anatomy and physiology of urinary system

1. URINARY SYSTEM
BY
SONI KUMARI SHAH

2. Functions Of Urinary System
 Eliminates metabolic waste products from body
 Regulates blood volume and hence blood pressure
 Electrolytes and metabolites balance
 Maintains acid-base balance

3. Organs Of Urinary System
 Kidney
 Ureter
 Urinary bladder
 Urethra

4. Kidney
Reddish Brown, Bean Shaped Retroperitoneal Organ
Weight: 150gm
Location: Posterior Abdominal Wall, T12 To L3
Right Kidney Is Slightly Lower Than Left.
Two Borders: Lateral And Medial
Two Surfaces: Anterior And Posterior
Two Poles: Upper And Lower
Covering: Fibrous Capsule(Renal Capsule)
Blood Supply: Renal Artery & Renal Vein

5. Organs Associated With The Kidneys
As the kidneys lie on either side of the vertebral column, each is
associated with different structures.
Right kidney
Superiorly – the right adrenal gland
Anteriorly – the right lobe of the liver, the duodenum and the
hepatic flexure of the colon
Posteriorly – the diaphragm, and muscles of the posterior
abdominal wall.
Left kidney
Superiorly – the left adrenal gland
Anteriorly – the spleen, stomach, pancreas, jejunum and splenic
flexure of the colon
Posteriorly – the diaphragm and muscles of the posterior
abdominal wall.

6. Kidney: Internal Structure
 Renal capsule
 Renal cortex
 Renal medulla
 Renal column
 Renal pyramids
 Renal papilla
 Renal pelvis

7. Kidney: Internal Structure
There are three areas of tissue that can be distinguished when a longitudinal
section of the kidney
 outer fibrous capsule, surrounding the kidney
 the cortex, a reddish-brown layer of tissue immediately below the capsule and
outside the renal pyramids
 the medulla, the innermost layer, consisting of pale conical-shaped striations,
the renal pyramids.
The hilum is the concave medial border of the kidney where the renal blood and
lymph vessels, the ureter and nerves enter.

8. Kidney: Internal Structure
Urine formed within the kidney passes through a renal papilla at the apex of a
pyramid into a minor calyx.
Several minor calyces merge into a major calyx and two or three major calyces
combine forming the renal pelvis, a funnel shaped structure that narrows
when it leaves the kidney as the ureter.
The walls of the calyces and renal pelvis are lined with transitional epithelium
and contain smooth muscle.
Peristalsis, intrinsic contraction of smooth muscle, propels urine through the
calyces, renal pelvis and ureters to the bladder.

9. Nephron
Structural and functional unit of kidney
Two Parts:
Renal Corpuscle-
Bowman’s Capsule
Glomerulus
Renal Tubule-
Proximal Convoluted Tubule(PCT)
Loop Of Henle (LH)
Distal Convoluted Tubule(DCT)
Collecting Duct

10. Structure of Nephron
Each nephron consists of two parts: renal corpuscle for filtration and renal
tubule for selective reabsorption of filtrate until urine is formed.
Renal Corpuscle
Renal corpuscle is also known as malpighian corpuscle. It is spheroid and
slightly flattened structure situated in the cortex of the kidney. The diameter of
the corpuscle is about 200µ. The renal corpuscle is formed by two portions.
Glomerulus
Bowman’s Capsule

11. Glomerulus
The glomerulus consists of many capillaries called glomerular capillaries. These
capillaries connect afferent arteriole with the efferent arteriole. Thus, the
vascular system in the glomerulus is purely arterial.
The capillaries of glomerulus arises from the afferent arteriole. Afferent
arteriole, after entering the glomerulus divides into 4 or 5 large capillaries.
Each large capillaries subdivides into many small capillaries. The small
capillaries are arranged in irregular loops and form anastomosis. All the smaller
capillaries finally reunite to form efferent arteriole.

12. Bowman’s Capsule
Bowman’s capsule encloses the glomerulus and it is formed by two layers,
both layers are composed of flattened epithelial cells.
The diameter is about 200µ. Its cavity has a network of blood capillaries
forming glomerulus.
An afferent arteriole from a branch of renal artery enters into the Bowman’s
capsule and exits as efferent renal arteriole. Afferent arteriole has wider
lumen than efferent arteriole.

13. Renal Tubule
The renal tubule is a duct that leads away from the glomerular capsule and
ends at the tip of a medullary pyramid. It is about 3cm long and divided into
four major regions.
Proximal Convoluted Tubule(PCT)
It is the coiled portion arising from Bowman’s capsule. This occupies the cortex
near glomerulus. The PCT is formed by single layer of cuboidal epithelial cells.
Its length is about 14mm and diameter is 55µ.

14. Loop of Henle
It dips down from cortex to medulla forming descending limb, then it bend
and forms ascending limb which runs from medulla to cortex.
Descending limb: it is the direct continuation of PCT. Its length is 6mm and
diameter 55µ.
Ascending limb: this segment of the loop is continued from descending loop
of Henle. This segment ascends to cortex and forms DCT.

15. Distal Convoluted Tubule(DCT)
It is the continuation of ascending loop of Henle and occupies the cortex of
kidney. It opens into collecting duct. The DCT is composed of cuboidal
epithelial cell with length about 14.5-15 mm and diameter 22-55µ.
Collecting Duct
It is composed of cuboidal or columnar epithelial cells. The length is about
20-22mm and diameter varies between 40-200µ. The DCT opens into
collecting duct.

16. Functions Of Different Parts Of Nephron
Renal Corpuscle: Generates Glomerular Filtrate Composed Of Water, Ions And Small Molecule
Bowman’s Capsule: Filtration Of Blood Forming First Step Of Urine Formation
Renal Tubule
PCT: About 70% Of Glomerular Filtrate Is Reabsorbed In PCT
ReabsorbsSodium,Chloride,Potassium,Water,Glucose,AminoAcids,Bicarbonate,CalciumAndPhosphate
Secretes Ammonium And Creatinine
LH: Descending Limb - Passive Transport Of Water
Ascending Limb - Reabsorbs Sodium And Chloride
Secretes Urea
DCT: Reabsorbs Sodium And Chloride
Collecting Duct: Reabsorbs Sodium, Chloride And Water
Secrets Ammonium, Hydrogen Ions And Potassium

17. Juxtaglomerular Apparatus
Specialized structure between glomerulus and renal arteries
Components:
Juxtaglomerular Cells
Extra Glomerular Mesangial Cells
Macula Densa

18. Components Of Juxtaglomerular Apparatus
Juxtaglomerular Cells
It is specialized smooth muscle cells situated in the wall of afferent arteriole
just before it enters the Bowman’s capsule.
It is also known as granular cell because the presence of secretary granule in
their cytoplasm.
Juxtaglomerular cells form a thick cuff known as polar cushion or polkissen
around the afferent arteriole before it enters the Bowman’s capsule.

19. Components Of Juxtaglomerular Apparatus
Extraglomerular Mesangial Cells
It is situated in the triangular region bound by afferent arteriole, efferent
arteriole and macula densa. These cells are known as agranular cells or lacis
cells.
Macula Densa
It is situated between afferent arteriole and efferent arteriole and opens
into DCT. It is formed by tightly packed cuboidal epithelial cells.
Juxtaglomerular apparatus secretes two hormones: renin and
prostaglandins.

20. Renal Circulation

21. Functions Of Kidney
 Regulation of blood volume
 Production of blood- by secreting erythropoietin
 Blood pressure regulation
 Blood pH regulation
 Regulation of osmotic pressure of blood
 Regulation of Ion composition of blood
 Vitamin D synthesis
 Excretion of unnecessary substances

22. Ureter
 Muscular tube from kidney to urinary bladder
 25cm long
Three constriction:
at pelviureteric junction
at pelvic brim
where it enters urinary bladder

23. Structure Of Ureter
The walls of the ureters consist of three layers of tissue :
 an outer covering of fibrous tissue, continuous with the fibrous capsule of
the kidney
 a middle muscular layer consisting of interlacing smooth muscle fibres that
form a functional unit round the ureter and an additional outer
longitudinal layer in the lower third
 an inner layer, the mucosa, composed of transitional epithelium

24. Functions Of Ureter
Propel urine from kidney to the urinary bladder by peristaltic
contraction
Ureter is a Common site of renal colic

25. Kidneys are abdominal organ lying
I. On the posterior abdominal wall
II. On each side of vertebral column
III. Behind the peritoneum
IV. All of the above
All are major functions of kidney except
I. Regulation of water content of body
II. Elimination of waste products from the body
III. Destruction of toxic substance in the body
IV. Regulation of body acidity alkalinity
The function of kidney are
I. WBCs production
II. Water and electrolyte balance
III. Metabolism of protein
IV. All of the above

26. Urinary Bladder
Pear shaped hollow muscular organ
Location: pelvic cavity
Capacity: 500-600ml
Interior of urinary bladder is folded into rugae when empty.
It has 3 orifices.
Trigone of bladder:
The base of the bladder contains three openings that form a triangular area
called the trigone. Two of the openings connect the bladder to the ureters,
while the third connects the bladder to the urethra

27. Gross Structure Of Urinary Bladder
Apex
Neck
3 surfaces:
2 inferolateral surfaces(right & left)
superior surface
Base or Fundus

28. Microscopic Structure
Four layers:
 Serosa
 Muscular layer
 Submucosa
 Mucosa

29. Organs Associated With Urinary Bladder- in Female

30. Organs Associated With Urinary Bladder- in Male

31. Capacity Of Urinary Bladder
Sense of filling: begins at 100-150 ml
first desire of micturition: 150-250 ml
Physiological capacity: 250-450 ml; in new born: 20-50 ml
Painful sensation: above 450 ml
beyond voluntary control: about 800ml
Anatomical capacity: about 1000ml

32. Functions Of Urinary Bladder:
Collects and temporarily stores the urine
Helps in expulsion of urine by contraction of detrusor muscle.

33. Urethra
Canal extending from neck of bladder to exterior
Length differs in male and female
Male: 18-20 cm
Female: 4cm

34. Parts Of Male Urethra:
I. Penile urethra: about 15-16 cm long and passes though the penis to
external urethral orifice.
II. Membranous urethra: short (1-2cm) thin walled portion where urethra
passes through the muscular floor of pelvic cavity.
III. Prostatic urethra: begins at the urinary bladder and passes about 3-4 cm
through the prostate gland.

35. Female Urethra
The external urethral orifice is embedded in the anterior vaginal wall
inferior to the clitoris, superior to the vaginal opening (introitus), and
medial to the labia minora.
Its short length, about 4 cm, is less of a barrier to fecal bacteria than the
longer male urethra and the best explanation for the greater incidence of
UTI in women.

36. Sphincter Of Urethra
Internal urethral sphincter
This sphincter is situated between neck of bladder and upper end of urethra.
It is made up of smooth muscle fibres and formed by thickening of detrusor
muscle. It is innervated by nerve fibres. This sphincter closes the urethra
when bladder is emptied.
External urethral sphincter
External sphincter is located in the urogenital diaphragm. The sphincter is
made up of circular skeletal muscle fibres, which are innervated by somatic
nerves.

37. Functions Of Urethra:
Passage way for passing urine to exterior
Male urethra also passes reproductive fluid.

38. Urine Formation
 Process of blood cleansing
 Urine is formed by filtering the blood at renal corpuscle and
reabsorption of necessary substances in renal tubule.
Mechanism Of Urine Formation
1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion

39. Glomerular Filtration
 Takes place through semi permeable membrane of glomerulus
and glomerular capsule.
 Water and large number of small molecules pass through
 Blood cells, plasma protein and other large molecules are
unable to filter so remain in the capillaries.
 Filtration is assisted by the
differences between blood
pressure in glomerulus and
pressure of filtrate in glomerular
capsule.

40. Because the efferent arteriole is narrower than the afferent arteriole, a
capillary hydrostatic pressure of about (55 mmHg) builds up in the
glomerulus. This pressure is opposed by the osmotic pressure of the blood,
provided mainly by plasma proteins, about (30 mmHg), and by filtrate
hydrostatic pressure of about (15 mmHg) in the glomerular capsule.
The net filtration pressure is, therefore:
Glomerular filtration pressure
= capillary hydrostatic pressure – (osmotic
pressure of blood + filtrate hydrostatic pressure)
GFP= 55 – (30+15) = 10mmHg

41. Glomerular Filtration Rate (GFR)
 Volume of filtrate formed by both kidney in one minute is GFR.
 GFR=125ml/min. i.e. 180 litres
 Most of the filtrate is reabsorbed.
 Less than 1% i.e. 1-1.5 litres is excreted as urine.

42. Tubular Reabsorption/Selective Reabsorption
 Process by which composition and volume of glomerular filtrate is altered during
passage through renal tubule.
 Reabsorb into blood those filtrate constituents needed by the body to maintain
fluid and electrolyte balance and pH balance.
 Reabsorption is achieved by active transport, passive transport, osmosis and
diffusion.
 Some constituents of glomerular filtrate do not appear normally in urine because
they are completely reabsorbed unless they are present in blood in excessive
quantities.
PCT: glucose, amino acid, vitamin, hormone, calcium, and some urea
PCT, LH and DCT: 99% water, Na+, Cl- ions

43. Renal Threshold/ Transport Maximum
 Kidneys maximum capacity for reabsorption of a substance.
 If the level rises above the transport maximum, the substance will appear in
urine.
Hormones Regulating Reabsorption:
 Parathyroid hormone and calcitonin regulates reabsorption of calcium and
phosphate.
 Antidiuretic hormone(ADH) increases permeability of DCT and collecting
tubule, increasing water reabsorption.
 Aldosterone increases reabsorption of sodium and excretion of potassium.
 Atrial natriuretic peptide(ANP) inhibits NaCl reabsorption.

44. Tubular Secretion
 Substances not required and foreign materials eg. Drugs
including penicillin and aspirin may not be cleared from the
blood by filtration because of short time it remains in the
glomerulus.
 Such substances are cleared by secretion into the convoluted
tubules and excreted from the body in urine.
 Tubular secretion of hydrogen ion (H+) is important in
maintaining homeostasis of blood pH.

47. The normal GFR is
i. 50 ml per min.
ii. 125 ml per min.
iii. 250 ml per min.
iv. 500ml per min.
Normal daily urine output of an adult is
i. 500ml
ii. 1000ml
iii. 1500ml
iv. 2500ml
In kidney glucose is mainly absorbed by
i. PCT
ii. Loop of Henle
iii. DCT
iv. Collecting tubule
Volume of urine is primarily controlled by
i. ADH or Vasopressin
ii. Oxytocin
iii. ACTH
iv. Growth Hormone

48. Formation Of Uric Acid
In the liver, purines are metabolized to uric acid.
The last step in purine metabolism involves an
enzyme called xanthine oxidase.

49. Formation Of Urea

50. Urine
Clear amber colored fluid of slight acidic reaction excreted by
kidney.
pH: around 6 (normal range: 4.5-8)
Color: light yellow
Volume excreted: 1-1.5 liters per day
The volume depends on:
i. Amount of water intake
ii. Environmental temperature
iii. Diet
iv. Mental state
Odour: faintly aromatic

51. Composition Of Urine
Water - 96%
Urea - 2%
Uric acid
Creatinine
Ammonia
Sodium
Potassium 2%
Chlorides
Phosphates
Sulphates
Oxalates

53. Colour Of Urine

56. Micturition
 Process of emptying of bladder
 Also called voiding
Structures Involved In Micturition:
1. Urinary bladder (detrusor muscle)
2. Urethra (sphincter muscle)
3. Parasympathetic nerves supplying urinary bladder and urethra

57. Mechanism Of Micturition
In infants, accumulation of urine in the bladder activates stretch receptors
in the bladder wall generating sensory (afferent) impulses that are
transmitted to the spinal cord, where a spinal reflex is initiated. This
stimulates involuntary contraction of the detrusor muscle and relaxation of
the internal urethral sphincter, and expels urine from the bladder – this is
micturition or voiding of urine.
In adult, micturition occurs when detrusor muscle contracts, and there is
reflex relaxation of internal sphincter and voluntary relaxation of external
sphincter.

58. Micturition Reflex
Filling of urinary bladder
Stimulation of stretch receptors
Afferent impulse passes via pelvic nerve
Sacral segments of spinal cord
Efferent impulse via pelvic nerve
Contraction of detrusor muscle and relaxation of internal sphincter
Flow of urine into urethra and stimulation of stretch receptors
Afferent impulses via pelvic nerve
Inhibition of pudendal nerve
Relaxation of external sphincter
Voiding of urine

59. Micturition

60. Stimulation of parasympathetic nervous system
i. Retains urine in bladder
ii. Helps voiding of urine
iii. Neither
iv. Both
Normal specific gravity of urine is
i. 0.980
ii. 1.000
iii. 1.010
iv. 1.020

61. Urinary Changes With Aging
As a person ages, changes in the kidneys and bladder can affect urinary
system function.
Kidneys
After age 40, kidney function may diminish; if the person lives to age 90, it
may decrease by as much as 50%. Age-related changes in kidney vasculature
that disturb glomerular hemodynamics result in a decline in glomerular
filtration rate. Reduced cardiac output and age related atherosclerotic
changes cause kidney blood flow to decrease by 53%. In addition, tubular
reabsorption and renal concentrating ability decline because the size and
number of functioning nephrons decrease. Also, as blood levels of
aldosterone and renin fall, the kidneys are less responsive to antidiuretic
hormone

62. Urinary Changes With Aging
Bladder
As a person ages, bladder muscles weaken. This may lead to incomplete
bladder emptying and chronic urine retention—predisposing the bladder to
infection.
And the rest Other age-related changes that affect renal function include
diminished kidney size, impaired renal clearance of drugs, reduced bladder
size and capacity, and decreased renal ability to respond to variations in
sodium intake. By age 70, blood urea nitrogen levels rise by 21%. Residual
urine, frequency of urination, and nocturia also increase with age