🔵 14.1 HUMAN URINARY SYSTEM
🟢 Introduction
The urinary or excretory system is responsible for excretion.
In biological terms, excretion is the process by which an organism eliminates the metabolic wastes.
The metabolic wastes include nitrogenous wastes, extra water, and extra salts etc.
The urinary system performs three essential roles simultaneously:
- Nitrogenous Waste Removal: Filtering out urea (a nitrogenous waste of protein breakdown in the liver).
- Osmoregulation: Maintaining the “water-to-salt” balance of the blood by adjusting how much water is reabsorbed or excreted.
- pH and Ion Regulation: Balancing levels of sodium, potassium, and hydrogen ions to keep blood slightly basic (around pH 7.4).
🟣 Organs of the Human Urinary System
The human urinary system consists of:
- Two kidneys
- Two ureters
- One urinary bladder
- One urethra
Location of Kidneys Kidneys are located high in the abdominal cavity, one on each side of the vertebral column, between the 12th thoracic and 3rd lumbar vertebrae. Due to the position of the liver, the right kidney is slightly lower and smaller than the left one. The upper parts of both kidneys are partially protected by the 11th and 12th ribs.
Ureters Ureters are about 25 cm long tubes. A ureter begins at the funnel-shaped renal pelvis in the kidney. Ureters from both kidneys extend downward and open into a single urinary bladder. They transport urine from the kidney to the urinary bladder.
Urinary Bladder It is a hollow and distensible (can stretch) muscular organ located within the pelvic cavity. It serves as a urine reservoir.
Urethra It is a tube that carries urine from the urinary bladder to the outside of the body.
Figure 14.1 – Human Excretory (Urinary) System Caption: The human urinary system consists of two kidneys, two ureters, one urinary bladder and one urethra. Attribution: Healthdirect / educational medical resources.
🔴 14.1.1 Structure of Kidney
A kidney is a reddish-brown, bean-shaped organ. Each kidney has an adrenal gland on its top. The kidney and its adrenal gland are surrounded by a fibrous renal capsule.
Each kidney has a convex and a concave side. A depressed area on the concave side is the renal hilum (also called hilus). At this point, the renal artery enters the kidney and the renal vein and ureter leave.
Internal Structure of Kidney
Internally, a kidney consists of two main portions:
- Renal Cortex (outer portion) – makes up about one-third of the kidney’s mass.
- Renal Medulla (inner portion) – makes up about two-thirds of the kidney.
The renal pelvis is a funnel-shaped structure in the centre of the kidney. Blood enters the kidney through a renal artery and leaves through a renal vein.
The renal medulla consists of a number of cone-shaped renal pyramids. Urine is collected in the renal pelvis and exits the kidney through the ureter.
Figure 14.2 – Internal Structure of Kidney Caption: Longitudinal section of the kidney showing cortex, medulla, pyramids, pelvis and hilum. Attribution: Lumen Learning / Anatomy & Physiology.
🔵 Structure of Nephron
Each kidney contains about one million microscopic tubular structures called nephrons. These are the functional units of the kidney.
A nephron consists of two main portions:
1. Renal Corpuscle Consists of two associated structures: (i) Glomerulus – a capillary network derived from an afferent renal arteriole. (ii) Bowman’s capsule – a cup-shaped, double-walled sac that surrounds the glomerulus.
2. Renal Tubule A long tubule that leads away from the Bowman’s capsule. It consists of three connected portions:
(i) Proximal Convoluted Tubule – the beginning portion; highly coiled. (ii) Loop of Henle – a U-shaped hairpin turn. It has two limbs: - Descending limb (goes toward medulla) - Ascending limb (returns toward cortex) (iii) Distal Convoluted Tubule – highly coiled again.
The distal convoluted tubules of multiple nephrons drain into a single collecting duct. As these ducts descend through the medulla, they merge to form larger papillary ducts, which ultimately discharge into the renal pelvis.
Types of Nephrons
Nephrons are categorized into two types based on their location:
(i) Cortical Nephrons (about 85%) Located primarily within the renal cortex. They possess relatively short loops of Henle.
(ii) Juxtamedullary Nephrons Originate deep in the cortex, near the medulla. They have long loops of Henle that extend deep into the renal medulla.
Figure 14.3 – Structure of Nephron Caption: Detailed structure of a nephron showing renal corpuscle and renal tubule with all parts labelled. Attribution: Encyclopaedia Britannica / educational resources.
⭐ Board Exam Tips
Frequently Asked Short Questions ✅ Outline the organs of the human urinary system. ✅ Describe the structure of the kidney. ✅ Explain the structure of a nephron. ✅ Differentiate between cortical and juxtamedullary nephrons.
Frequently Asked MCQs ✔ Functional unit of kidney is → Nephron ✔ Number of nephrons in each kidney ≈ → One million ✔ Outer portion of kidney is → Cortex ✔ Cup-shaped structure surrounding glomerulus is → Bowman’s capsule
📌 Quick Revision
✔ Urinary system = 2 kidneys + 2 ureters + 1 bladder + 1 urethra ✔ Kidney is bean-shaped and has cortex + medulla ✔ Nephron is the functional unit ✔ Nephron = Renal corpuscle + Renal tubule ✔ Two types of nephrons: Cortical (85%) and Juxtamedullary
30 MCQs – Human Urinary System
1. The functional unit of the kidney is: A) Neuron B) Nephron C) Neuron + Nephron D) Glomerulus Ans: B 2. Number of nephrons in each human kidney is approximately: A) 1 thousand B) 1 lakh C) 1 million D) 10 million Ans: C 3. The outer portion of the kidney is called: A) Medulla B) Cortex C) Pelvis D) Hilum Ans: B 4. The inner portion of the kidney is called: A) Cortex B) Medulla C) Capsule D) Hilum Ans: B 5. The cup-shaped structure that surrounds the glomerulus is: A) Loop of Henle B) Bowman’s capsule C) Proximal tubule D) Distal tubule Ans: B 6. Glomerulus is a network of: A) Veins B) Capillaries C) Arteries D) Lymph vessels Ans: B 7. Which part of nephron is U-shaped? A) Proximal tubule B) Distal tubule C) Loop of Henle D) Collecting duct Ans: C 8. Majority of nephrons (about 85%) are: A) Juxtamedullary B) Cortical C) Medullary D) Both equal Ans: B 9. Long loops of Henle are present in: A) Cortical nephrons B) Juxtamedullary nephrons C) Both D) None Ans: B 10. The depressed area on the concave side of kidney is: A) Cortex B) Medulla C) Hilum D) Pelvis Ans: C 11. Urine is collected in the: A) Cortex B) Medulla C) Renal pelvis D) Capsule Ans: C 12. Which organ stores urine? A) Kidney B) Ureter C) Urinary bladder D) Urethra Ans: C 13. Ureters carry urine from: A) Bladder to outside B) Kidney to bladder C) Bladder to kidney D) Kidney to urethra Ans: B 14. The tube that carries urine outside the body is: A) Ureter B) Urethra C) Renal pelvis D) Collecting duct Ans: B 15. Right kidney is slightly lower than left because of: A) Heart B) Liver C) Stomach D) Spleen Ans: B 16. Renal artery enters the kidney at: A) Cortex B) Medulla C) Hilum D) Pelvis Ans: C 17. Cone-shaped structures in medulla are called: A) Columns B) Pyramids C) Calyces D) Lobes Ans: B 18. Proximal convoluted tubule is: A) Straight B) Highly coiled C) U-shaped D) None Ans: B 19. Distal convoluted tubules open into: A) Bowman’s capsule B) Loop of Henle C) Collecting duct D) Glomerulus Ans: C 20. Each kidney is covered by a fibrous: A) Capsule B) Membrane C) Sheath D) Layer Ans: A 21. Adrenal gland is present on: A) Bottom of kidney B) Top of kidney C) Side of kidney D) Inside kidney Ans: B 22. The process of elimination of metabolic wastes is called: A) Digestion B) Excretion C) Secretion D) Absorption Ans: B 23. Main nitrogenous waste filtered by kidney is: A) Ammonia B) Urea C) Uric acid D) Creatinine Ans: B 24. Which is NOT a part of renal corpuscle? A) Glomerulus B) Bowman’s capsule C) Loop of Henle D) Both A and B Ans: C 25. Length of ureter is approximately: A) 10 cm B) 25 cm C) 50 cm D) 100 cm Ans: B 26. Urinary bladder is located in: A) Abdominal cavity B) Thoracic cavity C) Pelvic cavity D) Cranial cavity Ans: C 27. Blood leaves the kidney through: A) Renal artery B) Renal vein C) Ureter D) Aorta Ans: B 28. Collecting ducts ultimately open into: A) Cortex B) Medulla C) Renal pelvis D) Urethra Ans: C 29. Which nephrons help more in concentrating urine? A) Cortical B) Juxtamedullary C) Both equally D) None Ans: B 30. Human urinary system consists of: A) 2 kidneys + 2 ureters + 1 bladder + 1 urethra B) 1 kidney + 2 ureters + 1 bladder + 1 urethra C) 2 kidneys + 1 ureter + 1 bladder + 1 urethra D) 2 kidneys + 2 ureters + 2 bladders + 1 urethra Ans: A
FAQ (Compact)
Q1. What is the urinary system? The system responsible for excretion of metabolic wastes, osmoregulation and pH balance. It consists of two kidneys, two ureters, one urinary bladder and one urethra.
Q2. What is a nephron? Nephron is the structural and functional unit of the kidney. Each kidney has about one million nephrons.
Q3. Name the two main parts of a nephron.
- Renal corpuscle (Glomerulus + Bowman’s capsule)
- Renal tubule (Proximal convoluted tubule + Loop of Henle + Distal convoluted tubule)
Q4. Differentiate between cortical and juxtamedullary nephrons.
- Cortical nephrons (85%): Located mainly in cortex, short loops of Henle.
- Juxtamedullary nephrons: Located near medulla, long loops of Henle that go deep into medulla.
Q5. What is the function of renal pelvis? It is a funnel-shaped structure that collects urine from the collecting ducts and passes it into the ureter.
Q6. Why is the right kidney slightly lower than the left? Because of the position of the liver on the right side.
Q7. What is hilum of kidney? It is the depressed area on the concave side of the kidney where renal artery enters and renal vein + ureter leave.
Q8. Write the path of urine from kidney to outside. Kidney → Ureter → Urinary bladder → Urethra → Outside
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