Download “You Are What You Eat” The Digestion System

“You Are What You Eat”
The Digestion System
Jade Bennett
Jade Hoayun
Karla Burnett
Worryin’ Bout What Dey Eat
And How Dey Eat, You Nosy
Three Dietary Categories:
Herbivores – An heterotrophic animal that eats plants
Carnivores- eats other animals
Omnivores- heterotrophic animal that consumes both
meat and plant material
Four Main Feeding Mechanisms:
Suspension Feeders-sifts small food particles from the
water
Substrate Feeders- an organism that lives in or on its
food source, eating its way through the food
Fluid Feeders- suck nutrient rich food from the living
host
Bulk Feeders- an animal that eats relatively large pieces
of food
Guess Who’s Comin’ To Dinner
Herbivore
Carnivore
Omnivore
The Importance Of Being
Homeostasis
Nearly all ATP generation is based on the oxidation of organic fuel
molecules—carbohydrates, proteins, and fats—in cellular
respiration.
If more calories taken in than can be used for ATP production,
excess used to fuel biosynthesis
Example of homeostasis: glucose regulation
Body tends to store surplus energy
If body’s store of glycogen is full and caloric intake
exceeds expenditure, excess is stored as fat
If expenditure exceeds intake then fuel is taken out of
storage
Caloric imbalance
Undernourishment- a diet that is chronically deficient in
calories
Overnourishment- a diet that is chronically excessive in
calories
Gimme Gimme More
(Homeostasis cont’d)
Obesity
A major health problem for humans
Actually beneficial in some species such as petrel
Leptin:
One of several hormones that helps regulate body weight
As adipose tissue (fat) decreases, leptin levels fall, and
appetite increases
Inheritance also plays large factor in obesity
Evolution of obesity
Natural selection could have favored those with a physiology
that induced them to eat rich, fatty food on the rare occasion
they were available
Also, those with genes enabling them to better store highenergy molecules may have been more likely to survive
famines.
Mo’ Supply and Demand
Fuel as well as organic precursors (carbon skeletons) are
needed as material for biosynthesis
However, some materials (Essential nutrients) must
be obtained in preassembled form because the
animal’s cells can’t make them from any raw
materials
An animal whose diet is missing 1 or more essential
nutrients is said to be malnourished.
4 classes of essential nutrients: essential amino acids,
essential fatty acids, vitamins, and minerals.
Essential Nutrients
An essential amino acid cannot be synthesized by the
animal and must be obtained from food
Eight amino acids are essential in most animals’ diet.
Insufficient amounts of 1 or more essential amino acids
causes a protein deficiency
Ex. Kwashiorkor
Meat products are able to provide all essential amino
acids
Animals can synthesize most of the fatty acids they need.
The essential fatty acids, the ones they cannot make,
are certain unsaturated fatty acids
Ex. Linoleic acid
The diets animals generally furnish ample quantities of
essential fatty acids, and thus deficiencies are rare.
Essential Nutrients: Vitamins
Vitamins are organic molecules required in the
diet in very small amounts
Two categories: water-soluble vitamins and fatsoluble vitamins
Water-soluble vitamins – Vitamins B and C;
excesses of these are excreted in urine so
moderate overdoses are harmless
Fat-soluble vitamins – Vitamins A,D,E, and K;
excesses of these are deposited in body fat, so
overdose may lead to toxic level build up
The subject of vitamin dosage has aroused debate
Betta Get Dem Vitamins
Essential Nutrients: Minerals
Minerals are simple inorganic nutrients, usually
required in small amounts
Ingesting an excess of salt or several other
minerals can upset homeostatic balance and
cause toxic side effects
Most people ingest too much salt (sodium
chloride)
Too much sodium is associated with high
blood pressure
Also, excess Iron can cause liver damage
Betta Get Dem Minerals
The Main Stages of Food Processing
Organic material in food consists largely of
proteins, fats, and carbohydrates in the form of
starch and other polysaccharides
Animals cannot use these macromolecules directly
for two reasons (IB- Explain why digestion of large food molecules is essential)
First, polymers are too large to pass through membranes
and enter the cells of the animal
Second, the macromolecules that make up an animal are
not identical to those of its food
For these reasons food processing involves four
stages: ingestion, digestion, absorption, and
elimination
Put It In Yo Mouth: Ingestion
Ingestion – The act of eating, is a mechanical fragmentation
of the food, such as chewing
Breaking food into smaller pieces increases the surface area
exposed to digestive juices containing hydrolytic enzymes
Digestion
Digestion- food is broken down into molecules
small enough for the body to absorb
Macromolecules are cleaved into component
monomers, which the animal uses to make its own
molecules or for ATP production
Polysaccharides and disaccharides are split into simple
sugars, fats are digested to glycerol and fatty acids,
proteins are split into amino acids, and nucleic acids are
cleaved into nucleotides
Enzymatic hydrolysis is the process in digestion
that splits macromolecules by the enzymatic
addition of water.
The Final Two…Stages
In the third stage, absorption, the animal’s
cells take up (absorb) small molecules
such as amino acids and simple sugars
from the digestive compartments
And last but not least, elimination occurs,
as undigested material passes out of the
digestive compartments
Absorption versus Assimilation
Absorption occurs in the small
intestine. During this process the
food is truly inside the body .
Small finger-like projections called villi
line the small intestine and are adapted
to absorb food molecules
Assimilation occurs once food has
been absorbed and becomes part of
the tissues in the body.
Kitty
Small
molecules
Pieces
of food
Mechanical
digestion
Food
Chemical digestion
(enzymatic hydrolysis)
Nutrient
molecules
enter body
cells
Undigested
material!
Digestive Compartments
To avoid self-digestion animals process food in specialized
digestive compartments
Two types: Intracellular Digestion and Extracellular
Digestion
Intracellular digestion is the joining of food vacuoles and
lysosomes (organelles containing hydrolytic enzymes) to
allow chemical digestion to occur safely within the cytoplasm
of a cell
Begins after phagocytosis or pinocytosis
In most animals, at least some hydrolysis occurs by
extracellular digestion- the breakdown of food outside cells
Occurs within compartments that are continuous with the
outside of the animal’s body
Such animal able to devour much larger prey than can be
ingested by phagocytosis and digested intracellularly.
Some Like It Simple,
While Some Like It Complicated
There are two types of extracellular digestion
Animals with simple body plans such as cnidarians and
flatworms have a gastrovascular cavity
A digestive sac with a single opening, functions in both digestion and
distribution of nutrients throughout the body
Single opening functions as mouth and anus
Most animals have a digestive tube extending
between two openings, called a complete
digestive tract or an alimentary canal
Because food moves along the canal in a single direction,
the tube can be organized into specialized regions that carry
out digestion and nutrient absorption in a stepwise fashion
Ability to ingest additional food before earlier meals are
completely digested
Cnidarians called hydras
Tentacles
Mouth
Food
Gastrovascular
cavity
Epidermis
Mesenchyme
Gastrodermis
Nutritive
muscular
cells
Flagella
Gland cells
Food vacuoles
Mesenchyme
Earthworm. The digestive tract of
an earthworm includes a muscular
pharynx that sucks food in through the
mouth. Food passes through the
esophagus and is stored and moistened
in the crop. The muscular gizzard, which
contains small bits of sand and gravel,
pulverizes the food. Digestion and
absorption occur in the intestine,
which has a dorsal fold, the typhlosole,
that increases the surface area for
nutrient absorption.
Grasshopper. A grasshopper has several
digestive chambers grouped into three
main regions: a foregut, with an esophagus
and crop; a midgut; and a hindgut. Food is
moistened and stored in the crop, but most
digestion occurs in the midgut. Gastric ceca,
pouches extending from the midgut,
absorb nutrients.
Bird. Many birds have three separate chambers—
the crop, stomach, and gizzard—where food is
pulverized and churned before passing into the
intestine. A bird’s crop and gizzard function very
much like those of an earthworm. In most birds,
chemical digestion and absorption of nutrients
occur in the intestine.
The process of digestion:
Foods processing in all animals follow the same
general process so mammals will be
representative.
Consists of alimentary canal and accessory
glands: salivary glands, liver, pancreas, and
gallbladder.
Accessory glands secrete digestive juices through ducts
Peristalsis- rhythmic waves of contraction by smooth
muscles that move food down
Sphincters- ring- like modified muscles that close up
like drawstrings to modify the amount of material that
passes through the chamber of the canal
IB Important!: mouth, esophagus, stomach,
anus, liver, small intestine, large intestine, pancreas,
and gallbladder
Tongue
Salivary
glands
Salivary
glands
Cardiac
orifice
Oral cavity
Parotid gland
Sublingual gland
Mouth
Pharynx
Submandibular gland
Esophagus
Esophagus
Pyloric
sphincter
Liver
Ascending
portion of
large intestine
Stomach
Gallbladder
Gallbladder
Liver
Pancreas
Small
intestines
Pancreas
IIeum
of small
intestine
Small intestine
Duodenum of
small intestine
Large intestine
Rectum
Appendix
Anus
Cecum
Stomach
Large
intestines
Rectum
Anus
A schematic diagram of
the human digestive system
Elements to Digest: Oral Cavity,
Pharynx, and Esophagus
Physical and Chemical digestion begins in the mouth
Food in the oral cavity triggers a nervous reflex that cause
salivary glands to deliver saliva. Saliva important for mucin
that lubricates food and protects inside of mouth from
abrasion
Prevents tooth decay by neutralizing acids
Kills off bacteria
Salivary amylase- hydrolyzes starch and glycogen which helps
to break down carbohydrates for chemical energy
Swallowing moves food into a bolus and to back of oral
cavity to the pharynx (throat) then to esophagus and
trachea (windpipe) which has an opening called the glottis
covered by the epiglottis
The esophagus moves food from the pharynx to the stomach
by peristalsis. Muscles at top are voluntary (striated) but
become involuntary contractions
Let’s Begin (41.16)
Epiglottis
up
Bolus of food
Tongue
Glottis
down
and open
Epiglottis
up
Pharynx
Esophageal
Epiglottis
sphincter
down
contracted
Glottis
Larynx
Trachea
Esophageal
sphincter
relaxed
Esophageal
sphincter
contracted
Esophagus
To lungs
To stomach
Relaxed
muscles
Glottis up
and closed
Contracted
muscles
Relaxed
muscles
Stomach
Elements to Digest: Stomach
Stores food and does the beginning steps of digestion
Located in upper abdominal cavity below diaphragm.
Large and has elastic , accordion- like walls that can
stretch it to 2 liters. Secretes gastric juice - has a high
concentration of hydrochloric acid with a pH of 2
Breaks extracellular matrix that binds cells in meat and
plants
Kills most bacteria swallowed with food
Pepsin- enzyme that begins the hydrolysis of protein
Breaks peptide bonds adjacent to specific amino
acids, that cleave proteins into smaller peptides which
are later digested to amino acids in small intestines
Low pH of gastric juice unfolds the proteins that
increase exposure of peptide bonds to pepsin
Elements to Digest: Stomach
(Cont’d.)
Pepsin does not destroy the stomach due to
pepsinogens that are an inactive form.
In the gastric cell the chief cells produce pepsinogens
while the parietal cells secrete hydrochloric acid
The acid converts the pepsinogens to the active form by
removing a small part of the molecule and exposing it to
the active site
The two ingredients do not mix because they come from
different cells and pepsinogen is not activated until they
enter cavity (lumen) of stomach.
Example of positive biofeedback (nerves). Once a bit of
pepsinogens is activated, activation occurs rapidly
because pepsin can activate itself
Mucus also prevents self digestion A recent
meal becomes acid chyme (nutrient- rich broth)
that is regulated from the stomach to the small
intestine by the pyloric sphincter.
A meal can take 2-6 hours to leave stomach
Get in Mah Belly:
Stomach Lining (41.17)
Esophagus
Cardiac orifice
Stomach
5 µm
Pyloric
sphincter
Interior surface of stomach.
The interior surface of the
stomach wall is highly folded
and dotted with pits leading
into tubular gastric glands.
Small
intestine
Folds of
epithelial
tissue
Epithelium
3
Pepsinogen
Pepsin (active enzyme)
2
HCl
Gastric gland. The gastric
glands have three types of cells
that secrete different components
of the gastric juice: mucus cells,
chief cells, and parietal cells.
1
2 HCl converts
pepsinogen to pepsin.
Mucus cells secrete mucus,
which lubricates and protects
the cells lining the stomach.
3 Pepsin then activates
more pepsinogen,
starting a chain
reaction. Pepsin
begins the chemical
digestion of proteins.
Chief cells secrete pepsinogen, an inactive form of the
digestive enzyme pepsin.
Parietal cell
Parietal cells secrete
hydrochloric acid (HCl).
1 Pepsinogen and HCI
are secreted into the
lumen of the stomach.
Chief cell
Elements to Digest:
The Small Intestine
Name from diameter. More than 6 m in humans so it is longest part
of alimentary canal
Duodenum: 1st 25 cm, acid chyme mixes with digestive juices from
the liver, gallbladder, and pancreas, and glass cells of wall
Liver creates bile that has digestive enzymes and bile salts that aid
digestion and absorption of fats
As peristalsis moves the chime and digestive juices along the small
intestine, enzymatic digestion is completed
Most of the process is completed in the duodenum; the jejunum and
ileum absorb nutrients and water
Hormones help coordinate the secretion of juices
Most absorption of nutrients occurs here- some still occurs in
stomach and large intestine
Transport across epithelial cells can be passive like sugar fructose
with facilitated diffuson
Small peptides, amino acid, vitamins, and glucose are some
examples of nutrients that are pumped against the concentration
gradient by epithelial membranes.
Active transport helps intestine absorb a higher amount of proteins
Villi help a lot…
When acid chyme and digestive
juices get together… (41.19)
Liver
Bile
Gallbladder
Stomach
Acid chyme
Intestinal
juice
Pancreatic juice
Pancreas
Duodenum of
small intestine
What happens in the small intestines
(doesn’t) stay in the small intestines
Protein digestion
Carbohydrate digestion
Oral cavity,
pharynx,
esophagus
Polysaccharides
(starch, glycogen)
Nucleic acid digestion
Fat digestion
Disaccharides
(sucrose, lactose)
Salivary amylase
Smaller polysaccharides,
maltose
Stomach
Proteins
Pepsin
Small polypeptides
Lumen of
small intestine
Polysaccharides
Pancreatic amylases
Maltose and other
disaccharides
Polypeptides
Pancreatic trypsin and
chymotrypsin (These proteases
cleave bonds adjacent to certain
amino acids.)
Smaller
polypeptides
DNA, RNA
Pancreatic
nucleases
Nucleotides
Pancreatic carboxypeptidase
Small peptides
Dipeptidases, carboxypeptidase, and aminopeptidase
(These proteases split
off one amino acid at a time, working from opposite ends
of a polypeptide.)
Monosaccharides
Amino acids
Fat droplets (A coating of
bile salts prevents small droplets from coalescing into
larger globules, increasing
exposure to lipase.)
Glycerol, fatty
acids, glycerides
Nucleotidases
Nucleosides
Disaccharidases
Bile salts
Pancreatic lipase
Amino acids
Epithelium
of small
intestine
(brush
border)
Fat globules (Insoluble in
water, fats aggregate as
globules.)
Nucleosidases
and
phosphatases
Nitrogenous bases,
sugars, phosphates
Villus: The Importance Of Structure
Increases the surface area
from which food is absorbed
Microvilli also serves this
purpose
The epithelium is one thin
layer of cells- easy to pass
through
Protein channels have rapid
absorption because of active
transport and facilitated
diffusion
ATP is provided by
mitochondria in the epithelium
cells
Blood capillaries are close to
the epithelium (small distance)
A lacteal
Elements to Digest:
Large Intestines
From the liver, blood travels to the heart, which
pumps the blood and nutrients to all parts of the
body. RECLAIMING WATER IS A MAJOR
FUNCTION OF THE LARGE INTESTINE.
The large intestine, or colon, is connected to the
small intestine at a T-shaped junction where a
sphincter controls the movement of materials.
A major function of the colon is to recover water that
has entered the alimentary canal as the solvent to
various digestive juices.
Living in the large intestine is a rich flora of mostly
harmless bacteria.
Feces contain masses of bacteria and undigested
materials including cellulose.
The terminal portion of the colon is called the rectum,
where feces are stored until they can be eliminated.
Large Intestine is the Colon
Evolutionary Adaptations In Digestive
Systems In Vertebrates
Dental adaptations
Carnivores generally have pointed teeth to kill prey and rip flesh
Herbivores generally have teeth with broad ridged surfaces to
grind plants
Omnivores are a combination of both
Stomach and intestinal adaptations
Carnivores usually have large, expandable stomachs so they can
eat as much as possible
Herbivores and omnivores generally have longer alimentary
canals to give more time for digestion of plants and more surface
area for absorption of nutrients
Symbiotic adaptations
Symbiotic bacteria and protists in the fermentation chambers of
the alimentary canals are a way for herbivores to break down
cellulose
Ruminants- an animal such as a cow, or sheep, with an elaborate
compartmentalized stomach specialized for a herbivorous diet