M5 Renal Flashcards
What is the purpose of the renal system?
- regulate blood volume/pressure
- regulate water and solute balance
- filtration of blood
What is the renal system a part of?
Urinary system
What does the urinary system consist of?
Ureters - transport urine from kidneys to urinary bladder
Urinary bladder - temp storage of urine
Urethra - transporting urine out of body
Where are kidneys located?
Dorsally in lumbar vertebral region
What are the 5 major structures of the kidney?
Cortex - Outer
Medulla - spaces
Pelvis
Renal arteries and veins
Renal plexuses
What is filtrate?
Formed by kidney: blood plasma minus proteins
How much oxygen does the kidneys use?
20-25%
What does urine contain?
excess salts and metabolic wastes
How many times do kidneys filter the body’s entire plasma volume per day?
60
Path of blood flow through renal blood vessels
Aorta
renal artery
segmental artery
interlobar artery
arcuate artery
cortical radiate artery
afferent arteriole
glomerulus (capillaries)
efferent arteriole
peritubular capillaries or vasa recta
cortical radiate vein
arcuate vein
interlobar vein
renal vein
inferior vena cava
What are the nephrons
Network of tubules and vasculature across renal cortex and medulla through which filtrate is formed.
over 1 million nephrons per kidney.
What is the renal corpuscle?
Consists of glomerulus and glomerular capsule.
Efferent and afferent arterioles enter and lead to proximal convoluted tubule > nephron loop > distal convoluted tubule.
What is the glomerulus?
A ball of fenestrated capillaries
- highly porous, transporting large volumes of solute-rich,m protein-free fluid from the blood into the glomerular capsule. (some not others)
- Creates filtrate, processed by renal tubules to form urine.
What is the glomerular capsule?
Cup structure around glomerulus.
- external epithelium - simple squamous cells.
- visceral layer - attached to capillaries of the glomerulus.
(branching epithelial cells [podocytes] with filtration slits)
(Allows filtrate but not macromolecules to enter capsular space)
What is the purpose of renal tubules?
Reabsorption, secretion and urine formation
What are renal tubules?
Proximal and distal convoluted tubules, nephron loop.
- from renal cortex, into medulla and back to cortex)
- drains into collection ducts.
What is the purpose of collecting ducts?
site of water, sodium and acid-base balance maintenance.
What is the structure of proximal and distal convoluted tubule cells?
luminal surface (highly folded) lined by microvilli to increase surface area for water/solute reabsorption and secretion.
What is the structure of the nephron loop cells?
Thin-segment
What are the 2 cell types in the collecting duct?
Principle cells
- More numerous
- Fewer microvilli
- Water + Na+ balance
Intercalated cells
- More microvilli lining
- acid-base balance
(segmented alternating)
Does a single collecting duct receive filtrate from many nephrons?
Yes
Why does the renal pyramids have a stripy appearance?
side-by-side arrangement of collecting ducts.
What are the 2 types of nephrons?
Cortical - 85% of nephrons, situated in cortex, shallow tubules (proximal and distal)
Juxtamedullary - states at boundary, extend into medulla (only nephron)
What is glomerulus fed and drained by?
Afferent and efferent arterioles
- arrangement provides high-pressure blood supply to facilitate efficient filtration.
Where do efferent arterioles feed into?
Peritubullar capillaries (vasa recta)
What are the functions of peritubular capillaries?
Low-pressure porous capillaries for water and solute reabsorption
- wrapped around cortical renal tubules
What are the functions of Vasa Recta
Long, thin-walled vessels, run parallel to long nephron loops of juxtamedullary nephrons
- Contribute to the formation of concentrated or diluted urine.
What is the juxtaglomerular complex?
Regulates filtration rate and blood pressure, next to the glomerular.
What are the 3 types of cells in the juxtaglomerular complex?
Macula densa cells in nephron loop - chemoreceptors - monitor NaCl
Granular cells in arteriolar walls - smooth muscle cells - mechanoreceptors (secrete renin for BP regulation)
Extraglomerular mesangial cells
- Between arteriole and tubule cells, pass regulatory signals
What are the 3 renal processes that produce urine?
- Glomerular filtration - produce cell and protein-free filtrate
- Tubular reabsorption - selectively move 99% of substances from filtrate to blood in renal tubules and collecting ducts
- Tubular secretion - selectively moves substances from blood to filtrate.
Is Glomerular filtrate passive?
Yes
What forces fluids and solutes out of capillaries through the filtration membrane into the glomerular capsule?
Hydrostatic pressure (pressure gradient)
What does outward pressure promote?
Filtrate formation
- pushing water + solutes out of blood.
- Higher pressure in capillaries.
What does inward pressure promote?
inhibit filtrate formation (higher pressure in capsular space)
- Higher osmotic pressure in capillaries exerted by proteins in blood, blood sucked into capillaries.
What is the Glomerular filtration rate?
The volume of filtrate formed by both kidneys per minute
- determined by the volume of blood flowing into the glomerulus, regulated via the diameter of renal afferent arterioles
- the more flow + dilated arterioles, the more GFR
How is GFR regulated intrinsically?
- myogenic stretch of arteriole smooth muscle (Intrinsic)
- high BV stretch arteriole wall > vasoconstriction > GFR lower. - NaCl concentration
- High GFR reduces time for solute reabsorption, NaCl in filtrate stays high
- Vasoconstrictor signaling by macula densa cells constrict arterioles
- Decrease in blood flow into glomerulus
How is GFR regulated extrinsically?
SNS and RAAS
1. Baroreceptor reflex
- Sympathetic vasoconstriction of arterioles. when BP low, decreased GFR
- RAAS
- Granular cell release of renin in response to low BP
How is sodium reabsorbed?
Na is pumped into the interstitial space by ATPase at basolateral membrane, concentration gradient drive downhill Na entry at apical membrane.
How is water reabsorbed?
By osmosis through aquaporin (gateways)
- increases concentration of solute left behind, allowing them to be reabsorbed down concentration gradient.
How are organic nutrients and certain ions reabsorbed?
Cotransport at apical membrane
How are lipid-soluble substances diffused?
Transcellular route
How are Cl, Ca, K and urea diffused?
Paracellular route.
What do proximal convoluted tubules reabsorb?
Glucose, amino acids and 2/3 Na and water
What does the descending nephron loop absorb?
water (aquaporin only in descending)
What does the ascending nephron loop absorb?
solutes
What does distal convoluted tubule and collecting absorb?
Based on body’s needs
- Antidiuretic hormone inserts aquaporins in collecting duct (water)
- Aldosterone promotes Na reabsorption in DCT and collecting duct (water follows Na+ by osmosis)
What determines volume and concentration of urine?
Osmotic gradient in medulla
What is urine made up of?
what is not reabsorbed, water, capillary secretion, urea.
What is countercurrent?
The direction of flow of fluid in adjacent segments of a connected tube
What is a countercurrent multiplier?
the process of using energy to generate an osmotic gradient that enables you to reabsorb water from the tubular fluid and produce concentrated urine.
When does filtrate reach the highest concentration?
Dip of the nephron loop.
What drives reabsorption at the descending limb?
Changes in interstitial osmolarity (secreted solutes)
What affects solute secretion from the ascending limb?
Changes in filtrate concentration in descending limb
Why do Vasa recta perform countercurrent exchange?
Preserves osmotic gradients in renal medulla, maintain change in osmotic gradients
How do collecting ducts adjust concentration of urine?
Osmotic gradient
What happens if the body is well hydrated?
ADH release lowered, less aquaporin in the collecting duct, less water reabsorption
What happens if the body is dehydrated?
ADH from the posterior pituitary increased, with more aquaporins in the collecting duct, more water reabsorption, small amount of urine as 99% of water reabsorbed.
What is micturition
Urinating
What is the muscular sac of the urinary bladder lined by?
Circular and longitudinal muscle
What are the 2 sphincters that control micturition and which one is voluntary?
Internal and external urethral sphincter.
External
