DigestiveSystem2013 - holyoke

Download Report

Transcript DigestiveSystem2013 - holyoke

Digestive
System
Mouth
Liver
Esophogus
Stomach
Pancreas
Large intestine
Small intestine
Rectum
Anus
Digestion: Accessory Organs
• Liver
• Gall Bladder
• Pancreas
Why Do We Eat?
• Regardless of what an animal eats, an
adequate diet must satisfy three
nutritional needs
– Fuel for all cellular work
– The organic raw materials for biosynthesis
– Essential nutrients, substances such as
vitamins that the animal cannot make for
itself
• Nearly all of an animal’s ATP generation
– Is based on the oxidation of energy-rich
molecules: carbohydrates, proteins, and
fats
• Glucose is a major fuel for cells
• Its metabolism, regulated by hormone
action, is an important example of
homeostasis
1 When blood glucose
level rises, a gland called
the pancreas secretes insulin,
a hormone, into the blood.
2 Insulin enhances the
transport of glucose into body
cells and stimulates the liver
and muscle cells to store
glucose as glycogen. As a
result, blood glucose level
drops.
STIMULUS:
Blood glucose
level rises
after eating.
Homeostasis:
90 mg glucose/
100 mL blood
4 Glucagon promotes
the breakdown of
glycogen in the
liver and the
release of glucose
into the blood,
increasing blood
glucose level.
STIMULUS:
Blood glucose
level drops
below set point.
3 When blood glucose
level drops, the pancreas
secretes the hormone
glucagon, which opposes
the effect of insulin.
• When fewer calories are taken in than
are expended
– Fuel is taken out of storage and oxidized
Obesity as a Human Health
Problem
• The World Health Organization
– Now recognizes obesity as a major global
health problem
• Obesity contributes to a number of
health problems, including
– Diabetes, cardiovascular disease, and colon
and breast cancer
Caloric Imbalance
• Undernourishment
– Occurs in animals when their diets are
chronically deficient in calories
– Can have detrimental effects on an animal
• Overnourishment
– Results from excessive food intake
– Leads to the storage of excess calories as
fat
100 µm
The White House's
task force on
childhood obesity is
tackling obesogens
and the
Environmental
Protection Agency
has pumped $20
million into studying
them.
BONUS!!!!
http://www.motherearthnews.com/naturalhealth/atrazine-probable-obesogenzwfz1202zhun.aspx#axzz2NX2P5Mmb
• Researchers have discovered
– Several of the mechanisms that help
regulate body weight
• Over the long term, homeostatic
mechanisms
– Are feedback circuits that control the
body’s storage and metabolism of fat
• Several chemical signals called hormones
– Regulate both long-term and short-term
appetite by affecting a “satiety center” in the
brain
Secreted by the stomach
wall, ghrelin is one of the
signals that triggers feelings
of hunger as mealtimes
approach. In dieters who lose
weight, ghrelin levels increase,
which may be one reason
it’s so hard to stay on a diet.
Produced by adipose (fat)
tissue, leptin suppresses
appetite as its level increases.
When body fat decreases,
leptin levels fall, and appetite
increases.
Ghrelin
The hormone PYY,
secreted by the small
intestine after meals,
acts as an appetite
suppressant that
counters the appetite
stimulant ghrelin.
Insulin
Leptin
PYY
A rise in blood sugar level
after a meal stimulates
the pancreas to secrete
insulin (see Figure 41.3).
In addition to its other
functions, insulin suppresses
appetite by acting on the brain.
http://www.youtube.com/watch?v=BwqAel
WSgHk
• The complexity of weight control in
humans
– Is evident from studies of the hormone
leptin
• Mice that inherit a defect in the gene for
leptin
– Become very obese
Obesity and Evolution
• The problem of maintaining weight
partly stems from our evolutionary past
– When fat hoarding was a means of survival
– *Journal Entry – Article Summary! – TYPED
– DUE MONEY!
• A species of birds called petrels
– Become obese as chicks due to the need to
consume more calories than they burn
Figure 41.7
Digestion
• The process of PHYSICALLY
(mechanically) and CHEMICALLY…
Changing the composition of food
into simpler substances that your
cells can use for growth, repair
and maintenance.
Digestive System
• As food is digested, it passes through
a muscular tube leading from the
mouth to the (GASTROINTESTINAL
TRACT/ GI TRACT).
• The GI tract is about 25 to 30 feet
in length and each part plays very
important functions!
Digestion: Physical/Mechanical
Changes
• Grinding and mixing by teeth
(MASTICATION) in the mouth and
muscular actions of the stomach and
small intestine and…
• Liquefying by the addition of water
and digestive juices in the mouth,
stomach and small intestine
Digestion: Chemical Changes
• In Chemical Digestion, food is mixed
with powerful acids and enzymes!
• Complex nutrients are broken down
into particles usable by cells:
- Polysaccharides and disaccharides to
monosaccharides (carb chains)
- Proteins to amino acids
- Fats to fatty acids to glycerol
Chemical Environment of the GI
Tract
Neutral in mouth
- (pH approx 7)
Acid in stomach
- (pH approx 2)
Neutral in small
intestine
- (pH approx 7)
Enzymes
•Big food molecules can’t pass
through cell membranes.
•ENZYMES are types of proteins used
to break up big molecules into small
ones (they act like chemical scissors).
•These small molecules can pass
through the wall of the small
intestine into the blood. They then
pass into cells and are used.
Big food molecules
can’t pass through cell
walls.
These small
molecules can
pass through the
wall of the small
intestine into the
blood.
ENZYMES are used
to break up big
molecules into small
ones (they act like
scissors).
Digestion: Mouth
• Physical Changes:
- First step in
digestion
- Teeth grind food
-Salivary glands add
water (99%)
• Chemical Changes:
-Salivary amylase
(digests starch…big
sugars) aka.
polysaccharides
Digestion: Esophagus
• Transport tube (10
inches)
• Muscular (muscular
contractions move the
food - peristalsis)
• Enables swallowing to
move bolus (food) from
the mouth to the
stomach
• No enzymes added
• Other tube in the
throat region?
Digestion: Stomach (3 hrs)
• pH Shift
• Gastric Glands in Stomach produce gastric
juices containing 3 types of cells
1. Mucus – lubricates/protects
2. Chief – pepsinogen (inactive pepsin) + HCL
- pepsin
3. Parietal – secretes HCL (pH 2..STRONG)
• pH rapidly decreases
• Protein digestion begins in the stomach as
the major gastric enzyme that begins to
break down protein is PEPSIN.
• The mixture of food and gastric juices is
called chyme…and it moves to the SI next!!
Gastric Ulcers
• Lesions in the lining
• Mainly caused by bacterium Helicobacter
pylori
Bacteria
1 µm
Mucus
layer of
stomach
Digestion: Small Intestine(SI) –
5-14 hours
• About 95% of digestion takes place in SI
• Coiled and folded
• Made of 3 sections: duodenum (12 inches),
jejunum (4ft) and ilium (5ft)….can stretch
to over 20 feet!!
• Peristalsis moves food through the SI
• Another pH shift…what happens?
• Bile from the liver and digestive enzymes
from the pancreas (proteases ex: trypsin for
protein digestion, pancreatic amylase for
carbohydrate digestion and pancreatic lipase
for fat digestion) further break down food
Liver
Bile
Gallbladder
Stomach
Intestinal
juice
Acid chyme
Pancreatic juice
Pancreas
Duodenum of
small intestine
Small Intestine – Site of
Nutrient Absorbtion!!!
• Walls of intestine pleated with folds
covered with villi. (increase surface
area)
• Function is to absorb nutrients in to
the BLOODSTREAM 
Digestion: Large Intestine
(aka: colon) – up to 3 days
• The small intestine is
connected to the large
intestine (3-5 feet
long in the body…5-6
stretched)
• Chyme is very liquid
when enters the LI, so
main function is to
ABSORB WATER!!
• Solid wastes called
feces leave through
the rectum and then
finally out the anus
(mucus/bile/cells from
lining of LI and water)
Accessory Organs
• Pancreas – gland behind stomach – secretes
bicarbonate to neutralize environment of SI,
produces 3 digestive enzymes to break down
carbs, protein and fat.
• Carbs – Pancreatic Amylase
• Protein –
• Fat –
• Liver – large gland above stomach. Produces
digestive juice called bile. (Helps to digest
fat)
• Gall Bladder – muscular sac that stores bile
Match the organ to its function!!
Mouth
Esophogus
Stomach
Liver
1. This is where water is absorbed.
2. Makes bile which breaks up fats and it is alkaline to
give the right pH for the enzymes in the S. intestine.
3. Makes all 3 enzymes.
4. Mixes the food with enzymes that digest proteins
AND contains acid to kill bacteria.
Pancreas
5. Produces more enzymes AND this is where the food
is absorbed through the gut wall into the blood.
Small
intestine
6. Chew and mix the food with saliva (contains
enzymes).
Large
intestine
7. Links the mouth to the stomach.
Rectum
8. Here food that can’t be digested is stored as
faeces and then leaves through the anus.
Well
Done!!