Urinary System

Color the Urinary System | Color the Kidney | Color the Nephron

Case Study - The Case of the Crying Baby

Article: Kidney Swap

Urinary System Wordsearch

Urinary System Review Guide | Label the Kidney and Nephron (practice)

Renal Arteries & Veins

Arteries attach to the abdominal aortaVeins attach to the inferior vena cavaInterlobar arteries pass between the renal pyramidsAfferent arterioles lead to the nephronsNEPHRONS - functional unit of the urinary systemQuick Analogy: A nephron is to the urinary system as the ______________________ is to the nervous system-each kidney contains about 1 million nephrons-renal corpuscle: composed of a tangled cluster called a glomerulus which filters fluidPathway = glomerulus -» proximal tubulue --» nephron loop (also called loop of henle) --» distal tubule --» collecting duct --» ureter --» bladder

Also see Kidney and Nephron Coloring

Urine Formation

glomerular filtration - urine formation begins, plasma is filtered

tubular reabsorption - returns most of the fluid to the body - PROXIMAL TUBULE

tubular secretion - removes what is not needed; produces urine - DISTAL TUBULE

Urine Composition

95 % Water

Contains urea and uric acid (characteristic smell)

Can contain trace amino acids

Urine may also contain other chemicals that can be detected.

Hormones present in a pregnant woman are detectable in urine

*Diuretic – any substance that increases urine production

Urine Elimination

After urine forms in the nephrons, the ureters (starting with the renal pelvis) carry the urine away to the bladder

Bladder is an expandable structure that stores urine before it is eliminated from the body.

Transitional epithelial cells change shape to allow for expansion and contraction.

Micturation = urination; as the bladder fills this reflex occurs though it is also under voluntary control

Detruser Muscles – muscles that attach to bladder and sphincter that control urination

Urethra = tube carries urine to the outside of the body

Disorders Related to the Urinary System

Kidney Stones

Extracorporeal shock wave lithotripsy (ESWL) is a procedure used to shatter simple stones in the kidney or upper urinary tract. Ultrasonic waves are passed through the body until they strike the dense stones.

Kidney Failure – kidneys no longer filter substances from the blood. This can result in death if not treated withdialysis. Eventually a person will need a new kidney. Causes of kidney failure vary.

Cystitis = bacteria enters the bladder or kidneys (kidney infection); more common in women because the urethra is shorter

Commonly known as a "bladder infection"

Overactive Bladder = sudden contractions of the bladder produce sensation of urgency, also more common in women

Incontinence - inability to control urination (or defecation)

Gross Anatomy and Histology

Objectives:

After completing this tutorial the student will be able to:

list and identify the various parts of the kidney

describe the gross anatomy and histology of the kidney

Anatomy

The kidneys are two somewhat bean-shaped, reddish-brown organs located in the retroperitoneal space on either side of the vertebral column. Each kidney weighs about 150 gms, measures 11 cm long and 6 cm wide and lies between T11-12 and L3. Each kidney has a convex lateral border and a concave medial border with the two borders merging at the poles (superior and inferior portions). Surrounding each organ is the fibrous renal capsule, which is loosely adherent to it. Adipose tissue surrounds the capsule and is in turn surrounded by the renal fascia (Gerota's fascia), which secures the kidney to the posterior abdominal wall. Much of the medial border is occupied by an indentation, the hilum, through which the renal vessels, nerves, lymphatics and the renal pelvis enter or leave the renal sinus, the space enclosed by the renal parenchyma.

The bisected kidney through the hilum shows the parenchyma to consist of an outer cortex, which forms a continuous subcapsular band of tissue, and an inner medulla, which is discontinuous being interrupted by projections of the cortex towards the renal sinus, the renal columns (columns of Bertin). The medulla consists of several triangular structures, thepyramids, with their bases towards the cortex and their tips, called papillae, projecting into minor calyces.

Question: What is the name of the functional and structural unit of the kidney?

Each medullary pyramid with its overlying cortex forms the functional and structural unit called the lobe. This lobar structure is conspicuous in the fetal kidney, but becomes less so as the organ increases in size with age.

Question: Into what regional nodes do the renal lymphatics drain?

Lumbar lymph nodes in the para-aortic chain

Histology

The renal parenchyma is composed of functional units called the nephron, and connective tissue, the interstitium.

Each nephron consists of a tuft of anastomosing capillaries called the glomerulus, formed from the afferent arteriole and draining into the efferent arteriole, and a tubular system called the renal tubule. Epithelial cells called podocytes (or visceral epithelium of Bowman's capsule) invest the glomerulus, and are reflected to become continuous with the parietal epithelium of the Bowman's capsule. The Bowman's capsule is the bulbous, distended, closed proximal end of the tubular system and is invaginated by the glomerulus. The space between the glomerulus and capsule is the urinary space.

Extending from the capsule is the proximal tubule, which is lined by tall cuboidal-to-columnar epithelial cells containing many mitochondria and a prominent brush border. The proximal tubule is the longest portion of the tubular system and is made up of convoluted proximal and distal straight (pars recta) segments. The pars recta descends into the medulla, where it forms the U-shaped loop of Henle. The latter reenters the cortex within which it forms the straight and convoluted segments of the distal tubule. The distal tubule, at about the junction between its two segments, runs close to the glomerular hilum and forms a specialized segment called the macula densa (see below). The distal tubule is lined by cuboidal epit

helium that lacks a brush border.

Low magnification view of a section through the kidney. The cortex is the more darkly staining region at the top (outside of the kidney). the lower lightly stained tissue is the renal medulla ending in the pointed renal papilla. urine empties into the Y-shaped space made up of the renal calyces (the arms of the Y) and the pelvis (the base of the Y).Section through the cortex showing a group of cross-sectioned profiles of proximal (p) and distal (d) tubules. Both are composed of simple cuboidal epithelium but the epithelium of the proximal tubule is taller, has prominent brush border and contains clear vacuoles.

Question: Which hormone acts on the distal convoluted tubules?

Antidiuretic hormone (ADH). Lack of ADH leads to diabetes insipidus, in which large volumes of dilute urine are formed due to failure of water reabsorption at the distal convoluted tubules.

Question: What are the parts of the loop of Henle?

The thin descending and ascending limbs and the thick ascending segment.

The distal tubule empties into collecting tubules, which in turn drain into collecting ducts. The latter converge, as they approach the medulla, to form the collecting ducts of Bellini, which run vertically through the medulla to the papillae. The collecting tubules and ducts are lined by pale-staining, cuboidal epithelial cells called clear cells scattered amongst which are darker-staining intercalated cells.

Section through the renal papilla that extends into the renal calyx. The papilla contains a number of large, parallel ducts called papillary collecting ducts (ducts of Bellini).

Section of kidney showing cross-sectioned profiles of collecting ducts (1), distal tubules (2) and proximal tubules (3).

Longitudinal view of papillary collecting duct (duct of Bellini). The duct is lined by simple cuboidal epithelium with definite cell borders (not seen in proximal or distal tubules).

The straight portions of the proximal and distal tubules and the collecting ducts run in parallel arrays in a portion of the cortex devoid of glomeruli and inaccurately called the medullary rays (because they appear to emanate from the medulla). The medullary ray and the glomeruli and convoluted tubules on either side of it form the cortical subunit, the lobule.

The interstitium is made up of the interstitial cells, which are fibroblast-like, and matrix. In the cortex the interstitium is small and mainly occupied by small blood vessels and lymphatics and, at the hilum of glomeruli, lacis cells. However, in the medulla it increases considerably in amount. The lacis cells, together with the macula densa and specialized myoepithelial cells in the walls of afferent and efferent arterioles containing neurosecretory granules filled with renin form the juxtaglomerular apparatus.

Question: What is the role of the renal medullary interstitium in urine production?

There is a gradient of hypertonicity in the medullary interstitium from the cortico-medullary junction to the renal papilla created by the thin limbs of the loop of Henle (via the counter current multiplier mechanism). This allows urine in the collecting duct to become concentrated (via the counter current exchange mechanism) as the duct passes through the medulla.