Describe the overall gross and microanatomy of the kidney, including descriptions of: 

• contents of the cortex and medulla

• renal columns and medullary rays

• renal lobes vs. lobules

• renal papillae, renal pelvis & calyces, and renal sinus

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I. Cortex--outer portion that contains:

(a) Renal corpuscles - (glomerus + visceral & parietal epithelial capsule)

(b) Convoluted tubules (proximal and distal) -

(c) Collecting ducts

(d) Vascular network

(e) Medullary rays: regions of medullary-type tubules in the cortex, associated with "cortical nephrons"

II. Medulla--inner portion (when cut at proper angle, looks like a pyramid with base at cortical interface and apex pointed toward renal pelvis)

(a) Henle's loop (thick & thin portions)

(b) Vasa recta - form a series of straight capillaries  in the medulla that lie parallel to the loop of Henle.

(c) Collecting ducts

(d) Renal columns: regions of cortical-type tissue extending deep into the medulla, separating the medullary pryamids.

III. Renal Lobe - anatomic unit, than functional unit

(a) a medullary pyramid with its overlying cortex and surrounding renal columns.

IV. Renal lobule - the collecting ducts of a medullary ray and all the neophrons they drains

V. Renal papillae - The confluence of collecting ducts, which drain into thte renal pelvis

VI. Renal pelvis -> the region where urine accumulates to drain into the ureter, subdivided in calyces which ocver the tips of the renal papillae and receive the urine dripping form the collecting ducts. Lined by urothelium

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Renal artery

Interlobar arteries - b/w lobes, traveling in renal columns to cortex

Arcuate arteries- form arches running at interface b/w cortex and medulla

interlobular arteries- branches from arcuate

Afferent arterioles

Capillaries of the glomerulus

efferent ARTERIOES**

(i) -Peritubular capillaries (assoc. w/ convoluted tubules)

(ii) -Vasa Recta (assoc. w/ Henle's loop & CC exhange- concentrates the urine)

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peritubular capillaries

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vasa recta

Define "nephron" and describe its various parts. Identify each in photographs and diagrams. Include identification & discussion of distinguishing features & function of:

• structure of the renal corpuscle

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The nephron is the functional unit of the kidney composed of 5 major divisions. One of them is the renal corpuscle.

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arrow: "Vascular pole"--the point of entry/exit of the arterioles from the renal corpuscle

Renal corpuscle = glomerulus + glomerular (Bowman's) capsule

Glomerulus - is a loose knot of capillaries with afferent and efferent arterioles (not veins)

Glomerular epithelial capsule (Bowman's) - has two layers

(A) Visceral Layer - covering glomerular capillaries

(B) Parietal Layer - defining the outer layer of the renal corpuscle and continuing on to form the proximal convuluted tubule (simple squamous-> cuboidal at TP)

(C) Urinary space - space b/w the layers, where glomerular filtrate collects to drain into the prximal convoluted tubule

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TP: Exit of the proximal convoluted tubule
from the urinary space is the “tubular pole” or “urinary pole”

(D) Mesangium - pericyte-like cells & their extracellular matrix--they fill the interstices between capillaries that lack podocytes

Functions include:

Support the glomerular capillaries, including
contractile & phagocytic properties
Secrete cytokines (including IL-1),
prostaglandins, growth factors (including PDGF  [platelet-derived growth factor]) & other substances of innate defense

Lacis cells - Also extend beyond the renal corpuscle at the vascular pole to support the juxaglomerular apparatus

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MM: Mesangial matrix MC: Mesagnial cell

P: Podocyte PD: Pedicels

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Define "nephron" and describe its various parts. Identify each in photographs and diagrams. Include identification & discussion of distinguishing features & function of:

• Proximal convoluted tubule

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Proximal Convoluted tubule

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A. Composed of simple cuboidal epithelium with a prominent apical brush border (microvilli) and extensive basolateral plasma membrane infolding with numerous mitochondria

B. Are the major site for reabsorption of H2O and filtered solutes being returned to the blood, including essentially all filtered glucose

• Endocytosis (pinocytosis) - removes proteins & other macromolecules that have escaped the GCM border

• Secretion into the urinary filtrate

• Channels and pumps - transcellar movement

C. Peritubular capillaries directly take up the solutes and water transferred across the tubular wall.

D. Tubular secretion - to rid of foreign compounds and organic ions by moving them from the peritubular capillaries -> tubular lumen

E. Vitamin D hydroxylation

Define "nephron" and describe its various parts. Identify each in photographs and diagrams. Include identification & discussion of distinguishing features & function of:

• Loop of Henle

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Loop of Henle (Nephron Loop)

A. Thick descending portion - extension of proximal convoluted tubule
B. Thin descending portion - thin simple squamous epithelium
C. Thin ascending portion -
D. Thick ascending portion - cuboidal, returning to the vascular pole of its original glomerulus (where it is part of the juxtaglomerular appartus) -> distal convoluted tubule

• The ascending limb is impermeable to H2O, while allowing movement of electrolytes

• Vasa recta accompany the straight tubules

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thin limbs: simple squamous

thick limbs: simple budoial

collecting ducts: pale columnar cells

Define "nephron" and describe its various parts. Identify each in photographs and diagrams. Include identification & discussion of distinguishing features & function of:

• Distal convoluted tubule

Distal convoluted tubule

I. Composed of simple cuboidal but NO brush border, only scattered short microvilli;
II. Has extensive basolateral plasma membrane infolding with mitochondria, supporting the function of transporters; Na/K pumps in these cells are regulated by aldosterone

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D: DCT

P: PCT

G: glomerulus

U: Urinary space

TP: tubular pole

Arrows: pertubular capillaries and draining venules

Fibroblastic interstitial cells of cortex - source of erythropoietin--released in response to a prolonged decrease in local O2 concentration

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Juxtaglomerular Apparatus

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A. Macula densa of the distal tubule- thickened spot of the tubule wall

•Composed of modified tubular epithelial cells: larger, taller, more closely-packed than usual tubular

•Sense sodium and/or chloride concentrations in urinary fluid and transfer signal to glomerular arterioles

B. Juxtaglomerular (JG) cells of the afferent arteriole- Modified smooth muscle cells of tunica media of glomerular arterioles containing membrane-bound granules of renin

•Release renin by exocytosis into blood

C. Extraglomerular (Lacis) mesangial cells

•Connected by gap junctions and can communicate signals from extraglomerular environment to glomerulus
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D: distal tubule (at vascular pole)

G: glomerulus MD: Macula densa

AA: afferent arterioles

EA: efferent arteriole

P: proximal tubules

US: urinary space

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Connecting Tubules/Ducts

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VR: vasa recta

I. Tubules from multiple nephrons join to form ducts (no longer part of a nephron, since they are formed from the joining of tubules from several nephrons & have a different embryologic origin)

II. Composed of simple cuboidal epithelium
III. Two epithelial cells types (both are large cells with clear cytoplasm, sharply defined cell borders and scanty microvilli): 

Principal cells - few organelles, microvilli
Intercalated/Dark cells - abudant mitochondria, acid-base regulation; secrete H+, absorb HCO3-

IV. Rich in aquaporins for H2O transport
V. Arginine vasopressin (ADH) receptors of basolateral membranes of collecting duct cells respond to ADH => insertion of aquaporins into plasma membrane, changing permeability of tubule to water
VI. Permeability is modulated by anti-diuretic hormone (ADH) => inc. permeability of the collecting tubule epithelium so that the urine takes on the tonicity of the hypertonic medulla.

Cortical nephrons vs. juxtamedullary nephrons

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Cortical nephrons

• Located in outer cortex
• Have shorter loops of Henle which do not descend deeply into the medulla if at all
• Thick portion may begin even before the U-turn of the loop
Juxtamedullary nephrons
•Located just above the medulla (still located in cortex)
•Have long loops of Henle that descend deeply into medulla with accompanying vasa recta

Ureter: A muscular (smooth muscle) tube with a stellate lumen lined by urothelium

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Bladder -

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- A hollow muscular organ lined by urothelium
- Mucosa consists of urothelium, a loose lamina propria and an incomplete, ill-defined muscularis mucosa; underlying this is an ill-defined submucosa of
loose CT
-Muscularis propriais smooth muscle arranged in poorly-defined “three” layers, each spiraling in
different directions

Urethra - tube that carries the urine from bladder to exterior

The epithelium is variable
- It is urothelial near the bladder and is stratified squamous near the external orifice
- In between it may be columnar, pseudostratified
columnar or truly stratified columnar

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female

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male

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prostatic - extends through prostate gland

Define "nephron" and describe its various parts. Identify each in photographs and diagrams. Include identification & discussion of distinguishing features & function of:

• Glomerulus & Visceral epithelial capsule

The glomerulus & Visceral epithelial capsule - define the anatomic basis of glomerular filtration

A. Podocytes – visceral capsule epithelial cells that surround glomerular capillary loops

•Have cytoplasmic processes called “foot processes” or “pedicels” that terminate on the basal lamina of the capillary loop.
•The pedicels interdigitate with spaces in between
called filtration slits.

B. Glomerular capillary endothelial cells – highly
fenestrated, without diaphragms in the fenestrae

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Arrowhead: filtration slit

C. Glomerular basement membrane (GBM)-- a fusion of basal laminae of both endothelial & epithelial cells

•The laminin, fibronectin, type IV collagen, & negatively charged proteoglycans form a selective barrier against negatively charged molecules to filtration
•The GBM is the major barrier to filtration of large molecules & damage to the GBM can result in abnormal loss of large molecules into the urine

D. Afferent & efferent arteriole muscular walls -  allow control of local intraluminal capillary pressure, controlling flow and glomerular filtration rate

What does the cell type (indicated by the arrow produce)?

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Peritubular interstitial cells

produce growth hormone erythropoietin in response to a prolonged decrease in the local O2 concentration

Describe the ultrastructure of urothelium ("Transitional Epithelium")

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Urothelium - A specialized stratified epithelium characterized by surface epithelial cells called “umbrella cells” or “cap cells”

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- Umbrella cells are large, often multinucleated, cells
with unusual apical plasma membranes

- Apical plasma membrane has lipid rafts with uroplakins, integral membrane proteins that assemble into plaques that protect against the hyperosmotic damage of the urine contained in the bladder

- When the bladder is not expanded, these plaques can be internalized into the umbrella cells as vesicles, which can be re-inserted into the plasma membrane as the bladder expands