Renal system Flashcards
Between which vertebral levels do the kidneys sit?
Where are they positioned relative to the peritoneum?
T12-L3
Retroperitoneal
What passes through the hilum of the kidney?
- Blood vessels (arteries + veins)
- Lymphatics
- Ureter
- Nerves
Which liver is inferior and why?
Right bc of liver
Where are the kidneys surrounded by?
What glands sit above them?
- Fat pads
- Adrenal glands
What are the 3 regions of the kidneys and what makes up the outer surface?
- Cortex
- Medulla
- Pelvis
- Surrounded by fibrous capsule
What is the medulla arranged into? What do they end in?
- Pyramids
- Papilla
Urine passage through the kidneys into the ureter
Papilla –> minor calyx –> major calyx –> renal pelvis –> ureter
Blood supply to, through and from the kidneys
Abdominal aorta –> renal artery –> series of arteries –> afferent arteriole –> glomerular capillary –> efferent arteriole –> peritubular capillaries –> series of veins –> renal vein –> inferior vena cava
Nerve supply of the kidneys? Made up of?
- Renal plexus
- autonomic nerves + ganglia
Two types of nephron + defining features
- Cortical nephron
- 85%
- Lie mainly in cortex - Juxtamedullary nephrons
- Extend deep into medulla
- concentrated urine
Glomerulus:
- Specialised for?
- Endothelium?
- Supplied + drained by?
- Pressure?
- Filtration
- Fenestrated, simple squamous endothelium
- arterioles
- High pressure
Peritubular capillaries
- Specialised for?
- position?
- Arise from?
- Pressure?
- Absorption
- Adjacent to renal tubules
- Aries from arterioles draining glomeruli
- low P
Vasa recta
- structure
- associated w/
- long, straight vessels (extensions of peritubular capillaries)
- Associated w/ LoH in juxtamedullary nephrons
What makes up the renal corpuscle?
Glomerulus + bowman’s capsule
Structure of bowman’s capsule
Outer layer - simple squamous
Bowman’s space
Inner layer - podocytes
What facilitates filtration at the glomerular capillaries
Filtration slits formed by the pedicels of the podocytes
What is/isn’t filtered at the blood-urine barrier?
Filtered (usually): - Water and small molecules - Na+ and K+ - Glucose Cannot be filtered (usually): - Proteins - RBCs
Layers of the blood-urine barrier
- Fenestrated endothelium of glomerular capillary
- Fused basement membrane
- Filtration slits b/w pedicels of the podocytes
How does the outer cortex separate the medullary pyramids?
Renal columns
What forms a kidney lobe?
One medullary pyramid + all the cortex that surrounds it
Specialised cells of the afferent arteriole \+ form part of? \+ what type of receptor \+ detect? \+ How do they respond to stimulus?
- Juxtaglomerular cells
- JGA
- Mechanoreceptor
- BP
- Release renin, which stimulates angiotensin II formation
Proximal convoluted tubule (PCT)
- What type of reabsorption
- Surrounded by
- Epithelium (structure + what it contains)
- Bulk reabsorption
- Peritubular capillaries
- Cuboidal epithelial cells w/ dense microvilli on luminal membrane
- Many mitochondria + highly folded basolateral membrane
Loop of Henle
- Surrounded by?
- Why is length important?
- Position in kidney?
- Structure
- Which parts absorb what?
- Mechanism that helps create gradient?
- Vasa recta (juxtamedullary only)
- To produce highly concentrated urine
- Penetrates medulla
- Descending limb: thick section = cuboidal, thin section = simple squamous; reabsorption of water
- Ascending limb: thin = simple squamous, thick = cuboidal; reabsorption of salt
- Counter-current system
Distal convoluted tube
- What type of reabsorption?
- Epithelium (structure + what it contains)
- Fine tuning (regulated reabsorption)
- cuboidal epithelium
- Fewer mitochondria and few microvilli
Collecting duct
- What type of reabsorption?
- Receives filtrate from?
- Empties filtrate into?
- Epithelium
- Reabsorption influenced by?
- Fine tuning (regulated reabsorption)
- Multiple DCTs
- Papilla
- Simple cuboidal (principal cells for reabsorption + intercalated cells for acid/base balance)
- ADH and aldosterone
JGA:
- Where does it lie?
- Controls what?
- Stabilises what?
- Between efferent and afferent arterioles
- Controls GFR
- Stabilises BP
Specialised cells of the efferent arteriole
+ What type of cells?
+ What type of receptor
+ Detect?
- Macula densa cells
- Chemoreceptors
- Detect Na+ conc. in filtrate
What motility pattern moves urine through ureters?
- Peristaltic waves
Layers of the ureter + structure
- Mucosa
- transitional epithelium, stratified - Muscularis
- Inner longitudinal, outer circular - Adventitia
- Outer covering of FCT
- Protein plaques on inner surface (stops urine leakage)
How does the ureter act as a sphincter/valve?
Runs obliquely through bladder wall, thus compressed by muscles during increased bladder pressure –> prevents back flow of urine
3 openings of the bladder known as?
trigone
Male vs female bladder position
Male: - anterior to rectum - superior to prostate gland Female: - anterior to vagina + uterus
Layers of the bladder wall
- Mucosa
- Transitional epithelium
- Allows it to expand w/out great increase in P - Detrusor muscle
- Meshwork of oblique, longitudinal and circular muscle fibres - Adventitia
- Connective tissue
Epithelia transition in urethra
- Transitional near bladder
- Columnar
- Mucous protection from urine - Stratified squamous near anus
Female vs male urethra
Male: - Long - Part of repro. system - 3 sections: prostatic, membranous, spongy/penile Female: - Short - Separate from RS
Urethral sphincters
- Junction of?
- Composed of?
- Voluntary/involuntary control
Internal: - Urethra and bladder - Detrusor muscle - Involuntary control (parasympathetic) External: - Where urethra passes through urogenital diaphragm - Skeletal muscle - Voluntary control
Urination steps
Bladder expands –> APs to brain –> urgency –> inner sphincter relaxes –> conscious relaxation of external sphincter –> urination
Places in the urinary tract which contain transitional epithelium?
Ureter, bladder, urethra
Composition of normal urine
- Water (95-98%)
- Creatinine
- Urea
- H+
- Ammonia
- Na+
- K+
- Drugs
- Toxins
Composition of pathogenic urine
- Glucose
- Protein
- Blood
- Hb
- Leucocytes
- Bacteria
Look, taste + smell of normal urine
- Clear, light or dark amber
- Acidic (pH 5-7, depending on diet); NOT sweet
- No smell
Look, taste + smell of pathogenic urine
- Golden, red, brown, blue
- Sweet
- Smells like fruits (diabetes, etc.) or rotten (infection)
Functions of the kidneys
- Water + salt/ion homeostasis
- Filtration
- Reabsorption
- Hormone production (EPO)
- Metabolism
- Gluconeogenesis
- Excretion of drugs, urea, etc.
- pH regulation
Rate of filtration? (GFR)
125mL/min (180L/day)
Rate of blood supply to the kidneys?
1-1.2L/main
How does DCT monitor BP
Senses how much vol. is filtered
How to calculate effective filtration pressure?
(glomerular hydrostatic pressure + capsular osmotic pressure) - (glomerular osmotic pressure + capsular hydrostatic pressure)
What is renal clearance?
+ Formula
The RATE at which substances are cleared by the kidneys per unit time
C = (Conc. in urine x vol. of urine) / conc. in plasma
What is GFR?
+ Estimated how?
- VOLUME of fluid filtered per unit time
- estimated using creatinine or inulin (bc aren’t reabsorbed, secreted or metabolised)
What is filtration fraction?
GFR / renal plasma flow
ratio b/w blood flow and filtration
Filtered load
- Calculation
AMOUNT of a substance filtered per minute
FL = GFR x conc. in plasma
Solutes which are only reabsorbed
- Glucose
- Water
- Na+
- Cl-
- PO4-
- Ca2+
Solutes which are only secreted
Organic cations + anions (e.g. drugs - PAH)
How is water transported across different parts of the nephron?
- Paracellular
- PCT
- leaky epithelium (gaps b/w tight junctions are leaky)
- high permeability
- needs gradient - Transcellular
- tight epithelium; tight tight junctions
- low permeability
- 2 barriers, involves aquaporins (APQ1 in PCT + APQ2 in CCT))
What percentage of sodium, water and chloride are reabsorbed in the PCT?
66%
How much glucose + AAs are reabsorbed in the PCT
99%
How much sodium, phosphate and calcium are reabsorbed in the PCT?
most
How much bicarbonate is reabsorbed in the PCT
80%
How much urea is reabsorbed in the PCT?
50%
Proportions of sodium reabsorbed in different parts of the nephron
PCT - 66%
TAL - 25%
DCT - 5%
CCT - 3%
What is the apical transporter that allows glucose to be reabsorbed coupled to Na+?
SGLT1 or SGLT2
What is the basolateral transporter which allows glucose to diffuse into the interstitium? (facilitated diffusion)
GLUT1 or GLUT2
What membrane protein allows Na+ to maintain its coupling function?
Na+/K+ ATPase
How is the Hyperosmotic medullary gradient (HOMG) created?
- Salt is reabsorbed, causing the medulla interstitium to be hypERosmotic
- Filtrate becomes dilute; must be reabsorbed in CD
What does the DCT and CD reabsorb/secrete?
- Hormonal control?
- Reabsorb remaining salt + water
- Secrete K+ and H+
- Salt ions = aldosterone
- Water = ADH
What percentage of our body weight is our total body water (TBW)?
Women - 55%
Men - 60%
Components of TBW
ICF = 2/3
ECF = 1/3; divided into
- plasma = 1/5
- Interstitial fluid = 4/5
What is osmolarity
Number of ions per vol. of water
What is tonicity?
Effect of a solution on cells
Osmolarity in different parts of the nephron
PCT - isosmotic
tDLH/bottom of LoH - hypertonic
TAL - hypotonic
CD - hypertonic
Relative osmolarity of ECF and ICF?
Same; tightly regulated b/w 275-295mosmol/L
Movement of water during
- dehydration
- hyperhydration
- Water lost from ECF only
- Water gained by ECF only
How is body osmolarity regulated?
- Change in TBW detected by osmoreceptors in hypothalamus
- Stimulates pituitary gland to secrete more/less ADH
- ADH alters permeability of CD to water
- Water retained/excreted to balance initial TBW
- Plasma osmolarity stable
- Cell vol. stable
What does ADH do?
Insert aquaporins (AQP2) into luminal membrane of CD
Urine composition w/ ADH
Small vol of highly concentrated urine
Urine composition w/out ADH
large vol. of dilute urine
What are the 2 water homeostasis regulation systems?
What do they react to?
Correct via?
- What happens if not corrected?
- Fast
- Reacts to changes in osmolarity
- ADH system
- Problems w/ cell size + function - Slow
- React to changes in (isosmotic) volume
- Corrected via sodium retention/excretion
- Problems w/ circulating vol. + BP
What 3 main sites detect change in ECF vol.? Via what receptors?
- High pressure baroreceptors (“Pressure sensors”)
- aorta, carotid - Low pressure baroreceptors (“vol. sensors”)
- vana cava, right atrium - Intra-renal baroreceptors + macula densa
- JGA
Action of low pressure baroreceptors
High vol. = release ANP/ANH
- promotes loss of sodium in urine
Action of intra-renal sensors
Low BP/ECF vol = alters renin secretion
RAAS system
- Renin secreted by JGA
- Renin cleaves angiotensin –> angiotensin I
- Angiotensin I –> angiotensin II by ACE
- Angiotensin II = vasoconstrictor and Na+ reabsorption, also stimulates aldosterone release (from adrenal gland)
- Aldosterone = sodium reabsorption via sodium channels in DCT + CD
What does ANP do?
Decrease vol. by:
- Incr. sodium filtration
- decreased sodium reabsorption
- Decreased renin secretion
Net urinary excretion of a substance (calculation)
Amount filtered - amount reabsorbed + amount secretion
How much of the cardiac output does the kidney receive?
20%
Approximately how much of the plasma gets filtered out? (FF)
20%
Which 2 intrinsic mechanisms determine the amount of blood flow in the afferent arteriole?
- What happens if GFR is too high?
- Myogenic autoregulation of the smooth muscle surrounding the afferent arteriole
- incr. GFR = more vasoconstriction - Tubuloglomerular feedback, involving the JGA
- too much salt (macula densa cells) = vasoconstriction
Example of extrinsic modulation
Sympathetic vasoconstrictor nerves (e.g. constrict during exercise)
Approximately how much of the remaining water is reabsorbed in the DCT + CD?
2-8%
Approximately how much of the remaining sodium is reabsorbed in the DCT + CD?
8%
