Transport in Plants and Animals

The cellular level

The cellular level

The uptake and release of water and solutes by individual cells example water and mineral absorption by root cells

The tissue level

Short distance transport of substances from cell to cell at the level of tissues and organs example loading sugar from mature cells of leaves to sieve tube elements of phloem

The Whole plant

Long distance transport of sap within xylem and phloem over the whole plant

Lateral Movement

refers to movement of water and solutes from one place to another in a plant tissue or organ. It usually occurs along the radial axis of the plant e.g. From the outside (circumference of root) to inside (centre of root), or vice versa

Plasma membrane

Controls the passage of substances between the cell wall and the cytoplasm

Tonoplast

Controls the passage of substances between the cytoplasm and the large central vacuole

Apoplast

a continuous compartment forms by the cell walls of adjacent cells

Symplast

a continuous compartment forms by the cytoplasm of adjacent cells if plasmodesmata is present

Trans-membrane pathway

substances move out of one cell through the plasma membrane, across the cell walls, and into the neighbouring cell through its plasma membrane. These substances continue moving along adjacent cells by means of the same mechanism

Apoplast mathway

water flows through cell walls and extra cellular spaces and carries solutes with it. Substances will only move through the plasma membrane when the destination is reached

Symplast pathway

water (moves by osmosis) and solutes travel from cell to cell via plasmodesmata. Requires only one crossing through the plasma membrane. After entering one cell, solutes and water move from cell to cell via plasmodesmata

Vertical movement

Refers to movement of water and solutes from one place to another in a whole plant. It usually occurs along the vertical axis of the plant, in xylem or phloem

Bulk flow

The movement of a fluid driven by pressure

Transport in the root

Water and mineral salts from soil enter the plant through the epidermis of the roots, across the root cortex, pass into the stele, and then flow up xylem vessels to the shoot system

Nitrate ions

They are essential for the synthesis of amino acids, proteins, enzymes, and chlorophyll, which are crucial for plant growth and development. These compounds support the production of structural and functional components needed for transport mechanisms within the plant

Phosphate ions

They are key components of ATP (adenosine triphosphate), which provides energy for active transport processes in plant cells. Phosphates are also part of DNA and phospholipids, aiding cell division and membrane formation

Magnesium ions

They are central to the chlorophyll molecule, enabling photosynthesis to produce energy required for active transport. Magnesium also activates various enzymes involved in energy transfer and transport processes

Most of water absorption from the soil occurs:

• Near the root tip as the epidermis here is permeable to water

• Through the root hairs, which are extensions of epidermal cells that increase the surface area of the root.

• Through the mycorrhizae i.e. Symbiotic relationships between fungi and roots. The hyphae absorb water and selected minerals and then transfer them to the roots of the host plant.

two pathways of water flow

1. Water flows into the walls of epidermal cells and start flowing to the parenchyma cells of the cortex via the apoplast pathway. This process is not selective as the cell wall is permeable to all substances. It is the preferred pathway as it offers the least resistance.

2. Water flows across the plasma membrane of the epidermal cells and is transported to the parenchyma cells of the cortex via the symplast pathway. As the plasma membrane is selectively permeable, selective absorption of ions is possible

Uptake of mineral ions from soil to epidermis

As the root respires, CO₂ gas is released. It dissolves in the water film around the soil crumbs, rendering the solution slightly acidic. This causes the cations (+vely charged ions) to be released and hence the root will actively absorb them. The epidermal cells actively pump H⁺ ions out of them due to a proton pump.

The effects of proton pump

• The extracellular environment of the epidermal cells becomes positively charged compared to the intracellular environment.

• A difference in proton concentration results across the cell wall

  Positively charged ions such as K⁺ move into the cell through the specific ion channels on the membrane. (+ve ions move into a region of -ve charge) The difference in the proton concentration drives the active transport of -vely charged ions e.g. Cl^-, SO₄^2-, NO₃^-. In fact as H⁺ ions flow back into the epidermal cells, they drag in with them the –ve ions (example of co-transport).

Transport from epidermis to root cortex

Water and mineral ions move across the root cortex up to the enoddermis mainly via the symplast route and apoplast route

Symplast route

water crosses one cell wall and one plasma membrane and then runs through the plasmodesmata in the symplast

Apoplast route

water runs through the extracellular continuum formed by the cell walls, crosses into one cell wall, crosses no plasma membrane

Transport from root cortex to xylem

when water and mineral ions reach the endodermis (innermost layer of the root cortex), the Casparian strip (or band) blocks the apoplast pathway

Casparian strip

this is a belt of an impermeable waxy material called suberin that runs all around the endodermal cell. Therefore, all water and minerals that will be transported up the plant must cross into a cell and pass through a plasma membrane i.e. Enter the symplast pathway

Advantages of the Casparian Strip

• It slows down the flow of water through the root

• it controls the entry of toxic substances and fungal pathogens as water passes through the plasma membrane

• it enables the plant to control its chemical composition, thus striking a balance in the concentrations of essential nutrients

Root pressure

Refers to the  pressure exerted by root tissue that forces liquid up the xylem. This pressure arises due to the xylem sap (water) having a lower (more –ve) water potential than the soil. This arises from the accumulation of ions in the stele. The –ve potential draws water into the stele, which exerts pressure upwards

Vertical transport

Water rises up the xylem from to the root to the stem and shoots against gravity. Water rises up the xylem due to: Root pressure that pushes the xylem sap upwards and The transpiration-cohesion-tension mechanism that pulls the xylem sap upwards

The Transpiration- Cohesion-tention mechanism

The transpiration-cohesion-tension mechanism explains how water moves upward through plants. It relies on transpiration, cohesion, and tension. This process drives water transport from roots to leaves without requiring energy.

Transpiration

Refers to the evaporation of water at the stomata in the leaves

Cohesion

Refers to the tendency of water molecules to stick together due to the presence of hydrogen bonds. Cohesion is responsible for an unbroken column of water being pulled all the way from roots to the leaves

Adhesion

This refers to the tendency of water molecules to stick to the cell walls. Adhesion helps water to rise up the plant against gravity, as water adheres to the hydrophilic walls of the xylem vessels due to hydrogen bonds

Vessel Diameter

As xylem vessels have a small diameter they ensure a greater influence of adhesion forces thus helping water to rise up the plant against gravity. As water evaporates from the cells in the leaves and a resulting tension in the remainder of the xylem’s water owing to its cohesion, this pulls up more water to replace water that has been lost

Cavitation

This occurs when an air bubble gets blocked in the xylem vessel. In nature cavitation never occurs except When the plant is exposed to a lot of radiation or/and When the temperature falls below zero or it is very high

The role of xylem

Transport water and mineral ions for support

The cell types of xylem

It consists of 4 cell types: tracheids, vessel elements, parenchyma and fibres

Xylem vessels

Are mainly responsible for the transport of water in flowering plants. They are very long tubular structures formed when several vessel elements fuse together

Adaptation of xylem vessels for efficient transport of water

• Vessel diameter is wide to minimise frictional resistance.

• Vessels also lack cytoplasm that would impede water flow.

• Lignification prevents walls from collapsing because of tension.

• Lignin deposition may be annular, spiral or reticulate. Absence of cross walls.

• Formation of a continuous tube helps reduce frictional resistance

Lenticles

these are spaces between loosely arranged cork cells in the bark of trees

Transport of water in the leaf

Water arriving in the xylem vessels in the leaf has a higher water potential than the mesophyll cells. Thus water moves OUT of the xylem into the mesophyll cells largely through the apoplast pathway. Water evaporates and diffuses out of the leaf through the stomata

Stomata

It is a gap in the epidermis. A pair of specialized epidermal cells called guard cells control its opening and closing. The stomata lead to a honeycomb of air spaces. This increases the surface area through which: CO₂ diffuses to the photosynthetic cells in the mesophyll and H₂O evaporates and is then lost through the stomata

Functions of stomata

• Gaseous exchange of CO₂ and O₂ between the leaf and the atmosphere

• When water is lost, the plant cools down as heat is eliminated.

• Due to uptake of water, minerals are transported along the plant.

Structure of Stomata

Each stoma consists of a pore between a pair of guard cells. These are surrounded by subsidiary cells. Dicots generally have sausage shaped guard cells. Grasses and sedges have dumb-bell shaped guard cells

Adaptations of Guard cells

• Inner wall (cell wall closer to stoma) is thicker due to more cellulose deposited on it. Therefore it is less elastic than the outer wall.

• Unlike other epidermal cells they contain chloroplasts

Mechanism causing stoma open and close

In the majority of plants stomata are open during the day and closed at night. During the day, light is available and so the stomata open allowing CO₂ to diffuse into the leaf enabling photosynthesis. At night, in the absence of light, photosynthesis cannot proceed and so stomata remain closed thereby conserving water

Opening mechanism of the stomata

When stomata are about to open, H⁺ ions are actively pumped out of guard cells by means of a proton pump. This leads to the entry of K⁺ ions into the guard cells, via specific ion channels, from the surrounding epidermal cells. The guard cells’ increase in positive charge due to the entry of K⁺ is balanced by the entry of negatively charged ions e.g. Cl^-. These are dragged into the cells along with the H⁺ ions that diffuse back into the guard cells down a concentration gradient. This lowers the water potential within guard cells. Therefore, water enters by osmosis, rendering them more turgid. When water enters the guard cells their length remains constant but their volume increases. (Volume may increase by up to 50%). However, the thickness of the cell wall of the guard cells is not even: Outer wall is thinner and more flexible and the Inner wall is thicker and not so flexible

Closing mechanism of the stomata

The stomata close by reverse process. K⁺ ions diffuse out of the guard cells passively, decreasing the water potential of the neighbouring epidermal cells. Water flows out of the guard cells by osmosis. Turgidity is lost; guard cells collapse thus closing the stoma in between

Factors influencing stomatal movement

• Water: Some guard cells monitor their own water potential. If it is too low (i.e. Water is lacking), they release abscisic acid, a plant hormone. This causes K⁺ ions to move out of the guard cells leading to the closure of the stomata, preventing loss of H₂O from the plant

• CO₂: During the day CO₂ level in air spaces is low as the cells use it for photosynthesis. This favours the opening of the stomata, allowing CO₂ to diffuse in. At night only respiration occurs in the plant. This increases the CO₂ level in the air spaces in the leaf, leading to the closure of the stomata.

• Temperature: At low temperature guard cells behave sluggishly and tend to remain closed. As the temperature rises they act more rapidly, thus stomata tend to remain open. Yet is temperature rises further, the rate of respiration increases releasing a lot of CO₂ that causes stomata to close

• Light: Light activates the blue-light receptor on the plasma membrane of guard cells. This stimulates the active transport of H⁺ through the proton pumps leading to opening of stomata. Light also triggers off photosynthesis in chloroplasts in guard cells, making ATP available for active transport of H⁺

• Circadian rhythms: All eukaryotic organisms have internal clocks that somehow keep track of time and regulate cycles. Cycles that are repeated daily (i.e. Every 24 hours) are called circadian rhythms. Guard cells have a built-in circadian rhythm. In fact, if a plant is kept in the dark, its stomata will continue their daily rhythm of opening and closing.

The rate of diffusion depdens on

• the diameter of the stomata: diffusion rate is greater through small stomata than through large stomata

• the distance between stomata: when stomata are close together the diffusion shells of adjacent stomata overlap. This forms one large area from which water diffuses to the atmosphere and reduces transpiration rate

Factors affecting transpiration

• Light- indirectly affects transpiration as it leads to opening of stomata due to photosynthesis in guard cells.

• Humidity- high transpiration rate favoured by low humidity as concentration gradient of water vapour between leaf air spaces and air is large.

• Temperature- high temperature favours high transpiration rate as temperature lowers humidity of air, and provides latent heat of vaporisation, and increases kinetic energy of water molecules.

• Air movements- favour a high transpiration rate. Air movements sweep away water vapour in the air around stomata, increasing the concentration gradient of water vapour between the leaf air spaces and air.

• Atmospheric pressure- the lower the atmospheric pressure (e.g. In high altitudes) the greater the rate of transpiration.

• Water supply- if water in soil is lacking, the plant wilts and stomata close, thus transpiration stops.

• Leaf structure- influences transpiration depending on whether it shows adaptations against water loss or not.

Translocation of phloem sap

chemical analyses of phloem sap indicated that its main component is sucrose (may reach 30%). It may also contain minerals, amino acids and hormones. Phloem sap samples are extracted by means of aphids, small insects. The aphid drives its stylet, which is a sharp mouthpart that functions like a hypodermic needle, between the epidermal cells and withdraws sap from a sieve tube cell. If the aphid is anaesthetized using ether, its body can be carefully cut away, leaving the stylet. Phloem sap is then collected and analysed

Translocation

Refers to the transport of the products of photosynthesis by phloem to the rest of the plant. translocation may occur along the vertical axis of the plant or along its radial axis. in this process sieve tubes carry food from a sugar source to a sugar sink

Sugar source

Is a plant organ where sugars are produced by photosynthesis or by the breakdown of starches. Mature leaves are the primary sugar sources

Sugar sink

An organ where sugars are stored (as starches in tubers) or used (roots, stems, growing parts of plant)

Dodder

A parasitic plant. Sucker-like process that penetrate the host attach to the latter’s phloem

Aphid

Parasitic insect inserts stylet into phloem

Autoradiography

This technique may be used to determine the passage of substances through specimens, sites of reactions and their rates. A plant is enclosed in a perspex box in an atmosphere containing 14CO₂. The path of the 14C used to build sucrose is then traced by means of autoradiography. In this process plants of the same species are exposed to radioactive C-14 for varying amounts of time. Then they are fixed and processed. They are placed in contact with a photographic plate e.g. X-ray film. After sufficient time passed, the images obtained showed the distribution of the radioactive sucrose in phloem tissue because the regions where radioactivity was present appear ‘fogged’.

Phloem loading

Sucrose formed in the leaf mesophyll cells by photosynthesis, may reach the sieve tube elements via the symplast and/ or the apoplast pathways. When sucrose reaches the companion cells (sometimes called transfer cells) and the sieve tube elements, it switches from the apoplast to the symplast pathway by secondary active transport

Pressure flow model

as sucrose is formed in the leaf mesophyll cells by photosynthesis, may reach the sieve tube elements via the symplast and/ or the apoplast pathways. When sucrose reaches the companion cells (sometimes called transfer cells) and the sieve tube elements, it switches from the apoplast to the symplast pathway by secondary active transport. This decreases the hydrostatic pressure at the sink end of the tube. The building of pressure at one end of the tube (source) and reduction of that pressure at the other end (sink) cause water to flow from source to sink, carrying sugar along. This model may be used to explain why in the phloem movement is not uni-directional like xylem flow. In fact the phloem sap can move in any direction, as long as a hydrostatic pressure gradient exists.

Role of phloem

Transport organic solutes

Cell types

Sieve tube elements, companion cells, phloem parenchyma, phloem fibres and phloem sclereids

Sieve-tube elements

These are living cells, interconnected by perforations in their end walls formed from enlarged and modified plasmodesmata (sieve plates). Lateral walls are thickened due to higher amount of cellulose deposited. These cells retain their plasma membrane, but they have lost their nuclei and much of their cytoplasm. However, mature sieve elements retain a modified endoplasmic reticulum, mitochondria, numerous types of proteins and specialized sieve element plastids. Most of these components are arranged along the lateral walls of the sieve elements. The absence of a nucleus implies that sieve tube elements rely on associated companion cells for their maintenance. In fact they are connected together by means of plasmodesmata companion cells are smaller than sieve tube elements. They have thin cellulose walls, a nucleus and are very rich in organelles. This shows that companion cells are involved in the active transport of soluble food molecules into and out of sieve-tube elements through porous sieve areas in the wall

Adaptations of Xerophytes

• Small, thick leaves (reduces SA:V)

• Secrete a heavier layer of cuticle over the leaf epidermis.

• Dense covering of epidermal hairs to trap humid air around them.

• Leaves produced only if water is abundant, and shed them when it is scarce.

• Cacti have spines rather than typical leaves, so photosynthesis confined to fleshy stems.

• Succulents have fleshy leaves in which water is stored.

• Ammophila arenaria, marram grass, rolls up its leaves trapping the humid air around it.

• Some trees hang leaves vertically thus avoiding mid-day sun e.g. Eucalyptus.

• Stomata concentrated on the lower leaf surface.

• Fewer stomata in number but high stomatal density therefore less water lost due to overlapping of diffusion shells.

• Sunken stomata e.g. In Pinus (pine tree)

• Some plants have a tap root system. Roots grow to great depth, sufficient to reach underground water supplies e.g. Mesquite tree, acacia, oleander.

• Cacti have shallow but extensive fibrous root systems that effectively trap water at the surface of the soil following even light rains.

Adaptations of Halophytes

• Accumulate Na⁺ and Cl^- in leaves.

• Salt glands in leaves excrete salt thus reducing the danger of poisoning by accumulated salt e.g. Tamarisk.

• Succulence.

• Open stomata during the night and close them during the day. [CAM plants]

Adaptations of mesophytes

• Adapted to grow in well-drained soils with their aerial system exposed to moderately dry air. Loss of water is substantial but it is controlled by closure of stomata.

• Deficit of water created during the day is compensated as water uptake continues during the night.

• Woody perennial Mesophytes shed their leaves before winter sets in, thus water loss is reduced before water freezes.

• Herbaceous perennials lose aerial system during the unfavourable season, surviving as underground organs e.g. Bulbs, corms and rhizomes

• Survive winter as dormant seeds

Adaptations of Hydrophytes

• Tend to form thin leaves that lack characteristics to conserve water.

• Cuticle tends to be very thin.

• Have no stomata (if leaves are completely submerged in water.)

• Vascular tissue is reduced, especially xylem. Plants whose leaves float on the surface, e.g. Water lily: have stomata on their upper epidermis only.

• Tend to have large air spaces to provide buoyancy.

• Have several layers of palisade mesophyll cells above the spongy mesophyll cells.

Transport in Unicellular organisms

Unicellular animal-like protoctist have a high SA:V. Thus, they rely on diffusion for gas, nutrients and waste exchanges with the external environment that surrounds them.

Transport in Invertebrates with a cavity

Cnidarians, such as the sea anemone and the hydra, and flatworms, have a sac body plan. This makes a circulatory system unnecessary. In a sea anemone, the body wall is two cells thick. Thus, the cells are either part of an external layer, or they line the gastrovascular cavity. The gastrovascular cavity serves the dual functions of digestion and distribution of substances. In either case, each cell is exposed to water and can independently exchange gases and rid itself of wastes, by diffusion. Nutrients easily pass from the inner layer to the outer layer of cells because the distance they have to travel is short. Planarians and other flatworms also have gastrovascular cavities that exchange materials with the environment through a single opening. The flat shape of the body and the branching of the gastrovascular cavity throughout the animal ensure that all cells are bathed by a suitable medium.

The need for a circulatory system

a gastrovascular cavity is inadequate for internal transport within larger animals having many layers of cells as: their SA:V is small, distances that materials have to travel within the body increase and quantity of materials moving in and out of the body increases. This renders diffusion an inefficient method to distribute substances around the body. Thus, circulatory systems evolved.

Circulatory system

Transports fluid in one direction, powered by a pump that forces the fluid through vessels that reach throughout the body. All circulatory systems have 3 major parts:

• A fluid, blood that serves as a medium of transport

• A system of channels, or body vessels that conduct the blood throughout the body

• A pump, the heart that keeps blood circulating

Open circulatory system

the fluid is not contained in vessels. This system consists of a heart and blood vessels that lead to spaces where the fluid, haemolymph, directly bathes cells before returning to the heart. This means that blood and interstitial fluid (fluid filling spaces between cells) are not distinct from each other. When the heart contracts it pumps haemolymph through vessels out into the hemocoel. This is a network of blood-filled spaces (sinuses) that surround the internal organs. Here, chemical exchange occurs between the haemolymph and the body cells. When the heart relaxes, its volume increases while the pressure decreases. This causes suction of the haemolymph back into the circulatory system through pores called ostia. Valves prevent haemolymph from moving out of the heart through the ostia. Body movements of the organism help the haemolymph to circulate through the sinuses, as well. Molluscs and arthropods typically have an open circulatory system. Invertebrates with open circulatory systems can be fairly active as their respiratory system branches in a way that allows the outside environment to come close to internal tissues e.g. In insects the respiratory system is independent of the circulatory system.

Closed Circulatory System

here the blood remains within vessels and is distinct from interstitial fluid. A heart pumps blood around the body under high pressure. Distribution of blood to different tissues can be adjusted, depending on demand. The only entry and exit to the system are through the walls of the blood vessels. The arteries conduct blood away from the heart and branch into smaller vessels called arterioles. These diverge into a network of very tiny, thin vessels called capillaries. Materials diffuse between the interstitial fluid and blood across the walls of capillaries. Exchange also occurs between the interstitial fluid and body cells. Blood then collects into slightly larger vessels, called venules, which unite to form the veins. These carry blood back to the heart. Annelids are the simplest animals with a closed circulatory system. In an earthworm, three major vessels are present: the dorsal vessel and two ventral vessels. The dorsal vessel functions as the main heart, pumping blood forward by peristalsis. Near the worms’ anterior (front) end, 5 pairs of vessels loop around the digestive tract, connecting the dorsal and ventral vessel. The paired vessels function as auxiliary hearts, pumping blood ventrally. Blood flows towards the posterior end in the ventral vessel. Blood in annelids contains haemoglobin, dissolved in the plasma rather than being carried in red blood cells. It is responsible for the transport of oxygen. Most vertebrates, including humans, possess a closed circulatory system. A muscular heart is found in a ventral position towards the front end of the organism. It pumps blood rapidly through the various blood vessels in the system. Oxygen is carried by haemoglobin in red blood cells.

Single Ciculation

This is observed in fish. Blood flows in a one-circuit pathway. The heart has two chambers: One atrium- a chamber which collects blood from the body and One ventricle- a chamber which pumps blood to the body. The ventricle pumps blood under pressure to the gills, where it is oxygenated. Carbon dioxide is removed as well. Oxygenated blood then flows to the capillaries in all other parts of the body. When blood flows through a capillary bed, blood pressure, i.e. the hydrostatic pressure that pushes the blood through the vessels, drops substantially. Therefore, oxygen rich blood leaving the gills flows to other organs in the fish quite slowly, but the movements of the body whilst swimming aid the process.

Double circulation

Terrestirial vertebrates have adapted themselves to breathing air on land by developing a double circulatory system. Thus blood flows through two circuits. The heart pumps blood both to the lungs (pulmonary circulation) and to the tissues (systematic circulation).

Amphibian Heart

It have 3 chambers: a left and right atrium and one ventricle. It have a double circulation, with blood flowing to the tissues and to the lungs and skin. The presence of one ventricle implies that oxygeneted blood from the lungs mixes with deoxygentes blood from the body in the ventricle. Amphibians overcome this problem by obtaining much of their oxygen from the mouth surface and their skin surface. This limits amphibians to wet and a humid terrestrial environment, as their skin surface must be kept moist.

The Reptile heart

It is a 3 chambered heart, but the single ventricle is partially divided. This division helps to separate deoxygenated blood from oxygenated blood. Thus more oxygen can reach the body extremities. Hence reptiles are better adapted to surviving in a terrestrial environment

Efficiency of a circulatory system

1. Pressure Differences- The heart generates high pressure for systemic circulation to overcome resistance in long, extensive vessels. Pulmonary circulation operates at lower pressure to prevent damage to delicate lung capillaries. 

2. Fast Blood Flow-High pressure and rapid flow ensure quick delivery of oxygen and nutrients and the swift removal of wastes.  This sustains a high metabolic rate, essential for mammals' energy-demanding activities.

3. Steep Concentration Gradient- Continuous blood flow maintains a gradient for oxygen, carbon dioxide, nutrients, and waste, promoting efficient diffusion across exchange surfaces like alveoli and capillaries. Efficient diffusion is critical for gas exchange, nutrient uptake, and waste removal

Advantages of Double Circulation

1. Separation of Oxygenated and Deoxygenated Blood-Prevents mixing, allowing tissues to receive fully oxygenated blood for maximum efficiency. 

2. Efficient Oxygen Delivery- Systemic circulation delivers blood at high pressure, meeting the high oxygen demands of active tissues.Pulmonary circulation is maintained at a lower pressure to optimize gas exchange and protect lung structures. 

3. Flexibility in Blood Distribution- Blood flow can be adjusted based on tissue demands (e.g., increased flow to muscles during exercise). 

Adaptation for High Metabolism

Mammals, being endotherms, need a high metabolic rate to regulate body temperature, which double circulation supports through efficient oxygen and nutrient transport.

Outline Functions of the Circulatory System in Mammals

1. Transport of Respiratory Gases-Oxygen is transported from the lungs to tissues via hemoglobin in red blood cells. Carbon dioxide is carried back to the lungs as bicarbonate ions or dissolved in plasma. 

2. Transport of Metabolites-Glucose, amino acids, fatty acids, and other nutrients absorbed from the digestive system are delivered to cells. 

3. Removal of Metabolic Wastes- Waste products like urea and ammonia are transported to excretory organs (kidneys, liver) for elimination. 

4. Hormone Distribution- Hormones secreted by endocrine glands are distributed via the bloodstream to target organs and tissues.

5. Immune Function- White blood cells and antibodies circulate to defend against pathogens. 

6. Temperature Regulation-Blood helps distribute heat throughout the body, aiding thermoregulation. 

7. Clotting and Healing- Platelets and clotting factors in the blood prevent excessive bleeding and aid tissue repair.

The location of the human heart

It is found between the two lungs and just beneath the sternum in the thorax. It is about the size of a clenched fist.

Pericardium

Surroundes the heart and consist of: an inelastic white fibrous tissue layer that gives strenght and keeps the heart in its place and two membranes the outer membrane- attached to the fibrous tissue and the inner membrane attached to the heart

Pericardial fluid

Secretes by the two membranes in the pericardium which acts as a lubricant and it minimises friction when the heart beats

Function of pericardium

• prevents the heart from being over-streched

• prevents the heart from beinf overfilled with blood

Endocardium

A squamous epithelium lining the heart cavities. It provides a smooth surface for blood to pass over

Chambers of the mammalian heart

two upper thin-walled atria and two lower thick walled ventricles. The atria receive blood from the veins and pump it to the ventricles, which in turn pump it to the arteries. The right and left sides of the heart are completely separated

The right side of the heart

Deals with deoxygenated blood, which has a dark red colour. Right atrium receives blood from systematic circulation through the superior and the inferior vena cava. Right ventricle has a thin muscular wall. It pumps blood to the lungs, which are near the heart, via the pulmonary artery. Blood entering the pulmonary artery from right ventricle has a low pressure (2.1kPa).

The left side of the heart

Deals with oxygenated blood, which has a bright red colour. Left atrium receives oxygeneted blood from the lungs, through the pulmonary veins. Left ventricle has a muscular wall that is 3 times as thick. It pumps blood to the whole body through the aorta. Blood entering the aorta from the left ventricle has a high pressure (14.0kPa)

Chordae tendinae

fibrous chords attached to the flaps of the valves. These are attached to the papillary muscles that are extensions of the inner wall of the ventricles.

Coronary sinus

A small vein which transprts blood to the right atrium. It carries deoxygeneted blood which has been circulating in the heart.

Heartbeat

The heart beats about 70 times a minute, and each heartbreat lasts about 0.85s. Each beat of the heart is called a cardiac cycle. It consits of a sequenxe of contraction (systole) and relaxation (diastole).

Myogenic

The muscle cells contract on their own, without nervous stimulation

Intercalared disces

The gap junctions between the cardiac muscle cells, help spread electrical impulses from cell to cell.

Desmosomes

help attach muscle cells to each to enable the heart muscle withstand the pressure generated within.

Pressure curve

Show how pressure varies in atria and ventricles during a cardiac cycle

Pulse

A wave effect that passes down the walls of the atrial blood vessels when the aorta expands and then recoils following ventricle systole.

Factors affecting the heart rate

• Exercise- causes a faster pulse rate as more blood is needed around the body

• Age- Young children have a faster heart beat due to their high rate of growth and high SA:V ratio

• Emotions- The pulse rate increases when one is angry, afraid or excited

• Position- When standing the pulse rate is faster than when lying down

• Gender- Females tend to have a higher pulse rate than males

The heart is accelerated by

• Emotions: the pulse rate increases when one is angry, afraid or excited

• Decreased activity of baroreceptors in the arteries, left ventricle and pulmonary circulation

• Inspiration

• Most painful stimuli

• Hypoxia

• Exercise

• Epinephrine (adrenaline)

• Thyroid hormones

• Fever

The heart declearated by

• Increase activity of baroreceptors in the arteries, left ventricle and pulmonary circulation

• Expiration

• Fear

• Grief