Module 9: KUB, RBF, Tubules, Hormones And Renal Function Tests (a)

Question 1

Renal system Overview

-Primary Functions

Answer 1

1. Maintain stable internal environment for optimal cell tissue metabolism — Ex Blood pressure*
2. Balance solute and water transport
3. Excrete metabolic waste products
4. Conserve nutrients
5. Regulate serum pH

Question 2

Renal system Overview

-Endocrine Functions?

Answer 2

1. Renin — Important for regulation of BP
2. Erythropoietin — Production of erythrocytes in response to low oxygenation
3. 1,25-dihydroxyvitamin D3 — important in metabolism of calcium — performs gluconeogenesis in renal cortex
4. Forms urine

Question 3

Nephron

-Info

Answer 3

1. Functional unit of the kidney
   - Superficial cortical nephrons — 85% of all nephrons — located on outer edge
   - Midcortical nephrons
   - Juxtamedullary nephrons — Concentrate urine and secrete renin
2. EACH kidney contains 1.2 million nephrons

Question 4

Glomerulus

-Info

Answer 4

1. Afferent arteriole — Supplies glomerulus w/ blood
2. Efferent arteriole — Returns blood to systemic blood flow — Away from glomerulus
3. Juxtaglomerular apparatus **
   - Controls renal blood flow, glomerular filtration, and renin secretion

Question 5

Glomerulus

-Juxtaglomerular Apparatus

Answer 5

1. Control renal blood flow, glomerular filtration, and renin secretion
2. Juxtaglomerular cells — Specialized cells located around afferent arterioles
3. Macula densa — Specialized sodium and chloride sensing cells — Found in distal convoluted tubules where afferent and efferent arterioles enter glomerular space

Question 6

Glomerulus & Juxtaglomerular Apparatus

-Function

Answer 6

1. Juxtaglomerular cells — Surround afferent arteriole — Distal tubule and afferent arteriole come into contact
2. Macula Dens — Line the Distal tubule — Measure sodium concentration of urine being excreted — Regulates sodium concentration
3. Glomerulus — Tuft of capillaries surrounded by Bowman’s capsule —
   —Space between glomerulus and Bowman’s capsule is the Bowmans Space — Filtrate (Mostly water) is in this space
   —Filtrate in Bowman’s space should NEVER contain PROTEIN when kidney is healthy

Question 7

Glomerulus

-3 layers?

Answer 7

1. Endothelial cell layer — forms lumen and comes into contact with blood — contains pores that allow for particles to pass through
2. Basement Membrane — Selectively permeable & NEGATIVELY charged (Repels negatively charged material) Ex of Neg charged is: ALBUMIN
   —Damage to Basement membrane removes Negative charge — Allows proteinuria and hematuria**
3. Visceral Capillary Epithelium — Contains foot processes of podocytes — Interlocking fingers serve as filtration slits

Question 8

Bladder

-Components

Answer 8

1. Detrusor muscle — “basket weave” of smooth muscle — muscle fibers run in different directions to cause bladder to contract
2. Trigone — Smooth triangular region where 2 ureters and urethra sit
3. Transitional epithelium — Allows bladder to expand and contract — Provides interface between urinary space and underlying vasculature

Question 9

Urethra

-Components

Answer 9

1. Internal sphincters — autonomic regulation; parasympathetic fibers— smooth muscle located at junction of bladder & Urethra
2. External sphincter — Voluntary control — striated skeletal muscle — Skeletal motor neurons in pudendal nerve (L4 -S3)
3. Female Urethra — 3 to 4 cm long — Increased UTI’s in female
4. Male urethra — 18 to 20 cm long

Question 10

Renal Blood Flow

-Process

Answer 10

1. Kidneys receive 1000 to 2000 ml/min of blood
2. GFR
   - Filtration of plasma into bowman space
   - 120 to 140 ml of plasma per minute
   - DIRECTLY related to perfusion pressure in the glomerular capillaries**
3. If MAP decreases or renal artery vascular resistance increases, renal blood flow decreases*

Question 11

Glomerular Filtration

-Process

Answer 11

1. Glomerulus is freely permeable to water and relatively impermeable to large colloids such as plasma proteins
2. Size and electrical charge are important factors that affect permeability
   —Positive-charged particles permeate the membrane more readily than neutral or Negative-charged particles**

Question 12

Glomerular Filtration

-Net Filtration Pressure**

Answer 12

1. Combined effect of forces favoring and forces opposing filtration
2. Favoring Forces — Capillary hydrostatic pressure
3. Opposing Forces — Oncotic pressure in the capillary AND hydrostatic pressure in Bowman capsule
4. Glomerular Filtration Results in — NET POSITIVE FILTRATION 10mmHg leaving glomerulus into proximal convoluted tubule

Question 13

Renal Blood Flow Regulation Systems

-3 Methods

Answer 13

1. Auto regulation
   - Myogenic mechanism
   - Tubuloglomerular feedback
2. Neural Regulation
3. Hormonal Regulation
   - RAAS
   - Natruiretic Peptides

Question 14

Renal Blood Flow Regulation & GFR

-Auto-Regulation

Answer 14

1. Goal is to maintain constant GFR when atrial pressure is between 80 to 180mmHg
2. As SBP increases, afferent arterioles constrict preventing an increase in filtration pressure**
   —Also prevents wide fluctuations in the systemic arterial pressure from being transmitted to glomerular capillaries

Question 15

Renal Blood Flow Regulation

-Auto-regulation — Myogenic Mechanism (Stretch)

Answer 15

1. As atrial pressure declines, stretch on the afferent arteriolar smooth muscle decreases
   —Afferent arteriole relaxes and glomerular perfusion INCREASES

Question 16

Renal Blood Flow Regulation

-Auto-Regulation Tubuloglomerular Feedback

Answer 16

1. When sodium filtration increases (As sensed by the macula densa*), GFR needs to be decreased
2. Macula densa cells stimulate afferent arteriolar VASOCONSTRICTION

Question 17

Juxtaglomerular Granular Cells

-Function?

Answer 17

1. Related to Hormonal aspect of regulation — Also sense STRETCH
   —When BP is low, these cells release RENIN — This converts Angiotensinogen into Angiotensin-1 — SYSTEMIC vasoconstriction

Question 18

Renal Blood Flow Regulation

-Neural Regulation

Answer 18

1. Sympathetic Nervous System — Sympathetic stimulation causes Afferent arteriole to vasoconstrict, which decreased GFR
2. Baroreceptors Reflex — Measures BP in carotid artery and aortic arch — Activated with BP decreases — Causes afferent arteriole to vasoconstrict — Causes reduction of GFR and increase in BP
3. Severe hypoxia
   - Carotid and aortic chemoreceptors are stimulated d/t SEVERE HYPOXIA — Causes GFR reduction d/t sympathetic stimulation
   - Increased BP allows for increase blood flow and oxygenation to lungs

Question 19

Renal Blood Flow Regulation

-Hormonal Regulation

Answer 19

1. RAAS
   —Increases systemic arterial pressure & increases sodium reabsorption
2. RENIN — Enzyme is formed and stored in afferent arterioles of juxtaglomerular apparatus
   —Renin helps form angiotensin-1

Question 20

Renal Blood Flow Regulation

-Where is RENIN formed/Stored?

Answer 20

1. Renin enzyme is formed and stored in afferent arterioles of the juxtaglomerular apparatus
   —Renin helps form angiotensin-1**
2. Renin is released when:
   — BP decreases, Sodium decreases (Macula densa cells), Sympathetic stimulation, Prostaglandin stimulation

Question 21

Renal Blood Flow Regulation

-Renin Function

Answer 21

1. Converts Angiotensinogen into Angiotensin-1

Question 22

Renal Blood Flow Regulation

-Hormonal Regulation RAAS — Angiotensin-II

Answer 22

1. Stimulates secretion of aldosterone by adrenal cortex**
2. POTENT vasoconstrictor
3. Also stimulates ADH (AKA vasopressin) secretion and thirst
4. Aldosterone — Increases BP by increasing sodium/chloride reabsorption by distal convoluted tubules and collecting ducts
   —Fluid will follow the reabsorption and increase BP
5. Vasopressin — increases WATER permeability by distal convoluted tubule and collecting ducts
   —Causes Increase of WATER being reabsorbed instead of secreted

Question 23

Renal Blood Flow Regulation

-Hormonal Regulation — Aldosterone

Answer 23

1. Aldosterone — Increases BP by increasing sodium/chloride reabsorption by distal convoluted tubules and collecting ducts
   —Fluid will follow the reabsorption and increase BP

Question 24

Renal Blood Flow Regulation

-Hormonal Regulation — Vasopressin

Answer 24

1. Vasopressin — increases WATER permeability by distal convoluted tubule and collecting ducts
   —Causes Increase of WATER being reabsorbed instead of secreted

Question 25

Renal Blood Flow Regulation | -Hormonal Regulation — Natriuretic Peptides

Answer 25

1. Atrial Natriuretic Peptide (ANP) — Secreted by myocardial cells in the ATRIA 2. Brain Natriuretic Peptide (BNP) — Secreted by myocardial cells in the VENTRICLES **Released in response to dilation/stretch of the heart caused by elevated blood pressure —GOAL is to cause DIURESIS or loss of fluids

Question 26

Renal Blood Flow Regulation | -Hormonal Regulation — Natriuretic Peptides FUNCTION?

Answer 26

1. Inhibit Sodium and Water reabsorption from kidney tubules back into capillaries 2. Inhibit secretion of renin and aldosterone 3. Vasodilation of afferent arterioles 4. Constriction of efferent arterioles 5. Forces secretion and a DROP in BP

Question 27

Renal Tubules | -Vasarecta

Answer 27

1. Very slow moving network of capillaries — This allows for concentration gradient in interstitial space

Question 28

Rental Tubules | -Cortical Nephron Vs. JuxtaMedullary Nephron

Answer 28

1. Cortical nephrons are located higher than Juxtamedullary nephrons —The lower they connect to collecting duct, the more CONCENTRATED the urine will be

Question 29

Renal Tubules | -Filtration

Answer 29

1. ONLY occurs in the glomerulus — 20% of blood volume will be filtered

Question 30

Renal Tubules | -Reabsorption

Answer 30

1. Substances needed by the body move from the tubules BACK into the peritubular capillaries 2. 99% of filtrate is reabsorbed 3. Reabsorption includes — H20, Na, K, Glucose, Bicarb —H20, chloride and urea are reabsorbed PASSIVELY. All others are active. Even passive molecules follow sodium 4. Proximal Tubule Reabsorption - Transport capacity of active transport molecules can become SATURATED - Once 180mg/dL of glucose is reabsorbed, it is saturated and the rest goes out in urine — That is how diabetes was initially discovered

Question 31

Renal Tubules | -Secretion

Answer 31

1. Substances move FROM peritubular capillaries | - Secreted substances include — Ammonia, hydrogen, urea, creatinine

Question 32

Tubular Transport | -Loop of Henle

Answer 32

1. Provides kidney with ability to CONCENTRATE urine and conserve water for the body** WATCH Vídeo ON BRIGHTSPACE** Confusing**

Question 33

Tubular Transport | -Distal Convoluted Tubules & Collecting Duct

Answer 33

1. Units of the nephron that performs final adjustments in urine composition 2. Convoluted portion of Distal Tubule — Marginally permeable to water but Readily absorbs IONS — Contributes to dilution of tubular fluid - Positive IONS (Ex: ammonia & Hydrogen) need to be absorbed so they are EXCRETED in urine 3. Straight segment of distal tubule and collecting duct is — Permeable to water & controlled by VASOPRESSIN

Question 34

Hormones | -Vitamin D

Answer 34

1. Hydroxylation occurs first in LIVER then in the KIDNEYS — Renal hydroxylation is stimulated by parathyroid hormone 2. Necessary for absorption of calcium and phosphate absorption in small intestine 3. Pt’s w/ renal disease manifest disturbed calcium and phosphate balance** 4. Parathyroid hormone is responsible for regulating serum calcium levels

Question 35

Hormones | -Erythropoietin

Answer 35

1. Stimulates bone marrow to produce RBC’s 2. Stimulus to release erythropoietin is DECREASED OXYGEN delivery to kidneys ** 3. Comercial product is — EPOGEN

Question 36

Hormones | -Connection between Erythropoietin & Anemia of Chronic Disease

Answer 36

1. Anemia of Chronic disease — Occurs as a result of decreased erythropoietin production 2. Chronic diseases that cause renal failure and kidney cell death I.e Diabetes — Decreased Erythropoietin seen in these patients 3. Treatment for this is EPOGEN

Question 37

Tests of Renal Function | -4 tests

Answer 37

1. GFR — Best test 2. Urinalysis 3. Serum Creatinine 4. Blood Urea Nitrogen BUN

Question 38

Tests of Renal Function | -GFR?

Answer 38

1. BEST estimate of kidney function —Lost or damaged nephrons lead to corresponding decline in GFR —Determined by calculating creatinine clearance

Question 39

Tests of Renal Function | -Urinalysis

Answer 39

1. First and EASIEST test to check renal function 2. UA should NOT contain — Protein, glucose, RBC’s, Casts (Accumulation of cellular precipitates , or bacteria 3. Types of Casts - RBC casts — indicate bleeding and hematuria is accompanying Sx - WBC casts — May indicate inflammation - Epithelial cell casts — WORST — Degeneration or NECROSIS

Question 40

Tests of Renal Function | -Creatinine

Answer 40

1. Product of MUSCLE METABOLISM 2. Most Valuable for monitoring the progress of chronic rather than acute renal disease 3. Measures progressive renal dysfunction 4. BUN is not as accurate or reliable as serum creatinine - BUN/Creatinine ratio can help with fluid status needs

Question 41

Aging and Renal function

Answer 41

1. While aging, the number of nephrons decrease** 2. Over lifespan, there is a Linear decrease in Kidney size, renal blood flow and GFR 3. By age 75, nephrons are reduced by 30-50% w/ loss of cortical mass 4. Elimination/clearance of many drugs may be altered, resulting in need for dosage adjustments and monitoring of metabolic/fluid-electrolytes to avoid toxic reactions