Lecture 9 - Renal Systems

Front 1

What is the urinary system comprised of?

Back 1

Kidneys (urine forming organs) and structures that carry urine from the kidneys to the outside of the body -> ureters, urinary bladder, and urethra

Front 2

What is the function of the kidney?

Back 2

Regulations of body's water and solute composition (osmoregulation); filters waste (metabolic, foreign), produces urine to remove waste products and excess water, ions.

Front 3

Any other functions?

Back 3

Also has an endocrine function -> production of hormones (renin, erythropoietin) and activation of vitamin D.

Front 4

What are the kidneys referred to as?

Back 4

Guardians of the internal environment.

Front 5

How is the kidney supplied blood?

Back 5

Renal artery and renal vein

Front 6

Where does urine drain to as it forms?

Back 6

into the renal pelvis, located at the inner core of each kidney

Front 7

What is the function of the bladder?

Back 7

Temporary storage site for Urine; hollow, distensible sac with smooth muscle in the walls. periodically empties to the outside of the body through the urethra

Front 8

What is the function unit of the kidney? How many are there?

Back 8

The nephron; 10^6.

Front 9

How are nephrons arranged?

Back 9

The arrangement gives rise to two distinct regions in the kidney: the Renal cortex; outer region lighter in appearance, and renal medulla; inner region made up of striated triangles called renal pyramids.

Front 10

What are the two different types of nephrons?

Back 10

Cortical nephrons (80% of the nephrons are almost completely contained within cortex) and Juxtamedullary nephrons (20% of nephrons dip down into the medulla)

Front 11

Picture of nephron anatomy

Back 11

Front 12

How many afferent and efferent arterioles are associated with each nephron?

Back 12

1 of each.

Front 13

What is the dominant feature of a nephron?

Back 13

The glomerulus, a ball like group of capillaries

Front 14

What's special about efferent arterioles?

Back 14

They are the only arterioles in the body that drain blood FROM the capillaries.

Front 15

Which capillaries supply the renal tissue, and what occurs here?

Back 15

Peritubular supply the renal tissue, and this is where reabsorption and secretion occurs.

Front 16

A picture of the vessels in the Nephron

Back 16

Front 17

What does the Juxtamedullary nephron have that the cortical does not?

Back 17

The vasa recta.

Front 18

What is the vasa recta?

Back 18

A series of vessels which surround the collecting ducts and the Loop of Henle in Juxtamedullary nephrons.

Supplies O2 and nutrients to the nephron segments; allows for return of reabsorbed water and solutes to the circulatory system

Front 19

Picture of vasa recta?

Back 19

Front 20

What is a unique feature of the renal vasculature?

Back 20

The afferent and efferent arterioles have different diameters; the efferent arteriole is quite a bit smaller in diameter. Why is this important? It creates a 'backup' in the glomerulus which creates higher pressure in the glomerular cavity.

Front 21

Let's back up. What does the afferent arteriole do, and what does the efferent do?

Back 21

Afferent brings blood to the glomerulus, whereas the efferent takes blood away from the glomerulus.

Front 22

Where do the filtered components go after the glomerulus? What are these components?

Back 22

Bowman's capsule. Includes water, glucose, amino acids, and ions, and also waste (creatinine and urea).

Front 23

How much of the filtrate leaves the nephrons?

Back 23

1%

Front 24

Where does the efferent arteriole go after leaving the glomerulus?

Back 24

It branches out to form capillaries that wrap around the tubules.

Front 25

What is secretion? What materials tend to be secreted?

Back 25

Where some fluid leaves the capillaries and enter the tubules. Usually ammonia and medication (drugs) are secreted into tubules.

Front 26

What percentage of glucose and amino acids are reabsorbed?

Back 26

About 100%

Front 27

What happens in the descending limb of the loop of Henley?

Back 27

Permeable to water but low permeability to ions such as sodium and urea. Water leaves the tubule due to osmosis (due to salty environment in medulla)

Front 28

What is the main characteristic of the filtrate by the time it reaches the bottom of the loop?

Back 28

It is highly concentrated.

Front 29

What happens in the ascending limb?

Back 29

Impermeable to water, so any water remaining in the filtrate cannot escape. Sodium is actively pumped out of the thick portion of the ascending limb, and passively leaves out of the thin portion. About 25% of NaCl is reabsorbed. After these processes have occurred, the filtrate is dilute.

Front 30

How do efferent and afferent arterioles control blood flow to glomerulus?

Back 30

By constricting and dilating.

Front 31

Would glomerulus filtration rate be increased or decreased with the dilation of the afferent arteriole AND constriction of the efferent arteriole?

Back 31

GFR would increase because as the afferent arteriole dilates, more blood enters glomerulus. As the efferent arteriole constricts, the filtration pressure would increase and filtrate would enter the proximal tube (tubule immediately after glomerulus)

Front 32

Picture of material transport

Back 32

Front 33

What affects glomerular capillary blood pressure?

Back 33

contraction of the heart (Co = HR x SV) and the resistance to blood flow offered by afferent and efferent arterioles

Front 34

What is the net pressure calculation in glomerulus?

Back 34

55 mm Hg (BP) - 30 mm Hg (osmotic pressure) - 15 mm Hg (filtrate pressure) = net 10 mm Hg pressure into tubule.

Front 35

What is filtered during glomerular filtration? What cannot pass?

Back 35

Plasma is filtered. Protein cannot pass.

Front 36

What are the three main structures of the glomerulus and what do they do?

Back 36

Glomerular Capillary wall: single layer of endothelial cells that are more permeable to water and solutes than capillaries elsewhere in the body; Mesangial cells: specialized smooth muscle cells that can regulate blood flow through capillaries, and Podocytes: these wrap around the capillaries and leave slits between them. Blood is filtered through these slits.

Front 37

Detailed picture of Glomerulus Structure.

Back 37

Front 38

What is the basic nephron function?

Back 38

The maintenance of blood volume and electrolyte balance.

Front 39

What is the equation for total amount of solute excreted?

Back 39

Amount filtered - amount reabsorbed + amount secreted.

Front 40

What is the basic structure of the tubular nephron?

Back 40

A hollow, fluid-filled tube formed by a single layer of epithelial cells.

Front 41

What are the different function regions of the nephron?

Back 41

Bowman's capsule, proximal tubule, loop of Henle, distal tubule, collecting duct.

Front 42

What is the main function of Bowman's capsule? Proximal tubule?

Back 42

Collects glomerular filtrate; reabsorption and secretion of substances.

Front 43

What is the main function of the loop of Henle?

Back 43

Descending and ascending limbs: osmotic gradient established in Juxtamedullary nephrons.

Front 44

What is the main function of the distal tubule? Collecting duct?

Back 44

Regulated reabsorption; collects urine

Front 45

What is tubular reabsorption?

Back 45

Transfer of substances from tubular lumen into peritubular capillaries - essential 'stuff' returned to body. Highly selective, but variable - a highly regulated process.

Front 46

Picture of tubular reabsorption

Back 46

Front 47

What are the reabsorption steps?

Back 47

1) Leave tubular fluid by crossing luminal membrane of tubular epithelial cell

2) pass through cytosol from one side of tubular cell to the other

3) cross basolateral membrane of the tubular cell to enter interstitial fluid

4) diffuse through interstitial fluid

5) penetrate capillary wall to enter blood plasma

Front 48

How much of urea is reabsorbed? Phenol? Water, sodium, glucose?

Back 48

50, 0, 99, 99.5, 100

Front 49

What is the difference between passive and active tubular reabsorption?

Back 49

Passive requires no energy, occurs down electrochemical or osmotic gradients. Active reabsorption requires energy as movement occurs against electrochemical or concentration gradient.

Front 50

Describe the active Na reabsorption process

Back 50

Sodium potassium pump in basolateral membrane is essential for Na reabsorption. 80% of total energy spent by kidneys is used for Na transport. Water follows reabsorbed Na by osmosis. Mainly affects blood volume and pressure.

Front 51

Picture of Na reabsorption

Back 51

Front 52

Describe proximal tubule water reabsorption

Back 52

Water follows reabsorbed Na by Osmosis; mainly affects blood volume and pressure. Hypertonicity in lateral spaces, established by active extrusion of Na, is the force for water reabsorption.

Front 53

Picture of water reabsorption

Back 53

Front 54

Sodium absorption. How much is absorbed in the proximal tubule, the ascending limb, and the distal collecting tubes? What is the role of Na reabsorption in each section?

Back 54

Front 55

What really controls Na reabsorption?

Back 55

Hormones. Renin is secreted by Juxtaglomerular granular cells in response to low NaCl. Complicated system (slide 32)

Front 56

How does Aldosterone increase sodium retention?

Back 56

Front 57

What does Atrial Natriuretic Peptide (ANP) do?

Back 57

Inhibits Na reabsorption; secreted by specialized cells in the Atria in response to stretch caused by expansion of ECF (caused by Na retention) and increased arterial pressure. ANP release prompts additional effects (natriuretic, diuretic, hypotensive) that help correct original stimulus.

Front 58

What do natriuretic, diuretic mean?

Back 58

Natriuresis: discharge of sodium through urine

Diuretic: Elevates discharge of urine

Front 59

How can ANP increase Sodium excretion?

Back 59

Dilates the Afferent glomerular arteriole, constricts the Efferent glomerulararteriole, and relaxes the mesangial cells (this increases pressure in the glomerularcapillaries, thus increasing the glomerular filtration rate (GFR), resulting in greaterexcretion of sodium and water)

Front 60

How else can ANP increase sodium excretion?

Back 60

Increases blood flow through the vasa recta, which will wash the solutes (NaCl andurea) out of the medullary interstitium (the lower osmolarity of the medullaryinterstitium leads to less reabsorption of tubular fluid and increased excretion)-decreases sodium reabsorption in the Distal convoluted tubule and collecting ductby inhibiting the Epithelial Sodium Channel-Inhibits Renin secretion, thereby inhibiting the Renin–Angiotensin–Aldosteronesystem

Front 61

Discuss glucose reabsorption (Active)

Back 61

Some glucose is filtered and ends up in Bowman's capsule; but completely reabsorbed through Sodium Glucose Co-Transport proteins (SGLT)

Front 62

How is Urea passively reabsorbed?

Back 62

Firstly, urea is a nitrogen-containing waste product from the breakdown of protein in the liver. Reabsorption occurs mainly at Collecting Duct (50%). Indirectly linked to active Na reabsorption (Osmotic reabsorption of H2O in theproximal tubule produces a [gradient] forpassive reabsorption of urea)

Front 63

Picture of Urea Reabsorption

Back 63

Front 64

What is tubular secretion?

Back 64

Transfer of substances from peritubular capillaries into the tubular lumen for eventual excretion.

Front 65

Where is most K reabsorbed?

Back 65

In the proximal tubule; at the distal tubule only 5-10% of filtered load remains, mostly secreted at the distal tubule.

Front 66

Picture of K ion tubular secretion

Back 66

Front 67

How does K ion tubular secretion work?

Back 67

the same Na+-K+ ATPase that pumps Na+ out of epithelial cells pumps K+intothe cells;

K concentration gradient allow diffusion of K into the lateral spaces, andpassive movement into the tubules for excretion

Front 68

Another picture of K transport in the proximal tubule

Back 68

Front 69

A picture of K transport in the cortical collecting duct (the principal cell)

Back 69

Front 70

What regulates K secretion?

Back 70

Aldosterone from the adrenalcortex is most importantregulator of K+secretion;

Simultaneous Reabsorption ofNa+ and Secretion of K+

Front 71

Picture of Aldosterone regulating K secretion

Back 71

Front 72

H+ - Important tubular secretion systems

Back 72

Important in regulating acid-base balance

Secreted at proximal, distal, and collecting tubules

Front 73

K+ - Important tubular secretion systems

Back 73

Plasma [K+] kept at appropriate levels to maintain normal membraneexcitability in Muscles and Nerves

Secreted only at the Distal and Collecting tubules under control ofaldosterone (an adrenal hormone)

Front 74

Organic Ions - Important tubular secretion systems

Back 74

Secreted only at the proximal tubule

Includes blood-borne chemical messengers (i.e. histamine, NE);insoluble molecules initially bound to proteins; foreign organicmolecules such as drugs, food additives, pollutants, etc., etc.

Front 75

Why do Juxtamedullary nephrons have long loops of Henle?

Back 75

Important to establish Osmotic gradients.

Front 76

Flow through the nephron, specifically the loop of Henle, is influenced by....

Back 76

The gradient of osmolarity, which increases with toward the distal end of the loop of Henle.

Front 77

Picture of Loop of Henle reabsorption

Back 77

Front 78

What happens in the descending tube?

Back 78

Descending loop is highly permeable toH2O, but does not reabsorb Na+(Concentrates urine) -Osmotic pressure favors waterreabsorption

Front 79

What happens in the ascending tube?

Back 79

The Ascending limb actively transportsNa and Cl out of the tubular lumen intosurrounding ECF, but is impermeable toH2O (Dilutes urine)

Front 80

What is partially responsible for selective water reabsorption?

Back 80

Aquaporins (selective water channels)

Front 81

How can the GFR be regulated?

Back 81

By adjusting the glomerular capillary BP to suit the bodies needs. Two types: autoregulation (prevents spontaneous changes in GFR 1a, 1b) and extrinsic sympathetic control 2a, 2b (long term regulation of arterial BP)

Front 82

1a How does myogenic autoregulation work?

Back 82

kidneys can 'auto-regulate' blood flow to glomerular capillaries; arteriolar resistance is adjusted locally (vasoconstriction or dilation); occurs due to the myogenic properties (originating in muscle tissue) of the arterioles

Front 83

1b What about autoregulation via the Juxtaglomerular apparatus?

Back 83

The twisted configuration of the nephron causes the final portion of theAscending loop of Henle to pass between the Afferent and Efferentarterioles.

Front 84

How does this work?

Back 84

A decrease in sodium chloride concentration initiates asignal from the Macula Densa that has two effects:

(1) it decreases resistance to blood flow in the AfferentArterioles, which raises glomerular hydrostaticpressure, and

(2) it increases Renin release from the Juxtaglomerularcells of the afferent arterioles

Front 85

Picture of Tubuloglomerular feedback

Back 85

Front 86

2a) What is the importance of extrinsic regulation?

Back 86

Fight or flight; GRF can be changed due to vasoconstriction and decreased renal blood flow; mediated by SNS input to afferent arterioles of glomerulus

Front 87

Is there any parasympathetic input to the kidneys?

Back 87

NO.

Front 88

2b) Baroreceptor Regulation

Back 88

long term regulation of arteriole blood pressure; changes in BP are detected by aortic and carotid baroreceptors; mechanoreceptors are sensitive to changes in arterial pressure = pressure mechanoreceptors.

Front 89

What does the solute concentration of urine depend on?

Back 89

The body's state of hydration; too much water in the ECF establishes a hypotonic EFC (less concentrated urine) whereas a water deficit established a hypertonic ECF (more concentrated urine)

Front 90

How much blood plasma is filtered daily?

Back 90

~ 125 ml/min males, 115 females

so about 180 L per day, 166 L day in females

Front 91

What percentage of 180L is reabsorbed?

Back 91

99% - the body would rapidly dehydrate if reabsorption didn't occur. ~1.5 L of urine is excreted daily.

Front 92

How many times per day is overall plasma filtered?

Back 92

60x.

Front 93

What is renal failure?

Back 93

Kidney function Decreases with Age

GFR declines at a rate of ~10 mL/min/1.73 m2for each decade beyondthe age of 30

Front 94

What are some causes of renal failure?

Back 94

infectious organisms• toxic agents• inappropriate immune responses• obstruction of urine flow• an insufficient renal blood supply

Front 95

What are some engineering solutions?

Back 95

Hemodialysis; kidney transplant; bioengineered kidney.