ch. 17: physiology of the kidneys

renal

pertaining to the kidneys

renal system

regulation of ECF environment through urine

functions of renal system

1. regulates blood volume

2. eliminates organic waste products of metabolism (urea, uric acid, creatine)

3. regulates balance of electrolytes (Na+, K+, HCIO3-)

4. maintains acid-base balance/pH of plasma w/ respiratory system

function of kidneys (2)

1. formation of urine

2. water/electrolyte balance

3. secretion of toxins and drugs into urine

function of ureters (2)

transfer of urine to bladder

function of urinary bladder

storage and micturition (urination) via urethra

micturition (peeing)

contractions of smooth muscle in ureter wall cause urine to move from ureter to bladder

detrusor muscle

main muscle (smooth) of the bladder walls; contraction produces micturition

internal urethral sphincter

base of bladder (smooth, involuntary)

external urethral sphincter

contraction prevents urination (skeletal, voluntary)

contraction and relaxation of muscles is determined by

1. neuronal input due to stretching of the bladder when it fills

2. voluntary decision making

nephron

1. functional unit of the kidneys

2. > 1,000,000 nephrons per kidney

what does the nephron consist of

1. renal corpuscle (glomerular capsule + glomerulus)

2. tubule

how does blood enter and exit the kidney

enters through the renal artery and exits via the renal vein

glomerulus (glommeruli)

a capillary network in the renal corpuscle

glomerular filtration

first step of urine formation; blood is filtered in glomerulus

what happens to the 20% of plasma from glomerulus

it filters out and into the Bowman’s capsule and then moves into tubule

what happens to the remaining 80& of blood in glomerulus

it exits the real corpuscle through efferent arteriole to the peritubular capillaries and drains into veins that exit the kidney as the renal vein

glomerular/Bowman’s capsule

surrounds glomerulus and fluid filters out of glomerulus into capsule

proximal convoluted tube

reabsorption of salt, water, etc. into peritubular capillaries that surround tubule

collecting duct

distal convoluted tubule empties into it and duct drains into renal pelvis and then into ureters

fenstrae

large pores in glomerular capillaries for filtration

what is filtrate/ultrafiltrate free of

cell-free and mostly protein-free; similar to plasma

glomerular filtrate is around ? each day, but urine excretion is only around ? per day

180 L, 1-2 L

1% of glomerular filtrate is excreted as urine. what happens to the other 99%?

it returns to vascular system (reabsorbed) to maintain blood volume and pressure

reabsorption

movement of materials from the tubules into the peritubular capillaries (back into general circulation)

what does urine volume depend on

fluid needs of body to maintain blood volume/pressure = volume of fluid reabsorbed varies

filtration

movement of fluid and solutes from the glomerulus into the capsule and then into the tubules

for water to be reabsorbed into bloodstream by osmosis, ISF surrounding tubule must be ?

hypertonic, causing water to move out of tubule

fluid is hypertonic due to ?

countercurrent multiplier system

countercurrent multiplier system

opposite direction flow + close proximity of limbs allow them to interact to crate high osmotic pressure in ISF

what happens in descending loop of henle

1. water is reabsorbed (permeable to water, not salt)

2. filtrate concentrates as it descends

what happens in ascending loop of henle

1. Na+ is actively pumped out of filtrate and into ISF

2. Cl- follows because of electrical attraction

3. filtrate becomes diluted because not permeable to water as it ascends because of high osmolarity

what happens at the bend of the loop

1. fluid has a high osmolarity (1200 mOsm")

2. saltiness of ISF is mulitplied because lack of permeability to water

role of osmoreceptors in ADH secretion

1. osmoreceptors in hypothalamus detect changes in plasma osmolarity due to water intake (dehydration)

2. stimulates the release of ADH from the posterior pituitary gland to promote water absorption in the kidneys

3. reduces urine output and restores fluid balance

renal plasma clearance

volume of plasma that is cleared of a substance by kidneys per unit time

how are substances removed from plasma

via filtration from glomerulus or secretion into filtrate

secretion

movement of substances from the peritubular capillaries into the tubular fluid, for excretion in the urine

reabsorption of a substances ? its clearance

reduces

what happens to filtered glucose and AAs

they are completely reabsorbed in proximal tubule via active transport

transport maximum

when the concentration of glucose exceeds the capacity of the transporters

glucosuria

excess glucose is excreted in urine

when is most of the filtered Na+ and K+ reabsorbed and what does their concentration in the urine depend on

in the early part of nephron and depend on physiological needs/homeostasis and are adjusted later in the nephron

what activates the Renin-Angiotensin-Aldosterone system

decreased plasma [Na+]

Renin-Angiotensin-Aldosterone system

1. secretes aldosterone (adrenal cortex) when Na+ intake is low

2. stimulates Na+ reabsorption to increase plasma [Na+]

3. stimulates K+ secretion into filtrate when plasma [K+] is high

4. causes passive reabsorption of Cl-

ADH

regulates water reabsorption to regulate urine volume and blood volume

where is potassium filtered and reabsorbed

filtered from the glomerulus and some is reabsorbed in the proximal convoluted tubule

how do they kidneys regulate blood pH

by excreting H+ in the urine and reabsorbing bicarbonate into the bloodstream

is urine basic/acidic and why

acidic because almost all of the filtered bicarbonate is reabsorbed

acidosis

pH < 7.35; increased plasma [H+] and more H+ in filtrate. bicarbonate is synthesizd in the proximal tubule and absorbed into the bloodstream

alkalosis

pH > 7.45; decreased plasma [H+] and less H+ in filtrate, so less bicarbonate is reabsorbed to compensate