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Week 4 Lecture 10: Tissues and Homeostasis (Homeostasis (A multicellular…
Week 4 Lecture 10: Tissues and Homeostasis
Biological hierarchy
Cells
, when differentiated, all assemble into...
Tissues
, when multiple tissue types are organised, form into...
Organs
, whose functions are interrelated, can be grouped into...
(Organ) systems
For example, the digestive system includes the oesophagus, stomach and intestines
Most organs are composed of epithelial tissue and one or more other kind of tissue
Usually, at least 2
For example, the small intestine has
all 4 tissues
In order from top to bottom...
A sheet of columnar polarised epithelial cells
Connective tissue called the
mucosa
with fibroblasts scattered throughout (underneath the basal layer of the epithelial tissue)
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Circular fibre smooth muscle tissue
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Another network of neurons located between the smooth muscle layers called the
myenteric or Auerbach's plexus
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Network of neurons located in the submucosa, called the
submucosal or Meissner's plexus
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Longitudinal fibre smooth muscle tissue
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Serosa
A section through a tissue is called a
histology section
, and you would see the different layers
Over 200 different types of cells
Humans are made up of
thousands
of cells
1 billion cells in the human brain
Types of tissues
There are 4 types
Epithelial tissue
Densely packed and tightly connected cells
In layers or sheets
Functions
Creates barriers between the internal and external environment
Also regulates transport across the barriers
The 1st barrier against infection
Involved in secretion and absorption
Involved in smell and taste
Examples
Gut epithelial tissue (columnar)
Selectively transport ions and molecules from one side of an epithelial membrane to the other
This is done through...
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Respiratory epithelial tissue (ciliated pseudostratified columnar)
The cilia on the tissue move secreted mucus and particulate matter posteriorly towards the pharynx where it passes into the oesophagus and is digested in the stomach
Olfactory epithelial tissue (ciliated pseudostratified columnar)
Responsible for smell – for detecting odours
Types
Squamous (flattened)
e.g. skin and mouth lining (also
stratified
– layered)
Thin
Flattened
Nucleus in centre
Columnar (like a rectangle)
e.g. lungs, intestines and uterine cervix
Can have cilia
Can have absorptive and secretory functions
Tightly packed
Polarised
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Cuboidal (like a square)
e.g. kidney, trachea and oesophagus (also
stratified
)
Lines tubules and ducts (for kidneys)
Tightly packed
Can conduct fluids from one point to another
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Nucleus is in the centre
Secretory cells
e.g. stomach or intestine (also
columnar
)
The stomach lining has
epithelial cells that secretes
digestive juices and acids
Other secretory cells are
found in
the salivary, sweat, mammary, pancreatic and anterior pituitary
glands
.
Tight junctions
are areas between two cells where the plasma membranes are fused together
They are found in between adjacent cells in the epithelial lining of the stomach, intestine and urinary bladder
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The human skin is the largest organ
Muscle tissue
Most abundant tissue in body
Muscle cells contain long filaments of myosin and actin
This allows muscles to contract, relax and exert force
3 types
Skeletal muscle
Attached to bone
Allows for body movement (temporary/permanent displacement of body or its parts)
Intercostal muscles in chest aid in respiration
Facial expressions
Shivering
Regular arrangement of actin and myosin filaments
Results in
striated
appearance
Under
VOLUNTARY
control
"I decide when to move my arm."
Responsible for locomotion
Movement of a
whole
organism from one place to another
Cardiac muscle
Responsible for beating and contracting the heart
Branched cells form strong structural meshwork
Also
striated
Responsible for pumping blood within the heart
Under
INVOLUNTARY
control
However, some Buddhist monks have some control in lowering their heart rate
Smooth muscle
Forms the outer walls of hollow internal organs
Organs of the GI tract (for
motility
– peristalsis using metabolic energy)
Mouth
Oesophagus
Stomach
Small intestine
Large intestine
Anus
Bladder
Blood vessels
For
vasocontriction
and
vasodilation
(relaxation)
Under
INVOLUNTARY
control
Lack of striated appearance
Actin and myosin filaments are not regularly arranged
Connective tissue
Types
Blood
Unique type of
connective tissue
, because it is not static
It is a connective tissue because blood originated from the
mesoderm
during embryonic development
The embryonic tissues are...
Ectoderm
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Endoderm
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Mesoderm
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Blood cells float in plasma, the
liquid
extracellular matrix of blood (not net-like)
Plasma makes up
55%
of blood liquid volume
Fat
Adipose tissue is made of loose connective tissue
White fat
Stores lipids/energy
Cushions organs
Around the gonads
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On the front of our bodies to protect vital organs
Provides insulation against the cold
Brown fat
Produces heat when burned
Brown due to abundant mitochondria and rich blood supply
Bone
Collagen fibres hardened by calcium phosphate to form osseous tissue
Hardened collagen provides strong, rigid connective tissue to bones
The rigid connective tissue provides support
This makes movement possible
Cartilage
Fibroblast cells called
chondrocytes
secrete an ECM rich in collagen and elastin
This makes cartilage
firm
and
flexible
Ear
Joints (knee)
Trachaea
Loose cells (fibroblasts or stroma) embedded in an
extracellular matrix
The extracellular matrix (ECM) is a 'scaffold' or 'meshwork' that provides a structure for the connective tissue cells
Extracellular
, because the proteins in the ECM are secreted by the cells
The cells 'sit' on top of the ECM, and can MOVE along the ECM
Different connective tissues have
different compositions and properties
of the ECM
Many different types of proteins make up the ECM, but only two are considered for this course
Extracellular matrix proteins
Collagen
First protein that was made as the ECM
Allows multicellular organisms to evolve
Collagen only present in animals
Allows cells to 'stick together'
Most common
Long fibres
Strong
Resistant to stretch
Lots of collagen means a rigid ECM and little movement for the loose cells
Provides structural strength to organs
Bone
Skin
Elastin
Long fibres
Can stretch then recoil
Abundant in tissues that are regularly stretched
Lungs
Arteries
Nervous tissue
Two main types of cells
Neurons
Many shapes and sizes
Encode information as electrical signals
Communicate with other target cells via secretion of neurotransmitters
Conduct action potentials down the axon
Glial cells (glia)
Do
not
conduct electrical signals
Provide support and protection to neurons
Glial cells can create a barrier that protects the brain from chemicals in blood
e.g. astrocytes (a type of glial cell)
Play an important role in spinal cord injuries
The glial cells are stimulated to aid recovery
Homeostasis
In general, homeostasis is
"the maintenance of stable conditions in the internal environment"
A multicellular organism (e.g.
human
) must fulfil its nutritional needs by
maintaining stable conditions in the body's internal environment (i.e. the
interstitial fluid
)
Counters challenges from the external environment and those by the metabolic activity of our body's cells
Requires
control
and
regulation
Responding to changes
in both the external and internal environments
Done so through the
nervous
and
endocrine
systems (as the regulatory systems)
They control the activities of organs and organ systems
They achieve homeostasis through
feedback information
Negative feedback
Tells the regulatory system to
reduce or reverse
a process
e.g. reducing amount of glucose
Positive feedback
Tells the regulatory system to
amplify or increase
a response
beyond
the set-point
e.g. monthly menstrual cycle of female – just before ovulation, the level of oestrogen is very high, and this is countered
e.g. release of oxytocin to stimulate uterine contractions
Feedforward reflexes
are NOT a loop
They serve to prepare the body for an upcoming changes or events
e.g. the gastrocolic reflex causes an increase in large intestine motility in response to food in the stomach, which "prepares" the late intestine for incoming food
Certain factors in the interstitial fluid need to be maintained within the
set-points
Also known as
reference intervals
or
limits
If the values are beyond or below the
critical values
, then something is wrong
These factors include...
Vitamin B12
Thyroid stimulating hormones (TSH)
Glucose (fasting)
Protein
Potassium
Sodium
Cholesterol (total)
Low density lipoproteins (LDL)
High density lipoproteins (HDL)
Other 'things' need to also be regulated in our interstitial fluid
Hormone levels
Body temperature
pH
Oxygen levels
The interstitial fluid IS basically the extracellular fluid, but is
inside connective tissue, between cells
Each cell in tissue must be bathed in interstitial fluid
A stable internal environment of interstitial fluid is essential for complex multicellular animals
Intracellular fluid exchanges with interstitial fluid
Blood vessels, fibroblast/stromal cells and immune cells lie within the interstitial fluid
A unicellular organisms (e.g.
amoeba
) can fulfil its nutritional needs by regulating exchange of materials across its cellular membrane
O2 and
nutrients from the extracellular fluid
go into the
intracellular fluid
This is the cytoplasm or the internal environment
The extracellular fluid is the fluid found in...
Interstitial fluid
Plasma
Lymph
From the immune system
CO2 and waste from the intracellular fluid go out into the
extracellular fluid
This is the pond water or the external environment
Body temperature
How do animals regulate their body temperature?
Animals are temperature sensitive
Endotherms
Regulate body temperature by
producing heat
or
active mechanisms of heat loss
Body temperature is more or less
constant
e.g. mouse
They
alter the rates
of heat gain and heat loss via...
Metabolism
Generates heat in the body
Radiation
Heat moves from warmer objects to cooler ones via the exchange of infrared radiation
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Evaporation
Helps to release heat from the body
Evaporation of water from body surfaces or breathing passages cools the body (transfers heat away from the surface)
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Convection
Heat transfer to a surrounding medium such as air or water as that the medium flows over a surface
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Conduction
Heat transfer directly between two objects at different temperatures when they come into contact
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Blood flow to skin
Another way to reduce or dissipate body heat
Heat from body via blood to skin is lost to to the environment
In mammals, the
hypothalamus
is a neural tissue that regulates body temperature and many hormones
Controls/regulate metabolism
A lot of our enzymatic reactions requiring energy are inefficient and produce
heat
as a
by-product
– i.e. metabolism generates heat
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Basal metabolic rate (BMR)
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The hypothalamus is a sense organ that regulates metabolism and sends out signals to
effectors
– organs or cells that act in response to stimuli
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It integrates thermosensory information, establishes set points for body temperature, and regulates physiological thermal controls
Location
Put two fingers in both ears and take one under your nose – you will find the hypothalamus (centre of brain)
Ectotherms
Regulate body temperature by
equilibrating to temperature of the environment
or external sources of heat
e.g. lizard
Heterotherm
An animal that sometimes behaves as an endotherm and at other times as an ectotherm
Why is it important to study how temperature is regulated?
Our human bodies need to stay within the optimum body temperature range of
37.0-37.2˚C
Having too high of a body (
hyperthermia
) can lead to improper function of proteins and cell membranes
The tertiary structure of proteins unfold as a result of denaturation (40˚C for heatstroke)
This can
ultimately
lead to cell and organism death
Heat injury
is very important and common, especially in athletes
Occurs in different forms ('seriousness') of
hyperthermia
"Elevated body temperature"
From least serious to most serious...
1.
Heat cramps
Due to dehydration and loss of sodium via sweating
2.
Heat exhaustion
Also known as
exercise-associated collapse
Symptoms
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3.
Heatstroke
Life-threatening condition requiring immediate medical attention
Symptoms
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Symptoms (dangerous)
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Death in
20%
of cases