Physiology and human body

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The Body’s
Internal Environment
An Introduction to
Physiology
Levels of Physiological Organization
•
• Cells
Cells
•
• Tissues
Tissues
•
• Organs
Organs
•
• Organ systems
Organ systems
•
• Organism
Organism
Tissues
Primary types:
• Epithelial
• Connective
• Muscle
• Nervous
• Continuous sheet
or layers of cells
with direct cell-
cell junctions
Epithelial Tissue
Connective Tissue
• Cells are
suspended in an
extracellular
matrix.
– The matrix is
often largely
composed of
collagen fibers.
Muscle Tissue
• Specialized for
contraction.

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• Specialized to
conduct
electrochemical
nerve impulses.
Nervous Tissue Organ Systems
11 Organ Systems
• Descriptions on p. 66–67 of Human Biology, 9th ed.
Bauplan:
Ger. “Life Plan” (pl: baupläne)
The arrangement, pattern, and
development of tissues, organs, and
systems unique to a particular type of
organism.
Cell Differentiation
Cell Differentiation in Development
• From one original fertilized egg cell
(zygote), mitotic division has produced
all your body’s cells.
~50,000,000,000 cells in your body
• Each genetically identical!
But >200 cell types of cells
• (specialized [differentiated] tissues)
• Each type uses only ~20% of the total
genes in their nucleus
• Even fewer in more specialized cells
• Unused genes may be permanently
inactivated
permanently differentiated
cannot change into a different
type of cell
Cell Differentiation
Cell Differentiation in Development
• Undifferentiated
• Totipotent: able to become any cell type
• Cells may be separated and each
become a new identical embryo
• First differentiation:
cells separate into layers
1. Inner cell mass
2. Trophoblast
• Secretes hormone (hCG)
• Secretes enzymes
fi implant into uterine lining

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Cell Differentiation
Cell Differentiation in Development
• Second stage of
differentiation:
Inner cell mass divides into:
1. Extra-embryonic
membranes
• form the placenta and
“bag of waters” around
the embryo
2. Embryonic disc
• becomes the embryo
(day 8)
(day 12)
Epiblast
Ectoderm
Mesoderm Endoderm
Hypoblast
Embryonic
disc
Cell Differentiation
(day 14)
Neural tube
Endoderm
Mesoderm
Ectoderm
Cell Differentiation in Development
• Third differentiation stage:
Embryonic disc develops
into three basic
embryonic germ layers
1. Ectoderm
2. Mesoderm
3. Endoderm
Cell migration &
specialization
to form body
organs
(day 22)
Cell Differentiation
(day 56)
All organs formed.
(From now on called a fetus)
Cell Differentiation in Development
• Final differentiation: the three embryonic germ layers differentiate into the primary tissue
types and their subtypes.
Cell Differentiation
Cell Differentiation in Development
• Final differentiation: the three embryonic germ layers differentiate into the primary tissue
types and their subtypes.
ECTODERM MESODERM ENDODERM
• Epidermis of skin and its
derivatives (including sweat
glands, hair follicles)
• Epithelial lining of mouth
and rectum
• Sense receptors in
epidermis
• Cornea and lens of eye
• Nervous system
• Adrenal medulla
• Tooth enamel
• Epithelium or pineal and
pituitary glands
• Notochord
• Endoskeletal system
• Muscular system
• Muscular layer of
stomach, intestine, etc.
• Excretory system
• Circulatory and lymphatic
systems
• Reproductive system
(except germ cells)
• Dermis of skin
• Lining of body cavity
• Adrenal cortex
• Epithelial lining of
digestive tract
• Epithelial lining of
respiratory system
• Lining of urethra, urinary
bladder, and reproductive
system
• Liver
• Pancreas
• Thymus
• Thyroid and parathyroid
glands
• Nervous tissue from ectoderm.
• Muscle & connective tissues from mesoderm.
• Epithelial tissues from all three germ layers. (Embryonic tissue is epithelial-like.)
What about Stem Cells?
• Remain partially
undifferentiated
(embryonic).
– Most their genes not
permanently
deactivated.
• Can divide and
differentiate on
demand to replace
specialized tissue
cells.
What about Stem Cells?

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• Many organs are known
to produce stem cells in
adults
Adult Stem Cells
Bone Marrow Stem Cells
• Long known to have multipotential hematopoietic stem cells
– One stem cell has the potential to form any type of blood cell
• Recently discovered able to also differentiate into other types of connective tissue
– Adipose, bone, & cartilage
Embryonic Stem
Cells
• Preferred because they
are pluripotent
– More potential to be
induced to form any cell
type desired
“left over” embryos from
in vitro fertilization clinics
“human cloning”
Embryonic Stem Cell Research
• Current research
• Future proposal
Personalized Stem Cells
Nuclear Transfer Method:
1. Remove nucleus from egg
cell from donor
2. Replace with the nucleus
from your epithelial cell
3. Stimulate egg to develop into
embryo
– “Hello Dolly” … a clone
? If the nucleus of epithelial
cells is non-differentiated
enough to be used to form
embryonic stem cells, why
cannot epithelial cells be
induced directly to become
stem cells??
The Promise of Stem Cell Research

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Current Limitations
• Localization
• Tumor formation
• Rejection
• May not address
underlying problem
The Debate over Embryonic Stem Cell [ESC]
Research Funding
PRO
• Possible therapy replacement for
tissues that don’t regenerate
– Neurons, heart muscle
• No embryos created just for stem
cells
– IVF clinics may legally dispose of
extra embryos
CON
• Over-hyped
– Actual “cures” not attained
• Taxpayer subsidies for very
lucrative biomedical business
• Immoral to “destroy one life to
prolong another”
– Focus efforts on adult stem cell
research
Physiology
function and process: why and how
• Understanding the processes of life
• Physiology incorporates the
teleological approach and the
mechanistic approach
– Teleology = purpose/function = “Why?”
– Mechanism = “How?”
Function and process: an example
• Observation: red blood cells transport oxygen.
• Teleological (function) approach: Why does the system exist?
“…because red blood cells deliver oxygen to the cells that need it.”
This answer explains the reason blood cells transport oxygen but says nothing about
how the cells transport oxygen.
• Mechanistic approach: How does the system operate?
“…because there are hemoglobin molecules that combine reversibly with oxygen
molecules.”
This very concrete answer explains exactly how oxygen transport occurs but says
nothing about the significance of oxygen transport to the intact animal.
• One role of physiology is to integrate function and process into a cohesive picture.
• (modified from Human Physiology: An Integrated Approach, D. U. Silverthorn 3rd ed
Important physiological themes
• Homeostasis
• Regulation
• Compartmentalization
• Distribution of materials
• Communication, coordination, & integration
• Energy flow
Homeostasis: maintaining a
constant, optimal internal environment

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Homeostasis helps us adjust to
change
Homeo stasis
“same” “stay”
• Dynamic Constancy (= Dynamic Equilibrium):
– Fluctuate around set point.
– Set point may be reset for new situations.
Homeostatic Mechanisms
•Negative feedback loops
ÿIntrinsic — within an organ
ÿExtrinsic — integrating multiple organs
Negative Feedback Loop
Negative Feedback: Room Thermostat
Antagonistic Effectors
Pairs of effectors with opposing actions provide much tighter control.

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Negative Feedback: Body Thermostat
Effector Sets
Redundant effectors allow stronger responses to stronger deviations.
Table 1.2
Homeostasis & Regulation of
Blood Glucose
Negative Feedback: Body Glucostat
• Pancreas controls blood sugar levels
• Glucose is taken up or released by:
– liver as glycogen
• Glucagon from alpha cells ups it
• Insulin from beta cells drops it
GAC UP
BIN DOWN
GAC UP
BIN DOWN

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Body-Fluid Compartments
• 65-75% of total body weight is H20.
• Intracellular compartment:
– Fluid inside the cell.
• 2/3 of H20.
• Extracellular compartment:
– 2 Subdivisions:
• Blood plasma.
• Interstitial fluid.
• 1/3 H20.
Life is dynamic
• Constant exchange between internal and external
environments
Energy Flow The Body’s Internal Environment