Functional Anatomy

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Functional Anatomy

• Equine Science II

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Four Basic Surfaces

1. Dorsal refers to the upper surfaces of the animal
2. Ventral refers to the lower or abdominal area
3. Anterior or cranial refers to the head or front
4. Caudal or posterior refers to the tail or rear

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Dorsal
Anterior
Caudal
Ventral
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Nine Body Systems

1. Skeletal System- includes bone and cartilage that
   give the body shape and protect internal organs
2. Muscular system- provides movement both
   externally and internally

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

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1. 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.
2. Circulatory System- distributes blood throughout
   the body

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• 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.

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

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Two Divisions of Skeletal System and Articulations
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• 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.

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

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

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• 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

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• 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

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Muscular System

• red, lean meat
• compose about 50 of the equines 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

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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

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• 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

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• 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

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• 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.

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• 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.

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1. 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.

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1. Both are found mainly near joints

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Digestive System

1. 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

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1. 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.

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

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1. It is easy to overwhelm the digestive capacity of
   the equines 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

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1. 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.
2. 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.

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1. 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.

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1. 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.
2. 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.

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• 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.

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• 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.

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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

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• 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

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• 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

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• 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.

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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

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

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• 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.

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• 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.

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Circulatory System

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

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• 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

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• 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

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• 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

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• 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

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

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• 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.

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Nervous System

1. 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.
2. 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.

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• 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.

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Endocrine System

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

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• 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

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• Some hormones and glands
• Hypothalamus ADH (vasopressin) is the trauma
  hormone, oxytocin controls lactation and
  reproductive phases of the mare.

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• Pituitary
• FSH stimulates the ovaries of the mare and sperm
  production in the male,
• LH stimulates secretion of estrogen in the mare
  and testosterone in the male,
• LTH (prolactin) promotes lactation once the
  mammary system has been primed by estrogen and
  progesterone,
• TSH stimulates the thyroid gland to release
  thyroxin that regulates body metabolism

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• Pancreas insulin regulates glucose metabolism.

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Reproductive System
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Stallion

1. Testicles- Primary sex organ used to produce
   sperm and the male hormone testosterone
2. The seminal vesicles, prostrate gland and bulbo
   uretral gland are accessory sex glands that
   furnish fluid secretions for the semen.

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1. The epididymis carries sperm from the testes to
   the Vas deferens and provides a place for storage
   and maturation of sperm
2. The Vas deferens transports mature sperm from the
   epididymis to the urethra
3. The urethra takes sperm from the Vas deferens to
   the end of the male genitalia

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• The penis deposits the sperm into the female
  reproductive tract.
• Stallions can ejaculate from 60-300 milliliters
  of sperm with up to about 10 billion live
  spermatozoa per ejaculate
• A sperm cell may live in a mares reproductive
  tract for 24-48 hours.
• Sperm travel to the mares Fallopian tubes in as
  short a time as 15-18 minutes but normally
  requite 2-6 hours

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Mare

1. The ovaries produce eggs and secrete the hormone
   estrogen that causes heat (estrus) and stimulates
   the production of other hormones to condition the
   reproductive tract
2. The Fallopian tubes connect the ovaries to the
   uterus and are the normal site of fertilization
   of the egg by the sperm

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1. The uterus consists of the body, cervix and two
   horns. It is in one of the two horns that the egg
   normally develops after fertilization
2. The vagina receives the sperm during mating and
   serves as the birth canal

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1. The uterus is prone to infections due to its
   elongated shape
2. The mares reproductive system has an unusual
   placenta arrangement and inefficient cervical
   closure that may hinder full-term pregnancy.

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Functional Muscle Groups

• Flexors Bend the limb
• Decrease the angle of a joint
• Examples Teres major in the front leg and
  Iliacus in the hind leg
• Extensors Straighten the limb
• Increase the angle of a joint
• Examples Brachiocephalicus of the front leg and
  Gluteus medius of the hind leg

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• Abductors
• Move a limb away from the center plane of the
  equine
• The abductor of the front leg is the deltoid
• Adductors
• Pull a limb toward the center plane of the equine
• Adductors of the front legs are the pectoral
  muscles

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Terminology of Movement

1. A gait is an equines way of going or moving its
   legs during movement
2. A beat refers to the time a foot or two feet
   simultaneously hit the ground.
3. A step is the distance between the imprints of
   the two front legs or the two hind legs

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• A stride is the distance between successive
  imprints of the same foot
• Directness, also called trueness is the line in
  which the foot is carried forward during the
  stride.
• Spring is the manner in which weight settles back
  on the supporting leg at the completion of the
  stride.
• Balance refers to the ability of the equine to
  coordinate action, go composed and in form

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Components of a Stride

• A stride has two phases
• Stride stance is the weight bearing phase
• Stride suspension or swing is the non-weight
  bearing phase

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• The speed of a horse is affected by
• Length of stride, rapidity or frequency of stride
  and overlap time
• Overlap time is the time on the ground versus the
  time off the ground

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Natural Gaits(no training)

• Walk is a slow, even, four-beat gait
• The sequence of hoof-beats is first left hind,
  next, left fore, then- right hind, and finally
  right fore
• Both feet on one side strike the ground before
  the feet on the opposite side strike the ground

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Walk
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• Trot is a two-beat gait where the diagonal fore
  and hind legs act together
• A period of suspension when all four feet are off
  the ground occurs between each beat
• There are different styles of trotting road
  horse trot is fast-stepping, hackney trot and
  heavy harness trot are high-stepping forms of
  trotting

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Trot
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• Canter or lope is a three beat collected gait
  where the equine carries more weight on its
  haunches or rear quarter
• Sequence of hoof-beats for canter is first
  right rear hoof, next- left rear and right front
  striking the ground at the same time and last-
  left front hoof.
• Canter is performed in slow, animated, rhythm.

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Canter
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• Gallop or run is a fast, four-beat gait
• Sequence of hoof-beats is first- one hind foot,
  next- the other hind foot, then- the diagonal
  forefoot followed by the remaining forefoot
• A period of suspension follows the four beats.
• Racehorses use the gallop or run gait

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Other Gaits

1. Pace is a two-beat, lateral gait used for speed
   with the fore and hind legs on the same side
   moving together. The gait has a rolling motion.
2. Slow gait or stepping pace is a show gait that
   uses a lateral, four beat gait where the front
   foot on the right is followed by the hind foot on
   the right

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1. Rack (sometimes called the single foot) is an
   even, fast four-beat lateral gait that is hard on
   the equines forelegs due to increased amount of
   concussion from the excessive leg movement. Rack
   is easy on the rider

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1. Running walk is the fast walk of a Tennessee
   walking horse where the horse travels with a
   gliding motions as a result of extending its hind
   leg forward to overstep the forefoot print.
2. Back is actually trotting in reverse

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Gait Defects

• May interfere or cause injury to the equine
• Forging is the striking of the toe of the hind
  foot against the sole of the forefoot.
• Interfering is when the foot of the striding leg
  strikes the supporting leg and usually occurs
  between the supporting front leg a striding front
  leg or between a supporting hind leg and a
  striding hind leg

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1. Winding is twisting the front leg around in front
   of the supporting leg as each stride is taken and
   is common with wide-chested horses
2. Other gait defects include scalping,
   speedy-cutting, cross-firing, pointing, swelling,
   trappy, pounding and rolling

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Center of Gravity, Conformation and Gaits

1. Most commonly located in the middle of the rib
   cage just caudal to the line separating the
   cranial and middle thirds of the body
2. Because the center of gravity is located more
   cranially, the forelimbs bear 60-65 of the
   equines weight resulting in more stress and
   lameness in the forelimbs

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1. Conformation for structure of the horse can be
   generalized to say that basically an equine that
   stands straight is likely to move straight and
   true.