Urinary System Flashcards
What is excretion and secretion?
“Excretion” is the removal of material from a living thing while “secretion” is the movement of material from one point to another
Why do we need a urinary system?
protein catabolism yields toxic nitrogenous wastes
- NH2 → NH3 → Urea
water and essential ions tend to accumulate
What organs contribute to waste removal?
kidneys
lungs: CO2, water vapor
gastrointestinal tract (fiber or undigestible material, water,)
sudoriferous glands (sweat - salt, urea, water)
What organs does the urinary system consist of?
kidneys (2)
ureters (2)
urinary bladder
urethra
What are the general functions of the kidneys?
regulate blood volume and composition
regulate blood pressure (renin)
regulate RBC numbers with erythropoietin
synthesize vitamin D (calcitriol)
How do the kidneys regulate blood volume and composition?
water in excess will be filtered out
How do the kidneys regulate blood pressure (renin)?
water removal/retension affects BP
renin controls vasoconstriction too
How do the kidneys regulate RBC numbers with erythropoietin?
erythropoietin produced by kidneys
25% of blood passes through kidneys
monitors if you have enough O2 or not
not enough triggers erythropoietin secretion = more RBCs
How do the kidneys synthesize vitamin D (calcitriol)?
calcitriol: hormone version of vitamin D
controls absorption/reabsorption of calcium
produced by kidneys
Where are the kidneys located?
in between, retroperitoneal and abdominal wall, posterior to liver
What is the hilum?
indented side of kidney
- where ureter, lymphatic, arteries/veins enter/exits
What are the coverings of the kidneys?
renal fascia - anchor
adipose capsule - packing
renal capsule - thin layer of dense connective tissue on surface of kidney
- barrier to outside of kidney to protect it
What components comprise the internal anatomy of the kidney?
Renal Cortex
Renal Medulla
Renal Sinus
Renal Pelvis
What is the Renal Cortex?
Outer layer of the kidney
Renal Columns: spaces in between the pyramids
- still part of renal cortex
Nephrons begin in the renal cortex
What is the Renal Medulla?
Inner layer of the kidney
renal pyramids: in the medulla the corn shaped striated sections of medulla
- lots of ducts creates striated texture
- base of pyramid faces cortex
- apex of pyramid is called the renal papillae
Renal papillae: where pyramids empty urine into the minor calyx
What is the Renal Sinus?
space between everything entering/exiting hilum is called renal sinus
What is the Renal Pelvis?
Renal Pelvis big area right before ureter
Minor caliyce: cup like opening at end of renal pyramid (renal papillae)
Major calyce: Larger area that contains multiple minor calyces
What is the pathway of urine in the kidney?
Renal papillae → Minor Calyx → Major Calyx → Renal Pelvis → Lumen of Ureter
What is the nephron?
Functional unit of the kidney
Responsible for:
- filtration
- reabsorption
- secretion
What are the types of nephrons?
cortical (85%) located mostly in the cortex
juxtamedullary (15%) located close/adjacent to medulla
- start in cortex but tube dips down close to medulla
- the nephrons responsible for water retention or
excretion
What is the renal corpuscle?
glomerulus + bowmans capsule
What is the glomerulus?
glomerulus: bundle of capillaries (in kidneys, oxy blood enters as arteriole and leaves as arteriole too (different))
- afferent arteriole: brings oxy blood in
- efferent arteriole: leads blood away from glomerulus
What is the bowmans capsule?
filters the blood
surrounds the tuft of capillaries but has 2 layers
parietal layer: outer layer
capsular space between layers (par/visc): everything that is filtered out
see the filtrate inside the capsular space
from capsular space, filtrate travels into tubed ductwork of nephron (renal tubule)
visceral layer: innermost layer, covers every capillary in the glomerulus
What is the renal tubule? What are its parts?
renal tubule: filtrate from capsular space arrives here
Parts:
proximal convoluted: filtrate from capsular space arrives here first
loope of henle: becomes much thinner and dips down and comes back up
- Proximal Straight (descending loop)
- Distal Straight (ascending loop)
distal convoluted tubule
- leads right into the collecting duct for filtrate
What can pass through the membrane of the nephrons?
Water Electrolytes Glucose Fatty acids Amino acids Nitrogenous wastes Vitamins
What is the kind of epithelial cells are found in the:
Proximal tubule
Loop of Henle
Distal tubule
Collecting ducts
Proximal tubule = simple cuboidal + brush border (increase SA 90% reabsorption)
Loop of Henle = simple squamous
-water movement
Distal tubule = simple cuboidal + basal foldings (SA)
Collecting ducts = simple cuboidal
aquaporins in collecting ducts (ADG)
distal cells = secretion into filtrate (urine)
How does blood get supplied to the kidneys
~25% of cardiac output via
aorta → renal arteries →
segmental arteries →
interlobular arteries →
arcuate arteries →
afferent arteriole →(arrive)
glomerular capillaries →
efferent arteriole →(exit)
peritubular capillaries and
vasa recta capillaries →
ultimately the renal veins →
inferior vena cavaHow is the kidney innervated?
Nerve supply = sympathetic fibers
sympathetic NS)
What is the juxtaglomerular apparatus?
specialized structure formed by the distal convoluted tubule and the glomerular afferent arteriole
- regulates blood pressure and the filtration rate of the glomerulus
Where is the juxtaglomerular apparatus located?
next to glomerulus
What are macula densa cells?
special cells of the distal tubule
measure tubular flow rate and
NaCl in filtrate
secretes paracrine message (vasconstrictor substance)
What are Juxtaglomerular cells?
special cells of afferent arteriole
respond to paracrine message by causing vasoconstriction
secrete renin
What are the basic functions of the nephron? What do they accomplish?
Control blood concentration and volume
Regulate blood pH
Remove toxic wastes from the blood
filter blood, pull out good stuff and put back bad stuff
What are the 3 processes in urine formation?
Glomerular filtration by the renal corpuscle
Tubular reabsorption by the renal tubule
Tubular secretion by the renal tubule
How is urine formed?
- Glomerular filtration
- in glomerulus - Tubular reabsorption and tubular secretion
- in the descending loop of henle - Water conservation
- in the collecting duct
blood plasma → glomerular filtrate → tubular fluid → urine
What is the driving force behind glomerular filtration?
Blood Hydrostatic Pressure
-
What is filtrate?
Filtrate = all blood components except:
- formed elements
- plasma proteins
How much filtrate is made every day?
180 Liters/day 36 times a day
- urine = 1 – 2 Liters/day
- filtrate reabsorbed = 178 – 179 Liters/day
What Renal corpuscle adaptations that enhance filtration?
glomerular capillaries are long
endothelial-capsular membrane is porous
glomerular blood hydrostatic pressure is higher than normal blood pressure
What is the net filtration pressure (NFP) and what are its components?
Glomerular blood hydrostatic pressure (out of glomerulus)
- 60 mmHg
Capsular hydrostatic pressure (into glomerulus)
- 18 mmHg
Blood colloid osmotic pressure (into glomerulus)
- 32 mmHg
NFP = GBHP – (CHP + BCOP) = 60 – (18+32) = +10 mmHg
What is filtration fraction?
Filtration fraction = 10% (normally) = the percentage of plasma that will become filtrate.
25% cardiac output goes to kidneys = 1250 ml/min
1250 ml/min x 10% = glomerular filtration rate
GFR = 125 ml/min (Normal)
WHy important to have normal GFR?
If GFR faster: Filtering too fast, fluid flowing too fast in nephron = can’t reabsorb everything you need
If GFR slower: Filtering too slow, fluid flowing too slow in nephron = reabsorb a lot including waste you want to excrete
Need to control glomerular filtration rate (GFR)
What is Glomerular Filtration Rate (GFR)?
GFR = 125 ml filtrate produced every minute
GFR is directly related to the NFP
Homeostasis requires a relatively constant GFR
if GFR is too high, then what do you want to happen?
if GFR is too low, then what do you want to happen?
Too High = won’t filter everything out
Too Low = filter too much out
What does glomerular blood flow depend on?
systemic blood pressure: overall blood pressure (higher BP = higher GFR and vice versa)
afferent and efferent arteriolar diameters
- increase/decrease blood hydrostatic pressure in glomerulus
What mechanisms regulate the faactors that determine glomerular blood flow?
Renal autoregulation (part of juxtaglomerular apparatus)
- myogenic mechanism: smooth muscle of wall of areteriole
- tubuloglomerular feedback…
hormonal regulation
- renin-angiotensin-aldosterone system=
Neural
- sympathetic NS controls systemic BP w/ efferent / afferent arteriolar diamaters
- increase afferent diameter and decrease efferent diameter increases BP in glomerulus (vice versa)
Walk through the myogenic mechanism for renal autoregulation.
Increased blood pressure → Stretch of afferent arteriole → ateriolar vasoconstriction→ decreased glomerular blood pressure → decreased NFP → decreased filtration
Opposite mechanism for decreased blood pressure
Walk through the tubuloglomerular feedback mechanism for renal autoregulation.
Increased GFR → Increased flow of tubular fluid + increased NaCl concentration → macula densa cells secrete vasoconstrictor substance onto juxtaglomerular cells → vasoconstriction of afferent arteriole → decreased glomerular blood pressure → decreased NFP → decreased filtration
Works opposite way for decreased GFR
Walk through the hormonal regulation of regulating glomerular flow.
Blood Pressure too Low (Low GFR)
Liver secretes Angiotensinogen
Kidney secretes Renin which converts Angiotensinogen → Angiotensin I
Lungs secrete Angiotensin Converting Enzyme (ACE) which converts Angiotensin I → Angiotensin II
Angiotensin II
- signals hypothalamus to cause thirst
- signals cardiovascular system for vasoconstriction
- signals adrenal cortex to cause kidneys to secrete aldosterone
- stimulate antidiuretic hormone secretion by pituitary gland which activate aquaporins in the collecting duct
End Result: Raise BP → Raise GFR
What is atrial natriuretic peptide?
Higher blood pressure → ANP → dilates afferent arteriole while constricting the efferent arteriole→ increases GFR
Inhibits renin and aldosterone secretion
Inhibits ADH secretion and action of ADH on the kidney (less water retention)
Inhibits Na+ reabsorption in collecting duct
- no water following it = lower BP
What is the tubular maximum (Tm)?
Tubular maximum (Tm) - A reabsorption threshold
What are the active transport for tubular reabsorption?
maximum amount of a particular substance that can be reabsorbed by the kidneys
receptors (carriers)
glucose and amino acids
(100% of the time)
Na+ and K+
(aldosterone controlled)
Ca++
(PTH and CT controlled)
What is the passive transport for tubular reabsorption?
diffusion or electrochemical
Cl-, HPO4–
What are the types of tubular reabsorption of water?
Obligatory reabsorption (90%)
- indirect control of water
- osmosis related to solutes
- Na+ has major effects (aldosterone)
Facultative reabsorption (10%)
- direct control of water
- antidiuretic hormone (ADH)
- aquaporins
Walk through the negative feedback control of ADH?
Blood osmotic pressure (decreased water concentration) is increased in response to some stressor →
Hypothalamic osmoreceptors respond to increased blood osmotic pressure and send nerve impulses to appropriate neurons in hypothalamus →
Hypothalamic neurons, via the posterior pituitary gland, secrete ADH in the blood →
In response to ADH, aquaporins in distal tubules and collecting ducts become more permeable to water →
In response, there is increased water reabsorption, and blood osmotic pressure decreases
What is the main function of the loop of henle?
The loop of Henle’s main function is to generate a salinity gradient in the medulla.
This gradient will enable the collecting ducts to reabsorb more water if necessary.
What is the:
% of solute reabsorbed
% of water reabsorbed
for the
Proximal Convoluted Tubule
Loop of Henle
Proximal Convoluted Tubule
- % of solute reabsorbed: 65% reabsorption
- % of water reabsorbed: 2/3 of water
Loop of Henle
- % of solute reabsorbed: 25% reabsorption
- % of water reabsorbed: 15% water
How does the loop of henle establish the salinity gradient?
as loop of henle progresses the osmolarity increases toward bottom
- More salt continually added to ECF by PCT
- As ECF osmolarity rises, more water leaves descending loop of Henle
- As water leaves filtrate, filtrate becomes more concentrated
- Salt pumped out of ascending loop + ascending limb impermeable to water
- The more salt pumped out, the greater the osmolarity of the ECF in the medulla
What is tubular secretion?
Tubule cells extract from blood and secretes into filtrate
What purpose does tubular secretion serve?
waste removal – urea, uric acid, bile acids, ammonia, creatinine
acid-base balance – hydrogen ions or bicarbonate ions
- If H+ secretion = HCO3- filtration, then no change in ECF pH
- If H+ secretion > HCO3- filtration, then ECF pH increases (more H+ in urine)
- If H+ secretion < HCO3- filtration, then ECF pH decreases (less H+ in urine)
What is the net result of tubular secretion?
body directly rids itself of toxic wastes
body uses kidneys to make ECF pH changes (renal compensation)
What is renal clearance?
Volume of blood plasma from which a particular waste is completely removed (“cleared”) in one minute.
What is the summary of functions for the Proximal convoluted tubule?
Reabsorbs:
water (osmosis)
sodium (active transport
potassium (active transport)
glucose (active transport)
amino acids (active transport)
chloride (simple diffusion)
bicarbonate (simple diffusion)
urea (simple diffusion)
Secretes:
hydrogen
ammonium
urea
creatinine
What is the summary of functions for the Loop of Henle?
Reabsorbs:
water (osmosis)
sodium (active transport
potassium (active transport)
chloride (active transport)
Secretes:
urea
What is the summary of functions for the Renal Corpuscle?
Filtration = 125 ml/min
Filtrate includes all solutes in plasma except plasma proteins
Controlled by: autoregulation, angiotensin II, sympathetic neurons
What is the summary of functions for the Distal convoluted tubule?
Reabsorbs:
water (osmosis)
sodium (active transport
chloride (active transport)
Secretes:
potassium
What is the summary of functions for the collecting duct?
Reabsorbs:
bicarbonate
urea
water (aquaporins)
Secretes:
hydrogen
What path does urine take as it exits the kidneys?
Papillary ducts → Minor calyces → Major calyces → Renal pelvis → Ureter → Urinary bladder
What is the trigone region of the bladder?
triangular area between ureteral openings and the urethral opening
Where is the bladder located in males? In females?
Males
- bladder anterior to rectum
Females
- anterior to the vagina
- inferierior to uterus
- uterus/vagina anterior to rectum
What is the functional sphincter and detrusor muscle?
functional sphincter
no extra smooth muscle to open close
when bladder full of urine the opening to it closes off from ureter (functional)
Detrusor muscle
smooth muscle around urinary bladder
What is the internal and external sphincters of the urethra?
internal (involuntary)
external (voluntary)
How do the lengths of the urethra differ in males and females?
females: less than an inch
Males: longer
prostatic urethra: male urethra goes through the prostate
membranous urethra: goes through muscular pelvic floor (diaphragm)
penile urethra: urethra in the penis
