Embryology Flashcards
What is the Allantois?
A disposal sac for certain metabolic wastes produced by the embryo. The membrane of the allantois also functions with the chorion as a respiratory organ
What is the Chorion?
Together with the allantois, exchange gases between the embryo & the air. Allows oxygen & carbon dioxide to diffuse freely across the shell
What is the Yolk sac?
Contains the yolk, a stockpile of nutrients. Blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo
What is the Shell?
Protects the embryo and keeps it from drying out, but it flexible to allow gas exchange. Can be leathery
What is the Amniotic cavity?
Filled with the amniotic fluid, protects the embryo, cushions against mechanical shock
What is the amnion?
The membrane surrounding the amniotic cavity
At some stage of life, all vertebrata have 8 characteristics. Name three.
- Brain
- Mouth
- Dorsal, hollow nerve cord
- Pharyngeal slits or clefts
- Anus
- Notochord
- Muscle segments
- Muscular, post-anal tail
What three characteristics distinguish vertebrates from other chordates? Briefly describe.
- Vertebral column: vertebrae; series of bones that make-up the back bone and surround dorsal nerve cord
- Cranium: or skull; bone that surrounds and protects the brain
- Endoskeleton: internal skeleton of cartilage or bone
What is an embryo?
The phase between fertilisation and birth
To become an embryo, 4 things had to be done. What were they?
- Build from a single cell
- Respire before lungs
- Digest before a gut
- Form orderly arrays of neurons before “thinking”
Starting at Maturation, what is the vertebrate life cycle of fertilisation
(1) Maturation
(2) Spermatogenesis/Oogenesis
(3) Fertilisation (Zygote)
(4) Cleavage (Blastula)
(5) Gastrulation (Germ layers)
(6) Neurulation (Nervous system)
(7) Organogenesis (Organs)
(8) Cytodifferentiation (Specialised cells)
(9) Individual Life
(10) Growth
(1) Maturation
Steps 3 through 8 are part of EMBRYOGENESIS
Briefly describe the difference between Oviparous, Viviparous & Ovoviviparous
Oviparous: Develop & Hatch in egg
Viviparous: Develop within mother & produce live young
Ovoviviparous: Similar to viviparous & produce live young - NO PLACENTA e.g. sharks
What does isolecithal mean?
Large distribution of yolk - Nucleus & cytoplasm within yolk
Mammals
What does Telolecithal mean?
Yolk is found within the cytoplasm at the vegetal pole. Nucleus is found at the animal pole
Reptiles & birds
What does Centrolecithal mean?
Nucleus is within yolk, yolk is within cytoplasm
spiders
What does Microlecithal mean?
Small amount of yolk - mammals
What does Mesolecithal mean?
Small amount of yolk - amphibians
What does Macrolecithal mean?
Large amount of yolk - fish, reptiles & birds
Briefly describe cleavage
- Series of mitotic division
- From zygote to morula to blastula/blastocyst
What are blastomeres?
Individual cells during cleavage
What is a blastocoel?
cavity in the blastula
What is a holoblastic?
Full cleavage - microlecithal
What is a meroblastic?
- Partial cleavage - macro & telolecithal
What is the subgerminal space?
Cavity between blastoderm & yolk
What is a trophoblast?
Cell forming the outer layer of a blastocyst. Provides nutrients to the embryo and develops into a large part of the placenta
Amphibians and mammals use _______ cleavage.
Birds and reptiles use _________ cleavage.
Holoblastic
Meroblastic
What are the three embryonic germ layers?
- Endoderm
- Mesoderm
- Ectoderm
What is neurulation?
The folding process to form the neural tube which becomes the spinal cord and CNS. Notochord signals thickening the ectoderm germ layer to form the thick and flat neural plate which fold in upon itself to form the neural tube
What is organogenesis?
The series of organised integrated processes that transforms an amorphous mass of ells into a complete organ in the developing embryo
Briefly describe the ectoderm germ layer
- Skin (outer layer)
- Nervous system
- Neural crest cells
Briefly describe the endoderm germ layer
- Intestines
- Lungs
- Liver
- Pancreas
What is the archenteron?
Primary gut that is formed during gastrulation
Briefly describe the Mesoderm
Paraxial Mesoderm:
- Connective tissues of the back: Vertebrae, ribs
- Muscles of the back: ribs & limbs
- Dermis (skin)
Intermediate Mesoderm:
- Circulatory system; Heart, blood vessels
- Lining of body cavity
- Mesodermal components of limbs (not muscle)
What is considered the ectoderm?
- Epidermis of skin and its derivatives (including sweat glands, hair follicles)
- Epithelial lining of mouth and rectum
- Sense receptors in epidermis
- Cornea and lens of eye
- Nervous system
- Adrenal medulla
- Tooth enamel
- Epithelium or pineal and pituitary glands
What is considered the mesoderm?
- Notochord
- Skeletal system
- Muscular system
- Muscular layer of stomach, intestine, etc.
- Excretory system
- Circulatory and lymphatic systems
- Reproductive system (except germ cells)
- Dermis of skin
- Lining of body cavity
- Adrenal cortex
What is considered the endoderm?
- Epithelial lining of digestive tract
- Epithelial lining of respiratory system
- Lining of urethra, urinary bladder, and reproductive system
- Liver
- Pancreas
- Thymus
- Thyroid and parathyroid glands
In the timeline of organogenesis, what occurs at each one of these turn points:
Week 3?
Week 4?
Week 5?
Week 6?
Week 7?
Week 8?
Week 3:
Brain
Heart
Blood
Week 4:
Bones
Facial structure
Arm & leg buds appear
Week 5: Eyes Nose Kidneys Lungs
Week 6:
Hands
Feet
Week 7: Hair follicles Nipples Eyelids Sex organs Urine first formed
Week 8: Facial features more distinct Internal organs now more developed The brain can signal muscle movement External sex organs begin to form
What is Oestrous?
ADJECTIVE, refers to the entire cycle
What is Oestrus?
NOUN, refers to the phase in which the animal can get pregnant
What is a spontaneous ovulator?
Ovulates at a regular period
What is an induced ovulator?
Ovulates upon mating
i.e. felines, camels etc.
What is a polyoestrous animal?
Oestrous cycles throughout the year
What is a seasonal polyoestrous animal?
Multiple oestrous cycles at certain periods
What is a non-seasonal polyoestrous animal?
Cycles all year long
What is a monoestrous animal?
Single oestrous cycle per year
Give examples of steroids in the oestrous cycle.
What is the function of a steroid?
Can traffic entire body, BUT only act on specific cells
Oestrogen, Progesterone, Testosterone
Give examples of peptides in the oestrous cycle.
Follicle Stimulating Hormone & Luteinising Hormone
What does HPG stand for?
Hypothalamus/Pituitary/Gonadal
What does the hypothalamus produce?
GnRH
What is the role of the pituitary gland?
Key role in regulation of vital body functions, e.g. metabolism, growth, sexual maturation, reproduction
Briefly describe Testosterone
SEX SPECIFIC:
- Essential for spermatogenesis
- Develops sex drive
- Controls GnRH secretion
- Maintains reproductive tract through adulthood
SEXUAL CHARACTERISTICS:
- Induces male hair/feather growth
- Causes voice to deepen by thickening of vocal chords
- Promotes muscle growth
Briefly describe Oestrogen & Progesterone
- Triggered by GnRH
- Synthesised from the ovaries
- Prepare reproductive system for pregnancy
- If no fertilisation production stops and uterine lining breaks down
OESTROGEN:
- Dominates first half of cycle - FOLLICULAR PHASE
- Permits copulation and release of ova
- Promotes fertilisation
PROGESTERONE:
- Levels high in the LUTEAL PHASE
- Progesterone produced by the CORPUS LUTEUM
Briefly describe the Placenta
- 4000 described placental mammals
- The first of the foetal organs to develop
- Produces several hormones
- The placenta takes over as the main producer of progesterone & oestrogen
- TROPHOBLASTS are able to convert cholesterol from the mother’s bloodstream into progesterone
Briefly describe progesterone during pregnancy
- Establishes & eventually produced by PLACENTA
- Dominates throughout pregnancy
- Levels rise steadily until birth
- Increases blood flow to the womb
- Stimulates glands in the lining of the womb to produce nutrients that sustain the early embryo
- Stimulates the endometrium to grow and become thickened
- Maintains pregnancy by preventing womb contracting until ready
- Prepares for labour
- Prevents lactation
Briefly describe oestrogen during pregnancy
PRODUCED BY THE PLACENTA
- Levels of oestrogen increase steadily until birth
- Stimulates growth of uterus
- Controls the production of other pregnancy hormones
- Involved in development of many foetal organs; Lungs, liver & kidneys
- Promotes growth of maternal breast tissue (with progesterone)
- Contribute to mammal gland development & prepares for lactation
Briefly describe oxytocin
- “The love hormone”
- Is associated with feeling of bonding and motherhood
- Levels of oxytocin receptors rise triggered by oestrogen
- Causes regular CONTRACTIONS
A posterior pituitary hormone and the strongest simulator of uterine contractions. During labour, prostaglandins stimulate myometrial contractions.
Briefly summaries Parturition
Two things MUST happen:
- The muscles in the womb and abdominal wall have to contract
- The cervix needs to soften or ripen
Oestrogen is the most important hormone in preparation for parturition. It stimulates:
- Oxytocin receptors - increasing the activity
- The synthesis of prostaglandin
- Gap junctions
Pre-labour prostaglandins stimulate cervical ripening, the breakdown of cervical connective tissue allowing it to become soft and flexible and capable of dilation.
Briefly describe Prolactin
- A key hormone in preparation for lactation
- Has more than 300 functions in the body; Osmoregulation, Immunoregulation, behavioural functions etc.
- Produced in the anterior pituitary gland
- Also produced in the uterus, breasts prostate, immune cells, brain etc.
- Oestrogen also a key regulator of prolactin and increases the productions
What hormone causes milk to be squeezed out of the alveoli, into the ducts and out of the nipple?
What is the process called?
Oxytocin
Letdown or Milk Ejection Reflex (MER)
What are environmental factors that are key for successful reproduction?
- Photoperiod
- Season
