tissue repair

PRESENTED BY:

UZMA BATOOLSHAHRAIN SAFDAR

ABDUL SAMISAMINARABIA

PRESENTATION TOPICS:

TISSUE REPAIRPLATELETS

CLOTTING CASCADEBLOOD GROUPSHOMEOSTASIS

TISSUE REPAIR

The body has many techniques for protecting itself from uninvited “guests” or injury.

Tissue Repair

Intact mechanical barriers such as the skin and mucosae, the ciliary activity of epithelial cells lining the respiratory tract, and a strong acid (chemical barrier) produced by stomach glands represent three defenses exerted at the body’s external boundaries.

Tissue Repair

When tissue injury occurs these barriers are penetrated, this stimulates the body’s inflammatory and immune responses, which wage their battles largely in the connective tissues of the body.

Tissue Repair

Inflammatory Response:The inflammatory response is a

relatively nonspecific reaction that develops quickly and occurs whenever and wherever tissues are injured .Essentially, inflammation acts to get rid of the harmful agent, prevent further injury, and restore the tissue to a healthy condition.

Tissue Repair

Immune Response:The immune response, on the other hand,

is extremely specific, but takes longer to swing into action.

Cells of the immune system, programmed to identify foreign substances such as microorganisms, toxins, and cancer cells, mount a vigorous attack against specific recognized invaders, either directly or by releasing antibodies into the blood.

Steps of Tissues Repair

1.Inflammation sets the stage:Let us briefly examine the

inflammatory events that tissue injury sets into motion.

First , the tissue trauma causes injured tissue cells, macrophages, mast cells, and others to release inflammatory chemicals which causes the capillaries to dilate and become very permeable.

1.Inflammation sets the stage:

This allows white blood cells and plasma fluid rich in clotting proteins, antibodies, and other substances to seep into the injured area.

Then the leaked clotting proteins construct a clot, which stops the loss of blood, holds the edges of the wound together, and effectively walls in, or isolates, the injured area, preventing bacteria, toxins, or other harmful substances from spreading to surrounding tissues.

1.Inflammation sets the stage: The part of the clot exposed to air

quickly dries and hardens , forming a scab. The inflammatory events leave excess fluid, bits of destroyed cells, and other debris in the area.

Most of this material is eventually removed from the area via lymphatic vessels or phagocytized by macrophages during the repair process.

Tissue Repair

Tissue Repair

2. Organization restores the blood supply:

During organization the blood clot is replaced by granulation tissue.

Granulation tissue; is a delicate pink tissue composed of several elements.

It contains capillaries that grow in from nearby areas and lay down a new capillary bed.

2. Organization restores the blood supply:

Granulation tissue is actually named for these capillaries, which protrude nublike from its surface, giving it a granular appearance.

These capillaries are fragile and bleed freely, as demonstrated when someone picks at a scab.

Also present in granulation tissue are proliferating fibroblasts that produce growth factors as well as collagen fibers to bridge the gap.

2. Organization restores the blood supply:

Some of these fibroblasts have contractile properties that pull the margins of the wound together.

As organization proceeds, macrophages digest the original blood clot and the deposit of collagen fibers continues.

2. Organization restores the blood supply:

The granulation tissue, destined to become scar tissue (a permanent fibrous tissue patch), is highly resistant to infection because it produces bacteria-inhibiting substances.

3. Regeneration and fibrosis effect permanent repair:

During organization, the surface epithelium begins to regenerate, growing under the scab, which soon detaches.

As the fibrous tissue beneath matures and contracts, the regenerating epithelium thickens until it finally resembles that of the adjacent skin.

3. Regeneration and fibrosis effect permanent repair:

The end result is a fully regenerated epithelium, and an underlying area of scar tissue.

The scar may be invisible, or visible as a thin white line, depending on the severity of the wound.

Tissue Repair

The above process described above follows of a wound (cut,scrape,puncture) that breaches an epithelial barrier.

In pure infections (a pimple or sore throat), healing is solely by regeneration.

Only severe (destructive) infections lead to scarring.

Capacity for regeneration

The capacity for regeneration varies widely among the different tissues.

Epithelial tissues regenerate extremely well, as do bone, areolar connective tissue, dense irregular connective tissue, and blood forming tissue.

Smooth muscle and dense regular connective tissue have a moderate capacity for regeneration.

Capacity for regeneration

Skeletal muscle and cartilage have a weak regenerative capacity.

Cardiac muscle and the nervous tissue in the brain and spinal cord have no functional regenerative capacity ; hence they are routinely replaced by scar tissue.

Scar Tissue

In nonregenerating tissues and in exceptionally severe wounds, fibrosis totally replaces the lost tissue.

Over a period of months, the fibrous mass shrinks and becomes more and more compact.

The resulting scar appears as a pale , often shiny area composed mostly of collagen fibers.

Scar Tissue

Scar tissue is very strong, but it lacks the flexibility and elasticity of most normal tissues.

It cannot perform the normal function of the tissue it has replaced.

Platelets

Platelets are the smallest of the three major types of blood cells.

Platelets are only about 20% of the diameter of red blood cells, the most numerous cell of the blood.  The normal platelet count is 150,000-350,000 per micro liter of blood, but since platelets are so small, they make up just a tiny fraction of the blood volume.  The principal function of platelets is to prevent bleeding. 

Platelet Production

Platelets are produced in the bone marrow, the same as the red cells and most of the white blood cells.  Platelets are produced from very large bone marrow cells called megakaryocytes.  As megakaryocytes develop into giant cells, they undergo a process of fragmentation that results in the release of over 1,000 platelets per megakaryocyte.  The dominant hormone controlling megakaryocyte development is thrombopoietin (often abbreviated as TPO).

Platelets structure

Platelets are actually not true cells but merely circulating fragments of cells.

But even though platelets are merely cell fragments, they contain many structures that are critical to stop bleeding. 

They contain proteins on their surface that allow them to stick to breaks in the blood vessel wall and also to stick to each other. 

Platelets structure

They contain granules that can secrete other proteins required for creating a firm plug to seal blood vessel breaks.

Also platelets contain proteins similar to muscle proteins that allow them to change shape when they become sticky. 

Platelet Function

Platelets serve three primary functions: 1) sticking to the injured blood vessel

(called platelet adherence). 2) attaching to other platelets to enlarge

the forming plug (called platelet aggregation).

3) providing support (molecules on the surface of platelets are required for many of the reactions) for the processes of the coagulation cascade.

Platelet Function

Platelets are not only the smallest blood cell, they are the lightest.  Therefore they are pushed out from the center of flowing blood to the wall of the blood vessel.

There they roll along the surface of the vessel wall, which is lined by cells called endothelium. 

The endothelium is a very special surface, like Teflon, that prevents anything from sticking to it. 

However when there is an injury or cut, and the endothelial layer is broken, the tough fibers that surround a blood vessel are exposed to the liquid flowing blood. 

Platelet Function

It is the platelets that react first to injury. 

The tough fibers surrounding the vessel wall, like an envelop, attract platelets like a magnet, stimulate the shape change , and platelets then clump onto these fibers, providing the initial seal to prevent bleeding, the leak of red blood cells and plasma through the vessel injury.

Platelet Function

Clotting Cascade

Introduction: The process by which the body

prevents blood loss is referred to as coagulation. Coagulation involves the formation of a blood clot (thrombus) that prevents further blood loss from damaged tissues, blood vessels or organs.

Clotting Cascade

This is a complicated process with a cellular system comprised of cells called platelets that circulate in the blood and serve to form a platelet plug over damaged vessels.

A second system based upon the actions of multiple proteins (called clotting factors) that act in concert to produce a fibrin clot. These two systems work in concert to form a clot; disorders in either system can yield disorders that cause either too much or too little clotting.

Clotting Cascade

Process: When a break in a blood vessel occurs,

substances are exposed that normally are not in direct contact with the blood flow.

These substances (primarily collagen and von Willebrand factor) allow the platelets to adhere to the broken surface.

Once a platelet adheres to the surface, it releases chemicals that attract additional platelets to the damaged area, referred to as platelet aggregation.

Clotting Cascade

These two processes are the first responses to stop bleeding.

The protein based system (the coagulation cascade) serves to stabilize the clot that has formed and further seal up the wound.

Factors

Factor VII:Tissue factor and factor VIIa (the ‘a’ denotes the active form of

the factor)

Factor Xa, IIa , Ia:Activate factor X, forming factor Xa.Factor Xa is then able to

activate prothrombin (also referred to as factor II) to form thrombin (factor IIa). Thrombin converts fibrinogen to fibrin (factors I and Ia respectively).

Factor XIII: Fibrin forms a mesh that, in concert with the platelets, plugs the

break in the vessel wall. The fibrin mesh is further stabilized by factor XIII, which sews up the clot (much like forming an intricate network of cross-stitched strands of fibrin).

Factors

Factors that Accelerate Clot Formation: Factor V and factor VIII accelerate the conversion

of factor X to factor Xa by factor IXa (this is done by factor VIII) and accelerate the conversion of prothrombin to thrombin as done by factor Xa.

Factors that Inhibit (Slow Down) Clot Formation:

Protein C, protein S and thrombomodulin form a complex (group of proteins) that can inactivate factor VIII and factor V. The protein C, protein S and thrombomodulin complex is activated by thrombin.

FactorsAntithrombin:Antithrombin (formerly called antithrombin III) serves to block the actions of multiple clotting factors (called inhibition).

Blood Groups

Blood is a complex, living tissue that contains many cell types and proteins. A transporter, regulator, and defender, blood courses through the body carrying out many important functions.

PROTEINS & BLOOD TYPES:

Distinct molecules called agglutinogens (a type of antigen) are attached to the surface of red blood cells.

There are two different types of agglutinogens, type "A" and type "B".

Each type has different properties. The ABO blood type classification system uses the presence or absence of these molecules to categorize blood into four types.

Four Type Of Blood

Blood Transfusion

When conducting a blood transfusion, it is important to carefully match the donor and recipient blood types.

If the donor blood cells have surface molecules that are different from those of the recipient, antibodies in the recipient's blood recognize the donor blood as foreign.

This triggers an immune response resulting in blood clotting.

Blood Transfusion

If the donor blood cells have surface molecules that are the same as those of the recipient, the recipient's body will not see them as foreign and will not mount an immune response.

RH Factors

Scientists sometimes study Rhesus monkeys to learn more about the human anatomy.

While studying Rhesus monkeys, a certain blood protein was discovered.

This protein is also present in the blood of some people. Other people, however, do not have the protein.

A+ A-B+ B-

AB+ AB-O+ O-

RH Factors

The presence of the protein, or lack of it, is referred to as the Rh (for Rhesus) factor.

If your blood does contain the protein, your blood is said to be Rh positive (Rh+). If your blood does not contain the protein, your blood is said to be Rh negative (Rh-).

HOMEOSTASIS

Everyday your body is affected by many things

HOMEOSTASIS Is the way your body keep balance

Introduction

Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, relatively constant condition of properties.

All homeostatic control mechanisms have at least three interdependent components for the variable being regulated: The receptor The control center The effector

Three components of Homeostasis

Positive feedback &Negative feedback

Positive feedback

Positive feedback is a mechanism by which an output is enhanced.

Positive feedback mechanisms are designed to accelerate or enhance the output created by a stimulus that has already been activated.

Negative feedback

Negative feedback mechanisms consist of reducing the output or activity of any organ or system back to its normal range of functioning.

Negative feedback

Thermal Balance

Body temperature

Normal body internal temperature is 370C Temperatures above this:

denature enzymes and block metabolic pathways

Temperatures below this:slow down metabolism and affect the brain

We need to regulate internal body temperature in order to provide the optimum conditions for enzyme-catalyzed reactions to be carried out.

Control of homeostasis

When your body gets too hot, your body need cooling down by: sweating, vasodilation, etc…

When your body gets too cold, you also need warming up by: Shivering, vasoconstriction, etc…

Glucose Homeostasis

About glucose in the body

Glucose is a monosaccharide which represents an essential biological energy source, enabling the generation of ATP following glycolysis

Although many tissues can also use fats and protein as an energy source, the brain and red blood cells can only use glucose.

Glucose is stored in the body, importantly in the liver, as glycogen.

Circulating levels of glucose

Circulating levels of glucose are controlled by two enzymes, insulin and glucagon.

glucagon

insulin

High glucose levels

In response to high glucose levels, pro-insulin is released from pancreatic beta cells in the islets of Langerhans and is converted to the active form in the blood.

Insulin stimulates the uptake of glucose and storage in the tissues as glycogen (glycogenesis).

Low glucose level

In contrast, low glucose levels cause secretion of pancreatic peptide hormone glucagon from alpha cells.

Glucagon promotes the conversion of liver glycogen to glucose (glycogenolysis) and release of glucose back into the blood.

During starvation and intense exercise, glucose can also be generated from non-carbohydrate precursors (i.e. pyruvate, amino acids and glycerol), in a process called gluconeogenesis.

Diabetes mellitus

Disruption of glucose homeostasis is most commonly studied in the field of diabetes mellitus, a metabolic syndrome in which patients do not produce suffi cient levels of, or correctly respond to, insulin.

References

Human Anatomy & Physiology, Fifth Edition, Elaine N. Marieb, Chapter 4, Tissue: The Living Fabric ;Tissue Repair, Page No. 138-140

www.admin.med.uiuc.edu/hematology

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