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From Cell to Human …. http://www.youtube.com/watch?v=Q6ucKWIIFmg&feature=related. Cell. Cells. Cells are the smallest living unit of life Cells have a nucleus, cytoplasm, and plasma membrane Cells make proteins Cells have DNA in their nucleus Cells divide to make new cells.

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cells
Cells
  • Cells are the smallest living unit of life
  • Cells have a nucleus, cytoplasm, and plasma membrane
  • Cells make proteins
  • Cells have DNA in their nucleus
  • Cells divide to make new cells
genes and proteins
Genes and Proteins
  • Proteins do the work of the cell: growth, maintenance, response to the environment, reproduction, etc.
  • Proteins are chains of amino acids.
genes and proteins1
Genes and Proteins
  • The sequence of amino acids in each protein is coded in the DNA as a specific sequence of A, C, G and T bases: a gene.
  • Each gene codes for a different protein.
genes and proteins2
Genes and Proteins
  • All cells within an organism have the same genes.
  • What makes cells different from each other is that different genes are turned on and turned off in different cells.
cell division
Cell Division
  • The DNA must be copied and then divided exactly so that each cell gets an identical copy.
cell division1
Cell Division
  • Two types of cell division
    • Mitosis
      • For growth and repair
    • Meiosis
      • For formation of gametes - sperm and egg
cell division2
Cell Division

All complex organisms originated from a single fertilized egg.

cell division3
Cell Division

Every cell in your body started here, through cell division the numbers are increased

cell division4
Cell Division

Cell then specialise and change into their various roles

mitosis1
Mitosis
  • Mitosis is the process by which new body cell are produced for:
    • Growth
    • Replacing damaged or old cells.

This is a complex process requiring different stages

slide15

Parent cell

Chromosomes are copied & double in number

Chromosomes now split

2 daughter cells identical to original

mitosis2
Mitosis
  • All daughter cells contain the same genetic information from the original parent cell from which it was copied.
  • Every different type cell in your body contains the same genes, but only some act to make the cells specialize – e.g. into nerve or muscle tissue.
mitosis bone cell slides
Mitosis – bone cell slides

2

1

Parent cell

Chromosomes copied

4

3

5

2 daughter cells

Copies separating

slide19

Animated Mitosis Cycle

  • Interphase
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase & Cytokinesis

http://www.cellsalive.com/mitosis.htm

interphase occurs before mitosis begins
Interphaseoccurs before mitosis begins
  • Chromosomes are copied(# doubles)
  • Centrioles replicate

Nucleus

CELL MEMBRANE

Cytoplasm

interphase
Interphase

Plant Cell

Animal Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

early prophase
Early Prophase
  • Chromosomes appear as threadlike coils (chromatin) during interphase
  • At the start of prophase, (early prophase), chromatin condenses and coils into chromosomes.

CELL MEMBRANE

Nucleus

Cytoplasm

prophase 1 st and longest step in mitosis
Prophase 1st and Longest step in Mitosis
  • Mitosis begins (cell begins to divide)
  • Centrioles(or poles) begin to move to opposite ends of the cell.
  • Asters are seen

Centrioles

Sister chromatids

Spindle fibers

prophase
Prophase
  • Chromosomes are condensed into sister Chromotidsheld together by a button-like body called a centromere
  • Nucleolidissappear
  • Spindle fibersform between the poles.

Centrioles

Sister chromatids

Spindle fibers

prophase1
Prophase

Plant Cell

Animal Cell

Spindle fibers

Centrioles

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

metaphase 2 nd step in mitosis
Metaphase 2nd step in Mitosis
  • Chromatids(or pairs of chromosomes) attach to the spindle fibers.
  • Chromosomes cluster at the middle of the cells, with their centromeres aligned at the exact center, called the metaphaseplate

Centrioles

Spindle fibers

metaphase
Metaphase

Plant Cell

Animal Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

anaphase 3 rd and shortest step in mitosis
Anaphase3rd and shortest step in Mitosis
  • Chromatids(or pairs of chromosomes) separate and begin to move to opposite ends of the cell.
  • Cells elongate. Chromosomes look V-shaped

Centrioles

Spindle fibers

anaphase
Anaphase

Plant Cell

Animal Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

telophase 4th step in mitosis
Telophase4th step in Mitosis
  • Two new nuclei form, nuclear envelope forms from rough ER
  • Chromosomes uncoil and appear as chromatin (threads rather than rods).
  • Spindle dissappears. Mitosis ends.

Nuclei

Nuclei

Chromatin

telophase
Telophase

Plant Cell

Animal Cell

Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

cytokinesis
Cytokinesis
  • Cytokinesis begins during late anaphase and continues through and beyond telephase
  • A contractile ring of microfilaments forms at the cleavagefurrow and squeezes cells apart
cytokinesis1
Cytokinesis
  • Cell membrane moves inward to create two daughter cells – each with its own nucleuswith identical chromosomes.
mitosis3
Mitosis
  • Cells divide by mitosis to make identical daughter cells
cell division5
Cell Division
  • Mitosis – Division of the nucleus
  • Cytokinesis – Division of the cytoplasm
mitosis animation
MitosisAnimation

http://www.youtube.com/watch?v=NR0mdDJMHIQ&feature=fvwrel

summary of mitosis
Summary of Mitosis
  • Prophase:
      • Chromosomes condense
      • Nuclear envelope disappears
      • Centriolesmove to opposite sides of the cell
      • Spindle forms and attaches to centromereson the chromosomes
summary of mitosis1
Summary of Mitosis
  • Metaphase
      • Chromosomes lined up on equator of spindle
      • Centriolesat opposite ends of cell
summary of mitosis2
Summary of Mitosis
  • Anaphase
      • Centromeres divide: each 2-chromatid chromosome becomes two 1-chromatid chromosomes
      • Chromosomes pulled to opposite poles by the spindle
summary of mitosis3
Summary of Mitosis
  • Telophase
      • Chromosomes de-condense into chromatin
      • Nuclear envelope reappears
      • Cytokinesis: the cytoplasm is divided into 2 cells
meiosis video
Meiosis Video
  • http://www.youtube.com/watch?v=mKWxeMMFTEU
meiosis
Meiosis
  • There is a special type of cell division to make a sperm or egg
  • To make gametes, cells must undergo meiosis
why do we need meiosis
Why do we need meiosis?
  • Meiosis is necessary to halve the number of chromosomes going into the sex cells
  • Why halve the chromosomes in gametes?
why do we need meiosis1
Why do we need meiosis?

At fertilization the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents

meiosis1
Meiosis
  • The form of cell divisionby which gametes, with half the number of chromosomes,are produced.
  • Diploid (2n)  haploid (n)
  • Meiosis is sexual reproduction.
  • Two divisions (meiosis I and meiosis II).
meiosis2
Meiosis
  • Sex cells divide to produce gametes(sperm or egg).
  • Gametes have half the number of chromosomes.
meiosis3
Meiosis
  • Meiosis only in gonads (testes or ovaries).

Male: spermatogenesis

Female: oogenesis

meiosis4
Meiosis
  • Meiosis is similar to mitosis with some chromosomal differences.
meiosis5
Meiosis

Parent cell – chromosome pair

Chromosomes copied

1st division - pairs split

2nd division – produces 4 gametes

meiosis6
Meiosis

Gamete cells have ½ the original number of chromosomes

spermatogenesis

n=23

human

sex cell

sperm

n=23

n=23

2n=46

haploid (n)

n=23

n=23

diploid (2n)

n=23

meiosis I

meiosis II

Spermatogenesis
meiosis mouse testes
Meiosis – mouse testes

Parent cell

1st division

2nd division

4 gametes

interphase i
Interphase I
  • Similar to mitosisinterphase.
  • Chromosomes replicate (S phase)
  • Each duplicated chromosome consist of two identical sister chromatids attached at their centromeres.
  • Centriole pairs also replicate.
interphase i1
Interphase I
  • Nucleus and nucleolus visible.

chromatin

nuclear membrane

cell membrane

nucleolus

meiosis i four phases
Meiosis I (four phases)
  • Cell division that reduces the chromosome number by one-half. - Four phases:

a. prophase I

b. metaphase I

c. anaphase I

d. telophase I

prophase i
Prophase I
  • Longest and most complex phase (90%).
  • Chromosomes condense.
  • Synapsis occurs: homologous chromosomes come together to form a tetrad.
  • Tetrad is two chromosomes or four chromatids (sister and nonsisterchromatids).
prophase i synapsis

Homologous chromosomes

sister chromatids

sister chromatids

Tetrad

Prophase I - Synapsis
homologous chromosomes
Homologous Chromosomes
  • Pair of chromosomes (maternal and paternal) that are similar in shape and size.
  • Homologous pairs carry genes controlling the same inherited traits.
  • Each locus(position of a gene) is in the same position on homologues.
homologous chromosomes1
Homologous Chromosomes
  • Humans have 23 pairs of homologous chromosomes.

a. 22 pairs of autosomes

b. 1 pair of sex chromosomes

homologous chromosomes2

eye color

locus

eye color

locus

hair color

locus

hair color

locus

Paternal

Maternal

Homologous Chromosomes
crossing over
Crossing Over
  • Crossing over (variation) may occur between nonsisterchromatids at the chiasmata.
  • Crossing over: segments of nonsisterchromatids break and reattach to the other chromatid.
  • Chiasmata (chiasma) are the sites of crossing over.
crossing over variation

Tetrad

nonsister chromatids

chiasmata: site of crossing over

Crossing Over - variation

variation

sex chromosomes
Sex Chromosomes

XX chromosome - female

XY chromosome - male

prophase i1

spindle fiber

centrioles

aster

fibers

Prophase I
metaphase i
Metaphase I
  • Shortest phase
  • Tetrads align on the metaphase plate.
metaphase i1
Metaphase I
  • INDEPENDENT ASSORTMENT OCCURS:

1. Orientation of homologous pair to poles is random.

2. Variation

3. Formula: 2n

Example: 2n = 4, then n = 2

thus 22 = 4 combinations

metaphase i2

OR

metaphase plate

metaphase plate

Metaphase I
question
Question:
  • In terms of Independent Assortment -how many different combinations of sperm could a humanmale produce?
answer
Answer
  • Formula: 2n
  • Human chromosomes:2n = 46

n = 23

  • 223 = ~8 million combinations
anaphase i
Anaphase I
  • Homologous chromosomes separate and move towards the poles.
  • Sister chromatidsremain attached at their centromeres.
telophase i
Telophase I
  • Each pole now has haploid set of chromosomes.
  • Cytokinesis occurs and two haploid daughter cells are formed.
meiosis ii
Meiosis II
  • No interphase II

(or very short - no more DNA replication)

  • Remember: Meiosis II is similar to mitosis
prophase ii
Prophase II
  • same as prophase in mitosis
metaphase ii

metaphase plate

metaphase plate

Metaphase II
  • same as metaphase in mitosis
anaphase ii
Anaphase II
  • same as anaphase in mitosis
  • sister chromatids separate
telophase ii
Telophase II
  • Same as telophase in mitosis.
  • Nuclei form.
  • Cytokinesis occurs.
  • Remember: four haploid daughter cells produced.

gametes = sperm or egg

meiosis7

n=2

sex cell

sperm

n=2

n=2

2n=4

haploid (n)

n=2

n=2

diploid (2n)

n=2

meiosis I

meiosis II

Meiosis
variation
Variation
  • Important to population as the raw material for natural selection.
  • Question:

What are the three sexual sources of genetic variation?

answer1
Answer:

1. crossing over (prophase I)

2. independent assortment (metaphase I)

3. random fertilization

Remember: variation is good!

question1
Question:
  • A cell containing 20 chromosomes(diploid)at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?
answer2
Answer:
  • 10 chromosomes (haploid)
karyotype
Karyotype
  • A method of organizing the chromosomes of a cell in relation to number, size, and type.
actual human karyotype picture
Actual Human Karyotype Picture

Male or female?

Male!

fertilization

sperm

n=23

n=23

egg

2n=46

zygote

Fertilization
  • The fusion of a sperm and egg to form a zygote.
  • A zygote is a fertilized egg
question2
Question:
  • A cell containing 40 chromatids at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?
answer3
Answer:
  • 10 chromosomes
meiosis error fertilization
Meiosis error - fertilization

Should the gamete with the chromosome pair be fertilized then the offspring will not be ‘normal’.

meiosis error fertilization1
Meiosis error - fertilization

In humans this often occurs with the 21st pair – producing a child with Downs Syndrome

21 trisomy downs syndrome
21 trisomy – Downs Syndrome

Can you see the extra 21st chromosome?

Is this person male or female?

from cell to human2

From Cell to Human ….

Information about Chromosomal Disorders

mistakes in meiosis
Mistakes in Meiosis
  • About 1 in 150 babies is born with a chromosomal abnormality
mistakes in meiosis1
Mistakes in Meiosis
  • When a gamete (egg or sperm cell) with the wrong number of chromosomes joins with a normal gamete (egg or sperm cell), the resulting embryo has a chromosomal abnormality.
mistakes in meiosis2
Mistakes in Meiosis
  • Chromosomal abnormalities usually result from an error that occurred when an egg or sperm cell was developing
  • An egg or sperm cell may divide incorrectly, resulting in an egg or sperm cell with too many or too few chromosomes.
mistakes in meiosis3
Mistakes in Meiosis
  • In most cases, an embryo with the wrong number of chromosomes does not survive. The pregnant woman has a miscarriage. This often happens very early in pregnancy, before a woman may realize she's pregnant. Up to 75 percent of first trimester miscarriages are caused by chromosomal abnormalities in the embryo
mistakes in meiosis4
Mistakes in Meiosis
  • A baby can be born with too many or too few chromosomes
  • These errors in the number or structure of chromosomes can cause a wide variety of birth defects ranging from mild to severe.
mistakes in meiosis5
Mistakes in Meiosis
  • A common type of chromosomal abnormality is called a trisomy. This means that an individual has three copies, instead of two, of a specific chromosome.
trisomy 21 down syndrome
Trisomy 21 – Down Syndrome
  • Individuals with Down syndrome have three copies of chromosome 21.
  • Children with Down syndrome have varying degrees of mental retardation, characteristic facial features and, often, heart defects and other problems.
  • The risk of Down syndrome and other trisomies increases with maternal age.
trisomy 21 down syndrome1
Trisomy 21 – Down Syndrome
  • Down syndrome is one of the most common chromosomal abnormalities,
  • The risk of having a live-born baby with Down syndrome is about:
  • 1 in 1,250 for a woman at age 25
  • 1 in 1,000 at age 30
  • 1 in 400 at age 35
  • 1 in 100 at age 40
trisomy 13 trisomy 18
Trisomy 13 & Trisomy 18
  • Extra copy of chromosome 13 or 18.
  • More severe than Down syndrome, less common.
  • About 1 in 10,000 babies is born with trisomy 13 (Patausyndrome),
  • About 1 in 6,000 with trisomy 18 (Edwards syndrome)
  • Severe mental retardation &many physical birth defects. Most die before their first birthday.
x and y chromosomal abnormalities
X and Y chromosomal abnormalities
  • About 1 in 500 babies has missing or extra sex chromosomes
  • Sex chromosome abnormalities may cause infertility, growth abnormalities, and in some cases, behavioral and learning problems. However, most affected individuals live fairly normal lives.
turner syndrome
Turner Syndrome
  • Affects about 1 in 2,500 girls
  • Missing all or part of one X chromosome.
  • Usually infertile
  • Does not undergo normal pubertal changes unless treated with sex hormones.
  • Affected girls are short, though treatment with growth hormones can help increase height.
  • Other health problems may include heart or kidney defects.
  • Normal intelligence
triple x
Triple X
  • About 1 in 1,000 females have an extra X chromosome
  • Affected girls tend to be tall.
  • No physical birth defects, undergo normal puberty, fertile, normal intelligence
klinefelter syndrome xxy
Klinefelter Syndrome XXY
  • Affects about 1 in 500 to 1,000 boys
  • Normal intelligence
  • As adults, they produce lower-than-normal amounts of the male hormone testosterone (and often are treated with this hormone)
  • Infertile
xyy syndrome
XYY Syndrome
  • Affects 1 in 1,000 males
  • Affected males are sometimes taller than average
  • Normal sexual development
  • Fertile
  • Normal intelligence
from egg to embryo
From Egg to Embryo
  • Pregnancy – events that occur from fertilization until the infant is born
  • Conceptus – the developing offspring
  • Gestation period – from the last menstrual period until birth (280 days)
from egg to embryo1
From Egg to Embryo
  • Preembryo– conceptus from fertilization until it is two weeks old
  • Embryo – conceptus during the third through the eighth week
  • Fetus – conceptus from the ninth week through birth
  • At birth it is called an Infant
accomplishing fertilization
Accomplishing Fertilization
  • The oocyte is viable for 12 to 24 hours
  • Sperm is viable 24 to 72 hours
  • For fertilization to occur, coitus must occur no more than:
    • Three days before ovulation
    • 24 hours after ovulation
accomplishing fertilization1
Accomplishing Fertilization
  • Fertilization – when a sperm fuses with an egg to form a zygote
sperm transport and capacitation
Sperm Transport and Capacitation
  • Fates of ejaculated sperm
    • Milllions leak out of the vagina immediately after deposition
    • Millions are destroyed by the acidic vaginal environment
    • Millions fail to make it through the cervix
sperm transport and capacitation1
Sperm Transport and Capacitation
  • Those sperm that do reach the cervix
    • Dispersed in the uterus cavity by uterine contractions
    • thousands are destroyed by phagocytic leukocytes
    • Only a few thousand (sometimes less than 200) reach the uterine tubes
sperm transport and capacitation2
Sperm Transport and Capacitation
  • Sperm must undergo capacitation before they can penetrate the oocyte
  • Gradually over 6 to 8 hours membrane proteins are removed and cholesterol is depleted
  • Enables membranes to become fragile so the hydrolytic enzymes in their acrosomes can be released
acrosomal reaction and sperm penetration
Acrosomal Reaction and Sperm Penetration
  • An ovulated oocyte is encapsulated by:
    • The corona radiata and zonapellucida
    • Thick layer of extracellular matrix
acrosomal reaction and sperm penetration1
Acrosomal Reaction and Sperm Penetration
  • Sperm binds to the zonapellucida and undergoes the acrosomal reaction
    • Enzymes are released near the oocyte
    • Hundreds of acrosomes release their enzymes to digest the zonapellucida
    • The first sperm there will not be able to penetrate
acrosomal reaction and sperm penetration2
Acrosomal Reaction and Sperm Penetration
  • Once a sperm makes contact with the oocyte’smembrane its nucleus is pulled into the oocyte cytoplasm
blocks to polyspermy
Blocks to Polyspermy
  • Only one sperm is allowed to penetrate the oocyte
  • Two mechanisms ensure monospermy
    • Fast block to polyspermy
    • Slow block to polyspermy
  • If polyspermy does occur, embryos are nonviable and die
blocks to polyspermy1
Blocks to Polyspermy
  • Fast block to polyspermy – membrane depolarization prevents sperm from fusing with the oocyte membrane
  • Slow block to polyspermy – zonal inhibiting proteins (ZIPs):
    • Destroy sperm receptors
    • Cause sperm already bound to receptors to detach
completion of meiosis ii and fertilization
Completion of Meiosis II and Fertilization
  • Upon entry of sperm, the secondary oocyte:
    • Completes meiosis II
    • Casts out the second polar body
completion of meiosis ii and fertilization1
Completion of Meiosis II and Fertilization
  • The ovum nucleus swells, and the two nuclei approach each other
  • When fully swollen, the two nuclei are called pronuclei
  • Fertilization – when the pronuclei come together
preembryonic development
Preembryonic Development
  • The first cleavage produces two daughter cells called blastomeres
  • Morula – the 16 or more cell stage (72 hours old)
  • By the fourth or fifth day the preembryo consists of 100 or so cells (blastocyst)
preembryonic development1
Preembryonic Development
  • Blastocyst – a fluid-filled hollow sphere composed of:
    • A single layer of trophoblasts(large flat cells)
    • An inner cell mass (smaller round cells)
preembryonic development2
Preembryonic Development
  • Trophoblaststake part in placenta formation
  • The inner cell mass becomes the embryonic disc
cleavage from zygote to blastocyst
Cleavage: From Zygote to Blastocyst

Degenerating zona pellucida

Inner cell mass

Blastocyst cavity

Blastocyst cavity

Trophoblast

(a) Zygote(fertilized egg)

(c) Morula3 days

(b) 4-cell stage2 days

(e) Implanting blastocyst6 days

(d) Early blastocyst4 days

Fertilization(sperm meets egg)

(a)

(b)

(c)

Ovary

Uterine tube

(d)

Oocyte(egg)

(e)

Ovulation

Uterus

Endometrium

Cavity of uterus

Figure 28.4

implantation
Implantation
  • Begins six to seven days after ovulation when the trophoblasts adhere to a properly prepared endometrium
implantation1
Implantation
  • The trophoblasts then proliferate and form two distinct layers
    • Cytotrophoblast – cells of the inner layer that retain their cell boundaries
    • Syncytiotrophoblast – cells in the outer layer that lose their plasma membranes and invade the endometrium
implantation2
Implantation
  • The implanted blastocyst is covered over by endometrial cells
  • Implantation is completed by the fourteenth day after ovulation
placentation
Placentation
  • Formation of the placenta from:
    • Embryonic trophoblastic tissues
    • Maternal endometrial tissues
placentation1
Placentation

Figure 28.7a-c

placentation2
Placentation

Figure 28.7d

placentation3
Placentation

Figure 28.7f

germ layers
Germ Layers
  • The blastocyst develops into a gastrula with three primary germ layers: ectoderm, endoderm, and mesoderm
  • Before becoming three-layered, the inner cell mass subdivides into the upper epiblast and lower hypoblast
  • These layers form two of the four embryonic membranes
embryonic membranes
Embryonic Membranes
  • Amnion – epiblast cells form a transparent membrane filled with amniotic fluid
    • Provides a buoyant environment that protects the embryo
    • Helps maintain a constant homeostatic temperature
    • Amniotic fluid comes from maternal blood, and later, fetal urine
embryonic membranes1
Embryonic Membranes
  • Yolk sac – hypoblast cells that form a sac on the ventral surface of the embryo
    • Forms part of the digestive tube
    • Produces earliest blood cells and vessels
    • Is the source of primordial germ cells
embryonic membranes2
Embryonic Membranes
  • Allantois – a small outpocketing at the caudal end of the yolk sac
    • Structural base for the umbilical cord
    • Becomes part of the urinary bladder
  • Chorion – helps form the placenta
    • Encloses the embryonic body and all other membranes
gastrulation
Gastrulation
  • During the 3rd week, the two-layered embryonic disc becomes a three-layered embryo
  • The primary germ layers are ectoderm, mesoderm, and endoderm
  • Primitive streak – raised dorsal groove that establishes the longitudinal axis of the embryo
primary germ layers
Primary Germ Layers
  • Serve as primitive tissues from which all body organs will derive
quiz next time2

QuizNext time

Study Guide

remember
Remember
  • During the 3rd week, the two-layered embryonic disc becomes a three-layered embryo
  • The primary germ layers are ectoderm, mesoderm, and endoderm
  • Primitive streak – raised dorsal groove that establishes the longitudinal axis of the embryo
primary germ layers1
Primary Germ Layers
  • Serve as primitive tissues from which all body organs will derive
primary germ layers2
Primary Germ Layers
  • Ectoderm – forms structures of the nervous system and skin epidermis
  • Endoderm – forms epithelial linings of the digestive, respiratory, and urogenital systems
  • Mesoderm – forms all other tissues
  • Endoderm and ectoderm are securely joined and are considered epithelia
primary germ layers3
Primary Germ Layers

Figure 28.8a-e

primary germ layers4
Primary Germ Layers

Figure 28.8e-h

organogenesis
Organogenesis
  • Gastrulation sets the stage for organogenesis, the formation of body organs
  • By the 8th week all organ systems are recognizable
specialization of ectoderm
Specialization of Ectoderm
  • Neurulation – the first event of organogenesis gives rise to the brain and spinal cord
  • Ectoderm over the notochord thickens, forming the neural plate
  • The neural plate folds inward as a neural groove with prominent neural folds
specialization of ectoderm1
Specialization of Ectoderm
  • By the 22nd day, neural folds fuse into a neural tube, which pinches off into the body
  • The anterior end becomes the brain; the rest becomes the spinal cord
  • By the end of the second month brain waves can be recorded
specialization of endoderm
Specialization of Endoderm
  • Embryonic folding begins with lateral folds
  • Next, head and tail folds appear
  • An endoderm tube forms the epithelial lining of the GI tract
specialization of endoderm1
Specialization of Endoderm
  • Organs of the GI tract become apparent, and oral and anal openings perforate
  • Endoderm forms epithelium linings of the hollow organs of the digestive and respiratory tracts
specialization of the mesoderm
Specialization of the Mesoderm
  • First evidence is the appearance of the notochord
  • Three mesoderm aggregates appear lateral to the notochord
    • Somites, intermediate mesoderm, and double sheets of lateral mesoderm
specialization of the mesoderm1
Specialization of the Mesoderm
  • The 40 pairs of somites have three functional parts:
    • Sclerotome – produce the vertebrae and ribs
    • Dermatome – help form the dermis of the skin on the dorsal part of the body
    • Myotome – form the skeletal muscles of the neck, trunk, and limbs
specialization of the mesoderm2
Specialization of the Mesoderm
  • Intermediate mesoderm forms the gonads and the kidneys
  • Lateral mesoderm consists of somatic and splanchnic mesoderm
specialization of the mesoderm3
Specialization of the Mesoderm
  • Somatic mesoderm forms the:
    • Dermis of the skin in the ventral region
    • Parietal serosa of the ventral body cavity
    • Bones, ligaments, and dermis of the limbs
  • Splanchnic mesoderm forms:
    • The heart and blood vessels
    • Most connective tissues of the body
development of fetal circulation
Development of Fetal Circulation
  • By the end of the 3rd week:
    • The embryo has a system of paired vessels
    • The vessels forming the heart have fused
development of fetal circulation1
Development of Fetal Circulation
  • Unique vascular modifications seen in prenatal development include umbilical arteries and veins, and three vascular shunts (occluded at birth)
    • Ductusvenosus – venous shunt that bypasses the liver
    • Foramen ovale – opening in the interatrial septa to bypass pulmonary circulation
    • Ductusarteriosus – transfers blood from the right ventricle to the aorta
slide178

The umbilical vein delivers nutrient and oxygen rich blood to the embryo

  • Umbilical arteries return oxygen poor and waste laden blood to the placenta
from cell to human5

From Cell to Human ….

Part 5 (on part 4 note sheet)

8 weeks
8 weeks
  • End of embryonic period – now a fetus
  • Head as large as body – brain waves
  • Liver large and begins to form blood cells
  • Limbs present, digits were webbed, starting now to be free
  • Ossification of bones begin
8 weeks1
8 weeks
  • Cardiovascular system fully functional (Heart has been pumping since week 4)
  • All body systems present
  • Weight 2 grams
9 12 weeks
9-12 weeks
  • Body lengthening
  • Brain continues to enlarge
  • Retina of eye present
  • Facial features present
  • Blood cell formation begins in bone marrow
  • Sex able to be detected from genitals
13 16 weeks
13-16 weeks
  • Blinking of eyes and sucking motions of lips occur
  • Kidneys are formed
  • Most bones distinct, joints are apparent
17 20 weeks
17-20 weeks
  • Vernixcaseosa (from oil glands) covers body
  • Lanugo (fine silky hair) covers skin
  • Fetal position assumed
  • Mother feels muscular activity of fetus
21 30 weeks
21-30 weeks
  • Weight increases
  • May survive if born at 27-28 weeks, but temperature regulation and lungs not all way formed
  • Eyes are open
  • Skin is wrinkled and red
  • Fingernails and toenails present
30 40 weeks
30-40 weeks
  • Skin whitish pink
  • Hypodermis formed
  • Weight 6-10 pounds
is it a boy or girl
Is it a boy or girl?
  • Remember…
  • Females have two X chromosomes; males have one X and one Y
  • Hence, all eggs have an X chromosome; half the sperm have an X, and the other half a Y
  • A single gene on the Y chromosome, the SRY gene, initiates testes development and determines maleness
developmental aspects
Developmental Aspects
  • 5th week – gonadal ridges form and paramesonephric (Müllerian) ducts form in females, mesonephric (Wolffian) ducts develop in males
  • Shortly later, primordial germ cells develop and seed the developing gonads destined to become spermatogonia or oogonia
developmental aspects1
Developmental Aspects
  • Male structures begin development in the 7th week; female in the 8th week
  • External genitalia, like gonads, arise from the same structures in both sexes
development of external genitalia
Development of External Genitalia

male

female

In the absence of testosterone

Genital tubercle gives rise to the clitoris

The urethral groove remains open

  • In the presence of testosterone
  • Genital tubercle enlarges forming the penis
  • Urethral groove elongates and closes completely
development of external genitalia1
Development of External Genitalia

male

female

The urethral folds become labia minora

The labioscrotal swellings become labia majora

  • Urethral folds give rise to the penile urethra
  • Labioscrotal swellings develop into the scrotum
development aspects descent of the gonads
Development Aspects: Descent of the Gonads
  • About 2 months before birth and stimulated by testosterone, the testes leave the pelvic cavity and enter the scrotum
  • Ovaries also descend, but are stopped by the broad ligament at the pelvic brim
homeostatic imbalance
Homeostatic imbalance
  • Many substance cross placental barriers and enter fetal blood –dangerous!
  • Alcohol, nicotine, many drugs, infections (like measles) all cross barriers
homeostatic imbalance1
Homeostatic imbalance
  • When mother drinks, her fetus becomes inebriated
    • may result in fetal alcohol syndrome typified by a small head, mental retardation, and abnormal growth
homeostatic imbalance2
Homeostatic imbalance
  • Nicotine hinders oxygen delivery to the fetus
    • Impairing normal growth and development
homeostatic imbalance3
Homeostatic imbalance
  • The sedative thalidomide sometimes results in deformed infants with short flipperlike legs or arms
quiz next time test on thursday

QuizNext timeTest On Thursday

Complete Study Guide for next time

effects of pregnancy anatomical changes
Effects of Pregnancy: Anatomical Changes
  • Chadwick’s sign – the vagina develops a purplish hue
  • Breasts enlarge and their areolae darken
  • The uterus expands, occupying most of the abdominal cavity
  • Lordosis is common due to the change of the body’s center of gravity
  • Relaxin causes pelvic ligaments and the pubic symphysis to relax
  • Typical weight gain is about 29 pounds
effects of pregnancy metabolic changes
Effects of Pregnancy: Metabolic Changes
  • The placenta secretes human placental lactogen (hPL), also called human chorionic somatomammotropin (hCS), which stimulates the maturation of the breasts
  • hPL promotes growth of the fetus and exerts a maternal glucose-sparing effect
  • Human chorionic thyrotropin (hCT) increases maternal metabolism
  • Parathyroid hormone levels are high, ensuring a positive calcium balance
effects of pregnancy physiological changes
Effects of Pregnancy: Physiological Changes
  • GI tract – morning sickness occurs due to elevated levels of estrogen and progesterone
  • Urinary system – urine production increases to handle the additional fetal wastes
  • Respiratory system – edematous and nasal congestion may occur
    • Dyspnea (difficult breathing) may develop late in pregnancy
effects of pregnancy physiological changes1
Effects of Pregnancy: Physiological Changes
  • Cardiovascular system – blood volume increases 25-40%
    • Venous pressure from lower limbs is impaired, resulting in varicose veins
parturition initiation of labor
Parturition: Initiation of Labor
  • Estrogen reaches a peak during the last weeks of pregnancy causing myometrial weakness and irritability
  • Weak Braxton Hicks contractions may take place
  • As birth nears, oxytocin and prostaglandins cause uterine contractions
  • Emotional and physical stress:
    • Activates the hypothalamus
    • Sets up a positive feedback mechanism, releasing more oxytocin
stages of labor dilation stage
Stages of Labor: Dilation Stage
  • From the onset of labor until the cervix is fully dilated (10 cm)
  • Initial contractions are 15–30 minutes apart and 10–30 seconds in duration
  • The cervix effaces and dilates
  • The amnion ruptures, releasing amniotic fluid (breaking of the water)
  • Engagement occurs as the infant’s head enters the true pelvis
stages of labor expulsion stage
Stages of Labor: Expulsion Stage
  • From full dilation to delivery of the infant
  • Strong contractions occur every 2–3 minutes and last about 1 minute
  • The urge to push increases in labor without local anesthesia
  • Crowning occurs when the largest dimension of the head is distending the vulva
stages of labor expulsion stage2
Stages of Labor: Expulsion Stage
  • The delivery of the placenta is accomplished within 30 minutes of birth
  • Afterbirth – the placenta and its attached fetal membranes
  • All placenta fragments must be removed to prevent postpartum bleeding
extrauterine life
Extrauterine Life
  • At 1-5 minutes after birth, the infant’s physical status is assessed based on five signs: heart rate, respiration, color, muscle tone, and reflexes
  • Each observation is given a score of 0 to 2
  • Apgar score – the total score of the above assessments
    • 8-10 indicates a healthy baby
    • Lower scores reveal problems
first breath
First Breath
  • Once carbon dioxide is no longer removed by the placenta, central acidosis occurs
  • This excites the respiratory centers to trigger the first inspiration
  • This requires tremendous effort – airways are tiny and the lungs are collapsed
  • Once the lungs inflate, surfactant in alveolar fluid helps reduce surface tension
occlusion of fetal blood vessels
Occlusion of Fetal Blood Vessels
  • Umbilical arteries and vein constrict and become fibrosed
  • Fates of fetal vessels
    • Proximal umbilical arteries become superior vesical arteries and distal parts become the medial umbilical ligaments
    • The umbilical vein becomes the ligamentum teres
    • The ductus venosus becomes the ligamentum venosum
    • The foramen ovale becomes the fossa ovalis
    • The ductus arteriosus becomes the ligamentum arteriosum
transitional period
Transitional Period
  • Unstable period lasting 6-8 hours after birth
  • The first 30 minutes the baby is alert and active
    • Heart rate increases (120-160 beats/min.)
    • Respiration is rapid and irregular
    • Temperature falls
transitional period1
Transitional Period
  • Activity then diminishes and the infant sleeps about three hours
  • A second active stage follows in which the baby regurgitates mucus and debris
  • After this, the infant sleeps, with waking periods occurring every 3-4 hours
lactation
Lactation
  • The production of milk by the mammary glands
  • Estrogens, progesterone, and lactogen stimulate the hypothalamus to release prolactin-releasing hormone (PRH)
  • The anterior pituitary responds by releasing prolactin
lactation1
Lactation
  • Colostrum
    • Solution rich in vitamin A, protein, minerals, and IgA antibodies
    • Is released the first 2–3 days
    • Is followed by true milk production
lactation and milk let down reflex
Lactation and Milk Let-down Reflex
  • After birth, milk production is stimulated by the sucking infant

Figure 28.18

breast milk
Breast Milk
  • Advantages of breast milk for the infant
    • Fats and iron are better absorbed
    • Its amino acids are metabolized more efficiently than those of cow’s milk
    • Beneficial chemicals are present – IgA, other immunoglobulins, complement, lysozyme, interferon, and lactoperoxidase
    • Interleukins and prostaglandins are present, which prevent overzealous inflammatory responses
    • Its natural laxatives help cleanse the bowels of meconium
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