histo/embryo after midterm part II

• ova and ovarian hormones (estrogen and progesterone)
• cuboidal derived from visceral peritoneum - tunica albuginea immediately below surface
• Cortex - foliclles and corpora lutea (in various stages of development) loose CT
• Medulla - vessels, nerves, lymph, loose CT
• mare - cortex and medulla are switched

• primordial - primary, simle squamous
• primary -primary, simple cuboidal
• seconday - primary, granulosa cells stratified polyhedral folicular cells, secret Zona Pellucida around plasma membrane of primary oocyte
• Late secondary - theca cells form around granulosa cells, vascularised layer of spindle shaped stroma cells

• small fluid-filled clefts among granulosa cells and form large cavity Antrum containing liquor fluid
• ovulation - immediately before and after, primary oocyte completes first meiotic division (2nd oocyte and first polar body)
• antrum - enlarges, accumulates liquor folliculi, oocyte displaced in cumulus oophorus granulosa cells
• corona radiata - granulosa cells immediately surrounding oocyte become radially displaced
• theca - 2 layers
• inner vascualr theca interna - steroid secreting cells, abundant SER, mito and lipid droplets
• outer supportive theca externa - thin layer of loose CT, fibrocytes arranged concentrically

• rupture of follicle and release of oocyte
• caused by LH from anterior pituitary and increased pressure of antrum fluid
• atrtic follicles - some follicles atresia(degeneration), reabsorbed except for fibrous tissue scar corpus atreticum

• dog and cat - ovaries
• arise from epitheloid theca interna cells or from hypertorphied granulosa cells or atretic follicles
• polyhedral, epitheloid
• contain lipid droplets

• after ovluation
• ruptured follicle called this b/c of blood in antrum

• large luteal cells -hypertrophy, granulosa cells proliferate
• small luteal cells -hyperplasia, theca cells of corpus luteum
• luteinization - process which the granulosa and theca cells are converted into luteal cells
• cow, mares, carnivores - yellow lipid pigment accumulates in luteal cells

• polygonal
• produce progesterone
• abundant SER, mito and other steroid- cell characteristics
• mixed in CL and difficult to distinguish

• more lipid
• fewer steroid-syn types of organelles than large luteal cells
• produce Progesterone
• mixed in CL and difficulte to distinguish

• no fertilization - slowly degenerates and replaced by CT called corpus albicans
• fertilization - CL persists and actice for a variable time
• some species required for entire pregnancy
• mares - accessory corpus luteum

• embryonic remnant homologous to rete testi
• in medulla
• networks of irregular channels lined by cuboidal or solid cellular cords
• may differentiate inot follicular cells
• canivores and ruminants - prominent

• infundibulum, ampulla, isthmus
• mucosa - highly folded, simple columnar or pseudo w/ motile cillia
• nonciliated - secretory activity
• propria submucosa - loose CT, plasma cells, mast cells, and eosinophils
• T muscularis - cicular smooth m. bundles, few long and oblique bundles
• T serosa - vessels and nerves

• bilateral horns, body, neck (cervix)
• endometrium (mucosa-submucosa)
• myometrium (muscualris)
• perimetrium (serosa)

• simple columnar
• pig and cow - patches of pseudo columnar
• simple branched coiled tubular throughout endometrium, secret mucus, lipids, glycogen and protein,
• lamina propria - highly vascualar, loose CT, macrophages, and mast cells
• cow - caruncles, non glandular, circumscribed thickenings, highly vascular and rich in fibroblast
• mare - endometrial cups present in eary pregnancy

• thick inner circular layer
• outer longitudinal layer
• Stratu vasculare - between the two layers of smooth m

• T serosa - loose CT, rich in nerve fibers, blood and lymp
• covered by peritoneal mesothelium

• mucosa-submucosa - highly folded
• simple columnar
• many mucigenous cells - including goblet cells, secrete mucus during estrus, in pregnancy mucus thickens and forms cervical seal
• T muscularis - inner circular (elastic fibers predominate and reestablish cervix after parturition) and outer longitudinal,
• T serosa - loose CT

• mucosa - stratified squamous, increases in thickness during estrus
• propria submucosa - dense irregular CT containing lymphatic nodules
• T muscularis - inner circular and outer longitudinal layer
• T adventitia or serosa - loose CT, highly vascular and nerves
• pig and dog - additional thin layer of long m. resent inside of cirular layer
• cow - isolated foci of goblet cells in cranial part

• similar to caudal part of vagina except for - presence of more subepithelial lymphatic nodules
• glands - compound tubuloalveolar mucous glands
• mare and dog - erectile coprus cavernosum bulbus vestibuli beneath vestibular mucosa

• Proestrus - follicular growth, endometrial proliferation and increased vascularization
• Estrus - ovluation, endometrial proliferation and edema more apparent
• Metestrus - corpus luteum, endometrial gland hyperplasia
• Diestrus - active CL b/c of pregesterone, endometrial glandular hyperplasia and secretion are max, no pregancy : Cl regresses and converts to corpus albicans, endometrial involution including glandula region

• only left oviduct
• ovaries not as compact, cortex and medulla distinguishable
• cortex - follicles at various stages, no antrum develops, follicel stays in extremely large primary oocyte, a single layer of membrane granulosa cells, theca intena and externa
• medulla(not well develped and diffuse)
• ovluation - not followed by formation of CL

• infundibulum
• magnum
• isthmus
• shell gland(uterus)
• vagina

• funnel like cranial extension of duct,
• mucosa - highly folded
• pseudostratified ciliated

• deposition of majority of egg white
• ciliated and non ciliated columnar cells
• lamina propria - numerous branched, tubular glands, cuboidal or columnar and release ablumin

• ciliated and non ciliated columnar
• numerous branched, tubular glands extended into laimna propria
• formation of shell membrane

• shell gland
• diltution of albuminoids
• intermittently pseudo
• coiled tubular glands project into underlying CT

• mucosa - short mucosal folds and lined by cliated pseudo w/ few goblet cells
• nonglandular till utero-vaginal junction which have sperm host glands to nourish sperm stored

• ductless
• parenchyma cells - large, epitheloid, close contact with dense networks of capillaries,
• secrete hormones directly into intercellular or perivascualr connective tissue space to reach the circulatory system
• hormones - regulate functions of target tissues or organs

• Adenohypophysis - pars :distalis, intermedia, tuberalis
• Neurohypophysis

• Pars Distalis :
• Acidohils
• Basohiles
• Chromophobes

• Somatotrophs - production of somatotrophin/ growth hormone
• Lactotrophs/prolactin cells - induces secretion of mammary gland(lactogenic activity)

• Thyrotorphs - thyroid stimulating hormone, induces thyroid gland to release thyroxine
• Gonadotrophs - Follicle stimulating hormone (FSH) & LH
• Corticotrophs - Adenocorticoropic hormone (ACTH) acts on adrenal cortex

most are considered temorarily resting degranulated chromophils

• associated with neurohypophysis and is completely separated from pars distalis by hypophyseal cleft
• melanotropes - most abundant cells that may surround colloid-filled follicles produce melanocyte-stimulating hormone (MSH)

• cluster of epithelial cells forming small follicles
• morphological characteristic of peptide - secreting cells that are subject to seasonal variation and belived to play a role in seasonal reproductive cycle of some animals
• few gonadotrophins and thyrorophs are present

• hypothalmic component - supraoptic and paraventricular nuclei
• nuclei - large, neurosecretory granules concerned with the production of oxytocin and vasopressin/ADH
• axons - from hypothalamo-neurohypophyseal, transport to neurohypophysis
• Herring bodies - enlarged axon terminals in neural lobe containing neurosecretory granules that secrete into perivascular space or sinusoidal capillaries
• Pituicytes (modified astrocytes) - glial cells of neurohypophysis, form extensive network around axons and capillaries,
• microglia cells are present also

• thin capsule - dense irregular CT, trabecula extends into parenchyma, dividing lobules
• lobules - thyroid follicles, parafollicles, dense network of sinusoidal capillaries
• follicles - filled with gel like substance (colloid), lined by follicular cells
• resting - cuboidal, colloid appears dense
• stimulated - cuboidal or columnar, colloid dissolved, golgi on apical cell surface, colloid droplets at luminal surface, secrete thyroid hormones

• single cells enclosed in basal lamina of follicle
• dogs - may form groups outside the follicles
• light staining cytoplasm, abundant golgi, numerous small membrane bound vesicles
• secrete Calcitonin - lowers blood calcium level by supressing bone resorption

• Capsule - dense irregular CT
• parenchyma - highly vascularised, arranged in clusters of cords
• Light - inactive principal cells
• Dark - active principal cells
• horse and large ruminant - oxyphilic cells - large cells, light staining, unknown function
• Transtitonal cells - structure between principal and oxyphilic cells
• Function - Parathormone : maintains calcium and phosphorus levels in blood

• thin capsule
• parenchyma - cortex and inner medulla

• Ruminants - irregular clusters and cords of cells
• horse, carnivore and pig - zona arcuata, cells arranged in arcs, steroid secreting
• produce - mineralocorticoids (aldersterone), maintain sodium and potassium level in extracellular body fluid

• radially arranged cords of cuboidal or columnar cells
• large number of lipid droplets

production of glucocorticoids - participate in protein, fat and CHO metabolism

• irreglar network of anastomosing cell cords
• cells similar to zona fasciculata

production of glucocorticoids - participate in protein, fat and CHO metabolism

• cell - arranged in irregular cords and clusters, separate by dense network of sinusoidal capillaries
• chromaffin cells - affinity with chromium salts, 2 types
• one has stronger chromaffin reaction and secretes Norepi
• other has less affinity to chromium salt and secret Epi
• released under physical and psycoholical stress
• parasympathetic ganglion may occur among the chromaffin cells

• arranged irregular anastomosing cords composed of 5 different types of cells
• A
• B
• C
• D
• heterogenous population of small granulated cells, precursor of a variety of cells that produce various gastro-entero-pancreatic hormones, which inhibit motility and bile secretion

• 5-30%
• secretory granules, insoluble in alcohol
• nucleus is indented or lobulated
• stain brillian red with Mason's trichome and Gomori's aldehyde-fuchsin
• secrete glucagon - increases blood sugar levels

• 60-80%
• secretory granules - soluble in alcohol and satin dark orange with Mallor's trichome and deep purple with Gomori's aldehyde-fuchsin
• Produce insulin - reduces blood sugar levels
• diabetes mellitus - absence or insuffiencent secretion of insulin

• immature precursor cells to other type of islet cells
• nongranulated or sparsely granulated

• rare
• produce somatostatin - inhibitory action on the secretion of insulin and glucagon

• epidermis
• dermis (corium)
• Skin appendages - hair follicles, sweat and sebaceous gland
• Special skin structures - hoof, horn, claw

• stratified squamous keratinized
• Stratum basale - single layer of cuboidal or columnar rests on basal lamina, melanocytes (produce melanin, pigment)
• Stratum Spinosum - several layers of polyhedral cells tightly abhere by numberous desmosomes, melanocytes (produce melanin, pigment)
• Stratum germinativum = stratum basale + stratum spinosum
• Stratum granulosum - several layers of flattened cells, keratohyalin granules
• Stratum lucidum - only in non-hairy skin (foot pad)
• Stratum corneum - dead, keratinized cells : protein, keratin, which provide structural support
• Stratum disjunctum - most superficial layer of stratum conrum that undergo constant desquamation

• vessels, lymph and nerves, smooth m in specialized area such as scrotum, penis and teat
• skeletal m. fibers of cutaneous trunci penetrate the dermis and allow voluntary movement of skin
• Papillary layer - loose CT, network of fine collagen, elastic and reticular fibers, predominantly cell types are fibrocytes, mast cells, and plasma cells and macrophages
• Reticular layer - dense irregular CT, large bundles of collagen fibers

• loose arrangement of collagen and elastic fibers
• adipose tissue is present either in small clusters or large mass of fat = panniculus adiposus

• covers entire body except - foot pad, hoof, glans penis
• flexible keratinized structure produced by hair follicle
• free part - hair above the surface of skin is the hair shaft
• within follicle - hair root which has terminal end, hollow knob called the hair bulb, attached to the dermal papilla

• Cuticle - single layer of flat keratinized cells
• Cortex - layer of dense compact keratinized cells, with long axis parallel to hair shaft, pigment granules are present with in the cell
• Medulla - center of hair and is loosely filled with cuboidal or flattened cells, in root, medulla is solid, shaft has air vacoules among cells
• pattern of surface of cuticular cells - together with cellular arrangement of medulla is characteristic for each species and used for medicolegal purpose

• internal root sheath
• external rooth sheath
• dermal papilla
• hair matrix
• arrector pilli muscle
• sinus or tactile hair follicles

• internal root sheath cuticle - overlapping keratinized cells
• granular epith layer - 1-3 layers of keratinized cells rich in trichohyaline granule
• pale epith layer - single layer of keratinized cells

• several layers of cells similar to straum spinosum
• covered by glassy membrane
• enclosed by a connective tissue sheath

• connective tissue directly under the hair matrix
• richly supplied by vessels and nerves

• cells comparable to germinativum cells
• give rise to cells that keratinized (soft form) to form hair shaft

• most hair follicle
• bundles of smooth m. attached to CT sheath of hair follicle and connect to the papillary layer of dermis
• innervated by autonomic nerves

• (whiskers of cat)
• highly specialized tactile hairs
• blood filled sinus between inner and outer layer of dermal sheath
• skeletal m. attached to the outer sheath of follicle allowing some voluntary control
• numberous nerve bundles penetrate the dermal sheath

• simple compund alveolar gland
• associated with hair follicles - duct empties to form pilosebaceous canal
• hairless areas - empty directly onto surface of skin through a duct, release by Holocrine mode of sebum
• secretory unit - solid mass of epidermal cells encolsed by CT capsule
• mitotic activity - basal layer, cells move inward and enlarge and accumulate lipid droplets
• Sebum - derived from disinigartion of these cells
• Examples - infraorbital, inguinal and interdigital gland of sheep, preputial and circumanal glands of dog

• Apocrine - simpel coiled tubular, secretory portion has large lumen lined with flattend cuboidal to low columnar cells having characteristic of secretory activity
• myoepithelia cells - located between secretory cells and basal lamina
• domestic animals - located throughout most of skin
• horse - secrete abundantly and produce sweat during exercise and at high temperature
• Merocrine - simple tubular, in foot pad of carnivores, planum nasolabiale of cow, carpal pad of pig

• compound tubulo-alverolar gland
• secretory alveoli - lined by simple cuboidal or columnar,
• secretory stage - columnar cells conatin fat droplets and membrane bound vesicles filled with micelles of milk protein, released inot the lumen and enlarge the lumen, at end of cycle cells become cuboidal
• Myoepithelial cells - contract in response to oxytocin causing let down of milk into duct system
• Duct system - intralobular (simple cuboidal) - interlobular duct(stratified cuboidal) - lactiferous sinus (stratified cuboidal) - teat sinus and papillar duct (stratified squamous)
• interstitial CT - support and contains blood vessels and nerves

• keratinized portion - hard keratin ex. hooves, claws, horns
• digital pad - carnivores, highly keratinized hairless dermis, coild merocirn glands in dermis and subcutaneous masses of adipose tissues enclosed in collagen and elastic fibers
• Chestnut and ergot - tubular and intertubular horn

• Fibrous tunic - sclera and cornea (protctive)
• Vascular tunic - choroid, ciliary body and iris
• Nervous tunic - retina

• white layer
• dense irregular CT
• bundles of collagen fibers
• elastis fibers - few, arranged parallel to surface

• Anterior epith - non keratinized
• Subepithelial basement membrane
• Substantia propria - collagen fiber layers or lamellae
• Posterior limiting membrane - highly refractile thick basement membrane
• Posterior epthelium - (corneal) simple squamous

• Choroid - dense network of highly vascular layer, in heavy pigmented CT
• Tapetum Lucidum - dorsal half of fundus, crystaline rods for light reflection, (makes animals eyes shine when look at light)
• Ciliary body - rostal continuation of choroid
• Iris - highly vascular CT and pigmented epithelium (determines eye color)

• pigment epithelium
• photrecptive layer - cones (color during day) and rods (black and white at night)
• external limiting membrane
• outer nuclear layer - bipolar neurons
• outer plexiform layer
• inner nuclear layer (bipolar neurons)
• inner plexiform layer
• ganglionic cell layer (multipolar neurons)
• optic nerve fiber layer
• internal limiting membrane

• lens capsule
• epithleium
• fibers
• cataract - cloudy lens

• compund tubulo-alveolar gland
• Cow and cat - serous
• dog - seromucous

• External - auricle(pinna) and external auditory canal
• Middle - auditory ossicles (malleus, incus and stapes), tympanic cavity and auditory tube
• Internal ear - Bony labyrinth (filled with perilymph)
• Membranous labyrinth (filled with endolymph)

• membranous ampulla of each smicircular duct contains crista ampullaris - sensory epithelium
• Utricle and saccule - macula utriculi and sacculi - sensory epi
• balance(vestibular) - cristae ampullaris, macula utriculi
• and sacculi
• Spiral organ (corti) - hearing, sensory cells, supportive cell, afferent and efferent nerve terminals, tectorial membrane

• primary tissues of digestive tube - epith and glands from endoderm
• splanchnic mesoderm - CT and Muscular tissue covering

• endoderm lined yolk sac - longitudinal and transverse folding
• foregut and hind gut - cephalic and caudal part of primitive gut
• midgut - remains temporally connected to yolk sac by vitelline duct or yolk stalk

• Stomodeum - most cranial, external ectodermal depression
• buccopharyngeal membrane - bilaminar, endoderm of cranial end of forgut in contact with ectoderm of stomodeum, later will rupture and form a continous digestive tube
• Proctodeum - ectodermal depression (cloacal membrane)endoderm of caudal end of hindgut and proctodeal ectoderm

• from oral opening to buccopharyngeal membrane
• develops mouth

• buccopharyngeal membrane to cranial intestinal portal
• pharynx, esophagus, stomach, cranial part of duodeum

• cranial and caudal intestinal portion - reduces to vitello-intestinal duct
• caudal part of duodenum, jejunum, ileum, cecum and cranial part of colon

• caudal intestinal portal to the cloacal membrane
• caudal part of colong and rectum

• cloacal membrane to external opening
• anal canal and anus

• spindle shaped dilation of foregut in future neck region and later descends
• dorsal side grows faster to form greater and lesser curvature
• first rotation along the cranio-caudal axis shift greater curvature to left
• second roation along dorsal-ventral axis shift caudal end of stomach to right side and cranially
• fundus arises as a local bulge near in cranial end
• greature curvature directed to the left and caudoventrally
• lesser curvature directed to right and craniodorsally
• dorsal and ventral mesogastrium becomes the greater and lessser omentum

• mesoderm of dorsal mesogastrium
• gastro-splenic ligament - formed from mesoderm joining the spleen with the greater curvature of stomach

• from primordium
• similar to simple stomach
• except great and lesser curvatures are dorsal and ventral curvatures respectively

• outgrowth of dorsal surface of the fundus extending dorsally, cranially to the left
• free end - divides into caudodorsal and caudoventral blind sacs
• later - tubular rumen primordium turns caudally and grows back dorsal to rest of stomach

left ventral bulge at the origin of the rumen

from lesser curvature

primordium corresponding to the lower part of the corpus and pyloris part of the simple stomach

central axis from which the 4 compartments of the ruminant stomach develop

• new born calf - rumen and reticulum(not yet functional, and colapsed) half capacity of abomasum
• 8 weeks - rumen and reticulum equal to abomasum
• 12 weeks - rumen and reticulum have twice the capacity of abomasum
• Omasum grows very slowly - at 1 1/2 yr, capacity ~ equals abomasum

• Rumen - 80% L 75% S
• Reticulum - 5% L 8% S
• Omasum - 8% L 4% S
• Abomasum - 7% L 13% S

• suspended from dorsal abdominal wall by short mesentery and communicates with yolk sac by VItelline duct or yols stalk
• rapid elongation of gut and mesentary - forms primary intestinal loop
• rapid growth of intestinal loop - enters extraembryonic coelon in umbilical cord b/c of nto enough space in abdominal cavity
• cranial limb - distal part of duodenum, jejunum, part of ileum, expands faster than caudal, causing 290 degree loop rotation around cranial mesenteric artery
• rotation - herniated intestinal loop begins to return to the abdominal cavity and fusion occurs between the parts of mesentery suspending the ascending duodenum and descending colon
• cuadal limb - lower part of ileum, cecum, ascending colon and part of the transverse colon

• Dog and cat - ascending short and straight tube followed by transverse and descending
• Ruminant - ascending colon develops into the elongated loop which grows and coils to form proximal, spiral and distal loops of colon
• spiral - two centripetal turns, the central flexture, and 2 centrifugal turns, sheep and goats - spiral is more variable, 3 centripetal and 3 centrifugal turns
• Equine - ascending colon forms 2 limbs (ventral and dorsal) then become left and right ventral or dorsal
• Pig - ascending forms into centripetal and centrifugal coils

• at junction fo hindgut and allantois, endoderm and surrounding mesenchyme thickens and forming the urorectal septum
• septum - grows caudally, separates cloaca into dorsal rectum and ventral urogenital sinus, separtation continues until the urorectal septum contacts the cloacal memebrane dividing the dorsal anal meembrane and ventral urogenital memebrane
• tissue between these 2 thin plate is the perineal body and the external surface of which will become perineum
• bladder - proximal part of allantois together with adjacent cranial portion of the urogenital sinus, remainder allantois called urachus slowly degenerates
• proctodeum - later anal membrane and urogenital memebranes degenerate and form the continuity with the derivatives of the proctodeum

• foregut - celiac artery
• midgut - cranial mesenteric artery
• hindgut - caudal mesenteric artery

narrowing and atresia(closure) in pups, kittens, floals and calves

• imperforated anus
• failure of anal memebrane to break down
• calves and pig

• body organ develop opposite to their normal position
• ex. descending duodenum on left and descending colon on right
• not a problem unless a part is coiled or closed

• calves
• abnormalities in the development of the urorectal septum that permits communication between rectum and urogenital sinus
• feces can go into bladder

• horse and pig
• persistence of vitello-intestinal duct leads to a diverticulum
• yolk sac does not regress, feces come from midgut at yolk sac

failure of retraction of midgut loop produces a congenital hernia

urachus remains open and urine is excreted from this tube at umbilicus

• Hepatic bud or diverticulum - ventral outgrowth from the gut endoderm at terminal part of forgut, rapidly proliferating cells, 2 parts (pars hepatica and cystica)
• Pars Hepatica - liver parenchyma (liver cords) and hepatic ducts
• Pars Cystica - gallbladder and cystic duct, abscent in horse
• further development - epithelial liver cords (differentiate into hepatocytes) intermingled with vitelline veins form hepatic sinusoids
• Kupffer cells and CT cells - derived from mesoderm of septum transversum

• Hepatic lobules - regularity in proliferating and branching livercords
• Pars Cystica - gallbladder and cystic duct develop
• Bile duct - cystic duct and hepatic duct join, opens at the duodenum at major duodenal papilla
• Hepatic diverticulum - from ventral foregut, duodenum differenitates, unequal growth in the duodenal wall brings hepatic diverticulum to dorsal surface of duodenum
• CT capsule and ligaments - splanchnic mesoderm

• 2 buds from gut endoderm on opposite sides of the duodenum at terminal end of foregut
• Dorsal pancreatic bud - dorsal and grows into dorsal mesentery, Left Lobe of pancreas, enters duodenum at dorsal pancreatic diverticulum (accessory pancreatic duct)
• Ventral pancreatic bud - hepatic diverticulum near its originand forms Right Lobe, pancreatic duct opens into the duodenum on the major duodenal papilla, togeth form bile duct
• endoderm epithelium - pancreatic diverticulum proliferates and branch, clumps of cells from secretory pancreatic acini (exocrine part) at end of branches, groups of cells from pancreatic diverticulum form pancreatic islets (endocrine part)
• Further development - 2 pancreatic diverticulum partially fuse, forming a common body at site of crossing, ducts anastomose so that secretions can pass by either pancreatic or accessory pancreatic duct into the duodenum

• Dog : large - accessory pan duct, small - pancreatic duct
• Horse and cat : small, large
• Ox and pig : large, abscent
• sheep and goat : abscent, large

• outgrowth of ventral wall of foregut
• endoderm - larynx, trachea, bronchi and lungs
• splanchnic mesoderm - cartilaginous and muscular component
• pulmonary macrophages - mesoderm

• longitudinal diverticulum of endodermal epithelial cells grows ventrally from forgut in the median plane and form the laryngo-tracheal groove (grows ventrally and caudally into splanchnic mesoderm benethe the foregut)
• Tracheo-esophageal septum - ridges of mesenchyme proliferate on both sides of the groove and form this partition, divides the foregut into a dorsal esophagus and a ventral portion, laryngo-tracheal tube and lung bud

• extends caudally between the foregut and developing heart and split to become bilobed
• bilobed branches from left and right principal bronchi
• Tracheal bronchus - ruminants and pig, develop on right side
• continued growth and subdivision of principal bronchi form each lung, lobar bronchi, segmental bronchi and bronchioles
• Functional parenchymal unit on the end of this duct system is the alveolus

• Initially - formed as solid cords of cuboidal cells
• Later - when lumen of bronchioles expands into alveoli, it becomes hollow and lined by thin alveolar epithelium
• Some cells produce phospho-lipoprotein called surfactant, reduces surface tension and aid in maintaining potency of the lumen of alveolus

• cessation of umbilical blood flow results in rapid decrease of oxygen and increase of Carbon Dioxide in blood
• Stimulates respiratory centers in the medulla

• bronchial tree and alveoli - expand and maintained by surfactans that line alveoli surface
• sudden expansion of lungs produces a marked pulmonary vasodilation and at same time ducts arteriosus begins to constrict
• blood from pulmonary trunk now profuses lungs

• direct flow to pharynx and oral cavity
• evaporation into the respired air
• absorption into pulmonary lymphatics

• pericartidal cavity - and separation from pleural cavity initially related to gowth of common cardinal veins (pleuropericardial fold mesenchyme surrounding veins)
• pleuropericardial spetum - folds grow medially and fuse
• lungs grow laterally into the body wall along with a horizontal septum
• pericaridum - heavy sheath that surrounds heart

• primary defect in cartilage morphogenesis
• english bulldogs

improper separation of caudal portion of laryngotracheal groove from the foregut

• inability of alveolar epithelium cells to produce enough surfactant to prevent collapse of alveoli after initial distension with air
• cerebral hypoxia - insufficient respiratory function, seizures in foals, (make barking sound at onset) Barker foal syndrome
• newborn - insufficient volume of blood circulating, prevents normal full expansion of lungs and deprives the central nervous system of oxygen it needed to function

• Cranial part - intermediate mesoderm
• middle part - endoderm
• caudal part - ectoderm

• intermediate mesoderm
• grows and forms a longitudinal mass running cranio-caudal direction
• pronephros
• mesonephros
• metanephros
• emphasizes the Theory of Recaptitation

• pronephris tubules - 7 to 8 pairs, from cranial (neck region) of nephronic ridge
• one end of each tubule turns caudally to meet the next on to form pronephric duct
• tubules - not functional and regress, duct persists and continues as mesonephris duct

• develops in thoracic and lumbar regions of nephronic ridge
• size is correlated to type of placenta - larger size may be responsible for normal herniation of growing intestinal loop
• carnivores - smallest (endotheliochorial)
• pig - largest (epitheliochorial)
• sheep - intermediate
• Mesonephronic tubules - functional in embryonic life, then regress
• Bowman's capsule - one enlarged end of tubule forms double walled capsule
• Glomerulus - derived from branches of the dorsal aorta invaginated in the Bowman's capsule
• Mesonephric duct - other end of tubules joins the mesonephric duct (continuation of pronephric duct) provides and outlet for excretory product

• permanent and functional kidney from caudal nephrogenic ridge
• dual origin
• Ureteric bud - (metanephric diverticulum) caudal part of mesonephric duct, develops inot collecting system, grows in metanephric tissue and induces metanephris tissue to form the metanephric cap which develops into excretory system (nephron)
• 2 parts establish connections and communications
• outer part - forms capsule and interstitial tissue of kidney

• derived from metaneohric tissue cap
• Bowman's capsule, PCT, loop, and DCT

derived from a series of branches of the dorsal aorta, invaginated in the Bowman's Capsule

• derived from ureteric bud
• collecting tubules, major and minor calyces
• renal pelvis and ureter

• review - division of cloaca by urorectal septum into dorsal rectum and ventral urogenital sinus
• urogenital sinus - vesicular, pelvuc, and phallic parts
• bladder - proximal part of allantois together with vesicular part of urogenital sinus
• allantois - remainer degenerates and is called urachus
• lower part of mesonephric duct (deferent duct) and metanephric (ureter) duct are separated
• metanephric duct - opens into the bladder
• mesonephric duct - caudal w/in urogenital sinus (pelvic part)

absence of one of both kidney

two kidneys may fuse

failure of union between the developing nephron and collecting duct

• ureter opens into the urethra
• common in female dogs

• genetic sex determined at fertilization
• difficult to determine sex of embryo morphologically
• genital (gonadal) ridge - develops on the ventro-medial aspect of mesonephros, lined by coelomic epithelium which overlies a condensed mesenchyme
• primordial germ cells (originate in yolk sac) - migrate to the genital ridge, induces the development of the genital ridge to form primitive sex cords in mesenchyme

• Lateral to genital ridge is persisting mesonephric (Wolffian) duct - develops into male duct system
• Paramesonephric (Mullerian) duct - develops dorsolateral to mesonephric duct, develops into female duct system
• both ducts are present in each embryo

• XY : male Y - contains testis determining factor (TDF) genes
• Mullerian Inhibitory substance (MIS) produced by sertoli cells, causes regression of mullerian duct
• Testosterone - from Ledig cells, stimulates the development of Wolffian duct and causes the regression of mullerian duct

XX : female

• testis(gonadal) cords - develop into seminiferous tubules (peripheral part) and rete testis (central part)
• primordial germ cells - differentiate into gonocytes, after birth form spermatogonia
• mesenchyme - sertoli and leydig cells
• testis cords - separate from coelomic epithelium by a distinct mesenchymal sheet, develops into the tunica albugina
• efferent ductules - from some of the persisting mesopnephric tubules

• gonadal cords - break into many small clusters called follicles which contain primordial germ cells to develop into oogonia
• cortex - most clusters in peripheral
• medualla clusters degenerate
• tunica albugenia - poorly developed in ovary
• follicular cells - mesenchymal origin

M - Effernt Ductules

F - Vestigeal structures

M - Epididymis, Ductus deferens, Vesicular gland

F - Vestigeal Structure

M - Vestigeal Structures, Uterus Masculinus

F - Uterine Tube, Uterus and Vagina (partly)

M - Uninary bladder,

F - Urinary bladder

M - Pelvic urethra, Prostate

F - Urethra, Vagina (partly)

M - Penile urethra, bulbourethra gland

F - Vestibule, Vestibule gland

M - Medial ligament of bladder

F - Medial ligament of bladder

M - Ligament of Testis and epididymis

F - Round ligament of uterus

M - urethral fold of penile urethra

F - Labia minora

M - Scrotum

F - Labia

M - penis

F - Clitoris

• Gebernaculum testis - mesenchymal condensation extends from gonad to scrotal swelling
• swelling - of gebernaculum and intra-abdominal pressure are responsible for testis descent

• failure of testis to descent
• congenital inguinal and scrotal hernia

twins M and F

F - has male like characteristics

accumulation of fluid in the 2 layers of tunica vaginalis

• notochord - induces surface ectoderm to thicken, form neural plate
• neural plate - bounded laterally by elevations called neural folds
• median groove - develops in neural plate, allowing the neural folds to become apposed and subsequently fused to form a neural tube
• closures begins in the future cervical region and extends cranially and caudally until 2 small openings Rostal and Caudal neuropore close
• Fusion - group of cells are detached from the neural tube and differentiate into the neural crest cells

• Ganglia (sensory and autonomic)
• neurolemmal cells
• mesenchymal cells of head
• chromaffin cells of adrenal medualla
• melanoblasts
• pia mater
• arachnoid

• brain and spinal cord
• neuroepithelium - lines neural tube, proliferates outward to form neuroblast and gliablast (supporting cells)
• Neuroblast - begin to outgrow processes (axon and dendrites) which lie in peripheral region of the developing tube
• Mantle Zone - cell bodies of neuroblast, grey matter
• Marginal Zone - processed (axon and dendrites) white matter

• gliablast - astrocytes and oligodendrocytes
• Sulcus limitans - groove in the lateral wall of neural tube marks the division into dorsal (alar plate) and ventral (basal plate) halves
• Lateral plates - develop and combine with alar and basal plate, autonomic neurons, lateral horn
• Alar plate - sensory, dorsal horn
• Basal Plate - motor, ventral horn

• initially - spine and veterbral column equal, spinal nerves leave at the intervertebral foramina
• later - growth of veterbral column exceeds that of the cord
• Caudal end - tapers to form conus medullaris and most caudal spinal nerves passes obliquely (caudal equina)
• Dorsal and ventral Media fissure - separate white matter into dorsal, ventral, and lateral funiculus
• Central canal - spinal cord and cavity of neural tube
• Ependyma - proliferation od neuroepithlium ceases, lies in central canal
• Spinal nerves - formed at the union of dorsal and ventral roots
• Ventral root - Efferent, motor, axons originating from ventral horn
• Dorsal root - Afferent, sensory, axons originat from unipolar neurons of dorsal root ganglion (derived from neural crest cells)

• 4 cell columns
• Somatic Afferent - dorsal horn
• Visceral Afferent -lateral horn
• Visceral Effernt - intermediate horn
• Somatic Effernt - ventral horn

• Forebrain - Prosencephalon
• Midbrain - Mesencephalon
• Hindbrain - Rhombencephalon

cervical flexure - between the developing brain and spinal cord

Cranial flexure - or midbrain flexure

• Telencephalon :
• derivatives - olfactory bulb, and cerebral hemisphere
• Cavity - lateral ventricle
• Cranial nerve - first or olfactory nerve

• Diencephalon :
• Epithalamus, Thalamus, and Hypothalamus
• Cavity - Third venticle
• cranial nerve - Second or Optic nerve

Derivaties - Corpora quadrigemina, Cerebral peduncle

Cavity - Cerebral aqueduct

Cranial nerves - Occulomotor, Trochlear

• Metencephalon:
• Derivatives - Pons and Cerebellum
• Cranial nerve - 5th trigeminal

Pontine Flexure - between the metencephalon and myelencephalon

• Myelencephalon :
• derivative - medulla oblongata
• cranial nerve - 6 - 12
• cavity - 4 th ventricle

• piamater and arachnoid - from neural crest
• duramater - surrounding mesoderm

defective closure of the 2 halves of the vertebral arch through which the spinal cord and meninges may or may not protrude

cleft in spinal cord

panleucopenia virus

• abnormal accumulation of CSF with in vestibular ventricular system
• as ventricles enlarg the brain is diminutive

• absence of cranial vault
• cerebral hemispheres completely missing or reduced to small masses

• develops from 2 sources
• adrenal cortex - from intermediate mesoderm
• adrenal medulla - chromaffin cells, from neural crest cells (ectoderm)

• Dual origin
• Adenophyophysis - anterior pituitary, from stomodeal ectoderm as a dorsal evagination Rathke's pouch (joins infundibulum, and looses its connection with stomodeum) differentiates into pars, distalis, media, tuberalis
• Neurohypophysis - posterior pituitary, ventral outgrowth from floor of diencephalon, Infundibulum, retains its connection with hypothalamus and pars nervosa

• neuroectoderm - contibutes to the retina and optic nerve
• surface ectoderm - lens, lacrimal gland, corneal and conjunctival epithelium
• mesoderm - remaining structures

• develops - from developing forebrain(diencephalon) as lateral outgrowth
• makes contact with overlying ectoderm and induces it to thicken and form lens placodes
• optic cup - invaginations of optic vesicle, double walled, develops choroid fissure for the passage of hyloid artery
• retina - 2 walls of the optic cup, pigmented and sensory layers
• Lens placode - invaginates, becomes detached and round off into a lens vescile which occupies the mouth of optic cup
• Optic nerve - optic cup connected to the forebrain at optic stalk
• Corneal epithelium- surface ectoderm after detachemtn of lens vesicle
• Fibrous sclera and vascualr choroid - coats develop by local condensation of mesoderm
• Smooth m. of Iris - ectoderm at margin of optic cup
• Occular m. - paraxial mesoderm
• lid - skin fold above and below eye

faliure of choroidal fissure to close

• too small eye may result from intra-uterine infections
• toxoplasmosis

absence of eye as a result of exposure of the mother to toxic chemical during pregnancy

cloudiness of lens

• pharyngeal or brachial cleft - ectoderm
• pharyngeal arches - mesoderm and neural crest

Phayngeal pouches - endoderm

• pharynx - series of bilateral outpoketing from pharangeal endoderm, aka phayrngeal pouches
• pouches - causes adjacent mesenchymal tisse to becomes partially segreatated into a series of dorso-ventrally thickened masses called "brachial arches"
• branchial arch - supplied by aortic arch and specific cranial nerve
• brachial groove or cleft - ectoderm between arches develops a series of grooves

• out-pockets - lateral wall of most cranial part of the gut, from buccopharyngeal membrane to commencement of esophagus
• 1 - tympanic cavity and auditory tube
• 2 - tonsillar fossa
• 3 - parathyroid and thymus
• 4 - parathyroid and thymus
• 5 - ultimobrachial body : parafolicular cells

• thyroid bud - median endodermal downgrowth from floor of the pharynx, grows
• Thyroglossal - thyroid bud grows ventral and caudal and becomes canalised
• later - detaches and migrates to neck
• Foramen cecum of tongue - duct disappearsat its point of origin from the floor of the pharynx
• Thyroid follicles - endoermal, CT are derived from the invasion of surrounding mesoderm
• persistent thyroglossal duct

• series of grooves which demarcate the arches externally
• first cleft - forms external acoustic meatus
• 2-4 cleft - cervical sinus, regress and disappear

Skeletal - mandible (in part), malleus and incus

Muscle - muscles of mastication, digasticus (in part)

Innervation - mandibular division of trigeminal nerve

Skeleton - Hyoid apparatus (inpart), Stapes

Muscle - muscles of facial expression, digastricus (in part) Stapedius

Innervation - Facial nerve

Skeletal - hyoid apparatus (remaining part)

Muscule - pharyngeal muscles (in part)

Innervated - Glossopharyngeal nerve

Skeletal - most laryngeal cartilages

Muscle - pharyngeal and laryngeal muscles

Innervation - vagus, medullary part of accessory nerve

• Rostal 2/3 - ventral part of first pharyngeal arches, paired lateral swelling and median tuberculum impar
• Caudal 1/3 - from hypobrachial eminence (copula), from 2-4 pharyngeal arches and forms the root of the tongue
• Body - grows and project into the developing mouth cavity and lined by the stomodeal ectoderm, separated from the caudal part by the terminal sulcus, caudal part lined by occipital somites
• Occipital somites - striated muscles of tongue
• Innervation - trigeminal, facial, glossopharyngeal and hypoglossal

• Dental lamina - thickening ridge of oral ectoderm alond lenght of upper and lower jaw
• dental buds - lamina, deep surface invaginates and forming enamel cup which have outer and inner dental epithelium and central core, the Stellate Reticulum
• Neural crest - mesenchyme, forms dental papilla

• Enamel - ameloblast : form inner enamel epithelium, produce prisms of enamel that become calcified
• Dentine - odontoblast : specialized cells of dental papilla
• pulp - remaining cells of dental papilla
• Cementum - cemenoblast : mesenchymal cells located outside of toothe and incontact with the root
• Ligament - outside cement layer, mesenchyme gives rise to periodontal ligament
• Eruption and growth, deciduous teeth and permanent teeth
• Brachydont and Hypsodont

• Auricle - from a number of swellings in the dorsal region of pharyngeal arches 1 & 2
• External acoustic meatus - first pharyngeal cleft

• auditory tube and tympanic cavity - first pharyngeal pouch
• tympanic membrane - ectoderm of first cleft plus endoderm of first pouch
• malleus and incus - first pharyngeal arch
• Stapes - second pharyngreal arch

• Optic placode - thickening of surface ectoderm at level of rhombencephalon
• optic vesicle or otocyst - invagination of otic placode, detach from surface ectoderm
• membranous labyrinth - from otic vesicle, utericle saccule, endolymphatic duct, semicircular and cochlear duct
• bony labrinth - develops from chondrification and ossification of surrounding mesoderm

• around stomodeum - forward growth
• frontal process - dorsally, appears as a result of growth of the mesenchymal cells around the forebrain
• maxilary and madibular process - from division of manibular arch

• nasal placode - 2 ectodermal thickenings, covering ectoderm bounding the oral depression
• nasal pit - nasal placode invagination, excavation of mesoderm ventrally and communicates with stomodeum
• medial and lateral processes - proliferation regions of either side of the nasal pits
• mandibular processes - grow and develop into lower jaws
• maxillary process - fuses with medial nasal process to form the upper jaw
• cheek - fusion of mandibular and maxillary process at the corner of the mouth
• lacrimal duct - groove between the lateral nasal process and maxillary process

abnomalities of fusion of maxillary and mandibular process

• Study of abnormal development
• branch of study of embryology concerned with the study of malformations (abnomalities)

Genetical - mutation or by inheritance of dominant or recessive genes, inbreeding may produce genital defect

• Environmental - teratogens (agents that cause abnormal development)
• physical agents - x ray
• chemical - vitamin A deficiency (microphthalmai pigs)
• Drugs - Thalidomide in pups
• Infectious agents - Panleukopenia virus in kittens

Embryonic

• 50-60% Unknown
• 20-25% Multifactorial Inheritance
• 7-10% - Environmental Agents
• 7-8% - Mutant Genes
• 6-7% - Chromosomal Abnormalities