Question

Which chordate features can be found in the human embryo?

Short answer

The human embryo exhibits four key chordate features: a notochord, which provides support and eventually gets replaced by the vertebral column; a dorsal hollow nerve cord, which develops into the central nervous system; pharyngeal slits or clefts, which transform into structures such as the middle ear, Eustachian tubes, lymphatic system, and neck glands; and a post-anal tail, which later regresses to form the coccyx or tailbone in the adult human skeleton.

Step-by-step solution

1. Identifying Key Chordate Features

Chordates are characterized by having a notochord, a dorsal hollow nerve cord, pharyngeal slits or clefts, and a post-anal tail during some part of their life cycle. Let's discuss each of these features in the context of the human embryo.

2. Notochord

The notochord is a flexible, rod-shaped structure that provides support to the body and helps to maintain the shape of the embryo. In humans, the notochord is present during early embryonic development but is then replaced by the vertebral column as the embryo grows and develops further.

3. Dorsal Hollow Nerve Cord

The dorsal hollow nerve cord is a tubular structure present in all chordates. It is the precursor of the central nervous system in vertebrates. In the human embryo, the nerve cord is initially formed from the ectoderm tissue during development and eventually develops into the spinal cord and brain.

4. Pharyngeal Slits or Clefts

Pharyngeal slits or clefts are openings in the pharynx that can develop into gill slits for respiration in aquatic chordates, such as fish. In the human embryo, pharyngeal clefts are present during the early stages of development, but they eventually transform into different structures. For example, the first pair of clefts contributes to the formation of the middle ear and Eustachian tubes, while the others contribute to the development of the lymphatic system and glands in the neck.

5. Post-anal Tail

A post-anal tail is a muscular extension that is found posterior to the anus in chordates. While humans do not have a tail in their adult form, a post-anal tail is present during the embryonic stage. The human embryonic tail later regresses, with the remaining structure known as the coccyx, or tailbone, in the adult human skeleton. In conclusion, the four key chordate features - a notochord, a dorsal hollow nerve cord, pharyngeal slits or clefts, and a post-anal tail - can all be found in the human embryo, though they may undergo changes during development and eventually contribute to different structures in the adult human body.