physiology of the kidney

1. Physiology of Kidney
Deblina Roy
M.Sc Nursing 1st Year
King George’s Medical University
M.Sc. Nursing 1st year

2. Introduction
 Filtration
 Osmosis
 toxins and metabolites
 Wastes.

3. Longitudinal Section of the Kidney

4. Functional Anatomy
 Bean shaped
 Hilus( the renal artery and renal
nerves enter through this and the
renal vein exits from here, lymphatic
and the ureter leaves through this
region)
 layers (outer cortex and inner
medulla)

5. renal cortex
 Red in colour
 Highly vascular
 Granular
 Contains and bowman’s
capsule
 And tortuous convoluted
tubules.

6. Medulla
 Pink in colour
 Less vascular
 Striated appearance
 Contains the largely straight running
portions of the nephrons.

7. Nephron

8.  Structural and functional unit of the
kidneys
 Each kidney has 1 million nephrons
 They never divide during the lifetime.
 Each nephron is about 5 cm long
 The total length of the nephrons is
about 100 kms

9. Glomerulus and the Bowman’s
Capsule

10. Filtration surface
 It is composed of the loops of the capillaries.
 Arises from the afferent arteriole of each
nephron.
 Glomerular capsule is the bowman’s capsule.
 Glomerulus and the Bowman’s capsule are
together called the malpighian body.
 The endothelial wall shows some
fenestrations of 40-100nm in dia.
 This surface prevents the large molecules to
escape into the filtrate.
 This fluid after reabsorption and secretion
becomes urine.

11. Urinary tubule

12. Urinary tubule
 Urinary tubules are divided into
number of segments
 Basis of type of epithelium that lines
the lumen.
 Basement membrane is same except
in the macula densa .

13. Proximal convoluted tubules
 This is the first portion of the tubule
 It is lined by the cells which look like
truncated pyramids
 Basically it has a large no of microvilli
which increase the surface area and
reabsorb a lot of filtrate by active
transport carried out by a large
number Mitochondria.
 Absorbs 2/3 of the glomerular filtrate.

14. The loop of Henle
 The proximal convoluted narrows
abruptly to continue as the loop of
Henle .
 The majority of the nephrons originate
in the cortex the loops of Henle are
short .
 For the nephrons that originate in the
junction of cortex and medulla have
long loops of henle.

15. Distal convoluted tubules
 Not very high metabolic activity.
 Reabsorbs less than 15%of the filtrate.
 Poor permiability
 Reabsorbs against high electrochemical
gradients
 Important part in final composition of the
urine
 Small part of the distal tubule id near the
afferent areteriole is called the macula
densa.

16. Collecting ducts
 The proximal part of the collecting
tubules are very similar to the distal
part of the distal tubule
 And the cells become columnar and
less mitochondria are present.
 And this part shows less hormone
mediated reabsorption of the filtrate.

17. Renal Circulation

18. Functions of the kidney
 The mnemonic A WET BED aids in
memory of kidneys functions.
 A – maintaining ACID-base balance
 W – maintaining WATER balance
 E – ELECTROLYTE balance
 T – TOXIN removal
 B – BLOOD Pressure control
 E – making ERYTHROPOIETIN
 D – Vitamin D metabolism.

19. Non excretory function
 Secretion of hormones
 Secretion of erythropoietin, which
regulates red blood cell production in
the bone marrow.
 Secretion of renin, which is a key part
of the renin–angiotensin–aldosterone
system.
 Secretion of the active form of vitamin
D (calcitriol) and prostaglandins.

20.  Gluconeogenesis
 The kidney in humans is capable of
producing glucose from lactate, glycerol and
glutamine.
 The kidney is responsible for about half of the
total gluconeogenesis in fasting humans. The
regulation of glucose production in the kidney
is achieved by action
of insulin, catecholamines and other
hormones.
 Renal gluconeogenesis takes place in
therenal cortex.
 The renal medulla is incapable of producing
glucose due to absence of
necessary enzymes

21. Homeostasis
 The major homeostatic control point for
maintaining this stable balance is renal
excretion.
 Action of aldosterone,antidiuretic
hormone (ADH, or vasopressin), atrial
natriuretic peptide (ANP), and other
hormones.
 Abnormal ranges of the fractional
excretion of sodium can imply acute
tubular
necrosis or glomerular dysfunction.

22.  The kidney's ability to perform many of
its functions depends on the three
fundamental functions
of filtration, reabsorption,
and secretion, whose sum is renal
excretion. That is:
 Urinary excretion rate = Filtration rate
– Reabsorption rate + Secretion rate

23. Urine formation

24. Filtration
 The blood is filtered by nephrons,
 of ultrafiltration, leaving an ultrafiltrate
that resembles plasma (except that
the ultrafiltrate has negligible plasma
proteins) to enter Bowman's space.
Filtration is driven by Starling forces.
 The ultrafiltrate is passed through, in
turn, the proximal convoluted tubule,
the loop of Henle, the distal
convoluted tubule, and a series
of collecting ducts to form urine.

25. Reabsorption
 Tubular reabsorption is the process by which
solutes and water are removed from the tubular
fluid and transported into the blood. It is
called reabsorption (and not absorption) because
these substances have already been absorbed
once (particularly in the intestines).
 Reabsorption is a two-step process beginning
with the active or passive extraction of
substances from the tubule fluid into therenal
interstitium (the connective tissue that surrounds
the nephrons), and then the transport of these
substances from the interstitium into the
bloodstream. These transport processes are
driven by Starling forces, diffusion, and active
transport.

26. Indirect reabsorption
 bicarbonate (HCO3
−) does not have a
transporter,
 begins with the active secretion of a hydrogen
ion (H+) into the tubule fluid via a Na/H
exchanger:
 In the lumen
◦ The H+ combines with HCO3
− to form carbonic acid
(H2CO3)
◦ Luminal carbonic anhydrase enzymatically converts
H2CO3 into H2O and CO2
◦ CO2 freely diffuses into the cell
 In the epithelial cell
◦ Cytoplasmic carbonic anhydrase converts the
CO2 and H2O (which is abundant in the cell) into
H2CO3
◦ H2CO3 readily dissociates into H+ and HCO3
−
−

27. Hormones
 Some key regulatory hormones for
reabsorption include:
 aldosterone, which stimulates active
sodium reabsorption (and water as a
result)
 antidiuretic hormone, which stimulates
passive water reabsorption
 Both hormones exert their effects
principally on the collecting ducts

28. Secretion
 Tubular secretion is the transfer of
materials from peritubular
capillaries to renal tubular lumen.
Tubular secretion is caused mainly
by active transport.
 Usually only a few substances are
secreted. These substances are
present in great excess, or are natural
poisons.
 Many drugs are eliminated by tubular

29. Summary

31. Assignment
 What stops the proteins from escaping
into the glomerular filtrate ?
 Why is the urine acidic ?
 How does the kidney maintain the
electrolyte balance ?