Class Notes (807,038)
Australia (1,850)
BMS2011 (3)
Lecture 15

BMS2011: Anatomy: Lecture 15, 16 & 17

7 Pages
Unlock Document

Monash University
Biomedical Sciences
Colin Mc Henry

Lecture 15 Notes: Half the genetic information is carried in the gametes form each gender so when combined, they form the full genetic complement.  Germ cells produce gametes and are the only cells that undergo meiosis AND mitosis  A germ cell is defined as any biological cell that gives rise to the gametes of an organism that reproduces sexually Germ cells in the beginning:  Prior to gastrulation the germ cell lineage is set aside whilst other cells are being differentiated  Germ cell lineage needs to maintain a high level of pluripotency Primordial germ cell journey:  Around 6 cells in the mouse embryo express a gene called “Blimp1”.  Blimp1 is involved in transcriptional repression of somatic gene transcription: suppresses all genes suppressed in somatic cells to make sure germ cells remain pluripotent  A subset of blimp1 express a second gene called Stella and they commit to the germ line  After this they migrate: Primordial germ cell’s (PGC’s) undergo both passive (as the embryo shape changes) and active migration to the gonads (following a series of signals within the embryo)  If they get lost along the way they can cause teratomas (a tumor composed of tissues not normally present at the site (the site being typically in the gonads)  Colonisation: PGC’s colonise the gonad and undergo sex determination o Oogonia (female embryonic germ cells) enter meiosis, but stop at prophase 1 of meiosis until puberty o Gonocytes (male embryonic germ cells) undergo mitosis-arrest-mitosis, and don’t enter meiosis until puberty Sex determination:  The germ cells enter into a bi-potential gonad  If you are a male you have a Y chromosome and within the somatic cells of the gonad, it starts to switch a gene on called “SRY” and once it is switched on it sets on a whole cascade of events, which end up forming testes.  Formation of the testes will produce anti-mullerian hormone which causes mullerian ducts which are originally present to shrink/regress as it is a female ductal system, and will support the male ductal system (Wolffian system)  Leydig cells in the testes begin to produce testosterone (DHT)  DHT affects genitalia, anatomy/physiology, male brain/behavior  If you are a female: there’s no Y chromosome and therefore no SRY, so the gonadal tissue will form the ovaries. There are positive factors to help form the ovaries also (not mentioned)  The Mullerian system is supported and Wolffian system regresses  As the ovary develops and estrogen and other female hormones are produced, female external genitalia form, anatomy and physiology and brain and behavior  Reproductive anatomy:  Clitoris and penis are homologous i.e. develop from same tissues and underlying structure is very similar  Scrotum and labia majora are homologous What can go wrong in sex determination?  E.g. mutations in SRY  Gonadal dysgenesis: Swyer syndrome, 46XY o Mutation in SRY – without SRY setting off cascade of events to develop testes, so never make testosterone o Phenotypically female (external) o Streak ovaries (increased likelihood of cancer) o No post pubertal development of 2 sex characteristics (lack of hormone production o No germ cells – can become pregnant with donated egg/embryo Reproduction: sperm and Eggs: Spermatogenesis and oogenesis:  PGC’s (primordial germ cells) have undergone the journey to the gonad  Once in the gonad, surrounded by o Support cells: (SERTOLI/ GRANULOSA) and; o Hormone-producing cells (LEYDIG/ THECA)  Undergo significant maturation during development and are the only cell types to undergo meiosis  In spermatogenesis: you start with a spermatogonium and end up with 4 sperm cells  In oogenesis, you start with a oogonium and end up with 1 ovum  Human oocyte (egg) is 100,000 times the size of the sperm Maturation of the oocyte:  As the oocyte matures, you start to develop theca interna and externa  Theca cells also produce androgens (male hormone) but get converted into estrogens by aromatase enzyme produced by granulosa cells  As puberty approaches, continued follicular maturation requires follicle stimulating hormone (FSH) produced by the pituitary  Up to 50 follicles start the maturation process each month  One will dominate  Dominant follicle enlarges, becomes FSH-independent, secretes high levels of INHIBIN  Inhibin suppresses pituitary FSH production causing the remaining semi- maturated follicles to degenerate –atretic follicles Female germ cell maturation is under hormonal control Spermatogenesis: Sertoli cells support the maturation of the germ cell from the spermatogonium stem cell stage to spermiogenesis and ultimately until the sperm cells are released into the lumen of the seminiferous tubules.  They express SRY  Supply anti-mullerian hormone (AMH)  Produce inhibin and activins – regulate FSH secretion after puberty  Form blood-testis barrier – to protect them from autoimmune attack Male germ cells do not comp
More Less

Related notes for BMS2011

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.