Circulatory System – Blood Vessels (part 2 of 4)

Blood vessels are the highway system of the body.

They are tubular structures that transport blood throughout the body.

There are approximately 60,000 miles/100,000kilometers of blood vessels in the human body; this ensures that every cell is within diffusion distance from a capillary.

There are 5 different types of blood vessels:
1. Arteries
2. Arteriole
3. Capillaries
4. Venules
5. Veins

1. ARTERIES
– Arteries are thick-walled blood vessels that carry blood, under high pressure from the heart out toward the extremities of the body.
– The blood in the arteries is usually under high pressure because the blood had just left the heart.
– The arteries carry oxygen-rich blood from the left side of the heart.
– As the arteries bring blood to the outer extremities of the body, they become smaller and smaller in diameter.

2. ARTERIOLES
– The major arteries branch into smaller arteries, eventually becoming arterioles.
– These small blood vessels’ walls contract to control blood flow to the organs.
– The amount of blood that flows into a particular tissue depends on the diameter of the arterioles.
– If an organ needs oxygen the arterioles relax and the arterioles diameter increases in size, increasing the blood flow to that organ.
– The arterioles can also contract, reducing the diameter and therefore the blood flow when needed.

3. CAPILLARIES
– Eventually blood vessels become the thickness of one cell. These very narrow blood vessels are call capillaries.
– While the blood moves through the capillaries, gases, hormones and other nutrients diffuse in and out of the blood and the surrounding tissue.
– Capillaries also collect the waste produced from the cells of surrounding tissue and brings them back toward the heart.
– Capillaries gradually increase in size, becoming larger vessels called venules.

4. VENULES
– When several capillaries join, they form veins called venules.
– Venules are very small blood vessels that allow blood to return from the capillary beds to larger blood vessels called veins.

5. VEINS
– Veins are thin-walled vessels that bring the blood back to the heart.
– The lowest blood pressure is found in the veins.
– Most veins run upward or against gravity, therefore they rely on skeletal activity (like walking and breathing) and muscle contractions (in the legs and other parts of the body) to help move the blood back to the heart.
– Veins also have valves in them that allow the blood to move in one direction and prevent the back flow of blood.

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Circulatory System – Blood (Part 1 of 4)

The Circulatory System is made up of 4 parts:
1. Blood
2. Blood Vessels
3. Heart
4. Lymphatic System

1. BLOOD
Blood is the only liquid connective tissue in the body.

Human adults have 4.7 liters of blood in their bodies.

Blood has roles in transport, regulation and protection.
– It transports oxygen, carbon dioxide, nutrients, hormones, heat and waste.
– It is involved in the regulation of body temperature, PH and the water content of cells.
– The body is protected from blood loss through clotting and against disease by PHAGOCYTIC WHITE BLOOD CELLS and ANTIBODIES.

PLASMA
– Plasma makes up 55% of the blood.
– It is a clear; straw-colored liquid, which is mostly water.
– It is the bloods SOLVENT (able to dissolve substances).
– It transports nutrients, waste products of metabolism, respiratory gases and hormones.
– There are 3 main PLASMA PROTEINS:
1. ALBUMIN
– Is the smallest and most numerous protein.
– It helps recover water that has been lost.
– It transports some of the steroid hormones.
2. IMMUNOGOBULIN (antibodies)
– Aids the immune system by attacking bacteria and viruses.
– Other globulins help in the transport of iron, lipids and fat-soluble vitamins.
3. FIBRINOGEN
– It plays an essential role in the clotting of blood, by providing the necessary protein network.
– Various ions act as solutes in plasma; they play key roles in osmotic balance, PH buffering and the regulation of membrane permeability.

BLOOD CELLS
Blood cells make up about 45% of the blood.

There are 3 main types of blood cells:
1. RED BLOOD CELLS (ERYTHROCYTES)
– They transport oxygen to all cells.
– The oxygen-carrying protein HEMOGLOBIN is the pigment that gives blood its red color.
– They are the simplest cells in the body; mature red blood cells lack a nucleus, ribosomes and mitochondria.
– They are also the most numerous cells in the body; 5 million/ml of blood.
– About 2.5 million are made every second in the red bond marrow.
– Mature cells are flattened and disc-shaped with a central depression.
– They are non-reproducing sacks of oxygen binding hemoglobin.
– The hormone, ERYTHROPOIETIN, triggers transformation of skin cells in the marrow to produce red blood cells.
– After circulating for 3 to 4 months in the blood, red blood cells are engulfed by liver and spleen SCAVENGER CELLS.

2. WHITE BLOOD CELLS (LEUKOCYTES)
– They contain a nucleus.
– Most live only a few days, although some, particularly LYMPHOCYTES can live for several months or longer.
– During infections white blood cells may only live for a few hours.
– The shape of their nuclei and the staining properties of their granules distinguish white blood cells from each other.
– The number and type of white blood cells can indicate a person’s health. Most infections stimulate an increase in circulating white blood cells.
– There are 5 classes of white blood cells:
1. NEUTROPHILS and 2.MACROPHAGES
– Are active in PHAGOCYTOSIS (the engulfing of particles by phagocytes); ingesting bacteria and cellular debris.
– Certain chemicals released by bacteria and inflamed tissue attract the white blood cells to the site.
– After engulfing the bacteria, neutrophils lysozymes are released that destroy the bacteria.
– Strong oxidants are then released, like peroxide and proteins called DEFENSINS that have antibiotic activity.
– Monocytes arrive after the neutrophils and enlarge to become macrophages, which clean up cellular debris and bacteria after an infection.
3. EOSINOPHILS
– They enter tissue fluid from the capillaries and release enzymes to combat allergic reactions.
4. BASOPHILS
– Intensify the inflammatory response when they enter the tissue from the capillaries.
5. LYMPHOCYTES
– They are the major combatants in the immune response.
– They are the B-CELLS, T-CELLS and the natural killer cells.
– These cells are active in fighting infections caused by viruses, bacteria and fungi.
– They are also responsible for transfusion reactions, allergies and the rejection of transplanted organs.

3. PLATELETS
– They are the small cell-like fragments that come from special white blood cells, called MEGAKARYOCYTES.
– They have no nucleus and live for about 5 to 9 days.
– Aged and dead platelets are removed by macrophages in the liver and spleen.
– Platelets release chemicals in blood clotting.

BLOOD TYPE
Humans have highly individualized blood that is credited to proteins and other genetically determined factors located on the surface of red blood cells and the plasma bathing the red blood cells.

The main types of blood are A, B, AB, and O.

Transfusions of blood are possible only when the blood types of the donor and recipient are compatible.

If the blood types are not compatible, proteins in the plasma will recognize foreign antigens and respond by causing the cells to AGGLUTINATE (clump) which will block the small vessels.

Type AB is considered the UNIVERSAL RECIEPENT (this person can receive blood from any type in the ABO blood group).

Type O is considered the UNIVERSAL DONOR (this type of blood can be given to any blood type in the ABO blood group).

Homeostasis

To stay alive the cells of an organism need proper nutrients, oxygen and it’s metabolic waste must be removed. This goal affects the organism’s interactions with its environment.

The component parts of any organism (whether it is one-celled or a human being) must work together to maintain a stable fluid environment that all of its cells require. There must be a relative consistency (a controlled sameness) of the organisms internal environment. This is the basic concept of Homeostasis.

Multicellular organisms must regulate their internal environment. Maintenance of a stable internal environment is critical to the well-being of an organism; regulatory mechanisms must be carefully controlled.

It is important that an organism keep its chemical processes occurring at the correct rate and time.

When living things are able to regulate these chemical processes precisely, they can maintain a stable internal environment.

HOMEOSTATIC CONTROL mechanisms help maintain, both physical and chemical aspects of an organisms internal environment within ranges that are favorable for cells to function.

3 COMPONENTS OF HOMEOSTATIC CONTROL:
1. SENSORY RECEPTORS: Cells that can detect stimulus (a change in the environment).
2. INTEGRATOR: The BRAIN processes the information about the stimulus and selects a response.
3. EFFECTORS: Carry out the response to the stimulus (MUSCLES&/or GLANDS)

FEEDBACK MECHANISMS are the controls that operate to keep chemical and physical aspects of the body within tolerable ranges.

A VARIABLE in the environment triggers the mechanism. A variable triggers change.

A POSITIVE FEEDBACK mechanism amplifies positive change.

in a NEGATIVE FEEDBACK mechanism, something alters the condition in the internal environment, and this triggers a response to reverse the altered condition.

Homeostasis is dependent upon positive or negative feedback mechanisms.

Photosynthesis

Photosynthesis is the reverse of Cellular Respiration.

The main end products of respiration are CO2 (carbon dioxide) and water, which are used as the starting material for Photosynthesis, and photosynthesis converts them into glucose and O2 (oxygen).

Photosynthesis is the ultimate source of all energy rich carbon compounds used by all organisms; it is responsible for the continual supply of atmospheric O2 (oxygen), without which all the aerobic organisms, that use oxygen would not exist.

Green plants, algae, some unicellular green flagellates and 2 bacteria groups are the only organisms that photosynthesize. Each year they release half of all the O2 (oxygen) in the atmosphere.

Plants use CO2 (carbon dioxide) when they produce O2 (oxygen). CO2 is converted to O2 during photosynthesis. At the same time, animals through their respiration process use this O2 from their metabolism and replace it with CO2, which is then used by plants to begin the cycle again.

Photosynthesis is a solar powered process. SUNLIGHT is a key component of the process.

Light is a form of ELECTROMAGNETIC ENERGY. When light meets matter, it can be reflected, transmitted or ABSORBED.

PIGMENT absorbs light. Plant pigment, CHLOROPHYLL (the main light-absorbing molecule of green plants), is a pigment that absorbs LIGHT ENERGY.

Chlorophyll is found in specialized structures called CHLOROPLAST; they give plants their green color. Each chloroplast contains all the chlorophyll and enzymes needed to complete the complex chemical reactions of photosynthesis.

Chlorophyll participates directly in LIGHT REACTIONS.

The site of photosynthesis is typically the leaf of green plants. Each cell has about 30 to 40 chloroplast.

The large amount of chlorophyll in the leaves of plants allows it to produce most of their own FREE ENERGY, by using photosynthesis.

Cells of green leaves-> Contain chloroplast organelles-> Filled with chlorophyll molecules-> Absorb light energy during photosynthesis

Photosynthesis involves 2 linked sets of chemical reactions:
1. The 1st is called the LIGHT-DEPENDENT REACTIONS
2. The 2nd set, which does the actual synthesizing of chemicals, is called LIGHT-INDEPENDENT or the CALVIN CYCLE.

In these 2 processes green organisms use energy from sunlight to make sugar.

Photosynthesis = Light-dependent reactions (produce energy) + Calvin Cycle (produce sugar)

1. LIGHT-DEPENDENT REACTIONS
– Light-Dependent Reactions are the conversion of light energy into chemical energy.
– In the first set of reactions, the chlorophyll absorbs energy that is striking the plants surface from sunlight. The Light-Reactions absorb the energy of sunlight and converts it to energy that is stored in chemical bonds.
– Once the light is absorbed the electrons of the chlorophyll become excited (a process where an electron gains energy). This energy absorption agitates the electrons within the chlorophyll. Some of these energized electrons are transferred where they can be used by the organism.
– The energy released from the electrons in the chlorophyll is used to do 2 things:
1. Split water molecules. When the water molecule is split, O2 (oxygen) is released into the atmosphere.
2. Make ATP. Some of the energy from the electrons in chlorophyll is used to change ADP to ATP.
– This energy is passed along until it reaches a particular pair of molecules that can process the energy. The energy released by the transferred electrons helps add a phosphate group to ADP, creating more ATP.
– Some of the produced ATP provides energy to run the 2nd stage of photosynthesis, the Calvin Cycle.
– As a result of the Light-Dependent Reactions, water is split and O2 (oxygen ) is given off. The plant uses some of the O2 for CELLULAR RESPIRATION and some is released into the atmosphere.

2. CALVIN CYCLE
– The 2nd stage, called the Calvin Cycle, uses the ATP given off by the 1st set of reactions.
– This step involves the storage of chemical energy into sugar molecules.
– It is called a “CYCLE” because it begins and ends at exactly the same point: Carbon Dioxide (CO2) molecules.
– The Calvin Cycle takes place in the chloroplast. The simple inorganic molecules of CO2 (carbon dioxide) is used to make a complex organic molecule.
– In this step, CO2 (carbon dioxide) is chemically reduced from hydrogen ions and turned into a carbohydrate (sugar molecule/glucose).

CO2 (Carbon Dioxide) + H (Hydrogen Ions) = CH2O (Carbohydrate)

– One sugar molecule is to be used by the plant cell.
– Many plants make more sugar than they need; this sugar is converted to starch and stored in the roots, tubers and fruits of plants, food that other organisms eat.
– Most organisms need the food manufactured by green plants in the process of photosynthesis.

The following reaction summarizes the chemical process of Photosynthesis:

6 CO2(Carbon Dioxide) + 6 H2O(Water){REACTANTS} -> C6 H12 O6(Glucose) + 6 O2(Oxygen) + 6 H2O(Water){PRODUCTS}

Cellular Respiration

Where does the energy come from that power the recharging of the ATP molecule?

Cellular Respiration is a chemical process that occurs in all living cells, when trapped energy in the bonds of food molecules are converted to the stored energy in ATP molecules.

Cellular Respiration is a series of chemical reactions that frees the energy in food molecules, making it available to cells.

The chemical process of Cellular Respiration starts when a food molecule (i.e. glucose) enters the cell and is acted upon by the enzymes in the cytoplasm of the cell.

The steps of Cellular Respiration are controlled by ENZYMES.

This process takes place in the MITOCHONDRIA, in the presence of oxygen and is called AEROBIC RESPIRATION (oxygen requiring).

Respiration is generally defined as OXYGEN-REQUIRING; but respiration can also occur WITHOUT OXYGEN (ANAEROBIC RESPIRATION).

There are 2 steps to the Cellular Respiration Process:
1. GLYCOLYSIS (ANAEROBIC RESPIRATION)
– Glycolysis is the 1st series of chemical reactions in cellular respiration, in which glucose is converted to pyruvic acid.
– The entire process can take place whether or not oxygen is present. So Glycolysis is sometimes referred to as ANAEROBIC RESPIRATION.
– It is a series of reactions that take place in the CYTOPLASM of the cell.
– Each chemical reaction is catalyzed (to cause an action to begin) by an enzyme.
– The chemical reactions of glycolysis are anaerobic, because they occur without oxygen.
– All organisms can carry on glycolysis.
– Once GLUCOSE is present in the cell, its chemical bonds are broken down by glycolysis, with the help of enzymes, releasing free energy to make ATP.
– Glucose is not the only cellular fuel. ALL SIMPLE SUGARS in the diet are catabolized (process by which complex substances are converted to simpler compounds) and used in cellular respiration.
– To break down glucose, a small amount of energy is needed to get the reactions started, 2 ATP molecules supply this energy.
– In the initial reaction a glucose molecule is broken up into 2 new molecules of PYRUVIC ACID.
– Energy is released as the bonds of the glucose are broken to produce the 2 pyruvic acid molecules.
– During glycolysis one 6-carbon glucose molecule is broken down into two 3-carbon (pyruvic acid) molecules. Two ATP molecules are also produced.
– (1) 6-carbon glucose molecule -> (2) 3-carbon (pyruvic acid) molecules + (2) ATP molecules
– After the process of glycolysis has occurred, only about 10% of all available energy within the glucose molecule has been used.
– More energy can be extracted from the molecule, by using AEROBIC RESPIRATION.
– The KREB CYCLE is the aerobic process of cellular respiration.
– If oxygen is not present, the final product of glycolysis, PYRUVATE, is FERMENTED into ethanol and lactate.

2. There are 2 stages to AEROBIC RESPIRATION
1. KREBS CYCLE
2. ELECTRON TRANSPORT CHAIN

KREBS CYCLE
– The 2 pyruvic acid molecules enter the Krebs cycle.
– The Krebs cycle takes place in the MITOCHONDRIA of the cell, where the enzymes that run the reactions of the Krebs cycle are located.
– The Krebs cycle is a repeating cycle of aerobic reactions that breakdown the pyruvic acids produced by glycolysis.
– The Krebs cycle rotate twice, once for each of the pyruvic acid molecules and produces 2 ATP molecules, several CO2 (carbon dioxide) molecules, and HYDROGEN-CARRIER MOLECULES.
– The hydrogen-carrier molecules move to the ELECTRON TRANSPORT CHAIN in the mitochondria.

ELECTRON TRANSPORT CHAIN
– The molecules of the electron transport chain carry high-energy electrons from the hydrogen atoms down to lower and lower energy levels, releasing considerable amounts of energy along the way.
– A total of 34 more ATP molecules are produced from the electron transport process. The electron transport chain does not produce ATP directly, it produces a PROTON.
– The transported electrons, now deplete of most of their energy, are transferred to an OXYGEN ATOM.
– The oxygen atom combines with 2 hydrogen ions an creates WATER (H2O).
– C6 H12 O6 + 6 O2 -> 6 CO2 + 6 H2O + 36ATP
Glucose + Oxygen -> Carbon Dioxide + Water + Free Energy

FERMENTATION
When there is no oxygen available to complete the breakdown of glycolysis (the Krebs cycle requires oxygen) fermentation occurs.

Fermentation is the chemical release of energy from food without the use of oxygen.

The chemical process of fermentation does not release any more energy from the food (like the Krebs cycle and the electron transport chain) it only frees up molecules for continued respiration.

The process of converting pyruvate into ethanol and lactate is called fermentation.

Cellular Energy

Energy is the ability to do work.

All cells get their energy from their metabolism (food).

Energy required for motion is called KINETIC ENERGY.

Stored energy is called POTENTIAL ENERGY.

Energy can neither be created or destroyed (the 1st LAW OF THERMODYNAMICS), so the amount is always constant (the same).

Energy can be converted from one form to another. When energy is converted from one form to another, some of the energy ends up as heat (the 2nd LAW OF THERMODYMANICS).

ATP (ADENOSINE TRIPHOSPHATE)
– ATP is a molecule present in living organisms, it shuttles energy within the cells.
– ATP is one of the major energy-providing molecules that initiates biochemical reactions throughout the body.
– It is a source of potential chemical energy for most enzyme reactions.
– In the cell’s mitochondria, ATP is constantly generated from food.
– All chemical reactions are the transfer of energy from one molecule to another.
– ATP is an ADENOSINE MOLECULE chemically bonded to 3 PHOSPHATE MOLECULES.
– The chemical bonds connecting each phosphate molecule to the adenosine molecule hold energy.
– Energy is stored when bonds are formed to connect a phosphate molecule to an adenosine molecule. When these bonds are broken the energy is released.
– When a cell needs an ATP’s molecules energy, the last phosphate group breaks off and the energy in the bond is released for use by the cell.
– ATP molecules bind to chemicals within the cell that need the energy. This ensures that the energy is transferred from the ATP molecule to the proper place for use.
– Specialized proteins, called ENZYMES, use the energy released from ATP to do all the work of the cell.
– Enzymes are important biological catalysts; they function in lowering the activation energy needed for chemical reaction to occur.
– Enzymes are neither changed nor used up in the reaction.

ADP (ADENOSINE DIPHOSPATE)
– Once the ATP molecule has released energy by breaking off a phosphate molecule, the ATP molecule only has 2 phosphate molecules and is called ADP (ADENOSINE DIPHOSPATE).
– ADP is like an uncharged battery, it has no energy.
– ADP can have another phosphate molecule join it and become an ATP molecule again.

Types of Tissue

Tissues are groups of cells with a common structure and function.

They work together to perform a particular task.

ORGANS
– Organs are a collection of 2 or more of the basic body tissue types.
– Multiple tissues adapt as a group to perform specific functions and form structures called ORGANS.

ORGAN SYSTEMS
– A collection of 2 or more of the organs that together perform some complex body function.
– The human body is a cooperative of organ systems that are interdependent upon one another, either chemically or physically.

There are 4 main CATEGORIES OF TISSUE:
1.  EPITHELIAL TISSUE (covers and lines the body)
2.  CONNECTIVE TISSUE (binds and supports other tissue)
3.  MUSCLE TISSUE (is involved with movement)
4.  NERVOUS TISSUE (forms a communication network)

1. EPITHELIAL TISSUE

Epithelial tissue is covering and lining tissue, it covers body surfaces in general and lines cavities within the body.

It has little or no intercellular material between its cells.

The free surface of this tissue is exposed either to air or fluid.

The base of the cell is attached to a BASEMENT MEMBRANE (a dense layer of extra cellular material).

The cells are closely joined and may act as a barrier against injury, microbial invasion or fluid loss.

These cells may be specialized for absorption or secretion of chemical solutions.

Epithelial tissue is categorized by the number of LAYERS and the SHAPES of the free surface of the cells.

LAYERS can be:
1. SIMPLE: one layer of cells.
2. STRATIFIED: multiple tiers of cells.
3. PSEUDOSTRATIFIED: one layer that appears multiple because the layers vary in length.

SHAPES include:
1. SQUAMOUS
SIMPLE SQUAMOUS epithelial tissue is thin and leaky.
– These cells aid in the exchange of material by diffusion.
– They line blood vessels and air sacs in the lungs.
STRATIFIED SQUAMOUS tissue regenerates rapidly near the basement membrane.
– New cell are pushed to the free surface as replacements for the cells that are continually sloughed off.
– Stratified Squamous tissue is located on surfaces that are subject to abrasion, like the outer skin.

2. COLUMNAR
– They are like a cytoplasm filled water balloon.
– They are found where secretion or active absorption of substances is an important function, like the intestines, where they secrete digestive juices or absorb nutrients.
STRATIFIED COLUMNAR epithelial tissue line the inner surface of the urinary bladder.
PSEUDOSTRATIFIED CILIATED COLUMNAR epithelial tissue line the nasal passage.

3. CUBOIDAL
SIMPLE CUBOIDAL epithelial tissue is specializes for secretion.
– They can be found in the kidney tubules, the thyroid gland and the salivary glands.

2. CONNECTIVE TISSUE

Connective tissue binds and supports other tissue.

It has a sparse cell population scattered throughout an extensive extracellular matrix;  it has a lot of intercellular material between its cells.

The matrix contains long, slender rods and connective tissue fiber in a substance similar to soft-set gelatin.

This fiber helps connective tissue to do its job, to directly or indirectly connect body parts together.

3 types of FIBERS make up the various types of connective tissue:
1. COLLAGENOUS FIBERS
– They are bundles of fibers containing 3 collagen fibers each.
– These fibers are strong and resist stretching.
– The parallel lines on the palm of your hand are collagen bundles.

2. ELASTIC FIBERS
– They are long threads of the protein, elastin.
– If stretched, this tissue can return to its original shape.

3. RETICULAR FIBERS
– They are branched and tightly woven.
– They join connective tissue to neighboring tissue.

There are 6 CATEGORIES of connective tissue:
1. LOOSE CONNECTIVE TISSUE
– Contains all 3 fiber types; collagen, elastin and reticular.
– Holds organs in place and attaches the epithelium to underlying tissue.
– Contains 2 types of cells:
1. FIBROBLASTS: secrete proteins of extracellular fibers, like collagen.
2. MACROPHAGES: act as the “attack dogs” of the body’s immune system.

2. ADIPOSE TISSUE
– It is a loose connective tissue that is specialized to store fat.
– The fat is stored in adipose cells distributed throughout its matrix.
– Each adipose cell stores one fat droplet, which can vary in size.
– The stored fat insulates the body and is used for fuel when needed.

3. FIBROUS CONNECTIVE TISSUE
– Large numbers of collagenous fibers in parallel bundles makes this tissue very dense.
– This density gives it the great strength needed for tendons (to attach muscle to the bone) and ligaments (to attach bone together at joints).

4. CARTILAGE
– It is the strong and flexible connective tissue found in the skeleton of all vertebrate embryos.
– Most vertebrates convert the cartilage to bone, but they retain cartilage in the nose, ears and trachea.
– It is composed of collagenous fibers embedded in chondroitin sulfate (a protein-carbohydrate).

5. BONE
– Bone is hard, but not brittle or completely solid.
– It is mineralized connective tissue.
– OSTEOBLASTS (bone-forming cells) deposit a matrix of collagen and calcium phosphate that hardens into the mineral hydroxyapatite.

6. BLOOD
– Blood is the only liquid connective tissue in the body.
-It is a liquid extracellular matrix of plasma containing water, salt and proteins.
– Blood contains RED BLOOD CELLS (that transport oxygen), WHITE BLOOD CELLS (for the immune system) and PLATELETS (which are cell fragments that help in the clotting of blood).
– Blood cells are made in the red marrow of long bones.
– Blood vessels and nerve cells occupy slender canals in the bone tissue call HAVERSAIN CANALS.

3. MUSCLE TISSUE

There is more muscle tissue available in the human body than any other type of tissue.

It consist of long, slender muscle fibers, that contract or shorten to create body movement.

There are 3 types of muscle:
1. SKELETAL MUSCLE
– It is multinucleated and is usually attached to bones by tendons.
– Contractions are voluntary.
– This muscle appears striated under the microscope.

2. SMOOTH MUSCLE
– It is found in the walls of the internal organs and arteries.
– The spindle-shaped, uninucleated cells contract involuntarily.

3. CARDIAC MUSCLE
– It is located only in the wall of the heart.
– The cells are striated, uninucleated, and are joined by intercalated disks.
– Contractions are involuntary.

4. NERVOUS TISSUE
– It is the major tissue for communication and control within the body’s internal environment.
– It is designed to sense stimuli.
– It communicates by means of NEURONS (nerve cells).
– The neuron conducts impulses or bioelectric signals.
– It transmits signals from one part of the organism to another.