HUMAN DIGESTIONHUMAN DIGESTION

DigestionDigestion

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

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

Four Components of Four Components of DigestionDigestion

IngestionIngestion – this is the consumption of – this is the consumption of or taking in of nutrients.or taking in of nutrients.

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

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

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

IngestionIngestion Food enters the Food enters the

human digestive human digestive tract through the tract through the mouth or oral cavity. mouth or oral cavity.

Humans are Humans are considered chunk considered chunk feeders because they feeders because they consume chunks of consume chunks of food that are then food that are then mechanically broken mechanically broken down.down.

Alimentary CanalAlimentary Canal

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

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

Mechanical DigestionMechanical Digestion Physical breakdown of Physical breakdown of

food begins with the food begins with the teeth grinding the teeth grinding the food and increasing its food and increasing its surface area. An surface area. An increase surface area increase surface area allows for easier allows for easier chemical digestionchemical digestion

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

Saliva Saliva

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

Taste BudsTaste Buds

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

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

SwallowingSwallowing

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

EsophagusEsophagus

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

Peristalsis moves Peristalsis moves food all the way food all the way through the through the gastrointestinal tract.gastrointestinal tract.

StomachStomach

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

The stomach is also The stomach is also the site of initial the site of initial protein digestion.protein digestion.

StomachStomach Movement of food into and Movement of food into and

out of the stomach is out of the stomach is controlled by circular controlled by circular muscles known as muscles known as sphincters.sphincters.

One at the top of the One at the top of the stomach allows food from stomach allows food from the esophagus to enter and the esophagus to enter and prevents food from going prevents food from going back up into the esophagus.back up into the esophagus.

Another located at the Another located at the bottom slowly releases bottom slowly releases partially digested food into partially digested food into the small intestine. The the small intestine. The partially digested food is partially digested food is called called chymechyme..

StomachStomach Millions of cells lining the stomach secrete Millions of cells lining the stomach secrete

various fluids known collectively as gastric various fluids known collectively as gastric fluids.fluids.

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

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

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

Stomach pHStomach pH

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

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

Stomach UlcersStomach Ulcers An stomach ulcer is a An stomach ulcer is a

lesion in the lining of lesion in the lining of the stomach. It occurs the stomach. It occurs when the when the protective protective mucusmucus lining breaks lining breaks down and the cell down and the cell membranes are membranes are exposed to the HCl and exposed to the HCl and pepsinpepsin

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

EndoscopyEndoscopy

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

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

Small and Large IntestineSmall and Large Intestine The intestines are The intestines are

named for their named for their diameter, not diameter, not length.length.

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

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

Small IntestineSmall Intestine In mammals the length In mammals the length

of the small intestine is of the small intestine is directly related to their directly related to their diet. diet.

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

Anatomy of the Small Anatomy of the Small IntestineIntestine

The majority of chemical The majority of chemical digestion occurs in the digestion occurs in the first of three sections of first of three sections of the small intestine the small intestine known as the known as the duodenumduodenum..

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

Small IntestineSmall Intestine Food enters the small Food enters the small

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

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

PancreasPancreas The pancreas is an The pancreas is an

accessory organ of the accessory organ of the digestive system. It digestive system. It releases chemicals to releases chemicals to aid in digestion.aid in digestion.

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

Pancreas and DigestionPancreas and Digestion

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

Pancreas & ProteinsPancreas & Proteins TrypsinogenTrypsinogen, a protein-, a protein-

digesting enzyme is digesting enzyme is released into the small released into the small intestine where it is intestine where it is convertes into trypsin and convertes into trypsin and it breaks down large it breaks down large protein chains into protein chains into smaller chains. smaller chains.

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

Pancreas and Pancreas and CarbohydratesCarbohydrates

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

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

Pancreas and LipidsPancreas and Lipids The pancreas also The pancreas also

releases enzymes releases enzymes known as lipases that known as lipases that break down fats into break down fats into fatty acids and fatty acids and glycerol.glycerol.

The lipases include The lipases include pancreatic lipase and pancreatic lipase and phospholipase.phospholipase.

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

LiverLiver

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

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

Liver and Gall BladderLiver and Gall Bladder The presence of lipids The presence of lipids

in the small intestine in the small intestine trigger the release of trigger the release of the hormone the hormone cholecystokinin (CCK) cholecystokinin (CCK) which triggers the which triggers the release of bile from the release of bile from the gall bladder.gall bladder.

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

GallstonesGallstones Bile contains Bile contains

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

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

JaundiceJaundice Jaundice is a yellow Jaundice is a yellow

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

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

Detoxification and the LiverDetoxification and the Liver The liver is also able to The liver is also able to

detoxify many detoxify many substances in the body substances in the body by making them by making them soluble and they can soluble and they can then be dissolved in then be dissolved in the bloodstream and the bloodstream and eliminated in urine.eliminated in urine.

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

Absorption of MaterialsAbsorption of Materials

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

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

Large IntestineLarge Intestine

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

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

Large IntestineLarge Intestine

The large intestine The large intestine is home to several is home to several different types of different types of bacteria.bacteria.

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

CelluloseCellulose Cellulose is a long Cellulose is a long

chain carbohydrate chain carbohydrate found in the cell found in the cell wall of plant cells.wall of plant cells.

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

CelluloseCellulose Cellulose is more Cellulose is more

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

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

Absorption of NutrientsAbsorption of Nutrients Most nutrients are Most nutrients are

absorbed in the small absorbed in the small intestine.intestine.

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

Structure of the VillusStructure of the Villus Each villus contains a Each villus contains a

capillary network along capillary network along with a lacteal.with a lacteal.

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

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

MicrovilliMicrovilli