APPLIED A&P OF RENAL

The Express Revision Series

APPLIED ANATOMY
& PHYSIOLOGY OF
RENAL

By Malinda Kaur

TABLE OF CONTENTS

1 Macroscopic Structure
2 Microscopic Structure
3 Renal Physiology
4 Physiology of Urine Formation
5 Urine Composition & Characteristic

2

1. MACROSCOPIC STRUCTURE

• Solid, reddish, bean-shaped organ
• Located in retroperitoneal between T12 - L3 vertebrae (right lower position);

lie against ribs 11 and 12
• Each kidney weighs about 150g, 11cm long, 6cm wide, 3cm thick like a bar

soap size

3

• Lateral surface convex; medial concave with a slit: hilum where ureter
emerges along with blood vessels, lymphatic vessels & nerves

• Protected by 3 connective tissue as outer layer:
i. Renal fascia: a fibrous layer (dense irregular connective tissue) deep to

parietal peritoneum that binds kidney to abdominal wall (peritoneum
anteriorly; lumbar muscles posteriorly)
ii. Perirenal fat capsule: an adipose layer (loose connective tissue) that cushions
& holds kidney in place
iii. Fibrous capsule: a fibrous layer (dense irregular connective tissue) that
encloses kidney to protect from trauma & infection

4

5

• Renal parenchyma: glandular tissue that forms urine appears C-shape
(frontal section) that encircles medial cavity: renal sinus (hollow space),
occupied by blood & lymphatic vessels, nerves & urine - collecting structures
(papilla, minor & major calyx)

• Parenchyma divided 2 zones: cortex (outer) & medulla (inner)
• Extension of cortex: renal column that project toward sinus & divide medulla

into 6 – 10 renal pyramid
• Pyramid is conical with base facing cortex & apex facing sinus: renal papilla

6

• 1 pyramid with cortex makes 1 kidney lobe
• Papilla of each pyramid nested in a cup: minor calyx that collects urine
• 2-3 minor calyces form a major calyx
• 2-3 major calyces form a funnel - like: renal pelvis

7

Renal parenchyma: glandular tissue that forms
urine appears C-shape (frontal section)

8

2. MICROSCOPIC STRUCTURE

• Each kidney has about 1.2 million nephrons, functional units of kidney
• A nephron has 2 parts: renal corpuscle that filters blood plasma and renal

tubule that converts filtrate to urine
• 80-85% are cortical nephrons with their renal corpuscles lie in outer renal

cortex; 15-20% are juxtamedullary nephrons with renal corpuscles deep
inside cortex, near to medulla (juxta=near to)

9

• Renal Corpuscle consists of glomerulus and glomerular / Bowman’s capsule
• Glomerulus: a ball of capillaries (single layer endothelial cells) from afferent

arteriole
• Bowman’s capsule: 2 layers – parietal (outer) simple squamous epithelium &

visceral (inner) podocytes (modified simple squamous epithelium) that wrap
around glomerulus; these 2 layers separated by a filtrate-collecting capsular
space (C-shape)
• At vascular pole, afferent arteriole (larger) enters capsule bringing blood to
glomerulus & efferent arteriole (smaller) exits carrying blood away from
capsule
• At urinary pole, parietal wall of capsule ends, gives rise to renal tubule lined
with simple cuboidal epithelium

10

• 3 filtration layers:
i. Endothelium of glomerulus containing fenestrae (fenestrated capillaries) –

allow all solutes except blood cells
ii. Basement membrane of glomerulus from connective tissues, negatively

charged – allow water & small solutes except plasma protein
iii. Visceral layer of Bowman’s capsule containing podocytes (foot processes or

pedicels with negatively charged filtration slits) – allow water, glucose,
amino acid, vitamin, ammonia, urea & ion

11

• 2 filtration criteria:
i. Size of filtrate – blood cells, plasma proteins except
• albumin are too tiny to be filtered
ii. Charge of filtrate – basement membrane repel negatively charged filtrate:

albumin; cytokine released in inflammation can change electro-negativity
• Renal Tubule is a duct leads away from Bowman’s capsule & ends at apex of

medullary pyramid
• 3cm long
• 4 regions: proximal convoluted tubule (PCT), nephron loop, distal convoluted

tubule (DCT) & collecting duct
• First 3 are parts of a nephron, collecting duct receives fluid from many

nephrons

12

Histology of Renal Tubules

13

14

Histology of Renal Tubules

15

Blood Flow to Renal

16

Blood Flow to Renal 17

Nerve Innervation to Renal

18

3. RENAL PHYSIOLOGY

i. Excretion of wastes
• Excrete metabolic waste (substance produced by body)
• Most toxic metabolic wastes are nitrogenous wastes:
❖ Ammonia (more toxic) & urea (made up 50% nitrogenous wastes) - by-

product of protein catabolism (ammonia converted to less toxic - urea by
liver)
❖ Creatinine - by-product of creatine phosphate catabolism (in skeletal muscle
fibres)
❖ Uric acid - by-product of nucleic acids catabolism
❖ Urobilin - by-product of haemolysis
• Others - foreign substances e.g. drugs / toxins

ii. Regulation of electrolytes
• Most importantly ions level - sodium, potassium, calcium, chloride &

phosphate are adjusted via urine excretion

iii. Regulation of blood volume, pressure & osmolarity

• Blood volume adjusted by conserving / eliminating water in urine. ↑ blood
volume ↑ BP and vice versa

• BP is also regulated by enzyme renin that activates RAS to ↑BP via sodium
+ water absorption

• Constant blood osmolarity (a measure of total number of solutes in a

solution) achieved by regulating loss of water and solutes in urine 19

iv. Regulation of blood pH
• Variable amount of hydrogen ions (H⁺) excreted into urine
• Bicarbonate ions (HCO3¯) are conserved, an important buffer of H⁺
• Metabolic imbalance: HCO3 abnormal (Normal: 22 – 26mmol/L)
• Respiratory imbalance: PCO2 abnormal (Normal: 35 – 45mmHg)

20

v. Regulation of blood glucose
• As liver, kidneys can use amino acid in gluconeogenesis to release new

glucose into blood when needed
vi. Produce hormone: erythropoietin & calcitriol
• Produce calcitriol hormone, active form of vit D in regulating calcium

homeostasis (absorb calcium from gut) – PCT cells
• Produce erythropoietin hormone to stimulate erythropoiesis – peritubular

cells

21

4. PHYSIOLOGY OF URINE
FORMATION

• Kidney converts blood plasma to urine in 4 stages:
i. Glomerular Filtration
ii. Tubular reabsorption
iii. Tubular Secretion
iv. Water Conservation

• Fluid in capsular space, like blood plasma except has almost NO protein -

glomerular filtrate

• Fluid from PCT through DCT, differs from glomerular filtrate as substances

removed & added by tubule cells - tubular fluid

• Once fluid enters collecting duct, undergoes little alteration: change in water

content - urine

22

23

i. GLOMERULAR FILTRATION
• Process in which water & some solutes in blood plasma pass from

glomerulus capillaries into Bowman’s capsular space
• Filtrate pass through 3 barriers of filtration membrane
• Filtration pressure involved:
❖ Blood hydrostatic pressure (BHP) – about 60mmHg ( pressure) results

from glomerulus large inlet versus small outlet & arteriole capillary
(compared with 10 - 15mmHg in other capillaries)
❖ Capsular space hydrostatic pressure (CHP) – about 18mmHg results from 
filtration rate & continual fluid accumulation (compared with negative
interstitial pressure elsewhere)
❖ Colloid osmotic pressure (COP) – osmosis pressure of blood (protein
plasma) about 32mmHg, same elsewhere

• A high outward pressure of 60mmHg opposed by 2 inward pressures of 18
and 32mmHg gives a Net Filtration Pressure (NFP):

60 out –18 in –32 in = 10 out mmHg

• Glomerular filtration rate (GFR) - amount of filtrate formed per minute by 2
kidneys combined

• Filtration coefficient (Kf) - every 1mmHg of NFP, kidneys produce about
12.5ml filtrate/min (male adults) & 10.5ml/min (10% lower in female adults)

GFR = NFP x Kf
= 10 x 12.5 or 10.5 ml/min

• These rates equivalent to 150 L/day (female) – 180 L/day (males), 60 times
of blood amount in body

• From these, only 1% (1-2 L) eliminated as urine / day, 99% reabsorbed

24

• GFR regulation – if GFR too  → tubular reabsorption , GFR too  →
tubular reabsorption 

• Only way to adjust GFR is to change glomerular BP by 3 homeostatic
mechanism:

i. Renal autoregulation

• Ability of nephrons to adjust own (auto) blood flow & GFR to ensure stable

fluid & electrolyte balance

• Myogenic (more effective) + tubuloglomerular feedback mechanism

❖ Myogenic: BP  → renal perfusion  → GFR  → AA wall stretched →
AA vasoconstriction → GFR  back

❖ Tubuloglomerular feedback by juxtaglomerular apparatus: macula densa,
mesangial cells & granular / juxtaglomerular cells → GFR  back

25

Juxtaglomerular Apparatus

26

Characteristics of Juxtaglomerular Apparatus

27

ii. Sympathetic control
• Sympathetic nerve fibres richly innervate renal blood vessels
• In strenuous exercise or acute conditions e.g. circulatory shock - sympathetic

stimulation → adrenal medulla secretes epinephrine hormone → constrict
AA → GFR + urine output  (only a few ml/min) to redirect blood to heart,
brain & skeletal muscle
iv. Hormonal control
• Renin-angiotensin-aldosterone (RAS) mechanism
• Drop in BP detected by baroreceptor in aorta and carotid arteries → signal
sent to brainstem → sympathetic stimulation → granular cells secrete
enzyme renin → BP  + sufficient GFR
• In RAS, renin acts on angiotensinogen (protein plasma) convert to
angiotensin I (inactive protein hormone). In lungs & kidneys, angiotensin
converting enzyme (ACE) convert angiotensin I → angiotensin II (active
hormone)
• Angiotensin II actions in RAS:
i. Systemic vasoconstriction → ↑ arterial BP
ii. Constrict efferent > afferent arterioles → ensure sufficient GFR to continue
filtration of wastes from blood even BP falling + ↓ peritubular capillaries
pressure → ↑ Na + water absorption into nephron instead of lost in urine
iii. Stimulates adrenal cortex secretes aldosterone hormone → ↑ Na + water
absorption into nephron + collecting duct
iv. Stimulates posterior pituitary gland secretes antidiuretic hormone → ↑ Na
+ water absorption into collecting duct
v. Stimulates hypothalamus → sense of thirst → ↑ water intake

• Atrial Natriuretic Peptide (ANP) – hormone released by atrium →
relaxation of mesangial cells → ↑glomerular surface area → ↑ GFR

28

ii. TUBULAR REABSORPTION
• Process of returning water + solutes from tubular via transcellular +

paracellular route back to blood via peritubular capillaries osmosis +
diffusion
• Upon glomerular filtration,  COP  BHP in peritubular capillaries & 
hydrostatic pressure in tubular fluid cause peritubular capillaries
reabsorption
• Efferent Arteriol constriction via RAS activation when  BP help 
peritubular capillaries BP / resistance →  reabsorption
❖ PCT reabsorb most: 65% filtrate
❖ NL reabsorb another 25% filtrate
❖ DCT + CD reabsorb variable amount of water and salts

29

iii. TUBULAR SECRETION
• Process in which renal tubule extracts water and solutes from blood

capillary & secretes them into tubular fluid
• In PCT + NL it serves 3 purposes: secrete H⁺ + HCO3¯ for acid-base balance;

extract wastes (urea, uric acid, ammonia, bile acid, creatinine) from blood;
clear drugs (analgesic, antibiotic) & contaminants from blood
• DCT + CD secrete variable amount of water and salts

30

iii. WATER CONSERVATION
• NL primary function: generate osmotic gradient to concentrate urine and

conserve water in blood
• Urine in thick segment of NL ascending limb, DCT + cortical segment of CD is

hypotonic compared to peritubular capillary
• By the time urine reaches medullary segment of CD, it becomes hypertonic

(more permeable to water than solute)
• Urine concentration depends on hydration status where hormones act

accordingly
• E.g. Drinking  water produces hypotonic urine (water diuresis);

dehydration stimulates ADH to  water reabsorption but in extreme cases
 BP causes  GFR +  water reabsorption →  urine produced

31

32

5. URINE COMPOSITION &
CHARACTERISTIC

33

Abnormal • Albumin

urine • Glucose

composition • Rbc

• Wbc

• Ketone body (fatty acid breakdown in ATP

synthesis)

• Bile pigment: ↑bilirubin, urobilinogen

• Cast (hardened cells e.G. RBC, WBC, tubular

epithelium)

34

EXPRESS REVISION

1. Describe the 3 renal protective layers.
2. Describe the structure of a nephron.
3. Describe the structure and function of juxtaglomerular apparatus.
4. Explain the physiology of renal.
5. Describe the physiology of urine formation.
6. Describe the flow of urine using a flow chart.
7. State the characteristic of normal urine.
8. Complete the following table on hormones affecting renal function

35

EXPRESS REVISION

9. Calculate the Glomerular Filtration Rate (GFR) for Puan A given her Net Filtration
Pressure (NFP): 10mmHg and Filtration Coefficient (Kf): 10.5ml/min.

10. Label the following diagram.

36