BIOL 211: Unit 4 - Embryology of Sensory Organs, Integument, and Cardiovascular System

Comprehensive review flashcards covering the embryonic development of the eye, ear, integumentary system, teeth, and cardiovascular system based on BIOL 211 Unit 4.

From which embryonic germ layers do the optic nerve, retina, lens, and sclera develop?

The optic nerve and retina form from the optic cup via neural ectoderm of the diencephalon; the lens forms from skin (surface) ectoderm; and the sclera forms from head mesenchyme (neural crest and mesoderm).

What are the distinct derivatives of the outer and inner layers of the optic cup?

The thinner outer layer forms the pigmented retina (showing melanin granules by the $6\text{th}$ week) and the outer pigmented epithelium of the iris and ciliary body. The thicker inner layer forms the sensory retina (rods, cones, bipolar cells, and ganglion cells) and the inner unpigmented epithelium of the ciliary body and iris.

What is the optic (choroid) fissure, and what vessels does it enclose?

It is a gap in the ventral wall of the optic cup and a groove along the ventral surface of the optic stalk that partially engulfs the hyaloid artery and hyaloid vein. The hyaloid artery later gives rise to the central artery of the retina.

How does ciliary muscle contraction alter lens curvature for near versus distance accommodation?

Relaxation of the circular ciliary muscle tightens the suspensory ligaments and pulls the lens thin/flat for distance vision; contraction of the ciliary muscle slacks the suspensory ligaments, allowing the lens to bulge into its most rounded shape for close focus.

What are the embryonic origins and innervations of the iris sphincter and dilator muscles?

Both smooth muscles originate from neural tube neuroectoderm of the optic cup. The circular sphincter muscle is controlled by parasympathetic innervation via $\text{CN III}$, while the radial dilator muscle is controlled by sympathetic innervation.

In retinal histogenesis, which neural cell layer differentiates first and which differentiates last?

Ganglion cells differentiate first (forming at the inner surface closest to the center of the eyeball, sending processes through the optic stalk). Rods and cones differentiate last (located deepest, adjacent to the pigmented retina at around $7\text{ months}$).

From which embryonic tissue does the inner ear derive, and what are the two main functional divisions of the otic vesicle?

The inner ear derives entirely from surface ectoderm (via the otic placode and otic vesicle). The otic vesicle divides into a dorsal utricular division (forming the utriculus and semicircular ducts) and a ventral saccular division (forming the sacculus and cochlear duct).

What are the branchial arch origins of the auditory ossicles in the middle ear?

The malleus and incus develop from mesenchyme (neural crest) of the first branchial arch (mandibular arch), whereas the stapes develops from the second branchial arch (hyoid arch).

What nerves provide sensory innervation to the auricle (pinna) based on its pharyngeal arch origins?

Parts derived from the first pharyngeal arch are innervated by the mandibular branch of the trigeminal nerve ($\text{CN V}$); parts derived from the second pharyngeal arch are supplied by occipital and auricular nerves, with potential contributions from the facial nerve ($\text{CN VII}$).

What are the layers of the epidermis from deepest to most superficial?

Stratum basale (germinativum), Stratum spinosum, Stratum granulosum, Stratum lucidum (found in thick skin only), and Stratum corneum.

What is the origin and developmental journey of epidermal melanocytes?

Melanocytes originate from neural crest cells and migrate through the embryonic dermis to settle in the stratum germinativum (basale) of the epidermis.

What structural and functional features distinguish eccrine sweat glands from apocrine sweat glands?

Eccrine glands open directly onto the skin surface, produce a watery secretion for thermoregulation, and are widely distributed. Apocrine glands (sudoriferous/scent glands) open into hair follicles and are restricted primarily to the axilla and pubis.

Identify this paired embryonic structure extending from the axilla to the inguinal region at $6\text{ weeks}$.

The mammary ridge (milk line), from which definitive mammary gland primordia develop.

Which cells produce enamel and dentine, and what are their respective embryological origins?

Enamel is deposited by ameloblasts derived from inner enamel organ epithelium (surface ectoderm). Dentine is secreted by odontoblasts derived from the dental papilla (neural crest).

What is the chronological sequence of anatomical sites responsible for embryonic and fetal hemopoiesis?

Yolk sac (up to $\sim 10\text{ weeks}$) $\rightarrow$ body mesenchyme ($5\text{ weeks}$) $\rightarrow$ liver ($6\text{ weeks}$ until birth) $\rightarrow$ spleen, thymus, and lymph ($2\text{--}3\text{ months}$ onward) $\rightarrow$ bone marrow ($3\text{--}4\text{ months}$ onward).

What is the chronological sequence of erythrocyte development in the human embryo?

Hemoblasts $\rightarrow$ Megaloblasts ($6\text{ weeks}$, vesicular nucleus) $\rightarrow$ Normoblasts ($2\text{ months}$, compact nucleus) $\rightarrow$ mature, enucleated erythrocytes (by $3\text{ months}$).

What are the four primary segments of the tubular heart in craniocaudal order at $4\text{ weeks}$?

Truncus arteriosus, bulbus cordis, primitive ventricle, and primitive atrium (with the sinus venosus at the caudal venous inlet).

How is the interatrial septum formed, and what provides the valve of the foramen ovale?

The septum primum grows toward the endocardial cushions, forming the foramen primum and later foramen secundum. A thicker septum secundum grows to its right, creating the foramen ovale. The remaining flap of the septum primum acts as the one-way valve of the foramen ovale.

What structure partitions the truncus arteriosus and bulbus cordis into the ascending aorta and pulmonary trunk?

The spiral aorticopulmonary septum, formed by the fusion of opposing truncal and bulbar ridges.

What are the adult cardiovascular fates of the right and left horns of the sinus venosus?

The right horn enlarges to become the smooth-walled sinus venarum of the right atrium; the left horn regresses and becomes the coronary sinus (and oblique vein of the left atrium).

What are the adult arterial derivatives of the third, fourth, and sixth aortic arches?

Third arch: common carotid and proximal internal carotid arteries. Fourth arch: left forms the aortic arch; right forms the proximal right subclavian artery. Sixth arch: proximal parts form pulmonary arteries; distal left forms ductus arteriosus (ligamentum arteriosum).

What are the adult arterial derivatives of the embryonic vitelline and umbilical arteries?

Vitelline arteries give rise to the three unpaired visceral branches of the abdominal aorta: celiac artery, superior mesenteric artery, and inferior mesenteric artery. Proximal segments of the umbilical arteries persist as the internal iliac arteries.

What are the fates of the embryonic vitelline veins?

They form hepatic sinusoids within the liver; the posterior vitelline vein forms the hepatic portal vein; and the anterior right vitelline vein forms the hepatic vein that drains into the inferior vena cava.

What are the three vascular shunts of the fetal circulation, their functions, and their adult remnants?

1. Ductus venosus: shunts oxygenated umbilical vein blood past liver sinusoids into the IVC (remnant: ligamentum venosum). 2. Foramen ovale: shunts blood from right atrium to left atrium to bypass pulmonary circuit (remnant: fossa ovalis). 3. Ductus arteriosus: shunts pulmonary trunk blood into descending aorta (remnant: ligamentum arteriosum).