Ch. 26, The Kidney

Front 1

detrusor

Back 1

-muscularis in bladder

-contracted by parasymp. NS to urinate

-relaxed/inhibited by symp. NS when holding urine

Front 2

Function of Kidneys

Back 2

-regulation of:
pH
blood volume
blood pressure

-maintains water balance

-excretes:
excess ions (K+)

nitrogenous and other metabolic wastes

drugs & toxins

-produces hormones (renin, erythropoietin, vit. D)

Front 3

2 types of nephrons

Back 3

-short loop or corticol (most nephrons)

- long loop or juxtamedullary (15-20% of nephrons)

maintains the medulla's osmotic gradient

Front 4

Anatomy of kidney

Back 4

- retroperonital

- hilum medially (for artery, vein, nerve, ureter)

- cortex & medulla (pyramidal shape w/ apex toward hilum)

Front 5

Kidney's collecting system

Back 5

(MMPUBU)

Minor calyx
Major calyx
pelvis
ureter
bladder
urethra

Front 6

Main anion of ICF

Back 6

protein and phosphate

Front 7

Main anion in ECF

Back 7

Cl-

Front 8

Blood flow to nephron

Back 8

(AGEP)

afferent arteriole
glomerulus
efferent arteriole
peritubular capillary, vasi recti

Front 9

Main cation in ICF

Back 9

K+ with magnesium also high in concentration

Front 10

3 basic function of nephron

Back 10

(FRS)

Filtration (at glomerulus)

Reabsorption (at tubule)

Secretion (at tubule)

150-180 liters of fluid is filtered and almost all is reabsorbed

Front 11

Glomerular Filtration

Back 11

- driven by hydrostatic pressure

- is opposed by colloid osmotic pressure and capsular hydrostatic pressure

Front 12

gain of H20

Back 12

drinking governed by thirst center in Hypothalamus

Stimulated by:

- decrease volume of body fluids (dehydration)

- decrease flow of saliva causes dry mouth and stimulates thirst center

- decrease in BP stimulates thirst

Front 13

Loss of excess water and electrolytes

Back 13

governed by kidney:

body fluid volume depends on urinary NaCl loss (b/c water follows solutes in osmosis & body fluid osmolarity depends on urinary water loss

Front 14

Regulation of renal losses is by

Back 14

AAAA

Angiotensin II
Aldosterone
ANP
ADH

Front 15

trigone

Back 15

- located in bladder

- triangular area at base of bladder where R&L ureters enter

- anteriorly the internal orofice of the urethra

Front 16

Micturition

Back 16

- urination

- parasym. NS- contracts detrusor; relaxes sphincter

-stretch receptors in bladder wall send impulses to micturition center in sacral spinal cord (S2-S3)

Front 17

Holding urine

Back 17

Symp NS:

- inhibits detrusor

- contracts sphincter

Front 18

Peristalsis

Back 18

moves urine down ureters

Front 19

Urinary bladder

Back 19

- distensible holding chamber

- has internal (smooth M) and external (skeletal M) sphincter

- contents always under low pressure

- voiding occurs when parasymp. NS causes detrusor to contract and sphincter relaxes

Front 20

Urine analysis (kidney)

Back 20

SpGr- reflects concentration of solutes:
1.004= dilute
1.035=concentrated

Front 21

Glucosuria

Back 21

high blood glucose

Front 22

proteinuria

Back 22

glomerular disease

Front 23

Symporters and antiporters

Back 23

- use energy of a cation (Na+) following its concentration gradient

- glucose, aas, enter thru symporters

- H+ goes through an antiporter

Front 24

water absorption in kidney

Back 24

Water absorbed in PCT and descending limb of LOH (impermeable to Na+ but H20 is absorbed, thus tubular fluid is concentrated as it descends the LOH)

BUT NOT in ascending limb ("diluting segment") (which is impermeable to water but allows Na+ to continue being reabsorbed)

Front 25

Potassium (K+) in blood

Back 25

The more K+ in blood, the more K+ leaks into the lumen of the CD

Front 26

Efferent arteriole

Back 26

- narrower than afferent

thus

- increased resistance so

increased blood hydrostatic pressure in glomerulus which is greater than in capillaries elsewhere in body

Front 27

Reabsorption in kidneys

Back 27

- most reabsorption occurs in PCT

- all glucose, aas, ions, protein are reabsorbed

- H+, K+, creatinine, NH4+, toxic substances are secreted by tubules

Front 28

2 types of water absorption

Back 28

- obligatory (90%) water is obliged to follow solutes

- facultative (10%) according to body's needs, occurs in CD)

Front 29

male urethra

Back 29

3 regions:

prostatic
membraneous
penile (spongy)

- bladder infections very rare in males b/c of 8" urethra

Front 30

Main cation in ECF

Back 30

Na+ (sodium)

Front 31

Anatomy of nephron

Back 31

(RPLD)

Renal Corpuscle (glomerulus + Bowman's capsule) (in cortex)

PCT (cortex)
LOH (in renal medulla)
DCT- (cortex)

-then nephron connects to CD and that to PD

Front 32

Transitional Epithelium

Back 32

lines the mucosa of:

(CUBU)

- collecting systems (calyces & pelvis)

- ureters

- bladder

- most of urethra

Front 33

Nephron

Back 33

- functional unit of kidney

- mesangial cells can contract thus:

- regulating blood flow thru glomerulus

- regulating filtration

Front 34

Filtration membrane

Back 34

(GBP)

glomerular endothelium

basal lamina

podocytes (visceral layer or Bowman's capsule)

Front 35

In renal corpuscle:

Back 35

(EBPT)

- filtrate passes thru pores in endothelial cells

- then thru basal lamina

- then the filtration slits between pedicels of podocytes (which support glomerular loops) into Bowman's space

-then into tubule

Front 36

Kidney function tests

Back 36

Creatinine and BUN elevated when GFR is decreased

BUN can merely reflect hydration

BUT

increased creatinine indicates renal failure

Front 37

2 routes for reabsorption in kidney

Back 37

Paracellular
AND
Transcellular

tight junctions partition cell membrane into apical and basilateral regions

Front 38

JGA (Juxtaglomerular Apparatus)

Back 38

- maculadensa and JG cells

- microscopic structure in kidney

- regulation function of each nephron

- between afferent and efferent arterioles at glomerular hilum

- JG cells secrete renin, which autoregulates glomerulus (controls GFR by negative feedback)

Front 39

Regulation of GFR by:

Back 39

- autoregulation (myogenic and JGA)

- Neural (sympathetic NS)

- hormones (angiotensin II constricts a's and ANP relaxes mesangial cells)
(renin--->angiotenisin II)

Front 40

Paracellular vs. Transcellular reabsorption

Back 40

Paracellular- reabsorption of tubular fluid occurs BETWEEN tubule cells (leakage despite tight junctions)

Transcellular- reabsorption of tubular fluid occurs THROUGH the cells.

Front 41

GFR (Glomular Filtration Rate)

Back 41

total filtrate/min (i.e. from both kidneys)

normally= 105-125 ml/min

is constant w/in MAP range of 80 to 180 mmHg

Front 42

Regulation of GFR

Back 42

Autoregulation- (myogenic or tubulo-glomerular feedback)

Neural- (i.e. symp. NS constricts afferent arterioles)

Hormonal- (Angiotensin II constricts arterioles and ANP relaxes mesangial cells)

Front 43

threshold

Back 43

a threshold (blood glucose 180-200) exists for glucose reabsorption (Tmax) ie. limit on how much is reabsorbed

in normal person, kidney conserves all glucose (no glucosuria)

Front 44

Water reabsorption descending LOH and CD:

Back 44

driven by osmotic gradient of medulla's ISF, which is created by Na+, Cl and urea.

Front 45

ADH

Back 45

- puts aquaporin-2 water channels into principal cell's apical membrane in CD; thus water facultatively reabsorbed

- ADH secretion regulated by blood volume and osmolarity

Front 46

dilution/concentration of urine

Back 46

kidney must always rid wastes regardless of water balance

so small volume of concentrated urine is possible

or

dilute urine can be produced to get rid of excess water (in absence of ADH)

Front 47

kidney hormones

Back 47

Angiotensin II- causes afferent arteriole to vasoconstrict

PTH- causes Ca++ to be reabsorbed

Aldosterone- causes principal cells to reabsorb Na+ (and water with it) and to secrete K+

Front 48

Each kidney surrounded by:

Back 48

a capsule

surrounded by variable amt of adipose tissue

surrounded by Gerata's fascia which anchors kidney to wall of abdomen

Front 49

renal hilum

Back 49

in center of medial aspect

where nerves/vessels enter and ureter leaves

Front 50

nephrons

Back 50

1 million in each kidney

Consists of:
glomerulus surround by Bowman's capsule (aka renal corpuscle) which is attached to a tubule

-drain to papillary ducts (extend thru papillae to drain into minor calyx)

Front 51

glomerulus

Back 51

ball shaped, tight capillary bed in nephron; surrounded by bowman's capsule

single layer of squamous epithelium

parietal layer- outer wall of capsule

visceral layer- podocytes (support capillary endothelial cells)

between 2 layers is Bowman's space

drains by an efferent arteriole

Front 52

efferent arteriole

Back 52

drains glomerulus

surrounds tubular part of nephron in cortex, but branches also extend into medulla to supply tubular part of nephron in medulla

Front 53

Intercalated and principal cells are in the

Back 53

distal collecting duct (DCT)

Front 54

Macula densa + JG cells=

Back 54

JGA or juxtaglomerular apparatus

Front 55

JGs are from

Back 55

modified smooth M cells from afferent arteriole

Front 56

Most tubular epithelium is

Back 56

cuboidal with microvilli on apical surface

Front 57

descending limb and thin ascending limb is

Back 57

simple squamous

Front 58

collecting and papillary ducts

Back 58

receives outflow from several nephrons

several collecting ducts form larger papillary duct

these ducts extend from cortex to pelvis

Front 59

urinary excretion =

Back 59

filtration + excretion -reabsorption

Front 60

glomerular filtration

Back 60

the movement of water and solutes from plasma across glomerular capillaries to Bowman’s space

and then into lumen of renal tubule

Front 61

tubular reabsorption -

Back 61

almost all of filtered water and solutes are reabsorbed and return to the blood thru peritubular capillaries

Front 62

tubular secretion -

Back 62

wastes, drugs, toxins, excessive ions, etc, enter tubular lumen

Front 63

glomerular filtrate =

Back 63

the fluid that passes thru filtr’n membrane into glomerular space

(~150-180 l/day, of which 99+ % is then reabsorbed)

Front 64

the filtr’n membrane has three components:

Back 64

capillary endothelial cell that has large fenestr’ns

basal lamina

pedicels of podocytes; filtr’n slits, covered by a slit membrane, are between pedicels

Front 65

mesangial cells:

Back 65

regulate filtr’n by controlling how much blood flows thru the capillaries

Front 66

most reabsorption occurs in the

Back 66

PCT (proximal convoluted tubule)

Na+ transport drives much of process

Front 67

Loop of Henle

Back 67

further reabsorption of ions and water occurs here

the descending limb is totally permeable to water

the ascending limb however is impermeable to water, although it has symporters that continue to reabsorb Na+ and Cl-

thus the tubular fluid at the end of the ascending limb has low osmolarity

Front 68

the distal convoluted tubule

Back 68

further reabsorp’n of ions + water

here PTH regulates reabsorp’n of Ca2+

Front 69

the collecting duct

Back 69

principal cells here reabsorb Na+ and secrete K+

intercalated cells reabsorb K+ and HCO3- and secrete H+

Na+ is reabsorbed here thru leakage channels rather than by transporter channels

the body’s [K+] is controlled here: K+ leakage channels are in apical plasma membrane of principal cells; when  [K+], more K+ passively diffuses into tubular fluid, and vice versa

Front 70

angiotensin II has three roles:

Back 70

it vasoconstricts afferent arteriole, which decreases GFR

it increases reabsorp’n Na+, Cl- (and thus also water) in the PCT

it causes the adrenal cortex to secrete aldosterone, which causes principal cells to both increase reabsorp’n of Na+ (which increases reabsorp’n of water) and increases secr’n of K+

Front 71

ANP:

Back 71

minor role of inhibiting reabsorp’n in presence of increased blood volume, causing natriuresis and diuresis, which lower blood volume, BP

Front 72

antidiuretic hormone (ADH)

Back 72

stimulates principal cells to insert aquaporin-2 (a water channel protein) into cell’s apical membrane

causing increased reabsorp’n of water from tubular fluid into collecting duct, so that small volume of concentrated urine produced;

when no ADH, the aquaporin channels are removed (by endocytosis), so apical membrane is nearly impermeable to water, and a large volume of dilute urine is produced

negative feedback controls ADH secr’n involving osmoreceptors in hypothalamus

Front 73

glomerular filtrate has the same osmolarity as

Back 73

blood (~300 mOsm/L),

but urine produced can have osmolarity from 65 up to 1200 mOsm/L

Front 74

when fluid intake is plentiful, tubular fluid has

Back 74

low osmolarity at the end of the nephron and collecting duct

mostly due to low levels of ADH

Front 75

when water intake is not plentiful, or water losses are large (eg, xs sweating or diarrhea), the kidneys

Back 75

conserve water

the tubular fluid at the end of the collecting duct has a very high osmolarity