The Digestive System

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Transcript The Digestive System

The Digestive and
Excretory Systems
By. Emir Fils-Aimé, Alexis Murray, and
Melody Schwenk
AP Biology-Ms. Stein, Due 4/14/10
The Digestive System: Part I
“Food’s Highway”
• To be processed and expelled, food must
pass through various digestive organs
• Food goes through the following organs:
Mouth Esophagus  Stomach Small
and Large Intestines  Rectum  Anus
The Oral Cavity, Pharynx, Esophagus
Food begins digestion in the mouth
Both physical and chemical digestion
of food begin in the oral cavity
The food is broken down physically
by chewing, making it easier to
swallow and increase surface area.
The presence of food in the mouth
activates salivary glands.
The saliva starts the breaking down
of food.
-An enzyme, salivary amylase,
hydrolyzes starch and glycogen.
The tongue manipulates food into a
ball called the bolus. It is pushed into
the back of the throat to the pharynx
• To prevent choking, when we swallow the
epiglottis blocks the windpipe.
• From the pharynx the food is conducted to
the stomach by the esophagus.
• Swallowing begins voluntarily but is taken
over involuntarily by peristalsis.
• Peristalsis is the contraction of smooth
muscle to help move food along the
digestive tract.
The Stomach
The stomach stores food and
performs the preliminary
steps of digestion.
Before storing food, the
stomach secretes gastric
juice. This juice mixes with
the food.
Gastric acid binds cells
together in meat and plant
material. It also kills most
bacteria in food.
Pepsinogen, an inactive form
of pepsin is also secreted so
the gastric juice doesn’t burn
the stomachs lining.
• Every 20 seconds the stomachs contents are mixed by
the churning of smooth muscles.
• As a result of mixing and enzyme action, the food in the
stomach becomes a nutrient rich broth called acid
• The stomachs ends are usually both closed off. At the
top, its closed by the cardiac orifice, which only opens
when a bolus arrives.
– Backflow may occur, causing heartburn
At the bottom, the stomach is closed off by the pyloric
– It helps regulate the passage of chyme into the
intestine, one squirt at a time.
The Small Intestine
• Most of enzyme hydrolysis
occurs in the small
• Acid chyme from the
stomach mixes with
digestive juices from the
pancreas, liver,
gallbladder, and gland
cells of the intestinal wall
in the duodenum.
• The duodenum is the first
25 cm of the small
• The jejunum and ileum
function mainly to absorb
nutrients and water.
• The small intestine contains villi which also contain
microvilli. These structures help to increase the rate of
nutrient absorption.
• Small vessels of the lymphatic system called lacteal.
• Capillaries within the villi converge into the hepatic
portal vein, which leads to the liver.
– It ensures that the liver is the first to receive access to
sugars and amino acids
The Large Intestine
• The large intestine is also known as the colon.
• The appendix is located on the large intestine. It is
• The large intestines major function is to recover water
that has entered the alimentary canal.
• The wastes of the digestive tract, the feces, become more
solid as they move along the colon by peristalsis.
• The terminal portion of the colon is called the rectum.
Feces are stored here until they can be eliminated.
Key Terms
Mouth- the first part of digestion takes place here. Chemical and mechanical
digestion start here.
Esophagus- tube between mouth and stomach. Forces food down to stomach by
Stomach- sac like muscular organ attached to esophagus. Stores food and starts
Small Intestine- long tube winding from the stomach. Named small intestine for its
diameter not length
Large Intestine- tube that food travels through after the small intestine. Also called
the colon.
Gall-bladder-small sac like organ by the duodenum. Stores and releases bile.
Duodenum- the first 25 cm of the small intestine.
Liver- organ above the stomach. It filters toxins and makes bile and blood proteins.
The Excretory System:
Part II
Urine Production
• The process of producing the fluid waste “urine”
occurs in four steps:
– Filtration: Filtrate from the blood is collected
by the excretory tubule. Water and solutes
(which make up the filtrate) are forced across
the selectively permeable membranes of
capillary clusters and then into the excretory
– Reabsorption: The transport epithelium
reabsorbs valuable solutes from the filtrate
and returns them to the body fluids.
– Secretion: The remaining substances,
such as toxins and excess ions are
removed and added to the excretory
– Excretion: The filtrate leaves the system
and the body.
The Kidneys
• They are the principal site for water balance and
salt regulation; they are found in a pair
• Receive blood from the renal artery and it is
drained from the renal vein; blood flow through
the kidneys is voluminous
• Urine exits them through the ureters and they
drain into a single urinary bladder and from
there, the urine exits through the urethra (found
near the vagina in females and in the penis in
Consist of two different regions: the renal cortex (outer part) and the renal medulla
(the inner part)
Contains about a million nephrons; each nephron has a single long tubule and a ball
of capillaries called a glomerulus
The blind end of the excretory tubule forms a cup shaped swelling known as a
“Bowman’s capsule”-it surrounds the glomerulus
The initial filtration of blood, which is nonselective, occurs in the Bowman’s capsule
The filtrate then travels in spiraled direction to other regions including the
proximal tubule, the loop of Henle, and the distal tubule which empties into the
collecting duct
From the collecting duct, processed filtrate is transported to the renal pelvis and
drained by the ureters
ADH (Antidiuretic hormone) helps to regulate reabsorption levels and adjust the
volume and osmolarity of urine, by increasing and decreasing permeability in the
A special tissue known as the juxtaglomerular apparatus (JGA) affects blood volume
and pressure levels in the glomerulus
Activities: Part III
The Excretory System Crossword Puzzle
Fill in the Blank
1.After chewing, food goes down your throat or __________ .
2.Wave like muscle contractions called __________ move food through the digestive
tract from one processing station to the next.
3.The three sections, duodenum, jejunum, and ileum, in the __________ perform
similar but different functions. However, ultimately nutrients are absorbed through the
4.The __________ is located between the esophagus and small intestine; it’s primary
function is to process and break down food into small enough parts so that it is passed
through the rest of the digestive tract.
5.Salivary glands, pancreas, liver, and the gallbladder are all __________ of the
digestive system.
6.Partially digested food, called _________ , when combined with bile may be excreted
from the body as a bowel movement.
7.The __________ is the last part of the large intestine that ultimately releases fecal
matter from the body.
8.Waste products from the food you eat are stored in the __________ to be collected
and processed into feces.
9.Food and drinks are transported down the __________ into the stomach.
10. Not only do __________ offer protection for the small intestine, but they also
expand the space to allow molecules to enter easily.
Small Intestine
Large Intestine
Accessory Glands
Label the Diagram
The End!
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