Chapter 5: Functional Anatomy

Chapter 5: Functional Anatomy
Animal Surfaces and Body Systems
• Dorsal-Upper surface
• Ventral-lower/abdominal surface
• Anterior-front
• Cranial-toward head
• Posterior/caudal-tail/rear
• LOOK ON PAGE 97!!!

Nine Body Systems
1. Skeletal
2. Muscular
3. Digestive
4. Urinary
5. Respiratory
6. Circulatory
7. Nervous
8. Reproductive
9. Endocrine

Skeletal System
 Periosteum covers the surface of the bone
 Articulation/Joint=union of 2 bones
 Ligament= Connects Bone to Bone
 Tendon= Connects Bone to Muscle
 Stores minerals-Ca, Phoshorus
 Factory for manufacturing blood cells
 Classified as long, short, flat, and irregular
▸ Long-in limbs, support and act as levers
▸ Short-in knee and hock, shock absorption
▸ Flat-ribs, scapula, some skull, enclose cavities
▸ Irregular-unpaired/vertebrae, some skull
*Exostosis-Abnormal bony growth-result of injury to periosteum
*Cartilage-Dense, very smooth bluish substance covering joints
-Diminishes effects of concussion, minimizes friction
Two divisions of the skeleton: Axial vs. Appendicular

Axial Skeleton: Skull, spine, ribs, breastbone, pelvis, tail
□ Bones of the Skull
❏ Cranium and face
❏ Attached to the first vertebrae of spine
❏ Spinal cord passes through the foramen magnum, the large opening of the skull
❏ Maxillae and mandible, upper and lower jaws
□ Vertebral or Spinal Column
❏ basis of the skeleton
❏ Composed of irregularly shaped bones bound together with ligaments and cartilage that form a column of bones
❏ Elastic pad separates each vertebra
❏ Neural canal/spinal canal contains main trunk line of nerves to the brain=Spinal cord.
❏ Divided into five groups:
■ Cervical: 7 Vertebrae
■ Thoracic: 18 Vertebrae
■ Lumbar: 6 Vertebrae (sometimes 5)
■ Sacral: 5 Vertebrae fused together
■ Coccygeal/tail: 15-21 vertebrae
Appendicular Skeleton: Forelegs and hind legs
□ Used for locomotion, grooming, defense, feeding
□ Forelimbs have no skeletal attachment to the axial skeleton-only connected by muscles
❏ Scapula
❏ Humerus
❏ Ulna and radius
❏ Carpal Bones
❏ Splint Bones
❏ Cannon
❏ Sesamoids
❏ First phalanx
❏ Second phalanx
❏ Coffin
□ Hind Leg bones
❏ Femur
❏ Patella
❏ Tibia and fibula
❏ Tarsals
❏ Splint Bones
❏ Cannon
❏ Sesamoids
❏ First phalanx
❏ Second phalanx
❏ Coffin
❏ Attached to the bony pelvis at the hip joint

Joints/Articulations
Classified into three types:
□ Immovable: opposed surfaces of bon are united by connective tissue or fused bone and permit no movement: cranium
□ Slightly movable: pad of cartilage allows slight movement: vertebrae
□ Freely movable: joint cavity exists: joints of the legs
❏ Ends of bones held together by strong bands of tissue, called ligaments.
■ Ligaments allow only a slight degree of elasticity and have limited blood supply=this is why they heal slowly!!!
❏ Ends of bones covered with a smooth cartilage that absorbs concussion. Entire joint is enclosed in fibrous sac called the joint capsule. Lined with the synovial membrane that secretes synovia or joint water.

● Joints of the foreleg:
• Shoulder
• Elbow
• Knee
• Fetlock
• Pastern
• Coffin
● Joints of the hindleg:
• Hip
• Stifle
• Hock
• Fetlock

Important Ligaments:
▸ Suspensory: runs from back of knee and upper end of cannon bone down the back of the leg in a groove between the splint bones. Divides into 2 diverging rounded branches that are attached to the upper and outer part of the corresponding sesamoid bone.
▸ Extensor:
▸ Check:
▸ Deep Flexor tendon:
▸ Plantar:

The Muscular System:
Provides internal and external movement.
Muscles compose about 50% of total body weight
Composed of 3types:
▸ Smooth=involuntary
▸ Cardiac=involuntary striated
▸ Skeletal=striated

Smooth Muscle: Sometimes called “visceral”
Found in digestive system and female reproductive system
Capable of prolonged periods of activity
Peristalsis: wavelike contractions

Cardiac Muscle: Found only in the heart
Contraction is inherent and rhythmic, requires no nerve stimulus
Autonomic nervous system controls rate of contraction=no conscious control

Striated/Skeletal Muscle: Move the body voluntarily
Tendons: connect bone to muscle in order for movement
Set up in opposing manner: one set bends, one set straightens-one set acts as a “brake” for the other
Can only contract for short amount of time before becoming fatigued
▸ many elongated cells sitting side-by-side become shorter and thicker when stimulated
▸ Extensor: straightens
▸ Flexor: bends joint
Tendons, Sheaths, and Bursae
▸ Eliminate undue friction to allow muscle to work more efficiently
▸ Sheath is a synovial sac in which tendon passes
▸ A bursa is a synovial sac between tendon and surface over which is passes in a change of direction
▸ Found chiefly near joints

The Digestive System
☻ Converts feed into form that can be used for the body for maintenance, growth, and reproduction.
☻ Tube from mouth to the anus
☻ Includes mouth, esophagus, stomach, intestines, anus, and other associated organs:
▸ liver, teeth, pancreas, and salivary glands
☻ Herbivore vs. carnivores vs. onmivores
☻ Digestive tract of horse is ~100 feet with a capacity of 40-50 gallons
☻ Stomach makes up less than 10 percent of digestive tract; small intestine makes up 30%, the cecum makes up 65%
☻ Rapid passage rate through stomach and sm. intestine=easy to overwhelm
☻ Cecum and colon contain large microbial populations allowing for digestion of fibrous feeds. If large amounts of concentrates reach the cecum, they will be fermented rapidly and may produce excessive gas or lactic acid and cause founder or colic. KNOW THIS!!!!
□ Mouth
■ Extends from lips to pharynx
■ soft palate: separates mouth from pharynx=fleshy curtain suspended from back part of hard palate-permits passage of food and water from mouth to pharynx but prevents passage in opposite direction.
■ Saliva: moistens and lubricates food and begins digestion of starches and sugars
□ Pharynx
■ muscular tube between the mouth and esophagus that also serves as an air passage between nasal cavities and larynx
■ forces food into esophagus
□ Esophagus
■ muscular tube extending from pharynx down the left side of the neck and through the thoracic cavity and diaphram to the stomach.
■ Food and water are forced down by peristalsis.
□ Stomach
■ U-shaped sac
■ contents squeezed and pressed by muscular activity of the organ
■ Gastric juice is secreted by the walls
□ Small Intestine
■ ~70 feet long, holds ~12 gallons
 Duodenum, jejunum, ileum
■ ~2 inches in diameter
■ Folds and coils near left flank, being suspended from the region of the loin by and extensive fan-shaped membrane called mesentery.
□ Large Intestine
■ Divided into cecum, large colon, small colon, rectum, and anus.
■ Bacteria break up cellulose into substances absorbable into body.
■ Because of its large size, material moves through very slowly.
■ Contents of cecum always liquid, capacity about 8 gallons
■ Large colon holds about 20 gallons, bacterial digestion takes place here, also
■ contents of small colon are solid, here, the balls of dung are formed.
■ Rectum is about 12 inches long. Is the terminal end of digestive tract

Urinary System
□ Composed of kidneys, ureters, bladder, and urethra.
□ Kidneys: Paired organs on each side of backbone at 18th rib. Maintain water and mineral balance and excrete wastes of metabolism.
■ 6-7 inches in length. Right kidney is roughly triangular with the corners rounded, but left is more bean shaped and longer.
■ Blood passes through more than 400 times per day
■ Nephrons: tiny functional units of kidneys, filter the blood.
■ Urine is collected in the inner portion of the kidney (the renal pelvis) and is drained through the ureter to the bladder.
□ Urinary Bladder holds wastes till they are excreted.
■ muscular balloon that can expand
■ nerve endings signal that bladder needs to be emptied
■ Urine flows to the outside through the urethra. The urethra is short and wide in mares and long and narrow in males.

Respiratory System:
Takes Oxygen from the environment and delivers it to tissues and cells of the body. It also picks up carbon dioxide from body and delivers it to the outside environment.
■ Organs include nasal cavity, pharynx, larynx, trachea, bronchi, and lungs.
■ Larynx=voice box. It also regulates the amount of air passing into our out of the lungs.
■ Trachea=composed of cartiliginous rings
■ Bronchi=branches of the trachea that connect the trachea with each lung. Alveoli are tiny air sacs similar to bunches of grapes where the exchange of carbon dioxide and oxygen take place.
Respiration:
▸ Consists of Inspiration and Expiration.
▸ Inspiration: contraction of diaphragm and an outward rotation of the ribs.
▸ Expiration: relaxation of diaphragm muscles and contraction of rib and abdominal muscles
 Breathing rate of horse at rest: 8-16 breaths per minute

The Circulatory System
Consists of the heart, veins, and arteries.
✓ The Heart:
✓ in the left half of the thorax, between the lungs
✓ weighs from 7-8 pounds
✓ enclosed in the pericardium
✓ Composed of four chambers: Right atrium, right ventricle, left atrium, left ventricle
✓ Four valves keep blood pumping in one direction
1. Blood enters heart through superior vena cava
2 Right atrium holds deoxygenated blood
3 Mitral valve opens
4 right ventricle pumps blood into a blood vessel
5 Pulmonary artery carries blood to lungs
6 Gas exchange occurs
7 Blood is carried back to the heart throught the pulmonary vein
8 Oxygenated blood is held in the left atrium
9 Tricuspid valve opens
10 Left ventricle contracts and pumps blood through the aortic valve
11 Blood travel through the aorta to the rest of the body

Blood: red alkaline fluid composed of blood plasma and red and white blood cells.
• WBC’s are active agents in combating disease germs in body.
• RBC’s originate in bone marrow, liver, and spleen, and carry oxygen from lungs to the tissues and carbon dioxide from the tissues back to the lungs
• Regulator of the body

Vessels and Lymphatics
Arteries have thick, elastic walls and carry the blood from the heart to the tissues of the body.
The expansion and contraction of arteries is the pulse.
Veins-have thinner walls and are equipped with one-way valves opening toward the heart.
Veins are located between muscle masses and are squeezed as the horse moves, sending the blood back to the heart.
• Capillaries are the connecting tubes between arteries and veins. Exchange of food and oxygen for waste products takes place here.
• Lymph vessels and nodes connect to form one large duct that lies parallel to the aorta.

Circulation:
normal heart rate: 38-40 beats per minute.

The Nervous System:
Consists of the brain, spinal cord, many nerve fibers, and sensory receptors.
Divided into the autonomic and central nervous system.
★ Autonomic: automatic, control over respiratory and digestive systems, eyes, heart, and blood vessels, glandular products, and other automatic functions directed by the brain stem.
★ Central Nervous System: conscious or voluntary actions.
★ CNS divided into the spinal cord and the brain and the peripheral nerves.
▸ The brain is divided into three major portions: the brain stem (the primitive brain), the cerebrum, and cerebellum. Page 120
▸ Ganglia: secondary nerve centers located chiefly along the spinal cord-act like a subexchange in a telephone system.-heat, pain, excessive pressure-cause certain muscles to react almost instantly–Reflex.
The Reproductive System:
Zygote: formed after sperm meets and fertilizes the egg. Develops into a fetus
Mare:
 Ovaries: produce eggs, secretes estrogen (which induces estrus) and progesterone (maintains pregnancy)
 Fallopian tubes: site of fertilization, connecting link between ovary and UT
 UT consists of a body, cervix, 2 horns
 Vagina receives sperm and functions as passageway during parturition
 All reproductive functions are directed by hormones produced in the glands of her endocrine system.
Stallion:
 Seminiferous tubules:coiled tubes in the testes where sperm are produced-heat regulation is critical!
 Cryptorchid-one or both testes are not descended
 Accessory sex glands: seminal vesicles, prostate, and bulbourethral gland. These furnish fluid secretions.

The Endocrine System:
Influences vital functions of the horse from before birth until death.
Controls events leading up to and including conception, gestation (how long is gestation in a horse?), parturition, digestion, metabolism, growth, puberty, aging.
Homeostasis: Balance-under the control of the endocrine system.
Secretions are called hormones.
Hormones:
● Stimulate or inhibits organs
● regulate body reactions
● Operate at small levels in the body
● Often controlled by a feedback system
● Pituitary and Hypothalamus work together as functional unit to coordinate endocrine and nervous systems. The Hypothalamus is the “master” of the pituitary.
Posterior Pituitary:
● ADH: Vasopressin/Antidiuretic Hormone: triggered by hemorrhaging, trauma, pain, anxiety, and some drugs. Low environmental temperatures inhibit it.
● Oxytocin: controls lactation and reproductive phases. Neural stimulus triggers the release of oxytocin-suckling milk.
Anterior Pituitary:
● FSH and LH: necessary for gonadal function.
Prolactin:
● vital for proper development of lactation. Not necessary for continuation of lactation
ACTH:
● causes the release of adrenocorticoid steroids
● reduction of lipid levels
● Secretion of aldosterone
● Movement of fatty acids and neutral fats from fat deposits, ketogenesis, muscle glycogen levels, hypoglycemia, and amino acid levels in the blood.
TSH:
● release of thyroxin from thyroid gland
● increases rate of binding iodine w/in the thyroid
STH:
● stimulate body size
● important in protein synthesis
● exerts its effects on bone, muscle, kidney, liver, and adipose tissues and especially epiphyseal plates
Pineal:
● responsible for melatonin syntheses
● functions on photo-receptive basis
● affects development and function of the gonads
Thyroid:
● secretes thyroxin
• necessary for the maturing of animals-for the proper differentiation of body structures
• growth and eruption of teeth, also skin and hair affected
• Goiter-enlargement of thyroid area-either from hyper or hypo thyroid conditions. Common cause: deficiency of iodine
Parathyroid
● maintenance of proper calcium levels in the blood
● Parathormone increases calcium levels
● Thyrocalcitonin decreases calcium in blood serum during hypercalcemia
Pancreas
● Organ of digestive secretions
● Isles of Langerhans:
• rich blood supplies and consist of alpha and beta cells-beta cells produce insulin (lowers blood glucose), alpha cells produces glucagon (raises blood glucose)
Adrenal Cortex
● produces steroid hormones
Adrenal Medulla
● produces epinephrine and norepinephrine.
• epinephrine (adrenaline) helps horse adjust to stress and activates fight or flight mechanism
• norepinephrine maintains tone of vessels in the circulatory system.
Gonads
● androgens, estrogens, progesterone, relaxin
● Testosterone: develops and maintains accessory sex glands, stimulates secondary sexual characteristics, regulates sexual behavior and sperm production
● Estrogen: promotes female sexual behavior, stimulates secondary sexual characteristics, growth of repro. Tract, mammary growth, and feedback control
● Progesterone: prepares UT for pregnancy, maintains pregnancy, prepares mammary glands for lactation, provides feedback control
● Relaxin: facilitates dilation of birth control
Gastrointestinal Tract
● Secretin-stimulates pancreatic bile
● Enterokinin-causes increased rate of secretion of digestive juices and enzymes in the small intestine
● Controls secretions and motility of digestive tract

Required Extra Credit Assignment:
Diagram a leg and label the extensor ligament, the check ligament, the deep flexor tendon, and the plantar ligament. Explain what each of these do.