The document outlines the anatomy and functions of the renal system, detailing components such as kidneys, ureters, bladder, and urethra, as well as the processes involved in urine formation, including filtration, reabsorption, and secretion. It also discusses the hormonal regulation of fluid and electrolyte balance, emphasizing the kidneys' role in homeostasis and waste elimination. Additionally, the document covers fluid compartments, the significance of electrolytes, and the importance of maintaining acid-base balance.

1. BY. UNIS

2. Learning Outcomes
• Be able to label the renal system and internal
structure of the kidney
• State the functions of the renal system
• Label the parts of the nephron
• Describe the process of urine formation
– Filtration
– Reabsorption
– Secretion
• State two hormones involved in the regulation
of fluid and electrolyte balance
• Understand the basics of maintaining fluid and
electrolyte balance

3. Figure 15.1a
Organs of the Urinary System

4. Structures of the urinary system
 2 Kidneys
 1 million nephrons (functional units) per kidney
 2 Ureters: transport urine from the kidneys to the
bladder
 1 Bladder: A temporary storage for urine.
 1 Urethra: through which urine reaches the exterior.

5. Functions of the Renal System
 Formation of Urine
 Urine formed in the Kidneys
 Elimination of waste products
 Nitrogenous wastes
 Toxins
 Drugs

6. Funtions of the Renal System
 Regulates many aspects of homeostasis
 Water (fluid) balance
 Electrolyte balance
 Acid-base balance in the blood
 Involved in blood pressure regulation
 Red blood cell production: Kidneys produce
erythropoetin
 Activation of vitamin D

7. Renal System
 Consists of:
 Kidneys
 Ureters
 Bladder
 Urethra

8. The Kidneys
• 2 Kidneys
• Left kidney higher than right as
(large) liver above right kidney
• Position: upper, posterior
abdominal wall
• Well protected:
– Thick outer fibrous capsule
– Surrounded by bed of fat
– Also protected by lower ribs

9. The Kidneys
• Length 11cm, width 6cm,
depth 3cm
• Hilum: Concave border
of the kidneys:
– renal artery and nerves
enter
– Renal veins and ureters
leave
• 2 main parts
– Cortex (outer)
– Medulla (inner)

11. Kidney: Structure
• Renal or medullary pyramids: triangular regions of
tissue in the medulla
• Renal columns: extensions of cortex-like material
inward that separate the pyramids
• Calyces: cup-shaped structures that funnel urine
towards the renal pelvis
• Renal pelvis: funnels urine towards the ureter
• Ureters carry urine down to bladder

12. Ureters: Structure
• Drain urine from the kidneys to bladder
• About 25 – 30cm long
• Layers of both longitudinal & circular smooth muscle
which propel the urine along the structures
(peristaltic waves)
• Turn medially & enter posterior wall of bladder
– Renal pelvis & ureters, lined with a mucosal membrane,
layer of mucous protects the epithelial cells from urine
as the pH of urine can differ drastically and would
damage cells.

13. Bladder & Urethra

14. Bladder
• The bladder is a reservoir for urine. It is a muscular
sac that can expand considerably
• Situated in the pelvic cavity but extends when full up
into the abdominal cavity
• Outer layer of loose connective tissue.
• 3 layers of smooth muscle (detruser muscle) and
elastic fibres: inner & outer layers of longitudinal
muscle fibres & a middle layer of circular muscle
fibres.
• Lined with mucosal membrane.

15. Urethra
 The urethra is a muscular (smooth muscle) tube
carries urine from the bladder & out of the body
 At the bladder- urethral junction is a thickening of
the detruser muscle which acts as an internal
sphincter to prevent bladder leakage
 The external urethral sphincter (sphincter urethrae)
is striated muscle & under voluntary control

16. Renal System: Overview
 Urine is formed in the kidneys
 Formed by functional units called nephrons
 Once urine formed it drains from kidneys down
into bladder
 When 250-300 mls collects in bladder, bladder
empties and urine expelled from body via urethra

17. Nephrons: Structure
 About 1 million per
kidney
 Each nephron has 4
distinct parts
 Glomerular capsule or
Bowmans capsule
 Proximal convoluted
tubule (PCT)
 Loop of Henle (LoH)
 Distal convoluted
tubule (DCT)

18. Blood Flow in Kidney
• Renal artery enters the kidney:branches into arterioles
• An arteriole enters the glomerular (Bowmans) capsule of
each nephron & divides into capillary network called the
glomerulus.
– Afferent arteriole: Enters glomerulus (wider than efferent)
– Efferent arteriole: Leaves glomerulus
• The efferent arteriole then forms another capillary
network which surrounds the rest of the nephron before
reforming as veins
• This arrangement of blood vessels: (artery- capillaries,
artery – capillaries) is peculiar to the kidneys

20. Glomerular (Bowmans)
Capsule
The nephron is a tube, closed at 1 end, opens into a
collecting duct at the other end
Glomerular (Bowmans) Capsule
• Closed end: glomerular (Bowman’s) capsule
which is cup shaped.
– Endothelium of capsule: fenestrated (many pores)
– Afferent arteriole carries blood into depression of
capsule
– Divides into capillaries called the glomerulus:
• Glomerular capillaries very leaky, 1000 times more leaky
(permeable) than other capillaries
– Efferent arteriole carries blood away from glomerulus

21. Glomerular (Bowmans) Capsule

22. Formation of Urine: Overview
 The first stage is filtration: Water and solutes in blood
are ‘filtered’ out of the blood stream, into the
glomerular capsule
 Filtered fluid: called filtrate
 Filtrate flows out of glomerular capsule through tubule
 Much of filtrate is reabsorbed back into blood as it
passes through the tubule (reabsorption)
 Some substances pass from blood into filtrate
(secretion)

24. Filtration
• Blood pressure in glomerulus higher than in other
capillaries: blood pressure forces water and small
solutes out of capillaries
Filtration
– Nonselective, indiscriminate, passive process
– Water and solutes smaller than proteins are forced through
capillary walls into glomerulus to form filtrate
• Proteins and blood cells: too large to pass through the
filtration membrane, they remain in the blood
• Filtrate is collected in the glomerular capsule and
leaves via the renal tubule

25. Reabsorption
 As the fluid passes through the tubules much of the
water & solutes that were filtered out of the blood
are reabsorbed back into the blood stream
 Some by passive diffusion & some are actively
transported which is a more selective process and
depends on the bodies needs

26. Reabsorption
By the time filtrate leaves the PCT all glucose & amino
acids, 80-90% bicarbonate, 65% Na+, K+ & water &
varying amounts of other solutes have been
reabsorbed
In the loop of Henle 15% Water is reabsorbed in the
descending limb. Solutes such as Na+, K+, bicarbonate
& Cl- reabsorbed in the ascending limb
Water & solutes continue to be reabsorbed in the DCT
and collecting ducts

27. Secretion
 Not all substances are cleared from the blood into the
filtrate in the glomerular capsule, e.g. some drugs, H+,
urea and creatanine are secreted into the filtrate as it
passes along the tubule.
 Secretion of substances is regulated by amounts of
different substances present in the blood e.g. K+
secretion can vary depending on dietary intake, if
high more is secreted.

28. Hormonal Regulation
• Most water moves back into blood passively with
solutes
• Antidiuretic hormone acts on the collecting ducts, it
increases re-absorption of water from filtrate when
dehydrated so less urine passed
• Aldosterone increases reabsorption of sodium (Na+)
in the DCT and collecting duct, (water moves back
passively (osmosis) with Na+, not a direct effect of
aldosterone)

30. Filtrate and Urine
• Kidneys are very active 24 hours day, filtration takes place
constantly to maintain health
• The filtration rate of all nephron’s is 125mls/minute, this
is a lot, per hour, 125 X 60 is = 7,500mls/per hour which is
7.5L
• Per day (X 24) this amounts to 180,000 mls or 180L per day
• The average sized adult only passes 1–2L of urine per day,
so most filtrate is reabsorbed.

31. Urine
 After leaving the collecting duct the processes of re-
absorption & secretion are completed
 The fluid is now classed as ‘urine’
 Urine is what remains after the filtrate has lost most
of its water, nutrients, and necessary ions
 Urine contains nitrogenous waste and substances that
are not needed by the body

32. Urine
 Yellow colour due to the pigment urochrome (from
the destruction of hemoglobin) and solutes
 Sterile
 Slightly aromatic
 Normal pH of around 6
 Specific gravity of 1.001 to 1.035

33. Urine Contains
 Urine is mostly water
 Solutes normally found in urine are:
 Sodium and potassium ions
 Urea, uric acid, creatinine
 Ammonia
 Bicarbonate ions

34. Abnormal Constituents of
Urine
 Solutes NOT normally found in urine
 Glucose: this is filtered but rapidly reabsorbed in the
PCT
 Blood proteins
 Red blood cells
 Haemoglobin
 White blood cells (pus)
 Bile

35. Fluid Compartments
 Water is the ‘universal solvent’
In health fluid balance is maintained automatically
 Fluid Compartments
2 main compartments
Intracellular (about 66% of total body fluid2/3))
(=40% body weight)
Extracellular (about 33% of total body fluid (1/3))
Interstitial fluid & Blood Plasma
(=80% of ECF) (=20% of ECF)

36. Fluid Balance
• In health balance is normally well maintained
• When additional fluid is required we become aware
of this (thirst) and drink
• Excess fluid is excreted via the kidneys, urine
becomes more dilute
• To maintain normal levels of electrolytes and rid the
body of toxins and by products of metabolism the
kidneys must constantly remain active (24 hours/day)

37. Water Input & Output (Average)
Water Input: ml per day Water Output: ml per day
Drink 1500
Food 800
Metabolic Production: 200
Urine: 1400
Evaporation:
Lungs: 500
Skin: 400
(insensible loss, i.e. not
detected by senses)
Faeces: 200
Total 2500 Total 2500
Note: Values will vary with diet and environmental conditions

38. Electrolytes
• Defined as inorganic compounds which dissociate
into ions (carry a positive or negative charge) in
solution.
• Important regulators of nervous and metabolic
activity.
• Dissociate in solution to form + charged cations & -
charged anions
• Number of cations and anions must balance in body
fluids (intracellular & extracellular)
• Different fluid compartments contain different
electrolytes (see diagram)

39. Extracellular Fluid
ECF)
Sodium (Na+)
Chloride (Cl-)
Bicarbonate
(HCO3-)
Calcium (Ca++)
Intracellular
Fluid (ICF)
Potassium (K+)
Protein-
Phosphate
(HPO4-)
Magnesium
(Mg++)
Examples of Main Ions Found in
Intracellular Fluid and Extracellular Fluid
This separation of ions enables neuronal and muscular
activity.
The number of positive & negatively charged ions balance

40. Fluid & Electrolytes & pH
 Body fluids: a complex
mix of electrolytes
 + & - charged ions
always balance (same
number of each) in
fluid compartments.
 Not always the same
ions in each fluid
compartment
 Fluid & electrolyte
levels are closely
linked
 Hydrogen (H+) formed as by
product of metabolism of
amino-acids.
 Concentration of free H+
determines intra &
extracellular fluid pH (acid or
alkaline), it effects the activity
of many enzyme systems
 pH stands for pressure of
hydrogen

41. The Acid Balance
 The acid balance is related to the number of
hydrogen ions present (more H+ = more acidic).
pH must be kept within very narrow limits.
 pH in arterial blood is maintained between 7.35 –
7.45
 All metabolic reactions generate H+ so constantly
being produced.
 As H+, pH decreases, = acidosis (pH<7.35)
 As H+, pH increases, = alkalosis (pH>7.45)

42. Fluid and Electrolyte
Imbalance
• Dehydration may increase plasma concentrations of
ions.
• Sodium and Potassium depletion, could be due to:
– ( loss of) Gastric aspirate
– Vomiting, diarrhoea
• Acidosis or Alkalosis (H+)
• In health, the kidneys maintain fluid, electrolyte and
pH within very narrow ranges (balance)

43. Fluid Balance
• Fluid loss during breathing and from sweat cannot be
measured (800-1000mls/day)
• Fluid balance charts are normally in a ‘positive’ balance
(more in than out) as this fluid loss cannot be measured
• More water lost if temperature is high (pyrexia) resulting
in increased sweating and also increased respiratory rate
so:
• Intake should also be increased

44. Fluid Balance
 A constant fluid intake is vital to health if blood is to
maintain fluid, electrolyte and acid balance
 Fluid input and output often monitored closely in
hospital
 When unwell fluid intake must be maintained, if oral
intake is limited or restricted intravenous fluids can be
given
 Ensuring adequate intake is very important

45. Summary of lecture contents
 Structure and functions of the renal system
 Structure and function of the nephron
• Formation of urine
– Filtration
– Reabsorption
– Secretion
 Hormones involved in regulation of fluid and
electrolyte balance
 Basics of fluid and electrolyte balance

46. THANK YOU