Excretory System Flashcards
Excretion
Disposal of waste products
Liver function in excretory system
Excretes wastes by chemically modifying them and releasing them into bile
What waste does the liver deal with specifically?
Hydrophobic/large waste which can’t be filtered by the kidney
Liver synthesizes
Urea and releases it into bloodstream
Urea: Carrier of excess nitrogen from protein breakdown because ammonia is toxic so must be converted into Urea
Large Intestine role in excretory system
Re-absorb wafter and ions from feces
Processes wastes already destined for excretion
Colon role in excretory system
Can excrete excess ions into the feces using active transport
Skin role in excretory system
Produces sweat (contains water, urea and ions)
Similar to urine, but not controlled by amount of waste needing to be excreted, controlled by sympathetic NS and temperature
–Secondary role
Kidney function in excretory system
Excretes hydrophilic wastes (i.e., sodium, bicarbonate, water)
Homeostatic role: Sensitive regulator that must keep concentrations at optimum levels as opposed to just dumping things
Roles of the kidney (3)
- excretion of hydrophilic waste
- Maintain constant solute concentration and pH
- Maintain constant fluid volume (BP & CO)
Kidney: filtration
Passing pressurized blood over a filter
Cells and proteins remain in the blood while wanter and small molecules are squeezed out into the renal tubule (filtrate) to be made into urine
Kidney: Selective reabsorption
Take back useful items from the renal tubule (water, glucose, AA)
Leave wastes and some water in the tubule
Kidney: Secretion
Adding substances to the filtrate in the renal tubule
INC rate of elimination from the blood
Most substances are added to the filtrate after filtration
Last step of urine formation: concentration and dilution
Selective reabsorption of water and decide to make concentrated urine or dilute urine
Renal Artery
Blood enters kidney from renal artery
Direct branch of the lower portion of the abdominal aorta
Renal Vein
Purified blood from kidney is returned to the circulatory system and empties into the inferior vena cava
Ureter
Urine leaves kidney through the ureter into the urinary bladder
Two sphincters controlling release of urine from the bladder:
Internal sphincter and external sphincter
Internal sphincter
Bladder reflexively contracts when the wall is stretched
Smooth muscle
External sphincter
Relaxed when the time is appropriate to pee
Skeletal muscle
Cortex and medulla of the kidney
Cortex: Outer region
Medulla: Inner region
Medullary pyramids of the kidney
Striations within the medulla due to collecting ducts
Papilla
Urine empties from the collecting ducts and leaves the medulla at the tip of a pyramid (papilla)
Calyx
Space that each papilla empties into
Renal pelvis
Urine collects here and empties into the ureter
Nephron contains two components:
- Capsule
- Renal tubule
Capsule: filtration takes place
RT: receives filtrate from capillaries and empties into a collecting duct which dumps urine into the renal pelvis
Blood vessels surrounding the nephrons: function
Carry arterial blood toward the capsule for filtration then surround the tubule to carry filtered blood and reabsorbed substances away from the tubule
Blood from the renal artery flows into an ____ which branches into a ball of capillaries known as ____
Blood from the renal artery flows into an afferent arteriole which branches into a ball of capillaries known as glomerulus
Blood from the renal artery flows into an afferent arteriole which branches into a ball of capillaries known as glomerulus, from there the blood flows into an ____
Efferent arteriole
Constriction of the efferent arteriole results in
High pressure in the glomerulus which causes fluid (blood plasma) to leak out of the glomerular capillaries
The fluid that leaks out of glomerulus when efferent arteriole constricts then
passes through a filter (glomerular basement)
Glomerular basement
blood filter of leakage from glomerulus
After blood filters through the glomerular basement it enters
Bowman’s capsule
What substances DO NOT pass through the glomerulus basement / ARE NOT filtered, but rather remain in the blood in the glomerular capillaries and drain into the efferent arteriole?
Blood cells and plasma proteins do NOT get filtered
Filtrate in the kidney’s tubule consists of:
Some of these substances must be returned to the bloodstream via
Water and small hydrophilic molecules (sugars, AA, urea)
Active transport extracted materials out of tubule and into blood stream
Peri-tubular capillaries
Filtered blood transported out of tubule arrives here and is drained into venues that lead to renal vein
Proximal convoluted tube (PCT) of the nephron
Location of most reabsorption of filtered blood (nearest the bowman’s capsule)
All solute movement in the PCT is accompanied by ____
As a result:
Water movement
Water reabsorption occurs (70% of filtrate reabsorbed here)
Distal convoluted tube (DCT) of the nephron
More regulated reabsorption via hormones
Secretion in the kidney
Movement of substances into filtrate via active transport to increase removal from plasma
“Back up” to glomerulus that ensure everything that needs to get eliminated does get eliminated
Most secretion occurs
in the DCT and collecting duct
Secretion is the primary way that ___ and ____ are deposited into urine
drugs and toxins
Distal nephron (includes collecting duct and DCT) function:
Adjustments made to urine to get correct volume and osmolarity
Distal nephron is controlled by
ADH and aldosterone (hormones)
Condition: dehydration
___ blood volume and ____ blood osmolarity
Function of the hormone ____:
Condition: dehydration
Low blood volume and High blood osmolarity
Function of the hormone ADH/vasopressin: Released by posterior pituitary to prevent water loss in urine by increasing water reabsorption in distal nephron (by making nephron permeable to water)
Water flows out of the distal nephron into kidney tissue to be returned into the blood
Condition: After drinking a lot of water
___ blood volume and ____ blood osmolarity
Function of the hormone ____:
Condition: After drinking a lot of water
High blood volume and low blood osmolarity
need to deposit large volume of dilute urine
Function of the hormone ADH: not needed, collecting duct remains impermeable to water so water in filtrate remains in tubule and lost in urine (diuresed)
Diuresis
Water loss in urine
prevented in dehydration, promoted during hydration
Condition: BP Low
___ blood osmolarity
Function of the hormone ____:
Aldosterone released by adrenal cortex
Low blood osmolarity
Increased reabsorption of Na+ by distal nephron to increase osmolarity leading to increased thirst and water retention raising BP
Condition: BP High
____ blood osmolarity
Function of the hormone ____:
High blood osmolarity
Function of the hormone Aldosterone: not released
Na+ is lost in urine and plasma osmolarity decreases with BP
Triggers for release of aldosterone
Low BP, low blood osmolarity, low blood volume, and angiotensin II
To INC BP:
- Aldosterone:
- ADH:
- Aldosterone causes Na+ absorption which increases plasma osmolarity
- ADH is secreted which results in increased water reabsorption and increased plasma volume
PCT empties into the LOOP OF HENULE which is:
2 parts:
Loop that dips into the renal medulla (inner part of the kidney)
- Descending limb of the loop of henule dips in (thin)
- Ascending: heads out toward the cortex (thick and thin)
Loop of henule is a countercurrent multiplier meaning:
Makes the medulla very salty, and this facilitates water reabsorption from the collecting duct
This is how kidney is capable of making urine with a much higher osmolarity than plasma
Vasa Recta
Eager to reabsorb water released by the descending Loop of Henule because blood they contain is like coffee grinds which have been drained
Returns water reabsorbed by filtrate into the bloodstream
How is the vasa recta performing countercurrent exchange?
The vasa recta are moving in opposite directions as the filtrate in the nephron
Glomerular filtration rate (GFR) depends on
Pressure
Juxtaglomerular apparatus (JGA)
Contact point between the afferent arteriole and the distal tubule
At the JGA, cells at the afferent arteriole are called ____ and at the distant tubule are called _____
AA: juxtaglomerular (JG) cells
DT: macula densa
JG cells are
Baroreceptors monitoring systemic BP
When there is a decrease in BP, JG cells
secrete an enzyme called renin into bloodstream to catalyze conversion of angiotensinogen into angiotensin II by ACE in the lungs
ACT II is a powerful vasoconstrictor that immediately raises BP and stimulates release of aldosterone to INC BP by INC Na+ retention
Macula dense cells are
Chemoreceptors that monitor filtrate osmolarity in distal tubule
When filtrate osmolarity decreases, macula densa cells
stimulate JG cells to release renin
cause dilation of the afferent arteriole increasing blood flow to the glomerulus
How does the kidney regulate pH?
When plasma pH too high: releases HCO3-
When plasma pH is too low: H+ is secreted
What enzyme is involved in regulating pH in the kidney?
Carbonic anhydrase which catalyzes conversion of CO2 into carbonic acid which can dissociate into bicarbonate and a proton
Changes in pH regulated by the kidney are fast or slow?
Slow
