Download Chapter 18: Digestive and Excretory System

Chapter 16: Digestive System
and Nutrition
• The structure of the wall of the
small intestine allows it to move,
digest, and absorb food.
• Digestion is controlled by nervous
and hormonal mechanisms.
• A balanced diet is essential to
human health.
I. Digestion
A. Digestion is an enzyme-facilitated
chemical process
1. After eating, a series of events is started
that lead to your body cells being provided
with the nutrients that they need
a) Ingestion: eat the food
b) Digestion: series of chemical reactions,
whereby the ingested food is converted into
smaller and smaller molecular forms
c) Absorption: small molecular forms are
absorbed through the cells of digestive
system and pass into blood or lymphatic
vessels
d) Transport: circulatory system delivers
the small molecular nutrients to your body
cells
2. Food that we eat must be chemically digested
to a suitable size to cross cell membranes and
get into the bloodstream
3. Hydrolysis of food molecules into their
smallest components. Those components can
then be reassembled into macromolecules that
are useful to the body
B. Role of enzymes during digestion
1. Enzymes used for digestion are all
hydrolysis reactions
Enzyme
Location
Function
Lipase
Small intestine
Breakdown lipids
Amylase
Mouth: saliva and
small intestine
Breakdown starch
Endopeptidase
(trypsin)
Small intestine
Breakdown protein
Pepsin
Stomach
Breakdown protein
Note: Humans can’t digest cellulose from plants
since we don’t produce the enzyme cellulase
2. Enzymes are protein molecules that act as a catalyst
a) Reactions require a lower amount of energy to
react
b) Energy is typically in the form of heat
c) Enzyme reactions can occur at a lower
temperature
d) Humans maintain a stable body temperature of
98.6 °F or 37°C which is warm enough to maintain
good molecular movement and with help of
enzyme to provide enough activation energy for
reactions to occur
Section 38-2
The Digestive System
Mouth
Pharynx
Salivary glands
Esophagus
Liver
Gallbladder
(behind liver)
Stomach
Pancreas (behind
stomach)
Large intestine
Small intestine
Rectum
Interactive slide
Draw a diagram of the digestive system
• Zygote body Digital human
• Produce a large (A3 size or bigger), annotated diagram of the digestive
system. Include the following structures • mouth,
• esophagus,
• stomach,
• small intestines
• large intestine,
• anus,
• liver,
• pancreas and
• gall bladder.
Drawing video
C. Anatomy of the human digestive system: made
up of a long tube (alimentary canal) and two
accessory organs (pancreas and liver) connected
by ducts Overview clip
1. Mouth: teeth tear and chew food into small
particles
a) Mechanical digestion: chewing Digestion
b) Chemical digestion: involves a change in the
chemical nature of the nutrients Chemical
c) Salivary glands produce saliva: mixture of
water, mucus, and amylase (enzyme)
d) Saliva softens and lubricates food and breaks
down some starch
2. Esophagus: muscular tube that connects pharynx
with the stomach
a) Bolus: chewed up food that is swallowed into
the pharynx and then into the esophagus
b) Epiglottis closes over the trachea
c) Peristalsis: series of rhythmic muscular contractions
that move bolus through the esophagus
i) Smooth muscle that is controlled
by the autonomic nervous system
ii) Two layers of muscle: circular and
longitudinal
iii) Contracting fibers of the inner circular muscled
do make a circle
iv) Contracting fibers of the longitudinal muscles
are positioned at right angles to the circular
muscles
v) Peristalsis continues to move food through the
entire alimentary canal and is fast in esophagus and
slower in small intestines
vi) Peristalsis helps to churn the food in the
stomach
3. Stomach: sac like organ involved in mechanical and
chemical digestion
a) Three layers of smooth muscles turn and twist the
stomach to help churn the contents of the stomach
(mechanical digestion)
b) Inner lining of the stomach
is a thick, wrinkled mucus
membrane
c) Gastric pits: small openings in lining that release
secretions into the stomach
d) Acidic digestive fluid: mucus, enzymes, and
hydrochloric acid Stomach
e) Chemical Digestion: carried out by gastric fluid
i) Pepsin: enzyme that breaks down proteins
ii) Hydrochloric acid: lowers the pH for pepsin
to work and kills bacteria and dissolves minerals
iii) Mucus: forms protective coating for the
stomach against the hydrochloric acid
iv) Ulcer: sore in stomach because mucus lining
breaks down, caused by a bacteria
f) Formation of chyme: food and gastric fluid mixture
i) Cardiac sphincter: circular muscle between
esophagus and stomach
ii) Pyloric sphincter: circular muscle between
the stomach and small intestine that regulates the
flow of chyme
4. Liver: large organ located to the right of stomach
a) Many different functions
b) Secretes bile
c) Bile: breaks down fat into smaller pieces
d) Gallbladder: stores bile and releases it into the
small intestine
5. Pancreas: organ that lies behind the stomach
a) Produces two important hormones (insulin and
glucagon) involved in glucose metabolism
b) Three digestive enzymes: lipase, amylase, and
endopeptidase (trypsin) to make pancreatic juice
c) Contains sodium
bicarbonate that changes
the acidic chyme into a
base so enzymes can work
d) Fluids are released into the first portion of the
lumen (cavity) of the small intestine through a duct
The Liver and the Pancreas
Section 38-2
Liver
Bile duct
Gallbladder
Pancreas
Pancreatic duct
Duodenum
To small intestine
6. Small intestine: coiled tube 21 feet long that finishes
digestion and absorbs nutrients into the blood
a) Absorption: end products ( amino acids,
monosaccharides, glycerol, and fatty acids) of
digestion are transferred into blood and lymph
b) Three parts
i) Duodenum: first section that
finishes chemical digestion of chyme
ii) Jejunum: middle section
iii) Ileum: last section
c) Mucosa: cells in the inner lining of the small
intestine
d) Villi: small folds or projections inside
mucosa
i) Composed of many cells whose job
is to selectively absorb molecules
found in the lumen of the small
intestines
e) Microvilli: projections that extend into the
lumen and are from epithelial cells that are in
direct contact with the nutrients for absorption to
occur
Section 38-2
The Small Intestine
Villus
Small Intestine
Circular folds
Epithelial cells
Villi
Capillaries
Lacteal
Vein
Artery
f) Villi and microvilli greatly increase the
surface area for absorption
g) Interior of each villus contains a capillary
bed for nutrient absorption and transport of
digested monomers by the blood stream
h) Lacteal: small vessels of the lymphatic
system that absorbs some of the nutrients
and fatty acids Absorption
i) Substances absorbed through villi into
bloodstream or lymph fluid
• Water
• Glucose (other monosaccharides)
• Amino acids
• Nucleotides
• Glycerol
• Fatty acids
• Mineral ions
• Vitamins
Absorption small intestine clip Answers
7. Large intestine or colon
a) Minerals, vitamins, and water are absorbed from
the undigested material
b) Four parts: ascending, transverse, descending,
and sigmoid
c) Reflex contractions move the remaining material
out of the body through the anus
Digestive System Chart Prezi
D. Example of what happens as ingested food (starch)
moves through the system
1. Chemical digesting begins in mouth with saliva
containing amylase to hydrolyze starch into
maltose
2. Amylase stops working in the acidic environment
of the stomach
3. Chyme is released into the small intestine
4. Amylase is in the pancreatic juice
5. Slightly alkaline environment in the small
intestine allows amylase to work
6. Amylase continues to hydrolyze starch
into maltose and this continues as peristalsis
moves the chyme through the lumen of the
small intestine
7. Maltase (produced by inner lining of the
small intestine) catalyzes the hydrolysis of
maltose into 2 molecules of glucose
E. Transport mechanisms used by epithelial cells to
absorb nutrients
1. Passive mechanisms: no ATP used
a) Simple diffusion: movement of molecules
through cell membrane following a concentration
gradient (small molecules, fatty acids)
b) Facilitated diffusion: movement through cell
membrane following a concentration gradient using
a protein channel due to size and polarity of the
molecules (glucose and amino acids)
2. Active mechanisms: ATP is used
a) Membrane pumps: molecules move against the
concentration gradient by proteins using ATP to
pump the molecules across the membrane (glucose
and amino acids under certain conditions)
b) Endocytosis: molecules are trapped in an
infolding of the membrane and pass through to the
other side of the membrane as a vesicle
i) Pinocytosis: brings in a fluid (drinking)
ii) Phagocytosis: brings in particles (eating)
II. Exocrine secretions are fundamental to the
digestive process
A. Exocrine glands: produce a secretion that
is useful in a specific location in the body and
are taken to that location by a duct
1. Secretions to surface of the body
a) Lacrimal fluid: tears from lacrimal
glands and carried by a duct to the
surface of the eye
b) Perspiration: sweat glands and taken to the
skin
c) Milk: mammary glands for lactating
mothers
Comparison clip
2. Secretions to interior (lumen) of some parts of the
alimentary canal
B. Gastric secretions and their control
1. Stomach is a holding place for ingested
food and site of early steps of digestion
2. Some of the cells making up the lining of
the stomach are glandular (exocrine glands)
3. Three types of glandular cells located in gastric
pits extending down into the inner lining of the
stomach that secrete the components of gastric
juice
a) Hydrochloric acid
Clip
b) Pepsinogen
c) Mucus
4. Stomach prepares for digestion when the smell,
slight, or taste of food resulting in the autonomic
nervous system sending impulses to the medulla
oblongata
a) Medulla responds using the
parasympathetic division to send action
potentials through the cranial nerve (vagus
nerve) directly to the stomach
b) Stomach then produces and secretes HCl
and pepsinogen into stomach cavity
c) Same action potentials stimulate endocrine
cells in the lower portion of the stomach to
secrete gastrin
d) Gastrin: hormone that enters the blood and
is carried to other cells elsewhere in the
stomach and results in higher secretion of HCl
and pepsinogen
e) Pepsinogen is converted to pepsin (protein
digesting enzyme) when it comes in contact
with HCl Clip
5. Food enters the stomach
a) Walls of stomach become distended
(expanded due to internal pressure)
b) Autonomic nervous system signal by the
vagus nerve to the medulla oblongata
c) Medulla sends impulses back to glandular
cells of the stomach to continue and increase
production of HCl and pepsinogen
6. Valve at lower end of the stomach opens and
releases the chyme into the duodenum of the
small intestine
a) Set of signals that terminates the secretion of
HCl and pepsinogen from gastric pits
b) Secretin: hormone that enters the blood
and lowers the gastric pit activity
C. Role of HCl during the digestive process
1. Proteins enter the stomach in their 3D fibrous or
globular shapes: Many hydrogen and ionic bonds
between non-adjacent amino acids
a) Proteins will denature at pH conditions
outside their norm (low pH of the stomach)
b) Denatured: H and ionic bonds become
broken and protein opens up and digestive
enzymes are able to access the peptide bonds
between adjacent amino acids
2. Activating pepsinogen to pepsin
a) When pepsinogen comes into contact with
HCl, it undergoes a molecular modification
that activates the enzyme
b) Pepsin: catalyze the hydrolysis of large
polypeptide chains into smaller peptides and
works best in low pH environment
c) Small peptides are further digested by
enzymes later in the process Video
3. Control the ingestion of some pathogens
a) Highly acidic environment helps to kill
many harmful pathogenic bacteria
D. Stomach ulcers: sore in the stomach
1. Answers to scientific questions can sometime
change as it did with the cause of ulcers
a) Until the 1980’s it was believed that
nothing could live in the fluid of the
stomach due to its pH of 2
b) Ulcers were believe
to be caused by excess
production of HCl brought
on by stress
2. Researchers isolated living bacteria
(Helicobacter pylori) in the stomach
lining of patients suffering from ulcers
3. Summary of recent scientific information
a) H. pylori survives by burrowing beneath mucus
layer and infecting stomach lining cells
b) H. pylori uses urease enzyme to create ammonia to
neutralize stomach acid
c) H. pylori infections leads to gastritis and ulcers
d) Antibiotics can be used to treat infection
e) Patients infected for 20-30 years with H.
pylori are more prone to stomach cancer
f) H. pylori may be the most common bacterial
infection with 3 billion people infected
Video
Video
4. 1822, American physician, William Beaumont
saved the life of a Canadian trapper who had
suffered a shotgun wound to abdomen
a) Wound left a permanent hole in stomach wall
and allowed Beaumont to make observations and
take samples of the digestive process
5. Fistula: surgically implanted window that does
not harm the animal
a) Cow is fitted with a fistula for observing
and taking fluid samples from one of its
stomachs
E. Adaptations of villi epithelial cells for efficient
absorption
1. Epithelial villi cells: digested molecules must
pass through these cells in ordered to be absorbed
into either a capillary or lacteal on the interior of
each villus
2. Microvilli: microscopic finger-like projections
on the surface of each villus that faces into the
lumen of the small intestine
a) Function is to increase the surface area
for absorption
3. Epithelial villi cells contain mitochondria to
produce ATP for active transport of molecules across
the membranes of the villi
4.Pinocytosis: active transport mechanism used to
absorb molecules from the lumen of the intestine into
the interior of the villi cells and requires ATP from
mitochondria
5.It is the movement of digested molecules through
the selectively permeable membrane of the villi
epithelial cells that guarantees that the molecules
have completed the process of enzymatic digestion
6. Epithelial cells of villi are sealed to each other
by membrane-to-membrane protein seals
called tight junctions
7. Two cell membranes share some membrane
proteins and are held so tightly together that
most molecules cannot pass between them and
must be transported first into and then other of
the epithelial cells lining each villus
8. On the side of the villi epithelial cell closer to
the capillary bed (opposite the microvilli), the
plasma membrane has infoldings
(invaginations)
9. Basal labyrinth: infoldings increase the
surface area for transport out of the epithelial
cell
a) Similar function as the microvilli, but work
in the opposite direction
F. Importance of fiber in the diet
1. Almost all absorption of nutrients occurs
in the small intestine, some ingested
substance will never be digested and no
chance of being absorbed
2. Undigested substances continue into the large
intestine and become part of the solid wastes
(feces)
3. Materials that are not absorbed are egested
(become part of the waste material)
a) Cellulose: cell walls of ingested plant
material
b) Lignin: component of plant cell walls
c) Bile pigments
d) Bacteria: few survive the low pH in
stomach and become a constantly
regenerating population of billions of
mutualistic inhabitants of digestive tract
i) Bacteria provide vitamin K
ii) We provide undigested food for the
bacteria
3. Fiber: (roughage) is composed mostly of the
cellulose and lignin in plant material
a) Helps digestive system function better by
providing bulk in order for peristalsis to push food
through the intestines it needs sufficient volume of
material to apply pressure
b) Rate of movement of material through the
large intestine has a positive correlation with fiber
content
c) High fiber diets help people manage their body
mass better
i) Easy to lose excess weight with a diet
that includes fruits and vegetables because
the fiber fills up the stomach
ii) Recommended to eat a least 5 servings
of fruit or vegetables each day
Clip
III. Human nutrition
A. Nutrients: chemical substance found in
foods and used in the human body
1. Nutrients can be absorbed to
a) Give you energy
b) Help strengthen your bones
c) Prevent you from getting a
disease
2. Some molecules that make up living organisms
can be made by the human body and some
cannot
a) Essential nutrients: cannot be synthesized
from other molecules and must be a part of the
diet
b) Examples of essential nutrients
i) Essential amino acids
ii) Essential fatty acids
iii) Minerals
iv) Most vitamins
B. Dietary minerals: essential chemical elements
1. Minerals: inorganic substances that living
organisms need for a variety of purposes
a) Living organisms only need a very
small intake of these elements to
ensure good health
b) Each mineral has one or more specific role in making
structures or physiological roles (making important
molecules)
i) Calcium in bones
ii) Iron in hemoglobin
c) Structures and molecules are typically long lived
within the body so minerals are needed constantly but
in small amounts
i) Small amounts of calcium used for repairing bones
ii) Calcium also used for other purposes and needs
to replace those that are used
iii) Red blood cells with hemoglobin lasts 4
months and the components of the blood cells
are recycled in the liver and much of the iron is
recovered to produce more red blood cells
iv) Some iron is still lost.
Females need more iron due
to blood lost during menstruation
d) Minerals in our diet are often know as
electrolytes because they dissolve in fluid medium
(blood, cytoplasm, intercellular fluid)
i) Ca+2, Fe+2, Na+, Mg+2, and Cl-
ii) Electrolytes are important in sending
action potentials in the neurons and for
muscle contractions
iii) Muscle cramp occurs when there is an
electrolyte imbalance after exercise
2. Vitamins: essential organic compounds
a) Vitamins are synthesized by living organisms, but
many organisms rely on vitamins from other
organisms (often plants like fruits and vegetables)
b) Small amounts are need and are used to create
long-lived substances
c)Vitamin C (ascorbic acid): essential vitamin for
human (some primates, and guinea pigs) but non-essential
for most other animals
i) Scurvy: serious deficiency disease when
vitamin C is not consumed over an extended
period of time
ii) Vitamin C is produced from glucose in the
kidney tissue or liver and it requires 4 enzymes.
The gene coding for the 4th enzyme is defective in
all humans making it essential that vitamin C is in
our diet
iii) Important for protection against infections,
helping in wound healing, maintaining healthy
gums, teeth, bones, and blood vessels.
iv) Linus Pauling: chemist and biochemist in his
book How to Live Longer and Fell Better (1986),
he suggested large doses of vitamin C
•Radical idea since it was normally regarded as a
substance needed in small amounts
•Ideas not supported by conclusive results from clinical
trials and he was criticized by other scientists Clip
d) Vitamin D: essential component of the human diet for
the proper formation of bones
i) Rickets: develops when there is insufficient
supply of vitamin D and/or Ca+
ii) Develops in children when the bones near the
growth plates do not mineralize properly
iii) Lead to irregular, thick, and wide bones growth
iv) Children don’t reach their optimal height and
their legs bow inwards or outwards at the knees
v) Osteomalacia: soft bones in adults that
have a deficiency in vitamin D or calcium
vi) Epidermis of skin contains precursors that
are able to synthesize vitamin when
stimulated by UV rays of the sun
vii) Balance between getting rewards of
vitamin D from sun and sunburns and skin
cancer from UV radiation
3. Fatty acids: Two are essential
a) Fatty acids: carboxyl functional group and a
long hydrocarbon chain
i) Saturated fatty acid: single bonds in
hydrocarbon chain
ii) Unsaturated fatty acid: double bond in
hydrocarbon chain
iii) Identity of fatty acid is determined by its
number of C atom and location of double
bonds
b) Two fatty acids are required in our diet because
humans lack the enzymes to make these
i) Omega-3 and omega-6 are essential in the
diet and consuming them it is not necessarily
bad for your health
4. Amino acids: Nine of 20 are essential
a) Nine of the amino acids must
be in our diet throughout our lives to
make the necessary proteins
b) Some other amino acids essential for very young
people or those with certain diseases
c) Humans have no storage mechanisms for amino
acids, so essential amino acids must be a part of your
regular diet
d) Some cultures that depend on a single stable crop
for their diet may not be getting all 9 amino acids
i) Corn or maize is deficient in lysine and
tryptophan and people relying too much on maize
can suffer from a variety of symptoms due to the
low intake of those 2 essential amino acids
ii) Researchers are developing an improved variety
of maize that has increased levels of lysine and
tryptophan
C. PKU: phenylketonuria: genetically inherited disease
caused by a person’s chemical inability to metabolize the
amino acid phenylalanine
1. Mutated form of a gene that doesn’t break
down phenylalanine because it doesn’t make
enzyme phenylalanine hydroxylase
2. Phenylalanine builds up in tissues and
bloodstream
3. Excess phenylalanine can result in mental
deficiency, behavioral problems, seizures and other
developmental problems
4. Allele for PKU is autosomal recessive: both
parents contribute an allele for this homozygous
recessive condition to be expressed
5. If both parents are heterozygous, then they have a
25% chance of causing PKU in their child
6. Most common in European populations and less in
Asian, Latino, and African
7. No cure, but there is effective treatment if detected
early
a) Common for every newborn to be tested for
PKU
b) Treatment is based on a diet that limits
protein sources with high levels of
phenylalanine so the toxic levels do not
develop
D. Eating and nutrition disorders: lack of sufficient healthy
foods, behavioral, or physiological and are heavily
influenced by a person’s culture
1. Appetite is controlled by hypothalamus
a) Appetite: desire to eat
b) Hunger: body’s way of expressing its need
for food
c) Satiety: state in which you have eaten a
sufficient amount of food and stop eating
i) Mechanisms of appetite and satiety are quite
complex and not fully understood
ii) Combination of feedback loops from the nervous
system, digestive system, and endocrine system
(Ex: pancreas releases hormones that reduce appetite
after a meal)
d) Medical problem with hypothalamus can have
severe appetite problems (thin due to loss of appetite
or obese due to insatiable appetite)
i) Hypothalamus is the appetite control center
2. Steps that occur for appetite during meal
a) Stomach fills with food, expands,
and stimulates cells of vagus nerve
b) Signal is sent to hypothalamus to stop eating
c) Intestines produce hormones to send signals about
hunger and satiety to the brain
d) Cells of adipose (fat) tissue produce hormone
leptin that sends message to hypothalamus to suppress
appetite
i) Person with more body fat produces more leptin so
brain knows there is enough energy stored in fat
ii) During fasting, leptin levels decrease
3. Other hormones involved for appetite and other factors
such as compulsive eating and persuasive advertising seem
to override leptin’s effects
E. Consequences associated with being overweight
1. Perception of being underweight, normal, or
overweight is highly biased by cultural and personal
feelings about body shapes and expectations
2. Body mass index (BMI) is a better way to
determine appropriate weight: calculation of body
mass that is corrected for height
3. Hypertension: high blood pressure
a) Uncontrollable factors: age,
ethnic origin, and family history
b) Controlled factor: weight: positive correlation
between a higher BMI and hypertension
c) More you weight, the more blood you need to
supply oxygen and nutrients to cells, as volume of
blood through blood vessels increases, so does the
pressure on walls of arteries
4. Type II diabetes: body cell resistance to the normal
effect of insulin and decrease in insulin production
a) Insulin: hormone that allows
cells to remove glucose from blood
b) Positive correlation between
developing type II diabetes and obesity
c) Incidence of type II has increased as obesity has become
more common in children, teenagers, and adults
d) Blood glucose levels remain abnormally
high because cells are not receiving glucose for
normal metabolic activity
e) Need to control their carbohydrate intake to
keep their blood glucose level reasonably
stable
F. Nutrition problems and their consequences
1. Malnutrition: deficiency, imbalance, or excess of
nutrients
2. Deficiency: lacking many essential substances or
lack of calories in the diet
a) Glycogen stored in liver and muscles will be
used quickly as a source of glucose
b) Body fat will be used next
c) Use proteins as a source of energy
d) When energy is not available from
ingested carbohydrates, lipids, or proteins, the
body’s metabolism begins a series of
reactions that digest body tissues for energy
i) Skeletal muscle is used first
ii) Muscle gets thinner and is less useful
3. Imbalance: unequal amount of nutrients in the diet
a) Single staple crop is providing most of the nutritional
needs of a population
i) Lead to an overall imbalance of too many
carbohydrates or specific deficiency of one or
more essential nutrients
b) Parts of the world that have excellent sources of
nutrition available
i) Individual choice of what is in their
diet can lead to nutritional imbalances
4. Excess of nutrients: can lead to obesity
a) 2005, World Health Organization’s Obesity Task Force
estimated that 400 million people were obese and 1.6
billion were overweight WHO
b) Overweight and obesity: abnormal
or excess fat accumulation that may
impair health (use BMI calculation)
c) Number of people overweight and obese
has continued to increase in the last few
decades
i) Change in types and quantities of
food people eat ( low nutrition, highcalorie choices from many ready-to-eat
food products)
ii) Change in the amount of physical
activity (farming towards urban life)