D3. Exretory System

Question 1

Excretion

Answer 1

• Process of removing waste and excess water from the body
• One of the major ways the body maintains homeostasis

Question 2

Key Organs Involved in Excretion

Answer 2

• Kidneys (filter blood and produce urine)
• Lungs (expel CO₂ during respiration)
• Skin (sweating)
• Liver (excretion of certain metabolic products)

Question 3

Principle Organs of the Excretory System

Kidney

Answer 3

• Main organ of the excretory system
• Excretes waste products and regulates water and salt balance

Question 4

Principle Organs of the Excretory System

Ureter

Answer 4

Tube extending from each kidney that carries urine to the urinary bladder

Question 5

Principle Organs of the Excretory System

Urinary Bladder

Answer 5

Sac that stores urine until it is eliminated from the body

Question 6

Principle Organs of the Excretory System

Urethra

Answer 6

Tube leading from the urinary bladder through which urine exits the body

Question 7

Functions of the Excretory System

Answer 7

• Filtration of blood (remove waste and extra stuff)
• Balancing water and minerals (like sodium and potassium)
• Blood pressure regulation
• Balanced blood pH
• Makes blood cells (produces a hormone that tells your body to make red blood cells)
• Getting rid of waste (like urea and creatinine)
• Helping with detoxicification (help get rid of drugs/toxins)
• Small part in regulating blood sugar by managing how much glucose is kept or released

Question 8

Urine

Answer 8

Liquid waste product produced by the kidneys through the filtration of blood

Question 9

Urine Composition

Answer 9

• Water ~95%
• Urea
• Creatinine
• Uric Acid

Question 10

Urea

Answer 10

A nitrogenous waste product resulting from the breakdown of proteins

Question 11

Creatinine

Answer 11

A waste product from muscle metabolism

Question 12

Uric Acid

Answer 12

Formed during the breakdown of DNA and RNA

Question 13

Importance of Urea Formation

Nitrogen Elimination

Answer 13

Urea is a non-toxic compound that carries excess nitrogen, a by-product of protein breakdown, out of the body

Question 14

Importance of Urea Formation

Prevents toxicity

Answer 14

Ammonia, an intermediate in deamination, is toxic to cells. Converting it to urea in the liver prevents harmful effects on cellular function

Question 15

Importance of Urea Formation

Safe Excretion

Answer 15

Urea can be safely transported in the bloodstream to the kidneys for excretion in urine, efficiently eliminating nitrogen waste

Question 16

The Kidney

Answer 16

• About the size of your clenched fist
• The Cortex - outer layer
• The Medulla - inner layer
• Covered by a layer of connective tissue called the capsule
• The pelvis recieves urine from the collecting ducts and funnels it to the ureter

Question 17

The Kidney

Renal Artery

Answer 17

Oxygenated blood from the heart is transported to the kidneys through the renal artery

Question 18

The Kidney

Renal Vein

Answer 18

Dexoygenated blood is carried away from the kidney through the renal veins, returning to the circulatory system

Question 19

The Formation of Urine

Filtration

Answer 19

Mass movement of water and solutes from blood into the renal tubule

Question 20

The Formation of Urine

Reabsorption

Answer 20

Movement of water and essential solutes from the tubule back into the blood

Question 21

The Formation of Urine

Secretion

Answer 21

Movement of materials from capillary back to the tubule

Question 22

Glomerulus

Answer 22

A network of capillaries surrounded by a cuplike structure, Bowman’s capsule

Question 23

Flow Through a Nephron

Part A: Blood Filtration

Answer 23

1. Blood enters the glomerulus through the afferent arteriole

• Blood pressure pushes water and dissolved solutes from the capillary into Bowman’s capsule
• The filtration membrane is selectively permeable, blocking plasma proteins, erythrocytes and platelets from passing through, thus remaining in the blood

2. Fluid in the Bowman’s capsule is now called filtrate
3. What isn’f filtered out - moves out the glomerulus into the efferent arteriole

Question 24

Flow Through a Nephron

Part B: Reabsorption in the Proximal Tube

Answer 24

• The proximal convoluted tubule is the tubule that is neartest to the glomerulus
• Selective reabsorption by both active and passive transport occurs
• Sodium ions are actively reabsorbed
• Cl^- and HCO₃^- follow by electrostatic attraction
• Stops when threshhold is reached
• Glucose/amino acids are actively reabsorbed
• Solutes and proteins in the blood create an osmotic pressure that pulls water back into the blood
• Concentrates solutes in the nephron
• Some uric acid and urea returns to the blood

Question 25

Reabsorption

Answer 25

* Process that moves solutes and water out of the filtrate and back into your bloodstream * They are "reabsorbed" because the first time they were absorbed was when they went into your bloodstream via the digestive tract after your meal

Question 26

# Flow Through a Nephron Part B: Loop of Henle - Descending Limb

Answer 26

* Reabsorption of water by osmosis (lots of aquaporins) * High osmotic pressure in medulla forces water out * Membrane permeable to water but not to salt or other small solutes * No sodium channels to transport sodium out * Filtrate becomes highly concentrated

Question 27

# Flow Through a Nephron Part B: Loop of Henle - Ascending Limb

Answer 27

* Membrane permeable to salt but not water * Thin segment - NaCl diffuses out * Thick segment - NaCl reabsorbed

Question 28

# Flow Through a Nephron Part C: Secretion in Distal convoluted tubule

Answer 28

* Occurs along the distal tubule by active transport * Nitrogen wastes, histamines, excess H⁺, and mineral levels are balanced * The secreted ions combine with the remaining filtrate becomes urine

Question 29

# Flow Through a Nephron Part D: Water Reabsorption - Collecting Duct

Answer 29

* Water and urea may be reabsorbed (back into the blood) * Water reabsorption is controlled by hormones * If someone is dehydrated, more water must be reabsorbed back into the blood

Question 30

Kidneys and Blood pH

Answer 30

* The blood pH is maintained by acid-base buffer systems * The most important acid-base buffer system is bicarbonate-carbon dixoide buffer system: H⁺ + HCO₃^- ↔ H₂CO₃ ↔ H₂O + CO₂ * The kidneys help to maintain this balance by balancing H⁺ and HCO₃^- * If the blood is too acidic, H⁺ is excreted amd HCO₃^- is reabsorbed and returned to the blood

Question 31

Antidiuretic Hormone (ADH)

Answer 31

* Made in your hypothalamus and stored and releases from your pituitary gland * Helps regulate the water balance by controlling the amount of water your kidneys reabsorb * More ADH released when dehydrated, excess salt intake or losing blood pressure * Makes the collecting duct more permeable to water * Kidneys hold onto more water instead of releasing it in your urine

Question 32

Aldosterone

Answer 32

* Released from the adrenal glands in response to a drop in Na⁺ concentration, or an increase in potassium ions * Stimulates the distal tubule and collecting ducts to reabsorb Na⁺. The reabsorption of Na⁺ is followed by Cl^- and water, therefore has a net effect of retaining both salt and water * Also promotes the secretion of K⁺ into the tubule