2. LEARNING OBJECTIVES
3.4 Synthesising the concept of homeostasis in humans
LEARNING OUTCOMES
explain the necessity to maintain an optimal physical and chemical
condition in the internal environment
state the meaning of homeostasis,
design an experiment to study the effect of different quantities of
water intake on urine output,
relate changes in blood osmotic pressure to urine output,
describe the formation of urine,
relate the formation of urine to excretion,
describe briefly the mechanism of osmoregulation,
predict the consequences of impaired kidney function,
describe the regulation of blood sugar level,
describe the regulation of body temperature,
conceptualise homeostasis.
3. What is Homeostasis?
Body cells work best if they have the correct
Temperature
Water levels
Glucose concentration
Your body has mechanisms to keep the cells in
a constant environment.
4. Homeostasis:
Greek: ‘homoios’ = similar
‘stasis’ = standing still
Homeostasis is the
maintenance of a relatively
stable internal environment
The ‘internal’ environment is
the:
tissue fluid [interstitial fluid]
plasma
7. Examples of Physiological conditions
requiring homeostasis:
O2 and CO2 levels in the body
energy requirements
glucose level in blood
water / ion balance
pH
temperature
8. Living systems are seen to be open
systems. What does this mean?
Require a continuous exchange of matter
between the environment and themselves
Oxygen Carbon dioxide
Heat
Urea
Food
Water
9. We are a
complex system of chemical
processes
these processes are:
self-regulating
tend to maintain a steady state even though
the external environment changes
10. What is Homeostasis?
The maintenance of a
constant environment
in the body is called
Homeostasis
11. Why is homeostasis important?
We function more
efficiently if
conditions are
maintained within
optimum conditions
Fluctuations are caused by:
Changes in:
external
internal
Toprevent large
fluctuations from the
optimum
environments
12. Internal conditions may be maintained
constant within the body by:
developing a variety of mechanisms:
Structural
Physiological
Behavioural
16. LEARNING OBJECTIVES
3.4 Synthesising the concept of homeostasis in humans
LEARNING OUTCOMES
explain the necessity to maintain an optimal physical and chemical
condition in the internal environment
state the meaning of homeostasis,
design an experiment to study the effect of different quantities of
water intake on urine output,
relate changes in blood osmotic pressure to urine output,
describe the formation of urine,
relate the formation of urine to excretion,
describe briefly the mechanism of osmoregulation,
predict the consequences of impaired kidney function,
describe the regulation of blood sugar level,
describe the regulation of body temperature,
conceptualise homeostasis.
17. Principles of Homeostasis
Stimulus Receptors Self-corrective Mechanism Negative Feedback
Change in
internal
environment
Detect the
change
Regulation of
blood
glucose
concentration
Examples
To rectify
the change
Regulation
of blood
water
potential
Regulation of
body
temperature
The reverse
effect of the
change
HOMEOSTASIS
The maintenance of a constant internal
environment
18. Three basic components of a control
system:
1. Detector / Receptor / Sensor
2. Regulator / Control centre /
Co-ordinator / Integrating centre
3. Effector
24. Negative feedback also applies to the
regulation of a population size:
Death rate
increasesBirth rate
increases
25. Why is negative feedback very
common in the body?
increases the stability of
systems
26. Examples of Negative Feedback Control:
O2 and CO2 levels in the body
hormone levels, e.g. thyroxine
sex hormones
metabolic levels e.g. glucose
water balance
the regulation of pH
body temperature
29. Positive feedback:
a disturbance leads to events which
increase the disturbance even further
rare in biological systems
WHY rare?
lead to:
an unstable situation
extreme states
Time
Divergence
30. Examples of Positive Feedback Control:
1. Blood clotting
Activated platelet
releases chemicals
More platelets
are activated
A blood clot forms
31. Examples of Positive Feedback Control:
2. Child birth
Oxytocin stimulates
muscular contractions
of the uterus
More oxytocin is
released
32. Does the disturbance ever stop?
once the purpose of the feedback loop is
completed
Oxytocin level
drops once baby
is born
33. LEARNING OBJECTIVES
3.4 Synthesising the concept of homeostasis in humans
LEARNING OUTCOMES
explain the necessity to maintain an optimal physical and chemical
condition in the internal environment
state the meaning of homeostasis,
design an experiment to study the effect of different quantities of
water intake on urine output,
relate changes in blood osmotic pressure to urine output,
describe the formation of urine,
relate the formation of urine to excretion,
describe briefly the mechanism of osmoregulation,
predict the consequences of impaired kidney function,
describe the regulation of blood sugar level,
describe the regulation of body temperature,
conceptualise homeostasis.
34.
35.
36. LEARNING OBJECTIVES
3.4 Synthesising the concept of homeostasis in humans
LEARNING OUTCOMES
explain the necessity to maintain an optimal physical and chemical
condition in the internal environment
state the meaning of homeostasis,
design an experiment to study the effect of different quantities of
water intake on urine output,
relate changes in blood osmotic pressure to urine output,
describe the formation of urine,
relate the formation of urine to excretion,
describe briefly the mechanism of osmoregulation,
predict the consequences of impaired kidney function,
describe the regulation of blood sugar level,
describe the regulation of body temperature,
conceptualise homeostasis.
39. Urine Production
• Regulation of water
and salts in the body
- osmoregulation
• Rids body of waste –
excretion
• Maintaining blood pH
• Regulating blood
volume & pressure
45. The Job of the Kidneys
• cleans the blood
• by removing metabolic
wastes,
• excess solutes (eg. salts or
glucose)
• excess water
• and excreting them as urine
• maintain homeostasis in
blood solute concentration.
46. The Hard-working Kidneys
• The two kidneys in the body
receive between 1100 – 2000
liters (1160 – 2100 quarts or
500 gallons) of blood per day –
about the volume of a car!
• Because the body has only
about 5.6 liters of blood, your
blood runs through the kidneys
to be cleaned about once every
four minutes.
51. (b) Kidney structure
Ureter
Section of kidney from a rat
Renal
medulla
Renal
cortex
Renal
pelvis
Figure 44.13b
• Kidney has 2 internal layers
renal cortex - outer light red region
renal medulla – inner darker red-brown
region
54. The renal artery branches inside kidney
Renal
artery
Ureter
Renal
vein
Each capillary supplies blood to hundreds of thousands
of tiny filtration units called nephrons
Detail of a
nephron
55.
56.
57. Nephron
• functional unit of the kidney
• About a million in each kidney.
• Consists of 3 major parts : a) the glomerulus
• b) Bowman’s capsule
• c) Renal tubule
71. Ultrafiltration
• takes place in the glomerulus & Bowman’s capsule
• is filtration under pressure
• pressure comes from blood pressure (hydrostatic
pressure)
73. Hydrostatic pressure caused by:
Efferent
arteriole
Afferent
arteriole
Filtration
pressure
GFR maintained
• Diameter of the afferent
arterioles bigger than the
efferent arteriole
• blood enters
glomerulus under high
hydrostatic presssure
• Pushes/filters small
particles from the blood
into the capsular space.
74. Glomerular Filtrate (GF): is the filtered fluid
chemical composition is similar
to blood plasma, containing:-
Glucose
Amino acids
Vitamins
Ions
Nitrogenous waste
Some hormones
Water
Glomerular
filtrate
76. But can blood ever be detected in urine?
YES. But, this
shows that
something is
wrong .
77. Ultrafiltration takes place through three layers:
1) Endothelium of the
blood capillary
2) Basement membrane of
the blood capillaries
3) Epithelium of the
Bowman' capsule
88. Glomerular Filtrate
Molecule or ion Approx. concentrations / g dm-3
Plasma Filtrate
water
protein
glucose
amino acids
urea
inorganic ions
900.0
80.0
1.0
0.5
0.3
7.2
900.0
0.0
1.0
0.5
0.3
7.2
89. Where does the glomerular filtrate go to after
being formed?
90. Recap: What is ultrafiltration?
Ultrafiltration begins in the Bowman's Capsule.
a) Blood arrives in the kidney in the Afferent arteriole
(with a wide blood vessel) at high pressure.
b) Blood passes through the Glomerulus and passes out
the Efferent arteriole (with a narrow blood vessel).
c) Blood pressure increases in the Glomerulus.
d) High hydrostatic pressure forces the plasma (liquid in
blood - water, salts, amino acids, glucose and urea) out
of the blood vessel into the inside of the Bowman's
Capsule - This is called "Glomerular Filtrate."
92. Function of the nephron is to :
actively secrete
waste substances from
the blood capillaries to
the tubules
selectively
reabsorb
substances useful
to the body
93. The Proximal Convoluted Tubule
longest (14 mm)
and widest (60 m)
part of the nephron
carries filtrate from
Bowman’s capsule to
loop of Henle
CORTEX
MEDULLA
94. b) Reabsorption
• Selective reabsorption
takes place when
substances move across
the walls of the renal
tubule into the capillary
network.
• It mostly occurs in the
proximal convoluted
tubule
95. Why Reabsorbtion?
Molecule or ion Approx. concentrations / g dm-3
Plasma Filtrate
water
protein
glucose
amino acids
urea
inorganic ions
900.0
80.0
1.0
0.5
0.3
7.2
900.0
0.0
1.0
0.5
0.3
7.2
96. Selective reabsorption in the proximal convoluted tubule
In humans:
Glomerular filtrate production: 125 cm3 min-1
Urine production: 1 cm3 min-1
24 cm3
100 cm3
Urine 1 cm3
125 cm3
97. Proximal convoluted tubule
• 65% water reabsorbed by
osmosis into blood
capillaries
• All glucose, AA, vitamins &
some salts reabsorbed by
active transport
• Urea not reabsorbed
• GF – now only water, some
salts & urea
98.
99. Proximal Convoluted Tubule is composed of:
a single layer of cuboidal epithelial cells with
extensive microvilli forming a ‘brush border’ on the
inside surface of the tubule
Figure 44.9
100. Proximal Convoluted Tubule is adapted for
reabsorption in three ways:
1.large surface area for absorption due to:
Figure 44.9
Microvilli
Basal
channels
BLOOD FILTRATE
Tight
junction
Epithelial
cell
101. Proximal Convoluted Tubule is adapted for
reabsorption:
Figure 44.9
2. numerous mitochondria (M)
to provide
ATP for
active
transport.
102. Proximal Convoluted Tubule is adapted for
reabsorption:
Figure 44.9
3.closeness of blood capillaries
blood capillary
Glomerular
filtrate
Microvilli
Cuboidal
epithelium
103. Over 80% of filtrate is reabsorbed in the proximal tubule
REABSORBED
all the glucose, amino acids,
vitamins, hormones
about 80% water
about 80% sodium
about 80% chloride
about 80% potassium
about 40-50% urea
MECHANISM
diffusion + active transport
osmosis
diffusion
+ active transport
diffusion
104. Selective reabsorption of sodium and glucose
in the proximal convoluted tubule
Figure 44.9
Secondary
Active
Transport
106. Question:
Briefly describe the following processes in the context of urine
formation in humans.
a) Ultrafiltration. (2)
Filtration of blood occurs under high pressure. Small molecules
which can cross the glomerular lining, end up as glomerular
filtrate inside the Bowman’s capsule.
b) Selective reabsorption of glucose. (3)
Occurs in the proximal convoluted tubule. All glucose is
reabsorbed in a normal person but appears in urine in a
diabetic one. Active transport is involved in the reabsorption of
glucose.
107. THE LOOP OF HENLE
Function: to conserve water
the concentration of urine
produced is directly related to the:
length of the loop of Henle
thickness of the medulla
relative to the cortex
108. The longer the loop of Henle, the more concentrated the
urine that can be produced
BEAVER
(abundant water)
RABBIT
(moderate water)
SAND RAT
(scarce water)
109. Birds & Mammals are the only vertebrates:
which can produce a urine which is more
concentrated than the blood
[hypertonic]
with loops of Henle
Loop of Henle
110. Three distinct regions in the loop of Henle
Thin
ascending
limb
Descending
limb
Thick
ascending
limb
Thin walls
Thick walls
113. Permeability of the loop of Henle to water:
Highly
permeable
Descending
limb
Almost
totally
impermeable
to waterThin ascending
limb
Thick ascending
limb
114. Permeability of the loop of Henle to
Na+ & Cl-ions:
Not very
permeable
Descending
limb
Thin ascending
limb
Thick ascending
limb
Permeable
Active secretion
115. What happens to the concentration of the
fluid in the ascending limb as it reaches the
distal convoluted tubule?
The fluid becomes
very dilute
Distal convoluted tubule
Reason:
IONS are lost
116. WHY it is vital for ions to move out
of the tubule?
ions
117. To create an Osmotic Gradient From Cortex to
Medulla
PelvisMedulla
Cortex
The outer layer of the kidney is isotonic with the blood:
~300 milliosmoles/liter
The innermost layer (medulla) is very hypertonic:
~1200 milliosmoles/liter
123. Three Countercurrents:
1. the two limbs of the Henle's loop
2. the two limbs of the vasa recta
3. the descending limb of
Henle with the ascending
limb of the vasa recta;
the ascending limb of
Henle and the
descending vasa recta
126. To ureter
Collecting duct
•Several nephrons
empty into one
collecting duct.
•The collecting duct
passes through the
progressively more
concentrated
medulla, losing
water by osmosis.
This water is
reabsorbed by the
capillaries.
•This water is
conserved, and a
highly concentrated
urine is produced.
Water reabsorbed into vasa recta,
urine becomes more concentrated
Cortex
Medulla
127. Question: [SEP, 2009]
Briefly describe the role of each of the following in
osmoregulation in humans:
i) The descending limb of the Loop of Henle; (2)
Is permeable to water. Functions towards water
conservation.
ii) The ascending limb of the Loop of Henle; (2)
Is relatively impermeable to water but permeable to salts.
The tissue fluid inside the medulla becomes concentrated as
salts move out of the ascending limb. This causes water to be
drawn out of the descending limb.
128. Question:
The diagram below shows the
simplified structure of a human
nephron.the loop of Henle
Substance Quantity passing
through P
Quantity passing
through Q
%
reabsorbed
Water 180 dm3 1.5 dm3 99.17%
Glucose 180 g 0 g 100%
Urea 53 g 25 g 52.8%
The table below represents the quantities of water,
glucose and urea passing through P and Q over a
period of time, while the last column shows the
percentage reabsorption during the same period of
time.
129. Question:
a) Relate the role of structure R to the filtrate composition
as it passes through Q. (5)
Structure Q is permeable to water. Water is reabsorbed by
the vasa recta as fluid passes through Q. This is possible
because the ascending limb creates the ideal
concentration gradient within the medulla by losing ions.
The thin ascending limb of Structure R is permeable to ions
but impermeable to water. The thick ascending limb of
Structure R allows ions to move actively out of it and is
also impermeable to water. Loss of ions from the whole
ascending limb, creates an ever increasing salt
concentration on moving deeper into the medulla.
130. Question:
Substance Quantity passing
through P
Quantity passing
through Q
%
reabsorbed
Water 180 dm3 1.5 dm3 99.17%
Glucose 180 g 0 g 100%
Urea 53 g 25 g 52.8%
b) Explain the biological significance of the percentage
reabsorption of water and urea. (3)
Most of the water is reabsorbed to avoid dehydration.
Only half of the urea is reabsorbed so that it contributes to
the concentration of solutes in the medulla. A high solute
concentration is needed to ensure reabsorption of water from
the loop of Henle.
131. Distal convoluted tubule
Reabsorption & Secretion
occur
• More H2O reabsorbed
osmosis
• Na+ and Cl- , HCO3
- ions
are reabsorbed active
transport
• Secretion of NH4
-, H+,
some drugs & poisons
active transport
132. COLLECTING DUCT
• More water leaves the
tube by osmosis, since the
tube is surrounded by salty
tissue.
• Some urea leaves by
diffusion, and may be
cycled through the system.
• More Na+ and Cl-
reabsorbed by active
transport
133.
134. Summary: REABSORPTION
1. Proximal tubule
• Glucose, amino acid, Na+ and Cl- (active transport)
• Water, HCO3
- (passive transport)
2. Loop of Henle
• Na+ and Cl- (active transport)
• Water (passive transport)
3. Distal tubule
• Na+ and Cl- , HCO3- (active transport)
• Water (passive transport)
4. Collecting duct
• Na+ and Cl- (active transport)
• Water, urea (passive transport)
135.
136. 3. Secretion
• By active transport
• Occurs only in the PROXIMAL TUBULE &
DISTAL TUBULE
• Proximal tubule – NH4-, H+, some drugs
& poisons
• Distal tubule – K+, H+
• Substances not filtered in the glomerulus
are secreted into the renal tubule to be
excreted.
• Reason: 1. To get rid of certain substances
2. To regulate blood pH
137.
138. 1. Urine from collecting
duct drips into pelvis
2. passes via the ureter to
the bladder
3. Stored in bladder
4. Once ~200 cm3 urine
collected, stretch
receptor stimulated
desire to urinate
144. In this topic we mention TWO hormones that
affect the kidneys:
Urine
ADH
(antidiuretic
hormone)
Posterior
pituitary
Adrenal cortex
Aldosterone
145. ADH :
1. increases the permeability of the distal
convoluted tubule and collecting duct to
water
More ADH, more water is reabsorbed.
146. 2. increases the permeability of the collecting
duct to urea
1. Urea moves into
medulla
2. Medulla becomes
concentrated
RESULT:
3. Water moves out of
descending limb
147. ADH is released when osmoreceptors:
detect a low level
of water in blood
kidney
148. Water
Salts
Fig. 21 The effect of ADH on the permeability of the distal
convoluted tubule and collecting duct to water
Blood too concentrated
ADH level high
Blood too dilute
ADH level low
Dilute
urine
Urine
concentrated Water
Salts
149.
150. Reabsorbing water
If you have too
little water in your
blood, you will
produce very
concentrated urine.
(very little water in
it)
If you have too
much water in your
blood, you will
produce very dilute
urine.
(lots of water in it)
153. Water content
of the blood normal
Water content of
the blood HIGH
Water content of
the blood LOW
Too much water drunk
Too much salt
or sweating
Brain
produces
More ADH
Urine output
LOW
Brain
produces
Less ADH
Urine output
HIGH
High volume of water
reabsorbed by kidney
Low volume of water
reabsorbed by kidney
(small volume of
Concentrated urine)
(large volume of
dilute urine)
154. Release of ADH from the posterior
pituitary is inhibited by drinking
alcohol & caffeine.
How would this affect urination?
Increases
ADH
155. Failure to release sufficient ADH leads to a
condition: DIABETES INSIPIDUS
large quantities of dilute urine are produced
could lead to dehydration death
156. ALDOSTERONE:
is secreted by the adrenal cortex
stimulates sodium reabsorption in the
nephron
stimulates excretion of potassium
ions
Control of Blood Sodium Level:
Aldosterone is a:
Steroid hormone
157. Aldosterone causes:
2. K+ to move into
lumen & ends
in urine
1. Na+ ions to be pumped
from distal tubule into
the blood capillaries
TS distal
tubule
K+
Na+
RESULT OF more Na+ in
blood is….
More aldosterone secreted,
more Na+ ions reabsorbed
from distal tubule into the
blood capillaries
158. A decrease in blood Na leads to a
decrease in blood volume. WHY?
Because less water enters the
blood by osmosis.
Less water =
reduction in blood pressure
159. b) Complete the table below by filling in the empty
spaces with the appropriate answers: (3)
Hormone Site of
production
Effect
Antidiuretic
hormone
Hypothalamus
Stimulates distal
convoluted tubule and
collecting duct to
reabsorb water
Aldosterone
Adrenal
cortex
Stimulates excretion of
potassium ions and
reabsorption of sodium
ions in the nephron
160. Factors that affect kidney
function
• Antidiuretic hormone (ADH) – prevents excess
water loss from kidneys
• Alcohol – inhibits secretion of ADH = more
urine volume
• Aldosterone – prevents excess loss of sodium and
water from kidneys
• Caffeine – increases rate of salt and water loss
from kidneys
• Increased blood pressure – increase rate of water
loss from kidneys.
171. Cause of kidney stones
• Exact cause of kidney stones
cannot always be found,
although they are usually
formed following a build-up
of a substance such as
calcium.
• The leading cause of kidney
stones is a lack of water.
• A kidney stone is formed
when a small speck of
mineral settles out of the
urine into the kidney or the
ureter, a tube that links the
kidney to the bladder.
174. Longer-term adjustments in the ion balance of
the blood :
are made in the distal convoluted tubule
If the pH falls below 7.4:
distal tubule cells
secrete H+ into the urine
If the pH rises:
Distal tubule cells
secrete OH- & HCO3
-
into the urine
H+
HCO3
-
OH-