Reproduction Flashcards
Erection
penis becomes enlarged and firm
Sexual excitation initiates blood flow
ejaculation
Rhythmic contraction of epididymus, vas deferens, seminal vesicle, prostate gland
propels contents of the ducts and glands into the urethra and then out the body
Semen
provide nourishment
Neutralises acidic nature of urethra and female vagina, protecting sperm.
insemination
Sperm travel through cervix and body of uterus into uterine tubes
quickly reach upper portions of uterine tubes, often a few minutes
Along wt swimming, contractions in uterus walls and uterus tubes help sperm reach egg faster
sperm mortality
Death rate of sperm is high
only few 1000s reach uterine tube
Ova
Has two layers around it: corona radiata and zona pellucida
corona radiata
Follicle cells held together by cementing materials that contain acid
outer layer
Zona pelucida
glycoprotein matrix surrounding the plasma membrane of oocyte
Inner layer
Acro some (fertilisation)
acrosome of sperm head uses enzymes to break down acid in cementing material holding cells of corona radiata together.
1 acrosome’s enzymes are inefficient therefore 1000s of sperm needed to loosen layer to allow 1 sperm to reach egg.
Once sperm through corona radiata
encounters zona pellucida and initiates acrosomal reaction.
Release of digestive enzyme from acrosome, breaking down glycoprotein matrix of zona pellucida, giving access to plasma membrane of Oocyte, preventing entrance of any more sperm. This ensure only one haploid cell joins wt Oocyte.
once sperm entered oocyte
Tail is absorbed, head begins to move through cytoplasm to form male pronucleus, the haploid nucleus of sperm.
entrance of sperm stimulates secondary Oocyte to complete 2nd meiotic division.
Nucleus of Oocyte develops into female pronucleus, haploid nucleus of Oocyte, fuses with male pronucleus, forming single diploid nucleus.
Oocyte is now referred to as zygote.
Blastocyst formation (after fertilisation)
zygote travels down uterine tube and begins to divide by mitosis
Blastocyst
6 days after fertilisation, zygote has reached uterus and developed into blastocyst.
Hollow ball of cells that surround a cavity filled wt fluid
at one side is inner membrane (group of 30 cells), embryoblast. Inner cell mass composed of stem cells, differentiation develops embryo.
Implantation
blastocyst remains free within cavity pf uterus for 2-3 days then sinks into soft endometrium, to become firmly attached to wall of uterus.
Enables the blastocyst to gain nourishment for growth and development by absorbing nutrients from glands and blood vessels of uterine lining
hormone production
Blastocyst development depends on endometrium being maintained.
high levels of oestrogen and progesterone stop break down of endometrium, ceases menstrual cycle.
Corpus luteum secretes hormones until placenta is able to produce them, usually after 8-12 weeks.
1st 2 months referred as embryonic period, after 2 months embryo reffered to as foetus
Cell differentiation
cells making up inner cell mass of blastocyst are stem cells.
Genes and chemicals and contact wt other cells causes differentiation
totipotent stem cell
Has potential to create any type of cell necessary for embryonic development
pluripotent stem cells
Cells of inner cell mass
able to give to many, but not all, cell types necessary for foetal development
Multipotent stem cells
pluripotent that has undergone further specialisation
Give rise to cells that have particular function
primary germ layer
3rd week of development
Inner cell was undergoes changes as cells change to multipotent
resutlts in formation of 3 primary germ layers: Ectoderm, Mesoderm, Endoderm
Ectoderm
outermost germ layer
Form outer parts of body
(Eg. Skin, hair, mammary gland, nervous system)
Mesoderm
middle germ layer
Allows formation of stomach and intestines
(eg. Skeleton, muscles, connective tissue, heart, blood)
Endoderm
Innermost germ layer
(eg. Lining of digestive system, lungs, thyroid)
Embryonic membranes
4 embryonic membranes form: amnion, chorion, Yolk sac and Allantois
Lie outside embryo and serve to protect and nourish it as it develops
Amnion
First membrane to develop
8th day it surrounds embryo, enclosing cavity within which it secretes amniotic fluid, fluid is shock absorber, protecting baby, and helps maintain constant temp, and allowing foetus to move freely
Expands during growth, usually bursting at childbirth
chorion
Formed from outer cells of blastocyst together with layer of mesodermal cells
surrounds embryo and other 3 embryonic membranes
Amnion fuses with inner layer of chorion as it expands
eventually becomes main part of foetal portion of placenta
Yolk sac and Allantois
2 of the other membranes
Form outer structure of umbilical cord
placenta
Foetal and maternal tissues formed in first 3 months of gestation, foetal portion develops from chorion
placenta supplies nutrients to, and removes wastes from, the foetus
Also serves as endocrine gland
chorionic villi
Small, branching, finger-like projections
develops from chorion and contain blood vessels, grow into endometrium
Mother and foetal blood don’t mix, therefore exchange of materials occurs through diffusion and active transport
number of villi provide large surface for exchange
Umbilical cord
contains umbilical vein and artery
Vein carries blood from placenta through cord to foetus
Artery carries blood from foetus through cord to chorionic villi
blood passage from mom to baby
Uterine arteries -> chorionic villi -> umbilical vein -> foetus -> umbilical artery -> chorionic villi -> uterine veins
Gestation
time embryo or foetus is carried in uterus
About 280 days
embryo to foetus (1st month)
After 1 month embryo is under 4mm long
development of muscle segments on either side of the tube that is to become brain and spinal cord
Embryo to foetus (4th week)
arm/leg buds start to appear
Embryo to foetus (8th week)
all organs present
Recognisable human form
3cm length, 1g
Head half size of embryo, eyes appear as slits, moved from side to front of head
jaw almost developed
Foetal development (16th week)
uterus expands
Foetus 18cm long, 100g
posture more erect
Heart beats 120-160 bpm
foetal development (20th week)
Foetus is 25cm long, 300g
foetal movement clearly felt
Foetal development (24th week)
mother shows obvious signs of pregnancy
Foetus grown 27-35cm long, 565-680g
foetal development (28th week)
Foetus os 38cm long, 1000g
moves around rigorously in uterus
Brain enlarged
in males, testes descend into scrotum
Foetal development (32 weeks)
foetus is 41-45cm long, 1800-2200g
Foetal development (36th week)
46-48cm, 2700g
Circulatory system fully developed, ready for birth
foetal development (40th week)
Pregnancy at full term
foetus occupies all space in uterus, no room to move
50cm long, 3400g, males 100g more
Head smaller in proportion to body
nose well formed
Shortly before birth
head moves inside curved shape of pelvis
Growth is slow, placenta begins to fail and becomes more fibrous
late stages of pregnancy
Antibodies diffuse into placenta, give baby immunity to same diseases as mum
after 6 months affects of antibodies begin to decrease, baby builds own immunity
Pregnant mother changes
growing abdomen, growing uterus pushes organs upwards and outwards
Enlargement of breasts, hormones create milk-secreting tissue
increase is size of heart and blood volume
Greater blood volume results in increased blood flow to kidneys, therefore more urine production
uterine presses on bladder, less liquid can be contained
Emotional stated affected by hormonal imbalances
parturition
Process by which foetus is expelled from mother’s body at end of gestation
proceeded by a sequence of events called labour
Prior to labour
several hormone changes, changes cause ligaments in pelvis to soften, also increases response of uterus to stimuli, strengthening contractions.
Before labour begins cervix softened, shortened in length, begins to open
first stage of labour
Dilation of cervix
waves of contractions travel from upper part of uterus downward towards cervix, muscle fibres shorten wt each contractions
Cervix is 10cm when full dilation and head of baby pushed into dilating cervix, passage called birth canal.
complete dilation marks end of first stage of labour
Second stage of labour
involves delivery of foetus
Membrane surrounding foetus bursts, gushing liquid from vagina
Baby’s head turns to face mother’s back, distension stimulates mother to contract uterus
once head emerges, head turns to face mother’s hips, allowing shoulders and rest of body to move more easily
Pressure on head may change its shape, no brain damage, head returns to shape in a few days
third stage of labour
Contractions continue and placenta and remains are expelled, called afterbirth
umbilical cord clamped in 2 places and then cut between clamps
Baby first breath
if baby doesn’t breath on its own doctor will slap its bottom.
If this is unsuccessful umbilical cord is cut causing a buildup of CO2 in body stimulating lungs to breath.
Ductus Venosus
Before birth
Vein bypasses liver and enters inferior vena cava as blood is already filtered by mom.
Ductus Arteriosus
Lungs collapsed therefore causes resistance to blood flow, little blood reaches lungs.
Ductuce Arteriosus provides pathway from right ventricle into aorta, bypassing lungs
Foramen Ovale
Blood in right atrium may flow directly into left atrium through oval opening between both chambers
because blood from mom already oxygenated.
Closing of special vessels
after lungs expand no more resistance to blood flow therefore blood in arteriosus decreases, closing after a few weeks later
More blood returns from the lungs therefore pressure in aorta increases, pushing flaps of Foramen Oval against aorta walls, eventually completely shutting.
due to loss of placenta, blood need filtration through liver, therefore Ductus venosus contracts and eventually closes
Following birth
45 breathes per min, for 2 weeks, rate gradually slows
Heart rate 125-130 bpm, high rate due to need for oxygen for muscular activity, to keep warm due to environment being cooler then uterus
number of RBC increases
Maintaining healthy pregnancy (diet)
increase energy uptake, 850kj more per day
At least 65g of protein daily
increase folic acid essential for normal cell division and manufacture of proteins
Increase calcium for bone growth, teeth, heart, nerve and muscular development
increase fluoride prevents future dental problems
Increase vitamin A normal growth of cells
literiosis
Cause: contaminated foods
potential to cause miscarriage
Avoidance: eat freshly cooked foods, avoid packaged foods
Healthy pregnancy (exercise/weight)
exercise level should be maintained to same level as before pregnancy
0.5kg weight added per week, due to uterus and blood volume increase
Teratogens
agent that causes physical defects in the developing embryo
Foetal alcohol syndrome
describes effects of foetal exposure to alcohol
Smoking
increased rate of miscarriage, baby born lighter than supposed to
Thalidomide
morning sickness pill that formed deformities in babies, in legs and arms
Rubella
viral infections contracted by school-aged children
If contracted by pregnant mother baby may be born deaf, blind or heart malfunctions
