How and When Does the Upper Lip Close?
Which blocks must merge and fuse to close the upper lip, and when does this happen?
💡 The upper lip closes at about weeks 4 to 6 when the medial nasal and maxillary processes fuse, and that same seeds the front of the , so a lip failure often extends backward.
Prerequisite check
- After , cranial travel in organized migratory streams, each with a destination, not at random.
- The front of the face is filled by cells that migrate into the and the first pharyngeal arch, which becomes the maxillary and mandibular processes.
What you will learn
Goal: Explain that the upper lip closes when the medial nasal, lateral nasal, and maxillary prominences merge and fuse at about human weeks 4 to 6, forming the upper lip, , and primary , and identify this as the step that fails in a lip.
- The two medial nasal processes merge into the , which becomes the , the four upper incisors, and the primary .
- The upper lip closes at about human weeks 4 to 6 when each fuses with the medial nasal block beside it.
- When the medial nasal and maxillary processes fail to fuse, the upper lip does not close, producing a lip that can be or .
- Because the same seeds the primary , lip with cleft palate is treated as one developmental group.
Model: The fusion timeline, told as normal versus failed
Read the rows in order. At the end of week 4 nasal pits split the into medial and lateral nasal processes. During weeks 4 to 6 the medial nasal processes merge into the , the fuses with the medial nasal block on each side, and the upper lip closes. In weeks 5 to 6 the primary forms from the intermaxillary segment, the front triangle of palate to the . Putting it together, the lip closes at about human weeks 4 to 6 when these blocks come together.
Told as failure: if the maxillary and medial nasal processes do not fuse, the upper lip does not close, producing a lip that can be on one side or both and can extend up into the nostril and back through the gum. Because the same also seeds the primary , the failure often extends backward, which is why cleft lip with cleft palate is one developmental group. Mateo's chart says complete (left) cleft lip and palate with no other birth defects found, so the left-side fusion did not complete.
Explore (work the model before reading on)
- Which two medial blocks merge to form the ?
- At about what human week does the upper lip close?
- What is the name for the result when the upper lip fails to close?
- The becomes the , the upper incisors, and the primary . Use this to explain why a of the lip and a cleft of the front of the palate so often travel together.
- Mateo has a complete LEFT lip and . Using the timeline, name the specific (which two blocks, on which side) that did not finish, and predict what you would expect on his right side.
Guided notes
How and when the lip closes
- The becomes the , the four upper ____ (incisors), and the primary .
- The primary sits to the ____ foramen.
When fusion fails
- When the medial nasal and ____ processes fail to fuse, the upper lip does not close (a lip).
- Because the same seeds the primary , lip with cleft palate is one developmental ____.
An honesty note
- We now know which failed on Mateo's left side and roughly when, but we do not yet know ____ it failed.
- We also notice the rest of his body checked out normal, a clue we keep but do not yet turn into a ____.
Reading the Research
- Skim the title and abstract first to get the gist.
- Circle the one sentence that states the main claim.
- Box the evidence the authors give for that claim.
- Mark one sentence that confuses you, and move on.
Track your progress today
Check these off as you work through the lesson, then submit. This tells Mr. Mendoza how you're doing so he can help the class. It does not replace turning in your producible.
Use the code Mr. Mendoza gave you, not your name. Saved on this device.
- Read the Model and answered the Explore questions.
- Filled in the guided notes in my own words.
- Defined the new vocabulary with an example.
- Built the producible: On a labeled front-view diagram of the developing upper lip, outline the medial nasal blocks (intermaxillary segment) in one color and the maxillary processes in another. Draw the LEFT fusion line that did not seal for Mateo and the RIGHT line that did, then finish: "Mateo's upper lip is open on the left because the ____ and ____ processes did not fuse there at about week 4 to 6."
- Wrote my Claim, Evidence, and Reasoning exit ticket.
Exit ticket (Claim, Evidence, Reasoning)
- Claim: The upper lip closes when the medial nasal and maxillary processes fuse, at about human weeks 4 to 6.
- Evidence: The two medial nasal processes merge into the ____ segment, and each fuses to the medial nasal block beside it; failure here is a ____ lip.
- Reasoning: Because that same also seeds the primary , a left-side failure in Mateo can leave both the lip and the front of the palate open on that side, which matches his chart.
| Criterion | Proficient | Developing | Beginning |
|---|---|---|---|
| Complete | Every required part of the artifact is present and filled in. | Most parts are present, but one is missing or left blank. | Several parts are missing. |
| Accurate | The science and data are correct and match the evidence. | Mostly correct, with a small factual slip. | Key science or data is wrong. |
| Scientific reasoning (CER) | States a claim, backs it with specific evidence, and explains the reasoning. | Has a claim and evidence, but the reasoning is thin or missing. | Gives an answer with no evidence or reasoning. |
| Professional communication | Clear, organized, and labeled the way a clinician or scientist would write it. | Readable but disorganized or missing labels. | Hard to follow. |
| Submitted | Turned in the right way (Schoology for routine work) and confirmed. | Turned in, but in the wrong place or unconfirmed. | Not turned in. |
- CompleteProficient: Nothing is left blank: the model fills every part of "On a labeled front-view diagram of the developing upper lip, outline the medial nasal blocks (intermaxillary segment) in one color and the maxillary processes in another. Draw the LEFT fusion line that did not seal for Mateo and the RIGHT line that did, then finish: "Mateo's upper lip is open on the left because the ____ and ____ processes did not fuse there at about week 4 to 6."".
- AccurateProficient: Every number and claim matches the case evidence.
- Scientific reasoning (CER)Proficient: It names a claim, cites the specific evidence, and explains the reasoning, not just the answer.
- Professional communicationProficient: It is organized and labeled like a real chart note.
- SubmittedProficient: It would be turned in on Schoology and confirmed.
Where this leads: careers
What's next: The upper lip closes at about weeks 4 to 6, forming the lip and the small front triangle of . But that triangle is only the front of the roof of the mouth. Behind the , the palate is still wide open. So the next question is: how does the palate begin? We chase that next time.