Download The Endocrine System

The Endocrine System
&
Physiological
Feedback
Why an Endocrine System?
• Made up of glands which secrete
hormones directly into the bloodstream
• Regulates many physiological responses of
the body (homeostasis) as well as long term
changes (reproduction, growth,
development)
• Effects of endocrine system are usually
slower and longer lasting than those of the
nervous system.
Glands of the Endocrine System
Hypothalamus-Pituitary Connection
• Hypothalamus – tiny brain
structure receives internal
sensory info. Serves as link
between nervous and
endocrine system
• Nerve impulses from
hypothalamus sent to
pituitary gland which
releases hormones into
bloodstream
• Pituitary hormones can affect
target cells directly or turn on
other glands to release their
hormones
The pituitary is the master gland
Hormone Action
• Endocrine glands contain
cells which secrete
chemicals called
hormones directly into
bloodstream
• Hormones only interact
with target cells – cells
with right receptor to bind
the hormone
• Hormones turn on, turn
off, speed up, slow down,
specific activities of cells,
tissues, and organs.
Insulin: An Example of Hormone Action
Homeostasis = Maintaining Internal
Conditions Within Narrow Limits
Homeostasis = Maintaining Internal
Conditions Within Narrow Limits
temperature: 35.6-37.8 °C
blood pH: 7.35-7.45
blood glucose: 90mg /100 mL
calcium: 10mg /100 mL
carbon dioxide: 23-29 mmol/L
oxygen: 95-100% hemoglobin
saturation
Physiological Feedback Loops Maintain Homeostasis
Physiological Feedback Loops: Thermostat Analogy
Physiological Feedback Loops: Thermostat Analogy
Types of Feedback
• Negative Feedback – the
system responds to a stimulus
by adjusting the system away
from the stimulus (back to an
intermediate level)
• Positive Feedback – the
system responds to a stimulus
by adjusting the system toward
the stimulus. (further beyond the
intermediate level)
HOMEOSTASIS = NEGATIVE FEEDBACK
Positive Feedback
Negative Feedback