3b ­ Excretion.notebook
January 10, 2023
The Excretory System
Role of Excretion
1. The elimination of metabolic waste products from our body
(Not to be confused with secretion or egestion!)
2. The homeostatic regulation of chemical concentrations
Examples of substances to be controlled:
CO2
salts (eg. Ca2+, Na+, H+)
drugs, pesticides, food additives
nitrogenous wastes
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3b ­ Excretion.notebook
January 10, 2023
Nitrogenous Wastes
What are they?
Biochem Alert!!!
Cellular Respiration:
• converts food energy into usable cell energy (ATP)
• food energy sources are carbs, lipids, amino acids
• carbs' and lipids' composition: C,H,O
• amino acids' composition: C,H,O,N
• respiration deals with C,H,O byproducts alright, but NOT N
• so nitrogen is a problem, and must be dealt with prior to the
respiratory process
• amino acids must be deaminated before being broken down for
energy
• the amino groups are then excreted:
as ammonia (though this is toxic)
as uric acid (primarily birds, reptiles)
as urea
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3b ­ Excretion.notebook
January 10, 2023
Urea
H
H
N C
O
N
H
H
• urea is produced in the liver and can be excreted from
the body through our kidneys and sweat glands
• amino groups are non-toxic in this form
Organs of Excretion
Kidneys
Lungs
Skin
Liver
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3b ­ Excretion.notebook
January 10, 2023
The Urinary System
The Kidneys
Cortex
Medulla
• attached to the dorsal
wall of the upper abdomen
• highly vascularized
Pelvis
• three different regions:
Cortex: outermost layer, covered by a leathery capsule
Medulla: inner layer
Pelvis:
hollow chamber; entrance for blood vessels and ureter
• the kidney is composed of millions of individual units called nephrons
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3b ­ Excretion.notebook
January 10, 2023
Ureters
• muscular ducts through which urine flows out of each kidney, and
into the ...
Urinary Bladder
• muscular sac in which urine is temporarily stored
• openings are guarded by sphincters
Urethra
• duct through which urine is eliminated from the bladder
(urination)
The Nephron
cortex
medulla
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3b ­ Excretion.notebook
January 10, 2023
Glomerulus
• a ball of capillaries supplying
blood to the nephron
Bowmans Capsule
• a cup­like extension of the
nephric tube
• single layer of cells thick
• encloses the glomerulus
Proximal Tubule
• highly coiled hollow tube
joined to Bowmans Capsule
Loop of Henle
• U­shaped, narrow tube
• extends into the medulla region
of the kidney
Distal Tubule
• another highly coiled tube,
downstream of loop of Henle
Collecting Tubules
• tubules which several nephrons
empty into
• carry urine out of kidney toward
ureter
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3b ­ Excretion.notebook
January 10, 2023
Blood Pathway
• arteries carry blood to the kidneys for cleaning
• some of the blood leaves the blood vessels and
enters nephron; some remains in these blood vessels
renal artery
arterial branching
afferent arteriole
glomerulus
efferent arteriole
peritubular capillaries
venal branching
renal vein
Video ­ Amoeba sisters ­ 9 min ­ can watch up to 4 min
Video : 3 min ­ parts
F.Y.I.
(for urine formation ...)
Video : 3 min­ blood path
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3b ­ Excretion.notebook
January 10, 2023
Blood
What's in it?
• water
• cells
• protein
• ions (Na+, K+, ...)
• soluble nutrients (glucose, a.a., ...)
• urea
Glomerulus/Bowmans Capsule:
• blood pressure forces water and solutes into Bowmans
capsule
• this solution is called the nephric filtrate
• blood cells and proteins are too large, so remain in the
capillaries
Blood
Solutes, water
Blood cells, protein
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3b ­ Excretion.notebook
January 10, 2023
Proximal tubule:
• filtrate flows through here
• useful stuff is reabsorbed back into
blood capillaries by facilitated diffusion
and/or active transport
• because water concentration of the
filtrate increases, some of it is also
reabsorbed by osmosis
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