Transcript HumanDigSys

The Human Digestive System
The Mouth
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Structure: see diagram
Function: Ingest and Digest
Ingestion - the teeth and tongue
(taste buds) take in the
appropriate size and kind of food.
Digestion - the teeth (incisors,
canines and molars) cut, tear and
grind food (mechanical digestion)
Salivary glands add saliva (water,
mucous, amylase) to further aid
in mechanical breakdown
Amylase starts the chemical
digestion of starch
(polysaccharide)
The Mouth continued:
• Saliva moistens food, breaking it down
physically and also making it slippery
• The tongue rolls food around keeping it
between teeth (mechanical digestion)
• Food eventually becomes ball of chewed food
known as a bolus
• When swallowed, food is prevented from
entering the nasal cavity by the uvula
(pushed upwards) or the trachea by the
epiglottis (cartilage flap closes downward)
Esophagus
• Esophagus - tube joining the
pharynx to the stomach
• Lined with mucous and two
smooth muscle layers
(circular and longitudinal
muscles)
• Pathway for bolus to reach
the stomach
• Performs peristalsis (wave
like muscle contractions that
push and pull food to
stomach)
Stomach
• Stomach Structure
• J-shaped sac covered with
three muscle layers
(c,l,oblique)
• Rugae are the inner folds
with special gastric cells
• Gastric cells secrete
mucous, hydrochloric acid
and enzymes (pepsin)
• Two sphincters (cardiac,
pyloric) seal stomach tightly
Stomach lining
• Nice folds!!
Stomach Function
• The stomach completes mechanical digestion
• Muscle layers slosh food around with hydrochloric acid
(corrosive) breaks food down into small pieces
• Chyme = semi-liquid acidic food
• Pepsin (enzyme) initiates protein digestion (chemical digestion)
breaking peptide bonds within complex proteins producing
polypeptides (hydrolysis reactions)
• The acidic conditions of the stomach denatures amylase
(stopping chemical digestion of starch) and kills most
microorganisms ingested in your food
Stomach Cells (Gastric Pits)
Small Intestine
• Structure:
• Long tube (6 m), narrow
lumen lined with villi and
microvilli
• Includes rich blood supply
• Three main regions:
• Duodenum (25 cm)
• Jejunum (3 m)
• Ileum (3m)
• Function:
• Complete chemical digestion
• Absorb nutrients
Duodenum and accessory organs
• The duodenum is the first
part of the small intestine
• It is short (25 cm) and not as
highly folded as the other
regions of the s.int.
• The chyme from the stomach
is very acidic (pH 2) so the
duodenum is more mucous
lined then the rest of the
tube.
• It receives secretions from
the pancreas and liver (gall
bladder).
Liver and Gall Bladder
• Liver produces bile (gall
bladder stores it)
• Carried to duodenum
through the common
bile duct
• Bile emulsifies fats
(keeps them from
joining together)
• Increasing surface area
to improve the chemical
digestion of fats.
Pancreas
• Pancreas adds two main
secretions to the duodenum:
• A) Sodium bicaronate baking soda to neutralize
acidic chyme raising the pH
to over 7.
• B) package of 28 digestive
enzymes - protein,
carbohydrate and lipid
digesting enzymes to
continue and help complete
chemical digestion
Jejunum and Ileum
• The jejunum and the ileum are essentially the same continuous
tube lined with enzyme producing cells to complete chemical
digestion
• Carbohydrates - monosaccharides
• Proteins - amino acids
• Lipids - glycerol and fatty acids, cholesterol
Jejunum and Ileum
• Both are highly folded with villi and microvilli
• These increase the surface area to facilitate absorption
• Most nutrients absorbed by diffusion, some by facilitated
diffusion and active transport
• Amino acids and monosaccharides, along with most vitamins
and minerals (element ions) enter the capillary networks while
fatty acids and glycerol are picked up by the lacteals (lymph)
Large Intestine
• The remaining digested
liquid food material enters
the large intestine
• A wide tube lined with
circular and longitudinal
muscles
• The approximately 1-1.25 m
long tube has three main
parts: Ascending colon,
Transverse colon and the
Descending colon ending
with the anus (rectum).
Large Intestine Function
• The primary function of the
large intestine is to reabsorb
water! Water has been
added the entire length of
the tube to help with moving
the food along as well as
digestion and now has to be
returned to the body along
with some electrolytes
(minerals).
• The bacteria that live
symbiotically in the large
intestine also produce
vitamins K, B (B12),
riboflavin and niacin that are
also very useful to us and
are absorbed by the large
intestine.
Human Digestive System
• Peristalsis moves food,
chyme, liquid digestive food
throughout system
• There can be issues with
several (all) steps along the
way that interfere with
digestion/system.
• HW
QuickTi me™ and a
TIFF (U ncompressed) decompressor
are needed to see this pi cture.