Cardiovascular Respiratory Histology

Question 1

Cardiac Muscle Cells

Answer 1

Cardiac muscle (myocardium) is striated, involuntary muscle found in the heart wall. Cardiac muscle cells (cardiomyocytes) contain the same contractile filaments as in skeletal muscle (sarcomeres). They are intermediate in size compared to skeletal and smooth muscle.
cardiac muscle cells have rounded cross-sections with a centrally located nucleus
cardiac muscle cells are joined end-to-end are often branched
cardiac muscle cells have a single or occasionally two centrally located nuclei.
cardiac muscle cells are joined together by specialized junctions called intercalated discs. They appear as thin, dark stained linear structures dividing adjacent cells that are perpendicular to the direction of the muscle fiber
Lipofuscin Pigment - residue of lysosomal digestion that accumulates as yellow-brown granules near the nucleus of some cells. In this specimen, few cells have detectable amounts.

Question 2

Right & Left Atria histology

Answer 2

The right and left atria are on the low pressure side of the heart. The lower workload results in thinner walls than in the ventricles (compare with MH 070 Heart).

Right Atrium - receives venous blood from the systemic circulation. Pectinate muscles (bundles of muscle that protrude from the surface) are common in the right atrium.

Question 3

Endocardium

Answer 3

inner surface of a simple squamous epithelium (endothelium) supported by a thin layer of dense irregular connective tissue

Question 4

Myocardium

Answer 4

thickest, middle layer of cardiac muscle responsible for the pumping action of the heart. It also contains blood vessels, nerves and adipose cells

Question 5

Epicardium

Answer 5

outer surface of mesothelial cells supported by dense irregular connective tissue

Question 6

The wall of the right atrium is composed of three layers:

Answer 6

Endocardium - inner surface of a simple squamous epithelium (endothelium) supported by a thin layer of dense irregular connective tissue
Myocardium - thickest, middle layer of cardiac muscle responsible for the pumping action of the heart. It also contains blood vessels, nerves and adipose cells
Epicardium - outer surface of mesothelial cells supported by dense irregular connective tissue

Question 7

he wall of left atrium is composed of three layers:

Answer 7

Endocardium - thick in this part of the atrium - has three sublayers:
Endothelium - innermost layer of simple squamous epithelium (endothelium)
Subendothelial Connective Tissue - thick, middle layer of collagen fibers with scattered smooth muscle
Subendocardial Connective Tissue - outer layer of loose connective tissue often containing adipose cells
Myocardium - thickest, middle layer of the heart wall
Epicardium - outer surface of mesothelial cells (mostly missing on this specimen) supported by dense irregular connective tissue. An inner layer of loose adipose connective tissue is also found in some areas.

Question 8

Purkinje Fibers

Answer 8

Purkinje fibers are specialized cardiac muscle cells that conduct electrical impulses that allow coordinated contraction of cardiac muscle.

In this specimen, the aorta is on the left and the left ventricle on the right. Purkinje fibers are found in the inner ventricular wall beneath the endocardium.

Purkinje fibers are larger than normal cardiac muscle cells.
The cytoplasm of Purkinje fibers is more lightly stained (pink) than normal cardiac muscle cells (pink/red). This results from:
Higher content of glycogen
Lower content of myofibrils

Question 9

Elastic Artery

Answer 9

(Carotid Artery) - convey blood from the heart to systemic and pulmonary circulations. The tunica media is the thickest layer and contains prominent elastic tissue.
Tunica Intima - inner layer composed of the endothelium, subendothelial connective tissue, and a thin layer of elastic fibrils (the internal elastic membrane).
Tunica Media - middle layer composed of alternating layers of circumferentially arranged smooth muscle (bluish-pink) and wavy sheets of elastic tissue (unstained or light pink).
Tunica Adventitia - outer layer of dense irregular connective tissue containing loosely organized collagen fibers.

Question 10

Large Vein

Answer 10

(Brachiocephalic Vein) - have thinner walls than arteries with less distinct layers. The tunica adventitia is the thickest of the three layers.
Tunica Intima - inner layer composed of endothelium and a thin layer of collagen fibrils
Tunica Media - middle layer of only a few (3 to 8) layers of smooth muscle.
Tunica Adventitia - outer layer of dense irregular connective tissue containing mostly longitudinal or spiral arrangements of smooth muscle and collagen fibers.
Vasa Vasorum - blood vessels that supply the tunica adventitia and tunica media.

Question 11

Arterioles

Answer 11

small diameter blood vessel that branches out from arteries and leads to capillaries.
Their wall consists of endothelial cells, an internal elastic lamina apposed by one or two layers of smooth muscle, and a thin layer of collagen fibers. The inner elastic lamina is usually absent from smaller arterioles. The thickness of vessel wall is usually similar in size to the diameter of the lumen.
Arteriole #1 - one to two layers of smooth muscle and a remnant of an inner elastic lamina.
Arterioles #2 - adjacent arterioles.
Arteriole #3 - two layers of smooth muscle.
Small Arteriole #4 - nuclei of two endothelial cells and two smooth muscle cells are seen.
Arterioles are the primary site of vascular resistance.

Question 12

Venules

Answer 12

small diameter blood vessel that allows blood to return from capillary beds to veins
Their wall is composed of an endothelial cell, one or two layers of smooth muscle, and very thin adventitia.

Question 13

Capillaries

Answer 13

There are three types of capillaries; continuous capillaries, fenestrated capillaries and sinusoids. Capillaries form beds within tissues htat allow for nutrient and waste exchange.

Continuous capillaries have a continuous endothelium and basement membrane. Continuous capillaries are responsible for gas exchange.

Fenestrated capillaries have small pores in the endothelium called fenestrations.

Sinusoidal capillaries have discontinuous endothelium and basement membrane. Sinusoids allow for exchange of large macromol

Question 14

histology of the Trachea

Answer 14

The trachea is a tube that connects the larynx to the lungs allowing the passage of air. It is a fibromuscular tube supported by 15 to 20 “C”-shaped hyaline cartilages.

Respiratory Epithelium - the trachea is lined with a pseudostratified columnar epithelium with cilia and goblet cells.
Cilia - extend 5 to 7 µm from the surface of the columnar epithelial cells. The dark line at their base is from their basal bodies.
Goblet Cells - secrete mucus. They are difficult to identify in this specimen, but a thick layer of mucus (20 to 30 µm) is seen on the surface of the epithelium.
Basement Membrane - separates the epithelium from the underlying connective tissue. It is seen as a thick, eosinophilic band beneath the epithelium
Lamina Propria - dense irregular connective tissue supports the epithelium.
Sero-Mucous Glands - add moisture to air and aid in trapping contaminants. The cilia propel mucus towards the esophagus where it is swallowed.
Tracheal Cartilage - cross-section of a single, “C”-shaped hyaline cartilage that is open in its posterior aspect.
Trachealis Muscle - smooth muscle that spans the ends of tracheal cartilages. They control the diameter of the trachea.
Adventitia - loose connective tissue.

Question 15

histology of the lung

Answer 15

The lung consists of airways and structures for gas exchange.

The trachea divides into a primary bronchus for each lung. The smaller intrapulmonary airways are devoid of cartilage and glands in their walls.

Primary (Muscular) Bronchioles (not present in this specimen)
Epithelium changes from pseudostratified columnar to simple, ciliated columnar epithelium as they decrease in diameter.
Club Cells - dome-shaped secretory cells with short microvilli. (Do not have cilia.)
Smooth Muscle - variable amounts present.
Terminal Bronchioles - conducting airways.
Epithelium changes from simple, ciliated columnar epithelium to cuboidal epithelium.
Club Cells - become more prominent.
Smooth Muscle - variable amounts present.
Respiratory Bronchioles (#1, #2 and #3) - mixture of conducting epithelium and alveoli where respiration occurs.
Epithelium is a mixture of simple columnar and simple cuboidal epithelia.
Club Cells - become more prominent.
Smooth Muscle - only small amounts are present.

Question 16

Alveoli

Answer 16

Alveolar Ducts (#1 and #2)- arise from respiratory bronchioles and are passageways lined with alveoli and occasional regions of simple cuboidal epithelium.
Alveolar Sacs (#1 and #2) - spherical-like spaces with openings into multiple alveoli.
Alveoli - blind ending sacs that are the final termination of the airways.
Simple Epithelium (#1, #2, #3, #4 and #5) - contains two types of pneumocytes resting on a thin basal lamina.
Type I - flattened, simple squamous epithelial cells.
Gas exchange occurs through these cells.
Type II - dome-shaped, cuboidal epithelial cells that project into the lumen.
Secrete surfactant that covers the alveolar surface and reduces surface tension.
Macrophages (or Dust Cells) (#1, #2 and #3) - large, dark cells within alveoli that engulf dust particles, bacteria, and other pathogens.
Capillaries - dense network surround alveoli. They are usually seen in cross-section and can be identified by finding a red blood cell within a lumen next to an endothelial cell.
Smooth Muscle - often found at the ends of alveolar walls. (Not easily seen in this specimen.)