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Chapter 23

Bio 202

Human Anatomy & Physiology Part 2

Tim Pimperl

A & P Instructor

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Important Points in Chapter 23:Outcomes to be Assessed

23.1: Introduction

Distinguish between growth and development.

Distinguish between prenatal and postnatal.

23.2: Conception

Describe the movement of sperm toward an egg

Discuss fertilization.

23.3: Pregnancy/Prenatal Period

List and provide details of the major events of cleavage.

Describe implantation.

Discuss the hormonal and other changes in the maternal body during pregnancy.

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Important Points in Chapter 23:Outcomes to be Assessed

Describe the major events of the embryonic stage of development.

Explain how the primary germ layers originate, and list the structures each layer produces.

Describe the formation and function of the placenta.

Define fetus, and describe the major events that occur during the fetal stage of development.

Trace the path of blood through the fetal cardiovascular system.

Explain the role of hormones in the birth process and milk production.

23.4: Postnatal Period

Name the postnatal stages of development of a human, and indicate the general characteristics of each stage.

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Important Points in Chapter 23:Outcomes to be Assessed

Describe the major cardiovascular and physiological adjustments that occur in a newborn.

23.5: Aging

Distinguish between active and passive aging.

Contrast lifespan and life expectancy.

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23.1: Introduction• A sperm and a secondary oocyte unite, forming a zygote, and the journey of prenatal development begins• After 38 weeks of cell division, growth and specialization into distinctive tissues and organs, a new human being enters the world• Humans grow, develop and age

• Growth is an increase in size• Development, which includes growth, is the continuous process by which an individual changes from one life phase to another

• Prenatal period is from fertilization to birth• Postnatal period is from birth to death

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23.2: Conception

•The union of a secondary oocyte and a sperm cell is called fertilization, or conception• Fertilization takes place in a uterine tube

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Transport of Sex Cells• Before fertilization can occur, a secondary oocyte must be ovulated and enter a uterine tube• Only a few hundred of between 200 to 600 million sperm reach a secondary oocyte

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Infundibulum

Egg cell

Path of egg cellSperm cells

Cervix

Body of uterus

Ovary

Semen deposited in vaginaduring sexual intercourse

Path ofSperm cells

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From M. Tegner and D. Epel. 16 February 1973. "Sea Urchin Sperm." Science, 179:685-688. © 1973 American Association for the Advancement of Science

Vagina

Fertilization

• Several hundred sperm cells must be present at the secondary oocyte to release enough enzymes (from the sperms’ acrosomes) necessary to penetrate the corona radiata and zona pellucida that surround the oocyte

• As one sperm nucleus enters, the secondary oocyte completes meiosis II, producing a tiny polar body and an egg nucleus

• The sperm nucleus unites with the egg nucleus to form a zygote

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23.3: Pregancy/Prenatal Period

• Pregnancy is the presence of a developing offspring in the uterus• Pregnancy consists of three trimesters, each about three months long•The prenatal period usually lasts 38 weeks from conception• It can be divided into:

• 1. A period of cleavage• 2. An embryonic stage• 3. A fetal stage

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Period of Cleavage

• The rapid cell division and distribution of the zygote’s cytoplasm into progressively smaller cells is cleavage• The cells produced during cleavage are called blastomeres Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

(a) (b) (c)a: © A. Tsiara/Photo Researchers, Inc.; b: © Omikron/Photo Researchers, Inc.; c: © Petit Format/Nestle/Photo Researchers, Inc.

Period of Cleavage

• Zygote – fertilized egg• Morula – solid ball of cells• Blastocyst – hollow ball of cells that implants in

uterus

• Inner cell mass – gives rise to embryo

• Trophoblast – cells forming wall of blastocyst – develops into structures that assist embryo….also produces hCG

• Placenta – vascular structure formed by cells of trophoblast and endometrium 11

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Hormonal Changes During Pregnancy

• Secretion of hCG maintains the corpus luteum (remains of follicle after ovulation, stays in ovary) and inhibits FSH and LH• The corpus luteum secretes estrogens and progesterone• The placenta secretes large amounts of estrogens and progesterone• Estrogens and progesterone stimulate and maintain the uterine lining, inhibit FSH and LH, inhibit uterine contractions, and enlarge the reproductive organs• Relaxin from the corpus luteum inhibits uterine contractions and relaxes the pelvic ligaments• Placental lactogen stimulates breast development• Aldosterone promotes sodium retention• PTH maintains calcium concentrations in the blood

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Other Changes During Pregnancy

• Growth of the uterus can displace abdominal organs and disrupt meals, including the development of heartburn and increased urinary frequency• More oxygen is needed and more waste is excreted causing increases in blood volume, cardiac output, breathing rate, and urine production• To obtain adequate nutrition, intake must be sufficient to supply needed vitamins, minerals and proteins

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Embryonic Stage

• The embryonic stage extends from the beginning of the second week through the eighth week, when the placenta forms, the main internal organs develop, and the major external body structures appear Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chorion

Extraembryonic cavity

EctodermMesodermEndoderm

Chorionic villi

Connecting stalk

Amniotic cavity

Endometrium

Amnion

Lumen ofuterus

Yolk sacof embryo

Germ layers ofembryonic disc

Embryonic Stage

• Structures which help support and nourish the embryo:

• Chorion

• Amnion

• Yolk sac

• Placenta

• Umbilical cord• By the end of the 2nd week, the primordial embryo

has formed three primary germ layers and is termed a gastrula 15

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Chorion

Endometrium

Amniotic cavity

Amnion Allantois

Umbilicalcord Maternal

bloodvessels

Developingplacenta

Extraembryoniccavity

Yolksac

• As the amnion develops, it surrounds the embryo, and the umbilical cord begins to form from structures in the connecting stalk

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chorion

Placenta

Umbilical cord

Amniochorionic membrane

Endometrium Myometrium

Amniotic fluid

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Fetal Stage

• The fetal stage begins at the end of the eighth week of prenatal development • Here growth is rapid, and body portions change considerably• At the beginning of this stage, the head is disproportionately large, and the lower limbs are relatively short

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Birth Process• Pregnancy terminates with the birth process called parturition• The process is complex as noted in Table 23.5

Milk Production and Secretion

• During pregnancy, placental estrogens and progesterone stimulate further development of the mammary glands, and prolactin is released by the anterior pituitary

• But milk secretion does not begin until after birth • The “first milk” is a thin, watery fluid called

colostrum (rich in proteins and antibodies but has lower amounts of carbohydrates and fats)

• Mature milk is produced within a few days20

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23.4: Postnatal Period

• Following birth, both mother and newborn experience physiological and structural changes• The postnatal period lasts from birth until death• It can be divided into:

• The neonatal period• Infancy• Childhood• Adolescence• Adulthood• Senescence (including dying)

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Neonatal Period

• Neonatal period• From birth to the end of the 4th week• The newborn begins to carry on respiration, obtain nutrients, digest nutrients, excrete wastes, regulate body temperature, and make cardiovascular adjustments

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Infancy

• Infancy• From the end of the 4th week to one year• The growth rate is high• The teeth begin to erupt• The muscular and nervous systems mature• Communication begins

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Childhood

• Childhood• From one year to puberty• The growth rate is high• Permanent teeth appear• Muscular control is achieved• Bladder and bowel controls are established• Intellectual abilities mature

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Adolescence

• Adolescence • From puberty to adulthood• The person becomes reproductively functional and emotionally more mature• Growth spurts occur• Motor skills continue to develop• Intellectual abilities continue to mature

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Adulthood

• Adulthood• Adolescence to old age• The person remains relatively unchanged anatomically and physiologically• Degenerative changes begin

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Senescence

• Senescence • Old age to death• Degenerative changes continue• The body becomes less able to cope with the demands placed on it• Death results from various conditions and diseases

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The End of Life

• Nearing the end of life is a personal process, influenced by belief as well as circumstance• A person who has been chronically ill may show signs of impending death, often in a sequence• Two stages of the dying process include:

• Preactive dying which may take up to three months• Active dying with a distinct set of signs

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23.5: Aging

• The aging process is difficult to analyze• The medical field of gerontology examines the biological changes of aging at the molecular, cellular, organismal, and population levels• Aging is both active and passive

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Passive Aging

• Aging as a passive process is a breakdown of structures and slowing of functions

• Molecularly a degeneration of elastin and collagen proteins• Biochemically lipids breakdown• Cellular degradation is associated with free radicals

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Active Aging

• Aging also entails new activities or the appearance of new substances

• Lipofuscin granules from the breakdown of lipids• Autoimmunity• Apoptosis - the process of programmed cell death

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The Human Life Span

• The human life span is approximately 120 years• Life expectancy is a realistic projection of how long an individual will live• The current U.S. life expectancy is 75.4 years for men and 83.2 years for women• Medical advances contribute to improved life expectancy