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Physiology 3: Transport
Transcript of Physiology 3: Transport
Oxygen and Carbon Dioxide are subject to diffusion. This works in opposition at the leaf and at the root.
Soil nutrients must enter the plant in the roots.
To effectively photosynthesize, water must move in to the roots of the plant, through the stem and up to the leaves. Water Potential Revisited Water potential is a function of the pressure potential and the solute potential. Water will move from areas of less solute (higher solute potential) to areas of more solute (lower solute potential) Positive pressure (higher pressure potential) will push water into an area of negative pressure (lower pressure potential). More solute (lower solute potential) has an opposing effect on water movement to positive pressure (higher pressure potential). Plant Physiology is fundamentally dependent upon the movement of water into the plant at the roots and out of the plant at the leaves. By controlling internal solute concentration and pressure, plants control the direction of water and solute movement Root Tonicity: Roots are hypertonic to the soil.
Cells of the root cortex actively transport soil nutrients in to the root.
This maintains tonicity and keeps water (and dissolved nutrients) moving in to the root. Symplast vs. Apoplast Two routes of transport through plant cells:
Symplastic: transport through cytoplasm and plasmodesmata.
Apoplastic: transport through cell wall channels.
Material can also travel through both means (the "transmembrane route") Prior to transport into the vascular tissue of the root (and therefore into the rest of the plant), all material must move into the symplast of the endodermis that surrounds the vascular cylinder.
This is accomplished by the means of a waxy strip of material (the "Casparian strip") that lines the cell wall of the endodermis. Apoplastic material can not traverse the Casparian strip and must move into the symplast. This forcing of the symplastic route prior to transport to vessels serves a means of controling the material that moves in to the vessels of the plant The continual movement of water into the roots of a plant does not usually provide enough pressure to move water through the entire plant.
At some point (somewhere ~ 4 feet off the ground), gravity begins to counterbalance the positive root pressure.
And yet, there are plants taller than 4 feet....how is this possible?
Transpiration: The movement of water from roots to leaves and in to the atmosphere.
A major part of the water cycle. How transpiration happens... Root: The hypertonicity of the roots (low solute potential) keeps water moving in to the plant.
Water is sent to the xylem.
This process creates a positive root pressure, which keeps water moving up the xylem of the plant (to a point). Stem: Water continues to move through the stem in response to the the positive root pressure and cohesional attraction to water molecules that are moving up the xylem.
Water molecules also have adhesional attraction to the walls of the xylem, which keep them moving up (or at least not moving down) Leaf Water moves from the xylem in to the mesophyll of the leaf, where it can be used for photosynthesis.
Excess water moves in to the atmosphere via stomates in the leaf.
Cohesional attraction between water molecules keeps water moving through the stomates ("Transpirational Pull") Transpiration is made possible by the fact that as water moves through the plant, it is always moving to an area of lower water potential.
The area of highest water potential in the plant is the roots. Plants spend a lot of energy maintaining the osmotic potential of the roots by actively transporting solutes in to the roots (which keeps the roots hypertonic to the soil and serves as a source of nutrients).
As water moves up the plant, it is moving into increasingly lower water potential, due mainly to a decreasing pressure potential.
The atmosphere has the lowest pressure potential. At the leaf, water will saturate the cell wall fibers (micofibrils). As water evaporates into the air spaces of the leaf, adhesive attractions among water molecules and cohesive attractions to the cell wall fibers will bring more water in to the boundary between cells and the atmosphere. At night, transpiration does not typically occur.
As water continues to enter the roots of the leaf, the postive root pressure can cause water to be pushed out of the plant, forming droplets on the surface of the leaf ("guttation"). Stomatal Control Opening and closing stomates is the major way that plants are able to control transpiration and gas exchange. Stomates are controlled by guard cells, which line the opening of the stomate.
Turgid guard cells: Open stomate
Flaccid guard cell: Closed stomate. Typical stomatal density is anywhere from 100-1000 stomates per square millimeter of leaf surface (!) The active transport of potassium ions into guard cells leads to turgidity.
Flaccid guard cells stop actively transporting potassium ions, which causes water loss. Water loss prevention adaptations Xerophytes: Plants that have adapted to live in arid climates. The white bristles of the Old Man Cactus reflect sunlight. Ocotillo only leafs after heavy rainfall. The leaves are small and fall off quickly. Oleandar stomates are found in recessed "crypts", which increases humidity at the stomate and delays water loss. Phloem tissue transports sugars ("sap") made at the leaf through the rest of the plant. As sugar is produced by mesophyll, it travels through symplastic and apoplastic channels to the phloem.
Sugar is actively loaded into the phloem through proton/sucrose cotransporter proteins. Once loaded into the phloem, the high sugar concentration at the leaf (source), causes water to diffuse into the phloem.
This leads to a positive pressure which moves phloem sap through the plant until it reaches an area of low sugar concentration (sink), at which point the sap diffuses out of the phloem. Experiments that utilized aphid mouthparts (stylets) demonstrated evidence to support the "pressure flow" hypothesis of phloem transport.
Stylets closer to leaves had faster rates of sap extrustion. Evolutionary Trends The Mammalian Respiratory System Open vs. Closed Circulatory Systems Circulatory Systems Are Not (Necessarily) Required Circulatory systems are utilized for exchange of material with the environment and the body tissues.
Some animal plans are simple enough (a), or have enough internal surface area (b) that a distinct circulatory system is not required. In an "open" circulatory system (most arthropods and most molluscs), the circulatory fluid ("hemolymph") surrounds the body tissues for exchange, before collecting back in to the system. In an "closed" circulatory system (annelids, chordates), the circulatory fluid ("Blood") never leaves the vessels of the system.
Exchange is accomplished in small vessels that allow for diffusion of materials. Both systems require a heart! Single vs. Double Circulation: Chordates only Single loop circulation takes blood from the heart, to the respiratory surface, to the body, and back to the heart.
Double loop circulation takes blood from the heart, to the respiratory surface, back to the heart, to the body, and back to the heart. Double loop is more efficient than single loop The evolution of the chordate heart Fish have a two-chambered heart, which allows for single-loop circulation. Amphibians have a three-chambered heart, which allows for double-loop circulation, though oxygenated and deoxygenated blood mix in the heart. Reptiles have a three-chambered heart, which allows for double-loop circulation. Reptiles have partial seperation of oxygenated and deoxygenated blood due to a partial septum in the heart. Birds and mammals have a complete septum in the heart, which creates four chambers, and prevents any mixing of oxygenated and deoxygenated blood.
This allows for endothermy. Ectotherms Endotherms The human circulatory system is typical of mammals
red: oxygenated blood blue: deoxygenated blood. There are two circuits that blood follows:
Pulmonary circuit: From the heart to the lungs via the pulmonary arteries. Blood will pick up oxygen and deposit carbon dioxide (and some water) for exhalation. Blood returns to the heart from the lungs via the pulmonary veins.
Systemic circuit: From the heart to the body via the aorta. Blood will provide oxygen and nutrients in body cells, and pick up carbon dioxide and other waste products for excretion.
It takes about a minute for any one blood cell (on average) to make both circuits. The mammalian heart has particular structural features:
Blood enters the right side in the right atrium from the vena cava. This is the least oxygenated blood coming in to the heart.
From the right atrium, blood flows to the right ventricle, and leaves the heart via the pulmonary arteries to the lungs.
Blood enters the left side of the heart in the left atrium from the pulmonary arteries. This is the most oxygenated blood coming in to the heart.
From the left atrium, blood flows to the left ventricle and leaves the heart via the aorta to the systemic circulation (first stop is the cardiac arteries, which supply heart muscle with blood). All chambers of the heart are separated from eachother by one-way valves to prevent back-flow of blood.
The pumping of the heart moves blood through the circulatory system Heart Beat Heart beat is coordinated by a pacemaker region of the heart (the sinoatrial node).
The contraction impulse originates in the SA node, and spreads through the heard via the bundle branches to the purkinje fibers.
As signals are transmitted through the purkinje fibers, the walls of the heart contract, which pushes blood out of the heart.
When the walls of the heart relax, the heart fills with blood.
All phases of the heart beat impulse are visualized as distinct phases of an electrocardiogram on an EKG machine. Contraction moves from the atria to the ventricles.
Systole: Contracted, blood is forced out.
Diastole: Relaxed, blood is filling. The pressure of blood in the heart changes as the heart contracts (systolic) and relaxes (diastolic).
This can be measured with a sphygmomanometer, which dects when the external pressure of a cuff surrounding an artery is equal to the systolic pressure of the artery, and when it is equal to the diastolic pressure of the artery.
Blood pressure is correlated to heart and circulatory health. Blood Vessels Three major kinds:
Arteries- carry blood away from the heart. Muscular walls to allow for expansion and contraction due to heartbeat.
Capillaries- smallest blood vessels (diameter of a single blood cell). Allow for exchange of materials with other cells. The only exchange surface of the circulatory system.
Veins- carry blood back to the heart. Some muscle in their walls, but not as much as arteries. Unidirectional valves to prevent backflow of blood. All blood flows:
Heart Artery Arteriole Capillary Venule Vein Heart As blood moves through capillaries, bulk flow (due to pressure) causes materials to move out of circulation into the interstitial fluid (and from there to body cells).
Osmotic pressure causes materials to move from the interstitial fluid into circulation. The relationship between surface area, vessel diameter, velocity of blood flow and pressure all contribute to the exchange of materials between the circulatory system and the body.
All body cells are within a distance of a few cells of the circulatory system (capillaries).
Given the massive total surface area of capillaries, but their single-cell diameter, it is calculated that there are ~150000 kilometers (~60000 miles) of capillaries in the human body. It is physiologically impossible to have blood flowing through all capillaries in the body simultaneously. This would cause a precipitous decrease in pressure that stopped materials exchange ("shock").
To prevent this, blood flow through capillaries is modulated by precapillary sphincter cells that constrict or relax to prevent or allow blood to flow through the capillaries as required by the body. Since veins have the lowest blood pressure, they require valves to prevent the back-flow and pooling of blood.
This can become a problem as the body ages. Much of the fluid that returns to the circulatory system first moves to the lymphatic system before returning to the blood. Components of Blood Blood is a liquid tissue.
There are two major components:
Cells- 3 major kinds:
Plasma- The liquid portion of the blood, made of water, ions, nutrients, wastes, and proteins -Erythrocytes: red blood cells. Carry oxygen and carbon dioxide.
-Leukocytes: white blood cells. Involved in the immune system.
-Platelets: Involved in clotting. All blood cells originate from the same population of stem cells ("hematopoetic") in the bone marrow. Clotting: When a vessel is damaged, a blood clot forms.
Clot formation requires an elaborate cascade of proteins (mediated by platelets) that trigger the conversion of prothrombin to thrombin.
Thrombin triggers the conversion of fibrinogen to fibrin.
Fibrin forms a network of fibers that catch erythrocytes and forms a "scab". Embolism Aneurysm Atherosclerosis cause symptoms Treatment cause symptoms Treatment cause symptoms Treatment In animals, transport is the responsibility of the circulatory system and the respiratory system. The respiratory surface In order to exchange gas with the environment, animals need a respiratory surface.
Characteristics of a respiratory surface:
in contact with the circulatory system and the environment
large surface area.
Some respiratory surfaces: skin (amphibians), gills (fish), lungs (terrestrial vertebrates). Insects: Trachea Insects bring air into the body via a series of external openings (spiracles).
Air is brouch in to a system of tubes (tracheae), and air sacs which branch into tracheoles, where gas is exchanged with body cells. Fish: Gills Gills are adapted to exchange dissolved gases between the circulatory system and water.
Oxygen rich water flows into the mouth and past the gills.
As the water moves accross the gill, gas is exchanged. Animals with gills maximize exchange by having the direction of blood flow opposite the direction of water.
This type of system is known as a "countercurrent multiplier".
It allows for diffusion of oxygen into the blood, even at relatively high oxygen concentrations in the circulatory system. Fish are not the only animals who have gills. Birds: Lungs Birds and other terrestrial vertebrates bring air into the body through the mouth.
From the mouth, air enters the respiratory system where it travels to the lungs.
The lungs serve as the respiratory surface of the body.
Following gas exchange, air is expelled from the body the compressing the lungs.
Birds maximize gas exchange by keeping air in the body longer than mammals do. The human respiratory system is typical of mammals Air enters the system through the nose (into the sinuses) and mouth.
It moves into the respiratory system in the pharynx, passing in to the trachea.
From the trachea, air moves to the bronchi, which lead to the lungs.
Inside the lungs, the bronchi split into a series of bronchioles.
At the end of each bronchiole is a series of alveoli, which are the mammalian respiratory surface.
Larynx: a series of chords of tissue that cover the opening to the trachea and allow for vocalization (the "voice box").
The epithelium that line the respiratory system are covered in cillia and produce a mucus to trap foreign particles in the air. A group of alveoli Sinus Larynx Trachea Bronchi Diaphragm Breathing The inhalation and exhalation of air is controlled by the expansion and contraction of the diaphragm. When inhaling, the diaphragm causes the rib cage to expand, which makes the lungs negatively pressurized, and causes air to enter the system. To exhale, the diaphragm causes the rib cage to contract, expelling air. Alveoli Up Close: The alveoli are surrounded by a dense network of capillaries.
As blood moves into the alveolar capillaries, it exchanges oxygen and carbon dioxide with the air in the alveoli (other substances in the air and blood can be exchanged, too). Hemoglobin! The protein that carries oxygen in the blood.
Erythrocytes are essentially just bags of hemoglobin. They don't even have a nucleus at maturity! Gas Loading The diffusion of oxygen and carbon dioxide into and out of the blood is a function of the pressures of those gases at different points in the circulatory system.
Gases always go from higher partial pressure to lower partial pressure. Hemoglobin's affinity for oxygen is a function of pH and the partial pressure of Oxygen in the environment that hemoglobin is in.
Lower partial pressure of oxygen (due to the body using more oxygen), more likely to unload oxygen.
Lower pH (due to increased carbon dioxide concentration), more likely to unload oxygen. Carbon Dioxide The transport of carbon dioxide is also mediated by red blood cells.
Hemoglobin has some affinity for carbon dioxide.
The enzyme carbonic anhydrase will convert carbon dioxide and water into carbonic acid.
The carbonic acid is then converted into bicarbonate ions.
The bicarbonate ions exist in the plasma and function as a pH buffer.
At the lungs, the bicarbonate ions are converted back to carbon dioxide, before diffusion to the alveolar space for exhalation. Control The control of respiration is a function of both voluntary and involuntary nervous processes.
Sensors in the aorta and carotid arteries respond to changes in blood pH.
As carbon dioxide concentration in the blood increases, pH of the blood decreases.
This drop in pH will cause the medulla oblongata in the brain to increase breathing rate and depth.
Homeostasis is a blood pH of ~7.4. Blood pH lower than ~6.8 or higher than ~7.8 is Fatal. Asthma cause symptoms Treatment Emphysema cause symptoms Treatment Infant Respiratory Distress cause symptoms Treatment A buildup of a plaque of cells and cholesterol in blood vessels, decreasing the diameter of the vessel. The blockage of a vessel with a clot. The failure of a vessel wall. Frequently none until more serious complications develop.
Cholesterol monitoring is utilized.
Can be visualized in X-Rays, and other visualization techniques. medication, diet modification, lifestyle modification.
surgery: stents Depend on where the blockage occurs
Coronary embolism: "Heart attack"
Cerebral embolism: Ischemic stroke Depends on the nature of the blockage.
Surgical intervention may be required in life-threatening situations. Depend on where the aneurysm occurs
Cerebral aneurysm: hemmorhagic stroke. Depends on the location of the aneurysm.
Surgical intervention is usually required. Constriction of bronchioles, decreasing airflow. Sudden onset of wheezing, feeling of not being able to breathe. medication (inhalers, pills)
trigger avoidance. decrease in alveolar surface area.
Usually caused by smoking or other environmental influences. chronic shortness of breath. Chronic condition. Mediated by oxygen in extreme cases. Incomplete lung development in premature infants.
Lack of "surfactant" production in alveoli leads to collapse of alveolar airspaces. Difficulty breathing. Cyanosis (blueish purple coloration) Artificial surfactant administration.
The leading neonatal cause of death in the developed world. Big Questions: Make Sure You Can: Why do organisms need to internally transport substances?
How do organisms accomplish the process of transport?
What happens to organisms if they are unable to transport material? Plants: Explain how material is transported throughout a plant at the root, stem, and leaf.
Relate transport processes to aspects of water potential.
Explain how transpirational pull is generated and maintained.
Explain how sap is transported through the phloem from source to sink.
Describe adaptations that plants have made for arid climates. Animals Data showing relationship between body mass of infant and surface tension in lungs, correlated to cause of death Describe the evolutionary trends of circulatory and respiratory systems.
Explain the structure and functions of all parts of the mammalian circulatory and respiratory systems.
Relate the transport of material by the circulatory and respiratory system to changes in pressure.
Explain the causes, effects, and treatments of various disorders of the circulatory and respiratory systems Tell it to me proper! Speak to me of these things The Blood Mobile CLICK