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HOMEOSTASIS
Powerpoint@lecture Slides Are Prepared By Biology Lecturer, KMPk
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19.3 : HUMAN HOMEOSTATIC ORGANS: LIVER AND
KIDNEY
9.3.2 Structure and functions of Kidney
TOPICS
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PREVIOUS LESSON
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PREVIOUS LESSON
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OBJECTIVES
At the end of this lesson, students should be able to:
11. Describe the structure of kidney & its functional units.
2. Describe urine formation:
i) Ultrafiltration
ii) Reabsorption
iii) Secretion
3. Describe the concentration of urine by counter current
multiplier mechanism
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19.3.2 Structure and
Functions of Kidney
A major excretory and osmoregulatory organ
A pair, bean-shaped organ
About 10 cm in length
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Situated towards the back of
the lower part of the
abdominal cavity
Left kidney is slightly higherthan the right
Protected by a capsule offibrous connective tissue
Rich blood supply andregulates the bloodcomposition
Contributes to homeostasis
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Functions of Kidney
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Consists of:
Renal cortex
A light outer region
Renal medulla
A dark inner region
Renal pelvis
A whitish central
region
Leads to ureter
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Functions of Kidney
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The basic structural and
functional unit of the
kidney
Microscopic excretory
tubules
Packing the cortex and
medulla region
NEPHRON
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Functions of Kidney
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Each kidney
consists about a
million nephrons
Total tubulelength: 80 km
Enormous surface
area for the
exchange of
materials
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Functions of Kidney
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Structure of a nephron:
Glomerulus
A spherical cluster of
blood capillaries
Bowmans capsule
A double-walled, cup-shaped swelling capsule
Blind end of the tubule
Located in the cortex
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Functions of Kidney
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Proximal convolutedtubule
Lumen is continuouswith the Bowmanscapsule
Highly coiled
Located in the cortex
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Functions of Kidney
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Loop of Henle
Hair-pin shaped
Have descending
limb & ascending
limb
Located in themedulla
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Functions of Kidney
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Distal convoluted
tubule
Located in the
cortex
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Functions of Kidney
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Collecting duct
End of kidney
Eventually drain into
the pelvis of thekidney
from where the urine
flows into the ureter
Located in the
medulla
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Functions of Kidney
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19.3.2 Structure and
Functions of Kidney
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Main blood vessels
Renal artery : supplies oxygenated blood from
aorta
AortaRenal arteries
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Functions of Kidney
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Main blood vessels
Renal veins: carries deoxygenated blood to
posterior vena cava
Vena cavaRenal veins
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Functions of Kidney
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AortaRenal arteries
Vena cavaRenal veins
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Functions of Kidney
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An Individual Nephronand Its Blood Supply
Renal artery
afferent arteriole
Glomerulus
efferent arteriole
vasa recta
19.3.2 Structure and
Functions of Kidney
Renal vein
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Urine formation :
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1.Ultrafiltration
2. Reabsorption
3. Secretion
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Functions of Kidney
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.Ultrafiltration
2.Reabsorption
3.Secretion
URINE FORMATION
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Takes place in the glomerulus
and the Bowmans capsule
Occurs due to the hydrostatic
pressure caused by the bloodpressure
1. ULTRAFILTRATION
URINE FORMATION
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Blood enters the glomerulus
via afferent arteriole (larger
diameter) and leaves via efferent
arteriole (smaller diameter)
Produce high hydrostatic
pressure
ULTRAFILTRATION
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Forces small molecules through the walls of capillaries and
Bowmans capsule into the capsular space
Except RBC, plasma proteins and platelets
glucose, amino acids, sodium,
potassium, chloride,
bicarbonate, other salts, waterand urea,
ULTRAFILTRATION
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The wall of Bowmans capsule
consists of a specialized
epithelial cell called
podocytes (pod:foot)
Have numerous
cytoplasmic extension
called foot
Cover most of the
capillaries
STRUCTURE OF
BOWMANS CAPSULE
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Foot processes of adjacent podocytes are separated by
narrow gaps
Filtration slits
STRUCTURE OF
BOWMANS CAPSULE
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The perforated walls of the capillaries and thepodocytes form a filtration membrane
Permits fluid and small solutes to pass
glomerular filtrates
STRUCTURE OF
BOWMANS CAPSULE
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STRUCTURE OF
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STRUCTURE OF
BOWMANS CAPSULE
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The process ofabsorbing useful substances into
capillaries which wrapped around tubule
Glucose, amino acids, vitamins, most of the water,
sodium and chloride ions
2. REABSORPTION
Tubules Blood capillaries
URINE FORMATION
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REABSORPTION
Occurs in:
Proximal convoluted tubule
Loop of Henle
Distal tubule
Collecting duct
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Proximal convoluted tubule
Most reabsorption occurs : over 80%
All glucose, amino acids,
vitamins and hormones85% of NaCl and other ions
Active transport
REABSORPTION
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Proximal convoluted tubule
40-50% of urea
85% of water
As concentration of ions increase in plasmaWater moves out
Diffusion
Osmosis
REABSORPTION
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STRUCTURE OF
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STRUCTURE OF
PROXIMAL TUBULE
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Loop of Henle
Function:oTo create a water potential gradient
oBetween the filtrate and the interstitial fluid in the
medulla
Longer : urine produced is more concentrated
REABSORPTION
STRUCTURE LOOP OF
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Divided into 2:
Descending limb
Ascending limboThin segment
oThick segment
STRUCTURE LOOP OF
HENLE
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Descending limb
Thin walls
Highly permeable towater
Impermeable to NaCl and
other solutes
REABSORPTION
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Ascending limb
Thick segment
Thin segment
- thick wall
- transport NaCl actively
- thin wall
- transport NaCl passively
-impermeable to water
- permeable to NaCl
and urea
REABSORPTION
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Involves counter-current multiplier mechanism
Counter-currento
Filtrate past each other in opposite directionsoThe descending and ascending limb
REABSORPTION
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Involves counter-current multiplier mechanism
Multiplier
oFiltrate flow down the descending limboHigh concentration of NaCloMost hypertonic round the hairpin
Filtrate flow up the ascending limboLess concentration of NaCloHypotonic
REABSORPTION
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In the descending limb,
Water is drawn out by
osmosis Concentrates NaCl in the
tubule
Filtrate concentration is
highest at the bottom of
the loop of Henle
REABSORPTION
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As the filtrate flows up
the ascending limb
Thin segmentoNaCl passively diffuseout into the interstitialfluid
Thick segmentoNaCl is activelypumped out into theinterstitial fluid
REABSORPTION
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As the filtrate flows up the
ascending limb
Produce a high
concentration of NaCl
around the descending
limb
Filtrate concentration islower in the tubule
REABSORPTION
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Water potential in the
interstitial fluid is lower
Causes water in the
descending limb drawnout by osmosis
Creating a
concentration gradient
in the medulla
REABSORPTION
REABSORPTION
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The water and NaCl
moves into the vasa
recta surroundingthe loop of Henle
REABSORPTION
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The Distal Tubule
Receives a hypotonic filtrate
from the ascending limb
Not permeable to water butdepends on hormonal
controloBecomes permeable
under hormonal controloAnti-diuretichormone (ADH)
REABSORPTION
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The Distal Tubule
Active reabsorption of
Na+
oUnder hormonal
control
oAldosterone
REABSORPTION
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The Collecting Duct
Carries the filtrate from
cortex to medulla to the renalpelvis
Permeability to water and
urea is under hormonal
control
oAnti-diuretic hormone
(ADH)
REABSORPTION
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When the filtrate pass
along the collecting duct
Water moves out by
osmosis to the
interstitial fluid
REABSORPTION
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ome urea will also
diffuse out
Along with NaCl,contributes to the high
concentration of solute
(lower water potential)
in the interstitial fluid
REABSORPTION
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This urea is recycled
by diffusion into the
ascending limb of loop
of Henle
REABSORPTION
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REABSORPTION
URINE FORMATION
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Occurs in the distaltubule and the
proximal convoluted
tubule Mainly in distal tubule
3. SECRETION
Blood capillaries Tubules
URINE FORMATION
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Distal tubule secretes H+ and NH3from the blood into
the filtrate
Helps to maintain blood pH
Secretion of K+occurs under hormonal control:
aldosterone
SECRETION
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Proximal & distal tubule also actively
secretes harmful or toxic substances into
the filtrate
Removed by urine
Eg: drugs such as penicillin and caffeine
SECRETION
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CONCLUSION
VIDEO FUNCTIONS OF KIDNE
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