Embryology + Gametogenesis Flashcards
Describe the processes of mitosis and meiosis?
What are differences between the steps of mitosis and meiosis?
What are the main goals of meiosis?
- reduction of chromosome numbers from diploid to haploid in gametes
- crossing over and exchange of genetic material between male-female chromatids
- production of 4 daughter cells that are genetically distinct
What is gametogenesis?
- formation of male and female gametes (sperm and ova) from spermatogonia and oogonia
What occurs during mitosis?
- spermatogonia and oogonia (gonadal stem cells) multiply within the gonad with a full set or diploid number of chromosomes (2N)
What occurs during meiosis I + II?
- spermatocytes and oocytes are produced and exchange genetic material between male and female chromatids and divide t ensure a haploid number chromosomes (1N) in sperm/ova
What occurs during fertilization?
- a sperm penetrates an ovum to restore diploid number of chromosomes (2N) to produce a zygote
T/F: Primordial germ cell -> spermatocyte/oocyte -> spermatogonia/oogonia -> zygote
- False; Primordial germ cell -> spermatogonia/oogonia -> spermatocyte/oocyte -> zygote
What are functions of gonads?
- endocrine and gametogenic functions
What are primordial germ cells?
- primary undifferentiated stem cells that will differentiate into male and female germ cells (spermatogonia/oogonia) that will develop into male and female gametes (spermatozoa/ova) through spermatogenesis/oogenesis
- appear during early embryo development
- proliferate and migrate towards the genital ridge of the developing gonad
What are the parts of the male reproductive tract?
What are parts of the male testes?
What are key hormones in the male gonad?
- gonadotropic releasing hormone (GnRH)
- follicle stimulating hormone (FSH)
- luteinize hormone (LH)
- testosterone (and androgen binding protein)
- inhibin
What is the purpose of leydig cells? Sertoli?
- Leydig cells:
- responds to LH to produce testosterone or other androgens that aid in sexual development
- provides support to Sertoli cells
- Sertoli cells: (mother cells/nurse cells):
- respond to FSH to produce inhibin and androgen binding proteins
- help nourish developing sperm cells
What is this image? Label the terms
- testis
- A: sertoli cell
- B: primary spermatocytes
- C: spermatogonium
- D: elongating spermatids
- E: germinal epithelium
- F: lumen
- G: seminiferous tubule
- H: leydig cell
When does spermatogenesis start?
- puberty, when HPG axis matures and testosterone rises
Describe the steps of spermatogenesis
- mitosis: spermatogonia divide to produce dipooloid (2N) primary spermatocytes
- meiosis i: primary spermatocytes duplicate adrenal chromosomes, homologous chromosomes cross over, exchange DNA,and divide to produce haploid (1N) secondary spermatocytes
- meiosis ii: secondary spermatocytes divide to produce spermatids
- maturation: transformation of spermatids to spermatozoa or sperm
Describe sperm morphogenesis
T/F: spermatogenesis is a continuous process after puberty, with no pauses between stages
- true
What are important characteristics of sperm?
- each is genetically distinct and has either an X or Y chromosome
- acrosome of head contains enzymes to penetrate ovum
- midpiece is packed with mitochondria to produce ATP, energy needed to propel sperm to site of fertilization
Describe sperm morphology between species
- size and shape of sperm head is species specific
- disc-like: ruminants
- pear shaped: man, stallion
- hook-like: rodents
- spoon-like: guinea pigs
- filiform: birds
- length is also species specific
The 12 stages of the spermatogenic cycle follow an orderly sequence along the length of the seminiferous tubule. What is a spermatogenic cycle? A spermatic wave?
- cycle: time it takes for the appearance of one o the same 12 stages at a given segment of the tubule
- wave: distance between the same stages
What does seasonal breeder mean in regards to release of sperm?
- seasonal reduction of sperm production
How many weeks does it take for transport through the epididymides where spermatozoa will be stored the tail until ejaculation?
- 2 weeks
What is the path sperm travel?
- lumen of seminiferous tubule > rete testis > efferent ducts > head of epididymus > tail of epididymus (storage)
- upon ejaculation, sperm travels via vas deferens into urethra, mixes with seminal plasma, and exits glans penis
What are the features of the female reproductive tract?
What are features of the uterine tube/oviduct?
What are features of the ovary?
What are features of the preovulatory follicle?
What are features of the corpus luteum?
What is the functional unit of the ovary?
- follicle
What are the steps of folliculogenesis?
What hormones is folliculogenesis dependent on?
Describe oogenesis vs follicle development
Describe the steps of oogenesis and spermatogeneis. Which has steps before puberty?
What are differences between spermatogenesis and oogenesis?
What are the main steps of fertilization?
- sperm preparation: capaciation and acrosome reaction
- sperm-ovum fusion and penetration off sperm
- sperm and ovum pronuclei fusion
- activation of zygote
What is capacitation?
- maturation process in response to uterine and oviductal fluid secretions involving severalmolevular steps to prepare the Esperanto for the acrosome reaction and fertilization
What is the acrosome reaction?
- acrosomal digestive enzymes are released to facilitate fusion with ovum and penetration through zona pellucida and plasma membrane of ovum
What are the steps of sperm-ovum fusion?
What is polyspermy? What can it cause?
- a phenomenon in which an ovum is fertilized by more than one sperm
- too many centrosomes can be detrimental to survival of the zygote
What are the two mechanisms to block polyspermy?
- fast block: change in electric potential of plasma membrane preventing fusion of sperm, mediated by influx of Na ions
- slow block: cortical granules release enzymes that result in formation of a fertilization envelope around ovum, mediated by release of Ca2+
What are features of the pronuclear envelope? What is pronuclear fusion?
-fertilization
Describe fusion of male and female pronuclei
What are stem cells? What are some different classes?
- self-renewing cells from which all other cells with specialized functions are generated
Describe the timeline of cleavage
What occurs during cleavage?
- within the uterine tube, unicellular zygote divides by mitosis or CLEAVAGE to become a multicellular embryo
- each daughter cell is a blastomere
- no increase in size since the early embryo is encased in a zona pellucida
What is this structure?
- morula
- still within the uterine tube, blastomeres continue to divide into a compact ball of 16-32 cells within the zona pellucida
What are features of blastocysts?
- blastocyst enters the uterus and “hatches” from the zon pellucida
- develops a cavity (blastocoele) which becomes the yolk sac
- differentiation of the inner cell mass (embryoblast) surrounded by outer cells (trophoblast)
Why must blastocysts “hatch”
- to accommodate implantation
- hatching due o pressure of expanding blastocyst and enzymatic dissolution of the zona pellucida
What is the inner cell mass of the blastocyst? Outer cells?
- inner cell mass: embryoblast: forms entire embryo
- outer cells: trophoblast: will expand to form extraembryonic membranes (amnion, yolk sac, allantois, chorion), related to placentation
The embryoblast differentiates to form bile in ar disc of _________ and _________ . This establishes the dorsoventral axis
- epiblast (dorsal)
- hypoblast (ventra)
What is gastrulation?
- process that establishes all 3 germ layers
- ectoderm
- mesoderm
- endoderm
What is the trilaminar disc and primitive streak in gastrulation?
- trilaminar disc:
- bilaminar embryonic disc with ectoderm and endoderm that develops into a trilaminar disc as mesoderm embers between the layers
-primitive streak:
- epiblast thickens, cells ingress, streak lengthens along developing embryo establishing craniocaudal axis
Describe the path of gastrulation
T/F: outer cells > embryoblast > epiblast > germ layers
- false; inner cell mass > embryoblast > epiblast > germ layers
What do each of the 3 germ layers give rise to?
- ectoderm: epidermal structures (of skin), lining of oral,nasal cavity, and anus, corneal epithelium, nervous system
- mesoderm: connective tissues, muscle tissue, mesothelium, cardiovascular system, urogenital tract
- endoderm: epithelial lining and glands of digestive and respiratory systems
How is the notochord formed?
- derived from mesoderm as a transient structure that provides direction
- basis of vertebral column: provides direction and contributes to vertebra and intervertebral discs
- induces ectoderm to differentiate into neuroectoderm
What are functions of the notochord?
Describe formation of the neural tube
- derived from ectoderm (note: different levels of mesoderm)
- basis for central nervous system (brain, spinal cord)
In the notochord, the cranial portion is the _______ and the ventral portion is the ______
- brain, spinal cord
What are the parts of the intra-embryonic mesoderm?
What are features of the paraxial mesoderm?
- somitogenesis
- differentiates into somitomeres on each side of neural tube
- differentiates further to somites
What are major somites?
- sclerotome: vertebrae, portions of skull, axial skeleton
- myotome: striated muscles of head, trunk, limbs
- dermotome: dermis of dorsal regions
What are features of intermediate mesoderm?
- differentiate into the urogenital system:
- paired kidneys
- paired adrenal gland cortex
- paired gonads
- reproductive tracts
What are the two kinds of lateral plate mesoderm?
- somatic (parietal):
- dorsal and associates with ectoderm
- contributes to serous membranes lining the peritoneal, pleural, and pericardial cavities
- splanchnic (visceral):
- ventral and associates with endoderm
- contributes to cardiovascular system, blood, kidneys, smooth muscle
What are features of the extra-embryonic mesoderm?
- derived from epiblast that initially developed from inner cell mass or embryoblast
- contributes to formation of yolk sac, amnion, allantois, and chorion
- vital functions in maternal-fetal protection, nutrient and waste exchange
Summarize germ layer derivatives
What are the placenta types
What are teratogens?
- (gr: monster-producing)
- any agent or factor that can cause congenital (present at birth) anomalies during embryonic growth and development
What are features of teratogens?
- genetic factors
- radiation
- chemical agents
- ex: nicotine, drugs (thalidomide, tetracycline), alcohol
- infectious agents
- ex: bovine diarrhea virus, akabane virus
- hormones
- ex: anti-paramesonephric duct hormone
What are examples of congenital anomalies of teratogens
What are undifferentiated gonads?
- genital ridge: medial part of mesonephros (early kidney) and differentiate into capsule, stroma,and connective tissue of gonad
- coelomic epithelium: covers genital ridge and differentiate into sex cords (sertoli or granulosa cells) of gonad
- primordial germ cells (PGC): unipotent cells that migrate rom wall of yolk sac an differentiate into spermatogonia/oogonia between sex cords or sertoli or granulosa cells, respectively, in testes or ovaries
What are differentiated gonads?
- paired testes: in presence of Y chromosome (XY), there is a SRY gene that encodes for a testis determining factor and Sertoli cells produce an anti-mullerian hormone (AMH). Müllerian ducts degenerate and testes + wolffian ducts develop
- paired ovaries: in absence of Y chromosome (XX), wolffian ducts degenerate and ovaries + Müllerian ducts develop
