Chapter 17: Physiology of the Kidneys

what is the defintion of renal

pertaining to the kidneys

what is the main function of the renal system

regulation of extracellular fluid (ECF) environment in the human body through urine formation

the renal system regulates

blood volume

the renal system eliminates

waste products of metabolism: urea (protein breakdown), uric acid (nucleic acids), creatinine (muscle creatine), end products of hemoglovin breakdown

the renal system regulates balance of

electrolyes (Na+, K+, HCo3-, other ions)

the renal system, with the respiratory system maintains

acid-base balance/pH of plasma

how many kidneys do we have

2

what are the functions of kidneys

• urine formation

• water and electrolyte balance

• secretion of toxins and drugs into urine

• gluconeogenesis: synthesis of glucose from AAs during prolonged fasting (also occurs in liver)

how many ureters do we have

2

• one per kidney

what is the function of ureters

transfer of urine to bladder

what is the function of urinary bladder

storage and micturition (urination) via the urethra

function of urethra

flow of urine from bladder to outside (micturition)

what do paired kidneys form

a filtrate of the blood that is modified by reabsorption and secretion

how does urine that is destined for excretion move

from the kidneys along the ureters to the bladder

where is urine excreted

through the urethra

what is the outer layer of the kidney

renal cortex

what is the renal cortex the site of

glomerular filtration as well as the convoluted tubules

what is the inner layer of the kidney

renal medulla

what does the renal medulla contain

location of the longer loops of Henle, and the drainage of the collecting ducts into the renal pelvis and ureter

what is micturition

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

what kind of muscle do bladder walls contain

smooth muscle (detrusor muscle)

what is at the base of bladder

internal urethral sphincter (smooth muscle)

what is the external urethral sphincter (skeletal muscle)

is below this and surrounds the urethra.

• its contraction can prevent urination

what is contraction and relaxation of these muscles determined by (micturition)

• neuronal input, due to stretching of the bladder when it fills

• voluntary decision making

how does blood enter the kidney

via the renal artery

how does blood exit the kidney

via the renal vein

what is in the kidney

extensive branching and capillary networks including the glomeruli

what is the nephron

functional unit of the kidneys, consisting of a renal corpuscle (glomerular capsule + glomerulus) and tubule

how many nephrons are per kidney

> 1,000,000

how is blood brought back to the the glomeruli

branching of renal artery → afferent arterioles

what is a glomerulus

a capillary network in renal corpuscle

how much % of plasma does the glomerulus filter

20% filters out of glomerulus into glomerular capsule and then moves into tubule

pathaway of plasma being filtered in glomerulus

filtrate from glomerulus → glomerular capsule → tubule → collecting duct → renal pelvis → ureters

how much blood (%) remains in glomerulus

80% exits renal corpuscle through efferent arteriole to the pertibular capillaries

pathaway of blood remaining in glomerulus

80% of blood in glomerulus → efferent arteriole → pertitubular capillaries → renal vein

what is the glomerular capsule/Bowman’s capsule

• surrounds glomerulus

• fluid filters out of glomerulus into capsule

what is the proximal convoluted tubule

• filtrate from glomerulus enters lumen of tubule

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

• secretion of substances into filtrate

what is the collecting duct

• distal convoluted tubule empties into it

• duct drains into renal pelvis and then into ureters

pathaway of nephron

glomerular capsule/Bowman’s capsule → proximal convoluted tubule → descending limp of loop of Henle (some reabsorption) → ascending limp of loop of Henle → distal convoluted tubule → collecting duct

glomerular filtration

• filters thorugh large pores in glomerular capillaries called fenestrae

• filtrate (or ultrafiltrate) is cell-free and mostly protein-free; otherwise similar to plasma

glomerular filtrate is around 180 L each day, but urine excretion is only

around 1-2 L per day

how much of the filtrate is excreted and how much is absorbed

1% is excreted as urine and 99% of filtrate returns to vascular system (reabsorbed) to maintain blood volume and pressure

what is reabsorption

return of filtrate from tubules to pertibular capillaries, via osmosis

why does urine volume vary

depending on fluid needs of body (e.g. to maintain blood volume and pressure), so volume of fluid reabsorbed varies

where is most salt and water in filtrate reabsorbed

mostly in proximal tubule; some reabsorbed in descending limb of loop of Henle

what does filtratation refer to

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

what does reabsorption refer to

the movement of materials from the tubules into the pertibular capillaries, i.e. back into general circulation

Na+ and Cl- in proximal tubule

Na+ is actively transported out of filtrate and Cl- follows passively by electrical attration

why does water follow the salt into the pertibular capillaries

due to osmosis