Complete the analogy :
Ectoderm : Somatotropin : : Endoderm :

Options

A. Estrogen
B. Thyroxine
C. Epinephrine
D. Cortisol

Answer

To complete the analogy: Ectoderm : Somatotropin : : Endoderm : ?

### Step-by-Step Solution:

1. **Identify the Germ Layers**: Understand that ectoderm and endoderm are two of the three primary germ layers in embryonic development. The three germ layers are ectoderm, mesoderm, and endoderm.

2. **Understand the Hormone Association**: Somatotropin (growth hormone) is associated with the ectoderm because it is produced by the anterior pituitary gland, which originates from ectodermal tissue.

3. **Determine the Endodermal Glands**: Identify the glands that originate from the endoderm. The key glands include:
- Thyroid
- Parathyroid
- Thymus
- Pancreas

4. **Identify Hormones from Endodermal Glands**: From the glands listed, determine which hormones are produced:
- Thyroid gland produces thyroxin (T4).
- The pancreas produces insulin and glucagon.
- The thymus produces thymosin.
- The parathyroid gland produces parathyroid hormone (PTH).

5. **Select the Correct Hormone**: Since we are looking for a hormone that corresponds to the endoderm, we see that thyroxin is produced by the thyroid gland, which is derived from the endoderm. Therefore, we can complete the analogy with thyroxin.

### Final Answer:
Ectoderm : Somatotropin : : Endoderm : Thyroxin

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