Download X-Sheet10 Endocrine System and Thermo Regulation

X-Sheet10
Endocrine System and Thermo Regulation
Life Sciences X-Sheets
65
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
Terminology & definitions
Hormones: organic chemical messengers secreted directly into the blood by an
endocrine gland. Hormones cause target organs to perform a specific function.
Hyperthyroidism: Increased levels of thyroxin in the blood due to over-activity of the
thyroid.
Hypothyroidism: Decreased levels of thyroxin in the blood due to under-activity of the
thyroid.
Homeostasis: is the maintenance of a relatively balanced and constant internal
environment by means of the negative feedback mechanism.
Negative feedback mechanism: when there is an increase from normal, a corrective
mechanism causes a decrease and vice versa to maintain a balanced system.
Thermoregulation: a regulatory process to keep a constant body temperature in
homoeothermic animals like birds and mammals.
Hypothermia: when the body becomes so cold that the internal mechanisms cannot keep
the internal core body temperature constant.
Hyperthermia: when the body becomes too hot and the internal mechanisms are unable
to cool the internal core body temperature down sufficiently.
Key Concepts / Diagrams
The Endocrine system works in conjunction with the Nervous system. The endocrine
system is responsible for chemical coordination, regulating the functioning of all the
organs in the body. The endocrine glands produce organic chemical messengers called
hormones. All endocrine glands are ductless so hormones are secreted directly into the
blood. Each gland has a rich supply of blood to transport the hormones to the target
organs. Hormones generally consist of proteins and fats, but some (like the sex
hormones) consist of fats only. Hormones control the activities of a target organ, but do
not themselves perform the activity. Hormones work together as an integrated system
where they either stimulate or inhibit organs.
Processes are regulated by chemical co-ordination to ensure normal growth, development
and functioning of all the systems in a coordinated manner. This coordination ensures
the control of:
 tissue fluid
 nutrients
 blood pressure
 body temperature
 blood glucose levels
 osmoregulation (water)
 oxygen and carbon dioxide levels
 salt concentrations (electrolytes)
Life Sciences X-Sheets
66
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
Endocrine glands in the body and the hormones that they secrete:
Exocrine glands
Exocrine glands are glands that secrete substances into ducts that lead into cavities in
the body or lead directly to the external environment. Examples are sweat glands,
mammary glands, the liver, salivary glands and the pancreas.
Endocrine gland table (Learn Well):
Hormone
Gland
Growth
Anterior lobe
hormone
of the pituitary
(somatotrophin) gland
Follicle
stimulating
hormone (FSH)
Luteinising
hormone (LH)
Anterior lobe
of the pituitary
gland
Anterior lobe
of the pituitary
Location
Function
Effect of under- and
oversecretion
Base of the
For growth, repair
brain and
and replacement of
attached to
cells
the
hypothalamus
Oversecretion:
Children – giantism
Adults – acromegaly
Base of the
brain and
attached to
the
hypothalamus
In males:
stimulates
spermatogenesis
No over- or
undersecretion effects
Base of the
brain and
In males:
stimulates the
Undersecretion:
Children – pituitary
dwarf
Adults – premature
senility
In females:
stimulates the
development of the
follicle for process
of ovulation
No over- or
undersecretion effects
Life Sciences X-Sheets
67
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
gland
attached to
synthesis of the
the
hormone
hypothalamus testosterone by the
Leydig cells in the
testes
In females: LH
stimulates the
release of the
secondary oocyte
from the Graafian
follicle and then the
development into
the corpus luteum
Thyroidstimulating
hormone (TSH)
Anterior lobe
of the pituitary
gland
Stimulates the
production of
thyroxin by the
thyroid gland
Oversecretion: goitre
Antidiuretic
Neurosecretory In the centre
hormone (ADH) cells of the
of the brain
hypothalamus
(ADH is stored
in the posterior
lobe of the
pituitary gland)
Regulates
osmoregulation in
the kidneys (in the
distil convoluted
tubules and the
collecting tubules)
Oversecretion: water
retention and swelling
(oedema)
Thyroxin

Oversecretion: goitre
Thyroid gland
Base of the
brain and
attached to
the
hypothalamus
Below the
larynx in the
neck region



Regulates the
basal metabolic
rate of the cells
in the body
Affects growth
and functioning
of the heart and
the nervous
system
Stimulates
growth and
differentiation of
tissue in a
foetus and in
children
Regulates the
body
temperature
when stimulated
by the
Undersecretion: lack
of production of
thyroxin – thyroid gland
is understimulated
Undersecretion:
dehydration
Undersecretion:
Children – cretinism
Adults – myxodema
Life Sciences X-Sheets
68
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
hypothalamus
Aldosterone
Cortex of the
adrenal gland
Above the
kidney
Helps the uptake of
sodium ions in the
loop of Henle in the
kidneys
Oversecretion:
oedema (water
retention)
There are no known
over- or undersecretion
effects. The
sympathetic and
parasympathetic
nervous system
controls the release of
adrenalin
Undersecretion:
Addison’s disease
Adrenalin
Medulla of the
(fight-and-flight adrenal gland
hormone)
Above the
kidney
Prepares the body
to deal with stress:
 Increase in
heartbeat rate
 Increase in
breathing rate
 Increase in
blood pressure
 Increase in
muscle tone
 Increase in
blood sugar
levels
 Decrease in
blood supply to
the skin and
digestive system
 Causes pupils to
dilate
Glucagon
Islets of
Langerhans –
alpha cells
Endocrine
cells of the
pancreas
Controls the
No over- or
increase in the
undersecretion effects
blood sugar level by
causing the
conversion of
glycogen to glucose
Insulin
Islets of
Langerhans –
beta cells
Endocrine
cells of the
pancreas


Testosterone
Gonads: testes Leydig cells in 
the testes of
males located
in the scrotum
at the bottom
Controls blood
sugar by
causing the
conversion of
glucose into
glycogen
Inhibits the
functioning of
glucagon
Oversecretion:
obesity
Testosterone is
responsible for
the secondary
sexual
characteristics
Oversecretion:
aggression. In females,
it results in secondary
sexual characteristics
similar to that in males
Undersecretion:
diabetes
Life Sciences X-Sheets
69
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
of the pelvis


Oestrogen
Gonads:
ovaries
Located in the 
lower
abdominal
region with
each ovary
located within
the pelvic
bones (in line
with the balland-socket
joints of the
femurs)



Progesterone
Gonads:
ovaries
Located in the 
lower
abdominal
in males like a
deeper voice,
pubic hair, hair
on face
Necessary for
the normal
development of
sperm
Activates genes
in the cells of
Sertoli to
promote the
differentiation of
the
spermatogonia
Undersecretion: lack
of secondary sexual
characteristics and lack
of healthy sperm
production
Oestrogen
promotes the
development of
the secondary
sexual
characteristics
in females like
breasts, the
thickening of the
endometrium
(uterus) and the
female body
shape
Necessary for
the process of
ovulation
Oestrogen
inhibits the
secretion of
FSH by the
anterior pituitary
gland so that
only one follicle
is produced
during ovulation
High oestrogen
levels will trigger
the secretion of
luteinising
hormone (LH)
Oversecretion: may
cause cancer
Progesterone
prepares the
Undersecretion:
during pregnancy, will
cause a spontaneous
Undersecretion:
menstruation cycle is
affected, ovulation may
be prevented leading
to infertility, onset of
menopause may occur
Life Sciences X-Sheets
70
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
region with
each ovary
located within
the pelvic
bones (in line
with the balland-socket

joints of the
femurs)


Prolactin
Anterior lobe of Base of the

the pituitary
brain and
gland
attached to
the
hypothalamus 
endometrium of miscarriage
the uterus for
implantation
once fertilisation
of the egg cell
has occurred
Necessary for
the production
of the mucus
plug to prevent
sperm or other
substances from
entering the
uterus during
pregnancy
Decrease in
progesterone
levels causes
menstruation
Progesterone
improves
memory and
cognitive ability
Oversecretion: can
Stimulates the
cause impotence and
mammary
loss of libido
glands to
produce milk
Counteracts the
effect of
dopamine which
is responsible
for sexual
arousal
Homeostasis
Homeostasis is the maintenance of a relatively constant internal environment by
automatic control mechanisms. Cells will function normally, regardless of the external
environment. The nervous system controls all the systems in the body either directly or
indirectly. Homeostasis of the endocrine system occurs through the negative feedback
mechanism. Feedback systems are important because they ensure that all the systems
are interrelated and work together. When there is an increase from normal, a corrective
mechanism will cause it to decrease and vice versa. This ensures that a balance is
maintained within the body.
Life Sciences X-Sheets
71
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
Control of Thyroxin:
Life Sciences X-Sheets
72
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
Blood glucose control:
The blood glucose level is controlled by the Islets of Langerhans in the pancreas.
Diabetics take insulin by injection. It is absorbed into the bloodstream at a much faster
rate. If taken orally, there is a chance that digestive enzymes will denature insulin
because it is a hormone and therefore consists of proteins.
Life Sciences X-Sheets
73
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
Differences between the Endocrine System and the Nervous System
Endocrine system
Nervous system
1.
2.
3.
4.
5.
Made up of glands
Produces hormones
Hormones transported by the blood
Effects are slower and more general
Hormones control long-term changes
(e.g. growth)
1.
2.
3.
4.
Made up of nerves
Produces nerve impulses
Impulses transmitted along the nerves
Effects are very quick and very
specific
5. Nerve impulses control short-term
changes (e.g. sneezing, lifting your
arm)
Thermoregulation
Body temperature must be kept constant in homoeothermic organisms like birds and
mammals. Optimal body temperature in humans is between 36,6 ºC and 37 ºC. If the
temperature is too high, the proteins will denature and be unable to function. If the
temperature is too low, the proteins will become inactive – the body temperature must be
kept constant. The hypothalamus stimulates various systems to regulate the body
temperature. When the body is hot, the hypothalamus will stimulate the pituitary to release
more ADH and less thyroxin. When the body is cold, the opposite will take place.
Hot day
Cold day
The body gets hot:
 You need more water in the blood to
make more sweat to cool you down
 More ADH is released by the pituitary
gland to keep more water in the blood
 Blood vessels near the surface of the
skin dilate (vasodilation), so more
blood reaches the sweat glands
 More sweat evaporates, cooling the skin
and the blood in the vessels near the
surface of the skin
 This means that you will produce more
concentrated urine (less water in the
urine)
 The hairs in the skin lie flat so no heat is
trapped between the skin and the hairs
 The pituitary gland inhibits the thyroid
so less thyroxin is released causing a
decrease in cell metabolism, so less
energy is released – body cools down
The body gets cold:
 You need less water in the blood as you
do not need to produce sweat
 Less ADH is released by the pituitary
gland to keep less water in the blood
 Blood vessels near the surface of the
skin constrict (vasoconstriction), so
less blood reaches the sweat glands
 No sweat evaporates, so there is no
cooling of the skin and the blood in the
surface vessels
 This means that you will produce less
concentrated urine (dilute urine)
 The hairs in the skin are pulled upright
by the erector muscles to trap warm air
(goose bumps)
 The pituitary gland stimulates the
thyroid so more thyroxin is released,
causing an increase in cell metabolism.
More energy is released and causes
shivering – body warms up
Hypothermia (HypO – Ohhh, it is Cooooold): occurs when the body is exposed to cold
and the internal mechanisms cannot keep the internal core body temperature
constant. Preventative measures: keep the body warm, keep moving, exercise, dress
warmly, add more clothes and blankets, drink hot drinks, warm the body near a fire or
heater, stay in a warm, protected environment etc.
Life Sciences X-Sheets
74
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
Hyperthermia: occurs when the body becomes too hot and is unable to cool the internal
core temperature down sufficiently. This results in dehydration, heat stroke and heat
exhaustion. Preventative measures: the body can be cooled by changing the external
temperature, for example cold compressions on the neck and forehead, swimming, taking
a cold shower or bath, taking extra layers of clothes off, staying in the shade, wearing a
hat, moving into an air conditioned room etc.
Thermoregulation – animal adaptations
Various species of animals have behavioural, physical and physiological adaptations to
deal with thermoregulation:
 Panting – dogs.
 Insulation: fat layers under the skin e.g. blubber of marine mammals like whales and
seals; trapped air under the fur of their bodies e.g. rabbits and cats; thicker winter
coat of fur e.g. bears and squirrels and birds ruffle their feathers and trap the air
between the feathers and skin.
 Body size: the metabolic rate of a small animal is faster than that of a larger animal.
The smaller the animal, the larger the body surface in relation to mass - smaller
animals lose heat to a cold environment more rapidly than the larger animal. Larger
animals can retain more heat.
 Heat exchange mechanism: counter-current exchange mechanism involves two
blood vessels that are in close contact with blood flowing in opposite directions, for
example an artery and a vein. The body temperature may rise or fall, but the
temperature of the thoracic cavity and brain will stay constant.
 Body orientation: reptiles orientate their bodies to the sun, depending on whether
they need to warm up or cool down.
 Water conservation: kangaroo rat and camels.
 Behaviour patterns
o Hibernation: e.g. squirrels, bats, bears, rodents, hedgehogs, marsupials and
rattlesnakes.
o Aestivation: e.g. ladybeetles, some species of snails, land crabs, desert tortoises,
crocodiles, salamanders, some amphibians and lungfish.
o Burrowing
o Nocturnal behaviour: animals come out at night e.g. bats, bush-babies and
genets.
Life Sciences X-Sheets
75
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
X-ample Questions
QUESTION 1:
(Taken from Study and Master Grade 12, 2003)
Study the diagram and answer the questions that follow:
1.1.
1.2.
1.3.
1.4.
1.5.
1.6.
1.7.
Identify the organs marked A and B.
(2)
Identify the hormones numbered 1 and 2.
(2)
Name the exact structures that secrete hormones numbered 1 and 2
respectively.
(2)
How do the hormones mentioned in question 1.2 reach the target organ A? (1)
Which organ (A or B) monitors the blood sugar levels?
(1)
Name the abnormality that may develop from an under-secretion of the
hormone numbered 1.
(1)
What effect does the secretion of adrenalin have on the normal blood sugar
level?
(1)
Life Sciences X-Sheets
76
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
QUESTION 2:
(Taken from Study and Master Grade 12, 2003)
Study the diagram and answer the questions that follow:
2.1.
2.2.
2.3.
2.4.
2.5.
2.6.
2.7.
Identify the endocrine glands marked A and B.
Which interaction is depicted by this diagram?
Name the hormones numbered 1 and 2.
Name the specific function performed by hormone number 2 as shown
at point X in this interaction.
What effect will:
a) an over-secretion, and
b) an under-secretion of hormone number 2 have on the production of
hormone number 1?
Name the hormone secreted by endocrine A necessary for normal growth
and development.
List FOUR specific characteristics of hormones.
Life Sciences X-Sheets
77
(2)
(1)
(2)
(1)
(2)
(1)
(4)
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
QUESTION 3:
(Taken from BIOS BEST 2007 HG)
Study the diagram of the human skin and answer the questions that follow:
3.1.
3.2.
3.3.
Provide labels for structures A, B, D and E.
(4)
State ONE function of C and D respectively.
(4)
Describe the role played by the skin in regulating blood temperature on a
cold day.
(9)
X-ercise
Complete the following table.
Gland
Hormone
Adrenal Medulla
1
Pituitary gland
(Anterior lobe)
Thyroid
4
Beta cells of the
Islets of
Langerhans
Neurosecretory
cells of the
Hypothalamus
Alpha cells of the
Islets of
Langerhans
9
2
Function
Prepares the body for action in an emergency
situation
Stimulates the production of thyroxin
Thyroxin
3
Somatotrophin Regulates growth and development of muscle tissue
5
Causes the decrease of blood sugar levels
6
Regulates water levels in the blood
7
8
10
Necessary for the normal development of sperm cells
Life Sciences X-Sheets
78
Animal Responses to the Environment:
Endocrine System and Thermo Regulation
Answers to X-ercise:
1. Adrenalin
2. TSH
3. Regulates the basal metabolic rate
4. Pituitary gland (anterior lobe)
5. Insulin
6. ADH
7. Glucagon
8. Causes an increase in blood sugar levels
9. Testes / Male gonads
10. Testosterone
Life Sciences X-Sheets
79