Bio 219: Urinary System (Part 1)

Front 1

Urinary System Overview

Back 1

• 2 kidneys
• 2 ureters
• urinary bladder
• urethra

Front 2

What do the kidney's produce?

Back 2

urine

Front 3

What is the function of the ureter?

Back 3

transport urine from kidneys to bladder

Front 4

What is the function of the urinary bladder?

Back 4

temporary storage for urine

Front 5

What is the function of the urethra?

Back 5

transports urine from the bladder out of the body

Front 6

What are the functions of the the kidney?

Back 6

1. filter blood
2. regulate blood volume and blood pressure
3. regulate plasma ion concentrations
4. help stabilize blood pH
5. endocrine function - erythropoietin (EPO)
6. activation of vitamin D

Front 7

What are the regions of the kidney?

Back 7

cortex, medulla and renal pelvis (ureter)

Front 8

What is the functional unit of the kidney?

Back 8

nephron

Front 9

Each nephron can be divided into:

Back 9

a renal tubule of renal corpuscle

Front 10

What is a renal tubule?

Back 10

long tubule beginning at the renal corpuscle that's consisted of three regions: proximal convoluted tubule (PCT), Loop of Henle, Distal convoluted tubule (DCT)

Front 11

What is a renal corpuscle?

Back 11

spherical structure = Bowman's capsule + glomerulus

Front 12

The glomerulus is the site of _____

Back 12

filtration

Front 13

Each nephron empties into the:

Back 13

collecting system

Front 14

What is the collecting system?

Back 14

series of tubes that carry fluid away from the nephron

Front 15

What is the collecting duct?

Back 15

receives fluid from many nephrons; begins at cortex, descend into medulla

Front 16

What is the papillary duct?

Back 16

receives fluid from collecting duct - drains into minor calyx

Front 17

The regions of the _____ & _____ vary in their structure and function/role in the production of urine

Back 17

nephron & collecting system

Front 18

What is filtration?

Back 18

blood & all of its contents (except proteins & RBCs) are filtered into a nephron

Front 19

What is reabsorption?

Back 19

H₂O & important ions/nutrients are reabsorbed back into blood

Front 20

What is secretion?

Back 20

additional "unwanted" solutes, acids, toxins, etc transported further into forming urine

Front 21

The renal corpuscle is the production of _____

Back 21

filtrate

Front 22

What is the Bowman's capsule?

Back 22

double layered bag that collects urinary filtrate

Front 23

What is the parietal epithelium?

Back 23

outer wall; simple squamous epithelium

Front 24

What is the visceral epithelium?

Back 24

covers glomerular capillaries

Front 25

What is the capsular space?

Back 25

between parietal & visceral epithelia

Front 26

Blood supply to the glomerulus has two locations:

Back 26

afferent arteriole & efferent arteriole

Front 27

The _____ arteriole brings blood to the glomerulus

Back 27

afferent

Front 28

The _____ arteriole takes blood away from the glomerulus (after filtration has occurred)

Back 28

efferent

Front 29

What is the filtration membrane?

Back 29

filter that lies between the blood & capsular space

Consists of three layers:
• fenestrated endothelium
• fused basement membrane
• visceral layer of glomerular capsule

Front 30

What are the three layers of the filtration membrane?

Back 30

• fenestrated endothelium - of glomerular capillaries
• fused basement membrane
• visceral layer of glomerular capsule - podocytes form filtration slits

Front 31

What are the two 2 capillary beds in every nephron?

Back 31

glomerulus and peritubular capillaries

Front 32

Each glomerulus is:

Back 32

• fed by an afferent arteriole
• drained by an efferent arteriole

Front 33

What are peritubular capillary beds?

Back 33

low-pressure, porous capillaries adapted for absorption
• arise from efferent arterioles
• cling to adjacent renal tubules
• empty into renal venous system

Front 34

What is the vasa recta?

Back 34

long, straight efferent arterioles connected to peritubular capillaries (15% of nephrons) that follow Loops of Henle into medulla

Front 35

Cortical nephrons

Back 35

85% of all nephrons
• located in the cortex of the kidney
• short loop of Henle
• efferent arteriole connects with peritubular capillaries

Front 36

Juxtaglomerular nephrons

Back 36

15% of nephrons
• long loops of Henle extend deep into medulla
• peritubular capillaries (surround convoluted tubules) connect to vasa recta (long, straight capillaries parallel with loop of Henle)

Front 37

What are the three stages of urine formation?

Back 37

1. filtration - of H₂O & solutes across filtration membrane
2. reabsorption - removal of H₂O & solutes from filtrate into peritubular fluid
3. secretion - transport of solutes from peritubular fluid into tubular fluid

Front 38

Three processes of urine formation

1. Filtration - solutes travel from _____ to ______
2. Reabsorption - solutes travel from _____ to _____
3. Secretion - solutes travel from ______ to _____

Back 38

1. Filtration - solutes travel from _____ to ______
2. Reabsorption - solutes travel from _____ to _____
3. Secretion - solutes travel from ______ to _____

Front 39

Filtration

Back 39

H₂O & dissolved solutes move out of glomerulus → across filtration membrane → into capsular space
• requires glomerular hydrostatic pressure (BP generated by heart) to force H₂O and solutes through membrane pores
∙ small solute molecules pass through
∙ larger solutes (e.g. proteins, RBCs) can't pass through

Filtration → effective and passive
• major limitation — in addition to metabolic wastes & excess ions...
∙ glucose, fatty acids, amino acids & vitamins enter capsular space

These potentially useful materials are recaptured before the filtrate leaves the kidneys (reabsorption)

Front 40

Glomerular filtration is determined by a balance between:

Back 40

1. hydrostatic pressure (fluid pressure)
2. colloid osmotic pressure (of materials in solution)

Front 41

Glomerular hydrostatic pressure (GHP)

Back 41

(BP in glomerular capillaries) = 50 mm Hg

(arrows in purple)

Front 42

Capsular hydrostatic pressure (CsHP)

Back 42

15 mm Hg (pushes H₂O & solutes out of filtrate)

(arrows in red)

Front 43

Blood colloid osmotic pressure (BCOP)

Back 43

25 mm Hg (osmotic pressure due to suspended proteins)

(arrows in teal)

Front 44

Why do we not need to consider the colloid osmotic pressure in the filtrate?

Back 44

lack of proteins in filtrate (due to semipermeable membrane) ... BCOP draws H₂O out of filtrate - into plasma

Front 45

Net hydrostatic pressure (NHP)
NHP =

Back 45

GHP -CsHP

35 mm Hg = 50 mm Hg - 15 mm Hg

Front 46

Filtration pressure (NFP)
NFP =

Back 46

NHP - BCOP
10 mm Hg = 35 mm Hg - 25 mm Hg

10 mm Hg = average pressure forcing H₂O & dissolved solutes out of glomerular capillaries into capsular space

Front 47

Typical hydrostatic pressure in the peripheral capillaries is

Back 47

35 mm Hg

Front 48

Glomerular hydrostatic pressure is

Back 48

50 mm Hg

Front 49

How is the filtration pressure established/maintained?

Back 49

efferent arteriole diameter < afferent arteriole diameter

Therefore high pressures are needed to overcome the resistance

Front 50

Blood pressure in the glomerulus is high because:

Back 50

• arterioles are high-resistance vessels (high diameters)
• afferent arterioles have larger diameters than efferent arterioles

Fluids and solutes are forced out of the blood throughout the entire length of the glomerulus

Front 51

Glomerular Filtration Rate (GFR)

Back 51

amount of filtrate kidneys produce in 1 minute (~ 125 ml/min)
... about 10% of fluid delivered to kidneys - leaves bloodstream & enters capsular space

Front 52

Glomeruli generate about _____ L of filtrate/day but _____% is reabsorbed in renal tubules

Back 52

180 L; 99%

Front 53

Any factor that alters filtration pressure alters _____.

Back 53

GFR

Front 54

What are the three levels of GFR regulation?

Back 54

1. Autoregulation (local level)
2. Hormonal regulation (initiated by kidneys)
3. Autonomic regulation (by SNS)

Front 55

What level(s) of GFR regulation is under intrinsic control?

Back 55

Autoregulation (local level)

Front 56

What level(s) of GFR regulation is under extrinsic control?

Back 56

Hormonal regulation (initiated by kidneys) and Autonomic regulation (by SNS)

Front 57

What is intrinsic control?

Back 57

act locally to maintain constant GFR (despite fluctuations in blood pressure or MAP)

Front 58

What is extrinsic control?

Back 58

aimed at regulating blood pressure (MAP) ... and ultimately GFR (BP drives filtration in the kidneys)

Front 59

If we can regulate MAP, Renal BP and/or NFP → can control _____

Back 59

GFR

Front 60

Autoregulation of Glomerular Filtration Rate (GFR)

Back 60

Maintain GFR by changing diameters of afferent arterioles, efferent arterioles & glomerular capillaries

Front 61

Autoregulation of Glomerular Filtration Rate (GFR)

If we experience a ↓ in BP do we want to have dilation or constriction of ......
_____ of afferent arteriole
_____ of glomerular capillaries
_____ of efferent arterioles
... to raise BP to homeostatic levels

Back 61

_____ of afferent arteriole
_____ of glomerular capillaries
_____ of efferent arterioles

Front 62

Autoregulation of Glomerular Filtration Rate (GFR)

If we experience a ↑ in BP...
_____ of afferent arteriole
... to lower BP to homeostatic levels

Back 62

_____ of afferent arteriole

Front 63

Autoregulation of Glomerular Filtration Rate (GFR)

Under normal conditions, auto regulation maintains nearly _____ GFR

Back 63

constant

Front 64

Autoregulation of Glomerular Filtration Rate (GFR)

If systemic BP is HIGH → afferent arteriole will be stretched → response:

Back 64

Afferent arteriole & glomerular capillary constrict; efferent arteriole dilates → ↓ glomerular hydrostatic pressure → ↓ NFP → ↓ GFR

Front 65

Autoregulation of Glomerular Filtration Rate (GFR)

If systemic BP is LOW →

Back 65

Afferent arteriole & glomerular capillary dilate; efferent arteriole constricts → ↑ glomerular hydrostatic pressure → ↑ NFP → ↑ GFR

Front 66

Hormonal regulation of glomerular filtration rate (GFR) occurs by hormones of the:

Back 66

1. renin-angiotensin system
2. natriuretic peptide (ANP and BNP)

Front 67

Renin-Angiotensin System involves the _____.

Back 67

Juxtaglomerular Apparatus (JGA)

Front 68

Juxtaglomerular Apparatus (JGA) is an endocrine structure that secretes:

Back 68

• hormone erythropoietin (EPO)
-RBC production
• enzyme Renin
-converts angiotensinogen to angiotensis I

Front 69

Autonomic regulation of Glomerular Filtration Rate (GFR) under normal conditions

Back 69

(MAP ~ 80-180 mm Hg)
• SNS - at rest
• Autoregulatory mechanisms in control
• GFR remains relatively constant

Front 70

Autonomic regulation of Glomerular Filtration Rate (GFR) under extreme stress/emergency

Back 70

(acute drop in MAP ~ < 80 mm Hg)
• SNS - activated
• Neural mechanisms override autoregulatory control
• Blood is shunted to vital organs — decrease in GFR

After a crisis passes...
Sympathetic control decreases
↓
GFR returns to normal

Front 71

Effect of MAP of GFR

Group Questions
1. Why is the line "flat" between 80-180 mm Hg?
2. If MAP increased to 220 mm Hg what would happen?
3. If MAP decreased to 40 mm Hg what would happen?

Back 71

1. Why is the line "flat" between 80-180 mm Hg?
2. If MAP increased to 220 mm Hg what would happen?
3. If MAP decreased to 40 mm Hg what would happen?

Front 72

Reabsorption in the Proximal Convoluted Tubule (PCT)

Back 72

• "Mass reabsorption" ~ 70% of filtrate is reabsorbed at PCT
• H₂O, nutrients, ions vitamins, etc returned to blood via peritubular capillaries

Front 73

Epithelial cells of the PCT are specialized for transport:

Back 73

• transport proteins (pumps, carriers, channels) in apical & basolateral membranes
• microvilli on apical surface face into lumen of tubule (↑↑ surface area)

Front 74

Primary molecule that drives reabsorption at PCT is

Back 74

Na+

Front 75

[Na+] = PCT lumen > Tubule cell →

Na+/K+ ATP pump →

[Na+] = Peritubular fluid > Peritubular capillaries →

Back 75

[Na+] = PCT lumen > Tubule cell → passive diffusion into cell

Na+/K+ ATP pump → active transport into peritubular fluid

[Na+] = Peritubular fluid > Peritubular capillaries → passive diffusion into blood

Front 76

Movement of Na+ has 3 important effects:

Back 76

(1) creates osmotic gradient → results in water reabsorption called: obligatory water reabsorption ("water follows salt")

(2) Creates an electrical gradient that causes negatively charged ions to "follow along" with Na+ and be reabsorped

(3) Diffusion of Na+ into PCT tubule cells releases energy that is "captured" and "used" to pump other nutrients (e.g. glucose, amino acids) into cells or wastes out of cells (e.g. H+) = secondary active transport

• nutrients will then diffuse out the other side of PCT tubule cells into the ECF → and then into blood

Front 77

What is the osmotic gradient?

Back 77

water "follows" the diffusion and active transport of Na+ via osmosis

Front 78

What is the electrical gradient?

Back 78

negatively charged ions "follow along" with Na+ to be reabsorped

Front 79

What is the secondary active transport?

Back 79

movement of Na+ into tubule cells releases energy
• energy is "captured" and "used" to pump other nutrients (e.g. glucose, amino acids) into cells or wastes out of cells (e.g. H+) = secretion

Front 80

Secondary active transport also drives _____ transport

Back 80

HCO₃-

Front 81

Concept of Transport Maximum

Back 81

(Tm)
• Carrier proteins (active and passive) can become saturated (full)
∙ reflects number of carriers in the renal tubules available
∙ when carriers are saturated, excess of that substance is excreted in urine (e.g. diabetes mellitus - high [glucose] in filtrate)

Front 82

Substances are not reabsorbed if they:

Back 82

• Lack carriers
• are not lipid soluble
• are too large to pass through membrane pores

• Urea, creatinine and uric acid are the most important non reabsorbed substances