ESTROUS CYCLE: Reproductive cycle of female, generally defined as period from one estrus to the next.
Two phases:
Follicular Phase
Luteal phase
TYPES OF ESTROUS CYCLE
Reproductive behaviour: 1-Sexual behaviour in animalsrhfayed
Reproductive Behaviour involve behaviour patterns associated with courtship, copulation, birth, maternal care and with suckling attempts of newborn. It is species specific behaviour
Development of gonads (Gonad differentiation)male gonad and female gonadshallu kotwal
The development of the gonads is part of the prenatal development of the reproductive system and ultimately forms the testes in males and the ovaries in females. The gonads initially develop from the mesothelial layer of the peritoneum.
ESTROUS CYCLE: Reproductive cycle of female, generally defined as period from one estrus to the next.
Two phases:
Follicular Phase
Luteal phase
TYPES OF ESTROUS CYCLE
Reproductive behaviour: 1-Sexual behaviour in animalsrhfayed
Reproductive Behaviour involve behaviour patterns associated with courtship, copulation, birth, maternal care and with suckling attempts of newborn. It is species specific behaviour
Development of gonads (Gonad differentiation)male gonad and female gonadshallu kotwal
The development of the gonads is part of the prenatal development of the reproductive system and ultimately forms the testes in males and the ovaries in females. The gonads initially develop from the mesothelial layer of the peritoneum.
The term implantation is used to describe the attachment of the developing embryo to the endometrium.
After fertilization, the embryo reaches the uterus in the blastocyst stage. Then attached to the wall of the uterus. Though the implantation may occur at any period between the sixth to the tenth day after the fertilization generally it occurs on the seventh day after fertilization.
How 3 germ layers are formed in Chick that are endoderm, mesoderm and ectoderm.As Chick are polylecithal so cell movements are somewhat restricted and gastrulation is modified as compared to frog.
Vittelogenesis is a word developed from Latin vitellus-yolk, and genero-produce
Vitellogenesis (also known as yolk deposition) is the process of yolk formation via nutrients being deposited in the oocyte, or female germ cell involved in reproduction of lecithotrophic organisms. In insects, it starts when the fat body stimulates the release of juvenile hormones and produces vitellogenin protein.
Yolks is the most usual form of food storage in the egg.
Yolks appear in the oocyte in the secondary period of their growth called vittelogenesis.
Thus,the formation and deposition of yolks is known as vittelogenesis
Characteristic
Yolks is a complex variable assembled component.
The principle component are protein,phospholipid and fats in different combination.
Depending upon these component yolks is distinguished into protein yolks and fatty acid
For eg- the avian contain 48.19% water , 16.6 % protein, 32.6% phospholipids and fats and 1% carbohydrates.
The term implantation is used to describe the attachment of the developing embryo to the endometrium.
After fertilization, the embryo reaches the uterus in the blastocyst stage. Then attached to the wall of the uterus. Though the implantation may occur at any period between the sixth to the tenth day after the fertilization generally it occurs on the seventh day after fertilization.
How 3 germ layers are formed in Chick that are endoderm, mesoderm and ectoderm.As Chick are polylecithal so cell movements are somewhat restricted and gastrulation is modified as compared to frog.
Vittelogenesis is a word developed from Latin vitellus-yolk, and genero-produce
Vitellogenesis (also known as yolk deposition) is the process of yolk formation via nutrients being deposited in the oocyte, or female germ cell involved in reproduction of lecithotrophic organisms. In insects, it starts when the fat body stimulates the release of juvenile hormones and produces vitellogenin protein.
Yolks is the most usual form of food storage in the egg.
Yolks appear in the oocyte in the secondary period of their growth called vittelogenesis.
Thus,the formation and deposition of yolks is known as vittelogenesis
Characteristic
Yolks is a complex variable assembled component.
The principle component are protein,phospholipid and fats in different combination.
Depending upon these component yolks is distinguished into protein yolks and fatty acid
For eg- the avian contain 48.19% water , 16.6 % protein, 32.6% phospholipids and fats and 1% carbohydrates.
Hello. I am Shiba Hari Dhakal , undergraduate student of Agriculture science studying 8th semester in Agriculture and Forestry University, Rampur,Nepal. This slide was prepared when I was in Bsc.Ag 5th semester, as an assignment of LPM subject by compiling information from different sources.
Reproductive cycle by Rashmi Morey pdfRashmiMorey1
Reproductive cycle useful for undergraduate , post graduates and for secondary and higher secondary students science education.
It includes physiology of menstrual cycle and role of hormones in mammalian reproductive cycles
Similar to Estrous Cycle and Its Hormonal Regulation (20)
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
1. ESTROUS CYCLE AND ITS
HORMONAL REGULATION
PROF. JOGEN C. KALITA
MSc (Gau), PhD (King’s College London)
Professor in-Charge
Animal Physiology & Biochemistry Lab.
Dept. of Zoology, Gauhati University,
Guwahati, Assam, India
2. After going through this PPT the students will be able to learn the following:
• Know about Estrous cycle and the cyclic nature of reproductive activities
in female mammals
• Different phases of the estrous cycle in mammals
• They will know about physiological changes happening internally inside
animals body can be assessed by simple external observation using
vaginal smears technique (without using any invasive/aggressive
methods)
• Know about the hormonal feedback that exists among hormones of
Hypothalamus, Pituitary and Ovaries for regulation of the cycle
• Applied value of the earned knowledge in the field, animal husbandry
and in case of farm animals (induced breeding etc.)
LEARNING OUTCOMES
3. DEFINITION OF ESTORUS CYCLE
& RELATED TERMINOLOGY
• A cycle is a repetition of the same event (s) at a definite interval of
time.
• The Estrous or Oestrous Cycle is the reproductive cycle occurring in
non-primate mammals.
• The repetition of morphological/physiological and behavioural changes
occurs in female mammals at a definite interval of time. This duration
of time interval differs in species.
• The Estrous cycle has four distinct phases, proestrus, estrus,
metestrus and diestrus.
• During their reproductive life female mammals exhibit two types of
reproductive cycles, Estrous cycle and Menstrual cycle. Human
female and primates have Menstrual Cycle. Unlike estrous cycle the
Menstrual Cycle has a distinct bleeding phase.
4. DEFINITION OF ESTORUS CYCLE
& RELATED TERMINOLOGY
• We should not confuse with the term "estrus“. Estrus is just a phase
of the Estrous Cycle. The word “estrus” means psychological heat
period (psychic heat) of receptivity of female towards male for
mating. Only during this estrus period of the cycle a female receives
a male for mounting.
• Estrous cycle starts after sexual maturity in females and are
interrupted by anestrous (absence of estrous) phases or by
pregnancies.
5. The word “estrus” was first used by Heape (1900). This is a Latin form of
the Greek word “oistros” which means “sexual season”, “gadfly”, “frenzy”,
“sting” or “madness”. Heape further named and defined the phases of the
mammalian estrous cycle into proestrus, metestrus, diestrus and anestrus.
Proestrus is the preparatory stage for an animal coming into heat. Estrus
is the actual period of heat when females receive male for mounting.
Metestrus which is a brief period characterized with decline of corpus
luteum functions in the absence of conception when the activities of
reproductive organs gradually subside,
Diestrus which is a period of short rest during the breeding season, and
Anestrus which a non-breeding period when reproductive organs are
quiescent.
HISTORICAL BACKGROUND
6. Proestrus: The first stage in the estrous cycle immediately before estrus
characterized by development of both the endometrium and ovarian follicles.
Estrus: The second stage in the estrous cycle immediately before metestrus
characterized by a receptivity to a male and to mating, often referred to as "heat" or
"in heat". Pheromones may also be secreted only at this stage of her cycle.
Metestrus: The third stage in the estrous cycle immediately before diestrus
characterized by sexual inactivity and the formation of the corpus luteum.
Diestrus: The last stage in the estrous cycle immediately before the next cycle
proestrus characterized by a functional corpus luteum and an increase in the blood
concentration of progesterone.
Anestrus: Not a stage in the estrous cycle, but a prolonged period of sexual rest
where the reproductive system is quiescent (inactive).
STAGES OF THE ESTROUS CYCLE
The descriptions below refer to the "typical" estrous cycle
Proestrus - Estrus - Metestrus - Diestrus
7. DIFFERENCES BETWEEN
ESTROUS CYCLE AND MENSTRUAL CYCLE
Estrous cycles are named for the cyclic appearance of behavioral sexual
activity (estrus) that occurs in all mammals except for higher primates.
Menstrual cycles, which occur only in human female and primates, are
named for the regular appearance of menses due to the shedding of the
endometrial lining of the uterus.
8. ESTROUS CYCLE MENSTRUAL CYCLE
Estrous cycle occurs in Infra-primate female
mammals only, for example rats, mice, cat,
dog, cow, horse, pig etc.
Menstrual cycle occurs In human female
and primates
Estrous cycle has its four distinct phases,
proestrus, estrus, metestrus and diestrus,
where receptivity to males is limited to
estrus phase only.
Menstrual cycle has no such type of
proestrus, estrus, metestrus or diestrus
phases and female can mate with male
during the entire cycle period.
Estrous cycle is normally of short duration
starting from 4-days
Menstrual cycle duration is always of about
a months (28±2 days)
Estrous cycle has no distinct bleeding
phase
Menstrual cycle has a distinct bleeding
phase towards the end of each cycle
DIFFERENCES BETWEEN
ESTROUS CYCLE AND MENSTRUAL CYCLE
9. ESTROUS CYCLE
TYPES
In different mammals during their reproductive life, Estrous cycles vary between
species
Polyestrous Animals: Estrous cycles occurring throughout the time of the year
(e.g, cattle, pigs, mice, rats). They can become pregnant without regard to the
season of the year.
Seasonally Polyestrous Animals: Animals that have multiple estrous cycles only
during certain periods of the year (e.g, horses, sheep, goats, deer, cats). They
are classified as “short day breeders” when they present estrous cycles during
autumn when day length is decreasing (goats and ewes) and “long day breeders”
(mares and queens) when they show estrous mainly during spring, when day
length increases.
Monestrous Animals: Animals that have one estrous cycle per year (e.g, dogs,
wolves, foxes, and bear)
10. CHANGES IN REPRODUCTIVE PHYSIOLOGY
DURING ESTROUS CYCLE
Female mammals always exhibit different kind of
behavioural, as well as morphological, histological, cytological, and physiological changes in
the reproductive tract and also hormonal changes during each estrous cycle as stated below
PROESTRUS
Follicles in ovaries start developing further
Estrogen, the main female sex hormones of
ovary increases in circulation
Estrogen start acting on its target, uterus and
vascularity of the female reproductive tract
increases
Inside uterus endometrial thickness and
glands of endometrium begin to grow
Estrogen level becomes the highest (levels
peak)
11. ESTRUS
During this time of the cycle female allows
male to mate (mounting)
Estrogen in circulation slowly decreases
LH from anterior Pituitary level increases to
peak (surge occurs)
Ovulation occurs after few hours of surge of
LH or during the surge of LH
Uterine motility becomes high with
contractions moving toward the oviduct
Sperm transport is optimal during this time if
mating occurs and cervical mucus volume
increases
12. METESTRUS
Circulating Estrogen level becomes low
Corpus hemorrhagicum present
Ovulation may occur in some animals
FSH increases, triggering growth of
follicles
Uterus
contractions subside
endometrial glands continue to
grow and become coiled
13. DIESTRUS
Progesterone secreted from ovaries
become higher in circulation
FSH level becomes low
Uterus
• Secrets fluid but the volume of fluid
decreases over time
• Contraction stop
• Corpus luteum regresses at the end
of this period if female is not
pregnant
14. STUDY OF ESTROUS CYCLE USING
VAGINAL SMEARS IN RATS AND MICE
BACKGROUND
The estrous cycle in rats and mice averages 4–5 days and is a repetitive but
dynamic process whereby different cell types appear and recede in waves
throughout the cycle, reflecting changes in the levels of estradiol and
progesterone secreted by the ovarian follicles and further changes occurring in
the uterus, mainly endometrium, cervices, and vagina.
STOCARD & PAPANICOLAOU (19I7) dealt with the maturation process in the
Graafian follicles using the smear method with vaginal fluid in the guinea pig.
ALLEN (1923) and HISAW (1947) put forwarded a theory on the oestrous cycle in
the Muridae (largest family of rodents). Estrous cycles are characterized by
morphological changes in ovaries, the uterus and the vagina which occur during
different phases in the cycle (Goldman et al., 2007).
Vaginal smear method remains as the gold standard till date to study estrous cycle
in commonly used experimental animals.
15. VAGINAL SMEAR PROCEDURE
Estrous cycle can be studied by collecting vaginal smears with a sterile cotton
plugs putting in to the vagina or by a dropper. We in our Lab used a sterilized
stainless steel wire loop having a diameter of about 3.5 mm was dipped in
distilled water to create a diaphragm of water inside the loop. One drop of
distilled water was added on the middle of a clean microscopic slide. The loop
was then inserted into the vagina and rotated gently 2-3 times to collect the
vaginal cells and finally placed onto the water drop and spread softly to make a
smear. The slide was then allowed to air dry, fixed in methanol and stained for
10-15 min in Giemsa stain and observed under normal microscope. Four
distinct cell associations of vaginal cytology appear at four different stages of
the cycle.
18. Fig: Appearance of cytological changes in four phases of estrous cycle in mouse
The different phases of oestrous cycle are usually identified according to cell
types observed in vaginal smears
VAGINAL CYTOLOGICAL CHANGES DURING
OESTROUS CYCLE & IDENTIFICATION OF THE PHASES
19. Phase of the cycle Cell types
Proestrous Large rounded nucleated epithelial cells with distinct plasma
membrane (PM) and clear cytoplasm.
Estrus Entirely of cornified cells, in high numbers and usually forming
clumps and sheets. Cells are ells with granulated cytoplasm.
Cells with no distinct boundaries (PM) and nucleus.
Metestrous Large numbers of leucocytes and smaller numbers of mostly
large, non-granular and non-nucleated epithelial cells.
Diestrous Mainly of leucocytes but sometimes with quite variable
numbers of epithelial and small cornified cells
Table: Cytological changes during
4 different phases of estrous cycle
20. Estrous cycle is a hormonally controlled cycle of activity of the reproductive organs in
female mammals. The follicular stage (growth of the Graafian follicles, thickening of
the lining of the uterus, secretion of oestrogen, and ovulation, is succeeded by the
luteal phase (formation of the corpus luteum and secretion of progesterone), followed
by regression and a return to the first stage. The first half of the cycle is also termed
as Follicular phase or Estrogen phase due to estrogen dominance and the second half
of the cycle is called the Luteal phase, as corpus Luteum forms during this time or as
Secretary phase or Progesterone phase.
There are four major hormones involved in the oestrous cycle. These hormones
include
•Follicle-stimulating hormone
•Luteinizing hormone
•Estrogen
•Progesterone
HORMONAL REGULATION OF THE ESTROUS CYCLE
21. Fig: Relationship between circulating reproductive hormones, reproductive cycle stage, and
vaginal cytological outcomes through different phases estrous cycle in female mouse.
(Jessica G. et. al., 2018)
22. The cycle is regulated by the hypothalamic-pituitary-gonadal axis, which produces
hormones that dictate reproductive events. The reproductive axis is composed of the
hypothalamus, pituitary, and the ovary
HORMONAL FEEDBACK DURING ESTROUS CYCLE
Fig: Hypothalamic Pituitary gonadal Axis,
the interaction of the structures and
hormones involved within the oestrous cycle
23. The sequence of hormonal release essentially begins with the synthesis and release
of GnRH from the hypothalamus. This polypeptide hormone is transported to the
anterior pituitary through a highly specialized capillary network called the
hypothalamo-hypophyseal portal system. GnRH functions to stimulate the anterior
pituitary to produce and release FSH and LH. FSH and LH are transported through
systemic blood circulation to the ovaries, where they initiate a series of morphological
changes in the ovaries (ovarian folliculogenesis) that lead to ovulation (and
pregnancy if fertilization occurs). The primary hormones produced by the ovary are
Estrogen and Progesterone. These hormones are transported by the blood stream to
"target" tissues (mainly uterus and breast) to cause a development. As the follicle
grows, more estrogen is produced. As increasing amounts of estrogen are released
into the blood stream and travel to the anterior pituitary, it acts in a positive feedback
fashion, stimulating pulsatile LH release. The uterus found in the pelvic cavity also
contributes to reproductive control, as it produces prostaglandin F2a(PGF2a).
24. Changes occurring in the mouse estrous cycle are evident in the animal’s
physiology and anatomy. The cells lining the vagina of the female rat respond to
the levels of circulating hormones and can provide a valuable marker of the
stage of preparation of the ovary and uterus for mating and for ovulation.
Vaginal smears taken on consecutive days over a period of time can provide
detailed information on the oestrous cycle. The normal oestrous cycle in the rat
usually follows a 4-day pattern and the varying characteristics of the cells in the
smear allow the days of the cycle to be classified relative to the predicted time of
ovulation. Ovulation occurs at approximately midnight after the pro-oestrous
stage, when the females become receptive to the male.
IMPORTANCE OF STUDY OF ESTROUS IN ANIMALS
25. The stages of the vaginal cell cycle will normally correlate with changes
in the female reproductive organs e.g. ovary and uterus. This
knowledge can be used in many lab experiments to study reproductive
performances of animals under different situation and for testing drugs
etc. and in the field of induced breeding technology.
In farm animals and animal husbandry the detection of estrus and
ovulation time is very important for farmers to specifically apply mating
at the specific time.
IMPORTANCE OF STUDY OF ESTROUS IN ANIMALS
26. SUGGESTED READINGS
Essential Reproduction (Essentials): Amazon.co.uk: Martin H. Johnson,
8th Editon
Knobi and Neil’s Physiology of Reproduction, Vol. 2, 4th Edition
The murine female intestinal microbiota does not shift throughout the
estrous cycle
Jessica G. et al., Published: July 16, 2018
https://doi.org/10.1371/journal.pone.0200729