**3. Vasculature of the foot**

In addition to the bones, ligaments, tendons and other soft tissues of the foot, the vasculature is essential in the equine foot. The blood vessel system is a vital part of transport of dissolved gases, nutrients, waste, signalling chemicals such as hormones, and immune cells to and from other organs [13]. The vast vascular network underlying the hoof capsule and coursing through the bones, fed through branches from the medial and lateral digital arteries and returning to general circulation via the medial and lateral digital veins (**Figure 3**) [9].

The vascular blood supply of the hoof originates from the common palmar digital artery and the dorsometatarsal artery, these main branches giving rise to medial and lateral palmar/plantar digital arteries (**Figure 4**) [14, 15]. In the hind limb, the small plantar common digital arteries contribute to form the digital arteries. At the level of second phalanx, there are branches nourishing to the heel bulbs and coronary region [1].

The vascular arteries of the dermis are divided into three independent arterial blood supplies: the dorsal coronary corium; the palmar/plantar portion of the coronary corium and laminar corium; and the dorsal laminar corium and solar corium, as the blood flow is reversely directed from the distal part to the proximal part within the dermal lamina (also termed lamella/lamellae and lamellar in the

#### **Figure 3.**

*Vascularisation of the equine foot. Reconstruction of the vasculature of the equine foot from CT images, showing the coronary, sublamellar and solar plexuses, the terminal arch, the circumflex vessels of the sole, and the bulbar vessels.*

**23**

**Figure 4.**

*margin.*

*The Anatomy, Histology and Physiology of the Healthy and Lame Equine Hoof*

literature) [4]. The terminal branches of the blood supply enter the distal phalanx from the medial and lateral aspects and then form several anastomoses within the bone to make the terminal arch. At this arch, there are 8–10 blood vessels emerging distally to nourish the sole margin [1]. This is a highly important organisation of blood vessels in equine feet as the terminal arch and its branches are protected by the bony canal that can be altered in chronic laminitis, leading to ischemia and a

*Reconstruction of micro CT image illustrating vascularisation of equine foot. Computed tomography (CT) scan images showing the three-dimensional reconstruction of arterial supply of equine foot. (A) Shows arteries distributed throughout the dorsal surface of the distal phalanx and anastomoses located proximally with vessels of the coronet and distally forming the circumflex artery. (B) Represents the arteries distributed in the sole* 

The capillary network of the equine digit is complex due to the fact that the dorsal and palmar parts of the foot have different blood supplies and drainage routes [2]. For instance, the blood vessels of the dorsal lamella pass through the distal phalanx and the blood supply of these portions is directed in the distal to the proximal way, while the palmar lamella is from the proximal circumflex to dorsal lamella [17]. Thus, haemorrhage from the sublamellar circulation can result in the rotation of P3, as is observed in the case of founder [16, 18, 19]. Consequently, the blood vessels of

decrease in the growth rate of the corium [16].

*DOI: http://dx.doi.org/10.5772/intechopen.84514*

*The Anatomy, Histology and Physiology of the Healthy and Lame Equine Hoof DOI: http://dx.doi.org/10.5772/intechopen.84514*

#### **Figure 4.**

*Veterinary Anatomy and Physiology*

**3. Vasculature of the foot**

**Figure 2.**

and coronary region [1].

the medial and lateral digital veins (**Figure 3**) [9].

*Haematoxylin and eosin stained lamellae within the horse hoof.*

In addition to the bones, ligaments, tendons and other soft tissues of the foot, the vasculature is essential in the equine foot. The blood vessel system is a vital part of transport of dissolved gases, nutrients, waste, signalling chemicals such as hormones, and immune cells to and from other organs [13]. The vast vascular network underlying the hoof capsule and coursing through the bones, fed through branches from the medial and lateral digital arteries and returning to general circulation via

The vascular blood supply of the hoof originates from the common palmar digital artery and the dorsometatarsal artery, these main branches giving rise to medial and lateral palmar/plantar digital arteries (**Figure 4**) [14, 15]. In the hind limb, the small plantar common digital arteries contribute to form the digital arteries. At the level of second phalanx, there are branches nourishing to the heel bulbs

The vascular arteries of the dermis are divided into three independent arterial blood supplies: the dorsal coronary corium; the palmar/plantar portion of the coronary corium and laminar corium; and the dorsal laminar corium and solar corium, as the blood flow is reversely directed from the distal part to the proximal part within the dermal lamina (also termed lamella/lamellae and lamellar in the

*Vascularisation of the equine foot. Reconstruction of the vasculature of the equine foot from CT images, showing the coronary, sublamellar and solar plexuses, the terminal arch, the circumflex vessels of the sole, and the* 

**22**

**Figure 3.**

*bulbar vessels.*

*Reconstruction of micro CT image illustrating vascularisation of equine foot. Computed tomography (CT) scan images showing the three-dimensional reconstruction of arterial supply of equine foot. (A) Shows arteries distributed throughout the dorsal surface of the distal phalanx and anastomoses located proximally with vessels of the coronet and distally forming the circumflex artery. (B) Represents the arteries distributed in the sole margin.*

literature) [4]. The terminal branches of the blood supply enter the distal phalanx from the medial and lateral aspects and then form several anastomoses within the bone to make the terminal arch. At this arch, there are 8–10 blood vessels emerging distally to nourish the sole margin [1]. This is a highly important organisation of blood vessels in equine feet as the terminal arch and its branches are protected by the bony canal that can be altered in chronic laminitis, leading to ischemia and a decrease in the growth rate of the corium [16].

The capillary network of the equine digit is complex due to the fact that the dorsal and palmar parts of the foot have different blood supplies and drainage routes [2]. For instance, the blood vessels of the dorsal lamella pass through the distal phalanx and the blood supply of these portions is directed in the distal to the proximal way, while the palmar lamella is from the proximal circumflex to dorsal lamella [17]. Thus, haemorrhage from the sublamellar circulation can result in the rotation of P3, as is observed in the case of founder [16, 18, 19]. Consequently, the blood vessels of

the equine foot are predisposed to local vasoconstriction and the development of ischemic disease as the arteries from the plexus have thicker walls with small lumens and are unable to auto-regulate the volume variations that are involved in contraction of smooth muscle as well as encompassing arteriovenous shunts [18].

The equine hoof veins are divided into three groups depending on their location: wall dermis veins, which are separated into proximal and distal regions; coronary dermis veins; and frog and sole dermis veins [1]. The dermal lamella is drained by: the coronary vein; the independent superficial vein; the proximal branch of the caudal hoof vein; and the circumflex vein. The toe and quarters are drained via the circumflex vein [2, 20]. An additional feature of the blood circulation of the equine foot is the anastomoses of arteries and veins, which are blood vessels forming shunts [21]. Each dermal papilla in the periople, coronary band, frog, sole and terminal papillae contain a meshwork of anastomosing arteriovenous vessels located at the base of the papillae. These anastomoses are able to withdraw approximately 50% of the whole limb blood flow, and thus can be involved in ischemia due to blood flow diversion [22]. This could explain the relationship between laminitis and ischemia [3].
