Difference Between Endometrium and Myometrium

The main difference between endometrium and myometrium is that the endometrium is the inner glandular layer of the uterus wall whereas the myometrium is the middle muscular layer of it. Furthermore, endometrium undergoes cyclic changes such as thickening and menstruation throughout the menstrual cycle while myometrium is involved in the movements of the uterus during childbirth.

Endometrium and myometrium are two layers of the wall of the uterus. They perform unique functions while conceiving the baby.

Key Areas Covered

1. What is Endometrium
     – Definition, Anatomy, Role
2. What is Myometrium
     – Definition, Anatomy, Role
3. What are the Similarities Between Endometrium and Myometrium
     – Outline of Common Features
4. What is the Difference Between Endometrium and Myometrium
     – Comparison of Key Differences

Key Terms

Endometrium, Functional Zone, Myometrium, Parturition, Stratum Functionalis, Uterus

What is Endometrium

Endometrium is the inner layer of the uterus where the implantation takes place. It undergoes both morphological and functional changes during the menstrual cycle under the influence of sex hormones. But, in the absence of this cyclic hormone influence, that is before the puberty and after the menopause, the morphology and the thickness of the endometrium are constant. Hence, following the menarche in each menstrual cycle, the endometrium prepares for an implantation. If the implantation does not occur, the innermost layer of the endometrium is shed in the process called menstruation.  

Figure 1: Proliferative Phase Endometrium

Endometrium is made up of a simple columnar epithelium associated with endocrine glands and highly vascular connective tissue. The three layers of endometrium are stratum compactum, stratum spongiosum, and stratum basalis. Stratum basalis is close to the myometrium and does not change much. Stratum compactum and stratum spongiosum collectively make up the stratum functionalis, the layer involved in the implantation. During the proliferative phase of the menstrual cycle, the rising FSH and estrogen levels cause the thickening and vascularization of the stratum functionalis. Subsequently, in the secretory phase, the rising LH levels cause ovulation and the glands of the endometrium secrete glycogen. If the implantation does not happen with the decreasing levels of LH and progesterone, the contraction of the spiral arterioles in the stratum functionalis cause ischemia and the degradation of the stratum functionalis layer.  

What is Myometrium

Myometrium is the middle, smooth muscle layer of the uterine wall responsible for the muscular movement of the uterus during childbirth. The three layers of the myometrium are the outer layer of longitudinal smooth muscles, the middle crisscrossing muscle fibers in the figure of eight shape, and the inner circular fibers. The predominant proteins expressed in these muscle fibers are actin and myosin.

Figure 2: Anatomy of the Uterus

The inner layer of the myometrium is called the functional zone, which is the closest layer to the endometrium. The remaining two layers are responsible for the muscular contraction during parturition as well as abortion.   

Similarities Between Endometrium and Myometrium

• Endometrium and myometrium are two of the three layers of the uterine wall. The third is the perimetrium.
• Both perform important functions while conceiving a baby.

Difference Between Endometrium and Myometrium

Definition

Endometrium refers to the mucous membrane lining the uterus, which thickens during the menstrual cycle in preparation for possible implantation of an embryo while myometrium refers to the middle, smooth muscle tissue of the uterus. The main difference between endometrium and myometrium is this anatomical difference.

Made up of

Endometrium is made up of simple columnar epithelium, endocrine glands, and connective tissue while myometrium is made up of smooth muscles.

Layers

The three layers of endometrium are stratum compactum, stratum spongiosum, and stratum basalis while the three layers of myometrium are the longitudinal muscles, crisscrossing muscle, and circular muscles.

Function

The main functions of the endometrium are to undergo cyclic changes of the menstrual cycle and to provide a site for the implantation of the blastocyst and the development of placenta while the myometrium is responsible for the muscular movement of the uterus during parturition. This functional difference is the other important difference between endometrium and myometrium.

Conclusion

Endometrium is the innermost layer of the uterine wall, which undergoes cyclic changes during different stages of the menstrual cycle. The main function of the endometrium is to provide sites for implantation and the development of placenta. However, myometrium is the middle, muscular layer of the uterine wall responsible for the muscular contractions of the uterus during childbirth. The main difference between endometrium and myometrium is the anatomy and function.

Reference:

1. Paxton, et al. “Uterus.” Histology Guide, University of Leeds, 1 Jan. 1970, Available Here
2. “6.1 Role and Functional Anatomy of the Endometrium.” HUMAN EMBRYOLOGY, Embryology.ch, Available Here
3. “MYOMETRIUM.” Fertilitypedia, Available Here

Image Courtesy:

1. “Proliferative phase endometrium — high mag” By Nephron – Own work (CC BY-SA 3.0) via Commons Wikimedia 
2. “Blausen 0732 PID-Sites” By BruceBlaus – Own work (CC BY 3.0) via Commons Wikimedia