Exam 2 Histology- Heart and circulatory system

What does the circulatory system consist of?

- Heart -Blood vessels -lymphatic system

Pericytes what are they what is their function

- mesenchymal-like stem cells -in wound healing, they may differentiate into fibroblasts or smooth muscle cells

Venules what is their diameter -which tunicas do they have

-12micrometer- 1mm diameter diameter -tunica intima of endothelial cells tunica media of 1-2 layers of smooth muscle cells -tunica adventitia has several layers of collagen fibers

what are the physical characteristics of discontinuous (sinusoidal) capillaries

-Large (30-50 micrometers) -Irregular, tortuous walls -wide gaps between cells -incomplete basal lamina

what courses through lymphatic vessels?

-Plasma proteins -fluid -enzymes -lipids -antibodies -hormones -other macromolecules that leak from blood vessels and bathe tissues and interstitial spaces

describe the tunica media of small to medium sized veins

-Thin -has some reticular and elastic fibers interspersed with smooth muscle cells

what are the characteristics of continuous (somatic) capillaries?

-continuous endothelium and basal lamina -NO fenestrae -Numerous pinocytic vesicles (for transcytosis)

Tunica Intima of elastic arteries -What is it composed of -what does it include?

-endothelium + underlying sub-endothelial CT -includes internal elastic lamina in larger vessels

Septum Membranaceum (membranous septum) -what is it -what is it an attachment for

-fibrous portion of the interventricular septum -attachment sites of cardiomyocytes

Annuli Fibrosi (annulus fibrosus) -what is it? -what does it support?

-fibrous rings around the origins of the pulmonary artery, aorta, and atrioventricular canals support heart valves

Trigona Fibrosa (fibrous trigone) -what is it? -what does it support?

-fibrous tissue supports AV openings, and the base of the aorta

What does the subendothelial layer of the endocardium contain? What is below this?

-fine collagenous fibers -thin layer of dense fibroelastic CT

Parasympathetic nerves -where are they found -what is their function

-from Vagus to sinoatrial node -slow the heart

Sinoatrial Node (SA node) --function -made of -spread of impulse

-heart pacemaker -made of modified cardiac muscle cells concentrically arranged around a nodal artery -impulse spreads from this node via conduction fibers to the AV node

Atrioventricular Node (AV node) - location -cell composition -what does it form

-located beneath the septal wall endocardium of the right atrium -cells similar to those in SA node (modified cardiac muscle cells) -this node continues to form a common stem--> AV bundle of His

Underneath the mesothelium of the epicardium, it a subepicardial layer. What does this layer contain?

-loose CT -adipose tissue -coronary blood vessels and nerves

Subendothelial layer of an elastic artery -Type of CT -what does the CT contain

-made of loose CT -Contains collagen, elastic fibers, and fibroblasts.

describe the tunica media of a muscular artery

-media of up to 40 circular layers of smooth muscle interspersed with elastic fibers

Purkinje fibers -what are they -what do they contain -where do they travel? -what do they make contact with?

-modified muscle cells (cardiac conduction fibers) -contain glycogen -travel in the subendocardial layer to the heart apex. -then reverse direction and branch to make contact and form gap junctions with cardiac muscle cells

what do continuous capillaries have in the CNS? What is their contribution?

-occluding junctions that contributes to blood-brain barrier

Tunica Media of elastic arteries -what is it composed of and what does it contain?

-primarily smooth muscle cells -external elastic lamina

Atrial natriuretic peptide -where is it released from -why is it released -what are its primary effects?

-released from modified atrial muscle cells -released in response to high BP -primary effect is to increase sodium and water secretion from the kidney.

describe the adventitia of veins

-well developed -with multiple layers of collagenous fibers, a few smooth muscle cells, and elastic fibers

where are continuous (somatic) capillaries located?

1- Muscle 2- CT 3- CNS 4- Exocrine pancreas 5- Gonads My. Cat. Can't. Eat. Grapes

which are the controlling structures of the heart?

1- SA node 2- AV node 3- AV bundle of His 4- Parasympathetic nerves 5-Sympathetic nerves 6-Atrial cardiac muscle cells

what are the three tunics found in blood vessels?

1- Tunica intima 2- Tunica media 3- Tunica Adventitia

describe the flow of blood starting from the aorta

1- aorta 2- arteries 3- arterioles 4- capillaries 5- post-capillary venules 6- venules 7- veins 8- vena cava 9- right atrium 10-right ventricle 11- pulmonary artery 12- lung capillary bed 13- pulmonary vein 14- left atrium 15- left ventricle 16- aorta

the cardiac skeleton can become fibrocartilage in ________, hyaline cartilage in_______ ,or boney in ______________

1- dogs 2- horse 3- older animals (large ruminants)

What are the three ways in which arteries can be classified?

1- large (elastic) 2- Medium (muscular) 3- Small (arterioles)

What are the physical characteristics of capillaries -layer(s) of endothelial cells -diameter -surrounded by?

1- single layer of endothelial cells 2) 7-10 micrometer diameter 3- surrounded by thin sheath of reticular and collagenous fibers and some pericytes

What are muscular venules composed of?

1-2 layers of smooth muscle and thin tunica adventitia

describe the tunica media of an arteriole

1-3 layers of smooth muscle cells -occasional elastic fibers some references say 5-6 layers of SMC

which are examples of elastic arteries?

1-Aorta 2- Pulmonary 3- Brachiocephalic 4- Common carotid 5- Subclavian 6- Common iliac arteries

Which are the 4 different hormones that the ANP gene makes?

1-long acting natriuretic (sodium) peptide 2-vessel dilator 3-kaliuretic (potassium) peptide 4-ANP (atrial natriuretic peptide

where are fenestrated (visceral) capillaries located?

1. Mucosa of GI tract 2. endocrine glands 3. ciliary body 4. choroid plexus 5. renal glomerular and peritubular capillaries Mary. Eats. Chocolate. Chips. Rapidly

what is the diameter of lymphatic vessels?

10-50 micrometers

describe the tunica adventitia of muscular arteries

Adventitia may be as thick as media, with collagen and elastic fibers

what is diastole?

Arterial hydrostatic pressure between contractions

Which cells are the source of polypeptide hormones?

Atrial cardiac muscle cells and some cells in the interventricular septum (myoendocrine cells)

What are the tunics/layers of the circulatory system -Blood vessels -Heart

Blood vessels 1- tunica intima 2- tunica media 3- tunica adventitia Heart 1- endocardium 2- myocardium 3- epicardium

True/false arterioles always have an internal elastic lamina

False it may or may not be present

true/false the tunica adventitia of an elastic artery has a distinct external elastic lamina

False, it does not.

what is the first functional unit in the embryo?

Heart

Where are discontinuous (sinusoidal) capillaries found?

In the liver and hematopoietic organs (BM and spleen)

do muscular venules have pericytes?

NO

What is the epicardium? Which cells form the epicardium?

Outermost epicardial layer formed by mesothelial cells (simple squamous epithelium)

which protein in diaphragms of capillaries maintains the endothelial barrier integrity and controls permeability?

PV1

What is the function of postcapillary venules?

Receive blood from capillaries

what is the function of an arteriole?

Regulate blood flow to capillary beds via vasoconstriction/vasodilation important for regulation of BP

describe the tunica adventitia of an elastic artery

THIN adventitia -has elastic and collagen fibers -NO distinct external elastic lamina

which are the common sites for congenital defects in newborn animals?

The fusion of endocardial tubes and subsequent formation of the chambers, septa, and valves

Composite Blood vessel

The thickness and characteristics of different layers will change based upon vessel type: elastic or muscular artery, arteriole, vein, or venule

True/false All large blood vessels have tunics

True

true/false postcapillary venules have an incomplete layer of pericytes that becomes more complete as the vessel gets larger

True

True/false endothelial cells regulate the traffic of inflammatory cells

True early in inflammation, macrophages in surrounding CT secrete cytokines (TNF-alpha, IL-1) which induce expression of E-selectin by endothelial cells. -neutrophils bind to selectins and then extravasate by migration through the endothelium

what does the internal elastic lamina of an arteriole consist of?

a network of fibers that may not be visible at the level of LM can be seen with PAS or elastin stain

what is endothelin-1

a vasoconstrictor

what is the function of sympathetic nerves

accelerate the heartbeat innervate atrial and ventricular cardiac muscle cells.

How is the myocardium arranged in the ventricles?

arranged into deep and superficial layers

in an arteriovenous anastomoses, what happens when the shunt is closed?

arterial blood flows into the capillary bed

compare the shape of an arteriole to a vein

arterioles have a more regular round shape relative to venules

in an arteriovenous anastomoses, what happens when the shunt is open

blood bypasses the capillary bed and flows into a vein (i.e. cutaneous subpapillary plexus in skin)

what does nitric oxide do?

causes smooth muscle in the tunica media to relax--> vasodilation

what are endocardial cushions?

cell subset that forms the septa

what course do deep fibers of the myocardium have around the ventricle?

circular course

What do elastic arteries do?

conduct blood to muscular arteries.

what are arteriovenous anastomoses

connections primarily between arterioles and venules they have a specialized tunica media with a sphincter

medial endocardial tubes fuse into a single centrally located tubular, _____________ heart

contractile

what aids blood circulation through veins?

contraction of surrounding muscles

what is the function of muscular arteries?

deliver blood to organs

which type of arteries (muscular or elastic) stretch with ventricular contraction and store energy?

elastic arteries

Development of the heart begins as a pair of medial ______________________ tubes

endocardial

What is an atrioventricular canal

endocardial cushion defect

lymphatic vessels are an _____________________ lined vessel. lymph flows in ___________ direction, which is toward the base of the ____________

endothelial 1 neck

Endocardium -what is it -what is it lined by -what is it continuous with -What are its layers

endothelial surface layer of the heart and underlying connective tissue -lined by endothelium -continuous with blood vessels Consists of endothelium, sub-endothelial layer of thin collagenous fibers, thin layer of dense fibroelastic CT, and subendocardial layer of loose CT with nerves, blood vessels, and purkinje fibers.

what lines the entire circulatory system?

endothelium

true/false the cardiac skeleton always remains collagenous

false can range from loose collagen to bone depending on the age and species

true/false BM has lymphatics

false it does not

true/false fenestrated endothelium in the glomerular capillaries have diaphragms

false they do not

Tunica Adventitia -what is it made of

fibroelastic CT (dense irregular CT with small amounts of elastic fibers.)

what holds the lymphatic vessel open in smaller vessels?

fine anchoring filaments that attach to perivascular collagen

what is a patent foramen ovale?

hole between the right and left atrium

where do lymphatic vessels originate?

in CT as anastomosing capillaries capillaries have NO basal lamina

other than in veins, where can valves be found?

in larger lymphatic vessels

where would vasa vasorum (small vessels) be found in larger vessels?

in the tunica adventitia and outer part of the media

what does prostacyclin do?

inhibits platelet adhesion and clot formation

_____________________ in the intestine are an important route of fat absorption

lacteals

what does the heart differentiate from?

lateral plate mesoderm

describe the tunica adventitia of an arteriole

layer of loose CT with longitudinally arranged collagenous and elastic fibers

what is the diameter of an arteriole?

less than 0.5mm

postcapillary venules are similar to capillaries but have a wider __________

lumen

Apart from vasa vasorum, larger vessels may have ______________ and nerves (__________ ______________) in the adventitia

lymphatics nervi vascularis

subendocardial layer of the endocardium -What is it made of -What is it connected to -What does it contain?

made of loose CT, connected to the myocardium contains blood vessels, nerves, and portions of purkinje fibers

The visceral layer of the serous pericardium is the epicardial ______________

mesothelium

what is the myocardium

middle layer of cardiac muscle tissue

papillary muscles -what are they composed of -what is their function?

muscles composed of cardiomyocytes (contractile) prevent inversion/prolapse of the valve leaflets

apart from protstacyclin, what do endothelial cells secrete?

nitric oxide endothelin-1

do arterioles have an external elastic lamina?

no

does the subendothelial connective tissue of muscular arteries have smooth muscle cells?

no, it lacks them

which vessels are an important site of activity in inflammation?

postcapillary venules (vasoactive compounds- histamine and serotonin- affect fluid extravasation and migration of WBCs)

What is systole?

pressure increase in vessel during contraction

what do endothelial cells produce from arachidonic acid?

prostacyclin

Atrioventricular Bundle of His -formed by?

purkinje fibers (cardiac conduction fibers) that penetrate the skeleton and then branch to form the right and left bundle branches

what do the annuli around atrioventricular orifices result in and what does this control?

results in electrical discontinuity between myocardial cells of atria and ventricles controls communication between them via specialized conduction tissue (A-V bundle)

What is the Fibrous cardiac skeleton?

skeleton composed of: -dense irregular CT -Septum membranaceum -Annuli fibrosi -Trigona fibrosa

the intima of which vessel may have a thin subendothelial connective tissue layer

small to medium size veins (1-9mm diameter)

precapillary sphincter -what has this sphincter -what does it control

some microvascular beds (i.e. mesenteric) -control the amount of blood flowing into a capillary

what course does the superficial layer of the myocardium have around the ventricle?

spiral course

which are examples of large veins

superior and inferior vena cava portal trunk

How do elastic arteries maintain BP between heart contractions?

they recoil

Do muscular arteries have a thin or thick external elastic lamina? Where is it found?

thick, found at the edge of the tunica media

Is the tunica intima of muscular arteries thinner or thicker compared to elastic arteries?

thinner.

which are the 2 atrioventricular valves?

tricuspid and mitral valves

True/False heart layers are homologous to the tunics of blood vessels

true

True/false Elastic fibers of the intima of elastic arteries form an incomplete internal elastic lamina

true

true/false -all parts of the cardiac skeleton start out as irregular collagen and elastin

true

true/false arterioles have a thick wall relative to the lumen

true

true/false arterioles have sparse subendothelial connective tissue

true

true/false fluid is scavenged by the lymphatic system, filtered by lymph nodes, and recycled back into the venous circulation at the base of the neck

true

true/false purkinje fibers are portions of the impulse-conducting system of the heart

true

true/false valves have both dense and loose CT layers surrounded by endothelium

true

true/false venous valves are paired, semilunar folds of the tunica intima covered with endothelium

true

true/false larger vessels have an intima, media, and adventitia, like blood vessels, but these may be difficult to discern at LM level

true

true/false (visceral) capillaries are fenestrated

true -they have attenuated endothelium (very thin) with large 60-80 nm fenestrae fenestrae are closed by thin 4-6 nm diaphragms

describe the tunicas of large veins

tunica intima: similar to small veins tunica media: thin tunica adventitia: thick with collagenous fibers and longitudinal arranged smooth muscle cells

What happens to the fused heart tube?

undergoes bends and forms a heart loop with subsequent formation of the chambers, septa, and valves

which are the semilunar valves?

valves between the ventricles and aorta and pulmonary artery

Which vessels have more vasa vasorum?

veins

what is the function of venous valves?

veins operate under low pressure. -valves prevent backflow

what are the mitral and tricuspid valves connected to?

ventricle papillary muscles by fibrous cords (chordae tendineae)

does the tunica intima of muscular arteries have a well developed or poorly developed internal elastic lamina?

well developed

describe the tunica media of an elastic artery

~500 micrometers or 40-70 concentric elastic sheets