Structure

The ovaries are covered on the outside by a layer of simple cuboidal epithelium called germinal (ovarian) epithelium. This is actually the visceral peritoneum that envelops the ovaries. Underneath this layer is a dense connective tissue capsule, the tunica albuginea. The substance of the ovaries is distinctly divided into an outer cortex and an inner medulla. The cortex appears more dense and granular due to the presence of numerous ovarian follicles in various stages of development. Each of the follicles contains an oocyte, a female germ cell. The medulla is a loose connective tissue with abundant blood vessels, lymphatic vessels, and nerve fibers.

Oogenesis

Female sex cells, or gametes, develop in the ovaries by a form of meiosis called oogenesis. The sequence of events in oogenesis is similar to the sequence in spermatogenesis, but the timing and final result are different. Early in fetal development, primitive germ cells in the ovaries differentiate into oogonia. These divide rapidly to form thousands of cells, still called oogonia, which have a full complement of 46 (23 pairs) chromosomes. Oogonia then enter a growth phase, enlarge, and become primary oocytes. The diploid (46 chromosomes) primary oocytes replicate their DNA and begin the first meiotic division, but the process stops in prophase and the cells remain in this suspended state until puberty.

Many of the primary oocytes degenerate before birth, but even with this decline, the two ovaries together contain approximately 700,000 oocytes at birth. This is the lifetime supply, and no more will develop. This is quite different than the male in which spermatogonia and primary spermatocytes continue to be produced throughout the reproductive lifetime. By puberty the number of primary oocytes has further declined to about 400,000.

Beginning at puberty, under the influence of follicle-stimulating hormone, several primary oocytes start to grow again each month. One of the primary oocytes seems to outgrow the others and it resumes meiosis I. The other cells degenerate. The large cell undergoes an unequal division so that nearly all the cytoplasm, organelles, and half the chromosomes go to one cell, which becomes a secondary oocyte. The remaining half of the chromosomes go to a smaller cell called the first polar body. The secondary oocyte begins the second meiotic division, but the process stops in metaphase. At this point ovulation occurs. If fertilization occurs, meiosis II continues. Again this is an unequal division with all of the cytoplasm going to the ovum, which has 23 single-stranded chromosome. The smaller cell from this division is a second polar body.

The first polar body also usually divides in meiosis I to produce two even smaller polar bodies. If fertilization does not occur, the second meiotic division is never completed and the secondary oocyte degenerates. Here again there are obvious differences between the male and female. In spermatogenesis, four functional sperm develop from each primary spermatocyte. In oogenesis, only one functional fertilizable cell develops from a primary oocyte. The other three cells are polar bodies and they degenerate.

Ovarian Follicle Development

An ovarian follicle consists of a developing oocyte surrounded by one or more layers of cells called follicular cells. At the same time that the oocyte is progressing through meiosis, corresponding changes are taking place in the follicular cells. Primordial follicles, which consist of a primary oocyte surrounded by a single layer of flattened cells, develop in the fetus and are the stage that is present in the ovaries at birth and throughout childhood.

Beginning at puberty, follicle-stimulating hormone stimulates changes in the primordial follicles. The follicular cells become cuboidal, the primary oocyte enlarges, and it is now a primary follicle. The follicles continue to grow under the influence of follicle-stimulating hormone, and the follicular cells proliferate to form several layers of granulose cells around the primary oocyte. Most of these primary follicles degenerate along with the primary oocytes within them, but usually one continues to develop each month. The granulosa cells start secreting estrogen and a cavity, or antrum, forms within the follicle. When the antrum starts to develop, the follicle becomes a secondary follicle. The granulose cells also secrete a glycoprotein substance that forms a clear membrane, the zona pellucida, around the oocyte. After about 10 days of growth the follicle is a mature vesicular (graafian) follicle, which forms a “blister” on the surface of the ovary and contains a secondary oocyte ready for ovulation.

Ovulation

Ovulation, prompted by luteinizing hormone from the anterior pituitary, occurs when the mature follicle at the surface of the ovary ruptures and releases the secondary oocyte into the peritoneal cavity. The ovulated secondary oocyte, ready for fertilization is still surrounded by the zona pellucida and a few layers of cells called the corona radiata. If it is not fertilized, the secondary oocyte degenerates in a couple of days. If a sperm passes through the corona radiata and zona pellucida and enters the cytoplasm of the secondary oocyte, the second meiotic division resumes to form a polar body and a mature ovum

After ovulation and in response to luteinizing hormone, the portion of the follicle that remains in the ovary enlarges and is transformed into a corpus luteum. The corpus luteum is a glandular structure that secretes progesterone and some estrogen. Its fate depends on whether fertilization occurs. If fertilization does not take place, the corpus luteum remains functional for about 10 days; then it begins to degenerate into a corpus albicans, which is primarily scar tissue, and its hormone output ceases. If fertilization occurs, the corpus luteum persists and continues its hormone functions until the placenta develops sufficiently to secrete the necessary hormones. Again, the corpus luteum ultimately degenerates into corpus albicans, but it remains functional for a longer period of time.

The post The Ovaries appeared first on Medika Life.

Anatomical Structure

The uterus is a thick-walled muscular organ capable of expansion to accommodate a growing fetus. It is connected distally to the vagina, and laterally to the uterine tubes.

The uterus has three parts;

• Fundus – top of the uterus, above the entry point of the uterine tubes.
• Body – usual site for implantation of the blastocyst.
• Cervix – lower part of uterus linking it with the vagina. This part is structurally and functionally different to the rest of the uterus.

The Cervix

The cervix is the lower portion of the uterus, an organ of the female reproductive tract. It connects the vagina with the main body of the uterus, acting as a gateway between them.

The cervix is composed of two regions; the ectocervix and the endocervical canal. The ectocervix is the portion of the cervix that projects into the vagina. It is lined by stratified squamous non-keratinized epithelium. The opening in the ectocervix, the external os, marks the transition from the ectocervix to the endocervical canal.

The endocervical canal (or endocervix) is the more proximal, and ‘inner’ part of the cervix. It is lined by a mucus-secreting simple columnar epithelium. The endocervical canal ends, and the uterine cavity begins, at a narrowing called the internal os.

Functions of the cervix

The cervix performs two main functions:

• It facilitates the passage of sperm into the uterine cavity. This is achieved via dilation of the external and internal os.
• Maintains sterility of the upper female reproductive tract. The cervix, and all structures superior to it, are sterile. This ultimately protects the uterine cavity and the upper genital tract by preventing bacterial invasion. This environment is maintained by the frequent shedding of the endometrium, thick cervical mucus and a narrow external os.

Histological Structure

The fundus and body of the uterus are composed of three tissue layers;

• Peritoneum – a double layered membrane, continuous with the abdominal peritoneum. Also known as the perimetrium.
• Myometrium – thick smooth muscle layer. Cells of this layer undergo hypertrophy and hyperplasia during pregnancy in preparation to expel the fetus at birth.
• Endometrium – inner mucous membrane lining the uterus. It can be further subdivided into 2 parts:
  • Deep stratum basalis: Changes little throughout the menstrual cycle and is not shed at menstruation.
  • Superficial stratum functionalis: Proliferates in response to oestrogens, and becomes secretory in response to progesterone. It is shed during menstruation and regenerates from cells in the stratum basalis layer.

Ligaments

The tone of the pelvic floor provides the primary support for the uterus. Some ligaments provide further support, securing the uterus in place.

They are:

• Broad Ligament: This is a double layer of peritoneum attaching the sides of the uterus to the pelvis. It acts as a mesentery for the uterus and contributes to maintaining it in position.
• Round Ligament: A remnant of the gubernaculum extending from the uterine horns to the labia majora via the inguinal canal. It functions to maintain the anteverted position of the uterus.
• Ovarian Ligament: Joins the ovaries to the uterus.
• Cardinal Ligament: Located at the base of the broad ligament, the cardinal ligament extends from the cervix to the lateral pelvic walls. It contains the uterine artery and vein in addition to providing support to the uterus.
• Uterosacral Ligament: Extends from the cervix to the sacrum. It provides support to the uterus.

Vascular Supply and Lymphatics

The blood supply to the uterus is via the uterine artery. Venous drainage is via a plexus in the broad ligament that drains into the uterine veins.

Lymphatic drainage of the uterus is via the iliac, sacral, aortic and inguinal lymph nodes.

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Externally, each breast has a raised nipple, which is surrounded by a circular pigmented area called the areola. The nipples are sensitive to touch, due to the fact that they contain smooth muscle that contracts and causes them to become erect in response to stimulation.

Internally, the adult female breast contains 15 to 20 lobes of glandular tissue that radiate around the nipple. The lobes are separated by connective tissue and adipose. The connective tissue helps support the breast. Some bands of connective tissue, called suspensory (Cooper’s) ligaments, extend through the breast from the skin to the underlying muscles. The amount and distribution of the adipose tissue determines the size and shape of the breast. Each lobe consists of lobules that contain the glandular units. A lactiferous duct collects the milk from the lobules within each lobe and carries it to the nipple. Just before the nipple, the lactiferous duct enlarges to form a lactiferous sinus (ampulla), which serves as a reservoir for milk. After the sinus, the duct again narrows and each duct opens independently on the surface of the nipple.

Mammary gland function is regulated by hormones. At puberty, increasing levels of estrogen stimulate the development of glandular tissue in the female breast. Estrogen also causes the breast to increase in size through the accumulation of adipose tissue. Progesterone stimulates the development of the duct system. During pregnancy, these hormones enhance further development of the mammary glands. Prolactin from the anterior pituitary stimulates the production of milk within the glandular tissue, and oxytocin causes the ejection of milk from the glands.

Surface Anatomy

The breast is located on the anterior thoracic wall. It extends horizontally from the lateral border of the sternum to the mid-axillary line. Vertically, it spans between the 2nd and 6th intercostal cartilages. It lies superficially to the pectoralis major and serratus anterior muscles.

The breast can be considered to be composed of two regions:

• Circular body – largest and most prominent part of the breast.
• Axillary tail – smaller part, runs along the inferior lateral edge of the pectoralis major towards the axillary fossa.

At the centre of the breast is the nipple, composed mostly of smooth muscle fibres. Surrounding the nipple is a pigmented area of skin termed the areolae. There are numerous sebaceous glands within the areolae – these enlarge during pregnancy, secreting an oily substance that acts as a protective lubricant for the nipple.

Anatomical Structure

The breast is composed of mammary glands surrounded by a connective tissue stroma.

Mammary Glands

The mammary glands are modified sweat glands. They consist of a series of ducts and secretory lobules (15-20).

Each lobule consists of many alveoli drained by a single lactiferous duct. These ducts converge at the nipple like spokes of a wheel.

Connective Tissue Stroma

The connective tissue stroma is a supporting structure which surrounds the mammary glands. It has a fibrous and a fatty component.

The fibrous stroma condenses to form suspensory ligaments (of Cooper). These ligaments have two main functions:

• Attach and secure the breast to the dermis and underlying pectoral fascia.
• Separate the secretory lobules of the breast.

Pectoral Fascia

The base of the breast lies on the pectoral fascia – a flat sheet of connective tissue associated with the pectoralis major muscle. It acts as an attachment point for the suspensory ligaments.

There is a layer of loose connective tissue between the breast and pectoral fascia – known as the retromammary space. This is a potential space, often used in reconstructive plastic surgery.

Vasculature

Arterial supply to the medial aspect of the breast is via the internal thoracic artery (also known as internal mammary artery) – a branch of the subclavian artery.

The lateral part of the breast receives blood from four vessels:

• Lateral thoracic and thoracoacromial branches – originate from the axillary artery.
• Lateral mammary branches – originate from the posterior intercostal arteries (derived from the aorta). They supply the lateral aspect of the breast in the 2^nd 3^rd and 4^th intercostal spaces.
• Mammary branch – originates from the anterior intercostal artery.

The veins of the breast correspond with the arteries, draining into the axillary and internal thoracic veins.

Lymphatics

The lymphatic drainage of the breast is of great clinical importance due to its role in the metastasis of breast cancer cells.

There are three groups of lymph nodes that receive lymph from breast tissue – the axillary nodes (75%), parasternal nodes (20%) and posterior intercostal nodes (5%).

The skin of the breast also receives lymphatic drainage:

• Skin – drains to the axillary, inferior deep cervical and infraclavicular nodes.
• Nipple and areola – drains to the subareolar lymphatic plexus.

The post The Mammary Glands appeared first on Medika Life.

The testes are located within the scrotum, with the epididymis situated on the posterolateral aspect of each testicle. Commonly, the left testicle lies lower than the right. They are suspended from the abdomen by the spermatic cord – collection of vessels, nerves and ducts that supply the testes.

Originally, the testes are located on the posterior abdominal wall. During embryonic development they descend down the abdomen, and through the inguinal canal to reach the scrotum. They carry their neurovascular and lymphatic supply with them.

Anatomical Structure

The testes have an ellipsoid shape. They consist of a series of lobules, each containing seminiferous tubules supported by interstitial tissue. The seminiferous tubules are lined by Sertoli cells that aid the maturation process of the spermatozoa. In the interstitial tissue lie the Leydig cells that are responsible for testosterone production.

Spermatozoa are produced in the seminiferous tubules. The developing sperm travels through the tubules, collecting in the rete testes. Ducts known as efferent tubules transport the sperm from the rete testes to the epididymis for storage and maturation.

Inside the scrotum, the testes are covered almost entirely by the tunica vaginalis, a closed sac of parietal peritoneal origin that contains a small amount of viscous fluid. This sac covers the anterior surface and sides of each testicle and works much like the peritoneal sac, lubricating the surfaces of the testes and allowing for friction-free movement.

The testicular parenchyma is protected by the tunica albuginea, a fibrous capsule that encloses the testes. It penetrates into the parenchyma of each testicle with diaphragms, dividing it into lobules.

The epididymis consists of a single heavily coiled duct. It can be divided into three parts; head, body and tail.

• Head – The most proximal part of the epididymis. It is formed by the efferent tubules of the testes, which transport sperm from the testes to the epididymis.
• Body – Formed by the heavily coiled duct of the epididymis.
• Tail – The most distal part of the epididymis. It marks the origin of the vas deferens, which transports sperm to the prostatic portion of the urethra for ejaculation.

Vascular Supply

The main arterial supply to the testes and epididymis is via the paired testicular arteries, which arise directly from the abdominal aorta. They descend down the abdomen, and pass into the scrotum via the inguinal canal, contained within the spermatic cord.

However, the testes are also supplied by branches of the cremasteric artery (from the inferior epigastric artery) and the artery of the vas deferens (from the inferior vesical artery). These branches give anastomoses to the main testicular artery.

Venous drainage is achieved via the paired testicular veins. They are formed from the pampiniform plexus in the scrotum – a network of veins wrapped around the testicular artery. In the retroperitoneal space of the abdomen, the left testicular vein drains into the left renal vein, while the right testicular vein drains directly into the inferior vena cava.

Lymphatics

Since the testes are originally retroperitoneal organs, the lymphatic drainage is to the lumbar and para-aortic nodes, along the lumbar vertebrae. This is in contrast to the scrotum, which drains into the nearby superficial inguinal nodes.

Spermatogenesis

Sperm are produced by spermatogenesis within the seminiferous tubules. A transverse section of a seminiferous tubule shows that it is packed with cells in various stages of development. Interspersed with these cells, there are large cells that extend from the periphery of the tubule to the lumen. These large cells are the supporting, or sustentacular cells (Sertoli’s cells), which support and nourish the other cells.

Early in embryonic development, primordial germ cells enter the testes and differentiate into spermatogonia, immature cells that remain dormant until puberty. Spermatogonia are diploid cells, each with 46 chromosomes (23 pairs) located around the periphery of the seminiferous tubules. At puberty, hormones stimulate these cells to begin dividing by mitosis. Some of the daughter cells produced by mitosis remain at the periphery as spermatogonia. Others are pushed toward the lumen, undergo some changes, and become primary spermatocytes. Because they are produced by mitosis, primary spermatocytes, like spermatogonia, are diploid and have 46 chromosomes.

Each primary spermatocytes goes through the first meiotic division, meiosis I, to produce two secondary spermatocytes, each with 23 chromosomes (haploid). Just prior to this division, the genetic material is replicated so that each chromosome consists of two strands, called chromatids, that are joined by a centromere. During meiosis I, one chromosome, consisting of two chromatids, goes to each secondary spermatocyte. In the second meiotic division, meiosis II, each secondary spermatocyte divides to produce two spermatids. There is no replication of genetic material in this division, but the centromere divides so that a single-stranded chromatid goes to each cell. As a result of the two meiotic divisions, each primary spermatocyte produces four spermatids. During spermatogenesis there are two cellular divisions, but only one replication of DNA so that each spermatid has 23 chromosomes (haploid), one from each pair in the original primary spermatocyte. Each successive stage in spermatogenesis is pushed toward the center of the tubule so that the more immature cells are at the periphery and the more differentiated cells are nearer the center.

Spermatogenesis (and oogenesis in the female) differs from mitosis because the resulting cells have only half the number of chromosomes as the original cell. When the sperm cell nucleus unites with an egg cell nucleus, the full number of chromosomes is restored. If sperm and egg cells were produced by mitosis, then each successive generation would have twice the number of chromosomes as the preceding one.

The final step in the development of sperm is called spermiogenesis. In this process, the spermatids formed from spermatogenesis become mature spermatozoa, or sperm. The mature sperm cell has a head, midpiece, and tail. The head, also called the nuclear region, contains the 23 chromosomes surrounded by a nuclear membrane. The tip of the head is covered by an acrosome, which contains enzymes that help the sperm penetrate the female gamete. The midpiece, metabolic region, contains mitochondria that provide adenosine triphosphate (ATP). The tail or locomotor region, uses a typical flagellum for locomotion. The sperm are released into the lumen of the seminiferous tubule and leave the testes. They then enter the epididymis where they undergo their final maturation and become capable of fertilizing a female gamete.

Sperm production begins at puberty and continues throughout the life of a male. The entire process, beginning with a primary spermatocyte, takes about 74 days. After ejaculation, the sperm can live for about 48 hours in the female reproductive tract.

The post The Testes appeared first on Medika Life.

It secretes proteolytic enzymes into the semen, which act to break down clotting factors in the ejaculate. This allows the semen to remain in a fluid state, moving throughout the female reproductive tract for potential fertilisation.

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The prostate is positioned inferiorly to the neck of the bladderand superiorly to the external urethral sphincter, with the levator ani muscle lying inferolaterally to the gland.

Most importantly, posteriorly to the prostate lies the ampulla of the rectum – this anatomical arrangement is utilised during Digital Rectal Examinations (DRE), allowing physicians to examine the gland.

The proteolytic enzymes leave the prostate via the prostatic ducts. These open into the prostatic portion of the urethra, through 10-12 openings at each side of the seminal colliculus (or verumontanum); secreting the enzymes into the semen immediately before ejaculation.

Anatomical Structure

The prostate is commonly described as being the size of a walnut. Roughly two-thirds of the prostate is glandular in structure and the remaining third is fibromuscular. The gland itself is surrounded by a thin fibrous capsule of the prostate. This is not a real capsule; it rather resembles the thin connective tissue known as adventitia in the large blood vessels.

Traditionally, the prostate is divided into anatomical lobes (inferoposterior, inferolateral, superomedial, and anteromedial) by the urethra and the ejaculatory ducts as they pass through the organ. However, more important clinically is the histological division of the prostate into three zones (according to McNeal):

• Central zone –surrounds the ejaculatory ducts, comprising approximately 25% of normal prostate volume.
  • The ducts of the glands from the central zone are obliquely emptying in the prostatic urethra, thus being rather immune to urine reflux.
• Transitional zone – located centrally and surrounds the urethra, comprising approximately 5-10% of normal prostate volume.
  • The glands of the transitional zone are those that typically undergo benign hyperplasia (BPH)
• Peripheral zone –makes up the main body of the gland (approximately 65%) and is located posteriorly.
  • The ducts of the glands from the peripheral zone are vertically emptying in the prostatic urethra; that may explain the tendency of these glands to permit urine reflux.
  • That also explains the high incidence of acute and chronic inflammation found in these compartments, a fact that may be linked to the high incidence of prostate carcinoma at the peripheral zone.
  • The peripheral zone is mainly the area felt against the rectum on DRE, which is of irreplaceable value.

The fibromuscular stroma (or fourth zone for some) is situated anteriorly in the gland. It merges with the tissue of the urogenital diaphragm. This part of the gland is actually the result of interaction of the prostate gland budding around the urethra during prostate embryogenesis and the common horseshoe-like muscle precursor of the smooth and striated muscle that will eventually form the internal and external urethra sphincter.

Vasculature

The arterial supply to the prostate comes from the prostatic arteries, which are mainly derived from the internal iliac arteries. Some branches may also arise from the internal pudendal and middle rectal arteries.

Venous drainage of the prostate is via the prostatic venous plexus, draining into the internal iliac veins. However, the prostatic venous plexus also connects posteriorly by networks of veins, including the Batson venous plexus, to the internal vertebral venous plexus.

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