Transcript ADAPTATIONS FOR NUTRITION AND DIGESTION

THE HUMAN DIGESTIVE SYSTEM
Food passes through the digestive tube
in the following order
Oral cavity
(mouth)
pharynx
(throat)
esophagus
(gullet)
Stomach
small
intestine
large
intestine
Rectum
anus
HUMAN DIGESTIVE SYSTEM
• Liver, pancreas and salivary glands lie
outside of the digestive tract and they are
called as accessory organs.
• Food is never found within the alimentary
canal itself.
• These organs aid digestion by the
secretion of digestive fluids.
THE MOUTH AND PHARYNX
• Mechanical breakdown and chemical
digestion occur.
• Chunks of food are bitten of with the teeth
and ground into pieces small enough to
swallow
• The tongue moves and shapes the food
mass in the mouth
• Saliva is secreted into the mouth by three
pairs of salivary glands
TYPES OF SALIVA
Thin,
watery
secretion that
wets the food
Thicker,
mucuous
secretion that acts as
a
lubricant
and
causes
the
food
particles to stick
together to form a
food mass (bolus)
• Saliva also contains a digestive enzyme called
salivary amylase . (This enzyme breaks down
starch, which is
a polysacharide, into
maltose, which is a disaccharide.)
• When the food has been chewed sufficiently , it
is pushed by the tongue to the back of the throat,
or pharynx. This starts the automatic swallowing
reflex, which forces the food into the
esophagus, the tube leading to the stomach.
• To prevent food and liquids from entering the
larynx, it is automatically closed off during
swallowing by a flap of tissue called epiglottis.
• At the same time, breathing stops momentarily
and passageways to the nose, ears and mouth
are blocked
THE ESOPHAGUS
• The esophagus is a tube through which
food passes from pharynx to the stomach.
• Beginning in the esophagus, the
movement of food down the digestive tube
is aided by alternate waves of relaxation
and contraction in the muscular walls of
the alimentary canal. This is called
peristalsis.
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THE ESOPHAGUS
• Where the esophagus opens into the
stomach , there is a ring of muscle called
sphincter. There are two sphincters to
isolate the stomach.
Cardiac sphincter
Pyloric sphincter
is located between
the esophagus and
the stomach
is located between
the stomach and
the intestine
• When the wave of peristalsis reaches the
sphincter, it relaxes and opens, and the
food (bolus) enters the stomach.
• During vomitting, a wave of peristalsis
passes upward -reverse peristalsiscausing the cardiac sphincter to open, and
the contents of the stomach to be “thrown
up”
THE STOMACH
• The stomach is thick-walled muscular
sac.
• Food is stored temporarily in the stomach.
• Mechanical breakdown and the partial
digestion of protein occur.
• Churning of the stomach causes
mechanical break down and helps the
mixing of the food with its secretions.
GLANDS OF THE STOMACH
Pyloric glands
Gastric glands
•Secretes mucus
•Mucus
protects
the lining of the
stomach
from
being digested
•Secretes gastric
juice(pH 1.5 to 2.5)
GASTRIC JUICE
HCl
•HCl kills the bacteria
that are swallowed
with food
•Activates pepsinogen
Pepsinogen
• Inactive form of pepsin and
activated by HCl
•Breaks down large protein
molecules
into
shorter
chains
of
a.a
called
polypeptides.
GLANDS OF THE STOMACH
In stomach:
Gastric Gland
Pyloric Gland
Gastric juice = Hydrochloric acid + Pepsinogen + Mucus
HCl
Pepsin
Mucus
- kills most bacteria that
- starts digestion of
enter with food
proteins (breaks down stomach from HCl and
- activates pepsinogen
large protein
Pepsinogen
HCl
Pepsin molecules into smaller
polypeptide chains)
- protects the lining of
pepsin
GLANDS OF THE STOMACH
Control of Gastric Juice Secretion
thought/ sight/ smell/ taste of food
food in stomach
gastric juice is secreted
(touching the wall of stomach)
food in stomach
(stretching the wall of stomach)
gastrin (hormone)
blood
THE STOMACH
The breakdown of starch by salivary
amylase which begins in the mouth,
continues for some time after the food
mass reaches the stomach. Gradually
however, the low pH of the acid in the
stomach inactivates this enzyme and
starch breakdown.
THE STOMACH
There are three mechanisms involved in
stimulating the flow of gastric juice.
1. The thought, sight, smell or taste of food
stimulates the brain to send messages to
the gastric glands, causing them to
secrete moderate amounts of gastric
juice
THE STOMACH
2. Food touching the lining of the stomach
stimulates the secretion of moderate
amounts gastric juice.
3. When a food mass enters the stomach, it
stretches the stomach wall. The streching of
the stomach wall, as well as the presence of
proteins, caffeine, alcohol and certain other
substances, stimulates the lining of the
stomach to secrete a hormone called gastrin
directly into the blood. Gastrin further
stimulates the gastric glands in the stomach
to secrete large amounts of gastric juice.
THE STOMACH
•Liquids pass through the stomach in 20
minutes or less.
•Solids on the other hand, must first be
reduced to a thin, soupy liquid called chyme
THE SMALL INTESTINE
pyloric sphincter
6.5 meters in length
2.5 cm in diameter
chyme
duodenum
jejenum
ileum
Most of the digestion
takes place
FUNCTIONS OF THE SMALL INTESTINE:
1. Most of the chemical digestion takes
place and completed in it
2. It is the site of absorption
THE SMALL INTESTINE
It has a number of structural features that increase
the surface area for absorbtion.
a) It is very long
b) Its lining has many folds
c) The lining is covered with millions of finger-like
projections which are called villi
d) The epithelial cells that make up the intestinal
lining have brush borders. In the brush borders,
the membranes of cells that face into the intestinal
opening have tiny projections called microvilli
that further increase the surface area of the cells.
Within each villus , there is a
network of blood capillaries
and in the center of it there is a
lacteal. Fatty acids and
glycerol are absorbed into tiny
lacteals of the lymphatic
system.
THE SMALL INTESTINE
•
•
1.
2.
3.
4.
Absorption involves both diffusion and active
transport.
When food is present, the small intestine is in
constant motion. This peristaltic movements
have four effect:
They squeeze chyme through the intestine
They mix the chyme with the digestive
enzymes
They break down food particles mechanically
They speed up absorption of digestive end
products by bringing the intestinal contents into
contact with intestinal wall.
Chyme from the stomach is mixed with
Pancreatic
juice
from
pancreas
Bile from the
liver
Intestinal
juice
from
glands in the
wall of the
intestine
*** Fluids in the small intestine are generally alkaline
PANCREAS
• Pancreas is located in the abdominal
cavity between stomach and duodenum.
• It is both endocrine and exocrine gland.
• It secretes insulin and glucagon form the
Islets of Langerhans
• pH of pancreatic juice is 8.5
PANCREATIC JUICE
• When the acidic chyme from the stomach
enters the small intestine, it stimulates
cells in the intestinal lining to secrete two
hormones
SECRETIN
CHOLECYSTOKININ
stimulates
Pancreas to secrete pancreatic juice and pancreatic enzymes
pass throuh the
pancreatic duct
onto the ampulla of vater
in the duodenum part of
the small intestine
PANCREATIC JUICE
Bicarbonate ions
Enzymes
•Converts the acidic chyme into
alkaline solution
1. Amylase
•Chyme is neutralised by HCO3and turns into alkaline solution.
3. Lipase
H+ + HCO3 Acid from
stomach
Bicarbonate
from liver
and
pancreas
H2 CO3
Alkaline
because
medium of
intestine is
basic
2. Proteases
ENZYMES OF PANCREATIC JUICE
1. Pancreatic Amylase:
Starch + water
amylase
maltose + dextrin
2. Proteases
Trypsin
Trypsinogen
(inactive)
chymotrypsin
anterokinase
trypsin
(active)
They continue the break down of large protein molecules into amino acids
begun in the stomach
Trypsin and
chymotrypsin
Polypeptides + water
peptide + amino acids
ENZYMES OF PANCREATIC JUICE
3. Lipase
lipid
lipase
fatty acids + glycerol
4 . Nucleases
Nucleic acids
nucleotides
Digestion in small intestine
(pancreatic juice)
Acidic chyme
cells in intestinal lining
to secrete hormones
Secretin and cholecystokinin
stimulate
Pancreas
to secrete
Pancreatic juice
Pancreatic duct
given to
Small intestine
BILE
•
•
•
•
•
•
is secreted from liver
stored and concentrated in gall bladder
has no enzyme
is alkaline
consists of water, ions, cholesterol and bile salts, pigments
it passes from gall bladder to duodenum through the bile
duct
• the release of bile from the gall bladder is stimulated by
cholecystokinin hormone.
• it aids in the digestion of fats and oils by breaking them up
into tiny droplets. This is called emulsification. It increases
the surface area for enzyme action.
• since bile is alkaline, it aids in neutralizing the acidic chyme
from stomach.
Digestion in small intestine
(bile from gall bladder)
Hormone cholecystokinin
stored in the
Bile produced in the liver
gallbladder
releases bile into the
Bile duct
opens to
Small intestine
Bile is transfered from liver to duodenum through the choledoc
duct onto the ampulla of vater
Numerous oil
droplets are
physically
formed
as a result
of emulsification.
INTESTINAL JUICE
•
The wall of the small intestine contain millions of intestinal glands, which
secrete intestinal juice.
peptidase
1. Peptides
amino acids
(erepsin)
2. Maltose
3. Sucrose
maltase
sucrase
2 glucose
glucose+fructose
lactase
4. Lactose
glucose+galactose
DIGESTION IN INTESTINE
1.Remaining Polypeptide
2. Peptides
Trypsin
chymotrypsin
peptidase
peptides
amino acids
(erepsin)
3. Remaining starch
Pancreatic
amylase
disaccharides
DIGESTION IN INTESTINE
4.Maltose
5.Sucrose
6.Lactose
7. Lipids
maltase
sucrase
lactase
lipases
2 glucose
glucose+fructose
glucose+galactose
fatty acids+ glycerol
nucleases
8. Nucleic acids
nucleotides
HORMONAL CONTROL OF
DIGESTION
HORMONE
SOURCE
Gastrin
Stomach
(Mucosa)
Secretin
Small
intestine
(Duodenum
mucosa)
TARGET
TISSUE
Stomach
(Gastric glands)
Stimulates gastric
glands to
secrete
pepsinogen
Pancreas
Signals secretion of
sodium
bicarbonate
Liver
Cholecytokinins
Small
intestine
(Duodenum
mucosa)
ACTION
Pancreas
Gallbladder
FACTORS THAT STIMULATE RELEASE
Presence of food in stomach and certain
substances such as caffeine
Acidic chyme acting on mucosa of duodenum
(small intestine)
Stimulates bile
secretion
Stimulates release
of digestive
enzymes
Stimulates emptying
of bile
Presence of fatty acids and partially digested
proteins in duodenum
(small intestine)
LARGE INTESTINE
• Undigested and unabsorbed materials pass from
the small intestine through a sphincter into the
large intestine.
• No digestion occurs
• On the right side of the abdomen, where the small
intestine joins the large intestine, is a small pouch
the appendix.(It plays no part in the HDS)
• The appendix becomes infected or inflamed, a
condition known as appendicitis
FUNCTIONS OF THE LARGE
1. Reabsorbtion of water form the food mass ¾ of
water is reabsorbed.
• If too much water is reabsorbed, constipation
results.
• If too little water is reabsorbed , diarrhea
results.
2. The absorption of vitamins (vitamin K and
Vitamin B) that are produced by bacteria that
normally live in the large intestine.
3. The elimination- removal of undigested and
indigestible material from the digestive tract.
LARGE INTESTINE
• This material consists of cellulose,
bacteria, bile, mucus and worn-out cells
from the digestive tract. As this material
travels through the intestine, it becomes
feces.
• Fecal matter is stored in the rectum and
periodically eliminated, through the anus.
Check If Your Feces Are Healthy
Dietary fibers and lactobacillus bifidus are essential for a healthy and comfortable life.The best feces are like
bananas. They are modestly hard with no strong smell. Feces are like a barometer of your health and beauty. Check
the following questions to see if you have a healthy feces or not.
Do they float?
They float..................1 point
They sink...................2
points
How often do you evacuate?
Once a day............1 point
Not everyday.......2 points
How hard are they?
Like toothpaste.........1 point
Hard.............................2
points
What color are your feces?
Yellow.....................1 point
Dark brown..........2 points
How much do they weight?
( 2 pcs of feces a day, each
about 2cm in diameter and
about 15cm in length )
Over 200g.............1 point
Below 200g...........2 points
Do your feces smell?
Not much.................1 point
Bad smell................2 points
Like pebbles...2points
Like paste....1 point
Like banana....1 point
Very hard....2 point
Liquid....2 point
Like mud....2 point
If you score:
7 to 9 points..........You are quite healthy
10 to 12 points......Be careful what you eat everyday Take more dietary
fibres.
13 to 14 points......Warning! If these conditions continue long, you should
see a doctor.