Download 12 The Digestive and Excretory Systems

The Digestive System
MCAS STANDARDS
4.1 Explain generally how the digestive
system (mouth, pharynx, esophagus,
stomach, small and large intestines, rectum)
converts macromolecules from food into
smaller molecules that can be used by cells
for energy and for repair and growth.
Overview of Digestion
•  Function
–  To help convert foods into
simpler molecules that can
be absorbed and used by
the cells of the body.
•  Alimentary Canal- a one
way tube that passes
through the body
•  The digestive system
includes the mouth,
pharynx, esophagus,
stomach, small intestine,
and large intestine.
The Mouth
•  Mechanical digestion-the
physical breakdown of
food into smaller pieces
–  Teeth-anchored to bones of
jaw and are protected by
enamel
•  Chemical digestion-large
food molecules are broken
down into smaller food
molecules.
–  Saliva-contains enzyme
called AMYLASE-breaks
the chemical bonds in
starches to release sugars
The Esophagus and Stomach
•  From the throat the bolus
of food enters the
esophagus (food tube) to
travel to the stomach
•  Peristalsis- contractions
of smooth muscle that
squeeze food through the
esophagus down to the
stomach.
•  Food from the esophagus
enters a large muscular sac
called the Stomach
–  Mechanical and Chemical
digestion continue
Chemical & Mechanical
Digestion
•  Chemical Digestion
–  The lining of the stomach contains millions of
microscopic gastric glands that release a number of
substances into the stomach
•  Mucus that lubricates and protects the stomach wall
•  Hydrochloric acid which makes the contents of the stomach
very acidic
–  Activates pepsin, an enzyme that begins the digestion of protein
and is secreted by a third set of stomach glands
•  Mechanical Digestion
–  Stomach muscles contract to churn and mix stomach
fluids and food, gradually producing a mixture known
as chyme.
Small Intestine
•  Divided into 3 parts
–  Duodenum, Jejunum,
Ileum
•  Most of the chemical
digestion and absorption
occurs in the small
intestine
•  As chyme enters the
intestine it mixes with
enzymes and digestive
fluids from the pancreas,
the liver, and the lining of
the duodenum.
Absorption in Small Intestine
•  The folded surfaces of the small intestine are
covered with fingerlike projections called Villi.
•  The surfaces of the cells of the villi are covered
with thousands of fingerlike projections called
microvilli.
–  Provide for an enormous surface area for the absorption
of nutrients
•  Slow wavelike contractions of smooth muscle
move the chyme along the surface. Nutrient
molecules are absorbed into the cells lining the
small intestine
The Large Intestine
•  When chyme leaves the
small intestine it enters the
large intestine or colon
•  Function of the large
intestine is to remove
water from the undigested
material that is left
–  Absorbed through intestine
walls
•  Waste material that
remains passes through
the rectum and is
eliminated from the body.
Excretory System
•  The function of the
excretory system is to
help the body maintain
homeostasis.
Structures of the Excretory System
•  Skin
–  Excretes water, salts,
urea
•  Lungs
–  Excrete carbon dioxide
continued
•  Liver
–  Converts excess amino
acids into protein
compounds
•  Creating nitrogen
wastes – urea
•  Removed from blood
by kidneys
continued
•  Kidney
–  Removes waste from
the blood
–  Maintain blood pH
–  Regulate water content
of blood
Kidney Structure
•  nephrons
–  are located in the renal
cortex
–  their loops of Henle,
descend into the renal
medulla
•  As blood enters a nephron
through the arteriole, impurities
are filtered out and emptied into
the collecting duct. The purified
blood exits the nephron through
the venule.
Kidney Function
•  Blood purification
involves two distinct
processes:
–  Filtration (Bowman's
capsule)
•  filtrate contains water,
urea, glucose, salts, amino
acids, and some vitamins
–  Reabsorption
•  amino acids, fats, and
glucose, are removed from
the filtrate by active
transport
–  Loop of Henle- Urine
consentrated