The rectum lies between the terminal portion of the descending colon and anus. It is empty most of the time, except after the mass movements of the large intestine which move faeces into the rectum. This stimulates defeaction, which may happen when an animal is frightened.

A reflex arc represents a mechanism by which a physiological function is automatically managed or regulated. Reflex arcs can be found throughout the body, ranging from skeletal muscles to smooth muscle in glands. Reflex arcs are initiated via the excitation or stimulation of specific sensory cells that are directly connected to motor neurons thus enabling motor nerve impulses to be automatically passed on to that particular muscle or gland. Therefore a basic reflex arc consists of sensory cells and their associated nerve fibers, motor nerve fibres and the ultimate muscle or gland.

Reproductive hormones often have multiple roles and operate via negative feedback systems. The information below will provide the main reproductive hormones in domestic species and their functions.

Development of the reproductive system is a complex process relying on numerous systems and conditions to ensure appropriate structures are formed and the rate of development is maintained within the embryo. There are several important criteria that determine appropriate reproductive system development; genetic sex which determines the sex of the embryo, gonadal sex and phenotypic sex which both determine sexual differentiation. Genetic sex determines gonadal sex which in turn determines phenotypic sex. Sex determination relates to the genetic or environmental process which determines the sex of an individual whilst sexual differentiation represents the development of internal and external genitalia.

Reproduction is the complex set of biological processes that result in the formation of a new organism; it is crucial that we understand how these processes occur normally and have a good grasp of the role of hormones in the reproductive process. Pathology and disease are common within the reproductive system and can not only lead to a sick animal but also to a loss in production. In this section we hope to cover all the main processes in domestic animals, laying a foundation for understanding the associated pathological states.

Respiratory epithelium is a type of epithelium which lines both the upper and lower respiratory tracts. It consists of multiple layers of cylindrical epithelium, along with cilia and goblet cells.

The reticulum is the second chamber of the ruminant stomach. It has regular contractions which precede the biphasic ruminal contraction for digestion of food particles. Mechanical digestion and microbial fermentation occur to breakdown food particles for absorption. Volatile fatty acids are the major product of ruminant digestion.

The rumen is the first chamber of the ruminant stomach. It is the largest chamber and has regular contractions to move food around for digestion, eliminate gases through eructation and send food particles back to the mouth for remastication. The rumen breaks down food particles through mechanical digestion and fermentation with the help of symbiotic microbes. Volatile fatty acids are the main product of ruminant digestion.

The ruminant stomach is composed of 4 separate compartments. Food passes first into the rumen, then reticulum, omasum and finally into the abomasum before entering the duodenum. The first three compartments are adapted to digest complex carbohydrates with the aid of microorganisms which produce volatile fatty acids - the major energy source of ruminants. The last compartments, the abomasum resembles the simple monogastric stomach in structure and function.

Sensory information from the periphery of the animal ascends through the spinal cord and enters the higher levels of the brain. There are numerous pathways which allow different types of information to be passed to the brain. Types of general somatic sensation include pain, touch, temperature and kinaesthesia (conscious proprioception). This sensory information is sent to one of two destinations; the cerebral cortex or the cerebellum.

The epidermis is a stratified squamous epithelium and is composed of 4 cell layers anchored to a basal lamina of connective tissue. Keratinocytes migrate through the epidermis from the basal layer. This migration begins in the stratum basale, then moves up through the stratum spinosum, stratum granulosum and the stratum corneum.

Hormones have a large effect on the skin, details of which can be found at endocrine and nutritional influences on the skin. As a result, endocrine associated skin pathology is relatively common.

The small intestine extends from the pylorus of the stomach to the caecum. The small intestine recieves chyme from the stomach. It is the main site of chemical degradation and absorption of chyme. Fats are exclusively broken down in this part of the alimentary tract. Carbohydrates and proteins that are not degraded in the small intestine are available for microbial fermentation in the large intestine. The small intestine produces enzymes for digestion of protein, carbohydrate and fat and absorbs the products of their digestion. Enzymes are produced by glands in the intestinal wall and the pancreas. The gall bladder produces bile which emulsifies fats for digestion. Absorption is facilitated by ridges in the small intestine and by the presence of villi and microvilli.

n the verterbrate embryo, as the primitive streak is regressing, the paraxial mesoderm divides into blocks of cells called somites. These divisions can be seen either side of the notochord. Somites are transient structures that will give rise to cells of the vertebrae and ribs, dermis of the dorsum, skeletal muscle of the body wall, back and limbs. Somites begin to develop at the anterior of the embryo first, and appear at regular intervals.

Fusion of the two plates of the thyroid cartilage is incomplete forming a rostral pointing notch which is a good site for surgical entry into the larynx. The thyroarytenoid muscle is divided into 2 parts; the rostral and caudal vocalis, which are situated within the vocal folds and vestibular folds. The cuneiform processes are attached to the epiglottis.

The spinal cord is constructed of the marginal layer which has axons and white matter, the mantle which contains cell bodies and grey matter and the spinal canal. This canal conducts sensory information from the peripheral nervous system (both somatic and autonomic) to the brain, conducts motor information from the brain to various effectors and acts as a minor reflex center.

This page explains superficial anatomy through a guide to the superficial anatomy of a dog, including the head, forelimb, and hindlimb. Detailed Illustrations open in new tab.

Thermoregulation is the ability of an endothermic organism to maintain a relatively constant body temperature, despite fluctuations in temperature of the external environment. This is a vital part of homeostasis.

The thymus has a key role in the maturation of prothymocytes into mature T cells. In juvenile animals the thymus produces significant numbers of new T lymphocytes but as the animal matures this production decreases and T cell population is maintained by division of mature T cells.