Download The Alimentary System (The digestive system)

The Alimentary System
(The digestive system)
Alimentation
• Is the combined processes of
ingestion, digestion, absorption,
assimilation, and egestion.
• Process by which food
substances are chemically
changed into forms that can be
absorbed and assimilated by
the cells of the body.
Ingestion-process by which food
enters the digestive system.
(eating)
Digestion-The breakdown of
large food molecules into a
usable form.
Absorption
The process by which food molecules
move into the blood stream to be
carried to the cells of the body.
Assimilation
The incorporation of food molecules
into the cells of the body to be used
as energy, structural materials, or
storage products.
Egestion
The expulsion of undigestable
materials from the body.
Digestive System is divided into 2 parts.
1. Alimentary Canal- Organs in
which food passes through;
oral cavity, pharynx,
esophagus, stomach, small
intestine, and colon. (large
intestine) 30 ft. in length
2. Accessory Organs-glands or
organs which secrete
chemicals needed for the
digestion of food substances;
salivary glands, liver, gall
bladder, pancreas.
4 layers of the Alimentary Gland
1. Mucosa- innermost,
composed of simple columnar
epith.
• Functions in protection,
absorption and secretion
2. Submucosa-composed of
loose connective tissue and
blood and lymphatic vessels
and nerves.
• Functions in the nourishment of
the mucosa and surrounding
tissues and carries away
absorbed nutrients.
4 layers of alimentary canal
3. Muscularis 2 layers, inner
layer is a circular layer of
smooth muscle. Outer layer is
a longitudinal layer.
• Function is the movement and
mixing of the contents of the
tube.
• Peristalsis- coordinated
contraction of a tube.
Serosa visceral peritoneum,
composed of serous
epithelium and connective
tissue.
• Functions is to secrete fluid to
keep outer surfaces moist and
lubricated.
Organs of the Alimentary Canal
Mouth (oral cavity)
• Adapted to receive food and
prepare it for digestion.
• Lined with stratified squamous
epithelium.
• Tongue-muscular organ covered
with taste receptors.
• Functions in taste, speech, and
swallowing.
• Frenulum-attaches tongue to
the floor of the mouth
• Gingiva-gums Str. Squ. Epith.
• Vestibule is the space between
the cheek and gum
Roof of Oral Cavity the Hard and Soft Palate
Hard Palate is anterior. Palatine
bone of the skull.
Soft Palate is posterior extends to
the uvula. Muscular, functions
in swallowing.
• Cleft Palate- malformation of
the hard palate
Teeth
• Function in the mechanical
digestion of foods.
• Mastication is the chewing of
food into smaller pieces so that
enzymes can work at a faster
rate.
Teeth are composed of pulp,
•
•
1.
2.
dentine, and enamel. The
hardest substance in the human
body.
They are living tissue.
2 sets in your life time.
Deciduous set (baby teeth)
Permanent set (adult teeth)
Deciduous Teeth- 20
3 types of teeth in the baby set:
1. Incisors- flat, chisel like teeth
for cutting.
2. Canine- sharp pointed teeth
for tearing and shredding.
3. Molars- flat teeth for crushing
and grinding.
Dental Formula
I-8, C-4, M-4, M2-4.
Permanent Set-32
• Have the same make-up as baby
teeth.
• New tooth added:
• Bicuspid (premolar) - flat tooth
for grinding.
• Start to erupt by age 6 and usually
thru by age 12.
• 3rd Molar “Wisdom Tooth” erupts
usually between 17 and 22.
Dental Formula:
I-8, C-4, B-4, B2-4, M-4, M2-4, M3-4
Dental Caries Tooth Decay
• Bacteria living in the mouth
produce acids which breaks
down the enamel on teeth.
• Gradually forming holes in the
enamel.
• These are called cavities.
Salivary Glands
• Secrete saliva, composed of water,
mucous, amylase, and ions.
• Functions:
• in the digestion of carbohydrates
(amylase)
• lubrication of food
• maintains the pH of the mouth
• washes the teeth
• neutralizes acids in mouth.
3 sets of Salivary glands
1. Parotid-located anterior and
inferior to the ear.
• Secretes a concentrated saliva
with a great deal of amylase
• Secretes thru Stenson’s duct
opposite the 2nd Molar.
Submandibular gland
• About the size of a walnut.
• Lies along the medial aspect of
the mandibular body.
• Secretes a watery dilute saliva
thru Wharton’s duct that is
located at base of the frenulum
of the tongue.
Sublingual gland
Dilute saliva, located below the
tongue inferior to the floor of
the mouth.
• Excretes thru 10-12 ducts along
the vestibule of lower incisors
Swallowing-Deglutition
• The muscular act of swallowing.
• Reflex controlled by vagus
nerve.
Events of deglutition
1. Food is chewed and mixed
with saliva. (mastication) and
rolled into a ball (bolus) and
forced into the pharynx
2. The bolus upon reaching the
pharynx triggers sensory
receptors causing the muscular
contraction that cause
swallowing.
3. Food enters the esophagus
and is carried by peristalsis to
the stomach.
Peristalsis
• Wave like contraction of a
tube.
• Occurs in the alimentary
canal as well as in
arteries of the circ. system
• Involves the coordinated
contraction of both the
longitudinal and circular
planes of muscle.
Esophagus
• A straight muscular tube 10 in.
length.
• Serves as a passageway for food
to reach the stomach.
• Has a thick muscularis for forcing
food down into stomach
• Esophageal hiatus- a hole in the
diaphragm where the esophagus
enters the abdominal cavity.
• Site of a hernia, hiatal hernia
• Cardiac sphincter- circular
muscle serves as the door to the
stomach.
• Heartburn is when acid from the
stomach is splashed up into the
esophagus causing a burning
sensation in the chest.
Stomach
• J-shaped pouch
• Located upper left quadrant of
the abdominal cavity.
• Functions:
1. Receive food and mix it with
gastric juice.
2. initiate digestion of proteins
3. limited absorption
4. passes food to small intestine.
• Stomach is distendible, it
stretches, due to rugae, inner
folds of the mucosa.
Mucosa of the Stomach
• Contains gastric pits composed
of 3 cells:
1. Chief cell- secretes pepsin
(enzyme) which breaks down
proteins to polypeptides.
2. Parietal cell- secretes
hydrochloric acid (HCl) kills
germs and needed to maintain
a low pH so pepsin can work.
3. Mucous cell- protects the
mucosa so that pepsin will not
break down the proteins in the
stomach tissue.
These products mixed together
are known as gastric juice.
Gastric Ulcers
• also known as peptic ulcers
• Due to stress, hypersecretion of HCl,
or pepsin, or not enough mucous
produced.
• A bacteria, H. pylori. are also known
to be a cause of peptic ulcers.
• The mucosa is eaten away by the
action of pepsin.
Parts of the Stomach:
Stomachs
Small Intestine
• Starts at the pyloric sphincter and
extends some 18-20 ft. in length to the
cecum of the colon.
• It is the primary organ of
digestion and absorption.
• Functions:
1. Receives partially digested food
material (chyme) from the stomach.
2. Receives secretions from the pancreas,
liver and gall bladder.
3. digestion of carbs, proteins, and lipids
by enzymes.
4. Absorption of carbs, proteins, and
lipids into the blood stream.
5. Secretes and produces various
enzymes
6. Transports the remaining undigestable
material to the colon
Small Intestine (cont)
Divided into 3 segments:
1. duodenum- 25cm, primary
organ of digestion.
• The liver, gall bladder, and
pancreas all secrete their
products here thru the common
bile duct and pancreatic duct
2. jejunum- approx. 15 ft in length,
most absorption of nutrients
occurs here.
3. Ileum- last 2 ft. very little
absorbable materials left.
• Ileocecal valve controls the
passage of material into the
large intestine (colon)
Structure of the mucosa of the small intestine
• The entire mucosa is covered
with tiny microscopic finger-like
projections called villi.
• These increase the surface area
of the small intestine some 600
times so that absorption can
occur quickly.
• Each villus is covered with even
smaller microvilli which
increase the surface area even
more.
• Intestinal glands secrete
enzymes that break down;
carbs, proteins, and lipids.
• Brunner’s glands secrete
mucous
Mucosa of S.I. (cont)
• The muscularis is the force which
propels chyme thru the lumen of
the small intestine
• Within each villi are found, a
lacteal, a lymphatic capillary, and a
blood capillary.
• The lacteal absorbs fats, the blood
capillaries absorb other nutrients.
Which are carried by the
circulatory system to all the cells
of the body.
Enzyme Secretions of the S.I.
Peptidase -proteins
Sucrase-sucrose
Maltase-maltose
Lactase-lactose
Nucleases-nucleic acids
Lipase-lipids
The Peritoneum- Mesenteric Membranes
• These are membranes covering
most of the organs of the
abdominal cavity.
• They support them loosely.
• They also contain blood vessels,
lymphatic vessels and nerves
1. Mesentary- supports small
intestine
2. Greater omentum- supports
stomach and small intestine
3. Lesser omentum- supports the
stomach and liver
Large Intestine (Colon)
• 5-6 ft. in length, performs no
digestive functions.
• Functions:
1. Reabsorb water
2. Reabsorb electrolytes
3. Stores and forms feces for
defecation.
Parts of the Colon
Cecum-blind pouch
Veriform apppendix- lymphatic tissue
Ascending colon
Transverse colon
Descending colon
Sigmoid colon-holds and forms feces
Rectum- feces stored here
Anus- site of exit of feces
Colon (cont.)
• Large bacterial flora living in the
large intestine.
• This is a symbiotic relationship
• They produce a number of B
vitamins, and vitamin K.
• These are absorbed by the large
intestine and are used by our
bodies.
• Eschericia Coli is a predominant
bacterial species living in our
colons.
• Methane is a byproduct of
these bacteria, causes
flatulation
Defecation
• Is controlled by 2 sphincter
muscles.
1. Internal anal sphincterinvoluntary, must relax before
defecation can occur.
• Stimulated to relax by fullness
in the rectum
2. External anal sphinctervoluntary, must relax and
compression of the abdominal
organs by the abdominal
muscles must occur if
defecation is to occur.
Constipation- too little water
Diarrhea- too much water
Accessory Organs Of Alimentation
The Liver
• Largest gland in the body.
• Located in the upper right quadrant
of the abdominal cavity
Functions:
1.
2.
3.
Converts glucose to glycogen and stores it.
Converts non-carbohydrates to glucose.
Synthesizes cholesterol, phospholipids, and
lipoproteins.
4. Synthesis of proteins, carb’s into fat.
5. Deamination of amino acids
6. Formation of urea
7. Stores Vitamins A, D, B12, and Iron
8. Destroys worn out rbc’s
9. Detoxifies the blood (portal vein)
10. Produces Bile.
It actually has several more functions!!!!!
Structure of the Liver
• Liver is enclosed in a fibrous
capsule and divided into lobes.
• Lobes are further divided into
lobules
• Lobules are separated by
vascular channels called hepatic
sinusoids.
• Blood from the digestive tract
from the portal vein bring
newly absorbed nutrients into
the sinusoids and nourishes
hepatic cells.
• This immediately detoxifies the
blood from the small intestine
• Hepatic cells secrete a
substance called bile.
Bile
Bile
• A yellowish green liquid secreted
and produced continuously by
hepatic cells.
• Composed of water, bile salts, bile
pigments and cholesterol.
• Bile pigments are produced by the
destruction of rbc’s.
• Bile is an emulsifier. Like soap or
detergent.
• Breaks down large fat globules into
smaller fat globules.
• Exposing a greater surface area for
catalytic enzymes to break down
fats.
Gall Bladder
• Pear shaped sac attached to the
ventral surface of the liver.
• Bile produced in the liver enters
the gall bladder thru the cystic
duct.
• The cystic duct and hepatic duct of
the liver merge to form the
common bile duct.
• The common bile duct carries bile
from the gall bladder where its
secreted to the duodenum.
• The presence of fats in the
duodenum stimulates the
secretion of bile by the gall
bladder.
• Its controlled by the sphincter of
Odi at the terminal end of the
common bile duct.
Gall Bladder (cont.)
• The gall bladder stores and
secretes bile only. The liver
produces it.
• When bile is stored in the gall
bladder, water is continually
being reabsorbed from the bile.
• When water is reabsorbed, bile
become more concentrated.
• Sometimes when this occurs,
too much cholesterol can
crystallize forming gall stones.
• Gall stones block the flow of
bile from the gall bladder.
• The removal of these stones is
called a cholecystectomy,
removal of the gall bladder.
Pancreas
• Located slightly below and behind the
stomach.
• Closely associated with the duodenum of
the small intestine.
• Pancreatic cells produce pancreatic juice
which contains enzymes.
• They are passed to the duodenum thru the
pancreatic duct.
• Which joins the common bile duct to enter
the duodenum.
• Pancreatic juice contains enzymes which
break down proteins, carbs, and fats.
Pancreatic enzymes:
Pancreatic amylase-carbohydrates
Pancreatic lipase-fats
Trypsin-proteins
Chymotrypsin-proteins
Carboxypeptidase-proteins
We’ve already discussed the endocrine
function of the pancreas