By: Kaylie Corda, Finn Mahoney, & Liana Tabtiang

The Excretory System

The FUNction of the Excretory System

Source 2

The excretory system is a passive biological system that removes excess, unnecessary materials from an organism, so as to help maintain homeostasis within the organism and thus prevent damage to the body.

The Excretory System Source 1

The body’s blood filtration system begins with the kidneys. Blood is pumped in from the heart and filtered in the medullas of the kidneys. Cleaned blood is pumped back into the body and filtered solution is collected in the Renal Pelvis. Two tubes, the Ureters, drain the fluid from the renal pelvis and empty it into the Urinary Bladder. The urethra empties the urine from the bladder.

The Kidney Source 1

● Two bean shaped organs that act as the body’s blood filters and liquid waste generatorso the Cortex

spongy external tissue surrounding the kidney’s filters

o the Medulla pyramid shaped where blood is filtered

o the Renal Pelvis sac in the interior of the kidney collects filtered fluid from blood (liquid waste) drained by the Ureter into the Urinary Bladder

Summary of the Kidney Source 1, 3

Cortex (connective tissue surrounding the Medullas and Renal Pelvis)

Medullas (structures through which unfiltered blood is passed)

Renal Pelvis (sac in the interior of the kidney where urine is collected)

Renal Artery (passes unfiltered blood from the heart to medullas and nephrons (filtration units within the medullas)

Ureter (drains renal pelvis into urinary bladder)

Renal Vein (passes filtered blood out to the rest of the body)

The Medulla Source 1, 3

● Several pyramid shaped medullas for blood filtration within each kidney

● Within each medulla, unfiltered blood passes through thousands of specific blood vessel structures called nephrons

● The renal artery feeds blood to the medullas from the heart and the renal vein transports the blood that has already passed through the nephrons out to the rest of the body

The Nephron Source 1

● Located on the border between the Cortex and Medulla● Act as vessel filters for the blood● Functional units of the kidney● Made up of a Glomerulus, Bowman’s Capsule, Proximal tubule, Loop of Henle,

Distal tubule, and Peritubular Capillaries● Glomerulus (a semipermeable membrane):

o a collection of tightly packed, looped blood vessels that are about 100 times more permeable to water and small solutes

● The Glomerulus is surrounded by the Bowman’s Capsule (an impermeable cup):o Think of the glomerulus and Bowman’s Capsule as a permeable bag within an

impermeable one● Clean blood moves out of the Glomerulus and through the Peritubular Capillaries

back into the body● Waste filtrate (in the Bowman’s Capsule) moves through the Proximal tubule, Loop

of Henle, and Distal tubule, where the rest of the waste is added

Summary of the Nephron Source 1

Glomerulus (collection of Glomerular Capillaries)

Renal Artery (feeds unfiltered blood to the Nephron)

Renal Vein (carries cleaned blood to the rest of the body)

Peritubular Capillaries (capillaries carrying clean blood around the Distal and Proximal Tubules)

Bowman’s Capsule (surrounds glomerulus)

Proximal Tubule (carries filtrate)

Loop of Henle (carries filtrate)

Distal Tubule (carries filtrate)

Collecting Duct (collects filtrate and transports to Renal Pelvis)

Urine Formation Source 1, 3

Pressured Filtration: blood pressure generated by heart’s contractions filters blood by forcing water and all solutes except proteins through the walls of the glomerular capillaries. The protein-free filtrate moves out of the cupped part of the nephron and into the proximal tubule (first step in exit from the body)

● Utilizes facilitated diffusion (through channel proteins and membrane) out of the blood and into the filtrate along an artificially high pressure gradient

Tubular reabsorption: as the filtrate in the Bowman’s capsule passes along the proximal tubule, Loop of Henle, and distal tubule, most of the water in the filtrate is drawn out from tubule and into the peritubular capillaries surrounding the tubule and reabsorbed into the blood

● Utilizes facilitated diffusion (through channel proteins and membrane) out of the filtrate and into the blood along an osmotic pressure gradient

Tubular secretion: as the blood moves through the peritubular capillaries, hydrogen and potassium ions (H+ and K+) are pulled (diffused through the capillary wall and tubule wall) from the peritubular capillaries (filtered blood) and into the tubules (bodily waste)

● Utilizes facilitated diffusion (through channel proteins and membrane) out of the blood and into the filtrate along an electric charge gradient

Urinary Process Source 1

● After leaving the distal tubule, urine is collected in the Renal Pelvis

● Urine leaves the renal pelvis through the Ureter and travels into the Urinary bladder

● Urine exits the urinary bladder through the Urethra.

Homeostasis and Urine Function Source 3

● Regulates blood volume and pressure:

○ adjusts the volume of water in blood (through pressured filtration)

○ releases Erythropoietin (EPO) and Renin

■ EPO is a hormone that bonds with receptor proteins in the bone marrow to stimulate red blood cell production

■ Renin is an enzyme that mediates extracellular volume, and arterial vasoconstriction

● Regulates blood pH by balancing ion concentrations:○ Hydrogen, Sodium, Potassium, and Chloride ions lost in urine

● Prevents valuable nutrient loss while excreting organic waste products (solutes useless to the body)

Resources:

1. Starr, Cecie and Taggart, Ralph. Biology: The Unity and Diversity of Life. California: Brooks/Cole, 2001. Print.

2. Science Daily. “The Excretory System.” Science Daily. Web. 13 November 2014 <www.sciencedaily.com/articles/e/excretory_system.htm>

3. Napa Valley College. “The Urinary System.” Napa Valley College. Web 14 November 2014 <http://www.napavalley.edu/people/briddell/Documents/BIO%20105/_START_HERE_ch18_lecture.pdf>

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