Transcript The Digestive System

Chemical
Digestion
Breaking food into
useable pieces for
the cell.
Chemical Digestion
The body is VERY well suited to take
food in all of its complex forms and
break it down into its smallest pieces!
This process of organic macronutrients
returning back to their smallest pieces
is known as chemical digestion.
The Goals
Transform carbohydrates into monosaccharides.
Transform lipids (triglycerides) into fatty
acids.
Transform proteins into amino acids.
Transform nucleic acids into a sugar, base and
a phosphate group.
Mechanical versus Chemical Digestion
Mechanical
– Changes the physical form of
food
Chew
Tear
Grind
Mash
Mix
Mechanical versus Chemical Digestion
Chemical
– Changes the chemical composition of food
with the aid of digestive enzymes
Carbohydrate into monosaccharides
Protein into amino acids
Lipids into fatty acids
Nucleic Acids into sugar, base, phosphate
group
How is it possible to break down complex
food into simple molecules?
– Digestive enzymes are special proteins that
help break up large molecules of food into
very tiny molecules that can be absorbed
and used by the cells in the form of
nutrition.
Phases of Digestion
1. Ingestion - mouth
2. Movement
3. Digestion – stomach and small
intestine.
4. Absorption – small intestine,
large intestine (water)
5. Further digestion
Accessory Parts of the
Digestive System
Organs that are not in the digestive tract
but helps in the digestion
– Teeth
– Tongue
– Salivary glands
– Liver
– Gall bladder
– Pancreas
Mouth
Functions:
– Food enters in the mouth or oral
cavity
– Tasting
– Mechanical breakdown of food
– Secretion of salivary glands
(salivary amylase)
Mouth
Structures in the mouth that aids digestion:
Teeth – cut, tear, crush and grind food.
Salivary glands – 3 pairs produce and
secrete saliva into the oral cavity.
– Parotid (beneath the cheeks)
– Submaxillary (below the jaw bone)
– Sublingual (below the tongue)
Role of Saliva – the first chemical
digestion site!
To moisten the food and contains enzymes
(salivary amylase) that begins digestion of
starch (glycogen into small polysaccharides,
or disaccharides) into smaller
polysaccharides.
Carbohydrate digestion is the only
macronutrient digestion that begins in the
mouth! Cool!
Carbohydrate digestion isn’t complete in the
mouth but it is a nice start!
Bolus!
The bolus is the food that you eat
that has been mechanically
crushed with the tongue, teeth,
hard and soft palate, and then
mixed with saliva to start the
beginning of chemical
carbohydrate digestion.
Cracker Experiment
Let’s build a bolus!
Mechanism of Swallowing
Swallowing is a coordinated activity of the
tongue, soft palate, pharynx and esophagus.
Phases
– Food is pushed into the pharynx by the
tongue. (voluntary)
– Tongue blocks the mouth
– Soft palate closes off the nose
– Larynx (Adam’s Apple) rises so the
Epiglottis (a flap of tissue) can close the
opening of the trachea.
Esophagus
To pass through the esophagus the bolus
must travel down the 10 inch tube, this
takes 8 seconds.
The wall of the esophagus contain smooth
muscles that contracts in wavy motion
(Peristalsis).
What is PERISTALSIS?
Peristalsis propels food and liquid
slowly down the esophagus into the
stomach.
Cardiac Sphincter (ring-like valve) relaxes
to allow food into the stomach.
Video of Peristalsis….SO COOL!
Peristalsis
Once a bolus is made it needs to
travel to the stomach
In the stomach the bolus is mixed with
GASTRIC JUICE!
In the Gastic juice there is HCl – hydrochloric
acid that has a pH of 2 and Pepsin.
The HCl disrupts the extracellular matrix and
kills the bacteria that was living on the food.
The acidic environment created by the HCl
turns ON or activates Pepsinogen into PEPSIN.
Inside the Stomach
Churns and grinds together the bolus into
smaller pieces.
Food is mixed with gastric juices
(hydrochloric acid and enzymes) secreted
by the stomach walls.
HCl helps break down food and kills
bacteria that came along with the food.
Stomach
Enzymes in the Stomach
Pepsin and HCl are the major enzymes
in the stomach.
Pepsin – converts proteins into peptides
in the presence of HCl.
Converts the bolus into a liquid
(chyme) after 4 hrs of mechanical and
chemical digestion
Chyme passes through the pyloric
sphincter into the small intestine.
Movements in Stomach
Small Intestine
Inside the small intestine, triglycerides,
carbohydrates, proteins and nucleic acids
are all broken down into smaller digestible
products.
Remember that we want the
macronutrients to become smaller so they
can slip across the cell membrane into the
bloodstream.
Fats in the Small Intestine
Site of greatest amount of digestion and absorption
Triglycerides are broken down using bile from the
liver and the gallbladder into emulsified fats.
Pancreatic lipase from the pancreas takes the
emulsified fats and breaks them into fatty acids and
then down further into glycerol.
Fat digestion is complete in the small intestine thanks
to the actions of the bile and the pancreatic lipase.
Carbs in the Small Intestine
Carbohydrate digestion also happens in the
small intestine.
Pancreatic amylase from the pancrease breaks
polysaccharides down into disaccharides.
The Disaccharides can then be broken into
monosaccharides with the help of intestinal
enzymes.
We are talking about HYDRATION SYNTHESIS
Maltose is broken into glucose
Sucrose is broken into glucose
Lactose is broken into glucose
Protein in the Small Intestine
Peptidases from the pancrease help
convert polypeptides into dipeptides.
The intestinal enzymes from the intestinal
walls break dipeptides into amino acids.
Amino acids are the smallest part of a
protein. When the protein has been
digested into amino acids in the small
intestine, protein digestion is complete!
Nucleic Acids in the Small Intestine
We get nucleic acids from eating the DNA and
the RNA contained in food.
It is in the small intestine that we have nucleic
acid digestion.
Pancreatic enzymes from the pancreas break
nucleic acids down into nucleotides
The nucleotides are then converted into sugars,
bases and phosphates with the help from many
intestinal enzymes secreted from the intestinal
walls.
Nucleic acid digestion is completed in the small
intestine.
Small Intestine
Has folded inner walls covered with
fingerlike projections (villi; sing. – villus)
Each villus has tinier projections called
microvilli that absorbs digested food.
Villi and microvilli increases the surface
area of the small intestine for greater
absorption.
Peristalsis moves the undigested food to
the large intestine.
VILLI! 
Movement in small intestine:
Mixing: Segmental contraction that occurs in small intestine
Secretion: Lubricate, liquefy, digest
Digestion: Mechanical and chemical
Absorption: Movement from tract into circulation or lymph
Elimination: Waste products removed from body
Large Intestine
a.k.a. Colon
larger diameter, but shorter (5 ft)
Water is absorbed from the
undigested food making the waste
harder until it becomes solid.
Waste stays for 10 – 12 hours.
Large Intestine
Large Intestine
Waste is pushed into the expanded
portion (rectum) of the large intestine.
Solid waste stays in the rectum until it
is excreted through the anus as
feces.
Appendix hangs on the right side of
the large intestine.
Accessory Organs
Produce or store enzymes that helps in
digestion.
Liver
– Largest gland of the body
– Stores vitamins A,D,E,K
– Stores sugar and glycogen
– Produces bile (watery, greenish
substance)
– Secretes bile to the gall bladder via the
hepatic duct and cystic duct.
Accessory Organs
Gall bladder
– Stores bile in between meals
– Secretes bile to the duodenum through
the bile duct during mealtime.
Bile contains bile salts, pigments,
cholesterol and phospholipids.
Bile is an emulsifier NOT an enzyme.
Emulsifier – dissolves fat into the
watery contents of the intestine.
Accessory Organs
Pancreas
– Produces a juice that contains
enzymes (amylase and insulin) to
break down carbohydrates, fats
and protein.
– Secretes the juice into the
duodenum through the pancreatic
duct.
Path of Digestion
Mouth
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine
Anus