Week 12 (The Kidney)

Question 1

Organs in the Urinary System

Answer 1

2 Kidneys

2 Ureters

Urinary Bladder

Urethra

Question 2

Functions of the Urinary System (Excretory System)

Answer 2

Excretion: Removal of metabolic wastes

Elimination: Discharge via urination (micturition)

Homeostatic Regulation:
Blood volume and pressure
Plasma ion concentration
Extracellular fluid volume and osmolarity
Acid-base balance
Nutrient conservation
Assists the liver in detoxification

Question 3

The Kidney

Answer 3

Produces urine

Excretes metabolic waste

Homeostatic regulation

Question 4

Ureter

Answer 4

Tubular structure transporting urine from kidneys to bladder

Question 5

Urinary Bladder

Answer 5

Muscular sac for temporary urine storage

Smooth muscle contraction expels urine

Question 6

Urethra

Answer 6

Exit tube for urine

Note: Shorter in females than in males

Question 7

THE KIDNEY OVERVIEW

Answer 7

Primary excretory organ

Bean-shaped

Excellent blood supply

0.5–1% of body weight

Receives 20–25% of cardiac output

Question 8

Three Regions of the Kidney

Answer 8

Renal Cortex

Renal Medulla

Renal Pelvis

Contains nephrons (structural & functional units)

Question 9

Excretory Functions

Answer 9

Filters blood

Removes nitrogenous wastes (urea, uric acid, creatinine, ammonia)

Eliminates drugs and toxins

Question 10

Homeostatic Functions

Answer 10

Regulates:

Blood volume
Ion concentration (Na⁺, K⁺, Cl⁻, Ca²⁺, PO₄³⁻)
Extracellular fluid volume and osmolarity
Blood pressure (via renin and water volume)
Plasma pH (acid-base balance)

Conserves valuable nutrients

Assists liver in detoxification

Other Functions:
Produces hormones and enzymes:
Erythropoietin: Stimulates red blood cell production
Renin: Regulates fluid balance and blood pressure
Gluconeogenesis: Glucose from amino acids
Converts vitamin D to calcitriol for calcium absorption
Hormone degradation

Question 11

THE NEPHRON

Answer 11

Microscopic structure (1.25 million per kidney)

Starts in renal cortex; loops into medulla

Question 12

Functional Processes of the Nephron

Answer 12

Glomerular filtration

Tubular reabsorption

Tubular secretion

Question 13

Types of Nephrons

Answer 13

Cortical Nephron (85%): Short loop of Henle

Juxtamedullary Nephron (15%): Long loop deep into medulla

Question 14

Nephron Structure

Answer 14

1. Renal Corpuscle (Malpighian Corpuscle):

Glomerulus: Filters blood

Glomerular (Bowman’s) Capsule: Receives filtrate

2. Renal Tubule:

Proximal Convoluted Tubule:
Reabsorbs ions, glucose, vitamins, water

Nephron Loop (Loop of Henle):
Descending limb: Reabsorbs water
Ascending limb: Reabsorbs ions

Distal Convoluted Tubule:
Adjusts fluid by absorption/secretion
Reabsorbs water and sodium
Secretes acids, drugs, ammonia

Question 15

Collecting Duct

Answer 15

Transports tubular fluid

Reabsorbs water

Secretes or reabsorbs ions (Na⁺, K⁺, HCO₃⁻, H⁺)

Question 16

Papillary Duct

Answer 16

Collects from multiple ducts

Delivers to minor calyx (now termed urine)

Question 17

Glomerular Filtration

Answer 17

Passive process

Blood pressure forces substances through filtration membrane

Produces filtrate (water, ions, glucose, vitamins, metabolic wastes)

Excludes: Large proteins and blood cells

Question 18

GFR (Glomerular Filtration Rate)

Answer 18

Normal: 90–120 mL/min

Average: 125 mL/min (180 L/day)

Question 19

Tubular Reabsorption

Answer 19

Reclaims 99% of filtrate into blood

Main sites:
Proximal Tubule: 67%
Loop of Henle: 20%
Distal Tubule + Collecting Duct: 12%

Influenced by hormones (ADH, aldosterone)

Question 20

Tubular Secretion

Answer 20

Substances move from plasma → tubule

Sites: Proximal tubule, distal tubule, collecting duct

Substances: K⁺, H⁺, urea, creatinine, drugs, toxins

Question 21

Urine Output

Answer 21

Rate: ~1 mL/min

Daily Output: ~1.5 L/day