Urinary+System

=**Objectives**=


 * 1. List the organs of the urinary system and give their functions**

Kidney: Produces urine, located on posterior wall at level of T12 – L3 vertebrae Ureter: Carries urine from kidney to bladder Urinary Bladder: Located behind pubic bone, temporary storage of urine Urethra: Carries urine to exterior of body

5 functions of the system:
 * 1) Remove metabolic wastes from blood and excrete urine from the body
 * 2) Conserve salts, glucose, proteins and water for the body
 * 3) Helps to regulate blood pressure and acid-base balance of body
 * 4) One of organs that participates in the formation of Vitamin D
 * 5) Has endocrine function as well as exocrine function
 * [|Erythropoietin]: stimulates red blood cell production
 * [|Renin]: stimulates increase in blood pressure
 * Medullipin I: stimulates decrease in blood pressure


 * 2. List and describe the gross external structure of the kidney.**

Retroperitoneal, surrounded by a [|Renal Capsule] of dense irregular CT, supported by; Perirenal fat, Renal Fascia, and Pararenal fat. Clinical correlation: Nephrotosis “Floating kidney”, kidney drops into pelvis due to deficient renal fascia or adipose tissue.
 * Renal Hilum : Indentation on medial side, entrance for renal artery, vein, lymphatics and exit of ureter
 * Renal Sinus : Indentation into mass of kidney, which contains the renal pelvis
 * Renal pelvis: tapers to form ureter, contains branches of renal artery, vein & lymphatic vessels, filled with adipose tissue


 * 3. List and describe the gross internal structure of the kidney.**


 * [|Cortex] - darker staining material at periphery of gland, containing [|Renal Corpuscles] *//Diagnostic of cortex//
 * [|Medulla] - lighter staining material in central region composed of:
 * [|renal pyramid]: //apex// of pyramid points towards renal sinus, //renal papillae// apical tip of pyramid base of pyramid at //cortico-medullary junction//.
 * [|renal columns] (cortical columns): cortical material extending down into medulla between the pyramids
 * [|Lobes]: pyramid plus overlying cortical material, human kidney is multi lobar.
 * [|Lobules] are subdivision of cortex: //medullary rays// are located at center of lobule, //cortical labyrinth// is tubule material around ray, contains renal corpuscle
 * [|Minor calyx] (calyces)a cup-like structure which surrounds apex of each pyramid. 2-3 fuse to form single major calyx.
 * [|Major calyx] formed by the fusion of 2-3 minor calyces, fusion of all major calyces forms the renal pelvis which functions to drain urine from kidney as it is produced.


 * 4. Define, list, and contrast the parts of the subdivisions of the kidney.**

One Medullary Ray plus its cortical Labyrinth is a Lobule.
 * **Medullary Ray** || **Cortical Labyrinth** ||
 * Prox. straight tubule || Prox. convoluted tubule ||
 * Distal straight tubule || Distal convoluted tubule ||
 * Collecting tubule || Renal corpuscle. ||


 * 5. Define, list, and contrast the parts of the uriniferous tubule, nephron, and collecting duct.**

A Uriniferous Tubule is the structural and functional unit of the kidney. It consists of one nephron and its collecting tubule(duct).

A Nephron is comprised of four parts: Bowman's capsule, Proximal tubule, Loop of Henle, and Distal Tubule. Nephrons are very tightly packed together admist a small amount of very vascular connective tissue(stroma).

The collecting ducts are of three types: Cortical, Medullary, and Papillary ducts.


 * 6. Describe and contrast the two major types of nephrons based upon their location in the kidney.**

The collecting tubules are part of the uriniferous tubule, but not part of the nephron. They are made of transitional epithelium.
 * **Region:** || **Cortical Nephron** (80%) || **Juxtamedullary Nephron** (20%) ||
 * Cortex || Bowman's capsule, Distal and proximal (straight and convoluted) tubules || Bowman's capsule and convoluted portions of the distal and proximal tubules ||
 * Outer Medulla || Loop of Henle(thin) || Straight portions of proximal and distal convoluted tubules ||
 * Inner Medulla || None || Loop of Henle (may go as far as apex) ||

The collecting tubules are part of the uriniferous tubule, but not part of the nephron. They are made of transitional epithelium.

[|Juxtamedullary nephron:] occur at a deep position compared to most other nephrons. the Loop of henle runs deep into pyramid the Inner medulla zone contains mostly collecting ducts & thin segments of Loop of Henle and the Outer medulla zones contains //thick// segments of loop of Henle plus collecting ducts and thin segments. [|Cortical Nephron] : "Short" nephrons whose renal corpuscle is located in outer portion of cortex. Most of loop of Henle is still located within cortex or outer portion of medulla. Most common type of nephron (80%).


 * 7. Describe and relation the morphology of the various parts of the nephron and collecting ducts to their functions.**


 * **Region** || **Function** || **Notes** ||
 * Bowman's Capsule || Filtration of the blood to produce Glomerular Filtrate; houses the glomerulus || Has parietal(simple squamous epi) and visceral layer(podocytes) separated by Bowman's Space. Has a urinary pole (where prox tubule enters) and a vascular pole (where arterioles enter). ||
 * Proximal Tubule (convoluted and straight) || Resorption of 80% of water, sodium, chloride. Resorption of 100% of glucose, protein, amino acids and bicarbonate || Urine volume increases at this portion, but remains isotonic with the blood. The convoluted and straight portions are both lined with simple cuboidal epithelium. Its lumen is nearly obliterated by brush border. ||
 * Thin Loop of Henle || Descending portion completely permeable to water and salts; Ascending portion impermeable to water, but allows salts and chloride to leave. || Both portions are simple squamous epithelium, appearing histologically like a capillary, without RBCs in its lumen. The urine becomes hypertonic to the blood at this point. Urea enters the lumen at this point, as well as penicillin. ||
 * Straight Distal Tubule (Thick ascending LoH) || Impermeable to water || Lined with simple cuboidal epithelium. Chlorine pump establishes an osmotic gradient between lumen and renal interstitium. ||
 * Juxtaglomerular Apparatus || Macula Densa- monitors sodium and volume levels JG cells- make and release renin || Macula Densa are simple columnar epithelial cells that communicate with JG cells. MD is located between the straight and convoluted distal tubule. JG cells are located in the wall of the afferent arteriole, where it passes near the distal tubule. They are modified smooth muscle cells. Mesangial cells are also present in the JG apparatus/ ||
 * Distal Convoluted Tubule || Responds to aldosterone by resorbing sodium and chloride for lumen. || Simple cuboidal epithelium. ||

Cortical Ducts: - lined by simple cuboidal epithelium with two types of cells, Principal and Intercalated. Intercalated cells have clearly defined lateral membranes and actively transport H+ ions against the gradient.

Medullary Ducts- lined by cuboidal cells. Created by the convergence of several cortical ducts, in the outer medulla. Contain both principal and intercalated cells.

Papillary Ducts (of Bellini):- These are the largest of the three, formed by the convergence of several medullary ducts. Their outlet is at the tip of the renal papillae, into the minor calyx at the area cribrosa. Contain Interstitial cells in the CT space between ducts that appear histologically like rungs on a ladder. They secrete Medullipin I, a vasodilator.

The collecting ducts are sensitive to ADH and will reabsorb water out of the lumen in its presence.


 * 8. Describe the structure of the filtration barrier and relate it to its function.**

Filtration Barrier is the structural barrier that is between the blood and the glomerular filtrate.
 * Fenenstrated capillary: without diaphrams, contains fenestra prevents formed cellular elements from passing through barrier
 * Basal lamina: 300nm thick fusion of basal lamina of both epithelia. Made up of Lamina lucida - Lamina densa - Lamina lucida. Contains collagen IV, perlecan, laminin and fibronectin. It is negatively charged preventing large molecules (albumin, immunoglobulins & large proteins) to cross barrier.
 * Podocytes: visceral layer of Bowman's capsule, highly modified simple squamous epithelium covers outside of capillary (endothelium & BL). These cells have numerous processes that encircle the capillary called small foot processes (pedicels) that extend from larger processes. The pedicels //interdigitate// with each other.
 * Filtration slits: are the narrow space between the pedicels (20-40nm wide) that are covered by a slit diaphram (6nm thick) extends across filtration slit. Note that slit diaphram acts as part of filtration barrier. Filters out negatively charged ions & molecules < 1.8nm dia. (medium sized proteins). Intraglomerular mesangial cells keep barrier sieve clean by phagocytosis


 * 9. Describe and integrate the blood supply to the kidney with its function.**

Each kidney receives its blood supply from the [|renal artery], two of which branch from the abdominal aorta. Upon entering the hilum of the kidney, the renal artery divides into smaller interlobar arteries situated between the renal papillae. At the outer medulla, the interlobar arteries branch into arcuate arteries, which course along the border between the renal medulla and cortex, giving off still smaller branches, the cortical radial arteries (sometimes called //interlobular arteries//). Branching off these cortical arteries are the [|afferent arterioles] supplying the glomerular capillaries, which drain into [|efferent arterioles]. Efferent arterioles divide into peritubular capillaries that provide an extensive blood supply to the cortex. Blood from these capillaries collects in renal venules and leaves the kidney via the [|renal vein]. Efferent arterioles of glomeruli closest to the medulla (those that belong to [|juxtamedullary nephrons]) send branches into the medulla, forming the [|vasa recta].


 * 10. Describe and examine how the circulation to the cortex is different from that of the medulla of the kidney. Relate this to the function of the kidney.**

Although the source of blood for both the cortex and the medulla of the kidney come from the Efferent arteriole, their subsequent route and drainage differs.

The efferent arterioles of cortical nephrons form the Peritubular Capillary Network, which consists of small capillaries surrounding proximal and distal tubules in the cortical labyrinth. This Peritubular Capillary Network subsequently drains into interlobular veins.

The efferent arterioles of juxtamedullary nephrons form the Vasa Recta, long, large capillaries which run straight down into the medulla alongside the collecting ducts. The vasa recta drain into the arcuate veins directly, and are the only blood supply to the medullary region. The vasa recta are important for carrying resorbed water and ions back into the body from the kidneys.


 * 11. Describe the morphology of the ureter and relate the structure to its function.**

2 hollow cylindrical tubes, 25-30 cm long, 10-12 inches long ½” thick which extend from renal pelvis of kidney to posterior aspect of urinary bladder. It is lined by transitional epithelium making it impervious to liquid and functions to conduct urine from kidney to urinary bladder. The wall is composed of 3 layers: >
 * Mucosa: transitional epithelium, lamina propria with a star-shaped lumen * //diagnostic of ureter//
 * Muscularis: 2 layers of smooth muscle, inner longitudinal and outer circular (//reverse of digestive tract muscularis layers)//, lower 1/3 of ureter has 3rd layer of longitudinal muscle. Urine is moved by parastaltic contractions.
 * Adventitia: connective tissue layer


 * 12. Describe the morphology of the urinary bladder and relate the structure to its micturition function.**

The urinary is comprised of transitional epithelium and is a hollow, distensible muscular organ. Its wall is composed of three layers:

//Mucosa//: Transitional epithelium, consisting of dome cells, 12-16 layers thick when nondistended and 4-6 when distended. The transitional epithelium is impermeable to water. Lamina Propria: a thin layer of CT

//Muscularis//: The smooth Detrusor muscle and three layers: inner long, middle circ, outer long

//Serosa//: An outer CT coat of adventitia.

The trigone is a flattened area of smooth epithelium on the posterior wall (different embryo origin) bordered by imagined lines drawn between points of entry of the ureters, and the urethral exit. It is pear shaped, oriented downwards, and posterior to the pelvis. The ureters enter on the posterior aspect. At the area of urethral opening, there is an internal sphincter (extension of Detrusor Muscle) and an external sphincter, voluntary muscle of the UG diaphragm. When 200-400ml of urine is in the bladder, stretch receptors send signals to the spinal cord. The parasympathetic nervous system causes contraction of Detrusor and relaxation of internal sphincter, at which time the conscious brain becomes aware of the need for micturition, and is able to control the process via the external sphincter.


 * 13. Describe and contrast the structure of the male and female urethra and relate its structure to function.**

The male urethra is longer than the female urethra, and the distal portion of the male urethra is of different embryological origin. The male urethra also doubles as a conduit for the reproductive tract.


 * 14. Terms:**

__Erythropoietin__- A hormone regulating RBC production that is produced by the kidney.

__Renal Hilus__- The medial area of the kidney where the vessels, renal pelvis, and lymphatics enter.

__Retention__- The failure to completely void urine, leading to dilation of the renal pelvis and destruction of nephrons.

__Minor Calyx__- The portion of the duct collection system that receives urine from the Papillary ducts of the renal lobes.

__Renin__- A hormone product of the Juxtaglomerular cells of the afferent arteriole of the Renal Corpuscle. It is ultimately responsible for activation of angiotensin II.

__Renal Sinus__- The adipose-filled area that is the extension of the hilum of the kidney laterally.

__Cystitis__- Infection of the bladder. more common in females.

__Renal Pyramid__- The portion of the medulla that has its base oriented towards the outer cortex, known as the cortico-medullary junction. The pyramid of medulla then narrows, sloping inwards towards the renal sinus to form the apex, where the renal papilla is located.

__Renal Pelvis__- The renal pelvis is the area where the major calices come together in the hilum, proximal to the ureters.

__Fibrous Capsule__- A thin layer of Dense Irregular CT surrounding the kidney.

__Major Calyx__- The major calyx is the junction and common extension of the branching minor calices in the renal sinus.

__Renal Papilla__- The renal papilla is the apex of the renal pyramid, nearest the renal sinus.

__Area Cribrosa__- The area cribrosa is the sieve-like portion of the renal pyramid, where the papillary ducts of Bellini empty into the minor calices.

__Renal Lobule__- The renal lobule consists of a medullary ray and its surrounding cortical labyrinth.

__Multilobular__- Multilobar means "more than one lobe". Human kidneys are multilobar; some animal kidneys are unilobar. A lobe is one renal pyramid and its overlying cortex.

__Bowman's Capsule__- The Bowman's Capsule is the proximal portion of a nephron. It is comprised of simple squamous epithelium, and has a urinary pole (where the proximal convoluted tubule continues on) and a vascular pole (where the vascular Glomerulus enters via two arterioles to form a capillary tuft). Its parietal layer is an inner layer of epithelium, and its visceral layer is on the capillary tuft from where it invaginated into the capsule, forming a specialized cell called a Podocyte. It houses the Glomerulus, which is NOT part of the nephron.

__Renal Columns__- The renal columns are the portions of cortext between the medullary pyramids.

__Multilobular__- Multilobular means "more than one lobule". This refers to multiple units of (one medullary ray + its cortical labryinth). All kidneys are multilobular.

__Medullary Rays__- A medullary ray is the physiological unit comprised of the straight proximal tubule, the straight distal tubule, and the collecting tubule of a nephron.

__Proximal & Distal Convoluted Tubule-__ The proximal and distal convoluted tubule are in the cortex and comprise the cortical labyrinth, along with the renal corpuscle. They consist of simple cuboidal epithelium__.__

__Renal Lobe__- A renal lobe is a unit consisting of a medullary(renal) Pyramid and its overlying cortical region.

__Unilobar__- Unilobar means "one lobe". Some animal kidneys are unilobar; humans are not.

__Renal Corpuscle__- A renal corpuscle is the functional filtration unit consisting of a Bowman's Capsule ( a portion of the nephron) and a Glomerulus (a portion of the vascular system). It uses hydrostatic pressure created by differential flow from Afferent to Efferent arterioles to push liquid through the fenestrations in the capillary wall and the rest of the filtration system, ultimately producing Glomerular (ultra)filtrate in Bowman's Space.

__Loop of Henle__- The loop of Henle has an ascending and descending portion, lined with simple squamous epithelium. The portions are linked through a hairpin turn at the inferior aspect. The thin limbs are the main site for entry of urea (and penicillin) to the lumen, as well as a site for Sodium and Chloride to move out of the tubules through active transport. The thick portions of the limbs are overlapping terminology with the straight portions of the proximal and distal straight tubules.

__Glomerulus__- The capillary tuft inside a Bowman's Capsule, arising from the afferent and efferent arterioles. It is fenestrated.

__Glomerular Filtrate__- The fluid result that is filtered through a glomerulus into the Bowman's Space. It must pass through the fenestra, the basal lamina, the Filtration Slit, then the Slit Diaphragm. In a healthy Renal Corpuscle, it will not contain any large molecules such as albumin or protein.

__Vascular Pole__- The end of the Bowman's capsule where the afferent and efferent arterioles enter to form the glomerulus.

__Collecting Ducts__- The ducts that receive the urine from nephrons. There are three divisions: Cortical, Medullary, and Papillary.

__Visceral & Parietal Layer__- The parietal layer of the Bowman's Capsule is the lining of simple squamous epithelium just to the interior of the capsule structure. The visceral layer is actually on the glomerulus, in the form of the podocytes and their pedecils.

__Podocytes__- a specialized cell of the visceral layer of the BC, that extend out small pedecils that interdigitate with eachother to create filtration slits.

__Afferent & Efferent Arteriole__- the two arterioles responsible for supplying a glomerulus with blood inflow (afferent) and outflow (efferent).

__Papillary Ducts__- The papillary ducts of Bellini are the summation of multiple medullary collecting ducts. They carry urine to the apex of the medullary triangle to the area cribrosa.

__Vasa Recta__- The vasa recta are long, straight capillaries created by the efferent arterioles that run straight down the medulla alongside the collecting ducts to drain into the arcuate veins. They are important because they pick up resorbed water and ions from the CT and return it to the body.

__Urinary Pole__- The area of the Bowman's Capsule where the proximal convoluted duct joins it.

__Bowman's Space__- The space where glomerular filtrate accumulates between the visceral and the parietal layer of the BC.

__Slit Pore__- (Filtration Slit?) The space between two interdigitating pedecils(20-40nm).

__Slit Diaphragm__- The membrane covering a Filtration Slit. it is 6nm thick.

__Thick Segment__- The thick segments of the Loop of Henle are defined as such by the thickness of their epithelial cells. They are lined by simple cuboidal epithelium.

__Macula Densa-__ A specialized grouping of simple columnar cells that are tightly packed together in the portion of the distal tubule between the straight and convoluted ends. It comes into direct contact with the JG cells and induces them to release renin when it senses a low sodium concentration or low volume.

__Juxtaglomerular Cells-__ A specialized grouping of smooth muscle cells in the wall of the afferent (and sometimes efferent as well) arteriole that is in close contact with the Macula Densa of the Distal Tubule. They are responsible for the synthesis and secretion of Renin, which ultimately creates Angiotensin II, raising blood pressure and stimulating the release of aldosterone and ADH.

__Basal Lamina__- The basal lamina of the glomerulus is a fusion layer (Lamina lucida/Lamina densa/Lamina lucida) that assists in filtration by blocking large cellular components and molecules, as well as inhibiting negatively charged particles.

__Thin Segment__- The thin descending loop of Henle is completely permeable to water and salts, whereas the thin ascending loop of henle is impermeable to water. Both are lined with simple squamous epithelium. Their diagnostic feature is that they appear like capillaries, without RBCs present in their lumen. Urea can enter the urine at this point.

__Pedecil__ The small outgrowths of the podocytes that interdigitate to form filtration slits.

__J-G Complex__- The JG complex consists of Juxtaglomerular cells, the Macula Densa, and extraglomerular mesangial cells (lacis cells). It is responsible for monitoring and adjusting the Na concentration and volume of filtrate in the distal tubule.

__Mesangial Cell__- a phagocytic cell that can be either //intra//glomerular or //extra//glomerular (fixed). They are responsible for maintenance of the glomerular filter (intraglomerular).

__Arcuate Artery__- An arcuate artery is the arced extension of an interlobar artery over the medullary pyramid. It gives rise to many interlobular arteries.

__Interlobular Artery__- An interlobular artery is a small extension of an arcuate artery, supplying a medullary ray with arterial blood.

__Interlobar Artery__- an Interlobar artery is an extension of a segmental renal artery, running laterally along a medullary pyramid towards the base.

__Incontinence__- Incontinence is the loss of voluntary control of micturation(urination). This can be due to nerve damage, bladder irritation, or trauma to sphincter.

__Intralobular Artery-__ An intralobular artery may refer to the afferent and efferent arterioles associated with a nephron.

__Intertubular Capillary Network__- The efferent arteriole supplies the cortex via a peritubular capillary network, which then drain into the interlobular veins. The medulla has a different blood supply from the efferent arteriole (vasa recta to arcuates).

__Pyelonephritis__- An ascending urinary tract infection that has reached the renal pelvis. Can be used as a general term for inlammation of the renal pelvis.

__Dome Cell__- a dome-shaped cell diagnostic of transitional epithelium. Common to mucosa of bladder.

__Urethritis-__ Infection of the urethra