1/2 - Histology

Question 1

What are the layers of a blood vessel?

Answer 1

Tunica Intima - thin layer of endothelium lining the vessel lumen, bounded by internal elastic membrane
Tunica Media - thicker layer of smooth muscle and elastic fibers (some times)
Tunica Adventitia - external, vascularized connective tissue and some smooth muscle (sometimes)

Question 2

What are the differences between the structure of veins and arteries?

Answer 2

Arteries contain a more muscular tunica media, which may also contain layers of elastin (large/named arteries) to allow extension during systole.
Veins may have bundles of smooth muscle in the tunica adventitia. In large/named veins this layer will actually be almost filled with smooth muscle.
In histology - veins will also appear collapsed compared to the more rigid arteries.

Question 3

What are the types of capillaries? Where would they typically be found?

Answer 3

Continuous - muscle, lung, CNS
Fenestrated - endocrine glands, gallbladder, kidney, GI tract
Discontinuous - liver, spleen, bone marrow

Question 4

What are the muscles of inhalation and exhalation?

Answer 4

Inhalation - diaphragm, external intercostals, scalene, and sternocleidomastoids

Exhalation (usually passive) - rectus abdominis. external oblique, internal intercostals, pectoralis minor, rhomboids

Question 5

What are the components of the olfactory epithelium/mucosa?

Answer 5

(From lumen) Olfactory cells -> supporting cells -> basal cells -> basement membrane -> olfactory (Bowman’s) glands, vessels, neural bundles

Olfactory cells are bipolar neurons with non-motile cilia that lie on the lumen surface. Their axons extend through the basement membrane to collect in discrete bundles that will travel into the olfactory cortex.
Bowman’s Glands release serous secretions to moisten apical surfaces of the epithelium.
Basal cells are the stem cells that differentiate to replace olfactory and supporting cells on a regular basis (~monthly).

Question 6

Describe the location and differences between the vocal folds.

Answer 6

True Vocal Folds (Cords) - located distal to false folds and interventricular folds; surface is stratified squamous epithelium, under which is vocalis muscle and vocal ligament
False Vocal Folds (Cords) - located proximally; surface is psuedostratified ciliated columnar cells epithelium, under which are serous glands

Question 7

Differentiate the structure of:

1) main bronchus
2) segmented bronchus
3) terminal bronchiole
4) respiratory bronchiole.

Answer 7

1) Main bronchus has a core of discontinuous hyaline cartilage on top of a layer of smooth muscle. Inside this is a layer of elastic fibers. The inner surface is peudostratified ciliated columnar epithelium and goblet cells.
2) Same as above, but smaller with less cartilage
3) Same as above, but NO: cartilage, goblet cells
4) Same as above, but NO: ciliated cells

Question 8

What is the affect of PO2 on pulmonary resistance?

Answer 8

As PO2 drops in an alveolus, the resistance in the arterioles feeding the capillary beds increases.
Blood flow to non-ventilated sections of the lung decreases, matching perfusion to ventilation.

Question 9

What are the cells of alveolar epithelium?

Answer 9

Type I - flat, thin squamous cells that cover most (~90%) of the lumen surface
Type II - larger, round cells that secrete surfactant; these develop in the late stages of gestation

Question 10

Describe the blood flow within the kidney.

Answer 10

Entering the Kidney via the renal artery, it divides into the interlobar arteries that travel up through the medulla between the renal pyramids(also called lobes).
The interlobar arteries terminate in the arcuate arteries that arch over the renal pyramids and act to demarcate the division between cortex and medulla.
From the arcuate arteries come the interlobular arteries, which give off branches (glomerular arterioles), which in turn terminate in peritubular capillaries.

Question 11

Describe Bowman’s Capsule.

Answer 11

• double epithelium that surrounds the glomerulus.
• parietal epithelium -> simple squamous epithelium; doesn’t participate in filtration; continuous with the PCT
• visceral epithelium -> composed of podocytes and their interlinking foot processes; forms the outer lining of the glomerulus capillary and the last part of the glomerular filtration
• bowman’s space/urinary space -> space between visceral and parietal epithelium that serves to collect the filtrate from the glomerulus and empty into the PCT

Question 12

Describe the glomerulus.

Answer 12

• A collection of dilated capillaries with FENESTRATED (no-diaphram) epithelium residing with Bowman’s Capsule
• starts at the afferent and ends at the efferent arteriole
• contains the Glomerular Basement Membrane that is a key part of filtration -> a multi-layered, charged membrane

Question 13

Describe Mesangial Cells.

Answer 13

Intraglomerular Mesangial -> enclosed within the basement membrane, they are responsible for phagocytosis within the glomerulus
Extraglomerular Mesangial -> part of the juxtaglomerular apparatus that participates in autoregulation; lies between Macula Densa and the afferent/efferent arterioles

Question 14

Describe the cells of the PCT.

Answer 14

• simple cuboidal cells WITH a brush border
• contain numerous endocytotic vesicles at the apical border
• contain numerous mitochondria
• connected via tight junctoins
• responsible for majority of reabsortion within the kidney

Question 15

Describe the cells of the Loop of Henle.

Answer 15

Thick -> simple (low) cuboidal epithelium
Think -> simple squamous epithelium
-no brush border
-specialized for electrolyte/H2O resorption-> thin descending limb is impermeable to Na; thick ascending limb is impermeable to H2O

Question 16

Describe the cells of the DCT.

Answer 16

• simple cuboidal epithelium
• NO brush border
• nuclei tend to be close to the apical/tubular lumen
• DCT is impermeable to H2O, but Na is actively resorbed

Question 17

Describe the Juxtaglomerular Apparatus.

Answer 17

JGA:

1) Macula Densa (part of the DCT) -> hypercellular region sensitive to changes in [NaCl] and volume in distal tubule
2) extraglomerular mesangial cells -> receive signal from MC and communicate to each other via Gap Junctions, and then to the JG Cells to illicit a response; also contractile cells sensitive to antiotensin II and atrial natriuretic factor to help regulate GFR
3) Juxtaglomerular Cells -> specialized myoepithelium in the afferent arterioles; sensitive to signaling from macula densa and is acts as an intrarenal baroreceptor -> secretes Renin to

part of smooth muscle of the afferent/efferent arteriole; secrete Renin

Question 18

Describe the cells of the Collecting System.

Answer 18

Each DCT empties into a Collecting Tubule which is divided into Cortical and Medullary.  The MCT then empty into the Collecting Duct, which will empty into the Minor Calyx.
Principle Cells (LIGHT cells): mostly clear cells with basal foldings; present throughout collecting system participating in water regulation; ADH sensitive, leading to migration of AQP2 to the apical border (APQ3/4 are always on basolateral border)
Intercalated Cells (DARK cells): primarily in cortical and medullary collecting tubules; important for Acid/Base regulation (Type I/II cells); lots of mitochondria and apical vesicles; MUCH less numerous than the Principle Cells

Question 19

Describe the histology of the ureter.

Answer 19

• lumen is covered by Transitional Epithelium
• Mucosa = epithelium + lamina propria
• multiple layers of smooth muscle: starts as helical near the kidney, but becomes progressively more longitudinal as it approaches the bladder; outer layer is circular

Question 20

Describe the histology of the bladder.

Answer 20

• lumen is covered by Transitional Epithelium (thicker when relaxed)
• smooth muscle: three layers -> inner longitudinal, middle circular, and outer longitudinal smooth muscle
• inner smooth muscle becomes the inner sphincter at junction with urethra