chapter 42 notes circulation and gas exchange. circulation in animals diffusion alone is not enough...

Chapter 42 Notes

Circulation and Gas Exchange

Circulation in Animals

Diffusion alone is not enough to transport substances over long distances in animals- ex. moving O2 from the lungs to the brain

The circulatory system solves this by making sure substances only diffuse a short distance


Invertebrates have a gastrovascular cavity or circulatory system for internal transport

- ex. the body wall of the hydra is only 2 cells thick; the body cavity can serve for digestion and distribution


In animals with many cell layers, gastrovascular cavities are not enough because diffusion distances are too great

They will use an open or closed circulatory system- contains blood, blood vessels, and a muscular pump (heart)


In insects blood bathes the organs directly in an open circulatory system- no distinction between blood and interstitial fluid

In a closed circulatory system, blood is confined to vessels and is distinct from interstitial fluid


Humans have a closed system called the cardiovascular system- the heart has 1 atria or 2 atrium that receive blood returning to the heart- the heart also has 1 or 2 ventricles that pump blood out of the heart


- arteries, veins, and capillaries are the three main types of blood vessels- arteries are going to branch into arterioles pass blood to the capillaries- capillary beds infiltrate each tissue; here gasses are exchanged by diffusion


Metabolic rate is an important factor in the evolution of the circulatory system- animals with high metabolic rates have more complex circulatory systems and more powerful hearts- differences are associated with gill breathing versus lung breathing


A fish heart has 2 main chambers (1 atria and 1 ventricle)- blood pumps from the ventricle to the gills; from the gill capillaries the blood moves through all other parts of the body- problem is when blood pumps through a capillary, blood pressure will drop


- this constrains the delivery of O2 to body tissues and the maximum aerobic metabolic rate of fishes

Amphibians have a 3 chambered heart (2 atrium and 1 ventricle)- the ventricle pumps blood into a forked artery that splits the ventricle's output


- the pulmocutaneous circulation leads to capillaries for gas exchange- systemic circulation supplies the bodies organs with oxygenated blood- some mixing of blood occurs- reptiles have less mixing since they have a partially divided ventricle


Crocodiles, birds, and mammals have a 4 chambered heart- the left side of the heart receives and pumps oxygen-rich blood; the right side handles oxygen-poor blood- the evolution of this supported endothermic life- use 10X more energy than ectotherms


The mammalian heart- about the size of a closed fist- contracts and relaxes in a rhythmic cycle- cardiac cycle: one complete pumping and filling of blood


- systole: the contraction phase- diastole: the relaxation phase

Cardiac output depends on the heart rate (# of beats per min.) and stroke volume (amt. of blood pumped)


The heart has 4 valves that prevent backflow of blood- atrioventricular (AV) valve: between atrium and ventricle- semilunar valves: located at the 2 exits of the heart- the “lub-dup” sound is the of the valves closing


- heart murmur: a defect in the heart valves when blood squirts backward

The sinoatrial (SA) node or pacemaker sets the rate and timing at which cardiac muscles contract


The lymphatic system returns fluid to the blood and aids in body defense- fluid enters the system by diffusing into tiny lymph capillaries; the systems drains back into the circulatory system

Along the lymph vessel are lymph nodes: filter lymph and attack viruses and bacteria


Blood consists of several kinds of cells suspended in a liquid called plasma- blood plasma is 90% water- in the plasma are red blood cells (RBC), white blood cells (WBC), and platelets


RBC, or erythrocytes, are the most common blood cells- main fcn. is to transport O2

- lack nuclei; leaves more space for hemoglobin- lack mitochondria; no aerobic respiration


There are 5 major types of WBC’s or leukocytes- monocytes, neutrophils, basophils, eosinophils, and lymphocytes- monocytes and neutrophils are phagocytes

Platelets are important for blood clotting

Gas Exchange in Animals

Gas exchange: the uptake of oxygen and the release of carbon dioxide- don’t confuse with (cellular) respiration

Respiratory medium: source of oxygen- air and water


Respiratory surface: part of an animal where gases are exchanged- movement must be from diffusion- surfaces are thin w/ large surface areas- cells must be bathed in water (for plasma membrane)


The structure of the respiratory surface depends on the size of the animal and whether it lives in water or on land- also influenced by metabolic demands

ex. endotherms vs. ectotherms


In simple animals, the plasma membrane of every cell is able to have gases diffuse in and out

In other animals, their outer skin acts as a respiratory organ- animals are small and usually long and thin or flat


For most other animals, the body doesn’t have enough area for gas exchange- the solution is an organ that is highly branched and folded; enlarges the surface area for gas exchange

- ex. lungs, gills, and tracheae


Gills are respiratory adaptations of most aquatic animals

Gills are outfoldings of the body surface that are suspended in the water- total surface area of the gills is often much greater than the surface area of the rest of the body


As a respiratory medium, water has advantages and disadvantages- no problem keeping the cell membranes moist- low [O2] in water

Gills must be very effective to obtain enough oxygen


Ventilation: increases the flow of the respiratory medium over the respiratory surface


The arrangement of capillaries in a fish gill enhances gas exchange and reduces the energy cost of ventilation

Countercurrent exchange: blood flows in opposite direction to the movement of water past the gills


- as blood moves through the capillary, it becomes more and more loaded with oxygen. Simultaneously, it encounters water with even higher oxygen concentrations.- along the entire length of the capillary, there is a diffusion gradient


Tracheal systems and lungs are respiratory adaptations of terrestrial animals

Tracheal system: made up of air tubes that branch throughout the body- largest tube is called the tracheae; opens to outside


- for small insects, diffusion through the trachea brings in enough O2 and removes enough CO2 to support cellular respiration

- larger insects ventilate their tracheal systems with rhythmic body movements


Unlike the tracheal systems that branch throughout the insect’s body, the lungs are restricted to one location- not in direct contact with all cells- the circulatory system must transport gases between the lungs and the body- size is correlated to metabolic rate


Pathway of air to the lungs- the nasal cavity leads to the pharynx; when food is swallowed; the larynx moves upward and tips the epiglottis over the glottis; allows food to go to the stomach- the rest of the time the glottis is open


- from the larynx, air passes into the trachea (windpipe)- the trachea forks into two bronchi, one leading to each lung- within the lung, each bronchus branches repeatedly into finer and finer tubes called bronchioles


The system of air ducts looks like an inverted tree- the epithelium lining of the major branches are covered by cilia and a thin film of mucus

- traps and moves dust, and pollen away from lungs


At the tips of the bronchioles, there is a dead-end cluster of air sacs called alveoli- location of gas exchange across the epithelium-O2 and CO2 diffuse across the epithelium and the capillaries


Ventilating the lungs- needed to maintain high [O2] and low [CO2] at the gas exchange surfaces- breathing ventilates the lungs- mammals ventilate the lungs by negative pressure breathing

- pulls air instead of pushing it


Lung volume increases as a result of contraction of the rib cage muscles and the diaphragm

Because gas flows from high pressure to low pressure, through the nostrils and down the breathing tube to the alveoli

chapter 42 notes circulation and gas exchange. circulation in animals diffusion alone is not enough...

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