4. Intro to glomerulus

Question 1

What are 4 general functions of the kidney?

Answer 1

• Regulation: controls concentrations of key substances in ECF
• Excretion: excretes waste products
• Endocrine
• Metabolism

Question 2

Give examples of kidney endocrine function.

Answer 2

Renin, erythropoietin, prostaglandin

Question 3

Give examples of kidney metabolism function.

Answer 3

Activate VitD, catabolism of insulin, PTH and calcitonin

Question 4

How much water, Na, Cl, Bicarbonate, Glucose and Amino acids are reabsorbed?

Answer 4

• Over 99% of filtered water recovered
• Over 99% of filtered sodium and chloride ions recovered
• 100% of bicarbonate recovered
• 100% of glucose and amino acids recovered
• Just a few waste products not recovered

Question 5

Define euvolemic

Answer 5

fluid balance

Question 6

What is the glomerular filtration rate?

Answer 6

Rate at which kidneys filter plasma = 120mL/min/1.73m2

180L/day

Question 7

How much urine is produced each day?

Answer 7

approx. 1.5L

Question 8

Describe the electrolyte composition of intra cellular fluid

Answer 8

high K+, low Na+, many large organic anions

Question 9

Describe the electrolyte composition of extracellular fluid

Answer 9

low K+, high Na+, main anion Cl- and HCO3-

Question 10

what maintains the differences in intracellular and extracellular electrolyte composition and what happens if it is not controlled?

Answer 10

• Differences maintained by active transport
• Sodium pumps
• Failure to control extracellular electrolytes will affect transport and electrical functions

Question 11

What is the difference between osmolarity and osmolality?

Answer 11

Osmolarity = number of osmoles of solute per litre
Osmolality = solute particles per Kg of solvent

Question 12

What is oncotic pressure?

Answer 12

Osmotic force due to proteins

Question 13

What is normal renal plasma flow (RPF)?

Answer 13

800ml/min

Question 14

What is filtration fraction and what is the normal value?

Answer 14

percentage of total plasma volume that filters into the tubule = GFR/RPF = 20% usually

Question 15

what happens to 80% of blood that is not filtered at glomerulus?

Answer 15

exits via efferent arteriole (unfiltered)

Question 16

what are the two types of nephrons?

Answer 16

• Cortical

* Juxtamedullary

Question 17

What is the normal range for GFR?

Answer 17

90-120mL/min/1.73m2

Question 18

What is the normal composition for glomerular filtrate

Answer 18

• Contains no blood cells or platelets
• Contains virtually no proteins
• Is composed of mostly organic solutes with a low molecular weight and inorganic ions

Question 19

Compare the amount of glucose, Na+, urea and creatinine in blood and filtrate

Answer 19

Substance Plasma Ultra-filtrate
Glucose mg/100mL 100 100
Na+ mmol/L 140 140
Urea mg/dL 15 15
Creatinine mmol/L 60-120 60-120

Have the same concentration of each substance.

Question 20

What are the different components of the filtration barrier?

Answer 20

Capillary endothelium, basement membrane, podocytes

Question 21

What is a property of the glomerular capillaries endothelium?

Answer 21

They are fenestrated, to allow selective filtration of the plasma

Question 22

What is the basement membrane composed of and what charge does it have?

Answer 22

It is acellular gelatinous, made up of glycoproteins which have negative charges

Question 23

How is the basement membrane involved in selective filtration?

Answer 23

The negative charge makes it selective for positively charged substances.

Question 24

What are podocytes?

Answer 24

Specialised type of epithelial cell which directly invest the glomerular capillaries.

Question 25

What part of the podocytes make contact with the basement membrane and what is the opening between these called?

Answer 25

They have 'foot processes' (pedicels), between these are filtration slits which allow passage of substances into the bowman's space

Question 26

Molecules of what radius will pass through the filtration barrier?

Answer 26

1.48nm

Question 27

In disease where negative charge of basement membrane is lost, what can pass through?

Answer 27

In many disease processes the negative charge on the filtration barrier is lost so that proteins are more readily filtered - a condition called proteinuria

Question 28

What 3 forces determine net filtration pressure?

Answer 28

* Hydrostatic pressure in capillary (PGC) * Hydrostatic pressure in Bowman's capsule (PBC) * Oncotic pressure difference between the capillary and tubular lumen (piGC)

Question 29

How is Net Filtration calculated?

Answer 29

PGC – (PBS + PiBS)

Question 30

Which part of the glomerular capillaries have higher oncotic pressure?

Answer 30

End closer to efferent arteriole, same amount of protein in a smaller volume (as plasma has been filtered) so higher protein conc

Question 31

At what blood pressures is autoregulation able to maintain GFR within normal limits?

Answer 31

90-200mmHg

Question 32

What 2 mechanisms are responsible for autoregulation of GFR and RBF?

Answer 32

* Myogenic mechanism | * Tubuloglomerular feedback

Question 33

Which vessels does myogenic autoregulation predominantly occur in?

Answer 33

It is a property predominantly of the preglomerular resistance vessels • Accurate • Interlobular • Afferent arteriole

Question 34

What is myogenic autoregulation?

Answer 34

The ability of vascular smooth muscle to regulate its own state of contraction. When GFR increases vessels contract to reduce blood flow, vice versa

Question 35

Describe the myogenic mechanism when an increase in renal arterial pressure is detected

Answer 35

Afferent arterioles vasoconstrict so less blood entering capillary bed and Prevents transmission of ↑ BP to glomerular capillary and maintains normal glomerular capillary pressure and RBF efferent arterioles dilate so more blood leaving capillary bed so as to decrease GFR

Question 36

Describe the myogenic mechanism when a decrease in renal arterial pressure is detected

Answer 36

Efferent arteriole vasoconstrict so less blood leaving so GFR increases --> Maintains GFR and RBF Afferent arterioles dilate so more blood entering capillary bed

Question 37

What are the 3 types of cells that contribute to the juxtaglomerular apparatus?

Answer 37

1. the macula densa, a part of the distal convoluted tubule of the same nephron 2. juxtaglomerular cells, (also known as granular cells) which secrete renin 3. extraglomerular mesangial cells

Question 38

At what region does the juxtaglomerular apparatus exist?

Answer 38

At the vascular pole of the glomerulus

Question 39

In what part of the nephron does the macula densa exist?

Answer 39

Distal convoluted tubule (has larger nuclei than other cells of the DCT)

Question 40

What do the macula densa detect an increase in?

Answer 40

Increase in NaCl.

Question 41

What is the TG feedback if GFR increases?

Answer 41

• Macula densa cells of the DCT epithelium detect osmolality or the rate of movement of Na+ or Cl- movement into the cells. • Increase in BP increases RBF which increases hydrostatic pressure increasing GFR • The higher the flow of filtrate the higher the Na+ concentration in cells. • An ATP signal is sent via the juxtaglomerular cells, triggered by an increase in NaCl concentration of distal tubular fluid. • Further vasoconstriction of the smooth muscle of the adjacent afferent arterioles and therefore ↓ RBF which in turn ↓GFR.

Question 42

What is the TG feedback if GFR decreases?

Answer 42

* Decrease in BP decreases RBF which decreases hydrostatic pressure which decreases GFR * The lower the flow of filtrate the lower the Na+ concentration in cells. * Macula densa cells of the DCT epithelium detect low levels of Na or Cl- * reduced release of ATP signal from macula densa cells so reduced vasoconstriction of afferent arteriole * Release of prostaglandins from macula densa cells – attenuate systemic constriction of afferent arteriole * Renin released by juxtaglomerular cells

Question 43

What is the action of prostaglandins in low GFR?

Answer 43

When BP is low, systemic vasoconstriction occurs to direct blood flow to other organs, this is bad for renal function so prostaglandin released from macula densa cells acts to vasodilate afferent arteriole to reduce the effect of systemic vasoconstriction and increase GFR.

Question 44

what 3 stimuli cause renin release?

Answer 44

* Sympathetic nerve stimulation * ↓ stretch of afferent arteriole * Signals generated by macula densa cells in response to ↓NaCl delivery

Question 45

What is the action of rennin?

Answer 45

renin converts angiotensinogen to angiotensin 1 which is converted to angiotensin 2 in lungs. angiotensin 2 causes constriction of efferent arterioles so that GFR increases

Question 46

Why does increasing GFR help increase BP in severe low BP?

Answer 46

increased GFR means blood flowing to rest of body has higher oncotic pressure so reabsorbs more fluid and NaC| increasing volume of blood. angiotensin 2 also increases aldosterone which increases Na and water reabsorbtion