Hyperplasia and Hypertrophy Quiz

Study Notes

Increased stress causes organs to grow due to increased cell size (hypertrophy) and/or cell number (hyperplasia)
Hypertrophy involves activating genes, synthesizing proteins, and producing organelles
Hyperplasia involves producing new cells from stem cells
Hyperplasia and hypertrophy often occur together, such as in the uterus during pregnancy
Permanent tissues like cardiac, skeletal, and nerve tissue can only undergo hypertrophy due to their inability to produce new cells
In response to systemic hypertension, cardiac myocytes undergo hypertrophy rather than hyperplasia
Pathologic hyperplasia, seen in conditions like endometrial hyperplasia, can progress to dysplasia and eventually cancer
Benign prostatic hyperplasia (BPH) is an exception to this trend, as it doesn't increase the risk of prostate cancer

Decreased stress, including reduced hormonal stimulation, disuse, or decreased nutrient/blood supply, causes a decrease in organ size (atrophy)
This occurs due to a decrease in both cell size and number
Cell number decreases through apoptosis
Cell size decreases through ubiquitin-proteosome degradation of the cytoskeleton and autophagy of cellular components
Ubiquitin-proteosome degradation involves "tagging" intermediate filaments of the cytoskeleton with ubiquitin and destroying them via proteosomes
Autophagy of cellular components involves the formation of autophagic vacuoles that fuse with lysosomes containing hydrolytic enzymes to breakdown cellular components

A change in stress on an organ leads to a change in cell type (metaplasia)
Mostly involves changes in surface epithelium types (squamous, columnar, or urothelial)
Metaplastic cells are better adapted to handle the new stress
Barrett esophagus is a classic example, where the lining of the esophagus changes due to acid reflux
Metaplasia can sometimes progress to cancer, as seen in Barrett esophagus's potential progression to adenocarcinoma of the esophagus
Apocrine metaplasia of the breast is an exception as it doesn't increase cancer risk
Vitamin A deficiency can also cause metaplasia
Vitamin A is crucial for differentiating specialized epithelial surfaces, like the conjunctiva of the eye
In vitamin A deficiency, the conjunctiva's thin squamous lining changes to stratified keratinizing squamous epithelium, a condition called keratomalacia
Connective tissues can also undergo metaplasia
Myositis ossificans is a prime example where connective tissue within muscles changes to bone after trauma during healing

Characterized by disordered cellular growth
Often refers to the proliferation of precancerous cells, such as in cervical intraepithelial neoplasia (CIN), which precedes cervical cancer
Often emerges from long-standing pathologic hyperplasia or metaplasia
Dysplasia can be reversed by alleviating the underlying stress
If the stress persists, dysplasia progresses to carcinoma, which is irreversible

Aplasia is the failure of cell production during embryonic development, like in unilateral renal agenesis (absence of one kidney)
Hypoplasia is a decrease in cell production during embryonic development, resulting in a relatively small organ, such as the streak ovary in Turner syndrome