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
Components of the Digestive
System
Alimentary Canal
• Around 9 meters long
• Muscular tube that
passes through the
ventral cavity
• Lumen
Alimentary Wall Structure
• Mucosa
• Submucosa
• Muscular layer
– Circular fibers
– Longitudinal fibers
– Oblique fibers
• Serosa
Movements of the Alimentary
Canal
• Mixing movements
• Propelling movements
Mouth Structure
• Surrounded by lips,
cheeks, tongue, and
palate
• Oral cavity
• Vestibule
• Cheeks
• Lips
Tongue
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Frenulum
Papillae
Hyoid bone
Lingual tonsils
Palate
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Hard palate
Soft palate
Uvula
Palatine tonsils
Pharyngeal tonsils
(adenoids)
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
Tooth Types
• Incisors
– Chisel-shaped
– Bite off large pieces of
food
• Cuspids
– Cone-shaped
– Grasp and tear food
• Bicuspids and Molars
– Flattened surfaces
– Grind food
General Tooth Structure
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Crown
Root
Neck
Enamel
Dentin
Pulp
Root canals
Cementum
Periodontal ligament
Salivary Glands
• Secrete saliva:
– Moistens food particles
– Helps bind food
particles
– Begins chemical
digestion of
carbohydrates
– Dissolves food for
tasting
– Helps cleanse mouth
and teeth
Salivary Cells
• Serous cells
– Produce watery fluid
that contains amylase
– Amylase splits starch
and glycogen into
disaccharides
• Mucous cells
– Secrete mucus to bind
food particles and
lubricate during
swallowing
Major Salivary Glands
• Parotid glands
– Largest
– Mostly serous
secretions
• Submandibular glands
– Mostly serous
secretions
• Sublingual glands
– Smallest
– Mostly mucous
secretions
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
• Food is chewed 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.
Swallowing Reflex
• Soft palate rises to prevent 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
• Tongue presses against the soft palate,
sealing the oral cavity off from the pharynx.
• Longitudinal muscles in the pharyngeal wall
contract, moving the pharynx up toward the
bolus.
• Muscles in the lower pharynx relax, and the
esophagus opens.
• Peristalsis moves the bolus through the
esophagus.
Esophagus
• Straight, collapsible
tube
• Approximately 25 cm
long
• Passageway from
pharynx to stomach
• Cardiac sphincter
• Mucous glands for
lubrication
Movement through Esophagus Peristalsis
Stomach
• J-shaped, pouchlike
organ
• Hangs under the
diaphragm
• 1 liter capacity
• Rugae
Stomach Functions
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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
Stomach Regions
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Cardiac
Fundic
Body
Pyloric
Gastric Secretions
• Gastric pits
• Gastric glands
– Goblet cells
– Chief cells – pepsinogen
– Parietal cells – HCl and
intrinsic factor
• Gastric juice
• Regulated by ACh,
gastrin, and
cholecystokinin
Mixing and Emptying Actions of
the Stomach
Pancreas
• Secretes pancreatic
juice from acinar cells
• Mixed gland
• Pancreatic duct
• Hepatopancreatic
sphincter
Pancreatic Secretions
• Pancreatic juice
contains several
enzymes:
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Pancreatic amylase
Pancreatic lipase
Nucleases
Trypsin, chymotrypsin,
and carboxypeptidase
– Bicarbonate ions
• Release regulated by
secretin
Liver
• Located in upper right
quadrant below the
diaphragm
• Color from rich supply
of blood vessels
• Divided into left and
right lobes by fibrous
capsule
• Each lobe separated
into hepatic lobules 
functional units of
liver
Hepatic Lobule Structure
• Consists of many
hepatic cells radiating
out from a central vein
• Hepatic sinusoids
• Portal vein
• Central veins
• Kupffer cells
• Bile canals
• Common hepatic duct
Liver Functions
• Cells respond to insulin and glucagon to maintain
normal glucose levels
• Carbohydrate, lipid, and protein metabolism
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Glucose  Glycogen
Noncarbs  Glucose
Makes cholesterol and fats
Amino acids  Urea
Makes plasma proteins
Storage of glycogen, iron, vitamins A, D, and B12
Blood filtering
Detoxification
Secretion of bile
Bile
• Yellowish-green
liquid that contains:
– Bile salts – for
emulsification and
absorption of fatty
acids, cholesterol,
vitamins A, D, E, and
K
– Bile pigments –
bilirubin and biliverdin
– Cholesterol
– Electrolytes
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
• Stimulated by
cholecystokinin
Gallbladder and Liver Problems
• Jaundice
• Hepatitis
• Gallstones
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 products 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
– 25 cm long
– Most fixed portion of
the small intestine
• Jejunum
• Ileum
– Jejunum and ileum are
not distinctly separate
– Both are mobile
Mesentery
• Double-layered fold of
peritoneal membrane
• Suspends the jejunum
and ileum from the
posterior abdominal
wall
• Supports the blood
vessels, nerves, and
lymphatic vessels that
supply the intestinal
wall
Greater Omentum
• Filmy, double-layered
fold of the peritoneal
membrane
• Drapes like an apron
from the stomach over
the transverse colon
and the folds of the
small intestine
• May adhere to infected
areas of the alimentary
canal to wall it off
Intestinal Villi
• Tiny projections on the
inner wall off the small
intestine
• Densest in the duodenum
• Increase surface area for
absorption
• Lacteals – absorb fatty
acids and glycerol
• Goblet cells
• Intestinal glands
• Microvilli
– Secrete peptidases, sucrase,
maltase, lactase, intestinal
lipase
• Capillaries absorb simple
sugars, amino acids,
electrolytes, and water
Large Intestine
• Ileocecal valve
• 1.5 meters long
• Extends up right side,
crosses obliquely to
the left side, and
descends into the
pelvis
• Opens to the outside
of the body as the anus
Regions of Large Intestine
• Cecum
– Vermiform appendix
• Colon
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Ascending colon
Transverse colon
Descending colon
Sigmoid colon
• Rectum
• Anal canal
Anal Canal Structure
• Anal columns
• Anus
– Internal anal sphincter
– External anal sphincter
• Hemorrhoids
Large Intestine Anatomy
• Lack villi
• Teniae coli
• Many goblet cells
– Protect intestinal wall
– Bind particles of fecal
matter
– Help control pH
Large Intestine Functions
• Proximal end functions primarily in water
and electrolyte absorption
• Distal end functions primarily to store feces
• Little to no digestive function
• More sluggish movements – peristaltic
waves 2-3 times per day (mass movements)
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
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Water
Electrolytes
Mucus
Bacteria
• 75% water
• Color from bile pigments
altered by bacterial action
• Odor from compounds
produced by bacteria