Download Digestion - mvhs

Digestion
AP Biology
Unit 6
General Steps
• Ingestion = food is taken in
(eating )
• Digestion = Food is broken
down into smaller pieces
/molecules
• Absorption = Nutrient
molecules are absorbed into
body cells
• Elimination = undigested
material exits the body
Types of Digestion
• There are two kinds of digestion –
mechanical and chemical
• Mechanical = Food is broken down into
smaller pieces (chemical structure not
changed)
• Chemical = Food is broken down into
smaller molecules (chemical structure
changed)
Intracellular Digestion
• In the animal kingdom, only
sponges (Phyla Porifera) do
this exclusively.
• Steps:
– Cells engulf food via
phagocytosis or pinocytosis,
forming food vacuole.
– Lysosomes fuse with food
vacuoles; hydrolytic enzymes
break down food.
Extracellular Digestion
• All animals (except sponges)
perform this mode of digestion
• Digestion begins in a
compartment continuous with
the outside of the animal’s
body (gut).
• What is the advantage of
extracellular digestion?
– animal can take in a lot of food at
once and slowly digest it
Extracellular Digestion
• Enzymes are secreted to break food into
smaller molecules.
• After the food has been broken down, many
animals continue digestion intracellularly.
• Animals that perform extracellular digestion
can have a variety of different digestive
systems.
Gastrovascular Cavity
• Gastrovascular cavity =
digestive sac with a single
opening
• Animals that have a
gastrovascular cavity =
Hydra
– Phyla Cnidarian (includes
jellyfish, anemones, corals)
Digestion in Gastrovascular Cavities
• Tentacles sting prey and stuff it
into opening
• Digestive enzymes are secreted
to allow for extracellular
digestion
• Nutritive muscular cells then
engulf food particles and
complete digestion
intracellularly
• Undigestible material leaves
through mouth (no anus)
Complete Digestive Tracts
• Complete digestive tract =
digestive tube running
throughout body
• Organisms with a complete
digestive tract have both a
mouth and an anus
Question…
• Why would having a separate entry and exit
point be beneficial?
– digestion can be broken down into steps
– there can be specialization of digestive tissues
for these steps
Human Digestion
• Where do the four steps in food processing
occur?
Human Digestion
• Ingestion = mouth
• Digestion = mouth, Stomach,
Small Intestines
• Absorption = Small Intestines,
Large Intestines
• Elimination = End of large
intestines
Oral Cavity, Pharynx, Esophagus
• Participate in ingestion and
digestion
• Mechanical Digestion
– By teeth and tongue
(chewing)
• Chemical Digestion
– Salivary amylase begins
digestion of carbohydrates
(starch  glucose)
Oral Cavity, Pharynx, Esophagus
• Epiglottis = flap that covers the trachea
during swallowing, so food travels down
“right pipe” (the esophagus)
• Peristalsis (muscle contractions) will
involuntarily continue movement of the mass
of food (bolus)
Stomach
• Important in storage & digestion
• What advantage do folds in the stomach
tissue provide?
– Allows the stomach to expand to hold more
food
– Tissue is also very elastic so that it can stretch
Stomach
• Gastric juice continues
digestion:
• HCl converts pepsinogen
into pepsin (active enzyme)
• Pepsin hydrolyzes (breaks
down) protein.
• Gastric juice is churned
with bolus to break down
food and kill bacteria
Stomach: Pepsin
• What kinds of bonds are broken by pepsin?
– Peptide bonds
• What kind of reaction is this?
– Hydrolysis
Protection of the stomach
• Stomach protects itself
from self-digestion by
– keeping pepsinogen
stored away from HCl
until pepsin is needed
– lining stomach with
mucus
Small Intestine
• Participates in digestion and absorption
• Peristalsis allows for movement of chyme
and digestive juices down the small
intestine.
Digestion in the Small Intestine
• Digestion is usually completed in the
duodenum (first section) with the help of
digestive juices
Digestive Juices
• Digestive juices come
from 4 sources,
entering the
duodenum:
• Pancreas
– produces digestive
enzymes
– produce basic
bicarbonate solution
(buffer against stomach
acid)
Digestive Juices also come from
• Lining of duodenum
– produces digestive enzymes
• Liver
– Produces bile
• Gallbladder
– Stores bile
Bile
• contains bile salts
– breaks up fat droplets into
very small pieces
(emulsification)
• Increases surface area for
lipase to digest into micelles
– micelles are then absorbed
Question…
• Does bile perform mechanical or chemical
digestion?
– Mechanical– breaking it up into smaller pieces
Protection of Small Intestine
• Small intestine and adjacent organs are
protected from digestive enzymes by
producing inactive forms that are only
activated in the duodenum.
Absorption of Nutrients
• Occurs in the jejunum (mid-small intestine)
and ileum (end-small intestine)
• Nutrients are absorbed into the blood
vessels and lymph vessel (lacteals).
• Water is also absorbed here.
Absorption of Nutrients
• Villi and microvilli
– Projections of the lining of the small intestine
– Benefit?
– Increases the surface area in these regions 
increases amount of nutrient absorption
Digestion Summary
Biomolecule
Where Digested Key Enzymes
Carbohydrates
Mouth, Small
Intestine
Amylase, Maltase,
Lactase, Sucrase
Lipids
Small Intestine
Proteins
Stomach, Small
Intestine
Bile (not an enzyme
but helps process),
Lipase (from pancreas)
Pepsin (stomach),
Peptidases, Trypsin
Nucleic Acids
Small Intestine
Nucleases
Large Intestine
• responsible for water recovery from
digested material
• Feces = Waste of digestive tract
• Bacteria live here (including E. coli) that
live on feces and produce vitamins B and K
() and stinky gases
• End of colon = rectum
• End of rectum = anus
Control of
Digestive System
Food in the stomach
Stomach cells release GASTRIN
Lower pH inhibits
gastrin release
Increased secretion of:
HCl
Pepsin
Increased movement in stomach
CCK slows
movements of
stomach down
Faster delivery of chyme to small intestine
small intestine cells release
CHOLECYSTOKININ (CCK)
small intestine cells release
SECRETIN
pancreas releases
digestive enzymes
gallbladder
releases bile
Digestion of food
pancreas releases sodium
bicarbonate to neutralize acid
Nervous System Control of Digestion
• The Autonomic Nervous System controls
the internal environment by controlling
muscles in various organ systems
– Sympathetic division (“fight or flight”):
inhibits digestion, promotes release of glucose
from liver
– Parasympathetic division (“rest and digest”):
stimulates digestion
– Enteric division: neurons that control the
secretions of the digestive organs.
Diabetes
• Blood sugar levels are controlled by hormones
Diabetes (continued)
• Diabetes mellitus is a condition in which
insulin is not produced or cells are insulin
resistant
– Type 1 –
• can’t produce insulin
– Type 2
• cells no longer respond to insulin
– End result: glucose cannot be used by cells 
blood sugar is too high (homeostasis not
maintained)