Renal system

Question 1

What is the main function of a kidney

Answer 1

Concentrates urine.

Ensures there isn’t too much or little water in the body

Makes sure blood pressure isn’t too high or too low

Gets rid of urea, uric acid, toxins and other wastes

Maintains a balance of electrolytes (important for cardiac function and rhythm)

Maintains ACID-BASE balance. makes sure body isn’t too acidic or alkaline

Has capacity to produce different hormones (e.g RAS and EPO).

Question 2

What is chronic kidney disease?

Answer 2

Insufficient circulating vitamin D.
Suggested to contribute to development of bone fragility, fractures, and cardiovascular function, diabetes, multiple sclerosis, cancer, and reduced immunological response.

Question 3

What does Vitamin D supplementation do?

Answer 3

Improves production from kidney, stimulating calcium reabsorption.]

BUT Reduces PTH secretion (PTH is important for bone health)

Stimulates phosphate and calcium absorption

Question 4

What is Erythropoetin (EPO)?

Answer 4

Produced from the kidney.

Bone express the EPO receptor.

EPO receptor important for function of all the cells for bone (e.g bone cartilige)

Question 5

What happens when the EPO receptor in bone is removed?

Answer 5

Reduced bone mass

Question 6

Describe the main function of the kidneys (don’t remember all of these, name at least 3)

Answer 6

Homeostatic regulation of water and ion content of blood.

Regulation of extracellular fluid volume (this would drop because of not drinking enough so blood pressure would drop and CV function drop)

Regulation of osmolarity (kidneys are capable of telling brain when thirsty) - thirst

Maintain balance of ions (sodium, potassium, calcium, chloride) within normal range. Balancing dietary intake/urinary loss.

Homeostatic regulation of pH H+ or HCO3- (removal or preserving ions)

Excretion of wastes and foreign substances (by products of metabolism e.g creatinine) and drugs.

Production of hormones

Question 7

What is a nephron?

Answer 7

Kidneys are made up of a million filtering units called nephrons.

Each nephron includes a filter (called the glomerulus) and a tubule.

They work through a 2-step process: glomerulus filters blood and tubule returns needed substances to blood and removes waste

Question 8

Describe the key processes of the nephron

Answer 8

1) Filtration:

Glomerular filtration - ultra filtration of plasma in the glomerulus. Movement of fluid from blood into tubule lumen (results in urine production)

2) Reabsorption:

Tubular reabsorption, transport of substances out of tubular urine and returned to capillary blood (Solutes filtered through glomerulus is non-selective so good stuff will be filtered into lumen of nephron so body wants to take it back)

3) Secretion:

Tubular secretion - involves transport of substances into tubular urine movement into urine

4) Excretion elimination via urine

Question 9

What 3 barriers does filtrate have to pass through in the blood system?

Answer 9

1st: glomerular (high pressure and leaky)me

2nd: Basal lamina

3rd Epithelium of bowmans capsule

Question 10

How to calculate Net filtration pressure

Answer 10

Capillary blood pressure - ( Osmotic pressure + fluid pressure)

Question 11

Describe glomerular filtration rate

Answer 11

Should be 125ml/min allows for 180L/day

Question 12

Give examples of how Glomerular filtration rate (GFR) is regulated

Answer 12

Changes in afferent arteriole resistance is the most common physiological regulator of GFR.

if high BP then constrict afferent arteriole or dilate efferent

If low blood pressure then dilate (make bigger) afferent arteriole or constrict efferent (constricting efferent will act like a dam)

Question 13

What are the specialised cells in the glomerulus called and what do they do?

Answer 13

Endothelial cells and epithelial cells.

They act as a highly efficient filtration system

Question 14

What does autoregulation do to renal blood flow and GFR in response to arterial pressures from 80 to 180 mmHG and how does it do this?

Answer 14

It suppresses the changes in renal blood flow & GFR in response to mean arterial pressures

Control mediated by: myogenic response and tubulo-glomerular feedback

Question 15

What is the myogenic response?

Answer 15

A way to suppress the changes in renal blood and GFR in response to arterial pressures

Blood travels down pressure gradients.

Lining the sarcolemma of the smooth muscle cell on the blood vessel are “stress sensitive” calcium channels and voltage gated calcium channels (green on diagram).

When there’s high blood pressure to an organ (e.g a toe), this causes smooth muscle cell to stretch, activating the stretch sensitive calcium channel to open up the voltage gated calcium channels > influx of calcium > depolarise smooth muscle cells > vasoconstriction.

Vasoconstriction decreases volume & increases pressure so it cuts off/minimises blood flow to a specific area since blood flow doesn’t flow from high to higher.

DIAGRAM IN ON

Question 16

What cells cover blood vessels that allow vasodilation/constriction to happen?

Answer 16

Muscle cells

Question 17

Tubuloglomerular feedback

Answer 17

Macula desa cells sense the flow of fluid through the nephron and tubule. THeyc an produce vasoactive substances which can allow for vasoconstriction/dilation of efferent/afferent.

GFR increase > Increase in fluid flow through tubule > flow moves past macula densa cells and they produce vasoactive mediators to the afferent arteriol > afferent arteriol constricts in response > Resistance in afferent arteriole increases > hydrostatic pressure in glomerulus decreases > reduction in GFR

Question 18

What hormone is an example of a vasoconstrictor?

Answer 18

Angiotensin 2

Question 19

What hormone is an example of a vasodilator?

Answer 19

Prostaglandins

Question 20

How do we measure renal function(GFR)?

Answer 20

Through creatinine.

It’s a waste product from the normal breakdown of muscle tissue.

As it’s produced, it’s filtered through the kidneys and excreted in urine. So they reabsorb none of it.

Doctors measure the blood creatinine levels as a test of kidney function.

Under normal circumstances, the kidneys efficiently filter out creatinine, maintaining a stable level in the blood. However, if kidney function declines, the kidneys are less able to filter out creatinine, leading to an accumulation in the blood. Thus, the blood level of creatinine reflects how well the kidneys are functioning.

Blood creatinine levels are used to estimate the glomerular filtration rate (GFR), which measures how much blood the kidneys filter per minute. A higher blood creatinine level generally indicates a lower GFR and thus impaired kidney function.

Question 21

What is normal creatinine clearance in healthy women and men?

Answer 21

women: 88-128mL/min maybe remember as 90-130

Men: 97-137mL/min (maybe remember it as 100-140

Question 22

Explain the process of reabsorption and where it occurs
Describe the main mechanisms of solute reabsorption in the tubule
Describe the process of secretion and excretion, describe where in the nephron these processes occur

Question 23

What is reabsorption, how much fluid pass from glomerular capillaries into nephron?

Answer 23

Reabsorption is the movement of filtered solutes and water from the lumen of the tubule back into the plasma

180L of fluid pass from glomerular capillaries into nephron but only 1.5L are excreted into urine

99% of what goes through glomerulus filter is reabsorbed

The high filtration rate helps clear foreign substances quickly.

Question 24

Where does most of reabsorption happen?

Answer 24

In the proximal tubule

Question 25

At which point do most of the salts and nutrients get absorbed into the capillaries?

Answer 25

The loop of henle - Fine tuning of water balance

Question 26

How much of creatinine is reabsorbed and secreted?

Answer 26

None.

Question 27

What are the cellular type that comprise the proximal tubule?

Answer 27

Renal proximal tubular epithelial cells (PTECs)

Question 28

What to PTEC’s do

Answer 28

Responsible for the reabsorption fo numerous solutes from glomerular filtrate and excretion of metabolic waste products or xenobiotics from peritubular capillaries,

Have much more microvilli and lots of mitochondria to produce energy to drive reabsorption.

Question 29

Describe the process of reabsorption and where it occurs

Answer 29

For a substance to be reabsorbed, it needs to be transported across the tubular epithelial membranes into the renal interstitial fluid and then through the peritubular capillary membrane back into the blood.

Question 30

The concentration of a molecule determines the mechanism required to transport….

Answer 30

Any particular substance from the urine, across the epithelial cells, into the interstitial space, and then back into the blood stream.

Question 31

Transport can be active or passive, explain this.

Answer 31

Passive - molecules move with the gradient (high to low) VIA either diffusion or facilitated transport (e.g urea)

ACTIVE - molecules move against the gradient (low to high) with the help of a carrier and energy - primary and secondary

Primary active: - directly uses energy to transport molecules

Secondary active: uses energy from electrochemical gradient to drive transport e.g sodium accross epithelium and sodium linked glucose reabsorption

Question 32

In the medulla, water is diffused out of the loop of helne because of…

Answer 32

The salts attracting the water in the medulla. These salts come from the other end of the loop of henle where they are released.

Question 33

Is water reabsorbed at the end of loop of helne?

Answer 33

It can be, for example in response to dehydration so the kidneys save water and produce concentrated urine.

Question 34

How can we increase the osmolarity of the interstitium? DIAGRAM IN ON

Answer 34

Moving solutes/ions into it which creates favorable conditions for water reabsorption.

Question 35

How are sodium reabsorbed into the capillary?

Answer 35

Sodium transporters located in various segments of the nephron. 60-70% in PT, 15-20% LOH and 1-2% in collecting duct.

ATP is generated to move sodium out of the cell and into the space. It does this by modulation of potassium

The NA and K move against concentration gradients (low to high)

The pump maintains the gradient ofa higher concentration of sodium extracellularly and high level of potassium intracellularly

Question 36

Why can’t glucose molecules traverse the lipid membrane of the cell by diffusion?

Answer 36

Because of its polar nature and large size so it requires transport proteins (glucose transporters)

Question 37

What are the 2 glucose transporters?

Answer 37

Sodium-glucose linked transporters (SGLTs)

Facilitated diffusion glucose transporters (GLUTs)

These are expressed at the membrane of the early proximal tubule

Question 38

Describe a mechanism of solute reabsorption in the tubule

Answer 38

Sodium linked glucose reabsorption

Glucose is actively transported across the apical membrane by Na-linked active transport using an SGLT (sodium glucose co-transporter)

Na+ is kicked out of the tubule, into the intracellular space through the SGLT2 transporter and Glucose piggybacks with it. Then, glucose in transported into the plasma using the GLUT2 transporter. Na+ gets into the plasma via a Na+/K+ ATPase pump.

DIAGRAM IN ON

Question 39

Under normoglycemia, how much glucose is reabsorbed by the SGLT2 and SGLT1?

Answer 39

SGLT2 in early proximal tubule 97% of filtered glucose.
SGLT1 in late proximal tubule 3%

In individuals with genetic defect in SGLT2 gene, reabsorption of glucose is impaired so high concentration of glucose in urine

Question 40

Describe the process of secretion and excretion. Describe where in the nephron this occurs and how

Answer 40

Secretion is the transfer of molecules from the extracellular fluid into the lumen of the nephron. e.g drugs, urea.

Excretion: urine output result of all processes that take place in kidney

Amount of solute excreted = amount filtered - amount reabsorbed + amount secreted