Class 9
Digestive System
Digestive System Functions:
• Digestion
– Breaking down food into
usable nutrients
• Absorption
– Transferring nutrients into
bloodstream
• Excretion
– Expelling out non-digestible
and non-useable materials.
The Alimentary Canal
• Continuous
hollow tube
extending from
mouth to anus.
• Mouth, pharynx,
esophagus,
stomach, small
intestine, large
intestine, anal
canal
Accessory Organs
• Organs that contribute
to the digestive process,
but are not part of the
alimentary canal and
the food does not travel
through.
• Salivary Glands, liver,
gall bladder, pancreas
Four Layers
Four Layers
Movements of the Alimentary Canal
• Peristalsis
– Propels contents forward
– Alternates between circular
and longitudinal muscles.
• Mixing Movements
– Uses circular and longitudinal
muscles simultaneously to
cause a “mixing” or
“churning” type of movement.
– Mixing can be done all along
the canal, but is most
noticeable in the stomach.
The Mouth
Mouth Functions
• Small amount of
digestion (starch)
• Taste
•
•
Receive food
Moisten food and prepare
for further processing
Salivary Glands
Exocrine glands composed of mucous and serous cells
• Parotid
– Largest of the main glands,
secretes mostly serous fluid
• Submandibular
– secretes equal amounts of
serous and mucous fluids
• Sublingual
– secretes mostly mucous fluid
•Saliva components:
•98% water
•2% - antibacterial components,
mucus,
electrolytes (Na, Ca, K, Mg),
amylase (salivary)
•Salivary Amylase breaks down CHO,
therefore……..
•CHO DIGESTION BEGINS IN
THE MOUTH
The Pharynx
Swallowing
• known as deglutination
• allows food to pass from the mouth to
the pharynx to the esophagus
• can start as a “voluntary” action, but
quickly becomes involuntary
• “Bolus” passes along hard palate then
to soft palate with tongue pushing
towards oropharynx.
• bolus is prevented from gaining entry
into the larynx by the epiglottis
The Esophagus
• Pierces the diaphragm through the
esophageal hiatus
•Circular muscles that close off
before entering the stomach:
cardiac sphincter ( aka
gastroesophageal sphincter, lower
esophageal sphincter)
Function – propel food into stomach
THERE IS NO DIGESTIVE FUNCTION
The Stomach
Stomach
Gastric glands
Function
• temporary storage
tank for food
• site for mechanical
and chemical
breakdown of
proteins….
• Mucous cells
– secretes mucous
• Parietal cells
– secretes HCl (acid), intrinsic factor
(protein released to allow intestine
to absorb vit B12)
• PROTEIN DIGESTION • Chief cells
BEGINS IN THE
– secretes pepsinogen (an inactive
STOMACH
form of pepsin). Once this mixes
**cells in the lining of the mucosa continuously secrete
bicarbonate to protect the stomach lining from self
digestion. So this, along with mucous, protects the lining.
with HCl, it becomes pepsin and is
able to breakdown protein into
amino acids.
The Pancreas
Pancreas
Functions of the
Pancreas:
Pancreatic juice
•
pancreatic amylase breaks down
carbs
Releases enzymes that digest
fats, proteins, carbohydrates, • pancreatic lipase breaks down fats
and nucleic acids
• Produces alkaline (basic) fluid • proteinase (Trypsin) breaks down
to neutralize acidic chyme in
proteins
small intestine
• Produces insulin and glucagon • nuclease breaks down nucleic acid
into nucleotides (from DNA and RNA)
to regulate sugar metabolism
•
•
* Pancreatic juice is very alkaline, which
helps neutralizes the fluid and allows the
intestine to absorb properly.
Liver
Hepatic Portal System
Liver
• Lobes:
2 lobes, left and right
• Hepatic Lobules:
– cylindrical structures which are the
functional units of the liver.
– Contain:
•
•
•
•
hepatocytes,
bile canals and ducts,
artery (hepatic),
vein (hepatic portal on perimeter and
central vein draining sinusoids into
hepatic veins),
• sinusoids (blood filled spaces
between hepatocytes),
• Kupffer cells (specialized
macrophages).
Liver Functions
• Makes and secretes bile
• Stores some vitamins and iron
• Detoxification
• Stores glucose
• Modifies fats so the body can use them more efficiently
• Forms plasma proteins
• Helps excrete by-products of RBC (bilirubin) into bile
• Synthesizes urea (by-product of protein metabolism), released into blood and
sent out in urine
Bile
• Emulsify fats
• Stored in the gall bladder & becomes 5x more concentrated
• Produced by Hepatocytes
• Pasty yellow/green substance
• Contents: bilirubin, cholesterol, salts, water, sodium and
potassium and sometimes small amounts of copper and
other metals
• About 1 liter per day is made by the liver
• About 95% of all salts found in bile are reabsorbed in the
body in the lower small intestine
The Gallbladder
The Small Intestine
Structures of the Intestinal Wall
The Large Intestine
Defecation Reflex
Thank goodness!!!