Metabolic processes of kidneys

Question 1

what are the different processes at the renal cortex and medulla

how does structure relate to function

Answer 1

1. renal cortex = gluconeogenesis
   - structure: greater blood supply and cells have more mitochondria
   - more oxygen for mito to have AEROBIC respiration
   - more ATP produce to sustain high energy process such as gluconeogenesis
2. renal medulla = glycolysis
   - oxidation of glucose = pyruvate
   - less energy demand - less blood flow to regions

Question 2

what is the renal threshold of glucose absorption and briefly explain its implication

Answer 2

1. GFR: 90-140 ml/min
2. glucose all freely filtered (amount filtered is linear to plasma concentration)
3. all reabsorbed UNTIL renal threshold reached

this usually happens at the plasma level of 11mmol/L AND at the rate of 375mg/min

4. when this threshold is exceeded, GLUCOSE will be found in URINE (glucosuria)

Question 3

describe the process and location of glucose reabsorption from filtrate

Answer 3

at PROXIMAL tubule

1. LUMEN side: SGLT1 and 2 - mostly SGLT2
   - 2 active transport, using Na gradient
2. BASOLATERAL side: GLUT1 and GLUT 2
   - fascilitated passive diffusion - bidrectional
   - GLUT1 = early segment, GLUT2: later segment

Question 4

why do diebetic have increased renal TH for glucose

Answer 4

• increased expression of SGLT2 = more reabsorbed into blood = maintains hyperglycaemia

SGLT2 inhibitor = can inhibit this process but produces glucosuria

Question 5

GFR, plasma glucose and renal TH

Answer 5

High GFR = less plasma glucose concentration to reach renal threshold

opposite for low gfr

Question 6

what are the 2 hormones that regulate renal gluconeogenesis

Answer 6

insulin: inhibits
catacholamine: PROMOTES renal gluconeogenesis hence release

glucagon no influence

Question 7

what are the 2 substrates for renal gluconeogenesis

Answer 7

glutamine = muscle source, glutamate (cytosolic conversion to glutamine in most cells)
lactate

Question 8

describe the reciprocal hepatorenal release of glucose

Answer 8

FED state:
KIDNEY predominantly makes glucose and releases glucose to sustain body (contribute 60%)

• glucose in liver is converted to glycogen and stored

FASTED state:
LIVER predominantly makes glucose and releases (80%)
- 50% glycogenolysis, 50% gluconeogenesis

Kidney: gluconeogenesis only

Question 9

how does acidosis and liver disease affect the hepatorenal relationship in glucose release

Answer 9

Liver disease: body wont lack glucose (no hypoglycaemia), as kidneys can take over and release

Acidosis, especially diabetic acidosis:
low pH environment enhances muscle glutamine release = more substrate - renal -neo AND stimulate renal gluconeogenic pathway
INHIBIT LIVER gluconeogenesis

= MORE RENAL RELEASE

Question 10

Glutamine metabolism product and their uses

Answer 10

1. deamination = NH3 produced, used as H buffer in URINE (ammonia formed)
2. a-ketoguterate
   used as fuel - into TCA cycle produce ATP and CO2
   gluconeogenesis - produces GLUCOSE

Question 11

pathologies that interfere with glutamine handling

Answer 11

1 acidosis: increased glutamine availability AND more catabolised

2. normal acid base: glutamine MOSTLY REABSORBED into blood

Question 12

how does type 2 diebetic affect renal gluconeogenesis in fast and fed state

Answer 12

increases -neo in BOTH states because

• insulin insensitve
• impaired insulin release
• substrate level
• enzyme activation

Question 13

what does the kidney do with glucose

Answer 13

1. glycolysis

2. glycogen synthesis - glycosylation of proteins