouth and ends at the anus. This tube connects with the various organs and passages that play important roles in digestion. One of the most important things to know about the digestive system is the manner in which it propels food. Waves of muscle contractions move and push the contents continually downward in a process called peristalsis. In addition to moving your meal along its digestive path, these contractions also help churn food, liquid and different digestive juices together, rendering them into a gooey mix known as chyme. Stomach growling is the result of this process. Moving with those solid and liquid chyme ingredients are gasses and air. As all these ingredients get pushed around and broken down into easy-to-absorb bits, pockets of air and gas also get squeezed and create the noises we hear. Stomach growling can happen at any time -- not just when you're hungry -- but if there's food in your stomach or small intestine, the growling becomes quieter. It's like putting a pair of sneakers in the dryer by themselves versus with a load of towels. The towels muffle the noise of the shoes as they bounce around