http://www.mennellmedia.co.uk/Biology%20-%20Organisms.html
•HOW LONG ARE YOUR
INTESTINES? At least 25 feet in an
adult. Be glad you're not a full-grown
horse -- their coiled-up intestines are
89 feet long!
•Chewing food takes from 5-30 seconds
•Swallowing takes about 10 seconds
•Food sloshing in the stomach can last
3-4 hours
•It takes 3 hours for food to move
through the intestine
•Food drying up and hanging out in the
large intestine can last 18 hours to 2
days!
•Americans eat about 700 million
pounds of peanut butter.
•Americans eat over 2 billion pounds of
chocolate a year.
•In your lifetime, your digestive system
may handle about 50 tons!!
2 Main Groups
I. Alimentary : digests food, breaks it down into smaller fragments
and absorbs the digested fragments through its
lining into the blood
II. Accessory Digestive Organs : assist the process of digestion
I. Alimentary Canal
*Also called gastrointestinal (GI) tract, and is technically considered
to be outside the body b/c it is in contact with the external environment at both ends.
Includes the following organs:
-mouth
-pharynx
-esophagus
-stomach
-sm intestine -lg intestine
-anus
*Approx 30 feet in a cadaver but smaller in a living person b/c of its constant
muscle tone.
I. Alimentary Canal
4 Distinct Tissue Layers
p741 Fig 25-2
1. Mucosa – innermost layer that lines the cavity or lumen. It
secretes mucus and digestive enzymes. In some areas
it has folds and tiny projections that help inc the
surface area for absorption.
2. Submucosa – beneath the mucosa, contains blood vessels,
nerve endings and lymphatic vessels. It nourishes
and carries away absorbed material.
3. Muscular layer - a muscle layer made up of circular inner
layer and a longitudinal outer layer of smooth
muscle cells.
I. Alimentary Canal
4. Serous layer - (serosa) outer covering of the tube, composed
of visceral peritoneum. Its cells secrete serous fluid
to keep the tube’s outer surface lubricated and moist
so organs can slide freely against one another.
I. Alimentary Canal
Mixing and Propelling Movements
Mixing - muscular contractions along its walls from end to end
mix digestive juices secreted by the mucosa.
Propelling - wavelike motion called peristalsis pushes tubular
contents ahead.
Lips – protect anterior opening
A. Mouth
Cheeks – protect lateral walls
Hard palate – anterior roof
Soft palate – posterior roof
Uvula – finger-like projection of the
soft palate
Palantine tonsils – back of mouth on
either side of tongue
P747 Fig 25-8
Primary teeth & Secondary teeth
Tongue – muscular structure
A. Mouth
Food enters mouth and is chewed and mixed with saliva (bolus).
Cheeks and lips hold food between teeth during chewing. The
tongue mixes food w/ saliva during chewing and initiates swallowing.
Salivary gland – secrete saliva to help bind, moisten, and
digest food.
2 Types of Secretory Cells
1. Serous cells – watery fluid that contains amylase
2. Mucous cells – thick, stringy liquid which helps bind food
particles together and acts as a lubricant during
swallowing.
A. Mouth
3 Major Salivary Glands
1. Parotoid gland – largest, secretes a watery fluid rich in
amylase
2. Submandibular gland – mostly serous cells and some
mucous cells
3. Sublingual gland – floor of mouth under tongue, mostly
mucous cells
B. Pharynx
•A passageway that connects the nasal and oral cavities with
the larynx and esophagus
1. Nasopharynx – part of the respiratory
passageway
2. Oropharynx – posterior to oral cavity
where food moves from
the mouth and air to and
from the nasal cavity
3. Laryngopharynx – continuous with the esophagus
P689 Fig 23-6
C. Esophagus
p748 Fig 25-9
Esophagus – runs from pharynx through diaphragm to the
stomach (approx 10 in long). Contains mucosa
glands to keep inner lining moist and lubricated.
Epiglottis - keeps food out of the air tube
http://video.about.com/heartburn/HiatalHernia.htm GERD, and Hiatal Hernia
http://www.bidmc.org/YourHealth/Proced
uresInMotion.aspx
D. Stomach
Stomach - J-shaped or C-shaped pouchlike organ
just under the liver and diaphragm in the
upper left side of the abdominal cavity.
*approx 10 inches long, when full can hold
up to 1 gallon of food.
*inner lining marked by folds or rugae
*starts digestion of proteins, mixes food with
gastric juices
D. Stomach
1.
2.
3.
4.
Divided into 4 Regions
Cardiac - where food enters stomach from esophagus
Fundic - expanded part of stomach, acts as temporary storage
Body - midportion of stomach
Pyloric - terminal part of stomach continuous with the small
intestine
P749 Fig 25-10
D. Stomach
p749 Fig25-11
4 Different types of cells make up the gastric glands
1. Mucous cells - secrete mucus that protects and coats the inside
stomach wall
2. Chief cells - secrete digestive enzymes….pepsin….protein splitting
enzyme
3. Parietal cells - release HCl, makes stomach acidic and helps
activate enzymes.
4. Endocrine cells - secretes the hormone gastrin that functions in
increasing the gastric activity.
The Hormones That Control Digestion
1. Gastrin - stimulates the stomach cells to inc the sections of
the gastric glands. (gastric juice ….HCl & Pepsin)
2. Secretin - stimulates the release of pancreatic juice
3. Cholecystokinin (CCK) - stimulates the gallbladder to empty
due to the presence of fat in the sm
intestine.
D. Stomach
* In the pyloric region of the stomach where most digestive
activity occurs you will find chyme - digested food mixed with
gastric juices. The chyme leaves to the small intestine via the
pyloric sphincter.
Pyloric sphincter - a valve at end of pyloric canal that prevents
food from reentering the stomach.
E. Small Intestine Convoluted tube that extends from the
pyloric sphincter to the ileocecal valve…
where the ileum joins the cecum of the large
intestine
E. Small Intestine
Mesentery - supporting tissues that contains blood vessels, nerves,
and lymphatic vessels that supply the intestinal wall.
*this fan-shaped mesentary holds the intestines together
E. Small Intestine
P752 Fig 25-13
Intestinal villi - tiny projections that come in contact with the
intestinal contents and inc surface area for absorption.
*nutrients are absorbed through the capillaries
E. Small Intestine
1. Duodenum - curves around the head of the pancreas. The first
part of the small intestine.
2. Jejunum - extends from the duodenum to the ileum
3. Ileum - terminal part of the small intestine. Joins lg intestine
at ileocecal valve. Longest
portion of the sm intestine
E. Small Intestine
Small Intestine Secretions
* peptidase - split peptides into amino acids
* sucrase, maltase, lactase - split double sugars
* intestinal lipase - split fats
F. Large Intestine
*larger diameter than sm intestine and begins in the lower
right side of the abdominal cavity where the ileum joins the
cecum.
*functions in drying out indigestible food residue by absorbing
water so it can be eliminated from the body as feces.
F. Large Intestine
P754 Fig 25-16
*It frames the sm intestine on 3 sides and has the following
subdivisions.
1. Appendix - hangs from the cecum and has no digestive function
2. Cecum - a pouch like structure at the
beginning of the lg
intestine.
3. Colon –
Ascending: travels up right side
Transverse: turns left to travel across the
abdominal cavity
Descending: travels down the left side
Sigmoid: at pelvis where it make a S-shape
F. Large Intestine
P755 Fig 25-17 – 25-18
4. Rectum : just posterior to anal canal in the pelvis
5. Anal Canal : contains the anus which has an external voluntary
sphincter and an internal involuntary sphincter.
F. Large Intestine
*Large intestine doesn’t have villi but has goblet cells to produce
mucus. The mucus helps lubricate and prevent the intestine
from the abrasiveness of the feces as it passes through. It also
helps hold fecal matter together.
http://www.bidmc.org/YourHealth/ProceduresInMotion.aspx
II. Accessory Digestive Organs
A. Pancreas
*A soft pink, triangular gland that extends across the abdomen
from the spleen to the duodenum.
*It secretes enzymes into the duodenum
to neutralize the acidic chyme. The
pancreas also functions in producing
the hormones insulin and glucagon.
*secretin – hormone that stimulates
pancreatic secretions
B. Liver
P757 Fig 25-22
*Largest gland in the body. Located under the diaphragm more to
the right side of the body. Divided into lobes.
Functions in:
*Carbohydrate, lipid and protein metabolism
*Storage of iron and vitamins
*Blood filtering
*Detoxification
*Secretion of bile.
B. Liver
*Its digestive function is to provide bile.
-Bile is made up of salts and is pigmented b/c of red blood cell
breakdown.
-Bile salts emulsify fat
B. Liver
-Bile leaves the liver through the hepatic duct and enters the
duodenum through the common bile duct.
C. Gallbladder
-A small, green sac embedded in the inferior surface of the
liver.
*When digestion is not taking place the bile backs up
the cystic duct and enters the gallbladder to be stored.
*When fat is consumed a hormone (CCK) stimulates the
gallbladder to release bile.
C. Gallbladder
P759-760 Fig 25-25 – 25-26
*Gallstones – when bile is stored in the gallbladder too long
it crystallizes. The gallstones then prevent bile
from entering the sm intestine and it eventually
backs up into the liver and blood stream.
http://www.innerbody.com/image/digeov.html
http://www.medtropolis.com/VBody.asp