Transcript I. Digestion

In order to survive, organisms must
maintain constant interior conditions in a
changing environment.
• The interior environment that cells must
maintain includes:
– Water volume
– Salt concentration
– Oxygen, carbon dioxide levels
– Toxic metabolic waste levels
– Essential nutrients
• Organisms must respond to their
environment to avoid harm and to seek
beneficial conditions
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• Organisms must reproduce to ensure
survival of the species.
• Simple unicellular organisms like
prokaryotes and protists have simple
ways to meet their survival needs.
• Multicellular organisms have evolved
more complex body plans that provide a
variety of solutions to survival
challenges that all organisms face.
• As multicellular organisms have evolved
into larger more complex forms over
time, their cells have become more
removed from the external environment.
• These cells have become more
specialized to one specific function.
• Specialized cells with a common
function form tissues
• Different tissues come together
to form large anatomical
structures - organs.
• Organs are part of organ
systems.
• Organ systems include
– Reproductive
– Digestion
– Respiration
– Circulatory
–Immune
–Excretory
–Endocrine
–Nervous
• Intracellular using enzymes
• Extracellular using enzymatic secretions in
gut cavities and then absorbed into cells in
the lining of the gut
• The simplest example of digestion is
that of a single celled organism.
• Protists utilize intracellular digestion. In
Amoeba, pseudopods surround and
engulf food through phagocytosis.
• Phagocytosis
– Involves larger particles
– Cell membrane expands around a particle
– Lysosomes containing digestive enzymes break
down food.
– Resulting molecules duffuse into cytosol
– Undigestable particles are released from the
vacuoles.
• Pinocytosis
– Another form of endocytosis
– Smaller particles/liquids
– Vesicle fuses with a lysosome
Pinocytosis/Phagocytosis
• In the paramecium, cilia
sweep microscopic food
such as yeast cells into
its oral groove.
• A food vacuole forms
around the particles and
breaks off into the
cytoplasm
• Waste is eliminated
through an anal pore.
Paramecium
• Oral groove: cilia sweeps
food in body like a mouth
• Gullet: encloses food like
a stomach, forms a food
vacuole
• Anal pore: opening where
wastes are removed
• Trichocysts: structures
used for defense
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• Animals are multicellular heterotrophic
organisms that must acquire energy
from the consumption of food.
• Food must be digested and or absorbed
to be used by cells.
• Mechanical - cutting & grinding in the mouth
and churning in the stomach and small
intestines. Molecular structure is unchanged
• Chemical - enzymatic hydrolysis of food
particles (proteins, lipids, carbs, nucleic acids,
minerals, vitamins like Niacin for NADH)
• Absorption - glucose, fatty acids, amino
acids…)
DIGESTION IN
EARTHWORMS
• Earthworms have a complete one way
two-opening digestive tract.
• The digestive tract is a tube that moves
food through in one direction.
DIGESTION IN
EARTHWORMS
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Digestion in Earthworms
• Mouth - beginning of the digestive tract.
The earthworm takes in soil and organic
matter
• Pharnyx - the mixture enters the
pharnyx which which is the opening
between segments 1-6 of the worm.
• Esophugus - is the passageway
between the pharnyx and the crop.
Digestion in Earthworms
• Crop - stores food temporarily
• Gizzard - churns and grinds food
• Intestines - takes up 2/3 of the worms
body. Digestion and absorption takes
place
• Anus - Soil and indigestible matter
leaves through the anus
Digestion in Humans
Digestion of large food molecules is essential.
• large food molecules are usually polymers, such as
polysaccharides, proteins and lipids, which are too large to be
absorbed from the digestive tract into the circulatory system
for transport because they are simply too large to move
across the membranes of small intestine epithelial cells.
• after digestion, polysaccharides are broken down into
monosaccharides, polypeptides are broken down into amino
acids, and lipids are broken down into glycerol and fatty acid
• monomers, such as monosaccharides, amino acids, glycerol,
and fatty acids are small enough to be absorbed by small
intestine epithelial cells, moving these substances by either
diffusion, facilitated diffusion, or active transport through
membrane proteins
Enzymes are needed in digestion.
• at body temperature (37｡C in mammals), reaction rates
are too slow to be efficient at hydrolysis reactions of
large food molecules
• hydrolytic reactions in the digestion of large food
molecules, such as polysaccharides, proteins and lipids
into their monomers, are exothermic, but occur very
slowly due to considerable activation energy
• enzymes lower activation energy, catalyzing hydrolysis
reactions of large food molecules into their monomers
Amylase, protease, and lipase are important enzymes in
digestion
Enzyme
amylase
pepsin
phospholipase
Source
Salivary
glands
stomach
pancreas
Substrate
starch
proteins
phospholipids
Products
maltose
polypeptide
Glycerol
phosphate,
fa’s
Optimum
pH
7-8
2-3
8
Digestive System
Label your illustration
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
L.
Mouth
Pharnyx
Esophagus
Stomach
Small Intestine
Large Intestine
Rectum
Anus
Salivary glands
Liver
Gallbladder
pancreas
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Function of the Stomach;
• a large, expandable, muscular and glandular organ
• stores and mixes food, aiding in both physical and
chemical digestion
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Gastric Pits Secrete:
a) HCl - producing a stomach pH of about 2, facilitating
pepsin activity, and killing foreign pathogens, such as bacteria
b) pepsinogen - converted to pepsin under acidic conditions
c) pepsin - catalyzes the hydrolysis of large proteins and
polypeptides into smaller polypeptides
d) mucus - which protects stomach cells from acidic
conditions
e) chyme - product of stomach digestion, an acid fluid
released from stomach into small intestine via pyloric sphincter
Function of the small intestine:
I. Digestion
a) pancreas releases bicarbonate = NaHCO3-, which neutralizes
acidic chyme, producing a pH = 8
b) enzymes from pancreas, and small intestine epithelial cells
hydrolyze large molecules into smaller molecules
c) polypeptides & oligopeptides digested into amino acids
d) polysaccharides & disaccharides digested into
monosaccharides
e) triglycerides digested into fatty acids and glycerol
f) bile produced in liver, stored in gall bladder, released through
pancreatic duct
h) emulsifying fat droplets into smaller particles on which
pancreatic lipase can act more efficiently
II. Motility - by peristalsis: rhythmic contractions
of circular and longitudinal smooth muscles
lining small intestine slowly force chyme down
intestinal tract
III. Absorption - lining of small intestine is
folded, increasing surface area for absorption,
and each fold is folded again into villi, with
each villus acting as an absorptive unit.
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Function of large intestine:
a) Absorption of vitamin K produced by mutualistic
bacteria
b) Reabsorption of water, Na+, K+ from intestinal
lumen to capillaries
c) Motility by peristalsis: rhythmic contractions of
smooth muscles lining large intestine slowly force
fecal matter down intestinal tract