1- All are derived from ectoderm except?
1. Lens
2. Eustachian tube
3. Brain
4. Retina
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Answer 1 – 2
Explanation –
☆Eustachian tube originates from the first pharyngeal pouch i.e. Endoderm
☆ Lens ,brain and retina are derived from ectoderm.
Structure develops from different germ layers;-
Endoderm
The endoderm produces tissue within the lungs, thyroid, and pancreas.
Endoderm
The endoderm is one of the germ layers formed during animal embryonic development. Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm.
It forms the epithelial lining of the whole of the digestive tract except part of the mouth and pharynx and the terminal part of the rectum (which are lined by involutions of the ectoderm). It also forms the lining cells of all the glands which open into the digestive tract, including those of the liver and pancreas; the epithelium of the auditory tube and tympanic cavity; the trachea, bronchi, and alveoli of the lungs; the bladder and part of the urethra; and the follicle lining of the thyroid gland and thymus.
The endoderm forms: the pharynx, the esophagus, the stomach, the small intestine, the colon, the liver, the pancreas, the bladder, the epithelial parts of the trachea and bronchi, the lungs, the thyroid, and the parathyroid.
Mesoderm:-
The mesoderm aids in the production of cardiac muscle, skeletal muscle, smooth muscle, tissues within the kidneys, and red blood cells.
Mesoderm
The mesoderm germ layer forms in the embryos of triploblastic animals. During gastrulation, some of the cells migrating inward contribute to the mesoderm, an additional layer between the endoderm and the ectoderm. The formation of a mesoderm leads to the development of a coelom. Organs formed inside a coelom can freely move, grow, and develop independently of the body wall while fluid cushions and protects them from shocks.
The mesoderm has several components which develop into tissues: intermediate mesoderm, paraxial mesoderm, lateral plate mesoderm, and chorda-mesoderm. The chorda-mesoderm develops into the notochord.
The intermediate mesoderm develops into kidneys and gonads.
The paraxial mesoderm develops into cartilage, skeletal muscle, and dermis.
The lateral plate mesoderm develops into the circulatory system (including the heart and spleen), the wall of the gut, and wall of the human body.
The mesoderm forms: muscle (smooth and striated), bone, cartilage, connective tissue, adipose tissue, circulatory system, lymphatic system, dermis, genitourinary system, serous membranes, and notochord.
Ectoderm
The ectoderm produces tissues within the epidermis, aids in the formation of neurons within the brain, and constructs melanocytes.
The ectoderm generates the outer layer of the embryo, and it forms from the embryo’s epiblast.The ectoderm develops into the surface ectoderm, neural crest, and the neural tube.
The surface ectoderm develops into: epidermis, hair, nails, lens of the eye, sebaceous glands, cornea, tooth enamel, the epithelium of the mouth and nose.
The neural crest of the ectoderm develops into: peripheral nervous system, adrenal medulla, melanocytes, facial cartilage, dentin of teeth.
The neural tube of the ectoderm develops into: brain, spinal cord, posterior pituitary, motor neurons, retina.
Note: The anterior pituitary develops from the ectodermal tissue of Rathke’s pouch.
