The document provides an overview of the excretory system. It discusses the anatomy and functions of the kidneys, including their role in regulating blood composition, volume, and pressure. The kidneys filter blood to form urine, which passes through the ureters into the bladder and then exits the body through the urethra. The functional unit of the kidneys is the nephron, which filters blood in the glomerulus and reabsorbs or secretes substances along the renal tubule. The kidneys play an important role in homeostasis.

1. THE EXCRETORY
SYSTEM
By:
Mrs.Keerthi.K
Asst.Professor
Vijay Marie CON

2. INTRODUCTION
• The urinary system consists of 2 kidneys, 2 ureters one urinary
bladder and one urethra.
• Once the kidneys filter the blood plasma, they return most of the
water and solutes to the blood stream. The remaining water and
solutes constitute URINE which passes through ureters and is
stored in bladder until it is excreted from body through urethra.
• NEPHROLOGY: scientific study of anatomy , physiology and
pathology of kidneys.
• UROLOGY: branch of medicine that deals with male and female
urinary

3. FUNCTIONS OF KIDNEYS
Regulation of blood ionic composition
Regulation of blood PH
Regulation of blood volume
Regulation of BP
Maintenance of blood osmolarity
Production of hormones
Regulation of blood glucose levels
Excretion of wastes and foreign substances

4. 1.BLOOD IONIC COMPOSITION
• Regulates the levels of several
ions , mostly Na+,ca+2,cl-,Hpo4-
3.REGULATION OF BLOOD VOLUME:
• Kidneys adjust blood volume by
conserving or eliminating water in
urine.
• Increase in blood volume increases
blood pressure and decrease in blood
volume decreases blood pressure.
FUNCTIONS OF KIDNEYS
2.REGULATION OF BLOOD PH:
• They excrete a variable amount of
H+into the urine and conserve Hco3-
which is an important buffer of H+
ion balance.
• Both these activities helps to regulate
PH

5. 4. REGULATION OF BP:
• They secrete renin a hormone which
activates Renin-Angiotensin-
Aldosterone pathway.
• Increased renin causes increased BP
6.PRODUCTION OF HORMONES:
1.CALCITRIOL: active form of vitamin
D that regulates calcium homeostasis.
2. ERYTHROPOIETIN: helps in
production of RBC’s.
FUNCTIONS OF KIDNEYS
5.MAINTAIN BLOOD OSMOLARITY
• By separately regulating loss of
water and loss of solutes in urine.
Kidneys maintain blood osmolarity
to 300 mosm/lit.

6. 7. REGULATION OF BLOOD GLUCOSE
LEVELS:
• Like liver , kidneys can use amino acid
glutamine in gluconeogenesis which
releases glucose into blood to maintain
normal blood glucose levels.
8. EXCRETION OF WASTES AND FOREIGN
SUBSTANCES:
• By forming urine kidneys help excrete wastes. Some
wastes are formed from metabolic reactions in body-
NH4 and urea( from deamination of aminoacids).
• BILIRUBIN: from catabolism of hemoglobin.
• CREATININE: breakdown of creatinine phosphate
in muscle fibers.
• URIC ACID: catabolism of nucleic acids.
• OTHER WASTES: metabolism of diet , drugs and
environmental toxins
FUNCTIONS OF KIDNEYS

7. • GROSS APPEARANCE: paired, reddish and bean shaped.
• LOCATION: located just above the waist between peritoneum
and posterior wall of abdomen.
• Because their position is posterior to peritoneum of abdominal
cavity – hence they are called RETROPERITONEAL ORGANS.
• Located between levels of last thoracic and 3rd lumbar
vertebrae protected by 11th and 12th pair of ribs.
• Right kidney is slightly lower than the left because of the
presence of liver
ANATOMY OF KIDNEYS

8. • LENGTH : 10-12cms
• WIDTH : 5-7cms
• THICKNESS: 3cms and size of bar soap
• WEIGHT: 135-150grams
• THE CONCAVE BOARDER: faces the vertebral column. Near
the center of the concave boarder there is an indentation
called HILUM/RENAL HILUS through which ureter emerges
along with blood vessels, lymphatic vessels and nerves.
ANATOMY OF KIDNEYS-EXTERNAL

9. • Inner layer.
• Smooth
transparent sheet
of dense irregular
connective tissue.
• Barrier against
trauma and helps
to maintain shape
of the kidney.
RENAL
CAPSULE
• Middle layer.
• Mass of fatty
tissue
surrounding the
renal capsule.
• Protects from
trauma and
holds kidney in
place within
abdominal cavity
ADIPOSE
CAPSULE
• Superficial layer
• Thin layer of
dense irregular
connective tissue
that anchors
kidney to
surrounding
structures
RENAL
FASCIA
ANATOMY OF KIDNEYS-EXTERNAL

10. • A frontal section through kidney reveals 2 distinct
regions:
 RENAL CORTEX- superficial light red area
 RENAL MEDULLA – darker reddish brown inner
region
• The renal medulla consists of several cone shaped
structures- RENAL PYRAMIDS.
 BASE of renal pyramids – faces renal cortex
 APEX – is called RENAL PAPILLA –points towards
renal hilum.
INTERNAL ANATOMY OF KIDNEYS

11. • RENAL CORTEX: smooth textured area extending
from renal capsule to bases of renal pyramids and
into the spaces between them.
• It is divided into 2 zones:
 OUTER CORTICAL ZONE
 INNER MEDULLARY ZONE
• Portions of renal cortex that extends between renal
pyramids is called RENAL COLUMNS.
INTERNAL ANATOMY OF KIDNEYS

12. • RENAL LOBE: Renal Pyramid+ overlying area of renal cortex+ half
of each adjacent renal column.
• Together ,the renal cortex and renal pyramids of renal medulla-
RENAL PARENCHYMA or the functional portion of kidney.
• Within the parenchyma , millions of functional units of kidneys
called NEPHRONS are present.
• Filtrate formed from nephrons drains into large papillary ducts and
then into large cup shaped structures called minor and major
calyces.
INTERNAL ANATOMY OF KIDNEYS

13. • Each kidney has 8-18 minor calyces and 2-3
major calyces.
• Minor calyx receives urine from papillary duct of
one real papilla and delivers it to a major calyx.
• Once the filtrate enters calyces it becomes urine
as further reabsorption doesnot occur
INTERNAL ANATOMY OF KIDNEYS

14. • Kidneys are abundantly supplied with blood vessels
• In adults renal blood flow is 1200ml/min
• Within the kidney the renal artery divides into several SEGMENTAL
ARTERIES.
• Each segmental artery gives off several branches that enter расенсута b/w
renal pyramids and pass through renal columns as INTERLOBAR
ARTERIES.
• At the base of renal pyramid. the interlobar arteries arch between renal
medulla & content= hence called as ARCUATE –ARTERIES
• Division of arcuate arteries produce a series of INTERLOBULAR
ARTERIES - They pass between lobules into Afferent arterioles.
BLOOD SUPPLY TO KIDNEYS

15. Each nephron receives one afferent arteriole which
divides into a tangled ,ball shaped capillary network
called GLOMERULUS.
The glomerular capillaries reunite to form efferent
arteriole that carries blood out of glomerulus.
The efferent .A divides to form Peritubular capillaries
BLOOD SUPPLY TO KIDNEYS

16. Peritubular venules
Interlobular veins
Arcuate veins
Interlobar veins
Segmental veins
BLOOD SUPPLY TO KIDNEYS

17. • Nephrons are the functional units of kidneys .
• Each nephron has 2 parts:
 RENAL CAPSULE-where blood plasma is filtered
 RENAL TUBULE- into which filtered fluid passes
1.RENAL CAPSULE: there are 2 components
GLOMERULUS- capillary network
GLOMERULAR CAPSULE- double walled epithelial cup that surrounds
capillaries
• Blood plasma is filtered in the glomerular capsule and the filtered fluid passes
into renal tubule
THE NEPHRON

18. 2.RENAL TUBULE: there are 2 main sections
Proximal convoluted tubule (PCT)
Loop of Henle (LOH)
Distal Convulued tubule (DCT)
• PCT denotes a part of tubule attached to
Glomerular capsule .
• Distal denotes the part that is farther away .
• Convoluted means tubule is tightly coiled
THE NEPHRON

19. • Renal corpuscle and both CT’s lie within the renal cortex, whereas LOH
extends into renal medulla , make a hairpin turn and returns to renal
cortex.
• The DCT of several nephrons empty into a single collecting duct.
• Collecting ducts unite and converge into several hundreds papillary ducts
that drain into minor calyces.
• In a nephron the LOH connects PCT and DCT. The first part of LOH dips
into the renal medulla, where it is called descending limb of LOH.
• It makes a hairpin turn and returns to renal cortex as the ascending limb of
LOH.
THE NEPHRON

20. CORTICAL NEPHRONS
• About 80-85%.
• Their renal corpuscles lie in outer
portion of renal cortex.
• They have short LOH that lie in
cortex and penetrate only into the
outer region of renal medulla.
JUXTRA-MEDULLARY NEPHRONS
• The other 15-20%.
• Their renal corpuscles lie deep in
the cortex, close to medulla.
• They have long LOH that extends
into the deepest region of
medulla.
• These nephrons have 2 additional
portions:
 Thin ascending LOH
 Thick ascending LOH
THE NEPHRON-TYPES

21. VISCERAL LAYER:
• modified SSE cells called
PODOCYTES.
• The many foot like projections of
these cells wrap around a single
layer of endothelial cells of
glomerular capillaries and form
inner wall of capsule.
PARIETAL LAYER:
• Consists of SSE and forms outer wall
of capsule.
• Fluid filtered from glomerular
capillaries enters capsular space (the
space between 2 layers of glomerular
capsule)
THE NEPHRON
A single layer of epithelial cells forms the entire wall of the glomerular capsule , renal tubule
and ducts.
However each part has distinctive histological features and reflect its articular functions:
1.GLOMERULAR CAPSULE: 2 layers

22. • IN PCT: Simple cuboidal cells with prominent brush boarder
of microvilli on their apical surface.
• These microvilli increase surface area of reabsorption and
secretion.
• Descending limb of LOH and 1st part of thin AL of LOH –
simple squamous epithelium.
• Thick ascending limb of LOH- simple cuboidal to low
columnar epithelium.
RENAL TUBULE AND COLLECTING DUCT

23. • In the renal corpuscle –the columnar tubule cells are crowded and are
called as MACULA DENSA.
• The site where the A/L touches the afferent arteriole – specialized cells
(cuboidal cells are crowded ) called macula densa. Only in macula densa
area the aff.arteriole has JG cells.
• Along side of macula densa the wall of afferent arteriole contains
modified smooth muscle fibers called JUXTRA GLOMERULAR CELLS.
• Together with macula densa + JG cells= JG apparatus- very sensitive to
Na+and Cl- reabsorption
RENAL TUBULE AND COLLECTING DUCT

24. • There are two types of cells:
1. PRINCIPAL CELLS:
receptors for ADH and
aldosterone
2. INTERCALATED CELLS:
homeostasis of blood PH
DCT

25. • Each of 2 ureters transports urine from renal pelvis to the bladder.
• Peristalisis contractions of the muscular walls of the ureters push urine
towards the bladder, but the hydrostatic pressure and gravity also
contribute .
• Frequency of peristalitic waves – 5/min.
• LENGTH- 25-30cms
• DIAMETER- 1mm-10mm
• RETROPERITONEAL
URETERS

26. • There is no anatomical valve at the opening of each
ureter , into bladder , a physiological one is quiet
effective.
• As the bladder fills , pressure with in compresses the
oblique openings into ureters and prevents backflow of
urine.
• If the physiological valve is not functioning then the
microbes travel upto the ureter from bladder to infect
both kidneys.
URETERS

27. MUCOSA WITH
UNDERLYING
LAMINA PROPRIA
MUSCULARIS ADVENTITIA
• Deepest , lined with
transitional
epithelium and
goblet cells.
• Lamina propria is
the areolar
connective tissue
with collagen,
elastic fibers and
lymphatic tissue
• Middle layer
• INNER-
Longitudinal
• OUTER- circular
helps in peristalsis.
• Transitional
epithelium is able
to stretch- stretches
to accommodate
urine.
• Mucous secreted by
goblet cells
prevents cells of
mucosa to come in
contact with urine.
• Superficial layer-
areolar connective
tissue with blood
vessels, lymphatic
vessels and nerves
that serves
muscularis and
mucosa.
URETERS-LAYERS

28. • It is hollow , distensible muscular organ situated in pelvic cavity
posterior to the pubic symphysis.
• In males, it is anterior to rectum, in females it is anterior to
vagina and inferior to uterus .
• Folds of peritoneum holds bladder in position.
• SHAPE: spherical –when slightly distended due to accumulation
of urine.
• When it is empty , it collapses . As urine volume increases it
becomes pear shaped and rises into the abdominal cavity.
URINARY BLADDER

29. • Capacity-700-800ml
• It is smaller in females because the
uterus occupies the space just as
superior to urinary bladder.
URINARY BLADDER

30. • In the floor of bladder there is small
triangular area called the ‘TRIGONE’
• Posterior corners of trigone- has 2 ureteral
opening and 1 urethral opening called
internal urethral orifice.
• 3 coats makeup the wall of urinary
bladder.
URINARY BLADDER-ANATOMY&HISTOLOGY

31. 1.MUCOSA: deepest made of transitional epithelium +
underlying lamina propria similar to that of ureters.
• RUGAE- are also present to permit the expansion of bladder.
• Surrounding mucosa there is intermediate MUSCULARIS or
DETRUSOR MUSCLE- 3 layers of smooth muscles.
 Inner longitudinal muscle
 Middle circular muscles
 Outer longitudinal muscles
URINARY BLADDER-ANATOMY&HISTOLOGY

32. • Around the opening to the urethra the circular
fibers form an IU sphincter inferior to it there is
external urethral sphincter composed of skeletal
muscle.
3.ADVENTITIA: most superficial layer
• Areolar connective tissue
• Over superior surface of urinary bladder is SEROSA layer of
visceral peritoneum.
URINARY BLADDER-ANATOMY&HISTOLOGY

33. • A tubular structure emerging from the neck of
the bladder and opens to the exterior.
• It is the outlet of the bladder and eliminates
urine to outside.
• Present in both males and females but there
are some differences between the two.
URETHRA

34. MALE URETHRA FEMALE URETHRA
Long Short
Length = 18-20cms Length =4cms
Function: urination
and ejaculation of
semen
Only urination
Course – curved
(double)
Nearly straight –foleys
catheterization is easy.
DIFFERENCES BETWEEN MALE AND FEMALE URETHRA

35. MALE URETHRA FEMALE URETHRA
Long Short
Length = 18-20cms Length =4cms
Function: urination
and ejaculation of
semen
Only urination
Course – curved
(double)
Nearly straight –foleys
catheterization is easy.
PARTS OF URETHRA