Biol-102: Urinary System

Front 1

What is the urinary system composed of?

Back 1

kidney, bladder, ureter (2), urethra

Front 2

Kidney function

Back 2

is to regulate plasma & interstitial fluid homeostatis by formation of urine

Front 3

In the process of urine formation, kidneys regulate:

Back 3

1. volume of blood plasma, which contributes to BP
2. waste products in blood
3. concentration of electrolytes (including Na⁺, K⁺, HCO₃⁻ & others
3. plasma pH

Front 4

If you have a high blood pressure you and decrease it by taking a(n) ____.

Back 4

antidiuretic

Front 5

Filtration (Glomerulus)

Back 5

fluid is pushed out of the plasma passing through the glomerular capillaries
- plasma proteins and cells are retained in the blood
- small particles pushed out into glomerular capsule and nephron tubules (relatively non-selective)

Front 6

What are some things that get filtered into the glomerulus?

Back 6

H₂O, glucose, amino acids, bicarbonate & electrolytes

Front 7

Glomerular Filtration Rate (GFR)

Back 7

rate at which fluid is pushed out of the glomeruls and into the nephron tubules
- volume of filtrate produced by both kidneys each minute

Front 8

What are the two forces that influence filtration?

Back 8

1. blood pressure in capillaries
- increased pressure drives fluid out of glomerulus
2. osmotic pressure
- pulls water back into capillaries

Front 9

What is the percentage of substances that are reabsorbed in the PCT?

Back 9

65%

Front 10

True/False: The PCT is under hormonal control.

Back 10

False

Front 11

What is the total of blood osmolarity?

Back 11

~ 300 mOsm

Front 12

What is the DCT & CD important for?

Back 12

fine tuning
- DCT & CD are under hormonal control
- an increase in Na+ and H2O reabsorbed is aldosterone

Front 13

More ADH makes the urine ___ dilute.

Back 13

less

More ADH makes the urine less dilute because ADH causes us to absorb more water. (urine is more concentrated)

Front 14

Less ADH makes the urine ___ dilute

Back 14

more

Less ADH makes the urine more dilute because ADH causes our bodies to not absorb water. (urine is less concentrated)

Front 15

Reabsorption

Back 15

-Of the 180L fluid filtered each day, only about ~1.5L of urine is excreted (can be as low as 400mL)
- most of the material in the filtrate is reabsorbed
- selective movement of substances from fluid in tubules to blood in the peritubular capillaries
- active or passive transport mechanisms used to drive reabsorption

Front 16

Secretion

Back 16

- also occurs in tubules
- addtional materials transported from plasma in peritubular capillaries into tubule
- excess K⁺, Ca⁺, and H⁺, uric acid
- foreign compounds (e.g., penicillin)
- typically driven by active carrier transport

Front 17

What are some other functions of the kidneys?

Back 17

1. secrete erythropoietin
2. secrete renin
3. activate vitamin D₃ to calcitrol
3. gluconeogenesis

Front 18

In a 24 hour period, how much H₂O is filtered from the blood to nephrons?

Back 18

~180L

Front 19

function: kidney

Back 19

produce urine

Front 20

function: ureters

Back 20

transfer urine to urinary bladder to pelvic region

Front 21

function: urinary bladder

Back 21

stores urine

Front 22

function: detrusor muscle

Back 22

• smooth muscle in wall of the urinary bladder
• generates action potentials in response to stretch and parasympathetic innervation

Front 23

internal urethral sphincter

Back 23

smooth muscle, involuntary

Front 24

external urethral sphincter

Back 24

skeletal muscle, voluntary

Front 25

function: urethra

Back 25

canal leading to exterior of the body

Front 26

Micturation

Back 26

• Stretch receptors in bladder wall relay signals to the micturition center
• activates parasympathetic neurons to smooth muscle
- induces detrusor contraction and internal sphincter relaxation
• conscious relaxation of external sphincter to enable urination

Front 27

How many nephrons are there per kidney?

Back 27

~ 1 million

Front 28

Why is the afferent arteriole larger than the efferent arteriole?

Back 28

the afferent arteriole puts more pressure in the glomerulus

Front 29

anatomy: cortex

Back 29

outer granular region

Front 30

anatomy: medulla

Back 30

• inner striated region
• subdivided into renal pyramids

Front 31

anatomy: renal pelvis

Back 31

• central collecting cavity
• branches into calyces that associate with each renal pyramid

Front 32

nephrons

Back 32

• urine-forming units of the kidney
• over one miller per kidney
• consist of nephron tubules and associate blood vessels

Front 33

glomerular (Bowman's) capsule

Back 33

• receives plasma filtrate
• located in renal cortex

Front 34

proximal convoluted tubule

Back 34

located in renal cortex

Front 35

loop of Henle

Back 35

• descending limb conducts fluid into medulla region
• ascending limb conducts fluid back to cortex
• upper regions have thicker walls (thick segment)

Front 36

distal convoluted tubule

Back 36

located in renal cortex

Front 37

collecting duct

Back 37

• received fluid from several different distal tubules in cortex
• conducts fluid through medulla
• empties into the calyces

Front 38

arteries (renal, arculate, interlobar)

Back 38

bring blood into kidney and distribute it to the nephrons

Front 39

afferent arteriole

Back 39

conducts blood into the glomerulus

Front 40

glomerulus

Back 40

bed of capillaries surrounded by glomerular capsule

Front 41

efferent arteriole

Back 41

conducts blood from glomerulus into peritubular capillaries

Front 42

peritubular capillaries

Back 42

surround tubules

Front 43

venules

Back 43

collect blood from peritubular capillaries

Front 44

veins (arcuate, interlobar, renal)

Back 44

collect blood from nephrons and conduct it out of the kidneys

Front 45

What are the three processes to convert blood plasma into urine?

Back 45

1. filtration
2. reabsorption
3. secretion

Front 46

What is filtration?

Back 46

filter blood plasma to retain cells/plasma

Front 47

What is reabsorption?

Back 47

remove valuable materials from filtrate

Front 48

What is secretion?

Back 48

transfer additional wastes to filtrate

Front 49

What is the structure of a glomerulus?

Back 49

• fenestrated capillaries (small pores (fenestrae) between endothelial cells
• glomerular basement membrane (plasma protein retention)
• three layers of podocytes form capillary walls
• slits between podocyte pedicels contain slit diaphragms (retain plasma proteins)

Front 50

Reabsorption in the Proximal Tubule
Na⁺

Back 50

• Na⁺ pumped from the tubule wall cells into the blood of the peritubular capillaries by Na⁺/K⁺ pumps
• creates gradient for Na⁺ to flow into the cells from the filtrate

Front 51

Reabsorption in the Proximal Tubule
Cl⁻

Back 51

moves passively out of filtrate, through cells, and into blood by the electrical gradient created by pumping Na⁺

Front 52

Reabsorption in the Proximal Tubule
Water

Back 52

flows from filtrate to blood because of osmotic gradient created by moving Na⁺ and Cl⁻ from the filtrate to the blood

Front 53

True/False: Filtered glucose and amino acids are normally reabsorbed by the nephrons.

Back 53

true

Front 54

Where to concentrating mechanisms occur?

Back 54

in the loop of Henle

Front 55

Kidneys produce a ____ urine.

Back 55

hypertonic
• more concentrated than blood plasma
• allow reduction of water loss via urination when dehydrated

Front 56

ascending limb

Back 56

• impermeable to water
• thick segment lined with Na⁺/K⁺ pumps

Front 57

descending limb

Back 57

• permeable to water
• no active transport

Front 58

______ forms loops that can absorb water

Back 58

Peritubular capillaries (vasa recta)

Front 59

Countercurrent multiplier system

Back 59

interactions between ascending limb and descending limb

Front 60

What is the percentage of original glomerular filtrate volume is reabsorbed by the loop of Henle?

Back 60

~ 20%

Front 61

Reabsorption in the Loop of Henle

Back 61

• pumping of ions out of thick segment of ascending limb creates osmotic gradient in interstitial fluid of the medulla (gradient amplified by urea being recycled between loop and collecting duct)
• water flows out of descending limb along this osmotic gradient
• water subsequently absorbed by vasa recta
• fluid in the tubule becomes more concentrated as it passed down the descending limb (~1400 mOsm at the turn of the loop)
• removal of ions from ascending limb while water is retained causes fluid to become less concentrated in the ascending limb
• fluid leaving the loop of Henle is hypotonic (~100 mOsm)

Front 62

Reabsorption in the Distal Tubule

Back 62

• some water and Na⁺ reabsorption
• water reabsorption variable depending on permeability of tubule walls

Front 63

Reabsorption in the Collecting Duct

Back 63

• conducts fluid through medulla
• strong osmotic gradients favor reabsorption of water out of duct
• water reabsorption variable depending on permeability of tubule walls
→ If permeable, small amount of concentrated urine produced
→ If impermeable, large amount of dilute urine produced
• Some Na⁺ reabsorption

Front 64

ADH regulation of water reabsorption

Back 64

• insertion of aquaporins into the plasma membrane of tubule cells
‣ ↑ permeability of distal tubule and collecting duct walls to water
‣ ↑ H₂O reabsorption = ↓ urine volume, ↑ urine concentration
• secreted by posterior pituitary in response to stimulation of osmoreceptors in hypothalamus

Front 65

Collecting Duct

Back 65

The walls of the CD have a variable permeability to H₂O.
• H₂O is drawn out of the CD by osmosis.
• Rate of osmotic movement is determined by the # of aquaporins (water channels) in the cell membrane.
• Permeable to H₂O depends upon the presence of ADH.
• ADH binds to its membrane receptors on CD, incorporating water channels into cell membrane.

Front 66

Stimulus: ↑ Osmolarity (dehydration)

Back 66

Receptors: Osmoreceptors in hypothalamus
Secretion of ADH: Increase
Effect of Urine Volume: Decreased
Effects on Blood: Increased water retention; decreased blood osmolarity

Front 67

Stimulus: ↓ Osmolarity

Back 67

Receptors: Osmoreceptors in hypothalamus
Secretion of ADH: Decrease
Effect of Urine Volume: Increased
Effects on Blood: Water loss increases blood osmolarity

Front 68

Stimulus: ↑ Blood Volume

Back 68

Receptors: Stretch receptors in left atrium
Secretion of ADH: Decrease
Effect of Urine Volume: Increased
Effects on Blood: Decreased blood volume

Front 69

Stimulus: ↓ Blood Volume

Back 69

Receptors: Stretch receptors in left atrium
Secretion of ADH: Increase
Effect of Urine Volume: Decreased
Effects on Blood: Increased blood volume

Front 70

Aldosterone Influences Na⁺ and Water Reabsorption, K⁺ Secretion

Back 70

• Aldosterone stimulates Na⁺ reabsorption and K⁺ secretion by the distal tubule and upper (cortical) collecting duct
• Elevated plasma K⁺ directly stimulates adrenal cortex to secrete aldosterone
• Low Na⁺ concentrations indirectly stimulate aldosterone secretion via the renin-angiotensin-aldosterone system

Front 71

Juxtaglomerular apparatus

Back 71

region of the afferent arteriole that comes in contact with ascending limb of Loop of Henle

Front 72

Renin-Angiotensin-Aldosterone System

Back 72

Release renin (enzyme) into blood in response to ↓ blood pressure
‣ low Na⁺ levels contribute to low blood pressure

Front 73

What does angiotensin II stimulate?

Back 73

stimulates aldosterone release from the adrenal cortex

Front 74

What are the causes of Diabetes Insipidus?

Back 74

1. drinking too much water
2. inadequate secretion of ADH
3. inadequate ADH action due to generic defect in the ADH receptors or aquaporin channels.

‣ Without adequate ADH secretion or action, the collecting ducts are not very permeable to water.