Histology of Glands and Glandular Epithelium

Comprehensive review flashcards covering exocrine and endocrine gland histology, morphology, secretory modes, thyroid folliculogenesis, and adrenal gland zoning.

What is an example of a single-cell (unicellular) gland associated with surface epithelium?

A goblet cell.

From what developmental process do both exocrine and endocrine glands originate?

Proliferation of surface epithelial cells into underlying connective tissue (forming cords of ingrowing epithelial cells).

What is the primary structural difference in how exocrine and endocrine glands deliver their secretions?

Exocrine glands secrete their products through a duct system directly to where they will be used, whereas endocrine glands are ductless and secrete their products (hormones) directly into the blood.

Which four salivary glands are identified in this anatomical diagram of a dog's head?

Zygomatic gland, parotid gland (and duct), mandibular gland (and duct), and sublingual gland (and ducts).

What structural characteristic differentiates a 'simple' exocrine gland from a 'compound' exocrine gland?

A simple exocrine gland has an unbranched duct system, whereas a compound exocrine gland possesses a branching duct system.

What are three anatomical examples of 'simple' exocrine glands based on the shape of their secretory units?

Simple tubular glands: uterus; simple coiled glands: sweat glands; simple branched acinar glands: sebaceous glands.

How does the secretory unit of a sebaceous gland discharge its oily secretion in the absence of an independent duct?

The secretory unit opens directly into a hair follicle.

What are the contrasting histological characteristics of mucous cells versus serous cells?

Mucous cells are pale-staining columnar cells with flattened nuclei that form tubular units, whereas serous cells are pyramidal cells with darkly staining protein granules and rounded nuclei that form alveolar units.

In this histological section of a mixed mandibular salivary gland, what do the labels 'D', 'M', and 'S' indicate?

'D' represents the duct lumen (L.S.), 'M' represents a mucous secretory unit, and 'S' represents a serous demilune.

How is the secretory product released from the cell during merocrine secretion?

Via exocytosis of secretory vesicles into an epithelial tubule or duct without any loss of cytoplasm or destruction of the cell.

What morphological process characterizes apocrine secretion?

Membrane-bound vesicles containing the product pinch off from the apex, causing the gland cell to lose part of its cytoplasm with the secretion.

What happens to a secretory cell during holocrine secretion?

The plasma membrane ruptures and the entire secretory cell is destroyed and shed into the duct lumen to release its secretory product.

What type of epithelium lines thyroid follicles, and what substance is stored in their lumen?

Simple cuboidal epithelium; the lumen stores colloid containing iodinated thyroglobulin ($\text{TGB}$).

Where is thyroglobulin ($\text{TGB}$) synthesized, and how are active $\text{T}_3$ and $\text{T}_4$ released into blood capillaries?

$\text{TGB}$ is synthesized in the rough endoplasmic reticulum ($\text{rER}$); active $\text{T}_3$ and $\text{T}_4$ are liberated when lysosomes fuse with endocytosed colloid droplets and enzymes break down $\text{TGB}$.

How do circulating $\text{T}_3$ and $\text{T}_4$ regulate the hypothalamic-pituitary-thyroid axis?

Elevated $\text{T}_3$ and $\text{T}_4$ exert negative feedback that inhibits the release of $\text{TRH}$ (thyrotropin-releasing hormone) from the hypothalamus and $\text{TSH}$ (thyroid-stimulating hormone) from the anterior pituitary.

What condition is exhibited by this foal, and what hormonal imbalance causes the enlargement?

Goitre (enlarged thyroid gland), caused by reduced plasma $\text{T}_3$ and $\text{T}_4$ removing negative feedback, leading to elevated $\text{TSH}$ and $\text{TRH}$ signaling the thyroid to grow abnormally large to attempt to meet metabolic demands.

In this low-power section of an adrenal gland, which structures do the labels 'C', 'M', and 'V' designate?

'C' designates the adrenal cortex, 'M' designates the adrenal medulla, and 'V' designates the central medullary vein.

What hormone class is secreted by the zona glomerulosa of the adrenal cortex, and what controls this layer?

Mineralocorticoids (mainly aldosterone), which control water and electrolyte balance by reabsorbing $\text{Na}^+$ in response to signals from the kidneys.

What class of hormones is produced by the pale-staining cells of the zona fasciculata?

Glucocorticoids (specifically cortisol), which increase in response to stress under control of signals from the hypothalamus and pituitary.

What are the histological features, secretory products, and control mechanism of the adrenal medulla?

It consists of neuroendocrine cells with granular cytoplasm and abundant vesicles that secrete catecholamines (mainly adrenaline) in response to signals from the sympathetic nervous system.