week 8: how do you get rid of toxic waste? introduction to the renal system

structure is known as the 'functional unit of the kidney'?

the nephron

Which one of the following substances would you expect to find in the filtrate of a healthy individual?

a. red blood cells

b. sodium ions

c. large proteins

d. white blood cells

b. sodium ions

What is the name of the muscle found in the wall of the bladder?

detrusor

Which hormone promotes water retention in the body?

anti-diuretic hormone

What is the name of the reflex that controls urination?

micturition

two parts of renal corpuscle

glomerulus and glomerular capsule

cortical nephrons

Cortical nephrons have a glomerulus located nearer to the outer parts of the cortex and their loops of Henle are short

juxtamedullary nephrons

Juxtamedullary nephrons have a glomerulus near the junction of the cortex and medulla and their loops of Henle penetrate deep into the medulla

The kidneys have a role in:

1. Eliminating wastes from the body, such as urea and creatinine.

2. Regulating the concentration of solute in the blood, e.g. by regulating how much Na+ , Cl- , K+ , Ca2+ are reabsorbed or secreted into urine.

3. Regulating blood volume and blood pressure, by controlling the amount of water we excrete.

4. Regulating the pH of body fluids, e.g. by regulating the amount of H+ secreted in urine.

5. Contributing to the synthesis of red blood cells.

6. Contributing to the synthesis of Vitamin D.

The parts of the nephron are:

• Renal corpuscle

• Proximal convoluted tubule (PCT)

• Loop of Henle

• Distal convoluted tubule (DCT)

Process of urine formation

1. Filtration - occurs in the renal corpuscle.

2. Tubular reabsorption - occurs in the PCT and DCT.

3. Tubular secretion - occurs in the DCT.

How is filtrate reabsorbed?

diffusion, facilitated diffusion, active transport, symport and osmosis.

Reabsorption from the filtrate is a two-step process:

1. Movement of the filtrate into the cells lining the nephron through the apical surface of the cell or the apical membrane.

2. Then from these cells into the blood through the basal surface of the cell or basal membrane.

Sodium-potassium exchange pump: Is this pump an active or passive transport mechanism?

active

Sodium-potassium exchange pump: Does the Na+ /K+ pump move Na+ ions up or down their concentration gradient?

Up or against its concentration gradient

Sodium-potassium exchange pump: Which direction are Na+ and K+ ions being pumped (i.e. from the inside to outside of the cell or vice versa)?

Na+ is pumped out of the cell

K+ is pumped into the cell

Co-transport: (symport): Which molecule is moving with Na+ ?

Glucose

Co-transport: (symport): Are they moving in the same direction or in opposite directions?

Same (sym = same)

Co-transport: (symport): Na+ is moving down its concentration gradient from high concentration outside the cell (in the filtrate) to low concentration inside the nephron cell. Is glucose molecule moving up or down its concentration gradient?

Glucose is moving up or against its concentration gradient. i.e. from low concentration in the filtrate to high concentration inside the nephron cell.

Co-transport: (symport): What form of membrane transport removes Na+ to prevent it accumulating inside the cell and to set up a high Na+ gradient outside the cell?

Na+/K+ pump

Anti-port / counter transport: Which molecule is moving with Na+ ?

Ca2+

Anti-port / counter transport: Are they moving in the same direction or in opposite directions?

Opposite (anti = opposite)

Anti-port / counter transport: Na+ is moving down its concentration gradient. Is the other molecule moving up or down its concentration gradient?

Ca2+ moves up or against its concentration gradient

Facilitated diffusion: Describe the structure and function of the special carrier molecule?

Protein imbedded in cell membrane with a central channel. It helps move molecules across the cell membrane.

Facilitated diffusion: Does this carrier molecule bind to many different molecules or is it specific?

Specific

Facilitated diffusion: Name two molecules that move across the cell membrane via facilitated diffusion?

Specific sugars (glucose) and amino acids. K+ also exits the nephron cell in this manner

Facilitated diffusion: Is facilitated diffusion moving the molecule up or down its concentration gradient?

Down its concentration gradient. From high to low concentration.

Facilitated diffusion: Is facilitated diffusion an active or passive process?

Diffusion is passive - it does not require energy (ATP).

Facilitated diffusion: Is the movement of these molecules via facilitated diffusion only in one direction across the membrane?

Can occur in either direction across membrane depending on concentration gradient, but the molecule always moves from high to low concentration

Facilitated diffusion: In the case of the nephron, is glucose moving from the filtrate to the blood, or from the blood to the filtrate (i.e. is it being re-absorbed or secreted?)

Glucose is in high concentration within the nephron cell (remember it came into the nephron cell with Na+ via symport).

Glucose is moving from the filtrate to the blood. It is being reabsorbed into the body where it will be used by cells to make ATP.

Osmosis: The solution with the higher concentrations of solutes is:

hypertonic

Osmosis: The solution with lower concentration of solutes is:

hypotonic

Can you think of anything in the blood that would not move across the dialysis membrane?

Cells in the blood (red blood cells and white blood cells), platelets and plasma proteins

The urinary system is the most important for excretion of wastes. What other forms of waste removal can the body perform?

The digestive system removes waste products from food, and sweating removes Na+, Cl- and urea (and some other metabolites) but these are minimal. Most waste excretion is performed by the kidneys.

The kidneys are not exactly aligned. Which kidney is displayed slightly inferiorly? Can you think of a reason for this? (Hint: what organ is above this kidney?)

The right kidney is slightly lower. The liver is on the right, and it displaces the right kidney so it is lies slightly lower than the left kidney

anterior to left kidney

Pancreas and colon

anterior to right kidney

duodenum and colon

What is the difference in colour between the medulla and cortex?

The cortex is lighter than the medulla. The pyramids in the medulla are a darker red

How many nephrons per kidney?

1.3 million nephrons in each kidney

Average length of a nephron?

50 - 55 mm long

What are the two layers of the glomerular capsule?

parietal layer and visceral layer

Fenestrae of capillaries

Holes in the endothelial cells of the glomerular capillaries

Basement membrane

Found in between the endothelial cells and the podocytes

Filtration slits

Spaces between the podocyte cell processes

Why may the presence of blood or large amounts of protein in the urine indicate damage to the filtration membrane in the renal corpuscle?

The filtration membrane needs to be intact to prevent large particles like RBCs, WBCs and plasma proteins passing through.

If any of these are present in the urine this suggests there is damage to the renal corpuscle

What effect do you think a large increase in systolic blood pressure would have on the filtration of fluid within the renal corpuscle?

Increased overall blood pressure will lead to an increase in the pressure of blood coming in to the glomerulus. Increased blood pressure in the glomerulus will increase how much fluid is filtered into the nephron

Proximal convoluted tubule

Main area for reabsorption of water (80%) 100% reabsorption of amino acids and sugars

Distal convoluted tubule

Controlled secretion of wastes, toxin, excess ions Alters concentration of urine by varying water reabsorption

Loop of Henle

Reabsorbs ions and water

The distal convoluted tubule is the last segment of the nephron. What is the name of the segment following the distal convoluted tubule?

Collecting duct

What would happen to the volume of urine if you drank a bottle of water (600ml) in an hour while you were studying?

Urine volume will increase as you are taking in more water than you are losing to the environment.

Coffee and alcohol are diuretics. What does this mean?

Diuretics make you pass more urine by affecting the amount of water reabsorbed by the kidneys. This means, drinking too much coffee or alcohol can make you dehydrated because you lose more water in urine than you take in. Dehydration contributes to the symptoms one may experience from drinking too much alcohol

What do you predict would happen to the volume of urine if a person had been stranded out at sea for 24 hours with no fresh water?

Decreased urine output, as the person would be dehydrated. Some urine would still be produced because the body still needs to secrete waste products that can only be done in solution.

What abdominopelvic regions are the kidneys in?

Right kidney - right lumbar; left kidney - left lumbar

What organs lie superior to each kidney?

Right kidney - liver; left kidney - stomach and pancreas

Which body cavity does the bladder lie within when it is empty?

Pelvic

The bladder is a hollow structure that stores urine. What volume of urine do you think the bladder usually holds?

At capacity the bladder can hold up to 1 L. On average, you may get the urge to urinate at approximately 500 mls

As the bladder fills it expands, do you think there may be a change in the body cavity location when the bladder is full?

It moves upwards and lies across the border of the abdominal and pelvic cavities

What is the name of the tube that transport urine from the kidney to the bladder?

Ureter

What is the role of the muscular layer in the bladder wall?

The muscle of the bladder contracts to help expel urine.

Renal capsule

connective tissue surrounding each kidney

Adipose tissue

surrounds the outside of the capsule for protection

Renal fascia

thin layer of connective tissue surrounds the adipose tissue; anchor kidneys to abdominal wall

Bowman Capsule:

enlarged end of the nephron, double walled chamber. Filters blood/fluid, which then enters the proximal convoluted tubule.

Pressure forces urine through nephron

Smooth muscle forces urine through ureters. Peristalsis moves urine from the renal pelvis in the kidneys -> ureters -> urinary bladder.