The Excretory System Flashcards
Liver
Responsible for excreting many wastes by chemically modifying them and releasing them into bile
Deals with hydrophobic or large wastes
Urea
synthesized by the liver
Is a carrier of excess nitrogen resulting from protein breakdown
Large Intestine
reabsorbs water and ions from feces
Skin
Produces sweat which contains water, ions, and urea (similar to urine)
Sweat
Controlled by temperature and level of sympathetic nervous system activity
Kidneys
Responsible for the excretion of hydrophilic wastes like urea, sodium, bicarbonate, and water
Essential for the maintenance of constant blood pH
Homeostasis
Constancy of physiological variables
Three main roles of the kidney
Excretion of hydrophilic wastes
Maintenance of constant solute concentration and constant pH
Maintenance of constant fluid volume (important for blood pressure and cardiac output)
Filtration
Passage of pressurized blood over a filter
Cells and proteins remain in the blood while water and small molecules are filtered into the renal tubule
Filtrate
Fluid in the renal tubule
Selective absorption
Reabsorption of useful items like glucose, water, and amino acids
Secretion
the addition of substances to the filtrate
Can increase the rate at which substances are eliminated from the blood
Concentration and dilution
selective reabsorption of water to determine whether urine is going to be concentrated or dilute
Internal Sphincter
Made of smooth muscle (involuntary)
External Sphincter
Made of skeletal muscle (voluntary)
ADH
When dehydrated: ADH is released by the posterior pituitary and results in increasing water reabsorption in the distal nephron
When hydrated: ADH is not secreted
A drop in blood pressure can also trigger ADH release
Aldosterone
Low BP: aldosterone is released by the adrenal cortex and results in increased reabsorption of sodium by the distal nephron. This results in increased plasma osmolarity, increased thirst and water retention, and increases BP
High BP: aldosterone is not released
Other triggers for the release of aldosterone: low blood osmolarity, low blood volume, angiotenisogen II
Countercurrent multiplier
This makes the medulla very salty and this facilitates water reabsorption from the collecting duct. This is how the kidney is capable of making urine with a much higher osmolarity than plasma
Vasa Recta
form a loop that helps maintain the high concentration of salt in the medulla
Return to the bloodstream any water that is reabsorbed from the filtrate
Juxtaglomerular cells
In response to low BP, they release Renin –> converts Angtiotensinogen to Angiotensin 1 –> converted to Angiotensin II by ACE.
Angiotensin II
Baroreceptors that monitor systemic blood pressure
Is a vasoconstrictor and increases blood pressure
It also stimulated the release of aldosterone which helps raise BP by increasing water retention
Th cells of the macula densa
Chemoreceptions and monitor filtrate osmolarity in the distal tubule
When filtrate osmolarity decreases, the cells of the macula densa stimulate the JG cells to release Renin
Also cause a direct dilation of the afferent arteriole
Carbonic Anhydrase
Catalyzes the conversion of CO2 to carbonic acid
Calcitonin
Released by the C cells of the thyroid gland
Released in response to high blood Ca2+ levels
Causes Ca2+ to be removed from blood by deposition in bone, reduced absorption by the gut, excretion in the urine
