PowerPoint Summary of Chapters 23-25

• Use this PowerPoint along with the outline notes • If a term appears in bold and is not defined, be sure to go look on the text for it • Refer back to the text for any additional info you would like to have • Have fun!

Chapter 23 Reproductive System

• Meiosis – A form of cell division specific to gametes that results in only half the number of original chromosomes (fig 21-1) – Stem cells (46 chromosomes) divide into functional

gametes

chromosomes which only have 23 – For males, this process doesn’t start until puberty and continues throughout the rest of their life • Once started, males will produce 500,000

spermatozoa

per day.

• Spermatogenesis – creation of sperm – A single stem cell divides twice to produce four

spermatozoa

(sperm cell) – This process occurs along the nearly half mile of

seminiferous tubules

in each testis – The seminiferous tubules drain into the epididymus. There spermatozoa mature up to 2 weeks in the super coiled 23 ft of tubule.

– The next part of the pathway is the

ductus deferens

(vas deferens) that runs from the posterior of each testis to a single

ejaculatory duct

.

• Sperm can be stored in the ductus deferens for several months

• Spermatogenesis – (cont’d) – Accessory glands add to the

seminal fluid

at the ejaculatory ducts and proximal end of the urethra.

• Seminal Vesicles • Prostate Gland • Bulbourethral (see fig 23-1 for location of these glands) – What are the functions of semen?

• Spermatogenesis – (cont’d) – The

urethra

is the final path for seminal fluid as it travels through the penis and is ejaculated out of the body • A typical ejaculate is 2 to 5 ml of semen and contains 50-100 million sperm per ml –

Interstitial cells

between the seminiferous tubules produce the hormone

testosterone

.

• This production increase dramatically after puberty in the presence of

FSH

and

LH

– Refer back to Chapter 12 about the regulation and production of these hormones

• Oogenesis – formation of an egg (ovum) – Stem cells during prenatal development divide twice to produce an ovum with 23 chromosomes • Each female is born with nearly 2 million ovum, but by the time they will start being released at puberty, the number withers down to ~200,000. All are stored in a pair of

ovaries

.

– Levels of FSH and LH stimulate the development and release • Even so, she will only release less than 400 in a lifetime. One per month, alternating from the right or left ovary. • This process will end with

menopause

.

• Oogenesis – formation of an egg (ovum) – One ovum from the left or right ovary is ovulated into the

fimbriae

of the 5 inch

uterine tube

• Cilia in the tube draw the ovum towards the uterus; a trip that takes 3-4 days – This cycle usually lasts about 28 days, but can be longer or shorter per individual • Increased LH levels stimulate the development of a follicle, which will then release its ovum in 14days • Fertilization needs to occur in the first 48 hrs after ovulation or the ovum will disintegrate in the uterus and be flushed out during

menstration

. • If fertilizations does occur, then the cycle is stopped until after birth

• Read both the menstrual cycle which starts on page 466 • Review fig. 23-13 which summarizes the hormonal events and uterus development for this cycle.

• Read the Hot Topic (Box 23-3) and Birth Control Strategies on pages 468 and 469 • Be familiar with the types of cancer of this system – Prostatic, Testicular, Breast, Endometrial, Ovarian, Cervical

Chapter 24 Development

• Begins at fertilization, or

conception and ends at birth

– Gestation lasts approximately 38 weeks • Prenatal development is divided into two stages – Embryo for the first two months – Fetus from the ninth week to birth

• Fertilization – Fusion of egg and sperm – Each contain 23 chromosomes to form a

zygote

containing 46 chromosomes – 200 million sperm are released into the vagina, 10,000 make it into the uterine tube, and about 100 may actually make it to the egg.

– Penetration of the egg by a single sperm allows the chromosomes to combine

Gestation

• • Average prenatal period is 38 weeks or 266 days (divided into three trimesters)

First Trimester

– 40% of the eggs that are fertilized produce embryos that survive the first trimester – Embryo formation • Zygote undergoes rapid cell divisions called

cleavage

• By day 5, the cells have entered the uterus, and developed into a blastocyst

• First Trimester continued

– Implantation • About day 7, the blastocyst adheres to the surface of the uterus and will become completely embedded within its membrane – The outer cells of the blastocyst develops into the placenta • The placenta begins secreting

human chorionic gonadotropin (hGC)

which signals the corpus luteum to maintain production of estrogens and progesterone – This hormone maintains a functional endometrial lining • The inner cell mass of the blastocyst becomes organized into three

germ layers

that will form different body tissues

• First Trimester continued – Placenta (fig 24-2) • Extensions from the chorion extend into maternal tissue where chorionic blood vessels develop • These

chorionic villi

enlarge as the heart starts beating and extend further into the endometrium where they will come in close proximity of maternal blood vessels • The vessels develop into two umbilical arteries and a single umbilical vein • The chorionic villi provide the surface area for the exchange of gasses, nutrients and wastes between maternal and fetal blood flow.

•

First Trimester continued – Placenta (cont’d) • Also releases hormones (progesterone and estrogen) which will take over for the declining corpus luteum • Prevents menstration, prepares mammary glands to produce milk, and prepare the body for delivery • The following slide shows embryos at different stages and an early fetus – Interesting note: Picture b is during a phase where we don’t look too much different from fish or chicken embryo

• Second and Third Trimester – The framework for the major organ systems have formed by the start of the second trimester • The fetus grows from ~1oz to 1.4lbs

– Those organ systems become mostly functional in the third trimester • The fetus gains most its weight and shoots up to an average of 7lbs

Changes

• The fetus is totally dependant on the mother’s organ systems – That means that the mother has to increase all her norms to provide proper nutrition to the developing fetus • Increase CV activity, blood volume, Respiratory Rate, appetite, and excretion

Changes

• Early contractions of uterine smooth muscle are weak, short and painless – Late in development rising estrogen levels increase smooth muscle sensitivity and stimulate an rise in oxytocin levels.

– Oxytocin increases the force and frequency of contractions in response to a stretch in the uterine cervix – Uterine tissues also produce prostaglandins that increase contractions as well • Typically at 9 months, these changes lead to labor contractions that continue until delivery has been completed.

Stages of Labor

(Parturition) • First Stage – Cervix dilates and the fetus begins to slide down the cervical canal – Labor contractions are once every 10 to 30 min and at some point the amnion will rupture releasing amniotic fluid (“water break”) • Second Stage – Starts after the cervix has dilated completely and concludes when the fetus emerges from the vagina – Time varies but usually lasts two hours or less

Stages of Labor

(Parturition) • Third Stage – This stage ends with the ejection of the placenta (“afterbirth”) and an associated blood loss of 500 600ml.

• Along with the placenta, the amniotic sac membranes, and the umbilical cord (except the part attached to the baby which forms the

umbilicus

) are ejected • Fourth Stage – The period the body controls the bleeding after the birth – Involves uterine contractions and repair of an

episiotomy

, if conducted.

Stages of Labor

• An

episiotomy

can be performed to prevent perineal tearing if the vaginal opening is too small – This procedure enlarges the vaginal opening by placing an incision through the perineal musculature between the vagina and anus. It can be repaired with sutures after delivery • A

Cesarean (C) section

if complications arise can be performed – Here the abdominal wall is opened and a 6-7 inch incision is made in the uterus to allow the head (the widest part) to pass through

Multiple Births

• • • New stats on births reveals that twins occur 1 in 100 births and with African-Americans, the rate is greater (1 in 77)

Fraternal twins

are created when two eggs are released and fertilized at the same time. May or may not be the same gender.

Identical twins

are produced when the fertilized zygote cells split apart during development. The offspring’s genetic makeup is exactly the same.

– Fraternal twins are twice as common as identical twins and are increasing with the practice of fertility medicine.

Genetics and Inheritance

Chapter 25

•

Genetics

is the study of heredity, or how different traits are inherited.

• Families have similar traits because they are passed on from generation to generation through their chromosomes

Genes and Chromosomes

• Chromosomes contain DNA (Chapter 2 if you forgot) – No cell uses every bit of its genetic information – Genes are functional segments of DNA • Every somatic cell carries copies of the 46 original chromosomes that were in the zygote – Except gametes / RBCs figure 2

Genes and Chromosomes

•

Genotype

– Chromosomes and their component genes •

Phenotype

– physical expression of the genotype ►Arrangement of nucleotide bases – ATGCGCCCCATA or AGCCGCATAGCG… ►Hair color, skin tone, vision, bone structure * The genotype dictates the phenotype

• A gene’s position on a chromosome is called a

locus

– The locus helps map the DNA strand to indicate which section is responsible for certain traits • Each DNA strand has a “partner” within the nucleus – This pairing is referred to as

Homologous Chromosomes

, with one strand coming from paternal DNA and the other from maternal DNA

Karyotyping

• a sample of amniotic fluid is taken (

amniocentesis

) and fetal DNA is analyzed • a

Karyotype

displays homologous pairs of chromosomes

• Sampling procedures can be dangerous to the fetus and mother – Amniocentesis is only performed when known risk factors are present • I.e. Family history, age complications, drug user, etc.

– Amniotic fluid has to be sufficienct enough to be taken without implication to the fetus • Usually at a gestational age of 14 weeks • Results take several weeks

Patterns of inheritance

• Somatic cells contain 23 pairs of chromosomes – All 23 are Homologous chromosomes – 22 pair of autosomal and one pair of sex chromosomes

• Various forms of a gene are called

alleles

• Homozygous if homologous chromosomes carry the same alleles - AA, or aa • Heterozygous if homologous chromosomes carry different alleles - Aa • Alleles are either

dominant

– Always expressed in the phenotype – Usually represented by a capital letter (A) • or

recessive

– Expressed only when both alleles are present – Usually represented by a lowercase letter (a)

• Incomplete Dominance – Phenotype that is different from phenotypes of homozygous for either allele – Example: Sickle cell – Recessive trait (s) that causes RBCs to fold • ss: individual has the sickle cell disorder • Ss: individual has RBCs that fold only when tissue O 2 levels drop

• Codominance – Heterozygous allele that shows both traits in its phenotype – Example: Blood type • I A : antigen A present • I B : antigen B present • i: no antigen present • ii = Type O • I B I B or I B i = Type B • I A • I A I A I B or I A i = Type A = Type AB

•

Teratogens

– factors that disrupt normal development by damaging cells, altering chromosome structure, or by changing the pattern of gene activation and expression.

– Examples are nicotine, radiation, and alcohol – Fetal alcohol syndrome (FAS) produces developmental defects caused by mothers who drink during pregnancy • Number 1 cause of mental retardation in the U.S.

Punnett square diagram predicts probabilities of traits

 A = normal color, a = albino (see next slide)

• In diagram A, a homozygous dominate male mates with a homozygous recessive female – The probability of them having offspring with normal pigment is 100% (all are heterozygous dominant) • In diagram B, a heterozygous dominant male mates with a homozygous recessive female – The probability that they will have normal pigment offspring is 50%, the other 50% have albinism

Inheritance

• Simple inheritance – Phenotypic characteristics are determined by interactions between single pair of alleles • Polygenic inheritance – Phenotypic characteristics are determined by interactions among alleles on several genes

Inheritance

• More than 1200 inherited conditions have been identified that are linked to 1 or 2 abnormal alleles for a single gene

Sources of Individual Variation

• Genetic recombination – Gene reshuffling, common, creates variations within a gene pool • Crossing over and translocation (fig next slide) – Occurs during meiosis – May produce abnormal chromosomes • The production of chromosomes with extra or missing segments • Most result in miscarriages but some result in developmental disorders

Crossover and Translocation

• Spontaneous mutations – Random errors in DNA replication where extra or missing code occurs – Many of these errors are hidden as the recessive trait, and some don’t make it past the embryo stage – Heterozygous for the abnormal trait would be a

carrier

Sex-Linked Inheritance

• Sex chromosomes are X chromosome and Y chromosome – Male = XY – Female = XX – X chromosome carries X-linked (sex linked) genes • Affect somatic structures • The X chromosome is longer therefore no corresponding alleles on Y chromosome (i.e. no competition for traits)

Sex-linked Punnett

Human Genome Project

• Mapped ~24,000 of our genes – Including some responsible for inherited disorders click for more Human Genome info click for DNA sequence list

DNA Map

Genetic Disorders

• Mistakes caused during meiosis – Extra copies or missing pieces of DNA • Down Syndrome – Most common chromosomal abnormality – Caused by an extra copy of chromosome #21 – Marked by mental retardation of various levels and specific common physical features – Most die early of cardiovascular problems or develop neurological problems as they age – Incidence increases as the age of the mother being impregnated increases after age 35.

Genetic Disorders

• Klinefelter Syndrome – Male with an extra X chromosome – Reduces testosterone production so testis fail to mature, individuals are sterile, and breasts enlarge • Turner Syndrome – Female with a single X chromosome – Therefore a chromosome short – Causes an absence of development at puberty, ovaries are non-functional, and estrogen production is insignificant.

– Will require hormone injections to develop adult female characteristics

Ectopic (“displaced”) Pregnancies

• Normal implantation occurs in the endometrial lining of the uterus, ectopics implant somewhere else.

• 95% implant in the uterine tube which cannot expand like the uterus.

– The developing embryo ruptures the tube which causes internal bleeding and a risk to the mother – In some cases, the embryo can continue to develop full term and with surgical removal at birth • Incidence increases with regular douching or uterine tube infection

Placenta Problems

• Placenta Previa – Implantation occurs in the lower portion of the uterus – The placenta then may form near or over the cervical opening which increases the risk of tearing and bleeding out – Treatment includes bed rest for the mother and a scheduled C section when gestation has reached a safe point • Abrupto Placentae – Placenta tears away from the uterus after the fifth month of gestation – Internal bleeding may lead to maternal anemia or shock – Fetal mortality is between 30 and 100%