Download Chapter 26

Chapter 26
Drastic Measures
Morbidly obese
• How did Amy Jo become obese?
• A person is obese when they weigh 20% more
than their ideal body weight
– Body mass index about 30
• Morbid obesity is defined as being 100
pounds or more over one’s ideal body weight
or BMI of 40 or higher.
• What was Amy’s BMI?
Surgery
• Several types of bariatric, or weight-loss, surgery
– Adjustable gastric banding
• Surgeon wraps an adjustable band around the stomach to
make it smaller so it holds less food
– Gastric bypass
• Stomach is surgically made smaller and small intestine is
rerouted.
• Shrinks the size of stomach and alters the digestion and
absorption of food
– Some risk involved with either method. What are
limitation to gastric bypass? Why do the surgery?
The Digestive System
• Heterotrophic organism
• Digestion, the
mechanical and chemical
breakdown of food into
subunits so that nutrients
can be absorbed, begins
immediately after
ingestion (the act of
taking food into the
mouth).
The Digestive System
• The digestive tract is the central pathway of
the digestive system that transforms the food
we eat into a form our bodies can use and rids
the body of the waste left over once usable
nutrients and energy are removed from food
we have taken in.
The Digestive System
• The digestive tract is a long muscular tube
that pushes food between the mouth and the
anus.
• As the muscles relax and contract, the tube
pushes food along.
• The tube receives inputs from various other
organs including the salivary glands,
gallbladder, liver, and pancreas.
The Upper Digestive System
• When food enters the mouth, chewing
mechanically breaks it down into smaller pieces.
Salivary glands secrete enzymes into saliva,
which chemically dismantle macromolecules
into their subunits.
The Upper Digestive System
• The tongue, a muscular organ in the mouth
that aids in swallowing, compresses the food
into a ball and works it to the back of the
mouth.
The Upper Digestive System
• When we swallow, food is propelled along the
esophagus, the section of the digestive tract
between the mouth and the stomach, by
rhythmic waves of contracting muscles in a
process called peristalsis.
The Upper Digestive System
• The stomach is an expandable muscular organ
that stores, mechanically breaks down, and
digests proteins in food. The stomach
contains acid that can inactivate potentially
harmful bacteria ingested with our food.
The Upper Digestive System
• Stomach acid has a pH of close to 1, and its action
helps protect us against food-borne diseases.
• Stomach acid also denatures proteins in the
food, unfolding their three-dimensional
structures into linear strands.
• This makes it easier for the enzyme pepsin, which
is produced in the stomach, to chemically break
proteins apart into individual amino acids.
The Upper Digestive System
• Like the esophagus, the stomach is also
muscular, expanding and contracting as it
accepts food and churns it.
• Each time it contracts, stomach acid mixes
with food, creating a soupy mixture called
chyme.
The Upper Digestive System
• While the stomach can absorb some
substances, such as water, ethanol, and
certain drugs, directly into the bloodstream,
most of the chyme is pushed farther into the
small intestine, where it is further processed.
The Small Intestine
• The small intestine is the organ in which the
bulk of chemical digestion and absorption of
food occurs.
The Small Intestine
• The duodenum is the first portion of the small
intestine. The duodenum receives chyme
from the stomach and mixes it with digestive
secretions from other organs.
The Small Intestine
• The pancreas is an organ that helps digestion
by producing enzymes that act in the small
intestine, and by secreting a juice that
neutralizes acidic chyme.
The Small Intestine
• Because fats are hydrophobic, they don’t mix
well with the watery solutions in the small
intestine, making it difficult for fat-digesting
enzymes to break them down.
• The liver aids in digestion by producing bile
salts, which are chemically suited to dividing
large hydrophobic fat globules into smaller
droplets – that is, emulsifying them.
The Small Intestine
• Bile salts pass from the liver into the
gallbladder, which in turn stores them for
future use.
• Once fats are emulsified, a lipid-digesting
enzyme secreted by the pancreas called lipase
chemically breaks them down to release their
constituent fatty acids and glycerol.
The Small Intestine
• Once digested into
their smallest
subunits, food
molecules are
absorbed by
epithelial cells
lining the small
intestine in a stage
of digestion known
as absorption.
The Small Intestine
• The inner lining of the small intestine is folded
into finger-like projections called villi
(singular: villus) that are composted of many
densely paced epithelial cells.
• The folds greatly increase the surface area
through which the intestine can absorb
nutrients.
The Small Intestine
• The food molecules then pass into the blood
vessels of the circulatory system, which
transport them throughout the body,
• They are used as a source of nutrients and
energy to build and maintain cells.
The Large Intestine
• After chyme
passes through
the small
intestine, it
moves on to the
large intestine,
where remaining
water is absorbed
and solid stool is
formed.
The Large Intestine
• Within the colon – the first and longest
portion of the large intestine – fiber, small
amounts of water, vitamins, and other
substances mix with mucus and bacteria that
normally live in the large intestine.
The Large Intestine
• As waste travels through the colon, most of
the water and some vitamins and minerals are
reabsorbed into the body through the colon
lining.
• Bacteria chemically break down some of the
fiber to produce nutrients for their own
survival and also to nourish cells lining the
colon.
The Large Intestine
• As the large intestine expands and contracts, it
pushes what ultimately becomes stool (solid
waste material eliminated from the digestive
tract) into the rectum, from which is it
eliminated through the anus as feces.
Costs and Benefits of Surgery
• In 2007, Swedish researchers published results
from a study in which they followed about
2,000 obese patients who had undergone
weight-loss surgery – either gastric bypass or
surgical banding – over 15 years and
compared them to about 2,000 similarly
obese people who didn’t have surgery but
who were counseled in diet and exercise.
Costs and Benefits of Surgery
• After 10 years, those who had gastric bypass
surgery weighed 25% less than their
presurgery weight; those who had stomachbanding surgery were down about 15%.
Those who got traditional diet advice lost no
more than 2% of their weight.
• After 10 years, I’ve lost 15% of my weight
eating a traditional diet with light exercise.
Costs and Benefits of Surgery
• There were 129 deaths in the diet-only group,
mostly from weight-related heart disease and
cancer, and 101 deaths in the surgery group –
a large difference statistically.
• Deaths in the surgery group were also mainly
from heart disease and cancer, although there
were half the number of heart attack deaths
in this group compared with the diet group.
How do other organisms process food?
• Fungi do not have
digestive tracts. To
obtain nutrients, fungi
extend hyphae into
food sources.
• Individual hypha cells
then release digestive
enzymes directly onto
their food and absorb
the released nutrients
directly into their
cells.
How do other organisms process food?
• Sea anemones
digest their food
internally, but they
don’t have a
digestive tract like
humans. They have
a single,
multifunctional
digestive cavity
called a
gastrovascular
cavity.
How do other organisms process food?
• Photosynthetic
organisms do
not need
stomachs or a
digestive
system because
they are
autotrophs:
they make their
own food.