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Excretory systems

eliminate nitrogenous wastes; osmoregulation; include filtration, reabsorption, secretion, and elimination

Osmoregulation

regulation of solute concentration and water balance by a cell or organism

Forms of nitrogenous waste

ammonia, urea, uric acid

Ammonia

a small, very toxic molecule (NH3) produced by nitrogen fixation or as a metabolic waste product of protein and nucleic acid metabolism

Urea

a soluble nitrogenous waste produced in the liver by a metabolic cycle that combines ammonia with carbon dioxide

Uric acid

a product of protein and purine metabolism and the major nitrogenous waste product of insects, land snails, and many reptiles; this is relatively nontoxic and largely insoluble

Filtration

in excretory systems, the extraction of water and small solutes, including metabolic wastes, from teh body fluid; nonselective; blood pressure in afferent arterioles forces material into Bowman's capsule

Reabsorption

in excretory system, teh recovery of solutes and water from filtrate

Secretion

teh discharge of wastes from teh body fluid into the filtrate

Protonephridia

(simple tubes) an excretory system, such as the flame bulb system of flatworms, consisting of a network of closed tubules and lacking internal openings

Metanephridia

(tubes + capillaries) an excretory organ found in many invertebrates taht typically consists of tubules connecting ciliated internal openings to external openings

Filtrate

cell-free fluid extracted from teh body fulid by the excretory system

Bowman's capsule

a cup-shaped receptacle in teh vertebrate kidney that is the initial, expanded segment of the nephron where filtrate enters from the blood

Glomerulus

a ball of capillaries surrounded by Bowmans capsule in teh nephron and serving as the site of filtration in vertebrate kidney

Renal cortex

the outer portion of the vertebrate kidney

Renal medulla

the inner portion of the vertebrate kidney, beneath the renal cortex

Nephron

the tubular excretory unit of the vertebrate kidney

Proximal convoluted tubule

in the vertebrate kidney, the portion of a nephron immediately downstream from Bowman's capsule that conveys and helps refine filtrate; reabsorption of materials (from tubules into intertitial fluid and capillaries, water follows by osmosis); secretion of materials (especially for adjusting pH)

Loop of Henle

the hairpin turn, with a descending and ascending limb, between the proximal and distal tubules of the vertebrate kidney; functions in water and salt reabsorption

Distal convoluted tubule

in the vertebrate kidney, the portion of a nephron that helps refine filtrate and empties its into a collecting duct; regulate Na+, K+, Cl-; regulate pH (H+, bicarbonate); urine relatively dilute

Collecting duct

the location in the kidney where processed filtrate, called urine, is collected from teh renal tubules; NaCl reabsorbed; water reabsorbed by osmosis (hyperosmotic interstitial fluid); urea becomes more concentrated (most is excreted, some is reabsorbed from lower permeable tubule)

Renal pelvis

funnel-shaped chamber that receives processed filtrate from teh vertebrate kidney's collecting ducts and is drained by the ureter

Loop of Henle: descending limb

impermeable to NaCl; permeable to water >>> water is reabsorbed by osmosis

Loop of Henle: ascending limb

permeable to NaCl (thin segment - Nacl diffuses out; thick segment - NaCl actively pumped out); impermeable to water >>> reabsorption of NaCl

Interstitial fluid osmotic gradient

increasingly concentrated from cortex deeper into medulla; important for water reabsorption (water moves by osmosis from tubuel into interstitial fluid and capillaries)

Cortical nephron

in mammals and birds, a nephron with a loop of Henle located almost entirely in the renal cortex

Juxtamedullary nephron

in mammals and birds, a nephron with a loop of Henle that extends far into the renal medulla

Afferent arteriole

in the kidney, the blood vessel supplying a nephron

Regulation of kidney function affects

blood pressure, blood volume, blood osmolarity

Renin

release of renin stimulated by low blood pressure, low blood volume; angiotensinogen -----(renin)---> angiotensinogen II

Renin-angiotensin II-aldosterone system (RAAS)

a hormone cascade pathway that helps regulate blood pressure and blood volume

Juxtaglomerular apparatus

a specialized tissue in nephrons that releases teh enzyme renin in response to a drop in blood pressure or volume

Angiotensin II

a peptide hormone that stimulates constriction of precapillary arterioles and increases reabsorption of NaCl and water by the proximal tubules of the kidney, increasing blood pressure and volume; stimulates the release of aldosterone from the adrenal gland

Aldosterone

a steroid hormone that acts on tubules of the kidney to regulate teh transport of sodium ions and potassium ions; increases NaCl reabsorption and water reabsorption

Antidiuretic hormone

a peptide hormone, also knowns as vaspressing, that promotes water retention by the kidneys; prodcued in teh hypothaliamus and released from teh posterior pituitary, ADH also has activities in teh brain; released if blood osmolarity > 300mosm; increases water permeabllity of distal convoluted tubules and collecting ducts; alcohol inhibits release of ADH

Atrial natriuretic peptide

a peptide hormone secreted by cells of the atria of the heart in response to high blood pressure; ANP's effects on the kindey alter ion and water movement and thereby reduce blood pressure; stifles aldosterone, renin release and NaCl reabsorption

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