Chapter 47
This presentation is the property of its rightful owner.
Sponsored Links
1 / 28

Chapter 47 PowerPoint PPT Presentation


  • 72 Views
  • Uploaded on
  • Presentation posted in: General

Chapter 47. Animal Development. Development is determined by the zygote’s genome and differences between embryonic cells Cell differentiation is the specialization of cells in structure and function

Download Presentation

Chapter 47

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Chapter 47

Chapter 47

Animal Development


Chapter 47

  • Development is determined by the zygote’s genome and differences between embryonic cells

  • Cell differentiation is the specialization of cells in structure and function

  • Cytoplasmic determinants, the uneven distribution of maternal substances within the unfertilized egg, cause early embryonic cells to differentiate in some species.

  • Morphogenesis is the process by which an animal takes shape


Chapter 47

Concept 47.1: After fertilization, embryonic development proceeds through cleavage, gastrulation, and organogenesis

  • Important events regulating development occur during fertilization and the three stages that build the animal’s body

    • Cleavage: cell division creates a hollow ball of cells called the blastula.

    • Gastrulation: produces a 3-layered embryo called the gastrula.

    • Organogenesis: generates rudimentary organs from which adult structures grow.


Fertilization

Fertilization

  • Fertilization brings the haploid (1 set of chromosome) nuclei of sperm and egg together, forming a diploid (2 sets of chromosomes) zygote

  • The sperm’s contact with the egg’s surface initiates metabolic reactions in the egg that trigger the onset of embryonic development (“activates the egg”)


Le 47 3

LE 47-3

Contact and fusion

of sperm and egg

membranes

Entry of sperm

nucleus

Acrosomal

reaction

Sperm plasma

membrane

Sperm

nucleus

Cortical reaction

Contact

Acrosomal

process

Basal body

(centriole)

Sperm

head

Fertilization

envelope

Fused plasma

membranes

Cortical

granule

Actin

Perivitelline

space

Hydrolytic enzymes

Acrosome

Jelly coat

Cortical granule

membrane

Vitelline layer

Sperm-binding

receptors

Egg plasma

membrane

EGG CYTOPLASM


The acrosomal reaction

The Acrosomal Reaction

  • The acrosomal reaction is triggered when the sperm meets the egg.

  • This process begins when a specialized vesicle at the tip of the sperm called the acrosome, discharges hydrolytic enzymes.

    • This reaction releases hydrolytic enzymes that digest material surrounding the egg

    • This allows the acrosomal process (elongated sperm structure) to penetrate the jelly coat.


Chapter 47

  • Molecules of a protein on the tip of the acrosomal process adhere to molecules of a specific receptor proteins on the egg’s surface.

  • This gamete contact and/or fusion depolarizes the egg cell membrane and sets up a fast block to polyspermy (multiple sperm).

    • Depolarization occurs when the ion channels open on the egg’s plasma membrane allowing sodium ions to flow into the egg cell and change the membrane potential.

    • Depolarization occurs within 1-3 seconds after a sperm binds to an egg.


Chapter 47

  • Fusion of egg and sperm also initiates the cortical reaction

  • This reaction induces a rise in Ca2+from the egg’s ER into the egg’s cytosol. This causes cortical granules in the egg to fuse with the plasma membrane and discharge their contents. This leads to swelling of the perivitelline space, hardening of the vitelline layer, and clippling of sperm binding receptors.

  • These changes cause formation of a fertilization envelope that functions as a longer-term slow block to polyspermy.

    • Does occur in vertebrates (fishes and animals)


Activation of the egg

Activation of the Egg

  • The sharp rise in Ca2+ in the egg’s cytosol increases the rates of cellular respiration and protein synthesis by the egg cell

  • With these rapid changes in metabolism, the egg is said to be activated

  • Sperm cells do not contribute any materials required for activation. The unfertilized eggs of many species can be artificially activated by the injection of Ca2+ or by a variety of mildly injurious treatments, such as temperature shock.


Le 47 5

LE 47-5

1

Binding of sperm to egg

Acrosomal reaction: plasma membrane

depolarization (fast block to polyspermy)

2

3

4

6

Seconds

8

10

Increased intracellular calcium level

20

Cortical reaction begins (slow block to polyspermy)

30

40

50

Formation of fertilization envelope complete

1

2

Increased intracellular pH

3

4

Increased protein synthesis

5

Minutes

10

20

Fusion of egg and sperm nuclei complete

30

Onset of DNA synthesis

40

60

First cell division

90


Fertilization in mammals

Fertilization in Mammals

  • Fertilization in other species share the same timing as the sea urchin in the previous slide. However, timing differs with species.

    • Sea urchins meiosis is already completed when the egg is released from the female.

    • In humans, the unfertilized egg stays at metaphase of meiosis II. Meiosis is NOT completed until they are fertilized in the female reproductive tract.

  • Fertilization is generally internal.


Fertilization in mammals continued

Fertilization in Mammals continued

  • Secretions in the mammalian female trace alter certain molecules on the surface of sperm cells and also increase sperm motility.

  • The mammalian egg is cloaked by follicle cells released along with the egg during ovulation. The sperm must migrated through this layer of follicle cells before it reaches the zona pellucida.

  • In mammalian fertilization, the cortical reaction modifies the zona pellucida as a slow block to polyspermy


Le 47 6

3. Breakdown of the zona pellucida by these enzymes allows the sperm to reach the plasma membrane of the egg. Membrane proteins of the sperm bind to the receptors on the egg membrane, and the two membranes fuse

LE 47-6

4. The nucleus and other components of the sperm cell enter the egg.

2. This binding induces the acrosomal reaction, in which the sperm released hydrolytic enzymes into the zona pellucida.

1. Sperm migrated through the coat of follicle cells and binds to receptor molecules in the zona pellucida of the egg.

Follicle

cell

Sperm

basal

body

Cortical

ganules

Zona

pellucida

Sperm

nucleus

Egg plasma

membrane

5. Enzymes released during the cortical reaction harden the zona pellucida, which now functions as a block to polyspermy.

Acrosomal

vesicle

EGG CYTOPLASM


Fertilization in mammals continued1

Fertilization in Mammals continued

  • After the egg and sperm membrane fuse, the whole sperm, tail and all is taken into the egg.

  • The egg lacks a centrosome. The basal body of the sperm’s flagella now acts as the centrosome and wraps itself around the centriole.

  • This will allows mitotic spindles to form for the first cell division.

  • Fertilization is much slower in mammals. The first cell division occurs 12-36 hours after sperm binding in mammals.


Cleavage cell division creates a hollow ball of cells called the blastula

Cleavage cell division creates a hollow ball of cells called the blastula.

  • Fertilization is followed by cleavage, a period of rapid cell division without growth

  • Cells undergo S and M phases of the cell cycle but skip Gap 1 and Gap 2. Little or now protein synthesis occurs.

    • The embryo does not enlarge during this period of development.

  • Cleavage partitions the cytoplasm of one large cell into many smaller cells called blastomeres. Each with its own nucleus.


Le 47 7

LE 47-7

Fertilized egg

Four-cell stage

Morula

Blastula

  • First 5-7 divisions from a cluster of cells known as the morula

  • A fluid-filled cavity called the blastocoel begins to form within the morula and is fully formed in the blastula, a hollow ball of cells.

  • During cleavage, different regions of the cytoplasm end up in separate blastomeres. These regions may contain different cytoplasmic determinants, in many species this partitioning sets the stage for subsequent developmental events.


Gastrulation

Gastrulation

  • Gastrulation rearranges the cells of a blastula into a three-layered embryo, called a gastrula, which has a primitive gut.

  • Varies from one animal to another, the process is driven by change in cell motility, changes in cell shape, and changes in cellular adhesion to other cells and to molecules of the extracellular matrix.

  • This results in the three cell layers.


Chapter 47

  • The three layers produced by gastrulation are called embryonic germ layers

    • The ectoderm forms the outer layer

    • The endoderm lines the digestive tract

    • The mesoderm partly fills the space between the endoderm and ectoderm

  • Eventually, these three cell layers develop into all the tissues and organs of the adult animal.

Video: Sea Urchin Embryonic Development


Organogenesis

Organogenesis

  • During organogenesis, various regions of the germ layers develop into rudimentary organs

  • Early in vertebrate organogenesis, the notochord forms from mesoderm, and the neural plate forms from ectoderm


Chapter 47

  • Mesoderm lateral to the notochord forms blocks called somites

  • Lateral to the somites, the mesoderm splits to form the coelom

  • The neural plate soon curves inward, forming the neural tube

  • Many structures are derived from the three embryonic germ layers during organogenesis


Developmental adaptations of amniotes

Developmental Adaptations of Amniotes

  • Because all vertebrate embryos required an aqueous environment for development, embryos of birds, other reptiles, and mammals develop in a fluid-filled sac in a shell (birds & reptiles) or the uterus (marsupials & eutherian)

  • Organisms with these adaptations are called amniotes

  • In these organisms, the three germ layers also give rise to the four membranes that surround the embryo


Le 47 17

LE 47-17

Amnion

Allantois

Embryo

Amniotic

cavity

with

amniotic

fluid

Albumen

Shell

Yolk

(nutrients)

Yolk sac

Chorion


Mammalian development

Mammalian Development

  • Fertilization takes place in the oviduct, and the progresses as the embryo completes its journey down the oviduct to the uterus.

  • The eggs of placental mammals

    • Are small and store few nutrients

    • Exhibit holoblastic cleavage (complete cell division of egg, having little or moderate amount of yolk)

  • Gastrulation and organogenesis resemble the processes in birds and other reptiles

  • Early cleavage is relatively slow in humans and other mammals


Chapter 47

  • At completion of cleavage, the blastocyst forms

  • The trophoblast, the outer epithelium of the blastocyst, initiates implantation in the uterus, and the blastocyst forms a flat disk of cells

  • As implantation is completed, gastrulation begins

  • The extraembryonic membranes begin to form

  • By the end of gastrulation, the embryonic germ layers have formed


Le 47 18a

LE 47-18a

Endometrium

(uterine lining)

Inner cell mass

Trophoblast

Blastocoel

Blastocyst

reaches uterus.

Expanding

region of

trophoblast

Maternal

blood

vessel

Epiblast

Hypoblast

Trophoblast

Blastocyst

implants.


Le 47 18b

LE 47-18b

Expanding

region of

trophoblast

Amniotic

cavity

Amnion

Epiblast

Hypoblast

Chorion (from

trophoblast

Yolk sac (from

hypoblast)

Extraembryonic

membranes start

to form and

gastrulation

begins.

Extraembryonic mesoderm cells

(from epiblast)

Allantois

Amnion

Chorion

Ectoderm

Mesoderm

Endoderm

Yolk sac

Extraembryonic

mesoderm

Gastrulation has produced a

three-layered embryo with four

extraembryonic membranes.


Chapter 47

  • The extraembryonic membranes in mammals are homologous to those of birds and other reptiles and develop in a similar way


  • Login