Download 11-3noteskidneys

Topic 11.3
The Kidney & Osmoregulation
Excretory System
• Function is to rid the body of toxic waste through excretion
• Excretion: the removal of waste products of metabolic
processes in the body
Types of Regulation
• Osmoconformers: maintain solute concentrations in their
body tissues that are isotonic to the surrounding environment.
• Saltwater fish (sharks etc.)
• Osmoregulators: have adaptations to live in aquatic
environments that are not isotonic to their body tissues.
• Freshwater fish
Types of regulation Cont.
• Malpighian Tubules: osmoregulation by insects
• Absorb salt, water and waste
• Mammals: osmoregulation by mammals using the kidneys
• use nephrons to regulate concentration of substances
The Human Excretory System
• Consists of the following parts
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Kidneys
Ureters
Urinary Bladder
Urethra
• Kidneys carry out
Both excretion and
Osmoregulation
The filtrate eventually
Becomes urine
Parts of the Kidney
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•
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Outside is called the renal cortex
Middle is called the renal medulla
Inner funnel shaped section is called the renal pelvis
Renal artery brings blood into the kidneys
Renal vein takes blood away from the kidneys
The Nephron
• The functional unit of the kidney
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•
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Ultrafiltration
Selective reabsorption
Secretion
excretion
Functions of the Nephron
Function
Location
Process
Filters small molecules through fenestrations
(pores) in the capillaries from the blood into
the Bowman’s capsule (urea, salts, glucose,
amino acids). Large proteins & blood cells are
too large to fit in pores so they stay in the
blood capillaries
Ultrafiltration
Glomerulus
Selective
reabsorption
Proximal
convoluted
tubule
Glucose, amino acids & salts are reabsorbed
back into blood capillaries. Actively pumped
out of the proximal convoluted tubule &
water follow possibly by osmosis
Secretion
Distal
convoluted
tubule
Toxins & metabolites of drugs are pumped
into the tubule to be excreted from the body
Excretion
Collecting
duct
Urea, some salts, water, ammonia & toxins
are excreted from nephron & ultimately from
the body as components of urine.
The Glomerulus
• Helps with ultrafiltration
• 3 parts
• Fenestration: pores between cells in the wall of capillaries that
allow fluid to escape, but not blood cells
• The basement membrane: covers and supports the wall of
capillaries. Prevents plasma proteins from being filtered out.
• Podocytes: form inner wall of Bowman’s capsule (foot like
projections) prevents small molecules from being filtered out
of the blood
Glomerulus
The Proximal Convoluted Tubule
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•
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Selectively reabsorbs useful substances by active transport
Most filtrate from glomerulus is reabsorbed
Most happens in the PCT
By the end of the PCT all glucose and amino acids & 80% of
the water, sodium and other mineral ions have been
reabsorbed
The Loop of Henle
• Maintains hypertonic conditions in the renal medulla
• Sodium ions are pumped out of the filtrate to the fluid
between the cells in the medulla and the interstitial fluid
• The Ascending limb is permeable to salts, but impermeable to
water; water is retained
• The descending limb is permeable to water but impermeable
to sodium ions
• Longer loops of Henle are found in animals that need to
conserve more water
• Then moves to DCT Distal convoluted tubule
Loop of Henle
Role of ADH
• ADH = Antidiuretic Hormone
• Filtrate in the DCT concentration is lower than that of normal
body fluids (hypertonic)
• If the solute concentration of blood is too low litter water is
reabsorbed
• If the solute concentration of the blood is too high they
hypothalamus causes the pituitary to secrete ADH.
• ADH causes the walls of the DCT and collecting duct to
become more permeable to water
Protein, Glucose & Urea Filtration
Molecule
Present in Blood
Plasma
Present in
Glomerular
Filtrate
Present in Urine
Proteins
Yes
No (Too large to
undergo
ultrafiltration)
No
Glucose
Yes
Yes
No (selectively
reabsorbed since
it is vital for
cellular
respiration
Urea
Yes
Yes
Yes (excreted
since it is a toxin)
Glucose in Urine & Diabetes
• Presence of glucose in the urine is the main identifying feature
of diabetes
• High level of glucose present in glomerular filtrate and enters
the PCT
Nitrogenous Waste
• Organisms have evolved to excrete ammonia, urea or uric acid
• Directly related to the environment in which they live
• Freshwater organisms can easily secrete ammonia into their
environment
• Terrestrial animals need to convert ammonia to urea or uric
acid
Renal Arteries Vs. Renal Veins
• Composition of Blood in the Renal Artery & Renal Vein
Renal Artery
Renal Vein
Oxygen levels
High
Low (used for cellular respiration by
cells in the kidney)
Carbon Dioxide
levels
Low
High (given off by kidney cells
during cellular respiration
Urea
(nitrogenous
wastes)
Glucose
High
Slightly high
Low (removed during ultrafiltration
and remains in the filtrate for
excretion from the body)
Slightly low (most is actively
reabsorbed in the proximal
convoluted tubule – some is used
by the kidney for cellular respiration
Stuff to Know
Afferent: Going towards,
moving into
Efferent: Going away from,
moving out