chp. 14: circulatory system

circulatory system consists of

blood, blood vessels, and a muscular, pumping heart.

blood

a connective tissue made of:

• Formed elements (cellular part)

  • erythrocytes, leucocytes, and thrombocytes

• Plasma (extracellular part)

  • plasma proteins (albumen, globulins, fibrinogen)

formed element of blood

the cellular component of blood

3 types:

1. Erythrocytes (Red Blood Cells)

   • Most numerous blood cell.

   • Contain hemoglobin, which carries oxygen.

2. Leukocytes (White Blood Cells)

   • Protect the body from infection.

   • Two categories:

     • Granular leukocytes → neutrophils, eosinophils, basophils

     • Agranular leukocytes → lymphocytes, monocytes

3. Thrombocytes (Platelets)

   • Cell fragments involved in blood clotting.

formed by Hemopoiesis

erythrocytes

• a subclass of the formed element of blood

RED BLOOD CELLS

• they are the most numerous type of blood cell

• contain hemoglobin to carry oxygen

leucocytes

• a subclass of the formed element of blood

WHITE BLOOD CELLS

• Protect the body from infection.
  
  Two categories:

  • Granular leukocytes → neutrophils, eosinophils, basophils

  • Agranular leukocytes → lymphocytes, monocytes

agranular leukocytes

a subclass of leukocyte in the formed element of blood

includes

• lymphocytes (T and B cells)

• monocytes

granular leukocytes

a subclass of leukocyte in formed element of blood

Includes:

• neutrophils (most abundant + can tell gender)

• eosinophils

• basophils

thrombocytes

• a subclass of the formed element of blood

THE PLATELETS

• involved in the clotting response

Hemopoieses/Hematopoiesis

formation of all formed elements.

1. During embryonic/fetal development, hemopoiesis occurs in:

   • yolk sac, liver, spleen,  thymus, lymph nodes,  bone marrow

2. In adults, hemopoiesis occurs mainly in red bone marrow.

   • Found in: sternum, vertebrae, ribs, pelvis.

   • Agranulocytes leave the red marrow and finish maturing in lymphoid tissues (thymus, lymph nodes, tonsils).

   • Because red marrow produces formed elements, it is called myeloid tissue

agrunolocytes

a type of white blood cell that will migrate out of red marrow and mature elsewhere in lymphoid tissues (thymus, lymph nodes, tonsils).

myeloid tissue

red bone marrow!!

called this cuz red marrow produces all the  formed elements in adults

hemocytoblasts

undifferentiated stem cells of red bone marrow that become hemocytoblasts.

• are multipotent and form five stem cell lines that produce all formed elements.

plasma

extracellular component of the blood

liquid component of blood.
Mostly water, plus:

• nutrients, gases, hormones, electrolytes, wastes and

• plasma proteins, which include:

  • Albumen → contributes to blood viscosity

  • Globulins → include immunoglobulins (antibodies)

  • Fibrinogen → inactive form of fibrin, required for clotting

plasma proteins

the proteins of the blood

• in plasma (extracellular)

Include:

• Albumen → contributes to blood viscosity

• Globulins → include immunoglobulins (antibodies)

• Fibrinogen → inactive form of fibrin, required for clotting

albumen

• a type of plasma protein in plasma (liquid extracellular component of blood)

contributes to blood viscosity

globulins

• a type of plasma protein in plasma (liquid extracellular component of blood)

include immunoglobulins (antibodies)

fibrinogen

• a type of plasma protein in plasma (liquid extracellular component of blood)

inactive form of fibrin, the protein required for clotting

fibrin

protein req. for blood clotting

blood vessels

hollow organs that carry blood throughout the body.

3 types:

• arteries ( carry blood from heart to tissues of bod)

• veins (carry blood back to heart from tissues

• capillaries 

blood vessel tunics

have 3 layers (tunics):

1. Tunica Intima (Tunica Interna)

   • Innermost layer; touches the blood.

   • Made of endothelium on top of areolar c.t

2. Tunica Media

   • Middle layer; contains smooth muscle.

   • Thickest layer in arteries.

3. Tunica Externa (Tunica Adventitia)

   • Outermost layer; mostly loose connective tissue.

   • Contains small blood vessels called vasa vasorum, which supply nutrients to large arteries and veins.

tunica intima

innermost layer of blood vessels

• in direct contact w/ blood.

• Made of endothelium on top of areolar connective tissue.

tunica media

middle layer of blood vessels

• contains smooth muscle.

• Thickest layer in arteries!!!!

tunica externa/tunica adventitia

outermost layer of blood vessels

• composed of loose connective tissue.

• Contains small blood vessels called vasa vasorum, which supply nutrients to large arteries and veins.

  • These vessels enter the adventitia, the media, and sometimes partly the intima.

vasa vasorum

these r on the tunica advintitia/ externa 

are v small blood vessels that supply nutrients to large arteries and veins.

• These vessels enter the adventitia, the media, and sometimes partly the intima.

• “blood vessel of the blood vessel”

arteries

a blood vessel that carry blood from the heart to body tissues.

• Carry blood at high pressure, so they have the thickest walls.

• Tunica media(muscular layer) is thickest layer, filled with elastic fibers and/or muscle fibers.

3 subclasses (largest → smallest):

1. Elastic arteries

2. Muscular arteries

3. Arterioles

   • Smallest arteries.

   • Deliver blood into capillary beds

arterioles

the smallest arteries and deliver blood into capillary beds

• Entrance to each capillary bed is guarded by a precapillary sphincter (a circular muscle at the end of an arteriole).

  • Controls which organs receive blood based on metabolic needs.

  • When closed, blood bypasses the capillary bed through an arteriovenous shunt.

precapillary sphincter

guards the entrance into the capillary bed

• a circular cuff of muscle located on terminal arteriole

• Controls blood flow and which organs receive blood based on metabolic needs.

• When closed, blood bypasses the capillary bed through an arteriovenous shunt.

  • an abnormal or surgically created connection between an artery and a vein

capillaries

microscopic blood vessels where exchange occurs between blood and tissues.

• Very thin-walled for diffusion.

• ONLY made of endothelium LACK THE 3 TUNICS!!!!!

types of capillaries:

• Continuous Capillaries

  • Most common.

  • Endothelial cells form uninterrupted rings.

• Fenestrated (Discontinuous) Capillaries

  • Have pores (fenestrae) where cytoplasm is absent.

  • Allow easier diffusion.

• Sinusoids

  • Similar to capillaries but:

    • Wider lumen

    • Fenestrae guarded by macrophages

  • Still microscopic, still used for exchange.

continuous capillaries

• the most common and numerous subclass of capillaries

Endothelial cells form uninterrupted rings.

fenestrated/discontinuous capillaries

• a type of capillary

Have pores (fenestrae) in endothelial walls where cytoplasm is absent.

• Allow easier diffusion.

sinusoids

microscopic blood vessels found in certain regions that may or may not be true capillaries

like capillaries:

• microscopic

• involved in exchange of materials

• have wall of endothelium

unlike capillaries:

• have wider lumen

• their fenestrae (pores) are guarded by macrophages

Veins

Veins carry blood back to the heart from the tissues

• Thinner walls than arteries because they carry low-pressure blood.

Subclasses:

1. Venules

   • First vessels to receive blood from capillary beds.

   • Very thin walls; small venules may lack all three tunics.

2. True Veins (small → medium → large)

   • Wall thickness increases as blood approaches the heart.

   • Tunica externa is the thickest tunic, rich in collagen.

   • Blood pressure remains much lower than in arteries.

Important feature:

• Veins contain numerous valves to prevent backflow due to low pressure.

venules

smallest subclass of vein

• First vessels to receive blood from capillary beds.

• Very thin walls; small venules may lack all three tunics.

• this is when blood is at its LOWEST PRESSSURE

venules drain into “true veins”

vein bloodflow

blood drains from capillaries to very small venules where its at its lowest pressure

venules then drain intro “true veins” which can be small, medium, and large

• Wall thickness and blood pressure gradually increases as blood approaches the heart.

• Tunica externa is the thickest tunic, rich in collagen.

• Blood pressure in veins remains much lower than in arteries.

veins have valves to prevent backflow of blood

valves

Veins contain numerous valves projecting into lumen to prevent backflow due to low pressure.

• only in veins NOT arteries!

heart

a muscular pump

• It sits in the Pericardial Cavity and is surrounded by the Pericardium, a serous membrane.

pericardium

serous membrane covering heart

heart wall layers

1. Endocardium – inner lining; includes endothelium.

2. Myocardium – middle, thickest layer; rich in cardiac muscle, provides pumping force.

3. Epicardium – outer layer made of connective tissue and a serous membrane.

• The heart receives its own blood through coronary vessels.

endocardium

inner lining of heart wall

• contains endothelium

myocardium

the middle and THICKEST layer of the heart wall

• composed of cardiac muscle to pump blod

epicardium

outer layer of the heart wall

• composed of c.t. and a serous membrane

single circuit hearts (fish)

• Blood travels heart → gills → body → heart.

• Gills oxygenate the blood; tissues use the oxygen; deoxygenated blood returns to heart.

• This forms one continuous loop (single circuit).

double circuit hearts (amniotes)

2 separate pathways:

1. Pulmonary Circuit

   • Carries deoxygenated blood → lungs

   • Returns oxygenated blood → heart

2. Systemic Circuit

   • Carries oxygenated blood → body tissues

   • Returns deoxygenated blood → heart

pulmonary circuit

• one of the circuits in the double circuit heart

Carries deoxygenated blood → lungs to pu oxygen

Returns oxygenated blood → heart

systematic circuit

• one of the circuits in the double circuit heart

Carries oxygenated blood → body tissues

Returns deoxygenated blood → heart

Fish Hearts (Gill-Breathers, except Dipnoans)

fish have 2-chambered hearts: one atrium + one ventricle

Fish have 4 sequential structures:

1. Sinus Venosus – receives deoxygenated blood

   • Very little contraction; blood enters due to ventricular pressure

   • Blood passes through sinoatrial aperture (2 unidirectional valves)

2. Atrium – thin-walled muscular chamber

   • receives blood from sinus venosus to push to ventricle

3. Ventricle – thick-walled major pump

   • Main force for fish circulation

   • Sends blood to the conus arteriosus

4. Conus Arteriosus – leads blood to the gills

   • Has cardiac muscle + elastic CT

   • Contains semilunar valves to prevent backflow

   • Large in cartilaginous fishes; short in teleosts

sinus venosus

receives deoxygenated blood

• Thin-walled w/ little muscle, mainly fibrous CT

• Very little contraction; blood enters due to ventricular pressure

• Blood passes through sinoatrial aperture (2 unidirectional valves)

NOT IN MAMMALS OR BIRDS!

• ancestral location of sinus venosus in mammals is marked by location of the sinoatrial node

sinoatrial aperture

blood travels from the sinus venosus through the sinoatrial aperture into the atrium

• is guarded by a pair of unidirectional valves

• blood moves to atrium when atrium relaxes after emptying

atrium

thin-walled muscular chamber

receives blood from the sinus venosus and pushes it into ventricle

• Pushes blood through the atrioventricular aperture (also 2 valves) into the ventricle

atrioventricular aperture

inbtwn atrium and ventricle

• guarded by pair of unidirectional valves

ventricle

muscular thick-walled major pump

• Main pumping chamber of the heart!

• Sends blood to the conus arteriosus

• generates main force for fish

conus arteriosus

receives blood from the ventricle and conducts it to the gills

• Has cardiac muscle + elastic CT

• Contains semilunar valves to prevent backflow of blood back into ventricle

• Maintains steady blood pressure to ventral aorta

• Large in cartilaginous fishes; short in teleosts

  • Teleosts compensate with a muscular Bulbus Arteriosus

semilunar valves (in fish)

prevent backflow of blood going back to ventricle in the conus arteriosus

bulbus arteriosus

since bony fishes have a shorter conus arteriosus, they compensate with a muscular Bulbus Arteriosus

Dipnoan and Amphibian Hearts

Modified for air-breathing, allowing separation of oxygenated and deoxygenated blood.

Four Key Modifications:

1. Interatrial Septum (partial or complete)

   • Separates right and left atria

   • Left atrium receives oxygenated blood from lungs/swim bladder

   • Right atrium receives deoxygenated blood from sinus venosus

2. Interventricular Septum (partial) or Ventricular Trabeculae

   • Both reduce mixing of oxygenated/deoxygenated blood

3. Spiral Valve in Conus Arteriosus

   • Separates oxygen/deoxblood

   • Routes oxygenated blood → systemic arches

   • Routes deoxygenated blood → lungs or gills

4. Shortened Ventral Aorta

   • Blood goes straight from conus arteriosus to the correct vessel

   • Urodeles are the exception—they keep a prominent ventral aorta

interartial septum

• modification of amphibian heart from fish heart (adapted to land)

separates right and left atriums

• Complete in anurans, some urodeles

• Absent in lungless urodeles

• Left atrium receives oxygenated blood from lungs/swim bladder

• Right atrium receives deoxygenated blood from sinus venosus

Interventricular Septum (partial)/ Ventricular Trabeculae

• modification of amphibian heart from fish heart (adapted to land)

Both reduce mixing of oxygenated/deoxygenated blood. separates right and left ventricles

• Partial septum: dipnoans, sirens

• Trabeculae: most amphibians (ridges inside ventricle)

spiral valve

• modification of amphibian heart from fish heart (adapted to land) ONLY IN AMPHIBIANS

established spiral valve in cornus arteriosus to separate deoxygen/oxygen blood

• Routes oxygenated blood →aortic archesthat go to tissues

• Routes deoxygenated blood → lungs or gills

• Found in dipnoans and anurans

Shortened Ventral Aorta

• modification of amphibian heart from fish heart (adapted to land)

Blood goes straight from conus arteriosus to the correct vessel

• Urodeles are the exception—they keep a prominent ventral aorta

heart in amniotes

4-chambered hearts: 2 atria + 2 ventricles

• Turtles and squamates have a third ventricle (Cavum venosus)

• Birds and mammals lack a sinus venosus

  • Their veins dump directly into right atrium

  • The Sinoatrial node marks the ancestral sinus venosus position 

• Crocodilians partially incorporate sinus venosus into right atrium

atria (atriums) in amniotes

Separated by a complete interatrial septum in all amniotes

• Embryos have a temporary opening: Foramen Ovale

  • Closes before birth/hatching

  • Adult remnant in mammals = Fossa Ovalis

• Right atrium receives deoxygenated blood

  • From sinus venosus (reptiles) or

  • From superior/inferior vena cava (birds & mammals)

• Left atrium receives oxygenated blood via pulmonary veins

• Mammals have atrial outpocketings called auricles

foramen ovale/foramen ovalis

mbryos have a temporary opening: Foramen Ovale

• Closes before birth/hatching

• Adult remnant in mammals = Fossa Ovalis

right atrium

receives deoxygenated blood

• From sinus venosus (reptiles) or

• From superior/inferior vena cava (birds & mammals)

left atrium

Left atrium receives oxygenated blood via pulmonary veins

superior/inferior vena cava

the two largest veins in the body that collect deoxygenated blood from body and return it to the heart's right atrium

pulmonary veins

a vein carrying oxygenated blood from the lungs to the left atrium of the heart

auricles

the atriums in mammals have outpocketings 

ventricles in amniotes

• Crocodilians, birds, mammals: complete interventricular septum → true 4-chambered heart

• Most reptiles: incomplete septum → 3-chambered heart

  • Turtles + squamates have extra chamber: Cavum Venosus

    • Helps separate oxygenated vs. deoxygenated blood

IN MAMMALS: As the heart develops, the conus arteriosus is absorbed into the right ventricle

cavum venosus

3rd ventricle in hearts of turtles and scaled reptiles

• helpes separating deoxygen/oxygen blood

cardiac muscle in amniotes

All chambers use cardiac muscle

• Ventricles have more muscle (pump farther than atria)

• Ventricular walls reinforced by Trabeculae Carnae (interlacing ridges)

trabeculae carnae

muscular ridges and columns on the inner surfaces of the heart's ventricles. 

• These structures provide support

heart valves

Prevent backflow of blood

• each valve has flaps of fibrous c.t. called cusps

1. Atrioventricular (AV) Valves – between atria and ventricles

   • Mammals: attached via Chordae Tendineae to Papillary Muscles

2. Semilunar Valves – at exits of ventricles

   • Prevent backflow from aorta and pulmonary trunk

atrioventricular valves

between atria and ventricles

• Mammals: attached via c.t strands called Chordae Tendineae to Papillary Muscles (bundles of smooth muscle)

chordae tendinae

anchored c.t. strands in the heart that prevent backflow of blood by anchoring the atrioventricular (AV) valves

papillary muscles

connect to the mitral and tricuspid (atrioventricular) valves via tough fibrous cords called the chordae tendineae

• bundles of smooth muscle

semilunar valves in amniotes

two semilunar valves are the aortic valve and the pulmonary valve

• prevent the backflow of blood from the arteries back into the ventricles

semilunar valves in amniote vs fish

Fish:

• Many small semilunar valves in the conus/bulbus arteriosus.

• Prevent backflow into the single ventricle in a single-circuit system.

Amniotes:

• Two major semilunar valves (aortic & pulmonary), each with three cusps.

• Prevent backflow into ventricles in a double-circuit system.

innervation of heart

• Cardiac muscle is naturally rhythmic and can beat on its own.

Specialized cardiac muscle, called nodal tissue, controls and coordinates the heartbeat.

• The ANS (autonomic nervous system) adjusts heart rate based on the body’s needs.

nodal tissue

specialized cardiac muscle that controls and coordinates the heartbeat

• ANS stimulates nodal tissue for needs

development of innervation in Fish, Amphibians, Reptiles

• Keep the sinus venosus throughout life. ANS nerves grow into sinus venosus

ANS signals → received by sinus venosus → atria → ventricles → conus arteriosus (if present).

development of innervation in birds and mammals

Lose the sinus venosus, remains only as mass of nodal tissue called the Sinoatrial node in the right atrium!

• SA node gets ANS input and fires:

  • Sends depolarization through both atria → they contract.

  • Also activates the Atrioventricular node.

• Atrioventricular node sends depolarization through both ventricles → they contract.

• Ventricles use special conduction fibers (including Purkinje fibers) to spread the signal quickly.

sinoatrial node

in BIRDS AND MAMMALS this is what’s left of sinus venosus and is in the right atrium

• receives ANS innervation!

IS HEART’S PACEMAKER!

Sinoatrial node gets ANS input and fires:

• Sends depolarization through both atria → they contract.

• Also simultaneously activates the Atrioventricular node.

atrioventricular node

cluster of nodal tissue in right atrium

• sends depolarization through both ventricles → they contract.

conducts electrical signals from the atria to the ventricles, ensuring coordinated contractions

• stimulated by sinoatrial node

Purkinje fibers

specialized muscle fibers in the heart that rapidly conduct electrical impulses from the atrioventricular (AV) node to the ventricles, ensuring synchronized and efficient contraction

General Pattern of Arteries

Arteries carry oxygenated blood from the heart to body tissues.

• Exception: Pulmonary arteries carry deoxygenated blood to the lungs.

pulmonary arteries

only artery that carries deoxygenated blood instead of oxygenated blood cuz its carrying it to lungs

• the artery carrying blood from the right ventricle of the heart to the lungs for oxygenation.

primitive gnathostomes arterial channels

1. A ventral aorta under the pharynx emerging from heart.

2. A paired dorsal aorta above the pharynx that becomes single farther back.

3. 6 pairs of aortic arches connecting the ventral and dorsal aortae.

aortic arches in sharks

Ventral aorta grows forward and connects to developing arches.

• 6 pairs form, but changes occur:

  • 1st arch disappears early, leaving spiracular arteries.

  • 2nd arch forms first pretrematic arteries.

  • 3rd–6th arches form buds → posttrematic arteries, which also form more pretrematic arteries.

• Later, arches 2–6 develop occlusions (gaps):

  • Ventral segments → afferent branchial arteries (carry blood to gills).

  • Dorsal segments → efferent branchial arteries (carry blood away from gills).

• Gill capillaries form in demibranchs.

spiracular arteries in shark form from

first aortic arch

• 1st arch disappears early, leaving spiracular arteries.

first pretrematic arteries form from

form from second pair of aortic arches in sharks

postrematic arteries form from

from 3rd–6th aortic arches in sharks form buds → posttrematic arteries, which also form more pretrematic arteries.

afferent branchial arteries (fish)

arise from Ventral segments

(carry blood to gills)

efferent branchial arteries (fish)

arise from dorsal segments

(carry blood away from gills).

aortic arches in teleosts

Same basic pattern as sharks, but:

• # of afferent/efferent branchial arteries depends on number of gills.

• Usually arches 1 and 2 disappear.

aortic arches in dipnoans

Pulmonary artery develops from the right & left 6th aortic arch

• same pattern as tetrapods!

aortic arches in tetrapods

Embryos start with 6 pairs, like fishes.

• 1st and 2nd arches disappear early.

• 3rd arches + paired dorsal aorta → internal carotid arteries (“carotid arch”).

• 5th arch is lost in most amniotes.

• 6th arch → pulmonary arteries.(same as dipnoans)

internal carotid artery

• develops from the 3rd aortic arch in tetrapods!

a major artery in the neck that supplies oxygen-rich blood to the brain, eyes, and face

dorsal aorta

a paired embryonic (not in adults) blood vessel that eventually fuses into the single, descending aorta, which is the body's largest artery

• Embryonic vertebrates: dorsal aorta is paired.

  • Paired in the head → internal carotids.

  • single dorsal aorta becomes the main systemic artery and gives rise to almost all major arteries of the body.

-Somatic branches (to body wall & limbs):

Subclavian, axillary, brachial, radial, ulnar, vertebral, intercostal, lumbar, sacral, iliac, femoral, tibial, popliteal.

Visceral branches (to organs):

• Single: celiac, superior mesenteric, inferior mesenteric

• Paired: renal, gonadal, adrenolumbar

rete mirabilia (“wonderful maze”)

A specialized arterial structure where an incurrent artery branches into many small interconnecting vessels and drains into an excurrent artery.

• Examples & functions:

  • Glomeruli (kidney filtration)

  • Shark pseudobranch networks

  • Red gland of swim bladders (regulates gas levels)

  • Oxygen storage in deep-diving mammals

  • Heat retention in mammals, birds, lamniform sharks, tuna

major venous channels in all vert.

General vertebrate venous system includes:

• Cardinals (anterior, posterior, common)

• Renal portal (kidneys)

• Lateral abdominal

• Hepatic portal

• Hepatic sinus

• Coronary veins

Tetrapods + Dipnoans also have:

• Pulmonary veins (from lungs)

• Postcava (drains kidneys → heart)