MCDB 240: Testes I Flashcards
what are the two major components of the testes?
spermatozoa: transmit male’s genes to embryo
hormones: need for maintenance of male reproductive functions
go over the development of testes; define the role of SRY, TDF, and MIF
1) gonads are bipotential for two weeks
2) SRY gene on y-chromosome encodes testis determing factor (TDF)
3) TDF promotes mullerin inhibiting factor (MIF), prevents mullterian duct from forming
4) Wolfian duct forms
define the wolfian duct and mullerian duct
wolfian: vas deferens and epidydimis
mullerian: fallopian, uterus, cervix, upper cervix
describe the testes compartments; where do the spermatozoa reside, where do the androgens reside
spermatozoa develop w/i tubules, associated w/ Sertoli cells
androgens are synthsized between tubules IN leydig cells
both compartments are separated by cell barriers which develop puberty
describe the three phases for spermatogenesis
1) mitotic proliferation produces a large # of cells
2) meiotic divisions promote gene diversity, halves chromosome #
3) cytodifferentiation packs chromosomes for delivery to oocyte
list three types of cells in the testes
1) Sertoli
2) Leydig
3) germ cells: different stages of sperm development
explain the importance of Leydig cells
- produce testosterone (downregulated LH), located externally outside basement membrane (b/t tubules)
- are interstitial endocrinocyteses
- contribute <1% of total testis mass
- activated by LH
explain the origins of Leydig cells
1) differentiation from mesenchymal cells
2) leydig cells divide under influence influence of LH and FSH
explain the importance of Sertoli cells
- think of them as the nurse cells
- PART of tubules, activated by FSH
- equivalent to ovarian granulosa cells (surround oocyte and control its development)
- provide nutrients/ions to spermatogonia (support and protect)
- produces inhibin (downregulates FSH)
- don’t divide in adult testis
- consist of the blood-testes barrier,* because sperm is antigenic to the body
describe the blood-testes barrier
barrier b/t blood vessels and tubules, formed b/t Sertoli cells
describe the order of spermatogonia maturation
Basal lamina
1) spermatogonia
2) mitosis
3) spermatocyte, 1st order
4) meiosis
5) spermatocyte, 2nd order
6) meiosis
7) spermatid
8) spermatogenesis
9) mature spermatid
describe endocrine function
- occurs b/t tubules
- Leydig, again, important for production of androgens (testosterone)
HPT axis: what is it and why is it important?
hypothalamus-pituitary testicular axis. HPT axis deals w/ endocrines.
male fertility depends on endocrine (distant) and paracrine (local) functions of androgens testes produces
how do hormones work?
via cell membrane and sometimes nuclear receptors
what determines how and which receptor a hormones reacts with?
the chemical structure (ensures RECEPTOR-SPECIFICITY)
describe the feedback mechanisms in the HPT axis
1) hypothalamus
2) emits LHRH
3) pituitary
4) emits LH (Leydig) and FSH (Sertoli)
5a) Leydig produces testosterone (neg fb on pituitary and hypo)
5b) Sertoli produces inhibin (neg fb on pituitary and hypo)
define feedback mechanism
action of a hormone increases or decreases effect of a hormone or itself
go over testosterone in detail, from fetus to puberty, how it’s released, how it’s made, and how does it act
- testosterone is activated by maternal human chorionic gonadotropin (NCG) during fetal neonatal life
- low secretion until puberty
- puberty: increased testosterone b/c LH
- released in a pulsatile manner (as w/ LH)
- synthesized from cholesterol, obtained from blood-borned HDL’s
- acts via androgen receptors located in target cells to stimulated secondary characteristics
- negative feedback on Sertoli cells, acts to increase sperm
go over inhibin; how does it cross-talk w/ testosterone
both control plasma FSH levels
define hypogonadotropic hypogonadism
low testosterone + low FSH + low LH
what is the percentage of free, unbound testosterone?
2%
what are usually tested for hormones in a male?
FSH and testosterone; rare to see abnormalities in LH
what has higher levels in pituitary cancers?
prolactin has 2x-3x higher levels; prolactinoma is a type of pituitary cancer
what can be used to treat prolactinoma?
bromacriptine is used to treat elevation of prolactin
define spermatogenesis
the maturation of spermatogonia to spermatozoa
-mitosis AND meiosis are involved, w/ changes in both cytoplasmic and nuclear architecture
how is the outcome of spermatogenesis determined?
1) proliferation
2) differentiation
3) apoptosis
what crosses the blood-testes barrier?
spermatocytes pass via tight junction to become spermatids, then elongated spermatids, then mature spermatozoa (differentiation)
