Development of Multicellular Tissues – Key Concepts

Question-and-answer flashcards covering germ layers, epithelial properties, skin renewal, specialized epithelia (sensory, airway, gut), blood and muscle development, and key regulatory mechanisms.

From which germ layer does the skin’s epidermis arise?

Ectoderm

Name the three primary germ layers formed during gastrulation.

Ectoderm, Mesoderm, Endoderm

What is the basic definition of an epithelium?

A sheet of cells that forms a barrier between the internal and external milieus, lining all body surfaces, cavities, and lumens.

Which epithelial classification is best suited for absorption and filtration due to its single layer?

Simple epithelia

What are the three basic cell shapes used to classify epithelia?

Squamous, cuboidal, and columnar

What two components make up the basement membrane?

Basal lamina and reticular lamina

List two major mechanical functions of the basement membrane.

Provides structural support/tensile strength and guides cell migration during tissue repair

What is the upper, free surface of epithelial tissue called?

Apical surface

Which type of epithelial cell junction helps define apical versus basolateral domains?

Tight junction

Approximately how often are intestinal epithelial cells replaced?

About every week

Why don’t blood vessels penetrate the basement membrane of epithelia?

The membrane acts as a barrier; nutrients and gases must diffuse across it from underlying vessels.

What is the oxygen diffusion distance limit through tissue, beyond which cells become hypoxic?

About 140 µm

What are the four main functions of epithelia listed in the lecture?

Control permeability, absorption/secretion, physical protection, and containment

Which epidermal layer contains the dividing keratinocyte stem cells?

Basal layer

What is the approximate time required for a basal keratinocyte to reach the skin surface and be shed?

About one month

What are prickle cells characterized by in light microscopy?

Numerous desmosomes appearing as tiny prickles around the cell surface

What barrier property is formed by the granular layer of the epidermis?

A waterproof seal

What are squames?

Dead, flattened keratin-filled cells shed from the skin surface

Define terminal differentiation.

Process by which a precursor cell acquires its final specialized characteristics and permanently stops dividing.

What two broad cell categories exist in the epidermal lineage prior to differentiation?

Stem cells and transit-amplifying cells

Give one reason epidermal renewal must be tightly regulated.

To allow thickening into callus under stress or to repair wounds

Name four gland types that originate from embryonic epidermis.

Sweat, tear, salivary, and mammary glands

What hormones drive mammary duct proliferation during pregnancy?

Estrogen and progesterone

What is the functional secretory unit formed at the ends of mammary ducts?

Alveolus (plural: alveoli)

Which cell type in the olfactory epithelium serves as a neuronal stem cell?

Basal cell

How long does an individual olfactory sensory neuron typically survive?

About 1–2 months

What specialized apical structures detect sound in auditory hair cells?

Stereocilia (giant microvilli) arranged in graded heights

In mammals, do auditory hair cells regenerate after destruction?

No; loss is typically permanent.

Which two epithelial cell types line the alveoli and what are their key functions?

Type I cells – thin for gas exchange; Type II cells – secrete surfactant

What is the main role of pulmonary surfactant?

Reduce surface tension to prevent alveolar collapse

Around what gestational age does fetal surfactant production begin, allowing potential independent breathing?

Approximately 5 months (20 weeks) of pregnancy

List the three differentiated cell types of the respiratory epithelium in larger airways.

Goblet cells, ciliated cells, and endocrine (neuroendocrine) cells

What is the function of goblet cells in the airway?

Secrete mucus to trap debris and microorganisms

Where are intestinal epithelial stem cells located?

At the base of the crypts of Lieberkühn

What structural projection greatly increases absorptive surface area on intestinal epithelial cells?

Microvilli, forming the brush border

Which germ layer gives rise to endothelial cells, blood cells, and muscle?

Mesoderm

What stem cell in bone marrow gives rise to all blood cell types?

Hemopoietic (blood-forming) stem cell

Name the four main categories of muscle cells discussed.

Skeletal, cardiac (heart), smooth, and myoepithelial

What precursor cell fuses to form multinucleated skeletal muscle fibers?

Myoblast

Why can skeletal muscle fibers not increase in number by cell division?

They are multinucleated terminally differentiated cells that no longer undergo mitosis

Which protein provides negative feedback to limit muscle growth?

Myostatin

What are satellite cells in skeletal muscle?

Quiescent stem-like cells under the basal lamina that can proliferate and fuse for muscle repair or growth

Explain the difference between muscle growth in length versus girth.

Length growth adds myonuclei via myoblast fusion; girth growth enlarges fibers and increases myofibrils, often also adding nuclei

What epithelial derivative forms the dilator muscle of the iris?

Myoepithelial cells (ectoderm-derived)

In the stomach, what two main secretions create an acidic digestive environment?

Hydrochloric acid and digestive enzymes active at low pH

Why is continual renewal of the gut epithelium essential?

To replace cells damaged or digested by harsh lumenal conditions

Which lung cell type pumps and secretes surfactant?

Type II alveolar cells

What structure houses auditory hair cells and supporting cells in the cochlea?

The organ of Corti

What extracellular matrix overlay contacts stereocilia in the ear?

Tectorial membrane

What property of epithelial cells allows selective import or export of substances?

Control of permeability via specialized transport proteins and tight junctions