TOPIC 14: Coordination and control - The
human endocrine system
Hormones
A chemical (protein) produced by endocrine glands and carried in the bloodstream.
- Function:
- Alters the activity of one or more specific target organs
- Endocrine glands have good blood supply → Hormones are carried in the bloodstream to the
target cells/organs
- Their production and release from secretory cells in response to stimulation by nerves/other
chemical stimuli
- Only specialised cells respond to hormone (target cells have particular receptors)
- Once used, destroyed by liver
Nervous system
Endocrine system
Cells involved
Neurones
Secretory cells
Types of signals
Electrical impulses (some chemical at
synapses)
Chemical (hormones)
Transmission of signal
Along nerve fibers
Dissolved in blood plasma and
through bloodstream
Effectors
Muscle and glands
Target cells in particular organs
Type of response
Muscle contraction or secretion
Chemical change
Speed of response
Very rapid
Slower
Duration/longevity of
response
Short until nerve impulses stop
Long until hormone is broken
down
Glands & Hormones table
Hormones are secreted/released by specific glands and released into the bloodstream to create a certain
effect.
Hormone
Source
(gland)
Target organ(s)
Role
Effects
Oestrogen
Ovary
Reproductive
organs
Female sex hormone, controls
menstrual cycle
Develops female secondary
characteristics (e.g. developed
breasts, widened hips to prepare
for pregnancy, growth of pubic
hair)
Progesterone
Ovary
Uterus
Supports pregnancy
Maintains uterus lining
Testosterone
Testis
Reproductive
organs
Male sex hormone
Develops male secondary
characteristics (e.g. voice break,
increased muscle, growth of
pubic and facial hair)
Primary: growth of testes and
penis, increased sperm
production
Glucagon
Pancreas
(islets of
Langerhans)
1) Liver
Controls and balances blood
glucose levels
Increase blood glucose level by
causing the liver cells to break
down glycogen to glucose, and
release it into the blood
Insulin
Pancreas
(islets of
Langerhans)
1) Muscle
(respiration)
2) Liver (converted
to glycogen)
3) MOST
TISSUES
Controls and balances blood
glucose levels
After eating, pancreas (islets of
Langerhans) detects increase in
blood glucose levels > pancreas
secretes insulin into the blood >
insulin 1) stimulates glucose to
be stored as glycogen in the liver
2) stimulates glucose to be used
in respiration
Adrenaline
Adrenal gland
MOST TISSUES
Stimulates “fight or flight”
response
Increases:
- Heart rate
- Speeds up conversion
of glycogen to glucose
> increased blood
glucose levels >
increased respiration in
muscle cells
- Breathing rate
- Blood flow to muscles
Decreases/reduces:
- Blood flow to nonessential parts of the
body (e.g. digestive
system/alimentary
canal)
Other:
- Dilates pupils to allow
as much light as
possible to reach the
retina > more info can
be sent to brain
(T3) Triiodothyronine
Thyroid gland
MOST TISSUES
Metabolism regulation (by
stimulating the rate of
metabolism)
Affects growth and development
(T4) Thyroxine
Thyroid gland
MOST TISSUES
Metabolism regulation (by
stimulating the rate of
metabolism)
Increases/decreases:
- Heart rate
- Metabolism rate
(FSH) Folliclestimulating
hormone
Pituitary
gland/Master
gland
1) Ovaries
2) Testis
Female sex hormone
Matures egg cells and causes
ovaries to produce oestrogen
(GH) Growth
hormone
Pituitary
gland/Master
gland
ALL TISSUES
Maintains muscle/tissue growth
Fuels growth during childhood
(LH) Luteinizing
hormone
Pituitary
gland/Master
gland
1) Ovaries
2) Testis
Female sex hormone
Ovulation (stimulates eggs to be
released)
(TSH) Thyroidstimulating
hormone
Pituitary
gland/Master
gland
Thyroid gland
To stimulate TRH. Controls the
production of thyroid hormones
(T3 & T4)
Stimulates the thyroid to release
Thyroxine and Tri-iodothyronine
(ADH) Antidiuretic hormone
Pituitary
gland/Master
gland
1) Kidney tubules
2) Smooth muscle
in arterioles
Osmoregulation
Increases permeability of the
distal convoluted tube and
collecting duct to water,
allowing more water to be reabsorbed into blood
Negative feedback systems in hormonal control
Homeostatic control
-
Water concentration, temperature, blood glucose concentration, the control of thyroxine level
Homeostasis - to keep the internal environment of an organism constant so that the body can
work as efficiently as possible
Negative feedback mechanism
-
The negative feedback control system responds when the condition changes, it returns it back to
the ideal state (e.g. it reduces a rised level, vice versa)
A continuous cycle of events
Control of body temperature
-
-
-
-
●
Keep a constant temperature (~37°C) helps enzymes to work at their optimum rate
Endothermic
- Endo- means within
- Able to keep good control over own body temperature and keep it constant
- Core body temperature is kept within narrow limits
- Get heat energy from food, by respiration.
- At colder temperatures, it is active with high body temperature to keep metabolising. At
high temperatures, it is still active but less active to avoid heat stroke/overheating.
- E.g. mammals, human, birds
Ectothermic
- Failed to keep its body temperature constant when the temperature of the environment
changes
- At 0°C, their metabolic rate slows down, their body temperature is also 0°C and they
become inactive
- At 20°C, the body temperature rises to near 20°C and becomes active
Body temperature is controlled by hypothalamus in brain
- It contains temperature receptors that sense the temperature of the blood running through
it
- It sends electrical impulses to skin to bring out actions to regulate body temperature
Significance
- Too hot: the body will sweat to reduce body temperature, to avoid heatstroke (which will
denature the enzymes and alter metabolism)
- Too cold: the body will shiver to raise body temperature, to avoid hypothermia (body
temp. below 35°C) (which will make enzymes inactive)
Structure of the skin (organ for temperature regulation)
Epidermis (upper layer)
○ Cells undergo mitosis → new cells are made gradually move towards the surface of the
skin
As they go, they die → become keratin (a protein)
Top layer (cornified layer) = dead cells
■ Hard and waterproof
■ Protects the living cells underneath
■ Always being worn away and replaced
■ E.g. soles of the feet
○ With cells containing melanin (brown pigment) which absorbs the harmful UV light from
the sun
○ Hair follicles with hairs (made of keratin)
Dermis (lower layer)
○ Made of connective tissue (with elastic fibres and collagen fibres)
○ Sweat glands: produce sweat (water + salts + urea), it travels through sweat duct to the
surface of skin to lower body temperature through evaporation
○ Blood vessels and nerve endings (sensitive to touch, pain, pressure, temperature)
○ Adipose tissue (fat): to insulate the body against heat loss, energy reserve
○
○
●
Structure of a section through human skin
When temperature falls
When temperature rises
Shivering
- Contract and relax very quickly to produce
heat
- The heat generated can warm the blood
nearby, the blood helps distribute to other
body parts
Sweating
- Sweat glands secrete sweat
- Evaporation of water takes heat away
(facilitate heat loss)
Increase metabolism (to release more heat) e.g.
respiration
Might decrease metabolism (to avoid heatstroke)
Hair stands up
- Erector muscle contracts, pulling the hairs
up
- To trap a thick layer of warm air next to the
skin, prevent heat loss
- Acts as an insulator in hairy animals (not
human)
Hair lies flat
- Erector muscle relaxes
- Not to trap too much warm air
Vasoconstriction
- The arterioles near the skin surface are
narrowed/constricted → allow little blood
flow → reduce heat loss
- The blood flows through shunt vessels
(deeper) instead which has more insulation
from fatty tissue
Vasodilation
- The arterioles near the skin surface are
widened/dilated
- More blood flow → more heat loss from
the blood to the air
How skin helps with temperature regulation
Control of blood glucose concentration by pancreas and insulin
Low blood glucose
High blood glucose
Glucagon released by pancreas
Insulin released by pancreas
Liver releases glucose into blood
Body’s cells absorb glucose from blood
Glycogen is converted into glucose (for higher
blood glucose levels)
Glucose is either USED or STORED (Glycogen)
Glucose - simple sugar for cellular respiration
Glycogen - stored sugar in liver and muscle cells
Glucagon - HORMONE released from pancreas
Type 1 & Type 2 diabetes
Type 1 (insulin deficiency)
Genetic diabetes, where the pancreas is genetically unable to produce enough insulin.
- Causes:
- Passed down from person to person genetically
- Symptoms:
- Treatment:
CANNOT be cured, can be CONTROLLED
- Inject insulin - the amount is determined by monitoring blood glucose levels frequently
per day OR the amount of physical activity done per day
- Careful dietary planning
- Exercise
Type 2 (insulin resistance)
Diabetes obtained in life, where the cells in a person’s body are no longer able to respond to the insulin
produced by the pancreas.
- Common in elderly
- Overweight/obese people have an increased risk of developing type 2 diabetes
- Causes:
- Poor diet control - intake too much food with high glycemic index
- Lack of physical activity/exercise
- Symptoms:
- Treatment:
CANNOT be cured, can be CONTROLLED
- Inject insulin - the amount is determined by monitoring blood glucose levels frequently
per day OR the amount of physical activity done per day
- Careful dietary planning
- Exercise