Homeostasis refers to the maintenance of stable internal conditions in the body, such as temperature and blood glucose levels. It involves dynamic mechanisms that detect changes in physiological variables and initiate responses to restore optimal levels. Negative feedback systems oppose stimuli to maintain equilibrium, while positive feedback intensifies stimuli over a limited time to complete a process, like childbirth. The nervous, endocrine, respiratory, and circulatory systems all contribute to homeostasis through receptors, signals, and coordinated regulatory responses.

1. Modern aspects of regeneration
and transplantation.
Biological mechanisms of
homeostasis maintenance in
organism.

2. Regeneration
Regeneration is the sequence of
morphogenetic events that restores
the normal structure of an organ after
its partial or total amputation.

3. Regeneration in
invertebrates

4. Hydra: Cross amputation of hydra led every
part to regenerate to whole hydra species.

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6. Planaria: The planaria contains neoblast
cells which migrate toward the amputated
region and form the lossing parts

7. The blastema of the amputated region formed of
ectoderm , mesoderm and neoblast cells which co-
ordinated in regeneration of the lossing parts.

8. Regeneration of vertebrates
There are two types of
regeneration:
1. Epimorphosis or epimorphic
regeneration.
2. Morpholaxis or morphollactic
regeneration.
.

9. Epimorphosis or epimorphic
regeneration :
This type of regeneration involve the
reconstruction of the missing parts by
local proliferation from the blastema, or
addition of parts to remaining piece .
For example: regeneration of tail, limbs
and lens in anurans and urodels and
other vertebrates.

10. Morpholaxis or morphollactic
regeneration:
• This type of regeneration involving
reorganization of the remaining part of
the body of an animal.

11. Epimorphosis or epimorphic regeneration
Regeneration of Tail in amphibians & reptilia :
Amphibia : The tail lacks vertebrae and has an unsegmented
cartilaginous tube, which contains the regenerated spinal cord
which form mainly of the ependymal lining of the central canal .
At first very few cells accumulate under the wound epithelium .
The ependyma and the various connective tissues dermis,
muscle septa, adipose tissues and osteocytes of vertebrae are
the sources of cells for the generate. The non-nervous elements
proliferate behind the apex, forming both the muscle and
cartilage tube ,then, the ependyma proliferate and gradually
extend dorsally.
Reptilia : For example lizard, the regenerated tail is a quite
imperfect tail. It lacks vertebrae and in their place, has an
unsegmented cartilaginous tube. This tube contains the
regenerated spinal cord, including the extension of the
ependymal lining of the central canal of the spinal cord.

13. Regeneration of lens:
1. The dorsal region of the iris thickens and a cleft arises between
inner and outer lamellae of the iris.
2. Amoeboid cells move from the stroma into the cleft followed by
marked increase of RNA and DNA synthesis as well as of mitotic
cell division.
3. The pigmented cells of the dorsal region is engulfed by invading
amoeboid cells.
4. The formed non- pigmented cubical cells form hollow epithelial
vesicle and extends with inner and outer lamellae.
5. The vesicle inner wall cells elongated into the lumen and form
primary lens fibers.
6. The lens-specific crystalline proteins is formed.
7. The primary lens fibers push to the front of vesicle to form a
nucleus behind the lens epithelium which form the secondary
lens fibers.
8. The nucleus of primary lens fibers is enclosed by secondary
lens fibers.
9. In the central lens fibers the nucleus degenerate ,primary and
secondary lens fibers are the components of the lens.

15. Regeneration of Limb
Regeneration begins in 3 phases :
1. Phase of wound healing or pre -blastema stage :
Blood clotting and migration of epidermal cells from the
basal layer of epidermis toward the centre of the wound. The
wound is covered with epithelium which is thicker than the
epidermis of the limb .
2. Phase of blastema formation :
Cells accumulate beneath the epithelial covering and formed
the blastema. Mesenchymal cells accumulate beneath the cap .
Mesenchymal – blastemal cells differentiate into myoblasts and
muscle cells, early cartilage cells and cartilage. During the
dedifferentiate phase Hyaluronate (HA) increases in the distal
stump to form blastema . As the blastema forms, the HA will be
decrease. The production of HA and break down of collagen
represent the establishment of migration from stump tissues .
3. Phase of dedifferentiate and morphogenesis :
The blastema begins to restore the part of which the limb was
deprived. Specifically, if the fore arm is removed, the blastema
differentiated directly into the muscle, bone, cartilage and skin
of the fore arm.

17. Steps of regenerated limb

18. Factors Controlling
Regeneration
1. nervous system.
2. animal size .
3. pituitary gland .
4. Vitamin A and its derivatives.
5. Insulin .

19. 1. Defined as maintenance of a relatively stable
internal environment
-Does not mean that composition,
temperature, and other characteristics are
absolutely unchanging
2. Homeostasis is essential for survival and
function of all cells
3. Each cell contributes to maintenance of a
relatively stable internal environment
Homeostasis

20. Homeostasis is the maintenance of
stable, constant conditions of the body’s
internal environment which consists of
blood and intestitial fluid (tissue fluid).
EQUILIBRIUM

21. Homeostasis involves dynamic
mechanisms that detect and
respond to deviations in
physiological variables from their
“set point” values by initiating
effector responses that restore
the variables to the optimal
physiological range.

22. • Homeostasis occurs in
ALL living organisms,
Uni-cellular & Multi-
cellular.

23. • Uni-cellular organism don’t have an
internal environment. They are cells
directly placed in fluids of their external
environment, their cell membrane
regulates their cytoplasm.

24. An advantage for multi-cellular organisms is that their
cells are protected from the organisms external
environment by the extracellular fluid.
This internal environment allows conditions inside the
organism to be maintained for efficient cell functioning.

25. 25
Homeostasis
All organ systems
contribute to maintain
within normal limits
the internal conditions
as body temperature,
water content, pH,
Glucose and CO2
concentrations.

26. External environment Internal environment
The medium surrounding
an organism
The extracellular fluid: is
the fluid that surrounds
cells in multi-cellular
organisms.

27. For optimal functioning, cells regulate:
1. Concentration of particular salts
2. Temperature
3. Nutrient levels
4. Waste levels
5. PH

28. • Tight regulation of extracellular fluid & a stable
internal environment is vital for optimal cellular
function in multi-cellular organisms.
Examples of processes used to stabilise the internal environment
include:
1. Lungs & exchange of carbon dioxide & oxygen
2. Animal circulatory systems
3. Removal of wastes
4. Root absorption of water & minerals

30. Homeostasis is achieved by three
important mechanisms:
STRUCTURAL – the organism has
particular physical features to maintain
homeostasis.
FUNCTIONAL – the metabolism of the
organism is able to adjust to changes.
BEHAVIOURAL – the actions of the
organism individually or with others help
the organism to maintain homeostasis.

31. There are three components to a
homeostatic system:
1. The Sensor which detects the stress.
2. The Control Center which receives information
from the sensor and sends a message to adjust
the stress.
3. The Effector which receives the message from
the control center and produces the response
which reestablishes homeostasis

32. Homeostatic Mechanisms
The most complex organisms to regulate their
internal environment are the mammals and
birds.
The mechanism used by these organisms is
called ‘The Stimulus-Response mechanism’
The 3 main types are:
1. Simple Stimulus-response
2. Negative Feedback systems
3. Positive Feedback systems

33. Stimulus-Response
• The general pattern of a stimulus–
response mechanism is the withdrawal
reflex.

35. Negative Feedback
• Most common type of biological feedback system.
• Activity of effector opposes stimulus
• Effector produces opposite effect of stimulus.
• Example:
– Home heating system. The temperature of the home is
monitored and heating will be turned off until the temperature
returns to set level.
• Biological examples: body temperature and blood
glucose levels

36. Negative Feedback System
• Negative feedback systems are stimulus–
response mechanisms that act to restore
the original state. The response produced
reduces the effect of the original stimulus;
that is, the response provides feedback
that has a negative effect on the stimulus.

37. 37
effect
effect
Control center
Control center
Sensor
Sensor
Negative feedback
The negative feedback mechanisms is the principal
mechanism in homeostasis and is composed of a sensor
and a reaction center (i.e. blood glucose levels).

38. Hyperglycemia Pancreas-beta cells
Sensor and Control center
Insulin is released
into blood
Liver and Muscle cells
take up glucose from
the blood
Effectors
Blood glucose
is reduced
Stress is reduced
shutting down
mechanism
Stress
Homeostatic Regulation of Blood Sugar through
Negative Feedback

40. Positive Feedback
• Not particularly common in biological
systems.
• Activity of effector reinforces stimulus.
• Effector produces response in same
direction as stimulus
• Must have a mechanism to halt the cycle
• Biological examples: childbirth and blood
clotting

41. Positive Feedback Mechanisms
Homeostatic systems utilizing positive feedback exhibit two primary
characteristics:
1. Time limitation – Processes in the body that must be completed within a
constrained time frame are usually modified by positive feedback.
2. Intensification of stress – During a positive feedback process, the initial
imbalance or stress is intensified rather than reduced as it is in negative
feedback.
Typical Positive Feedback Process
Stress Sensor Control Center
EffectorIntensifies

42. Positive feedback increases change
Example: Torn blood vessel stimulatesExample: Torn blood vessel stimulates
release of clotting factorsrelease of clotting factors
growth hormones stimulate cell divisiongrowth hormones stimulate cell division
platelets
fibrin
white blood cell
red blood cell
blood vessel
clot

43. Homeostatic Regulation of Child Birth through
Positive Feedback
Pressure of Fetus on
the Uterine Wall
Nerve endings in the uterine
wall carry afferent messages
to the Hypothalamus
Production and Release
of Oxytocin into the
Blood
Increasing strength of
uterine contractions
Intensifies
The birth of the child will bring this process to a close. Other
examples of positive feedback regulation occur during milk
letdown and blood clotting.

44. Types of signals
Physical Stimuli
•Light
•Heat
•Touch/mechanical
Chemical Stimuli
•Nutrient molecules-
glucose
•Hormones
•Neurotransmitters
•Pheremones

45. Regulating responses to stimuli
1. To coordinate all the
different activities a
multicellular organism
will integrate and
coordinate the
activities of their cells.
2. There are two major
systems for this:
- ENDOCRINE SYSTEM
(hormones) and
- NERVOUS SYSTEM
(nerves).

46. Types of Receptors
• Chemoreceptors - detect chemicals
– Olfactory lining in nose; taste buds; oxygen concentration
receptor in aorta; osmoreceptors in hypothalamus; glucose level
receptors in pancreas; pH/CO2 receptors in medulla, aorta and
carotid arteries
• Mechanoreceptors – detect pressure and movement
– Ear; touch & pressure receptors in skin muscles, joints and
connective tissue; muscle length receptors in skeletal muscle;
muscle tension receptors in tendons; joint receptors; venous
pressure receptors; arterial pressure receptors; lung inflation
receptors; lung deflation receptors; lung irritant receptors.
• Photoreceptors – detect light
– Eye.
• Thermoreceptors - detect temperature
– Heat receptors and cold receptors in skin; body temperature
receptor in hypothalamus.

47. Homeostatic Control Systems
In order to maintain homeostasis, control
system must be able to
 Detect deviations from normal in the internal
environment that need to be held within narrow
limits
 Integrate this information with other relevant
information
 Make appropriate adjustments in order to
restore factor to its desired value

48. Some systems controlled by
homeostasis
Control of Requires regulation of
nutrient levels
(e.g. glucose)
•nutrient intake
•digestive and circulatory system functions
•storage and mobilisation of nutrients
•behaviour
body temperature
•general metabolism
•blood flow to tissues
•muscle activity and sweating
•behaviour
water and salt
balance
•excretion of water and salts to maintain correct
osmotic concentration of internal body fluids
•behaviour
metabolic rate
•lung ventilation and circulation to deliver adequate
oxygen to tissues
•nutrient intake and storage
•behaviour

49. Body systems involved in regulation
of homeostasis
• Nervous system
– Receives and transmits information about both the external and internal
environment. Transmits electrical impulses to body cells that respond in
various ways.
• Endocrine (hormonal) system
– Produces hormones that are secreted directly into the bloodstream and
transported throughout the body where they regulate cell activities.
• Respiratory system
– Obtains oxygen from air and eliminates carbon dioxide which is a waste
product of metabolism of cells. Assists in regulation of pH through
removal of carbon dioxide.
• Circulatory system
– Transports O2 to cells, CO2 away from cells, and hormones, wastes and
nutrients such as glucose, amino acids and fatty acids throughout the
body.