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Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
30 
Fig. 17: Vasculature of Human uterine endometrium. 
Source: ILLL in house 
Cyclic Changes in the Endometrium   
Both the structure and function of the endometrium, including the epithelium, lamina 
propria, glands and blood vessels are subjected to the influence of ovarian steroid hormones 
(Figure 18). Generally, three stages of cellular reorganization are observed during each 
menstrual cycle.  
These are 1) a proliferative phase, 2) a secretory phase, and 3) a menstruation 
phase. During the estrous cycle the uteri also undergo progressive enlargement and 
become distended owing to the accumulation of luminal fluid (next chapter).  
The endometrium of the uterus undergoes pronounced cyclical changes every month during 
a woman’s reproductive years (Figure 18). These changes consist of a gradual building of 
tissue in preparation for receiving a fertilized egg followed by abrupt breakdown of this layer 
and a menstrual flow if pregnancy does not occur.  The endometrial and superficial 
connective tissue layers of the uterine lining are at their maximum height (nearly 6-mm) 
during the fourteenth to twenty-sixth days of menstrual cycle.  At this time, the endometrial 
glands are well developed and secrete a fluid that nourishes the embryo.  Therefore, this 
period is referred to as the secretory phase.  There are abundant blood vessels present in 
the superficial layer of endometrium at this stage.  These are elongated and follow a spiral 
course as they extend from the basal portion to the surface epithelium.  If no pregnancy 
occurs, drop in estrogen and progesterone levels makes the terminal portions of these 
vessels constrict.  This deprives the superficial layers of the uterine lining of a supply of 
oxygen (ischemia) and results in their degeneration.  About two days after the 
vasoconstriction takes place, the affected parts of the uterine lining begin to shed resulting 
in bleeding called the menstrual flow.  This constitutes the menstruation phase.  The 
menstrual fluid consists of epithelium, connective tissue, and blood.  This blood normally 
clots in the uterus and the clots are broken up by enzyme action before flowing from the 
cervix. However, if menstruation at any given time is abnormally rapid, the blood may clot 
in the vagina.  The normal blood loss during a menstrual period is variable, with an average 
of about 50 ml.  Menstruation normally takes four days, with an average of three to six 
days.  At this stage, the endometrium is only about 1 mm thick (Figure 10).  It goes in to a 
three-day repair phase during which i) continuity of the epithelium is re-established, ii) the 
Page 2


Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
30 
Fig. 17: Vasculature of Human uterine endometrium. 
Source: ILLL in house 
Cyclic Changes in the Endometrium   
Both the structure and function of the endometrium, including the epithelium, lamina 
propria, glands and blood vessels are subjected to the influence of ovarian steroid hormones 
(Figure 18). Generally, three stages of cellular reorganization are observed during each 
menstrual cycle.  
These are 1) a proliferative phase, 2) a secretory phase, and 3) a menstruation 
phase. During the estrous cycle the uteri also undergo progressive enlargement and 
become distended owing to the accumulation of luminal fluid (next chapter).  
The endometrium of the uterus undergoes pronounced cyclical changes every month during 
a woman’s reproductive years (Figure 18). These changes consist of a gradual building of 
tissue in preparation for receiving a fertilized egg followed by abrupt breakdown of this layer 
and a menstrual flow if pregnancy does not occur.  The endometrial and superficial 
connective tissue layers of the uterine lining are at their maximum height (nearly 6-mm) 
during the fourteenth to twenty-sixth days of menstrual cycle.  At this time, the endometrial 
glands are well developed and secrete a fluid that nourishes the embryo.  Therefore, this 
period is referred to as the secretory phase.  There are abundant blood vessels present in 
the superficial layer of endometrium at this stage.  These are elongated and follow a spiral 
course as they extend from the basal portion to the surface epithelium.  If no pregnancy 
occurs, drop in estrogen and progesterone levels makes the terminal portions of these 
vessels constrict.  This deprives the superficial layers of the uterine lining of a supply of 
oxygen (ischemia) and results in their degeneration.  About two days after the 
vasoconstriction takes place, the affected parts of the uterine lining begin to shed resulting 
in bleeding called the menstrual flow.  This constitutes the menstruation phase.  The 
menstrual fluid consists of epithelium, connective tissue, and blood.  This blood normally 
clots in the uterus and the clots are broken up by enzyme action before flowing from the 
cervix. However, if menstruation at any given time is abnormally rapid, the blood may clot 
in the vagina.  The normal blood loss during a menstrual period is variable, with an average 
of about 50 ml.  Menstruation normally takes four days, with an average of three to six 
days.  At this stage, the endometrium is only about 1 mm thick (Figure 10).  It goes in to a 
three-day repair phase during which i) continuity of the epithelium is re-established, ii) the 
Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
31 
remaining blood vessels start to grow upward again, and iii) development of glands is 
initiated as invaginations of epithelium.  Rapid growth of the epithelium, blood vessels, and 
connective tissue takes place during the next week.  This is called the proliferative phase.  
It is followed by another secretory phase.  All these changes are closely timed with those 
occurring in the maturing follicle of the ovary. 
 
 
 
 
 
 
 
 
 
 
Page 3


Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
30 
Fig. 17: Vasculature of Human uterine endometrium. 
Source: ILLL in house 
Cyclic Changes in the Endometrium   
Both the structure and function of the endometrium, including the epithelium, lamina 
propria, glands and blood vessels are subjected to the influence of ovarian steroid hormones 
(Figure 18). Generally, three stages of cellular reorganization are observed during each 
menstrual cycle.  
These are 1) a proliferative phase, 2) a secretory phase, and 3) a menstruation 
phase. During the estrous cycle the uteri also undergo progressive enlargement and 
become distended owing to the accumulation of luminal fluid (next chapter).  
The endometrium of the uterus undergoes pronounced cyclical changes every month during 
a woman’s reproductive years (Figure 18). These changes consist of a gradual building of 
tissue in preparation for receiving a fertilized egg followed by abrupt breakdown of this layer 
and a menstrual flow if pregnancy does not occur.  The endometrial and superficial 
connective tissue layers of the uterine lining are at their maximum height (nearly 6-mm) 
during the fourteenth to twenty-sixth days of menstrual cycle.  At this time, the endometrial 
glands are well developed and secrete a fluid that nourishes the embryo.  Therefore, this 
period is referred to as the secretory phase.  There are abundant blood vessels present in 
the superficial layer of endometrium at this stage.  These are elongated and follow a spiral 
course as they extend from the basal portion to the surface epithelium.  If no pregnancy 
occurs, drop in estrogen and progesterone levels makes the terminal portions of these 
vessels constrict.  This deprives the superficial layers of the uterine lining of a supply of 
oxygen (ischemia) and results in their degeneration.  About two days after the 
vasoconstriction takes place, the affected parts of the uterine lining begin to shed resulting 
in bleeding called the menstrual flow.  This constitutes the menstruation phase.  The 
menstrual fluid consists of epithelium, connective tissue, and blood.  This blood normally 
clots in the uterus and the clots are broken up by enzyme action before flowing from the 
cervix. However, if menstruation at any given time is abnormally rapid, the blood may clot 
in the vagina.  The normal blood loss during a menstrual period is variable, with an average 
of about 50 ml.  Menstruation normally takes four days, with an average of three to six 
days.  At this stage, the endometrium is only about 1 mm thick (Figure 10).  It goes in to a 
three-day repair phase during which i) continuity of the epithelium is re-established, ii) the 
Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
31 
remaining blood vessels start to grow upward again, and iii) development of glands is 
initiated as invaginations of epithelium.  Rapid growth of the epithelium, blood vessels, and 
connective tissue takes place during the next week.  This is called the proliferative phase.  
It is followed by another secretory phase.  All these changes are closely timed with those 
occurring in the maturing follicle of the ovary. 
 
 
 
 
 
 
 
 
 
 
Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
32 
 
Page 4


Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
30 
Fig. 17: Vasculature of Human uterine endometrium. 
Source: ILLL in house 
Cyclic Changes in the Endometrium   
Both the structure and function of the endometrium, including the epithelium, lamina 
propria, glands and blood vessels are subjected to the influence of ovarian steroid hormones 
(Figure 18). Generally, three stages of cellular reorganization are observed during each 
menstrual cycle.  
These are 1) a proliferative phase, 2) a secretory phase, and 3) a menstruation 
phase. During the estrous cycle the uteri also undergo progressive enlargement and 
become distended owing to the accumulation of luminal fluid (next chapter).  
The endometrium of the uterus undergoes pronounced cyclical changes every month during 
a woman’s reproductive years (Figure 18). These changes consist of a gradual building of 
tissue in preparation for receiving a fertilized egg followed by abrupt breakdown of this layer 
and a menstrual flow if pregnancy does not occur.  The endometrial and superficial 
connective tissue layers of the uterine lining are at their maximum height (nearly 6-mm) 
during the fourteenth to twenty-sixth days of menstrual cycle.  At this time, the endometrial 
glands are well developed and secrete a fluid that nourishes the embryo.  Therefore, this 
period is referred to as the secretory phase.  There are abundant blood vessels present in 
the superficial layer of endometrium at this stage.  These are elongated and follow a spiral 
course as they extend from the basal portion to the surface epithelium.  If no pregnancy 
occurs, drop in estrogen and progesterone levels makes the terminal portions of these 
vessels constrict.  This deprives the superficial layers of the uterine lining of a supply of 
oxygen (ischemia) and results in their degeneration.  About two days after the 
vasoconstriction takes place, the affected parts of the uterine lining begin to shed resulting 
in bleeding called the menstrual flow.  This constitutes the menstruation phase.  The 
menstrual fluid consists of epithelium, connective tissue, and blood.  This blood normally 
clots in the uterus and the clots are broken up by enzyme action before flowing from the 
cervix. However, if menstruation at any given time is abnormally rapid, the blood may clot 
in the vagina.  The normal blood loss during a menstrual period is variable, with an average 
of about 50 ml.  Menstruation normally takes four days, with an average of three to six 
days.  At this stage, the endometrium is only about 1 mm thick (Figure 10).  It goes in to a 
three-day repair phase during which i) continuity of the epithelium is re-established, ii) the 
Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
31 
remaining blood vessels start to grow upward again, and iii) development of glands is 
initiated as invaginations of epithelium.  Rapid growth of the epithelium, blood vessels, and 
connective tissue takes place during the next week.  This is called the proliferative phase.  
It is followed by another secretory phase.  All these changes are closely timed with those 
occurring in the maturing follicle of the ovary. 
 
 
 
 
 
 
 
 
 
 
Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
32 
 
Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
33 
 
Fig.18: Changes in uterine endometrium during menstrual cycle of 
women. 
Source: 
http://www.lab.anhb.uwa.edu.au/mb140/CorePages/FemaleRepro/femalerepro.htm#Uterus © 
Lutz Slomianka 
Free for educational purpose 
 
 
 
Page 5


Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
30 
Fig. 17: Vasculature of Human uterine endometrium. 
Source: ILLL in house 
Cyclic Changes in the Endometrium   
Both the structure and function of the endometrium, including the epithelium, lamina 
propria, glands and blood vessels are subjected to the influence of ovarian steroid hormones 
(Figure 18). Generally, three stages of cellular reorganization are observed during each 
menstrual cycle.  
These are 1) a proliferative phase, 2) a secretory phase, and 3) a menstruation 
phase. During the estrous cycle the uteri also undergo progressive enlargement and 
become distended owing to the accumulation of luminal fluid (next chapter).  
The endometrium of the uterus undergoes pronounced cyclical changes every month during 
a woman’s reproductive years (Figure 18). These changes consist of a gradual building of 
tissue in preparation for receiving a fertilized egg followed by abrupt breakdown of this layer 
and a menstrual flow if pregnancy does not occur.  The endometrial and superficial 
connective tissue layers of the uterine lining are at their maximum height (nearly 6-mm) 
during the fourteenth to twenty-sixth days of menstrual cycle.  At this time, the endometrial 
glands are well developed and secrete a fluid that nourishes the embryo.  Therefore, this 
period is referred to as the secretory phase.  There are abundant blood vessels present in 
the superficial layer of endometrium at this stage.  These are elongated and follow a spiral 
course as they extend from the basal portion to the surface epithelium.  If no pregnancy 
occurs, drop in estrogen and progesterone levels makes the terminal portions of these 
vessels constrict.  This deprives the superficial layers of the uterine lining of a supply of 
oxygen (ischemia) and results in their degeneration.  About two days after the 
vasoconstriction takes place, the affected parts of the uterine lining begin to shed resulting 
in bleeding called the menstrual flow.  This constitutes the menstruation phase.  The 
menstrual fluid consists of epithelium, connective tissue, and blood.  This blood normally 
clots in the uterus and the clots are broken up by enzyme action before flowing from the 
cervix. However, if menstruation at any given time is abnormally rapid, the blood may clot 
in the vagina.  The normal blood loss during a menstrual period is variable, with an average 
of about 50 ml.  Menstruation normally takes four days, with an average of three to six 
days.  At this stage, the endometrium is only about 1 mm thick (Figure 10).  It goes in to a 
three-day repair phase during which i) continuity of the epithelium is re-established, ii) the 
Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
31 
remaining blood vessels start to grow upward again, and iii) development of glands is 
initiated as invaginations of epithelium.  Rapid growth of the epithelium, blood vessels, and 
connective tissue takes place during the next week.  This is called the proliferative phase.  
It is followed by another secretory phase.  All these changes are closely timed with those 
occurring in the maturing follicle of the ovary. 
 
 
 
 
 
 
 
 
 
 
Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
32 
 
Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
33 
 
Fig.18: Changes in uterine endometrium during menstrual cycle of 
women. 
Source: 
http://www.lab.anhb.uwa.edu.au/mb140/CorePages/FemaleRepro/femalerepro.htm#Uterus © 
Lutz Slomianka 
Free for educational purpose 
 
 
 
Female Reproductive System: Structure of Organs and Duct System 
 
              Institute of Life Long Learning, University of Delhi  
 
34 
Many other tissues of the reproductive tract of the female also undergo changes during the 
menstrual cycle, but to a much less extent.  These changes are i) in motility of cilia of the 
oviduct (it is maximal at ovulation), ii) in the viscosity of the cervical mucus, and iii) in the 
cells of vaginal epithelium (next chapter). 
In general, the secretions that line the uterine mucosa during the progestational (secretary) 
phase are rich in carbohydrates, mucopolysaccharide, and proteins.  Ionic composition of 
the uterus also undergoes marked alteration during the preimplantation stages of 
pregnancy.  Also, in species in which capacitation of spermatozoa is a prerequisite for 
fertilization, the uterine secretions may be involved in an alteration of the plasma 
membrane overlying the spermatozoa acrosome, and change it to the fertilizable state.  
Unlike the oviduct, the uterus contains a reduced population of ciliated cells.  Although the 
function of the ciliated cells of the uterus is not as apparent as that of the oviduct, it seems 
likely that these elements participate in the release and distribution of secretory material 
throughout the mucosa. 
 
 
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FAQs on Lecture 7 - Female Reproductive System:Structure of organs and Duct System ( Part 2 ) - Animal Physiology and Functional Histology- I - MBBS

1. What are the main organs of the female reproductive system?
Ans. The main organs of the female reproductive system include the ovaries, fallopian tubes, uterus, cervix, and vagina. These organs work together to produce and carry eggs, facilitate fertilization, and support the growth and development of a fetus.
2. How does the duct system of the female reproductive system function?
Ans. The duct system of the female reproductive system consists of the fallopian tubes and the uterus. The fallopian tubes are responsible for transporting eggs from the ovaries to the uterus. Fertilization of the egg by sperm usually occurs within the fallopian tubes. Once fertilized, the egg implants itself into the lining of the uterus, where it can develop into a fetus.
3. What is the structure and function of the cervix?
Ans. The cervix is the lower part of the uterus that connects it to the vagina. It has a tubular shape and is lined with mucus-producing cells. The cervix acts as a barrier, preventing bacteria and other harmful substances from entering the uterus. It also produces mucus that changes in consistency throughout the menstrual cycle to facilitate or inhibit sperm transport.
4. How does the uterus support the growth and development of a fetus?
Ans. The uterus is a hollow, muscular organ that provides a suitable environment for the growth and development of a fetus. It undergoes dynamic changes during pregnancy to accommodate the growing fetus. The lining of the uterus, called the endometrium, thickens and becomes rich in blood vessels to support the implantation of a fertilized egg. The uterus also contracts during labor to facilitate the delivery of the baby.
5. What is the role of the vagina in the female reproductive system?
Ans. The vagina is a muscular tube that connects the uterus to the external genitalia. It serves as the birth canal during childbirth, allowing the passage of the baby from the uterus to the outside world. The vagina also plays a crucial role in sexual intercourse, as it provides a passageway for the penis and acts as a receptacle for semen. Additionally, the vagina is lined with mucus-producing cells that help maintain its moisture and pH balance.
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