The document provides an overview of the urinary system, including its main organs and functions. It describes the anatomy and histology of the kidney, nephron, ureters, and urinary bladder. It explains the three main processes of urine formation - glomerular filtration, reabsorption, and secretion. It also discusses some common urinary tract diseases and the relationships between the urinary system and other body systems.

1. BIOLOGY
URINARY SYSTEM
Block 4, Case 1, G5, PBL

2. Objectives
● What is Urinary System
● Organs: kidney, ureters, urinary bladder and urethra
● Anatomy of kidney
● Definition of nephron
● Structure of Nephron
● The process of filtration
● Relationship of urinary with other systems
● Diseases of urinary system

3. The Urinary System
The urinary system is the organ system of the body that plays a major role in maintaining the
salt, water, and pH homeostasis of the blood. It include: pair of kidney and ureters and a
urinary bladder. Collectively, these organs carry out the process of excretion, or the removal of
metabolic waste from the body. These metabolic waste materials are the by -products of the
normal activities of the cells and tissues.

4. Function of the Urinary System
A) Maintenance of Water–Salt Balance
A principal function of the kidneys is to maintain the
appropriate water–salt balance of the blood.
B) Maintenance of Acid–Base Balance.
The kidneys regulate the acid–base balance of the blood.
For a person to remain healthy, the blood pH should be just
about 7.4. The kidneys monitor and help control blood pH
C) Secretion of Hormones
The kidneys assist the endocrine system in hormone
secretion. The kidneys release renin, an enzyme that
leads to aldosterone secretion
d) Excretion of Metabolic Wastes
The kidneys excrete metabolic wastes, notably nitrogenou
wastes. Urea is the primary nitrogenous end product of
metabolism in human beings

5. Kidney histology
Two bean shaped kidneys are attached to the posterior abdominal wall, one on
each side of the vertebral column.
The kidneys have a tough fibrous capsule (irregular dense connective tissue) for
protection. Otherwise they have very little connective tissue between the
nephrons.
The kidney has a granular cortex (outer region). It has this appearance because it
is full of ovoid filtration units.
And a medulla (inner region) which has a more striated appearance.The kidney is
organised into many lobes, organised in a pyramidal structure, where the outer
portion is made up of cortex, and the inner portion is made up of the medulla.

6. Ureters
Ureter:is a tube that carries urine from the kidney to the urinary bladder.
*There are two ureters.The upper half of the ureter is located in the abdomen and
the lower half is located in the pelvic area.
*The ureter is about 25 cm long in the average adult.
*The tube has thick walls composed of a fibrous, a muscular, and a mucus coat,
which are able to contract.

7. Histology
The wall of the ureter have 3 layers:
1- The outer layer: the fibrous coat.
2 - The middle layer: the muscular coat./ The main function of this layer is peristalsis to
……..push the urine.
3 - The inner layer (the mucosa): is transitional epithelium./This layer secretes mucus which
……. coats and protects the surface of the cells.
* smooth muscle layers in the walls contract to propel urine into the bladder.
* once urine has entered the bladder, it is prevented from flowing back into the ureters by small
valve.

8. The Urinary Bladder
● The urinary bladder stores urine
until it is expelled from the body.
● The bladder has three openings:
two for the ureters and one for
the urethra.
● The bladder wall is expandable.
● It is lined with mucosa of
transitional epithelium.

9. ● The muscularis layer of the urinary bladder has 3 layers of smooth muscle .

10. Kidney anatomy
● Renal Capsule – outer membrane that surrounds the kidney; it is thin but
tough and fibrous
● Renal Pelvis – basin-like area that collects urine from the nephrons, it
narrows into the upper end of the ureter
● Calyx – extension of the renal pelvis; they channel urine from the pyramids
to the renal pelvis
● Cortex – the outer region of the kidney; extensions of the cortical tissue,
contains about one million blood filtering nephrons
● Nephron – these are the filtration units in the kidneys

11. ● Medulla – inner region of the kidney contains 8-12 renal pyramids. The
pyramids empty into the calyx.
● Medullary pyramids – formed by the collecting ducts, inner part of the
kidney
● Ureter – collects filtrate and urine from renal pelvis and takes it to the
bladder for urination
● Renal Artery – branches off of the aorta bringing waste-filled blood into the
kidney for filtering in the nephrons; the renal artery is further subdivided into
several branches inside the kidney. Each minute, the kidneys receive 20% of
the blood pumped by the heart. Some arteries nourish the kidney cells
themselves.
● Renal Vein – removes the filtered blood from the kidneys to the inferior vena
cava

12. Anatomy of Kidney

13. Nephron
The nephron is the main functional unit of the
kidney which is responsible for filtering the blood
and concentrating the solution to produce urine.
● Types of Nephron :
1-Cortical nephron: Located entirely in the
cortex and includes most nephrons.
2-Juxtamedullary nephron:Found at the
margin of the cortex and medulla.

14. Nephron
There are two parts of a kidney nephron: the renal
corpuscle, and the renal tubule.
(1) Renal Corpuscle:
Each renal corpuscle consists of :
1- glomerulus: is a knot of capillaries
2-the glomerular capsule or Bowman’s capsule: a
cup shaped hollow structure that completely surrounds the
glomerulus like a well-worn baseball glove encloses a ball.
Glomerular filtration: Water and solutes smaller than
proteins are forced through the capillary walls and pores of
the glomerular capsule into the renal tubule.

15. Nephron
(2) Renal Tubule
They are the :
● proximal convoluted tubule
(PCT)-nearest the glomerulus; have
permeable cell membranes that reabsorb
glucose, amino acids, metabolites.
● The distal convoluted tubule
(DCT) – farthest from the glomerulus;
helps regular potassium excretion.

16. The collecting ducts:
Each of which receives urine from many nephrons, They deliver the final urine
product into the calyces and renal pelvis.
The nephron loop, or loop of Henle
Has an ascending and descending limb, these loops along with their blood
vessels and collecting tubes form the pyramids in the medulla.

17. The Process of Filtration.
The kidneys filter unwanted substances from the blood and produce urine to
excrete them. There are three main steps of urine formation:
● Glomerular filtration,
● Reabsorption,
● Secretion.

18. Glomerular filtration
● Glomerular filtration is the process by which the kidneys filter the blood,
removing excess wastes and fluids.
● Blood enters the kidney via the renal artery.It forms many afferent
arterioles, each of which delivers blood to an individual kidney
nephron.each consist of microscopic filter called glomerulus.
● The pressure of the blood inside the glomerulus is increased due to the
difference in diameter of the incoming and out-going arterioles
● The diameter of the afferent arteriole is greater than the diameter of the
efferent arteriole.

19. ● This increased blood pressure helps to force water,salts,glucose and urea from
the blood out of the glomerular capillaries.
● The components of blood are filtered based on their particle size.
● The water and salts forced out of the glomerular capillaries pass into the
Bowman's Capsule and are called the glomerular filtrate.
● The glomerular filtrate then passes from the renal corpuscle to the renal
tubule.

21. Reabsorption
Occurring more commonly within the nephron system than filtration, this is a form of
active transport which takes the useful substances for the body from the tubules and
places them back into the blood filled capillaries.
Within the PROXIMAL CONVOLUTED TUBULE reabsorption occurs when pH needs to be
maintained and bicarbonate ions are reabsorbed back into the bloodstream. Glucose,
Amino Acids and Potassium Ions are all beneficial for the body so they are actively
transported into the blood as well. Sodium and Chlorine Ions are also moved back into
the capillaries so that some salt regulation can occur. On the other end of the scale,
substances such as hydrogen ions and toxins are actively secreted from the blood into
the tubule.

22. Reabsorption
Within the LOOP OF HENLE, the descending limb allows for the reabsorption of water
through osmosis whereas the ascending limb allows for the passive and active transport
of salts such as sodium to move out of the tubules and be reabsorbed.
The DISTAL CONVOLUTED TUBULE is where the final adjustments are made to the
passing urine within the tubule systems. This is where highly selective reabsorption takes
place allowing for small adjustments to be made especially between the presence of
Potassium and Sodium.

23. Secretion
The third process by which the kidneys clean blood (regulating its composition and volume) is called
tubular secretion and involves substances being added to the tubular fluid. This removes excessive
quantities of certain dissolved substances from the body, and also maintains the blood at a normal
healthy pH (which is typically in the range pH 7.35 to pH 7.45).
The substances that are secreted into the tubular fluid (for removal from the body) include:
● Potassium ions (K+
),
● Hydrogen ions (H+
),
● Ammonium ions (NH4
+
),
● creatinine,
● urea,
● some hormones, and
● some drugs (e.g. penicillin).

24. Tubular secretion occurs from the epithelial cells that line the renal tubules and collecting
ducts.
It is the tubular secretion of H+
and NH4
+
from the blood into the tubular fluid (i.e. urine -
which is then excreted from the body via the ureter, bladder, and urethra) that helps to
keep blood pH at its normal level. The movement of these ions also helps to conserve
sodium bicarbonate (NaHCO3
).
The typical pH of urine is about 6.
Urine formed via the three processes outlined above trickles into the kidney pelvis. At this
final stage it is only approx. 1% of the originally filtered volume but includes high
concentrations of urea and creatinine, and variable concentrations of ions.
The typical volume of urine produced by an average adult is around 1.5 - 2.0 dm3
per
day.

25. Relationship between urinary system and other
systems
Nervous System:
◄ Kidneys dispose of nitrogenous wastes;maintain fluid,electrolyte, and acid-base balance of blood;
renal regulation of Na+, K+, and Ca2+ content in ECF essential for normal neural function
◄ Neural controls involved in micturition;sympathetic nervous system activity triggers the
renin-angiotensin mechanism
Endocrine System
◄ Kidneys dispose of nitrogenous wastes; maintain fluid, electrolyte, and acid-base balance of blood;
produce the hormone erythropoietin; renal regulation of Na+ and water balance essential for blood
pressure homeostasis and hormone transport in the blood
◄ ADH, aldosterone, ANP, and other hormones help regulate renal reabsorption of water and electrolytes

26. Relationship between urinary system and other
systems
Respiratory System
◄ Kidneys dispose of nitrogenous wastes; maintain fluid, electrolyte, and acid-base balance of blood
◄ Respiratory system provides oxygen required by kidney cells; disposes of carbon dioxide; cells in
the lungs convert angiotensin I to angiotensin II
Lymphatic System/Immunity
◄ Kidneys dispose of nitrogenous wastes; maintain fluid, electrolyte, and acid-base balance of blood
◄ By returning leaked plasma fluid to cardiovascular system, lymphatic vessels help maintain
normal systemic blood pressure needed for kidney function; immune cells protect urinary organs
from infection, cancer,and other foreign substances

27. Relationship between urinary system and other systems
Cardiovascular System
◄ Kidneys dispose of nitrogenous wastes; maintain fluid, electrolyte, and acid-base balance of blood; renal
regulation of Na+ and water balance essential for blood pressure homeostasis. Na+, K+, and Ca2+
regulation help maintain normal heart function
◄ Systemic arterial blood pressure is the driving force for glomerular filtration; heart secretes atrial
natriuretic peptide; blood vessels transport nutrients, oxygen, etc. to urinary organs
Digestive System
◄ Kidneys dispose of nitrogenous wastes; maintain fluid, electrolyte, and acid-base balance of blood; also,
metabolize vitamin D to the active form needed for calcium absorption
◄ Digestive organs provide nutrients needed for kidney cell health; liver synthesizes most urea, a
nitrogenous waste that must be excreted by the kidneys
Reproductive System
• Kidneys dispose of nitrogenous wastes ;maintain fluid, electrolyte, and acid-base balance of blood

28. Relationship between urinary system and other
systems
Muscular System
◄ Muscles of pelvic diaphragm and external urethral sphincter function in voluntary control of micturition;
creatinine is a nitrogenous waste product of muscle metabolism that must be excreted by the kidneys
Integumentary System
◄ Kidneys dispose of nitrogenous wastes; maintain fluid, electrolyte, and acid-base balance of blood
◄ Skin provides external protective barrier; serves as site for vitamin D synthesis and water loss (via
perspiration)
Skeletal System
◄ Kidneys dispose of nitrogenous wastes; maintain fluid, electrolyte, and acid-base balance of blood
◄ Bones of rib cage provide some protection to kidneys

29. Urinary Tract Infections (UTI)
● The UTIs occur mainly in women and affect the bladder and urethra. A woman has a
shorter urethra than a man does, which shortens the distance that bacteria must
travel to reach the bladder.
● Infection of the bladder is cystitis. Escherichia coli by far is the most common
pathogen of UTIs. Most common symptoms include dysuria, frequent urination,
hematuria and lower abdominal pain.
● Infection of the urethra is urethritis. Because the female urethra is close to the
vagina, sexually transmitted infections, such as herpes, gonorrhea, chlamydia and
mycoplasma, can cause urethritis. The main symptom of urethritis is dysuria.

30. ● The infection of kidneys is called pyelonephritis. The causative agents of pyelonephritis
are similar to those of cystitis, with E.coli accounting for more than 75% of the
infections. Catheterization can also cause pyelonephritis. Symptoms of pyelonephritis
are lower back or abdominal pain, fever, sweat, headache, vomiting and malaise and
often include symptoms of cystitis.

31. Benign Prostatic Hyperplasia
➔ It is the enlargement of the prostate gland
➔ The prostate gland surrounds the urethra, the tube that carries urine from the
bladder out of the body. As the prostate gets bigger, it may squeeze or partly block
the urethra. This often causes problems with urinating.
➔ As prostate compresses the urethra the bladder cannot force itself to empty
completely.
➔ The prostate gland continues to grown throughout a man’s life. Hence BPH is
common in aging men. Up to 90% of men over age 80 have BPH.
➔ Its symptoms include:
◆ Nocturia
◆ Frequent urination
◆ Urinary retention
(Also known as Benign prostatic Hypertrophy)

32. References :
Books:
◆ Essentials of Human Anatomy Physiology - Marieb, Elaine N. chapter 16 page534. , 516 .
◆ Human biology Mader/Windelspecht 14 edition ,chapter 11 , page 218
◆ Essentials of Human Anatomy Physiology - Marieb, Elaine N. chapter 15 page520 .

33. References :
Wibesites:
● http://www.healthhype.com/nephron-glomerulus-and-tubule-structure-diag
ram-functions.html