Transcript VERTEBRATE DIGESTIVE SYSTEM

Mrs. Ofelia Solano Saludar
Department of Natural Sciences
University of St. La Salle
Bacolod City
1. Name the divisions of the coelomic cavities of a
fish, amphibian, reptile/bird, mammal.
2. Name the linings of the coelom, and the remnants
of some of its regions in the mammalian gut.
Discuss the phylogeny of the following vertebrate
structures:
3.
4.
5.
6.
7.
8.
9.
Mouth
Teeth
Tongue
Pharynx
Stomach
Small intestine
Large intestine
10. Describe the ruminant way of eating.
• The digestive
tract is formed
from
splanchnic
mesoderm.
• Epithelial
lining is
derived from
endoderm
lining the
primitive gut.
 Digestive tube
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differentiates
into foregut,
midgut, hindgut
Organs arise as
diverticula from
these regions.
Stomodeal and
proctodeal
invaginations
establish an
entrance
(mouth), and
exit (anus or
vent)
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In all vertebrates except birds & mammals, the
COELOM is divided into 2 compartments: the
pericardial cavity (heart), & the pleuroperitoneal
cavity (viscera). The transverse septum separates the
2 cavities
In cyclostomes, fishes & urodeles, the pericardial
cavity is anterior to the pleuroperitoneal cavity.
Due to the posterior descent of the heart, it lies ventral
to anterior part of the latter starting with anurans.
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With the transverse septum, a pericardial sac forms
around the heart. Dorsal to the heart are the pleural
cavities.
In birds & mammals, folds join the transverse
septum to produce the oblique septum in birds, or
the muscular diaphragm in mammals.
Birds & mammals have 4 coelomic cavities:
pericardial, 2 pleural, peritoneal
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The COELOM has 2 linings: Parietal peritoneum &
Visceral peritoneum
The dorsal and ventral mesenteries are the 2 folds of
peritoneum
The dorsal mesentery supports the digestive tract in
all vertebrates.
 The ventral mesentery is absent in adult
vertebrates except in the regions of the liver
and the gall bladder (falciform ligament)
 There are special mesenteries for the
gonads and
their ducts.
 In mammals,
the mesentery
of the stomach
develops a
special
prolongation
called the
greater
omentum.
 Accessory organs
include the tongue,
teeth, oral glands,
pancreas, liver, and
gall bladder.
 Differences in the
anatomy of vertebrate
digestive tracts is
often correlated with
the nature and abundance of food:
o readily absorbed (e.g., hummingbirds) vs.
requiring extensive enzymatic activity (e.g.,
carnivores)
o constant food supply (e.g., herbivores) vs.
scattered supply (e.g., carnivores)
Filter-feeding is the oldest craniate method of
acquiring food. It is still employed by lampreys,
a few jawed fishes, and baleen whales
The oral cavity
begins at the mouth
& ends at the
pharynx.
 FISHES have a very
short oral cavity,
while tetrapods
typically have longer
oral cavities.
 Primary palate- roof
of the oral cavity of
fishes & amphibians;
20 palate in reptiles &
mammals

 Nasal passageways open into the
oropharyngeal cavity in lobe-finned fishes,
and into the oral cavity in tetrapods with
primary palate.
 Multicellular oral glands open onto the roof,
walls & floor of cavity
 May contain: venom,
saliva, including
several enzymes,
anticoagulant
(lampreys, bats)
nutrients in catfish,
mucus
 Oral glands are scarce in fishes
MAMMALS:
 The mouth is specialized to serve as a suckling
and masticatory organ (with muscular cheeks).
 An oral vestibule separates the
gums or alveolar ridges from
the cheek and the mouth.
 Oral cavity leads to pharynx;
transition passageway is
called the isthmus of
fauces with 2 pillars
 A fleshy uvula hangs from
the caudal border of soft
palate into oral pharynx.
 Pharygeal & lingual tonsils are
present.
 Mammals have 3 pairs of salivary glands that can
differ in both the volume & composition of their
secretions.
 Parotid glands secrete a serous fluid; largest
gland in many herbivores
 Submaxillary
(submandibular)
and sublingual
glands tend to
contain large
amounts of mucus;
the submaxillary
gland of the giant
anteater is
extremely large
and provided with a storage bladder.
In rodents an opening leads from the
vestibule into the cheek pouch in
which grains maybe stored. It is emptied
by shaking the head vigorously.
A hamster with
mumps!
Gnathostomes &
primitive amphibians:
primary tongue is a
simple crescentshaped elevation in
the floor of the oral
cavity caused by the
underlying hyoid skeleton
Most amphibians - primary tongue (hypobranchial
eminence) + glandular field (tuberculum impar) is
stuffed with hypobranchial musculature
Reptiles & mammals - primary tongue + glandular field
(tuberculum impar) + lateral lingual swellings (more
hypobranchial muscle)
Birds - lateral lingual swellings are suppressed &
intrinsic muscle is usually lacking
Functions of vertebrate tongues: capturing &
gathering food, taste, manipulate fluids & solids
in oral cavity, swallowing, grooming,
thermoregulation, human speech
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Tongue mobility:
Turtles, crocodilians, some birds, & whales - tongue
is largely immobilized in the floor of the oral cavity &
cannot be extended
Snakes, insectivorous lizards, amphibians, & some
birds - tongue is sometimes long and may move in
and out of the oral cavity
Mammals- tongue is attached to the floor of the oral
cavity (via the frenulum) but can still be extended
out of the oral cavity
Derivations of the fish
dermal armor
 Odontoblasts
deposit dentin;
crown of enamel
from the
ameloblasts of the
enamel organ, & the
cementum (anchors
teeth to jaw)
 Placoid scales show gradual
transition to teeth at
the edge of the jaw
 Vary in number, distribution, degree of
permanence, mode of attachment, & shape
 Have tended toward reduced numbers &
distribution
 Fishes - teeth are numerous & widely
distributed in the oral cavity & pharynx
 Early tetrapods - teeth widely distributed
on the palate; most amphibians & some
reptiles still have teeth on the vomer,
palatine, & pterygoid bones
 Crocodilians, toothed birds, & mammals teeth are limited to the jaws; diastema are
toothless areas on the jaw
1. POLYPHYODONT – many sets,
typical of most vertebrates
2. DIPHYODONT – two sets, most
mammals
3. MONOPHYODONT– one set,
platypus
 Most vertebrates have
succession of teeth
 Most vertebrates (except
mammals) replace teeth in
‘waves’ (back to front; every
other tooth)
 Mammals generally develop 2
sets of teeth: milk (deciduous)
teeth & permanent teeth
HOMODONT- all shaped alike
HETERODONT- varied
 Incisors: cutting plant food
 Canines: slicing and tearing
meat
 Molars: grinding grass and other plants
What’s
on
your
menu?
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ACRODONT –
peak of jaws,
teleosts
PLEURODONT –
inner surface of
jaws,
amphibians,
lizards
THECODONT–
sockets,
crocodiles,
extinct birds and
mammals
- tricuspid cusps
Secodont- 2 or 3 cusps
interconnected by sharp
ridges of enamel (carnivores)
 Selenodont- sharp, crescentric enamel
ridges; side-to-side, forward-backward
chewing movements (bovine molars)
 Lophodont- long, grinding teeth
(proboscidians)
 Bunodont- have low rounded cusps
instead of sharp edges & pointed cusps
(higher primates)
Examples of
modified incisors
 Specialized fangs
(Viperidae) deliver
venom which kills prey,
as well as starts
digestion
 In other venomous
snakes, teeth are less
derived but can deliver
venom
 Some lizards (Gila
monster) deliver
neurotoxin
 Others have bacteria
that takes down prey
(Komodo dragon)
Toothless
vertebrates:
agnathans,
sturgeons, some
toads, turtles, birds
(jaw modified into
beaks), & baleen
whales.
Pharyngeal pouches
may give rise to gill slits
Fishes – gills & gill slits
Tetrapods- includes:
 Glottis (slit leading
into the larynx)
 Openings of auditory
(Eustachian) tubes
 Opening into esophagus
 Location of tonsils in mammals
Caudad to the pharynx, the wall of the gut are
composed of 4 layers:
A distensible muscular
tube connecting the
pharynx & the stomach
 Fishes - closes so
stomach doesn’t
become filled with
respiratory water
 Birds- may have a
diverticulum called the
crop which has
digestive enzymes &
allows hoarding of food
 Pigeon milk is an
esophageal secretion
in doves for nestlings
Muscular chamber(s) at end of esophagus that serves as
storage & macerating site for ingested solids & secretes
digestive enzymes
Vertebrate
stomachs:
Cyclostomes weakly developed;
similar to
esophagus
Fish, amphibians,
& reptiles increasing
specialization
(more differentiated from the esophagus)
Birds - store large quantities of
food temporarily in the crop,
releasing it for digestion as
needed.
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Stomach is divided into:
proventriculus (glandular
stomach) and ventriculus
(muscular stomach, or gizzard)
Lacking teeth, they swallow
small stones which lodge in the
muscular gizzard (the opening
of the pyloric sphincter is very
tiny, preventing these gizzard
stones from escaping).
As the gizzard churns, the
stones grind against the food
like numerous tiny millstones.
Birds must constantly replace
their gizzard stones by
swallowing new gravel.
1. Mouth – usually
relatively simple
2. Esophagus – may be widened at
midpoint to form crop (storage area)
3. Proventriculus – glandular
stomach which is highly acidic
4.Gizzard – thick muscular walls and
sandpaper like surface
stomach
5.Small intestine – food digestion
and absorption
6. Caecum – bacterial breakdown
of cellulose
7. Large intestine
8. Cloaca – final holding area
Herbivorous Bird
Carnivorous
Bird
Gizzard
Grain
Substantial Substantial
Fruits and
Berries
Reduced in
size
Small
intestine
Shorter,
less
complex
Longer,
more
complex
Shorter,
less complex
Caeca
Small or
absent
Well
developed
Less well
developed
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Stomach serves mainly as a storage sac for large
quantities of vegetable matter.
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In the absence of cellulase, little digestion takes
place in the small intestine, and food is diverted
into a long dead end side branch, the caecum.
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The caecum houses a huge population of
bacteria, some of which produce enzymes that
convert cellulose to sugars, while others
manufacture amino acids and other nutrients.
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Micromolecules are absorbed directly through
the epithelium of the caecum, and the waste
material is released into the colon for disposal.
A relatively inefficient system, but since the
supply of cellulose is so great, herbivores
modified the lower part of the esophagus and
the stomach into "four stomachs".
Four compartment
stomach
1. Reticulum – form
food bolus and initiate
regurgitation
2. Rumen – digestive
and fermentation vat,
contains anaerobic microbes,
site of fatty acid absorption
3. Omasum – lined by muscular
folds, reduces particle size,
absorbs water (and any
leftover fatty acids)
4. Abomasum – true
glandular stomach where
bacteria and pathogens
are killed
What do the microbes
provide to the ruminants?
1. Digestion of cellulose
Symbiotic
Microorganisms
2. Provision of organic acids
3. Provision of protein by
recycling waste nitrogen
X
4. Provision of B vitamins,
essential amino acids
5. Detoxify compounds
What do the ruminants
provide to the microbes?
1. Housing with reliable heat
Symbiotic
Microorganisms
2. Adequate nutrition
3. Garbage removal
4. Neutral environment
Located
between the
stomach & the
cloaca or
anus
Vertebrate
intestines are
differentiated
to varying
degrees into
small & large
intestines
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Cartilaginous fishes- have
a short, thick, tapering
intestine with a spiral
valve where food passes
slowly as it moves toward
the colon.
The colon is not required
for resorption of water,
since a shark is
essentially isotonic with
its environment.
Specialized salt glands,
which remove excess
ocean salts from the blood
dump their waste into the
colon, where it can be
eliminated.
 Amphibians - intestines
differentiated into coiled
small intestine and short,
straight large intestine
 Reptiles & Birds - coiled
small intestines & a
relatively short large
intestine that empties
into the cloaca
 Mammals - small
intestine is long & coiled
and differentiated into
duodenum, jejunum, &
ileum. The large intestine
is often relatively long.
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Typhlosoles, coils, villi
and CECA increase
absorptive area of
intestines
Fishes - pyloric &
duodenal ceca are
common in teleosts;
these are areas for
digestion & absorption
(are not fermentation
chambers)
Tetrapods - ceca are
present in some
herbivores; may contain
bacteria that aid in the
digestion of cellulose
• Enlarged caecum or
colon- rodents,
horses, zebras,
sheep, rhinos, apes,
elephants
• Break down of
cellulose and
carbohydrates
• Forms short-chain
fatty acid
• B vitamins- not
utilized, lost in feces
• Coprophagy– rabbits
eat special soft feces
 Chamber at end of
digestive tract that
receives the intestine, &
urinary & genital ducts
below placental mammals;
opens to the exterior via
the vent
 Lampreys, ray-finned
fishes, & mammals (except
monotremes)- shallow or
non-existent
 If no cloaca is present, the
intestine opens directly to
the exterior via anus.
EVOLUTIONARY
ADAPTATIONS
OF VERTEBRATE
DIGESTIVE SYSTEMS
GI TRACTS OF FISHES: Articulated jaws are absent in cyclostomes,
and located in the pharynx (1) of some species. The esophagus (2)
varies in length and the stomach is absent in cyclostomes and some
advanced species. Where present, the stomach (3) may be straight
(pike), U-shaped (trout), or Y-shaped with a gastric cecum (eel). The
absorptive surface and digesta retention time of the midgut (4) is
increased by a spiral valve (5) or pyloric ceca (6) in a number of
species.
GI TRACTS OF ADULT AMPHIBIANS: The gastric region of the
digestive tract forms a thickened sheath, which produces mucus, a
proteolytic cathepsin, and a low pH, but pepsin has been rarely
reported. The intestine is relatively long, with no distinct separation
into a midgut and hindgut. Adult amphibians are carnivores with a
weak dentition that serves for the grasping of food while it is being
swallowed. A distensible tongue is used for the capture of prey by
some species, and the mouth contains multicellular glands that
secrete mucous. Esophageal glands that secrete pepsinogen have
been described in frogs and toads.
GI TRACTS OF REPTILES: The mouth parts of are used for grasping,
cutting, or tearing their food. Some species have a distensible
tongue that serves as a sensing organ. The oral cavity contains
mucus secreting cells, and in some snakes & lizards, complex oral
glands secrete venoms and digestive enzymes. Salivary glands are
usually absent. The stomach tends to be tubular. The hindgut of
most herbivores is longer and it includes a blind sac or cecum at its
juncture with the midgut.
GI TRACTS OF BIRDS: The relative size of the crop, and gizzard are
smaller in carnivores, absent in the herbivores, but granivores
generally have a large crop and a large, muscular gizzard. The
gizzard is smaller and less muscular in carnivores and species that
feed principally on nectar, fruit, or pollen, or small
vertebrates. The most well-developed ceca are found in birds that
fed on high levels of plant fiber or invertebrates. The ceca serve as
a major site for microbial fermentation of plant fiber and chitin in
birds that feed on invertebrates.
MAMMALIAN HEADGUT: Mammals have an extremely efficient
masticatory apparatus. Teeth, a mobile tongue, the articulation of
the jaws and a complex musculature sling all allow rotational,
vertical & lateral movements of the mandible. However, a few
species have lost their teeth (replaced in baleen whales with sieve
for filter-feeding). Echidna, aardvarks, scaly anteaters, edentate
anteaters have weak jaws, relatively simple teeth, and a long tongue
that are adapted for feeding exclusively on ants or termites (the
giant anteater's tongue can measure as long as 2 feet).
MAMMALIAN FOREGUT: The stomach of these taxa includes an
expanded segment of sacculated or compartmentalized
forestomach. Therefore, the terms cardiac, body, and fundus that
are used to describe segments of the human stomach are useless
for comparisons with many other species.
E: esophageal entrance, P: pylorus, 1: omasum, 2: abomasum.
MAMMALIAN HINDGUT: The hindgut varies from a simple structure
with no cecum or valvular separation from the midgut to a
multicompartmental organ. It tends to be longer than that of other
vertebrates, consisting of a colon, rectum, and often a cecum that
is paired in a very few species. The colon of humans can be
subdivided into ascending, transverse, and descending segments
according to the direction it takes in the abdominal cavity. The
"ascending" colon is the segment of hindgut that has lengthened in
most mammals & vary considerably in its length, volume, and
course of direction. Anatomical terms assigned to the human colon
have little comparison to most other species.
CARNIVORES: The stomach consists of a unilateral dilatation of the
digestive tract. Cetaceans have a large multicompartmental
stomach, which is believed to have been conserved from herbivorous
ancestors. The hindgut is very short and indistinct in Insectivora,
cetaceans, and marsupials, and it lacks a valvular separation from
the midgut in some of these species. The hindgut of many
carnivores includes a cecum, but neither the cecum nor colon are
haustrated in most species.
HERBIVORES: The tract includes an expanded colon, cecum, or
forestomach. An enlarged colon is the principal site for microbial
fermentation. Haustrations extend over the cecum & the entire length
of the colon of most of these species. Bulk & roughage eaters (cattle
and sheep), tend to have the most well developed forestomach and
smallest cecum. Concentrate feeders have the smallest rumen and
omasum, & largest cecum. Some herbivores show combinations of
an expanded forestomach, cecum & hindgut.
OMNIVORES: The stomach is simple & noncompartmentalized. The
intestine varies in both its relative length & the ratio between midgut
and hindgut. The hindgut includes a cecum. The cecum & varying
lengths of the colon are haustrated in some species, and the colon is
haustrated throughout its length (pig, human). The human cecum
becomes well-developed during gestation. By the time of birth it is
represented by only a small distention in the proximal colon, which
does not correspond to the apex of the fetal cecum, and a vermiform
appendix.
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