It is about human excretory system

1. EXCRETORY SYSTEM

2. • Excretion is the process of removing wastes and
excess water from the body. It is an essential process in
all living things, and it is one of the major ways
the human body maintains homeostasis. It also helps
prevent damage to the body.
• Wastes include by-products of metabolism — some of
which are toxic — and other non-useful materials, such
as used up and broken down components. Some of the
specific waste products that must be excreted from the
body include carbon dioxide from cellular
respiration, ammonia and urea from protein cataboliS
m, and uric acid from nucleic acid catabolism.

3. EXCRETORY PRODUCTS
• Carbon dioxide -lungs
• Excess mineral and water salt- sweat-skin
• Bile pigments- Bile juice- liver
• Nitrogenous waste-urine -kidney
Digestive system excrete food residues in the form
of faeces
Lungs remove carbon dioxide and water vapour
Liver excrete many substances like bile pigments
heavy metals drugs toxins through bile
Kidney excrete urea in the form of urine

5. SKIN
• SKIN : The skin is part of the integumentary
system, but it also plays a role in excretion
through the production of sweat by sweat
glands in the dermis.
• The main role of sweat production is to cool
the body and maintain
temperature homeostasis, sweating also
eliminates excess water and salts, as well as a
small amount of urea.

6. LIVER
• The liver (shown in Figure 16.2.4) has numerous major
functions, including secreting bile for digestion of
lipids,
• The liver transforms ammonia — a poisonous by-
product of protein catabolism — into urea, which is
filtered from the blood by the kidneys and excreted in
urine.
• The liver also excretes in its bile the protein bilirubin, a
byproduct of hemoglobin catabolism that forms when
red blood cells die. Bile travels to the small
intestine and is then excreted in feces by the large
intestine.

7. LARGE INTESTINE
• As an organ of excretion, its main function is to
eliminate solid wastes that remain after the
digestion of food and the extraction of water
from indigestible matter in food waste.
• The large intestine also collects wastes from
throughout the body.
• Bile secreted into the gastrointestinal tract, for
example, contains the waste
product bilirubin from the liver.
• Bilirubin is a brown pigment that gives
human feces its characteristic brown colour.

8. LUNGS
• They are responsible for the excretion of
gaseous wastes from the body.
• The main waste gas excreted by the lungs is
carbon dioxide, which is a waste product
of cellular respiration in cells throughout the
body. Carbon dioxide is diffused from the
blood into the air in the tiny air sacs
called alveoli in the lungs

10. KIDNEYS
• The kidneys are paired, bean-shaped organs
located in the abdomen, on either side of the
spine, under the diaphragm. They are made of
a large number of structural and functional
subunits called nephrons. These nephrons
perform the primary task of filtering blood
and removing waste products.

12. URETER
• The ureter is a tube that carries urine from the
kidney to the urinary bladder. There are two
ureters, one attached to each kidney. The
upper half of the ureter is located in the
abdomen and the lower half is located in the
pelvic area.
•

13. URINARY BLADDER
• The urinary bladder is a hollow, stretchy
organ in the lower part of your abdomen that
stores urine before it leaves your body
through your urethra. Conditions that affect
your bladder include incontinence, cystitis and
bladder stones. They can make urinating
painful, difficult or uncontrollable.

14. URETHRA
• The urethra is the tube that lets urine leave
your bladder and your body.
• If you were assigned male at birth, your
urethra passes through your prostate and into
your penis.
• If you were female at birth, your urethra is
much shorter. It runs from your bladder to
open in front of your vagina.

17. Internally, the kidney has three regions—an
outer cortex, a medulla in the middle, and
the renal pelvis in the region called
the hilum of the kidney.
 The hilum is the concave part of the bean-
shape where blood vessels and nerves enter
and exit the kidney; it is also the point of exit
for the ureters.
The renal cortex is granular due to the
presence of nephrons—the functional unit of
the kidney.

18. . The medulla consists of multiple pyramidal
tissue masses, called the renal pyramids.
In between the pyramids are spaces
called renal columns through which the blood
vessels pass.
 The renal pelvis leads to the ureter on the
outside of the kidney.
 On the inside of the kidney, the renal pelvis
branches out into two or three extensions called
the major calyces, which further branch into the
minor calyces.
The ureters are urine-bearing tubes that exit
the kidney and empty into the urinary bladder.

22. BLOOD SUPPLY
• The kidneys receive blood from the renal arteries
left and right, which branch directly from
the abdominal aorta.
• Each renal artery branches into segmental arteries,
dividing further into interlobar arteries, which
penetrate the renal capsule and extend through the
renal columns between the renal pyramids.
• The interlobar arteries then supply blood to
the arcuate arteries that run through the boundary
of the cortex and the medulla. Each arcuate artery
supplies several interlobular arteries that feed into
the afferent arterioles that supply the glomeruli.

24. • Blood drains from the kidneys, ultimately into
the inferior vena cava
• After filtration occurs, the blood moves through
a small network of small veins (venules) that
converge into interlobular veins.
• As with the arteriole distribution, the veins
follow the same pattern: the interlobular
provide blood to the arcuate veins then back to
the interlobar veins which come to form
the renal veins which exit the kidney.

27. NEPHRONS
• Nephron is the basic structural and functional
unit of the kidney. They are the microscopic
structure composed of a renal corpuscle and a
renal tubule. The word nephron is derived
from the Greek word – nephros , meaning
kidney. There are about millions of nephrons
in each human kidney.

28. Structure of Nephron
THEmammalian nephron is a long tube-like
structure, its length varying from 35–55 mm long. At
one end, the tube is closed, folded and expanded,
into a double-walled, a cuplike structure called the
Bowman’s capsule or renal corpuscular
capsule, which encloses a cluster of microscopic
blood vessels called the glomerulus. This capsule and
glomerulus together constitute the renal corpuscle.

29. Small molecules from the blood pass freely into
Bowman’s space, but as long as the kidney filter is
working normally, cells and large proteins stay in
the blood. The small molecules then pass through
tubes in the kidney, and the kidney regulates
which molecules get absorbed back into your
blood and which leave your body in urine.

30. • The structure of nephron comprises two major portions:
• Renal Tubule
• Renal Corpuscle
• Renal Tubule
• The renal tubule is a long and convoluted structure that
emerges from the glomerulus and can be divided into three
parts based on function.
• The first part is called the proximal convoluted tubule (PCT)
due to its proximity to the glomerulus; it stays in the renal
cortex.
• The second part is called the loop of Henle, or nephritic loop
because it forms a loop (with descending and ascending
limbs) that goes through the renal medulla.
• The third part of the renal tubule is called the distal
convoluted tubule (DCT) and this part is also restricted to the
renal cortex.

31. PCT
• Proximal Convoluted Tubule (PCT)
• The blood brought by the renal artery is filtered by
the glomerulus and then passed to the PCT.
Maximum reabsorption takes place in PCT of the
nephron.
• PCT is the region of renal tubule where reabsorption
of essential substances like glucose, proteins, amino
acids, a major portion of electrolytes and water takes
place. Reabsorption takes place at the expense of
energy, i.e., the process is active.
• PCT selectively secretes ions such as hydrogen,
ammonia, and potassium into the filtrate and
absorbs HCO3
–from it. Thus, PCT maintains the
electrolyte and acid-base balance of the body fluids.

32. HENLES LOOP
• Henle’s loop has a descending and an ascending limb.
Being parts of the same loop, both the descending and
ascending limbs show different permeability. The
descending limb is permeable to water but
impermeable to an electrolyte, while the ascending
limb is permeable to electrolytes but impermeable to
water. Since the electrolytes get reabsorbed at the
ascending loop of Henle, the filtrate gets diluted as it
moves towards the ascending limb. But reabsorption is
limited in this segment.

33. DCT
• Distal Convoluted Tubule (DCT)
• The DCT, which is the last part of the nephron, connects and
empties its contents into collecting ducts that line the
medullary pyramids.
• Similar to PCT, DCT also secretes ions such as hydrogen,
potassium, and NH3 into the filtrate while reabsorbing the
HCO3
–from the filtrate. Conditional reabsorption of sodium
ions and water takes place in DCT. Thus, it maintains the pH
and sodium-potassium level in the blood cells.

34. Collecting Duct
• Collecting duct is a long, straight tube where
H+ and K+ ions are secreted to maintain the
electrolyte balance of the blood.
• This is also the region where the maximum
reabsorption of water takes place to produce
concentrated urine.

35. Types of Nephron
• There are two types of nephron:
• Cortical nephron
• These are the nephrons present within the
cortex. These are short and comprise about
80% of the total nephrons.
• Juxtamedullary nephron
• These have long loops of Henle and extend
into the medulla. These are about 20%.

37. NEPHRON FUNCTION
• Nephrons filter blood and then reabsorb useful materials
from the filtrate before eliminating the remainder as urine
• This process occurs over three key stages:
• Ultrafiltration – Blood is filtered out of the glomerulus at
the Bowman’s capsule to form filtrate
• Selective reabsorption – Usable materials are reabsorbed
in convoluted tubules (both proximal and distal)
• Osmoregulation – The loop of Henle establishes a salt
gradient, which draws water out of the collecting duct
•

40. MECHANISM OF URINE FORMATION
• The mechanism of urine formation involves the following steps:
• Glomerular Filteration
• Glomerular filtration occurs in the glomerulus where blood is
filtered. This process occurs across the three layers- the epithelium
of Bowman’s capsule, the endothelium of glomerular blood vessels,
and a membrane between these two layers.
• Blood is filtered in such a way that all the constituents of the
plasma reach the Bowman’s capsule, except proteins. Therefore,
this process is known as ultrafiltration .
• The filteration of blood through glomerulus under high pressure is
known as ultrafiltration.THE FILTERATE IS CALLED GLOMERULAR
FILTERATE

41. REABSORPTION
• Reabsorption
• Around 99 per cent of the filtrate obtained is
reabsorbed by the renal tubules. This is known
as reabsorption. This is achieved by active and
passive transport.
• Substances like glucose,amino acids are
reabsorbed actively by active absorption,while
the nitrogenous waste are absorbed by
passive absorption.

42. SECRETION
Secretion
• The next step in urine formation is tubular
secretion.
• Here, tubular cells secrete substances like
hydrogen ions, potassium ions, etc into the
filtrate. Through this process, the ionic, acid-base
and the balance of other body fluids are
maintained. The secreted ions combine with the
filtrate and form urine. The urine passes out of
the nephron tubule into a collecting duct.

43. URINE
• Urine
• The urine produced is 95% water and 5%
nitrogenous wastes. Wastes such as urea,
ammonia, and creatinine are excreted in the
urine. Apart from these, the potassium,
sodium and calcium ions are also excreted.

44. OSMOREGULATION
• Osmoregulation
• Osmoregulation is the process of regulating body fluids
and their compositions. It maintains the osmotic
pressure of the blood and helps in homeostasis. This is
why it is recommended to consume more water about
2-3 litres, which helps in the proper functioning of our
kidneys. For example, we consume lots of water during
summers, but still, we urinate fewer times in summers
than in winters and the concentration of the urine is
also more. The reason is that we lose lots of water
from our body in summer through sweating. Thus, to
maintain the fluid balance in the body our kidneys
reabsorb more water.

45. FUNCTIONS
1. Excretion of waste product :kidneys excrete
urea, uric acid ,creatinine, bilirubin which are
form during metabolic activities
Urea: End product of amino acid metabolism
Uric acid: End product of nucleic acid metabolism
Creatinine: end product of metabolism in muscles
Bilirubin: End product of haemoglobin
degradation

46. 2. Maintenance of water balance
Kidneys conserve water when it is decreased and excrete
water when it is excess in the body
3. Maintenance of electrolyte balance
Kidneys retain sodium if the osmolarity of body water
decreases and eliminate sodium when osmolarity increases
4. Hemopoietic function: kidney stimulate the production of
erythrocytes by secreting erythropoietin
5. Endocrine function: kidney secrete many hormones like
erythropoietin ,thrombopoetin and renin.
6. Regulation of blood pressure: kidney play and important
role in the long term regulation of arterial blood pressure.