Paper - The early appearance of the anlagen of the pars tuberalis in the hypophysis of the chick (1918)

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Atwell WJ. and Sitler I. The early appearance of the anlagen of the pars tuberalis in the hypophysis of the chick. (1918). Anat. Rec. 15(4): 181-187.

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This historic 1918 paper by Atwell and Sitler describes development of the pars tuberalis in the hypophysis (pituitary) of the chick




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The early appearance of the anlagen of the pars tuberalis in the hypophysis of the chick

Atwell WJ. and Sitler Ida.

Five Pictures


[t is now well n'('()>riuz((l lli:it tlic cpithcliiil portion of tlip hypophysis consists of three ilistinct parts. The pars anterior propria is the principal cpitheHal lobe and constitutes the main l)iilk of the ulaml, the i);'.rs int(>nii( dia is a thin layer. epithelial in iiatun". which becomes iiitiniately associated with the neural lobe. 'rh(» nicst recenth" rec(jgnizeil epithelial lobe is the pars tuberalis — so named by Tilney ('13) on account of its close relation to the tuber cinereum. It extends forward from the junction of the pars intermedia anil the pars anterior propria, surrounding the infundil)ular stalk and spreading out for some distance under the brain floor.

The jnirs tubcralis has been .sometimes confu.sed with the pars intermedia- Lothringer ('86) and Herring ('08) — but recent studies have .shown conclusively that these two parts are different both in adult structure and in developmental historj-. Tilney, in summarizing the develo])ment of tlie pars tuberalis in the chick and the cat, states:

In atUlition to (In- histological ditTorcnccs between these two parts, llic ontogenesis of tlie organ as observed in the cat and the fowl still furtluT einpiiasizes the fact .that the pars tubcralis and the pars infmnlibularis (pars inlernuMlia) are morphologically distinct elements. Till- |)ars infiiiidibularis makes its appearance inniiediately after the aiiianc of the buccal portion of the liypopliysis is fornietl. The pars tubcralis ai'ises as a relatively late stniciiirc. It has its origin in two sccond.aiy ilivcrliciila or sprouts from the ImkIv of the pituitary sac. These sprouts, the tubcral processes, ultimately fuse with each other across the median line, displace the body of the pituitary sac vcntrad and thus secondarily a.ssume their juxta-iiein-al position.


Out" (if lis Al\V(>ll CIS) — ill ;i recent study of tlie tlevelopiiii'iit of tlie liypopliysis in the nil)l)if has obtainod somewhat (lifTereiit results. Wliile afireeiiifi with Tilney as to the distinctness of the pars tul)erahs and the pars intermedia, and also confirming the statement tliat the pars tulieralis is late in acquiring its adult relationship with the tuber cinereum, it has been found thai in the rabbit the anlagen of the pars tuberalis may 1)1' discerned \erv early. They were found to precede* the definite pars intermedia by a considerable period of time.

It was with the lio|)e of throwiiifi some light upon this point that the j)resent study was imdertaken. Accordingly we have been led to construct a luimber of wax-plate models of the epillielial hypophysis from chick emiiryos, l)eginning with .stages in whicii the tuberal processes might be recognized easily and then j)roceeding to succes.sively younger (>mbryos in an effort to determine the earliest appearance of th<' anlagcu.

Tlie literature relating to the lateral lobes and the pai's tuberalis in the hypophysis of the chick is not extensive.

Rossi ('{)()) speaks of a median and two lateral parts in the early hypophj'sis of the chick embryo, .\ccording to Ro.ssi the lateral lobes are secondary structures.

iM'onomo ('!)!)) observed a pair of "Seitenspro.ssen' in the hypophysis of the dove and of the domestic fowl. In dove embryos the sprouts appear b(>tween the fourth and seventh days of incubation. \o definite statement is made concerning the first ai)pearance of the sprouts in the chick.

Tilney ('13) first ob.served the 'tuberal processes' in a chick embryo of o days and 20 hours of incubation. From this stage the jiroces.ses were traced to the formation of the pars tuberalis of the adult fowl, .\lthough a reconstruction was prepared from an embryo of fourda3's of incubation the tul)eral proces-ses were not seen in this stage. Embryos younger than four days were not studied.

Woerdeman ('14) notes that the lateral lobes are forming in a chick embryo of about 72 hours of de\-elopment. The thickened epithelium which lies in front of Hathke's pocket is constricted off from the mouth cavity by two lateral folds. Woerdeman considers that the lateral lobes so formed arise independently of Rathko's pocket.

Bruni ('15) observes the presence of two 'lobi laterali' in the chick at 82 hours of incubation. He also figures and describes the latrral lobes in older embryos but does not trace them into the formation of the pars luberalis.

Observations

We have prcpan-d wax-plate reconstructions of the epithelial portion of the hypophj'sis from cliick embryos of 48, 59, 67, 72, 96, 120 and 144 hours of incubation. A relatively high magnification was chosen for the construction of the models in order that all details of structure might be shown as accurately as possible. For all younger stages, including the 72 hour embryo, the magnification was 300 diameters. For the older embryos the magnification was reduced to 200 diameters.

Chick embryo, 4^ hours of incubation {21-2 pairs of primitive segments). Fig. 1. The hj^jophyseal pouch is well formed but opens widely into the mouth invagination. There is no indication of the lateral lobes. The anterior end of the fore-gut, which will later form Seessel's pouch, extends farther cranially than does the hj-pophyseal pouch. At this time the oral membrane is intact.

Chick embryo, 59 hours of incubation (30 pairs of segments). The hypophyseal pouch (Rathke's pocket) has deepened and now exhibits two lateral enlargements near its attachment to the oral epithelium. As later models show, these are theanlagen of the lat«'ral lobes from which the tuberal processes develop. .As may be seen from figure 2, Rathke's pocket is shghtly constricted just above the lateral lobes. The lateral lobes have the fomi of blunt ridges which protrude laterally and also somewhat nas^iUy. Their long axes lie parallel with the long axis of the entire h.vpophyseal pouch. This embryo shows one small perforation in the oral membrane.

Chick embryo, 67 hours of incubation. The lateral lobes are more prominent at this stage due to the fact that the hypophyseal pouch is beginning to be constricted somewhat from the oral ojivity. The constriction of Rathkc's pocket dorsal to the lateral lobes is also more distinct than previously. Each lateral lobe contains a lumen communicating with the cavity of the main h}7iophyseal sac. Seessel's pouch is in contact with the dorsal wall of Hathke's pocket for a considerable area. This is the eeto-entodennal fusion which has been recorded by numerous observers.

Chick embryo, 72 hours of incubnlion, figure 3. The hypophysis anlage is closely appUed to the brain wall, causing the nasal surface of the pouch to be sharply concave. The lateral lobes are more prominent than in the preceding .stage. The lumen of the pouch extends well into each lateral lobe. One striking feature is the extensive degree of communication between the cavity of Seessel's pouch and the hypophyseal sac. The two open into each other almost to the summit of the ecto-entodemial fusion. This cau-ses the opening of the hypophyseal sac into the oro-phuryn.\ to be relatively larger than in pre\-ious stages. From an examination of embryos of this age alone the impression might be gained that the lateral lobes are being added to Rathke's pocket. A critical comparison of this and younger stages, however, indiates strongly that the lateral lobes of the chick do not arise independently of Rathke's pouch, but that they are formed from it. In this we support the observations of Rossi.

Chick cinhryo, 96 hours of incubaUon. The principal feature of interest in this stage is the beginning recession of Seessel's pouch and its separation from the hj'pophyseal .sac. The lateral lobes are more sharply marked off from the superior part of the hypophysis, but otherwise this stage does not exhibit any striking differences from the preceding. .

.\11 figures represent wux-pliite recon-structions of the epithelial hypophysis as viewed from in front and from the left side. S, Seessel's pouch, R, Rathke's pouch, /./., lateral lobes, t.p., tuberal processes, st., hypophyseal stalk.

Fig. 1. Hypophysis region from chick embryo of 21-2 pairs of primitive segments (end of second day of incubation). X 100.

Fig. 2. Hypophysis from chick embryo of 30 pairs of primitive segments (59 hours of incubation). X 100.

Fig. 3. Hypophysis from chick embryo of 72 hours of incubation. X 100.

Fig. 4. Hypophysis from chick embryo, o days (120 hours) of incubation. X 75.

Fig. 5. Hypophysis from chick embryo, 6 days (144 hours) of incubation. X 75.


Chick embryo. 5 days (ISD hoiirn) of incubation. By tliis lime a definite h yp< )pliysoal stalk has been fonned. It is hollow and affords a coniniunioation between the lumen of the hypophysis and the oral cavity. The lateral lobes have increased in size so that the transverse diameter of the gland, measured between the lateral extremities of the two lobes, is almost twice the transverse diameter of the superior part of Rathke's pocket. The lateral lobes ar<^ united by a prominent ridge around the inferior and nasal enil of the hj-jiophysis. This solid median protuberance doubtless corresponds to a vestigial '\'orraum' or 'corpus I«)buli bifiu-cati' of other vertebrates as described by Woerdeman. The lateral lobes are beginning to be solid, also. At this stage they sometimes contain lumina, which, however, no longer conmiunicate clearlj- with the main h3^pophyseal cavity.

Seessel's pouch is represented by a solid bud of epithelial cells just dorsal to the hypophyseal stalk (S, fig. 4). Curiously enough Economo labels this bud the remains of Rathke's pocket.

Chid: embryo. 6 days (144 hours) of incubation. The hypophyseal stalk is much elongated and has become solid. Near its connection with the oral epithelium may be seen the bud-like remains of Seessel's pouch. The superior, or distal, half of the hjT)ophysisis is bent dorsalh" and forms an angle of about ninety degrees with the inferior or proximal half of the gland. The constriction near the middle of the gland is pronounced. Distinct 'tuberal processes' have formed from the lateral lobes. Instead of projecting so much laterally-, thej' are now directed toward the brain wall. The tuberal processes are not located at the extreme nasal end of the gland but are seen to protrude from about the middle of the inferior half (fig. 5).

Summary

The lateral lobes, from which the tuberal processes arise, may be distinguished in a chick embryo having 30 pairs of primitive segjiients. From a careful study of stages preceding and following the rupture of the oral membrane it is evident that the lateral lobes are not fonned independently of Rathke's pocket and later added to it, but are rather fonried secondarily from the nasjil wall of the early hypophyseal anlaK*'.

The lateral lobes, in all foniis studied, appear earlj- in devel«»pment. This would indicate that they and their derivative in higher vertebrates, the pars tuberahs, are of fundamental phylf>genetie importance. Thus gwat interest is attached to the broad homologies drawn by Woerdeman ('14).

Literature

Atwell, Wayne J. 1918 The development of the hypophysis cerebri of the rabbit (Lepus cuniculus L.). Amer. Jour. Anat., vol. 24, p. 271.

Brum, A. C. 1915 Sullo sviluppo del lobo ghiandolare dell' ipofisi negli Amnioti. Internat. Monutschr. f. Anat. u. Physiol., Bd. 31, S. 129.

EcoNOMO, C. J. 1899 Zur Entwicklung der Vogelhj-pophyse. Sitzber. d. kais. Akad. d. Wiss., math.-naturw. Classe, Bd. 108, Abth. 3, S. 381.

Herring, P. T. 1908 The histological appearances of the mammalian pituitary body. Quar. Jour. Ex. Physiol., vol. 1, p. 121.

LoTBRiNGER, S. 1886 Untersuchungcn an der hypophyse einiger Saugetbiere und des Menschen. Arch. f. mikr. Anat., Bd. 28, S. 257.

Rossi, U. 1896 Sui lobi latcrale della Ipsofisi. Monit. Zool. itul., 7, p. 240.

TiiJJET, Frederick 1913 An analysis of the ju.xtra-neural epithelial portion of the hypophysis cerebri, with an embryological and histological account of an hitherto undescribed part of the organ. Internat. Monatschr. f. Anat. u. Physiol.. Bd 30. S. 258.

Woerdeman, Martin W. 1914 Vergleichende Ontogenie der Hypophysis. Arch. f. mikr. Anat., Bd. 86, ,S. 108.


Cite this page: Hill, M.A. (2021, May 13) Embryology Paper - The early appearance of the anlagen of the pars tuberalis in the hypophysis of the chick (1918). Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_The_early_appearance_of_the_anlagen_of_the_pars_tuberalis_in_the_hypophysis_of_the_chick_(1918)

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