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Kidneys and Excretion
Structures and Functions
Kidney has 3 main parts
1. Adrenal cortex outer part of kidney
2. Adrenal medulle middle part of kidney
3. Renal pelvis - inner
part of kidney
Parts of the Kidney
Nephron
• functional unit of the kidney, performing the filtering of the blood.
• over 1 million per kidney
• Extend between the adrenal cortex and the medulla
• parts of the nephron:
Parts of the Nephron
1. Glomerulus
• microscopic glob of capillaries
• blood circulates at increased
pressure, causing fluids to leak
out.
• this is the process called
FILTRATION.
A.
Filtration
• materials are forced out of the
blood and into the nephron’s
tubules
• materials move OUT of the
glomerulus and INTO
Bowman’s Capsule
• the filtrate contains both “good” and “bad” materials
•
•
•
•
•
•
water
salts
sugars
amino acids
uric acid
urea
•
two arterioles are involved in increasing
the pressure of blood in the glomerulus:
1.
Afferent arteriole:
controls blood flow into the
glomerulus
dilates to allow for increased
volume.
2.
Efferent arteriole:
controls blood flow out of the
glomerulus
constricts to increase pressure
Proximal Tubule
2. Bowman’s Capsule
• cup-like structure that collects the
filtrate
3. Proximal Tubule
• some filtrate is put back into the
blood = REABSORPTION
B.
Reabsorption
Proximal Tubule
• the “good” materials are pulled back
out of the tubule into the blood.
• water, glucose, amino acids,
vitamins, minerals, salts
Active Transport is used to reabsorb
materials.
• special carrier proteins in the walls of
the proximal tubule use ATPs to
move what is needed.
• 70% of reabsorption occurs in the
proximal tubule.
4. Loop of Henle
•
long tube that extends into the medulla
•
creates an environment that encourages
WATER REABSORPTION (C)
•
the ascending loop actively transports out
sodium ions (Na+)
•
the positive ions draw negative chlorine ions
out after them (Cl-)
•
the salty environment that results sets up an
osmotic gradient for water to move out of the
nephron
•
the descending loop actually absorbs some of
the chlorine and sodium ions so that they can
be used again.
Descending
Loop of Henle
Ascending
5. Distal Tubule
• a winding tube that is found in the
cortex
• some reabsorption occurs here.
• able to remove materials from the
blood.
• Process is called SECRETION.
Distal tubule
D.
Secretion
• actively transports waste materials from the blood.
• carrier proteins in the walls of the capillaries near the distal tubule aid in
secretion.
6. Collecting Duct
• sends the waste (urine) out of the
nephron and toward the renal
pelvis.
• some secretion occurs here.
- urine will then travel down the ureters
to the bladder and then down the
urethra and out of the body =
EXCRETION