AnP Chapter 24 (LO4) Flashcards
Fertilization
Sperm can remain viable within the female reproductive tract for as long as six days
The egg is only available for 24 hours
It takes 72 hours for the egg to reach the uterus fertilization typically occurs in the distal third of the fallopian tubes
A team of sperm help make fertilization possible by clearing a path
Zona pellucida
layer of cells in glycoprotein membrane encasing the ovum
how fertilization works
- Hundreds of sperm swim the egg the acrosomes on the sperm heads release enzymes that break down the cells in the zona pellucida
- Because of the efforts of multiple sperm a path through the Zona eventually results allowing a single sperm to penetrate
- The nucleus of the sperm is released into the ovum as its tail degenerates and falls away
- –The nucleus of the sperm fuses with the nucleus of the egg creating a single cells 46 chromosomes
Zygote
is a fertilized egg
Stages of pregnancy
First trimester last from conception through the first 12 weeks
Second trimester ranges from week 13 through week 24
Third trimester last from week 25 until birth
Preembryotic stage
Embryotic stage
Fetal stage
Preembryotic stage: which begins at fertilization and last for 16 days
Embryotic stage: which begins after the 16th day and last until the eighth week
Fetal stage: which begins the eighth week and last until birth
Cleavage
The fertilize cell divides by mitosis to produce two identical daughter cells
how the preembryotic stage works
- Prebiotic stage begins in fertilization forms a zygote with 46 chromosomes
- Within 24 to 36 hours the zygote divides by mitosis to form two daughter cells called blastomeres
- The mitotic division continue with the cells doubling with each division
- —finally a BlackBerry like cluster of 16 cells called morula results
- —Approximately 3 to 4 days after fertilization the morula enters the uterine cavity where it floats for two or three days - As the morula continues to divide a hollow cavity forms and the morula is now called a blastocyst
- —The blastocyst consists of an outer layer of cells called the trophoblast and an inner cell mass
- —The trophoblast eventually formed the placenta and the inner cell mass becomes the embryo - Implantation: About six days after ovulation the blastocyte attaches to the endometrium
Implantation
The process of implantation takes about a week
- Open the blastocyst attaches to the endometrium the trophoblast cells on the side of the endometrium divide to produce two layers of cells
- –The outer layer secretes enzymes that erode a gap in the endometrium
- –As these other cells penetrate the endometrium the inner soul that separates from the trophoblast creating a narrow space called the amniotic cavity - Inner cell mass flattens to form the embryonic discs
- –Some of the cells on the interior portion of the embryonic disk multiply to form another cavity called the yolk sac
- –Meanwhile the rapidly growing endometrium covers the top of the blastocyte burying it completely - Embryonic desk gives rise to three layers called Jim layers which produce all the organs and tissues of the body
- –The three germ layers are the ectoderm, mesoderm and endoderm
germ layers
each germ layer gives rise to specific organs (organogenesis)
Ectoderm
Mesoderm
Endoderm
develops into the upper dermis, nervous system, pituitary gland, optic lens and salivary glands
develops into bones, muscle, cartilage, blood in the kidneys
develops into the epithelial lining of the digestive and respiratory tract, parts of the bladder and urethra, thyroid and parathyroid glands, liver, and thymus
forms the basis for pregnancy tests and may be detectible with an 8 to 10 days after fertilization
Detection of HCG in the mothers blood or urine
Embryo
when the germ layers forms the blastocyte enters the embryonic stage
2 key events occur during embryonic stage
the germ layers differentiate into organs and organ systems and several accessory organs emerged to add the developing embryo
how long does the embryonic stage last
6 weeks
The accessory organs of the embryonic stage
include four extra embryonic membranes the amnion, chorion, allantois, yolk sac, placenta and umbilical cord
Amnion
transparent sac that completely envelops the embryo
Filled with amniotic fluid which prevents the embryo from trauma as well as changes in temperature
Later the fetus will breed the fluid and swallow it
The volume remain stable because the fetus regularly urinates into the amniotic sac
Chorion
the outermost membrane that surrounds the other membranes
Fingerlike projections penetrate the uterus
In the area of the umbilical cord it forms what will become the fetal side of the placenta
Allantois
serves as the foundation for the developing umbilical cord later becomes part of the urinary bladder
Yolk sac
produces red blood cells until the sixth week contributes to the formation of the digestive tract and provides nutrients and handles waste disposal
when does the placenta develop
11 days after conception
The placenta plays at dual role
it secretes hormones necessary to maintain the pregnancy it also becomes increasingly important in supplying the embryo and fetus with oxygen and nutrients
Lucunae
As the villi project deeper into the endometrium they penetrate uterine blood vessels causing maternal blood to pull around the villi in sinuses
The umbilical cord contains two umbilical artery’s and one umbilical vein
Umbilical arteries: fetal heart pumps blood into the placenta
Umbilical veins: blood returns to the fetus
Fetal stage
Encompasses the period from the eighth week until birth
Primarily a stage of growth as organs that formed during the embryonic period grow and mature
The fetus the lungs snort delivery quite a great deal of blood amongst our non-functioning in the liver is still immature therefore the Fetus circulatory system contains three Sean Circle of blood to bypass these organs
3 shunts
the Ductus venosus
The foreman ovale
The ductus arteriosu
the Ductus venosus
The foreman ovale
The ductus arteriosus
Ductus venosus: Shunts blood around the liver
The foreman ovale: an opening between the two atria Shunts blood directly from the right atrium to the left
The ductus arteriosus: verts blood from right ventricle to the pulmonary artery bypass in the lungs play have a nice here
how circulatory system works during fetal stage
- Oxygen rich blood enters the fetus through the umbilical cord Vein
- Most of the blood bypasses delivered by flowing through the ductus venosus into the inferior vena cava
- —Placental blood from the umbilical vein then merges with fetal blood from the IVC as it flows to the heart - Blood flows into the right atrium most of the blood cells directly into the left atrium through the foramen ovale bypassing the lungs
- Blood that does not flow through the foramen ovale flows into the right ventricle and then into the pulmonary trunk
- —From there the blood flows through the ductus arteriosus and into the descending aorta again bypassing the lung - Oxygen depleted waste filled blood flows through to umbilical arteries to the placenta
- —The placenta than cleanses the blood reading of carbon dioxide and waste products reoxygenating it and returns it to the fetus through the umbilical vein
Week 4
The brain spinal cord and heart begin to develop
The GI tract begins to form
The heart begins to beat about day 22
Tiny buds that will become arms and legs are visible
Length 0.25inch
Week 8
The embryo is now a fetus
Eyes, ears, nose, lips tongue and tooth buds take shape
Head is nearly as large as the rest of the body
Brain waves are detectable
Arms and legs are recognizable
Blood cells and major blood vessels form
Bone calcifications begins
Genitals are present but gender is not distinguishable
Length 1.2 inches
Week 12
The face is well formed
Arms are long and thin gender distinguishable
The liver produces bile
The fetus swallows amniotic fluid and produces urine
Eyes are well developed but the eyelids are fused shut
Length 3.54 inches
Week 16
The scalp has hair
Lips begin sucking movements
The skeleton is visable
The heartbeat can be heard with a stethoscope
Kidneys are well formed
Length 5.5 inches
Week 20
Lanugo: covers the body which in turn is covered by vernix caseosa
vernix caseosa: a white cheese like substance
fetal movement (quickening) can be felt
nails appear on fingers and toes
length 8 inches
week 24
the fetus has a startle reflex
lungs begin producing surfactant
skin wrinkled and translucent
the fetus gains weight rapidly
length 11.8
week 28
eyes open and close
the respiratory although immature is capable of gas exchange at 28 weeks
testes begin to descend into the scrotum
the brain develops rapidly
length 14.8 inches
week 32
The amount of body fat increases rapidly
Rhythmic breathing movements began although lungs are still immature
Bones are fully formed although they are still soft
Length 16.7 inches
Week 36
More subcutaneous fat is deposited
Lanugo has mostly disappeared although its still present on the upper arms and shoulders
Length 18.5 inches
Week 39 and 40
The fetus is considered full-term
The average full term infant measures approximately 20 inches long and weighs 7-7.5lbs
Physical changes during pregnancy
digestive system
- Nausea and vomiting commonly occur during the first three months the cause is unknown
- Constipation often results from decreased intestinal motility
- Heartburn frequently occurs later in the pregnancy as the enlarged uterus presses upward on the stomach
- Basal metabolic rate rises about 15% during the second half of the pregnancy and the mother appetite increases
Physical changes during pregnancy
Circulatory system
- Mothers blood volume increases 30% to 50%
- Cardiac output increases 30% of 40% by week 27 as the uterus demands more blood heart rate also increases
- —-Later in the pregnancy the uterus exerts pressure on the pelvic blood vessels interfering with venous return hemorrhoids, varicose veins, and swelling in the feet may result
Physical changes during pregnancy
Respiratory system
- Ventilation increases about 50% to meet the developing fetus increased demand for oxygen
- Late in the pregnancy the enlarged uterus pushes against the die from often cousin shortness of breath
- —Increased estrogen levels cause the nasal mucosa to swell resulting in nasal stuffiness
Physical changes during pregnancy
Urinary system
- An increase in Aldosterone Promotes water and salt retention by the kidneys
- Glomular filtration rate increases to deal with the added burden of disposing pf the fetus’ waste this leads to a slightly elevated urine output
- —Later in pregnancy the enlarged uterus presses on the bladder and reduces its capacity; this leads to increased frequency of urination
Physical changes during pregnancy
Integumentary system
- The skin of the abdomen grows and stretches to accommodate the expanding uterus often leading to stretch marks or striae
- Skin over the breasts also grows as breasts enlarge in preparation for milk production
- An increase in melanocyte stimulating hormone and estrogen darkens areola and creates a line of pigment from the umbilicus to the pubis called linea nigra
- –Melanin production may also discolor skin on the face to create chloasma or “mask of pregnancy”
Physical changes during pregnancy
Uterus
- The uterus enlarges dramatically during first 16 weeks of gestation it grows from the size of a fist until it occupies most of the pelvic cavity
- As pregnancy continues the uterus expands until it reaches the level of the xiphoid process and fills most of the abdominal cavity
- —The uterus increases from its nonpregnant weight of 0.1lbs to about 2lbs by the end of pregnancy
The onset of labor is thought to result from several factors including:
A decline in progesterone:
The release of oxytocin (OT):
A decline in progesteron
progesterone inhibits uterine contractions
After 6 months of gestation the level of progesterone declines
The level of estrogen which stimulates uterine contractions continues to rise
Falling levels of progesterone combined with rising levels of estrogen lead to uterine irritability
The release of oxytocin (OT)
toward the end of the pregnancy the posterior pituitary releases more oxytocin at the same time the uterus becomes increasingly sensitive to oxytocin Peking just before labour
Oxytocin causes the fetal membranes to release prostaglandins
Uterine stretching: stretching increases contractility
3 stages of labour
dilation, expulsion and placental stages
Parturition
the process of giving birth
Stage 1: dilation of the cervix
Lasts 6 to 18 hours
Primipara
Multipara
Primipara: women giving birth for first time
Multipara: women who have previously given birth
Cervical effacement
the progressive thinning of the cervical walls
Stage 2: expulsion of the baby
Begins when cervix is fully dilated- ends when baby is born
Lasts 30-60mins in primiparous women but can be much shorter in multiparous women
Episiotomy
a surgical incision is sometimes made between the vagina and anus to enlarge the vaginal opening
Stage 3: delivery of the placenta
Involves the delivery of afterbirth: the placenta, amnion and other fetal membranes
Lasts 5 to 30 minutes
changes in neonates cardiovascular system
pressure changes in the heart cause the foramen ovale to shut and pressure changes in the pulmonary artery and aorta lead to the collapse of the ducts arteriosus
changes in neonates respiratory system
although most neonates begin breathing spontaneously the first few breaths require considerable effort as they work to inflate collapsed alveoli
changes in neonates immune system
neonates have weak immune systems at birth placing them at risk for an infection
changes in neonates thermoregulation
neonates risk becoming hypothermic because their surface area in relationship to their size is larger than in a adult
changes in neonates fluid balance
neonates require a fairly high fluid intake because their immature kidneys do not concentrate urine adequately
