Functional Anatomy

Functional Anatomy Equine Science II

Four Basic Surfaces • Dorsal refers to the upper surfaces of the animal • Ventral refers to the lower or abdominal area • Anterior or cranial refers to the head or front • Caudal or posterior refers to the tail or rear

Dorsal Anterior Caudal Ventral

Nine Body Systems • Skeletal System- includes bone and cartilage that give the body shape and protect internal organs • Muscular system- provides movement both externally and internally

Digestive System- converts feed into a form that can be used by the body for maintenance, growth and reproduction • Urinary System- maintains water and mineral balance while holding and excreting wastes when needed

Respiratory System- takes in oxygen and delivers it to the tissues and cells and picks up carbon dioxide from the tissues and cells to deliver to the environment. • Circulatory System- distributes blood throughout the body

Nervous System- supplies the body with information about its internal and external environment through electrical impulses between the brain, spinal cord, and other parts of the body.

Reproductive System- contains the organs necessary for the creation of new organisms. • Endocrine System- produces hormones that influence vital functions.

Two Divisions of Skeletal System and Articulations

The axial skeleton consists of the bones in the trunk area which includes the skull, spine (vertebral column), ribs and breastbone (chest cavity), pelvis and tail • Bones of the skull are flat or irregular in shape and form the framework for the brain, mouth, eyes and nasal cavities.

The vertebral column consists of a flexible column of small bones (vertebrae) that form the basis of the skeleton • Hip bones are two large flat bones attached to the spine and sacrum that form the pelvis or pelvic girdle and cavity

The ribs and breast bone (sternum) along with the thoracic vertebrae form the chest cavity.

Appendicular skeleton consists of the forelegs and hind legs that are used for locomotion, grooming and to some extent for defense and feeding • The forelimbs have no skeletal attachments to the axial skeleton or trunk, but are connected by muscles. • The hind limbs are attached to the pelvis at the hip joint

Articulations or joints are the union of two or more bones or cartilages held together by ligaments, tendons, or a tough fibrous capsule. • Joints are classified by their structure and movability. • Freely movable joints have a joint cavity between the two surfaces, the bones are covered with a smooth cartilage and the bones are held by ligaments

Muscular System • red, lean meat • compose about 50% of the equine’s total body weight • stimulated to contract or change shape by nerve impulses from the brain • send nerve impulses back to the brain indicating the degree of contraction so that movement is smooth

Three Basic Muscle Types • Smooth muscles are involuntary muscles. • Sometimes called visceral muscle • Found in the digestive system and in the uterus of females • Capable of prolonged activity without fatigue

Cardiac muscles in involuntary striated muscle • Found only in the heart • Contractions of the cardiac muscle require no nerve stimulus • Contractions are rhythmic and require no conscious control

Striated or skeletal muscles are usually attached to bones of the skeletal system either directly or by tendons and act voluntarily. • Bones serve as levers and the muscles move the body voluntarily under the direct control of the will

Skeletal muscles are usually arranged in opposite sets so that one set of muscles bends the limb (flexor muscle) and the other set straightens it (extensor muscle) • Voluntary muscles become fatigued and need rest after a short period of time.

Tendons eliminate undue friction to allow muscles to act more freely • The tendon sheath is a synovial sac through which a tendon passes and which provides synovia to lubricate the surrounded tendon.

The tendon bursa does the same thing as the sheath except the tendon does not pass through it. The tendon bursa is a synovial sac interposed between the tendon and the surface over which it comes in contact which lubricates and cushions the tendon.

Both are found mainly near joints

The parts of the digestive system work together to convert feed into a form that can be used by the body for maintenance, growth and reproduction. Parts include: Mouth Pharynx Esophagus Stomach Intestines Anus Associated Organs Liver, teeth pancreas and salivary glands Digestive System

Rate of feed passage through the stomach (30 minutes to 2 hours) and small intestine is very rapid so that any feed not digested and absorbed in the small intestine passes on to the cecum and colon within 24 hours.

Grinding or chopping decreased feed size which increases the rate of passage but decreases the absorption of nutrients by the equine

It is easy to overwhelm the digestive capacity of the equine’s stomach and small intestine with large amounts of concentrates, which if pass through to the cecum, become fermented and produce gas or lactic acid causing colic or founder

The mouth extends from the lips to the pharynx. It is bounded on the sides by the cheeks, above by the hard palate and below by the tongue. • The pharynx is the muscular somewhat funnel shaped tube from the back part of the mouth to the esophagus. It directs food and serves as an air passage.

The esophagus extends from the pharynx down the left side of the neck through the thoracic cavity and diaphragm to the stomach at an angle which makes regurgitation impossible.

The stomach is a U-shaped muscular sac at the front of the abdominal cavity close to the diaphragm and makes up less than 10% of the total digestive capacity for an adult equine. • The small intestine is a tube about 2” in diameter and is the site of most nutrient absorption but makes only 30% of the total digestive capacity.

The large intestine consist of the cecum, large colon, small colon, rectum and anus. • The cecum and colon make up 65% of the digestive system capacity and are greatly enlarged to allow bacteria time to break down the large quantities of cellulose from plant material.

The small colon extends from the large colon to the rectum and is the place where the balls of dung are formed. The contents are solid as most of the moisture in the food is reabsorbed in this part of the large intestine.

Urinary System • The urinary system is made up of the kidneys, ureters, bladder and urethra which filter the blood and dispose of waste products • All the blood in the body passes though the two kidneys more than 400 times per day and is filtered of nitrogenous wastes each time

The kidneys are from 6-7 inches long, 4-6 inches wide about 2 inches thick and are located on each side of the backbone at about the 18th rib

Millions of tiny nephrons in the outer cortex of the kidneys filter about 200 gallons of liquid per day, rejecting blood cell and proteins but permitting fluid, salts and other chemical waste to pass through them

The kidneys return about 198 gallons of the 200 gallons to the bloodstream, including salts, sugars and most of the fluids • The two gallons of waste fluid, urine is collected in the inner portion of the kidney, the renal pelvis and drained drop by drop through the ureters to the bladder.

Respiratory System • The respiratory system takes in oxygen and delivers it to tissue and cells and removes carbon dioxide from those same tissues and cells. • The lungs are the essential organ of respiration • Air is taken into the lungs where oxygen is removed by diffusion into the blood

Supporting parts of the respiratory systems carry air to and from the lungs and include the nasal cavity, pharynx, larynx, trachea and bronchi

The pharynx is common to both the digestive and respiratory systems • The larynx serves as the voice box, allowing equine to make sounds such as neighing, whinnying, nickering and regulates the amount of air passing into or out of the lungs.

The trachea is a long tube connecting the larynx with the lungs and branches into bronchi in each lung containing minute air sacs called alveoli where the gaseous exchange of carbon dioxide takes place between the circulating blood and air.

Circulatory System • The circulatory system distributes blood throughout the body to nourish each cell with food substance and oxygen while removing waste products

The parts of the circulatory system include the: • Heart- A muscular organ of about 7-8 pounds in ordinary sized equine that is the main pump of the circulatory system that creates blood flow

Arteries- Vessels with rather thick elastic walls that carry blood from the heart to the tissues of the body. • Veins Vessels that carry blood from the tissues back to the heart

Capillaries connect the arteries carrying blood cells and the veins carrying blood away from the cells • It is through the walls of the capillaries that the exchange of food and oxygen for waste products takes place • Capillaries are microscopic in size

Blood is the red alkaline fluid tissue that is the regulator of the body. It is composed of blood plasma and red and white blood cells • White blood cells are the active agents in fighting disease germs in the body • Red blood cells originate in the bone marrow, liver and spleen and carry oxygen from the lungs and carbon dioxide from the tissues

Lymph is the fluid that assists in carrying food from the digestive tract to the tissues and waste products back to the bloodstream

Lymph vessels are ducts that transport lymph and lymph nodes or lymphatics, are gland-like bodies found in the lymphatic vessels that act as filters. • The vessels converge to form on large ducts that lies parallel to the aorta, the main artery from the heart and empties into one of the large veins near the heart.

Nervous System • The nervous system is a complex system that uses electrical-chemical changes to send impulses to and from the brain or spinal cord, nerve fibers and sensory receptors. • The nervous system is the communication system of the body made up of the brain, spinal cord, ganglia (secondary nerve center along the spinal cord) and nerves.

The nervous system has two main portions • The autonomic or automatic nervous system is directed by the brain stem to control respiration, digestion and major organs like the heart automatically. • The central nervous system is directed by the brain to control the conscious or voluntary actions of the body like movement.

Endocrine System • Consists of ductless glands producing internal secretions called hormones that control and promote homeostasis (balance) between physiologic functions • Hormones regulate bodily reactions by slowing or speeding the rate of organ functions

The pituitary and hypothalamus work together to coordinate the endocrine and nervous system • The hypothalamus is the center of the autonomic nervous system • The hypothalamus releases hormones that regulate the pituitary

Functional Anatomy