System

The body systems collections within OVAM are subdivided into the category items described here.

Alimentary

The alimentary system is responsible for prehension, digestion and absorption of food as well as excretion of waste products of this system in the form of faeces. The structures involved in this system include the oral cavity, oesophagus, stomach, small intestine, large intestine, liver and gall bladder and the pancreas. There are species differences within this system, as it is optimised for the diet consumed by that particular species.

Cardiovascular

The components of the cardiovascular system include the heart, arteries, arterioles, capillaries and veins. This system, in conjunction with the respiratory system, primarily provides tissues of the body with oxygen and removes carbon dioxide. It also has metabolic and heat exchange roles. The heart is a muscular organ that functions to pump blood around the body, it contains four chambers. In mammals, the two upper chambers are the atria and the two lower chambers are the ventricles. Deoxygenated blood from the systemic circulation flows into the right atrium then through the tricuspid valve into the right ventricle. Deoxygenated blood then passes from the right ventricle, through the pulmonary valve to the pulmonary artery and pulmonary trunk; which conveys the blood to the lungs to be oxygenated. Oxygenated blood from the lungs flows into the left atrium via the pulmonary veins. Blood passes. Blood passes from the left atrium to the left ventricle through the mitral valve. It subsequently passes from the left ventricle to the ascending aorta through the aortic valve. From here some of the blood flows into the coronary arteries, which carry blood to the heart wall. The remainder of the blood travels throughout the body in the systemic circulation.

Endocrine

The endocrine system is comprised of a group of glands which act to control metabolic activity through secretion of hormones into the vascular system. The endocrine system integrates with, and is under the control of the nervous system with close association between the hypothalamus and the pituitary gland; which acts to co-ordinate many of the body's other endocrine glands. The endocrine glands are the hypothalamus, pituitary gland, thyroid gland, parathyroid glands, adrenal glands and the pineal gland. Several tissues and organs have important endocrine functions, including the pancreas, gut, kidney, heart, adipose tissue, liver, skin, thymus, testes, ovaries and placenta.

Integumentary

The integumentary system is often the largest organ system. It forms a protective covering and comprises the skin (including glands and their products), haircoat or feathers, scales, nails, hooves and horns. The integumentary system has a variety of functions; it serves to waterproof, cushion and protect the deeper tissues, excrete waste, regulate temperature and is the location of sensory receptors for pain, pressure and temperature. Generally mammalian skin is covered with hair and is termed hirsute skin. Where hair is absent, it is termed glabrous skin. Small-bodied invertebrates of aquatic or continually moist habitats also respire using the integument (integumentary exchange). The skin is an organ that shows complex adaptations many of which are species specific.

Lymphoreticular

The lymphatic system can be divided into the lymphatic vessels that carry lymph around the body, and the lymphoreticular system which describes the lymphoid tissues. The lymphatic system has three functions - immune defense, removal of interstitial fluid from tissues and the transport of fats. The lymphoreticular system produces immune cells and removes senescent cells. Primary lymphoid tissues can also be referred to as primary lymphoid organs. Maturation of lymphocytes and lymphopoiesis occurs in the primary lymphoid tissues, with different tissues responsible for maturing different types of lymphocyte. The primary lymphoid tissues are the bone marrow, thymus, foetal liver and the Bursa of Fabricius (exists only in birds). Secondary lymphoid tissues or secondary lymphoid organs provide a site for immune responses to occur and are populated by relatively mature T cells and B cells, macrophages and dendritic cells; each tissue seems to be preferentially populated by lymphocyte types that specialize in the antigens that are most likely to be presented at that site. The secondary lymphoid tissues are the lymph nodes, spleen, mucosal associated lymphoid tissue (MALT), tonsils, appendix/caecal pouch and the ileal Peyer’s Patch.

Musculoskeletal

The musculoskeletal system includes bones, joints, cartilage, muscles, ligaments and tendons. The function of this system is to enable locomotion of body parts or the whole animal, as well as provide a framework for protection of vital organs. The bone marrow also serves as the site of blood cell production. All components of this system are integrated with the circulatory, lymphatic and nervous systems. There are many species differences within this system, as it has evolved and adapted to optimal locomotion of the individual species.

Nervous

The nervous system can be divided into the central and peripheral nervous systems. The central nervous system is comprised of the brain and spinal cord. The brain is contained within the skull, and the spinal cord is contained within the spinal vertebral canal. The brain is covered and protected by the meninges. Cerebral Spinal Fluid (CSF) is the fluid surrounding the brain as well as the central canal of the spinal cord which helps cushion the CNS, acts as a chemical buffer, provides immunological protection and transports waste products and nutrients. Nerves arising from the brain and brain stem are the cranial nerves whilst those arising from the spinal cord are the peripheral nerves. The Peripheral Nervous System includes both cranial nerves and spinal nerves, and is commonly divided into the somatic nervous system and the autonomic nervous system. The somatic nervous system co-ordinates body movements and also receives external stimuli; regulating activities that are under conscious control. The autonomic nervous system contains the sympathetic and the parasympathetic nervous system as well as an enteric division. The sympathetic nervous system is the ‘fight or flight’ system which is triggered when an animal is under threat; its main neurotransmitter is adrenaline. The parasympathetic nervous system is the ‘rest and digest’ system which is responsible for digestion; the primary neurotransmitter is acetylcholine.

Reproductive

Reproduction is the complex set of biological processes that result in the formation of a new organism. The reproductive system is different according to the sex of the animal and may be divided into external and internal genitalia. The male external genitalia include the scrotum and penis. The male internal genitalia include the testes, epididymis, ductus (vas) deferens and the accessory sex glands (prostate, seminal vesicles, bulbourethral glands, ampullary glands). The female external genitalia comprise the vulva. The female internal genitalia include the vagina and vestibule, cervix, uterus, oviducts and ovaries. The male and female gonads are sex organs that produce gametes (reproductive germ cells). The female gonad is the ovary, while the male gonad is the testis. The ovaries produce the ova in a process known as oogenesis, while the testes produce spermatozoa in the processes spermatogenesis and spermiation. Mammals also produce milk from the mammary glands in a process known as lactation.

Respiratory

The respiratory system, in connection with the cardiovascular system, provides the tissues of the body with oxygen and removes carbon dioxide. It also has metabolic and heat exchange roles. Inhaled air passes through the upper respiratory tract via the nares, nasal cavity, pharynx, larynx and trachea. It then passes to the lower respiratory tract, traveling through the lungs via the bronchi, bronchioles and alveoli. The alveoli are the site of gas exchange where oxygen diffuses across the alveolar wall and into the blood, combining with haemoglobin in red blood cells for transport to tissues of the body. The active process of continuous gas exchange in the lungs is known as ventilation. Other associated structures of veterinary interest within the respiratory tract include the paranasal sinuses, the pleural cavity & membranes and the guttural pouches.

Special Senses

In anatomy, there are four major senses which have specialised organs associated with them. They are the eye, the ear, the nose and the tongue. These organs process visual, auditory, olfactory and taste sensations respectively. This information is then relayed to the central nervous system, where it can be interpreted and acted upon.

Urinary

The urinary system includes the kidneys, the ureters which join the kidneys to the bladder, the bladder itself and the urethra which permits urine excretion from the bladder- a process termed micturition. The function of the kidneys is to maintain the volume and composition of plasma, regulate water, ion and pH levels, retain nutrients and excrete waste, toxins and excess electrolytes. The kidneys achieve these functions via glomerular filtration, solute reabsorption, tubular secretion, water balance and acid-base regulation. The kidneys are responsible for the production and release of two hormones - erythropoietin and renin, which are produced in the juxtaglomerular cells. The kidneys also regulate the activation of vitamin D. The renal anatomy and physiology of fish, amphibians, birds and reptiles is significantly different to that of mammals.

View the Body Systems pages.

 

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