The study of cells and tissues forms the foundation for understanding the anatomy and physiology of a horse. Cells are the smallest functional units of the body, while tissues are composed of specialized cells that work together to perform specific functions. In this first part of our series, we will take a detailed look at cytology and histology, as well as the specific tissue types found in horses.
Cytology – The Study of Cells
Cytology deals with the structure, function, and development of cells. Each cell contains:
Nucleus: Stores genetic material and controls cell activity.
Cell membrane: Regulates the exchange of substances and protects the cell.
Mitochondria: The "powerhouses" of the cell, providing energy through cellular respiration.
Endoplasmic reticulum (ER): Involved in protein and lipid synthesis, divided into rough and smooth ER.
Golgi apparatus: Modifies and transports proteins.
Vacuoles: Store nutrients and waste products.
Cell division and differentiation are essential for growth, regeneration, and specific functions within the horse's body.
Histology – The Study of Tissues
Histology examines the structure and function of tissues, which consist of different cell types. There are four primary types of tissue:
Epithelial tissue: Covers internal and external surfaces, provides protection, and regulates substance exchange.
Connective and supportive tissue: Provides structural support, stores energy, and offers protection.
Muscle tissue: Enables movement and contraction.
Nervous tissue: Transmits impulses and processes information.
Histology of Cartilage and Bone
Cartilage Tissue
Cartilage is a specialized supportive tissue composed of chondrocytes embedded in a firm yet flexible matrix. In horses, hyaline cartilage is particularly important as it is found in joints, ensuring smooth, friction-free movement.
Bone Tissue
Bone consists of a mineralized matrix maintained by osteocytes. Osteoblasts facilitate bone formation, while osteoclasts are responsible for bone resorption. Compact bone tissue provides stability, whereas spongy bone tissue ensures flexibility and lightness.
Histology of Muscle Tissue
Muscle tissue is essential for movement and posture. There are three primary types:
Skeletal muscle (striated muscle): Voluntarily controlled, enabling precise movements. In horses, skeletal muscles are highly developed for endurance and rapid response.
Cardiac muscle: Involuntary, with specialized cell connections for synchronized contraction.
Smooth muscle: Involuntary, mainly active in digestion.
Muscle Contraction Using the Example of Skeletal Muscle
Muscle contraction occurs through the interaction of actin and myosin filaments. In horses, skeletal muscles are particularly well-perfused to support high endurance and power output.
General Structure of the Stomach and Intestinal Wall
The equine gastrointestinal tract is adapted for continuous food intake. The walls of the stomach and intestines consist of multiple layers:
Tunica mucosa (mucous membrane): Contains glands that secrete digestive enzymes and mucus.
Tunica submucosa: Loose connective tissue with blood and lymphatic vessels.
Tunica muscularis: Composed of smooth muscle, facilitating peristalsis.
Tunica serosa: Outer connective tissue layer that protects and stabilizes the organs.
Histology of the Stomach Wall
The horse's stomach is monogastric (single-chambered) and divided into different regions:
Pars cardiaca: Transition to the esophagus, preventing reflux.
Fundus & corpus: Contain glands producing gastric acid and digestive enzymes.
Pars pylorica: Regulates the passage of chyme into the small intestine.
The stomach wall contains specialized cells such as chief cells (enzyme production), parietal cells (acid secretion), and mucus-producing cells.
Histology of the Intestinal Wall
The equine intestinal wall is optimized for nutrient absorption and features microscopic structures:
Villi & crypts: Increase surface area for enhanced absorption.
Goblet cells: Produce mucus to protect the mucosa.
Enterocytes: Absorb nutrients and transport them into the bloodstream.
Distinct Features of the Three Sections of the Small Intestine
Duodenum: The site of enzymatic digestion, supported by pancreatic and bile secretions.
Jejunum: The main site of nutrient absorption, with numerous villi.
Ileum: The transition to the large intestine, containing specialized Peyer’s patches for immune defense.

About the Author
Harriet Charlotte Schulz is an equine nutrition manager, stable owner, and has over 20 years of experience in handling horses. Her expertise is based on both practical experience and in-depth knowledge of equine nutrition, anatomy, and physiology.
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