Histology of the reproductive system Flashcards
What are the histological structures of the testis?
1) Tunica albuginea
2) Mediastinum of the testis
3) Fibrous septa
4) Seminiferous tubules
5) Straight tubules
6) Rete testis
What is the tunica albuginea?
The tough fibrous outer surface of the testis
What is the mediastinum of the testis?
Thickening of the internal aspect of the tunica albuginea
What is the fibrous septa of the testis?
Fibrous tissue that extends from the mediastinum inwards between the lobules
What is the seminiferous tubule?
Coiled tubules within the lobules in which sperm are produced
What are the straight tubules?
Tubular structures that join the seminiferous tubules to the rete testis
What is the rete testis?
A network of canals in the mediastinum of the testis, which then travels through the efferent ductules to reach the epididymis, then the vas deferens
Describe the histology of the seminiferous tubules
1) Highly convoluted
2) Lines with stratified epithelium (due to the various layers of the spermatogenic cells)
3) It contains two types of cells (spermatogenic cells and Sertoli cells)
4) Its basal layer is supported by a membrane surrounded by myofibroblasts and fibroblasts, which aids in contraction
What is the function of the Sertoli cells?
It helps in the nourishment and support of the spermatogenic cells
What are the types of spermatogenic cells?
- Found in the basal compartment of the seminiferous tubules
- First one is the spermatogonia (which is an undifferentiated germ cell), it then forms either
1) Type-A (Large round/oval nucleus with condensed chromatin), it then undergoes mitosis and forms Type-A and Type-B (cycle repeats)
2) Type-B (nucleus with a dispersed chromatin), it undergoes mitosis to form a primary spermatocyte (44-chromosome + XY)
- The primary oocyte then undergoes meiotic division 1, forming a secondary oocyte, then meiotic division 2, forming 4 spermatids, then it forms a spermatozoa
What is the process that forms spermatozoa from spermatids?
Spermiogenesis (it is the maturation process)
How can the different germ cells of the testis be differentiated in histology?
1) Rounded large, dark cells = Type A spermatogonia
2) Rounded large, pale cells = Type B spermatogonia
3) Little deeper, slightly smaller cells = Primary spermatocytes
4) Secondary spermatocytes = hard to find without special tools.
5) Spermatids = elongated nuclei
How can we identify the Sertoli cells in histology?
- They are the triangular/Ovoid nuclei that are found towards the basement membrane
- Their cytoplasm extends to the lumen of the tubule, and it encloses the cells of the spermatogenic series
- Its function is to support the developing spermatozoa
Describe the blood-testis barrier
Sertoli cells are connected to each other via their cytoplasm through tight junctions, which disconnect the spermatogonial cells from the rest of the tubule, creating the blood-testis barrier
- This junction divides the seminiferous tubules into a basal compartment and an Adluminal compartment (closer to the lumen)
Describe the histology of the leyding cells
- Seen in the interstitial tissue between the seminiferous tubules
- It can occur in singles or clumps (embedded in the rich plexus of capillaries)
- It produces testosterone
- FYI: they’re endocrine cells
Describe the histology of the epididymis
- Long, extremely convoluted tubule
- It stores and (semi-matures) the sperm
- It is richly innervated by sympathetic fibers for the intense contraction during ejaculation
- The epididymis is pseudostratified columnar with stereocilia (smooth muscle is below the epithelium, “between it and the testis”)
- The smooth muscle starts as a single layer and then increases to three layers as it forms the vas deferens
- Its lumen is filled with spermatozoa (dense clusters)
What is the function of the stereocilia?
It helps with the movement of the sperm and absorbs the excess fluid
Describe the histological structure of the vas deferens
1) Muscularis layer: Very thick compared to its lumen, composed of inner longitudinal, middle circular, and outer longitudinal, and it is richly innervated by the sympathetic fibers
2) Mucosa: formed of pseudostratified columnar epithelium with stereocilia and lamina propria, and we can see some longitudinal folds
Describe the histological structure of the seminal vesicles
- Convoluted single tubule
- Its mucosa is folded a lot with a highly irregular lumen (honeycomb appearance)
- The epithelium is pseudostratified columnar, and it appears foamy due to the lipid droplets in the cytoplasm
- Its muscular layer is thinner than that of the vas deferens, formed of two layers (inner circular and outer longitudinal)
Describe the histology of the prostate
- It is a tubulo-alveolar gland, with ducts that open into the urethra (these secretory ducts are lined by a simple columnar epithelium), changing to a transitional epithelium near the opening of the ducts into the urethra
- The glands are embedded into a fibromuscular stroma (smooth muscle separated by collagenous and elastic fibers
- Their muscle layer forms a dense mass around the urethra beneath the thin capsule
- Their epithelium is either cuboidal or columnar
What is the epithelium of the prostatic urethra?
Urothelium (transitional epithelium)
What is the corpora amylacea?
They are rounded eosinophilic bodies of the prostate seen in the secretory alveoli (increase with age and might undergo calcification)
What are the different histological zones of the prostate?
1) Transition zone/Median lobe: BPH occurs here
2) Central zone (posterior and lateral lobes) consists of 20-25% of the glandular tissue
3) Peripheral zone: forms 70% of the glandular tissue and it is the most common site for an adenocarcinoma
4) Anterior fibromuscular stroma (non-glandular region)
Next, we are going to talk about the females
Describe the histological structure of the female uterus
1) Adventitia/Serosa/Perimetrium
- Outermost covering (aka serosa if peritoneal & adventitia if not)
= Both together are termed “perimetrium” regardless of peritoneal covering
2) Myometrium
3) Endometrium
- Undergoes cyclical changes and sloughs off during menstruation
- Supplied by uterine artery branches, especially spiral and radial arteries
- Contraction of circular muscles around these arteries cuts off blood flow ->ischemia -> sloughing
Describe the structure of the myometrium of the uterus
- It forms the bulk of the wall of the uterus
- It is formed of smooth muscles that are ill-defined (undergo hypertrophy and hyperplasia during pregnancy)
- Its longitudinal layer is expulsive in function
- Its circular layer constricts the blood supply to the placenta, for its detachment, and they form the sphincters at the internal OS and the uterine tube
What forms the sphincters at the opening of the uterine tubes and the internal OS?
The circular smooth muscle layer
What type of epithelium lines the endometrium?
Simple columnar epithelium with cilia/microvilli
- It dips into the endometrial stroma to form the endometrial glands, and its thickness varies in different stages of the menstrual cycle
What are the different anatomical layers of the endometrium?
1) Functional layer (superficial): Undergoes cyclic changes and sloughs off during menstruation.
- Formed of the stratum spongiosum and compactum (responds to the hormones)
2) Basal layer (deep): Remains intact.
Responsible for regenerating the functional layer after menstruation
- Stratum basalis
What are the histological layers of the endometrium?
(Deep to superficial “BSC”):
1) Stratum basalis:
- It is the deepest layer, adjacent to the myometrium, and it is not shed (acts as the regenerative layer)
2) Stratum spongiosum:
- Broad intermediate layer, and its stroma has a spongy appearance (edematous stroma)
- Sheds during menstruation
3) Stratum compactum (stratum functionalis)
- It is the thinner superficial layer, and it has a compact stroma
- Sheds during menstruation
What are the endometrial changes that occur during menstruation?
1) Proliferative stage:
- The thin endometrium doubles in thickness
- The glands change from sparse/straight to coiled
- Highly cellular stroma to edematous
2) Secretory phase: (after ovulation)
- The glandular epithelium synthesizes glycogen (nutrition for the fertilized ovum), forming vacuoles
- The stroma increases in vascularity and interstitial fluid
Describe the endometrial blood vessels
- Branches of the endometrial artery pass through the myometrium and divide into:
1) Straight arteries:
- Short, and forms a plexus supplying the stratum basalis
2) Spiral arteries
- Long and coiled
- Forms a capillary network around the glands
- It responds to the hormonal changes, in the sense that it constricts, ischemia, and menstruation
What is the artery that forms the plexus in the stratum basalis?
The straight arteries
Which ovarian arterial branch forms a plexus around the glands and is responsible for menstruation?
The spiral arteries
What is the course of the ovarian artery and its supply to the endometrium
1) Uterine A
2) Arcuate A
3) Radial A (penetrate& surround by circular muscle)
4) A. straight A: S.BASALIS (Stable) / B. Spiral artery: S.functionalis (yes to shedding)
How to identify the phase of the menstrual cycle based on a histological section of the endometrium?
1) Menstrual Phase
-> Sloughed-off endometrium
Poorly defined structures:
- Glands are not visible
- Spiral arteries are not distinct
Overall, a disorganized appearance
2) Proliferative Phase
Early :
Endometrium = thin
Glands = straight and narrow
Stroma = dense and compact
Late :
Endometrium = thicker
- Glands show BEGINNING of coiling
- Slight sawtooth appearance may start to appear
3) Secretory Phase
- Endometrium: Thickest
- Glands are highly coiled → sawtooth appearance.
- The glandular lumen appears hollow due to glycogen
- Spiral arteries are prominent and coiled
Describe the histology of the fallopian tube
1) Serosa: Vascular supporting tissue (derived from the broad ligament)
2) Mscularis: Inner circular and outer longitudinal layers (performs peristalsis to propel the ovum towards the uterus
3) Mucosa:
- Longitudinal folds
- Simple columnar epithelium (ciliated cells, wave-like beating to propel the ovum
- Non-ciliated cells (peg cells), project into the lumen, and it is secretory in function (nutrition and protection to the ovum)
Describe the histology of the ovary
1) Germinal epithelium
2) Tubica albuginea (fibrous tissue layer)
3) Cortex:
- Its outer layer contains (ovarian follicle in various stages of development), it is the site of oogenesis, and it contains follicles of various stages (corpus luteum, corpus albicans, etc)
4) Medulla (inner vascular part, which contains nerves and lymphatics)
5) Stroma (collagen fibers, stromal cells “resemble fibroblasts”, smooth muscle cells)
What is the mesovarium?
- It is the region where the ovary attaches to the broad ligament (via the parovarium)
- It serves as the entry point for the blood vessels and nerves
What are the different stages of follicular development?
1) Primordial follicle (located in the cortex, surrounded by a single layer of flat stromal cells)
2) Primary follicle (early, the flat cells become cuboidal granulosa cells, and later, the multiple layers of granulosa cells appear)
3) Secondary follicle (antral follicle, fluid fluid-filled space starts forming between the granulosa cells, and it gets surrounded by the theca cells)
4) Tertiary follicle (graffin follicle)
- The antrum enlarges significantly
- The oocyte gets pushed to the periphery, connected to the follicle by the cumulus oophorus
- It gets surrounded by the corona radiata
5) Ovulation occurs (-Follicle ruptures, the oocyte with corona radiata is released into the peritoneal cavity near the fimbriae)
6) Corpus luteum (represents the remaining follicular cells, and it secretes progesterone)
7) Corpus albicans (fibrous scar tissue)
Describe the process of ovarian oogenesis
1) Primordial germ cells (PGC) originate in the yolk sac, it then migrate into the ovarian cortex during early fetal development
2) Primordial germ cells then differentiate into an oogonium
3) The oogonia proliferate mitotically, increasing their numbers
4) During the fetal period, the oogonia begin meiosis-1, but it gets arrested in prophase-1 (forming the primary oocyte), until puberty
5) After puberty, and at ovulation, one primary oocyte completes meiosis-1 forming a secondary oocyte and the first polar body
6) The secondary oocyte then gets arrested at the metaphase-2 of meiosis-2
7) If fertilization occurs, the oocyte completes meiosis 2 forming an OVUM and a second polar body
In which state is the primary oocyte arrested?
PROPHASE-1 OF MEIOSIS-1
In which state is the secondary oocyte arrested?
Metaphase-2 of Meiosis-2, completes only if fertilization occurs
When does meiosis 1 complete?
At puberty, as the primary oocyte forms a secondary oocyte
How many primordial follicles undergo maturation?
Up to 20, however, only one of them reaches full maturity and ovulates; the rest become atretic (degenerate)
Describe the histological structure of the primary follicle
- Formed of cuboidal follicular cells
- The follicular cells will multiply via mitosis, forming:
1) Zona granulosa: several layers of granulosa cells
2) Zona pellucida: Thick homogenous layer of glycoproteins and proteoglycans (between the oocyte and the follicular cells)
3) Theca cells appear in further development, which are derived from the fibroblast-like cells of the ovarian stroma, and it is located around the ovum
Describe the histology of the secondary follicle
- Situated deeper into the ovarian cortex, it zona granulosa contains small fluid-filled spaces that fuse to form the follicular antrum
- The oocyte will get situated eccentrically in a thickened area of zona granulosa called the cumulus oophorus
- The theca cells will form two layers:
1) Theca internal (TI)
- Several layers of rounded cells
- It has an endocrine function
2) Theca external (TE)
- Spindle-shaped cells
- It merges with the surrounding stroma
- It has no endocrine function
Describe the histology of the tertiary (graffin) follicle
- The first polar body remains within the zona pellucida
- The follicular antrum enlarges
- The zona granulosa forms a layer of even thickness around the periphery of the follicle
- The cumulus oophorus diminishes
- Corona radiata of several layers surrounds the oocyte, which floats freely inside the follicle
- At ovulation, it gets rupture,d releasing (secondary oocyte, the zona pellucida, and the corona radiata)
Describe the histology of the granulosa cells
- Forms following ovulation, representing a collapsed, ruptured follicle
- It contains the remnant of post-ovulatory blood clots
- The granulosa cells increase in size to become the granulosa lutein cells (steroid-secreting cells)
- The theca interna cells increase in size, becoming the theca lutein cells (pale cytoplasm due to the presence of lipid droplets)
- Theca external, zone of condensed stromal tissue, with darker-stained
cytoplasm - 12-14 days after ovulation, it regresses if pregnancy does not occur 🡪 functionless corpus albicans.
