Digestive System
Download
Report
Transcript Digestive System
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
•
•
•
•
•
•
•
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
•
•
•
•
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
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
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