Agriscience 102
Applied Agricultural Science and Technology
Anatomy and Physiology of Animals
8392
Class Notes Key
TEKS: (c)(4)(B)
INTRODUCTION
Animal anatomy and physiology are useful for a variety of health management issues. In addition, knowledge of anatomy can aid in evaluating and selecting animals.
Anatomy is the study of form and structure. The study of anatomy includes gross anatomy and microscopic anatomy. Gross anatomy is the study of structures that can be seen with the naked eye. In comparison, microscopic anatomy is the study of structures that require a microscope to be seen. Physiology is related to the functions of the body and all its parts, including cells, tissues, and organs.
The study of anatomy and physiology is generally divided into the functions and integration of ten organ systems within the body, including -
§ Integumentary system (skin)
§ Skeletal system (bones)
§ Muscular system (muscles)
§ Circulatory system (heart and blood vessels)
§ Digestive system (stomach and intestines)
§ Nervous system (nerves)
§ Respiratory system (lungs and passageways)
§ Urinary system (kidneys and bladder)
§ Endocrine system (glands and hormones)
§ Reproductive system (organs involved in producing offspring)
integumentary system
The integumentary system is the exterior covering of the body that is essential for regulating body temperature, balancing water, and protecting internal organ systems. It consists of the skin and skin appendages, which include hair, nails, horns, sebaceous glands, and sweat glands.
The skin is an essential organ for animal health because it is the external barrier between internal organs and the environment. Its primary function is to act as a protective layer against disease, infection, sun, and other potentially harmful elements. The skin of animals consists of two layers, the epidermis and dermis. The epidermis is the outer layer of the skin and contains no blood cells. It is a superficial covering of stratified epithelial tissue that is comprised of an external layer of dead cells sitting on a lower layer of living cells. The dermis is the inner layer of the skin and contains blood vessels, lymph vessels, nerves, glands, hair follicles, and muscle fibers. It is a deeper layer of dense, irregular connective tissue.
Hair, scales, hooves, feathers, claws, horns, and nails are modified extensions or structures derived from the skin. Coat coverings differ among animal species; goats, horses, cattle, and swine have hair, sheep have wool, and poultry have feathers. Hair, wool, and feathers are composed of protein. Hairs are essential for regulating body temperature. Each hair follicle has a small bundle of smooth muscle fibers that can contract to pull the hair perpendicular to the skin surface. These muscles are known as the arrector pili muscles, which are stimulated to contract involuntarily by the nervous system in times of stress or cold. When all hairs stand perpendicular, they trap more air and keep the animal’s body warmer.
The principal glands of the skin are sweat glands and sebaceous glands. Sweat glands release water to cool the body when internal temperatures rise. Sebaceous glands secrete oily substances to lubricate the skin and hair. Other special types of glands may also be found in the dermis, such as mammary glands, which are found in all mammals.
Sensory receptors in the dermis of the skin detect touch, pain, heat, and cold. They include Merkel cells, free nerve endings, Meissner’s corpuscles, and Paccinian corpuscles. Merkel cells respond to very light pressure. Meissner’s corpuscles are also sensitive to touch and are found in greater numbers in delicate areas such as the lips and fingertips. Paccinian corpuscles mainly detect pressure.
Brahman cattle originally came from India and their integumentary system (skin) has adapted to hot, dry, pest-ridden environments. They have more highly developed sweat glands and less hair than European cattle such as Hereford, Angus, Limousin, or Charolais. As a result, they can release body heat more effectively by sweating. This allows them to live in hot, humid environments such as those found in Australia, India, Africa, and the southern parts of the United States. An oily secretion that they produce and secrete from their sebaceous glands has a strong odor and will repel insects.
skeletal system
The skeletal system is the framework of the body and provides structural support for all other organ systems. It is made up of bones and connective tissues. All domestic animals are vertebrates and therefore have an internal endoskeleton. Other animals such as insects have an exoskeleton.
An essential function of the skeletal system is the protection of other organs. The skull protects the brain, ribs protect the lungs and vertebrae protect the spinal cord. The skeleton also works in conjunction with the muscles to allow movement of the different body parts. Individual bones are sites for blood formation and mineral storage (particularly phosphorous and calcium).
The skeleton is made up of the axial skeleton and the appendicular skeleton. The axial skeleton consists of those bones on the midline of the body and can be thought of as all the bones other than the pelvis and limbs (appendages). It includes the skull, vertebrae, ribs, and sternum. The appendicular skeleton is comprised of those bones coming off the midline of the body. It is the limbs or appendages of the body including the forelegs (arms) and hindlegs (legs) as well as bones in the pelvic region.
Based on their functions and shapes, bones are divided into four classes. Long bones are found in the limbs and serve as supporting columns and levers for the skeletal system and the body. Flat bones protect the body’s organs and serve as an area of muscle attachment. Short bones, such as the bones in the knee and hock joint, diffuse concussion, diminish friction, and change the direction of tendons. Irregular bones are those found in the vertebral column.
Bone is made up of organic matter and inorganic matter. The inorganic matter is mostly tricalcium phosphate [Ca3(PO4)2] and gives bone rigidity and hardness. The organic matter, which is mostly collagen, is a matrix of fibrous tissues and cells that gives bone flexibility and resilience. The inner core of the bone is soft tissue called bone marrow. Some of the bone marrow consists of yellow fat, called yellow marrow. The other portion of bone marrow is comprised of red tissue, called red marrow. The red marrow is responsible for blood cell and platelet formation.
Bone is living tissue that changes constantly. After an animal reaches mature body size, bones do not elongate any further but they continue to turnover cells. Bone undergoes continuous deposition (creation of new bone material) and resorption (removal of old bone material). Bone is formed from cartilage that is laid down when the animal is an embryo during a process known as endochondral ossification (bone formation). The bone forming cells known as osteoblasts become embedded in a matrix of osteoid material. Osteoblasts develop into osteocytes, or mature bone cells. Bone formation occurs at growth plates: primary ossification occurs at the metaphyseal growth plate and secondary ossification occurs at the epiphyseal growth plate. The secondary ossification site is in the center of the epiphysis, and therefore the growth plate is spherical in shape.
Connective tissues connect other tissues together to give form and strength to organs and to provide protection and leverage. Four types of connective tissue within the skeletal system are ligaments, tendons, cartilage, and fascia. Tendons connect muscle to bone, and ligaments connect bone to bone.
Three types of cartilage have different functions within the body: hyaline cartilage is found on the ends of bones and acts as cushioning in joints; elastic cartilage makes up body parts such as the ears; and fibrocartilage provides cushioning between the intervertebral discs. Fascia, located between the skin and the underlying muscle or bone, is comprised of two layers. The top layer, superficial fascia, is attached to the skin while the bottom layer, deep fascia, covers the muscle or bone.
Joints are articulations (unions) between bones. Three types of joints are found in the body: fibrous, cartilaginous, and synovial. Joints can be highly movable (for example, the shoulder), partially movable (for example, the ribs) or immovable (for example, the suture joints between plates of the skull). Synovial joints allow the greatest range of movement and are commonly referred to as true joints. The various movements that can be performed by synovial joints include gliding, flexion, extension, hyperextension, rotation, adduction, abduction, and circumduction.
muscular system
The muscular system, in conjunction with the skeletal system, allows movement of internal structures, limbs and the body as a whole. Furthermore, in food-producing animals, muscles are the lean portion of the carcass used for human consumption.
Muscles can be categorized by their function (skeletal, visceral, or cardiac) by the way they are activated (voluntary or involuntary) or by their physiology (smooth, striated, or unstriated). This can lead to some confusion of terms, but the three types of muscles are commonly classified as skeletal, smooth, and cardiac. Skeletal muscles are striated, voluntary muscles involved in the movement of the skeleton and can be intentionally controlled by the animal. Smooth or visceral muscles are involuntary, unstriated muscles found in the digestive organs and blood vessels of the body; they function automatically and can not be controlled by the animal. Cardiac muscle is involuntary, striated muscle that is found only within the heart. It has no conscious control by the animal but can be regulated by the autonomic nervous system. The hormones epinephrine and norepinephrine stimulate autonomic nerves, which control involuntary muscles, to cause relaxation and contraction, respectively.
Depending on the movements they perform, skeletal muscles are divided into four functional groups: flexors, extensors, abductors, and adductors. Many muscles work in pairs so that when one contracts (flexes or shortens) the other one relaxes (extends or lengthens). This relationship is known as antagonism. In comparison, muscles that work together to perform a movement are referred to as synergists. The bicep and tricep muscles of the foreleg are antagonists. Biceps work as abductors and pull the lower leg toward the body. Triceps work as adductors and move the lower limb away from the body. Several muscles work together in the shoulder region to move the foreleg. For example, the deltoid muscles in the shoulder have a synergistic relationship with the biceps to move the whole foreleg (arm).
Most skeletal muscles attach to two different bones. The point of origin is on the most stable or least movable bone while the insertion point is on the more movable bone. For example, the pectoral muscles, which are involved in adduction of the foreleg, originate from the sternum (chest) and insert on the humerus (foreleg/arm).
Skeletal muscle is made up of bundles of fibers or cells that stretch from one tendon, or connective tissue, to the other tendon. These bundles of fibers lie parallel to each other within the muscle sheath making the muscle appear striped, or striated. Each bundle consists of fibers, which are individual cells with multiple nuclei. Individual muscle fibers are made up of bundles of myofibrils enclosed in a series of sarcomeres. Sarcomeres are the functional units of muscle and extend from Z line to Z line. They are made up of thick filaments of myosin and thin filaments of actin.
Muscle contraction occurs as a result of a process known as sliding-filament action. Each individual sarcomere contracts as a result of the actin and myosin filaments sliding over each other. Consequently, the fibers contract, causing the bundles of fibers to contract, which results in the whole muscle contracting. The physiology of muscle action is quite complex. Energy utilized for muscle contraction comes primarily from non-protein sources such as adenosine triphosphate (ATP), glycogen, and body fats. However, if food intake is insufficient, energy for muscle contraction may be taken from protein sources as well, resulting in weight loss.
Two different types of muscle affect the athletic ability of animals such as horses. These muscle types are fast-twitch and slow-twitch. Fast-twitch muscle fibers can contract rapidly because they break down glycogen in the absence of oxygen (anaerobic conditions). However, they produce lactic acid, which causes muscle soreness. In comparison, slow-twitch fibers convert fats to energy under aerobic conditions. They can not contract as quickly but they do not produce lactic acid, and they can continue to function for much longer periods than fast-twitch fibers. Quarter horses have more fast-twitch fibers than do Thoroughbreds and Arabians, which is why they are so fast over a quarter of a mile but do not perform as well over longer distances. Thoroughbreds have the ideal combination of slow and fast twitch fibers for middle distances. Arabians have more slow-twitch fibers, which is why they are better suited to long distance or endurance events.
CIRCULATORY SYSTEM
The circulatory system is responsible for distributing blood throughout the body, removing wastes, and mounting immune responses to infections. It also plays a role in regulating temperature. Blood provides organs, tissues, and cells with oxygen, nutrients, gases, hormones, and antibodies, and removes carbon dioxide and metabolic wastes. The lymphatic system works closely with, and is considered a part of, the circulatory system. It is responsible for draining fluid from the body and is also an important defense mechanism against infection. The circulatory system includes the heart, veins, capillaries, arteries, lymph vessels, and lymph glands.
The heart is a muscle having a left side and a right side. Each side is made up of an atrium and a ventricle. The atrium receives blood, either from the lungs or the remainder of the body. Blood then passes into the ventricle before being pumped out of the heart again. Deoxygenated or venous blood coming from the body enters the right atrium, passes through the right A.V. (atrioventricular) valve and into the right ventricle. It is then pumped through the pulmonary artery to the lungs. Oxygenated or arterial blood returns from the lungs via the pulmonary vein and enters the left atrium; it then passes through the left A.V. valve and into the left ventricle before being pumped out of the heart to the remainder of the body via the aorta.
The circulatory system includes five types of blood vessels: arteries, arterioles, veins, venules, and capillaries. Arteries take blood away from the heart. Arteries usually carry oxygenated blood, except for the pulmonary artery, which takes deoxygenated blood away from the heart to the lungs. Veins carry blood back to the heart, and they always carry deoxygenated blood, except for the pulmonary vein, which carries oxygenated blood from the lungs back to the heart.