ap2 #4 renal Flashcards
what are the 8 functions of the Kidney?
- Regulate blood ionic composition
- Regulate blood pH
- Regulate blood volume
- Regulate blood pressure
- Maintain blood osmolarity
- Produce certain hormones
- Regulate blood glucose levels
- Excrete wastes and foreign substances
What ions do the kidneys regulate to keep a good blood ionic composition?
Helps to regulate blood levels of ions like sodium (Na+), potassium (K+), calcium (Ca2+), chloride (Cl-), and phosphate (HPO42-)
How do the kidneys regulate blood pH?
Kidneys excrete variable amount of hydrogen ions (H+) into urine and conserve bicarbonate ions (HCO3-); bicarb is important buffer of H+
How do the kidneys regulate blood volume?
Adjust blood volume by conserving or eliminating water into the urine
How do the kidneys regulate blood pressure?
Kidneys excrete enzyme renin, this activates renin-angiotensin-aldosterone pathway; increased renin = increased blood pressure
How do the kidneys regulate blood osmolarity?
Separately regulates loss of water and loss of solutes in urine, kidneys maintain relatively constant osmolarity close to 300mOsm/liter
What hormones are produced by the kidneys
Kidneys produce the hormones calcitriol (metabolite of Vitamin D), erythropoietin (stimulates production of RBC’s), and renin (hormone/enzyme in RAAS)
How do the kidneys regulate blood glucose levels?
Like the liver, the kidneys can use amino acid glutamine in gluconeogenesis, which can then release new glucose into the blood stream to help maintain normal level
Very small contribution to glucose homeostasis
what types of waste do the kidneys rid?
Ammonia and urea- from deamination of amino acids
Bilirubin- catabolism of hemoglobin
Creatinine- breakdown of creatine phosphate in muscle fibers
Uric acid- catabolism of nucleic acids
Metabolites from hormones
what types of foreign substances do the kidneys rid?
From diet (asparagus, beet color, many other foods) Drugs (amphetamines, opioids, nicotine, alcohol, etc) Environmental toxins (pesticides, etc)
where are the kidneys located?
retroperitoneal space
kidney anatomical location
last thoracic and 3rd lumbar verterbrae
What gives the kidneys protection?
11th and 12th ribs
what is the border of the kidney that faces the spinal column?
Concave medial border (hilum)
what are the external layers of the kidney?
Renal Fascia
Adipose Capsule
Renal Capsule
What anchors the kidney and adrenal gland to surrounding structure and retroperitoneal wall
Renal fascia
Fatty tissue surrounding renal capsule, protection and holds kidney and adrenal glands in place in cavity
Adipose Capsule
what is the color of renal capsule connective tissue?
transparent
Smooth, covering that is continuous with ureters; helps maintain shape of kidney and offers protection; found surrounding the kidneys only
Renal Capsule
3 parts of the renal hilum
vein
artery
pelvis
4 parts of the internal anatomy of the kidney?
cortex
medulla
pyramid
papilla
Contains all of the glomeruli and convoluted tubules of nephrons
Also makes the columns that lay between pyramids
Cortex
Collection of all renal pyramids comprise the _______
Contains all of the loops of Henle and collecting ducts
Medulla
How many pyramid are there per kidney?
8-18
narrow apex of the pyramid
Contains the papillary duct leading to minor calyx
Papilla
what is the space between renal pyramids called?
columns
what makes up the kidney lobe?
Medulla+
overlaying cortex+
each adjacent column
What does the minor calyx do?
small chambers that collect urine directly from the papilla
where does the major calyx collect urine?
from multiple minor calyces
what are contained inside the renal sinus
adipose tissue, the blood vessels, and nerve supply
where does the ureter emerge and what is also here?
The hilum
with blood and lymphatic vessels, and nerves
where is the first place blood flows in the kidney? and where next?
The corpuscle and then the glomerulus
are things removed or added in the glomerulus?
removed only
what acts as a secondary filter?
Capillary reabsorb/secrete action
what is known as filtrate
As blood flows through, certain substances are removed from blood and placed into the urinary tubular system
where is filtrate first found
Glomerular Capsule
when is filtrate termed urine?
when the filtrate leaves the collecting duct
what are the two parts of the nephron?
Renal Corpuscle-
Renal Tubule-
what is the job of the renal corpuscle
It is where blood is filtered
what is the job of the renal tubule?
Controls filtered contents from blood
3 main contents inside the renal tubule.
Proximal Convoluted tubule (PCT)- attached to capsule
Loop of Henle (nephron loop)- middle section
Distal Convoluted tubule
(DCT)- distant from capsule, empty into collecting duct
what is the only structure that extends into the renal medulla
Loop of Henle
Note:The collecting ducts are also in the medulla, but they are NOT part of the nephron
what are the two nephrons
Cortical, Juxtademedullary
Characteristics of the cortical nephron
Renal corpuscles lie in outer portion of renal cortex
Short loops of Henle
Just barely reach into outer region of medulla
Peritubular capillaries only
85% of nephrons
Characteristics of the Juxtademedullary nephron
Renal corpuscles lie deep in the renal cortex
Long loops of Henle
Reach deep into medulla
Peritubular capillaries that give rise to the Vasa recta
Vasa recta: capillary bed that extends into medulla surrounding the Loop of Henle
Cortical-Short Nephron characteristics
Renal corpuscles lie in the outermost portion of the cortex
Descending limb of loop of Henle barely dips into the renal medulla
After a hairpin turn, the ascending limb of the Loop of Henle returns to the cortex
Cortical-Peritubular Capillary Characteristics
Arise from the efferent arteriole
Intermingle throughout the proximal and convoluted tubules
These then flow into interlobular veins and eventually back into systemic circulation
Juxta-Long Nephron characteristics
Renal corpuscles lie in the cortex
Descending limb of loop of Henle dives deep into the renal medulla
Anatomy lends to very dilute and/or concentrated urine
After a hairpin turn, the ascending limb of the Loop of Henle climbs back to the cortex
Juxta-Peritubular Capillary Characteristics
Arise from the efferent arteriole
Intermingle throughout the proximal and convoluted tubules
In the juxtamedullary nephrons only, a specialized capillary system exists coming off of these peritubular capillaries (see next slide)
Juxta-Vasa Recta Characteristics
Coming from the peritubular capillaries, dives deep into the renal medulla
Flows side by side each of the loops of Henle
Designed to keep a constant osmotic (pressure) gradient so that things can flow in and out
Afferent
Into Something
Efferent
Out of Something
Afferent Arteriole Characteristics
Wider lumen, thicker walls
Has much more capability to constrict or dilate when compared to efferent arteriole
Describe the Glomerulus
Ball of twine-like capillary structure that buds off of the afferent arteriole
Modified simple squamous epithelial cells called podocytes
Efferent Arteriole Characteristics
Brings blood with larger solutes (i.e. proteins) into the peritubular capillaries (or vasa recta) and then back into systemic circulation
Smaller lumen size, thinner walls (back-pressure sometimes needed for glomerular filtration)
Leftover unfiltered blood exists the corpuscle via what?
efferent arteriole
3 Main functions of Nephrons and Collecting Ducts
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
How much filtrate is reabsorbed back into the blood stream?
99%
What is the GFR
sum of all functioning nephrons
What forms the “leaky” barrier in the capsule?
Glomerular capillaries and podocytes
What is mostly prevented from entering the capsular space?
plasma proteins, blood cells, platelets
what are the three layers of filtration?
Fenestrations of endothelial cells
Basement membrane/Basal lamina
Slit membranes between pedicels
what happens when mesangial cells contract?
reduced area available
what happens when mesangial cells contract?
surface area is maximal
pressure is _____ in glomeruli than in any other capillaries in the body.
higher
GBHP
Glomerular Blood Hydrostatic Pressure,
push
outward from the glomerulus into capsular space
BCOP
Blood colloid osmotic pressure,
Pulls
on fluid/solutes to keep them in the glomerulus if possible
What does NFP =
GBHP - CH - BCOP
What is a normal NFP for the kidneys
10 mmHg
Homeostasis of body fluids requires a ____ _______ GFR
near constant
how does renal blood flow indirectly determine GFR
Modifying the rate of solute and water reabsorption by proximal tubule
Participates in concentration/dilution of urine
Delivers oxygen, nutrients, hormones to cells along the nephron
Delivers waste for excretion in urine
Constriction of afferent arteriole does what to GFR ? and RBF
decreases ,
increases
Constriction of efferent arteriole does what to GFR
increases ,
increases
5 stages of kidney failure
- Kidney damage (protein in the urine) with normal GFR
- Kidney damage with mild decreases of GFR
- Moderate decrease of GFR 45 to 59 mmHg 3b= 30-44mmHg
- Severe reduction in GFR 15-29mmHg
- Kidney failure Less than 15
what is considered when calculating GFR
Age Race Weight/body size Gender Creatinine levels
Why is Creatinine used to calculate GFR
the kidney neither reabsorbs nor metabolizes this substance
Should FREELY pass through the filtration membrane and be urinated out
3 mechanisms that regulate GFR
- Renal autoregulation
- Neural regulation
- Hormonal regulation
what is the main reason GFR can remain constant in high blood pressure situations
This is usually accomplished by variable changes in resistance at the afferent arteriole
Explain the Myogenic mechanism-
Response to to changes in blood pressure
The acute increase in BP causes stretching of the afferent arteriole
Allows for a very brief (millisecond) increase in RBF and GFR
Renal blood flow reduced.
what blood pressure turns on myogenic regulation
This occurs automatically between the systolic blood pressures of 90 and 180
Tubuloglomerular feedback
Responds to changes in sodium-chloride (NaCl-) and water
what happens to the tubules when GFR increases
rate through the tubules increase
what is the role of macula densa cells when GFR is high
macula densa cells release ATP and adenosine which has direct action upon receptors at the mesangial cells and afferent arteriole.
Causes both to constrict which then lowers GFR to normal level
Role of JGA
A complex structure that has the ability to affect systemic blood pressure through the autoregulation of tubuloglomerular feedback
one per nephron
3 types of cells in hte JGA
Juxtaglomerular cells (aka granular cells) -walls of the afferent arteriole
Macula densa cells
-walls of the late thick ascending limb of LOH
Extraglomerular mesangial cells (aka Lacis cells)
-between afferent arteriole, efferent arteriole, and DCT
2 functions of granular cells
Detect when blood pressure is too low (by sensing the lack of stretch of the afferent arteriole wall)
They synthesize, store, then secrete hormone/enzyme Renin (described later in RAAS)
2 functions of macula densa cells
Detect increase in NaCl (Sodium Chloride) concentrations in the filtrate
In response to this concentration check, these cells release
Function of Extraglomerular Mesangial cells(Lacis cells)
Contract or relax to make small regulatory changes in response to the signals that the other JGA cells are sending
When blood pressure or ECFV changes, the systems that have a larger role in attempting to maintain constant GFR are ?
Nervous system
Endocrine hormones
Paracrine hormones
What type of fibers feed blood vessels of the kidney
sympathetic nervous system fibers only
what is sympathetic stimulation when a person is at rest as long as ECFV is normal
low
As sympathetic stimulation increases….
ECFV begins to reduce (fluid being used in increased metabolism)
sympathetic stimulation (exercise, fight/flight) causes what?
This triggers sympathetic system to tell adrenal medulla to release epinephrine / norepinephrine
Vasoconstriction of the afferent arteriole
Blood flow decreases into glomerulus
GFR decreases until the kidney compensates with autoregulation
3 characteristics of angiotensin 2?
Very potent vasoconstrictor
At low concentration levels (when RAAS just activated), efferent arterioles constrict first
As levels of hormone continue to rise, causes vasoconstriction of afferent arterioles
Natriuretic peptide (ANP/BNP) hormone regualtion can do what?
Secreted by the atria (ANP) or the brain (BNP)*
Usually secreted in response to increase in volume (pressure)
Both dilate the afferent arterioles but constrict the efferent arteriole
GFR increases to hopefully offload more fluid to help lower systemic blood pressure
Prostoglandin hormone regualtion
Secreted by the atria (ANP) or the brain (BNP)*
Usually secreted in response to increase in volume (pressure)
Both dilate the afferent arterioles but constrict the efferent arteriole
GFR increases to hopefully offload more fluid to help lower systemic blood pressure
Helps to counteract vasoconstriction caused by angiotensin II and certain catecholamine’s
Nitric Oxide (NO)
Much more dilation at afferent arteriole compared to efferent
Endothelin
Potent vasoconstrictor released by endothelial cells of renal vessels, mesangial cells, and distal tubular cells
Stimulated by angiotensin II, bradykinin, epinephrine
Bradykinin
Vasodilator that stimulates subsequent release of NO and prostaglandins
what is the effect of Bradykinin on GFR
increases
Produced within kidneys (Tubuloglomerular feedback)
Causes vasoconstriction at afferent arteriole
Adenosine
what is the effect of Adenosine GFR
Decreases
Located on surface of endothelial cells lining afferent arteriole, glomerular capillaries, and lungs
Converts angiotensin I to angiotensin II (which is a vasoconstrictor)
Angiotensin converting enzyme (ACE)
, reduces GFR
what do granular cells secrete
renin
when is renin released
Activated in response to low afferent arteriolar pressure
low afferent arteriolar pressure =
low perfusion pressure
Explain Sympathetic nervous system activation
beta-1 adrenergic receptors found at juxtaglomerular cells are stimulated (beta-1 adrenergic receptors found at juxtaglomerular cells are stimulated )
Explain Tubuloglomerular feedback
Activated by a decrease in luminal sodium chloride concentration at the macula densa cells (renin gets released)
What two things happen when RAS is activated
Causes the juxtaglomerular (granular) cells to secrete the hormone/enzyme renin into the bloodstream
Angiotensinogen is released by hepatocytes (liver cells) into the blood at regular intervals
What happens to Angiotensin 1 in the lungs
angiotensin-I is converted to angiotensin-II by lung endothelial angiotensin converting enzyme (ACE)
what is the active form of Angiotensin
Angiotensin II
What happens to Angiotensin 1 in the kidneys
angiotensin-I is converted to angiotensin-II by kidney endothelial angiotensin converting enzyme (ACE)
4 functions of Angiotensin II
- Decreases GFR by causing stronger vasoconstriction of afferent arteriole, minor vasoconstriction of efferent arteriole
- Enhances Na+, Cl- and water reabsorption in the PCT
- Stimulates the adrenal cortex to release aldosterone
- Simulates posterior pituitary gland to release ADH
what does reabsorption and secretion throughout the nephron determine
volume and composition of urine
what 4 things are controled by the kidneys?
volume, osmolality, composition, and pH of extracellular and intracellular fluid compartments
what mediates reabsorption and secretion
Transport proteins positioned in cell membranes
what in the cell membrane is a good target for pharma drugs
transport proteins
what lines the renal tuble for reabsoprtion
Epithelial cells
________ cells make the largest contribution to reabsorption
proximal convoluted tubule (PCT) cells
what cells fine tune the reabsorption process
Loops of Henle, DCTs, Collecting ducts
what happens if small proteins are passed through the Glomerular filter
They are usually reabsorbed by pinocytosis
what are two ways reabsoprtion can occur?
Paracellular reabsorption - between adjacent tubule cells
Transcellular reabsorption - through the tubule cell itself
Apical membrane-
the lumen side of the cell
Basolateral membrane-
the interstitial side of the cell
90% of actual water reabsorption by the kidneys occurs with the reabsorption of
Sodium (Na+)
Chloride (Cl-)
Glucose
what segments are always permeable to water
PCT and the descending limb of the loop of Henle
Reabsorption of the remaining 10% of water occurs by
facultative water reabsorption
2 features of facultative water reabsorption
Regulated by ADH
Occurs in the late DCT and collecting ducts
Secreted substances include (but not limited to)
Hydrogen ions Potassium Ammonium ions Creatinine Certain drugs like penicillin
WHAT TYPE OF CELL FORMS THE wall of the glomerular capsule, renal tubule, and ducts
A single layer of epithelial cells
PCT- proximal convoluted tubule
Simple cuboidal epithelial cells with prominent microvilli brush-border facing lumen (apical surface)
what do microvili do?
increase surface area for absorption and secretion
(LOH) Loop of Henle
(thin descending and thin ascending limb portions)-
Simple squamous epithelial cells
(thick ascending limb portion)-
Simple cuboidal to low columnar epithelial cells
DCT- distal convoluted tubule
Most of DCT – simple cuboidal epithelial cells
with the last part containing :
Principal cells- receptors for ADH and aldosterone
Intercalated cells- help play a role in blood pH
Collecting Duct
Simple cuboidal epithelial cells that also contain
w/ Principle cells and Intercalated cells
Acidosis
when acids are added faster than they are excreted
Alkalosis
when acid excretion exceeds addition
pH varies when either what two things happen
bicarb (HCO3-) or the partial pressure of carbon dioxide (PCO2 ) is altered
When change in pH is caused by HCO3- , it is termed
___________________
When change in pH is caused by PCO2, it is termed
___________________
“metabolic”… KIDNEYS
“respiratory”… LUNGS
First “line of defense” against acid-base abnormalities
extracellular and intracellular buffer systems
Second line of defense is the_______
the respiratory system
Blood PCO2 and pH are important regulators
of ventilation RATE
What signals a change in the ventilatory rate to compensate for either acidosis or alkalosis
Chemoreceptors near the brain and in the periphery sense a change in PCO2 and pH
Third line of defense is________
the renal system
Certain tubule portions allow for secretion of hydrogen ions which will ______ the pH
raise
why can we never get a net-charge equilibrium of water and solutes
There is a constant turnover of new blood coming into the kidney’s
The body signals the need for certain elements to be reabsorbed or secreted based on an attempt for homeostasis
The constant movement of IF between tubules and capillaries does what?
Generates an osmotic gradient as well as an electric gradient (+/-)
Allows the kidney to engage in exchange
where does the largest amount of solute and water reabsorption from filtered fluid occur?
PCT
As Na+ moves into peritubular capillaries/vasa recta, this creates what?
a much more positively charged environment
what helps balance the charges
Chloride (Cl-) ions
when sodium and chloride move into the interstitium in large numbers, what happens?
water is obligated to move out of filtrate and into interstitium
water always follows
protein water channels that increase the rate of water movement
aquaporin-1 channels
solvent drag
The osmosis of water bringing often bring K+ and Ca++
what parts of the nephron are impermeable to urea
Thick ascending limb LOH, proximal DCT,
when are the Distal portion of DCT and collecting ducts impermeable to urea
only under the influence of ADH
3 parathyroid actions of the PCT
stimulates cells in the PCT to secrete phosphate
stimulates calcitriol (active form of Vitamin-D) to be made in PCT cells and then be absorbed into blood
stimulates cells in the DCT to reabsorb more calcium
The entire LOH is _____ regulated
independently
what is happening in the Descending limb of the LOH
mostly water reabsorption and solute secretion (concentrates the filtrate)
what is happening in the Ascending limb of the LOH
no water reabsorption, but reabsorption of solutes occurs (dilutes the filtrate)
This region is passively permeable to water and solutes
Descending Limb LoH
(hyperosmotic)
More solutes and less water causes the “first” concentration of filtrate inside the tubule
Thin portion
This region is passively permeable to small solutes, but impermeable to water (no water reabsorption occurs here)
Thick portion
Active reabsorption (movement out of tubule) of Na+, K+, Cl- occurs here, but this region is still impermeable to water
By the time filtrate reaches this portion, 90-95% of filtered solutes/water have been reabsorbed and returned to interstitium/bloodstream
Late portion of the DCT
Specialized cells found intermixed in the DCT and throughout the collecting ducts
Principal cells
Intercalated cells
what controls the amount of reabsorption of solutes and water
Hormonal (ADH, Aldosterone, Atrial Natriuretic Peptide, etc)
Osmoreceptors throughout the body
how does water flow through the DCT
water does not follow Na+ via osmosis
selectively absorb/reabsorb water
what does ADH do to principle cells
causes principal cells in the DCT and collecting ducts to become permeable to water
Triggers these cells to generate aquaporin-2 channels in the apical membrane
, in the presence of ADH, we produce
a small quantity of highly concentrated urine
where does ADH target?
principal cells in the DCT and collecting ducts
When blood pressure/volume stabilizes
ADH levels decline causing what?
The aquaporin-2 molecules to be removed from principal cells
Normal volume of normal to dilute urine produced
influence of aldosterone, principal cells cause what?
Sodium reabsorption (usually brings water with it)
Potassium secretion
What causes aldosterone to be released?
Hyperkalemia
Presence of angiotensin II
What stimulates intercalated cells?
various osmoreceptor readings in reference to pH and potassium levels
Type A
Intercalated Cells
Causes secretion of hydrogen (H+) ions
Causes reabsorption of bicarb
Causes reabsorption of potassium (K+)
Type B
Intercalated Cells
Causes reabsorption of hydrogen (H+) ions
Causes secretion of bicarb
Causes secretion of potassium (K+)
Stretached atrial/ventricular cells increase bp and/or blood volume and realease_______
ANP
What are the two direct actions of ANP/BNP on the cells located in the DCT and the Collecting Ducts?
- Inhibits the reabsorption of sodium and water
2inhibits the renin-angiotensin-aldosterone system
how does the Descending limb of LOH
regulate plasma osmolarity and volume?
Permeable to water mostly, therefore concentrating the filtrate
how does the Thick ascending limb of LOH
regulate plasma osmolarity and volume?
Impermeable to water only, therefore diluting the filtrate
how do the DCT + Collecting Ducts
regulate plasma osmolarity and volume?
this is Where final dilution/concentration occurs
Where the majority of ADH has its action
Who is responsible for the regulation of plasma osmolarity and volume
the Loop of Henle, the DCT, and the collecting ducts
What controls th Dilution/Concentration in the DCT and the collecting ducts
presence or absence of ADH :
In absence of ADH,
Urine is diluted
In presence of ADH,
Urine is concentrated
Explain the odor of urine
mildly aromatic, becomes ammonia-like with time
Bacteria turning urea back into ammonia
pH range of urine
from 4.6-8.0, average is 6.0, varies with diet, high protein increases acidity, vegetarian increases alkalinity
Specific gravity-
density (ratio of weight of solutes vs water) usually 1.001-1.035 (the higher the solutes the higher the value)
Urine is mostly _____
water
where does uric acid come from?
breakdown of nucleic acids
where does urobilinogen come from ?
breakdown of hemoglobin
The 2 blood tests that provide urine function information
- Blood Urea Nitrogen (BUN)- measures urea (uremia)
2. Plasma creatinine- catabolism of creatine phosphate in skeletal muscle
Renal Plasma Clearance of Glucose
the clearance of glucose is normally zero because normally 100% of glucose is reabsorbed, nothing gets excreted
reported in mL/min
Drugs with high RP clearance =
the dosing of the medication must be high to be effective
Inulin
plant polysaccharide, easily passes through the filter and is excreted in urine 100%
Great measure of true GFR
why is the inulin test difficult
inulin is not produced in the body
Creatinine Clearance
As creatinine is filtered, not reabsorbed, its clearance is a good estimate of GFR
Urine Transportation
Collecting ducts –papilla - papillary ducts - minor calyces – major calyces – renal pelvis – ureters – urinary bladder – urethra – toilet
what action performs urine transport
peristalsis
Location and morphology of ureters
Ureters are 10-12in long
Ureters are thick walled, narrow (1-10mm lumen)
Ureters are retroperitoneal
anti-reflux mechanism
When the bladder fills with urine, it pulls the bladder down which closes these valves so no “backflow” occurs
3 layers of ureters
Adventitia- anchors ureters to surrounding tissues, contains blood vessels, nerves, lymphatic vessels
Muscularis (peristalsis)-outer circular, inner longitudinal smooth muscle
Mucosa-transitional epithelium with goblet cells that secrete mucous (to protect mucosa from acidity)
Location of ureters in females
Posterior to pubic symphysis
Inferior and slightly anterior to uterus in females
Held in place by peritoneal folds
Location of ureters in males
Immediately anterior to rectum in males
Held in place by peritoneal folds
3 layers of urinary bladder wall
- Serosa
- Muscularis(Detrusor muscle)
- Mucosa(uroepithelium)
Difference between serosa and adventitia
Serosa: covers superior surface, visceral peritoneum
Adventitia: covers posterior and inferior surfaces,
continuous with the ureters
3 layers of the detrusor msucle
Inner longitudinal
Middle circular
Outer longitudinal
How doe the detrusor work
When the detrusor is relaxed, it allows for filling
When the detrusor is contracted, it forces urine into the urethra
2 parts of the Mucosa/uroepithelium
Rugae: allows bladder to expand when it is filling
Transitional epithelium – shape of these epithelial cells changes with the degree of stretch placed on them
Trigone: smooth, triangular area in bladder floor
ureteral openings in posterior corners
internal urethral orifice in anterior corner
Internal urethral sphincter
(inferior aspect of bladder)
Circular smooth muscle (extension of the detrusor muscle) near internal urethral orifice
External urethral sphincter
Skeletal muscle (composed of deep perineal muscles/pelvic floor)
Voluntary
Sits just below the prostate (in males)
Is at the opening of the external urethral orifice (in females)
Male urethra characteristics
4-5x longer than female, dual function (urine, semen), consists of mucosa (deep) and muscularis (superficial)
In total, urethra is usually 8in long
Prostatic - urine and sperm transport (smooth muscle)
Membranous - shortest region skeletal muscle forms EXTERNAL SPHINCTER
Spongy- longest region , Bulbourethral (Cowper’s gland)-delivers alkaline fluid to help neutralize acidity of urethra
Female urethra characteristics
Short tube that conveys urine from bladder to exterior
located between clitoris and vaginal orifice
Mucosa: consists of epithelium and lamina propria
Muscularis: circular, smooth muscle
What type of reflex is the micturation
Parasympathetic reflex
what does micturation cause
Involuntary contractions of the detrusor muscle
Internal urethral sphincter to open
[This causes the sensation that we perceive as our body telling us we need to urinate soon]
How is urine held vs. released
Held-voluntary contraction of the external urethral sphincter helps to prevent urination until the appropriate time
Released-Voluntary relaxation of this sphincter allows the flow of urine to occur
what are the reasons for Increased incidence of calculi, acute and chronic renal inflammation, urinary tract infections
Thought to be due to loss of thirst sensation as people age
What are the reasons for urine retention with age?
BPH and prostate cancer, hematuria (kidney stones), dysuria (UT infection, kidney stones)
