This document discusses homeostasis and feedback mechanisms in the body. It defines homeostasis as the condition of equilibrium in the body's internal environment that is maintained through feedback systems. Feedback systems involve detectors that monitor a controlled condition, a control center that processes this information and directs effectors to respond and correct any changes. Negative feedback is the most common type and acts to reverse changes, while positive feedback reinforces changes. Key feedback mechanisms discussed include regulating blood glucose levels through insulin and glucagon, body temperature through heat receptors and effectors, and blood pressure through baroreceptors. Signs of failed homeostasis include symptoms of illness and complete failure can result in serious events like stroke or death.

1. HOMEOSTASIS AND THE
CONCEPT OF FEEDBACK
MECHANISM
R.E.J. MASESE

2. Study Objectives
Define Homeostasis
Describe the Concept of Feedback
Mechanism.
Identify types of the Feedback
Mechanism.

3. Cont’
Explain the importance of Feedback
Mechanism.
Identify signs of altered and failed
homeostasis.

4. Definition of Homeostasis
It is the condition of equilibrium in the
body’s internal environment.
The body’s internal environment
should be maintained within fairly
constant state for an individual to
survive.

5. It is continuously being disturbed by
both internal and external insults.
Failure to achieve this equilibrium
will lead to serious risk of illness and
eventually death.
Homeostasis is maintained by the
nervous and endocrine systems
through the process of Feedback
System or Mechanism.

6. Feedback System/Mechanism
Is a cycle of events in which the status
of the body condition is continuously
monitored, evaluated and changed.
Each monitored variable is called a
Controlled Condition- body
temperature, BP, BS.

7. Any disturbance that changes the
controlled condition is called a
Stimulus- fever, extreme heat or
cold.
Homeostasis is maintained by the
Control System which detects and
responds to changes in the controlled
condition as a result of stimulus.

8. The Concept of Feedback
Mechanism
 Feedback Mechanism is composed of
three basic components;
i. Detector/Receptor
 Body structure that monitors changes
in the controlled condition.
 It sends nerve impulses (Input) to the
central nervous system (Control
Centre).

9. It is a component of the control
system that senses stress or stimulus.
The stimulus can be external or
internal e.g. extreme environmental
temperature or Fever, BP.

10. ii. Control centre
This is the central nervous system.
It sets the limits within which a
variable factor (controlled condition)
should be maintained.
Evaluates input (information) from
receptors and gives command
(Output) when needed.

11. When the information (input)
indicates that an adjustment is
needed, the control centre sends the
Output to the Effectors for
appropriate actions.
Output is in a form of nerve
impulses, hormones and other
chemical signals.

13. iii. Effector
Body structure that receives output
from the control centre and produces
a response or effects the needed
change.
Reacts from the sensor’s output by
modifying the internal environment
so that it remains constant.
Every tissue in the body can act as
effectors.

14. Types of Feedback Systems
a. Negative Feedback System
 This is whereby the response of the
effector reverses a change in the
controlled condition or stress.
 The result is that the effectors
produce a physiological response
that is able to return the controlled
condition to its normal state.

15. This type of feedback mechanism is
the commonest in the body.
It is used to maintain normal levels
of:
body temperature,
Blood Pressure,
Blood Sugar,
Blood pH etc.

16. HOMEOSTASIS OF BLOOD
GLUCOSE
Homeostasis of blood glucose is largely
achieved by the specialised cells
located in the pancreas.
These cells are called the isletes of
Langerhans.

19. Islet of Langerhans Anatomy
Cells that make up the islets of
Langerhans are found in clusters
distributed throughout the pancreas.
Are made up of Beta () cells, which
produce the hormone insulin and
Alpha () cells that produce the
hormone glucagon.

20. Islet of Langerhans

21. Ct…
Secretions pass directly into pancreatic
veins and circulate in the blood
throughout the body.
Secretions pass directly into pancreatic
veins and circulate in the blood
throughout the body.

22. Insulin & Glucagon
Secretion of glucagon and insulin is
controlled by blood glucose level.
Normal blood sugar levels (pre-meal)
are 60-120mg/dL or 3.5-6.6 mmol/L.
After a meal, concentration of glucose
in the blood rises.
 cells are stimulated to increase
insulin secretion.

23. Ct…
Insulin:
stimulates the storage of glucose,
lowers blood glucose level.
Insufficiency of insulin or cell resistance to
insulin in the body leads to diabetes
mellitus (DM).
DM is characterized by disturbances in
both glucose and fat metabolism.

25. Ct….
When one has not eaten for several
hours, the blood sugar level begins to
fall.
The  cells are stimulated to secrete
glucagon.

26. Ct…
Glucagon:
raises the blood sugar by stimulating
the liver cells to convert glycogen to
glucose.
It also stimulates liver cells to make
glucose from non-carbohydrates
sources.

27. Pancreas
 Endocrine
 Exocrine
 Endocrine – islets of Langerhans
 Three types of cells
1. Alpha cells - secrete glucagon
2. Beta cells - secrete insulin
3. Delta cells – somatostatin
(inhibits growth hormone)

28. 1. Glucagon
 Blood glucose
 Conversion of liver glycogen  glucose
“Glycogenolysis”
Converts amino acids + glycerol + lactic acid  glucose
“Gluconeogenesis”
Liver releases glucose into blood. Negative feedback
controls release of hormones

29. 2. Insulin
Secreted by beta cells
a.  blood glucose
 Accelerates transport of glucose into cells especially
muscle (skeletal) cells
 Converts glucose in glycogen
“glycogenesis”
 Decreases glycogenolysis
 Decreases glyconeogenesis
 Stimulates converson of glucose or other nutrients 
fatty acids
“lipogensis”
b. Stimulates protein synthesis

30. ‘Normal’ Blood glucose control

31. HOMEOSTASIS OF BODY
TEMPERATURE
Normal cellular metabolism requires a
core body temperature of 35.8 – 37.5
degrees C.
This is regulated by:
Heat/cold-sensitive receptors
Heat regulation centre (hypothalamus)
Effectors (heart, blood vessels, skeletal
muscles)

33. HOMEOSTASIS OF BLOOD
PRESSURE
Blood pressure is the force exerted by
the blood against the walls of the blood
vessel.
Blood pressure is normally described as
the sum total of cardiac output (CO) in
relation to peripheral resistance (PR).
BP= CO X PR

35. Ct….
 Cardiac output:
The total blood flow through the
systemic or pulmonary circulation per
minute.
It is calculated by multiplying the
stroke volume by the heart rate per
minute.

36. Cont.
 Stroke volume:
It is the amount of blood pumped out
of the left ventricle per beat.
It is estimated to be 70mls.

38. Ct…
Peripheral resistance (PR):
This is the force opposing movement of
blood within the blood vessels.
Vasoconstriction reduces the lumen
and therefore increases resistance.
BP= CO X PR

39. Cont.
In order to maintain homeostasis
reduced CO e.g. during hemorrhage,
causes a corresponding increase in PR
to maintain normotensive BP.
Conversely, increased CO e.g. during
exercise, causes a corresponding
decrease in PR to maintain normal BP.

41. Ct…
Detection and correction of
fluctuations in BP is initiated by
special cells called baroreceptors.
Baroreceptors are pressure or stretch-
sensitive receptors located in the big
arteries (aortic arch and carotid
sinuses).

43. Ct….
An increase in BP causes its walls to
stretch and stimulate activity of
sensory nerve endings.
A fall below normal pressure causes a
decrease in action potentials produced
by these sensory nerve fibres.

44. Ct…
Sensory nerve activity from the
baroreceptors ascend via the vagus and
glossopharyngeal nerves to the medulla
oblangata.
The cardiac and vasomotor areas in
the medulla oblangata direct the
autonomic system to respond
appropriately.

45. Ct…
Cardiac control centre regulate the
cardiac rate.

47. Ct….
Vasomotor control centre regulate
vasoconstriction or vasodilation which
controls peripheral resistance, blood
circulation and hence the blood
pressure.

49. Ct…
The vasomotor center receives
information about the level of your
blood pressure from pressure-sensitive
nerves in the aorta and the carotid
arteries, and then sends out
instructions to the arterioles.

50. b. Positive Feedback System
A situation whereby the response of the
effectors increases change in the
controlled condition.
The effectors produce the response that
reinforces the change.

51. Command given to the effectors
produces a physiological response
that reinforces the initial change in
the controlled condition.
The action continues until it is
interrupted by an external event.
It is a rare type of feedback
mechanism e.g. initiation of labour:

52. Slide
Figure 16.18

54. Importance of Feedback Mechanism
Helps in regulation of the body
temperature.
Maintains normal levels of water and
electrolyte concentrations in the
body.
Maintains normal ranges of
circulatory volume and blood pH.

55. Helps in maintenance of normal
blood glucose levels in the blood.
Maintenance of normal blood
pressure.
Helps women in labor during
delivery by reinforcing uterine
contractions.
Helps in elimination (urination,
defecation, vomiting)

56. Signs of failed homeostasis
When homeostasis is disturbed, one
feels symptoms of illness or disease
like;
- Fever, pain, nausea and vomiting etc
Complete failure of homeostasis
results in serious events like
- Stroke, Diabetes Mellitus
- Febrile convulsions
- Death

57. MBWENU VYAMARA