Human excretory system for Nurses Class 1

1. Class 1

2. • Homeostasis is the process of maintaining the ideal internal
conditions (i.e. correct temperature, right amount of water and
glucose & other solutes) for the body to work at it’s optimum.
• Excretion is the process of removing metabolic waste products
and other toxins.
• Osmoregulation is maintaining the correct balance between
water and solutes.
• Excretion, which includes osmoregulation, is thus extremely
important in maintaining homeostasis.
• Secretion is the release of useful substances, e.g. hormones,
from the body. Thus, it is not excretion. Egestion, i.e. defecation,
is also not excretion.

3.  Metabolic processes give rise to chemical
products which are of no use to the body.
 In fact, some of them may prove detrimental to
health, and accumulation of these waste
products can even be fatal.
 Hence waste products are removed from the
body by the process of excretion.
 The digestive and respiratory systems have
been dealt with separately.

4. • Certain waste products would become highly toxic if they
were to accumulate. This could damage tissues.
• An excess of water could also lead to a number of
complications.
• Thus, the waste products must be removed – they continually
move into the bloodstream, which carries them to the
excretory organs.

5. • There are four main excretory organs:
– Lungs
– Colon
– Skin
– Kidneys
• The liver is not an excretory organ, but produces many
products which are excreted elsewhere. Toxins and drugs as
well as alcohol, is broken down in the liver. Hence, an excess
of smoking, medication and alcohol is extremely harmful to
the liver.

6. Raw Materials
(Food and 02)
Useful Materials
Useless Materials
Egested (faeces) Metabolised
Metabolic Waste
Products (urea and CO2)
Excreted
Useful Products

7. • The carbon dioxide released from cellular respiration is
carried to the lungs in the blood. It then diffuses across the
respiratory membrane and is exhaled.
• A small amount of heat and water is excreted this way.
• Bile pigments, from the break down of haemoglobin, and
cholesterol are synthesised in the liver.
• They pass into the small intestine as bile and are finally
excreted in the faeces as bile salts, from the colon.
• Mucus and bacteria are too excreted through the colon.

8. • Sweat, which is excreted through the skin, contains water,
salts and some urea.
• As the water in the sweat is excreted, heat is lost and the
body is cooled.
• Sweat is a form of excretion as it rids the body of waste, as
well as a form of secretion as it maintains the body
temperature.

9. • When amino acids and nucleic acids are broken down,
nitrogenous wastes are released as ammonia, urea, uric acid
and creatinine. Ammonia is toxic if it accumulates and is
therefore converted to less toxic urea in the liver.
• The following substances are made in the liver and excreted
by the kidneys:
– Urea, the main nitrogenous waste compound secreted. It is formed by
the breakdown of excess amino acids in the process of deamination.
– Uric acid, the nitrogenous end product of nucleic acid metabolism.
– Creatinine is formed from creatin phosphate, found in the muscle
cells.
– Non-nitrogenous waste, e.g. CO2, excess water, ions, hormones,
poisons and drugs.

10. URINARY SYSTEM
METABOLIC WASTES INCLUDE
1. EXCESS WATER AND SALTS
2. CARBON DIOXIDE FROM CELLULAR RESPIRATION
3. NITROGENOUS COMPOUNDS FROM THE
BREAKDOWN OF PROTEINS
4. UREA.

11. KIDNEY

12.  The kidneys lie towards the back of the
abdomen, one on each side of the spinal column.
 A tube – the ureter – connects each kidney with
the bladder, where urine collects to be passed
through the urethra.
 The 2 important functions are to remove waste
products from the blood and to regulate the salt
and liquid content of the body.

13.  The kidneys also act as endocrine organs, secreting
substances which have the following effects:
 Formation of red blood cells.
 Regulation of blood pressure.
 Involvement in the control of calcium
metabolism.
 The main function of the kidneys is to filter waste
products out of the blood passing through them.
 Blood enters through the renal arteries, and passes
back to the circulation through the renal veins.

14.  The wastes, such as urea, and excess water, are
secreted from the kidneys as urine.
 The urine passes through the ureters to the
urinary bladder, where it is stored and
periodically released.
 Each kidney contains about a million filtering
units, called nephrons.
 Filtration, selective resorption, and secretion
processes occur in the nephrons.

15. • Glomerular Filtration
– The fluid part of the blood is filtered from the glomerulus into the
cavity of the Bowman’s capsule.
• Tubular Reabsorption
– As the fluid flows along the renal tubule, useful substances are
reabsorbed back into the bloodstream according to the body’s needs.
• Tubular Excretion/secretion
– In addition, certain unwanted substances in the blood are actively
excreted into the tubules.

16. • A passive, non selective process.
• Fluids and solutes are forced through the glomerular
membrane by hydrostatic pressure.
• The glomerular filtrate has the same composition as blood,
without the blood cells and plasma proteins. These are too
large to fit through the glomerular membrane.
• Substances in glomerular filtration: Blood plasma without
protein molecules which includes:
– Useful substances – water, glucose, amino acids, vitamins, hormones,
and ions.
– Waste substances – e.g. nitrogenous waste such as urea, uric acid and
creatinine.

17.  filtration.
 Water and dissolved molecules pass from the
blood to the nephron.
 In a normal kidney this filtrate should not contain
protein or red blood cells.
 Hence, if protein is found in the urine it is a sign
of abnormal kidney function.

18. Filtration
• Aided by difference in pressure
• Efferent arteriole narrower than afferent arteriole
• Capillary hydrostatic pressure more than the osmotic
pressure of blood (plasma proteins) & the pressure in
glomerular capsule
• Capillary hydrostatic pressure-55mmHg, Osmotic
pressure of blood-30mmHg, Filtrate hydrostatic
pressure -15mmHg ,so net filtration pressure is
10mmHg
• GFR 125 ml /mt
• 180 L filtrate ,only 1% excreted –rest reabsorbed

19. Filtration
• Auto regulation
• Renal blood flow is kept constant
• Irrespective of autonomic nerve supply
• Severe shock ,blood flow will be affected

20.  The first part of the nephron is called the
proximal tubule.
 This part is 15 mm long, and begins with a cup
like expansion (Bowman’s capsule).
 A small bunch of renal capillaries (very narrow
vessels, arising from the renal artery) is ‘pushed’
into this cup like capsule.
 The blood in these capillaries is under pressure,
hence fluid and some dissolved substances enter
the nephron, while large molecules – such as
proteins remain in the blood vessels.

24. The other parts of the nephron are:
 Loop of Henle (descending limb)
 Loop of Henle (ascending limb)
 Distal tubule
 Collecting duct
The first three are approximately 12 mm in length.
The collecting duct is 5 mm in length.

25.  Selective resorption occurs chiefly in the proximal
tubule, but also occurs in the other segments, right
up to the collecting duct.
 The following substances are taken up from the
tubule, back into the interstitial spaces or into the
blood stream (i.e. resorbed), useful substances such
as glucose, vitamins, and amino acids; and salts such
as sodium, potassium, chloride.
 A considerable amount of water is taken up once
more as well.
 In fact out of 180 liters/day, which pass through the
kidney, only 1 to 1.5 liters is excreted as urine
everyday.

26. • Substances are reabsorbed in the following ways:
– Active reabsorption
– Passive reabsorption

27. This is the process by which substances are reabsorbed.
• Carrier molecules on the microvilli join up with certain
molecules from the filtrate and actively transport them
through the epithelial cells to the blood.
• Energy from ATP is used to join the molecule to the
carrier molecule. The following are actively reabsorbed:
– All organic nutrients such as glucose, amino acids and water
soluble vitamins are completely reabsorbed.
– Sodium ions and fat soluble vitamins are selectively reabsorbed,
according to the needs of the body.
– Calcium , potassium , phosphate & chloride

28. Glucose reabsorption
• Kidneys maximum capacity for reabsorption of
a substance is transport maximum
• Glucose transport maximum is 160mg
• When blood sugar is more than that glucose
appears in urine
• All carrier sites will be occupied and the active
transport mechanism will be overloaded

29. • Passively = no energy needed.
• About 65% of the water is passively reabsorbed from the
filtrate in the proximal convoluted tubule by osmosis.
• Chloride ions passively follow the path of sodium ions.
• Urea, uric acid and creatinine is not reabsorbed.

30. Reabsorption
• PTH & Calcitonin regulate reabsorption of
Calcium & Phosphate
• Aldosterone increases Sodium absorption &
Potassium excretion
• ANP decreases Na absorption

31. • Takes place in proximal and distal tubules and is reabsorption
in reverse.
• The following molecules and ions are taken from the blood
and deposited into the filtrate:
– Hydrogen and potassium ions (secreted directly)
– Creatinine and uric acid
– Drugs, preserves and colourants (actively excreted)

32.  Secretion of certain substances in the distal
tubule and collecting duct, such as hydrogen
ions and ammonia are added to the urine in the
nephron.
Urine
formed
Filtrate
(water &
substances
like urea)
Substances
resorbed
(glucose,
amino acids)
Substances
secreted
(H+, NH4+)
=
__
+

33.  The collecting ducts open into large collecting
ducts.
 There are about 250 in each kidney, which collect
urine from more than 4000 nephrons each.
 These open into the ureters.

34.  Among other factors which influence the
resorption of water in the collecting duct, the
Anti Diuretic Hormone (ADH), which is stored in
the posterior pituitary.
 This ADH is released to conserve body fluid by
decreasing the urine output.
 This may be required when considerable fluid or
blood has been lost.

35. URINE
 The average daily output of urine is 1.0 to 1.5
liters/day.
 Apart from excess water, urine contains
nitrogenous substances (chiefly urea) –
approximately 32 g and mineral salts containing
sodium, chloride, phosphorus, and potassium.
 Urea and other nitrogen containing substances are
derived from protein.
 These compounds undergo further changes in the
liver before passing to the kidneys to be excreted
in the urine.

36. Urine
• Clear &amber colour due to urobilinogen
• Specific gravity-1020-1030
• pH around 6 (4.5-8)

37. • About 96% of urine is water.
• 2% is salts, mainly sodium chloride.
• Uric acid ,creatinine ,ammonia ,potassium ,phosphate ,
sulphate ,oxalate etc
• Urea makes up 2%
• Small quantities of drugs, colourants, hormones and
preservatives.
• About 1.5 litres of urine is produced daily.

38. The urinary system thus regulates
 Fluid volume by excreting excess water or
conserving water when needed.
 Acid level (pH) by excreting appropriate amounts
of acid or alkali.
 This is very important as most of the enzymes,
and other processes in the body require the pH
to be as close to the normal (i.e. 7.4 in arteries;
slightly lower in veins) to function correctly.

39. MODIFYING THE FLOW
 An increase in the flow of urine can be stimulated by
substances called diuretics. These act in different ways.
 Alcohol is a diuretic which stimulates both the blood
circulation and the kidneys, directly.
 Caffeine, which is present in both coffee and tea is also a
diuretic which acts on the kidneys.
 Temperature is another factor which influences the
production of urine.
 The lower the temperature the greater the volume of
urine produced.
 This is because less water is lost by evaporation through
the skin and through sweat.

40. Water, Electrolyte, & Acid-Base Balance
A. To be in balance, the quantities of fluids and
electrolytes leaving the body should be equal
to the amounts taken in.
B. Anything that alters the concentrations of
electrolytes will also alter the concentration
of water, and vice versa.
C. Distribution of Body Fluids
A. A. Fluids occur in compartments in the body, and
movement of water and electrolytes between
compartments is regulated.
B. Fluid Compartments

41. WATER BALANCE
A. Water balance exists when water intake equals water output.
B. Water Intake
C. Regulation of Water Intake
D. Water Output
E. Regulation of Water Output

42. ELECTROLYTE BALANCE
A. An electrolyte balance exists when the quantities of electrolytes gained equals
the amount lost.
B. Electrolyte Intake
C. Regulation of Electrolyte Intake
D. Electrolyte Output
E. Regulation of Electrolyte Output

43. ACID-BASE BALANCE
A. Electrolytes that ionize in water and release
hydrogen ions are acids; those that combine
with hydrogen ions are bases.
B. Maintenance of homeostasis depends on
the control of acids and bases in body fluids.
C. Sources of Hydrogen Ions.
D. Strengths of Acids and Bases.
E. Regulation of Hydrogen Ion Concentration.

44. URETERS
 There are 2 muscular tubes, 25 to 30 cm in
length, with a very small inner diameter of about
3 mm.
 They convey urine from the kidneys to the
bladder.

45. URINARY BLADDER
 Pear shaped organ, which lies in the pelvis.
 Though the 2 ureters, the bladder receives waste
products, including urea from the kidneys.
 The average capacity of the bladder is up to 400
or 500 mL.
 The need to pass urine is usually felt when the
bladder is filled to about 280 mL.
 Sometimes up to 500 mL can be tolerated.
 Filling above 500 mL leads to pain.

46. URETHRA
 Is a passage way through which urine is
discharged from the bladder.
 In men the urethra is longer than in females.
 It passes through the penis, and also has a
passage for the discharge of semen.
 In women the shorter urethra opens
immediately in front of the vagina.
 It serves solely for the discharge of urine.

47. EMPTYING THE BLADDER
 Emptying the bladder (via the urethra) takes
place by contraction of the smooth muscle –
detrusor.
 On either side of the urethra there are muscle
bundles, called the internal urethral sphincter.
 There is a significant difference between the 2
sphincter – the internal sphincter is not under
voluntary control, i.e. we are unable to prevent it
relaxing and allowing urine to pass through.
 In contrast, the external sphincter is under
voluntary control.

48.  Thus it is possible to learn to empty the bladder,
at appropriate times and places.
 Occasionally, in adults there may be involuntary
voiding of the bladder contents, when the
intraabdominal pressure is raised – during
coughing, sneezing, or laughing.
 Sometimes this may also be brought on by
emotional stress.

49.  Parasympathetic nerves which arise from the
sacral part of the spinal cord, send messages to
empty the bladder, by causing contraction of the
detrusor muscle, and relaxing the internal
sphincter.
 Sympathetic nerves also supply the internal
sphincter.
 It was believed that sympathetic nerves relax the
detrusor, contract the internal sphincter, and
prevent emptying.

50.  The sympathetic nerves to the bladder are
believed to be chiefly important – in males – in
preventing semen from entering the bladder
during ejaculation.
 The voluntary (somatic) nerves regulate the
external sphincter.
 These nerves also arise from the sacral part of
the spinal cord.

51. Some of the “higher” centers involved:
 The frontal and prefrontal cortices.
 Parts of the hypothalamus
 Brainstem (pons, midbrain)
Scientific studies have proved that the parts of the
brain are involved in initiating and conducting
micturition

52. THE SKIN (INTEGUMENT)
 The skin is the outer covering of the body.
 It is a major organ of the body, forming about
8% of the total mass.
 The average area (depending on the body
build) may range from 1.2 to 2.2 sqm.
 The total thickness is 1.4 to 4.0 mm.

53. SKIN STRUCTURE

54. The integument has a number of functions:
1. It is a barrier against germs.
2. It acts as a touch, resilient cushion – protection
for the structures beneath.
3. It helps to regulate the body temperature. When
it is hot, glands in the skin secrete perspiration on
sweat. When sweat evaporates, cooling occurs.
When it is cold, constriction of the blood vessels
in the skin cuts down the flow of blood near the
body’s surface. Hence it is decreased heat loss.

55. 4. The skin is also a sense organ. Nerve ending
(and other receptors) in the skin respond to
pain, heat, cold, touch, and pressure.
5. The skin supplies much of the body’s needs
for Vitamin D. a substance is produced in the
skin, which changes into Vitamin D, when
exposed to sunlight.
6. The skin gives rise to specialized structures
such as hair and nails.

56.  The skin has two distinct layers – the epidermis
– outer covering and the inner dermis, or true
skin.
 The uppermost part consists of flat, old cells
which are constantly being shed, or ‘sloughed
off’.
 The underlying part of the epidermis is made
up of rapidly dividing cells.
 These cells continuously push upward to
replace dead cells.

57.  Tiny blood vessels and nerve ending are
densely woven into the flexible connective
tissue which makes up the dermis.
 Sweat and oil (sebaceous) glands are
embedded in it.
 There are also various types of receptors for
the touch sensation, beneath the skin.

58. SWEAT GLANDS
 There are approximately 2 million sweat glands all
over the skin.
 They are tiny, coil shaped tubes.
 They extend from the deepest layer of the skin to
the surface.
 These glands help to regulate the body temperature
and also contribute to the excretion of water and
salt from the body.
 Sweat contains about 98-99% of water.
 Certain inorganic salts – specially sodium chloride
along with small make up the remaining 1-2%.

59.  During exercise more blood moves through the
vessels surrounding the sweat glands.
 This increases the sweat secretion, helping to lose
heat and to remove waste products.
 In offering protection to the internal organs against
germs and injuries, the skin itself is vulnerable to
various insults.
 In particular, the skin of certain persons is usually
sensitive.
 In extreme cases this hypersensitivity can lead to an
allergic reaction.
 This is observed in certain skin conditions, such as
eczema.

60. SWEAT GLAND