pathophysiology-lec 7-renal structure and function

8/7/2019 Pathophysiology-lec 7-Renal Structure and Function

http://slidepdf.com/reader/full/pathophysiology-lec-7-renal-structure-and-function 1/35

1

Renal Structure and Function



2

Anatomy

� Hilum (hilus)

� Renal artery and vein

� Cortex� Medulla

� Renal pyramids and renal papillae

� Major and minor calyces

� Renal Pelvis

� Ureters



3



4



5

2. Regulation:

Blood volume and compositionElectrolytes

Blood pH

Blood pressure



6

Nephron

� Functional unit of the kidney

� Filtration, tubular reabsorption, tubular

secretion� Renal corpuscle:

± Glomerulus ± capillaries

± Glomerular or Bowman¶s capsule



7

� Bowman¶s capsule

± Receives filtrate

� Proximal convoluted tubule

± Reabsorption of water and solutes

� Nephron loop or Loop of Henle

± Regulates concentration of urine

� Distal convoluted tubule and Collecting

duct

� Reabsorption of water and electrolytes

±ADH, aldosterone, ANP

± Tubular secretion



8



9



10



11

Forces that influence filtration

� Glomerular blood hydrostatic pressure

� Opposing forces:± Plasma colloid osmotic pressure

± Capsular hydrostatic pressure



12



13

Glomerular Filtration Rate

� Volume of plasma filtered / unit time

� Approx. 180 L /day

� Urine output is about 1- 2 L /day� About 99% of filtrate is reabsorbed



14

GFR influenced by:

� Blood pressure and blood flow

� Obstruction to urine outflow

� Loss of protein-free fluid� Hormonal regulation

± Renin ± angiotensin

± Aldosterone± ADH

± ANP



15

Juxtaglomerular apparatus

� Juxtaglomerular cells lie in the wall of

afferent arteriole

� Macula densa in final portion of loop of Henle ± monitor Na+ and Cl- conc. and

water

� Control blood flow into the glomerulus

� Control glomerular filtration



16



18



19

� In addition to reabsorption, also have

tubular secretion ± substances move fromperitubular capillaries into tubules ± a

second chance to remove substances

from blood.



20

� By end of proximal tubule have

reabsorbed:� 60- 70% of water and sodium

� about 100% of glucose and amino acids

� 90 % of K+, bicarb, Ca++, uric acid� Transport maximum ± maximum amount

of a substance that can be absorbed per

unit time

� Renal threshold ± plasma conc. of a

substance at which it exceeds Tm.



21

Loop of Henle

� Responsible for producing a concentrated

urine by forming a concentration gradient

within the medulla of kidney.

� When ADH is present, water is reabsorbed

and urine is concentrated.

� Counter-current multiplier



22



23

Distal convoluted tubule and

collecting ducts

� What happens here depends on ADH

� Aldosterone affects Na+ and K+

� ADH ± facultative water reabsorption� Parathyroid hormone ± increases Ca++

reabsorption



24



25

Distal convoluted tubule and

collecting ducts

� Tubular secretion to rid body of

substances: K+, H+, urea, ammonia,

creatinine and certain drugs

� Secretion of H+ helps maintain blood pH

(can also reabsorb bicarb and generate

new bicarb)



26

Renal diagnostic procedures

� Urinalysis is non-invasive and inexpensive

� Normal properties are well known and

easily measured



27

pH

� Normally 4.8 ± 8.0

� Higher in alkalosis, lower in acidosis

� Diabetes and starvation pH� Urinary infections pH

± Proteus and pseudomonas are urea splitters



28

Specific gravity

� Normal values 1.025 -1.032

� High specific gravity can cause

precipitation of solutes and formation of kidney stones

� When tubules are damaged, urine specific

gravity approaches that of glomerular

filtrate ± 1.010 ± remains fixed = 2/3 of

nephron mass has been lost



29

Microscopic analysis

� Red blood cells ± should be few or none

± Hematuria ± large numbers of rbc¶s in urine

± Catheterization± Menstruation

± Inflamed prostate gland

± Cystitis or bladder stones



30

� Casts ± precipitate from cells lining the

renal tubules± Red cells ± tubule bleeding

± White cells ± tubule inflammation

± Epithelial cells ± degeneration, necrosis of

tubule cells



31

� Crystals ±

± Infection± Inflammation

± stones



32

Substances not normally present in

urine

� Acetone

� Bile, bilirubin

� Glucose� Protein ± albumin

± Renal disease involving glomerulus



33

Blood Urea Nitrogen BUN

� Urea produced by breakdown of amino

acids - influenced by diet, dehydration,

and hemolysis

� Normal range 10-20 mg/ dL

� If the GFR decreases due to renal disease

or blockage, or decreased blood flow to

kidney - BUN increases

� General screen for abnormal renal

function



34

Creatinine clearance

� Creatinine is an end product of muscle

metabolism

� Muscle mass is constant; creatinine isconstant

� Normal 0.7 ± 1.5 mg/ dL in plasma

� Can then be compared to creatinine inurine over 24 hour period to determine

clearance



35

� Creatinine clearance is an indirect

measure of GFR and renal blood flow� Creatinine is neither reabsorbed nor

secreted, just freely filtered.

�A

mount excreted = amount filtered� Useful to monitor changes in chronic renal

function

� Increases with trauma with massivemuscle breakdown

pathophysiology-lec 7-renal structure and function

Documents