Digestive System
By: Isaías Quezada, Emely
Rivera, Carlos Sandoval
Per.5
Overview
 The digestive system consists of the Alimentary canal:
1.Mouth
2.Pharynx
3.Esophagus
4.Stomach
5.Small intestine
6.Anal canal
 Accessory structures:
1.Salivary glands
2.Liver
3.Gallbladder
Structure of the Alimentary
Canal’s Walls
 Its' walls consist of four distinct layers that are developed to
different degrees from region to region. Certain regions are
specialized for certain functions. These layers are:
1.Mucosa
2.Submucosa
3.Muscular Layer
4.Serosa
Mucosa
 formed of surface epithelium, lamina propria(connective
tissue), and a small amount of smooth muscle
 Function are protection, secretion, and absorption
Submucosa
 Contains loose connective tissue, glands, blood vessels,
lymphatic vessels, and nerves
 Function is to nourish surrounding tissues and carry away
any absorbed materials
Muscular Layer
 consists of two coats of smooth muscle tissue arranged in
circular and longitudinal groups
 Provides movement of the tube and its contents
Serosa
 outer covering of the tube and comprised of visceral
peritoneum, which is formed of epithelium on the outside and
connective tissue beneath
 Its function is both protection and lubrication
Types of Movement
There are two main motor functions of the
alimentary canal; mixing & propelling
Types of Movement: Mixing
 Occurs when smooth muscles in small segments of the tube
contract rhythmically
 When the stomach is full, waves of muscular contractions
move along its wall from one end to the other.
 The waves occur every twenty seconds and they mix foods
with the digestive juices that the mucosa secretes
Types of Movement: Propelling
 a wave-like motion called peristalsis occurs
 a ring of contraction appears in the wall of the tube, yet just
ahead the muscular wall relaxes
 This action begins when food expands the tube
Mouth
 First portion of alimentary canal
 Receives food
 Begins mechanical digestion
 Breaks food into smaller pieces
 Organ of sensory and speech
Cheeks
 Lateral walls of mouth
 Consist of outer layers of skin
 Pads of subcutaneous fat
 Muscles that help with expressions and chewing
 Moist inner layers moist, stratified squamious epithelium
Lips
 Mobile structures surrounding mouth
 Contain skeletal muscle
 Judges temperatures and texture of food
 Reddish color comes from amount of blood cells
 External borders mark boundaries between skin of face and
mucous membrane that lines in alimentary canal
Tongue
 Muscular organ rest on the bottom of the mouth
 Covered by mucous membrane
 Connected by midline to the floor by membranous fold,
lingual frenulum
 Composed of skeletal muscle fibers that run in several
directions
 Papillae
 Root held by hyoid bone
Palate
 Roof of oral cavity
 Hard anterior , soft posterior
 Hard palate formed by palatine processes of maxillary
 soft palate forms a muscular arch
 Uvula
 Muscles here help with swallowing
 Palatine tonsils
 Pharyngeal tonsils.
Teeth
 Hardest structures in body
 Not considered part of the skeletal system
 Develop in sockets in alveolar process of mandibular and
maxillary bones
 Permanent teeth come at about six years old
 They break food into smaller particles, thus beginning the
mechanical process
 Helps mix food with saliva
Salivary Glands
 Secretes saliva
 minor glands are found on mucosa of the mouth
 Constantly secreting fluid to keep mouth moist
 There are 3 pairs of major glands, parotid, submandibular,
sublingual
Secretion
 Secretory cells within the glands, Serous, and Mucous cells
 Serous cells contain salivary amylase.
 Enzymes split starch and glycogen molecules, they then
become disaccharides
 This begins chemical digestion
 Mucous cells secrete mucus
 Glands have parasympathetic and sympathetic nerves
Pharynx
 Connects nasal and oral cavity with larynx and esophogus
Nasopharynx
o Located: superior to the soft palate
o Communicates with the nasal cavity and provides a
passageway for air during breathing
Oropharynx
o Located: posterior to the mouth
o Passageway from the mouth for air moving to and from the
Pharynx (continued)
Laryngopharynx
o Located: inferior to the oropharynx
o Extends from the upper boarder of the….downward to the
lower boarder of the cyroid cartilage of the larynx and is a
passageway to the esophagus
Esophagus
 Straight, collapsible tube that is about 25 cm. long
 Provides a passageway for food
Cardiac Sphincter
 Remain contracted
 Close entrance to the stomach
 Prevents regurgitation
Parts of the Stomach: Cardiac
Region
 A small are near the esophageal opening, or cardia
 This is where the contents of the esophagus empty into the
stomach
Parts of the Stomach: Fundic
Region
 Serves as a temporary storage area and sometimes fills with
swallowed air
 This produces a gastric air bubble which may be used as a
landmark on a radiograph of the abdomen
Parts of the Stomach: Body
Region
 The main portion of the stomach and located between the
fundic and pyloric portions
 The main chamber for containing food
Parts of the Stomach: Pyloric
Region
 Funnel-shaped
 Shape narrows and becomes the pyloric canal as it approaches the
small intestine
 At the end, the circular layer of fibers in its muscular wall thickens
and forms the muscle Pyloric Sphincter, which acts as a valve that
controls gastric emptying
Gastric Secretions
 The stomach’s mucous membrane is studded with gastric
pits, located at the ends of tubular gastric glands
 Their structure and composition of their secretion vary in
different parts of the stomach
 All gastric glands generally contain 3 types of secretory cells
Secretory Cells
 Mucous Cells: found in the necks of the glands near the
openings and is responsible for lining the stomach from
digestive juices
 Chief Cells: also known as peptic cells are a key component
of gastric juices
 Parietal Cells: also known as oxyntic cells. When the chief
cells secrete enzymes and parietal cells release a
hydrochloric acid solution, they form the gastric juices
Major Components of Gastric
Juices
Components
Source
Function
Pepsinogen
Chief Cells of the Gastric
glands
Inactive form of
pepsin
Pepsin
Pepsinogen in the
presence of hydrochloric
acid
Protein-splitting
enzyme that
digests all dietary
protein
Hydrochloric acid
Pepsinogen in the
presence of hydrochloric
acid
Protein-splitting
enzyme that
digests all dietary
protein
Mucus
Goblet cells and mucous
glands
Provides viscous
alkaline protective
layer on the inside
of the stomach
wall
Intrinsic factor
Parietal cells of the
gastric glands
Aids in vitamin
B12 absorption
Phases of Gastric secretions
Phase
Action
Cephalic phase
Sight, taste, or thought of food
triggers parasympathetic reflexes.
Gastric juice is secreted in
response
Gastric phase
Food in stomach chemically &
mechanicaly stimulates release of
gastrin, stimulating secretion of
gastric juice; reflex response also
stimulate gastric juice secretion
Intestinal phase
As food enters small intestine, it
stimulates intestinal cells to
release intestinal gastrin,
promoting the secretion of gastric
juice from the stomach wall.
Pancreas
 Endocrine Gland/exocrine function
 Secretes pancreatic juices
Pancreas (structure)
 Located posterior to parietal peritoneum
 Pancreatic acinar cells: produce pancreatic cells
 Aclai: clusters around tiny tubes which release their
secretions
 Small tubes connect to pancreatic duct
 Pancreatic duct connects with duodenum
Stomach
 A J-shaped pouch like organ in the abdominal cavity
 It receives food from the esophagus, mixes it with gastric
juices, initiates the digestion of proteins, carries on limited
absorption, and transports food into small intestine
 Divided into four sections;
1.Cardiac region
2.Fundic section region
3.Body regions
4.Pyloric regions
Liver
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•
•
•
•
•
•
Largest gland in the body
Weights 3.2 – 3.7 pounds
Detoxifies blood
Creates bile for stomach
Stores vitamins, iron, simple sugar glucose
Converts ammonia to urea
Very Likely to get disease due to the mass of functions it
carries out
Gallbladder
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•
•
•
Pear shaped
Stores conventrate bile
Stores any bile that is not used
Cholecystokinin causes the release of bile to
small intestine
• Cholestoral, bile salts, can create Gallstones
Regulation of Bile Release
Small Intestine
 A tubular organ that extends from the pyloric sphincter
to the beginning of the large intestine
 Recieves secretions from the pancreas and liver
 Completes digestion of the nutrients in chym
Macromolecules
Carbohydrates
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Begins in the mouth
Parctially digested carbs travel to esophagus and then the
stomach
Move to the small intestine where they are broken down by
enzymes from the pancreas
Then absorbed into the blood stream
Fiber passes through undigested
Lipids
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Some digested in mouth and stomach
Mainly in the small intestine
Bile produced in liver is sent to gallbladder
Fatty acids combine with cholesterol and bile
Transported to veins of chest and the blood carries fat to be
stored in adipose tissue
Macromolecules (cont)
Proteins
 Digested into amino acids
 Begins in stomach with gastric juice
 Potent enzymes from pancreas
 Continues to the small intestine
 Amino acids absorbd into the blood
Duodenum
Shortest and most fixed portion of the small intestine
C-shaped
Recieves the partly digested food
Jejunum
Greater diameter
Thicker wall
More vascular
More active
Support absorption of carbohydrates and protiens
Ileum
More lymph nodules
Higher bacterial population
Absorb chyme
Large Intestine
 1.5 meters long
 Consists of cecum, colon, rectum, and anal canal
 Begins in iliac region of pelvis
 Joined together with small intestine
 Continues across and down the abdominal cavity, and ends
at the anus
 Takes 16 hours to digest
 Transports waste and re-absorption of water before it gets
secreted.
 Absorbs water and vitamins
 Reduces Acidity
Cecum
 Tube like structure in lower abdominal cavity
 Receives undigested food from small intestine
 Absorbs fluids and salts that remain after intestinal digestion
and absorption
 Mixes the contents with mucus
 Has a thick layer of mucous membrane
 Layer of muscle that makes churning and rubbing
movements
Colon
 Removes water, salt, and nutrients that form stool
 Muscles squeeze the contents through the intestine
 Bacteria is found along the walls of the colon
 4 parts, descending, ascending, transverse, and sigmoid
 Supported by peritoneum
Rectum
 10 to 12 cm
 Dilates towards the anus
 Stores feces
 Stretch receptors in walls tell when the body needs to
defecate
 When the rectum storage is full, the pressure pushes the
feces to the anus
 Body temperature can checked from rectum area
Anal Canal
 3-5 cm
 Lubricates feces as it comes from rectum
 Has muscular sphincter system that closes lumen
 External anal sphincter surrounds anal canal and acts like a
clamp. Similar to the puborectalis muscles that covers rectum
from behind.
 Both of which are voluntarily controlled
 Internal anal sphincter relaxes so blood in anal cushions
drain, which allows feces to go through
Hormones
Hormone
Function
Hormone
Function
Gastrin
Produce acid to
dissolve food
Ghrelin
Stimulates
appetite
Paptide YY
Inhibits
appetite
Leptin
Tells the
body it is full
Intestinal gastrin
Increase activity of
gastric glands
Inner/Somatostatin
Inhibits secretion of
acid
Cholecystokinin
Decrease activity of
gastric glands;
stimulates
pancrease;
stimulates
gallbaldder
Secretin
Stimulates pacreas
to secrete fluid