BIOLOGY 03048, ANATOMY: WEEKS 8, 9, 10:
PELVIS AND PERINEUM; HISTOLOGY OF ABDOMINOPELVIC REGION 10/21/99
W. Crone (303 FTZ, 629-7439, cronewil@hvcc.edu, www.hvcc.edu/academ/faculty/crone/index.html)
Readings: Moore and Dalley, Ch.3; Cormack, Chs. 7, 8, 9
possible web site: http://vh.radiology.uiowa.edu/Providers/Textbooks/pelvis/muscle.html (pelvic muscles)
histology samplers: http://www-medlib.med.utah.edu/WebPath/TUTORIAL/IBD/IBD.html
(tutorial on inflammatory bowel disease)
http://www-medlib.med.utah.edu/WebPath/TUTORIAL/PROSTATE/PROSTATE.html (prostate pathology)
http://www-medlib.med.utah.edu/WebPath/TUTORIAL/CYTOPATH/CYTOPATH.html
(pap smears and cervical histology)
THE THIRD LECTURE EXAM ON TUESDAY, NOVEMBER 9, WILL COVER THROUGH THIS MATERIAL
PELVIS: Hip bone (os coxa) made of ilium, ischium, and pubis. Ischial features of the ischial tuberosity, upon which we sit, and ischial spine useful for today's discussion. Strong hip bone connections to the sacrum allow for a stable pelvis. The sacrum is prevented from tilting by attached ligaments, e.g., the sacrospinous ligament (to the ischial spine) and the sacrotuberous ligament (to the ischial tuberosity). These ligaments convert the greater and lesser sciatic notches into greater and lesser sciatic foramina. The greater sciatic foramen is the main way that vessels and arteries leave/enter the pelvis, and the lesser sciatic foramen is the pathway to external genitalia and superficial structures. The female pelvis has distinctive features compared to the male pelvis to ease childbirth, e.g., longer pubic rami, greater pubic arch angle, less curved sacrum.3
PELVIC DIAPHRAGM: Inside the pelvis, the layer we knew as transversalis fascia continues downward from the abdominal cavity, becoming obturator fascia (when covering obturator internus). Along down the inner surface of obturator internus muscle, muscle fibers spring from the obturator fascia to form a thin muscular cone, the levator ani, the main muscle of the pelvic diaphragm. The levator ani muscle consists of two U-shaped slings that loop around the gut and attach at either end to the pelvis and obturator fascia. An important part of the levator ani loops around behind the anus to form a puborectal sling. The kink (perineal flexure) it creates separates the rectum from the anus (so a short anal canal), and acts as a supplementary voluntary sphincter. Anal columns and the associated pectinate line indicate the difference between painless internal hemorrhoids and painful external hemorrhoids.3
Perineum: the diamond-shaped region below the pelvic diaphragm, between the ischia, and containing the external genitalia and hypaxial muscles that anchor and move them (and the anus). It is often considered as an anterior urogenital triangle (region) and a posterior anal triangle (region) divided by a line between the ischial tuberosities.
Levator ani is a cone, and between it and the bony pelvis is stuffed with fat in the ischioanal (ischiorectal) fossa, through which nerves and vessels of the perineum travel. The pudendal nerve and internal pudendal vessels leave through the greater sciatic foramen, and enter the ischiorectal fossa through the lesser sciatic foramen, and are the major suppliers to the perineal region. A pudendal nerve block in the perineal region sounds appropriate for childbirth--why would you want to include the distribution of the ilioinguinal nerve to anaesthetize in addition?3
The anterior gap in levator ani needs to be"guarded" so that pelvic viscera don't fall through it. A sheet of hypaxial muscle with fascia wrapped on either side of it is the urogenital diaphragm. Some of the fibers of the muscle wrap around the urethra that passes through it to form a voluntary urethral sphincter. The urogenital diaphragm does not extend beyond the ischial tuberosities, leaving a free edge. This is tied to the anus behind by hypaxial fibers that form the external anal sphincter. Lots of other fascia and anchorings tie into where these meet each other, thus forming the perineal body or central tendon of the perineum. Episiotomy is often done so as to lessen damage to this support point during childbirth.3
ERECTILE TISSUE: Superficial (i.e., inferior) to the urogenital diaphragm are the erectile organs and associated musculature of the external genitalia. Two masses of erectile tissue: midline bulbs and lateral crura. The bulbs are connected to the underside of the urogenital diaphragm, while the crura are attached underneath the obturator foramen.
The urethra passes through the urogenital diaphragm, and so is surrounded by the corpus spongiosum, or tubular prolongation of the bulb of the penis in males. At its tip the corpus spongiosum expands into the glans penis (head). The crura travel alongside as corpora cavernosa. Failure of the developmental fusion of urethral folds results in hypospadias.3
Major female exceptions to the homology: with the vagina, the bulbs don't fuse midline, but instead are separate bulbs of the vestibule. Also, the female urethra isn't surrounded by a corpus spongiosum. In both sexes, these erectile tissues are overlain with thin layers of hypaxial muscle (ischiocavernosus around crura and the bulbospongiosus overlies bulb(s)). In females, skin on either side of vaginal opening is elaborated into labia majora and labia minora. The labia majora are homologous to the scrotum, while the labia minora meet over the clitoris to form a prepuce (yes, it's homologous to the male prepuce or foreskin). Circumcision in men involves removal of the prepuce around the glans penis, but typically involves removal of the clitoris and labia minora in women (African/middle Eastern culture)--which sounds like more extensive and disfiguring surgery?3
The superficial fascia on the abdominal wall has a superficial fatty layer and a membranous deep layer. In the perineum, the deep membranous layer is known as Colles' fascia. Colles' fascia is connected to the rear and side edges of the urogenital diaphragm. Hence, if the penile bulb or spongy (bulbous) urethra is hurt in a straddle injury, urine and blood will accumulate inferior to the urogenital diaphragm in the superficial perineal space, but not spread into the thighs or towards the anus.3
The bladder is hollow, made of four sides of equilateral triangles. The urethra leaves near where the ureters enter, forming a triangular trigone. Pelvic organs are draped from above by peritoneum. Males will have a rectovesical pouch lined by peritoneum between bladder and rectum, whereas females with their uterus will have both vesicouterine and rectouterine pouches. The sides of the uterus are covered by the broad ligaments. The ovary hangs from the rear surface of the broad ligament via the mesovarium. Additional extraperitoneal fascia surrounding the female pelvic viscera is condensed to form several supportive ligaments, e.g., sacrouterine ligaments, and transverse cervical ligaments. Stretching of and weakening of levator ani with childbirth predisposes to urinary stress incontinence and uterine prolapse.3
VESSELS AND NERVES: The internal iliac artery is the supply to the pelvic region, e.g., internal pudendal artery to perineal region. The ventral rami of L4 - S4 form the sacral plexus. Most of this sacral plexus forms the sciatic nerve (L4-S3) to the lower extremity via the greater sciatic foramen (also, pudendal nerve (S2-4) to the perineum). Preganglionic sympathetic (S) fibers originate from T1-L2 and will synapse in a ganglion, so that the sympathetic fibers entering the pelvis are postganglionic. Parasympathetic (P) motor pathways to the pelvic viscera orginate from S2-S4, enter inferior hypogastric plexuses and continue to their target organs. P and S functions:3
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Rectum and anus:bladder: |
P empties, but S constricts outlets. |
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male genitals: |
S impulses constrict arterial supply to erectile tissue, hence keeps it limp, but P cause the trabecular and coiled aterial walls to dilate, allowing more blood flow to create erection. S discharges allow ejaculation, and this predominance of S after orgasm leads to back to flaccidity. |
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female genitals: |
P, clitoral erection and increased vaginal secretion |
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MALE REPRODUCTIVE ORGANS: An outgrowth of the vas deferens, the seminal vesicle, is on the backside of the bladder. A common ejaculatory duct traverses the prostate and opens into the urethra. The prostate is inferior to the bladder, surrounding the first 3 cm of the urethra, but superior to the urogenital diaphragm. Autonomic fibers run along lateral to the prostatic capsule, and so are at risk with extensive surgery. The prostate, particularly the posterior lobe (often involved in cancer), is palpable in rectal examination.
FEMALE REPRODUCTIVE ORGANS: The ovary is covered by a germinal layer instead of peritoneum, allowing ovulation. As an ovum matures it ruptures through the surface of the ovary to end up in the trumpet-shaped mouth of the uterine (fallopian) tube. The fimbriae or fringes of the mouth help to attract ova.
The open communication along the female reproductive tract can lead to the spread of disease from more external organs, e.g., pelvic inflammatory disease (PID). The uterus has a fundus, a body, an isthmus, and a cervix. Its endometrial lining is partially shed in menstruation (or may spread pelvically as part of endometriosis).
The smooth muscle myometrium extends during pregnancy, but can be the site of fibroids (leiomyomas, or benign smooth muscle tumors).2 The vagina is a muscular sheath that leads downward and forward from the cervix, with interior fornices around the cervix. The greater vestibular glands (Bartholin's glands) [homologues to bulbourethral glands], supplying lubricating mucus during copulation, are a likely site for infection.3
HISTOLOGICAL ASPECTS OF GASTROINTESTINAL TRACT:
Generally speaking, digestive tract a hollow tube with a lumen and four layers:
1) mucosa (mucous membrane): an epithelial lining with a lamina propria of loose CT (with glands and lymphoid accumulations) and muscularis mucosae separating it from the submucosa. This muscularis mucosae, innervated by Meissner's complex, is responsible for mucosal motility.
2) submucosa: dense CT, with blood and lymph vessels
3) muscularis externa: responsible for gut motility, inner layer of circular smooth muscle, outer layer of longitudinal smooth muscle, with Auerbach's nerve plexus to innervate and blood vessels, in between these layers.
4) serosa vs. adventitia, whether outer layer is visceral peritoneum or adhering connective tissue.
SALIVARY GLAND
(check a web site)
In this round of histology, we will discuss the difference between exocrine and endocrine glands. While both originate from a cuboidal epithelium that proliferates into the underlying mesoderm, exocrine glands will maintain their contacts to form branching ducts, while endocrine glands will separate from their originations and instead be surrounded by blood vessels--hence their different appearances histologically.5
To appreciate a purely exocrine gland, let's look at the submandibular gland, which has both serous and mucinous acini. Serous cells are secretory and darker staining than the larger, clear staining mucinous cells. Acini (acinus-sing.) are the arrangements of pyramid-shaped cells around a lumen.
ESOPHAGUS
(Fig. 8-8)
Lined initially by nonkeratinized stratified squamous epithelium, with esophageal (mucous) glands in the submucosa. This epithelium is not protective to stomach contents, so that GERD (gastroesophageal reflux disease) is damaging to it, potentially causing such changes as a Barrett's epithelium (metaplasia).2 Note also that the muscularis [externa] of the proximal esophagus is skeletal muscle progressing to smooth muscle by the distal esophagus--skeletal muscle dysfunction may affect swallowing, but peristalsis for most of the esophageal length should be involuntary.1
STOMACH WALL
(Fig. 8-10)
Turns food into chyme with acidity and pepsin. Rugae flatten as stomach fills. Noticeable are gastric pits, or invaginations of surface epithelia of mucosa. Fundic glands extend from the bottom of the pits to the muscularis mucosae. In fundic glands are stem cells for cell proliferation, mucous neck cells, parietal cells (HCl), chief (zymogenic) cells (pepsinogen). Submucosa with reasonably dense CT, blood and lymph vessels. Muscularis with oblique, circular, and longitudinal layers (as befitting the most muscular part of the GI tract).
DUODENUM
(Fig. 8-15)
The small intestine is the site of food digestion, absorption. Absorptive epithelium of simple columnar epithelium, with microvilli (brush border). Villi or outgrowth of mucosa (only found in the small intestine). Duodenal (Brunner's glands in submucosa (mucous, alkaline secretion). Blood vessels plentiful and a central lacteal (lymphatic) as befits absorptive role. Loss of villi in nontropical sprue (gluten sensivity), so loss of absorptive surface area and malabsorption as a result.2
ILEUM
(Fig. 8-16)
As compared to the duodenum, no Brunner's glands in the submucosa, but instead multiple lymphoid nodules (MALT, remember?), or where organized these are organized, they're called Peyer's patches.
LIVER
(Fig. 8-23)
Apparent morphology of liver lobules, with sinusoids lined by hepatocytes draining into central veins. Portal areas between lobules contain portal vein, bile duct, hepatic artery branches. The current physiological understanding is that of the acinus, where the portal triad is in the"middle," and the central veins (now better known as terminal hepatic venules) represent the drainage edge. Hence, Zone 3 hepatocytes near the terminal hepatic venules are more vulnerable to anoxic damage, which indicates the usefulness of this acinar modeling.1
GALL BLADDER
(check a web site)
Multiple folds of the mucosa (but not villi) when the muscularis is contracted (as is typical in histological preparations). Only tall columnar epithelial cells (with a delicate striated border) seen lining the lumen (no glands except in neck). Functions in storing, concentrating, and releasing bile.4
PANCREAS
(Fig. 8-19)
The exocrine portion of the pancreas consists of cells packed into secretory serous acini with intralobular septae. Pyramidal zymogenic cells make up the acini. The endocrine cells are in pancreatic islets demarcated by reticular tissue. Special staining is necessary to distinguish between the insulin-producing beta (B) cells (70%) and glucagon-producing alpha (A) cells (yeah, there are somatostatin-producing D cells there as well). Capillaries should be common in the islets, as per the difference between exocrine and endocrine cells.
LARGE INTESTINE
(Fig. 8-17)
No villi, but the mucosa is indented by long intestinal glands (crypts of Lieberkühn). Many goblet cells seen in epithelium ("lubing the load"), and see many lymphatic nodules in the submucosa (especially in the appendix).
KIDNEY
(Fig. 7.5)
kidney: outer cortex, inner medulla.
cortex: renal corpuscles (glomerulus + Bowman's capsule), surrounded by PCT and DCT. PCT: brush border, larger outside diameter, more of them than for DCT. May also see juxtaglomerular apparatus near the glomerulus.
Hence, renal corpuscular changes (e.g., a glomerulonephritis) could correlate with filtration problems.
medulla: pyramid with collecting ducts, loops of Henle, and blood vessels
ENDOCRINE SYSTEM:
Production and secretion of hormones, so likely to see a lot of ducts (lined with simple cuboidal epithelium) and capillary spaces. Distinct endocrine glands (e.g., thyroid), vs. mixed endocrine/exocrine glands (pancreas, already"admired").
PITUITARY
(hmm, probably Fig. 9-8)
Dual origin of pituitary, so that there is an adenohypophysis (from pharyngeal cavity) and neurohypophysis (downward growth of brain, still connected via infundibular stalk).
adenohypophysis: chromophils (active) vs. chromophobes (inactive)
chromophils: acidophils (alpha cells) and basophils (beta cells). Acidophils produce GH and prolactin; basophils produce TSH, FSH, LH, and ACTH.
neurohypophysis: ADH and oxytocin secreted from here, with pituicytes (glial-like cells specific to here) surrounding the hypothalamic neurosecretory neurons4
ADRENAL
(Fig. 9-22)
Outer cortex, inner medulla. Connective tissue trabeculae reach from the outer capsule, often carrying arteries. In cortex are three zones producing steroid hormones: (outer) zona glomerulosa with mineralcortocoids (esp. aldosterone), (middle) zona fasciculata with glucocorticoids (esp. cortisol, cortisone), and zona reticularis to some extent produce sex steroids. The medulla consists of modified sympathetic postganglionic neurons that secrete epinephrine and norepinephrine. Most medullary cells appear polyhedral (secretory), but sympathetic ganglion cells should stand out.
THYROID/PARATHYROID
(Figs. 9-18, 9-32)
Thyroid characterized by spherical follicles containing colloid, which represents thyroglobulin. When stimulated by TSH, the follicular cells hydrolyze thyroglobulin to produce T3 (triidothyronine) and T4 (thyroxine). These follicles of colloid can vary in size depending on the level of thyroid activity.1 Parafollicular cells in the periphery of the follicles secrete calcitonin (to lower blood calcium levels, although probably not of major importance in counteracting PTH).
The parathryoid gland is only a thin connective tissue capsule away. Parathyroid contains chief cells that make parathyroid hormone that raises calcium levels in the blood. Larger, less numerous oxyphil cells have an unknown function. No follicles in parathyroid.
REPRODUCTIVE SYSTEM: as with other mammals, the human reproductive system...
1) produces gametes (eggs and sperm)
2) provides a home for fetal development (uterus)
3) produces sex steroids (estrogen, testosterone)
4) is involved in feeding the young (mammary gland)
MAMMARY GLAND
(Figs. 9-44, 9-45)
Modified sweat glands, showing lobules of cuboidal epithelial tubules, divided by septa of connective tissue. Proliferating mammary tissue during pregnancy can show alveoli and larger lactiferous ducts.
OVARY
(Fig. 9-33)
The outer part (cortex) of an ovary is coated with a simple cuboidal epithelium, the germinal epithelium, with a tunica albuginea underneath (connective tissue). Surrounded by CT stroma are follicles, with an oocyte surrounded by a single layer of follicle cells (at least in primordial follicles).
Maturation of follicles with enlarging follicular cavity (antrum). Granulosa and theca interna cells around these maturing/mature follicles combine to produce estrogen, in addition to progesterone. The granulosa cells are the ones with the aromatase function to produce estrogens.1 Theca externa cells are fibrous.
UTERUS
(Fig. 9-41)
Endometrium or mucous membrane consists of simple columnar epithelium and very cellular CT. Many tubular uterine glands and coiled arteries run the length of the endometrium. During menstruation, the (luminal) stratum functionalis sloughs off, and the (basal) stratum basalis remains. Deep to the stratum basalis is the myometrium. Myomas (fibroids) are benign smooth muscle tumors, which show swirling interlocking bundles of cells histologically.2
CERVIX
(Fig. 9-42)
The mucosa here does not exofoliate during menstruation, and the cervical walls can be made more flexible by relaxin during pregnancy. The outer side of the cervix is made of a nonkeratinizing stratified squamous epithelium, hence the squames that are scraped and are studied with a pap smear. Cells with large, irregular nuclei would be indicative of a cancerous process.1
TESTIS
(Fig. 9-50)
Sperm are produced in seminiferous tubules, with prominent lumina. A capsule (the tunica albuginea) surrounds the testis, and septa break it up. In the wall of the seminiferous tubules are the spermatogenic cells (spermatogonia > primary spermatocytes > secondary spermatocytes > spermatids), with mostly spherical nuclei, and Sertoli cells, which are fewer in number and with ovoid, indented nuclei. Sertoli cells support and protect the developing spermatozoa (and secrete androgen-binding protein and inhibin). In between the tubules is CT and interstitial Leydig cells (polygonal/ovoid), which make testosterone.
PROSTATE
(Fig. 9-56)
Surrounding the first part of the urethra, the prostate consists of about 40 glands in a fibromuscular stroma, that secretes among other items, acid phosphatase. The acini are variable in shape and size. Also, in older individuals, precipitates or prostatic concretions are typically present in the lumina of the prostate lumini. BPH (benign prostatic hypertrophy) compresses the urethra with hyperplastic glandular tissue and fibromuscular stroma. In prostatic cancer is typically an adenocarcinoma with small irregular acini.2
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This page updated on October 25, 1999