Physiology - Kidney part 1 Flashcards
Name functions of kidneys
- Regulation of water and salt
- Regulation of acid-base balance
- Excretory function
- Endocrine function
- Blood pressure regulation
- Gluconeogenesis
Explain regulation of water and salt
Balances the salt and water intake and excretion. In case of sudden change in salt consumptions, kidneys adapt within 2-3 days.
Explain regulation of acid-base balance
Kidneys can excrete H+ ions into the tubular fluid where it will then be neutralised by a buffer system and then excreted out of the body.
Acidosis - kidney with stimulate H+ into urine to decrease acidity of blood.
Alkalosis - kidney will decrease H+ excretion which will cause more HCO3- excretion.
Explain excretory function
Kidney excretes waste products such as:
Urea - from amino acid metabolism and will be high in concentration in blood if the kidney is not functioning properly.
Creatinine - comes from muscle creatine and high will be high in concentration in blood if the kidney is not functioning properly.
Uric acid - comes from nucleonic acid metabolism. Accumulation will lead to gout attack and joint pain.
Drugs and food additives - toxic substances in food or drinks are excreted.
Explain endocrine function
Erythropoietin:
- Produced in peritubular cells in case of hypoxia and stimulation of sympathetic nervous system.
Renin:
- Produced in case of low blood pressure, low Na+ and high K+ in blood.
- Produced by juxtaglomerular cells
- Activate renin-angiotensin-aldosterone system which releases angiotensin II and aldosterone and increases blood pressure.
Vitamin D3:
- Activation occurs in tubular epithelial cells.
- Vitamin D3 is necessary for calcium and phosphate equilibrium regulation in blood.
Explain blood pressure regulation
Intermediate blood pressure control:
- renin is released
- activation of angiotensin system
- production of angiotensin II
- vasoconstriction
- increased blood pressure.
Slow blood pressure control:
- Pressure volume diuresis or high blood pressure
- Filtration increases, reabsorption decreases.
- Decreases blood plasma volume and blood pressure.
Explain gluconeogenesis
Fat state = low gluconeogenesis.
Fasting state = intense gluconeogenesis.
Gluconeogenesis gets a-ketoglutarate from glutamine produced in tubular epithelial cells.
How many nephrons are in each kidney
Around 1 million nephrons
How much of the nephron is needed for normal kidney function
1/4
What does nephrons consist of
Tubular part and vascular part
Are dead nephrons substituted
No, the number of nephrons decreases throughout life.
What happens to nephrons in case of glomerulonephritis or infection
The nephrons are destroyed very rapidly leading to kidney failure.
What does the tubular part of nephron consist of
- Renal corpuscle
- Bowmans capsule
- Proximal convoluted tubule
- Nephron loop
- Distal convoluted tubule
- Collecting duct
- Calyces
What are the types of nephrons
Cortical nephrons (85%) and Juxtamedullary nephrons (15%)
What are cortical nephrons
- Control filtration and reabsorption
- Located in superficial layer fo cortex
- Small
- Have short nephron loops which only go to the outer part of the medulla.
What are juxtamedullary nephrons
- Control osmolarity gradient in medullary part
- Bigger corpuscle that are located deeper in the cortex
- Long loops that go into the inner part of the medulla.
What is the juxtaglomerular complex
Consists of the macho dense cells in the distal convoluted tubule and the juxtaglomerular cells in the afferent and efferent arterioles.
What does the juxtaglomerular complex do
- Control general arterial blood pressure
- Control of blood in glomerular capillary network
- Control of renal blood flow
What do macula densa cells do
- Control Na+ and Cl- concentration in urine that transports through distal convoluted tubule.
- Signals juxtaglomerular cells in the arterioles of renin production needs to be stimulated or inhibited.
What are the three events of urine formation
- Filtration
- Reabsorption
- Secretion
Urine formation - explain filtration
Goes down the concentration gradient from the glomerular capillary to the bowman capsule.
The primary urine then flows along the tubular system.
How much primary urine does kidneys filter per day
180 L of primary urine
Urine formation - explain reabsorption
Substances are transported from the urine —> peritubular capillaries
Substances: Na+, Cl-, K+, HCO3-, H2O
Urine formation - explain secretion
Substances are transported from peritubuar capillaries —> tubular system
Substances: K+ and H+ is excreted into the urine.
What is the product produced when filtration, reabsorption and secretion has occurred
Secondary urine
What formula is used to calculate excretion of secondary urine
E = Filtration - reabsorption + secretion
How much of secondary urine does kidneys filter per day
1.5 L of secondary urine
What is dialysis
Procedure that removes waste products and excess glue from the blood when the kidneys do not work properly.
Explain hemodialysis
Persons blood runs through a machine with big surface area of semipermeable membranes.
Substances that are in too high concentration leave the blood, pass the membrane and then travel to the dialysate.
Blood from the machine then returns back to the circulatory system.
What does dialysate consist of
Na+ = 135 - 145 (normal)
Cl- = 102 - 106 (normal)
Potassium = 0 - 4 (low so that excessive K+ can be removed from blood)
HCO3- = 30 - 39 (high to control acid base regulation)
Acetate = 2 - 4
Calcium = 0.0 - 3.5
Magnesium = 0.5 - 1.0
Dextrose = 11 (higher to keep glucose in blood)
pH = 7.1 - 7.3
Life of patient with kidney failure
Go to dialysis every second or third day, get attached to the machine for 4-6 hours.
Explain peritoneal dialysis
More advanced method. Dialysate is transported into the peritoneal cavity.
The peritoneal membrane acts as a semipermeable membrane = substances in high concentration go into the dialysate.
The bag of waste fluid can then be emptied after several hours.
This method can be used at home, day or night.
Explain general idea of glomerular filtration
Occurs from the glomerular capillary network into the Bowman’s capsule.
Goes down the concentration gradient and depends on filtration pressures.
What are the components of filtration pressure
- Hydrostatic pressure in the glomerulus.
- Colloid osmotic pressure in glomerular capillaries.
- Capsule pressure.
Explain hydrostatic pressure in glomerulus
P(h) = 50 - 70 mmHg
It shows the pressure in the glomerular capillary network.
Regulated by the vasoconstriction or vasodilation of afferent or efferent arterioles.
The higher the hydrostatic pressure the greater the filtration intensity.
Explain colloid osmotic pressure in glomerular capillaries
π = 20 - 30 mmHg
It shows the amount of plasma proteins.
Since plasma protein cannot cross the wall of capillaries it will attract water to the plasma = inhibiting filtration.
What happens to colloid osmotic pressure in case of liver cirrhosis
The filtration membrane is broken = protein leak into Bowman’s capsule = decreased colloid osmotic pressure = increased filtration rate.
Explain capsule pressure
P(c) = 10 - 20 mmHg
Shows the hydrostatic pressure in nephron/Bowman’s capsule.
The less fluid leaves the proximal convoluted tubule the greater the capsule pressure.
Inhibits filtration.
What happens to capsule pressure in case of kidney stones or accumulation of haemoglobin
Renal tubules will be obstructed = capsule pressure rises and inhibits filtration.
What formula determines effective filtration pressure
Pef = P(h) - (π + P(c))
Should be around 10 mmHg to clear blood plasma from unwanted substances and to maintain normal water and salt balance.
How does effective filtration pressure affect filtration rate
The higher the effective filtration pressure the higher the filtration intensity.
How does filtration membrane affect filtration rate
Surface area:
The greater the surface area = greater filtration intensity
Permeability:
Greater permeability = greater filtration intensity
The filter membrane consists of fenestrated endothelial cells that provide great water-soluble substance transport. Basement membrane of Bowman’s capsule consists of pericytes. Damage to these = increased permeability.
What happens in glomerular nephritis
The basement membrane is damaged.
Greater diameter of pores = more proteins are filter into urine.
Protein are NOT supposed to be found in urine.
So this shows that proteins are unable to be transported back into the bloodstream.
How does properties of substance affect filtration rate
Molecular weight:
- Substances greater than 70,000 Daltons are not passed through the filter membrane.
- Proteins are not filtrated.
Charge:
- Basement membrane is negatively charged.
- Negative substances are inhibited.
- Positive substances are facilitated.
Radius:
- the greater the radius the lower the filtration rate.
- Maximum radius of 45 angstroms are filtered.
What is ultra filtrate
It is primary urine
What is the ultrafiltrate level in males vs females
M: 125 ml/min or 180 L/day
F: lower
What does ultrafiltrate consist of
- Blood plasma
- Molecules less than 70,000 Daltons
- Blood should not be present in the urine = if fresh blood is present most likely from lower urinary tract. If blood appears in cylinders = damage of the glomerular capillaries.