Histology of small intestine of ox for veterinary anatomy
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histology small intestine ox bovine veterinary anatomy layers villi crypts
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Histology of the Small Intestine of the Ox (Bos taurus)
The small intestine of the ox (and ruminants generally) follows the standard four-layered wall plan of the GI tract but has several species-specific and segment-specific features. The three segments - duodenum, jejunum, and ileum - share the same basic architecture with important regional differences.
General Wall Structure (Inside to Outside)
The wall of the small intestine is composed of four concentric layers:
| Layer | Components |
|---|---|
| Mucosa | Epithelium + Lamina propria + Muscularis mucosae |
| Submucosa | Loose connective tissue + vessels + Meissner's plexus |
| Muscularis (Muscularis externa) | Inner circular + Outer longitudinal smooth muscle + Auerbach's plexus |
| Serosa | Inner fibrous + Outer mesothelial layer (peritoneal reflection) |
1. MUCOSA
The mucosa is the most functionally complex layer and contains the absorptive surface specializations.
Surface Adaptations for Absorption (three levels):
- Plicae circulares (Valvulae conniventes / Valves of Kerckring) - Circular folds of mucosa projecting into the lumen; best developed in the jejunum.
- Villi - Minute finger-like projections of mucosa projecting into the lumen. Lined by simple columnar epithelium. Each villus has a core of lamina propria containing a central lacteal (lymphatic capillary), blood capillaries, and smooth muscle fibers.
- Microvilli (Brush border / Striated border) - Projections on the apical surface of enterocytes. Appear as a uniform ~1 µm faintly staining layer in H&E sections.
Epithelium
Lined by simple columnar epithelium containing five main cell types:
| Cell Type | Location | Features |
|---|---|---|
| Enterocytes (Absorptive cells) | Villi surface | Tall columnar, brush border, basal nuclei; digest and absorb nutrients |
| Goblet cells | Villi + crypts | Unicellular mucin-secreting; pale apical cup on H&E; increase in density from duodenum → ileum |
| Paneth cells | Base of crypts | Absent or rare in the ox/ruminants (present in horses but NOT a feature of ox) - coarse eosinophilic apical granules; produce lysozyme and α-defensins |
| Enteroendocrine cells | Crypts | Secrete hormones (secretin, CCK, somatostatin); not visible on routine H&E |
| M cells (Microfold cells) | Over Peyer's patches | Antigen transport from lumen to lymphoid tissue; basal lamina is more porous |
Ox-specific note: Paneth cells are absent or very sparse in ruminants including the ox, unlike the horse (where crypts have conspicuous Paneth cells with eosinophilic granules) - Ohio State Veterinary Histology.
Crypts of Lieberkühn (Intestinal Glands)
- Simple tubular glands extending from the muscularis mucosae, opening at the base of villi.
- Contain stem cells (mitotically active; mitotic figures commonly seen) that generate all villous epithelial cells.
- Cells migrate from crypt base → villus tip, then shed into the lumen (continual cell renewal).
Lamina Propria
- Loose collagenous connective tissue forming the core of each villus.
- Contains:
- Central lacteal (lymphatic capillary for fat absorption as chylomicrons)
- Dense capillary network
- Lymphocytes, plasma cells, macrophages, eosinophils
- Smooth muscle fibers (from muscularis mucosae) extending into the villus - their contraction "pumps" lymph through the lacteal
Muscularis Mucosae
- Inner circular + outer longitudinal layers of smooth muscle.
2. SUBMUCOSA
- Loose connective tissue with blood vessels, lymphatics, adipocytes, and nerves.
- Contains Meissner's plexus (submucosal plexus) - parasympathetic ganglia regulating mucosal secretion.
- In the duodenum only: contains Brunner's glands (submucosal/duodenal glands) - simple branched tubulo-alveolar glands. They secrete alkaline mucus to neutralize acidic chyme entering from the abomasum. Their ducts open into the crypts of Lieberkühn.
3. MUSCULARIS EXTERNA
- Inner circular layer - thicker; responsible for segmental contractions.
- Outer longitudinal layer - thinner; responsible for peristaltic contractions.
- Myenteric plexus (Auerbach's plexus) - located between the two muscle layers; coordinates motility.
4. SEROSA
- Outermost layer; reflection of the peritoneum.
- Consists of an inner layer of fibrocollagenous tissue and an outer single layer of mesothelial cells (simple squamous epithelium).
Segment-Specific Differential Features
| Feature | Duodenum | Jejunum | Ileum |
|---|---|---|---|
| Brunner's glands | Present (submucosa) | Absent | Absent |
| Villi shape | Short, broad (leaf-like) | Long, slender (finger-like), best developed | Short, club-shaped |
| Plicae circulares | Developing | Well developed | Less developed |
| Goblet cells | Fewer | Moderate | Numerous (most abundant) |
| Peyer's patches | Absent | Occasional solitary nodules | Present (aggregated lymphoid nodules); extend into submucosa |
| Paneth cells | Absent/rare in ox | Absent/rare in ox | Absent/rare in ox |
| Openings | Bile duct + pancreatic duct open here | - | Opens into large intestine at ileocecal junction |
Villi Morphology in the Ox
In the ox and ruminants, villi show considerable variation in shape across the length of the small intestine:
- Duodenum: Low and broad (sometimes leaf or tongue-shaped)
- Jejunum: Tallest and most slender - maximum absorptive surface area
- Ileum: Short, club-shaped, fewer in number
Peyer's Patches (Aggregated Lymphoid Nodules) - Key Ox Feature
Peyer's patches are particularly prominent in the bovine ileum and are an important immunological structure:
- Consist of aggregated lymphoid follicles (B-cell zones) + parafollicular T-cell areas.
- Located in the lamina propria and extend into the submucosa of the ileum.
- The overlying epithelium is the follicle-associated epithelium (FAE), which:
- Has fewer goblet cells (thinner mucus layer)
- Contains M cells that sample luminal antigens by endocytosis and deliver them to APCs
- Has a more porous basement membrane
- In calves/bovines, Peyer's patches are entry points for pathogens like Mycobacterium avium subsp. paratuberculosis (causing Johne's disease).
Summary Table: Histological Layers of Small Intestine (Ox)
| Layer | Key Structure | Staining/Appearance |
|---|---|---|
| Mucosa - Epithelium | Simple columnar; enterocytes, goblet cells | Eosinophilic brush border; goblet cells pale (mucin) |
| Mucosa - Lamina propria | Loose CT, lacteal, capillaries, lymphocytes | Pale staining, cellular |
| Mucosa - Muscularis mucosae | Thin smooth muscle layer | Eosinophilic band |
| Submucosa | Loose CT; Brunner's glands in duodenum | Pale; glands basophilic |
| Muscularis externa | Inner circular + outer longitudinal smooth muscle | Eosinophilic bands |
| Serosa | Mesothelium over connective tissue | Thin, flat cells |
Sources:
- Histology: A Text and Atlas with Correlated Cell and Molecular Biology, 9e - Chapter 17 (Small Intestine, Duodenum plates)
- Ohio State University Veterinary Histology - Small Intestine
- Practical Manual of Veterinary Anatomy, MJF College of Veterinary & Animal Sciences (B.V.Sc. curriculum), Unit VIII
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