Nursing program- Human physiology (REHS243)
Lec -1 : Introduction to physiology
Mrs: Hoyam Abdelbagi
Introduction to Physiology
• Physiology – the study of how the body and its
parts work or function
• Physiology has many subdivisions.
• For example, neurophysiology explains the
working of the nervous system , and cardiac
physiology studies the function of the heart.
Homeostasis
• Describes the body’s ability to maintain stable
internal conditions even though the outside
world is continuously changing
• Communication within the body is essential
for homeostasis.
Control Mechanisms
The control system can be divided into:
- A receptor
- A controller : The central nervous system and
The endocrine system
- The controlled system : The effector organs
- Regulated variable : eg, blood pressure
Homeostatic Control Mechanisms
• Homeostatic control mechanisms are
TWO:
1. Negative feedback mechanisms:
shut off of the original stimulus or to reduce
its intensity
• E.g. – body temp, blood chemical levels
2. Positive feedback mechanisms:
increase the original disturbance (stimulus)
• E.g. – ovulation, blood clotting, birth
Cells
• Smallest living unit
• Most are microscopic
Cell composition
Cell membrane
- a structure that surrounds cytoplasm
- consists of double layer of phospholipids and proteins
Function: separates cell contents from environment, so acts as
a protecting layer
Proteins in cell membrane have functions:
1. Provide structural support.
2. Transport molecules across the membrane.
3. Enzymatic control of chemical reactions at cellular
surface.
4. Some serve as receptors for hormones.
5. Some serve as ‘markers’ (antigens),
that identify tissue type of an individual.
Types of membrane transport
2. Active transport
1. Passive transport
The movement of
molecules & ions across
a membrane from higher
to lower concentration
(down concentration


The movement across
a membrane against
concentration gradient.
(to region of higher
concentration )
gradient)
doesn’t require
metabolic energy

.

Requires metabolic
energy (ATP)
Movement Across the cell Membrane
Passive transport mechanism: (Diffusion )from high to low
concentration, doesn’t require energy
1. Simple diffusion: Lipid-soluble molecules, gases
(Carbon dioxide, Ammonia, Oxygen)
2. Facilitated diffusion: needs carrier molecules (Sugars
and amino acids)
3. Osmosis : is diffusion of water
Diffusion
diffusion
Osmosis is diffusion of water
• Is the movement of water from an area of low solute
concentration to one of high concentration across a
semi-permeable membrane
movement of water
osmosis
How about large molecules?
• Moving large molecules into & out of cell
– through vesicles & vacuoles
– endocytosis
• phagocytosis = “cellular eating”
• pinocytosis = “cellular drinking”
– exocytosis
exocytosis
Cytoplasm
Gel like substance surrounded by cell membrane and
contains organelles.
• Nucleus
• Mitochondria
• Golgi Body Complex
• Endoplasmic Reticulum
• Vacuole
• Lysosome
• Centrioles
 Nucleus:
Separated from cytoplasm by nuclear membrane
,contains genetic material – DNA and surrounds by
nuclear membrane
Chromosomes found in nucleus .made of DNA
Human cells contain 23 pairs.
 Endoplasmic Reticulum:
Network of interconnected membranes
Helps move substances within cells
Two types:– Rough endoplasmic reticulum (Manufacture protiens)
– Smooth endoplasmic reticulum(Carbohydrates and Lipids
Ribosomes:• sites of protein synthesis in the cytoplasm
• may be free in the cytoplasm or attached to
the endoplasmic reticulum(rough
endoplasmic reticulum)
Mitochondria:• Produces energy (ATP) through chemical
reactions
Golgi complex:• Flattened membranous sacs
• Synthesizes carbohydrates & packages
molecules for secretion.
• Secretes lipids & glycoproteins
Lysosome:
• membranous sac, containing digestive
enzymes
 Digest bacteria and some foods entering the cell
centrioles:Pairs of microtubular structures
Play a role in cell division
Cells in an isotonic solution
isotonic solution:- (= concentrations)
the concentration of dissolved substances in the
solution is the same as the concentration of
dissolved substances inside the cell
Water and dissolved substances diffuse into and
out of the cell at the same rate.
• hypotonic solution: dilute solution ( low
solute concentration)
• In a hypotonic solution, water enters a cell by
osmosis, causing the cell to swell
 hypertonic solution:
concentrated solution, thus a high solute
concentration
In a hypertonic solution, water leaves a cell by
osmosis, causing the cell to shrink
Isotonic
hypotonic
Hypertonic
Cell Life Cycle
 Cells have two major periods
 - Interphase
Cell grows
Cell carries on metabolic processes
 - Cell division
Cell replicates itself
Function is to produce more cells for growth and repair
processes
Events of Cell Division
• Mitosis
– Division of the nucleus
– Results in the formation of two daughter nuclei
• Cytokinesis
– Division of the cytoplasm
– Begins when mitosis is near completion
– Results in the formation of two daughter cells
Stages of Mitosis
• Interphase
– No cell division occurs
– The cell carries out normal metabolic activity and
growth
• Prophase
– First part of cell division
– Centromeres migrate to the poles
– Chromosomes condense and nuclear membrane
disappear.
• Metaphase
– Spindle from centromeres are attached to
chromosomes that are aligned in the center of the
cell
• Anaphase
– Daughter chromosomes are pulled toward the
poles
– The cell begins to elongate
• Telophase
– Daughter nuclei begin forming
– A cleavage furrow (for cell division) begins to
form
Stages of Mitosis
Meiosis
is the process by which ”gametes” (sex cells) ,
with half the number of chromosomes, are
produced.
- During Meiosis diploid cells are reduced to
haploid cells
Diploid (2n)  Haploid (n)
- Meiosis in males is called spermatogenesis
and produces sperm.
- Meiosis in females is called oogenesis and
produces ova.
Cell metabolism
In the human body.
 carbohydrates are converted into glucose.
proteins are converted into amino acids.
fats into fatty acids.
• glucose, fatty acids, and amino acids—all
entering the cell and react with oxygen
• Chemical Processes in the Formation of
ATP—Role of the Mitochondria.
• in side the cells:
• glucose is subjected to enzymes in the
cytoplasm that convert it into pyruvic acid (a
process called glycolysis).
• A small amount of ADP is changed into ATP by
the energy released during this conversion
• pyruvic acid, fatty acids from lipids, and
amino acids from proteins are converted into
the compound acetyl-CoA in the
mitochondrion.
• about 95 per cent of ATP , is formed in the
mitochondria
Uses of ATP for Cellular Function
• Energy from ATP is used to:
(1) transport of substances through multiple
membranes in the cell.
(2) synthesis of chemical compounds
throughout the cell.
Chemical messengers
Mechanisms of intercellular
communication
1.Direct through gap
junctions
Cells exchange chemicals
through connections
between cytoplasm
2. Indirect through
chemical messengers
The messenger must bind
to a matching receptor
and stimulate a
response
Indirect messengers
• Autocrine: the cell
secretes a chemical
which can bind on its
own membrane and
stimulates a response
• Paracrine: a cell
secretes a chemical
which can bind to a
receptor on a
neighboring cell 
trigger a response
Figure 5.1a
• Neurotransmitter:
influences a distant
organ by secreting
chemicals which travel
through axons.
• Hormone: a chemical
travels long distance
through the blood
before binding to its
own target organ and
stimulating a response
• The hormones must
bind to a matching
receptor.
• The binding of the
hormone to its
receptor can trigger
the opening of a
channel, induce
enzymatic activation