Histology of the urinary system Flashcards
Describe the histological structure of the outer cortex of the kidney
- It is granular in apperance, and it consists of:
1) Cortical arches
2) Renal columns (invagination of the cortex between the medulla)
What are the cortical arches?
- Found between the base of the pyramids and the surface of the kidneys, each arch consists of:
1) Medullary/cortical rays (rays of the medulla “referring to their destination” that contain the collecting tubule and the collecting ducts)
2) Plain convoluted part (contains the renal corpuscle “cortical and juxtra medullary nephrons” and the proximal and distal convoluted tubules)
What is the renal column?
- The area between the adjacent cortical arches
- It extends into the medulla between the two pyramids
- It contains few renal corpuscles and inter-lobar blood vessels
Describe the general distribution of the blood vessels in the parenchyma of the kidneys
1) Renal artery
2) Segmental/lobar artery
- Once they reach into the renal column, they become
3) Interlobar artery
- Once they reach the base of the pyramidal medulla
4) Arcuate artery
5) Interlobular artery (projects from the base of the pyramid to the cortex)
6) Afferent arterioles will then arise from the interlobular artery (which branches into a tuft of capillaries inside the glomerulus capsule)
- Then they join together, forming:
7) Efferent arterioles
- The efferent arterioles descend with the loop of Henle, forming:
8) Vasa recta
Summarize the blood supply of the kidney
renal artery - segmental/lobular - interlobar to arcuate - interlobular - afferent - capillary bed - efferent - vasa recta
Describe the venous drainage of the kidney
Starts from the interlobular vein - arcuate vein- interlobar vein - lobar/segmental vein - renal vein
What are the types of glomeruli?
1) Cortical glomerulus (Glomerulus of the cortex)
2) Juxtamedullary glomerulus (the clomerulus seen between the base of the pyramid and the cortex)
What is the artery that lines the base of the medullary pyramid?
The arcuate artery
What is the artery found in the renal column?
Interlobar artery
What is a kidney lobe?
The area of cortical arch that is bounded on either side by an inter-lobular BV and 1 medullary ray in the center
- 1 medullary ray between two interlobular blood vessels (this area is known as the lobule of the kidney)
What is the functional unit of the kidney?
- AKA uriniferous tubule, formed of two parts:
1a) Nephron
- Renal corpuscle (filtration)
- Glomerulus: Tuft of capillaries surrounded by:
- Glomerular (Bowman’s) capsule formed of a visceral and parietal part
- Renal tubule (selective reabsorption and secretion), formed of:
- Proximal convoluted tubule (PCT)
- Loop of Henle:
1) Thick descending portion
2) Thin descending portion
3) Thin ascending portion
4) Thick Ascending portion - Distal convoluted tubule (DCT)
- Collecting tubule
- As the collecting tubule goes down towards the medulla, they become larger and thicker, and they are called:
2b) Collecting ducts (papillary duct of Bellini)
What type of tissue forms the bowman’s capsule?
Simple squamous epithelium
Which parts of the uriniferous tubule are found in the renal cortex?
1) Renal corpuscle
2) Proximal convoluted tubule (most abundant)
3) Distal convoluted tubule
4) Medullary rays (bundles of collecting tubules and ducts that radiate towards the medulla)
Which parts of the uriniferous tubule are found in the renal medulla?
1) Loop of Henle
- Papillary ducts (the most distal)
2) Collecting ducts
3) Ducts of Bellini
What is the are cribrosa?
It is a porous area found at the apex of the pyramid where the ducts of Bellini opens
What are the types of nephron?
- Based on the location of their renal corpuscle in the cortex
1) Cortical nephrons
- 85% of all nephrons
- They are located in the cortex
- Short loop of Henle
2) Juxtamedullary nephrons
- Closer to the renal medulla
- Loops of Henle that extend deep into the renal pyramids
- Long loop of Henle
What is a renal corpuscle?
- Formed by the glomerulus (tuft of capillaries) and the bowman’s space
1) The vascular pole is formed by the afferent arteriole, which enters the corpuscle to supply the glomerulus
2) Urinary pole where substances leave the capillaries to enter into the renal tubule
Nuclei seen in a renal corpuscle belong to which cells?
1) Edothelial cells lining the capillaries
2) Mesangeal cells (the cells between the capillaries that are used for cushioning and support)
3) Podocytes (cells found on top of the capillaries that have a spider-like appearance)
4) Flattened nuclei of the squamous cells
What are the components of the glomerulus?
1) Glomerular capillaries
- They might contain erythrocytes
- They have a prominent basement membrane
- The nuclei of the endothelial cells might bulge into the lumen of the capillary
2) Mesangium
- Specialized connective tissue
- The mesangial substance is a densely stained extracellular substance that provides support for the capillary loops
3) Podocytes
- It invests the surface of the glomerular capillary loops, and it is exposed to the bowman’s capsule
- They have an extensive branching cytoplasm
What are the structural components of the glomerular filter?
1) Capillary endothelium
- It is fenestrated to permit the passage of all the non-cellular elements of the blood
2) Capillary basement membrane
- Non-fenestrated layer that acts as a glomerular ultra-filter; smaller molecules pass freely while the larger molecules are retained
3) Podocytes
- They envelop the glomerular capillaries
- They have a long cytoplasmic primary process, which give rise to short secondary foot processes (pedicles) that interdigitate and are directly applied to the glomerular basement membrane
- They have a slit pore (gaps between the interdigits, restricting the passage of the larger molecules
What are the components of the glomerular filter?
1) Plasma from the glomerular capillaries filtrates into the bowman’s space through the capillary endothelium, the capillary basement membrane and the slit pores of the podocytes
2) The podocytes have a phagocytic function to remove any large molecules that become trapped in the outer layer of the filter
3) The mesangial cells phagocytose molecules that are trapped in the endothelial side
Describe the proximal convoluted tubule
- Fund within the cortex
- Its reabsorptive function is reflected in the structure of the epithelial lining (which is simple, tall cuboidal epithelium
- It has a prominent brush border, which increases the surface area of the plasma membrane for the reabsorption of the flomerular filtrate
- It has a deeply stained cytoplasm due to the high content of the organelles (mainly the mitochondria)
- It is the longest and most convoluted part of the nephron, consisting of the bulk of the renal cortex.
- irregular lumen due to brush border, narrower lumen, not prominent nuclei due to ‘bipolar staining
What is the major constituent of the renal cortex?
The proximal convoluted tubule
What is the distal convoluted tubule?
- Found within the cortex
- Differentiated from the surrounding PCT via: (1. The absence of a brush border, 2. It contains a larger and more clearly defined lumen, 3. More nuclei are seen since the DCT cells are smaller, 4. They have a lesser affinity to the cytoplasmic stains due to lower content of organelles)
- Smooth border, larger lumen, prominent well-spaced nuclei
What is the key histological differences between the PCT and the DCT?
The distal convoluted tubule has a smoother border, larger lumen, and a prominent well-spaced nuclei, while the PCT has an irregular lumen, narrower lumen, and their nuclei are not prominent due to the biplar staining
Describe the histological structure of the loop of Henle
- They are found mainly in the renal medulla, composed of thin and thick segments
- The thin segments are made of simple squamous epithelium, they have a regular rounded shape, and there are no erythrocytes
- The thick segment is made up of low cuboidal epithelium, they are rounded in cross-section
- Loop of henle has no brush border
What type of tissue lines the thin segment of the loop of Henle?
Simple squamous epithelium
What type of tissue lines the thick segment of the loop of Henle?
Cuboidal epithelium
How do we differentiate between the thin and arteriolar segments of the loop of Henle? (since both of them are composed of simple squamous epithelium)
The arterioles have a collapsed lumen (lumen that is not well-defined) and RBC, while the thin segment is rounded in shape
How do we differentiate between the thick segment and the PCT of the loop of Henle? (since both of them are composed of cuboidal epithelium)
The proximal convoluted tubule has a tall cuboidal epithelium with a brish border, while the thick segment has low cuboidal epithelium with no brush border
Describe the histology of the collecting tubules
- Made of low cuboidal epithelium
- They have a wider and a less regular diameter than the ascending limb
Describe the histological structure of the collecting ducts
- Made of tall columnar epithelium (which is pale in stain)
- Mainly present in the medulla
- They have a larger diameter
- They have no brush border
How do we differentiate between the thick segment of Henle’s loop and the collecting tubule?
The thick segment has a smaller lumen, while the collecting tube has a larger lumen
What is the difference between the collecting tubule and collecting ducts?
The tubules are made of low cuboidal while the duct is made of columnar. The other thing is that the tubule has a narrower lumen, while the duct has a larger lumen
What is the juxtaglomerular apparatus?
- It lies adjacent to the renal corpuscle and the DCT, made by the cells of the afferent arterioles that touch the DCT (as they change, cells that lie in this vicinity become the juxtaglomerular cell) which are the:
1) Juxtaglomerular cells (cells of the afferent arteriole that touches the DCT)
2) Mecula densa (cells of the DCT that touch the arteriole)
- They regulate the systemic blood pressure via the renin-angiotensin-aldosterone mechanism
What are the juxtaglomerular cells?
- Modified smooth muscle cells of the afferent arteriole in the vascular pole of the renal corpuscle
- They contain secretory granules of renin
What is the macula densa?
- Modified DCT cells
- They are taller cells with a more prominent nuclei towards the luminal surface
Describe the histological layers of the urinary tract epithelium
- The urinary tract arises from the minor calyx - major calyx - renal pelvis - ureter - urinary bladder - and (till the) urethra
- Except for the urethra, they have the same general structure:
1) Mucosa
2) Muscularis
3) Adventitia/Serosa
Describe the histological components of the mucosa of the urinary tract
- Lined by transtional epithelium (except for the urethra), and it is also called the urothelium
- Stratified epithelium; which begins in the minor calyx (as two cell layer) and increases up to six in the empty bladder
- It has certain characteristics:
- Distensible: When relaxed, the surface epithelial cells are cuboidal and bulge into the lumen (“dome-shaped” cells), Interdigitating cell junctions permit great distension of the epithelium without damage to the surface integrity
- Impermeable: Does not modify urine, but specialized for storage and passage, and it has thick plasma membrane
Describe the histological structure of the transiotional epithelium?
- Surface surface
- Lamina propria
- Collagen fibers
- Fibroblasts
- Arteriole
- Venule
What is the histological structure of the ureter?
- They transport urine from the kidney to the bladder
- It has a stellate lumen (star-shaped)
1) Mucosa
2) Muscularis
3) Adventitia
Describe the mucosa of the ureter
- It is folded and gives the star-shaped lumen
- Made of transitional epithelium (transitional epithelium “lamina propria”, fibro-elastic connective tissue)
Describe the muscularis layer of the ureter
It consists of an inner longitudinal and outer circular layer (opposite to the GI tract), and in the distal part of the ureter, there is a third outer longitudinal layer that does peristaltic contractions (creating a star-shaped lumen)
Describe the adventitia of the ureter and its contents
- Made of loose connective tissue
- It contains blood vessels, lymphatics and nerves
Describe the histological structure of the urinary bladder
1) Mucosa
2) Muscularis
3) Adventitia/Serosa
Describe the structure of the mucosa of the urinary bladder
- Transitional epithelium, which are thrown into folds in the relaxed state
- It has a lamina propria (which might contain glands)
Describe the structure of the muscularis of the urinary bladder
- Smooth muscle that is irregularly arranged into layers (this irregular arrangement allows mass contraction for emptying “and not peristalsis”)
- Formed of 3-ill defined layers of smooth muscle (inner longitudinal, middle circular, and outer longitudinal)
How is the lamina propria of the urinary bladder different from that of the ureter
It can contain mucous glands at the neck of the bladder
Describe the histology of the urethra
- Its epithelium starts as transitional as it exits the bladder; it then changes to stratified columnar cells and stratified squamous cells near the external urethral orifice
- Transitional “as it exits the bladder” - stratified columnar - stratified squamous (near the external urethral surface”
- Three parts (1.Prostatic urethra, 2.Membranous part “surrounded by the muscle”, 3. The penile part “passes through the penic”)
Describe the histology of the prostatic urethra
- The prostate is a fibromuscular-gandular structure
- It is the portion of the urethra that passes through the prostate gland, just after the bladder
- It receives the ejaculatory ducts from the seminal vesicles and transports urine and semen
- It is lined by the transitional epithelium and surrounded by the prostate gland
- The prostatic urethra is made of (transitional epithelium which contains (prostatic glands) “Tubulo-alveolar, alveoli are wide, irregular, and have epithelial folds, they contain secretory products and a fibromuscular stroma
- The secretory products are seen as concretions due to calcification as someone ages (corpora amylasa), lamellated glycoprotein masses
What type of epithelium lines the prostatic urethra?
Transitional epithelium
What forms the fibromuscular stroma of the prostatic urethra?
1) Dense collagen
2) Fibroblasts
3) Irregularly arranged smooth muscle fibers
