Download - Role of Hormones in Humans
Role of Endocrine System
• Endocrine system : controls the body’s activity by
releasing chemicals in the blood stream that can regulate
the activities of organs and tissues
• Endocrine system : made up of endocrine glands (does
not have ducts)
• Produce and release hormones directly into the
bloodstream
• Body’s responses to hormones are slower and longer-
lasting than the responses to nerve impulses 2
Endocrine Glands
• Major glands of the endocrine system include the
pituitary gland, thyroid gland, adrenal glands, pancreas
and gonads (testes and ovaries)
• The pituitary glands is controlled by the hypothalamus in
the brain
• It secretes several hormones that directly regulate many
body functions and control the activities of another
endocrine glands 3
Regulation of hormone
secretion
• An endocrine gland released its hormones more
frequently when stimulated, thus increasing their
concentration in the blood
• Hormone secretion is regulated by;
• a.) signals from the nervous system
• b.) other hormones
• c.) the level of specific substances in the body 10
Secretion of Hormones
regulated by another hormone
• Hormone thyroxine : regulated by the thyroid-stimulating
hormone
• A high level of thyroxine inhibits the release of the
thyroid stimulating hormone and stops the release of
additional thyroxine
• A low level of thyroxine? 11
Secretion of hormones
regulated by levels of certain
substances
• Substances in the blood such as the level of glucose can
control the secretion of hormones.
• A high level of glucose stimulates the pancreas to secrete
insulin
• The excess glucose is then converted to glycogen and this
decreases the level of glucose in the blood
• When the level of glucose gets too low?
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Secretion of hormones
regulated by nervous system
• Some endocrine glands are controlled by the nervous
system
• The hypothalamus receives nerve impulses from the
receptors which then stimulate the pituitary gland to
release hormones
• The adrenal gland is also stimulated to release hormones
by the nervous system
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Neurosecretory cells in the
hypothalamus
ADH and Oxytoxin
These hormones pass through the axons into the posterior pituitary cells (stored in the
synaptic terminals)
ADH and Oxytoxin are secreted from the synaptic
terminals into the bloodstream
Hypothalamus RH and IH
These hormones are carried in the bloodstream
to the anterior pituitary
RH : stimulate the secretion of the anterior pituitary hormone
IH : suppress the secretion of anterior pituitary hormone 18
Coordination Involving Both
Nervous System and Endocrine
System (Fight or Flight situation)
• During a threatening situation, for example when fierce
dog suddenly barks at you, the hypothalamus sends nerve
impulses directly to the adrenal medulla
• The adrenal medulla, the innermost region of the adrenal
gland has neurones from the sympathetic division of the
ANS
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Sequence of events that take place
during fight or flight situations
• 1. Nerve impulses from the hypothalamus
• 2. Stimulate the neurones from the sympathetic division
• 3. Stimulate the cells of the adrenal medulla to secrete adrenaline and noradrenaline
• 4. Adrenaline and noradrenaline cause…..
• 5. The heartbeat and breathing rates, blood pressure, blood glucose level and metabolic activity to increase
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• When a person is in a stressful situation, the nervous and
endocrine systems both work together to bring about
immediate responses to cope with the situation
• Once these mechanisms successfully counteract the
danger, the bodily changes that occurred return to normal
23
Effects of Hormonal
Imbalance
• Improper functioning of an endocrine gland may result in
a disease or a disorder
• Goitre : enlargement of the thyroid gland due to iodine
deficiency. Too little thyroxine is produced which causes
the thyroid gland to enlarge to compensate for this
deficiency
• Cretinism : lack of thyroxine in children; results in
mental retardation and dwarfism. In adults, a condition
called hypothyroidism / myxedema 24
• Hypothyroidism : characterised by an enlarged thyroid gland, slow heart rate, fatigue and weight gain
• Hyperthyroidism : too much of thyroxine; enlarged thyroid gland, nervousness, rapid heart beat, bulging eyes, hand tremor and weight loss
• Gigantism : too much of growth hormones are produced during childhood, body grow quickly/ abnormally tall. Acromegaly?
• Dwarfism : too little of growth hormones is produced during childhood; the organs often fail to grow and the size of body is like that a child
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• Diabetes insipidus : lack of the antidiuretic hormone;
large volume of urine is excreted and body loses a lot of
water
• Oedema : too much of antidiuretic hormone; due to
accumulation of excess fluids in the body
• Diabetes mellitus : imbalance of insulin; amounts of
glucose in the blood may rise so high that the kidneys
excrete glucose in the urine
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Homeostasis in Humans
• Homeostasis : The regulation of the physical and chemical factors in the internal environment to maintain a constant internal environment.
• Involves monitoring changes in the external and internal environments by means of receptors and adjusting the change through a negative feedback mechanism
• Physical factors : body temperature, blood pressure
• Chemical factors : partial pressure of oxygen, carbon dioxide, osmotic pressure and sugar levels
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The Excretory system
• Plays an important role in homeostasis
• Primary organs of the excretory system are the kidneys
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Kidneys • Help to regulate the water and salt balance in the body by
excreting more or less salt, and increasing the intake or
loss of water
• Regulate the osmotic pressure and ionic levels in the
blood
• Excrete waste products
• Regulate the blood pH 30
Waste products
• From metabolic reactions in the body, example : urea,
creatinine (break down of amino acids), uric acid (break
down of nucleic acids)
• Foreign substances in the diet : drugs or toxins.
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Kidneys
• Filter blood and form urine which exits the body through
the ureters, urinary bladder and urethra
• Urine: consists of water, urea and other dissolved wastes,
and some excess nutrients.
• Has two distinct regions : a) outer light-red region (renal
cortex)
b) inner dark red region (renal medulla)
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• The renal artery supplies oxygenated blood and nutrients
to the kidney
• The renal vein carries away filtered blood to the body
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The nephron
• The functional unit of a kidney is the nephron
• Each human kidney consists of about one million
nephrons
• A nephron consists of three major parts:
• a) the glomerulus and its associated blood vessels
• b) the Bowman’s capsule
• c) a long narrow tube called the renal tubule 36
The nephron
• The renal tubule is made up of the ;
• a) proximal convoluted tubule
• b) loop of Henle
• c) distal convoluted tubule
• The distal convoluted tubules of several nephrons join to a common collecting duct
• The Bowman’s capsule and both convoluted tubules lie within the renal cortex, whereas the loop of Henle extends into the renal medulla
• http://www.dnatube.com/video/2754/Nephron-Function 37
The nephron
• Within the kidney, each nephron is supplied with blood
by an afferent arteriole which is a branch of the renal
artery
• Each afferent arteriole divides further into a tangled
capillary network called the glomerulus
• The capillaries of the glomerulus reunite to form an
efferent arteriole 40
The nephron
• Each efferent arteriole divides to form a network of blood
capillaries surrounding the kidney tubules
• These blood capillaries are called peritubular capillaries
or the capillary network which eventually join together
into the renal vein
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The formation of Urine
• The formation of urine involves three processes namely
ultrafiltration, reabsorption and secretion.
• Ultrafiltration occurs at glomerulus
• The high hydrostatic pressure in the glomerulus causes
many constituents of the blood to be filtered out from the
glomerulus into the Bowman’s capsule
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Ultrafiltration
• The glomerular filtrate has the same composition as the
plasma except that it does not contain any of the larger
components such as RBC and plasma proteins
• The glomerular filtrate contains water, glucose, amino
acids, urea, mineral salts and other small molecules
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Reabsorption
• As the filtrate passes along the length of the nephron,
reabsorption occurs
• Reabsorption occurs at the proximal convulated tubule
(PCT), loop of Henle, distal convulated tubule and
collecting duct
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Reabsorption
• At PCT, about 65% of the water in the filtrate is
reabsorbed back into the surrounding blood capillaries by
osmosis
• All the glucose, amino acids, vitamins and some salts
are reabsorbed by active transport
• Water, salts and urea passes along the loop of Henle,
about 20% of water and some salts are reabsorbed into
the capillaries 46
Reabsorption
• At the DCT and collecting duct, the amount of water and
salts that are reabsorbed into the blood capillaries
depends on the content of water and salt in the blood
• The absorption of water and salt regulated by the
endocrine system.
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Secretion
• Secretion occurs at the DCT
• Along the tubule, waste products such as urea, uric acid
and ammonia are pumped out of the blood capillaries into
the DCT by active transport
• Some drugs and other toxic substances are also secreted
out of the blood capillaries by simple diffusion
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Secretion
• The final glomerular filtrate which remain in the
collecting duct is called urine
• The major constituents of urine are approximately 96%
water, 2.5% nitrogenous products such as urea, uric acid,
ammonia and creatinine, 1.5% salts and other trace
elements such as bile pigments
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Secretion
• Secretion helps to ;
• a) eliminate and increase the rate of waste removal from
the body
• b) regulate the levels of certain ions in the blood.
( Kidneys can regulate the chemical composition of the
blood – by adjusting the amount of ions to absorb or to
secrete)
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Osmoregulation
• The kidneys also function as an organ of osmoregulation
by regulating the salts and water balance in the body; to
maintain the blood pressure
• The water and salt content in the blood determines the
osmotic pressure in the blood
• The osmotic pressure is high when is an excess of salts
and less water in the blood 53
Osmoregulation • Osmoregulation : The process of maintaining the water
content of the blood at the constant level
• Osmoregulation : achieved mainly by regulating the
volume of urine production and excretion from the
kidneys
• This process is achieved by a negative feedback
mechanism 54
Mechanism of Osmoregulation
• Controlled by two hormones that are the ADH and
Aldosterone
• Work through a negative feedback mechanism to regulate
water and salt content in the blood by the process
Reabsorption
• The reabsorption of both water and salts determine the
final concentration and volume of urine
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Mechanism of Osmoregulation
• When very salty food is eaten/ too much water is lost by
sweating = Osmotic pressure in the blood increases
• Osmoreceptor (sensory cells) detect the change in
osmotic pressure and trigger the pituitary gland to secrete
the ADH
• ADH increases the permeability of the walls of DCT and
collecting duct towards the reabsorption of water
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• As a result, more water is reabsorbed back from the
tubule into the blood capillaries
• This lowers the osmotic pressure to its normal level. It
also decreases the volume of urine produced. Hence the
urine produced is little but concentrated
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Consequences of Impaired
Kidney Function
• Kidneys fail to function? – cannot carry out their function
as an excretory organ and as organ of osmoregulation
• Metabolic wastes such as urea, excess water and salts
cannot be excreted out and osmotic pressure in the blood
cannot be regulated
• How can patients with impaired kidney function be
treated? 61
Haemodialysis
• Process whereby a dialysis machine is used to remove
metabolic wastes such as excess water, urea and excess
mineral salts from the blood
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Haemodialysis • The machine has a coiled tubing with a semi-permeable
wall bathed in a sterile dialysis fluid.
• The concentration of dialysis fluid in the machine is
maintained at a concentration similar to the blood
plasma
• The dialysis fluid is constantly flowing and changed
regularly to remove the waste substances and to maintain
the diffusion gradient between the patients’ blood and
dialysis fluid
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Haemodialysis
• The blood from the radial artery in the patients’ arm
passes into the machine and then flows out into a vein in
the same arm
• Blood flows through the coiled tubing, the urea and salts
which are higher in concentration in the blood diffuses
across the tubing walls into the dialysis fluid which has
a lower concentration of urea and salts
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Regulation of Blood Sugar
level
• The normal blood glucose concentration in humans is
about 90mg of glucose in 100 cm³/ (75-110mg/100ml)
• The high concentration of glucose stimulates the ß-cells
of the Islets of Langerhans in the pancreas to secrete
insulin into the bloodstream
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Regulation of Blood Sugar
level
• If the glucose level falls below the normal level, ᾳ-cells
of the Islets of Langerhans are stimulated to secrete
glucagon
• Both these hormones work in opposition to each other to
regulate the blood glucose level
• Defects in the production , release and reception of
insulin by target cells can lead to diabetes mellitus 67
Regulation of Blood Sugar
level
• As the PCT of the kidney cannot reabsorb all the glucose
from the kidney filtrate, glucose is excreted in the urine
• Diabetes can be controlled by insulin injections, tablets
that lower the blood glucose levels and careful diets
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Regulation of Body
Temperature
• The skin plays an important role in regulating the body
temperature; regulating heat gain and heat loss = maintains a
constant temperature
• Thermoreceptors (cold and warm receptors) in the skin detect
changes in the environmental temperature. Hypothalamus
(temperature regulatory centre) detect changes in the temperature
of the blood flowing pass it
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Regulation of Body Temperature
• The hypothalamus acts as the temperature regulatory
centre.
• It causes the effectors to respond by negative feedback
through corrective mechanism to restore the temperature
back to its normal level
• The effectors respond by physical means (involving the
skin) and by the process of metabolism (which involves
the endocrine glands) 74
Practising a Healthy Lifestyle
• Drugs can alter brain functions and the rates at which
neurones release neurotransmitters
• The abuse of drugs normally results in a tolerance of the
drug. This means that more and more of the drugs is
needed to produce the same initial effect on the person
• A person who is addicted to drugs will experience
withdrawal symptoms such as shivering, sweating and
nausea when he is deprived on the drug 77
Plant Hormones
• In plants, response is controlled by chemicals called plant
hormones or plant growth regulators
• A plant hormone : a chemical substance which is
produced by the plant and influences the growth and
development of the plant
• It brings about its effect near the site of its formation or it
may be transported to other parts of the plant where it
acts 79
Plant Hormones
• Plants hormones : Auxins and Ethylene
• Plants respond to stimuli by growing in a certain
direction. This growth response is called tropism –
Auxins
• Auxins are produced in the apical meristems of the
shoots.
• Auxins promote the elongation of cells in the shoot
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Role of Auxins in Tropism
• Auxins control the growth movements of shoots and roots
in plants
• This type of response where the direction of growth
movement is determined by the direction of the stimulus
is called tropism
• Phototropism (Direction of light from one side) : Shoots
bend towards light (+ve)
• : Roots grow away from light (-ve)
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• Geotropism : Shoots grow upwards against the force of
gravity (negative geotropism)
• : Roots grow downwards in the direction of gravity
(Positive geotropism)
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Phototropism
• From the experiments, we can conclude that,
• a) the tip of the coleoptile is the light-sensitive region
• b) the meristem cells at the tip of the shoot produces
auxins
• c) auxins move away from the light and accumulate in the
shaded side
• d) high concentration of auxins in shoots promote
elongation of cells in shoots
• e) auxins can diffuse through the agar block (liquid base)
but not through metals and solids 90
Geotropism • Gravity causes the tip of growing shoots and roots to
produce auxins
• Auxins diffuse into zone of elongation
• Owing to gravity, auxins move to lower side of shoot and
root
• The lower side of shoot and root has a higher
concentration of auxins that the upper side 91
Geotropism
• A high concentration of auxins in the shoot promotes
elongation of cells. Hence the lower side of the shoot
with a higher concentration of auxins will grow faster that
the upper side. (negative geotropism)
• A high concentration of auxins inhibits the elongation of
cells in the root. The upper side of the root grows faster
that the lower side. (positive geotropism)
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Ethylene
• Synthesised during the ripening of fruits
• Occurs in fruits, leaves and stems
• Function/role : speed up the ripening of fruits by
stimulating the production of cellulase.
• Cellulase hydrolyses the cellulose in plant cell walls,
making the fruit soft 94
Ethylene
• Function/Role : promotes the breakdown of complex
carbohydrates into simple sugar. That is why a ripe fruit
tastes sweeter that an unripe fruit
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Topical Test
• a) What is ultrafiltration? (1 mark)
• b) Explain where and how it occurs.(3 marks)
• c) What are the substances being filtered out? (3 marks)
• d) Describe how the components of the filtrate are
reabsorbed along the tubule of the nephron. (3 marks)
• e) What are the components of the filtrate that are
reabsorbed back into the capillaries? (2 marks)
• f) Describe how secretion occurs. (3 marks)
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