BIO211 Weekly Guide #9
URINARY
SYSTEM
After completing this laboratory you should be able to:
1) Identify the major organs of the urinary system in anatomical models
2) Recognize the kidney in histological section and be able to distinguish between the cortical and medullary regions
3) Describe the components of the nephron and be able to recognize each in histological section
4) Describe the microvascular structures associated with each nephron; as well as the functions of each
5) Localize and describe the urine formation processes of filtration, secretion, reabsorption, and concentration
6) Recognize transitional epithelium and describe its function in the ureters and bladder
7) describe the processes of urine collection, storage, and release
8) Describe the hormonal and nervous control of renal function
9) Describe how renal mechanisms function to regulate whole body blood volume, osmolarity, electrolyte concentrations, pH regulation, and nitrogenous waste elimination
Guide to Gross Anatomy Guide to Histology Guide to Physiology
Outline
I. Urinary System Overview [FAP 26-1]
A. Major regions/organs
kidneys, ureters, urinary bladder, urethra
B. Major functions
filtration of blood, blood volume regulation, osmolarity maintenance, pH balance,
elimination of wastes
C. Common physiological processes
filtration, secretion, reabsorption, concentration, collection and storage,
excretion/mincturition
II. Kidneys [FAP 26-2, 26-3; Spotlight Fig 26-16]
A. Nephron - structural and functional unit of kidney
renal corpuscle
Bowman's capsule
structure -visceral and parietal layers, simple squamous
epithelium, podocytes, Bowman's space
function - selective filtration
[afferent arteriole, glomerulus, efferent arteriole]
proximal convoluted tubule
simple cuboidal epithelium w brush border
function - selective reabsorption and secretion
[peritubular capillaries]
loop of Henle
descending loop - simple squamous epithelium
ascending loop - simple cuboidal epithelium
function - generates osmotic gradient (countercurrent multiplier)
[vasa recti- volume return, maintains gradient]
distal convoluted tubule
simple cuboidal epithelium
function - selective reabsorption and secretion
juxtaglomerular apparatus - j.g. cells and macula densa -->renin
[peritubular capillaries]
collecting tubule
simple cuboidal epithelium
function - concentrates urine under ADH control
[vasa recti]
B. Gross anatomy of the kidney
location - retroperitoneal
capsule - 3 layers
subserous fascia - loose C.T.
adipose capsule (perirenal fat)
fibrous capsule - dense irregular C.T.
lobes (fetal only)
cortex
renal arches and columns
glomeruli, convoluted tubules, loops of Henle (cortical nephrons)
medulla
medullary pyramids and renal papillae
loops of Henle (medullary nephrons), collecting tubules
pelvis
minor calyces --> major calyces --> proximal end of ureter
renal circulation
renal artery and vein
interlobar arteries and veins
arcuate arteries and veins
interlobular arteries and veins
III. Ureters [FAP 26-6]
A. Location
B. Wall structure - 3 layers
mucosa - transitional epithelium
muscularis -2 muscle layers - inner longitudinal, outer circular
adventitia
IV. Bladder [FAP 26-6]
A. Location
B. Wall structure - 3 layers
mucosa - transitional epithelium
muscularis - 3 muscle layers inner long., middle circ., outer long.
adventitia (lower part) and serosa (upper aspect)
C. Features
trigone - 2 ureter openings, 1 urethra opening
internal sphincter - (smooth muscle)
V. Urethra [FAP 26-6]
A. Female
4 cm. long
mucosa - transitional epithelium --> stratified squamous moist epithelium
external sphincter - (skeletal muscle)
B. Male
20 cm. long
regions
prostatic - transitional epithelium
membranous - stratified or pseudostratified columnar epithelium
cavernous - stratified/pseuostratified columnar epithelium
-->stratified squamous moist epithelium
external sphincter - (skeletal muscle)
VI. Urinary Control
A. Kidney physiological control [FAP 26-4, 26-5]
ADH/vasopressin
the juxtaglomerular apparatus (JGA)
renin-angiotensin-aldosterone system
single nephron control
auriculin/atrial naturetic hormone
ammonium hydrogen trapping
erythropoetin
B. Bladder control/micturition [FAP 26-6]
mechanoreceptors
urinary sphincters
parasympathetic control
C. Homeostatic consequences [FAP Ch 27]
fluid balance
electrolyte balance
pH balance
nitrogenous waste elimination
Gross Anatomy List
Kidney:
capsule
cortex
renal arches
renal columns
arcuate arteries and veins
interlobular arteries and veins
medulla
medullary pyramids
renal papillae
interlobar arteries and veins
minor calyces
major calyces
hilus
renal pelvis
renal artery
renal vein
Other Urinary Structures:
ureters
bladder
trigone
urethra - male and female
Key: Know location and function of all structures
Guide to Gross Anatomy
[APL Exercise 24-1]
Kidneys [FAP Figs 26-2 to 26-5; APL Figs 25.5, 25.6]
The kidneys act as blood filters - regulating blood volume, chemical composition, osmolarity, electrolyte balance, and pH in the process. About 20% of the blood that leaves the heart with each stroke is destined for the kidneys. They lie posteriolateral in the abdominal cavity, extending from about T12 to L3. The left kidney is usually slightly higher than the right.
a) Locate the following regions and structures on the models, charts, and prosected kidneys:
hilus medullary pyramids renal artery
capsule renal papillae renal vein
cortex minor calyces interlobar arteries and veins
medulla major calyces arcuate arteries and veins
renal arches pelvis interlobular arteries and veins
renal columns ureter
- The structural and functional unit of the kidney is the nephron. What portions of the nephron lie within the cortex and what portions lie in the medulla?
- Trace the path of urine from the nephrons through the papillae and calyces into the pelvis of the ureter.
- Note that the major veins and arteries of the kidneys branch in a parallel fashion. Trace the flow of blood through the kidneys.
- Identify the three major tubular structures of the renal hilus - the renal artery, the renal vein, and the ureter.
b) Notice that the kidneys are retroperitoneal, and therefore not suspended by mesenteries. Each kidney is invested in, and held in place by a three layered capsule. The layers are (from most superficial to deepest):
perirenal (subserous) fascia
perirenal fat
fibrous renal capsule
c) The urine volume and osmolarity are controlled by three hormones - ADH (vasopression), aldosterone, and auriculin (atrial naturietic hormone). Review how each of these hormonal control systems operates. What is diabetes insipidis?
Distal Urinary Structures [FAP Figs 26-18, 26-19; APL Figs 25.10 to 25.12]
The urinary structures distal to the kidneys do not substantially alter the makeup of the urine, but rather serve to store it and convey it out of the body.
a) Identify the ureters in the models and charts. Trace their course as they pass retro- peritoneally from the renal pelvis, descend just anterior to the psoas major, cross over the common iliac arteries, and turn anteriomedially to enter the bladder.
- Note the relationship of the distal ureter to the vas deferens in the male.
- What propels urine along the ureter?
b) Locate the bladder in the models and charts. It lies in the true pelvic cavity.
- What organ lies just posterior to the bladder in the male? In the female?
- Locate the triangular pattern (trigone) formed by the openings of the ureters and the urethra in the cut-away bladder model. The ureters pass obliquely through the bladder walls, forming a flap which prevents urine reflux. Outflow of urine into the urethra is regulated by the internal sphincter.
c) Study the course of the female urethra in the charts and models. It descends anteriorly from the trigone of the bladder to its exit just anterior to the vaginal orifice. Note the external sphincter surrounding the ureter where it passes through the urogenital diaphragm of the pelvic floor.
d) Study the course of the male urethra in the charts and models. Identify the three regions of the urethra:
prostatic urethra - from the bladder through the prostate to the pelvic floor
membranous urethra - through the urogenital diaphragm - surrounded by external sphincter
penile (cavernous) urethra - through the corpus spongiosum of the penis
Guide to Histology
[APL 24 Exercise 2]
The urinary system is the primary exocrine system of the body for homeostatically maintaining the osmolarity, specific ionic makeup and pH of the bodily fluids, as well as eliminating nitrogenous wastes and toxins. However, you should recognize that the integument (via sweat glands), the digestive system (primarily via bile), and the respiratory system all have significant exocrine, homeostatic, and waste elimination functions.
a) Kidney [FAP Figs 25-8,25-9; APL Fig 25.16]
The structural and functional unit of the kidney is the nephron - a highly convoluted tube lined with a simple (single cell thick) epithelium. The regions of the nephron may be distinguished by the nature of this epithelium. Specifically, you should be able to:
1) Identify the following regions of the nephron and its associated circulatory vessels: Bowman's capsule, glomerulus, proximal convoluted tubule, loop of Henle, vasa recti, distal convoluted tubule, collecting tubule, collecting duct. For each, give a brief description of its role in determining urine content.
2) Identify and distinguish the cortical and the medullary regions of the kidney.
3) Briefly describe the circulatory system and endocrine control of the kidney.
In the slides of the kidney:
- Identify the cortex, medulla, and hilus regions of the kidney under low power.
- In the cortex, identify glomeruli, Bowman's capsules, proximal and distal convoluted tubules. What process takes place across the border between each glomerulus and its associated Bowman's capsule? How can you distinguish proximal and distal convoluted tubules?
- Try to find a juxtaglomerular apparatus; the region of interaction between an afferent arteriole to a glomerulus and a segment of the distal convoluted tubule of the same nephron. What is the function of this structure? What is the macula densa? Review the renin-angiotensin-aldosterone and ADH systems for renal function and blood pressure control.
- In the medulla identify loops of Henle, collecting tubules and ducts, and vasa recti capillaries. Note that the loop of Henle generates an extracellular ionic concentration gradient, while the vasa recti maintains this gradient. How is this gradient used to concentrate urine in the collecting tubules?
- Review the microcirculatory pathway(s) by which blood passes by the nephron.
b) Ureter and Bladder [FAP Fig 26-19; APL Figs 25.14, 25.15]
The ureter and bladder may be identified by the transitional epithelium, and the prominent folding of the walls in histological preparations. In the ureter, the epithelium is thinner, and the muscular walls are proportionately much thicker.
- Examine the transitional epithelium of the ureter. How could you distinguish the ureter from the esophagus, in a histological section? Is the muscle of the ureter wall striated or smooth?
Guide to Physiology
APL Exercise 25-3 is a good review of kidney physiology.