Pancreas histology
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histology of normal pancreas showing exocrine acini islets of Langerhans and ducts
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pancreas histology
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pancreas histology exocrine acini islets centroacinar cells site:nih.gov OR site:ncbi.nlm.nih.gov
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Pancreas histology
The pancreas is a mixed gland with:
- Exocrine portion - produces digestive enzymes and bicarbonate-rich fluid
- Endocrine portion - the islets of Langerhans, which release hormones into blood
1. Exocrine pancreas
This accounts for most of the organ and is made of closely packed, purely serous acini.
- Acinar cells are pyramidal.
- Their basal cytoplasm is basophilic because it contains abundant rough endoplasmic reticulum.
- Their apical cytoplasm is eosinophilic/granular, due to enzyme-containing zymogen granules.
- The round nucleus is usually basal.
- Digestive enzyme precursors include trypsinogen, chymotrypsinogen, lipase, amylase, and nucleases.
Slide appearance: Dark-staining, tightly packed grape-like acini with very small lumina.
2. Centroacinar cells
A hallmark of the pancreas.
- They are pale, flattened or cuboidal cells seen within the lumen of an acinus.
- They represent the beginning of the intercalated duct.
- Together with duct cells, they contribute bicarbonate-rich secretion, helping neutralize acidic chyme in the duodenum.
Exam point: Centroacinar cells are characteristic of pancreas and are not found in salivary glands.
3. Pancreatic duct system
Flow of secretion:
Acinus → centroacinar cells/intercalated duct → intralobular duct → interlobular duct → main pancreatic duct → duodenum
- Intercalated ducts are lined by low cuboidal cells.
- Larger ducts have cuboidal to columnar epithelium.
- Striated ducts are absent, unlike in major salivary glands.
4. Endocrine pancreas: Islets of Langerhans
Islets are scattered, rounded clusters of pale-staining cells embedded among the darker exocrine acini.
- They are more numerous in the tail of the pancreas.
- Cells are arranged in cords around many fenestrated capillaries.
- They have no ducts.
| Cell type | Main hormone | Major action |
|---|---|---|
| Beta cells | Insulin | Lowers blood glucose |
| Alpha cells | Glucagon | Raises blood glucose |
| Delta cells | Somatostatin | Inhibits insulin, glucagon, and GI secretion |
| PP/F cells | Pancreatic polypeptide | Modulates pancreatic and GI activity |
On routine H&E, individual endocrine cell types cannot be identified reliably without immunostaining.
How to identify pancreas on an H&E slide
Look for:
- Dark serous acini
- Pale islets of Langerhans
- Centroacinar cells inside acini
- Absence of striated ducts
- No mucous acini or serous demilunes
The exocrine pancreas consists mainly of serous acini; its acinar cells have basal rough ER and apical zymogen granules. The distinctive duct system starts inside the acinus through centroacinar cells. Junqueira's Basic Histology - Text and Atlas, 17e, p. 848. Islets are dispersed endocrine clusters that contain alpha, beta, and delta cells. Histology: A Text and Atlas with Correlated Cell and Molecular Biology, p. 1735.
Ureter histology
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normal ureter histology cross section urothelium lamina propria muscularis layers
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ureter histology
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ureter histology urothelium muscularis externa layers
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Ureter histology
The ureter has three layers:
- Mucosa
- Muscularis
- Adventitia
1. Mucosa
- The lumen is usually stellate (star-shaped) in cross-section because the mucosa is thrown into prominent longitudinal folds.
- It is lined by transitional epithelium (urothelium), specialized to withstand and distend with urine.
- Urothelium has:
- Basal cells: small cells resting on the basement membrane
- Intermediate cells: cuboidal to low columnar cells
- Superficial umbrella cells: large, dome-shaped, sometimes binucleate cells that form the urine barrier
- Beneath it is a dense connective-tissue lamina propria.
- There is no muscularis mucosae and no submucosa.
2. Muscularis
The muscular coat propels urine by peristalsis.
- In most of the ureter:
- Inner longitudinal smooth-muscle layer
- Outer circular smooth-muscle layer
- In the lower/distal one-third, an additional outer longitudinal layer develops.
The muscle bundles are not sharply separated into perfect sheets and are intermixed with connective tissue.
3. Adventitia
- Outer layer of fibroelastic connective tissue
- Contains blood vessels, lymphatics, nerves, and surrounding adipose tissue
- The ureter is retroperitoneal, so it normally has an adventitia, not a serosa.
Identification points on a slide
Identify ureter by:
- Star-shaped lumen
- Longitudinal mucosal folds
- Urothelium with umbrella cells
- Thick smooth muscle wall
- Adventitia
- No glands and no muscularis mucosae
Important distinction
The ureter is lined by urothelium, like the renal pelvis and urinary bladder. Its thick muscularis produces peristaltic waves that move urine to the bladder. Junqueira's Basic Histology - Text and Atlas, 17e, pp. 984-985. The distal ureter has three muscle layers, unlike the more proximal ureter, which generally has two. Histology: A Text and Atlas with Correlated Cell and Molecular Biology, pp. 1935-1936.
Uterus histology
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normal uterus histology endometrium myometrium perimetrium proliferative secretory phase
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endometrium histology
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uterus histology endometrium myometrium proliferative secretory phase site:ncbi.nlm.nih.gov
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Uterus histology
The uterine wall has three layers, from lumen outward:
1. Endometrium
The endometrium is the mucosa lining the uterine cavity. It has:
- Simple columnar surface epithelium, with ciliated and secretory cells
- Endometrial stroma, a cellular connective tissue
- Simple tubular uterine glands that extend from the surface toward the myometrium
It is divided into:
| Layer | Features and fate |
|---|---|
| Stratum functionalis | Superficial two-thirds. Contains most of the glands and spiral arteries. It undergoes cyclic change and is shed during menstruation. |
| Stratum basalis | Deep one-third, adjacent to myometrium. Supplied by straight arteries. It is retained during menstruation and regenerates the functionalis. |
Menstrual-cycle appearances
| Phase | Hormonal influence | Histological features |
|---|---|---|
| Proliferative phase | Estrogen | Thin-to-thickening endometrium; straight, narrow tubular glands; frequent mitoses; compact cellular stroma. |
| Secretory phase | Progesterone | Thick endometrium; tortuous, coiled “saw-toothed” glands with secretion in their lumina; edematous stroma; prominent spiral arteries. |
| Menstrual phase | Fall in estrogen and progesterone | Spiral-artery constriction, ischemia, breakdown, and shedding of the stratum functionalis. |
2. Myometrium
The myometrium is the thickest layer of the uterus.
- Made of interlacing bundles of smooth muscle with connective tissue.
- Its layers are not sharply demarcated.
- The middle vascular layer, the stratum vasculare, contains large blood vessels.
- During pregnancy, smooth-muscle cells undergo hypertrophy and hyperplasia.
- At delivery, myometrial contraction expels the fetus and compresses blood vessels to reduce bleeding.
3. Perimetrium
The perimetrium is the external covering.
- Where covered by peritoneum, it is a thin serosa consisting of mesothelium and loose connective tissue.
- Parts of the uterus not covered by peritoneum have an adventitia instead.
Identification points on a histology slide
Look for:
- A lumen lined by simple columnar epithelium
- Numerous uterine glands in endometrial stroma
- A very thick layer of irregularly arranged smooth muscle forming the myometrium
- An outer thin serosal layer when present
- Endometrium that changes substantially with the menstrual phase
The uterine wall consists of endometrium, myometrium, and perimetrium; the endometrium and myometrium both undergo cyclic changes in preparation for implantation. Histology: A Text and Atlas with Correlated Cell and Molecular Biology, pp. 2237-2238.
Fallopian tube histology
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normal fallopian uterine tube histology cross section mucosal folds ciliated cells secretory cells ampulla
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fallopian tube histology
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fallopian uterine tube histology ciliated secretory cells mucosal folds site:ncbi.nlm.nih.gov
Fallopian tube histology
The fallopian tube, also called the uterine tube or oviduct, transports the oocyte, is the usual site of fertilization, and carries the early embryo toward the uterus.
Its wall has three layers:
- Mucosa
- Muscularis
- Serosa
1. Mucosa
The mucosa is highly folded into complex longitudinal folds, especially in the ampulla, the widest part and the usual site of fertilization.
- Lined by simple columnar epithelium
- Lamina propria: loose, vascular connective tissue
- No submucosa and no muscularis mucosae
Two principal epithelial cell types occur:
| Cell | Histological feature | Function |
|---|---|---|
| Ciliated cells | Apical cilia | Beat toward the uterus, moving the oocyte or zygote uterineward |
| Nonciliated secretory cells, or peg cells | Narrow apex, lack cilia | Produce nutritive tubal fluid for sperm, oocyte, and early embryo |
The proportion of ciliated cells is greatest toward the ovarian end, especially the infundibulum and ampulla. Both ciliary activity and secretory activity vary during the menstrual cycle.
2. Muscularis
The muscularis is smooth muscle arranged as:
- Inner circular layer - thicker
- Outer longitudinal layer - thinner
The layers are often indistinct. Peristaltic contractions of this muscle, aided by ciliary movement, propel the oocyte or zygote toward the uterine cavity.
3. Serosa
The outer layer is a serosa consisting of:
- Mesothelium, or simple squamous epithelium
- Thin underlying connective tissue
It is continuous with the peritoneum of the broad ligament.
Regional differences
| Segment | Histological appearance |
|---|---|
| Infundibulum | Numerous mucosal folds and many ciliated cells |
| Ampulla | Widest lumen; most elaborate, branched mucosal folds; usual site of fertilization |
| Isthmus | Narrower lumen, fewer and lower folds; relatively thicker muscular wall |
| Intramural part | Very narrow lumen; minimal folding; passes through uterine wall |
How to identify it on a slide
Look for:
- A very irregular, folded or labyrinth-like lumen
- Simple columnar epithelium with cilia
- No glands in the mucosa
- Smooth-muscle wall beneath the mucosa
- Outer serosa
Key distinction: The fallopian tube may resemble intestine because of the folded mucosa, but it has no goblet cells, no intestinal crypts, and no villi. It is recognized by ciliated simple columnar epithelium and its highly branched mucosal folds.
The uterine tube has a highly folded mucosa, a thick muscularis, and an external serosa. Its mucosal epithelium contains ciliated cells and nonciliated secretory or peg cells. Histology: A Text and Atlas With Correlated Cell and Molecular Biology, pp. 2231-2233.
Histology of testis
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