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.

Your circulatory system consists of a pump (your heart) and a network of tubes that conduct blood throughout your body (your blood vessels). With each heartbeat, blood is forced into your arteries, which carry blood away from your heart and toward all of your tissues and organs. As your arteries travel farther from your heart, they divide into progressively smaller vessels called arterioles, which themselves divide into tiny, thin-walled, somewhat leaky vessels called capillaries.

As blood travels through your capillaries, oxygen, nutrients, and fluid are pushed into the surrounding tissues, and carbon dioxide and cellular wastes are retrieved. The blood then proceeds on its way, coursing into progressively larger vessels called venules and then into even larger veins, which finally return the blood to your heart. If the fluid that leaked into your tissues from your bloodstream remained there, your cells would soon drown in the excess. That’s where your lymphatic system picks up the ball.

Function of the Lymphatic System

Mingled among the blood capillaries throughout your body is another network of tiny, thin-walled vessels called lymphatic capillaries. Lymphatic capillaries are designed to pick up the fluid that leaks into your tissues from your bloodstream and return it to your circulatory system.

Nature has ingeniously devised your lymphatic and circulatory systems so the pressure in your blood capillaries is slightly higher than the pressure in your lymphatic capillaries. This pressure gradient from blood capillary to tissue to lymphatic capillary gradually moves fluid from your circulatory system to your lymphatic system, much like water in a river flows downhill.

Just like their neighboring blood capillaries, your lymphatic capillaries join into progressively larger tubes called lymphatic vessels, which transport the fluid from your tissues (this fluid is now called lymph) toward the center of your body. Eventually, the lymph is returned to your bloodstream through two large ducts in the upper central portion of your chest.

The largest of these lymphatic ducts, the thoracic duct, originates in your abdomen, where it collects lymph from your legs, intestine, and other internal organs. As it proceeds upward into your chest, the thoracic duct collects lymph from your thoracic organs, your left arm, and the left side of your head and neck.

The right lymphatic duct, which is much shorter than the thoracic duct, begins high in the right side of your chest. It collects lymph from the right side of your chest wall, your right arm, and the right side of your head and neck. The thoracic duct and the right lymphatic duct reintroduce lymph to your bloodstream through the large veins returning to your heart from your arms: the left and right subclavian veins.

Structure

The general structure of lymphatics is based on that of blood vessels. There is an inner lining of single flattened epithelial cells (simple squamous epithelium) composed of a type of epithelium that is called endothelium, and the cells are called endothelial cells. This layer functions to mechanically transport fluid and since the basement membrane on which it rests is discontinuous; it leaks easily.

The next layer is that of smooth muscles that are arranged in a circular fashion around the endothelium, which by shortening (contracting) or relaxing alter the diameter (caliber) of the lumen. The outermost layer is the adventitia that consists of fibrous tissue. The general structure described here is seen only in larger lymphatics; smaller lymphatics have fewer layers.

The smallest vessels (lymphatic or lymph capillaries) lack both the muscular layer and the outer adventitia. As they proceed forward and in their course are joined by other capillaries, they grow larger and first take on an adventitia, and then smooth muscles.

The lymphatic conducting system broadly consists of two types of channels—the initial lymphatics, the prelymphatics or lymph capillaries that specialize in collection of the lymph from the ISF, and the larger lymph vessels that propel the lymph forward.

Unlike the cardiovascular system, the lymphatic system is not closed and has no central pump. Lymph movement occurs despite low pressure due to peristalsis (propulsion of the lymph due to alternate contraction and relaxation of smooth muscle), valves, and compression during contraction of adjacent skeletal muscle and arterial pulsation.

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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.

The post The Prostate Gland appeared first on Medika Life.

The external genitalia are the accessory structures of the female reproductive system that are external to the vagina. They are also referred to as the vulva or pudendum. The external genitalia include the labia majora, mons pubis, labia minora, clitoris, and glands within the vestibule.

The clitoris is an erectile organ, similar to the male penis, that responds to sexual stimulation. Posterior to the clitoris, the urethra, vagina, paraurethral glands and greater vestibular glands open into the vestibule.

The vulva (pudendum) refers to the external female genitalia. Its functions are threefold:

• Acts as sensory tissue during sexual intercourse
• Assists in micturition by directing the flow of urine
• Protects the internal female reproductive tract from infection.

Structures of the Vulva

The vulva is a collective term for several anatomical structures:

• Mons pubis – a subcutaneous fat pad located anterior to the pubic symphysis. It formed by the fusion of the labia majora.
• Labia majora – two hair-bearing external skin folds.
  • They extend from the mons pubis posteriorly to the posterior commissure (a depression overlying the perineal body).
  • Embryologically derived from labioscrotal swellings
• Labia minora – two hairless folds of skin, which lie within the labia majora.
  • They fuse anteriorly to form the hood of the clitoris and extend posteriorly either side of the vaginal opening.
  • They merge posteriorly, creating a fold of skin known as the fourchette.
  • Embryologically derived from urethral folds
• Vestibule – the area enclosed by the labia minora. It contains the openings of the vagina (external vaginal orifice, vaginal introitus) and urethra.
• Bartholin’s glands – secrete lubricating mucus from small ducts during sexual arousal. They are located either side of the vaginal orifice.
• Clitoris – located under the clitoral hood. It is formed of erectile corpora cavernosa tissue, which becomes engorged with blood during sexual stimulation.
  • Embryologically derived from the genital tubercle

Vascular Supply and Lymphatics

The arterial supply to the vulva is from the paired internal and external pudendal arteries (branches of the internal iliac).

Venous drainage is achieved via the pudendal veins, with smaller labial veins contributing as tributaries.

Lymph drains to the nearby superficial inguinal lymph nodes.

Male External Genitalia

The penis is an external organ of the male reproductive system. It has two main functions:

• Sexual intercourse – During erotic stimulation, the penis undergoes erection, becoming engorged with blood. Following emission, (mixing of the components of semen in the prostatic urethra) ejaculation can occur, whereby semen moves out of the urethra through the external urethral orifice. Finally, the penis undergoes remission, returning to a flaccid state.
• Micturition –The penis also has an important urinary role. It contains the urethra, which carries urine from the bladder to the external urethral orifice, where it is expelled from the body.

Structure of the Penis

The penis can be anatomically divided into three parts:

• Root – the most proximal, fixed part of the penis. It is located in the superficial perineal pouch of the pelvic floor, and is not visible externally. The root contains three erectile tissues (two crura and bulb of the penis), and two muscles (ischiocavernosus and bulbospongiosus).
• Body – the free part of the penis, located between the root and glans. It is suspended from the pubic symphysis. It is composed of three cylinders of erectile tissue – two corpora cavernosa, and the corpus spongiosum.
• Glans –the most distal part of the of penis. It is conical in shape, and is formed by the distal expansion of the corpus spongiosum. This contains the opening of the urethra, termed the external urethral orifice.

Erectile Tissues

The erectile tissues fill with blood during sexual arousal, producing an erection. The root and body of the penis are spanned by three masses of erectile tissue.

In the root, these tissues are known as the left and right crura, and the bulb of the penis. The bulb is situated in the midline of the penile root, and is traversed by the urethra. The left and right crura are located laterally; attached to the ipsilateral ischial ramus, and covered by the paired ischiocavernosal muscles.

The erectile tissues continue into the body of the penis. The left and right crura continue anteriorly into the dorsal part of the penis – they form the two corpora cavernosa. They are separated by the septum of the penis, although often incompletely. The bulb forms the corpus spongiosum, which lies ventrally. The male urethra runs through the corpus spongiosum – to prevent it becoming occluded during erection the corpus spongiosum fills to a reduced pressure.

Distally, the corpus spongiosum expands to form the glans penis.

Muscles

There are four muscles located in the root of the penis:

• Bulbospongiosus (x2) – associated with the bulb of the penis. It contracts to empty the spongy urethra of any residual semen and urine. The anterior fibres also aid in maintaining erection by increasing the pressure in the bulb of the penis.
• Ischiocavernosus (x2) – surrounds the left and right crura of the penis. It contracts to force blood from the cavernous spaces in the crura into the corpus cavernosa – this helps maintain erection.

Fascial Coverings

Each mass of erectile tissue has two fascial coverings. The most superficial layer, immediately under the skin, is the external fascia of Colles (which is in continuity with the fascia of Scarpa which covers the abdominal wall).

A deeper stratum is the deep fascia of the penis (also known as Buck’s fascia). This is a continuation of the deep perineal fascia, and forms a strong membranous covering which holds all three erectile tissues together.

Underneath the deep fascia is the strong fascia called tunica albuginea, forming an individual capsule around each cavernous body and fused in the midline. The incomplete septum between the two corpora is comprised of tunica albuginea.

Ligaments

The root of the penis is supported by two ligaments, which attach it to the surrounding structures:

• Suspensory ligament – a condensation of deep fascia. It connects the erectile bodies of the penis to the pubic symphysis.
• Fundiform ligament – a condensation of abdominal subcutaneous tissue. It runs down from the linea alba, surrounding the penis like a sling, and attaching to the pubic symphysis.

Skin

The skin of the penis is more heavily pigmented than that of the rest of the body. It is connected to the underlying fascias by loose connective tissue.

The prepuce (foreskin) is a double layer of skin and fascia, located at the neck of the glans. It covers the glans to a variable extent. The prepuce is connected to the surface of the glans by the frenulum, a median fold of skin on the ventral surface of the penis. The potential space between the glans and prepuce is termed the preputial sac.

Neurovascular Supply

The penis receives arterial supply from three sources:

• Dorsal arteries of the penis
• Deep arteries of the penis
• Bulbourethral artery

These arteries are all branches of the internal pudendal artery. This vessel arises from the anterior division of the internal iliac artery.

Venous blood is drained from the penis by paired veins. The cavernous spaces are drained by the deep dorsal vein of the penis – this empties into the prostatic venous plexus. The superficial dorsal veins drain the superficial structures of the penis, such as the skin and cutaneous tissues.

The post The External Genitilia appeared first on Medika Life.

The inner lining of the urinary bladder is a mucous membrane of transitional epithelium that is continuous with that in the ureters. When the bladder is empty, the mucosa has numerous folds called rugae. The rugae and transitional epithelium allow the bladder to expand as it fills.

The second layer in the walls is the submucosa, which supports the mucous membrane. It is composed of connective tissue with elastic fibers.

The next layer is the muscularis, which is composed of smooth muscle. The smooth muscle fibers are interwoven in all directions and, collectively, these are called the detrusor muscle. Contraction of this muscle expels urine from the bladder. On the superior surface, the outer layer of the bladder wall is parietal peritoneum. In all other regions, the outer layer is fibrous connective tissue.

There is a triangular area, called the trigone, formed by three openings in the floor of the urinary bladder. Two of the openings are from the ureters and form the base of the trigone. Small flaps of mucosa cover these openings and act as valves that allow urine to enter the bladder but prevent it from backing up from the bladder into the ureters. The third opening, at the apex of the trigone, is the opening into the urethra. A band of the detrusor muscle encircles this opening to form the internal urethral sphincter.

Shape of the Bladder

The appearance of the bladder varies depending on the amount of urine stored. When full, it exhibits an oval shape, and when empty it is flattened by the overlying bowel.

The external features of the bladder are:

• Apex – located superiorly, pointing towards the pubic symphysis. It is connected to the umbilicus by the median umbilical ligament (a remnant of the urachus).
• Body – main part of the bladder, located between the apex and the fundus
• Fundus (or base) – located posteriorly. It is triangular-shaped, with the tip of the triangle pointing backwards.
• Neck – formed by the convergence of the fundus and the two inferolateral surfaces. It is continuous with the urethra.

Urine enters the bladder through the left and right ureters, and exits via the urethra. Internally, these orifices are marked by the trigone – a triangular area located within the fundus.

In contrast to the rest of the internal bladder, the trigone has smooth walls (this is explained by the different embryological origin: the trigone is developed by the integration of two mesonephric ducts at the base of the bladder).

Musculature

The musculature of the bladder plays a key role in the storage and emptying of urine.

In order to contract during micturition, the bladder wall contains specialised smooth muscle – known as detrusor muscle. Its fibres are orientated in multiple directions, thus retaining structural integrity when stretched. It receives innervation from both the sympathetic and parasympathetic nervous systems.

The fibers of the detrusor muscle often become hypertrophic (presenting as prominent trabeculae) in order to compensate for increased workload of the bladder emptying. This is very common in conditions that obstruct the urine outflow such as benign prostatic hyperplasia.

There are also two muscular sphincters located in the urethra:

• Internal urethral sphincter:
  • Male – consists of circular smooth fibres, which are under autonomic control. It is thought to prevent seminal regurgitation during ejaculation.
  • Females – thought to be a functional sphincter (i.e. no sphincteric muscle present). It is formed by the anatomy of the bladder neck and proximal urethra.
• External urethral sphincter – has the same structure in both sexes. It is skeletal muscle, and under voluntary control. However, in males the external sphincteric mechanism is more complex, as it correlates with fibers of the rectourethralis muscle and the levator ani muscle.

The Bladder Stretch Reflex

The bladder stretch reflex is a primitive spinal reflex, in which micturition is stimulated in response to stretch of the bladder wall. It is analogous to a muscle spinal reflex, such as the patella reflex.

During toilet training in infants, this spinal reflex is overridden by the higher centres of the brain, to give voluntary control over micturition.

The reflex arc:

• Bladder fills with urine, and the bladder walls stretch. Sensory nerves detect stretch and transmit this information to the spinal cord.
• Interneurons within the spinal cord relay the signal to the parasympathetic efferents (the pelvic nerve).
• The pelvic nerve acts to contract the detrusor muscle, and stimulate micturition.

Although it is non-functional post childhood, the bladder stretch reflex needs to be considered in spinal injuries (where the descending inhibition cannot reach the bladder), and in neurodegenerative diseases (where the brain is unable to generate inhibition).

The post The Urinary Bladder appeared first on Medika Life.

Healthy kidneys filter about a half cup of blood every minute, removing wastes and extra water to make urine. The urine flows from the kidneys to the bladder through two thin tubes of muscle called ureters, one on each side of your bladder. Your bladder stores urine. Your kidneys, ureters, and bladder are part of your urinary tract.

Each of your kidneys is made up of about a million filtering units called nephrons. Each nephron includes a filter, called the glomerulus, and a tubule. The nephrons work through a two-step process: the glomerulus filters your blood, and the tubule returns needed substances to your blood and removes wastes.

Kidney Structure

The kidneys are encased in complex layers of fascia and fat. They are arranged as follows (deep to superficial):

• Renal capsule – tough fibrous capsule.
• Perirenal fat – collection of extraperitoneal fat.
• Renal fascia (also known as Gerota’s fascia or perirenal fascia) – encloses the kidneys and the suprarenal glands.
• Pararenal fat – mainly located on the posterolateral aspect of the kidney.

Internally, the kidneys have an intricate and unique structure. The renal parenchyma can be divided into two main areas – the outer cortex and inner medulla. The cortex extends into the medulla, dividing it into triangular shapes – these are known as renal pyramids.

The apex of a renal pyramid is called a renal papilla. Each renal papilla is associated with a structure known as the minor calyx, which collects urine from the pyramids. Several minor calices merge to form a major calyx. Urine passes through the major calices into the renal pelvis, a flattened and funnel-shaped structure. From the renal pelvis, urine drains into the ureter, which transports it to the bladder for storage.

The medial margin of each kidney is marked by a deep fissure, known as the renal hilum. This acts as a gateway to the kidney – normally the renal vessels and ureter enter/exit the kidney via this structure.

Arterial Supply

The kidneys are supplied with blood via the renal arteries, which arise directly from the abdominal aorta, immediately distal to the origin of the superior mesenteric artery.  Due to the anatomical position of the abdominal aorta (slightly to the left of the midline), the right renal artery is longer, and crosses the vena cava posteriorly.

The renal artery enters the kidney via the renal hilum. At the hilum level, the renal artery forms an anterior and a posterior division, which carry 75% and 25% of the blood supply to the kidney, respectively. Five segmental arteries originate from these two divisions.

The avascular plane of the kidney (line of Brodel) is an imaginary line along the lateral and slightly posterior border of the kidney, which delineates the segments of the kidney supplied by the anterior and posterior divisions. It is an important access route for both open and endoscopic surgical access of the kidney, as it minimizes the risk of damage to major arterial branches.

The segmental branches of the renal undergo further divisions to supply the renal parenchyma:

• Each segmental artery divides to form interlobar arteries. They are situated either side every renal pyramid.
• These interlobar arteries undergo further division to form the arcuate arteries.
• At 90 degrees to the arcuate arteries, the interlobular arteries arise.
• The interlobular arteries pass through the cortex, dividing one last time to form afferent arterioles.
• The afferent arterioles form a capillary network, the glomerulus, where filtration takes place. The capillaries come together to form the efferent arterioles.

In the outer two-thirds of the renal cortex, the efferent arterioles form what is a known as a peritubular network, supplying the nephron tubules with oxygen and nutrients. The inner third of the cortex and the medulla are supplied by long, straight arteries called vasa recta.

Venous Drainage

The kidneys are drained of venous blood by the left and right renal veins. They leave the renal hilum anteriorly to the renal arteries, and empty directly into the inferior vena cava.

As the vena cava lies slightly to the right, the left renal vein is longer, and travels anteriorly to the abdominal aorta below the origin of the superior mesenteric artery. The right renal artery lies posterior to the inferior vena cava.

Lymphatics

Lymph from the kidney drains into the lateral aortic (or para-aortic) lymph nodes, which are located at the origin of the renal arteries.

The post The Kidneys appeared first on Medika Life.

Male Urethra

The male urethra is approximately 15-20cm long. In addition to urine, the male urethra transports semen – a fluid containing spermatozoa and sex gland secretions.

According to the latest classification, the male urethra can be divided anatomically into three parts (proximal to distal):

• Prostatic urethra:
  • Begins as a continuation of the bladder neck and passes through the prostate gland.
  • Receives the ejaculatory ducts (containing spermatozoa from the testes and seminal fluid from the seminal vesicle glands) and the prostatic ducts (containing alkaline fluid).
  • It is the widest and most dilatable portion of the urethra.
• Membranous urethra:
  • Passes through the pelvic floor and the deep perineal pouch.
  • Surrounded by the external urethral sphincter – which provides voluntary control of micturition.
  • It is the narrowest and least dilatable portion of the urethra.
• Penile (bulbous) urethra:
  • Passes through the bulb and corpus spongiosum of the penis, ending at the external urethral orifice (the meatus).
  • Receives the bulbourethral glands proximally.
  • In the glans (head) of the penis, the urethra dilates to form the navicular fossa.

Female Urethra

In females, the urethra is relatively short (approximately 4cm). It begins at the neck of the bladder, and passes inferiorly through the perineal membrane and muscular pelvic floor. The urethra opens directly onto the perineum, in an area between the labia minora, known as the vestibule.

Within the vestibule, the urethral orifice is located anteriorly to the vaginal opening, and 2-3cm posteriorly to the clitoris. The distal end of the urethra is marked by the presence of two mucous glands that lie either side of the urethra – Skene’s glands. They are homologous to the male prostate.

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Cardia

The cardia is the portion of the stomach surrounding the cardioesophageal junction, or cardiac orifice (the opening of the esophagus into the stomach). Tumors of the cardioesophageal junction are usually coded to the stomach.

Fundus

The fundus is the enlarged portion to the left and above the cardiac orifice.

Body

The body, or corpus, is the central part of the stomach.

Pyloric antrum

The pyloric antrum is the lower or distal portion above the duodenum. The opening between the stomach and the small intestine is the pylorus, and the very powerful sphincter, which regulates the passage of chyme into the duodenum, is called the pyloric sphincter.

The stomach is suspended from the abdominal wall by the lesser omentum. The greater omentum attaches the stomach to the transverse colon, spleen and diaphragm.

The common mesentery suspends the small intestine. The parietal peritoneum lies over the duodenum and other structures, such as the abdominal aorta. Because they lie behind the peritoneum, they are called retroperitoneal structures.

Layers of the stomach wall

The stomach is made up of several layers of tissue:

• The mucosa (mucous membrane) is the inner lining of the stomach. When the stomach is empty the mucosa has a ridged appearance. These ridges (rugae) flatten out as the stomach fills with food.
• The next layer that covers the mucosa is the submucosa. It is made up of connective tissue that contains larger blood and lymph vessels, nerve cells and fibres.
• The muscularis propria (or muscularis externa) is the next layer that covers the submucosa. It is the main muscle of the stomach and is made up of 3 layers of muscle.
• The serosa is the fibrous membrane that covers the outside of the stomach. The serosa of the stomach is also called the visceral peritoneum.

Function

The stomach has 3 main functions:

• temporary storage for food, which passes from the esophagus to the stomach where it is held for 2 hours or longer
• mixing and breakdown of food by contraction and relaxation of the muscle layers in the stomach
• digestion of food

The mucosa contains specialized cells and glands that produce hydrochloric acid and digestive enzymes to help digest food. The mucosa in the cardiac and pyloric regions of the stomach release mucus that helps protect the lining of the stomach from the acid produced for digestion. Other specialized cells in the mucosa of the pylorus release the hormone gastrin into the blood. Gastrin helps to stimulate the release of acid and enzymes from the mucosa. Gastrin also helps the muscles of the stomach to start contracting.

Food is broken down into a thick, acidic, soupy mixture called chyme. The pyloric sphincter relaxes once chyme formation is complete. Chyme then passes into the duodenum. The duodenum plays a big role in absorption of the food we eat. The stomach does not play a big role in absorption of food. It only absorbs water, alcohol and some drugs.

The post The Stomach appeared first on Medika Life.

Layers of the Heart Wall

Three layers of tissue form the heart wall. The outer layer of the heart wall is the epicardium, the middle layer is the myocardium, and the inner layer is the endocardium.

Chambers of the Heart

The internal cavity of the heart is divided into four chambers:

• Right atrium
• Right ventricle
• Left atrium
• Left ventricle

The two atria are thin-walled chambers that receive blood from the veins. The two ventricles are thick-walled chambers that forcefully pump blood out of the heart. Differences in thickness of the heart chamber walls are due to variations in the amount of myocardium present, which reflects the amount of force each chamber is required to generate.

The right atrium receives deoxygenated blood from systemic veins; the left atrium receives oxygenated blood from the pulmonary veins.

Valves of the Heart

Pumps need a set of valves to keep the fluid flowing in one direction and the heart is no exception. The heart has two types of valves that keep the blood flowing in the correct direction. The valves between the atria and ventricles are called atrioventricular valves (also called cuspid valves), while those at the bases of the large vessels leaving the ventricles are called semilunar valves.

The right atrioventricular valve is the tricuspid valve. The left atrioventricular valve is the bicuspid, or mitral, valve. The valve between the right ventricle and pulmonary trunk is the pulmonary semilunar valve. The valve between the left ventricle and the aorta is the aortic semilunar valve.

When the ventricles contract, atrioventricular valves close to prevent blood from flowing back into the atria. When the ventricles relax, semilunar valves close to prevent blood from flowing back into the ventricles.

Pathway of Blood through the Heart

While it is convenient to describe the flow of blood through the right side of the heart and then through the left side, it is important to realize that both atria and ventricles contract at the same time. The heart works as two pumps, one on the right and one on the left, working simultaneously. Blood flows from the right atrium to the right ventricle, and then is pumped to the lungs to receive oxygen. From the lungs, the blood flows to the left atrium, then to the left ventricle. From there it is pumped to the systemic circulation.

Blood Supply to the Myocardium

The myocardium of the heart wall is a working muscle that needs a continuous supply of oxygen and nutrients to function efficiently. For this reason, cardiac muscle has an extensive network of blood vessels to bring oxygen to the contracting cells and to remove waste products.

The right and left coronary arteries, branches of the ascending aorta, supply blood to the walls of the myocardium. After blood passes through the capillaries in the myocardium, it enters a system of cardiac (coronary) veins. Most of the cardiac veins drain into the coronary sinus, which opens into the right atrium.

Physiology of the Heart

The conduction system includes several components. The first part of the conduction system is the sinoatrial node . Without any neural stimulation, the sinoatrial node rhythmically initiates impulses 70 to 80 times per minute. Because it establishes the basic rhythm of the heartbeat, it is called the pacemaker of the heart. Other parts of the conduction system include the atrioventricular node, atrioventricular bundle, bundle branches, and conduction myofibers. All of these components coordinate the contraction and relaxation of the heart chambers.

Cardiac Cycle

The cardiac cycle refers to the alternating contraction and relaxation of the myocardium in the walls of the heart chambers, coordinated by the conduction system, during one heartbeat. Systole is the contraction phase of the cardiac cycle, and diastole is the relaxation phase. At a normal heart rate, one cardiac cycle lasts for 0.8 second.

Heart Sounds

The sounds associated with the heartbeat are due to vibrations in the tissues and blood caused by closure of the valves. Abnormal heart sounds are called murmurs.

Heart Rate

The sinoatrial node, acting alone, produces a constant rhythmic heart rate. Regulating factors are reliant on the atrioventricular node to increase or decrease the heart rate to adjust cardiac output to meet the changing needs of the body. Most changes in the heart rate are mediated through the cardiac center in the medulla oblongata of the brain. The center has both sympathetic and parasympathetic components that adjust the heart rate to meet the changing needs of the body.

Peripheral factors such as emotions, ion concentrations, and body temperature may affect heart rate. These are usually mediated through the cardiac center.

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