Embry and phys exam Flashcards
Prenatal development, what is the embryonic period and the foetal period?
Embryonic period = the establishment of all major organ systems.
Foetal period = Growth of embryo and organ refinement.
What is a zygote?
The zygote is a one cell embryo in which the maternal and paternal pronuclei fuse in a process called syngamy.
What is syngamy?
The fusion of the maternal and paternal pronuclei.
Describe the blastomere and the process of its formation?
Second stage of embryo.
The first process of mitosis when the one cell zygote first develops into the two cell blastomere. Progresses through to the eight cell stage.
This occurs through the process of cleavage, where an increase in cell number is not accompanied by an increase in cell volume. Overall volume of embryo remains constant.
What are the general events associated with gastrulation.
It is the formation of three somatic germ layers ectoderm, mesoderm and endoderm (primordial cells).
recognised by the initial formation of the primitive streak.
Conversion of the bilaminar disk to the trilaminar disc. This occurs by the folding of the trophectoderm over the bilaminar layer resulting in the three somatic germ layers.
Describe amnion formation?
Results from a gradual upfolding of the trophectoderm.
What are mes-endodermal precursers?
Cells which are capable of developing into endoderm or mesoderm
What will the epiblast develop into?
The epiblast will develop into all of the embryonic cell lineages ectoderm, endoderm and mesoderm.
During gastrulation what happens to the endoderm ?
The endoderm gradually displaces the hypoblast and develops into the upper protion of the yolk sac.
At a later stage these endodermal cells will develop into the primative gut.
What is the primitive streak?
Accumulation of epiblast cells at the caudal pole that gather along the midline.
ngression of epiblast cells into the space between epiblast and hypoblast.
- First morphological sign of gastrulation
- Cresent shaped thickening of the embryonic disk
- Epiblast cells which ingress through the streak become mes-endodermal precursors
- Defines the cranio-caudal axis
- primitive node develops at the end of the streak
- ingression of epiblast cells to the sapace is initiated
Describe what happens to the mesoderm germ layer?
Mes-endodermal cells differentiate into endoderm and mesoderm under the epiblast and trophectoderm.
The mesoderm cells then
- Intraembryonic mesoderm develops into connective tissue, bone, muscle and stays within the embryo.
- Extraembryonic mesoderm develops into visceral mesoderm and somatic mesoderm
- Somatic mesoderm = trophectoderm
- viseral mesoderm = part of hypoblast and definitive yolk sac
The extraembryonic mesoderm grows out of the periphery of the embryonic disk.
Describe the development of the notochord?
Epiblast cells ingress through the primitive streak and form the notochord.
- Rod of mesoderm directly below the primitive streak
- primary inducer of neuraltion in the underlying epiblast
- induced via sonic hedgehog
- runs the entire length of the embryo
Describe the formation of the amnion ?
Amnion cavity
- Chorion forms fold that fuse above the embryonic disk which forms the amnion.
- The chrion forms from trophectoderm lined with somatic mesoderm
- sealed amniotic cavity
- fluid filled cavity which insulates foetus from shocks
Describe the formation of the allantois membrane?
Out pocket of hypoblast cells
- Forms umbilical cord and allantoic - chorionic placenta
- develops between the second - third week of development.
- respiratory of waste products.
How does the yolk sac develop ?
The yolk sac develops from the hypoblast and visceral mesoderm.
The yolk sac develops as a fluid filled cavity which provides a brief period of nutrient support to the embryo.
Describe the process of neuralation?
Neurulation is the develpment of the neural tube. eg. the central nervous system brain and spinal cord.
Process
- Notochord sonic hedgehop signaling molecule induces overlying epiblast to differentiate into neuroectoderm
- neural folds form on either side of the midline depression
- neural plate becomes elevated to form neural folds which fuse over to form the neural tube.
- neural crest above - neural tube - notochord.
- process of the embryos first embryonic organ system the neural system, brain and spinal cord
- neural tube seperates from overlying ectoderm
Describe what paraxial mesoderm is, and what it develops into?
Paraxial mesoderm is the mesoderm which surrounds the notochord.
The paraxial mesoderm proliferates into paird thick clustors of
Somitomeres = head region
Somites = body region
- somites differentiate in sclerotomes (bone and vertebrae), myotome (skeletal muscle), and dermatome (dermis).
- Somitomeres head region develop into connective tissue and cartilage together with lateral plate mesoderm
What is the central nervous system?
The brain and spinal cord
What is the peripheral nervous system? and what two systems can it be diveded into?
The peripheral nervous system includes all nerves which attach the central nervous system to the limbs and organs.
The peripheral nervous system can be divided into
Somatic nervous system = volunatry control of skeletal muscle
efferent or motor nerves and afferent sensory nerves.
The parasympathetic nervous system
= involunatry physiological responses.
Describe the parasympathetic nervous system?
The parasympathetic nervous system is derived from the parasympathetic nervous system
- responds to relaxation
- preganglionic neurons cranial and sacral regions
- brain stem and and lateral column of sacral region of spinal cord.
Describe the sympathetic nervous system?
The sympathetic nervous system is derived from the autonomic nervous system.
- responds to fight or flight
- paravertebral ganglion
- from cranial to sacral regions all along the spine.
Describe the enteric nervous system?
Consist of a mesh like network of neurons from the neural crest to the hind brain (rhombencephalic) and sacral regions.
- Operates autonomously from the brain and spinal regions.
- vagus nerve
- embedded in the linning of the gastrointestinal system (submucosa and myenteric plexuses), between smooth muscle layers in the gut linning
Describe the (5) steps of neuralation ?
- Notochord releases sonic hedgehog inducing the columnar epithelium to become pseudostratified neuroepithelium cells forming a neural plate.
- The lateral edges of the neural plate form neural folds, while the midline of the neural plate forms a neural groove.
- Neural crest cells migrate from the neural fold
- Neural folds eventuallly met at the midline and fuse foring the neural tube structure.
Describe the steps from development of the neural tube to development of the spinal cord ?
The neuroepithelium of the neural tube becomes thickened and differentiated into three layers.
Inner most layer epidymal layer
middle layer Mantle layer
- conatins cell bodies of neuroblast and presumptive glia cells
- becomes inner grey matter of the spinal cord
- dorsal thickness of mantle layer = alar plate or dorsal horn
- ventral thickness of mantle layer = basal plate or ventral horn
The two alar and basal plates eventually expand and the four plates fuse forming the characteristic butterfly shape of the spinal cord.
Outer = marginal layer
- inner grey matter migrates to form marginal layerof the white matter of the spinal cord
- white matter consist of mylinated axons.
Sulcus limitans = left and right longitudinal groove which eventually disappear, as the neural canal eventually reduces becomming the central neural canal
During development of the spinal cord what is the Sulcus limitans, and what dose it do?
The sulcus limitans forms left and right longitudinal grooves from the inner cell wall of the central neural canal.
During development the neural canal becomes reduced and the sulcus limitans disappear, becomming the central canal.
During development of the spinal cord, what happens to the neural crest cells?
During fusion of the neural folds, a population of specialised cells develop from the neuroepithelium - lateral side of folds
the neural crest
- extends along the neural tube
- dorsal position
- develops into the root ganglion of the spinal nerve (autonomic nerve and glia cells)
- peripheral processes from the marginal layer of the spinal cord joins the root ganglion to form the trunk of spinal nerves.
Describe the three brain flexures which occur during development?
Brain flexure = bend
Differential growth of the five brain parts leads to the development of three brain flexures.
- Cephalic flexure, occurs in mid brain (mesencephalon)
- Cervical flexure, occurs between the Rhombencephalon and spinal cord
- Pontine flexure, occurs dorsally bending between metencephalon and myelincephalon of the hind brain.
What is the choroid plexus?
Develops within the fourth ventrical and produces cerebrospinal fluid
Describe the myelencephalon ?
The myelincephalon is part of the Rhombencephalon caudal to the pontine flexure.
- Develops into the medulla oblongata
- Medulla oblongatat acts as a relay centre for neurological signals spinal to the brain
- vital centre for HR, BP and RR
- consist of alar and basal plates seperated by the roof and floor of the fourth ventricle. (alar plate located laterally to basal plate).
Describe the metencephalon?
The metencephalon is part of the hind brain ( Rhombencephalon), which is cranial of the pontine flexure.
Characterised by the pressence of basal and alar plates.
Pon
Serves as a pathway for nerve fibres between the cerebrum and cerebellum.
Sleep, respiration and sallowing
Cerebellum
Motor control, posture, auditory and visual reflexes
Describe the mesencephalon ?
Forms four aggregations of neuroblast the rostral and caudal colliculi.
- associated with visual and auditory functions respectively
- serves as a pathway for nerve tracts descending from cerebrum to pon and spinal cord CN3 and CN4
Due to expansion of the alar and basal plate the neural canal is reduced in size forming the aqueduct.
Describe the Diencephalon ?
Derived from the forebrain (Prosencephalon)
Basal plate are absent
formed via left and right alar plates.
A cavity within the diencephalon is known as the third ventricle.
Consist of three
- Epithalamus = includes pineal gland melatonin
- Thalamus = relay centre for sensory impulses (visceral)
- Hypothalamus = regulates hormones of endocrine glands
- Optic cups vesicles = gives rise to the retina CN2
Describe the Telencephalon?
Located dorsally over the dicephalon, mesencephalon and rostral area of the hind brain.
Develops into the cerebral hemispheres and olfactory bulbs (CN1)
There are paired cavities within the Telecephalon known as lateral ventricles which communicate with the third ventricle through the interventricular foramen.
The L and R cerebral hemispheres are seperated by the longitudinal fissure.
What is the ectomenix and endomenix?
Ectomenix
- Dura matter
- derived from axial mesoderm
Endomenix
- Arachnoid matter and pia matter
- derived from the neural crest
What tissues from the subarachnoid space, subdural space and epidural space?
Subarachnoid space
- arachnoid matter - pia matter
- contains cerebrospinal fluid CSF
Subdural space
- Dura matter - arachnoid matter
- no cerebrospinal fluid
Epidural space
- between dura matter and vertebral wall
- contains cerebrospinal fluid
- There is no epidural space within the brain as the dura matter is fused with the periosteum of the cranium skull.
Somites produce Sclerotomal, dermomyotome and myotome cells what do these become, and where are they located?
Sclerotomal cell
Transform into mesenchymal cells which migrate toward the notochords and neural tube becomming vertebral columns.
Dermomyotomes
Becomes the dermis of skin
Myotomes
Dorso medial becomes epimere, and dorso lateral becomes hypomere
What will the somite, lateral plate mesoderm and cranial neural crest develop into?
Somite = axial skeleton
Lateral plate mesoderm = limb skeleton
Cranial neural crest = craniofacial bones and cartilage + branchial arches.
Describe cartilage ?
- Forms from sclerotomes
- special connective tissue
- Stronger than other connective tissues and more flexible
- ECM = collagen, proteoglycan produced by chondroblast
- surrounded by connective tissue sheet perichondrium
- Two types of cartilage growth interstitial and appositional.
What is interstitial growth?
Interstitial growth
One pattern of cartilage growth
Chondroblasts grow into chondrocytes dividing by mitosis into isogeneous groups
daughter cells produces new ECM to create more cartiliginous mass.
What is appositional growth?
Appositional growth
Is a pattern of cartiliginous growth
- Where mesenchymal cells in the perichondrium differentiate into chondroblasts and eventually chondrocytes
- formation of new chondrocytes
Describe bone ?
Bone is a specialised tissue which has mineralisation in the matrix ( high strength and low flexability)
- Osteoblast osteoprogenitor cell from sclerotomes and mesenchymal cells
- Osteocyte mature osteoblast more embedded within the mineralised ECM
- Osteoclast large multinucleated cell which reasorbs mineralised bone
There are two types of ossification intramembranous ossification and endochondral ossification.
What is intramembranous ossification?
This is when mesenchymal cells produce bone
from periosteum - osteoblast - osteocyte
= flat bones
What is endochondral ossification?
Mesenchymal cells differentiate into cartilage which is replaced by bone tissue (epiphyseal growth plate).
long bone from cartilage template eg growth plates
Describe a morula and the process of compaction?
A small berry like cluster of cells know as a morula
- more than 8 ceells, next step after blastomere
- initially the morula is characterised by bulging blastomeres.
Compaction
- the outer cells interconnect and flatten forming a more uniform surfaceof the morula = trophectoderm
- outer cells connected by tight cell junctions / desosomes, the inner cells are connected by gap junctions.
What does CDX2 initiate as a transcription factor ?
Developement of the outer cells = trophoblast
differentiation (foetal placenta chorion).
Describe the process of blastulation, and bilaminar disc formation ?
The first step of differentiation
- Outer cells develop into the trophectoderm (foetal placenta)
- inner cells develop into the inner cell mass (ICM) or embryo proper, which gather at one pole of the embryo
- usually occurs within the uterine lumen
- first differentiation event
Process of blastulation
- A fluid filled cavity develops inside the trophectoderm, and a blastocyst is formed.
- Na+ pumped into morula = water influx
- expanding of the blastocyst eventually leads to rapture of the zona pellucida
Bilaminar disc formation
- expanded blastocyst hatches from the zona pellucida (polyspermy barrier)
- Towards the end of blastulation the ICM forms a epiblast and hyperblast
- Erosion of the overlying trophectoderm forms the bilaminar disc
What does Oct 4 transcription factor initiate ?
Differentiation of the inner cell mass into the embryo proper.
What does the nanog transcription factor do ?
Nanog specifies epiblast development into the embryo proper
What does the Gata 6 transcription factor do ?
Specifies development of the hypoblast into the epithelium of the yolk sac.
The hypoblast eventually develops into the ?
The hypoblast expands to line the trophoblast forming the primitive yolk sac.
Describe the diffuse placenta ?
Diffuse placenta
- Chorion is diffusely distributed over the entire chorioallantoic surface
- simplified chorionic villi
- uterine contact occurs over most of its surface.
- horse and pig
Describe the coteldonary placenta ?
Cotelydonary placenta
- cotyledons foetal, caruncles maternal
- coteldons and carnuncles = placentomes
- conves cow, concave sheep
Zonary placenta?
Zonary placenta
- Zonary in the dog, double in the ferret
- band like zone of chorionic villi around the middle of the conceptus
Describe the discoid placenta ?
Discoidal placenta
- spherical disc of chorionic villi that invades the endometrium
- trophectoderm is highly invasive
- the blastocyst penetrates the endometrial epithelium
- the trophoblast covered foetal villi are directly surrounded by maternal blood.
What is the epitheliochorial placenta ?
Epitheliochorial placenta
- contains all six tissue layers
- least invasive type of attchment
- horse and pig
Describe the six tissue types within the histological structure of the placenta?
Histological structure there are six tissue types.
Maternal
- maternal capillary endothelium
- maternal connective tissue
- maternal epithelium
Foetal
- chorionic epthilium
- foetal connective tissue foetal capillary endothelium
Describe the synepitheliochorial placenta ?
Synepitheliochorial
- six layers present
- more invasive due to binuclear trophoblast into uterine lumen epithelium
- cow
Describe the syndesmochorial placenta ?
Syndesmochorial placenta
- Five layers present
- small ruminants (sheep)
- loss of uterine epithelium
Describe the endotheliochorial placenta ?
Endotheliochorial placenta
- 4 layers
- 3 foetal, one maternal remaining
- loss of maternal epithelium, and connective tissue
- dogs and cats
Describe the Haemochorial placenta ?
Haemochorial placenta
- highly invasive
- only three layers remaining all foetal
- loss of maternal connective, epithelium and endothelium
- rodent, monkey and man
Describe the haemoendothelial placenta ?
Haemoendothelial placenta
- very extreme only one layer remaining
- maternal blood in contact with the foetal endothelium
- lagomorphs rabbits
What is the resting membrane potential and how is it maintained (3) ?
The electrical potential measured across the cell membrane, when a cell is at rest
negative inside / outside positive polarised.
excess of negative ions inside the membrane
How is this maintained
- more K+ leak channels, than NA+, thus more K+ leaks outside the cell
- proteins are predominantly found within the cell (negatively charged)
- Na+/K+ pump inside 2K+ / outside 3Na+
What is an action potential
Action potential
- rapid change in membrane potential, which is followed by a return to resting membrane potential.
- ability of a cell to produce an action potential = excitability
- caused by voltage gated ion channels.
- all or none law- must reach threshold
- amplitude is independant of stimulus, all AP is of identical magnitude
- refractory period = unidirectional
- self perpetuating
- no summation
Describe the four phases of an action potential and what causes them ?
The four phases of an action potential
Polarised state
- resting membrane potential
Depolarisation
- voltage gated Na+ channels open, results in a influx of Na+ into the cell
Repolarisation
- voltage gated Na+ channels close
- K+ voltage gated channels open, thus K+ leaves neuron repolarising it
Hyperpolarisation
- Voltage gated K+ channals are slow to close
- eventually Na+/K+ pump restores RMP
What is the absolute refractory, relative refractory and refractory period ?
Refractory period
The refractory period is the time after an action potential has been elicited, the membrane will resist eliciting a further AP until RMP has been restored
Absolute refractory period
- period from depolarisation until 2/3rd of repolarisation.
- can not induce a second AP
- Na+ channels open or inactivated
Relative refractory period
- end of absolute refractory to RMP is achieved
- may be elicited if a stronger than normal stimulus is applied
- some Na+ recovered and closed
What is the synapse, and how dose it work?
The synapse
- junctional region between two neurons
- electrical direct contact, chemical gap junctions neurotransmitter
- majority of neurons receive signals from a multitude of neurons.
Process
- action potential arrival in presynaptic neuron opens voltage gated Ca2+ channels allowing Ca2+ to enter the cell.
- Ca2+ causes fusion of the synaptic vessicles within the presynaptic membrane releasing neurotransmitter into the gap junction.
- Neurotransmitter causes chemical gated ion channels to open allowing for the influx of Na+ generating a postsynaptic AP.
- degradation of neurotransmitter and closure of the ion channel.
Discuss what EPSP and IPSP means ?
Postsyaptic potentials
Excitory synaptic potential (EPSP)
- induces influs of positive ions Na+
- depends on the type of ion channel enclosed by the receptor on the postsynaptic membrane
Inhibitory postsynaptic potential (IPSP)
- neurotransmitter causes influx of negative ions (CL-) or efflux of positive ions
- inhibits potential
Describe the structure of a sacromere ?
Sacromere
actin = a thin filament
myosin = thick filament with myosin heads
elastin filaments connect the two = spring
Describe the process of muscle contraction ?
Muscle contraction
- Sliding filament mode os muscle contraction
- cross bridge attachments form and break several times during contraction
- thin filaments moved in towards the centre of the sacromere
- Calcium binds to tropinin which shifts the tropomyosin exposing the G actin
- myosin binds to actin and complets a power stroke
- actin filament slides
- myosin cross brideges rotate towards the centre of the sacromere
- as the myosin head binds ATP it detaches the cross bridge from actin
- pre stroke = high energy.
Describe a neuromuscular junction and its innervation of a muscle fibre ?
Excitation of a muscle fibre through a neuromuscular junction.
- AP arrives at neuromuscular junction, depolarisation causes the opening of voltage gated calcium ion channels Ca2+.
- Ca2+ binds with the synaptic vessicles causing them to fuse with the presynaptic membrane releasing acetylcholine into the synaptic cleft.
- Acetylcholine binds to receptors on the sarcolemma causing ligand gated Na+ channels to open. This causes depolarisation and an action potential in the muscle fibre.
- AP travels along T tubules
- AP is transmitted along the T tubules causing the voltage sensitive proteins within the T tubule to change shape.
- This causes the SR calcium release into the cytosol.
Note - Ca2+ is continually pumped back into the SR by active transport.
Describe the length tension relationship ?
The forcefulness of contraction depends on the length of the sacromeres within a muscle before contraction begins.
- optimal resting length
- when thick and thin filaments have optimal overlap
- maximum force is geneerated at 80-120% of its optimal resting length
- increase or decrease in overlap reduces force of contraction produced by the muscle
Describe the various energy sources for muscle contraction ?
4-6 seconds
- ATP only energy source used directly by the muscle must be regenerated quickly (as fast as it is broken down).
10-15 sec
- creatine phosphate, high energy molecule used to restore ATP
- 100m dash
seconds - minutes
- glycogen is broken down within muscle to glucose, which is then oxidised (anerobic pathway)
hours
- aerobic pathway
- ATP is produced via several nutrient energy pathways to fuel the muscle
Discuss the histological structure of smooth muscle, and how contractions occur?
Histology of smooth muscle
- fusiform in shape
- centrally located nucleus
- no striations
- dense body
- T tubules are absent
Contraction of smooth muscle
- in most cases two sheets of smooth muscle exist, orientated at right angles to each other (intestines)
- peristalsis (mixing contents in the lumen of an organ)
- sacroplasmic reticulum is rduced (half T tubules), only some Ca2+ is released from the SR, the majority enters through calcium channels from the extracellular space. (caveolae)
Describe how smooth muscle contracts, how is this different to skeletal muscle?
Smooth muscle contraction
- no troponin
- calmodium acts as the binding site for calcium
- Dense bodies act as anchoring points for thin filaments, tethered to the sarcolemma.
- Ca2+ enters cytosol from extracellular fluid via voltage gated Ca2+ channels
- Ca2+ binds calmodulin
- activates myosin light chain kinase enzymes catalyze the transfer of phosphate to the myosin head, activating the myosin ATPases
- activated myosin forms cross bridges - shortening begins.
Binding to endomysium outside the cell transmitting the pulling force to the surrounding connective tissue.
Gap junctions - between smooth muscle cells allow action potentials to be transmitted from fibre to fibre.
Problems encountered with equine IVP embryos ?
Similar pregancy rates achieved, but higher rates of embryo loss
- smaller embryos, with delayed development
- higher rates of aneuplody (pressence of extra chromosomes), and apoptosis
- indistinct skeleton
- abnormal capsule formation
- most problems span the period of blastocyst formation
Explain what somites are ?
Somites
Epithelial like cells of the somite (medial and ventral walls)
Sclerotomes
- differentiate into connective tissue and bone
- Sclerotomes also transform into mesenchymal cells migrate towards the notochord and neural tube eventually developing into vertebral columns.
Dermomyotomes
- differentiates into the dermis + the major contributor somatic mesoderm
Myotome
- differentiates into skeletal muscle
- dorso medial = epimere and dorso lateral = hypomere
Describe the three distinct linages which generate the skeleton ?
Three distinct lineages form the skeleton
- Somite (sclerotomes) = provides the axial skelton (vertebral)
- lateral plate mesoderm = provides limb skeleton
- Cranial nerve crest = branchial arches and craniofacial bones + cartilage.
Describe the two different growth patterns of cartilage ?
Growth patterns of cartilage
special connective tissue develops from sclerotomes
Interstitial growth
- chondroblasts grow into chondrocytes which divide by mitosis into isogenous groups.
- daughter cells produce new ECM
- newly divided groups 2-8 cells
Appositional growth
- where mesenchymal cells of the perichondrium differentiate into chrondroblast, and eventually chondrocytes.
- formation of new chondrocytes
Describe the two different growth patterns of bone ?
Two types of bone pattern
Forms from sclerotomes
Intramembranous ossification
- mesenchymal cells form bone
- from periosteum - osteoblast- osteoclast
Endochondral ossification
- mesenchymal cells differentiate into cartilage, which is replaced by bone tissue (epiphyseal growth plate)
Describe the rhombencephalon ?
Rhombencephalon
- fourth ventricle = choroid plexus
- pontine flexure
myelencephalon = caudal pontine flexure
- medulla oblongata
- relay centre for neurological centres spinal cord to brain
- vital centre (HR, BP and RR)
Metencephalon
- rostral of pontine flexure
- pon = pathway for nerve fibres between the cerebrum and cerebellum
- cerebellum = motor control, posture and auditor and visual reflexes
Describe the mesencephalon ?
Mesencephalon
- paired rostral and caudal colliculi
- 4 aggregations of neuroblast
- associated with visual and auditory function respectively
Due to medial expansion of the basal and alar plates the neural canal is reduced to the aqueduct.
Also serves as a pathway for tracts CN3,4 descending from cerebrum to pon and spinal cord.
Describe the prosencephalon ?
Basal plates are absent, it is formed via left and right alar plates.
Diencephalon
- Epthalamus = pineal gland (epiphysis), produces melatonin, and serotonin
- Thalamus = relay centre for sensory impulses, visceral function sleep, digestion and body temperature etc.
- Hypothalamus = metabolic processes body temp, hunger. Works with pituitary gland produces hormones to control the fluctuation of endocrine glands.
Telencephalon
- located dorsally over diencephalon and mesencephalon
- develops into crebral hemispheres and olfactory bulbs
- lateral ventricles
- seperated by longitudinal fissure
- hippocampi = memory
- corpus callosum
