Regulation and
Control in humans and
plants
BIOL0012 Lecture 27
Regulation & Control Outline
• Explain the need for control in biological systems;
1
concept of homeostasis
• Receptors, effectors, normal/optimal condition
(range), feedback/equilibrium
• Describe homeostatic functions, as shown by the –
Liver: carbohydrate metabolism, deamination, detoxification,
breakdown of erythrocytes
– Skin: thermoregulation
• Explain how the nervous and endocrine systems
function in coordination of body systems •
Coordination in plants: plant growth substances as
demonstrated through:
– Auxin & growth
– Ethylene & fruit ripening
Objectives
2
• Explain the concept of, and reasons
for homeostasis
• Explain the feedback mechanisms •
Outline homeostatic functions of the
human liver
• Describe how human body
temperature is regulated
• State how processes in plants are
coordinated.
Regulation and Control
3
•A properly functioning body
maintains an internal
equilibrium.
•Physiological
mechanisms in body maintain
equilibrium ‘steady state’ in spite
of changes in the
environment.
Regulation and Control
• Homeostasis
– the maintenance of the internal
environment of the body within tolerable
limits.
– also the mechanism by which this internal
equilibrium is maintained.
4
– involves regulation of the concentration of
molecules and ions that are essential to life
within the blood and tissue fluid
– involves maintenance of physical
parameters
Regulation and Control
parameters controlled by homeostasis –
Concentration of oxygen and carbon
dioxide
– pH of the blood and tissue fluid –
Concentration of nutrients and waste
products
5
– Concentration of salts and ions – Volume
and pressure of extracellular fluid –
Temperature of blood and tissue fluid.
Regulation and Control
6
Negative feedback
• means by which a constant value (set point,
norm or optimal condition) of a factor is
achieved.
• whenever a change occurs in a system it is
detected by receptors and automatically
causes a corrective mechanism involving
effectors to occur, resulting in a reversal of the
original change, bringing the system back to
the norm.
• the desired level constantly fluctuates around
the set point. Equilibrium steady state
negative feedback
control
7
http://www.biology-online.org/4/1_physiological_homeostasis.htm
Temperature Homeostasis
Thermoregulation
• important in body since enzymes
8
require particular constant
temperatures for optimal metabolic
reactions.
– If temperature exceeds 40°C,
enzyme activity declines.
•brain affected first
– Abnormally low temperatures also
slow metabolic activities and impair
brain function.
9
Temperature status of organisms
• Endothermic: controlling body
temperature by internal metabolism
Homeothermic: maintaining constant
body temperature
• Exothermic, Ectothermic: controlling
body temperature by external
mechanisms.
• Poikilothermic: having varying body
temperature
Temperature
10
Homeostasis • Endothermic animals
(endotherms)
– e.g., birds and mammals
– maintain a fairly constant internal body temperature
around 37°C irrespective of the environment – employ
physiological mechanisms to maintain a steady
internal temperature (homeothermic).
• Exothermic animals (exotherms)
– eg. reptiles
– are not independent of the environmental changes
– maintain a body temperature by physical
mechanisms
11
Temperature Homeostasis
in mammals
12
Temperature Homeostasis
Thermoregulatory
centre in humans is
the hypothalamus
• part of the autonomic nervous system,
so the various responses are all
involuntary
• functions as a thermostat
• is sensitive to blood flowing through it,
and responds by sending messages to
appropriate effectors
Temperature Homeostasis
of
13
Hypothalamus
• receives input from 2 sets
thermoreceptors
1. receptors in hypothalamus itself monitor
temp. of blood as it passes through the
brain (the core temperature)
2. receptors in skin monitor external
temperature (Krause’s end bulb for cold
and Organs of Ruffini for heat).
• sends impulses to several different
effectors to adjust body
temperature
14
Temperature
Homeostasis Response to low
temperature
1.Hairs on skin raised to a more
vertical position.
– ‘Goose pimples’
– Air gets trapped in the spaces between the
hairs and serves as an insulator.
– Not
very
effective in humans.
2.Arterioles to the
superficial capillaries constrict
reducing blood flow to the surface
of the skin.
– Prevents loss of heat from blood
– Extremities can turn blue and feel cold and
can even be damaged (frostbite).
Temperature
15
Homeostasis • Response to low
temperature
3.Metabolic rate increases
– Involves hormonal action: adrenaline
(adrenals) and thyroxine (thyroid).
– Produces heat inside the body by involving
organs:
•skeletal muscles contract & relax
repeatedly (shivering) to generate
heat •metabolic reactions occur in the
liver. •heart rate and blood pressure
increase
Temperature
Homeostasis • Response to high
temperature
1.Hairs lowered.
– Less air trapped so heat energy readily lost.
16
2.Arterioles to superficial capillaries dilate –
more blood flows to skin surface where heat is lost
by convection and radiation.
3.Glands secrete sweat onto surface of skin
– sweat evaporates, cooling the skin.
4.Adrenal and Thyroid glands stop releasing
adrenaline and thyroxine
– metabolism decreases so less heat generated.
Temperature Homeostasis in Man
17
Effectors:
Effect:
Homeostatic Functions of
18
Liver
• Liver
– works closely with most systems and
processes in the human body for many
homeostatic functions.
– receives a dual blood supply; blood from
both sources intermingle
•hepatic portal vein from small intestines
•hepatic artery from heart.
19
Homeostatic Functions of Liver
• Blood from hepatic portal vein – has
already supplied SI, pancreas & spleen – has
most of its oxygen removed.
– but contains nutrients and other materials
absorbed in the intestine, blood cells and
their breakdown products from the spleen,
as well as endocrine secretions from the
pancreas.
• Blood from hepatic artery
– supplies liver with oxygen.
20
Organization of the liver
• Liver contains many lobules.
• Liver lobules have
– a branch of the hepatic vein in the center
– hepatocytes (liver cells) arranged in rows
radiating out from the centre
•sinusoids carry blood between hepatocytes
•canaliculi carry bile from hepatocytes to branch of
bile duct
– branches of the hepatic artery, hepatic portal
vein and bile duct between them.
•Blood flows from hepatic artery and hepatic portal
vein, through the liver and into the branch of the
hepatic vein.
Organization of the liver
21
branch of hepatic portal
vein
bile duct
central vein (branch of
hepatic vein)
chains of
sinusoids
hepatocytes
branch of
hepatic artery
http://www.ariess.com/s-crina/liver-anatomy.htm
Homeostatic functions of
liver 1. Regulation of blood sugar
22
• excess glucose from small intestine is stored
as glycogen in liver by the influence of
insulin (from pancreas).
2. Regulation of lipids
• lipids are extracted from blood by liver and
changed to carbohydrates if required, or sent
to fat storage sites (external to the liver).
• liver also converts excess carbohydrates
and proteins to fat for storage.
23
Homeostatic functions of liver
3. Regulation of amino acids
• excess amino acids in the blood cannot be
stored so
– some amino acid molecule are converted to
carbohydrates.
– some converted into urea by the liver and
transported to the kidneys for excretion in urine. 4.
Production of heat
• Heat produced by physiological process in
the liver is carried around the body in the
blood to warm less active regions.
24
Homeostatic functions of liver
5. Removals of hormones, toxins, drugs.
• Liver extracts many harmful materials from
the blood and excretes them in the bile or
via the kidneys.
6. Removal of haemoglobin molecules
• Haemoglobin from dead red blood cells is
converted into bile pigments and the Fe
atoms saved for future use.
25
Homeostatic functions of liver
7. Storage of blood
• Liver can swell to hold huge volumes of
blood which can be released into the
circulation if needed e.g. in cases of blood
loss due to wounding.
8. Storage of vitamins
• Liver stores vitamin D and B12.
• Liver manufactures vitamin A from carotene
and stores it.
Homeostatic functions of
Kidney
26
Two main homeostatic functions
1. Removes metabolic waste
(especially nitrogenous wastes) from
the body (excretion)
2. Regulates the water and salt content
in the blood (osmoregulation).
27
Regulation and Control In Plants
Coordination in Plants
•Plants
– respond to various types of stimuli
28
e.g., light, touch and gravitational
force.
– do not have special structures for
perception of external stimuli.
– controlled and coordinated by plant
growth regulators (chemical).
Coordination in Plants
• Plant growth regulators (plant hormones)
– include abscisic acid (ABA), auxins,
gibberellin, cytokinin, and ethylene.
29
– can interact with each other causing various
results in plant growth and development. –
have different effects depending on their
concentration, the plant’s stage of growth, as
well as the site of action.
–
involved in
the
regulation of functions such as growth of
roots, stems & leaves, flowering, germination
of seeds, ripening of fruits, movement of
stomata and tropisms.
Coordination in Plants
Plant response to stimuli
• Tropism - movement of a plant in the
direction of stimulus.
– Phototropism - growth of a plant towards
a unidirectional light source.
– Geotropism - downward movement of
the roots of plants in response to
gravitational force
– Chemotropism - movement in response
30
to a chemical stimulus
Coordination in Plants
31
Auxins
• regulate phototropism and geotropism.
• promote stem growth by stimulating cell
elongation
• control differentiation of xylem and
phloem • stimulate lateral root growth and
root initiation on stem cuttings
• inhibit lateral bud sprouting
• produced primarily in shoot tips and growing
leaves and fruits.
Coordination in Plants
32
Phytochrome
• pigment which allows plant to respond to
photoperiodic stimuli
– Flowering and seed germination are regulated by
duration of light (photoperiodism).
Cytokinins
• promote cell division
• stimulate lateral bud growth (determined by
relative concentrations of auxin & cytokinin) •
are produced mainly in roots.
• used extensively in plant tissue culture.
Coordination in Plants
Gibberellins
• promotes stem elongation (enhance the
effects of auxin)
• stimulate germination in buds and seeds.
• produced in embryonic tissues
(meristems)
Abscisic Acid
• cause stomatal closure during water stress
33
• promotes dormancy in seeds and buds •
produced in leaves, stems, and green fruits.
Coordination in Plants
34
Ethylene
• promotes abscission; dropping of
leaves, fruits, or flowers from a plant •
causes aging and fruit ripening – ripening
results from the increased activity of enzymes
that soften fruit
– ethylene stimulates the production of
cellulase which hydrolyses cellulose in
plant cell walls
• only gaseous growth regulator.
35