Phys: Renal Physiology Flashcards
What is the functional unit of the kidney?
Nephron
Can kidneys regenerate new nephrons?
No
Functions of kidney:
-homeostatic function
-excretion of metabolic waste
-excretion of bioactive substances
-regulation or arterial BP
-endocrine function
What does each nephron consist of?
-Glomerular corpuscle
-renal tubule
-collecting ducts
What is the average renal blood flow in adult?
1.2L/min
What percentage of cardiac output goes to the kidneys and how?
20% via renal arteries
What are the three physiological processes of the kidneys?
-glomerular filtration
-tubular reabsorbtion
-tubular secretion
What makes up the renal corpuscle?
-glomerular capillaries
-glomerular (bowman’s) capsule
What are the glomerular capillaries?
Tuft of capillaries formed by afferent arterioles and drained by efferent arterioles
What is the bowman’s capsule?
A double wall capsule with a visceral and parietal layer
Where does filtration occur?
The glomerular filtration barrier
What are the three layers of the glomerular filtration barrier?
-endothelium of glomerulus
-basement membrane of glomerulus
-epithelium of bowman’s capsule
Know the renal blood flow:
-Renal artery
-segmental artery
-interlobar artery
-arcuate artery
-interlobular artery
-afferent arteriole
-glomerular capillaries
-efferent arterioles
-peritubular capillaries
-interlobular vein
-arcuate vein
-interlobar vein
-renal vein
Endothelium of glomerulus:
Single layer of fenestrated capillary endothelium preventing blood cells
Basement membrane of glomerulus:
-between endothelium and visceral layer of bowman’s capsule
-prevents passage of large protein molecules
What is found within the epithelium of the bowman’s capsule?
Podocytes
What are podocytes?
-Specialized epithelial cells of the visceral layer that surround glomerular capillary
-have filtration slits between extensions and restrict passage of medium sized proteins
What determines glomerular filtration?
-net glomerular filtration pressure
-filtration coefficient
What is the net glomerular filtration pressure?
-hydrostatic and osmotic pressure gradients across capillary wall
-hydrostatic pressure very high compared to other capillaries
What is the filtration coefficient?
What determines the amount filtered through the membrane
What is the filtration coefficient determined by?
-effective filtration surface area
-permeability of the capillaries
What happens in kidney disease?
Functional glomeruli are lost and leads to reduction in surface area and fall in glomerular filtration rate
What factors affect filtration through the glomerular filtration membrane?
Size, weight, and charge
What can damage the filtration membrane? What happens when damaged?
Infections and trauma, allow some proteins, albumin, and rbc to pass through
What are some characteristics of glomerular ultrafiltrate?
-no cellular element
-protein free
-iso-osmotic to plasma
-[ ] to smaller solutes is similar to plasma
-less Ca2+ and FA
What is the glomerular filtration rate?
The amount of fluid filtered from the glomerulus each minute
What is the normal glomerular filtration rate?
180L/day
What factors affect glomerular filtration rate?
-total SA available for filtration
-filtration membrane permeability
-net filtration pressure (NFP)
what is the formula for glomerular filtration rate?
GFR = NFP X filtration coefficient
What is glomerular filtration pressure determined by?
Net filtration pressure
Glomerular capillaries hydrostatic pressure(HPGC) (value):
55mmHg
Blood osmotic (oncotic) pressure(OPGC) (value):
30mmHg
Hydrostatic pressure in bowman capsule(HPBC) (value):
15mmHg
What is the net filtration pressure equation?
NFP = HPGC - (OPGC + HPBC)
55 - (30 + 15) =10mmHg
What factors affect the GFR?
-glomerular capillary hydrostatic pressure
-plasma protein concentrations
-bowman’s capsule hydrostatic pressure
-glomerular coefficient
What affects the glomerular capillary hydrostatic pressure? (3 things)
-renal blood flow
-systemic blood pressure
-afferent or efferent arteriolar constriction
What affects the plasma protein concentration?
-dehydration
-hypoproteinemia
What affects bowman’s capsule hydrostatic pressure?
-ureteral obstruction
-edema of kidney inside the renal capsule
What affects the glomerular coefficient?
-glomerular capillary permeability
-effective filtration surface area
The larger the molecular weight of the substance the ________ they are filtered
Less
What happens to the GFR if there is an increase in hydrostatic pressure of the bowman’s capsule?
Decreased GFR
What causes increased hydrostatic pressure in the bowman’s capsule?
-renal stones
-ureteric obstruction
-constriction of the ureter
What are the requirements for a substance used to measure GFR?
-freely filtered
-neither reabsorbed or secreted
-creatinine or insulin
When is creatinine used to measure GFR? Insulin?
Creatinine is used in clinical practice, insulin is used for experimental purposes
Transport mechanisms in the nephron:
-passive transport
-active transport
-endocytosis
Passive transport in the nephron:
-down the [ ] gradient
-simple
-facilitated
-osmosis
Active transport in the nephron:
-primary active
-secondary active
Endocytosis in the nephron:
Small proteins and macromolecules are reabsorbed in the proximal tubules -> is a form of active transport
What is the tubular transport maximum?
-maximum rate at which a substance can be actively transported
**limit is due to the saturation of the transport system
Where do transport maximums exist?
For every substance that is actively transported
What does the transport maximum value represent?
The available number of carriers in the renal tubules
If the transporters are saturated, will the excess substance be transported?
No
What is the transport max (Tm) for men adn women?
Men: 375mg/min
Women: 300mg/min
How is glucose filtered?
By the glomerulus into the glomerular filtrate
Where is almost all glucose reabsorbed under normal conditions?
Proximal convoluted tubule
What helps glucose absorption occur?
Na+/glucose cotransporters SGLT1 and SGLT2
What cotransporters are in the early proximal convulsed tubules and reabsorbs 90% of glucose?
SGLT2 and GLUT2
What cotransporters are located in the late proximal convulsed tubule and absorb the remaining 10%?
SGLT 1 and GLUT1
What is the renal threshold for glucose?
The point where the kidneys can’t absorb any more glucose (typically 180 mg/dL)
What happens if your glucose is below the threshold?
All glucose is re-absorbed and none appears in urine
What happens if you exceed the renal threshold for glucose?
Excess glucose remains in the filtrate and appears in the urine because the SGLT1 and 2 cannot carry any more urine
What is it called when there is glucose in the urine?
Glucosuria
What conditions lead to glucosuria?
DM
Consequences of glucosuria:
-Increased urine output (leads to dehydration)
-thirst (polydipsia)
What is function of proximal tubules?
Reabsorbtion of numerous solutes coupled to the sodium reabsorption
