The Digestive System

Biology 11 McIntyre

Fun Facts

We eat about 500kg of food per year.1.7 liters of saliva is produced each dayYou can swallow even if you are standing on your head.

Every day 11.5 liters of digested food, liquids and digestive juices flow through the digestive system, but only 100mls is lost in feces. 

Food stays in your stomach for 2-6 hours.Small intestine, 5-6 meters longEsophagus is 25 cm longThe food stays in the small intestine from 1-4 hours

The food stays at the colon for 10 hours or for a several days

Fart FactsMost of us pass somewhere between 200 and 2,000 ml of gas per day (average, about 600 ml) in roughly 13-14 passages. Theseemissions are composed of five gasses: nitrogen (N2), oxygen (O2), carbon dioxide (CO2), hydrogen (H2), and methane (CH4).

produce more gas than meat-eaters because the intestinal enzymescan't digest the cellulose in vegetables' cell walls

Does your poop float? If so, that means bacteria in your gut are producing methane

The noise created by passing gas is not from the two buttocks vibrating together, as many believe. The noise created occurs as the gas passes through the anal sphincter. It's influenced by a combination of the volume of gas, the force with which it's expelled and the tightness of the anal sphincter.

Draw a Picture of the Digestive System!

Draw and label all the organs you can think of!

HUMAN DIGESTION

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter26/animation__organs_of_digestion.html

Digestion

Digestion is the breakdown of large, complex organic molecules into smaller components that can be used by the body.

Molecules need to be small enough to diffuse across plasma membranes.

Four Stages of DigestionIngestion – this is the consumption of or taking in of nutrients.

Digestion – the chemical breakdown of large organic molecules into smaller components by enzymes.

Absorption – the transport or delivery of digested nutrients to body tissues.

Egestion – the elimination of food waste materials from the body.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html

The Importance of Mechanical Digestion

Enzymes must make contact with the surface of food in order for chemical digestion to occur.

Why is chewing your food important?

Stuck? Consider this:what is the surface area of the Rubic’s cube?

What would be the surface area if you could break all the little cubes apart?

Alimentary CanalThe human digestive tract is often referred to as the alimentary canal.

The alimentary canal of a normal adult is approximately 6.5 to 9 meters long.

It runs from mouth to anus!

What organs/structures make up the alimentary canal? Which contribute to digestion? Which don’t?

Mechanical DigestionPhysical breakdown of food begins with the teeth grinding the food and increasing its surface area. An increase surface area allows for easier chemical digestion

Bacteria living in the mouth can feed off of nutrients sticking to the teeth and cause tooth decay.

youtube endoscopy

Saliva Saliva is released from the salivary glands and begins chemical digestion of starches. Saliva contains the enzyme salivary amylase which breaks down starches into simpler carbohydrates. (chemical digestion)

Saliva also moistens and lubricated food, making it easier to swallow.

Do the cracker challenge!!!!

Taste Buds As the food particles dissolve in the saliva they penetrate the cells of the taste buds located on the tongue and cheeks.

Humans can differentiate between sweet, sour, salty and bitter.

It used to be thought that specific regions of the tongue were responsible for bitter/sweet/sour and salty

SwallowingSaliva also lubricates the food and helps to form a bolus, the ball of food that is swallowed.

youtube swallowing

EsophagusThe bolus of food moves down the esophagus propelled by wave-like muscular contractions known as peristalsis.

Peristalsis moves food all the way through the gastrointestinal tract.

StomachThe stomach acts as a temporary storage site for food. Food usually spends about 4 hours in the stomach. It has ridges which allow it to expand to store about 1.5 litres of food.

The stomach is also the site of initial protein digestion.

endoscopy youtube

StomachMovement of food into and out of the stomach is controlled by circular muscles known as sphincters.

The cardiac (lower esophageal) sphincter allows food from the esophagus to enter and prevents food from going back up into the esophagus.

The pyloric sphincter slowly releases partially digested food into the small intestine. The partially digested food is called chyme.

stomach pyloris youtube.com

StomachMillions of cells lining the stomach secrete various fluids known collectively as gastric fluids.

Gastric fluid consists of mucus, hydrochloric acid, pepsinogens and other substances.

Mucus coats and protects the lining of the stomach. Hydrochloric acid kills any harmful substances that have been ingested and it also converts pepsinogen into pepsin.

Pepsin is a protein digesting enzyme that breaks large protein chains into smaller chains.

Stomach pHThe pH environment of the stomach normally ranges between 2.0 and 3.0 on the pH scale.

The high acidity allows pepsin to work and makes the HCl effective at killing pathogens

Stomach UlcersA stomach ulcer is a lesion in the lining of the stomach. It occurs when the protective mucus lining breaks down and the cell membranes are exposed to the HCl and pepsin

Most stomach ulcers are linked to the bacterium shown on the right known as Heliobacter pylori.

EndoscopyAn endoscope (shown on the right) can be used to view things such as stomach ulcers or as shown below, a tumor growing in the large intestine.

The endoscope can also extract small pieces of tissue for a biopsy.

Small and Large IntestineThe intestines are named for their diameter, not length.

The small intestine is up to 7 m in length but only 2.5 cm in diameter.

The large intestine is only 1.5 m in length but 7.6 cm in diameter.

Small IntestineIn mammals the length of the small intestine is directly related to their diet.

Due to the fact that meats are easier to digest than plant materials, carnivores (lion) will have a shorter intestine than herbivores (rabbit). The length of the digestive tract of omnivores falls somewhere in the middle.

Anatomy of the Small IntestineThe majority of chemical digestion occurs in the first of three sections of the small intestine known as the duodenum.

This section also contains an opening from the bile duct and pancreatic duct through which bile and pancreatic enzymes enter the small intestine.

Small IntestineFood enters the small intestine as a semi-solid mixture known as chyme. The chyme is acidic due to the HCl in the stomach so it needs to be neutralized.

The presence of the acidic chyme in the small intestine triggers the conversion of prosecretin into secretin which is absorbed into the blood stream and carried to the pancreas

http://www.youtube.com/watch?v=D76qndUOSz4&feature=fvwrel

PancreasThe pancreas is an accessory organ of the digestive system. It releases chemicals to aid in digestion.

Secretin will stimulate the pancreas to release a solution containing bicarbonate ions into the small intestine where it will neutralize the acidic chyme and raise the pH from 2.5 to 9.0. This inactivates the pepsin.

Stop & ThinkAcidic chyme is released from the stomach into the duodenum. How is this chyme neutralized? How is this process regulated?

Pancreas and Digestion

The pancreas also releases digestive enzymes that break down the three macromolecules: carbohydrates, lipids and proteins.

Pancreas & ProteinsTrypsinogen, a protein-digesting enzyme is released into the small intestine where it is converted into trypsin by enterokinase (another enzyme) and it breaks down large protein chains into smaller chains.

The final step in protein digestion occurs with the release of erepsins from the pancreas and they break the smaller chains into individual amino acids.

Stop & ThinkFill in the graphic organizer that summarized the complete breakdown of long chain polypeptides in the duodenum.

Use the following terms:Enterokinase, Individual amino acids, trypsin, trypsinogen, Long- chained polypeptides, Shorter-chained polypeptides, erepsin

Stop & Think

trypsinogen

Long-chained

polypeptides

trypsin

Shorter-chained

polypeptides

erepsin

Individual amino acids

enterokinase

Fill in the graphic organizer that summarized the complete breakdown of long chain polypeptides in the duodenum.

Use the following terms:Enterokinase, Individual amino acids, trypsin, trypsinogen, Long- chained polypeptides, Shorter-chained polypeptides, erepsin

Pancreas and CarbohydratesAmylase enzymes are released from the pancreas that break large carbohydrate chains into small chains called disaccharides.

Then the small intestine releases disaccharide enzymes which break those small chains into individual sugars.

Pancreas and LipidsThe pancreas also releases enzymes known as lipases that break down fats into fatty acids and glycerol.

The lipases include pancreatic lipase and phospholipase.

Before lipids can be broken down by lipases they must first be emulsified.

LiverThe liver is a large accessory organ of the digestive system that is constantly producing a fluid known as bile.

Bile is stored in the gall bladder until it is needed in the small intestine.

Liver and Gall BladderThe presence of lipids in the small intestine trigger the release of the hormone cholecystokinin (CCK) from cells that line the duodenum. CCK is carried in the blood to the gall bladder which triggers the release of bile.

Bile contains bile salts that emulsifies fats which means it breaks them into smaller droplets so they can be digested.

Stop & ThinkSummarize the role of CCK in the emulsification of fat in the duodenum.

GallstonesBile contains cholesterol which can acts as a binding agent and cause bile salts to crystallize into gallstones.

Gallstones can block the bile duct and inhibit fat digestion while causing a lot of pain.

JaundiceJaundice is a yellow discoloration of the skin and tissues caused by a collection of bile pigments in the blood.

The pigments are a result of the liver breaking down hemoglobin from red blood cells and the products are stored in the gall bladder.

Detoxification and the Liver

The liver is also able to detoxify many substances in the body by making them soluble and they can then be dissolved in the bloodstream and eliminated in urine.

One example would be alcohol. Alcohol can damage liver cells which are replaced by connective tissues and fat. The result is cirrhosis of the liver (shown left).

Absorption of MaterialsChemical digestion of nutrients is completed by the time it reaches the large intestine.

Now that nutrients are small enough they need to be absorbed into the blood stream so they can diffuse inside cells.

Large IntestineThe large intestine or colon stores waste products long enough so that water can be reabsorbed from the wastes.

Along with the water, some inorganic salts, minerals and vitamins are absorbed.

Large IntestineThe large intestine is home to several different types of bacteria.

These bacteria use waste materials to synthesize vitamins B and K. This is an example of a symbiotic relationship.

CelluloseCellulose is a long chain carbohydrate found in the cell wall of plant cells.

Humans cannot digest cellulose however it provides bulk which promotes the movement of the waste products out of the colon.

CelluloseCellulose is more commonly known as fiber. Fiber helps to remove wastes and therefore toxins from the body.

If you have a diet low in fiber you will have fewer bowel movements which means toxins remain in your body for longer periods of time.

Absorption of NutrientsMost nutrients are absorbed in the small intestine.

The small intestine is lined with millions of small finger-like projections known as villi. The villi increase the surface are of the small intestine which increases its ability to absorbed digested nutrients.

Structure of the VillusEach villus contains a capillary network along with a lacteal.

End products of protein and carbohydrate digestion enter the capillary network.

End products of fat digestion are absorbed into the lacteal. The lacteal is a vessel of the lymphatic system.

Microvilli