The theca externa is the outer layer of the
theca folliculi. It is derived from connective tissue, the cells resembling
fibroblast
A fibroblast is a type of cell (biology), biological cell typically with a spindle shape that synthesizes the extracellular matrix and collagen, produces the structural framework (Stroma (tissue), stroma) for animal Tissue (biology), tissues, and ...
s, and contains abundant
collagen
Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...
.
During ovulation, the surge in
luteinizing hormone
Luteinizing hormone (LH, also known as luteinising hormone, lutropin and sometimes lutrophin) is a hormone produced by gonadotropic cells in the anterior pituitary gland. The production of LH is regulated by gonadotropin-releasing hormone (G ...
increases
cAMP which increases
progesterone
Progesterone (; P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the ma ...
and
PGF2α production. The PGF2α induces the contraction of the
smooth muscle
Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. It can also be found in invertebrates and is controlled by the autonomic nervous system. It is non- striated, so-called bec ...
cells of the theca externa, increasing intrafollicular pressure. This aids in rupture of the mature
oocyte
An oocyte (, oöcyte, or ovocyte) is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ger ...
, or immature oocyte at the germinal vesicle stage in the canine, along with
plasmin
Plasmin is an important enzyme () present in blood that degrades many blood plasma proteins, including fibrin thrombus, clots. The degradation of fibrin is termed fibrinolysis. In humans, the plasmin protein (in the zymogen form of plasminogen) i ...
and
collagenase degradation of the follicle wall.
References
External links
*
* - "Mammal, canine ovary (LM, High)"
* - "Mammal, bovine ovary (LM, Medium)"
* - externa
*
Slide at trinity.edu
Mammal female reproductive system
{{genitourinary-stub