MODULE 6

what does the renal system consist of

kidneys and ureters

what is the overall function of the kidneys

filter out blood, returning water and solutes back to the body

what does urine consist of

excess water and solutes which are not returned to the body

what are the 4 regions of the kidney

renal cortex

renal medulla

renal sinus

hilum

what does the renal sinus consist of

minor calyces

major calyces

renal pelvis

what makes up the renal medulla

8-18 renal pyramids separated by cortical renal columns

what are the components of the nephron

renal corpuscle

renal tubules

what does the renal corpuscle consist of

the glomerulus and bowman’s capsule

what does the renal tubule consist of

proximal convoluted tubule

loop of henle

distal convoluted tubule

where do nephrons empty into

collecting ducts

where do collecting ducts drain into

they drain into papillary ducts

describe the path of urine once it exits the nephron

collecting duct

papillary ducts

minor calyces

major calyces

renal pelvis

ureter

describe the structure of the bowmans capsule

simple sqaumous parietal layer

visceral layer of podocytes over glomerular capillaries

describe glomerular capillary path

arise from afferent arteriole

empty into efferent arteriole

what does the filtration membrane consist of

fenestrated endothelium of glomerulus

basement membrane

podocyte cell layer with filtration slits

what is the role of fenestrated endothelium

prevents filtration of blood cells but allows all components of blood plasma to pass through

what is the role of the basement membrane

prevents filtration of larger proteins

what is the role of filtration slits

prevents filtration of medium sized proteins

what is the glomerulus

a length of capillary where glomerular filtration occurs in the nephron

describe the adaptations of the glomerulus

large length

fenestrated endothelium

thin wall

decreasing diameter from afferent to efferent to increase filtration pressure

describe the structure of the proximal convoluted tubule

convoluted tube made of cuboidal epithelium with many microvilli

packed with mitochondria

what occurs in the proximal convoluted tubule

reabsorption

describe the structure of the loop of henle

made of ascending limb and descending limb

thick cells in ascending limb and thin cells in descending limb

can loops of henle differ in size

yes

cortical nephrons have short loops of henle

juxtamedullary nephrons have long loops of henle

what are the 2 types of nephrons

80% of nephrons are cortical

20% of nephrons are juxtamedullary

describe the structure of the distal convoluted tubule

made of cuboidal epithelium with few microvilli

some mitochondria

describe the structure of collecting ducts

attached to DCT’s of several nephrons

begins in cortex and then passes into the renal pyramids

they open into minor calyces

made of cuboidal epithelia with mitochondria

what are the 4 specific function of the kidney

1. excretion

2. regulate blood volume

3. regulate blood pressure

4. release erythropoietin and calcitrol

what is the function of erythropoietin

it increases red blood cell production in bone marrow when oxygen levels are low

what is calcitrol

activated vitamin D

what are the 3 phases of urine production

glomerular filtration of plasma

tubular reabsorption

tubular secretion

what drives glomerular filtration

filtration pressure

what is glomerular capillary pressure

the blood pressure within the glomerulus which moves fluid from the blood into the bowman’s capsule

what is capsular hydrostatic pressure

the pressure inside the bowmans capsule which moves fluid from the bowman’s capsule into the blood

what is blood collid osmotic pressure

pressure produced by the concentration of blood proteins, it moves fluid from the bowmans capsule into the blood by osmosis

what do filtration pressure equal

the glomerular capillary pressure minus the capsular hydrostatic pressure and the blood colloid osmotic pressures

how much of filtrate is reabsorbed

about 99.5%

what does it mean to say that reabsorption is discriminating

only the substances we need are reabsorbed

where does most of reabsorption occur

in the proximal convoluted tubule with microvilli and mitochondria

by what methods are substances reabsorbed

actively and passively, and water follows by osmosis

describe symporting

Na+ symporters help reabsorb materials from the filtrate

what substances are completely reabsorbed in first half of PCT

glucose

amino acid

lactic acid

water soluble vitamins

describe where reabsoprtion of sodium occurs

67% in PCT
25% in LOH

8% in DCT and collecting duct

what controls Na+ reabsorption in DCT and collecting duct

aldosterone

therefore the 8% is variable

describe where reabsorption of water occurs

65% in PCT

15% in LOH

20% in DCT and dollecting duct

what controls water reabsorption in the DCT and collecting duct

ADH action and Na+ movement

describe the process of tubular secretion

transfer of solutes from blood into tubular fluid (filtrate)

what is the function of tubular secretion

controls pH by H+ secretion

eliminates specific substances quickly like ammonium, creatinine, potassium and drugs

how do kidneys influence blood pressure

by altering extracellular fluid composition and volume

what are the 2 subdivisions of blood pressure regulation

intrinsic

extrinsic

what are the 2 intrinsic blood pressure mechanisms

autoregulation

renin-angiotensin-aldosterone system

what is the extrinsic blood pressure mechanism

sympathetic nervous system control

what makes up the juxtaglomerular apparatus

juxtaglomerular cells of afferent arteriole and macula densa of the distal convoluted tubule

what is the role of the juxtaglomerular apparatus

regulate glomerular blood pressure and the rate of blood filtration

describe how autoregulation works

variable blood pressure results in variable glomerular filtration rate, and hence variable urine output

glomerular filtration rate is monitored and the afferent arteriole changes diameter accordingly

a decreased GFR will cause dilation to increase blood flow/GFR
an increased GFR will cause constriction to decrease blood flow/GFR

what can override the juxtaglomerular apparatus

the sympathetic nervous system

describe how the RAA mechanism works

juxtaglomerular cells release renin upon detected blood pressure drop

renin interacts with angiotensinogen to form angiotensin I

angiotensin I passes through the lngs where a pulmonary converting enzyme turns it into angiotensin II

what are the effects of angiotensin II on the body

1. vasoconstrictor

2. increase ADH release

3. increase thirst

4. influence cardiovascular system to increase blood pressure

5. stimulate adrenal cortex to release aldosterone (increases Na+ reabsorption, increases water retention, increase extracellular fluid volume and therefore increase BP)

how does aldosterone increase sodium reabsoprtion

it induces DNA to code mRNA to manufacture Na+ and K+ transport proteins

this increases the Na/K ATPase pumps in the basolateral membranes and increases the Na+ channel proteins in luminal membranes

what is the mechanism for urine production

counter current multiplier mechanism

why is it called the counter current multiplier mechanism

counter current because the flow in the LOH and vasa recta are in opposite directions to one another

multiplier mechanism because the movement of ions is achieved in small steps which will multiply into an overall big effect

which nephrons are responsible for concentrating urine

juxtamedullary nephrons which set up a steep osmotic gradient

how do juxtamedullary nephrons set up an osmotic gradient

by movement of water and ions from filtrate, and relative permeabilties of tubular cells in descending and ascending limbs of LOH

describe permeability of the descending limb

permeable to water

impermeable to Na+ and Cl-

describe permeability of the ascending limb

impermeable to water

permeable to Na+ and Cl-

describe active sal extrusion in the loop of henle

the thick ascending loop has salt pumps that reabsorb ions from filtrate

potassium leaks back into tubular fluid, whilst sodium and chloride move into the vasa recta

what does the counter current flow allow

it allows provision of nutrients and oxygen without affecting osmolality of interstitial fluid

it also removes any excess water and salt that has been extracted from the LOH

what is the net effect of the counter current multiplier mechanism

increase Na+ and Cl- in the descending limb

decrease Na+ and Cl- in the ascending limb

establish osmotic gradient in interstitium

how does ADH affect urine concentration

increased ADH means more water reabsorbed and hence urine more concentrated and vice versa

how is ADH release stimulated

osmoreceptors in the hypothalamus monitor osmotic pressure of plasma and hence blood volume

ADH will be secreted if there is water deficit in body (high osmotic pressure of plasma)