nvc bio105 lect22 development - napa valley college · fetal development fetal development 9th –...

2/6/13

1

Human Development

Biol 105 Lecture 22 Chapter 18

Copyright © 2009 Pearson Education, Inc.

Outline - Development

I.  Fertilization


Terminology

§  When a sperm and an egg fuse = fertilization

§  The product of fertilization is a zygote. The zygote is a diploid cell.

§  This zygote begins to divide into multiple cells.

§  After the zygote divides it is an embryo.


Sperm

§  Sperm have a cap called the acrosome which contains enzymes. The environment of the female body activates the acrosome

§  Several sperm may go through the corona radiata, which is the outer layer surrounding the secondary oocyte

16-2


Fertilization

§  Sperm need to penetrate two layers surrounding the secondary oocyte

1.  The corona radiata, which is the outer layer 2.  The zona pellucida which surrounds the egg

16-2 Copyright © 2009 Pearson Education, Inc.

Fertilization

§  The enzymes from the acrosome digest the zona pellucida which surrounds the egg, the sperm needs to penetrate this layer in order to enter the egg.

§  One sperm enters the egg—immediately the zona pellucida and the egg plasma membrane changes.

16-2

2/6/13

2

Copyright © 2009 Pearson Education, Inc. Figure 18.4a

Fertilization


Fertilization

§  The secondary oocyte now completes its second meiotic division and is considered an ovum


Zygote

Figure 18.2a Copyright © 2009 Pearson Education, Inc.

Morula

§  The zygote divides and by day 4 it is now a solid ball of 12 or more cells called a morula


The Prenatal Period

Figure 18.9

Morula: Solid ball of cells formed as

the zygote undergoes cleavage

Early blastocyst: Hollow ball of cells

with a fluid-filled cavity

Late blastocyst: Pre-embryo, with the embryonic disk, two layers of cells that

become the embryo proper

Gastrula: Embryo with three primary

germ layers (ectoderm, mesoderm, and

endoderm)

Inner cell mass

Day 4

Day 6

Day 10

Day 16

Trophoblast Blastocyst cavity

Embryonic disk Amniotic cavity

Mesoderm

Yolk sac

Endoderm Ectoderm


The Prenatal Period

Figure 18.3

Step 1: Ovulation A secondary oocyte is

released from the ovary and swept into the

oviduct.

Step 2: Fertilization A single sperm penetrates the secondary oocyte. Eventually, the sperm and egg nuclei will fuse, resulting in a fertilized

egg, or zygote.

Step 3: Cleavage The zygote soon undergoes rapid mitotic cell divisions as it moves

along the oviduct toward the uterus, becoming a pre-embryo

that consists of two cells, then four cells, then eight cells, and so on.

Step 4: Morula By day 4, successive divisions produce a

morula, a solid ball of cells that enters the uterus.

Step 5: Blastocyst By day 6, the pre-embryo

becomes a blastocyst, a hollow ball of cells with a fluid-filled

cavity. The blastocyst has freed itself from the zona pellucida

and can increase in size.

Step 6: Implantation The blastocyst attaches to the

uterine lining (endometrium) and begins to digest its way inward. The cells of the inner cell mass

begin to form primary germ layers.

Oviduct

Fimbriae Ovary

Secondary oocyte

Zona pellucida Secondary

oocyte nucleus

2-cell stage 4-cell stage 8-cell stage

Morula

Blastocyst

Blastocyst

Inner cell mass

Trophoblast

Endometrium Inner cell mass

Uterus

2/6/13

3


Embryonic development

§  Embryonic development is divided into three phases:

1.  Cleavage – division that results in a hollow ball of cells = blastocyst.

2.  Gastrulation – the cells rearrange into three layers.

3.  Organogenesis –organs begin to form.



Stem Cells

§  Early in embryonic development the cells are very adaptable – they can become many different types of cells = stem cells.

§  But as the embryo develops and the cells become committed to a certain type, they loose the ability to be adaptable – they become differentiated.

§  Some cells in adults still retain this adaptability


Stem Cells

§  For the first few days after fertilization the cells in the embryo can form a whole new embryo – this is how identical twins happen. These cells are called totipotent cells

§  It is these cells that are embryonic stem cells. §  These embryonic stem cells can be taken

from the embryo and cultured in a lab. §  They have shown more promise than adult

stem cells.


Stem Cell Debate

§  Where do researchers get embryonic stem cells?

§  One source is fertility clinics. Remember the movie and the ethics concerning creating embryos to be implanted in a woman.

§  Usually more embryos are created than are implanted in the woman, the rest are frozen in case they are needed later.


It is the blastocyst that implants in the uterus, usually on day 6.

2/6/13

4

The blastocyst is implanted in the uterus.

The blastocyst is implanted in the uterus.

Pregnancy begins after implantation.

The blastocyst has outer cells called trophoblasts that becomes the embryonic part of the placenta.


When the cells rearrange into three layers

1 2 3

45% 45%

9%

1.  Cleavage

2.  Organogenesis

3.  Gastrulation

There are three layers: ectoderm, mesoderm, and endoderm.


Three Layers of the Embryo

§  Part of the ectoderm becomes the nervous system and skin

§  The mesoderm becomes support tissues including bone, muscle, cardiovascular system, urinary system

§  The endoderm becomes many of the digestive and respiratory organs

2/6/13

5


The notocord is for support and the neural tube becomes the nervous system.


The Placenta

§  The placenta contains both blood vessels from both the mother and the embryo.

§  This allow carbon dioxide, oxygen, nutrients and wastes to pass between the mother and embryo.

§  The umbilical cord connects the embryo to the placenta.


Fetal Circulation

§  The placenta produces human chorionic gonadotropin (HCG) to tell the body to stop ovulating and stop menstruation

§  Blood from the mother and the fetus never meet, the exchange of materials between the maternal and fetal blood takes place across the walls of the chorionic villi.

§  Harmful chemicals can pass from mother to fetus

16-13

2/6/13

6


Extraembryonic Membranes

1. Chorion - develops into the fetal half of the placenta.

2. Yolk sac - contains very little yolk and is the first site of RBC formation.

3. Allantosis - the allantosis blood vessels become the umbilical blood vessels.

4. Amnion - contains amniotic fluid to cushion and protect the embryo.



Develops into the fetal half of the placenta

1.  Allantosis

2.  Yolk sac

3.  Chorion

4.  Amnion


Embryonic Development

Embryonic development—begins with the 2nd week and lasts until the end of the 2nd month of development. § Nervous system—first to become

visually evident. § Heart begins development the third

week and begins beating the 4th week. § All organ system have been

established by the end of embryonic development.

16-9

Table 16.1a


Fifth Week

16-10

2/6/13

7


Fetal development Fetal development 9th – 38th weeks of

development. §  Fetus has visible human characteristics. §  Cartilage begins to be replaced by bone. §  3rd month—possible to distinguish males

from females. §  4th month—heartbeat is loud enough to

be heard with a stethoscope. §  9th month - Fetus is about 20 1/2 inches

long and weighs about 7 1/2 pounds at the end of fetal development. 16-11

Table 16.1b


Development of Male and Female Sex Organs §  Sex of an individual—determined at

conception. Males have XY chromosomes, females have XX chromosomes

§  Gonads start developing at 7 weeks. §  SRY gene—sex determining region of the Y

chromosome. §  Hormones control the development of sex

organs.

16-14 16-15


Note that the neural tube begins to form very early in embryonic development. This is why proper nutrition is important from the beginning of a pregnancy. Folic acid in particular is needed early in the pregnancy.


2/6/13

8


Comparison of different animals Copyright © 2009 Pearson Education, Inc.

Copyright © 2009 Pearson Education, Inc. Copyright © 2009 Pearson Education, Inc.


Limbs and organs are formed by a process of certain cells dying.

Programmed cell death is called apoptosis


Pregnancy and Diabetes

§  Hormones cause mother to develop increased insulin resistance – can lead to gestational diabetes

16-16

2/6/13

9

Pregnancy and Birth


Aging

§  Stages of Life: §  Infancy, Childhood, Adolescence,

Adulthood §  Aging—progressive changes that

contribute to an increased risk of infirmity, disease, and death. §  Genetic in origin—aging has a genetic basis. §  Whole-body process—decline in hormonal

system affects many organs. §  Extrinsic factors—poor health habits and

exercise program.

16-18


Effect of Age on Body Systems

§  Effect of Age on Body Systems: §  Skin becomes thinner and less elastic. §  Decline in bone density. §  Weight gain occurs because metabolism

decreases and inactivity increases. §  Females undergo menopause.

§  Biologically successful old age begins with the health habits developed when we are younger.


Important concepts

§  Know how the sperm fertilizes the oocyte – what layers does it need to go through to do it.

§  Three phases of embryo development §  Know what stage of embryonic development

implants in the uterus §  Know what the three layers of the embryo are §  The main tissues that the three layers give

rise to


Important concepts

§  What hormone does the placenta produce that prevents ovulation and menustration

§  What is the role of the placenta §  What are the four extraembryonic

membranes and their functions §  Does the blood from the mother and fetus

mix? §  What is gestational diabetes


Definitions

§  Fertilization, zygote, embryo, stem cells, Zona pellicuda, acrosome, corona radiata, differentiate, differentiation, blastocyst, placenta

nvc bio105 lect22 development - napa valley college · fetal development fetal development 9th –...

Documents