Download Digestive System Function Breaking down of food Absorption of

Digestive System
Function
Breaking down of food
Absorption of nutrients
Origin
Stomodeum (inpocketing from the anterior portion of the body or embryo) and
Proctodeum (posterior end)
Keeps invaginating till it reaches the primitive gut (middle part) itself
Once it reaches the gut it starts forming the membrane
Buccopharyngeal membrane (anterior) and cloacal membrane (posterior)
degenerate, disappear to form the mouth pharynx alimentary canal and anal
Major Components
Digestive Tract (in adult)
Buccal Cavity (discuss subcomponents) includes the mouth and anterior part
Pharynx for swallowing
Alimentary Canal (esophagus towards anus or cloaca)
Accessory Glands
Not just a one way tract
Components: Buccal Cavity
Teeth, Tongue, Palate (Primary palate upper wall of respiratory tract and lower
palate which is lower part of mouth)
Primary and secondary palate – Main significance is to breathe while eating
Functions: Mechanical (attributed to teeth) and chemical breakdown of sugar
amylase
For palate – forms the roof of the mouth, In most vertebrates and amphibian
the palate would be the roof of the mouth, If the nares (mammals or
reptiles with secondary palate) there will be separation for entry of
air and food
Primary palate and secondary palate roof of mouth
Main significance of having secondary palate is to breathe while
eating
Animals without secondary palate – find internal nares are located –
main significance mammals and reptiles can chew – increase
need to keep food in their mouths, separate air and food tract
Nares – holes that can lead to the respiratory tract
Mammals and reptiles can masticate have and increase need in
keeping food in their mouths have to have something to allow them
another area to prevent mixing of food and air is the back of mouth –
where air can enter
Components: Buccal Cavity – Palate
Forms roof of the Mouth
Primary Palate: contains internal nares
Medial Series: Vomer, Pterygoid, Parasphenoid (middle)
Lateral series: Palatine, Ectopterygoid (upper)
Secondary Palate: Some reptiles and mammals
Hard and Soft palate
Cleft Palate – happens during gestation, before both, failure for secondary
palate to close, forming vault, primary palate exposed
Components: Buccal Cavity – Teeth
Origin: ectodermal
For Mechanical Breakdown, holding, hunting
Mammals and reptiles
Ex. Frogs and Salamanders - inner part of mouth hooklike structures inside
the mouth called vomerine teeth, for holding and keeping prey inside
their mouth, why do they need to do that? Tongue does not kill the
prey, will be most likely alive so prevent the prey from escaping, just
Release tongue to catch prey drag it back and leave it inside mouth for
a while
Muscular organ projecting outwards bringing the prey back using its
sticky structure keeping it inside, they don’t chew, tongue and mouth
doesn’t kill the prey, swallow it alive
Not just for mechanical breakdown usually happens in mammals and reptiles
Another modification got hunting a lot of carnivores have teeth modified to
be a bit sharper or curved to directly kill prey before ingestion
Ingestion entry of food and water to buccal cavity
Anatomy of the Tooth
Crown – exposed part above the gumline
Root – hidden by the gumline
Enamel – outermost covering, hardest substance in the body
Dentin – right under, next hardest to enamel
Pulp – supplied by nerves and blood vessels to keep the teeth alive to supply with
minerals and nutrients
Gums
Roots canals – supplying blood vessels and nerves directly to the pulp
Three types of tooth attachment found in vertebrates
Acrodont tooth is shallowly attached to upper part of bone
Ex. Snakes
Pleurodont also embedded but at the side
Ex. Lizards
Thecodont directly embedded
Ex. Crocodiles
Set of teeth for fish - very small, food are microscopic
Molluscs eat algae, can be used for scraping algae off rocks
Dormally flattened - vegetarian, for grinding, not only for proper swallowing, another
reason is it breaks the cell walls exposing the cytoplasm, in order to properly digest
the cells, have to be broken down first
Modification of tooth of great white sharks, serrated for more damage
Labyrinthodonts
carnivores need the teeth to properly attach on their prey and damage it , several
grooves on tooth itself, if look at it it will look ribbed, significance of having tooth
like that provides more piercing power, better penetration of muscle and skin
makes it more efficient
Front fangs of a snake
Shape is cone-shaped has certain modification that makes it significant, curved
backwards then curves forward again, very advantageous, how do snakes
strike, after pointing forward starts to pierce the meat
Advantage of the first curvature is for piercing the other is for anchorage to prevent
the prey from escaping makes them very efficient
Curvature is not found in some snakes
Most will have hollow fangs releasing the venom
Components: Buccal Cavity – Tongue
Evolution: Hypobranchial muscles resting on Hyoid Apparatus – lower part of the
head, musculature there
Sensory, feeding
Tongue is for sensory purposes, also important for feeding purposes
Chameleons and frogs – to get prey
Components: Buccal Cavity - Tongue
Ingestion where food water is ingested to buccal cavity, tongue can be used to bring
food inside the buccal cavity
Transport from outside environment to buccal cavity
Intraoral transport transport of food and water from buccal cavity to
pharynx,
Slow opening of the mouth in order to curve the tongue, wraps around
the food, quicker action snapping jaw open, bring the tongue inside,
closing and opening organism to bring food to next area
Deglutition – Swallowing gets food to alimentary canal
Components: Buccal Cavity – Tongue
Lingual Feeding – being sticky or having small parts
Woodpecker
Have accelerator muscles in the tongue
Allow it to contract tongue will move forward in a very fast manner
Proved to be very efficient
Components: pharynx not part of Buccal cavity
Common Passage for food and air notable in some reptiles and mammals
Derivatives: Pharyngeal pouches meeting w/ branchial grooves, further developing
into other organs
Separation before pharynx is notable for mammals and reptiles
Start to form branchial grooves
Start to meet forming a wall, in fishes and in some earlier amphibians in larval
stages, wall ruptures to form the gills, In reptiles, mammals and most birds
fail to rupture forming a wall does not allow gills to develop
When brancial groups close
Components: pharynx
Swallowing/ deglutition mostly modified in a lot of vertebrates
Air vs food – common passage for air and food
Muscular flap – Glottis
Movement of tongue against the soft palate of mouth or throat will allow the
glottis to close or open
Esophagus can accommodate larger sizes of food by being extended when
organisms swallow
When glottis closes air enters
Components: Alimentary Canal extends from esophagus (passageway of air and food)
stomach (storage of food, breakdown of proteins mostly, being acidic it kills
bacteria) small intestine (absorption of most nutrients and a bit of digestion) Large
intestine (reabsorption of water,storage of wastes) Cloaca (common passage way
for waste and reproductive cells) and anus (fecal wastes)
Alimentary Canal Design multiple layers within their organs
Mucosa – inner part inner lining or epithelium, find simple columnar lining/ tissue
Submucosa – under mucosa, layer of connective tissue attaching mucosa to
muscularis
Muscularis externa – layer of smooth muscles in the alimentary canal, smooth for
peristalsis - involuntary
Adventitia – connective tissue outside, can be modified to serosa – for mucus
secretion
Multiple Layers
Origins
Endoderm – inner lining
Mesoderm – muscles connective tissues, Blood vessels
Cross section of organ – different layers have diff. origins mostly endodermal thicker
layer endodermal
Alimentary canal
Esophagus, stomach, small intestine coiled, large intestine, rectum or anus
Alimentary Canal Components: Esophagus
Distendible
Secretes mucus – for bringing down food
passage way to stomach
Modifications:
For abrasion (histologic) psudostratified columnar tissue
Three types of tissues simple (1layer) stratified (multiple layers) pseudostratified (1
layer looks like multiple depending on nucleus found inside)
For secreting mucus for abrasion, Main Modification stratified, if have multiple
layers even if there is high amount of abrasion, still have cells under that layer to
allow organism to regenerate whatever layers in the area, Still provides degree of
protection
For ingesting large amounts of food (histologic and behavioral) ingestion of this,
histologic esophagus more distensible
behavioral modification keep food in esophagus before swallowing to
stomach, allows to digest food before swallowing big cavity where it
can store food
Alimentary Canal Components: stomach
Storage, absorption, digestion of proteins
Gastric Juice – mixture of HCL acidify to kill organisms aid in digestion, mucus more
slippery for food be better digestion, enzymes breaking down the food
Histologically if you look at stomach cross section epithelial lining folded
Rugae – folds, for increasing the surface area, modification of mucosal lining
Distends when there’s a large amount of food
Three Sections:
Cardiac – mucus, separated from esophagus by cardiac sphinchter – prevents
food from going back, it is a valve, why do you need to prevent it? area
is rich in HCl so its very corrosive, linings of stomach wall very thick
Prevent acidity of gastric juice to get to outside parts
Fundus- parietal and chief cells, most digestion happens, parietal cells
produce HCl provides acidity
chief cells – produce pepsin a lot of proteolytic enzymes
Pylorus – neutralize, mucus, end with pylorus sphinchter – prevents
backflow of food from small intestine to stomach
Have several glands and cells that neutralize acidity of stomach before
reaches small intestine,
Releases food gradual
Filled with mucus for better passage of food
Alimentary Canal Components: Small Intestine
Absorption
Ribbed
Areas have villi – larger, microvilli (found in villi for absorption of nutrients)
Crypts of Lieberkuhn (pit like areas found within mucosa for enzymatic functions)
provide enzymes that breakdown other components of food
Instestinal Juice that can break down food
Duodenum, jejunum, ileum
Duodenum - most anterior, pancreatic and hepatic secretions, Brunner’s
glands (neutralize acidity from stomach carried by the bolus – acidic
neutralized here) differences will be histological mostly glands and cells,
secretion of the pancreas and liver in order to digest the food
Jejunum - middle partwhere most of the absorption happens
Ileum – ileocolic valve separates small intestine to large intestine
Alimentary Canal Components: large intestine
Simple columnar (absorption and secretion) reabsorb water in digested food to
properly prevent dessication, excretory part for mucus
Terminus needs to be stratified drier it gets more abrassive, at terminal part of
small intestine starts forming stratified tissue since the waste is a lot more
abrassive since its dry
At the anal part there is an Internal (involuntary) and external anal spinchther
(voluntary)
Appendix area for fermentation in latter part
Accessory Glands (most portions of the entire digestive tract have glands)
Oral Glands
Buccal cavity mixture of mucus and other fluids, mucus provide better movement
for food going down
Mucus and serous fluid (enzymes for digestion msotly amylase)
More common in tetrapods
Fish – watery medium, don’t really need
Example: salivary glands produce saliva containing amylase and other mucus,
lacrimal glands in snakes and reptiles, venom glands for venoms
Accessory Glands
Liver
Developmental: RBC Production
Adults: RBC destruction, filtering wastes, bile production (exocrine)
Alcohol – waste poison by the body
Origin: hepatic diverticulum – invagination, outpocketing that lead to development
of liver cells, once outpocketing happens hepatocytes form
Liver cells are hepatocytes
Two types of excretion
Endocrine - directly lead to blood streams ducts for transport
Exocrine – leads to more distant areas
Bile – liver produces it and leads directly to small intestine, gall
bladder store bile
Leads directly to more distant areas
Accessory Glands
Pancreas
Origin: formation of Dorsal and ventral pancreatic diverticulum, more outpocketing
to facilitate development of cells of the organism
Ducts lead to duodenum, contains trypsin and chymotrypsin (enzymes that can
breakdown food, exocrine excretion)
Two Parts of Pancreas
Exocrine Chymotrypsin and trypsin
Endocrine mostly produced by Islets of langerhands: production of insulin
that detect high levels and glucagon detect low levels of sugar
Adaptations and Specialization of Gastrointestinal tract
Adaptations and Specialization Fish
Ileal modification – spiral valve – primitive ostechthyans, elasmobranches,
larger surface area less food is wasted,
If cut open the ileum of the shark there are spiral structures similar function
to rugae in the stomach for increasing surface area for better digestion,
larger surface area more food is in contact with mucosa which contains the
tissues directly absorbing the nutrients
Rectal gland – sharks, since they live in marine environments able to excrete excess
salts in their bodies using this gland, directly situated next to excretory parts
Pyloric cecum/ceca (absorption) – like appendix but more functional and
absorption of nutrients osteichthyes mostly in bony fishes
Adaptations and Specialization Extended ceca in other organisms
Cecum for fermentation
Cecum for absorption (exception)
Koalas (herbivores) only eat eucaliptus, not enough, so they have extended
cecum house a lot of bacteria to further ferment food to produce more
nutritional benefits
Cecum of carnivores very short almost non functional
Adaptations and Specialization Terrestrial vertebrates
Large intestine of terrestrial vertebrates longer in large intestine of aquatic
In large intestine there is water absorption, There is better conservation of water to
prevent dessication of water, more surface area more sites for water
absoprtion
Water absorption, prevent dessication, more surface area, more sites of watery
absorption
Adaptations and Specialization Gizzards
Very muscular and edible, Normally birds or reptiles swallow stones to store inside
the gizzard for further mechanical breakdown, internal teeth not part of the
body
Adaptations and Specialization Coprophagia
Ingestion of one’s own feces
Happens in Herbivores especially rabbits
There are two areas where they can digest:
Cecum for fermentation by bacteria
Small intestine and stomach main tract
Food they digest is from the cecum
After fermentation by feces comes from cecum have products of fermentation have
more nutrients not absorbed by organism
Reingest food from the cecum, Don’t reingest food that comes from main digestive
tract
Feces of koala
Herbivores reabsorb or reingest their feces in order to hide themselves from
predators, done by mothers
Baby rabbits don’t have very developed hind muscular, reingests feces of
baby animal to mask the smell
Reabsorp nutrients and protection