1. Homeostasis and homeostatic regulation. Control systems, negative feedback
and levels of physiological regulation.
Homeostasis
- maintenance of a constant internal environment within the body by coordinated
physiological mechanisms
- internal environment, cells do not communicate with external world directly
- they are surrounded by an internal environment: extracellular uid
- cells are capable of living, growing and performing their special functions only if proper
and constant condition ( e.g. pg, temperature, chem. compositions usw) is maintained
- if homeostasis fails: death or diseases may occur
Control systems and homeostatic regulation
- all organs and tissues of the body perform functions that help maintain the constancy
of internal environment
- control system def: device or set of devices managing, commanding, directing or
regulation the behavior of other devices or systems
Types:
1) open loop control system
2) closed loop control system
- goal of homeostatic control: maintain constancy of the parameters of the internal
environment
- homeostatic control systems are basically closed- loop control systems with a negative
feedback
fl
, Positive feedback
- output enhances original stimulus
- e.g. some features of hormone action causes more secretion of the hormone
- examples: delivering ( Oxytocin) , ovulation ( FSH), blood clotting
Negative feedback
- output inhibits original stimulus
- almost all homeostatic control mechanism are neg. feedback
- examples: control of blood sugar caused by insulin. When blood sugar rises, receptors
sense a change. in turn, the pancreas secretes insulin to lower the blood sugar. Once
blood sugar levels reach homeostasis, the pancreas stops secreting insulin
Levels of physiological regulation
Types of regulation:
proportional
derivative
integral
anticipatory
Levels of regulation:
intracellular
local
organ/system
whole body
Neural regulation:
- involved in fast adaption to changes in external and internal environment
- regulation of movement
- precise targeting and adaption
- e.g. neural regulation of blood pressure
Endocrine regulation:
- slower responses
- more di use in uences
- involved in long- term regulation of metabolism, growth, reproduction
- neural and endocrine control systems interact and regulate each other
- neuro- endocrine re exes
- endocrine glands are controlled by hypothalamus and autonomic nerves
- hormones modulate neuronal activity
ff fl fl
,2. Structure and function of the cellular membrane. General characteristics of
membrane transport, Passive transport across the cellular membrane.
Structure and function of the cell membrane
- separates the cytoplasm from the cell environment
- participates in binding and signaling ( chemical and electrical) to be integrated in a
complex living organism
- regulation of what enters and leaves the cell. Creates di erences in extra and
intracellular uid composition—> for biochemical
processes
- Lipids ( phospholipids, cholesterol, sphingolipids)
- proteins ( integrated and peripheral)
- carbohydrates ( outside): glycoproteins,
glycolipids
Cell junctions in epithelial cells. Cell adhesion proteins
fl ff
, - lipid rafts and caveolae: specialized membrane microdomains enriched in sphingolipids
and cholesterol
- function in variety of cellular processes: endocytosis, transcystosis, signal
transduction and receptor recycling
Membrane transport
- plasma membrane is selectively permeable to gases, hyrophobic molecules, small polar
molecules
- large polar molecules and ions can penetrate the cell membrane via membrane
channels or carrier proteins ( integral)
Ion channels:
- selective for particular ions or groups of ions
- regulation: gating, trafficking
- voltage- gated
- ligand- gated
- mechano- gated ( stretch activated)
- non- gated ( always open)
- water can move through phospholipid bilayer or membrane channels—< aquaporins
( gating or trafficking)
Passive transport
- No metabolic energy required
- down the electrochemical gradient
- simple diffusion
- facilitated diffusion
- osmosis
- filtration
Simple diffusion:
- driven by concentration difference between both side of the membrane and direction of
the net movement is down the electrochemical gradient
- net diffusion stops when the concentration on both sides of the membrane is equalized
- energy is released during the movement of a solute down its concentration gradient
- factors affecting: First Ficks law for free diffusion —> J= -D(dc/dx)
for diffusion across membrane—> J= -P(C1-C2)
- Diffusion of ions: electrical potential differences are created during ion diffusion
net diffusion of ions stops when concentration and the electrical
gradients are in equilibrium, the electrochemical gradient = 0
- liner in graph
Facilitated diffusion:
- requires carrier proteins-> binding to carrier increases rate of diffusion
- no metabolic energy
- driving force is concentration gradient ( electrochemical gradient) of solute
- characterized by: 1) specificity 2) competition 3) saturation ( non- liner in graph)
and levels of physiological regulation.
Homeostasis
- maintenance of a constant internal environment within the body by coordinated
physiological mechanisms
- internal environment, cells do not communicate with external world directly
- they are surrounded by an internal environment: extracellular uid
- cells are capable of living, growing and performing their special functions only if proper
and constant condition ( e.g. pg, temperature, chem. compositions usw) is maintained
- if homeostasis fails: death or diseases may occur
Control systems and homeostatic regulation
- all organs and tissues of the body perform functions that help maintain the constancy
of internal environment
- control system def: device or set of devices managing, commanding, directing or
regulation the behavior of other devices or systems
Types:
1) open loop control system
2) closed loop control system
- goal of homeostatic control: maintain constancy of the parameters of the internal
environment
- homeostatic control systems are basically closed- loop control systems with a negative
feedback
fl
, Positive feedback
- output enhances original stimulus
- e.g. some features of hormone action causes more secretion of the hormone
- examples: delivering ( Oxytocin) , ovulation ( FSH), blood clotting
Negative feedback
- output inhibits original stimulus
- almost all homeostatic control mechanism are neg. feedback
- examples: control of blood sugar caused by insulin. When blood sugar rises, receptors
sense a change. in turn, the pancreas secretes insulin to lower the blood sugar. Once
blood sugar levels reach homeostasis, the pancreas stops secreting insulin
Levels of physiological regulation
Types of regulation:
proportional
derivative
integral
anticipatory
Levels of regulation:
intracellular
local
organ/system
whole body
Neural regulation:
- involved in fast adaption to changes in external and internal environment
- regulation of movement
- precise targeting and adaption
- e.g. neural regulation of blood pressure
Endocrine regulation:
- slower responses
- more di use in uences
- involved in long- term regulation of metabolism, growth, reproduction
- neural and endocrine control systems interact and regulate each other
- neuro- endocrine re exes
- endocrine glands are controlled by hypothalamus and autonomic nerves
- hormones modulate neuronal activity
ff fl fl
,2. Structure and function of the cellular membrane. General characteristics of
membrane transport, Passive transport across the cellular membrane.
Structure and function of the cell membrane
- separates the cytoplasm from the cell environment
- participates in binding and signaling ( chemical and electrical) to be integrated in a
complex living organism
- regulation of what enters and leaves the cell. Creates di erences in extra and
intracellular uid composition—> for biochemical
processes
- Lipids ( phospholipids, cholesterol, sphingolipids)
- proteins ( integrated and peripheral)
- carbohydrates ( outside): glycoproteins,
glycolipids
Cell junctions in epithelial cells. Cell adhesion proteins
fl ff
, - lipid rafts and caveolae: specialized membrane microdomains enriched in sphingolipids
and cholesterol
- function in variety of cellular processes: endocytosis, transcystosis, signal
transduction and receptor recycling
Membrane transport
- plasma membrane is selectively permeable to gases, hyrophobic molecules, small polar
molecules
- large polar molecules and ions can penetrate the cell membrane via membrane
channels or carrier proteins ( integral)
Ion channels:
- selective for particular ions or groups of ions
- regulation: gating, trafficking
- voltage- gated
- ligand- gated
- mechano- gated ( stretch activated)
- non- gated ( always open)
- water can move through phospholipid bilayer or membrane channels—< aquaporins
( gating or trafficking)
Passive transport
- No metabolic energy required
- down the electrochemical gradient
- simple diffusion
- facilitated diffusion
- osmosis
- filtration
Simple diffusion:
- driven by concentration difference between both side of the membrane and direction of
the net movement is down the electrochemical gradient
- net diffusion stops when the concentration on both sides of the membrane is equalized
- energy is released during the movement of a solute down its concentration gradient
- factors affecting: First Ficks law for free diffusion —> J= -D(dc/dx)
for diffusion across membrane—> J= -P(C1-C2)
- Diffusion of ions: electrical potential differences are created during ion diffusion
net diffusion of ions stops when concentration and the electrical
gradients are in equilibrium, the electrochemical gradient = 0
- liner in graph
Facilitated diffusion:
- requires carrier proteins-> binding to carrier increases rate of diffusion
- no metabolic energy
- driving force is concentration gradient ( electrochemical gradient) of solute
- characterized by: 1) specificity 2) competition 3) saturation ( non- liner in graph)
