General Biology2 Summers

Respiration and oxygen availability Heart and Circulation/Transport Nutrition, Digestion, Metabolism Excretion and Elimination

Chemical Messengers Sexual Reproduction Neuronal Structure & Signals Sensory Reception

text:Biological Science 5th Edition - Freeman ..: Read Chapters 42 & 45 for this lecture Integration of Neural Function Neuromuscular Action - Behavior syllabus Figures acronyms    end

I. Respiration and oxygen availability 			

	A. Oxygen diffusion 

		1. Concentration x surface area x solubility / diffusion distance

			a. \ the greater the distance the smaller the amount of O2 diffuses

	B. Single Cell or very small multiple cell organisms 
	
		1. simply diffuse oxygen in from surrounding medium

		2. medium inside cell is mostly water

		3. membranes must remain wet to be functional

		4. medium outside cell must be wet

		5. therefore O2 must be dissolved in water to diffuse

	C. Large Organisms must have a respiratory system to bring O2 to each cell

		1. Insects have tubes (tracheae) to bring oxygen to all cells

			a. tubes must be moist inside

		2. Plants have leaf pores
		
			a. Stomata: CO2, O2 & H2O exchange
			
				i. each surrounded by 2 guard cells
			
			b. gas exchange must be balanced with H2O vapor loss
			
				i. guard cells swell - stoma opens
				
					(1) K+ + H2O Ü guard cells
					
						(a) H2O follows K+
				
					(2) CO2 enters, O2 + H2O leave leaf
					
				ii. guard cells shrink - stoma closes
				
					(1) plant protected from water loss
		
		
		3. Vertebrates

			a. respiratory organ coupled with a circulatory system

			b. fish - gills

			c. amphibians - skin

			d. amphibians, reptiles, mammals, birds - lungs

			
II. Ventilation and Respiratory System - Lungs

	A. Nostrils, Pharynx

		1. Warms the air as it comes in

		2. Moistens the air to 100%

		3. These two things protect the lungs and allow diffusion

	B. Trachea

	C. Bronchi

	D. Bronchioles

	
	E. Alveoli

		1. a hollow sac into which the air flows

		2. each sac (alveolus) is surrounded by capillaries

			a. alveolus is thin walled

			b. capillaries are thin walled

			c. diffusion distance is small

			d. [O2] (concentration) is greater in alveoli than blood 
			
				i. \ O2 diffuses into blood

			e. [CO2] greater in blood

				i. carried in the blood as H2CO3 (carbonic acid) 
				
				ii. and as ionic bicarbonate (HCO3-) and H+

				iii. converted to CO2 by carbonic anhydrase

			f. alveoli membranes are moist, air is 100% humid

	F. Circulatory system  (more later)

		1. carries the O2 to the capillaries at the tissues
		
			a. where the  diffusion distance is again small

		2. [O2]  greater in the blood; [CO2] greater in cells

III. Alternative ventilation

	A. Gills

		1. water flows over gill arches

			a. colder water normally contains more O2

			b. flow is unidirectional: front to back

				i. pump = buccal constriction + opercular opening

				ii. ram-jet ventilation

					(1) sharks/rays/skates force water across gills
					    by swimming

				iii. simple gills may just sit in the water

		2. deoxygenated blood flows across gill arch in the opposite direction of H2O

			a. blood with the least O2 is near H2O with the most O2 already removed

			b. still more O2 in the water than in the blood 

			c. oxygenated blood encounters more oxygenated water 
			   as it moves forward through the gill

				i. counter-current exchange

	B. gas bladder - primitive lungs

		1. fish have gas bladders

			a. usually for balance

		2. gas must be exchanged to maintain bouyancy

			a. usually exchanged from the blood

		3. a few species have connections between the esophagus and air bladder

			a. oxygen may be taken in by gulping air

			b. the swim bladder may act as a primitive lung

				i. it is highly vascularized and oxygen exchange occurs

				ii. sac like

				iii. more developed lungs (e.g. with alveoli)
				     are more highly vascularized

			c. lung-fish gain much of their oxygen this way

			d. even amphibian lungs work much this way

	C. Counter-current Lungs - Birds

		1. birds have air sacs which receive the inspired air

		2. the air travels across the lungs unidirectionally to another set of air sacs

			a. this allow for cross-current exchange

				i. similar to counter-current exchange
                
				ii. blood travels at a 90° angle to air flow
                
		3. the air is exhaled from the forward air sacs


IV. Gas Exchange

	A. Partial Pressure of Gases

		1. Partial Pressure ¹ concentration

			a. gases will diffuse against [gradient] if partial pressure is favorable

		2. diffusion occurs down partial pressure gradients

			a. at sea level Pb = 760 mmHg  Total Pressure
			
			

			
molecule
% X total =
Partial Pressure = Pmolecule
			
O2
0.2095 X 760 =
159 mmHg =  PO2
			
CO2
0.0003 X 760 =
0.23 mmHg = PCO2
 
			
N2
0.78 X 760 =
593 mmHg = PN2
			
etc.
< 0.01 X 760 =
+ 7.8 mmHg
 
			
760 mmHg



	B. Blood Oxygen Transport

		1. only 1.5% of blood O2 is physically dissolved

			a. hemoglobin carries 98.5%

		2. Hemoglobin affinity for O2 dependent on PO2

			a. Ý PO2 È affinity 

		3. animals at altitude produce more hemoglobin and more red blood cells

		4. myoglobin

			a. stores O2 in vertebrate muscles

			
	C. Oxygen Dissociation Curve

		1. Hemoglobin binds oxygen reversibly

			a. binds O2 when PO2 is high

				i. like at alveoli

			b. releases O2 when PO2 is low

				i. at tissues

			c. myoglobin binds O2 even when PO2 is low

			
	D. Regulation of Ventilation

		1. respiratory centers in medulla and pons of brainstem

			a. sensitive to: PCO2, H+

				i. centers Ý or ò ventilation to affect change
				   in blood gas partial pressures

		2. modified by cortex and central and peripheral chemoreceptors

			a. carotid/aortic bodies

			b. sensitive to gas and pressure changes
			   right after the blood is pumped out of the heart