Veterinary Abdominal Viscera (Animal)

 Abdominal Viscera

Alimentary Canal  (esophagus, stomach, intestine)

A.  Esophagus — cervical,  thoracic,  abdominal regions

                           (all striated in dog;  proximal 2/3’s striated in cat )

B.  Stomach:

                      Sphincters: 1) Cardiac (at cardia) and

                                         2) Pyloric (at pylorus)

                        Region:   a) Cardiac (surrounding cardia)

                                         b) Fundic (fundus = blind end)

                                         c) Body

                                         d) Pyloric (antrum & canal)

also, lesser curvature — LESSER OMENTUM

greater curvature —  GREATER OMENTUM

C. Small Intestine:

1)   Duodenum  — MESODUODENUM

regions: a) Cranial flexure

               b) Descending duodenum

               c) Caudal flexure

               d) Ascending duodenum

                e) Duodenal-jejunal flexure

2) Jejunum — MESOJEJUNUM      ----->MESENTERY

3) Ileum   — MESOILEUM      ----->  MESENTERY

                      antimesenteric vessel; ileocecal fold ileal (ileocolic)      

                      orifice

D. Large Intestine:

1) Cecum (blind end; no appendix)

                   cecocolic orifice; ileocecal fold

2) Colon  — MESOCOLON

                       Regions: a) Ascending colon

                                       b) Right colic flexure

                                       c) Transverse colon

                                       d) Left colic flexure

                                        e) Descending colon

3) Rectum  — MESORECTUM

4) Anal canal  (retroperitoneal)

                Anus = external opening

                Sphincters — a) Internal anal sphincter (smooth m.),

                                       b) External anal sphincter (striated m.);

Liver —

                  Secretes bile salts which emulsify ingested fat; bile is        

                  tored in the gallbladder develops in ventral 

                  mesogastrium:

                 (Diaphragm / LIGAMENTS / LIVER / LESSER  

                  OMENTUM / stomach)

Six lobes:

                Rright lateral lobe

                Right medial lobe

                Gallbladder

                Quadrate lobe

                 Left medial lobe

                 Left lateral lobe

                 Caudate lobe —

                                           Papillary process

                                      Caudate process

Pancreas —

                     Secretes proteolytic enzymes into duodenum;

                           also, endocrine secretions (insulin, etc.)

Structure:

                left lobe + body + right lobe;

                located in GREATER OMENTUM &   

                MESODUODENUM

Ducts:

                Pancreatic duct (smaller) empties with bile duct —>   

                major duodenal papilla.

              Accessory pancreatic duct (larger) empties —>  minor  

              duodenal papilla.

Kidney:

                — removes waste products from blood (urine);

—   regulates fluid/salt balance (blood osmotic pressure)

Topography —

                        Right kidney is more cranial than the left;

                       Cranial pole of right kidney is cupped by liver;

                       Left kidney is more loosely attached;

                       Feline kidneys are positioned more caudally.

Surface features —

                                cranial / caudal poles

                                dorsal / ventral surfaces

                                medial / lateral borders:

 medial border has a hilus (where vesselsand the ureter enter) that leads to aspace (renal sinus) where the renal pelvis is located.

Kidney structure —

                                    A fibrous capsule surrounds the kidney (capsular veins are prominent in the cat)

renal cortex = superficial tissue that contains vascular glomeruli

renal medulla =  deep tissue (an outer part and a less vascular inner part can be distinguished)

renal pyramid = the medulla between interlobar vessels (belonging to a renal lobe)

renal papilla = the free tip of a renal pyramid (not present as such in carnivores)

renal crest = median ridge produced by fusion of renal papillae in the carnivore

Ureter — (forms branches and calyces in multilobar kidneys)

                     conveys urine from kidney to urinary bladder.

renal pelvis = expanded proximal end of ureter ( located within renal sinus of unilobar kidney)

pelvic recess = lateral expansion of renal pelvis between interlobar vessels.

Spleen:

Structure

               — develops in dorsal mesogastrium;

               — becomes enlarged when capsular & trabecular smooth      

                     muscle relax (e.g., under barbiturate anesthesia)

Function

                — serves as a reservoir for blood cells (blood storage)

—   filters particles from blood, particularly over-aged

erythrocytes.

 Abdominal  Vessels

 Aorta:

A.  Branches to the abdominal wall:

1) lumbar aa. —  supply vertebral column, spinal cord, epaxial m., & skin over the back.

2) common trunk (previously, phrenicoabdominal a.) — supplies abdominal wall &  adrenal gland via cranial abdominal a. and diaphragm

3) deep circumflex iliac aa. — supply abdominal wall (caudally)

B.  Branches to paired organs:

1) renal a. — supplies kidney

2) ovarian a. or testicular a. — supplies gonad

C. Branches to unpaired organs (digestive system & spleen):

1) celiac a.

              — supplies cranial abdominal viscera (esophagus,

                    stomach, duodenum, liver & gall bladder,pancreas,

                      spleen)

               — the stomach has a quadrant blood supply(right/left &

                    gastric/gastroepiploic aa.)

2) cranial mesenteric a.

                                 — supplies duodenum to descending colon

                                      also pancreas

3) caudal mesenteric a.

                                  — supplies descending colon & rectum

D. Terminal branches of the aorta:    (within pelvic cavity)

1) external iliac a. (paired) — pelvic limbs

2) internal iliac a. (paired) — pelvis (wall & viscera)

3) median sacral a. (unpaired)

                                       — becomes median caudal a. of the tail

Portal Vein:

The portal vein conveys blood between two capillary beds (between alimentary tract capillaries and liver sinusoids).

Cranial and caudal mesenteric veins anastomose to from the portal vein which receives a splenic vein (left side) and the gastroduodenal vein (right side) before entering the liver.

The circulation sequence is . . .

Celiac and cranial and caudal mesenteric arteries and their branches

—> alimentary, etc. capillaries

—> satellite veins

—> portal vein

—> hepatic sinusoids

—> hepatic veins

—> caudal vena cava

Lymphatics:

Mesenteric lymph ducts converge to form a lymph "lake" (cysterna chyla)

Veterinary Autonomic Nervous System (Animal)

Autonomic Nervous System (ANS)

Visceral Efferent (VE) Pathway:    nvolves 2 neurons

  1. Preganglionic neuron   —   cell body located in CNS;  axon synapses in an autonomic ganglia

 

  2. Postganglionic  neuron — cell body in an autonomic ganglion;  axon innervates smooth muscle, cardiac muscle or gland           

dia......

.

ANS Divisions:   basis for recognizing two divisions

 Feature        Sympathetic            Parasympathetic

Distribution: ---------whole body--------- viscera in body cavities; in head

Preganglionic origin: --- thoracolumbar spinal cord --- sacral spinal cord &              

                                                                                              brainstem

Postganglionic neuron:  ------ usually adrenergic ------- always cholinergic

 

Functional role: ------------fight or flight------------ routine visceral operations

Functional Differences:

Structure --------- Sympathetic-----------Parasympathetic

iris (pupil)  ----------------------dilate  ------------------------ constrict

heart----------increase rate & force of contraction  ----------- decrease rate

bronchi -------------------dilate  ------------------------------ constrict

gut & bladder wall  -----------inhibit motility ------------ excite contraction

gut & bladder sphincters  --------------------contract ------------------- relax

cutaneous vessels -------------------constrict ------------------- doesn’t innervate

muscle vessels  -----------dilate (cholinergic)  -------------- doesn’t innervate

sweat glands -----------------------secrete -------------------- doesn’t innervate

Autonomic Pathways

Parasympathetic pathways:

dia..........

   1. Cranial nerves III, VII, and IX .... later in the course.

  2. Cranial nerve X (vagus nerve) innervates thoracic and abdominal viscera:

Preganglionic pathway:  the vagus n. branches travel to organs being innervated

Synapse:  occurs within organs innervated, in microscopic   terminal ganglia

Postganglionic pathway:  axons course in submucosal or myenteric plexuses to reach innervation targets.

   

3. Sacral spinal cord innervates pelvic viscera:

Preganglionic pathway: from the sacral cord to pelvic plexus.

 synapse:  occurs in a pelvic ganglion within the pelvic plexus.

Postganglionic pathway: branches from the pelvic plexus run 

directly to pelvic viscera.

Sympathetic Preganglionic Pathways

dia.......

Sympathetic Pathways to Six Regions

Head Region

Preganglionic path: ventral root; spinal n.; ramus communicans; sympathetic trunk; ansa subclavia; and cervical sympathetic trunk.

Synapse:  cranial cervical ganglion.

Postganglionic path: nerve plexuses run on external & internal carotid arteries and their branches to reach target structures.

Neck Region

Preganglionic path: ventral root; spinal n.; ramus communicans; sympathetic trunk.

Synapse: cervicothoracic ganglion.

Postganglionic path: vertebral nerve; rami communicantes; cervical spinal nn.; dorsal or ventral branches to muscles & skin.

Body Wall and Limbs and Tail

Preganglionic path: ventral root; spinal n.; ramus communicans; 

  sympathetic trunk.

Synapse: sympathetic trunk ganglia.

Postganglionic path: Rami communicantes;  spinal nn.; dorsal or ventral branches to muscles & skin

Thoracic Viscera

Preganglionic path: Ventral root; spinal n.; ramus communicans; sympathetic trunk.

Synapse: Cervicothoracic & middle cervical ganglia

Postganglionic path: Cardiosympathetic nn. branch from ansa subclavia

Abdominal Viscera

Preganglionic path: Ventral root; spinal n.; ramus communicans; sympathetic trunk; splanchnic nn

.

Synapse: Prevertebral ganglia (left/right celiac, cranial mesenteric, caudal mesenteric, renal, and gonadal ganglia) located in nerve plexuses along the aorta

Postganglionic path:  nerve plexuses on abdominal arteries supplying particular organs

Pelvic Viscera

Preganglionic path:   ventral root; spinal n.; ramus communicans; sympathetic trunk lumbar splanchnic nn.; caudal mesenteric plexus

Synapse caudal mesenteric ganglion (also, synapses in pelvic ganglia)

Postganglionic path:  hypogastric n.; pelvic plexus; branches directly to pelvic viscera (left/right)

Veterinary Female Genital Tract (Animal)

Female Genital Tract

 Ovary —  source of ova & hormones (estrogen and during a      

                        pregnancy progesterone (CL))

Uterine tube: ( Oviduct; “Fallopian tube” )

 - Exits laterally from uterine horn (extends cranially, arcs      

     ventrally, runs caudally, hooks dorsomedially)

-         Terminates medial to ovary in a funnel-shaped infundibulum  

that has fimbriae (villi) 

Uterus:

           1. Cervix  — short, thick muscular wall & narrow  canal

           2. Body  — relatively short in carnivores       

           3. Uterine horns — paired, relatively long

          

Vagina:

  - extends from the vestibule to a fornix at the level of the cervix

  - displays longitudinal folds when not expanded

 Vestibule: 

  - extends from vulval cleft to the transverse fold (hymen) that

     marks the vestibulo-vaginal junction

  - receives the external urethral opening, on a tubercle (dog) or in

     a slit (cat)

        

  - constrictor vestibuli m. (striated) is in the wall of the vestibule

         

  - the wall contains vestibular glands (mucous) — a major

     vestibular gland in the cat

        

-         in the dog, the wall contains an accumulation of erectile tissue = vestibular bulb

Clitoris:    homologue of the penis

         

  - located deep (cranial) to the fossa of the clitoris

  - composed of:  glans = erectile tissue

                             body = fat in a connective tissue capsule

                             crus  = scant erectile  tissue enclosed in        

                                         fibrous c.t.( right & left crura)

Vulva:

   - is composed of left & right labia which bound a vulval cleft

   - constrictor vulvae   m. (striated) is in the wall of each  labium      

   - an indentation, the fossa of the clitoris, is present ventrally

Ligaments associated with the female genital tract:

  1) suspensory ligament of the ovary — extends from ovary to

       dorsal body wall

  2) proper ligament of the ovary — extends between ovary &

       cranial end of uterine horn

  3) round ligament of the uterus — extends from cranial end of

       uterine horn thru inguinal canal

  4) broad ligament (lateral ligament of uterus), which has the

       following subdivisions:

           a) mesometrium;    b) mesovarium;    c) mesosalpinx

Veterinary Nervous System (Animal)

Nervous System  

Neuron = functional cell of Nervous System:

             — receives excitation (at a synapse or at a receptor);

             — conducts excitation (along an axon);

              transmits excitation (via release of chemical at a       

              synapse).

Most neurons are multipolar  — cell body is located where input

                                                     excitation occurs

Sensory neurons are unipolar — cell body is located along the

                                                     axon 

Definitions:

  Nerve = bundle of axons ensheathed by supporting cells and enveloped by connective tissue,.

  Root = nerve that is adjacent to the CNS and enveloped by meninges

Ganglion = localized site where a nerve is enlarged due to a collection of cell bodies:

        Spinal ganglia — contain unipolar cell bodies (located on

                                      dorsal roots of spinal nn.)

        Autonomic ganglia — contain multipolar cell bodies that

                                             innervate viscera.

Nervous System Divisions:

 Central (CNS): brain  and  spinal cord

  Peripheral (PNS): 12 pairs of cranial nerves (attached to brain);

36 pairs of spinal nerves in the dog & cat (attached to

spinal cord). [8 cervical; 13 thoracic; 7 lumbar; 3 sacral; & 5 caudal]

Spinal Nerve:

The spinal cord and spinal roots are located within the vertebral

canal of the vertebral column. Dorsal and ventral spinal roots unite toform a spinal nerve (bilaterally). Adjacent vertebrae combine to form an intervertebral foramen (dorsal to an intervertebral disc). The spinal nerve is found within theintervertebral foramen, from which it exits the vertebral canal.The spinal nerve is enveloped by connective tissue (epineurium,perineurium, & endoneurium). In contrast, the spinal cord and the dorsal and ventralspinal roots are surrounded by cerebrospinal fluid enclosed within meninges.

Spinal Nerve:  typical pattern

 — short (<1 cm); located at an intervertebral foramen

—   connected to the spinal cord by two roots (each comprised of

      rootlets):

dorsal root — composed of afferent (sensory) axons; the site of a

                        spinal ganglion

ventral root — composed of efferent axons that innervate muscle

                         & gland

                    — divides into four primary branches:

meningeal branch — small; sensory to meninges

ramus communicans — connects to sympathetic trunk & innervates viscera

ventral branch — largest branch; hypaxial mm. & lateral and ventral cutaneous nn.

dorsal branch — medial & lateral branches.; epaxial mm. & dorsal cutaneous nn.

Fiber types:  types of nerve fibers (axons) found in a spinal nerve and its branches

  • Afferent (sensory) — axons associated with receptors and unipolar cell bodies in spinal ganglia

General Somatic Afferent (GSA): receptors in skin & muscles, tendons, joints

General Visceral Afferent GVA): receptors in viscera

  • Efferent (motor) — axons that innervate muscle & gland;

 cell bodies are located in the spinal cord (or in some cases autonomic ganglia)

          Somatic Efferent (SE): innervates skeletal muscle

          Visceral Efferent (VE): innervates cardiac m., smooth m., &         

          gland

Cutaneous innervation:

Neck — series of dorsal and ventral cutaneous nn.

Thorax — series of  dorsal, lateral and ventral cutaneous nn.

Abdomen — series of dorsal and lateral cutaneous nn.

Limbs — individually named cutaneous branches of regional

                nerves thatoriginate from nerve plexuses (brachial or

                lumbosacral) to the limbs.

Face — named cutaneous branches of cranial nerves.

Brachial and Lumbosacral nerve plexuses:

Individual muscles are composed of multiple myotomes that overlap in forming the muscle.In the case of trunk muscles, which are generally broad, multiple dorsal or ventral branches of spinal

nerves can be seen to serially innervate each individual muscle. The innervations overlap within the muscle because of myotome overlap. In the case of limb muscles, each muscle is innervated by the branch of a single regional nerve. Because of multiple myotomes per muscle, the regional nerves must contain axons from ventral branches of multiple spinal nerves. The exchange of axons among ventral branches as they form regional nerves produces a nerve plexus for each limb.

Veterinary Pelvis and Perineum (Animal)

  Pelvis and Perineum

Pelvis  =  caudal region of trunk

                     The  pelvis consists of pelvic viscera within   pelvic                                         cavity that is bounded on five sides.

     

Pelvic Viscera:  

                                rectum & anal canal;  distal ureters, urinary  

                                bladder & urethra;

                                male or female genitalia;  blood vessels, 

                                lymphatics & nerves

 Pelvic Cavity Boundaries:

  cranial opening— pelvic inlet, bounded by sacrum, ilium &  

                                  pubis (rigid boundary)

   cavity walls— osseous pelvis + obturator & gluteal mm. &       

                            sacrotuberous ligament (dog)

     

   caudal boundary — perineum

Perineum  =    both a region & a wall

                                As topographic region:  from tail to scrotal  attachment or entire vulva; between ischiatic tuberosities.

As caudal wall of trunk: muscles,  fascia   &  skin  surrounding anal canal    and urogenital tract; includes

 1. Pelvic diaphragm = levator ani & coccygeus mm. associated

                                       deep fascia

2. Urogenital diaphragm = external urethral sphincter  associated    

                                               deep fascia                                                                                                                                                            3 External anal  sphincter m.

 4 Genital striated mm:

           

                 male    — bulbospongiosus m. & paired ischiocavernosus  

                                mm. 

                 female — constrictor vestibuli, constrictor vulvae &

                                  ischiocavernosus mm.

                                                 

 5. Smooth mm.: rectococcygeus  m.& retractor penis m.

  Micturition

Anatomy:

Urinary Bladder — apex; body; neck (trigone   = region of neck  demarcated by ureters & urethra).

Urethra — female: terminates in vestibule;

                      male: pelvic urethra  [preprostatic (cat); prostatic; &   

                       postprostatic regions] & penile urethra  

Musculature:

Detrusor m. = smooth muscle coat of apex & body; innervated by pelvic n  (S2 +S1 & S3 ) 

Internal urethral sphincter = smooth    m.; innervated hypogastric    n. (L2,  L3,  L4) 

               female   — vesical neck & cranial half of urethra 

               male      — neck (dog);  neck & preprostatic urethra (cat) 

External    urethral     sphincter   = urethralis m. (striated);       innervated  by pudendal n. (S2 & S3 + S1 ) 

               female — caudal half of urethra

               male — postprostatic urethra 

Urine Storage:

Sphincters  active via spinal  reflexes and detrusor    m. inhibited        

     - internal sphincter exerts tonic activity after bladder is half full 

     - external sphincter is activated voluntarily or reflexly during          phasic pressure increase

Micturition:

Requires prolonged detrusor contraction and sphincter inhibition 

    - free nerve endings (receptors) —>    GVA fibers in pelvic n.          —>   ascending          pathways —> pons —> descending spinal pathways —> activate detrusor & inhibit sphincters

Pain:

GVA pain   fibers travel through the hypogastric nerve to reach the spinal cord and brain.