Introduction of Physiology

1. University of Burao
Faculty: veterinary medicine and
animal production
Course: Physiology I
Semester: II

2. Course outline
• Introduction to physiology
• Homeostasis
• Cell physiology and cell organelles
• nervous system
• hormones
• blood and blood forming organs
• Muscles and nerves. Special senses.
Cardiovascular system.
• Kidney and body fluids.

3. Physiology I
Learning objectives
At end of this chapter you should be able to:
• 1. List different protein categories
• 2. Properties of protein and their functions
• 3. explain the mechanism of allosteric shape
• 4. Re-state muscular protein activities
• 5. Transportation

4. Cellular level of physiology
Physiology is the study of the regulation of change
within organisms, in this case higher animals. All
physiological change is mediated by a single class
of polymeric macromolecules (large molecules),
The proteins.

5. cellular level of physiology
Protein function can be subdivided
into a number of categories:
Catalysis:
The ability to increase the rate of a chemical
reaction without altering the equilibrium of the
reaction. The majority of biochemical reactions
occur at a physiologically useful rate only
because of protein catalysts, called enzymes.

6. Reaction coupling:
two reactions are joined together with the
transfer of energy.

7. Transport structure:
Proteins provide a pathway for the membrane
transport of most molecules and all ions into
and out of the cell.

8. Structural proteins
Proteins that form filaments and that glue
cells to each other and to their environment
are responsible for the structure and
organization of cells and multicellular
assemblies (i.e., the tissues and organs of
animals). The internal structure of the muscle
cell, as well as its ability to do work, is a result
of the properties of the muscle proteins

9. Protein Function Depends on Protein
Shape and Shape Changes
Protein function is founded on two molecular
characteristics:
- Proteins can bind to other molecules very
specifically; and proteins change shape, which
in turn alters their binding

10. How protein functions.
Binding site:
Grooves or indentations on the surface of protein
molecules Permit specific interactions with a molecule
of a complementary shape, called the ligand.
Ligand:
it is a molecule of complementary shape

11. Cont..
This complementary shape mechanism
underlying binding is similar to the shape
interaction between a lock and key. As with a
lock, only a small part of the protein is engaged
(involved) in binding. The binding is very
specific; small changes in the shape of the
binding site (keyhole) or the shape of the ligand
(key) can cause major changes in protein (lock)
behavior.

12. Cont…
Similar to the lock and key, the complementary-
shape interaction serves a recognition function;
only those molecules with the right shape affect
protein function. This recognition function plays
a primary role in Information transfer.

13. Mechanism of allosteric shape change
ligand binding
ligand binding to allostric site(site B) on a
protein changes the protein’s conformation such
that binding site A is altered; ligand no longer
binds at site A because of the binding event at
site B.

15. Voltage-dependent proteins.
The conformation of some proteins, particularly
ion channels, is altered by the electrical field
surrounding the protein. Shown here is the
opening (activation) of a voltage-dependent,
gated Ca2+ channel when the membrane
depolarizes.

16. Tyrosine conversion into three
different singling molecules
Farther looking how protein shape and its function related,
dopamine shape conversion will affect its function.
 dopamine, a brain neurotransmitter;
 norepinephrine, a neurotransmitter of the brain and
peripheral autonomic nervous system;
 epinephrine, an autonomic neurotransmitter and hormone.

17. Cont..
Dopamine, norepinephrine, and epinephrine share a
similar structure. All contain a phenyl (benzene) ring with
two hydroxyl groups (i.e., catechol) and an amine group
(thus catecholamines). They are among the large number
of molecules that function as neurotransmitters. That is,
the electrically coded information sent along nerve cells
causes the release of a chemical, the neurotransmitter, at
the terminal of the neuron, which is next to a target cell,
such as another nerve, a muscle, or an endocrine cell.
The electrically encoded information of the nerve is
transmitted to the target cell by the binding of the
neurotransmitter to proteins on the surface of the target

18. Epinephrine biosynthetic pathway
The amino acid tyrosine is metabolized to the
neurotransmitters dopamine, norepinephrine,
and epinephrine. The diagram shows the
names and structural formulas for each
compound in the path and the names of the
enzymes that catalyze each reaction. DOPA,
Dihydroxyphenylalanine.

20. Muscle Contraction and its Initiation and
Cessation Depend on the Binding Specificity and
Allosteric Properties of Proteins
• There are three types of muscle tissue in
vertebrates:
• (1) Skeletal muscle, responsible for the animal’s
ability to move;
• (2) Cardiac muscle, a muscle type found only in
the heart but structurally similar to skeletal
muscle; and
• (3) smooth muscle, which surrounds hollow
organs such as blood vessels, gut, and uterus.

21. Muscle cont….
- All three produce tensile force by contracting
- shortening the length of the muscle.
- All muscle contraction occurs by the binding and the
allosteric properties of two proteins, actin and
myosin.
- Starting and stopping the contraction process
depends on two additional proteins in skeletal
cardiac muscle, troponin and tropomyosin.
- Contraction initiation and cessation in smooth
muscle depend on a different system with different
proteins.

22. Biological Membranes Are a Mosaic of
Proteins Embedded in a Phospholipid
Bilayer
- Phospholipids make up the basic structure of a
cell membrane.
- A single phospholipid molecule has two different
ends:
a head and
a tail.
The head end contains a phosphate group and
is hydrophilic. This means that it likes or is attracted
to water molecules.

23. Cont..
The tail end is made up of two strings of
hydrogen and carbon atoms called fatty acid
chains. These chains are hydrophobic, or do not
like to mingle with water molecules.

25. Cell membrane arrangement
The phospholipids of a cell membrane are
arranged in a double layer called the lipid
bilayer. The hydrophilic phosphate heads are
always arranged so that they are near water.
Watery fluids are found both inside a cell
(intracellular fluid) and outside a cell
(extracellular fluid). The hydrophobic tails of
membrane phospholipids are organized in a
manner that keeps them away from water.

27. Cell membrane structure serves three
broad functions:
(1) Compartmentation
(2) Selective transport,
(3) Information processing and transmission

28. Compartmentation
- Compartmentation is the ability to separate and
segregate different regions by composition and
function.
- For example, the lysosome is membranous
organelle within cells that contains hydrolytic
(digestive) enzymes that can potentially digest the
cell.
- The lysosomal membrane compartmentalizes these
potentially harmful enzymes, segregating them
from the bulk cytoplasm.

29. Selective transport
Selective transport results partly from the
Properties of the phospholipid bilayer but
mostly from transport proteins embedded in the
membrane. These proteins are characteristically
selective in their transport functions; for
example, the protein that is the specialized ion
channel underlying neuronal signaling is 15
times more permeable to sodium ions (Na+)
than to potassium ions (K+).

30. Information processing
If the cells of an organism are to respond to
external changes, they must receive information
about the state of the outside world. Just as we
higher animals have our sensory organs—eyes,
ears, nose, and so forth—arrayed on our outside
surface, so to do cells have most of their
environmental information processing and
transmission apparatus on their external surfaces.
These are intrinsic membrane proteins of the
plasma membrane, called membrane receptors,
that serve a purely informational function,

31. Transport
Some molecules are not able to pass through the cell membrane
 Charged particles (i.e., ions): because of the hydrophobic regions of
the bilayer
 Polar molecules (molecules with no net charge but with electrical
imbalances) with a molecular weight greater than about 100
daltons are also unable to pass readily through a pure lipid bilayer,
thus excluding all sugar molecules (monosaccharides), amino acids,
nucleosides, as well as their polymers (polysaccharide, proteins,
nucleic acids).
On the other hand, some crucially important polar molecules (e.g.,
water, urea) are small enough to pass through the lipid bilayer.

32. Cont..
Molecules those can pass freely
Small, moderate-size
large molecules that are soluble in oily solvents
readily pass through a pure lipid bilayer.
O2, N2
 the steroid hormones
many toxic
synthetic molecules, such as insecticides, are also
in this category.

33. What is the protein pathway across
the biomembrane
Molecules those cannot pass across the
membrance needs:
1. Protein pathways
2. Energy factors that drive the transport