Human Physiology Stuart Ira Fox Chapter 17

Filling of bladder activates stretch receptors that:

send impulses to micturition reflex center of pons

efferent arteriole

small artery that carries blood away from the capillaries of the glomerulus; delivers blood to peritubular capillaries

In process of urine formation, kidneys regulate:

*volume of blood plasma (contributes to BP)
*waste products in blood
*concentration of electrolytes (including Na+, K+, HCO3- and others)
*Plasma pH

Bladder has a smooth muscle lining the wall called the __________ __________

detrusor muscle

Actions of internal and external urethral sphincters are regulated by:

reflex center located in sacral part of cord

nephron

the functional unit of the kidney responsible for removing wastes from the blood and producing urine

arcuate arteries

small vessels found at the base of the renal pyramids

vasa recta

the capillary system in the kidney that serves the loop of Henle

Loop of Henle

section of the nephron tubule that is responsible for conserving water and minimizing the volume of the filtrate

Tubular parts of nephron begins with __________ __________ which transitions into proximal convoluted tubule then to __________ and __________ limbs of Loop of Henle and distal convoluted tubule

glomerular capsule; descending; ascending

Nephron Tubules: Tubule ends where it empties into __________

collecting duct

Bowman's capsule

cup-shaped strucutre of the nephron of a kidney which encloses the glomerulus and which filtration takes place

proximal convoluted tubule (PCT)

the first segment of a renal tubule; walls consist of single layer of cuboidal cells with millions of microvilli (increases surface area for reabsorption)

Kidney function:

regulate plasma and interstitial fluid by formation of urine

Structure of Urinary System

-Paired kidneys are on either side of vertebral column below diaphragm
-About size of fist
-Urine flows from kidneys into ureters which empty into bladder

Major calyces are:

large branches of the renal pelvis

Structure of Kidney: Conducts urine to ureters which empty into __________; passes through the __________ to exit the body; transported using __________

bladder, urethra, peristalsis

Micturition reflex: Stretch can cause spontaneous APs and contraction to __________ regions of spinal cord

S2-S4

guarding reflex

prevents involuntary emptying of the bladder

Drugs for overactive bladders target __________ receptors

muscarinic

Micturition Reflex: Parasympathetic neurons cause contraction of detrusor muscle that relaxes internal urethral sphincter creating:

sense of urgency

T/F: Micturition Reflex: There is involuntary control over external urethral sphincter

False

Blood enters kidney through __________ __________ which divides into interloper arteries

renal artery

Interlobular arteries give rise to afferent arterioles which supply:

glomeruli

Glomeruli are mass of capillaries inside glomerular capsule that gives rise to filtrate that enters:

nephron tubule

cortical nephrons

85% of nephrons; almost entirely in cortex

juxtamedullary nephrons

originate in inner 1/3 cortex; have long LHs; important in producing concentrated urine

T/F: Glomerular capillaries are fenestrated having large pores between its endothelial cells

True

Glomerular filtration: To enter, tubule filtrate must pass through:

capillary fenestrae, glomerular basement membrane, narrow slit diaphragms formed between pedicels of podocytes of glomerular capsule

Plasma proteins are mostly excluded from the filtrate because of:

large size and negative charge

As fluid moves out of the glomerular capillaries, it passes through gaps in the podocytes called slit pores, whose size is regulated by what?
A) slit muscle
B) corpuscle
C) slit diaphragm
D) fenestrations
E) glomerular capillary

slit diaphragm

proteinuria

presence of protein in urine

Glomerular Filtration: Some protein normally enters the filtrate but most is reabsorbed by:

receptor-mediated endocytosis

Glomerular Ultrafiltrate

fluid that enters glomerular capsule, whose filtration was driven by hydrostatic blood pressure, colloid osmotic pressure, very permeable capillaries

glomerular filtration rate

amount of filtrate formed in all the renal corpuscles of both kidneys/minute; averages 125 mL/min

T/F: Total blood volume is filtered every 40 minutes so most filtered water must be reabsorbed or death would ensue from water lost through urination

True

Regulation of GFR is controlled by:

*extrinsic mechanism via sympathetic NS
*intrinsic mechanism via signals from kidneys (auto regulation)
*vasoconstriction or dilation of afferent arterioles affects rate of blood flow to glomeruli and thus GFR

_________ activity constricts afferent arteriole

sympathetic

T/F: Parasympathetic activity helps maintain blood pressure and shunts blood to heart and muscles

False

Sympathetic effects: Urine formation decreases compensating for?

blod pressure drop

renal autoregulation

*Allows kidney to maintain a constant GFR over wide range of BP's
*Achieved via effects of locally produced chemicals on afferent arterioles

Renal Autoregulation: If BP <70 mmHg afferent arteriole ________

dilate

Renal Autoregulation: If BP increases, afferent arterioles ________

constrict

Renal autoregulation is also maintained by _________ _________ between afferent arteriole and volume of filtrate

negative feedback

tubuloglomerular feedback

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

Renal Autoregulation: Increased flow of filtrate sensed by _________ _________ in thick ascending LH; signals afferent arterioles to _________

macula densa; constrict

obligatory water loss

the minimum amount of water required to dissolve urine wastes; 400 mL/day

About 180 L/day of ultra filtrate produced; how many liters of urine is excreted every 24 hours?

1-2 L

reabsorption

return of filtered molecules to the blood

T/F: Water is never transported

True

Filtrate in PCT is isosmotic to blood plasma; thus, reabsorption of H2O by osmosis cannot occur without:

active transport

Reabsorption of H2O is achieved by AT of _________ out of filtrate into interstitial space and into peritubular blood; loss of + charges causes _________ to passively follow Na+

Na+; Cl-

_________% of Na+, Cl- and H2O is reabsorbed in PCT and returned to bloodstream; an additional _________% is reabsorbed in descending LH

65; 20

85% of filtered H2O and salt are reabsorbed early in tubule; this is constant and independent of?

hydration levels

In order for H2O to be reabsorbed, interstitial fluid must be _________

hypertonic

Osmolality of medulla interstitial fluid is 4x that of:

cortex and plasma

Descending limb LH is permeable to _________ and does not actively transport salt

H2O

Ascending limb LH has a _________in depths of medulla and thick part toward cortex

thin segment

T/F: Ascending limb is impermeable to water and permeable to salt

True

Ascending limb LH: thick part actively transport _________ out of filtrate into interstitial fluid

salt

countercurrent multiplier system

mechanism associated with loops of Henle that creates a region having high interstitial fluid osmolarity in renal medulla

countercurrent mechanism

raises osmolality of filtrate in descending limb which causes more concentrated filtrate to be delivered to ascending limb

Positive feedback of countercurrent mechanism

concentrated filtrate is subjected to AT of salts, it causes even higher osmolality around descending limb; process repeats until equilibrium is reached when osmolality of medulla is 1400

Steps of countercurrent mechanism

- Interstitial fluid is hypertonic due to
NaCl pumped out of the ascending limb
- Water leaves descending limb by
osmosis, making the filtrate hypertonic
going into the ascending limb
- More NaCl in the ascending limb can
now be pumped out into the interstitial
fluid
- The greater concentration of the
interstitial fluid draws more water from
the descending limb
- Filtrate in ascending limb now more
concentrated
- Continues until the maximum NaCl
concentration of the inner medulla is
reached.

Vasa Recta: Specialized blood vessels around LH that also have ascending and descending limbs; help create _________ _________; take in salt in descending portion but lose them again in ascending region, keeps salt in _________ _________; high salt concentration at beginning of ascending region pulls in H2O removed from interstitial space

counteract system; interstitial space

Urea transporters and aquapourins present in descending region aid in?

counter current exchanges

Countercurrent mechanism recirculates ________, trapping some medulla interstitial fluif

salt

What is a waste product of protein metabolism?

urea

Effects of urea: Transported out of collecting duct and into ________ ________, diffuses back into ascending limb and cycles around continuously

interstitial fluid

What plays an important role in water conservation?

collecting duct

T/F: Collecting duct is impermeable to salt in medulla

True

Collecting duct permeability to H2O depends on levels of ________

ADH

ADH is secreted by ________in response to dehydration

posterior pituitary

ADH stimulates insertion of ________ into plasma membrane of collecting duct

aquaporins

When ADH is high, H2O is drawn out of collecting duct by:

high osmolality of interstitial fluid (and reabsorbed by vasa recta)

renal clearance

refers to ability of kidney to remove substances from blood and excrete them in urine

Renal clearance occurs by ________ and by ________

filtration; secretion

secretion

opposite of reabsorption; substances from vasa recta are transported into tubule and excreted

Reabsorption ________ renal clearance; secretion increases clearance

decreases

exertion rate

(filtration rate + secretion ratea) - reabsorption rate

Xenobiotics

chemical substances that are foreign to the biological system

Insulin, a fructose polymer, is useful for?

measuring GFR because it is neither absorbed nor secreted

renal plasma clearance (RPC):

volume of plasma from which a substance is completely removed/min by excretion in urine

If substance is filtered but not absorbed then all filtered will be ________; If substance is filtered and reabsorbed then ________; if substance is filtered but also secreted and excreted then ________

excreted RPC = GFR; RPC < GFR; RPC will be > GFR (=120mL/min)

Clearance of urea is a passive process because of:

presence of carriers for facilitative diffusion of urea

Not all blood delivered to glomerulus is filtered into glomerular capsule; ________% is filtered; rest passes into efferent arteriole and back into circulation

20

PAH clearance

used to measure renal plasma flow because it is filtered, not reabsorbed and almost completely secreted.

Filtered glucose and amino acids are normally ________% reabsorbed from filtrate; occurs in PCT by carrier-mediated cotransport wit Na+

100

transport maximum (Tm)

the maximum transport rate that occurs when all carriers are saturated

glycosuria

glucose in the urine

renal plasma threshold

more glucose is in the filtrate than active transport can handle

hyperglycemia

exceeds renal plasma threshold

diabetes mellitus (DM)

insulin is not secreted adequately or tissues are resistant to its effects

Kidneys regulate levels of Na+, K+, H+, HCO3+, Cl- and PO4 by:

matching excretion to ingestion

The control of plasma Na+ is important in the regulation of:

blood volume and pressure

Control of plasma K+ is important in proper functions of:

cardiac and skeletal muscles

Role of Aldosterone in Na+/K+ Balance

90% filtered Na+ & K+ reabsorbed before DCT

Remaining is variably reabsorbed in DCT & cortical CD according to bodily needs

Regulated by aldosterone (controls K+ secretion & Na+ reabsorption)

In the absence of aldosterone:
80% of remaining Na+ is reabsorbed in DCT & cortical CD

When aldosterone is high: all remaining Na+ is reabsorbed

K+ secretion is only way K+ ends up in urine; is directed by:

aldosterone and occurs in DCT and cortical CD

T/F: High K+ or low Na+ will increase aldosterone and K+ secretion

True

juxtaglomerular apparatus

Specialized cells next to the glomerulus that help to regulate blood pressure