Physiology is the scientific study of the mechanisms of living things. Physiology reveals how cells, tissues, organs, and systems help to maintain normal bodily functions in healthy animals, as well as examining how an animal responds to changes in its environment. A physiologist is an expert in physiology. Changes to normal physiology imply that disease is present in the animal. A good knowledge of physiology, therefore, can help an owner to maintain their animal’s health.
The horse is an athletic animal, which means that it is ever more crucial to understand equine physiology. A physiologist can help to increase your horse’s athletic performance, prevent injuries and identify problems in their early stages. Doing so can prevent injuries from becoming severe and can increase the strength of the animal. This can be of great economic value to the owner of a sporting horse! Physiological analysis can also be a helpful factor in assessing new horses before buying them. Following the advice of a physiologist, a horse owner can ensure that they choose and purchase an animal that is healthy and strong.
Basic equine anatomy
Anatomy is the scientific study of the body structure of a healthy animal. Anatomy can be subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of healthy structures in the body which can be seen using the naked eye, whilst microscopic anatomy is the study of healthy body structures that cannot be seen with the naked eye and require the use of microscopes. In basic anatomical terms, the horse’s body is made up of skin, the musculoskeletal system, the central nervous system, the cardiovascular system, the gastrointestinal system, the lymphatic system, the endocrine system, and the urinary system.
Skin
Skin is the largest organ in the horse, made up of haired areas, non-haired areas, pigmented areas, and non pigmented areas. The skin is divided into three layers.
ï Epidermis
ï Dermis
ï Hypodermis
The epidermis is the outermost layer of the horse’s skin. It is a keratinised stratified squamous epithelium. ‘Stratified’ implies that there is more than one cell layer. The outer cell layers are keratinised. Keratin is a protein which is an essential part of the epithelial cells in the epidermis. Keratin helps the skin cells form a barrier and forms the outermost layer of the skin. The only living layer of the skin is the basal layer, which lies on the basal membrane. The basal layer continuously forms new cells, and these cells replace those cells which are sloughed off due to friction and physical damages in the outermost layers. The epidermis acts as a barrier and prevents pathogens entering into the body.
The dermis lies directly under the epidermis, and is divided into the papillary and the reticular layers. The papillary layer is located directly under the epidermis. The dermis is a connective tissue layer consisting of blood vessels, nerve endings, hair follicles, glands, collagen fibres, and elastic fibres. The blood vessels in the dermis have a thermoregulatory function. The thickness of the dermis differs by body region and horse breed.
The hypodermis is located at the very bottom of the skin, and is a loose connective tissue storing a large amount of adipose tissue. The hypodermis is absent in the lips, cheeks, and eyelids of the horse.
A Horse’s Skeleton
The horse’s skeleton consists of two parts.The Axial skeleton
The Appendicular skeleton
The axial skeleton of the horse is made up of the skull, vertebral column, sternum, and ribs.
The skull is formed of connecting skull bones called the frontal bone, parietal bone, interparietal bone, temporal bone, ethmoid bone, occipital bone, sphenoid bone, incisive bone, palatine bone, pterygoid bone, mandible, and the maxilla.
The vertebral column of the horse consists of 7 cervical, 18 thoracic, 6 lumbar, 5 sacral, and about 20 caudal vertebrae.
The sternum is formed from the interconnecting of sternebrae. Ribs are connected to the sternum via cartilage.
Two forelimbs and two hindlimbs form the appendicular skeleton of the horse. A horse’s limbs are highly adapted for fast running, and the horse can make long strides via the straightening and lengthening of its limbs.
The skeleton of the forelimbs contain the scapula, humerus, radius, ulna, carpal bones, metacarpal bones, phalanges, and sesamoid bones. The scapula connects the forelimb to the axial skeleton. The humerus connects with the scapula, forming the shoulder joint. The radius and ulna form the antebrachial skeleton. The radius supports the humerus to form the elbow joint. The ulna is fused with the radius, but this fusion is interrupted at an interosseous space.
There are eight carpal bones arranged in two rows, 4 bones per row. The radial carpal bone, the intermediate carpal bone, the ulnar carpal bone, and the accessory carpal bone located in the proximal row from medial to lateral. There are four carpal bones in the distal row arranged from medial to lateral.
There are also 3 metacarpal bones, called metacarpal 2,3 and 4. Metacarpals 1 and 5 have disappeared over time whilst metacarpals 2 and 4 have significantly reduced in size. These are called splint bones. Metacarpal 3 is the prominent metacarpal bone in a horse, and is called the cannon bone. It is well adapted to carry weight.
The horse has three phalanges called the proximal, middle, and distal phalanges. There are two sesamoid bones called the proximal sesamoid bone and the distal sesamoid bone. The distal sesamoid bone is also called the navicular bone.
The skeleton of the pelvic limb/hind limb of a horse contains the pelvic girdle, femur, tibia, fibula, tarsal bones, metatarsal bones, phalanges, and sesamoid bones. The pelvic girdle connects the hind limb to the axial skeleton.
The pelvic girdle is formed by connecting three bones; the ilium, the ischium, and the pubis. The femur connects with the pelvic girdle, forming the hip joint. The hip joint of the horse is well adapted to weight-bearing. The tibia connects with the femur and forms the knee joint. The fibula articulates with the lateral condyle of the tibia.
There are six tarsal bones; the talus, the calcaneus, the central tarsal bone, and the three distal tarsal bones. Metatarsal bones, phalanges, and sesamoid bones are similar to their corresponding bones in the forelimb.
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