Urinary Apparatus Flashcards
Describe the Kidney structure from a longitudinal cut.
- organization into Renal pyramids separated by renal columns (lobe organization)
- Medullary region and cortical region.
- medullary rays!
What are the surface features of the Kidney?
- Hilus
- Ureter
- Pelvis
- Papilla
- Collecting Ducts perforating each papilla ducts
What are medullary rays?
Extensions of the medulla into the cortex (contains aggregation of straight tubules and collecting ducts).
What surrounds the medullary rays?
Cortical Labyrinths (contains renal corpuscles and associated proximal and distal convoluted tubules)
What are the components of a Nephron?
Renal Corpuscle
Proximal Convoluted Tubule (PCT)
Loop of Henle (Thin and Thick segments)
Distal convoluted Tubule (DCT)
Describe the Renal Corpuscle and the structures it contains.
Contains Bowman’s Capsule in parietal/visceral layers Capillaries invade the Capsule through its visceral layer.
(Balloon example from class)
What are the 3 types of Nephrons discussed?
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
Describe the polarity of the Renal Corpuscle.
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.
What is the space containing the ultrafiltrate called?
Bowman’s Space.
How do you differentiate between an Afferent Arteriole and an Efferent Arteriole in the Renal Corpuscle?
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.
What cell types comprise the visceral layer of Bowman’s capsule?
Podocytes.
- Major processes (extend from nuclear region)
- Minor processes (extend from Major processes)
What special feature do the podocytes give the Capsule?
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.
What are the layers of filtration between the capillaries and Bowman’s space?
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
What are the factors that cause ultrafiltration to occur?
- Pressure gradient (afferent arteriole > efferent arteriole)
- large surface area for filtration
- barrier separating blood from Bowman’s Space is very thin
How do the filters stay ‘clean’?
Mesangial cells actively maintain the filters through phagocytosis, contraction, secretion of cytokines and growth factors, and structural support.
What are the functions of the Juxtaglomerular Apparatus? What are its two major components?
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
Where is the Macula Densa? What is its specific function?
Region at the end of the distal straight tubule. It samples Na+ concentration of tubular fluid (ultrafiltrate)
Where are the Juxtaglomerular Cells? What is their specific function?
They are smooth muscle cells in tunica media of the Afferent Arteriole. They synthesize/secrete/store Renin, the protease that cleaves angiotensin.
What is the Proximal Tubule (PT), and what is its function? Describe some of its characteristics as well.
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.
What is actively transported in the PT?
NaCl (water will follow through aquaporin type 1)
Is the Collecting Duct part of the Nephron?
NOPE.
How does one differentiate the PCT from the Distal Convoluted Tubule (DCT) on a slide?
PCT will still contain matter in its lumen (process of resorbing), while DCT lumen will be clear.
What is the Loop of Henle comprised by?
- 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.
Is there active transport in the Loop of Henle?
No, it requires no ATP.
Describe the permability of various regions of the Loop of Henle to water and NaCl.
Descending thin loop:
- Permeable to water
- Low permeability to NaCl
Ascending thin loop
- Impermeable to water
- High permeability to NaCl
Describe the thick segment of the ascending portion of Loop of Henle.
- 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+)
What is the Distal Convoluted Tubule (DCT)?
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.
What are Collecting Ducts? Describe their location and structure.
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.
Where do Papillary Ducts drain?
Into the apex of a Papilla, which opens into minor Calyx at the Area Cribrosa.
How do you identify the different cells of the Collecting Duct’s epithelium?
Lighter cells contain Aquaporins
Darker cells secrete H+ or Bicarb as required.
What is the Area Cribrosa?
The “tip” of a Renal Pyramid where all the capillaries/collecting ducts(?) empty into the Minor Calyx.
Describe the Blood Supply of the Kidney.
Renal Artery -> Segmental Arteries -> Interlobar Arteries -> Arcuate Arteries -> Interlobular Arteries -> Afferent Arterioles -> NEPHRON -> Venules -> Interlobular Veins -> Arcuate veins -> Interlobar Veins -> REnal Veins.
What happens to Efferent Arterioles?
They arise from the Glomeruli and give rise to a Peritubular Capillary Network in Cortical Nephrons, and Vasa Recta in Juxtamedullary Nephrons.
What happens in the Countercurrent Exchange System for blood?
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.
What fibers is the Renal Plexus mostly composed of?
Sympathetic division. They cause contraction of vascular smooth muscle and consequent vasoconstriction.
What does constriction of the Afferent/Efferent Arterioles do to Urine production?
Afferent constriction = reduce (due to less blood flowing in)
Efferent constriction = increase (due to increased resistance of flow out)
Describe the flow of urine.
Renal Papilla -> Minor Calyx -> Major Calyx -> Renal Pelvis -> Ureter -> Bladder -> Urethra
All the excretory structures of urination have what three layers?
Mucosa (very thin lamina propria)
Muscularis
Adventitia
Note lack of Submucosa
What is Transitional Epithelium?
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.
Describe a cross-section of the Ureter.
Muscularis Externa is opposite of GI tract: Inner layer is Longitudinal, Outer Layer is Circular.
Lumen is stellate.
Describe the Bladder walls.
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.
Compare the Male and Female Urethras.
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.
