Describe the structure and function of the conjunctiva
Nathaniel Knox Cartwright, Petros Carvounis in Short Answer Questions for the MRCOphth Part 1, 2018
The conjunctiva is a transparent mucous membrane lining the ocular surface, linking the globe and eyelids. It is derived from ectoderm and has three parts: bulbar: the bulbar conjunctiva lies loosely over the sclera and merges with the corneal epithelium about 1 mm anterior to the corneoscleral limbus and fuses with Tenon’s capsule approximately 3 mm posterior to the limbuspalpebral: this is firmly adherent to the tarsal platesforniceal: the tarsal conjunctiva forms outpouchings between the bulbar and palpebral conjunctivae. The superior fornix extends about 10 mm from the limbus, inferior 8 mm and lateral 14 mm (i.e. behind the equator). There is no medial fornix.
Developmental Diseases of the Nervous System
Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw in Hankey's Clinical Neurology, 2020
This chapter is divided into two sections: (1) developmental malformations of the nervous system and (2) neurocutaneous disorders. Many of the neurocutaneous disorders could easily be considered in a discussion of tumors of the nervous system. However, several of the disorders show significant developmental abnormalities that justify their inclusion in this chapter. Furthermore, as discussed below, the nervous system emerges from the ectoderm of the primitive embryo from which the skin, as well as portions of the skull and face, also develops. As a consequence, germline or early somatic mutations of the ectoderm may produce defects in both the skin and nervous system resulting in neurocutaneous disorders.
Duplications of the alimentary tract
Prem Puri in Newborn Surgery, 2017
The most satisfactory of several theories of the origin of GI duplications is that relating to the development of the neurenteric canal. Saunders,15 in 1943, noted that thoracic duplications are frequently associated with abnormalities of the cervical and thoracic vertebrae. These duplications may be attached to the vertebral bodies or connected to the spinal canal. These findings gave rise to the Bentley and Smith split-notochord theory.16–18 The embryo initially has two layers: ectoderm and endoderm. Mesoderm forms between the two, but for a short time, these two layers remain adherent. A transient opening (the notochordal plate) appears, connecting the neural ectoderm with the intestinal endoderm. This notochordal plate normally migrates dorsally and becomes “pinched” off from the endoderm by the ingrowth of mesodermal cells from each side. If the notochordal plate fails to migrate as a result of adhesions to the endodermal lining, the spinal canal cannot close ventrally, and a tract resembling a diverticulum is established with the primitive gut. This tract may remain open, leaving a fistula between the gut and the spinal canal, or close, leaving only a fibrous tract. However, in the majority of cases, it disappears completely, leaving only the duplication of the GI tract. This theory explains the formation of thoracic and caudal duplications, which may be associated with vertebral anomalies. However, the absence of spinal defects in many alimentary tract duplications makes this theory less tenable as a unifying model of their origin.
Advances in understanding vertebrate nephrogenesis
Published in Tissue Barriers, 2020
Joseph M. Chambers, Rebecca A. Wingert
Vertebrate development entails the formation of three germ layers, the ectoderm, mesoderm, and endoderm, which provide cellular blueprints for embryonic organogenesis. Ectoderm gives rise to the central nervous system and skin cells, and endoderm derivatives encompass cells that line the respiratory and digestive tracts. The mesoderm, or middle layer, produces cells that are most abundant in the human body constituting skeletal muscle, cartilage, heart, gonads, and blood, among other tissue types.1 This review will focus on a member of the mesoderm lineage: the kidney. Much of our understanding about kidney development stems from rodent models, but also has benefited from studies in other vertebrates such as fish, frogs, and birds.2The inception of mesoderm development begins with the differentiation of pluripotent epiblast cells into a transient ‘primitive streak’ zone.1Position along the anterior-posterior embryonic axis and other instructive signals regulate the regionalization of paraxial, intermediate, and lateral plate mesoderm.3
Embryonic skin development and repair
Published in Organogenesis, 2018
Michael S. Hu, Mimi R. Borrelli, Wan Xing Hong, Samir Malhotra, Alexander T. M. Cheung, Ryan C. Ransom, Robert C. Rennert, Shane D. Morrison, H. Peter Lorenz, Michael T. Longaker
The adult epidermis has important barrier and protective functions. It is formed from the embryonic ectoderm via a multi-step process, involving distinct signaling patterns, and constant communication with the underlying dermis. In order to fulfill its important functions and maintain tissue homeostasis, stem cells in the basal layer of the epidermis continually reproduce to replace cell loss during turnover or after trauma. Adult skin is able to repair itself but through a process of fibrosis which results in scarring and loss of dermal appendages. The fetal epidermis has a unique ability to heal without scarring, and differences in extracellular proteins, signaling, and inflammatory and cell responses underlie this different healing capacity in fetal and adult skin. A greater understanding of the fetal tissue regeneration process has stimulated a variety of tissue engineering approaches to recapitulate this environment. However, more high-quality randomized controlled trials are required to demonstrate the clinical efficacy of many of the therapies in development for effectiveness in reducing or preventing scarring in human skin.
Biodegradable composite porous poly(dl -lactide-co-glycolide) scaffold supports mesenchymal stem cell differentiation and calcium phosphate deposition
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
Serena Casagrande, Roberto Tiribuzi, Emanuele Cassetti, Francesca Selmin, Gian Luca Gervasi, Lanfranco Barberini, Marco Freddolini, Maurizio Ricci, Aurélie Schoubben, Giuliano G. Cerulli, Paolo Blasi
Chorioallantoic membrane assay showed high biocompatibility of both uncoated and coated scaffolds. Digital images captured five days after the deposition of coated scaffolds on CAM surface showed a normal vascular growth without adverse reactions or inflammation, generally recognized as bleeding, ghost vessels and neoangiogenesis, around the scaffold (Figure 4(a)). The absence of adverse reactions was also confirmed by observing the CAM under the scaffolds after sampling for histology (data not shown). Histological examination confirmed the absence of toxicity and revealed just a slight thinning of the CAM due to the scaffold weight [33,34]. CAM had a normal histology without modification of the ectoderm, mesoderm, or endoderm. Nucleated red blood cells were normal as well. Of note, the coated scaffold showed important and deep cell invasion, as evident in Figure 4(b,c). Cells were found not only in the biopolymer in direct contact with the biological substrate but also in the scaffold porosity (Figure 4(c)). By a combination of capillarity and biopolymer cell adhesion, cells penetrated the 3 D structure of the scaffold deeper than 0.5 mm. The scaffold acted on CAM like a tissue graft [35]. The presence of the scaffold on the CAM caused localized hypertrophy of the membrane that reached more than 1 mm thickness. In addition, the ectoderm in contact with the scaffold manifested the classical reaction due to tissue fragment implantation. Ectoderm cells started to proliferate very rapidly (presence of numerous mitoses and multinuclear cells) and to invade the tridimensional structure.
Related Knowledge Centers
- Endoderm
- Epidermis
- Epithelium
- Germ Layer
- Mesoderm
- Nervous System
- Spinal Cord
- Brain
- Animal Embryonic Development
- Nerve