lecture 11 - renal physiology 1

Question 1

gross anatomy of the kidney

Answer 1

• left is slightly higher up due to the presence of the liver
• enclosed in fibres capsule
• outer layer = cortex
• inner later = medulla
• calyx feeds into the ureter
• rich blood supply
• aorta branches into each kidney
• inferior vena cava takes blood away from kidneys

Question 2

what is the functional unit of the kidney?

Answer 2

nephrons

1 million nephrons per kidney

Question 3

what are the 2 kinds of nephrons?

Answer 3

cortical
• mainly in cortex
• 80% of all nephrons

juxtamedullary
• fewer
• important in controlling urine concentration

Question 4

main structures in the nephron

Answer 4

• bowmans capsule
• PCT
• loop of henle
• DCT
• collecting tubes

Question 5

renal blood supply

Answer 5

input - renal artery

output - renal vein

Question 6

vascular supply to the nephrons

Answer 6

1) renal arteries branch into afferent arterioles
2) afferent arterioles feed into glomeruli
3) efferent arterioles leave the glomeruli and wrap around the nephron
4) peritubular capillaries or vasa recta
5) renal veins
6) inferior vena cava

Question 7

functions of the kidney

Answer 7

homeostatic regulation of water and ion content of blood

excretion of metabolic waste products and foreign substances

production of hormones

Question 8

how do the kidneys control homeostasis?

Answer 8

regulation of osmolarity - maintenance of ion balance

regulation of extracellular fluid volume - BP

regulation of pH

Question 9

what metabolic waste products does the kidney excrete?

Answer 9

• urea
• creatinine
• urobilinogen
• breakdown products of haemoglobin

Question 10

what hormones does the kidney produce?

Answer 10

erythropoietin - RBC synthesis

renin - sodium balance

activation of vitamin D - Ca++ balance bond prostaglandins and kinins

Question 11

what happens in glomerular filtration?

Answer 11

all plasma constituents filtered except proteins > 67 kDa

filtration barrier restricts solute movement on basis of shape and charge

kidneys receive 25% of CO
filtration fraction = 20%

Question 12

what pressures control the filtration process?

Answer 12

hydrostatic pressure of blood flowing through glomerular capillaries - P(H) - promotes movement of fluid into capsule

colloid osmotic pressure

hydrostatic pressure of fluid in bowmans space

Question 13

what substances aren’t filtered?

Answer 13

RBCs

serum albumin

Question 14

what is RBF?

Answer 14

renal blood flow

Question 15

what happens if you increase afferent resistance?

Answer 15

• decreased RBF
• decreased P(H)
• decreased GFR

Question 16

what happens if you decrease afferent resistance?

Answer 16

• increased RBF
• increased P(H)
• increased GFR

Question 17

what happens if you increase efferent resistance?

Answer 17

• decreased RBF
• increased P(H)
• increased GFR

Question 18

what happens if you decrease efferent resistance?

Answer 18

• increased RBF
• decreased P(H)
• decreased GFR

Question 19

control of GFR and RBF

Answer 19

remain relatively constant over a wide range of article pressure

this is a protective mechanism

maintained constant by:
• auto-regulation
• neural control
• tubuloglomerular feedback

Question 20

what does auto-regulation do?

Answer 20

maintains GFR and RBF within narrow limits during fluctuations in mean arterial blood pressure

Question 21

control mechanisms of auto-regulation

Answer 21

myogenic response 
• increased BP 
• stretch of smooth muscle 
• vasoconstriction 
• decreased RBF 
• decreased P(H)
• decreased GFR

tubuloglomerular feedback
• fluid flow through tubule influences arteriole resistance and GFR

Question 22

what are macula densa cells?

Answer 22

specialised epithelial cells

important for tubuloglomerular feedback

detect concentrations of Na+ in the tubule

Question 23

process of tubuloglomerular feedback

Answer 23

• GFR increases
• flow through tubule increases
• flow past macula densa cells increases - Na+ and Cl- conc sensed
• paracrine factors released from macula densa
• afferent arteriole constricts
• resistance in afferent increases
• hydrostatic pressure in glomerulus decreases
• GFR decreases

Question 24

what paracrine factors are released from the macula densa?

Answer 24

adenosine
ATP
NO