Chapter 26: The Urinary System Part 1 Flashcards
What are the 3 general functions of the Urinary System?
- Excretion: removal of organic wastes from body fluids
- Elimination: discharge of waste products
- Homeostatic regulation: of blood plasma volume and solute concentration
What are the 8 functions of the kidney?
- regulation of blood ionic concentrations
- regulation of blood pH
- regulation of blood volume
- regulation of blood pressure
- maintenance of blood osmolarity
- production of hormones
- regulation of blood glucose level
- excretion of wastes and foreign substances
Kidney Function: regulation of blood ionic concentrations
help regulate blood concentrations of several ions: sodium, potassium, calcium, chloride and phosphate
Kidney Function: regulation of blood pH
controlling amounts of hydrogen ion excretion and bicarbonate ion reabsorption
Kidney Function: regulation of blood volume
controlling amounts of water excreted or reabsorbed
Kidney Function: regulation of blood pressure
secretion of renin (enzyme) which is part of the RAAS pathway
Kidney Function: maintenance of blood osmolarity
(number of particles/L solution) iso-osmotic concentration: 300 mOsm/L
regulates excretion of water and solutes
Kidney Function: production of hormones
erythropoieten (EPO)
converts vitamin D to active form: Calcitriol
Kidney Function: regulation of blood glucose level
if necessary, gluconeogenesis from glutamine (an amino acid)
Kidney Function: excretion of wastes and foreign substances
urine: excretion of waste
- ammonia and urea (deamination of amino acids)
- catabolism of bilirubin (urobilin), creatine phosphate (creatine), and uric acid (nucleic acid)
- by products of drug and toxin degradation from the liver
location and external anatomy of the kidney
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3 Layers of Supportive Tissue Surrounding Kidney
- Renal Fascia
- Perirenal Fat Capsule (Adipose Capsule)
- Fibrous Capsule (Renal Capsule)
Renal Fascia
anchoring outer layer of dense fibrous irregular connective tissue
Perirenal Fat Capsule (Adipose Capsule)
mass of fatty cushion (protects and holds kidneys in place)
Fibrous Capsule (Renal Capsule)
- transparent, fibrous (dense irregular CT), smooth capsule that prevents spread of infection to kidney
- continuous with outer coat of ureter
renal ptosis or nephroptosis
condition in which one or both kidneys drop to a lower position
renal ptosis is caused by
• Can be caused by loss of surrounding fatty tissue capsule that holds kidneys in normal position or renal fascia is deficient
– Seen with emaciation or rapid weight loss
– Renal ptosis may cause a ureter to become kinked, causing urine to back up and exert pressure on kidney tissue
– Common (1 in 4) affect with some degree of weakening of fibrous bands (10X more common in females)
Hydronephrosis
-backup of urine from ureteral obstruction or other causes
–Can severely damage kidney, leading to tissue death and renal failure
Internal gross anatomy of the kidney
- Renal Cortex
- Renal Medulla
- Renal Pelvis
Renal Cortex
granular-appearing superficial region
Renal Medulla
deep to cortex, composed of cone-shaped Renal (Medullary) Pyramids
• Broad base of pyramid faces cortex
• Renal Papilla, tip of pyramid, points internally
• Renal pyramids are separated by renal columns, inward extensions of cortical tissue
• Lobe: medullary pyramid and its surrounding cortical tissue
Renal Pelvis
Funnel-shaped chamber continuous with ureter
• Minor calyces
• Major calyces
Minor calyces
– Cup-shaped areas that collect urine draining from
pyramidal papillae
Major calyces
– Areas that collect urine from minor calyces – Empty urine into renal pelvis
Pyelitis
Infection of renal pelvis and calyces
Pyelonephritis in females
- Infections in females are usually caused by fecal bacteria entering urinary tract
– Severe cases can cause swelling of kidney and abscess formation, and pus may fill renal pelvis
– If left untreated, kidney damage may result
– Normally is successfully treated with antibiotics
Renal Calculi
kidney stones in renal pelvis
– Crystallized calcium, magnesium, or uric acid salts
Large stones block ureter, causing pressure and pain
Renal Calculi cause and treatment
May be caused by: – Chronic bacterial infection – Urine retention – Increased Ca2+ in blood – Increased pH of urine • Treatment—shock wave lithotripsy—noninvasive procedure involving shock waves to shatter calculi
Blood supply of the kidneys
- kidneys cleanse blood and adjust its composition, so it has a rich blood supply
- Renal arteries deliver about one-fourth (1200 ml) of cardiac output to kidneys each minute
Nerve supply of the kidneys
via sympathetic fibers from renal plexus
Pathway of blood through the kidney
renal artery -> segmental arteries -> interlobar arteries -> arcuate arteries -> cortical radiate arteries -> afferent arterioles -> glomerulus (capillaries) -> efferent arteriole -> pertibular capillaries or vasa recta -> venules -> cortical radiate veins -> arcuate veins -> interlobar veins -> renal vein
Nephrons
structural and functional units that form urine
> 1 million per kidney
2 Parts of Nephrons
i. Renal Corpuscle
ii. Renal Tubule
2 Parts of Renal Corpuscle
- Glomerulus
2. Glomerular Capsule (Bowman’s Capsule)
Glomerulus
– Tuft of capillaries composed of fenestrated endothelium
• Highly porous capillaries
• Allows for efficient filtrate formation
Filtrate
plasma-derived fluid that renal tubules process to form urine
Glomerular Capsule (Bowman’s Capsule)
– cup-shaped, hollow structure surrounding glomerulus
– Consists of 2 layers: Parietal layer and Visceral layer
Parietal Layer of Glomerular Capsule
simple squamous epithelium
Visceral Layer of Glomerular Capsule
clings to glomerular capillaries; branching epithelial podocytes
– Extensions terminate in foot-like processes (pedicels) that cling to the basement membrane
– Filtration slits between foot processes allow filtrate to pass into capsular space
Renal Tubule
is about 3 cm (1.2 in.) long
• Consists of single layer of epithelial cells: each region has its own unique histology and function
3 Major Parts of the Renal Tubule
- Proximal Convoluted Tubule (PCT): Proximal, closest to renal corpuscle
- Nephron Loop
- Distal Convoluted Tubule (DCT): Distal, farthest from renal corpuscle. Drains into collecting duct
Proximal Convoluted Tubule (PCT)
- Simple cuboidal cells with dense microvilli that form brush border (increases surface area)
- Contain large mitochondria
- Functions: reabsorption and secretion
- Confined to renal cortex
Nephron loop
– Formerly called Loop of Henle
– U-shaped structure consisting of two limbs: Descending and Ascending Limb
Descending Limb
– Proximal part of descending limb is continuous with proximal tubule
– Distal portion also called descending thin limb:
simple squamous epithelium
-H2O reabsorption
Ascending Limb
– Thick ascending limb
» Thin in some nephrons
– Simple cuboidal or simple columnar cells
-reabsorption of ions (NO H2O REABSORPTION)
Distal Convoluted Tubule (DCT)
– Simple cuboidal cells with very few microvilli
– Function more in secretion than reabsorption
– Confined to renal cortex
2 Types of Collecting Duct Cells
- Principal Cells
2. Intercalated Cells
Principal cells
– Sparse with short microvilli
– Maintain water and Na+ balance
-receptors for ADH and aldosterone
Intercalated cells
– Simple cuboidal cells with abundant microvilli
– 2 types of intercalated cells » A and B: both help *maintain acid-base balance of blood
Collecting Ducts
– receive filtrate from many nephrons
– Run through medullary pyramids: give pyramids their striped appearance
– Ducts fuse together to deliver urine through papillae into minor calyce
2 Major Classes of Nephrons
- Cortical Nephrons
2. Juxtamedullary nephrons
Cortical Nephrons
- Make up 85% of nephrons
* Almost entirely in renal cortex
Juxtamedullary nephrons
- Long nephron loops deeply into renal medulla
- Ascending limbs have thick and thin segments
- Important in production of concentrated urine
- Associated with vasa recta
Ureters
- slender tubes that convey urine from kidneys to bladder: begin at L2 as continuation of renal pelvis
- Retroperitoneal
- Enter base of bladder through posterior wall: as bladder pressure increases, distal ends of ureters close, preventing backflow of urine
3 Layers of Ureter Wall (from inside out)
- Mucosa: consists of transitional epithelium
- Muscularis: smooth muscle sheets contract in response to stretch
- Adventitia: outer fibrous connective tissue
Function of muscularis layer of Ureter Wall
- Propels urine into bladder: gravity & hydrostatic pressure are not enough - must also be pushed by peristaltic wave
- action of smooth muscle
- Rate of peristalsis adjusted to rate of urine formation
Urinary Tract Infections (UTI’s)
– Improper toilet habits, such as wiping back to front after defecation
• Short urethra of females can allow fecal bacteria to easily enter urethra
Most UTIs occur in
sexually active women
• 40% of women get urinary tract infections
• Intercourse drives bacteria from vagina and external genital region toward bladder
• Use of spermicides magnifies problem
Urethritis
inflammation of urethra
Cystitis
inflammation of bladder
pyelonephritis
Infection or inflammation of entire kidney
dysuria
painful urination
Symptoms and Treatment for dysuria
Symptoms: urinary urgency and frequency, fever, and sometimes cloudy or blood-tinged urine
-Back pain when kidneys are involved
Treatment: antibiotics can cure most urinary tract infection
Urinary Bladder
- Hollow, distensible muscular sac for temporary storage of urine
- Has openings for ureters and urethra: Trigone
Where is the urinary bladder located? (in females and males)
On pelvic floor posterior to pubic symphysis
• Males: prostate inferior to bladder neck
• Females: anterior to vagina and uterus
Trigone
– Smooth triangular area outlined by openings for ureters and urethra
– Infections tend to persist in this region
Layers of the bladder wall
- Mucosa: transitional epithelial mucosa
- Muscular layer: thick detrusor muscle—contains three layers of smooth muscle (Inner and outer longitudinal layers with circular middle layer)
- Adventitia: areolar connective tissue except on superior surface where it is covered by peritoneum
Urine Storage Capacity
– Collapses when empty
– Rugae appear
– Expands and rises superiorly during filling without significant rise in internal pressure
– Moderately full bladder is ~12 cm long (5 in.) and can hold ~ 500 ml (1 pint)
• Can hold twice that amount if necessary but can burst if over distended
Micturition Reflex
Micturition = Urination or Voiding
- stretch receptors in bladder wall send signal to S2 and S3 of sacral spinal segments
What 3 simultaneous events occur during microturition reflex?
- Contraction of detrusor by ANS
- Opening of internal urethral sphincter by ANS
- Opening of external urethral sphincter by somatic nervous system (SNS)
Reflexive urination
(urination in infants)
– Distension of bladder activates stretch receptors
– Causes excitation of parasympathetic neurons in micturition center in sacral region of spinal cord
– Leads to contraction of detrusor and opening (relaxation) of internal urethral sphincter
– Inhibition of somatic motor pathways (somatic motor neurons) to external sphincter allow its relaxation and open
Pontine control centers mature between ages
2 and 3
Pontine storage center
inhibits micturition
• Inhibits parasympathetic pathways
• Excites sympathetic and somatic motor efferent pathwa
Pontine micturition center
promotes micturition
• Excites parasympathetic pathways
• Inhibits sympathetic and somatic motor efferent pathway
Glomerular Filtration Rate (GFR)
volume of filtrate formed per minute by both kidneys (normal = 120–125 ml/min)
Renal failure
-defined as GFR
Symptoms and Treatment for Renal Failure
– Symptoms: fatigue, anorexia, nausea, mental changes, cramps
– Treatment: hemodialysis or transplant
Urethra
Thin-walled muscular tube that drains urinary bladder
Lining Epithelium of the Urethra
- Pseudostratified columnar epithelium to stratified columnar (midpoint)
- Transitional epithelium near bladder
- Stratified squamous epithelium near external urethral orifice
Sphincters of the Urethra
– Internal urethral sphincter: Involuntary (smooth muscle) at bladder-urethra junction
– External urethral sphincter: Voluntary (skeletal) muscle surrounding urethra as it passes through pelvic floor
The Female Urethra
3–4 cm; ~1.5 inches): tightly bound to anterior vaginal wall
– External urethral orifice: anterior to vaginal opening; posterior to clitoris
The Male Urethra
- a (18-20cm; ~8 inches): carries semen and urine
- Has 3 regions
What are the three regions of the male urethra?
- Prostatic Urethra (2.5 cm): within prostate
- Intermediate Urethra (membranous urethra) (2 cm): passes through urogenital diaphragm from prostate to beginning of penis
- Spongy Urethra (penile urethra) (15 cm): passes through penis; opens via external urethral orifice
Urinary Incontinence
- in adults, usually caused by weakened pelvic muscle
- 3 Types: Stress incontinence, Overflow incontinence, and Functional incontinence (Automatic Bladder)
Stress incontinence
- Increased intra-abdominal pressure forces urine through external sphincter
- Laughing, coughing, or sneezing can cause incontinence
Overflow incontinence
- Urine dribbles when bladder overfills
* Blockage (enlarged prostate or kidney stones) or weak musculature contractions (detrusor muscl
Functional incontinence (Automatic Bladder)
- Alzheimer disease, stroke, spinal cord injury
* Voluntary control of the external urethral sphincter is loss
Urinary Retention
- bladder is unable to expel urine
- Damage to the pelvic nerve: micturition reflex is lost affecting both afferent and efferent fibers
- Common after general anesthesia
- Insertion of a catheter is necessary
the deeper the nephron the
more it is able to concentrate urine
Describe the path urine follows from formation to exiting the body.
Urine starts out as filtrate from the glomerular capsule in the kidney. It then enters the proximal convoluted tubule, then the loop of Henle, then the distal convoluted tubule. It then become urine as it enters the renal pelvis and then it travels down the ureters to the bladder until it is convenient to eliminate through the urethra.
Macula Densa
is a collection of specialized epithelial cells in the distal convoluted tubule that detects sodium concentration of the fluid in the tubule.
If salt content is high, or the volume of fluid is low, the macula densa cells do two things:
1) tell the granular cells to release renin
2) dilate the afferent arteriole of the glomerulus (by secreting a little vasopressive hormone).
