theca

anatomy and physiology

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July 14, 2026

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The term "theca" refers to an enveloping sheath or case, often found in anatomical contexts. In the physiology of the female reproductive system, the term "theca" is used to describe layers within the ovarian follicle. Specifically, the theca interna and theca externa are layers of stromal cells surrounding the developing egg. These layers play a role in hormone production, with the theca interna contributing to estrogen synthesis. The theca interna is rich in blood vessels and is involved in the conversion of androgens to estrogens.1234

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Ceratium
The theca, or armour, is composed of many textured plates that form one anterior horn and usually two posterior horns, which may help to slow the sinking of the cells. The spines tend to be shorter and thicker in cold salty water and longer and thinner…
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The theca, or armour, is composed of many textured plates that form one anterior horn and usually two posterior horns, which may help to slow the sinking of the cells. The spines tend to be shorter and thicker in cold salty water and longer and thinner…
Read More

animal reproductive system
Ovaries
…hagfish, is surrounded by a theca, or sheath, composed of two concentric layers of stromal cells. The outer layer (theca externa) is chiefly connective tissue but may contain smooth muscle fibres. The inner layer (theca interna) has more blood vessels and, in vertebrates that produce heavily yolked eggs, the largest…
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…hagfish, is surrounded by a theca, or sheath, composed of two concentric layers of stromal cells. The outer layer (theca externa) is chiefly connective tissue but may contain smooth muscle fibres. The inner layer (theca interna) has more blood vessels and, in vertebrates that produce heavily yolked eggs, the largest…
Read More