Renal Physiology

True or false: The body does not care about the concentration of urine

True

The renal system focuses on maintaining the components present in the

ECF

The renal system varies the excretion of _______, _________, and __________ to maintain consistency of ECF

1. Water

2. Electrolytes

3. Other hydrophilic molecules

The renal system plays the most important role in

Long-term regulation of BP

The renal system plays an important role in excretion of

1. K+

2. Ca2+

3. Mg2+

Kidneys are _________ cm long and located in ___________

1. 12 cm

2. Posterior abdominal wall

Outer region of the kidney

Cortex

Darker inner region of the kidney

Medulla

The inner region of the kidneys contain triangular structures called

Renal pyramids

Functional unit of kidneys

Nephron

How many nephrons are in each kidney?

500k - 800k

Nephron pathway

1. Glomerulus

2. Bowman's capsule

3. Proximal tubule

4. Loop of Henle

→ Thin descending tubule

→ Thin ascending tubule

→ Thick ascending tubule

5. Distal tubule

6. Cortical collecting duct

The glomerulus is located in

Bowman's capsule

Primary urine formation takes place in

Glomerulus

Receives filtrate from the Bowman's Capsule

Proximal tubule

U shaped tubule that descends variable distances

Loop of Henle

How many distal tubules converge with a single collecting duct?

6

Two types of nephrons

1. Cortical

2. Juxtamedullary

85% of the nephrons are __________ nephrons. The other 15% are _________ nephrons

1. Cortical nephrons

2. Juxtamedullary nephrons

Cortical nephrons have glomeruli located in the

Outer cortex

Do the cortical nephrons have a short or a long loop of Henle?

Short

Juxtamedullary nephrons have glomeruli located

Deep in the cortex

Do juxtamedullary nephrons have a long or short loop of Henle?

Long

Which type of nephrons extend all the way into the medulla?

Juxtamedullary nephrons

What structure surrounds the juxtamedullary nephrons' loop of Henle in the medulla? Function?

Vasa recta: A network of capillaries

Function: Stave off hypovolemia by holding onto blood

Which type of nephrons are important for urine concentration?

Juxtamedullary nephrons

Which type of nephron reabsorbs a higher proportion of glomerular filtrate?

Juxtamedullary nephrons

→ Salt conserving

When effective circulating blood volume is low, a higher proportion of renal blood flow is directed to _________ to help conserve __________

1. Juxtamedullary nephrons

2. ECF

How much plasma is filtered daily by the glomeruli?

150-200 liters per day

What are the values used to assess kidney function?

1. BUN

2. Creatinine clearance

3. GFR

What is the best/most sensitive value used to assess kidney function?

GFR

What happens when GFR is low?

Renal insufficiency

Is GFR a fixed or variable process?

GFR is a fixed process

→ Kept relatively constant

What are the GFR ranges for each stage of chronic kidney disease?

Mild: 60-89 mL/min

Moderate: 30-59 mL/min

Severe: 15-29 mL/min

Filtration only occurs in the

Glomerulus

_________% of the filtrate is reabsorbed back into the blood

98-99%

The rate of reabsorption for most substances is highest in the __________ and is reduced as flow becomes more _________

1. Proximal tubule

2. Distal

Fine control of excretion usually occurs in which parts of the nephron?

→ Distal convoluted tubule

→ Collecting duct

Reabsorption does not occur in

Bowman's capsule

What is reabsorption?

The process of moving substances in the filtrate from the lumen of the tubule back into the blood

Any solute dumped into the tubular lumen beyond Bowman's capsule

Secretion

Secretion usually occurs in

Proximal tubule

Urine dilution/concentration occurs in which part of the nephron?

Loop of Henle

Which part of the nephron is under hormonal control?

→ Distal tubule

→ Collecting duct

What is being filtered in Bowman's capsule?

1. Water

2. Nutrients

What is being secreted and reabsorbed in the proximal tubule?

Reabsorbed

→ Na

→ K

→ Nutrients

→ Water

Secreted

→ H+

(Most H+ ions filtered here)

Which part of the nephron acidifies urine (metabolic compensation)?

Proximal tubule

What is being secreted and reabsorbed in the loop of Henle?

Reabsorb

→ Water (Descending)

→ Na (Ascending thick)

→ Cl (Ascending thick)

→ K (Ascending thick)

What is being secreted and reabsorbed in the distal tubule?

Reabsorb

→ Na (if needed)

→ Water (if needed)

Secreted

→ H+ (if needed)

→ K+ (if needed)

What is being secreted and reabsorbed in the convoluted tubule/collecting duct?

Reabsorb

→ Na

→ Water

→ H+

→ K+

Secreted

→ H+

→ K+

Renal blood receives what percent of CO?

20-25%

RBF is autoregulated across

Wide range of MAP

RBF can be reduced by____________ if the ECF must be conserved

Sympathetic vasoconstriction

Why is a high renal blood flow (RBF) necessary?

To supply enough plasma for glomerular filtration

The glomerular capillary bed is supplied by __________ and drained via ____________

1. Afferent arteriole

2. Efferent arteriole

What maintains the pressure that drives glomerular filtration?

Resistance vessels at both ends of the glomerulus (afferent and efferent arterioles)

Which capillaries surround the entire nephron and receive reabsorbed water and solutes?

Peritubular capillary bed

Peritubular capillary bed are supplied by

Efferent arterioles

How does filtration of protein-free fluid affect blood osmolarity?

Increases blood osmolarity, creating a driving force for water

Persistently low renal perfusion may result in

Acute renal failure

True or false: In states of shock, kidney is easily injured

True

Function of the macula densa? Where is it located?

Function: Sense blood volume

Location: Distal convoluted tubule

____________ is released if the blood volume is low by _______________

1. Renin

2. Juxtaglomerular apparatus

Released in response to low renal interstitial PO2

EPO

We get vitamin D from

1. Sunlight

2. Diet

Which organ produces the inactive form of vitamin D?

Liver

Which organ converts inactive vitamin

D to active form?

Kidney

Why can kidney failure lead to osteoporosis?

Kidneys stop converting the inactive form of vitamin D to the active form = ↓ Calcium

Why can kidney failure lead to anemia?

No EPO production

Glomerular filter should not allow passage of

1. Plasma proteins

2. Blood cells

True or false: GFR is generally stable due to autoregulation, but can be varied by active changes in afferent and efferent arterioles

True

In the glomerulus, substances below _______ are freely filtered

10 kDa

In the glomerulus, substances above _______ are not filtered

70 kDa

__________ is the largest contributor to plasma oncotic pressure

Albumin

How does electrical charge affect glomerular filtration?

Negatively charged molecules are filtered less than neutral molecules of the same size

Hydrostatic pressure of glomerular capillaries

60 mmHg

Oncotic pressure of glomerular capillaries

29 mmHg

Bowman's capsule hydrostatic and oncotic pressure

Hydrostatic: 15 mmHg

Oncotic: 0 mmHg

What are the three layers through which the solute passes during glomerular filtration?

1. Glomerular capillary endothelial cell

2. Glomerular basement membrane

3. Podocytes

Glomerular capillary endothelial cells have __________ that only exclude __________

1. Large fenestrations

2. Blood cells

The glomerular basement membrane creates a _________ which acts like a sieve for __________

1. Fiber meshwork

2. Macromolecules

In the glomerulus, podocytes are specialized endothelial cells that provide _____________

Narrow filtration slits

Podocyte filtration slits are bridged by a protein called

Nephrin

Why do the basement membrane and filtration slits in the glomerulus contain fixed negative charges?

Repulsion of negatively charged molecules like proteins

What two main factors determine GFR?

1. Net driving pressure (PUF) forcing fluid out of the glomerular capillary

2. Permeability of the filtration barrier (Kf)

True or false: The hydrostatic pressure is variable in the Bowman's capsule

False

→ The hydrostatic pressure is constant in the Bowman's capsule

How does the process of filtration affect glomerular hydrostatic and oncotic pressure?

Hydrostatic pressure ↓

→ Due to the filtration of fluid

Oncotic pressure ↑

→ Due to an increase in protein concentration

Changes in afferent or efferent arteriolar tone alter

1. Vascular resistance

2. Glomerular capillary hydrostatic pressure

3. RBF

4. GFR

NE preferentially constricts ___________, leading to a reduction in ____________

1. Afferent arterioles

2. RBF, GFR, and Na excretion

Angiotensin II preferentially constricts ___________, leading to a reduction in ____________

1. Efferent arterioles

2. RBF

Why does Angiotensin II have no effect on GFR?

GFR is maintained because the efferent arteriole is located after the glomerulus

ACE inhibitors inhibit the activity of

Angiotensin

How will the vasodilation of the afferent arteriole affect GFR?

Vasodilation = ↑RBF = ↑Glomerular hydrostatic pressure = ↑GFR

How will the vasoconstriction of the afferent arteriole affect GFR?

Vasoconstriction = ↓RBF = ↓Glomerular hydrostatic pressure = ↓GFR

How will the vasodilation of the efferent arteriole affect GFR?

Vasodilation = ↑RBF

Blood flows out of the capillary too quickly = ↓ Glomerular hydrostatic pressure = ↓GFR

How will the vasoconstriction of the efferent arteriole affect GFR?

Vasoconstriction = ↓RBF

Blood collects in capillaries = ↑Glomerular hydrostatic pressure = ↑GFR

How will the extreme vasoconstriction of the efferent arteriole affect GFR?

Extreme vasoconstriction = ↓RBF

Lot of blood collects in capillaries = Protein buildup = ↑ Capillary oncotic pressure = ↓GFR

The volume of plasma rendered free of a given substance in 1 minute

Clearence

Renal clearance is often applied to specific marker molecules as a means of estimating

1. GFR

2. RBF

→ For example, creatinine

Creatinine is a product of

Muscle metabolism