Introduction

The slides for this lab are located in the “” folders on the Virtual Microscope. In

this lab, you will learn about the structures within the required to filter the blood and the tubes required to transport the resulting waste products outside the body.

The journey begins in the unit of the kidney called the . Here the blood is filtered, products are reabsorbed and then some are secreted again, based on the body’s current state. Dissolved in water, these products then travel through the conducting portion of the kidney to the . The ureters insert on the obliquely and posteriorly. The urinary bladder temporarily stores urine until it can be conveniently evacuated. Urine exits the body through the .

Learning objectives and activities Using the Virtual Slidebox:

A Outline a renal lobe and identify the structural components of a renal lobule

B Examine the components of the : and Bowman’s capsule

C Classify the different areas of the renal tubules based upon their histological appearance and location

D Compare the structures of the excretory passageways and use this information to identify them

E Complete the self-quiz to test your understanding and master your learning

Outline a renal lobe and identify the structural components of a renal lobule

Examine Slide 1 and approximate a renal lobe in the kidney by identifying the following:

Each kidney can be divided into somewhere between 8-15 renal lobes. Each lobe consists of a medullary pyramid capped by the cortex and flanked by renal columns with a renal papilla at its apex. The lobe is not readily seen histologically because it is a large, gross structure. This slide is a slide of a mouse kidney. The tiny lobes in a mouse kidney are actually all fused together to form a single large lobe. As a result you will not see any renal columns in this section. i. General organization Identify the renal a. capsule in A thin outer layer of connective tissue. Slide 1a

b. Identify the renal The outer layer of functional tissue containing glomeruli, proximal cortex in and distal convoluted tubules and medullary rays. Slide 1b

c. Identify the renal The inner layer of functional tissue that contains the Loops of medulla in Henle and collecting ducts as they course through the kidney. Slide 1c d. Cortico-medullary junction Identify the cortico- The junction between cortex and medullary. The arcuate arteries medullary junction in run along this junction as they send intralobular arteries into the Slide 1d cortex.

e. Renal papilla Identify the renal The region of medulla that forms the apex of a renal pyramid. The papilla in papilla protrudes into the minor calyx. The collecting ducts Slide 1e terminate here and urine drips through tiny holes (area cribrosa) into the calyx.

f. Minor calyx Identify the minor The initial part of the urinary passageways that convey urine to calyx in the bladder. Minor calyces unite to form major calyces which Slide 1f drain to the and then .

ii. Renal lobe Remember that the lobe is not readily seen histologically because it is a large, gross structure. This slide is a slide of a mouse kidney. The tiny lobes in a mouse kidney are actually all fused together to form a single large lobe. As a result you will not see any renal columns in this section.

a. Renal cortex The cortex forms the base of the approximately triangular renal lobe.

b. Renal pyramid The medullary pyramids extend from the base and taper to form the renal papilla. Identify the components of a renal c. lobe in Slide 1 The lateral aspects of a renal lobe in a human kidney are formed by half a renal column on each side. Refer to the lecture notes to see these as the images in the lab are not from human kidneys.

d. Renal papilla The renal papilla is the apex of a renal lobe.

iii. Renal lobule

Use Slide 2 to outline a renal lobule

The kidney lobe can further be divided into lobules. A renal lobule is centered about a series of straight collecting ducts called a medullary ray. It is flanked on either side by .

a. Interlobular artery Identify the Branches of the arcuate artery (this runs along the cortico- interlobular arteries medullary junction) that extend in to the cortex. They form the that flank a lobule in outer limits of a renal lobule. Slide 2a

b. Medullary ray Multiple located between the interlobular arteries all Identify the medullary drain into a common group of collecting ducts that run within a rays within a lobule in medullary ray. The medullary rays radiate into the medulla and Slide 2b lie centrally within a lobule.

Examine the components of a renal corpuscle The renal corpuscle is composed of a capillary ball engulfed by the proximal end of a nephron known as a Bowman’s capsule. This develops in much the same way as the lungs are engulfed by the pleura during embryonic development. As a result the capillaries are covered in a visceral layer of the Bowman’s capsule (these cells are called ). The outer layer of the glomerulus is formed by the parietal layer of the Bowman’s capsule.

Use Slide 3 to identify all the components of a renal corpuscle i. Glomerulus Examine a glomerulus a. Vascular pole and find the vascular The region where the afferent and enter the pole in Slide 3a renal corpuscle to form the glomerulus

b. Glomerulus The capillary ball engulfed by the visceral layer of the Bowman’s Examine a glomerulus capsule (podocytes). The endothelial cells and podocytes are and look at its cellular indistinguishable from each other histologically. components in Slide 3b ii. Bowman’s capsule

c. Visceral layer (podocytes) Look at the cells The podocytes surround the endothelial cells of the glomerular covering the capillary ball. They are a specialized mesothelial cells, glomerular capillaries indistinguishable from the underlying endothelial cells Slide 3c histologically. (some are podocytes)

d. Urinary space The space surrounding the glomerulus into which the glomerular Identify the urinary filtrate flows space in Slide 3d

e. Parietal layer Find the parietal layer The outermost layer of mesothelial cells that encloses the urinary of the Bowman’s space. capsule in Slide 3e f. Urinary pole The point where the Bowman’s capsule becomes the proximal Locate the urinary convoluted tubule. It is always opposite the vascular pole. pole in Slide 3f

Classify the different areas of the renal tubules based upon their histological appearance and location

The renal tubule is a long looping tube that emerges from the urinary pole of the renal corpuscle before descending, ascending and then finally descending for a final time through the cortex and medulla.

Use Slide 4, Slide 5 and Slide 6 to practice identifying all of the following regions of the renal tubule. a. Proximal Convoluted Tubule (PCT) PCTs are the most prevalent tube in the renal cortex. You can find them by looking for a tube with:

Simple cuboidal epithelium 4a o o Microvilli (occludes lumen) o Basal striations (stacks of mitochondria for ATP) o Large cells with ‘missing’ nuclei

Find PCTs in Slide 4a and Slide 5a

b. Thick limbs of 4b Upon reaching the cortico-medullary junction the PCT turns into the descending thick limb. When the LoH returns to the cortex after making its hairpin turn it has a thick ascending limb. Thick limbs look just like PCTs or DCTS but are located in the medulla.

Find thick limbs in Slide 4b and Slide 5b

c. Thin limbs of Loop of Henle Have a descending and ascending part that are

continuous proximally and distally with the thick 4c

limbs. It forms the hairpin region of the loop. You can find them because they are located in the medulla and have a simple squamous epithelium.

Find thin limbs in Slide 4c and Slide 5c d . (DCT) Found in the renal cortex, this section of the renal 4d tube is less prevalent than the PCT so you won’t see as many examples in the cortex of the kidney. The DCT is characterized by:

o Simple cuboidal epithelium o Sparse microvilli (open lumen) o Small cells (nucleus is almost always present) Find DCTs in Slide 4d and Slide 5d e. The specialized region of the DCT located at the 4e vascular pole of the renal corpuscle. It is these cells that are involved in monitoring sodium ion concentration in the ultra-filtrate.

Find a macula densa in Slide 4e and Slide 5e f . Collecting duct The collecting ducts receive filtrate from the DCTs of multiple nephrons in the medullary rays within the 5f center of a renal lobule in the cortex. The ducts then descend into the medulla. Look for:

o Simple cuboidal epithelium o Large central nucleus o Prominent intercellular limits

Find collecting ducts in Slide 5f and Slide 6f g. Ducts of Bellini Several collecting ducts converge onto one Duct of Bellini in the inner medulla. You can find them by 6g looking for:

o Simple cuboidal epithelium o Large central nucleus o Prominent intercellular limits

Find ducts of Bellini in Slide 6g

Compare the structures of the excretory passageways and use this information to identify them Once the urine exits the medulla of the kidney at the area cribrosa of the renal papilla, it enters into the minor calyces, the major calyx and renal pelvis before making its way through the ureter to the bladder where it is stored until urination occurs. From here it passes through the urethra to the outside world. All of these structures are specialized for transport and/or storage of urine. They majority of these structures are lined with transitional epithelium to accommodate stretch and resist urine toxicity.

i. Ureter

Use Slide 7 to identify the following features of the ureter

Examine the a. Mucosa epithelium of the - lined with a transitional epithelium mucosa in Slide 7a - is characteristically folded

b. Muscularis externa Examine the smooth - thick layer of smooth muscle muscle in the - inner loose spiral muscularis in Slide 7b - outer tight spiral

ii. Urinary bladder

Use Slide 8 to identify the following features of the urinary bladder

Examine the a. Mucosa epithelium of the - when empty is folded into rugae that permit stretch as the mucosa in Slide 8a bladder fills. - lined by transitional epithelium Examine the smooth b. Muscularis externa muscle in the - three layers of smooth muscle form a . muscularis in Slide 8b

iii. Urethra (female)

Use Slide 9 to identify the following features of the urethra

a. Mucosa Examine the - lined with transitional epithelium proximally. epithelium of the - progresses to non-keratinized stratified squamous epithelium mucosa in Slide 9a as it approaches the exterior of the body

b. Muscularis externa Examine fibro- - layers of smooth muscle are mixed with connective tissue muscular muscularis in making the muscularis a fibromuscular stroma. Slide 9b

c. External urethral sphincter Can you find evidence - If the section is made in the appropriate region it may be of the external possible to locate a region of skeletal muscle that forms the urethral sphincter in voluntary sphincter. Slide 9c iii. Penile urethra (male)

Use Slide 10 to determine that the penile urethra runs through the corpus spongiosum and has non-keratinized stratified squamous epithelium in this region.

a. Penis - observe the paired corpus cavernosa (erectile tissue). - observe the unpaired corpus spongiosum - note that the penile urethra runs through the c. spongiosum

b. Mucosa - The mucosa of the penile urethra has already transitioned to a ‘moist’ protective lining mucosa. Similar to that seen in other ‘moist’ areas of the body: non-keratinized stratified squamous.

In addition to all the basic tissues in slides you must be able to identify the following structures and their features:

Kidney Renal lobe Renal cortex Renal pyramid Renal column Renal papilla Renal lobule Interlobular artery Medullary ray Renal cortex Renal corpuscle Glomerulus Visceral layer of Bowman's casule () Parietal layer of Bowman’s capsule Urinary space Urinary pole Vascular pole Proximal convoluted tubule (PCT) Distal convoluted tubule (DCT) Macula densa Interlobular artery Cortico-medullary junction Arcuate artery Renal medulla Loop of Henle (thick limb) Loop of Henle (think limb) Collecting ducts Ducts of Bellini Renal papilla

Excretory pathways Minor calyx Major calyx Renal pelvis Ureter Urinary bladder Urethra Penile urethra Transitional epithelium