This document provides an overview of the urinary system. It discusses the organs of the urinary system including the kidneys, ureters, urinary bladder and urethra. It describes the internal and external anatomy of the kidneys and nephrons. It explains the functions of the urinary system such as removal of waste, regulation of water, electrolytes and acid-base balance. It also discusses the blood supply of the kidneys and reviews key concepts about the urinary system.

1. URINARY SYSTEM
Dr Wairimu Mwaura

2. REVIEW QUESTIONS
1.List five functions of the respiratory system. (5
marks)
2.Which of the following parts of the respiratory
system produces sound for speech?
a.Oropharynx
b.Nasal cavity
c.Larynx
d.Trachea

3. OBJECTIVES
◦Organs of the urinary system
◦Functions of the urinary system
◦Kidney- parts and functions
◦Ureters
◦Urinary bladder
◦Urethra

4. ORGANS OF THE URINARY SYSTEM
◦2 Kidneys
◦2 Ureters
◦Bladder
◦Urethra

5. ORGANS OF THE URINARY SYSTEM
Primary organ is the kidney
i. Filters waste products from the blood stream
ii. Converts filtrate into urine
◦The urinary tract : transports urine out of the
body
- Includes the ureters, urethra and urinary bladder

8. FUNCTIONS OF THE URINARY SYSTEM
i. Removal of waste products from the body-
urea, uric acid
ii. Storage of urine- urinary bladder can store up
to 1 litre of urine
iii. Excretion of urine through the urethra
iv. Blood volume regulation
v. Regulation of acid base balance

9. FUNCTIONS OF THE URINARY SYSTEM
vi. Blood pressure maintenance- renin angiotensin
aldosterone system
vii.Regulation of electrolyte balance e.g. Na+, K+
viii.Regulation of erythrocyte production
-Erythropoietin stimulates red blood cell
production in the bone marrow
viii.Vitamin D production

10. EXTERNAL ANATOMY OF THE KIDNEYS
◦ Two bean shaped organs that lie on either side of the spine
◦ Located in the retroperitoneal space
-Anterior surface covered by the peritoneum
-Posterior surface is against the posterior abdominal wall
◦ Left kidney T12-L3 vertebrae
◦ Right kidney is 2cm lower due to displacement by the liver
◦ Upper portions of the kidneys are protected by the 11th and 12th
ribs
◦ Adrenal glands are found at the superior pole

11. EXTERNAL ANATOMY OF THE KIDNEYS
◦Hilum- found medially, on the convex indentation of the
kidney
-Is the passage way for blood vessels, nerves, lymphatics
and ureters
The layers that surround the kidneys include:
i. Renal capsule- dense connective tissue that helps the
kidneys maintain their shape and protects them
ii. Renal fat pad- protection
iii. Renal fascia- anchors the kidney to the posterior
abdominal wall

12. INTERNAL ANATOMY OF THE KIDNEYS
◦Divided into an outer region called the renal cortex and an
inner region called the renal medulla
◦The medulla contains 5-18 renal pyramids that are
separated by renal columns
◦Each pyramid synthesizes urine and terminates into a renal
papilla
◦Renal papilla drains into a minor calyx
◦Several minor calyxes connect to form a major calyx
◦All major calyxes drain into the renal pelvis which connects
to the ureter

13. INTERNAL ANATOMY OF THE KIDNEY

14. THE NEPHRON
◦Structural and functional unit of the kidney.
◦Each nephron consists of a blood supply and a
specialised network of ducts called a tubule.
◦Average number is 1 million nephrons per kidney.

15. THE NEPHRON
◦Parts of the nephron:
i. Renal corpuscle: glomerulus within the Bowman’s
capsule
ii. Renal tubule:
-Proximal convoluted tubule
-Descending limb, loop and ascending loop of Henle
-Distal convoluted tubule
iii. Collecting ducts

16. THE NEPHRON

17. THE NEPHRON
◦ All nephron glomeruli are found in the renal cortex
◦ Cortical nephrons- have short loops of Henle
- Penetrate only the outer renal medulla
- 85% of all nephrons in the human body
- Perform the excretory and regulatory functions of the kidney
Juxtamedullary nephrons: have long loops of Henle
- Extend deep into the medulla
- 15% of all nephrons
- Concentrate or dilute urine

18. CORTICAL VS JUXTAMEDULLARY

19. BLOOD SUPPLY OF THE KIDNEYS
◦Kidneys receive 20-25% of the cardiac output
◦Renal arteries: 1200 ml of blood per minute

20. FUNCTIONS OF THE KIDNEY
i. Regulating Acid base balance- through absorption/ secretion
of H+ AND HCO3
-
ii. Regulating Water balance- the kidney ensures that there is
an adequate supply of plasma to keep blood flowing to vital
organs
iii. Maintaining Electrolyte balance
iv. Removes Toxins and waste products from the body
v. Controlling Blood pressure through the RAAS
vi. Produces the hormone Erythropoietin
vii. Activating vitamin D

39. URETERS
◦Long fibromuscular tubes, 25 cm in length
◦Retroperitoneal
◦Originate at the renal pelvis
◦Extend inferiorly to enter the posterolateral wall
of the base of the urinary bladder
◦Function: transport urine from the kidneys to the
urinary bladder

40. URINARY BLADDER
◦Expandable muscle container
◦Serves as reservoir for urine
◦Located posterior to the pubic symphysis
◦Trigone :triangular area of the urinary bladder
wall
-Connects the two ureteral openings and the
urethral opening
-Functions as a funnel that directs urine into the
urethra as the bladder wall contracts

41. URINARY BLADDER
Detrusor muscle – 3 layered smooth muscle
Internal urethral sphincter – made up of smooth
muscle
-Involuntary control
-Controlled by the autonomic nervous system
External urethral sphincter- skeletal muscle
-Voluntary control
-The muscle children learn to control when they are
toilet trained

42. URINARY BLADDER
Bladder capacity is 400-600ml
At 200-400ml we become conscious of the need to urinate
-Stretch receptors initiate micturition reflex.
-Micturition is the action of urination.
◦ During micturition:
◦ Detrusor muscle contracts
◦ Muscles of pelvic floor and abdominal wall contract
◦ External urinary sphincter relaxes and urine moves from bladder to the
outside

43. URINARY BLADDER

44. URETHRA
◦Fibromuscular tube
◦Conducts urine to the exterior of the body
◦Has two sphincters: internal and external
◦Female urethra: 3-5 cm long
-The external urethral orifice is located in the
anterior vaginal wall, between the clitoris and the
vaginal opening

45. FEMALE URETHRA

46. URETHRA
◦Male urethra: passageway for both urine and semen
◦Approximately 18-20 cm long
◦Has 3 segments:
i. Prostatic urethra : 3-4 cm long
ii. Membranous urethra- shortest portion
iii. Spongy/penile urethra: longest part,15 cm
-Encased within a cylinder of erectile tissue known as
the corpus spongiosum
-Extends to the external urethral orifice

47. MALE URETHRA

48. REVIEW QUESTIONS
1. The right kidney is slightly lower than the left
kidney because?
a. It is slightly smaller
b. It is displaced by the liver
c. It is displaced by the heart
d. It needs protection of the lower ribs

49. REVIEW QUESTIONS
2. The renal pyramids are separated from each
other by extensions of the renal cortex called?
a. Medullary cortices
b. Renal columns
c. Renal medulla
d. Minor calyces

50. THANK YOU