Histology Final

• the digestive system consists of the lips, oral cavity, esophagus, stomach, small intestine, large intestine, rectum, and anal canal
• the accessory digestive organs are the salivary glands, liver, and pancreas; they are all located outside the digestive tract

• mucosa - epithelium, lamina propria of loose CT
• muscularis mucosae - thin layer of smooth muscle between lamina propria and submucosa
• submucosa (tela submucosa) - dense irregular CT, site of numerous blood and lymph vessels and also Meissner nerve plexus
• muscularis externa - think inner circular and then outer longitudinal layers of smooth muscle
• serosa (adventitia) - simple squamous called mesothelium and underlying thin loose CT

• the lips are lined with a think skin covered by stratified squamous keratinized epithelium
• red color comes from blood vessels close to the lip surface
• dermis contains hair follicles, sebaceous glands, and sweat glands

• the oral cavity is lined with stratified squamous epithelium non-keratinized
• tissue has many mucus glands, taste buds, and is site of the three salivary glands
• in the oral cavity, food is ingested, masticated, and lubricated  by saliva for swallowing

• parotid
• submandibular
• sublingual

• the tongue is a muscular organ that at its core consists of CT and interlacing bundles (or crossing pattern) of skeletal muscle fibers
• dorsal side has more papillae and a rougher surface than ventral side
• the tongue perceives taste and assists with mastication and swallowing of food

four types are filiform, fungiform, circumvallate, and foliate

• papillae are elevations of epithelium on the dorsal surface of the tongue with underlying lamina propria
• filiform is needle-shaped, keratinized, do not have taste buds, and found on the entire anterior dorsal surface of the tongue
• fungiform are mushroom-shaped (taller and broader than filliform) and found interspersed with filiform papillae in the anterior and tip of the tongue
• circumvallate are larger than the previous two, have deep furrows that encircle them, have many serous glands, and are located in the posterior region of the tongue
• foliate are rudimentary in humans

• taste buds have a pear shaped structure and have an opening in the epithelium called a taste pore
• taste buds are found on fungiform and circumvallate papillae, and on the soft palate, pharynx, and epiglottis
• epithelium has microvili that protrude through the taste pore
• three cell types are support (sustentacular) cell, basal cell, and neuroepithelial (taste or gustatory) cell

substances dissolved in saliva enter the taste pore where they are perceived by gustatory or taste cellsthe basic taste sensations are sour, salt, bitter, sweet, and unami

• three cell types
• neuroepithelial (taste) cells are elongated cells, have light staining cytoplasm, and have microvilli that extends into the taste pore; synapses at its base connect to afferent axons 
• support (sustentaclar) cells have darker staining cytoplasm, a more oval nucleus, and are less numerous than taste cells; they provide structural support
• basal cells are located near the basement membrane and serve as undifferentiated stem cells for the other two cell types

palatine, lingual, and pharyngeal

• there are two general types of salivary glands - those that secrete saliva without contact with food and those that secrete saliva upon contact with food
• the former is made up of small salivary glands
• the latter are the parotid, submandibular, and sublingual salivary glands

• salivary glands secrete saliva which is composed of mucus, water, protein, and the enzyme ptyalin (AKA amylase)
• saliva serves as a lubricant, has digestive functions (amylase or ptyalin), and antimicrobial functions (lysozyme)

• acini (sing. acinus) are secretory units of salivary glands, pancreas, and other exocrine glands; they can be serous, mucous, or mixed
• CT septa divide acini into lobes and lobules
• secretory cells form the sac of each acinus

• the parotid gland exists as a pair, with one at each side of the head below the ears
• classified as a compound tubular alveolar gland
• this gland only has serous glands (no mucus glands), is subdivided into lobules by interlobular CT septa, and have a duct system terminating with the parotid duct that secretes saliva into the oral cavity

• serous acini empty their product into intercalated ducts (simple or low cuboidal epi.) that are located between cells, they empty into striated ducts
• striated ducts (simple columnar epi. with basal striations) have larger lumen and empty into interlobular excretory duct
• interlobular excretory ducts (columnar and pseudostratified to stratied columnar epi.) are between parotid lobules and have progressively wider lumens

• myoepithelial cells are flattened, highly branched cells that surround the serous and mucus acini, as well as the initial portion of the duct system
• they have a contractile function

• lingual tonsils are located on the dorsal surface of the posterior third of the tongue
• they are composed of lymphatic nodules with germinal centers, have tonsillar crypts, and are lined with stratified squamous epithelium
• deep in its lamina propria are the mucus acini of posterior lingual glands

the three major salivary glands are the parotid (paired), submandibular (paired), and sublingual

• the esophagus is a tube that extends from the pharynx to the stomach
• its mucosa layer is lined with stratified squamous epithelium, its submucosa has esophageal glands proper that release mucus, and the lamina propria of its proximal and distal parts have esophageal cardiac glands that also secrete mucus
• gastroesophageal spinchter at lower end prevents regurgitation of swallowed material

• the esophagus conveys liquids or mass of chewed food (bolus) from the oral cavity to the stomach
• its esophageal cardiac and proper glands secrete mucus that protect and lubricate the lumen

• the stomach is a hollow organ between the esophagus and the small intestine
• its three parts are the cardiac, fundus and body, and pylorus
• it is lined with simple columnar epithelium with many mucus secreting cells, and it forms many openings called gastric pits
• it has rugae which are longitudinal folds of the mucosa and submucosa

mucus neck cells are located in the upper region of gastric glands near the gastric pits of the fundus and body of the stomach; they are interspersed between parietal cells and secrete mucus

parietal cells are located mostly in the upper half of gastric glands and appear as large, polygonal cells and are distinctive acidophilic (red/pink) staining; they secrete HCl

chief (zymogenic) cells are located mostly in the lower region of gastric glands and appear as cuboidal basophilic staining cells; they secrete pepsinogen that becomes pepsin in an acidic environment

argentaffin (enteroendocrine) cells can only be seen with silver stain and they secrete the vasoconstrictor serotonin

• the main function of gastric secretions is the chemical reduction or digestion of food in the stomach
• its main components are pepsin, HCl, mucus, water, lysozyme, and electrolytes
• mucus secreted by the mucous neck cells functions to cover, lubricate, and protect the stomach surface from acidic gastric juices
• pepsinogen from chief cells is an inactive precursor of pepsin, which acts as a protease
• lysozyme acts as an anti-bacterial agent

• the three sections of the small intestine are duodenum, jejunum, and ileum
• it joins the stomach with the large intestine

• the villi in the duodenum are broad, tall, numerous, and with fewer goblet cells in its epithelium which is simple columnar
• it has intestinal glands (crypts of Liberkuhn) that are located between the villi; cells in these glands include goblet cells, Paneth cells, and stem cells
• it has Brunner (duodenal) glands in its submucosa that contain light-staining mucous cells; this gland secretes alkaline phosphatase which helps to neutralize acidic chyme from the stomach

• the villi in the jejunum are thinner, and there are more goblet cells in its epithelium which is simple columnar
• it has intestinal glands but no Brunner glandsrest of structure is similar to duodenum

• the ileum is noted for its aggregations of lymphatic nodules called Peyer patches, which can be found from in the lamina propria and the submucosa
• it has intestinal glands but no Brunner glands

the main function of the small intestine is the digestion of gastric components and absorption of nutrients into blood capillaries and lymphatic lacteals

Paneth cells have red-staining granules and are located at the base of intestinal glands; they secrete amylase, lipase, protease as well as lysozyme

goblet cells are light staining cells found in the intestinal epithelium that increase in number towards the ileum; they secrete mucus

argentaffin (enteroendocrine) cells contain fine secretory vesicles and are located at the basal side of intestinal glands near the lamina propia; they secrete regulatory hormones

• the lining epithelium (simple columnar) of the appendix has many goblet cells, its lamina propria has intestinal glands that are shorter and less well developed, and has many lymphatic nodules with germinating centers 
• the appendix is serves as a site of storage and formation of macrophages, lymphocytes, and plasma cells

• the large intestine consists of the colon (ascending, transverse, and descending), rectum, and anal canal
• the colon has fewer Paneth and argentaffin cells but many more goblet cells than small intestine
• its muscularis externa layer has taeniae coli, which are three longitudinal muscle strips that make up the outer longitudinal smooth muscle layer 
• functions to absorb water via mesenteric vein, to produce mucus for lubrication, and to shape and form the feces 

• above, thin blue vein is mesenteric vein

• the rectum is similar in structure to the colon/large intestine
• it does not interact with the mesenteric vein and so does not participate in absorption
• it functions only to pass along the feces

• epithelium continues as simple columnar and transitions to stratified squamous which then becomes keratinized once the anal canal reaches the skin
• the internal anal sphincter is involuntary (smooth muscle) and external is voluntary (striated muscle)

• the liver receives nutrients and liquids from the intestines via the hepatic portal vein, and receives lipids from lymph vessels
• the liver is made up of hepatic lobules (together make up the 4 lobes of liver) divided by interlobular CT, each lobule has a central vein that is surrounded by hepatocytes (cuboidal shaped)
• caniculi ducts collect bile secreted by hepatocytes and join to form ducts of Hering, these then joing to form hepatic ducts
• the 4 hepatic ducts from each lobe combine into the common hepatic duct that connects with the gall bladder

• exocrine - hepatocytes produce bile
• endocrine - liver stores glycogen which it can release as glucose into the bloodstream
• phagocytic - Kupffer cells are specialized macrophages that detoxify the blood of drugs and other harmful substances, and also filter old or damaged RBCs

• the gall bladder has simple columnar epithelium in its mucosa membrane, a fibromuscular coat, and a premuscular coat
• it functions to concentrate and store bile made by hepatocytes in the liver, and releases it when stimulated by cholecystokinin (CCK) from I cells of the small intestine 

• bile is made up of water, salt, green pigment, cholesterol, and fat
• it functions to increase the activity of intestinal and pancreatic lipase, emulsify fat, and facilitate absorption of fat in intestine

• the common hepatic duct from liver joins with cystic duct from gall bladder to form the common bile duct
• the common bile duct joins with the main pancreatic duct (duct of Wirsung) to form hepatopancreatic duct (duct of Vater)
• hepatopancreatic duct empties into duodenum through the sphincter of Oddi

• the pancreas has exocrine secretory units (acini) called acinar cells that are pyramid shaped; these cells are divided into lobules separated by loose CT and excrete their enzyme precursor products into a duct network
• the enodcrine portion of the pancreas are divided into units called the islet of Langerhans and contains alpha, beta, and delta cells

• individual acinus excrete their products first through intercalated ducts that are lined by low cuboidal epithelium; pale-staining centroacinar cells that the middle of each acinus is continuous with this epithelium
• the intercalated ducts drain into interlobular ducts (with simple cuboidal epithelium), then these ducts drain into the main pancreatic duct
• the pancreas does not have striated ducts

• exocrine - acini secrete granules that contain (inactive) pancreatic enzyme precursors collectively called pancreatic juices; this is controlled by the hormones cholecystokinin (CCK or pancreozymin) and secretin
• endocrine - cells of islets of Langerhans produce glucagon, insulin, and somatostatin

the exocrine acini secrete the inactive forms of the proteases trypsin, chemotrypsin, carboxypeptidase; also lipase and amylase

• exocrine portion
• acinar (zymogenic) cells are pyramid-shaped surround the small acinus lumen
• centroacinar cells are pale-staining and are found in the center of the acinus

• endocrine portion
• alpha cells stain red/pink/acidophilic and are found more in the islet periphery
• beta cells stain blue/basophilic and are found more centrally in the islet
• delta cell are light staining and are peripherally located

this system is composed of two kidneys, two ureters, a bladder, and a urethra

the kidney is surrounded by a dense irregular CT capsule and has a cortex and medulla

its functional unit is the nephron, which combined with collecting ducts make up a uriniferous tubule

cortex is site of nephrons and medulla is site of renal pyramids; apex of pyramids called papillae Bellini connect to minor calyxes which combine to form major calyxes, these drain to the renal pelvis

a nephron begins at the renal corpuscle, which is made up of a glomerulus and Bowman’s capsule (simple squamous)

next is the proximal distal tubule, the descending loop of Henle, the thin then thick ascending loop of Henle, and lastly the distal convoluted tubule; nephron drains into the collecting duct

the ureter has a mucosa membrane, a muscularis externa, and a serosa membrane

the bladder has transitional epithelium, three smooth muscle layers (longitudinal, inner, longitudinal) in its externa muscularis, and adipose tissue around its serosa

transitional epithelium appears squamous when the bladder is stretched (filled with fluid) and low cuboidal or columnar when contracted (empty)

the male urethra functions to remove urine from the body as well as to carry semen during ejaculation

the male urethra has three parts named (from proximal to distal) the pars prostatica, the pars membranosa, and the pars cavernosa

epithelium of male urethra starts proximally as transitional, becomes pseudostratified columnar, and distally is stratified squamous

underlying CT has goblet cells and glands of urethra that both secrete mucus to protect the epithelium from urine 

smooth muscle in the pars prostatica transitions into striated muscle

the female urethra functions to expel urine from the body

its epithelium begins proximally as transitional, becomes pseudostratified columnar, and distally is stratified squamous

the underlying tissue contains mucus-secreting glands of urethra, and the urethra exits the body between the clitoris and vagina

the testes are house in the scrotum and each are surrounded by a thick CT capsule called the tunica albuginea, which capsule extends inward to form the mediastinum testis (a network of fibrous CT)

thin CT called septum (or septula testis) extends from the mediastinum to divide the testis into testicular lobules, each containing seminiferous tubules

the seminiferous tubules attaches to the rete testis via the tubuli recti, both are lined with simple columnar epithelium; the rete testis connect to the epididymis via the duct efferentes (efferent ducts)

it functions as the site of sperm production (spermatogenesis) and testosterone synthesis

the three main accessory glands of the MRS are the prostate, the pair of seminal vesicle glands, and the paired bulbourethral glands

seminal vesicles produce fructose that serves as an energy source for sperm motility; they produce most of the fluid found in the semen 

prostate gland produces fibrolysin, citric acid, acid phosphatase; also the anti-microbial agents zinc chloride and zinc sulfate

Cowper (bulbourethal) glands produce mucus, galactose, and galactoamine

Sertoli cells are located in the seminiferous tubules of the testes

they appear as flat cells with a large centrally-located nucleus

they function to provide nutrition to developing sperm cells

Leydig cells are located in the interstitial CT between seminiferous tubules

they have a large single nucleus and stain acidophilic/red

they produces testosterone in males which is responsible for secondary sex characteristics including bone growth, muscle growth, hair growth, and enlargement of vocal cords

the epididymis is lined with pseudostratified columnar epithelium with specialized stereo cilia that are immobile

it functions as site of sperm storage and maturation

the vas deferens is lined with pseudostratified columnar epithelium and has three muscle layers (inner longitudinal, middle circular, outer longitudinal); it exhibits a narrow and irregularly shaped lumen

it functions to pass sperm from epididymis to the ejaculatory duct and eventually to the urethra

the two seminal vesicle glands are located on the posterior side of the bladder

this gland has outpockets lined with stratified (two cell layers) columnar epithelium and has two smooth muscle layers (inner circular, outer longitudinal)

basal cells produce basic alkaline, muscus, and fructose

these glands have excretory ducts that join the ampulla of each vas deferens to form the ejaculatory duct

it functions as a source of fructose for nutrient energy for spermatozoa, as well as seminal fluid which is alkaline and helps neutralize the acidity of the vaginal tract

the prostate gland is located posterior to the neck of the bladder; the pars prostatica of the male urethra passes through the prostate

it has cuboidal or squamous epithelium, is surrounded by fibromuscular CT, and has prostatic glands within it that contain prostatic concretions that store Ca+2

it functions to produce citric acid, acid phosphatase, fibrolysin (liquifies the sperm), zinc chloride and zinc sulfide (anti-microbial agents)

the two Cowper's glands are located posterior to the pars membranosa of the male urethra

they are pea-shaped and lined with squamous or columnar epithelium

they function to produce mucus (for urethra lubrication), galactose, and galactosamine; the glands are under the control of androgens from zona reticularis of adrenal cortex

the penis has two dorsally-located corpus cavernosa, and ventrally-located uretha which is in the corpus spongiosum

• has sweat glands and sebaceous gland
• (called Tyson gland in penis and are not attached to hair follicle), tunica albuginea is a CT layer that surrounds the three corpus bodies; epidermis is stratified squamous

deep arteries in corpus cavernosa fill with blood during erection

nitric oxide functions as a vasodilator of smooth muscle in the deep arteries within the corpus cavernosas of the penis, which leads to erection

sperm formation consists of two processes called spermatogenesis and spermiogenesis

spermatogenesis starts with diploid spermatagonia cells which undergo mitosis and differentiate to become primary spermatocytes

these undergo the first meiotic division to become haploid secondary spermatocytes, these undergo the second meiotic division to become round-shaped spermatids

spermiogenesis is the phase in which spherical spermatids (haploid) undergo a complex morphological transformation into elongated sperm cells called spermatozoa (haploid)

the sperm has three parts – head region, middle piece, and tail

the head region includes the acrosomal cap which contains several enzymes and houses the chromosomes

the middle piece contains mitochondria that supply energy for movement of the tail

the tail region contains the axonemal complex of flagellum

during female embryonic development, primordial germ cells from germinating epithelium differentiate into oogonia via mitosis, and enter but do not complete the first phase of meiotic division; these arrested germ cells are called primary oocytes

primordial follicles are also formed during fetal life, and these follicles consist of a primary oocyte surrounded by a single layer of follicular cells, a nucleus, and cytoplasm

during menarche (first menustral cycle), the primordial follicle grow and enlarge to become primary follicles, then secondary follicles, and finally mature (Graafian) follicles

the changes that occur to the ovaries during the menustral cycle is called the ovarian cycle; this cycle is under the control of the hormones FSH and LH, which are synthesized by alpha cells of the anterior pituitary; FSH and LH are under the control of gonadotropin-releasing hormone from the hypothalamus 

the ovarian cycle of typically runs for 28 days, with ovulation or rupture of an oocyte occurring around the 14th day

the first 14 days of the cycle is called the follicular phase, during which a primordial follicle matures into a Graafian follicle that ruptures during ovulation, resulting in release of an oocyte into the space near the fimbrae of the fallopian tube (oviduct)

the second 14 days is called the luteal phase, and beings with the formation of a corpus luteum and ends with either pregnancy or degradation of the corpus luteal into the corpus albicans

during menustration, the follicle that ruptures during ovulation becomes the corpus luteum, a process facilitated by the activity of FSH and LH

it produces estrogen and progesterone, which in turn suppressed the production of FSH and LH and thus preventing a second oocyte from ovulating

in the absence of pregnancy, the continued low levels of FSH and LH will cause the corpus luteum to atrophy and eventually become a corpus albicans, which in turn causes progesterone and estrogen levels to decrease, and FSH and LH are no longer inhibited and the menstrual cycle starts over

if implantation of a fertilized embryo occurs, a hormone called human chorionic gonadotropin produced by the embryo can sustain the corpus luteum

the corpus albicans is the regressed form of the corpus luteum

as the corpus luteum is being broken down by macrophages, fibroblasts lay down type I collagen, forming the corpus albicans; the remains of the corpus albicans may persist as a scar on the surface of the ovaries