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Unit 4 – part 1
•We eat about 500kg of food per year.
•We make approximately 1.7 liters of saliva every day.
•Every day 11.5 liters of digested food, liquids and digestive
juices flow through the digestive system, but only 100 mL is lost
in feces.
•Digestive problems cost Americans $50 billion each year in
both direct costs and absence from work.
•By age 50, many people will produce only 15% of the
Hydrochloric Acid (stomach acid) they released at age 25.
•Most of us pass somewhere between 200 and 2,000 ml of gas
per day (average, about 600 ml) in roughly 13-14 passages.
•How big is your stomach ?
An adult’s stomach holds about 1 liter of food. A child’s stomach
holds a little bit less. Your stomach gets bigger the more you eat. A
large adult can eat and drink up to 4 liters of food and liquid at one
meal!
•How long are the intestines ?
The small intestine is more than three times as long as the whole
body ! In an adult, this is about 21 feet long. The large intestine is
another 5 feet long. The whole tube from the mouth to the anus is
about 30 feet long. Wow !
•As a group, vegetarians produce more gas than meat-eaters
because the intestinal enzymes can't digest the cellulose in
vegetables' cell walls
Functions of the Digestive
System
• Ingest food
• Secretes (enzymes, bile, HCl) to assist in digestion
• Digests macromolecules
• Absorbs food
•to make energy
•to help us grow and repair ourselves
•
Eliminates indigestible waste
Four Steps of Digestion
1.
2.
3.
4.
Ingestion of food in mouth
Mechanical & Chemical digestion
Absorption of molecules
Elimination of indigestible substances
PATHWAY
Mouth ->Pharynx>Esophagus->Stomach->
Small Intestine->Large
Intestine-> Rectum->Anus
3 Accessory Organs
Assist in digestive process
Liver, Gall Bladder
Pancreas
Mechanical digestion
– Large piece of food become smaller ones
without creating a new product
– Examples:
• Chewing of food in the mouth
• Churning and mixing of food in the stomach
Chemical digestion
– Enzymes chemically break down
macromolecules into smaller products that can be
absorbed
– Example: polymer → monomer
Functions:
1. Ingestion
2. To begin digestion:
a) mechanical
b) chemical
1) Teeth
• Begins mechanical
digestion to increase SA
of food for enzymes to
act
2) Salivary Glands: produce
saliva, which:
a) Liquifies food
b) chemically digests - contains
salivary amylase (optimal pH 7)
c) Lubricates and softens the
BOLUS (saliva + chewed food).
d) Enzymes that kill bacteria
Starch
SALIVARY AMYLASE
maltose
3) Tongue (a muscle):
a. Contains taste buds
b. Moves the food
c. Pushes the BOLUS to the
back of the throat to the
‘swallow reflex center’.
Structure: region at the back of the throat.
Function: Swallowing: When food is placed on the ‘reflex
center’, the following things happen:
a) the soft palate covers nasopharynx
b) the epiglottis covers the trachea
(respiratory)
c) peristalsis of the esophagus begins
A flap of tissue that covers the trachea when we
swallow food and liquid
•Long muscular tube
•No digestion occurs here
•that connects to stomach via the
cardiac sphincter (ring of muscle
which stops acidic chyme from reentering the esophagus)
Dissected esophagus – notice the
thick, ribbed lining of the tract.
BOLUS moves through the
esophagus by PERISTALSIS (a
slow, rhythmic contraction)
Peristalsis continues down the
length of the entire digestive
tract.
Structure:
• thick walled, ‘J’ shaped organ
Functions:
1) churns & mixes food (mechanical
digestion)
•aided by the ridges or rugae in
the stomach layer
2) Stores food & releases slowly to
small intestine
3) Makes gastric juice – secreted by
gastric glands (chemical digestion)
RUGAE
Gastric Juices contain:
1. water (solvent)
2. Pepsinogen (protein digestion)
3. Hydrochloric Acid (strong acid)
4. Mucous
HCl released when proteins enters
•creates pH of 2.5 - kills bacteria & denatures salivary amylase
• transforms pepsinogen (inactive) to PEPSIN (active
enzyme)
HYDROCHLORIC ACID
PEPSIN
•Pepsin hydrolyses proteins into smaller
called peptides
chains for aa
Pepsinogen
Protein
PEPSIN
peptides
Mucous secretions
protect stomach
cells from HCl
• An ULCER can
result if acid
penetrates the
mucous layer
Bolus leaves the stomach as an acidic liquid called CHYME.
pyloric sphincter, at the base of the stomach, will release
the chyme into small intestine at a slow, controlled rate.
3 regions:
1. Duodenum:
2. Jejenum:
The rest of chemical
digestion
3. Ileum: absorbs nutrients into BLOOD
& LYMPH
•increased rate of absorption
•the highly folded walls
creating a very large
surface area.
• folds in layer of small
intestine called VILLI.
• villi also have smaller folds
called MICROVILLI.
• Villi contains:
– Blood capillaries
absorb glucose,
aa and nucleotide
components
– Lacteals (lymph
capillaries) absorb
glycerol & fatty
acids
Chemical Digestion – from pancreatic
and intestinal juice
Physcial Digestion – with assistance
from gallbladder
• Small intestine connected to 2 accessory organs
1) Pancreas
2) Gallbladder
The pancreas is a dual organ
a) ENDOCRINE GLAND which makes hormones
insulin and glucagon.
b) EXOCRINE GLAND which make the enzymes to
digest carbs, fats, proteins and nucleic acids.
high blood sugar → insulin secreted
•
insulin removes glucose from the blood which:
1. causes the liver to store it as glycogen
2. promotes formation of fats
3. causes cells to absorb glucose
low blood sugar → glucagon secreted
•
glucagon causes the liver to break down glycogen
and release glucose into the blood
Diabetes
Type 1 (juvenile onset)
Type 2 (adult onset)
• Deficiency in insulin
• Not enough insulin or
enough but a problem
with insulin receptors
on cell membranes
•Results in high blood
glucose levels
•Controlled with diet
SALT + N (memory trick):
1. Sodium Bicarbonate
- neutralizes acidic chyme;
changes pH to 8.5 (basic)
2.Pancreatic Amylase - an enzyme that converts
starch to maltose.
3.Lipase - enzyme that converts lipids into fatty acids
and glycerol
4. Trypsin - an enzyme that converts proteins into
peptides.
5. Nucleases - enzymes that convert nucleic acids (DNA
and RNA) into nucleotides.
…and of course, water to hydrolyze these reactions
• Connected to Liver and small
intestine
• Function – store & send BILE
to SI via bile duct
• BILE is NOT an enzyme
• Helps in physical digestion of
LIPIDS
• Breaks LIPIDS into smaller
particles this is called
EMULSIFICATION
• Bile is made by liver
•largest internal organ.
•blood from the villi travels via
the hepatic portal vein to the
liver.
•liver acts as a ‘gatekeeper’ to
the blood by keeping levels of
various nutrients in the blood
constant.
Hepatic Portal System
• Absorbed nutrients
(from small intestine)
are taken to liver via
hepatic portal vein.
• Liver stores excess
glucose and glycogen,
releasing it as needed.
Liver – 6 functions – KNOW!!!
B.B.B.B.B.U.
1.
2.
3.
4.
5.
6.
Blood Sugar -regulates through insulin & glucagon
Blood detoxify – e.g. turns alcohol into fatty acids
Bile produce
Blood proteins produce – e.g. albumin, fibrinogen
Blood Cells red break down
Urea – produce
Regulates the blood glucose level
High blood sugar
Glucose
INSULIN
Glycogen
Low blood sugar
Glycogen
GLUCAGON
Glucose
Urea production
If necessary the liver can convert amino
acids into glucose to maintain glucose
concentration of plasma.
• this process produces urea
• removed by the kidneys in the
production of urine.
Cells of small intestine (duodenum) make and secrete
intestinal juices that will finish chemical digestion
1. Peptidases digest
peptides into a.a.’s
2. Nucleosidases digest
nucleotides into sugar,
phosphate & N-base
3. Maltase digests the
maltose into 2 glucose
molecules
Villi are finger-like projections
that cover the lining of the sm.
Intestine
•Increases SA & absorption
rate
Capillaries of the villi absorb
sugars, amino acids, &
nucleotides
Lacteals of the villi absorb
glycerol & fatty acids and transfer
to lymph.
Junction of Small and Large Intestine
Appendix
• Has lymph tissue to help fight infection
• Subject to inflammation = appendicitis
• May be removed
large in diameter, but short (1.5 m long) in length
It consists of:
1. colon
2. rectum
3. anus
Absorption of the water and salts
And receives & stores undigestible wastes & fibres
• has anaerobic bacteria, E.Coli , that:
1. eat the wastes and produce useful things that we need
to survive (ie: vitamin K and amino acids)
2.produce growth factors (proteins that stimulate cell
growth)
3. Produce waste of their own (methane gas) Phew!
At the end of the large intestine, wastes are transformed
into pasty ‘feces’ which build up in rectum until
message is sent to central nervous system to stimulate
bowel movement
The entire process
of digestion from
the mouth to the
anus lasts 24 hours.
• Sphincter muscle through which feces exits
the body
If feces moves through too slowly:
• Too much water is absorbed.
• feces become hard and you are constipated.
THE END...GET IT...
“THE END”