Module 7: The Renal System

How many kidney functions are there?

8

What are the 8 functions of they kidneys?

1. regulation of blood ionic composition

2. regulation of blood pH

3. Regulation of blood volume

4. regulation of blood pressure

5. maintenance of blood osmolarity

6. regulation of blood glucose levels

7. production of hormones

8. excretion of wastes & substances

What are the 5 key ions that the kidneys regulate blood levels of?

Sodium ions (Na+)

Potassium ions (K+)

Calcium ions (Ca2+)

Chloride ions (Cl-)

Phosphate ions (HPO42-)

In what 2 ways do the kidneys regulate blood pH?

Excretion (excrete hydrogen ions into urine) & conservation (bicarbonate ions)

Kidneys will try to ___ water

reabsorb

How do the kidneys regulate BV & BP?

Conserve vs. eliminate water

decrease volume = decrease BP

constriction of blood vessel = increase BP

(fluid reduction & vasoconstriction)

How do the kidneys maintain blood osmolarity & regulation of blood glucose (functions 5 & 6)?

Gluconeogenesis -> release glucose into blood

What hormones are produced by the kidneys?

Calcitriol & Erythropoietin

Calcitriol

Active form of Vitamin D & helps with Calcium homeostasis

Erythropoietin

Stimulates production of RBC

Where are calcitriol & erythropoietin secreted/produced?

Adrenal glands

What wastes do the kidneys excrete?

Metabolic reaction wastes, drugs & toxins

What are the metabolic reaction wastes that the kidneys excrete?

Ammonia, urea, bilirubin, creatine, uric acid

How much of a person's daily water loss happens in the kidneys (under normal conditions)

total loss: 2500 mL

kidney water loss: 1500 mL

What 3 hormones control reabsorption & secretion?

RAAS, ADH, ANP

RAAS

Aldosterone causes reabsorption of Na & Cl & secretion of K in the collecting duct

ADH

Increases permeability to water in cells of the distal tubule & collecting duct -> higher water reabsorption

ANP

Decreases Na & water reabsorption, inhibits aldosterone & ADH release

Renin-angiotensin pathway

Dehydrated/Na+ deficiency/hemorrhage -> decrease in BV & BP -> increased renin -> increaed angiotensin I -> ACE -> increased angiotensin II -> adrenal cortex -> increased aldosterone -> increased Na+ & water reabsorption in kidneys -> increase BV & BP

What happens for urine to become more concentrated?

1. symporters in thick ascending limb establish an osmotic gradient

2. principal cells in collecting duct reabsorb more water when ADH is present

3. urea recycling causes buildup of urea in the renal medulla

How does your body/kidneys respond to dehydration?

1. decreased flow of saliva -> dry mouth & pharynx

2. increased blood osmolarity → stimulates osmoreceptors in hypothalamus

3. decreased BV → decreased BP → increaed renin release → increased angiotensin II formation

ALL will lead to:

stimulates thirst center in hypothalamus → increases thirst → increases water intake → increases body water to normal level & relieves dehydration

What 5 factors maintain body water balance?

Thirst center for hypothalamus, angiotensin II, aldosterone, ANP, ADH/vasopressin

Thirst center in hypothalamus

Stimulates desire to drink fluids

Angiotensin II

Stimulates secretion of aldosterone -> reduces loss of water in urine

Aldosterone

Promotes urinary reabsorption of Na+ & Cl- which increases water reabsorption through osmosis -> reduces water loss in urine

Atrial Natriuretic peptide (ANP)

Promotes natriuresis, elevated urinary excretion of Na+ (and Cl-) accompanied by water -> increases loss of water in urine

ADH/vasopressin

Promotes insertion of water-channel proteins (aquaporin-2) into the apical membranes of principal cells in the collecting ducts of the kidneys -> water permeability of these cells increases -> more water is reabsorbed -> reduces loss of water in urine

How does your body (& kidneys) respond to salt intake?

Increased release of ANP/decreased formation of angiotensin II/decreased release of aldosterone -> reduced reabsorption of NaCl by kidneys -> decreased blood volume

Excretion equation

Excretion = filtration + secretion - reabsorption

Where does blood flow into the nephron?

Afferent arteriole (into glomerulus)

What happens in the glomerulus?

Filtration from blood plasma into nephron

Where does filtration happen?

ONLY in the glomerulus

What is the name of fluid in the renal tubule?

filtrate

Tubular reabsorption

reabsorption from filtrate back into blood

Return to blood = ?

reabsorption

What happens to filtrate if it stays in the renal tubule?

It becomes urine

Tubular secretion

Secretion from blood into fluid (in renal tubule)

Where does secretion happen?

Everywehre except the glomerulus

Where does fluid go if it returns & stays in the blood?

The blood contains reabsorbed substances & goes to the renal vein then IVC

What is excreted?

urine

What are filtration & secretion composed of?

What you have put into the nephron/urine

What is reabsorption composed of?

What you have taken out of the nephron

What are the 4 major processes in the nephron?

1. filtration

2. reabsorption

3. secretion

4. excretion

Filtration

Movement of water & solutes from the blood plasma across the wall of the glomerular capillaries, into the glomerular capsule & into the renal tubule

Solutes

Anything that is dissolved in the solution

What 3 pressures drive filtration?

1. glomerular blood hydrostatic pressure (BGHP) = 55mmHg

2. Capsular hydrostatic pressure (CHP) = 15 mmHg

3. Blood colloid osmotic pressure (BCOP) = 30mmHg

What are the promoting pressure(s) (promotes filtration)?

Glomerular blood hydrostatic pressure (GBHP) -> wants solutes to leave the blood & enter the nephron

What are the opposing pressure(s) of filtration?

Capsular hydrostatic pressure (CHP) & Blood colloid osmotic pressure (BCOP) -> want solutes to stay in the blood

Increase in blood -> ?

Increase in GBHP pressure

Colloid

proteins

The more proteins in the blood (BCOP) -> ?

the more water they want to keep w/ them -> decrease in filtration

What leaves in the efferent arteriole?

Not filtered blood to the peritubular capillaries

Net Filtration Pressure (NFP)

GBHP - CHP - BCOP
55mmHg - 15 mmHg - 30 mmHg

= 10 mmHg -> filtration wins since it's positive (if number is - then it would be pulling filtrate into the efferent arteriole)

Glomerular filtration rate (GFR)

Volume of plasma filtrate that passes through the glomeruli every minute (rate of plasma we filter per minute)

What is the blood flow to the kidneys @ rest?

1200 - 1300mL/min (1.2-1.3L/min)

What is filtered?

Plasma

How much plasma is filtered?

720-780 ml/min (Hct = 40%)

What is the maximum filtration?

125 mL/min (17% of plasma)

Reabsorption

Return/retain

Movement of substances from the renal tubule to the blood stream (filtrate -> blood)

How much of the filtered water & solutes do cells reabsorb?

99%

Where do the water & solutes travel when reabsorbed?

Through the peritubular capillaries & vasa recta to eventually return to the IVC

Secretion

See ya!

The removal of a substance from the blood into the renal tubule (filtrate)

What is included in secretion?

What we want to get rid of: drug residuals, excess ions from blood, etc.

What happens in the proximal tubule?

Reabsorption of 99% of what was just filtered (mostly Na & glucose, also amino acids, K, Cl, bicarbonate ions) & secretion of H ions & drug residues

proximal tubule acid-base balance

Maintaining the acid-base balance

Co2 & H2O start the process by getting rid of H+ (in blood) & keeping bicarbonate (in blood) while also reabsorbing Na+ & getting rid of CO2

Why do we reabsorb HCO3- (bicarbonate)

Acts as buffers & helps get rid of H+

How much bicarbonate ions (HCO3-) are reabsorbed?

80-90% of bicarbonate ions

What happens in the descending loop of Henle?

Reabsorbs water back into blood

Secretes NaCl (salt/sodium chloride) into urine

What happens in the ascending loop of Henle?

Water impermeable (does not cross membrane/no water movement)

Reabsorbs NaCl back into blood through vasa recta

What happens if you increase osmolarity in the loop of Henle?

Increase solutes

What happens if you decrease osmolarity in the loop of Henle?

Decrease solutes & increase dilute

Where is there lower osmolarity in the loop of Henle?

At the beginning of the descending loop

where is there higher osmolarity in the loop of Henle?

At the bottom of the descending loop/beginning of the ascending loop

What happens in the distal tubule & collecting duct?

Secretion of K & H ions

Reabsorption of NaCl & water

(last chance to match solute & water to physiological needs)

What is water completely dependent on (for reabsorption in the distal tubule/collecting duct)?

On the presence of ADH & aldosterone

What is water inhibited by?

ANP (opposite of ADH & aldosterone)

Atrial natriuretic peptide (ANP)

Hormone that is release if you have high BP/BV or overhydrated that stretches the heart/atria and puts sodium into the urine (in which water will follow)

Aldosterone

Puts Na in blood (water will follow because of osmosis)

When it comes to the distal tubule/collecting duct, what determines what is reabsorbed?

If aldosterone -> Na

If ADH -> water

What does the renal system consist of?

2 kidneys

2 ureters

1 urinary bladder

1 urethra

What are the general functions of the renal system?

Filters blood to:

• keep necessary fluids & components

• excrete wastes

What is the size of the kidneys?

"size of a fist"

4-5 inches long

2-3 inches wide

1 inch thick

Where are the kidneys located?

Lateral to T12-L3 (right & slightly lower)

what cavity are the kidneys in?

Retroperitoneal cavity

What are the 3 kidney tissue layers?

Renal Fascia (superficial)

Adipose Capsule (intermediate)

Renal capsule (deep)

Renal Fascia function

anchor kidney to surrounding structures & posterior abdominal wall

Adipose capsule function

Protection, holds kidney in place

Renal capsule function

Protects from trauma & infection, maintenance of shape, continuous w/ ureter

How much blood supply to do the kidneys get?

25% of cardiac output @ 1200 ml/min

How many arterioles supply the kidneys & what are they & their function?

2 arterioles

Afferent & efferent → resistance vessels

How many capillaries do the kidneys have & what are they?

2 capillaries

Glomerular & peritubular

What is the order of the blood supply to the kidneys?

Renal artery -> afferent arteriole -> glomerular capillaries -> efferent arteriole -> peritubular capillaries and/or vasa recta -> renal vein

Renal artery

delivers blood into kidney

Afferent arteriole

delivers blood into glomerulus

Efferent arteriole

delivers blood away from glomerulus

peritubular capillaries

surrounds renal tubule to collect the filtered blood

renal vein

delivers blood away from kidney

vasa recta

specialized peritubular capillaries that surround the loop of Henle

Nephron

Functional unit of the kidney that filters blood & produces urine

How many nephrons do we have?

Millions!