The presentation explains in detail the excretion process in humans, it contains all the processes occurring inside human kidney. It also gives an insight about different types of excretory waste secreted by animals in general. In all, it is a physiological summary of human kidney and excretion
2. INTRODUCTION
The process of separation, collection and elimination of toxic waste products (especially
nitrogenous wastes) from the body
Waste products are formed due to catabolism of amino acids, glucose, glycerol and fatty acids.
Unwanted substances like Drugs, pigments, excessive vitamins, CO2, H2O
Excess of inorganic salts, hormones Bilirubin and biliverdin.
Kidneys play a major role as an excretory organ in all vertebrates. Skin helps in elimination of
urea; inorganic salts and water through sweat glands.
Lungs help in the elimination of CO2 and H2O
10. KIDNEYS
Kidneys are a pair of bean shaped, chocolate brown
structures situated in the dorsal side of the abdominal
cavity behind the peritoneum (retroperitoneal)- one
on either side of the vertebral-column between the
12th thoracic and 3rd lumbar vertebrae.
The right kidney is slightly lower than the left kidney-
11 cms long, 6 cms broad and 3 cms thick-150 grams
in males and 135 grams in females
Blood enters the kidneys through renal arteries and
leaves through renal veins.
Tubes called ureters carry waste products from the
kidneys to the urinary bladder for storage or for
release. During urination, urine is expelled from the
urinary bladder through the urethra
11. PARTS OF KIDNEY
❏ MEDULLA :
It is the inner, pale, striated part. It is made up of
about 4-14, striated conical masses called the renal
pyramids.
Each pyramid has its base directed outwards(towards
the cortex) and its apex inwards (called renal-
papillae)
❏ CORTEX :
It forms the outer (peripheral), reddish-brown,
granular part.
Parts of the cortical tissue invade the medulla and lie
between adjacent pyramid and are called renal-
columns (Bertini’s columns).
12. ❏ HILUM :
A depression located in the middle of the concave
side of the kidney where blood vessels, nerves, and
the ureters enter and exit the kidneys Cortex-Medulla
Hilum.
The cortex is where the blood is filtered.
The medulla contains the collecting ducts which carry
filtrate (filtered substances) to the pelvis.
The pelvis is a hollow cavity where urine accumulates
and drains into the ureter.
13. ❏ RENAL-SINUS :
Internally, the hilum leads to aspace called the
renal-sinus, which is occupied by the upper,
expanded part of the ureter called the renal-pelvis.
The renal-pelvis divides into two or three parts
called major-calyces (single calyx→cup of a
flower). Each major calyx divides into 6-20 minor-
calyces.
Each minor-calyx is shaped like a cup. The papilla
of a medullary pyramid fits into the minor calyx.
Each kidney consists of closely packed microscopic
coiled tubular structures called nephrons. The
nephrons are the structural and functional units of
the kidney.There are about 1.2 million nephrons in
each kidney.
15. NEPHRON
Two parts
1. Renal Corpuscle
a. a. Bowman Capsule
b. Glomerulosa.
i. Fenestrae - pore in endothelial
walls of glomerulus.
ii. Podocytes - specialized cells.
iii. Filtration slits
16. 2. Renal Tubule - Series of single layer
tubules
a. Proximal Convoluted tubule
b. Loop of Henle
c. Distal Convoluted tubule
Kidneys are made up of nephrons. Blood
enters the nephron, where impurities are
filtered out and emptied into the
collecting duct.
The purified blood leaves the nephron
through the renal vein.
17. ❏ GLOMERULUS (BLOOD-SUPPLY) :
It is a rounded tuft of blood capillaries found in the cup of the
Bowman’s capsule.
The renal artery (a branch of the abdominal aorta) enters
through the hilum, divides and re-divides to for many branches.
One branch called the afferent renal arteriole enters the cup
and divides to form the Glomerulus.
The capillaries reunite to form the efferent renal arteriole. It
leaves the glomerulus. The diameter of the efferent arteriole is
lesser than that of the afferent one.
18. ❏ THE PROXIMAL CONVOLUTED TUBULE (P.C.T) :
It is a highly coiled structure,connected to the neck and
lies in the cortex.
It is lined by cuboidal cells, rich in mitochondria, and
having microvilli (brush border to increase surface area)
and thus help in active reabsorption.
19. ❏ THE MIDDLE LOOP OF HENLE :
The renal tubule now descends into the
medulla (thin walled descending
limb),takes a hair- pin turn (the U-shaped
loop) and ascends back towards the cortex
(thick walled ascending-limb).
The ascending limb is not permeable to
water.The Henle’s loop is mainly meant for
concentration of urine.
20. ❏ THE DISTAL CONVOLUTED TUBULE (P.C.T)
The D.C.T leads to a straight, large collecting-tubule.
Nephrons open into the same collecting tubule.
Many collecting tubules join to form a collecting duct
which descends into the medullary pyramids.
The medullary pyramids are a bunch of these
collecting ducts.
About 7-8 collecting ducts draining different
nephrons join to form ducts of Bellini, each of which
opens into a minor calyx at the apex (papilla) of a
medullary pyramid.
23. MECHANISM OF FILTRATION
As blood enters a nephron through the arteriole, impurities are filtered out
and emptied into the collecting duct.– The purified blood exits the nephron
through the venule
The mechanism of blood filtration involves 2 processes
● Filtration
● Reabsorption
24. FILTRATION
Filtration : Passing a liquid or gas through a filter to remove wastes called filtration
The filtration of blood mainly takes place in the glomerulus.
The glomerulus is a small network of capillaries encased in the top of the nephron by
a hollow, cup-shaped structure called Bowman’s capsule.
Fluid from the blood flows into Bowman’s capsule.
The materials filtered from the blood include water, urea, glucose, salts, amino acids,
and some vitamins.
Plasma proteins, cells, and platelets remain in the blood because they are too large
to pass through the capillary walls.
25. REABSORPTION
Most of the material removed from the blood at Bowman’s capsule makes its way
back into the blood.
The process in which liquid is taken back into a vessel is called reabsorption.
Almost 99% of the water that enters Bowman’s capsule is reabsorbed into the
blood.
When the filtrate drains in the collecting ducts, most of the water and nutrients
have been reabsorbed into the blood.
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27. URINE
Remaining material, called urine, is emptied into a collecting duct.
Urine is primarily concentrated in the loop of Henle.
The loop of Henle is a section of the nephron tubule in which water is
conserved and the volume of urine is minimized.
As the kidney works, purified blood is returned to circulation while urine is
collected in the urinary bladder.
Urine is stored here until it is released from the body through a tube called
the urethra.
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31. URETERS
It is a tube approximately 6 to 7 inches
long attached to each kidney.
Made up of three layers of tissue
● Smooth muscle
● Fibrous tissue
● Mucous Layer
Peristalsis, a rhythmiccontraction of the
ureter smooth muscle which helps to
move the urine into the bladder.
32. URINARY BLADDER
It is a hollow, muscular organ that stores urine
Sphincter muscles hold the urine in place
Holds 300 to 400 milliliters of urine before
emptying
Walls contain epithelial tissuethat stretch to
allow the bladder to hold twice its capacity.
The trigone is a triangular area at the base of
the bladder where the ureters enter and the
urethra exits
33. URETHRA
A tube of smooth muscle with a mucous lining that carriesurine from the bladder to
the outside of the body.
Urethra Female Urethra Male
8 inches long 1.5 inches long
Passes through 3 different regions Opens through meatus
● Prostate Gland
● Membranous portion
● Penis
