Germ Layer Derivatives

Front 1

Epidermis

Back 1

Surface ectoderm

Front 2

Hair

Back 2

Surface ectoderm

Front 3

Nails

Back 3

Surface ectoderm

Front 4

Inner and external ear

Back 4

Surface ectoderm

(but NOT middle ear)

Front 5

Tooth enamel

Back 5

Surface ectoderm

(but NOT odontoblasts and the dentin they produce)

Front 6

Lens of eye

Back 6

Surface ectoderm

Front 7

Anterior Pituitary

Back 7

Surface ectoderm

(Rathke's pouch from oral ectoderm that grows upward)

Front 8

Parotid Gland

Back 8

Surface ectoderm

Front 9

Mammary Glands

Back 9

Surface ectoderm

Front 10

Anal canal below the pectinate line

Back 10

Surface ectoderm

Front 11

Central Nervous System

Back 11

Neuroectoderm of the neural tube

Front 12

Retina and optic nerve

Back 12

Neuroectoderm of the neural tube

(The optic nerve is an outgrowth of the CNS and therefore covered not only by oligodendrocytes but all three meningeal layers. As a result it can fall victim to pathologies of any of those structures. Ex: Multiple Sclerosis)

Front 13

Pineal Gland

Back 13

Neuroectoderm of the neural tube

Front 14

Neurohypophysis (Posterior Pituitary)

Back 14

Neuroectoderm of the neural tube - it is a downward outgrowth of the CNS

Front 15

Astrocytes

Back 15

Neuroectoderm of the neural tube

(The only glial cells that are not neuroectodermal in origin are microglia which are derived from monocytes that migrate to the CNS at birth)

Front 16

Oligodendrocytes

Back 16

Neuroectoderm of the neural tube

(The only glial cells that are not neuroectodermal in origin are microglia which are derived from monocytes that migrate to the CNS at birth)

Front 17

Adrenal Medulla

Back 17

Neural Crest

(The adrenal medullary cells - chromaffin cells - are basically modified post-synaptic sympathetic ganglion cells. Presynaptic (preganglionic) neurons release acetylcholine onto chromaffin cells, eliciting release of catecholamines (especially epinephrine) into the blood, rather than releasing norepinephrine onto a synapse)

Front 18

Ganglia (Both pseudounipolar sensory ganglia (DRG) and postganglionic autonomic ganglia)

Back 18

Neural Crest

Front 19

Pigment cells (Melanocytes)

Back 19

Neural Crest

(This is why neurofibromatosis --> cafe au lait spots)

Front 20

Schwann Cells

Back 20

Neural Crest

Front 21

Leptomeninges (Pia and Arachnoid only)

Back 21

Neural Crest

(The Pia and Arachnoid are derived from the neural crest. The Dura, however, is derived from mesoderm)

Front 22

Pharyngeal Arch Cartilage

Back 22

Neural Crest

Front 23

Odontoblasts

Back 23

Neural Crest

(But remember, the enamel of teeth is derived from surface ectoderm)

Front 24

Parafollicular Cells of the Thyroid

Back 24

Neural Crest

(Compare to the follicles of the thyroid which are endodermal in origin)

Front 25

Aorticopulmonary Septum

Back 25

Neural Crest

(Defects in migration --> Tetralogy of Fallot)

Front 26

Endocardial Cushions

Back 26

Neural Crest

(Problems in migration --> VSDs and A/V valvular defects, as in Down Syndrome)

Front 27

Muscle

Back 27

Mesoderm

(Smooth, cardiac and skeletal muscle are all derived from mesoderm)

Front 28

Connective Tissue

Back 28

Mesoderm

Front 29

All serous membranes

Back 29

Mesoderm

The epithelial layer (mesothelium) is a SIMPLE SQUAMOUS EPITHELIUM which produces lubricating serous fluid. These cells are bound tightly to the underlying connective tissue, which provides the blood vessels and also serves as the binding layer which allows the whole serous membrane to adhere to organs and other structures.

Do not confuse serosa with adventitia - which, rather than reducing friction between structures, adheres them to one another.

Front 30

Bone and cartilage

Back 30

Mesoderm

Exceptions: pharyngeal arch cartilage which is derived from neural crest cells and produces the mandible and bones of the ear.

Front 31

Blood, Lymph and cardiovascular organs

Back 31

Mesoderm

Do not get confused by the fact that blood vessels and the heart are lined with endothelium.

Front 32

Adrenal Cortex

Back 32

Mesoderm

(Contrast with the adrenal medulla which is of neural crest origins)

Front 33

Gonads and internal reproductive organs

Back 33

Mesoderm

(In females, the lower vagina is derived from endoderm, similarly to the bladder and urethra)

Front 34

Kidney and Ureter

Back 34

Mesoderm

(In addition, the region of the bladder where the ureters enter the bladder, the trigone, is also mesodermal)

Front 35

Dura Mater

Back 35

Mesoderm

(Unlike the leptomeninges, which are derived from neural crest. Think of the dura as being one with the bone which is also mesodermal)

Front 36

Nucleus Pulposus of the spinal column

Back 36

Notochord mesoderm

This means that many structures in the spinal column are mesodermal: The vertebrae, the nucleus pulposus between them, and the dura mater

The anulus fibrosus is also mesodermal (fibrocartilage)

Front 37

GI epithelia

Back 37

Endoderm

Note that smooth muscle and connective tissue are mesodermal

Front 38

Lower respiratory tract epithelium (larynx, trachea, bronchi and lung)

Back 38

The lower respiratory tract begins as an outgrowth of the gut endoderm - the respiratory diverticulum)

Note that the smooth muscle, connective tissue and cartilage are all mesodermal

Front 39

Genitourinary epithelium (Bladder, urethra, and lower vagina)

Back 39

Endoderm

An exception to this is the trigone of the bladder which is mesodermal. The upper vagina is also mesodermal.

Front 40

Auditory tube and middle ear

Back 40

Pharyngeal pouch endoderm

Front 41

Palatine Tonsils

Back 41

Pharyngeal pouch endoderm

Front 42

Parathyroid Glands

Back 42

Pharyngeal pouch endoderm

The thyroid follicles are also endodermal in origin. The only exception in the thyroid is the Parafollicular (C-cells) which are of neural crest origins.

Note: In DiGeorge Syndrome you see CATCH-22 due to deletions on chromosome 22q:

Cardiac Abnormality (especially tetralogy of Fallot)
Abnormal facies
Thymic aplasia
Cleft palate
Hypocalcemia

Front 43

Thymus

Back 43

Pharyngeal pouch endoderm

Note: In DiGeorge Syndrome you see CATCH-22 due to deletion on chromosome 22q:

Cardiac Abnormality (especially tetralogy of Fallot)
Abnormal facies
Thymic aplasia
Cleft palate
Hypocalcemia

Front 44

Liver parenchyma

Back 44

Endoderm

Front 45

Pancreatic parenchyma

Back 45

Endoderm

Front 46

Submandibular and Sublingual Salivary Glands

Back 46

Endoderm

(Compare to the parotid gland which is derived from surface ectoderm)

Front 47

Follicles of Thyroid Gland

Back 47

Endoderm

(Note: The thymus, thyroid parenchyma, and parathyroids are all endodermal. The C-cells of the thyroid, however, are of neural crest origins)

Front 48

Spleen

Back 48

Mesoderm

Think of the spleen as an extension of the cardiovascular system. The heart, major blood vessels and blood are all mesodermal.