Digestive and Excretory
Systems
Did you know that
your digestive
system measure
about 30 feet long
– from end to end?
Before you start
• In a healthy diet you
should have:
–
–
–
–
–
–
Proteins
Healthy Fats
Vitamins
Minerals
Water
Carbohydrates
• Healthy sugars
• Starches
• Fiber
3 Functions of the Digestive
System
1. Breaks down food into molecules the
body can use = Digestion
2. Molecules are absorbed into the blood
and carried throughout the body =
absorption
3. Wastes are eliminated from the body
2 types of Digestion
• Mechanical Digestion
• Begins with your first bite
of food
– Teeth cut, slice and grind
the food
– Saliva makes it slippery
– Swallow food to continue
digestion
• Chemical Digestion
• Breaks down food with
the help of enzymes – a
protein that speeds up
chemical reactions in the
body
• Each enzyme in the body
has a specific function
– Spit – contains an enzyme
to break down starches into
sugar molecules
– Have a cracker
Organs of the Digestive System Esophagus
• At the back of your mouth there are two
openings:
– Epiglottis – a flap of tissue that seals off your
windpipe when you eat
– Esophagus – a muscular tube that connects your
mouth to your stomach
• Lined with mucus (a thick, slippery substance) that makes
food easier to be swallowed
• Food is in your esophagus for about 10 seconds.
• Peristalsis – involuntary waves of smooth muscle contraction
that pushes food to the stomach
The Stomach
A J-shaped muscular pouch.
As you eat it expands to hold your
food – average about 2 liters.
• Mechanical
Digestion
– 3 layers of
muscles contract
to churn food
– Similar to they
way a washing
machine works –
mixing the
contents with
water
• Chemical
Digestion –
food is
further
broken down
by digestive
juices –
produced by
cells lining
the inside of
the stomach
Digestive Juices
• Pepsin – enzyme that chemically digests
proteins in your food
• Mucus – protects your stomach lining
from…
• Hydrochloric Acid –
– provides an acidic environment for the pepsin
to function
– Kills bacteria you swallow along with your
food.
Small Intestine – 6 meters long
• So now your food is a
thick liquid…it enters the
small intestine
• Starches and Proteins
have been broken
down…but fats haven’t
• Almost all chemical
digestion and absorption
of nutrients takes place
here…with help from the
liver and pancreas
Held together by the
mesentery
Help from the liver…
• Largest and heaviest
organ inside your
body
• Produces bile (a
substance that breaks
down fat molecules)
• Bile moves from the
liver to the gall
bladder – stores bile
until its needed in the
small intestine
Help from the Pancreas…
• Between the stomach
and the small
intestine
• Produces 3 enzymes
that continue the
process of breaking
down starches,
proteins, and fat
Back to the small intestine
• After chemical digestion –
nutrients are absorbed
into the villi of the small
intestine
• Villi line the walls and
contain blood vessels
• The amount of villi greatly
increases the surface
area of the small intestine
= greater absorption.
What’s left?
• By now most nutrients have been
absorbed – except fiber (thickens the
liquid material in the intestines and allows
it to be pushed forward)
• The liquid food also still contains water
• It is pushed by involuntary muscle action
into the large intestine.
Large Intestine
• A horseshoe shaped
organ – 1.5 meters long
• Contains bacteria that feed
on the material passing
through = make vitamin K
• Water is absorbed into the
bloodstream
• Remaining material enters
the rectum and is
compressed into solid
waste
• Waste is pushed out
through the anus
Traveling Tapeworms
• Traveling Tapeworm
Excretory System
The Excretory System…
• …is
the system
of the body that
collects wastes
produced by
cells and
removes the
wastes from the
body.
What is the waste that we need to
get rid of?
1. Carbon Dioxide – more on this later with
the respiratory system
2. Excess Water
3. Urea – a chemical that comes from the
breakdown of protein
If your body didn’t take away these wastes,
they would pile up and make you sick.
Organs of the Excretory System
• Kidneys – you have 2 of them – eliminate
urea and excess water through urine.
– As blood flows through the kidney they
remove waste from the blood
– Urine flows from the kidney through 2 narrow
tubes called the ureters…..
– To the urinary bladder – a sac-like muscular
organ that stores urine
How do you know you have to go?
• When the bladder is full enough that its
walls are stretched – you feel a need to
urinate.
• Urine flows out of the body through a small
tube called the urethra.
What do the Kidneys actually do?
• Every drop of blood
travels through your
kidneys 300 times a
day.
• Your kidneys contains
about a million
nephrons – tiny
structures that
remove waste from
the blood and
produce urine
Urine formation – 4 steps
1. Blood flows into a nephron
2. In the capillaries inside a nephron – urea,
water, glucose, and other substances are
filtered out of the blood. The filtered
material passes into a capsule
surrounding the capillaries
Urine formation – 4 steps
3. From the capsule – the materials that
were removed from the blood pass into a
long twisting tube. As the filtered material
flows through the tube – glucose and
water are reabsorbed, urea stays in the
tube
4. After the re-absorption is complete – the
liquid that remains in the tube is urine.
Urine and Disease
• What happens when you pee in a cup?
– Normal urine contains no glucose or protien
– Presence of glucose could = diabetes
– Presence of protein = kidneys aren’t
functioning
Why is water so important?
• Remember that as urine
is being formed, water is
absorbed back into the
bloodstream. The amount
absorbed depends on…
– Hot day - Sweat a lot with
little to drink – almost all of
the water will be absorbed
– little urination
– Cool Day – Little Sweat
with a lot to drink – less
water will be absorbed –
more urination
– You need about 2 liters of
water to maintain balance