SJSU BIOL 66 Final Exam (Ch. 17, 18, 19, 20)

Renal

pertaining to the kidneys

Main function of renal system:

regulation of ECF environment in the human body through urine formation

Renal System functions:

1. regulate blood volume

2. elimate organic waste products of metabolism: urea, uric acid, creatinine, end products of hemoglobin breakdown

3. regulate balance of electrolytes (Na+ , K+, HCO-3, other ions

4. maintain acid-base balance/pH of plasma

Kidney (2)

formation of urine, water and electrolyte balance, secretion of toxins/drugs into urine, gluconeogensis

Gluconeogensis

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

Ureters (2)

transfer of urine to bladder

Urinary Bladder

storage and micturition (urination) via urethra

Urethra

flow of urine from bladder to outside (micturition)

The paired kidneys form a filtrate of the blood which is modified by what?

reabsorption and secretion

Urine destined for excretion moves from

kidneys --> ureters --> bladder --> urethra

Outer layer of kidney

Renal cortex

Renal cortex

site of glomerular filtration and the convoluted tubules

Inner layer of kidney

renal medulla

Renal Medulla

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

Micturition (urination)

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

Bladder walls = smooth muscle (detrusor muscle)

contraction of detrusor produces micturition

Internal uretheral sphincter (smooth muscle)

base of bladder

External urethral sphincter (skeletal muscle)

below and surrounds the urethra, its contraction can prevent urination

contraction/relaxation of these muscles are determined by

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

2. voluntary decision making

Blood enters kidneys via

renal artery

Blood exits kidney via

renal vein

Nephron

functional unit of the kidneys, consisting of renal corpuscle and tubule (>1M nephrons per kidney)

Renal corpuscle

glomerular capsule + glomerulus

Step 1: How does blood enter the kidney

blood enters through renal artery

Step 2: What does the renal artery branch into?

renal artery branches into afferent aterioles, which carry blood to glomeruli

Blood flow into nephron order:

renal artery -> afferent arterioles -> glomeruli

What happens at the glomerulus?

about 20% of plasma filters out of the glomerulus into the glomerular capsule

Where does filtrate go after leaving the glomerulus?

glomerulus -> glomerular capsule -> tubule

What is the full flow of filtrate through the nephron?

filtrate: glomerulus -> glomerular capsule -> tubule -> collecting duct -> renal pelvis -> ureters

What does the collecting duct drain into?

the renal pelvis, which drains into the ureters

Blood remaining in glomerulus (80%)

exits renal corpuscle through efferent arterioles to peritubular capillaries to renal vein

Glomerular capsule/Bowman's capsule

- surrounds glomerulus

- fluid filters out of glomerulus into capsule

Proximal convoluted tubule function #1:

1. filtrate from gomerulus enters lumen of tubule

Proximal convoluted tubule function #2:

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

Proximal convoluted tubule function #3:

secretion of substances into filtrate

Glomerular Filtration

filters through large pores in glomerular capillaries called fenestrae

Filtrate

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

Reabsorption of Salt and Water

glomerular filtrate is around 180L/day, urine excretion is around 1-2L/day

What percentage of filtrate becomes urine?

1% urine, 99% reabsorbed back to vascular system

Why is reabsorption important?

maintains blood volume and blood pressure by returning most filtrate to the bloodstream

What is reabsorption?

return of filtrate from tubules to peritubular capillaries via osmosis

Why does urine volume change?

it varies depending on the body's fluid needs

Where does most salt and water reabsorption occur?

proximal tubule

Where else is some water reabsorbed?

descending limb of the loops of Henle

How is Na+ reabsorbed in the proximal tubule?

actively transported out of filtrate

Why does Cl- follow Na+?

electrical attraction (passive transport)

Why does water follow NaCl?

Osmosis -> water moves into peritubular capillaries

Countercurrent Multiplier System

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

What is countercurrent flow?

opposite-direction flow in ascending and descending limbs

Why is countercurrent important?

allows interaction between limbs to create high osmotic pressure in ISF

Is ascending limb permeable to water?

No, impermeable to water

What happens in the ascending limb?

Na+ is actively pumped out, Cl- follows passively due to electrical attraction

What happens to the tubular fluid in the ascending limb?

becomes more concentrated (hypertonic)

NaCl accumulates in the ISF here

increasing osmolarity of ISF so that reabsorption occurs in the descending limb

Is descending limb permeable to water?

Yes, but not salt

How does water leave descending limb?

osmosis -> ISF -> capillaries

What happens after fluid enters the ascending limb?

Na+ is actively pumped out and Cl- follows, creating diluted tubular fluid and more concentrated ISF

Step 1 of Countercurrent Multiplier System

ISF becomes more concentrated, Na+ is pumped out, Cl- follows due to electrical attraction

Step 2 of Countercurrent Multiplier System

water diffuses out via osmosis, this increases osmolarity of tubular fluid and decreases its volume as the fluid descends

Step 3 of Countercurrent Multiplier System

fluid at the bend of the loop has a high osmolarity (1200 mOsm). saltiness of ISF is multiplied due to lack of permeability to water

Osmoreceptors

a change in water intake alters plasma osmolarity, which is sensed by hypothalamic osmoreceptors

ADH secretion

altered to effect water reabsorption in the kidneys.

How does this affect volume of urine excreted?

to maintain blood pressure

Renal Plasma Clearance

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

How are substances removed from plasma?

by filtration or secretion into the tubules

What is secretion?

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

How does reabsorption affect clearance?

decreases clearance

Filtered glucose and AAs =

completely reabsorbed in proximal tubule via active transport

What happens when glucose concentration exceeds the transport maximum?

excess glucose is excreted in the urine -> glucosuria

Glucosuria

the presence of glucose in the urine due to exceeded transport maximum

When does glucosuria occur?

when plasma glucose concentration is too high (around 180-200 mg/dL) like diabetes mellitus

What is transport maximum?

maximum rate at which glucose transporters can reabsorb glucose before excess appears in urine

Where is most filtered Na+ and K+ reabsorbed?

early part of nephron

What determines Na+ and K+ concentrations in urine?

physiological needs/homeostasis, adjusted late in nephron

What activates the renin-angiotensin-aldosterone system (RAAS)?

decreased plasma Na+ concentration

What does activation of RAAS cause?

secretion of aldosterone from adrenal cortex

What does aldosterone do to Na+?

stimulate Na+ reabsorption --> increases plasma Na+

What happens to Cl- when aldosterone increases Na+ reabsorption?

Cl- is passively reabsorbed

Why does blood volume increase with aldosterone?

water follows NaCl via osmosis, increasing blood volume

What does aldosterone do to K+?

stimulates K+ secretion into filtrate when plasma K+ is high

What happens to potassium at the glomerulus?

potassium is filtered from the blood into filtrate

Where is some potassium reabsorbed?

in proximal convoluted tubule

Where does potassium secretion occur in nephron?

in collecting duct

What hormone stimulates potassium secretion?

aldosterone

when does aldosterone stimulate potassium secretion

when plasma K+ concentration is high

What is the effect of aldosterone on potassium?

increases K+ secretion into the filtrate, leading to more K+ excreted in urine

What is cortical collecting duct responsible for in K+ balance?

it secretes potassium into the filtrate under aldosterone's control

What happens to potassium that is secreted into the collecting duct?

it is excreted in the urine

What does ADH regulate?

water reabsorption to control urine volume and blood volume

What stimulates aldosterone secretion when Na+ intake is low?

The RAAS

Aldosterone stimulates Na+ reabsorption

in the cortical collecting duct

Acid/Base Balance

CO2 + H2O -> H2CO3 -> H+ + HCO-3

Kidneys regulate blood pH by

excreting H+ in urine and by absorbing biocarbonate into bloodstream

Why is urine acidic?

all of the filtered biocarbonate is reabsorbed

Acidosis (pH < 7.35)

increased plasma (H+) and more H+ in filtrate

Alkalosis (pH > 7.45)

decreased plasma (H+) and less H+ in filtrate