Digestive System
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Transcript of Digestive System
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Digestive System
By: Isaías Quezada, Emely Rivera, Carlos SandovalPer.5
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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
4.Pancreas
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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
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Mucosa formed of surface epithelium, lamina propria(connective
tissue), and a small amount of smooth muscle
Function are protection, secretion, and absorption
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Submucosa Contains loose connective tissue, glands, blood vessels,
lymphatic vessels, and nerves
Function is to nourish surrounding tissues and carry away any absorbed materials
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Muscular Layer
consists of two coats of smooth muscle tissue arranged in circular and longitudinal groups
Provides movement of the tube and its contents
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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
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Types of Movement
There are two main motor functions of the alimentary canal; mixing & propelling
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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
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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
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Mouth
First portion of alimentary canal
Receives food
Begins mechanical digestion
Breaks food into smaller pieces
Organ of sensory and speech
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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
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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
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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
Posterior covered in lingual tonsils
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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.
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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
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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
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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
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Pharynx
Connects nasal and oral cavity with larynx and esophogus
Nasopharynx
oLocated: superior to the soft palate
oCommunicates with the nasal cavity and provides a passageway for air during breathing
Oropharynx
oLocated: posterior to the mouth
oPassageway from the mouth for air moving to and from the nasal cavity
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Pharynx (continued)
Laryngopharynx
oLocated: inferior to the oropharynx
oExtends 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
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Esophagus
Straight, collapsible tube that is about 25 cm. long
Provides a passageway for food
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Cardiac Sphincter
Remain contracted
Close entrance to the stomach
Prevents regurgitation
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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
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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
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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
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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
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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
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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
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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
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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.
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Pancreas Endocrine Gland/exocrine function
Secretes pancreatic juices
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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
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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
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Liver
• 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
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Gallbladder
• 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
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Regulation of Bile Release
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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
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Macromolecules
Carbohydrates 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 LipidsSome digested in mouth and stomach Mainly in the small intestineBile 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
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Macromolecules (cont)
ProteinsDigested into amino acids Begins in stomach with gastric juicePotent enzymes from pancreasContinues to the small intestineAmino acids absorbd into the blood
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Duodenum
Shortest and most fixed portion of the small intestine C-shapedRecieves the partly digested food
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JejunumGreater diameterThicker wall More vascularMore activeSupport absorption of carbohydrates and protiens
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IleumMore lymph nodules Higher bacterial populationAbsorb chyme
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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
Produces antibodies
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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
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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
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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
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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
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HormonesHormone Function
Gastrin Produce acid to dissolve food
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
Hormone Function
Ghrelin Stimulates appetite
Paptide YY Inhibits appetite
Leptin Tells the body it is full