Transcript Slide 1

Digestion
Mechanical and Chemical Breakdown of
Ingested Food
3 Stages in Digestion
Digestion - breakdown of food into
particles/molecules small enough to pass
into the blood stream.
1.
2 types of digestion



2.
3.
mechanical (Mastication)
chemical (Enzymes)
Absorption of nutrients into the blood
stream
Elimination of indigestible nutrients
Organs and Glands of the Digestive
System










Mouth
Salivary Glands
Esophagus
Stomach
Small intestine
Liver
Pancreas
Gall bladder
Intestinal Glands
Large intestine
Enzymes of the Digestive System




Salivary amylase (starch  sugar)
Pepsin (proteins  peptones and proteoses)
Bile (emulisification of lipids)
Pancreatic Juice




Amylase (polysacchardies  disacchardies)
Trypsin (peptones and proteoses  peptides)
Lipase (lipids  gylcerol and fatty acids)
Intestinal Juice


Peptidase (peptides  amino acids)
Maltase (Disaccharide  Monosacchardies)
The Mouth

Mechanical breakdown of nutrients begins in the
mouth by chewing (Mastication).





The purpose of chewing is to increase the surface area of
food.
Chemical breakdown of starch also begins in
mouth. Starch is converted into glucose by salivary
amylase (secreted by the salivary glands)
This mixture of food and saliva is made into a mass
of food called a bolus and then pushed into the
pharynx by the tongue which triggers involuntary
swallowing.
The esophagus is a muscular tube whose muscular
contractions (peristalsis) propel food to the stomach.
Peristalsis – the wave action of muscle that moves
food through the digestive system.
The Stomach ( Churn, Churn, Churn)




During a meal, the stomach gradually fills to a capacity of 1 liter,
from an empty capacity of 50-100 milliliters.
 At a price of discomfort, the stomach can distend to hold 2 liters
or more.
The stomach secretes about 2 liters of gastric juices per day.
 Gastric juice contains hydrochloric acid, pepsinogen, and mucus
Hydrochloric acid (HCl) lowers pH of the stomach to activate
pepsinogen  pepsin. The acidic environment also helps to
liquefy foods.
 Pepsin is an enzyme that controls the hydrolysis of proteins into
peptides.
The stomach also mechanically churns the food. Chyme,
(liquefied food) the mix of acid and food in the stomach, leaves
the stomach and enters the small intestine.
The Small Intestine



The small intestine is the major site for
digestion and absorption of nutrients.
98% of digestion and 100% of absorption of
nutrients occurs in the small intestines.
Small intestine is made up of 3 parts



Duodenum
Jejunum
Ileum
From Stomach to Duodenum



Chyme – Liquefied food
Acidic Chyme is pushed from the lower part
of the stomach through the pyloric sphincter
into the Duodenum (first part of small
intestines).
The stomach empties over a 1 to 2 hour
period.
Small Intestines (Doudenum)



Chyme is pushed out of the stomach into the
small intestines. The acid chyme stimulates the
Liver and the Pancreas.
The pancreas secretes digestive enzymes and
stomach acid-neutralizing sodium bicarbonate.(2
pH  8 pH)
 Enzymes - Lipase, Amylase, Trypsin
The liver produces bile, which is stored in the
gall bladder before entering the bile duct into the
duodenum.
 Bile emulsifies fats (breaks fats into little pieces)
Carbohydrate Digestion step by step



The chyme is pushed into your small intestines
(duodenum) which triggers the release of
Pancreatic juice from the pancreas
Amylase is one of the enzymes in the pancreatic
juice which breaks down Polysaccharides into
disaccharides
Finally the intestinal glands release intestinal
juice which includes the enzyme maltase.
(jejunum)


Maltase breaks down the disaccharides into
monosaccharide which are absorbed by the blood
stream.
Monosaccharides are absorbed into blood
stream and carried to the cells (ileum)
Protein Digestion Step by Step





Proteins begin to be digested by Pepsin in the
stomach while being liquefied by the acid HCL.
The chyme is pushed into your small intestines
(duodenum) which triggers the release of
Pancreatic juice from the pancreas
Trypsin is one of the enzymes in pancreatic juice
which continues the breakdown of proteins into
Peptide bonds
Finally the intestinal glands release intestinal
juice which includes peptidase which breaks
peptide bonds into amino acids. (jejunum)
Those amino acids are absorbed into the blood
stream and carried to the cells (ileum)
Digestion of Lipids




The chyme is pushed into your small intestines
(duodenum) which triggers the release of
Pancreatic juice from the pancreas and bile from
your gall bladder.
Bile emulsifies (chews) the lipids to increase
surface area
Lipase that is found in pancreatic juice
hydrolyses lipids into a glycerol and 3 fatty acids
The products are absorbed by the small
intestines and carried to the cells for use.
(jejunum and ileum)
Enzymes and were they are Used




Salivary amalyase (starch  sugar) MOUTH
Pepsin (proteins  Polypeptides) STOMACH
Bile (emulisification of lipids) DUODENUM
Pancreatic Juice DOUDENUM




Amylase (polysacchardies  disacchardies)
Trypsin (peptones and proteoses  peptides)
Lipase (lipids  gylcerol and fatty acids)
Intestinal Juice JUJUMIN and ILEUM


Peptidase (peptides  amino acids)
Maltase (Disaccharide  Monosacchardies)
Villi and MircoVilli


The small intestine is lined with vill and microvilli
The purpose of villi and microvilli are to increase
surface area in the small intestines. Increase the
speed at which nutrients are absorbed


The small intestines a 6 meter long tube has a surface
area of 300 square meters or the surface area of a
500-600m long tube.
Each villus has a capillary network supplied by a
small artery. Absorbed nutrients pass through
the microvilli into the capillary (blood stream),
usually by passive transport (diffusion).
The Large Intestine






The large intestine is made up by the cecum, appendix,
colon, and rectum.
Digested food is pushed from the small intestines into
the large intestine.
No digestion takes place in the large intestines
Material in the large intestine is mostly indigestible
residue and liquid.
Water, and salts are absorbed, the remaining contents
form feces (mostly cellulose, bacteria, bilirubin).
Bacteria in the large intestine, such as E. coli, produce
vitamins (including vitamin K) that are absorbed.
There are 3 parts to
the Colon
1. Ascending Colon
2. Transverse Colon
3. Descending Colon
The Liver and Gall Bladder



The Liver makes Bile and stores it in the gall
bladder.
The Gall bladder sends bile to the small
intestine when the acidic chyme from the
stomach. Bile contains bile salts, which
emulsify fats, making them susceptible to
enzymatic breakdown.
The liver also stores excess glucose in the
form of glycogen.
The Pancreas


When the acidic chyme is pushed out of the
stomach into the small intestines. IT
simulates the pancreas to send pancreatic
juice, which neutralizes the chyme, begins
digestions of Carbohydrates, Lipids and
continues digestion of protein.
Pancreatic juice also contains Lipase which
digested emulsified Lipids
Stomach HCl

Hydrochloric acid does not directly function in
digestion:






it kills microorganisms that cause food poisoning.
lowers the stomach pH to between 1.5 and 2.5
activates pepsinogen (to pepsin) Pepsin is an enzyme
that starts protein digestion.
HCl inhibits further carbohydrate breakdown
started by salivary amylase.
HCl aids in the liquefaction of masticated food
Epithelial cells secrete mucus that forms a
protective barrier between the cells lining the
inside of the stomach and the stomach acids.
Ulcers




Peptic ulcers result when the protective mucus
fails and the HCl eats away at the lining of the
stomach.
Bleeding ulcers result when tissue damage is so
severe that bleeding occurs into the stomach.
Perforated ulcers are life-threatening situations
where a hole has formed in the stomach wall.
At least 90% of all peptic ulcers are caused by
Helicobacter pylori (bacteria). Other factors,
including stress and ibuprofen, can also produce
ulcers.