Lecture/Lab: Circulatory System

Question 1

tunica intima

Answer 1

inner endothelial layer

Question 2

tunica media

Answer 2

muscular layer

Question 3

tunica adventitia

Answer 3

layer of binding connective tissue.

The name “tunica adventitia”, in particular, bows to the fact that the circulation is a system derived from the mesodermal layer of the embryo, and is by default surrounded by mesodermal structures in the adult.

Question 4

arteries

Answer 4

function is to control and partition the flow of blood, and buffer the pressure differential in the blood stream caused by the heart’s pumping action. The arterial system controls blood distribution down to the sub millimeter level in most organs, normally terminating in capillary beds

Question 5

Capillary beds

Answer 5

function is to allow the transfer of gases and nutrients to those target organs

Question 6

Veins

Answer 6

Blood is returned to the heart at relatively low pressure by a network of veins, that increase in diameter. The largest of the veins must work to buffer any change in blood volume, lest the heart be made to work against an excessive pressure gradient.

Veins tend to travel with companion arteries and nerves. Remember that an artery will always have a thicker tunica media than its companion vein. The companion vein usually appears larger in diameter.

Question 7

What are the four possibilities for vessels of small size?

Answer 7

arterioles (the smallest branches of the arterial system), capillaries (whose lumen is comparable to the size of a single red blood cell), venules, and lymphatic vessels

Question 8

Arterioles

Answer 8

have smooth muscle in their walls, a continuation of the circular smooth muscle of the muscular arteries that feed them.
Generally, arterioles have only one or two layers of smooth muscle.
Notice that the smooth muscle cell, which is a cigar-shaped cell has a nucleus that is elongated in a direction perpendicular to that of the endothelial cell nucleus, whose cell is shaped like an oval pancake. The contrast between the two adjacent nuclei, one cut longitudinally and one cut transversely, is often crucial to the identification of the arteriole.
Note also that the smooth muscle is more eosinophilic than the surrounding connective tissue. That layer (which may be only one cell thick) forms the tunica media of the arteriole. The endothelial cell forms the bulk of the tunica intima layer.

Question 9

How to distinguish venules and capillaries?

Answer 9

Capillaries and venules are distinguished primarily on their size. Blood cells pass through capillaries in single-file. Thus, a capillary is roughly equal to, or less than the diameter of a red blood cell. Anything larger is a venule.

Question 10

Venules

Answer 10

Whereas the venous system begins to attain a distinct tunica media as the vessels grow larger, smooth muscle is absent in the smallest venules, so the tunica media is also absent.
For comparably sized elements of the arterial and venous systems, the venous vessel will have a much thinner tunica media than the arterial vessel. One must develop an expectation for how much smooth muscle to see in a given sized vessel.

Question 11

How to distinguish between continuous, fenestrated and sinusoidal capillaries?

Answer 11

can not be made in the LM, except perhaps indirectly, by inference based on the vessel’s location. (A capillary in the brain or among skeletal muscle will be of the continuous variety. A capillary in the intestines, or in an endocrine organ will be fenestrated. Sinusoidal capillaries are often larger in diameter, but even then you must infer from position within an organ that the vessel is a sinusoidal capillary. They are morphologically indistinguishable from venules in standard preparations).

Question 12

Lymphatic vessel

Answer 12

The wall of a lymphatic vessel, even the large ones, consists only of the endothelium and a small amount of subjacent connective tissue.

The cells are not held in place as well as those of the veins, and their nuclei usually protrude into the vessel lumen. The smaller vessels have an angular appearance to their walls that is not apparent in veins, and the larger vessels may have valves within them.

Question 13

Elastic arteries

Answer 13

The bulk of the wall forms the tunica media

Question 14

Elastic lamellae and Lamellar units

Answer 14

alternating layers of smooth muscle and elastic fibers (elastic arteries).

The elastic fibers, if they were to be seen in a tangential section, would look like a fenestrated sheet (i.e., a solid layer with holes in it). Thus these layers are referred to as elastic lamellae. One of the repeating units, consisting of one layer of smooth muscle and one of its adjacent elastic lamellae, forms a structure referred to as a lamellar unit.

Question 15

What is the difference between an elastic artery and a muscular artery?

Answer 15

From Google:
An elastic artery, like the aorta, is located closer to the heart and has a larger proportion of elastic tissue in its walls, allowing it to expand and recoil with each heartbeat to maintain steady blood flow, while a muscular artery has a thicker layer of smooth muscle, enabling it to actively regulate blood flow by constricting or dilating depending on the body’s needs

From Lab Doc:
Unlike the elastic artery, which is designed to buffer the pressure difference between systole and diastole, the muscular artery is primarily designed to control the distribution of blood as it branches. The lamellar units of the tunica media in muscular arteries are replaced with continuous layers of smooth muscle. The innermost elastic lamella, at the border of the tunica intima, is retained and strengthened, and is referred to as the internal elastic lamina (sometimes called internal elastic membrane). In larger muscular arteries, the outermost layer is also retained. It is termed the external elastic lamina.

Question 16

internal elastic lamina

Answer 16

(sometimes called internal elastic membrane)
In muscular arteries, the innermost elastic lamella, at the border of the tunica intima, is retained and strengthened

Question 17

Special veins

Answer 17

The largest veins, such as the vena cava, portal vein, and some select other veins, have a special morphology. They have the function of buffering changes in blood volume, and thus the capability to reduce their lumenal volume by contracting along their length. To carry out such contraction, smooth muscle fibers must be longitudinally arranged. Such longitudinal smooth muscle fibers are found in the tunica adventitia, and are characteristic of the largest veins.

Question 18

epicardium

Answer 18

The outermost layer of the heart proper, the epicardium (visceral pericardium) is a serosa. It is a simple squamous epithelium plus a thin layer of subjacent collagenous connective tissue.

Question 19

subepicardium

Answer 19

a layer of connective and adipose tissue, of varying thickness, that importantly contains the major cardiac vessels.

Question 20

vasa vasorum

Answer 20

The vasculature of the tunica adventitia layer of very large vessels (aorta)

Question 21

nervi vascularis

Answer 21

The innervation in the tunica adventitia of very large vessels

Question 22

coronary sinus

Answer 22

draining deoxygenated blood from the heart muscle into the right atrium

Blood from the heart wall drains into the coronary sinus, then into the right atrium

Question 23

Embolus

Answer 23

a thrombus, detached atheromatous plaque, or other foreign body that travels within the cardiovascular
system and lodges in a vessel, fully or partially occluding the vessel

Question 24

arterial embolus

Answer 24

travels away from the heart through progressively smaller vessels

Question 25

venous embolus

Answer 25

travels toward the heart through progressively larger vessels.

Question 26

left and right CORONARY ARTERIES

Answer 26

the first branches of the aorta, supply the heart itself

Question 27

FIBROUS PERICARDIUM

Answer 27

A dense connective tissue sleeve, the FIBROUS PERICARDIUM, rises from the central tendon of the diaphragm to surround the heart and blend with the outer connective tissue layer (adventitia) of the great vessels entering and leaving the heart.

Question 28

SEROUS PERICARDIUM

Answer 28

A closed mesothelial sac that lines the inner surface of the fibrous pericardium as "parietal serous pericardium" and covers the outer surface of the heart as "visceral serous pericardium". The nearly constant motion of the heart is eased by a thin layer of lubricating pericardial fluid between the parietal serous pericardium and visceral serous pericardium. The visceral serous pericardium is called the epicardium in histology slides.

Question 29

Fibrillation

Answer 29

spontaneous and irregular contraction of cardiac myocytes

Question 30

CARDIAC "SKELETON"

Answer 30

a pretzel-like configuration of dense connective tissue between the atria and ventricles of the heart. The annuli (rings) of the cardiac `skeleton’ surround and stabilize the valve cusps and provide attachment for both atrial and ventricular cardiac muscle. The non-excitable dense connective tissue`skeleton’ also acts as an insulator, preventing spontaneous depolarization of adjacent ventricular myocytes during atrial contraction.

Question 31

What is another word for epicardium?

Answer 31

visceral serous pericardium

Question 32

What is the order of the layers of the heart tissue going from outside to inside?

Answer 32

fibrous pericardium --> parietal serous pericardium --> visceral serous pericardium (epicardium) --> subepicardial CT (can be innervated and vascularized) --> cardiac muscle (myocardium) --> Subendocardial CT (where Purkinje fibers are located) --> endothelial cells (endocardium)

Question 33

What are the roles of each type of blood vessel in maintaining homeostasis?

Answer 33

Elastic and Muscular artery- high pressure conducting vessels Arteriole- Blood pressure control vessels Capillary- Gas, nutrient exchange with interstitial fluid vessels Post capillary venules- Leukocyte escape vessels Muscular vein, vein, special vein- Low pressure capacitance vessels

Question 34

Elastic artery

Answer 34

Functions: Accommodating a large volume of blood at high systolic pressure, damping flow pulsations, and passively propelling blood with elastic recoil. Location: Aorta, brachiocephalic trunk, common carotid, subclavian, common iliac, pulmonary and vertebral arteries. Intima: Endothelium, basal lamina, subendothelial connective tissue, and elastic fibers. Media: Thickest layer. Fenestrated elastic lamellae (52 in aorta) arranged *concentrically*, alternating with circular interlamellar smooth muscle. Lamellar unit = 1 smooth muscle layer and 1 adjacent lamella. Adventitia: Well-developed. Primarily collagen type I and elastic fibers, with vasa vasorum and nervi vasorum.

Question 35

vasa vasorum and nervi vascularis

Answer 35

Only in large vessels Comes in from outside to meet metabolic needs of everything that can't be supplied by diffusion Vascular smooth muscle is innervated by noradrenergic neurons of the the sympathetic nervous system. These are the nervi vascularis, which often can be spotted in the tunica adventitia along with vasa vasorum, blood vessels that supply the outer walls of the larger vessels where diffusion from lumenal blood would be inadequate. NE and, somewhat uniquely, NPY (neuropeptide Y) are transmitters used at this second sympathetic synapse. Local factors secreted by endothelial and other cells also affect the vascular smooth muscle.

Question 36

Elastic lamellae

Answer 36

Fenestrated elastic lamellae (52 in aorta) arranged *concentrically*, alternating with circular interlamellar smooth muscle. Lamellar unit = 1 smooth muscle layer and 1 adjacent lamella. On Verhoeff's stain: Yes, there are some elastic fibers in the subendothelial CT, but those are not lamellae Lamellae = THICK elastic fibers in tunica media

Question 37

ANEURYSM

Answer 37

a localized dilation resulting from acquired or congenital weakness of the vessel wall. All 3 layers bulge outward on one or both sides

Question 38

DISSECTION

Answer 38

an extravasation of blood into the tunica media, most often through an intimal tear. Blood tracks longitudinally through the media. break in tunica intima. blood goes from the lumen to a false lumen in subendothelial CT blood dissects intima off vessel wall dangerous because it can shut off flow to a branched artery

Question 39

Muscular artery

Answer 39

Function: Controlled distribution of blood to muscles, organs, and other tissues. Location: Named arteries, excluding elastic arteries. (ex: femoral artery, radial artery, brachial artery, splenic artery, and mesenteric artery) Intima: Endothelium, basal lamina, subendothelial connective tissue, and a prominent internal elastic membrane. External elastic membrane may also be present in larger muscular arteries Media: Thickest layer. Circular or obliquely circular smooth muscle (8-10 cell layers), and collagen fibers. NO ELASTIC LAMELLAE Adventitia: Connective tissue and elastic fibers. Vasa vasorum and nervi vascularis.

Question 40

internal elastic membrane

Answer 40

The innermost elastic lamella, at the border of the tunica intima, is retained and strengthened, and is referred to as the internal elastic lamina (sometimes called internal elastic membrane)

Question 41

External elastic membrane

Answer 41

In larger muscular arteries, the outermost elastic lamellae layer is also retained. It is termed the external elastic lamina.

Question 42

Arteriole

Answer 42

Function: Vasoconstriction, controlling arterial blood flow into capillary bed. Location: All body regions adjacent to capillary beds. Intima: Endothelium, basal lamina, subendothelial connective tissue. Smooth, non-thrombogenic Media: Thick circular smooth muscle (1-2 cell layers), relative to lumen size. Adventitia: Thin connective tissue.

Question 43

One way to differentiate the arterioles from the venules?

Answer 43

Look at the ratio of diameter to wall thickness Higher ratio in venules

Question 44

Continuous capillary

Answer 44

Most capillaries are continuous capillaries Function: Exchange between blood and body tissues, capillaries are permeable but selectively permeable. Location: Muscle tissue, connective tissue, lung, skin, the central nervous system, and the placenta. Intima: Thin continuous endothelium, usually a single endothelial cell joined by tight junctions, and a continuous basal lamina. Endothelial cells have numerous transport vesicles. The thin capillary wall is supported by pericytes. No media or adventitia. Instead surrounded by pericytes Continuous capillaries, found in the lung, placenta, muscle and CNS, allow no passive transport across their endothelium.

Question 45

pericytes

Answer 45

mesenchymal stem cells that can differentiate into either endothelium or smooth muscle They share the basal lamina with the endothelial cells Capillaries and other smaller vessels often have pericytes, cells with contractile properties, associated with their basal surface. Brain vasculature has the highest density of pericytes - almost 1:1 with endothelial cells. There, they appear to provide a slow (minutes to hours) modulatory control of blood flow compared to arterioles which can regulate local blood flow on the order of seconds.[5] For example, in the retina, pericytes cover over 90% of the capillaries, and are key to regulating the pressure-induced vascular damage of glaucoma.[6] They may also play a role in maintenance of the endothelial basement membrane, or even angiogenesis. Evidence suggests that pericytes are organ-specific. Pericytes in the brain derive from neural crest cells, whereas pericytes in gut organs derive from mesoderm. Similarity of pericyte cell surface markers suggests a relation with vascular smooth muscle and MSC, both of which also reside in the perivascular space. In culture, pericytes show a high degree of plasticity, similar to MSC.

Question 46

Fenestrated capillary

Answer 46

Function: More permeable. Location: Intestinal mucosa, gallbladder, endocrine and exocrine glands (pancreas), and kidney. Intima: Endothelial cells have numerous fenestrations or pores, usually closed by diaphragms that restrict passage of large molecules such as proteins (may be absent in renal glomeruli). Although the endothelial cells are fenestrated, the *basal lamina is continuous*. Supported by pericytes No media or adventitia: Fenestrated capillaries are found in endocrine glands, kidney, gallbladder and intestinal tract and have openings large enough to allow free passage of small molecules.

Question 47

Sinusoidal (discontinuous) capillaries

Answer 47

Function: Maximal molecular exchange between blood and surrounding tissue. Blood plasma proteins and cells can move easily across endothelium. Structural features of sinusoids vary from organ to organ. Location: Liver, spleen, bone marrow, adenohypophysis, and suprarenal medulla. Intima: Endothelial cells with large fenestrations which are also separated by large intercellular junctions. Basal lamina discontinuous or absent (liver). No media or adventitia Sinusoidal capillaries, found in the liver, spleen and bone marrow, are those that have openings large enough to admit cells, although sometimes the term is used to indicate merely large diameter capillaries.

Question 48

Postcapillary venule

Answer 48

exit of capillary beds Function: Extravasation of fluids and leukocytes. Postcapillary venules are relatively permeable, with few tight junctions. Inflammatory agents increase permeability, *facilitating leukocyte extravasation* and causing tissue edema. Loose intercellular junctions Location: Adjacent to capillary beds throughout the body. Intima: Continuous endothelium with loose intercellular junctions, basal lamina, subendothelial connective tissue. Walls supported by pericytes. No media or adventitia:

Question 49

What do immature intravascular neutrophils mean?

Answer 49

Immature neutrophils (nuclei not separated) tell you that an infection has been going on form some time They have graduated from the bone marrow early

Question 50

Vein

Answer 50

Function: Capacitance vessels that hold 60-70% of total blood volume. Vascular smooth muscle regulates lumen size, mediating blood volume and pressure. Location: Veins accompanying muscular arteries. May be paired as venae comitantes. Intima: Endothelium, basal membrane, and subendothelial connective tissue, and some veins have an internal elastic lamina. Valves in veins form by two layers of endothelium surrounding a connective tissue core. Valves are prominent in the limbs and absent in the larger thoracic and abdominal veins. Media: Smooth muscle, collagen fibers. (Smooth muscle gets progressively thicker) Adventitia: *Thickest layer*. Connective tissue some elastic fibers. Most of it is adventitia

Question 51

What are the names of the Special ‘caval-type’ veins

Answer 51

superior vena cava, inferior vena cava, renal vein, sometimes adrenal veins, brachiocephalic veins, portal vein, subclavian veins, common iliac veins

Question 52

Special ‘caval-type’ vein

Answer 52

Function: Return deoxygenated blood to heart, capacitance, and mediating blood volume. Location: Large veins closer to heart including the superior vena cava, inferior vena cava, brachiocephalic veins, portal vein, subclavian veins, common iliac veins. Intima: Endothelium, basal membrane, subendothelial connective tissue. Media: Circular smooth muscle (2-15 layers), collagen fibers. Adventitia: Thickest layer. Dense connective tissue, longitudinal smooth muscle. Cardiac muscle may extend into areas nearest heart (myocardial sleeves). Vasa vasorum, nervi vascularis.

Question 53

Lymphatic capillaries

Answer 53

Function: Absorption of tissue fluid, waste products, and cell debris. Location: All tissues except cartilage, bone, bone marrow, thymus, placenta, cornea, and teeth. Intima: Thin endothelium and subendothelium with valves. Media: Smooth muscle in larger lymphatic vessels, not in lymphatic capillaries. Adventitia: Thin connective tissue attached to anchoring filaments in surrounding connective tissue. The anchoring filaments help maintain lumen patency.

Question 54

Larger lymphatic vessels

Answer 54

asymmetrical LYMPH re-enters the blood vascular system through large lymphatic vessels that drain into large veins at the base of the neck. The lymphatic drainage of the body is asymmetrical. The right lymphatic duct drains lymph from the right side of the thorax, right upper limb, and right side of the head and neck. The right lymphatic duct drains into veins on the right side of the neck. The thoracic duct drains lymph from the rest of the body (both lower limbs, the abdominopelvic cavity inferior to the umbilicus, the left side of the thorax, left upper limb, and left side of the head and neck. The thoracic duct drains into large veins on the left side of the neck.

Question 55

right lymphatic duct

Answer 55

drains lymph from the right side of the thorax, right upper limb, and right side of the head and neck. The right lymphatic duct drains into veins on the right side of the neck.

Question 56

thoracic duct

Answer 56

drains lymph from the rest of the body (both lower limbs, the abdominopelvic cavity inferior to the umbilicus, the left side of the thorax, left upper limb, and left side of the head and neck. The thoracic duct drains into large veins on the left side of the neck.

Question 57

Edema

Answer 57

accumulation of excess fluid in tissue spaces. An increase in capillary hydrostatic pressure or a decrease in plasma osmotic pressure may lead to EDEMA, excess fluid accumulation in tissue spaces.

Question 58

Describe the process by which atherosclerosis occurs

Answer 58

Endothelial injury causes INCREASED PERMEABILITY and INCREASED PLATELET AND MONOCYTE ADHESION. Low density lipid (LDL) and monocytes enter the subendothelial connective tissue. Monocytes are activated as MACROPHAGES which engulf lipids and oxidized lipids. Factor release from endothelial cells, platelets, and macrophages induces SMOOTH MUSCLE CELL RECRUITMENT from tunica media and/or circulating SMC precursors. Ongoing EXTRACELLULAR AND INTRACELLULAR LIPID ACCUMULATION. Intracellular lipid in both smooth muscle cells and macrophages (now foam cells). Fatty streaks are now apparent on the artery lumen. Raised ATHEROSCLEROTIC PLAQUES protrude into the vessel lumen, reducing flow within the lumen or causing compensatory expansion and weakening of the vessel wall. Weakening or the vessel wall can also cause ischemic death resulting from increased diffusion distance from blood in the vessel lumen. Plaque may calcify or may rupture and embolize. Vessel wall may form aneurysm and potentially catastrophic rupture.

Question 59

What does each layer of the blood vessels correspond to in the heart?

Answer 59

In the heart, the tunica intima corresponds to the endocardium and subendocardium. The tunica media is the myocardium. The tunica adventitia corresponds to the subepicardium.

Question 60

Where does the pericardial cavity originate?

Answer 60

The pericardial cavity, along with the pleural cavity of the lung and the peritoneal cavity of the GI system are the three cavities that result from the embryonic coelum, the original cavity formed in the lateral mesoderm.

Question 61

Caveolae

Answer 61

Caveolae are small, flask-shaped invaginations of the plasma membrane in many vertebrate cells. They are a type of lipid raft and are most abundant in endothelial cells, adipocytes, and embryonic notochord cells. (from Google)

Question 62

lymph nodes

Answer 62

lymph passes through one or more lymph nodes for filtration and immune surveillance before returning to the blood circulation

Question 63

Thrombus

Answer 63

A THROMBUS is a clot that forms within the cardiovascular system during life.

Question 64

baroreceptor

Answer 64

A baroreceptor is a specialized sensory innervation of the larger arteries (carotids and the aortic arch) that senses information about stretching of the vascular wall (which correlates with blood pressure) and sends it to the brainstem. The baroreflex is crucial for maintaining blood pressure through postural changes, for example transitioning from sitting to standing.[10] The typical baroreceptor is a fine-scale nerve ending located in the inner portion of the tunica adventitia. Because the descending pathways of the baroreflex involve the spinal cord, the reflex may be lost with spinal injury. Loss of the baroreflex produces orthostatic hypotension.

Question 65

chemoreceptors

Answer 65

chemoreceptors present in the aortic bodies along the aortic arch (and a few select other locations) contain specialized cells that signal elevated blood CO2 to the brainstem.

Question 66

What is the difference between vasculogenesis and angiogenesis?

Answer 66

The process by which vessels are formed is called vasculogenesis, and is distinct from the process by which vessels elaborate from existing vessels, which is termed angioogenesis.