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Transcript
. 14.10
Phylum Platyhelminthes
General Characteristics
Bilateral symmetry: body can be
divided along one plane of symmetry to
yield 2 mirrored halves (anterior,
posterior, dorsal, ventral, left and
right)
 Has 1 digestive cavity
 Acoelomates: lack a coelom (body
cavity)
 Exhibit cephalization: has a head region
with sensory structures

Body Cavity
Classification
General Characteristics

Triploblastic: contain 3 well defined
germ layers
◦ Has mesoderm: region between endo- and
ectoderm made of parenchyma
◦ Mesoderm enables the formation of some
internal organs (muscular, excretory,
and reproductive)
◦ Mesoderm also gives rise to the
Parenchyma- a form of solid tissue
containing cells and fibers
General Characteristics
Reach the organ system level of
organization
 Has a central nervous system

Platyhelminthes “Firsts”
Bilateral symmetry
 Has digestive cavity
 Triploblastic
 Reach the organ system level of
organization
 Cephalization
 Central nervous system
 First with an excretory system

How are Platyhelminthes
different from cnidarians?
Cnidarians
Platyhelminthes
Mesoglea
Mesoderm
No organ systems
Organ systems
Diploblastic
Triploblastic
GVC
Digestive cavity
Radial Symmetry
Bilateral Symmetry
Not cephalized
Cephalized
Nerve net
Nervous system with brain
Cnidocytes
No cnidocytes
Gonads
Complex reproductive system
General Structure: Epidermis

Most general characteristics are
describing Turbellaria class

Epidermis: made from the ectoderm
◦ Ciliated: especially on the ventral surface
to aid in movement
◦ Contain many gland cells that secrete a
mucous covering to help move
General Structure: Epidermis

Epidermis has rhabdites: rod-like
structures in the cells of the epidermis
that are discharged and form a
protective mucous covering by
expanding when released
General Structure: inside the
epidermis

Contains layers of muscle cells (fibers)
◦ Run circularly, longitudinally, and
diagonally
◦ Come from the mesoderm

Parenchyma cells:
◦ Develop from the mesoderm
◦ Fills the space between the muscle cells and
the visceral organs
◦ Layer that prevents them from being
coelomates
Locomotion
Movement is a concerted effort of ciliary
action, mucous, and muscular
movements
 Most movement accomplished by
Turbellaria …. Why?
 The head (superior) is raised while
the other portion (inferior) is kept against
the surface
 Glides slowly
 Anterior end bends from side to side

Nutrition and Digestion

Class Cestoda are the exception to the
following notes on nutrition and digestion
◦ Cestodes have no digestive tract because
they are parasites that depend on their host
for nutrients- they absorb nutrient from
their host
Nutrition and Digestion
Other classes have:
 Mouth: near the middle of the ventral
surface; opens to the pharynx
 Pharynx: tubular muscular organ

◦ Contains many gland cells
◦ Can be extended from the mouth during
the feeding process
◦ Secrete enzymes to help soften prey
◦ Sucking action from the pharynx breaks off
small pieces of the prey
Class Turbellaria Ingesting Food
Pharynx
Nutrition and Digestion

Intestine
◦ Tri-clad Intestine (3 trunks)= class
Turbellaria
◦ Bi-clad (2 Trunks)= Class Trematoda
◦ No digestive tract= Cestoda)
Excretion and Osmoregulation


Platyhelminthes are the first organism with
an excretory system
Consists of Protonephridium: first
kidney
◦ System lies in the parenchyma and consists of a
network of tubules that run the length of the
worm on each side and opens to the surface
by minute pores
◦ Side branches terminate in tiny enlargements
called flame bulb: cup shaped terminal end that
contains flagella to propel the fluid
throughout the network to the exit pores
(nephridiopores)
Excretion and Osmoregulation

Primary function of the flame bulb system
is to remove the excess water from
the tissues
Circulatory and Respiratory
System
Platyhelminthes contain no circulatory or
respiratory system
 Respiration occurs through epidermal
cells of the whole body surface
(diffusion)
 To allow enough oxygen to pass in and
carbon dioxide to pass out through
diffusion-> the thickness can’t be too great
 This is the reason why the organism is
so FLAT!!!!

Nervous System
Consists of the simplest nervous system
called the sub-epidermal nerve plexus
 Resembles the nerve net of the
cnidarians
 Functions to send the nerve impulses
from one end to the other

◦ Consists of a brain, nerve cords, and side
branches
Nervous System

Brain: a mass of ganglion cells at the
anterior end
◦ Centered anteriorly
◦ Not needed for muscular coordination
involved in locomotion
◦ Functions to initiate behavior and receives
stimuli from sensory organs and sends it to
the rest of the body



Nerve cord: run from the brain to the
posterior
Side branches: come off the nerve cord
and directed toward the inside of the body
Forms a ladder type of system
Sense Organs
Ocelli: light sensitive eye spots
 Statocysts
 Have tactile and chemoreceptive cells
over entire body
 Have organs called auricles (ear-like
lobes on the side of their head)

◦ Functions in finding food
(chemoreceptive)
◦ If they are cut off they have a hard time
finding food
Reproduction and
Regeneration
Most information about class Turbellaria
 Can reproduce asexually and sexually


Asexual reproduction accomplished by
fission
◦ The area behind the pharynx constricts and
the organism separate into 2 animals
◦ Each part will regenerate missing parts
Regeneration

29
Many species have remarkable powers of
regeneration and repair wounds
Phylum Platyhelminthes
Reproduction and
Regeneration

Sexual reproduction
◦ Almost all flatworms are hermaphroditic:
contain both male and female sex organs in every
organism
◦ Have discrete testes and ovaries
◦ Have a system of tubes and chambers in which
fertilization occur
◦ Do not practice self-fertilization-> they
reproduce by cross-fertilization
◦ After breeding season the organs degenerate
and regenerates new at the beginning of the
next season
Protandry
Mutualistic insemination
 Sperm is produced first and the
organisms exchange sperm with
another
 The organism holds the sperm until the
eggs are ready
 Eggs develop later

Platyhelminthes Classification

Class Turbellaria
◦ Free living planarians & marine flatworms

Class Trematoda
◦ Internal Flukes

Class Cestoda
◦ Tapeworms
Classification
Platyhelminthes
Trematoda
Planaria
Aspidobothrea
Digenea
Monogenea
Cestoda
Class Turbellaria








Most free living flatworms
Marine or freshwater
Class of the planaria
Can regenerate
Not parasitic
Planaria class are carnivorous- feeding on small
crustaceans, nematodes, rotifers, and insects
Most have chemoreceptors to trap prey in
mucous (rhabdites)
The notes previously taken were on class
Turbellaria
Form Fits Function
The idea that the structure of an
organism/part of an organism is related to
its function
 Examples:

◦ Location of the mouth on the Platyhelminthes
◦ Lack of a digestive tract in the Cestoda Class
◦ Shape/depth of the planaria
◦ Turbellaria is the only class highly motile
Pretty planaria, not all flatworms
are ugly parasites
Types and Adaptations of
Parasites


Endoparasites: Parasites that live inside their host
Exoparasites: Parasites that live outside their host

Adaptations to a parasitic lifestyle:
◦ Small size- to be undetected
◦ High reproductive capacity
◦ Takes only what they need from the host- not all kill their
host
◦ Protective/stabilizing features for attachment
◦ Contains only necessary organ/features
◦ Forms protective cysts for when its outside a host
◦ Penetration glands
◦ Structures (hooks and suckers) for attachment
Class Trematoda
Class of the parasitic fluke
Endoparasites
Leaf-like in structure
No->little external cilia (does not want
to move)
 Oral and Ventral suckers (attachment)
 Poorly developed sense organs
 Biclad digestive tract
 Require 2 or more hosts
 Muscular pharynx to permit worm to pump
food into gut




Sub-Class Digenea
Parasitizes all types of vertebrates in a wide range
of sites
 Most cycles include:

◦ Intermediate host: site of asexual reproduction to
increase in number of individuals (Mollusc)
◦ Definitive host: site of sexual reproduction where
eggs are released (vertebrate)
◦ Some have a Secondary intermediate host

Examples are:
◦ Clonorchis sinensis- Liver Fluke
◦ Schistosoma- Blood Fluke
◦ Paragonimus- Lung Fluke
Generalize Fluke Body Plan
Types of Transmission

Passive Transmission: transmission into
the host that requires no action from the
parasite
◦ Ingestion

Active Transmission: transmission into
the host that requires the parasite to
“actively” work to gain entry into the
host
◦ Burrowing
Example #1 Clonorchis sinensisLiver Fluke



Infects humans, dogs, cats, pigs
Found in China, Japan, SE Asia
Life Cycle:
◦ Definitive Host: adult parasite found in the bile
duct of humans and other fish eating
mammals
◦ Intermediate Host:
 Primary: Snail
 Secondary: Fish
◦ Mode of Infection: Passive transmission by
eating raw/poorly cooked infected fish
◦ Causes: abdominal pain, cirrhosis of the liver,
blockage of the bile duct, death
Trematode Lifecycle
Vocabulary
Definitive Host: site of sexual reproduction
Miracidium: free swimming ciliated larvae
Intermediate Host: site of asexual repro.
Sporocyst: produced inside Intermediate host;
reproduce asexually to make more sporocysts or
redia
 Redia: 2nd asexual phase to produce redia or
cercaria
 Cercaria: free swimming larval form that emerges
from the snail; contains motile tail to swim to next
host
 Metacercarial Cyst: juvenile flukes that burrow
into muscle of (secondary) host




Fluke Life Cycle







Every: Egg
Mirror: Miracidium (in water)
Spotted: Sporocyst (in snail- primary
intermediate host)
Red: Redia (in snail- primary intermediate
host)
Certainly: Cercaria (in snail and water)
Met: Metacercaria (in 2nd intermediate host)
Approval: Adult (definitive host)
Fluke Life Cycle
Fluke Life Cycle
Clonorchis sinensis- Liver
Fluke
Example #2: Schistosoma
Affects 200 million people in Africa, S.
America, Middle East, and Far East
 Not hermaphroditic: have separate male
and female species
 Dimorphic: the male and female body are
structurally different

◦ Male: is larger(width) and contains a
gynecophoric canal (groove in the body of the
male to contain the female
◦ Female: longer and more slender; “snuggles” in
the male canal
Species of Schistosoma
S. mansoni: adult found in the veins of the
large intestine and feeds on blood
 S. japonicum: found in veins of small
intestine; most severe
 S. haematobium: found in veins of urinary
bladder

Side Effects of Schistosoma
Eggs in the intestinal wall can cause
ulceration, abscesses, bloody
diarrhea, and pain
 Eggs can travel to the liver or other sites
and cause problems at those sites and can
impede circulation
 If liver is affected it can cause cirrhosis

Blood Flukes:
Schistosoma japonicum &
Schistosoma mansoni
Schistosoma Life Cycle

Schistosomiasis
◦ Deadly prominent disease in
many regions of the world
◦ Bores into the skin of the
definitive host and travels in the
circulatory system to the heart
the lungs and the kidneys where
it feeds and grows
◦ Inflammation is caused by eggs
becoming trapped in the hosts
tissues
62

Chinese liver fluke
◦ Lives in the bile duct of
humans, cats, and dogs (1-2
cm.)
◦ Goes through two
intermediate hosts
◦ Infection occurs from
ingestion of raw fish
Phylum Platyhelminthes
Life Cycle of Schistosoma
Swimmer’s Itch

Encysted metacercaria
of avian schistosomes
Example #3: Paragonimus







Lung Flukes
Parasitizes wild carnivores, humans, pigs, rodents
Humans(vertebrates) are the definitive host
Snail is the primary intermediate host
Crab is the secondary intermediate host
Humans get infected by passive transmission > eating raw crab
Upon eating the metacercaria encysts itself in the
intestine then penetrates the lung and
diaphragm can cause chronic bronchitis
Human Lung Fluke Life Cycle
Class Cestoda
Class of the tapeworms
 Have long, flat bodies
 No digestive system…Why???
 No cilia in adults
 Contain microtriches: covering surface of
their body serves to increase surface area
providing greater absorption
 Hermaphroditic
 Well developed muscles
 No sense organs

Class Cestoda
Has a scolex: organ for attachment (hooks
and/or suckers)
 Most are polyzoic: body is divided up into
a series of proglottids
 Proglottid: individual segment of a
tapeworm body; contains their own set of
reproductive organs (can be 3-4,000/animal)
 Strobila: the length of the tapeworm body
behind the scolex consisting of a chain of
proglottids

Tapeworm
Anatomy
Growth of a Tapeworm

Germinative zone: located behind the
scolex; location where new proglottids are
formed
◦ As the younger proglottids differentiate each
moves posteriorly in the strobila (because of the
creation of new proglottid) and its gonads mature
◦ The proglottids can be fertilized by another
proglottid in the same or different strobila
◦ Mature eggs can be released through an opening
in the proglottid or leave the host when the
proglottids are separated from the main body of
the worm
General information on the
lifecycle of tapeworms

2 Hosts
◦ Definitive host: carnivore
◦ Intermediate host: herbivore
Adults live in the intestine of the
definitive host
 Larval stages (cysticercus) encyst in
muscle of intermediate host
 Causes : weight loss, indigestion,
diarrhea, intestinal blockage, pain

Examples of Class Cestoda

Taenia saginata: Beef tapeworm
◦ Humans get infected by eating raw/undercooked beef

Taenia solium: Pork tapeworm
◦ Humans get infected by eating raw/undercooked pork

Diphyllobothrium latum: Fish tapeworm
◦ Humans get infected by eating raw/undercooked fish
◦ Largest tapeworms in humans; common in Great
Lakes

Echinococcus granulosus: Dog tapeworm
◦ More later
Taenia saginata
Life Cycle
- Human/Beef
Tapeworm
Pork Tapeworm
Taenia solium – Human/Pork
Tapeworm
Pork Tapeworm

More dangerous than beef tapeworm
because the larva can encyst in the
definitive host rather than
intermediate host (by accident)
◦ Causes the formation of bladder worms called
cysticerci in human host outside of intestine
◦ Causes a condition called cysticercosis:
formation of cysticerci in several organs (eyes and
brain)-> leads to blindness, neurological problems,
and death
◦ May also form hydatid cyst (more later)
Hydatid Cysts in Human Brain
Fish Tapeworm
Dog Tapeworm
Definitive host: Dog
Intermediate host: humans, sheep, cattle, deer
Humans get infected because dogs can carry
tapeworms on their tongues
 Causes the formation of a special kind of
cysticercus called a hydatid cyst: has a single large
chamber with daughter cysts inside each
containing thousands of scolices
 Each scolex will produce a worm when eaten by a
dog (dog would need to eat human to continue
cycle-> usually dead end for parasite)
 Hydatid cysts can grow slowly and reach the size
of a basketball if not detected



Hydatid cyst in human heart
Comparison of Digestive System
Class
Feeding
TURBELLARIANS FEED ON SMALL
INVERTEBRATES
Digestion
 Mouth is used for both ingestion
& excretion.
 Mouth leads to pharynx and is
followed by the gut
Cestodes
FEED ON HOST
(INTESTINE OF A
VERTEBRATE
ANIMAL)
 Possess no gut or simple gut
 No mouth or digestive tract
 Absorb food from environment
 Digestion is intracellular
Trematodes
FEED ON HOST
TISSUE THROUGH
PHARYNX.
 Contain mouth and simple gut
 Digestion is extracellular and
then intracellular