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General Biology: Ecology & Physiology
Gas Exchange & Circulation

Glucose Homeostasis
● Insulin is produced in the pancreas when blood glucose levels are high
Glucose -> glycogen -> glucose levels decline
● Glucagon is produced in the pancreas when blood glucose levels are too low
Glycogen -> glucose -> glucose levels rise

2 Forms of Diabetes
● Type 1: autoimmune disease ; immune system destroys insulin producing cells = insulin
injections needed
● Type 2: prevalent in people who are resistant to insulin ; lowered / no function of insulin
receptors due to high amounts of sugar diets
● Higher glucose can lead to a higher urine volume due to an increased osmolarity in the
filtrate (kidney)

Respiratory & Circulatory Systems
● Gas exchange involves 5 steps:
1) Ventilation is the movement of air or water through a specialized gas-exchange
organ
2) Diffusion at the respiratory surface (O2 in/CO2 out)
3) Circulation of dissolved CO2 and O2 throughout the body
4) Diffusion at the tissues - O2 moves from blood into tissues & CO2 moves from
tissues into blood
5) Cellular respiration is the cell’s use of O2 & production of CO2

● Ventilation and diffusion at the respiratory surface are accomplished by the respiratory
system
● Circulatory system is responsible for the movement of O2 & CO2 throughout the body
(heart)
● Gas exchange based on diffusion ; O2 levels high in environment / CO2 levels high in
tissues, thus CO2 is produced and O2 is consumed

Organs of Gas Exchange
● Small animals - gas exchange through direct diffusion across body surface (wet
environment)
● Large animals - gas exchange through specialized organ (lungs) (dry environment)
● Fish gills can be internal or external

Ventilation Through Gills
● Fish ventilate gills by opening/closing their mouths & operculum (flap over gills) which
creates pressure for water movement
● Tuna swim fast w/ open mouths to force water through their gills ; process called ram
ventilation
● Water moves through gills in one direction over thin structures (gill filaments) ; each gill
filament is composed of 100s-1000s of gill lamellae

Insect Tracheae
● Insects have tracheae which open to the environment through pores (spiracles) ; spiracles
can close to minimize water loss

● In larger insect species, tracheae alternatively open and close as many muscles contract
and relax

Ventilation of the Bird Lung
● 4 steps to ventilation:
1) Inhale - air flows through tracheae into posterior air sacs
2) Exhale - lungs fill w/ air from posterior air sacs (posterior of lungs: parabronchi)
3) Next inhalation - anterior air sacs fill w/ air
4) Next exhalation - anterior air sacs empty out, air moves out to atmosphere

Open Circulatory System
● Hemolymph (fluid equivalent to blood in invertebrates - pumped throughout body in
open vessels)
● Open system characteristic of invertebrates
1) Heart pumps hemolymph into vessels that empty into open, fluid-filled spaces
2) Heart internal pressure drops & hemolymph moves into heart through holes in
surface
3) Body movements help move hemolymph to/from heart
4) Hemolymph is under low pressure, best for sedentary organisms w/o high O2
demands
● Crustaceans are an ​exception​: they use small vessels to send hemolymph to tissues w/
high O2 demand

Vertebrate Lungs
● Tracheae carries inhaled air to narrow tubes called bronchi ; bronchi branches off into
bronchioles

● Frogs & other amphibians: lung is a simple sac lined w/ blood vessels
● Mammalian lungs divided into tiny sacs (alveoli)
● Alveoli provides interface between air and the blood consisting of thin, aqueous film,
epithelial layer, extracellular matrix (ECM), wall of capillary

Ventilation of Human Lung
● Pressure inside human chest cavity is about 5mmHg less than atmospheric pressure
● Change in volume caused by downward motion of diaphragm (inhale - diaphragm down,
exhale - diaphragm up)

Transportation of O2 & CO2 in Blood
● Blood is a connective tissue consisting of:
1) White blood cells (immune system)
2) Red blood cells (transport O2 from lungs to tissues and CO2 from tissues to
lungs)
3) Platelets (cell fragments that minimize blood loss ; involved in clotting)

Structure & Function of Hemoglobin
● Red blood cells contain an oxygen-carrying molecule called hemoglobin:
1) Contains 4 iron molecules that can each bond to an O2 molecule
2) Hemoglobin molecule: 4 O2 molecules
3) 98
...
O2 in blood within tissues (demand)
● Binding of first O2 molecule -> more binding likely *cooperative binding

Circulation
● Larger animals need a closed circulatory system b/c they have less surface area to body
volume preventing direct flow of gas across body surface

Types of Blood Vessels
Arteries -> Arterioles
● Tough, thick-walled vessels
● Take blood away from the heart under high pressure
● Walls of arterioles consist of muscle fibers that relax to increase diameter,
increasing blood flow
● Muscle fibers contract, decrease diameter, & slow down blood flow
Aorta (large artery)
● Receives blood directly from the heart
● Consists of elastic fibers that expand for blood flow under high pressure and
propels blood forward through elastic recoil
Capillaries
● Thin walls, allowing gas exchange between blood and tissues in networks called
capillary beds
Veins -> Venules
● Thin-walled (for blood leaving tissues under low pressure)
● Returns blood to heart
● Larger veins contain one-way valves which prevent backflow of blood

● Veins contain some muscle fibers which contract in response to nervous system
signals
● Blood pressure in a closed circulatory system is partially regulated by adj

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