Digestive System Flashcards
Dietary categories
- herbivores
- carnivores
- omnivores
- saprophagous
Four main stages of food processing
- ingestion
- digestion
- absroption
- elimination
act of eating
ingestion
breaking food down into molecules small enough for the body to absorb
Digestion
small molecules are taken in by the animal’s cells
Absorption
undigested material passes out of the digestive compartment
Elimination
Feeding adaptations
- suspension feeder
- deposit feeder
- substrate feeder
- fluid feader
- bulk feeder
sifts through food particles in the water
Suspension feeder
filter out plankton, mainly large crustaceans called krill, with whalebone or baleen
whales
use gill rakers to strain plankton
- herring
- other suspension-feeding fishes
eats its way through dirt or sediments and extract partially decayed organic material (detritus) consumed along with the soil or sediments
Deposit feeder
lives in or on its food source, eating its way through the food
Substrate feeder
sucks nutrient-rich fluids from a living host and is considered a parasite
Fluid feeder
eats relatively large pieces of food
Bulk feeder
ability of some animals to move their skull bones relative to each other, in addition to the movement of the upper and lower jaws.
Cranial kinetism
what do birds lack
teeth
tube from mouth to vent or anus
Digestive tract
functions of Digestive tract
- ingestion
- digestion
- absorption
- egestion
major subdivisions of Digestive tract
- oral cavity
- pharynx
- esophagus
- stomach
- intestine (small, large)
- anus or cloacal opening
accessory organs
- tongue
- teeth
- oral glands
- pancreas
- liver
digestive organ in fishes, amphibians and most reptiles, lungs in tetrapods
Pleuroperitoneal cavity
lungs in few reptiles, birds and mammals
Pleural cavity
digestive organs beyond esophagus
Peritoneal or abdominal cavity
heart
Pericardial cavity
covering of digestive system
- visceral peritoneum
- parietal peritoneum
outer covering of the digestive tract
Visceral peritoneum
lines the body wall
Parietal peritoneum
embryonic digestive tract
- foregut
- midgut
- hindgut
posterior portion of the oral cavity, pharynx, esophagus, stomach, most of small intestines
Foregut
little remains in adult
Midgut
large intestine and cloaca
Hindgut
- midventral invagination of the ectoderm of thehead
- will give rise to the oropharynx in fishes
- guarded by oral plate (provide an anterior entrance tothe digestive tract
Stomodeum
exit from the hindgut when cloacal plate ruptures
Proctodeum
begins at the mouth and ends at the pharynx/ esophagus
Oral cavity
complete secondary palate (cleftless) that provides floor for separate nasal passageway from the external nares and pharynx
Crocodilians and mammals
- separates the gums of mammals from cheeks and lips
- specialized to serve as a suckling and masticatory organ
oral vestibule
- capturing and gathering food
- taste
- manipulate fluids and solids in
- oral cavity swallowing
- thermoregulation
- grooming
- human speech
tongue
tongue assist the jaw in holding the prey
- Elasmobranches
- bony fishes
- primitive amphibians
lateral lingual swellings are suppressed and intrinsic muscle is usually lacking
Birds
tongue immobilized in the floor cavity and cannot be extended
- turtles
- crocodilians=
- some birds
- whales
tongue sometimes long and may move in and out of the oral cavity
- snakes
- insectivorous lizards and amphibians
- some birds
attaches tongue to the floor of the oral cavity
frenulum linguae
perception of the shape, weight and texture of a solid food by feeling, handling and lifting it; in amniotes
Stereognosis
secrete a variety of substances
oral glands
- lubrication and binding- solubilizes dry food
- oral hygiene
- initiates starch digestion
- provides alkaline buffering and fluid
- evaporative cooling
Saliva
- (lizards, snakes and mammals)
- venom tranquilizes the prey or dispatches them
Poison
vampire bats
anticoagulant
Kinds of oral glands
- labial glands
- molar glands
- infraorbital glands
- palatal glands
- sublingual and submandibular glands
- intermaxillary
opens into the oral vestibule at the base of the lips
Labial glands
lie near the molar tooth
Molar glands
in the floor of the orbit
Infraorbital glands
opens into the palatine
Palatal glands
opens via a common papillae under the tongue
Sublingual and submandibular glands
lie near the premaxillary bone
Intermaxillary (internasal) glands
are derivations of bony dermal armor
Teeth
show gradual transition to teeth at edge of jaw
placoid scale
composition of teeth
primarily dentin surrounded by enamel or enameloid
teeth are numerous and widely distributed in the oral cavity and pharynx
fish
- teeth are widely distributed on the palate
- most amphibians and some reptiles – vomer, palatine, pterygoid bones
Early tetrapods
teeth are limited to the jaws
- crocodilians
- tooth birds
- mammals
Classification of teeth based on:
morphological variation
- homodont dentition
- heterodont dentition
- all teeth are shaped alike
- in vertebrates other than mammals
Homodont dentition
teeth exhibit morphological variation
Heterodont dentition
Heterodont dentition
- incisors
- canines
- premolars and molars
cutting
incisors
piercing and tearing
canines
macerating
premolars and molars
Classification of teeth based on:
attachment of tooth
- acrodont dentition
- pleurodont dentition
- thecodont dentition
attach to the surface or summit of the jawbone; in teleosts
Acrodont dentition
attach to the inner side of the jawbone; in anurans, urodeles and lizards
Pleurodont dentition
occupy bony sockets or alveoli; in fishes, crocodilians, extinct toothed birds and mammals
Thecodont dentition
Classification of teeth based on:
succession of teeth
- polyphyodont dentition
- diphyodont dentition
- monophyodont dentition
- number of replacements during a lifetime is indefinite but numerous
- in crocodiles
Polyphyodont dentition
- develop two sets of teeth
- deciduous or milk teeth and permanent teeth
- in most mammals
- definite sequence in which the teeth erupt
- humans: 6,1,2,4,3,7,8
Diphyodont dentition
sequence of human teeth
6,1,2,4,3,7,8
- develop only a first set of teeth
- in few mammals
- toothless whales – first set although form within the jaw bone do not erupt or are shed.
Monophyodont dentition
replaced platypus deciduous teeth
horny epidermal teeth
teeth being replaced throughout life byforward migration of new teeth formed at therear of the jaw
manatee
morphological variants in shark
- fish eaters
- shellfish eaters
numerous rows of teeth, flat, sharp, notched triangles that are used for cutting; single or multiparated tusks that are curved towards the pharynx for holding prey
Fish eaters
teeth at the entrance are with curved caudally directed spines while the rest form rounded denticles
Shellfish eaters
morphological variants in Actinopterygians, amphibians, reptiles
simple pointed cones attached to one or more membrane bones; small teeth between larger ones
morphological variants in venomous snake
fangs are curved or bladelike, grooved on the rear surface or tubular (for injecting venom)
morphological variants in mammals
- incisors
- canines
- premolars
- molars
- with one horizontal cutting edge and a single root and grows throughout life
- located on either side of the mandibular symphysis- grow throughout life
Incisors
well developed incisors, used for holding, cropping and gnawing
herbivorous mammals
tusks are modified incisors
elephant and mastodon
lacking incisors on the upper jaw only
bovines
incisors lacking on the lower jaw
vampire bats
no incisors
sloth
elephant tusk
modified upper incisor
male wild boar
modified canines
lie next to incisors
Canines
canines and incisors are similar in appearance
mammals
spearlike and used for piercing flesh
carnivores
tusks
walrus
absent canines
lagomorphs
space between the incisor and cheek tooth
Diastema
mammals and ungulates; with two prominent cusps (bicuspid; in most mammals) and 1-2 roots
Premolars
3 or more cusps (tricuspid) and usually three roots
Molars
Some varieties of mammalian cheeck cell
- secodont teeth
- carnassial teeth
- seledont teeth
- lophodont teeth
- bunodont teeth
- triconodont teeth
- trituberculate teeth
- crowns are laterally compressed, roots are long and cusps are interconnected by sharp ridges of enamel
- carnivores
Secodont teeth
first lower molar teeth usually larger and longer
Carnassial teeth
- with enamel disposed in crescentric fold
- wider and longer providing a broad surface for grinding, short roots, ungulates
Seledont teeth
- enamel and dentin are intricately interfolded
- in proboscidians, can reach a foot or more in length
Lophodont teeth
- low rounded cusps and crown
- wear down evenly
- omnivores, some herbivores, mammals (rhinos, some hogs, primitive ruminants)
Bunodont teeth
three conelike prominences arranged in a straight line; early prototherians
Triconodont teeth
- three conelike prominences are arranged in a triangle
- early therians
- forerunners of tricuspids
Trituberculate teeth
keratinized (horny) teeth that sometimes take the place of bony ones
Epidermal teeth
horny teeth in the buccal funnel and tongue used for rasping
Agnathans
buccal cavity is pressed tightly into the flesh of the host
Lampreys
several rows on temporary lips used for rasping algae; replaced by bony ones during metamorphosis
Anuran tadpoles
deciduous bony teeth are replaced by horny epidermal teeth
Platypus
- used for cracking the shell
- found in Turtles, crocodilians, birds and monotremes
Egg tooth
- had pharyngeal pouches in the embryo
- part of the foregut immediately preceding the esophagus
- fishes – part of the respiratory system
Pharynx
features of a tetrapod pharynx
- glottings
- openings of auditory tubes
- opening to esophagus
slit leading to the larynx
glottis
Pharynx of mammals
- nasal pharynx
- oral pharynx
- epiglottis
where the nasal passageway empty via choanae (internal nares) and the two auditory tubes open into its lateral walls.
Nasal pharynx
between the oral cavity and the glottis; where the oral cavity leads to
Oral pharynx
- fibrocartilage flap that overlies the glottis
- prevents foreign substances from entering the pathway to the lungs when swallowing
Epiglottis
transition between the oral cavity and the oral pharyn
Isthmus of fauces
side of the tongue to the soft palate
Glossopalatine arch
pharynx to the soft palate
Pharyngopalatine arch
- hangs from the caudal border of the soft palate into the oral pharynx
- humans and some primates
Uvula
hollow, between the pillars of the fauces
Palatine tonsils
develop in the mucosa of the nasal pharynx
Pharyngeal tonsils (adenoids)
- develop on the tongue near its attachment to the hyoid bone
- defense against infective agents that have entered the mouth and internal nares
Lingual tonsils
Morphology of the gut wall
- mucosa
- submucosa
- muscularis externa
- serosa
- glandular epithelium lining of endodermal origin
- underlying layer of not so very dense connective tissue supporting the base of cryptlike epithelial gland, lymph nodules, and blood and lymph capillaries that service the glandular epithelium
- thin coat of smooth muscle fibers
mucosa
thin coat of smooth muscle fibers
muscularis mucosae
secretes lubricant that fascilitates the passage of the content during peristalsis
mucous glands
- thicker layer of connective tissue
- supports the base of compound alveolar glands, plexus of arterioles, venules and lymphatics that service the capillary beds of mucosa.
Submucosa
- consist of smooth muscle tissue
- produces the macerating, peristaltic and segmenting action of the gut
- neural stimuli supplied from autonomic (visceral) nerve plexuses
muscularis externa
smooth muscle fibers that encircle the gut, constricting the lumen on neural demand
Inner circular layer
muscle fibers that contracts short segments of the gut
Outer longitudinal layer
- loose connective tissue (adventitia) and visceral peritoneum
- exudes small amount of a serous fluid that lubricates the surface of the viscera
Serosa
ciliated digestive tract
Larval craniates
ciliated stomach
Teleosts
ciliated oral cavity, pharynx, esophagus and stomach
Adult amphibians
gut movement
alternate constriction of rings of smooth muscle
relaxation in gut movement
in front of bolus
- distensible muscular tube
- extends between the pharynx and the stomach
- conducts foodstuffs to the stomach
- lined by a stratified squamous epithelium
Esophagus
entire length of esophagus consist of striated muscle
ruminants
line by horny papillae that are directed downward
marine turtles
paired or unpaired diverticulum or sac used for hoarding grain or seed until there is room for them in the stomach
crop
under the stimulus of prolactin, cells of the glandular area of the lining sac undergo fatty degenaration and are shed as holocrine secretion + partially digested food
pigeon
pigeon’s milk
holocrine secretion + partially digested food
narrow lumen
vampire bats
muscular chamber or series of chambers at the end of the esophagus
Stomach
partially liquify solid foods before they are injected into the small intestine
lubricatory mucus and digestive enzymes
gastric glands that are branched and tubular
Glandular epithelium
three divisions of the stomach
- cardia
- fundus
- pylorus
- transition between the esophagus and stomach;
- mammals- glands secretes mucus (cardiac glands)
- no zymogenic cells but few parietal cells are present
Cardia
- lateral to the cardiac region in humans
- presence of fundic glands composed of mucus cells, parietal cells (HCl), chief cells of zymogenic cells (proteolytic enzymes; synthesize and release the pre-enzyme pepsinogen) and goblet cells.
Fundus
action of HCl
pepsinogen to pepsin
- opening from the stomach leading into the duodenum
- presence of pyloric glands composed of mucus cells whose secretion helps to neutralize the acidic chyme as it moves next to the intestine
- with many goblet cells and few parietal cells
Pylorus
devoid of glandular glands
Non-glandular epithelium
Mesenteries in the stomach
- mesogaster
- greater omentum
dorsal mesentery that connects the stomach to the coelomic roof
mesogaster
mesentery attached to the greater curvature and draped like a curtain between the ventral body wall and the intestines
greater omentum
small part of the coelom, within the double walled omentum
lesser peritoneal cavity
small passageway that connects the coelom with the lesser peritoneal cavity
epiploic foramen (foramen epiploicum)
variations in the stomach
- cyclostomes
- fishes
- frogs
- crocodile and birds
- humans
- ruminants
no definitive stomach
Cyclostomes
variety of shapes and epithelium is sometimes ciliated
Fishes
no definitive stomach or have that is poorly differentiated and lacks digestive glands
Chimaeras and lungfishes
one large cavernous chamber lined with mucus and digestive gland
Frogs
- Proventriculus – secretes digestive enzymes
- Gizzard – lined with horny membrane; grinding mill that makes a mash of food mixed with gastric secretions
crocodilians and birds
secretes digestive enzymes
Proventriculus
lined with horny membrane; grinding mill that makes a mash of food mixed with gastric secretions
Gizzard
base of the esophagus
cardiac portion
lateral to the cardiac region
fundus
region between the lesser and greater curvatures
body
preceding the pylorus (stomach to the duodenum)
pyloric portion
ring of smooth muscle that surrounds the pylorus
pyloric sphincter
folds inside the stomach that increases its surface area
rugae
stomach is adapted in digesting cellulose
Ruminants
Chambers of ruminant stomach
- rumen
- reticulum
- omasum
- abomasum
- layer is like the esophagus, contains cellulase (enzymethat digests cellulose) secreting anaerobic bacteria
- interior surface forms numerous papillae that vary in shapeand size from short and pointed to long and foliate
rumen
- cellulose fermentation continues, cuds or small boluses are formed to be regurgitated for further maceration of the teeth
- Reticular epithelium - thrown into folds that form polygonal cells that give it a reticular, honey-combed appearance.
- Numerous small papillae stud the interior floors of these cells.
reticulum
thrown into folds that form polygonal cells that give it a reticular, honey-combed appearance.
Reticular epithelium
- temporary holding site of thoroughly masticated mash
- Inside is thrown into broad longitudinal folds or leaves reminiscent of the pages in a book
omasum
packed with finely ground ingesta, have been estimated to represent roughly one-third of the total surface area of the forestomachs.
omasal folds
true glandular stomach where gastric enzymes are added to the mash release pepsin & acids for typical protein digestion
abomasum
- commences at the pyloric sphincter and ends in the cephalic end of the cloaca or anus
- presence of microvilli increases the surface area for absorption
- with intestinal glands that secretes digestive enzymes
- morphology is affected by the type of diet, frequency of meals and their volume
- small and large
intestine
where intestine commences
pyloric sphincter
where intestine ends
cephalic end of cloaca or anus
increase surface area of intestine
microvilli
secretes digestive enzymes in the intestine
intestinal glands
chief site for digestion and absorption of nutrients
small intestine
- splits polypeptides to amino acids, disaccharides into monosaccharides
- pancreatic enzymes help in the final digestion that results in absorbable nutrients.
intestinal juices
where is water absorbed
colon
quite straight intestine
Cartilaginous and basal bony fishes
- with typhlosole or spiral valve
- suspended within the lumen (increases the surface area for absorption)
Spiral intestine
leads to the cloaca
Postvalvular intestine
extracts and excretes excess sodium chloride from the blood
rectal gland
increases the absorptive area (pyrolic ceca)
intestinal ceca
- lengthy but smaller in diameter
- with villi (small surface projections that increases the surface area of the mucosa for better absorption)
Small intestine
small surface projections that increases the surface area of the mucosa for better absorption
villi
Parts of small intestine of tetrapods
- duodenum
- jejunum
- ileum
- receives chyme from the stomach and exocrine secretions from the liver and the pancreas
- receives one or more ducts that drain the pancreas, liver and gallbladder delivering pancreatic juices and bile salts
Duodenum
acts on CHO;
amylase
digests lipids yielding absorbable fatty acids and glycerol
lipase
digests proteins
proteolytic enzymes
- middle part of the small intestine
- between the duodenum and the ileum
jejunum
- last part of the intestine
- presence of large masses of lymph nodules (Peyer’s/Payer’s patches)
Ileum
large masses of lymph nodes in ileum
Peyer’s/Payer’s patches
sphincter that regulates the movement of food to the large intestine
ileocecal valve
Three structures in the wall of the small intestine
- microvilli
- villi
- circular folds (plicae circulares)
tiny projections of the plasma membrane of the mucosal cells
microvilli
fingerlike projections of the mucosa that give it a velvety appearance and the feel
villi
deep folds of both mucosa and submucosa
circular folds (plicae circulares)
enter dead-end lymph vessels within the villi
lacteals
movement of absroption in intestine
- hydrolyzed lipids
- lacteals
- chyle larger lymphatic
- major vein near heart
- liver and other tissues
- diameter is bigger and the mucosa lacks villi
- rarely coiled but caeca is common
- smooth muscle sphincter within the muscularis of the nal canal controls the release of waste products
- presence of goblet cells that secrete mucus (acts as a lubricant to ease the passage of feces to the end of the digestive tract)
- absorbs water to dry out the undigestible food residue
- to eliminate these residues from the body as feces
Large intestine
common in large intestine
caeca
controls release of waste products
smooth muscular sphincter
secrete mucus
goblet cells
acts as a lubricant to ease the passage of feces to the end of the digestive tract
mucus
rare in fishes and amphibians but common in amniotes (ileocolic aceca)
Caecum
terminates the caecum in arthropods, rodents, rabbits and other mammals
vermiform appendix
where fermentation of food by enzymes secreted by cellulase secreting anearobicbacteria takes place (koala)
Caeca
sac that opens into the alimentary tract
Caecum
- commences at the ileocolic sphincter; where absorption of water takes place.
- ascending, transverse, descending with pronounced flexures between them
Colon
where the descending colons end in humans
sigmoid flexure
straight terminal portion of pelvic cavity
rectum
rumbling sound caused by gas moving through the intestine
borborygmi
- largest gland in the body
- arises from the midventral aspect of the midgut as a hollow caecumlike diverticulum (liver bud)
Liver
drain the lobes of the liver
hepatic ducts
mesenteries of the liver
- hepatoduodenal ligament
- gastrohepatic ligament
- falciform ligament
connects the duodenum and the liver
Hepatoduodenal ligament
connects the pyloric stomach to the liver
Gastrohepatic ligament
suspends the liver from the diaphragm and abdominal wall
Falciform ligament
- composed hepatoduodenal & gastrohepatic ligaments
- conducts the common bile duct to the duodenum and the hepatic artery and hepatic portal vein to the liver
lesser omentum
- small green sac embedded in the inferior surface of the liver
- develops in most vertebrates; none in many birds, lamprey, whales, some rodents
- stores bile secreted by the liver
Gallbladder
drains the gallbladder
cystic duct
where the hepatic and cystic ducts converge and empties to the duodenum
common bile duct
short terminal segment of the common bile duct embedded in the wall of the duodenum
ampulla of Vater
produces digestive enzymes in the alveoli (acini) which is transported via pancreatic ducts to the duodenum
exocrine portion
bears pancreatic islets (islets of Langerhans), lacks ducts; secretes its hormonal products, insulin and glucagon, into the bloodstream
endocrine portion
Kinds of pancreas
- diffuse
- compact
- teleosts and many higher vertebrates
- pancreas tissue is distributed along the blood vessels
Diffuse pancreas
may consist of several discrete lobes
compact pancreas
chamber into which the digestive, urinary and genital ducts usually empty in many fishes and most tetrapods other than therian mammals
Cloaca
cloaca becomes shallow and disappears thus digestive tract opens independently to the exterior
- lampreys
- chimaeras
- living female coelacanths
- ray finned fishes
in placental mammals, the cloaca becomes partition into how many ways
2 or 3 separate passageways
