Renal system

Question 1

Describe the Renin-angiotensin aldosterone mechanism

Answer 1

1. Renin is produced by the kidneys, it is released when low BP is detected via the juxtaglomerular complex
2. Renin splits into angiotensinogen which activates enzymes to convert into Angiotensin I
3. Angiotensin I circulates the blood and is converted to Angiotensin II in the lungs via ACE (enzyme)
4. Angiotensin II causes vasoconstriction of BV to increase BP. release of aldosterone from the adrenal cortex via k+ levels in zona glomerulus. (release of ACTH can speed up aldosterone secretion)
5. Release of aldosterone promotes reabsorption of Na+ as well as H2O, It stimulates the excretion of K+ in urine, this creates an increase in blood volume so BP is increased

ANP (atrial natriuretic peptide, secreted via heart) inhibits RAS mechanism as it blocks renin & aldosterone secretion, ANP decreases BP allowing Na+ to leave in the urine

Question 1

Define the nephron

Answer 1

A functional unit of the kidney, each kidney has 1 million nephrons each. It contains the: glomerulus, Bowmans capsule, 1st & 2nd convoluted tubule (distal), collecting duct, loop of henle, afferent & efferent arterioles, peritubular capillaries

Question 2

Describe the process of filtration

Answer 2

Blood is filtered at high pressure, allowing small molecules to be filtered out of the blood, and filtrate is produced.
It occurs within the Bowman capsule. The glomerulus is separated by two layers of cells and a basement membrane.
Basement membrane acts as a filter & only allows small molecules e.g., glucose to pass through to the filtrate, the rest e.g., RBC stay in the glomerulus, the basement membrane is supported via podocytes, finger like projections that allow filtrate to pass through, contain slits called pedicels that catch any large molecules that have managed to pass through the basement membrane, preventing access to tubules

Question 3

Describe the process of selective reabsorption

Answer 3

Occurs in the PCT
1. Na/K pump is actively pumping out Na+ ions and pumping in K+ ions, (needs ATP), Na+ concentration is higher outside the cells of the CVT
2. Glomerular filtrate arrives at PCT (H2O, glucose, A.A’s) As Na+ is pumped out concentration decreases inside cells, so Na+ moves in via facilitated diffusion along with glucose, A.A’s (need transport protein)
3. Increased solute concentration in PCT lowers the water potential in cells and so H2O moves in via osmosis from filtrate
4. Glucose & A.A’s build up inside PCT & diffuse out again into tissue fluid to enter the blood
More water absorbed from filtrate equals less urine produced

Question 4

Describe the process of secretion

Answer 4

Fluid flows in opposite directions in the tubules

Question 5

Describe the process of osmoregulation

Answer 5

1. Low water potential detected by osmoreceptors in the hypothalamus, stimulates production of ADH from neurosecretory cells that pass along axon to PPG to secrete ADH
2. ADH travels in the blood and acts on the walls of the collecting duct in the nephron, ADH increases the permeability of the by binding to receptors on DCT, more water is reabsorbed
3. CAMP triggers a cascade of enzyme reactions that produce phosphorylase
4. Water is reabsorbed, thirst receptors are stimulated, small dark concentrated volume of urine is produced.
   Rise in water potential and ADH secretion is reduced, more water removed, larger paler volumes of urine produced

Question 6

Define autoregulation

Answer 6

Autoregulation- if pressure is high afferent arteriole constricts to reduce pressure entering the glomerulus, if pressure is low the efferent arteriole will constrict to increase pressure in the glomerulus, low pressure in afferent arteriole stimulates release of renin, to retain water & salt to increase blood volume.

Question 7

Define the function of aquaporins

Answer 7

are proteins that enable the act as water channels found in tubule membranes, allows water to be reabsorbed by the collecting duct

Question 8

Name the functions of the kidney

Answer 8

• produces erythropoietin
• Regulates calcium, phosphate & vitamin D metabolism
• secretes hormones
• removes waste products of metabolism
• production of Renin
• produces urine
• regulates electrolytes
• maintains osmoregulation (fluid balance)

Question 9

Describe the acid-base balance mechanism

Answer 9

(haldane effect)
Normal pH range is 7.35-7.45
H+ ions are constantly produced during metabolism and need to be removed to prevent pH change, more H+ more acidic the blood becomes, causes a change in tertiary structure of Hb
More OH- causes more alkaline blood. The blood acts as a buffer as it contains carbonic acid & a concentration of bicarbonate ions. When any H+ ions are present in the blood the HCO3- ions neutralize them by forming carbonic acid & water.
Lungs also detect increase in H+ increasing BR to remove H+
Kidney acidiosis results in H+ in urine, H+ combines with buffer in the urine & is removed

Question 10

Describe the erythropoietin production mechanism

Answer 10

EPO is made by kidneys
EPO stimulates red bone marrow to produce RBC’s
Hb is needed to carry O2
EPO production is stimulated by hypoxia (low O2 in tissues) detected by peritubular cells in kidney
Stem cell divides to form myeloid cells, then become normoblasts, lose their nucleus to become reticulocytes, these mature to form RBC’s

Question 11

Describe the composition of urine

Answer 11

5% solutes & 95% water
Urea is formed in the liver from the breakdown of amino acids, protein is deaminated in the liver forming urea.
Sodium, potassium, water, creatine, uric acid found in the urine
NH3 is toxic so is converted to urea which is converted to uric acid
Urea & creatine concentration can give us an indication of renal function
Creatine is normally higher in men (more muscle mass)
Osmolarity: number of solutes per kg of H2O
1 osmol = 1 mole of particles per kg of H20

Question 12

Describe the structure of podocytes

Answer 12

the basement membrane is supported via podocytes, finger like projections that allow filtrate to pass through, contain slits called pedicels that catch any large molecules that have managed to pass through the basement membrane, preventing access to tubules.

Question 13

What is GFR and what is normal range?

Answer 13

60-90mg/mol

Question 14

What does the adrenal medulla produce and what does the adrenal cortex produce?

Answer 14

Adrenal medulla- adrenaline & noradrenaline
cortex- androgens, mineralocorticoids, glucocorticoids, adolsterone

Question 15

Describe the process of calcium, phosphate & vitamin D regulation

Answer 15

Hormonal control of calcium is caused via PTH released from parathyroid

Reabsoprtion of Ca2+ enables metabolism of vitamin D

Calcium is reabsorbed and phosphates are excreted

Hypocalcemia is detected which stimulates parathyroid to secrete PTH

This affects the bones & kidneys

PTH activates osteoclasts to break down bone to release calcium & phosphates into the bloodstream

Calcium reabsorption is activated in the kidneys as well as vitamin D metabolism

Question 16

Why does Potassium need to be removed?

Answer 16

Potassium is toxic for the body causing hyperkalemia, can cause MI & muscle weaknesses

Question 17

What is calcium needed for?

Answer 17

Strong teeth & bones
Transmission of nerve impulses
muscle contraction
blood clotting

Question 18

What causes filtration to occur at high pressure?

Answer 18

The efferent arteriole is narrower than the afferent arteriole so blood entering the kidney from afferent can not all leave via the efferent. This creates pressure pushing small molecules out of the blood to produce filtrate

Question 19

What are the adaptations of the primary convoluted tubule?

Answer 19

They contain microvilli which increase the SA for absorption, has lots of mitochondria to generate ATP for movement of Na+
Capillaries are close together providing a short diffusion distance

Question 20

Describe the structure of the Bowmans capsule, glomerulus, afferent & efferent arterioles

Answer 20

Bowman capsule: Cup-shaped, contains the glomerulus, has an inner layer made of podocytes in cortex region, it is the site if ultrafiltration
Glomerulus: a knot of capillaries found in the capsule, from where fluid is forced out of the blood
Afferent arteriole: tiny vessel that branches of renal artery & supplies nephron with O2 blood at high pressure from aorta, wider lumen than efferent
Efferent arteriole: a tiny vessel that leaves the renal capsule, smaller in diameter, carries blood away from the capsule to join inferior vena cava

Question 21

Describe the structure of the primary & secondary convoluted tubules & peritubular capillaries

Answer 21

PCT: a series of loops surrounded by capillaries, made of cuboidal cells with microvilli to increase SA for selective reabsorption
DCT: series of loops surrounded by fewer capillaries involved in osmoregulation, has cuboidal cells, permeability varies with ADH, regulates ion & H2O
PC: a dense network that surrounds PCT, DCT & loop of Henle, from which glucose, A.A’s, H2O are absorbed, merges into renal vein

Question 22

Describe the structure of the collecting duct & loop of Henle

Answer 22

CD: tube where convoluted tubules enter into, lined with cuboidal cells, widens before entering renal pelvis, collecting duct leads down into medulla into the pelvis to join to ureter, involved in osmoregulation.
LOH: a long loop from renal cortex to medulla then back to cortex, surrounded by blood capillaries, the filtrate is concentrated

Question 23

Describe the counter current multiplier mechanism

Answer 23

The fluid flows in opposite directions in opposing limbs, the ascending limb is impermeable to water, and pumps out Na+, inverse for the descending limb
1. Ascending limb pumps Na+ & Cl into tissue fluid surrounding limb space
2. high Concentration of Na+ & Cl- in tissue fluid, causes H2O in glomerular filtrate travelling down descending limb to be drawn out & moves into capillaries surrounding loop of henle
3. Na+/Cl- diffuse into descending limb at top, when it reaches bottom of limb concentration of Na+/Cl- is highest at base of loop
4. Some of Na+/Cl- diffuse out into the medulla at bottom of ascending limb
5. High up in AL Na+/Cl- are being pumped out, AL is impermeable to H2O, filtrate is diluted in AL
6. Concentration difference of 200 units is needed between intersitial fluid and ascending limb, effect is multiplied to ensure constant removal of Na+/Cl-

Question 24

What does blood in the urine indicate?

Answer 24

It indicates damage to the basement membrane in the Bowmans capsule as large molecules are not supposed to be allowed to pass through into the filtrate

Question 25

Define T(m)

Answer 25

Known as transport medium. It is the maximum volume of substance that can reabsorbed.
If glucose exceeds T(m) it is lost in the urine, occurs in diabetes

Question 26

Define the function of the: Fibrous capsule, cortex, medulla, renal pelvis & ureter

Answer 26

FC: the outer membrane that protect the kidney, e.g., from infection
RC: most superficial region, made up of convoluted tubules, BV’s & renal capsules
RM: holds the loop of henle, collecting ducts & BV’s
RP: funnel shaped cavity that collects urine & has calyces that drain into the ureter
Ureter: carries the urine to the bladder

Question 27

Define the function of the: Renal artery, Renal vein & urethra

Answer 27

RA: supplies kidneys with O2 blood from heart via aorta
RV: drains the kidney of DO2 blood, returns it to the heart via inferior VC
U: the tube where urine exits the body

Question 28

Define structure of the renal medulla

Answer 28

The medulla is deep within the kidney it contains a renal pyramid which are cone-shaped, the point facing inwards.
Pyramids are separated by renal columns made of cortical tissue. This creates 8 lobes of the kidney
Calyces branch off the renal pelvis which collect urine and flow into the ureter, urine moves by peristalsis.