Download The Digestive System

The Digestive
System
Digestion
• Digestion
• the mechanical and
chemical breakdown of
foods into nutrients
that cell membranes
can absorb
• 2 Components of the
digestive system:
• Alimentary canal –
mouth, pharynx,
esophagus, stomach,
small intestine, large
intestine, anal canal
• Accessory organs –
secrete products into the
canal; salivary glands,
liver, pancreas,
gallbladder
Alimentary Canal
• Around 9 meters (30
feet) long
• Muscular tube that
passes through the
ventral cavity
Alimentary Wall Structure
• Mucosa-innermost
layer
• Submucosa- 2nd layer
• Muscular layer-3rd
• Circular fibers
• Longitudinal fibers
• Oblique fibers
• Serosa-Outside layer
Mouth Structure
• Surrounded by lips,
cheeks, tongue, and
palate
• Oral cavity
• Vestibule
• Cheeks
• Lips
Tongue
• Frenulum
• Secures
tongue to
floor of
mouth
• Papillae
• Hyoid bone
• Lingual tonsils
Palate
•
•
•
•
•
Hard palate
Soft palate
Uvula
Palatine tonsils
Pharyngeal tonsils
(adenoids)
• Tonsils are
lymphatic tissue
used to protect
you from infection
Primary and Secondary Teeth
• Primary teeth
• Deciduous teeth
• Erupt between 6
months and 2-4 years
• 20 teeth
• Secondary teeth
• Appear around 6
years
• 32 teeth
All teeth have a coating
of enamel (hardest
substance in human
body)
Salivary Glands
• Secrete saliva:
• Moistens food particles
• Helps bind food particles
• Amylase (enzyme) begins
chemical digestion of
carbohydrates (used first for
energy)
• Dissolves food for tasting
• Helps cleanse mouth and teeth
• Mucus softens food &
lubricates G.I tract
Regions of the Pharynx
• Nasopharynx
• Open to nasal cavity
• Passage for air
during breathing
• Oropharynx
• Behind soft palate
• Passage for air and
food
• Laryngopharynx
• Passage for food to
the esophagus
Swallowing Reflex= deglutition
1.
2.
3.
Food is chewed
(mastication)and
mixed with saliva to
form a mass called a
bolus.
Bolus is forced into the
pharynx.
Swallowing reflex is
stimulated by sensory
receptors around the
pharyngeal opening.
4.
5.
6.
Soft palate rises and
seals the nasal
cavity off with the
uvula to stop food
from entering the
nasal cavity.
Hyoid bone and
larynx are elevated,
and the epiglottis of
the larynx closes off
the top of the
trachea.
Breathing is briefly
inhibited.
Swallowing Reflex
7. Tongue presses against the soft palate, sealing the
oral cavity off from the pharynx.
8. Longitudinal muscles in the pharyngeal wall
contract, moving the pharynx up toward the bolus.
9. Muscles in the lower pharynx relax, and the
esophagus opens.
10. Peristalsis moves the bolus through the
esophagus.
Swallowing Reflex
Esophagus
Disorders:
Acid Reflux
Ulcers
Heart Burn
• Straight, collapsible
tube
• Approximately 25 cm
long
• Passageway from
pharynx to stomach
• Cardiac or esophageal
sphincter (entry to
stomach)
• Mucous glands for
lubrication
Stomach
Disorders:
Ulcers
Tortion
• Receives food from the
esophagus
• Mixes food with gastric
juices
• Initiates protein digestion
• Performs limited
absorption of water, salts,
alcohol, and lipid-soluble
drugs
• Moves food into the small
intestine
• Bolus now turns into
chyme (creamy paste)
• Food enters through
esophageal sphincter
and exits via pyloric
sphincter
Exploratory Surgery
• Gastric pits
• Gastric glands
Gastric Secretions
• Goblet cells
• Chief cells – pepsinogen
• Parietal cells – HCl
• Gastric juice
• HCl
• Pepsin-digest protein
• Regulated by ACh, gastrin,
and cholecystokinin
Mucosal layer of stomach
prevents stomach acid from
eating through itself and
releasing acid into the
abdomen
Lower pH (Acids)
Pancreas
• Secretes pancreatic
juice from acinar cells
• Mixed gland
• Pancreatic duct
• Hepatopancreatic
sphincter
• Helps digest
carbohydrates,
proteins, fats & nucleic
acids
Pancreatic Secretions
• Pancreatic juice
contains several
digestive enzymes:
•
•
•
•
Pancreatic amylase
Pancreatic lipase
Nuclease
Trypsin,
chymotrypsin, and
carboxypeptidase
• Bicarbonate ions
What does the Pancreas do?
Liver
• Carbohydrate, lipid,
and protein
metabolism
• Storage of glycogen,
iron, vitamins A, D,
and B12
• Blood filtering
• Detoxification
• Secretion of bile
(emulsifies/breaks
down fats)
How does the Liver work?
Gallbladder
• Pear-shaped sac on the
inferior liver surface
• Connects to the cystic
duct which feeds into
the common hepatic
duct
• Stores bile between
meals
• Reabsorbs water to
concentrate bile
• Releases bile into the
small intestine
• Common bile duct
Small Intestine
• Extends from pyloric
sphincter to the large
intestine
• Receives secretions from
the pancreas and liver
• Completes digestion of
nutrients in chyme and
absorbs nutrients of
digestion
• Mixing movements and
peristalsis – chyme moves
through in 3-10 hours
• Transports digestive
residue to the large
intestine
Regions of the Small Intestine
• Duodenum
• Portion closest to
stomach
• 25 cm long
• Most fixed portion of
the small intestine
• Jejunum-middle
portion
• Ileum
• Final portion of small
intestines prior to large
intestines
Intestinal Villi
• Tiny projections on the
inner wall off the small
intestine
• Densest in the
duodenum
• Increase surface area
for absorption
• Microvilli
• Secrete peptidases,
sucrase, maltase,
lactase, intestinal lipase
• Capillaries absorb
simple sugars, amino
acids, electrolytes
(coenzymes that help
control metabolism),
and water
Large Intestine
• Ileocecal valve
• 1.5 meters long
• Proximal end
functions primarily in
water and electrolyte
absorption
• Distal end functions
primarily to store
feces
• Little to no digestive
function
Regions of Large Intestine
• Cecum
• Vermiform appendix
• Colon
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•
•
•
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
• Rectum
• Anal canal
To Gas or not to Gas?
Anal Canal Structure
• Anal columns
• Anus
• Internal anal
sphincter
• External anal
sphincter
• Hemorrhoids
Defecation Reflex
• Can be initiated by person (deep breath
and abdominal contraction)
• Forces feces into rectum
• Reflex involves relaxation of the internal
anal sphincter and peristaltic waves
through the descending colon
• Can be prevented by contraction of the
external anal sphincter
Feces
• Made of materials
not digested or
absorbed
•
•
•
•
Water
Electrolytes
Mucus
Bacteria
• 75% water
• Color from bile
pigments altered by
bacterial action
• Odor from
compounds
produced by
bacteria