Anatomy of Muscles PDF

MYOLOGY Traditionally, muscles are given Latin names, and are italicized The Latin names are usually highly descriptive of the function, and/or appearance of the muscle In Latin, the noun is written first, followed by adjectives that describes it (e.g. musculus triceps brachii)...

MYOLOGY Traditionally, muscles are given Latin names, and are italicized The Latin names are usually highly descriptive of the function, and/or appearance of the muscle In Latin, the noun is written first, followed by adjectives that describes it (e.g. musculus triceps brachii) Smooth (involuntary or unstriated) muscle In English, the nouns are generally preceded by their ○ Composed of muscle cells that have no striations visible descriptors, so the abbreviation for muscle is placed at the end with a microscope of the string of adjectives (deep digital flexor m.) ○ Found in systems of the body with autonomic function ○ Major component of the wall of organs of the digestive and urogenital system and most blood vessels ○ Contraction is an intrinsic property of the fibers themselves, which means that contraction does not generally require stimulation by a nerve ○ The contractility of smooth muscle is regulated and coordinated by the autonomic nervous system Cardiac muscle ○ Characterized by fibers with visible striations, so it is considered a type of striated muscle ○ Cardiac muscle, like smooth muscle, contracts intrinsically and is not under voluntary control ○ Restricted to the heart, where it constitutes most of the thickness of the wall ○ Its rhythmic contraction is responsible for the circulation of Blood Muscle Attachments SKELETAL MUSCLE Origin - the less movable of the two attachments ○ Bulk of the muscle in the body ○ In the limbs, this is usually the more proximal attachment ○ Responsible for producing the voluntary movements of the limbs, trunk and head Insertion - the more movable of the two attachments ○ The muscle tissue with which we are most familiar as the meat ○ In the limbs, this is usually the more distal attachment of our domestic animals Head(s) - muscle divisions that have separate origins ○ Muscle cells (fibers) are grouped into distinct organs of ○ e.g. triceps - a muscle with multiple heads (3) variable size identified as individual muscles Fleshy attachments - the apparent direct attachment of ○ Usually attached to the bones of the skeleton and are under muscles to bone voluntary control of the animal ○ They attach to the periosteum of the bone by very short tendons. e.g. scapular muscles ○ Under the microscope, skeletal muscle fibers exhibit a Tendinous attachments - the dense connective tissue characteristic striped pattern arising from the orderly connecting spindle-shaped or pennate muscles to bone arrangement of the contractile proteins within the cells Aponeurotic attachments (Aponeurosis) - the flat, tendinous sheets associated with flat muscles such as those ○ As a consequence, skeletal muscle is also called striated of the abdominal wall. Muscle to muscle. muscle  Functions of the Muscular System fibers Vertebrae muscle only has one function: contraction Epimysium - the connective tissue around an entire muscle Relaxation is a passive process, a lack of contraction The varied functions of the of the muscular system are all based on contraction (or shortening) of muscle fibers Functional Grouping of Muscles Flexor - if a muscle is on the side of the limb toward which a joint bends (decreasing the angle between the segments) Extensor - increases the angle between segments (extend) Adductors - muscles that tend to pull a limb toward the median plane (pull towards body) Abductors - muscles that tend to move the limb away from the median plane (move away from the body) Parallel muscle - the muscle bundles (fascicles) run Muscles that pass over more than one joint often have parallel to each other the entire length of the muscle different classifications, depending on the joint on which they are acting This allows greatest shortening of the muscle, but less strength of contraction ○ The m. gastrocnemius (the large muscle in the gaskin or calf of the leg) is a flexor of the stifle and an extensor of the hock e.g. sartorius and abdominal muscles Sphincters - muscles that encircle an opening, whether Pennate Muscle – muscle bundle converge on a tendon at an they are striated or smooth angle. Cutaneous muscle - occur in the superficial fascia (a layer Unipennate muscle – a pennate muscle whose tendon of connective tissue) between the skin and the deep fascia runs along one side covering the skeletal muscle Bipennate muscle - a pennate muscle whose muscle ○ The cutaneous muscle attach to the skin and are responsible bundles converge on a tendon from two directions for movement of the skin ○ When a fly rests on a horse, the cutaneous muscles enable the horse to shake the skin and dislodge the fly Prime mover or agonist - produces the characteristic movement ar a joint ○ The biceps brachii muscle is the prime mover for flexion of the elbow joint Antagonist - opposes the movement of a prime mover ○ It aids the prime mover by slowly relaxing so the movement produced is smooth and controlled ○ The triceps brachii muscle, the prime mover for extension of the elbow joint, is the antagonist to the biceps brachii during flexion of the elbow Synergist - a muscle that indirectly aids the action of a prime mover Sphincter - a muscle whose fibers encircle an opening Fixator - a muscle that stabilizes the proximal end of a limb Contraction of its fibers close the opening while the distal end moves This type of muscle is found at the entrance and exit of a Skeletal Muscle Organization Passageway. e.g. urinary and digestive system Muscle fibers are arranged in bundles surrounded by fibrous connective tissue Synovial Structures Endomysium - the connective tissue between individual Include joint capsules, bursae and synovial (tendon) sheaths muscle fibers Bursa - a synovial sac between two structures that tend Perimysium - the sheath surrounding bundles of muscle to rub against each other ○ Bicipital bursa - between the biceps brachii tendon and Syssarcosis - the muscle connection, as opposed to a bone to bone joint, between the thoracic limb and the body the proximal end of the humerus Intrinsic muscles - the muscles having both attachments ○ Atlantal bursa - between the ligamentum nuchae and atlas (origin and insertion) on the thoracic limb bones ○ Supraspinous bursa - between the ligamentum nuchae Intrinsic muscles of the shoulder - act primarily on the and the spinous process of the second thoracic vertebrae shoulder ○ Superficial bursa - between the skin and olecranon Intrinsic muscles of the arm - act primarily on the elbow process of the ulna at the point of the elbow and between joint, and are divided into flexor and extensor groups the skin and superficial digital flexor tendon at the point of the hock Craniolateral forearm (antebrachial) muscles - extend the digits and carpus, and supinate the paw ○ Navicular bursa - between the deep digital flexor tendon and the navicular (distal sesamoid) bone Caudal antebrachial muscles - the flexors of the carpus and digits and pronators of the forearm Synovial sheath - found where the tendon passes under ligaments and through osseofibrous tunnels ○ Most of them originate on or around the medial (flexor) epicondyle of the humerus and are innervated by the median ○ They reduce friction between the tendon and their and ulnar nerves surrounding structure Extrinsic Muscles - Shoulder MUSCLES OF THORACIC LIMB Trapezius (G. trapezion, and irregular, four-sided figure) ○ The triangular muscle extending from the dorsomedial neck and thorax to the spine of the scapula ○ Elevates the scapula, thus, the forelimb ○ Has two heads: the cervical part (trapezius cervicis) and the thoracic part (trapezius thoracis) Latissimus dorsi (L. widest of the back) ○ The broad, flat, fan-shaped muscle extending from the dorsal thoracolumbar region to the medial side of the humerus ○ Flexes the shoulder Brachiocephalicus - the wide muscle extending from the head and neck to the arm ○ The clavicular intersection divides the muscle into the Extrinsic muscles of the Thoracic Limb (thoracic girdle cleidocephalicus and cleidobrachialis muscle muscles) - muscles that attach to the thoracic limb and some other part of the body (i.e. to the head, neck or trunk) The cleidocephalicus is further divided in all species, except the horse, where it is called the cleidomastoideus  The brachiocephalicus acts to advance the limb or draw It functions to draw the limb caudally to adduct it the head laterally Clavicular (tendon) intersection - the fibrous remnant of the clavicle located cranial to the shoulder, traversing the brachiocephalicus muscle Omotransversarius - extends from the shoulder region to the cervical vertebrae Rhomboid or rhomboideus – the extrinsic muscle lying deep to the trapezius ○ Extends from the median raphe of the neck, the thoracic Extrinsic Muscles - Shoulder vertebral spines, and the skull to the dorsal border of the scapula and scapular cartilage ○ Elevates the forelimb Serratus ventralis (L. serratus, a saw) - the serrated, fan- shaped muscle extending from the last five cervical vertebrae and first seven or eight ribs to the medial surface of the scapula ○ Supports the trunk Superficial pectoral - the flat muscle extending from the sternum to the cranial surface of the humerus Divided into two parts based on their fiber direction ○ Superficial descending pectoral ○ Deeper transverse pectoral Adducts and advances the limb Deep (ascending) pectoral – the broad muscle extending from the sternum to the greater and lesser tubercles of the humerus Intrinsic Muscles - Shoulder Supraspinatus - a shoulder extensor  It originates from and fills the supraspinatus fossa Curving over the shoulder joint, it inserts on the greater tubercle of the humerus Acts as the shoulder’s lateral collateral ligament Deltoid - extends from the scapular spine over the shoulder joint to the deltoid tuberosity of the humerus Its aponeurosis covers the infraspinatus muscle Acts to flex the shoulder Infraspinatus - lies deep to the aponeurosis of the deltoid muscle, originating from and filling the infraspinatus fossa Its strong tendon crosses the shoulder joint to insert on the Subscapularis - the large muscle originating from greater tubercle of the humerus subscapular fossa Flexes the shoulder joint and acts with the supraspinatus Crosses the shoulder joint and inserts on the lesser tubercle muscle as the joint’s lateral collateral ligament of the humerus Brachialis - originates on the caudal surface of the It adducts the shoulder and serves as the shoulder’s medial proximal humerus, just distal to the humeral neck and collateral ligament extends over the lateral surface of the humerus in the spiral groove of humerus Triceps brachii - composed of three or four heads Inserts on the radial and the ulnar tuberosities Its long head crosses the shoulder, and all heads cross the elbow joint to insert on the olecranon Flexes the elbow joint It extends the elbow and its long head flexes the shoulder Teres minor - a round muscle in carnivores Biceps brachii - arises from the supraglenoid tubercle, Lies deep to the deltoid muscle on the caudolateral aspect of crosses the shoulder and elbow, and inserts on the radial the shoulder tuberosity of the radius Originates from the distal third of the caudal margin of It extends the shoulder, and more importantly, with the the scapula and crosses over the flexor side of the shoulder brachialis muscle, flexes the elbow joint joint to insert on the tuberosity of minor teres muscle Coracobrachialis - the small muscle extending from the Flexes the shoulder joint coracoid process over the shoulder to the humerus on the medial side of the axilla Anconeus - crosses the lateral aspect of the elbow joint under the triceps brachii muscle Teres major - arises from the caudal border of the scapula and inserts with the latissimus dorsi muscle on the medial Extends the elbow and tenses the antebrachian fascia side of the humerus Intrinsic Muscles - Shoulder Tensor fasciae antebrachii – the thin, insignificant muscle arising from the latissimus dorsi muscle and covering the medial surface of the triceps brachii muscle Extrinsic Muscle - Shoulder Extrinsic Muscles – Shoulder  Dorsolateral Forearm (antebrachial) muscles - extensors Muscles - Pelvic Limb of the digits and carpus, and supinators of the paw ○ Most arise on or near the lateral (extensor) epicondyle of the humerus and are innervated by the radial nerve Extensor carpi radialis – the largest extensor muscle Inserts on the metacarpal tuberosity Extends the carpus and flexes the elbow Common digital extensor – the long muscle inserting on the Mextensor process of the third phalanx (phalanges) ○ Extends the digits and carpus Lateral digital extensor - originating from the proximal end of the radius and inserting on the lateral digits ○ Extends the digits and carpus Ulnaris lateralis (lateral ulnar, extensor carpi ulnaris) - the most caudal extensor muscle ○ Inserts on the proximal part of a metacarpal bone and the accessory carpal bone ○ Although grouped under extensors, it flexes the carpus in most positions Muscles of the Forearm Muscles - Hip and Thigh  ARTHROLOGY Synostosis Symphysis term used when fibrous/cartilaginous tissues are replaced by a bone e.g.syndesmosis, synchondrosis, symphysis When one bone connects to another they form an articulation or union also known as an arthrosis or joint COMPONENTS OF SYNOVIAL JOINTS Arthrology (syndesmology) Articular Surface Study of articulations (unions) between bones specialized layer of compact bone on the surfaces that articulate with other bone Commonly called joints Articular Cartilage Articulations/joints Union or junction between two or more bones of the skeleton A layer of hyaline cartilage covering the articular surface CLASSIFICATION OF JOINTS Joint (articular) cavity Fibrous joints (synarthrosis) space between adjacent bones of the joint surrounded by joint capsule Bones a reunited by fibrous tissue. Joint capsule No joint cavity, most are temporary. Fibrous layer/capsule– outer Practically no movement; immovable joint superficial layer for protection and Syndesmosis strengthening Permits only slight movement; e.g. union of radius and ulna and union of metacarpals Synovial membrane– secretes fluid for lubrication (synovial fluid) Sutures Ligaments– connective tissue bonds that extend from bone to Ossify after maturity; e.g. junctions between skull bone Gomphosis Intracapsular (intra-articular) - Found within joints, Specialized articulation of teeth in their alveoli surrounded by synovial membrane TYPES OF SUTURES E.g. cruciate ligaments of the stifle Squamous Extracapsular (periarticular)---- External to joint capsule where the edges overlap–ex. parieto-temporal joint. collateral ligaments– lies in the medial and lateral aspect of joint Serrated dorsal and palmar/plantar ligaments– lies in front and behind where the edges are irregular–ex. Frontal joint the joint Harmonious annular ligaments– surrounds the joint , fibers circle the joint to where the edges are straight–ex. nasal joint. strengthen and protect capsule CLASSIFICATION OF JOINTS Menisci (fibrocartilage disc) Cartilaginous joints (amphiarthrosis) C-shaped piece of cartilage which is located between the major weight bearing bones United by cartilage with no joint cavity. Functions include stability, lubrication, nutrition, and shock Limited movements or no movement at all absorption Synchondrosis Only in stifle and temporomandibular joint Hyaline cartilage joint OTHER SYNOVIAL STRUCTURES Immovable joint e.g.epiphyseal plates Bursa Fibrocartilaginous joint A small, fluid-filled sac lined with synovial membrane e.g. pelvic symphyses, vertebrae and sternebrae Act as cushions and are generally found where tendons cross over a bony prominence Synovial joints Synovial sheath formerly diarthrodial joints (diarthrosis) A synovial membrane– lined tube that wraps around the true joints characterized by presence of joint cavity and tendon’s circumference mobility  Mostly in the distal limbs where long tendons pass over A convex articular condyle articulates with somewhat joints concave articular surfaces MOVEMENTS OF JOINTS Like hinge joint but with more movement; Allows movement in two planes (extension, flexion, hyperextension) Gliding or sliding– the articular surfaces of a joint slide over one another e.g. temporomandibular joint, stifle joint Flexion– decrease of angle between segments Ellipsoid joint Extension– increase of angle between segments Characterized by an articular surface expanded more in one direction than another forming an ellipse Hyperextension– angles between segments are beyond 180 degrees or a straight line e.g. joint between distal end of radius + proximal row of carpal bones Rotation– twisting movement of a segment around its own axis Saddle joint Adduction– movement of extremity towards the median Joints with an English or flat saddle–shaped articular plane surface Abduction– movement of extremity away from the median Perform all movement except rotation plane e.g. carpometacarpal joint. of human thumb, Circumduction– combination of above mentioned interphalangeal joints of dogs movements except rotation JOINTS OF THE AXIAL SKELETON Pronation/Inversion– rotation of extremity so that the ARTICULATIONS OF THE SKULL dorsum is up 1. Temporo-mandibular joint only synovial joint of the skull Supination/Eversion– rotation of extremity so that the palmar/plantar aspect is up 2. Mandibular Symphysis(intramandibular joint) TYPES OFSYNOVIAL JOINTS synchondrosis with an interdigitating surface that Ginglymus or hinge persists throughout life in the dog joints move only in the sagittal plane (extension, flexion) 3. Sutures Allows movement in one plane only e.g. elbow joint 4. Synchondrosis Arthrodial (plane/gliding) joint 5. Gomphosis Joint with slight gliding movement between relatively flat ARTICULATIONS OF THE RIBS opposed surfaces (facets) A. Synchondrosis Allows sliding of one bony surface over the other costochondral junction (fibrous joint between e.g. joints between adjacent carpal bones (Intercarpaljt), vertebral column, costotransverse joint ribs and cartilage) Pivot (trochoid) joint B. Synovial joints Rotary movement around one axis 1. Costovertebral joint Consists of a peg sitting within a ring; allows rotation Between ribs and vertebral column e.g. atlantoaxial joints “no joints”, proximal radioulnar joint Two portions: Spheroid (enarthrodial or ball & socket) joint 1. articulation of costal head with Joint which moves in almost all directions; allows a great vertebral column range of movement 2. articulation of costal tubercle with Aspherical head of 1 bone fits into a cup-shaped depression transverse process of the other bone Four ligaments: Consists of a rounded end or ball, sitting within a socket or cup 1. Ligament of costal head e.g. hip joint and shoulder joint 2. Intercapital Ligament– absent Condylar joint between 1st and last two pairs of ribs 3. Ligament of tubercle (costotransverse  ligament) strongest individual ligament uniting the ribs with B. Short Ligaments vertebral column 1. Interspinous Ligament– attach spinous process to each other 4. Ligament of the neck 2. Intertransverse Ligament– only in lumbar region, connect 2. Sternocostal joint transverse process of lumbar region Between ribs and sternum 3. Yellow Ligament– extends across open spaces between arches of vertebrae, elastic fibers that form these ligament give ARTICULATIONS OF THE VERTEBRAL them yellow color; must be punctured when accessing the COLUMN epidural or subarachnoid spaces Two Articulations: JOINTS AND LIGAMENTS OF THE THORACIC 1. Intercentral– between vertebral bodies,amphiarthrosis Synsarcosis 2. Interneural– between articular process, no true bony connection, held in place by muscles and ligaments diarthrosis e.g. scapula or shoulder blade JOINTS OF THE VERTEBRALCOLUMN 1. SHOULDER JOINT (GLENOHUMERAL JOINT, 1. Atlanto-Axial articulations SCAPULOHUMERAL JOINT) between dens of axis and fovea of atlas; “no” joint; pivot Motion: Spheroid/ ball and sockets in quadrupeds mainly joint extension and flexion 2. Atlanto-Occipital joint Bones: scapula (glenoid cavity) and head of humerus “yes” joint; synovial joint between the atlas and paired Ligaments: occipital condyles medial and lateral glenohumeral ligaments- weak ligaments 3. Intervertebral symphysis (intercentral articulations) transverse humeral ligaments movablejoint, between bodies of adjacent vertebra (BRACHIOANTEBRACHIAL, CUBITAL 4. Zygapophyseal joint (interneural articulations) Motion: hinge/ginglymus, mainly flexion extension with small synovial joint between articular process, mostly sliding gliding component and small amount of rotation motion A complex joint formed by the humerus, radius and ulna MOVEMENTSOFVERTEBRALCOLUMN 2. ELBOW JOINT mainly dorsal, ventral and lateral flexion and rotation THREE SUBJOIN' limited in thoracic and lumbar region 1. Humeroulnar joint freest movement in cervical and caudal region Humeral trochlea and trochlear notch of ulna LIGAMENTS OF VERTEBRALCOLUMN Main flexion- extension of elbow A. Long Ligaments 2. Humeroradial joint 1. Nuchal Ligament Humeral capitulum and radial head originates from spinous process of T1-T10, extends from the tip of spinous process of T1 to insert on the caudal broadened Provides major weight bearing function of the elbow area of the spinous process of the axis (C2); do not have 3. Proximal radioulnar joint contact with C7 to C3 powerful elastic apparatus, serves to support the head w/o muscular effort Formed by articular circumference of radius and radial notch ulna 2. Supraspinous Ligament– attach along Contributes for rotary motion of the elbow dorsal tip of vertebral spinous process from T1-Cd13 helps prevent excessive spreading of spinous process when vertebral Joint capsule: single cavity serving all three subjoints column is flexed ventrally Ligaments: 3. Dorsal Longitudinal Ligament– lies directly on the dorsal Medial and lateral collateral ligaments-stout thickening of joint surfaces of the vertebral bodies; thus lies on the floor of capsule, steadies the joint against excessive transverse motion vertebral canal, extends from axis to the caudal region toward the opposite side of the limb 4. Ventral Longitudinal Ligament– lies on ventral surface of Annular ligament of radius- thin ligamentous band, surrounds ventral bodies, extend from axis to sacrum the radius and maintain its position against the ulna when the radius rotates  Oblique ligament- minor ligament on cranial 6. INTERPHALANGEAL JOINTS ji. flexor retinaculum Proximal and distal (flexor) surface of joint, assist in prevention of hyperextension Digit I: only single interphalangeal joint- 2 Olecranon ligament- short band, assist in retaining proximity phalanx; digit II-V- 3 phalanx Motion: saddle of the olecranon and humerus joint (modified gynglymus) mainly 3. RADIOULNAR JOINT flexion-extension Bones: head of more proximal Motion: limited degree of rotation phalanx and base of more distal phalanx Joint 1. distal radioulnar joint- formed by articular circumference of capsule: individual ulna and ulnar notch of radius Ligaments: 2. proximal radioulnar joint Motion: condylar joint, ginglymus (hinge) joint. 4. CARPAL JOINTS Restricted to flexion and extension. Three main joint medial and lateral collateral ligament 1.Antebrachiocarpal- between radius and ulna proximally and proximal row of carpal bones distally. dorsal ligament- present in distal 2.Middle Carpal Joint- between proximal and distal row of interphalangeal joint, serve to hold the claw in carpal bones. passive semiretraction 3. Carpometacarpal joint- between distal row of carpal bones and metacarpal bones JOINTS AND LIGAMENTS OF THE PELVIC Motion: ginglymus, mainly extension, flexion, limited gliding LIMB Most mobile: antebrachiocarpal and middle carpal joints, 1. Sacroiliac Joint opens widely when The region where the pelvic limb articulates firmly with the Very limited movement: carpometacarpal and intercarpal vertebral column. joints Motion: Capable of small range of motion.( Its flexibility allows Joint capsule: extends like a sheat across entire carpal area the joint to absorb shock transmitted when the pelvic limb with cavities consisting of three separate compartments- contacts the ground.) middle carpal and carpometacarpal compartment communicate Structure: Mostly synarthrosis (fibrous) with a small portion of with each other but not with antebrachiocarpal compartment synovial. Ligaments: 2. Coxofemoral (Hip) Joint i. extensor retinaculum Motion: ball and socket joint. iii. palmar carpal fibrocartilage-Prevents collapse of the carpus Structure: os coxae (at the acetabulum) and femur (head). when limb is weight-bearing Ligament: ligament of the head of femur.-- thick and well- Provides origin site for most of digital muscles iv. special developed ligament extending between fovea capitilis and ligament of the carpus acetabular fossa. there are no collateral ligaments at the hip 5. METACARPAL JOINTS joint. 1. intermetacarpal joint- lies between adjacent metacarpal 3. Stifle (knee) joint bones at their proximal ends, motion is limited Most complex joint in the body 2. metacarpophalangeal joint Bones: femur, patella, tibia, fibula (not all are mobile) Motion: ginglymus, mainly extension, flexion Sesamoid bone THREE MOBILE SUBJOINTS (proximal sesamoid bones on palmar surface of joints II-V (weight bearing digits) 1. Femorotibial Joint Joint capsule: each has its own separate synovial joint Oriented proximal to distal capsule Formed by femoral condyles and tibial condyles Ligaments: Provides flexion and extension motion medial and lateral collateral ligaments 2. Femoro patellar Joint sesamoid and ligaments both dorsal and palmarly present Oriented cranial to caudal  Formed by patella and femoral trochlea Proximal tibiofibular joints- small with minimal movement. Protects the quadriceps femoris muscle Distal tibiofibular joint– small and tight. 3. Proximal Tibiofibular Joint 5. Tarsal Joints Formed by caudo lateral surface of the lateral tibial condyle 3 Main Joints and medial surface of fibular head Talocrural joint (ankle)– between tibia and fibula and Little to no motion proximal tarsal bones and provides greatest range of motion at tarsal region (hock). MENISCI OF THE STIFLE JOINT-- Intertarsal joints C–Shape fibrocartilages interposed between the femur and tibia to improve fit of two incongruous bones Six ligaments Two subjoints: attach the menisci to the tibia and to each other a. Proximal intertarsal joint– lies between talus and central (2)Cranial tibial ligaments (lateral and medial)– attach the tarsal medially and calcaneus and tarsal bone IV laterally with cranial edge of the open part of the “C” of each meniscus to small degree of motion. the cranial intercondylar area of the tibia caudal displacement b. Distal intertarsal joint– lies between central tarsal bone and of femur and tibial relative to each other. tarsal bones II and III medially. (2)Caudal tibial ligament– attach the caudal edge of the Tarsometatarsal joints– lies between distal row of tarsal open part of the “C” of each meniscus to the caudal bones and metatarsal bones. intercondylar area of the tibia Motion: functions as ginglymus joint. only the talocrural joint is Intermeniscal ligament (transverse) extends between free accessible to needle puncture. cranial ends of the 2 menisci LIGAMENTS OF THE TARSAL JOINT Meniscofemoral ligament (femoral ligament of the lateral meniscus) extends dorsally from the caudal open edge of the Collateral Ligaments (medial and lateral) lateral meniscus to the medial (“inner”) side of the medial femoral condyle Extensor retinacula (3) as opposed to thoracic JOINT CAPSULE OF THE STIFLE JOINT— limb (1) - composed of three subparts (Medial and lateral Crural (proximal) extensor retinaculum binds the tendons of femorotibial joint sacs Femoro patellar joint sac) long digital extensor and cranial tibial muscles. intercommunicate simplifying diagnostic and therapeutic Tarsal (distal) extensor retinaculum attach to calcaneus, manipulations of the joint (note: this is not the care in large retains the tendon of long digital extensor muscle. animals) Peroneal muscle retinacula– retains tendons of peroneous LIGAMENTS OF THE STIFLE JOINT longus and brevis muscles as well as lateral digital extensor. There are 13 ligaments associated with the Stifle Joint Flexor retinaculum– attaches plantarly to calcaneal tuber and Collateral ligaments (medial and lateral)– prevent to medial medially to distal tibia and tarsal bones. and lateral displacement of femur to tibia relative to each other. Plantar tarsal fibrocartilage– smooths the plantar surface of Cruciate ligament (cranial and caudal)forms an “X” and the tarsal bones, providing an even surface for the passage of prevent cranial to the flexor tendon over the hock. Ligament associated with patella: Special ligament of the tarsus– long plantar ligament associated with lameness when strained. Femoropatellar ligaments (medial and lateral)– prevents medial and lateral displacement of the patella. TARSAL CANAL-- Patellar ligament– portion of the tendon of the quadriceps - Positioned on the plantar surface of the joint. femoris muscle. - Lies between sustentaculum tali of the tarsus and flexor retinaculum. Maintains the position of the patella. - Passageway transmits several structures. Simply the continuation of the parent muscle (as opposed to Muscular structures- tendons of lateral head of deep digital a specialized ligament). flexor. Ligament associated with the menisci (6) Vascular structure- plantar branches of saphenous artery and veins. 4. Tibiofibular Joints Nervous structure- medial and lateral plantar nerves. 2 synovial joints are present between the tibia and fibula. A stiff membrane connects much of the medial surfaces of the two 6. METATARSAL and bones where they are separated from each other. 7. INTERPHALANGEAL JOINTS  CARDIOVASCULAR SYSTEM In the living animal, the right side of the Consists of heart and a system of vessels for the heart is on the right side of the body but distribution of blood to the tissues of the body and the lungs oriented more cranial than the left side, for exchange of gases which is left and somewhat caudad Arteries - carry blood away from the heart Veins - carry blood towards the heart Pulmonary circulation - circulation to the lungs Systemic circulation - circulation to the body Two principal divisions: ○ Blood vascular system - includes a powerful pump, the heart Arteries leave the left side of the heart They branch into progressively smaller arteries Pericardium. until they form microscopic vessels called Fibroserous sac enclosing the heart capillaries Composed of fibrous and serous pericardium, Capillaries feed into small veins that join to form larger veins, all carrying oxygen-depleted blood covered by mediastinal (pericardiac) pleura back to the right side of the heart The heart pumps this blood to the lungs again via arteries, where CO2 is exchanged for oxygen Newly oxygenated blood returns through veins to the left side of the heart that pumps it to the rest of the body and heart via the aorta ○ Lymphatic system - removes wastes and bacteria from the interstitial fluid and returns protein-rich fluid to the bloodstream Heart Fibrous pericardium - a tough, fibrous sac surrounding Cone-shaped, hollow muscular structure the serous pericardium, the heart and the pericardial cavity The base is directed dorsad or cranio-dorsad ○ It is closed above by its attachment to and is attached to other thoracic structures by the great vessels of the heart large arteries, veins and the pericardial sac ○ When discussing the pericardial serous The apex is directed ventrad and is entirely free membranes, the fibrous pericardium within the pericardial sac will be considered as a wall ○ Sternopericardiac ligament – connects the ○ Endocardium - thin, mesothelial layer lining the atria pericardium to the floor of the thorax and ventricles; continuous with the endothelium lining the great vessels entering and leaving the heart ○ Phrenicopericardiac ligament - connects the pericardium to the diaphragm Serous pericardium - a serous membrane forming a closed cavity ○ It covers the heart (visceral layer) and lines the inner surface of the fibrous pericardial sac (parietal layer) ○ Parietal layer of the serous pericardium - lines the inner surface of the fibrous pericardium. It reflects onto the surface of the heart as the visceral layer The heart is divided into right and left sides ○ Visceral layer of the serous pericardium - covers which correspond to the low-pressure (pulmonary the myocardium of the heart closely circulation) and high pressure (systemic circulation) It is also called the epicardium systems Each side has two chambers: ○ Atrium - receives blood by way of large veins ○ Ventricle - pumps blood from the heart through a large artery Auricle - a pectinated muscular structure which forms a distinctive pouch visible on the exterior of the heart and overlaps the pulmonary trunk ○ The auricles increase the holding capacity of the atria when needed but are not considered part of the main Pericardial cavity heart chamber ○ A potential space between the visceral and parietal layers of serous pericardium ○ It has approximately one ml of yellow fluid between the contacting layers, which acts as a lubricant to allow the heart freedom of movement during contraction Major blood vessels: ○ Cranial vena cava - the large vein returning blood from the head, neck and thoracic limbs to the right atrium ○ Caudal vena cava - the large vein returning blood from part of the thorax, the viscera and the caudal part of the Cardiac Anatomy body to the right atrium Three layers of the heart: ○ Right atrium - the chamber of the heart receiving deoxygenated blood from the body ○ Epicardium - the outer serous covering; thin layer of mesothelium covering the surface of the heart ○ Right ventricle - the chamber receiving blood from the right atrium and sending it to the lungs ○ Myocardium - the muscle layer making up the majority of the thickness of the heart wall; between the The conus is the funnel shaped end of the right endocardium and epicardium ventricle leading to the pulmonary trunk ○ Pulmonary trunk - the large vessel carrying blood from the right ventricle to the pulmonary arteries, thus, to the lungs ○ Pulmonary arteries - the two branches of the pulmonary trunk carrying blood to the lungs; one to the right lung, one to the left Semilunar valve - ensures that blood flows only from the ventricle into the artery and not in the opposite direction ○ Has three cuplike leaflets, with convex side facing the ventricle ○ Pulmonary veins - the numerous vessels emptying oxygenated blood from the lungs into the left atrium of the ○ Aortic valve - lies at the junction of the left ventricle and heart aorta ○ Left atrium - receives oxygenated blood from the lungs ○ Pulmonary valve - at the junction of the right ventricle via the pulmonary veins and pulmonary trunk ○ Left ventricle - sends oxygenated blood to the body and heart ○ Aorta - the major outflow from the left ventricle into the systemic circulation Atrioventricular valve (A-V valve) - between the atrium and the ventricle of each side ○ Bicuspid valve - left A-V valve, because in humans, it has two distinct flaps or cusps ○ Mitral valve - left A-V valve, because of its imagined resemblance to a bishop’s miter, or two-sided hat ○ Tricuspid valve - right A-V valve, because in humans it has three flaps or cusps Blood Vessels Resembles the branching of a tree in that the arteries start as large vessels and divide into smaller and smaller branches The smallest arteries are arterioles, which are continuous with the smallest blood vessels, capillaries Capillaries unite to form small venules that come together to form larger and larger veins Chordae tendineae - strong, fibrous connections The largest veins empty into the atria of the between the valve leaflets and the papillary muscles heart The chordae tendineae attach to small muscular Arteries and Arterioles protrusions called papillary muscle that project into the Tubular structures that carry blood away from lumina of the ventricle the heart These CT prevent the valve from everting into They are lined with endothelium the atrium when the ventricle contracts and closes the A-V valve by forcing blood against the ventricular side of the Walls are thick and elastic, properties that are valve important in maintaining blood pressure  Smooth muscle in the walls of smaller arteries Pulmonary Circulation controls the diameter of these vessels Capillaries Tiny tubes composed almost entirely of endothelium, a continuation of the simple squamous epithelium that lines the heart and blood vessels These thin-walled vessels are only large enough in diameter to accommodate a single file of erythrocytes Part of the vascular system that circulates the The wall acts as a selectively permeable blood through the lungs membrane that permits water, oxygen and nutrients to Deoxygenated blood is delivered into the leave the blood for tissue cells and permits waste pulmonary system by contraction of the right ventricle products from tissue cells to enter the blood After passing the pulmonary trunks, blood Much of the fluid that passes out of the enters the right pulmonary artery to go to the right lung and capillaries into tissue spaces again returns to the blood by the left pulmonary artery to go to the left lung passing back through the capillary walls Each pulmonary artery subdivides into lobar Veins and Venules arteries going to individual lobes of the lungs Veins are larger in diameter than the arteries The lobar arteries again subdivide many times, they parallel and have much thinner walls finally forming arterioles that supply the extensive capillary beds of the lungs, where gaseous exchange takes place Venous blood pressure is typically quite low After the blood passes through the capillary bed Contraction of the skeletal muscles in the limbs of the lungs, it enters and trunk squeezes the thin-walled veins, assisting the flow of venous blood back toward the heart venules, which combine to form pulmonary veins A valve frequently is present where two or more These pulmonary veins, after leaving the lungs, veins unite to form a larger vein deliver oxygenated blood to the left atrium, completing the pulmonary circulation The valves ensure a unidirectional flow of venous blood toward the heart As gases are exchanged, the color of the blood changes from the bluish maroon color of deoxygenated Lymphatic Vessels blood to the bright red of oxygenated blood ECF that does not reenter the vascular space In the adult, the pulmonary circulation is the only directly is recovered by thin-walled lymphatic vessels place where deoxygenated blood is found in arteries and Resemble veins in that they contain numerous oxygenated blood is found in veins valves permitting flow only toward the heart Refers to the movement of oxygenated blood to The smallest lymphatic vessels are blind all areas of the body and the return of deoxygenated blood capillary-sized structures that begin in intercellular spaces, to the heart where they accumulate extracellular fluid Aorta Lymph - the fluid within the lymphatic vessels; are The largest artery transported to larger and larger lymph vessels and finally emptied into the cranial vena cava or one of its tributaries ○ The left ventricle receives oxygenated blood from the left atrium and pumps the blood Tracheal trunks - two large lymph vessels draining the throughout the systemic circulation by way of the head and neck, usually terminate in the jugular veins aorta Thoracic duct - where lymph from the caudal half of the body is delivered ○ Traverses the thoracic cavity adjacent to the aorta to empty its lymph into the cranial vena cava  Aortic valve - found at the junction of the left ventricle Thoracic Aorta and aorta and prevents backflow of blood from the aorta Passes caudad just ventral to the vertebral into the left ventricle when the ventricle relaxes bodies Coronary arteries (left and right) – two large vessels that arise from the aorta immediately distal to the aortic valve ○ The arterial blood supply for the myocardium Coronary veins - where most of the venous blood from the myocardium passes as they are returned to the right atrium Coronary sinus - responsible for draining most of the deoxygenated blood leaving the myocardium; adjacent to the opening of the caudal vena cava After emerging from the base of the heart, the aortic arch courses dorsad and then caudad, just ventral to the bodies of the thoracic vertebrae As it does so, pairs of segmental arteries arise The aorta continues as the thoracic aorta until it from its dorsal aspect to supply the thoracic wall and passes through the aortic hiatus of the diaphragm to epaxial muscles become the abdominal aorta Each of these intercostal arteries enters the corresponding intercostal space, giving off a spinal branch that enters the vertebral canal to supply the spinal cord and spinal nerve roots After it passes through the aortic hiatus of the diaphragm Subclavian arteries (left and right) - main blood supply to the thoracic limbs Costocervial trunks (left and right) - provide arterial blood to regions of the neck and cranial thoracic wall Common carotid arteries (left and right) - main source of blood for the head and brain, arise together from a single bicarotid trunk Ventral to the last few lumbar vertebrae, it terminates by dividing into two external iliac arteries (supplying the pelvic limbs) and two internal iliac arteries (supplying the gluteal and perineal region)  ○ Left gastroepiploic artery - pases to the greater curvature of the stomach ○ Short gastric arteries - arise from the splenic artery and pass to the fundus of the stomach ○ Right gastric artery - anastomoses with the left gastric artery to supply the lesser curvature of the stomach ○ Gastroduodenal artery - crosses the stomach to branch into right gastroepiploic and cranial pancreaticoduodenal arteries ○ Cranial pancreaticoduodenal artery - passes distally along the descending duodenum to supply it and the pancreas Cranial mesenteric artery - immediately caudal to the Phrenic arteries - supply the diaphragm celiac artery Median sacral artery - small midline continuation of the ○ Large, unpaired artery branching into smaller aorta that continues ventral to caudal vertebrae as the arteries that supply blood to most of the small intestine and median caudal artery much of the large intestine Medial caudal vein - tail vein; used for collection of blood from adult cattle Lumbar arteries - arises from the dorsal side of the abdominal aorta and supplies the abdominal wall and epaxial muscles and giving off spinal branches that supply the spinal cord and spinal nerve roots of the lumbosacral region Paired visceral branches: ○ Renal arteries - provide arterial blood to the kidneys ○ Testicular or ovarian arteries - provide arterial blood to the gonads Caudal pancreaticoduodenal artery - anastomoses Unpaired visceral branches - supply nearly all the with the cranial pancreaticoduodenal artery abdominal viscera; from cranial to caudal: Ileocolic artery - branches to: ○ Celiac artery ○ Middle colic artery - supplies the transverse ○ Cranial mesenteric artery (“middle”) colon ○ Caudal mesenteric artery ○ Right colic artery - supplies the second half of the ascending colon Celiac artery - arises shortly after the aorta pases through the diaphragm ○ Colic branch of the ileocolic artery - supplies the first part of the ascending colon ○ Large unpaired artery that supplies the stomach (left gastric artery), the spleen (splenic artery) and the liver ○ Antimesenteric ileal artery - travels on the (hepatic artery) antimesenteric side of the ileum in the ileocecal fold Jejunal and ileal branches - come off the continuation of the cranial mesenteric artery ○ These branches anastomose, making arcades from which short jejunal and ileal arteries extend to reach the organs  Facial artery - convenient for taking a pulse as it passes across the mandible The internal carotid arteries or their derivatives enter into an anastomotic ring of vessels on the base of the brain called the cerebral arterial circle (formerly circle of Willis) Caudal mesenteric artery - supplies the caudal part of the large intestine and the rectum Arterial Distribution to the Head The cerebral arterial circle gives rise to arteries Common carotid arteries (right and left) - supplies that supply the cerebral hemispheres and rostral parts of most of the structures of the face, head and cranial neck the brainstem ○ Each runs craniad in a connective tissue sheath More caudal parts of the brainstem and the with the vagosympathetic trunk of the same side cerebellum receive most of their blood supply from Carotid sheath - lies in a groove dorsolateral to the branches of the basilar artery trachea Vertebral arteries - left and right joins to form the single ventral artery The robust vertebral arteries ascend from their origin in the thoracic inlet, run alongside the cervical vertebrae, enter the foramen magnum of the skull, and there coalesce into the basilar artery (coursing rostrad) and the ventral spinal artery (running caudad) Maxillary artery - the direct continuation of the external carotid artery to the space below the orbit (pterygopalatine fossa) ○ Branches supply the orbit, teeth, chin, nose, nasal cavity and palate Internal carotid artery - branch of the CCA that Arterial Distribution to the Thoracic Limb branches from the region of the larynx The right and left subclavian arteries follow the same course on each side of the body and each gives off similar branches Within the thorax, each subclavian artery gives off a number of branches that supply blood to the caudal part of the neck, much of the thoracic wall, and the dorsal part of the shoulder The subclavian artery passes cranial to the first rib on the respective side, passing into the axilla (armpit) ○ Primary source of blood for the brain of the thoracic limb, where it is called axillary artery External carotid artery - continuation of the Subscapular artery – passes dorsocaudally between common carotid artery whose many branches supply the the subscapular and teres major muscles face, tongue, and structures of the oral and nasal cavities ○ It gives off the caudal circumflex humeral artery and thoracodorsal artery Palmar arches - give off palmar metacarpal arteries (deep) and palmar common digital arteries (superficial) Brachial artery - the continuation of the axillary artery that supply the palmar aspect of the forearm and manus on the medial aspect of the arm, which it supplies Digital arteries - blood vessels of the metacarpus and ○ It continues as the median artery in the forearm digits after it gives off the common interosseous artery ○ Number the digital arteries from medial to lateral Major branches: ○ Palmar common digital arteries – the superficial Deep brachial - to the triceps brachii muscle arteries located on the palmar side of the metacarpus. Bicipital - to the biceps brachii muscle Carnivores also have dorsal common digital arteries Collateral ulnar - toward the olecranon ○ Dorsal and palmar metacarpal digital arteries - the deep arteries of the metacarpus travelling next to the Transverse cubital - under the biceps brachii metacarpal bones. They parallel the larger common digital muscle arteries and usually contribute to the formation of the proper digital arteries ○ Proper digital arteries - the distal branches of the common digital arteries past the proximal end of the digits. They extend down the sides of the digits as axial and abaxial proper digital arteries The axillary artery enters the limb, becoming the brachial artery in the region of the brachium and then the median artery as it continues distal to the elbow Bronchoesophageal artery – arises from the aorta or from one of the dorsal intercostal arteries Common interosseous artery – dives through the interosseous space between the radius and the ulna ○ It has caudal and cranial interosseous branches ○ In dogs, the caudal interosseous can’t be occluded with a tourniquet in the mid-forearm because it is ○ Bronchial branch is the nutritional supply to the protected between the radius and ulna tissues of the lung Median artery - the continuation of the brachial artery Dorsal intercostal arteries - the first few arise as past the common interosseous artery branches if the costocervical trunk, the rest arise directly from the aorta ○ It supplies the forearm by its branches: ○ Their main branch courses on the caudal aspect Deep antebrachial - to the caudomedial of the ribs to anastomose with the ventral intercostal muscles arteries Radial - to the digits Arterial Distribution to the Pelvic Limb ○ It passes through the carpal canal to join Each internal iliac artery and its many branches branches of the common interosseous artery to form supply the region of the pelvis, the hip and much of the palmar arterial arches genitalia  ○ Branches into cranial and caudal (small) tibial arteries Cranial tibial artery - the larger branch of the popliteal artery, passing in the interosseous space between the tibia Femoral arteries - located on the inner thigh and fibula to the cranial surface of the crus ○ Easiest place to find the dog’s pulse Dorsal pedal artery - the direct continuation of the cranial tibial artery over the tarsus ○ It is a continuation of the external iliac artery below the level of the inguinal ligament Common digital arteries – the superficial arteries (dorsal and plantar) in the metatarsal region The femoral artery descends on the medial aspect of the limb, giving branches to the large thigh Metatarsal arteries - the deep arteries (dorsal and muscles, and continues in the region of the caudal stifle as plantar) of the metatarsal region the popliteal artery Proper digital arteries (dorsal and plantar) - formed After a very short course, the popliteal artery from the joining of the common digital and metatarsal divides into cranial and caudal tibial arteries arteries ○ The small caudal tibial artery supplies the muscles of the crus or true leg ○ The cranial tibial artery is larger External Iliac Arteries Saphenous artery - arises from the femoral artery in the femoral triangle ○ Passes subcutaneously with a vein and nerve on the medial side of the thigh ○ Gives off the descending genicular artery of the stifle ○ Past the stifle it divides into cranial and caudal branches in the carnivores and horse Popliteal artery - the continuation of the femoral artery behind the stifle and between the two heads of the gastrocnemius muscle  ○ They have “axial” or “abaxial” added to their ○ Terminates as the ventral perineal artery and name, depending on which side of the digits they pass the artery of the penis or clitoris Prostatic or vaginal artery - the branch of either the internal pudendal or internal iliac, depending on which is longer ○ Supplies the urogenital organs in the pelvic cavity ○ It’s branches are named for the organs they supply Internal iliac arteries - the terminal aortic branches supplying the pelvic viscera and part of the hip and thigh External iliac arteries – the branches of the terminal aorta supplying the pelvic limb Uterine artery - the main blood supply to the uterus Deep femoral artery - the only branch of the external ○ Arises differently in the different species iliac artery present in all species. It has the following branches: ○ Pudendoepigastric trunk - a short branch off the deep femoral artery giving rise to the caudal epigastric and external pudendal arteries ○ Caudal epigastric artery - courses cranially on the deep surface of the straight abdominal muscle (rectus abdominus) ○ External pudendal artery - passes through the inguinal canal and branches into the superficial caudal epigastric and ventral scrotal or ventral labial arteries Umbilical artery - arises from the internal iliac or internal pudendal (horse) artery and passes to the apex of the ○ Superficial caudal epigastric artery - courses urinary bladder cranially under the skin of the ventral abdominal wall to anastomose with the cranial epigastric artery ○ In the fetus, the umbilical arteries were the vascular return from the fetus to the mother Internal Iliac Arteries ○ After birth, they regress from the umbilicus to Internal pudendal artery - can be “short” or “long”, the bladder depending on where it and the caudal gluteal artery separate ○ The last branch of the umbilical artery is the cranial vesical artery  Round ligament of the bladder - the part of the umbilical artery in the edge of the lateral ligament of the bladder ○ Its lumen is usually obliterated Veins With some notable exceptions, veins accompany arteries of the same name These “satellite” veins are always larger than their respective arteries and frequently duplicated Some veins are superficial, visible in the Artery of the penis - the continuation of the internal subcutaneous tissues, and these are particularly of interest pudendal artery in the male as they may be accessed via venipuncture ○ It rounds the arch of the ischium and trifurcates: Artery of the bulb - supplies the corpus spongiosum penis Deep artery of the penis - enters and supplies the corpus cavernosum penis Dorsal artery of the penis – travels along the dorsal surface of the penis External jugular vein - large vein in the neck returning blood from the head to the heart Cephalic - arises from the digital veins on the palmar aspect of the paw Artery of the clitoris - analogous to the artery of the penis ○ It extends proximally around the medial side of the forearm just above the carpus to reach the cranial ○ Branches into the artery of the vestibular bulb, surface of the limb the deep artery of the clitoris (except in horses) and dorsal artery of the clitoris (except in horses) ○ Here, it is joined by the accessory cephalic vein Ventral perineal artery - the other terminal branch of ○ Continues up the limb crossing the flexor the internal pudendal artery surface of the elbow and lateral side of the arm ○ Supplies the perineum ○ Empties into the external jugular vein Accessory cephalic vein - arises from the digital veins on the dorsal surface of the paw  ○ Extends proximally to join the cephalic vein above the carpus in the carnivores and ox and near the elbow in the horse Veins - Thoracic Limb ○ The median saphenous vein travels on the medial side of the limb and empties into the femoral vein in the femoral triangle ○ Travels on the lateral side of the limb and empties into the caudal femoral vein behind the stifle Portal System Portal vein - formed by the joining of the cranial and caudal mesenteric veins ○ Receives the gastroduodenal and splenic veins ○ Drains into the liver allowing intestinal blood to be processed and cleaned before it is sent on to the general circulation Liver sinusoids - spaces in the liver where the portal blood is processed Subclavian vein - the vessel returning blood from the thoracic limb to the heart Brachiocephalic vein - found only in the carnivores and pig, formed by the intersection of the external jugular and subclavian veins Cranial vena cava - the great vessel emptying into the cranial part of the right atrium, returning blood from the head, neck and thoracic limbs and cranial part of the walls of the thoracic cavity Caudal vena cava - the great vessel emptying into the caudal part of the right atrium, returning blood to the heart from the abdomen, pelvis and pelvic limb Veins - Pelvic Limb Deep veins parallel the arteries of the same name One in which a vessel divides into capillaries, recombines to form another vessel, and then redivides into ○ Superficial drainage occurs via the saphenous a second capillary bed vein Hepatic portal system - blood that has perfused the Medial and lateral saphenous vein – the superficial capillary beds of the viscera is brought to the liver by a drainage of the pelvic limb single large vein, the portal vein, and then redistributed into ○ Do not parallel similarly-named arteries a secondary capillary bed within the substance of the liver Tributaries include: ○ Similar to veins, the lymphatic vessels differ in having thinner walls, more valves, and lymph nodes along ○ Gastric vein - from the stomach their course ○ Splenic vein - from the spleen Lymph nodes - the ovoid or bean-shaped, ○ Mesenteric vein - from the intestines encapsulated structures located along the course of the medium-sized lymphatic vessels ○ Pancreatic vein - from the pancreas ○ Lymph nodes function as filters and germinal LYMPHATIC SYSTEM centers for lymphocytes Consists of lymphatic tissues and vessels ○ Each node has a capsule of fibrous connective This system returns protein-rich fluid to the blood tissue circulation that escapes from the blood capillaries into ○ Trabeculae extend from the capsule into the lymph node tissue spaces ○ The outer cortex and inner medulla make up the Involved in lymphocyte and antibody production, parenchyma of the node. phagocytosis of particulate matter, and movement of fats from the digestive system to the circulation Lymph nodes Lymph vessels are not present in the brain, spinal cord ○ Lymph enters the periphery of the lymph node or bone marrow by afferent lymphatic vessels, passes through the parenchymal sinuses, and out the hilus of the lymph node The pumping of the heart causes hydrostatic pressure by a single efferent lymphatic vessel that filters out all components of the blood, except blood cells and platelets, from the capillaries into the surrounding ○ Lymph picks up lymphocytes and is subjected tissue to macrophages as it passes through the node The lymphatic vessels have greater permeability than Primitive cells - located in the lymph nodes, they the capillaries, easily “picking up” proteins and large differentiate into lymphocytes and/or plasma cells molecules Macrophages - the phagocytic cells lining the walls of Muscle contractions compress the lymphatic vessels, the sinuses moving the “lymph” along LYMPHOCENTERS Group of lymph nodes draining the same region of the body in all species ○ Trunks and ducts drain the lymphocenters back to the general circulation at the so-called “venous angle” Lymph capillaries - blind-ended tubes located ○ The “venous angle” is where the ducts or trunks throughout the body empty into the large veins in the thoracic inlet ○ More permeable than blood capillaries, they “pick up” the excess interstitial fluid, which is then called lymph Lymphatic vessels - the larger vessels formed by the convergence of lymph capillaries  ○ Present in all species and palpable in dog, ox and horse ○ Located in front of the shoulder joint under the superficial neck muscles ○ Drain the superficial neck and dorsal thorax along with the proximal part of the forelimb Deep cervical lymph nodes - the chain of deep lymph nodes (cranial, middle and caudal) along the length of the trachea ○ Drains the deep and ventral structures of the neck into the thoracic duct on the left side or into the lymphatic duct on the right Right and Left Tracheal (Jugular) Trunks ○ Traveling along the trachea, draining the lymph nodes of the head and neck ○ Empty into the thoracic duct on the left side, LYMPHOCENTERS - HEAD AND NECK the right lymphatic duct, or the vessels of the thoracic duct Parotid lymph node - represents the parotid lymphocenter LYMPHOCENTERS - THORACIC LIMB AND THORAX ○ It is located under the cranial edge of the parotid gland The thoracic lymphocenters can be divided into: ○ It drains the dorsal part of the head, including ○ Parietal - dorsal and ventral thoracic the orbit and parotid gland, then the lymph continues to the lymphocenters represented by the intercostal and sternal retropharyngeal nodes lymph nodes ○ It is palpable in the dog and ox ○ Visceral - mediastinal and bronchial lymphocenters Mandibular lymph node - represents the mandibular lymphocenter and consists of nodes located ventral to the Mediastinal lymphocenters - consist of the cranial angle of the jaw mediastinal lymph nodes in all species ○ They drain that part of the head not drained by ○ Carnivores lack the caudal mediastinal lymph the parotid gland to the medial retropharyngeal node nodes that are huge in ruminants ○ Present in all species, they are palpable in the Bronchial lymphocenters - consists of nodes located dog, ox and horse around the tracheal bifurcation Retropharyngeal lymphocenter – drains the deeper Axillary lymph node (part of the axillary structures of the head and neck, including the pharynx lymphocenter) - constantly present in all species and and larynx palpable in dog ○ Also receive lymph coming from the parotid ○ Located in the axilla, it drains the forelimb and and mandibular lymph nodes the thoracic wall, including the first three pairs of mammary glands in the dog ○ Medial retropharyngeal lymph node – the largest lymph node of the head and neck, present in all ○ The accessory axillary lymph node is present species in the cat and inconstant in the dog and ox ○ Lies between the larynx and the wing of the LYMPHOCENTERS - ABDOMEN atlas and is not normally palpable Lumbar lymphocenters - consist of lumbar lymph ○ Lateral retropharyngeal lymph node - nodes located along the abdominal aorta usually absent in dog and palpable in the ox ○ Drains the kidney, loins, adrenal glands, and Superficial cervical lymph nodes - represent the abdominal portion of the urogenital system, including superficial cervical lymphocenter testes, into the lumbar trunks or cisterna chyli  ○ Carnivores lack renal lymph nodes Hilus - the area where vessels and nerves enter the spleen ○ Cisterna chyli - a lymphatic structure found at the caudal end of the thoracic duct that receives lymph ○ A long groove in the carnivores, horse and pig draining from the abdominal and pelvic viscera and lower and a small indentation in ruminants limbs NERVOUS SYSTEM Celiac lymphocenters - consist of splenic, gastric, hepatic and pancreaticoduodenal lymph nodes that drain Consists of the brain, the spinal cord, and the associated structures to the cisterna chyli peripheral nerves, which connect various parts of the body to either brain or spinal cord. Cranial mesenteric lymphocenters - consist of Neuron – primary functional cell of the nervous jejunal, cecal, and colic lymph nodes system. ○ Located near these organs and drain into the Glia / Neuroglia – other cells types that functions to cisterna chyli maintain the cellular environment to support the activity of the neurons. Cranial mesenteric lymph nodes – large node located in the root of the mesentery of the dog Basic Functions: Caudal mesenteric lymphocenters - represented by Initiate and/or regulate movement of the body the caudal mesenteric lymph nodes draining the parts by initiating and/or regulating the descending colon contraction of skeletal, cardiac, and smooth muscles. THORACIC DUCT Regulate secretions from glands. Gather inf