Urinary Apparatus

Question 1

Describe the Kidney structure from a longitudinal cut.

Answer 1

• organization into Renal pyramids separated by renal columns (lobe organization)
• Medullary region and cortical region.
• medullary rays!

Question 2

What are the surface features of the Kidney?

Answer 2

• Hilus
• Ureter
• Pelvis
• Papilla
• Collecting Ducts perforating each papilla ducts

Question 3

What are medullary rays?

Answer 3

Extensions of the medulla into the cortex (contains aggregation of straight tubules and collecting ducts).

Question 4

What surrounds the medullary rays?

Answer 4

Cortical Labyrinths (contains renal corpuscles and associated proximal and distal convoluted tubules)

Question 5

What are the components of a Nephron?

Answer 5

Renal Corpuscle
Proximal Convoluted Tubule (PCT)
Loop of Henle (Thin and Thick segments)
Distal convoluted Tubule (DCT)

Question 6

Describe the Renal Corpuscle and the structures it contains.

Answer 6

Contains Bowman’s Capsule in parietal/visceral layers Capillaries invade the Capsule through its visceral layer.

(Balloon example from class)

Question 7

What are the 3 types of Nephrons discussed?

Answer 7

Subcapsular/Cortical

• renal corpuscle in outer cortex
• short loops of Henle pass to outer medulla

Juxtamedullary

• renal corpuscles near cortico-medullary junction
• long loops pass to inner pyramid

Intermediate/Midcortical

• renal corpuscles in mid-region of cortex
• loops are intermediate length

Question 8

Describe the polarity of the Renal Corpuscle.

Answer 8

There is a Vascular Pole, where the capillaries bring blood in/out and the Efferent/Afferent Arterioles communicate with the Capsule.

There is a Urinary Pole, where the ultrafiltrate that is the precursor to urine is ultimately drained into the PCT.

Question 9

What is the space containing the ultrafiltrate called?

Answer 9

Bowman’s Space.

Question 10

How do you differentiate between an Afferent Arteriole and an Efferent Arteriole in the Renal Corpuscle?

Answer 10

The diameter of the Afferent Arteriole is greater than that of the Efferent.

Note: This should clue you into the pressure gradient inherently present in the Capsule.

Question 11

What cell types comprise the visceral layer of Bowman’s capsule?

Answer 11

Podocytes.

• Major processes (extend from nuclear region)
• Minor processes (extend from Major processes)

Question 12

What special feature do the podocytes give the Capsule?

Answer 12

Due to their interdigitation, they offer another layer of filtration on top of the fenestrated epithelium and the basal lamina.

The structure in between each podocyte is called a filtration slit diaphragm.

Question 13

What are the layers of filtration between the capillaries and Bowman’s space?

Answer 13

Fenestrated Epithelium
- restricts blood cells and other formed elements

Basal Membrane of capillaries
- restricts movement of particles larger than 70 kD like hemoglobin

Slit membrane in filtration slits
- physical barrier to free diffusion

Question 14

What are the factors that cause ultrafiltration to occur?

Answer 14

• Pressure gradient (afferent arteriole > efferent arteriole)
• large surface area for filtration
• barrier separating blood from Bowman’s Space is very thin

Question 15

How do the filters stay ‘clean’?

Answer 15

Mesangial cells actively maintain the filters through phagocytosis, contraction, secretion of cytokines and growth factors, and structural support.

Question 16

What are the functions of the Juxtaglomerular Apparatus? What are its two major components?

Answer 16

Regulation of blood pressure via renin-angiotensin-aldosterone system, acts as both baroreceptor and chemoreceptor.

AKA: Regulate BP and regulate salt levels!

Macula Densa and Juxtaglomerular Cells

Question 17

Where is the Macula Densa? What is its specific function?

Answer 17

Region at the end of the distal straight tubule. It samples Na+ concentration of tubular fluid (ultrafiltrate)

Question 18

Where are the Juxtaglomerular Cells? What is their specific function?

Answer 18

They are smooth muscle cells in tunica media of the Afferent Arteriole. They synthesize/secrete/store Renin, the protease that cleaves angiotensin.

Question 19

What is the Proximal Tubule (PT), and what is its function? Describe some of its characteristics as well.

Answer 19

It is the tube that begins at the urinary pole of the Renal Corpuscle. It has a straight portion and a convoluted portion

It is the major site of resorption (proteins, amino acids, and glucose). It is lined with a single layer of cuboidal cells a brush border and folds to increase its surface area.

CONSTITUTES BULK OF RENAL CORTEX and ONLY runs in the cortex.

Question 20

What is actively transported in the PT?

Answer 20

NaCl (water will follow through aquaporin type 1)

Question 21

Is the Collecting Duct part of the Nephron?

Answer 21

NOPE.

Question 22

How does one differentiate the PCT from the Distal Convoluted Tubule (DCT) on a slide?

Answer 22

PCT will still contain matter in its lumen (process of resorbing), while DCT lumen will be clear.

Question 23

What is the Loop of Henle comprised by?

Answer 23

• Straight part of the proximal tubule in descending limb
• thin segment in descending and ascending limbs
• straight part of the distal tubule in ascending limb.

Question 24

Is there active transport in the Loop of Henle?

Answer 24

No, it requires no ATP.

Question 25

Describe the permability of various regions of the Loop of Henle to water and NaCl.

Answer 25

Descending thin loop: - Permeable to water - Low permeability to NaCl Ascending thin loop - Impermeable to water - High permeability to NaCl

Question 26

Describe the thick segment of the ascending portion of Loop of Henle.

Answer 26

- Squamous cells -> Cuboidal cells - Macula Densa formed! - Basal infoldings with mitochondria (indicative of active transport) - NO BRUSH BORDER - Active transport of Na+ from urine to Interstitium (other ions resorbed as well: Cl-, K+, Ca2+, Mg2+)

Question 27

What is the Distal Convoluted Tubule (DCT)?

Answer 27

Begins at macula densa and empties into collecting tubule which empties into the collecting duct. Resorbs Na+, which is followed by water. (Note: Aldosterone will increase Na+ resorption). K+ secreted into lumen to maintain ionic equilibrium. Urine becomes acidic from H+ secretion and Bicarbonate resorption.

Question 28

What are Collecting Ducts? Describe their location and structure.

Answer 28

Collecting tubules from the Nephron will empty into Collecting Ducts: long ducts that descend in Medullary Rays into the Medulla, where several collecting ducts will join to form larger Papillary Ducts.

Question 29

Where do Papillary Ducts drain?

Answer 29

Into the apex of a Papilla, which opens into minor Calyx at the Area Cribrosa.

Question 30

How do you identify the different cells of the Collecting Duct's epithelium?

Answer 30

Lighter cells contain Aquaporins Darker cells secrete H+ or Bicarb as required.

Question 31

What is the Area Cribrosa?

Answer 31

The "tip" of a Renal Pyramid where all the capillaries/collecting ducts(?) empty into the Minor Calyx.

Question 32

Describe the Blood Supply of the Kidney.

Answer 32

Renal Artery -> Segmental Arteries -> Interlobar Arteries -> Arcuate Arteries -> Interlobular Arteries -> Afferent Arterioles -> NEPHRON -> Venules -> Interlobular Veins -> Arcuate veins -> Interlobar Veins -> REnal Veins.

Question 33

What happens to Efferent Arterioles?

Answer 33

They arise from the Glomeruli and give rise to a Peritubular Capillary Network in Cortical Nephrons, and Vasa Recta in Juxtamedullary Nephrons.

Question 34

What happens in the Countercurrent Exchange System for blood?

Answer 34

Arterial side of the Loop will lose water to/gain salt from the interstitium. Venous side of the Loop will lose salt to/gain water from the Interstitium. This occurs WITHOUT energy expenditure.

Question 35

What fibers is the Renal Plexus mostly composed of?

Answer 35

Sympathetic division. They cause contraction of vascular smooth muscle and consequent vasoconstriction.

Question 36

What does constriction of the Afferent/Efferent Arterioles do to Urine production?

Answer 36

Afferent constriction = reduce (due to less blood flowing in) Efferent constriction = increase (due to increased resistance of flow out)

Question 37

Describe the flow of urine.

Answer 37

Renal Papilla -> Minor Calyx -> Major Calyx -> Renal Pelvis -> Ureter -> Bladder -> Urethra

Question 38

All the excretory structures of urination have what three layers?

Answer 38

Mucosa (very thin lamina propria) Muscularis Adventitia Note lack of Submucosa

Question 39

What is Transitional Epithelium?

Answer 39

Specialized epithelium that resists any kind of absorption of salts and water and allows for distensibility, especially in ureter and bladder. 2-3 cells thick at level of Calyces 4-5 cells thick in ureter and bladder. Note: you can observe binucleation in some cells.

Question 40

Describe a cross-section of the Ureter.

Answer 40

Muscularis Externa is opposite of GI tract: Inner layer is Longitudinal, Outer Layer is Circular. Lumen is stellate.

Question 41

Describe the Bladder walls.

Answer 41

There is a lot more smooth muscle in the walls of the Bladder (3 Layers), particularly a prominent middle layer. Fusiform Vesicles in the Bladder walls will 'unfold' into the epithelial layer when the Bladder needs to distend, giving more surface area to the wall.

Question 42

Compare the Male and Female Urethras.

Answer 42

Male: 20 cm long with 3 distinct segments - Prostatic: 4 cm - Membraneous: 1 cm - Penile: 15 cm Note: Stratified/Psuedostratified Columnar in Membraneous and Penile Urethra Female: 3-5 cm long - epithelium goes from transitional to stratified squamous epithelium.