Download Ch. 9: Homeostasis (9.1) Humans (thin skin, warm

Ch. 9: Homeostasis (9.1)
Humans (thin skin, warm-blooded & relatively hairless) can
survive in extreme conditions and this makes us successful as a species.
Homeostasis- the tendency to keep the internal environment relatively
constant. Examples: blood pH, blood glucose, blood pressure, body
temp.
Our cells are bathed in interstitial fluid with a salt concentration
close to that of ocean water; the salinity and pH of interstitial fluid must
remain relatively constant for our cells to be healthy and to work
together. There are slight differences (i.e. temp & blood pressure)!
Homeostasis is an example of dynamic equilibrium.
Dynamic equilibrium- state of balance achieved within an environment
as a result of internal control mechanisms which continuously oppose
outside forces tending to change that environment. The constancy in
the internal environment is achieved through a series of many small
changes. Therefore, equilibrium is maintained as long as system is
active or dynamic.
A variety of factors affect the homeostasis of an organism. Our
body systems interact in order to maintain homeostasis. See fig. 9.2 p.
301.
For example:
What happens to your body as you run?
Why would the body respond in these ways?
What body systems would be involved?
What happens to your body when you are frightened?
What happens to your body when you have a cold? The flu?
Temperature regulation is important in maintaining homestasis.
Homeotherms- keep temp. relatively constant, warm-blooded
(birds & mammals).
Poikilotherms- temp. fluctuates with temp. of animal’s
environment, cold-blooded (fish, reptiles).
Most animals fall somewhere between these 2 extremes.
Homeotherms generate heat as a by-product of their metabolism
(all chem. processes of body) and use different mechanisms to control
the rate at which this heat is lost and dynamic equilibrium maintained:
Behavioral- hot day stretch out in sun, cold day by fireplace
desert animals primarily nocturnal (night feeders)
Physiological- circulatory system impt. in heat regulation
Examples of Physiological Mechanisms:
vasoconstriction- constriction of blood vessels when body
needs to conserve heat; blood flow limited close to skin
(extremities go numb with bluish tinge)
vasodilation- dilation of blood vessels when body needs to
remove excess heat; increased blood flow just under skin (skin
flushed and hot to touch); promoted by alcohol
Our body’s reactions to increased/decreased temperature are
examples of negative feedback loops.
Negative feedback loop- process that detects and reverses deviations
from normal body constant; reverse effects of stimuli; moves system
toward balance & stability. Consists of 3 parts:
Sensory receptors (skin, eyes, ears, nose, taste)- detect changes
and send nerve impulses to the brain
Integrator (brain)- interprets & sends messages to effectors
Effectors (tissues/organs)- cause change in internal conditions
A good example of a negative feedback loop is the thermostat in
your house. In our bodies, these loops help regulate our body
temp. (see fig. 9.4 p. 303) and prevent blood sugar, blood
pressure, and other body constants from becoming too high or
too low.
Positive feedback loop- act to increase the strength of the stimuli;
pushes system away from balance & stability; usually disastrous &
causing disease or serious changes/health issues; rare in healthy bodies
(i.e. high blood pressure, drug addiction)
Hmwk: When someone is sick, he or she often feels tired. How is this
tiredness feeling related to the maintenance of homeostasis?
Circulation (9.2):
Pre-17th Century- see theories on p. 304
17th Century- Harvey established mammals had cyclic circ. system
where blood flows in one direction only, but he couldn’t find the place
where it stopped flowing from the heart & began its return trip
1657- problem solved...Malpighi identified capillaries under microscope
Transportation in Animals
transport- process of moving substances into & out of cells or
distributing them within cells
The circular movement of materials b/w the heart and body cells is
the circulatory system and it acts as a link between the cells of complex
organisms and their environments.
Mammalian circulatory systems are closed systems (closed in the
sense that blood is always enclosed in vessels).
Blood vessels are organized into 3 primary cycles (pathways):
1. Cardiac Circulation - pathway of blood within heart
2. Pulmonary Circulation - carries blood b/w heart & lungs (most of
rest of blood)
3. Systemic Circulation - carries blood b/w heart & body (80-90% of
all blood in body)
Average adult male has 5-6 L of blood; average adult female has 4-5 L.
Circulatory Systems must have the following 3 components:
 a network of vessels through which fluid moves
 fluids (medium) to carry the nutrients and gases...blood
 pumping mechanism for fluid...heart(s)
Blood vessels- there are 3 types:
arteries- thicker, elastic walls; carry oxygenated blood from ventricle
away from the heart to the rest of the body (* 1 exception-pulmonary)
arteriole- small artery
veins- thin, slightly elastic walls; take unoxygenated blood from body
cells to the atrium (*1 exception...pulmonary); have valves inside
which prevent blood from flowing away from the heart (varicose veins
occur when valve doesn’t work)
venule- small vein
capillaries- microscopic; thin walls to allow for diffusion of gases,
foods, wastes & hormones b/w blood and interstitial fluid around cells
Circulatory systems have evolved b/c of the need to keep blood
flowing as quickly as possible through the cycle. In smaller vessels (i.e.
capillaries), friction ↑ and blood pressure ↓ so blood moves very slowly.
Heart doesn’t have enough pumping pressure to move blood
around entire system so each of blood vessels is adapted to help keep
blood moving (See fig. 9.8 p. 306 and 9.9 p. 307):
- elasticity of arteries, thick walls (pulse is expansion and
contraction of arteries as blood moves through)
- veins are thinner and lack elasticity, but have a greater capacity
(twice as much blood in veins as arteries) and one-way valves to
keep blood flowing in right direction
- capillary walls are one layer of cells; small size so largest blood
cells can fit through in single file
→If laid all blood vessels in our body end to end in straight line they
would wrap around Earth 2.5 times.
Blood consists of 2 main parts:
- 55% is yellow fluid called plasma (non-living) which is over 90%
water along with dissolved gases, proteins, sugars, vitamins, minerals,
wastes
- The other 45% of blood is the solid or formed living portion which
contains 3 types of cells:
1. red blood cells (erythrocytes) which contain hemoglobin
(iron-containing protein) that carries O2; hemoglobin picks O2 up
& releases it depending on the conc. of O2 and acidity of
surrounding fluid. When O2 is low and acidity high, then O2 will
be released.
Red blood cells (rbc’s)live for about 3-4 months. One drop of
blood has about five million rbc’s. They are produced in the bone
marrow and stored in the liver and spleen. Mature rbc has no
nucleus, disk-shaped.
2. white blood cells (leucocytes)
- 8000 in single drop of blood, live about 10 days, cells have nuclei,
larger than rbc’s
- fight infections:
macrophages- phagocytic cells that pass thru capillary walls to
ingest pathogens
lymphocytes- non-phagocytic cells involved in body’s acquired
immune response which enables it to recognize & fend off certain
pathogens (formation of antibodies)
- remove dead cells like rbc’s
3. Platelets
- cell fragments which produce fibrin to clot blood, 7-8 days,
250,000 in a drop of blood, no nucleus.
- Steps in clotting process (see p. 312...fig. 9.15)
Blood also links all body cells and organs (therefore, it’s called
connective tissue) and it transports:
- hormones (chemicals) to control body functions
- urea (waste products) from the liver which is transported to the
kidneys for processing & excretion
- basic nutrients from digestion (minerals, vitamins, glucose,
amino acids and fats) are absorbed by capillaries in walls of small
intestine
Human Heart (9.3)
- ‘pump’; little larger than your fist; found slightly left of the middle of
your chest cavity; its regular contractions force blood through blood
vessels
- muscular organ; consists mostly of cardiac muscle which is individual
cells (each cell has 1 nucleus) that branch and interlock to form a
network that allows them to contract more strongly
- pericardium is the tough membrane that covers the heart (protection)
- 2 upper, thin-walled atria (atrium is singular) and 2 lower, thick walled
ventricles
- left and right sides separated by a wall called the septum; this prevents
oxygen-poor blood on the right side from mixing with oxygen- rich
blood on the left side
- direction of blood flow inside heart is controlled by valves:
atrioventricular (A-V) valves- 2 of these allow blood to flow only from
atria into ventricles; right side is tricuspid valve and left side is
bicuspid or mitral valve
semilunar valves- 2 of these allow blood to move from ventricles into
arteries when they are open and prevent blood from flowing back into
ventricles when closed.
- ‘double’ pump; right side sends oxygen-poor blood to lungs and left
side sends oxygen-rich blood to all body cells
Blood Flow through the heart:
1. Unoxygenated blood enters the right atrium through the superior
and inferior vena cava which are two large veins at the top
(superior vena cava) and bottom (inferior vena cava) of the
heart. This blood flows from skeletal muscle contractions and is
not under pressure like blood in arteries.
2. Contractions of the right atrium force blood into the right
ventricle thru tricuspid valve.
3. Right ventricle contracts forcing blood into the left & right
pulmonary arteries. These arteries carry blood to the capillaries
in the lung where oxygen is picked up and carbon dioxide is given
off.
4. The now oxygen-rich blood comes back via the left & right
pulmonary veins to the left atrium.
5. Blood is then forced into the left ventricle through bicuspid valve.
6. The blood is then pumped into the dorsal aorta (large blood
vessel) by the left ventricle (through semi-lunar valve).
7. Arteries from the dorsal aorta (branches off) go to all parts of the
body carrying oxygenated blood to the capillaries.
8. Cells use O2 and then capillaries take unoxygenated blood which
is high in CO2 to veins that drain into the superior and inferior
vena cava. Cycle starts again
Recall that valves in the ventricles, atria and veins prevent blood from
reversing its flow.
Remember: blood travels to the heart twice in a circulation.
Unoxygenated blood travels to the right side of the heart and all
oxygenated blood travels to the left side of the heart AND there is no
mixing of the oxygenated and unoxygenated blood in the heart.
The Heart Beat
The pumping of the heart has 2 periods:
diastole- period when heart muscle is relaxed; A-V valves open so blood
flows from atria into ventricles
systole- period when heart muscle contracts; starts with contraction of
atria which forces more blood into ventricles to completely fill them
The source of each heartbeat is in the heart itself. The sinoatrial
or S-A node is found in the right atria and is a piece of muscular tissue
also called the pace maker. A flow of ions acts as an electrical impulse
that causes the atria to contract. The contraction forces blood into the
ventricle. The impulse then reaches another small bundle of muscle
tissue called the atrioventricular or A-V node located between the
ventricles and atria. The electrical impulses sweep down the muscle of
the ventricle causing the contraction. This contraction increases the
pressure on the blood and forces it out the aorta (left ventricle) or to the
lungs (right ventricle).
The closing of the heart valves makes a lub-dup sound. “lub” is
from closing of A-V valves while “dup” is from closing of semilunar
valves. The adult heart beats about 70 times a minute. It beats faster
when the heart is being exercised. When valves or septum are
damaged, blood leaks or flows backward which is a heart murmur.
Heart rate is under hormonal control (adrenalin) from the nervous
system; this controls the physical activity of the organism.
Blood Pressure- given as systolic pressure/diastolic pressure
-normal in a resting adult is 120/80
Circulatory System Disorders (p. 324-326)
High blood pressure is called hypertension and the most common cause is a
disease called atherosclerosis or “hardening of the arteries”. Cholesterol and fats
build up on the inner walls of the arteries and narrow them making it harder for
blood to flow and increasing the pressure. This disease can lead to heart attack and
stroke. To prevent...diet low in saturated fats & cholesterol; high in fruits &
veggies
Arteriosclerosis- cholesterol or other fatty material deposits under inner lining of
arteries usually b/c of poor diet over many years; plaque blocks blood flow in artery
which can damage platelets causing them to form blood clots. Blood clots can clog
arteries and cause body tissues to die or it can break free and travel to heart or
brain...an embolism. In the brain, this can lead to stroke and in the heart, a heart
attack. To prevent...aspirin a day
Treatment of Circulatory Disorders
- Treatments have improved over time
Coronary Artery Bypass Surgery- removing healthy blood vessel from
other part of body and using it to create new pathway around blockage in a
vessel near heart; 1 end of new segment joined to aorta and other end to point
in blood vessel beyond blockage.
Double- 2 vessels blocked; triple- 3; quadruple- 4
Shunt- tube used to redirect blood away from the suturing site during
coronary bypass; clear, bloodless field of view for surgeon & uninterrupted
blood flow during surgery
Angioplasty- surgery in which cardiologist inserts a fine plastic catheter into
a clogged artery; a tiny balloon is pushed out from its tip when it reaches
blockage; once inflated, the balloon forces vessel open by pushing on wall of
artery
Clot-busting drugs:
Thrombolytics- medicines which open up the coronary arteries, restore
blood flow to heart, ↑ O2 level in heart, prevent tissue death
The Lymph Network
interstitial fluid- colorless, watery fluid consisting of water, salts,
proteins and nutrients which bathes ALL body cells; it helps move
materials between capillaries and cells
lymphatic system- series of vessels that picks up excess fluid and
proteins and transports materials throughout the body via the blood.
Eventually, this fluid ends up back in the heart and therefore, the body
does not lose its water content.
lymph- intercellular fluid (colorless or pale yellow)inside the lymphatic
system
lymph nodes- important in defence against disease; filter out foreign
materials from blood (i.e. bacteria and other pathogens). Many bacteria
are destroyed in our lymph nodes.
There are over 100 areas of lymph tissue around the body where
lymph fluid collects.