Development in utero Flashcards
Describe the stages in utero
- Zygote (fusion of gametes, 46 chromosomes) consists of 16 cells
- Morula (day 3), cells clump and divide via mitosis
- Blastocyst (day4-20) formation of bilaminar disc
- Embryo (day21-56) somite’s from orogenesis
- Fetus (9 weeks)
Describe the process of fertilization
Fertilization is the fusion of female and male gametes to form a zygote
1. The sperm is released and swims to the ovum in the oviduct, before the sperm can fertilize it must undergo capacitation, changes that make the sperm to be able to penetrate the egg.
2. The sperm must penetrate the corona radiata & zona pellucida, the sperm releases digestive enzymes from its acrosome to digest the CR, once ZP is reached more digestive enzymes are released
3. When the sperm has penetrated CR & ZP it makes contact with egg & releases its genetic information, egg and sperm fuse and causes depolarization of the cell to prevent polyspermy via release of calcium iond
4. gametes fuse to form a zygote, this occurs within 2-3hrs of fertilisation
Define the cleavage process
Is the following stage after fertilization & consists of many cell divisions, without embryo growing in size
Describe the cleavage process
- Cell begins to divide via mitosis rapidly, embryo does not grow, leads to blastomeres being formed
- Holoblastic cleavage occurs, the zygote divides into smaller cells, blastomeres divide to form a cluster of cells known as morula (16 cells), cell remains in ZP preventing implantation
- Cells continue to divide to form a blastula/blastocyst which is filled with blastocoel fluid, consists of 2 components, inner cell mass (embryoblast) & outer layer of cell (trophoblast)
- cellular differentiation: cleavage does not differentiate, but sets the cells, The blastomeres will start to undergo differentiation and specialization as they prepare for the next phase of embryonic development, known as gastrulation, where the basic body plan of the organism starts to form.
Define embryoblast and trophoblast
Embryoblast (inner cell mass) differentiates into epiblast & hypoblast to form a bilaminar embryonic disc, disc differentiates endoderm, mesoderm & ectoderm, these are the germ layers
Trophoblast: formed during the formation of the blastocyst, the trophoblast consists of 16-32 cells, it becomes the fetal part of the placenta. These cells secrete HCG to maintain the corpus luteum
Describe the implantation process
Describe the process of decidualisation
The process the endometrium undergoes to support implantation & pregnancy forms 3 layers:
1. Decidua basalis: beneath embryo where the placenta forms
2. Decidua capsularis: covers the embryo
3. Decidua parietalis: remaining lining of the uterus
This process is triggered via progesterone from the corpus luteum to prevent menstruation
Endometrial cells enlarge & accumulate glycogen to deliver nutrients to embryo before placenta is formed
Describe what the germ layers develop into
Ectoderm: The outermost layer, which will develop into the skin, CNS, enamel of teeth, dermis, hair, nails, mammary & pituitary glands
Mesoderm: The middle layer, which will give rise to muscles, bones, blood vessels, kidneys, cartilage, gonads and the heart.
Endoderm: The innermost layer, which will form the digestive system, lungs, liver, and other internal organs.
Describe the gastrulation process
Where the blastocyst forms the gastrula, making of the 3 germ layers, Gastrulation is complete when the 3 layers have been formed
1. Blastula undergoes movement & reorgansiation, cells move to form the primitive streak (invagination) , cells fold & flatten to form 3 layers
2. Primitive streak is beginning stage in gastrulation, notochord is formed (body’s oreintation)
3. Cells migrate to form germ layers, ectoderm cells remain on the surface while epiblast cells move towards mesoderm & endoderm
4. Gastrulation is pivotal because it lays the foundation for the overall body plan, setting up the basic organization of tissues and organs in the embryo.
Secondary & tertiary villi begin to form, a yolk and amniotic cavity is formed
Describe the structure of the extra-embryonic membrane
Chorion formed from trophoblast, is a part of the placenta & enables exchange of gases, nutrients & waste
Blood cells are found in the yolk sac, (1st formation of RBC)
Amnion contains fluid that cushions & protects the embryo
BV’s of allantois form sections of the umbilical cord (waste removal & temp resp organ)
Define organogenesis and the key components
Occurs after Gastrulation, where the 3 germ layers develop into organs
Key stages:
1. Neurulation: formation of the NS starting with the neural tube which becomes brain & SC, ectoderm forms the neural plate which folds to form the neural tube
2. Somite formation: In the mesoderm, somites form on either side of neural tube, somites form vertebrae & muscles of trunks & limbs
3. Vasculogenesis: The development of blood vessels begins with vasculogenesis (the formation of blood vessels from endothelial cells) and is followed by angiogenesis (the growth of new blood vessels from existing ones). This is important for supplying nutrients and oxygen to growing tissues.
Describe how organogenesis is regulated
It is regulated via cell signaling pathways & molecular cues
They regulate stem cell & pattern tissues
1. Growth factors like FGFs (Fibroblast Growth Factors), BMPs (Bone Morphogenetic Proteins), and Wnts guide the development of specific organs.
2. Homeobox genes (Hox genes) play a significant role in defining the body’s structure, controlling the positioning of limbs and organs along the anterior-posterior axis.
Describe the importance of germ layers
The 3 germ layers of mesoderm, endoderm & ectoderm develop into organs and tissue during organogenesis
endoderm-digestive system, lungs, liver, and other internal organs.
mesoderm- muscles, bones, blood vessels, kidneys, cartilage, gonads and the heart.
ectoderm-which will develop into the skin, CNS, enamel of teeth, dermis, hair, nails, mammar3ry & pituitary glands
all are involved in enabling cell signaling allowing the development of organs to be regulated
Describe hematopoiesis in embryonic development
Yolk sace: yolk sac is the earliest source of RBC (3rd week), and contains stem cells that give nourishment and give rise to erythrocytes
Liver: At 5th week of development yolk sac begins to decline and liver becomes site of RBC production for several months
Bone marrow: By the end of development the bone marrow has taken on the responsibility of producing RBC & WBC, this continues after birth & through life
Describe Vasculogenesis:
This process refers to the initial formation of BV’s from angioblasts & precursors cells to form endothelial cells that line BV’s
1. Mesodermal cells differentiate to form angioblasts when then cluster together into networks to form blood islands
2. In these islands the angioblasts develop to form endothelial cells which form the walls of BV’s
3. Some cells in island become Haemopoietic stem cells that go on to form RBC
4. Angioblasts form small tubes that fuse into networks, these networks serve as the initial circulatory system allowing oxygenated blood to be delivered to the embryo
Describe the stages of development in the heart during embryonic development
Heart develops from specialized mesoderm known as cardiogenic mesoderm.
1. Day 18/19 Endocardial tubes develop either side of the embryo, lie in front of the embryo, they fuse eventually and form a single primitive heart tube by day 22/23, first heartbeat can be heard around this time
2. The tube undergoes further changes, it loops to form the basic shape of the heart, creating space for an atria & ventricle
3. day 27-30 the septum forming more distinct chambers & valves from endocardial cushions
4. day 38 the conductions system begins to develop including SAN, foramen ovale & ductus arteriosus directs blood flow
5. Heart continues to mature during pregnancy and after birth. By the 8th week the heart is fully functioning allowing oxygen and nutrients to be delivered
Define the ductus arteriosus
A vessel that connects the pulmonary artery to the aorta allowing blood to bypass the lungs, after birth the DA constricts and closes causing blood flow to be redirected
Describe the development of the lungs
The lungs are formed from the endoderm (foregut)
1. At 4th week of development the laryngotracheal groove appears, deepens & forms the laryngotracheal tube which develops into the lungs & trachea
2. At 5th week Bronchioles develop from resp buds, these elongate to form 1st, 2nd & 3rd bronchi
3. Week 16 bronchioles become more specialized and form terminal bronchioles, these are the last branches in the conduction zone
4. At 24 weeks resp bronchioles develop & divide further to form alveolar ducts, aveloar ducts cluster to form alveolar sacs, they are immature and do not have a fully developed blood barrier
5.At week 24-28 lung surfactant is produced via type 2 alveolar cells to reduce alveolar tension & prevent collapse, the alveoli continue to develop and increase in number
6. : By 36 weeks of gestation, the lungs are mature enough to function after birth, though they continue to develop during the first few years of life. The lungs are fully capable of gas exchange at birth, although the alveolar structures will continue to mature.
Describe a baby’s first breath
Lung Volume Expansion: At birth, the lungs expand rapidly as the baby begins to breathe air. The transition from fluid-filled lungs (in utero) to air-filled lungs requires a significant physiological change.
The first breath is typically a deep, powerful inhalation, The baby’s lungs expand for the first time, and the air pressure helps to push out the amniotic fluid that had been in the lungs, especially from the alveoli
Ductus arteriosus & foramen ovale close to redirect bloodflow to the lungs, placental connection is no longer needed
Describe the development of the gut
On day 28 the GI bulges out to form the stomach
Endoderm forms gut tube which is divided into for, mid and hindgut (colon & rectum)
Midgut (small intestine/cecum) undergoes rotation & returned to abdominal cavity, the gut becomes fixed via peritoneum
Liver, gallbladder & pancreas develop from buds in the foregut
The gut becomes specialized, villi and lymphoid tissue is developed
Describe what occurs during 9-12 weeks in foetal development
Eyelids meet & fuse, fingernails form
Gut develops
Uterus is still a pelvic organ
up to 12 weeks infectious diseases e.g., HIV can be screened
up to 10 weeks sickle cell can be screened
10-14 weeks genetic syndromes e.g., down syndrome can be detected
Describe the events that occur during 13-16 weeks
Ossification occurs (bone tissue is formed) uterus becomes an abdominal organ, fetal movment can be detected 16+ weeks
Lanugo hair forms over fetal body
Describe the events that occur during 17-20 weeks
Myelination of the spinal cord, signals are able to be transmitted, eyelids still closed, sebaceous glands are active
screening for congenital heart defects is possible
Describe the events that occur during 21-25 weeks
They are viable at 24 weeks, baby born after 24 weeks will be kept in NICU as lungs are not fully developed so need assistance
Describe the events that occur during 26-29 weeks
Eyes open, hair thickens, testes in scrotum and skin thickens
Describe the events that occur during 30-34 weeks
Growth
Describe the events that occur during 34-37 weeks
Brain becomes myleinated
Brown fat stores are laid down and lungs are fully developed
Describe the events that occur during 37-42 weeks
Foetus is fully developed and in gestation
Define the role & importance of the placenta
The placenta is made from uterine wall & embryonic tissue, developed from trophoblasts
Needed for:
1. Nutrient & gas exchange to allow the foetus to receive glucose, A.A’s etc & O2
2. Hormone production: e.g., HcG, HPL, oestrogen, progesterone etc, to enable uterus thickening and preparing body for birth
3. immune protection: Placenta acts as a barrier to certain pathogens, providing a level of immune protection, enable transfer of antibodies from mother to baby
4. Removes waste: e.g., urea & creatine to mothers kidneys for filtration
Describe the structure of the placenta
1.Maternal side: Connected to uterine wall, has spongy decidua that has BV’s to enable exchange of nutrients & waste, highly vascularised to enable exchange of gases between baby & placenta
2. Fetal side: Connected to the foetus via the umbilical cord which has 2 arteries and a vein, vein carries oxygenated blood and nutrients to foetus from placenta. Arteries carry waste and CO2 to placenta, BV’s embedded in villi to increase the SA for nutrient and gas exchange
Maternal side: brings oxygenated blood to the placenta from the mother.
Fetal side: carries oxygenated blood from the placenta to the fetus via the umbilical vein.
- Placental barrier: A thing barrier that seperates the maternal & foetal blood, prevents mixing of blood to give a strong diffusion gradient
Describe the 3 labor stages
Stage 1: Early labor, lasts 6-12 hrs, involves cervix dilating from o to 10cm, strong contractions, water breaking
Stage 2: delivery of baby, lasts 1-2 hours, cervix is dilated to 10cm, intense contraction push baby through cervical canal, baby is born
Stage 3: delivery of placenta, takes 5-30 mins, placenta detaches from uterine wall & is expelled from uterus after birth of baby
Describe the role of FSH, LH, progesterone & oestrogen in pregnancy
FSH: Stimulates the maturation of the primary follicle & production of oestrogen
LH: Stimulates ovulation, formation of corpus luteum, stimulates oestrogen & progesterone production
Oestrogen: Grows & matures reproductive organs, stimulates uterine & mammary gland growth, enables sperm capacitation, enables oogenesis, promotes feminization of bone skeleton, promotes female fat deposit & libido
progesterone: released via corpus luteum 6 weeks after pregnancy, increases body temp, quietens myometrium, promotes secretory phase and breast growth
Describe the role of HcG, HPL, relaxin & prolactin in pregnancy
HcG: produced via placenta, Maintains corpus luteum enabling secretion of progesterone, detected in pregnancy tests, stimulates progesterone and oestrogen production
HPL: Promotes maternal metabolism to enable nutrient supply to foetus, stimulates breast development in preparation for milk
Relaxin: relaxes the joints/ligaments in pelvis to prepare for childbirth, inhibits uterine contractions to prevent premature labor
Prolactin: stimulates milk production in breasts after birth & supports breast tissue
Describe the role of testosterone, oxytocin, CRH & thyroid hormones in pregnancy
Testosterone: promotes growth of genitalia in males & brain development in both sexes
Oxytocin: stimulates uterine contractions during labor & promotes milk production & bond between mum and child
CRH: Regulates timings of labor & development of foetal adrenal glands
TSH: Regulates metabolism during pregnancy & promotes normal growth & development
