Chapter 19: The Kidneys Part 1単語カード | Quizlet

What is the most important function of the kidney?

homeostatic regulation of water and ion content of the blood

(salt and water balance/fluid and electrolyte balance)

What are the six general areas that kidney function is divided into?

1. Regulation of extracellular fluid volume and blood pressure

2. Regulation of osmolarity

3. Maintenance of ion balance

4. Homeostatic regulation of pH

5. Excretion of wastes

6. Production of hormones

Kidney Function: regulation of extracellular fluid volume and blood pressure

ECF vol decreases, BP decreases

If ECF vol and BP fall too low, body can't maintain adequate blood flow to the brain/essential organs.

kidneys work with CV system to ensure that BP and tissue perfusion remain at homeostatic ranges

Kidney Function: Regulation of osmolarity

Integrates kidney function with behavioral drives (like thirst) to maintain blood osmolarity at 290-300 mOsm

related to plasma volume

Kidney function: maintenance of ion balance

kidneys keep concentrations of key ions within normal range by balancing dietary intake with urinary loss.

Na+ is the major ion involved in regulation of ECF volume and osmolarity.

K+ and Ca2+ concentrations are also closely regulated

related to plasma volume

Kidney function: homeostatic regulation of pH

pH of plasma is kept within a narrow range

if ECF is too acidic, kidneys remove H+ and conserve bicarbonate ions (buffers)

if ECF is too alkaline, kidneys remove bicarbonate and conserve H+

kidneys do not correct pH disturbances as quickly as lungs do

Kidney function: excretion of wastes

Kidneys remove metabolic waste products and xenobiotics (aka foreign substances like drugs/toxins)

Metabolic wastes include:

creatinine from muscle metabolism

nitrogenous wastes like urea and uric acid

urobilinogen from hemoglobin (gives urine the yellow color)

Some hormones

Kidney function: production of hormones

Kidneys are NOT endocrine glands, but play a role in 3 endocrine pathways

Kidney cells synthesize:

erythropoietin

- cytokine/hormone that regulates RBC synthesis

renin

- enzyme that regulates the production of hormones involved in sodium balance and blood pressure homeostasis

vitamin D production enzymes

help convert vit. D3 into a hormone that regulates Ca2+ balance

What structures does the urinary or renal system consist of?

Kidneys (2)

- paired

- have nephrons: hollow tubules where urine production begins

- involved in urine production

- retroperitoneal

Ureters (2)

- urine transport

- retroperitoneal

Urinary Bladder

- urine storage

Urethra

- urine transport

How much of the cardiac output do the kidneys receive?

20-25% even though they constitute only 0.4% of total body weight

What are the structures of the kidney?

Renal capsule surrounds kidney

the interior is arranged into an outer cortex and inner medulla

- formed by the organized arrangement of nephrons

- 80% nephrons in kidney are in the cortex (cortical): efferent arteriole --> peritubular capillary

- 20% nephrons in kidney dip into the medulla (juxtamedullary): efferent arteriole --> peritubular capillary & vasa recta and collecting ducts

medulla contains renal pyramids

renal pelvis

What is the functional unit of the kidney?

the nephron

smallest structure that can perform all the functions of the kidney

1 million nephrons in kidney

nephrons are divided into sections, each section is closely associated with specialized blood vessels

Kidney blood vessels form a portal system, explain

blood flows from renal arteries into afferent arteriole. From afferent arteriole to the first capillary bed (glomerulus). Blood leaving the glomerulus flows into an efferent arteriole, then into the second set of capillaries, peritubular capillaries that surround the tubule. In juxtamedullary nephrons, the long peritubular capillaries are called vasa recta. Finally peritubular capillaries converge to form venules and small veins sending blood out of the kidney through the renal vein

renal artery --> afferent arteriole --> glomerulus --> efferent arteriole --> peritubular capillaries (vasa recta) --> venules --> renal vein

What is the function of the renal portal system?

to filter fluid out of the blood and into the lumen of the nephron at the glomerular capillaries, then to reabsorb fluid from the tubule lumen back into the blood at the peritubular capillaries

Where does the nephron begin?

in the Bowman's capsule: surrounds the glomerulus and is hollow/ball like

- endothelium of glomerulus is fused to the Bowman's capsule epithelium so that fluid filtering out of the capillaries passes directly into the lumen of the tubule.

glomerulus + Bowman's Capsule = renal corpuscle

From the Bowman's Capsule, where does filtered fluid flow?

into the proximal tubule, then into the loop of Henle (dips down toward medulla and back up)

Loop of Henle is divided into 2 limbs:

thin descending limb

ascending limb w/thick and thin segments

- contains the juxtaglomerular apparatus: where it passes between afferent and efferent arterioles

fluid then passes into the distal tubule

Where does fluid flow after it passes through the distal tubule?

The distal tubules of up to 8 nephrons drain into the collecting duct which pass from the cortex through the medulla and drain into the renal pelvis

from the renal pelvis, the filtered and modified fluid (URINE) passes into the ureter and is on its way to excretion.

Nephron blood supply comes from where?

renal corpuscle

- afferent arteriole

- glomerulus

- efferent arteriole

nephron tubules

- efferent arteriole

- peritubular capillary network

- cortical nephrons

- vasa recta

- juxtamedullary nephrons: speicialized - countercurrent exchange

What are the structures of the renal corpuscle?

glomerulus

- endothelium

- fenestrated capillaries

- basement membrane

Bowman's capsule

- parietal layer

- Bowman's space

- visceral layer

- podocytes: filtration slits

- basement membrane

Filtration membrane

- endothelium

- fused basal lamina

- podocytes

What is the juxtaglomerular apparatus?

Contains the Macula Densa: junction of ascending loop of Henle and renal corpuscles

contains juxtaglomerular or granular cells

- afferent arteriole

- produce renin

What are mesangial cells?

smooth muscle cells (modified)

- between and around loops of glomerular capillary

- regulate blood flow by contractile activity

- they contract and alter blood flow through the capillaries

- also secrete cytokines associated w/immune and inflammatory processes

What are the 3 basic process that take place in the nephron?

filtration, reabsorption, secretion

Urine formation

What is filtration or glomerular filtration?

the movement of fluid from blood into the lumen of the nephron.

Takes place ONLY in the renal corpuscle where the walls of the glomerular capillaries and Bowman's capsule are modified to allow bulk flow of fluid

What is the standard glomerular filtration rate or GFR?

for a 70 kg person

180L/24 hours

7.5L/hour

125mL/min

3L of plasma filtered sixty times per day

300 mOsm

Is all of the plasma filtered?

filtration fraction = 20%

is the percentage of total plasma volume that filters into the tubule

What are filtration barriers?

substances leaving the plasma must pass through 3 of them before entering the tubule lumen

- the glomerular capillary endothelium

- fenestrated capillaries w/large pores that allow most components of plasma to filter through

- pores are small enough to prevent blood cells from leaving the capillary though.

- a basal lamina: acellular layer of extracellular matrix

- excludes plasma proteins from the fluid that filters through it

- epithelium of Bowman's capsule

- podocytes: long foot processes that leave narrow filtration slits

After filtrate leaves Bowman's capsule, what happens?

it is modified by reabsorption and secretion.

What is reabsorption and where does it occur?

process of moving substances in the filtrate from the lumen of the tubule back into the blood flowing through the peritubular capillaries

filtrate to blood

- only reabsorbs good material

occurs in the Proximal tubule, loop of henle, and distal convoluted tubule

What is secretion and where does it occur?

selectively moves molecules from the blood and adds them to the filtrate in the tubule lumen

Blood to filtrate

occurs ONLY in the distal convoluted tubule

How much filtrate is removed from the body per day via secretion?

1.5L/day

at 50-1200 mOsm (lower or higher than normal)

removes unwanted material from the blood

Amount excreted equation

Amt excreted = amt filtered - amt reabsorbed + amt secreted

E = F-R+S

amounts vary w/physiological control

What does it mean when excretion>filtration?

glomerular filtration and tubular secretion

NO reabsorption

What does it mean when excretion

glomerular filtration and some tubular reabsorption

- no secretion

What does it mean when excretion = 0?

glomerular filtration and total tubular reabsorption

NO secretion

How do you calculate filtration of a solute?

filtration of solute = [solute] in plasma x GFR

What is the glomerular filtration rate?

amount of plasma filtered per time

70 kg person -

180 L/24 hrs or 7.5 L/hr or 125 mL/min

3 L of plasma filtered 60 times per day

What are 2 influencing factors of GFR?

Net filtration pressure: hydrostatic and colloid osmotic pressures

Filtration coefficient:

- surface area for filtration

--- glomerulus surface area

- action of mesangial cells

- permeability of the filtration membrane

--- size barrier: cellular components of blood, proteins, chemicals bound to proteins won't pass usually

--- permeability of the substanc

How does hydrostatic pressure influence blood flow through glomerular capillaries?

forces fluid through the leaky endothelium

averages 55 mmHg and FAVORs FILTRATION into Bowman's capsule

How does colloid osmotic pressure influence blood flow through glomerular capillaries?

it is inside the glomerular capillaries

higher than that of fluid in Bowman's capsule

avg 30 mmHg and Favors fluid movement BACK INTO THE CAPS

How does hydrostatic fluid pressure influence blood flow through glomerular capillaries?

opposes fluid movement into the capsule

avg 15 mmHg

opposes filtration

How do you calculate the net filtration pressure in the glomerulus? NFP

Pc = capillary hydrostatic pressure (filtration): 55 mmHg

Pf = glomerular capsule fluid hydrostatic pressure (absorption): 15 mmHg

πc = capillary colloid osmotic pressure (absorption):

NFP = Pc- πc - Pf

or

NFP = Pc - (Pf + πc)

Pc = out

Pf+πc = in

What is the net driving force pressure in the direction favoring filtration?

10 mmHg

GFR is relatively constant over a wide range of blood pressures...explain.

As long as mean arterial blood pressure remains between 80 and 180 mmHg, GFR averages 180L/day

What is GFR primarily controlled by?

regulation of blood flow through the renal arterioles

if overall resistance of renal arteriole increases, renal blood flow decreases, and blood is diverted to other organs.

Effect of increased resistance on GFR depends on WHERE the resistance change takes place.

What is the general rule for GFR in the afferent arteriole?

it has a direct relationship with NFP

increase blood flow into glomerulus --> increase GFR

decrease blood flow into glomerulus --> decrease GFR

why?

NFP = PC - (PF + πC)

Alter capillary hydrostatic pressure (PC)

What happens if you vasodilate the afferent arteriole?

Vasodilate afferent → ↓ resistance → ↑ flow in afferent → ↑ pressure (PC) → ↑ filtration rate

What happens if you vasoconstrict the afferent arteriole?

Vasoconstrict afferent → ↑ resistance → ↓ flow in afferent → ↓ pressure (PC) → ↓ filtration rate

blood follows the path of least resistance and pressure dissipated in overcoming resistance

What is the general rule for GFR for the efferent arteriole?

indirect relationship with NFP

decreased blood flow out of glomerulus --> increased GFR

increased blood flow out of glomerulus --> decreased GFR

Why?

NFP = PC - (PF + πC)

Alter capillary hydrostatic pressure (PC)

What happens if you vasoconstrict the efferent arteriole?

↑ resistance → ↓ flow in efferent → ↑ pressure (PC) → ↑ filtration rate

- Blood backs up

What happens if you vasodilate the efferent arteriole?

Vasodilate efferent → ↓ resistance → ↑ flow in efferent → ↓ pressure (PC) → ↓ filtration rate

- Blood drains

What is autoregulation of glomerular filtration rate?

local control process in which the kidney maintains a relatively constant GFR in the face of normal fluctuations in BP.

(maintains GFR w/MAP variability: 80-180mmHg)

myogenic response

tubuloglomerular feedback

What is the myogenic response?

intrinsic ability of vascular smooth muscle to respond to changes

same as any arteriole

↑ blood flow → ↑ smooth muscle stretch → ↑ Ca2+ influx

if BP decreases, contraction disappears and arteriole becomes maximally dilated....but vasodilation is not as effective at maintaining GFR as vasoconstriction because normally the aff. arteriole is fairly relaxed.

Consequently, when MAP drops below 80 mmHg, GFR decreases - which helps body conserve blood volume

What is Tubuloglomerular feedback?

paracrine signaling mechanism through which changes in fluid flow through the loop of Henle influence GFR

the macula densa monitors Na+ in filtrate as a measure of GFR

↑ Na+ in filtrate → ↑ paracrine release → afferent arteriole vasoconstriction → ↓ GFR

How does the sympathetic system control GFR?

through the use of NE and E and alpha adrenergic receptors

Smooth muscle contraction → vasoconstriction → ↓ GFR

What hormones control GFR?

angiotensin II

prostaglandins

atrial natriuretic peptide (ANP)

How does Angiotensin II control GFR?

Causes Vasoconstriction → ↓ GFR

↓ filtration coefficient → ↓ GFR

How do prostaglandins influence GFR?

Vasodilation → ↑ GFR

↑ filtration coefficient → ↑ GFR

How does ANP influence GFR?

Vasodilation → ↑ GFR

↑ filtration coefficient → ↑ GFR

What is the process of reabsorption?

basic processes of nephron = remove then absorb

Filtration: 180L/day, 300 mOsm

excretion: 1.5L/day, 50-1200 mOsm

Why go so overboard?

- filtration is fast

- reabsorb to homeostatic balance

- only reabsorb what is needed, excrete the rest