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Comparative Anatomy
Exam 6 @ MO State
Undergraduate 4

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Circulatory System Functions
-Transportation of materials that are needed for the sustenance and activity of cells, including oxygen and food materials

-Removal of metabolic waste products from cells, including carbon dioxide, nitrogenous wastes and excess metabolic water

-Transportation of hormones from one organ to another

-Transportation of substances produced by the immune system

-Transportation of heat
Circulatory System Components
The blood-vascular system and the lymphatic system

Blood-vascular system


Anatomical Structures: 

-Heart: muscular pumping organ
-Arteries: vessels that carry blood from the heart to the body tissues; arteries have very muscular and elastic walls because of the high pressure exerted by the blood immediately after leaving the heart
-Veins: vessels that return blood from the tissues to the heart; Veins have much thinner walls because of reduced blood pressure.  Surrounding muscles may squeeze the veins, helping to propel the blood back to the heart.  Veins have one-way valves to prevent   backflow.
-Capillaries (Fig. 12.4): a network of vessels within the tissues that connect small arteries (arterioles) and veins (venules); physiological exchange between blood and tissues takes place through the thin walls of the capillaries.


Components of Blood:



-Plasma: 90% water - 10% dissolved solids (proteins, glucose, fat, amino acids, ions, enzymes, antibodies, hormones, waste products).
-Red blood cells (erythrocytes), specialized for oxygen transport (hemoglobin is the oxygen-binding protein). 
    -Shape: Nonmammales—oval with nuclei; mammals—concave and anucleate.
    -Site of production:  liver and spleen; in mammals,  the bone marrow is also an important
Embryonic blood formation
-Blood islands (Figure 12.7) form within the mesoderm

-Blood islands link together forming blood vessels and cells
Development of the heart
-> Develops from the splanchnic layer of the hypomere  (mesoderm) that is just posterior to the pharynx and ventral to the gut.

-> The embryonic heart has two primary layers (Fig. 12.8c):

• Endocardium: internal; composed of a thick layer  of connective tissue under an endothelial lining.

• Myocardium: muscle of the heart

Taxonomic comparisons of the heart


Primitive condition





-> Fishes (Fig. 12.26): a straight or curved tube with four chambers: Sinus venosus, atrium, ventricle, conus.  It pumps a single stream of unoxygenated blood forward to gills and then to the body tissues (Fig. 12.6a). 
-> Lungfishes, Amphibians, and Reptiles (Fig.s 12.30a) 
•  Two atria and a single ventricle (note: crocodilians have 2 ventricles).  The sinus venosus and conus are somewhat reduced.   
• Atria receive blood that is both oxygenated (from lungs) and deoxygenated (from body tissues).  The 2 streams are kept largely separate in the ventricle in trabeculae (amphibians; Fig. 12.30a) or cavae (reptiles; Fig. 12.32b).

Taxonomic comparisons of the heart


Birds and Mammals 

-> 2 atria and 2 ventricles, separating oxygenated and deoxygenated streams
-> Right side: low-pressure pulmonary circuit (Fig. 12.6b)
      Left side: high-pressure systemic circuit (larger ventricle) (Fig. 12.6b)
-> Blood flow: right atrium-> right ventricle-> pulmonary artery-> lungs-> pulmonary veins-> left atrium-> left ventricle-> aorta
-> Sinus venosus: birds – vestigial; mammals—merged with right atrium.
-> Conus arteriosus: divides into a pulmonary trunk joining the right ventricle and a systemic trunk joining the left ventricle.
Aortic Arches
Primitive number of pairs: The exact number is the subject of debate, but probably was somewhere between 6 and 10 (Fig. 12.12). Embryologically, there are 6 pair, and numbers below coincide with the number of embryological pairs (See Fig. 12.13).
Aortic Arches of Fishes
- Ventral aorta takes de-oxygenated blood away from the heart
- Afferent arteries branch off, taking blood to the gills
- Blood flows through capillaries in the gills through collector loops and then into efferent arteries
- The number of aortic arches supplying the gills varies from 4 (most ray-finned fishes) to 15 (hagfishes)    
- Oxygenated blood leaves the gills and travels to the heart via the external and internal carotid arteries and to the rest of the body through paired dorsal aortae
- Lungfishes are the only fishes with a separate pulmonary circuit.  In lungfishes the efferent vessel of the last arch (VI) gives rise to the pulmonary artery (Fig. 12.14b).
Aortic Arches of Amphibians
- Arches I and II disappear early in development
- In larvae, the next 3 arches (III-V) supply the gills and the last arch (VI) forms the pulmonary artery (Fig 12.14C)
- In metamorphosed adults (Fig. 12.14 D & E):
-> The section of dorsal aorta between arches III and IV closes, so that the carotid arteries are fed by the ventral aorta; this section of ventral aorta becomes the common carotid artery
-> The next two arches (IV and V) form major systemic vessels that join the dorsal aorta
-> The last arch (VI) may (salamanders) or may not (frogs) retain the connection to the dorsal aorta
-> The last arch (VI) develops a branch which becomes the pulmonary artery

Aortic Arches of




- Arches III, IV, and VI persist (I, II, and V disappear)
- The ventral aorta splits during development, forming the left aortic arch, the right aortic arch, and the pulmonary trunk
- Arch IV forms left & right systemic arches that unite behind the heart to form the common dorsal aorta
- Therefore, reptiles have one pulmonary circuit and two systemic circuits, each of which arises independently from the heart

Birds - right systemic arch becomes predominant; left never fully develops

Mammals - The left systemic arch becomes predominant
Lymphatic system
Collects fluids ("lymph") that have accumulated in the tissues due to diffusion, osmosis and the hydrostatic pressure produced by the heart.
Lymphatic vessels, hearts, and nodes
- Lymphatic vessels (Fig. 12.47a).  These vessels empty into veins at various locations in the body.
- Lymphatic hearts (found in fishes, amphibians, reptiles and embryonic birds): muscular swellings within the lymphatic vessels that help propel lymph  though the vessels.
 - Lymph nodes (Fig. 12.47a) (found in birds and mammals): filters the lymph of bacteria and foreign particles which are ingested by phagocytes; also filter out cancerous cells, although these cannot be broken down.  Lymph nodes are hemopoietic ("blood forming"), producing the white blood cells known as lymphocytes (phagocytic).
Lymphoid masses
    -> Spleen: formation, storage and destruction of blood cells (including rbc and some wbc in mammals, only lymphocytes are produced by the spleen); also functions in phagocytosis of infectious materials. 
     -> Thymus: rapid production of lymphocytes during development and early life and in the establishment of immune reactions.
    -> Bursa of Fabricius: found only in birds; develops as a dorsal pouch off of the cloaca; functions similar to the thymus.
    -> Tonsils: found in amphibians and in many mammals; lymphocytic function
    -> Peyer's patches: knots of lymphoid tissue in the walls of the intestine and, in some taxa, in the walls of the appendix.
Cell body

an oval or star-shaped body containing the nucleus and distinctive granules

(nissl granules) that contribute to a high rate of protein synthesis (Fig. 16.2)


bodies have one, (unipolar), two (bipolar) or more (multipolar) filamentous processes 

- Dendrites are processes that receive impulses from other dendrites or directly from sense organs  (Fig. 16.2)

- Impulses are transmitted away from dendrites (and the nerve cell body) by a single process, the axon (Fig. 16.2).  Axons may be very short or as long as one meter (!).  They branch less than dendrites, but may give off collaterals and usually have short branches called telodendria at their far ends where they communicate with other cells.

- In vertebrates, the length of the axons of neurons are usually sheathed with insulating cells (Figure 16.4b)
    -Schwann cells: in peripheral nerves
    -Oligodendroglia on nerves within the brain and spinal cord     
- The insulation is formed a coating called myelin (Figure 16.4b). 

- Unmyelinated portions, called nodes of Ranvier, occur at intervals.  (Figure 16.4b)

- The entire axon is covered by a second sheath (external to the myelin) called the neurilemma.

nerve impulse


- A nerve impulse is an electrical phenomenon that proceeds as a wave of depolarization down the axon.  Because the myelin insulates the axon, the impulse skips from node (of Ranvier) to node, greatly increasing the speed of the transmission (critical for large animals).
- The functional union of an axon of one neuron with a dendrite or nerve cell body of another neuron is called a synapse (Figure 16.5).  Some neurons have few synapses, others have thousands.



- The axon telodendria releases chemicals called neurotransmitters (Figure 16.5) that alter the permeability of the dendrite to the ions bathing it, resulting in depolarization of the dendrite and propagation of the nerve impulse.  Neurotransmitters include acetylcholine, noradrenalin, serotonin, dopamine and many others.  

- Within the brain and spinal cord, neurons typically are in contact with supporting cells called neuroglia that function in ion transport, nutrition, excretion, regeneration and repair of neurons.  The 4 types of neuroglia are astrocytes, oligodendroglia, microglia and ependymal cells.

Groups of nerves



white/gray matter


    - Functionally related neurons mass together forming bundles of parallel fibers called tracts within the spinal cord.
    - Myelinated tracts =white matter, whereas nerve cell bodies and associated unmyelinated fibers=gray matter.  Gray matter is found in the center of the nerve cord with the white matter surrounding it (Figure 16.7).
    - Outside of the brain and spinal cord, groups of fibers are supported by a membrane called the perineurium.  Several bundles of fibers which are enveloped by a tough epineurium make up a nerve (no figure)
Some divisions of the nervous system
    - The brain and spinal cord comprise the central nervous system (CNS).
    - The nerves and ganglia comprise the peripheral nervous system (PNS).
    - Afferent (or sensory) fibers of the PNS carry impulses from receptor organs to the CNS.  Efferent (or motor) fibers carry impulses from the CNS to effector organs (often muscles).  Nerves are sensory, motor, or mixed.
    - Some association neurons (aka interneurons) make up local circuits within the CNS and are not themselves afferent or efferent.
    - Somatic fibers (sensory and motor) related to the skin and its derivatives and to voluntary muscles.  Visceral fibers (sensory and motor) relate to involuntary muscles and glands.  Visceral fibers comprise the autonomic system.
Spinal Nerves of
->  Dorsal and ventral nerves do not join.

->  Distribution of fibers:

--Dorsal spinal nerves: contain all sensory fibers and visceral motor fibers.               
--Ventral spinal nerves contain only somatic motor fibers.
Spinal Nerves of
Fishes, and Amphibians
->  Dorsal and ventral roots join outside the vertebral column.

->  Close beyond the union of the dorsal and ventral  roots, the spinal nerve divides into a dorsal ramus that goes to structures of epaxial origin, a ventral  ramus that goes to the appendages and structures of  hypaxial origin

->  Distribution of fibers: similar to lamprey
Spinal Nerves of
->  Dorsal and ventral roots join inside the vertebral column.

->  Distribution of fibers:

    -Dorsal roots: contain sensory fibers

    -Ventral roots: contain motor fibers

->  Brachial and lumbosacral plexi tend to be more complex.


Cranial Nerves

Most cranial nerves evolved from dorsal and ventral roots of anterior spinal nerves
Numbered nerves
-Fishes: 10 (+1)
-Sarcopterygians/early amphibians: 12 (+1)
-Modern amphibians: 10 (+1)
-Reptiles, birds, mammals 12 (reptiles, mammals: +1)
-The terminal nerve at the anterior end is numbered "0" (it was discovered after the conventional number system was firmly established).
- Dorsal root derivatives:
-Terminus (0): innervates some of the olfactory epithelium.
-Trigeminal (V): Formed of 3 branches (in amniotes): ophthalmic, maxillary, and mandibular; innervates derivatives of the mandibular (first) arch
-Facial (VII): innervates derivatives of the hyoid (second) arch
-Glossopharyngeal (IX): innervates derivatives of the third gill arch
-Vagus (X): innervates mouth, pharynx, and viscera ("vagus" is Latin for "wandering").
-Spinal Accessory (XI): innervates derivatives of the cucullaris (cleidomastoid, sternomastoid and trapezius)
- Ventral root derivatives:
-Oculomotor (III): innervates several extrinsic eye muscles.
-Trochlear (IV): innervates an extrinsic eye muscle
-Abducens (VI): innervates an extrinsic eye muscle
-Hypoglossal (XII): Innervates hyoid and tongue muscles

Other nerve derevations

and origins 

- Olfactory (I), optic (II) and auditory (VIII) nerves: derived separately in conjunction with their respective sense organs

- Cranial nerves arise from the following regions of the brain (Fig. 16.14):
         -> Forebrain: Nerves I and II
         -> Midbrain: Nerves III and IV
         -> Hindbrain: Nerves V – XII
I    Olfactory                  On
II   Optic                        Old
III  Oculomotor             Olympus'
IV  Trochlear                 towering
V    Trigeminal               top
VI    Abduscens             a
VII    Facial                   Finn
VIII   Auditory               and
IX     Glossopharyngeal   German
X      Vagus                   vent
XI      Spinal                  some
XII     Hypoglossal          hopps
On old Olympus' towering top a Finn and German vent some hopps!

The Brain




Anterior end of nerve cord

Anterior end of nerve cord forms vesicles separated by constrictions:
->  Forebrain or prosencephalon (anterior to the notochord)
->  Midbrain or mesencephalon  (dorsal to the notochord)
->  Hindbrain or rhombencephalon (dorsal to the notochord)

The Brain Functions

Hindbrain and Midbrain 

1) Hindbrain: Forms 1st; little taxa variation; similar to spinal cord structure.  
- Medulla: controls vegetative functions of the body, including auditory activity,  heartbeat, respiration and intestinal motility.
- Cerebellum: coordinates motor functions.
- Pons: a crossroads for information flow.
2) Midbrain: Roof is the tectum (= the colliculi in mammals); sensory input
            - Floor is the tegmentum; initiates motor output.  is Most prominent region in fishes and amphibians
Brain Membranes
(“meninges”) surround the brain and spinal cord: derived from neural crest cells. (Fig. 16.26)
- Fishes: one membrane, the primitive meninx (meninx is the singular of meninges)
- Amphibians, reptiles, and birds: two membranes
•dura mater (derived from mesoderm): tough outer layer
•secondary meninx: thin, inner layer
- Mammals: three membranes:
•dura mater
•arachnoid mater
•pia mater

Componants of Blood



-White blood cells (leukocytes)much less  numerous than RBC's and include granular  (eosinophils, basophils neutrophils) and agranular (lymphocytes, monocytes) cells.  Function in immune and allergic responses.
-Thrombocytes are associated with the process of blood clotting.
    -Nonmammals: called spindle cells; small, oval structures with central nuclei which  appear to be related to WBC's.
    -Mammals: called Platelets;  anuclear and are formed by the fragmentation of giant cells called megakaryocytes.

The Brain Functions


3) Forebrain  - Cerebrum; controls voluntary motor responses, decision-making, memory; phylogenetic trend: becomes larger
- Thalamus (Hypo-, ventral and dorsal): coordinates sensory neurons
    -Pineal gland:  anamniotes: affects skin pigmentation and detects light changes; amniotes: regulates biological rhythms

The Brain



secondary vesicles 

Additional constrictions divide the brain further into five secondary vesicles.
->  Telencephalon: anterior part of prosencephalon; cerebral hemispheres
->  Diencephalon: posterior part of prosencephalon.
->  Mesencephalon remains undivided.
->  Metencephalon: anterior end of  rhombencephalon; cerebellum and pons
->  Myelencephalon: posterior part of the rhombencephalon; medulla.
The neurocoel forms expansions within the vesicles called ventricles. 

Groups of nerves:




    - Aggregates of nerve cell bodies cause swellings on nerves and are termed ganglia in the PNS and nuclei in the CNS.  
    - Adjacent to the appendages, adjacent nerves usually exchange bundles of fibers thus weaving to form a plexus.
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