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ISLAMIC MEDICAL EDUCATION RESOURCES 04

0102-PROTECTIVE SYSTEMS

By Professor Omar Hasan Kasule Sr.

1.0 SURFACES AND MEMBRANES

A. Skin

B. Surface Membranes

C. Nails

D. Secretions

E. Hair

 

2.0 BONY SKELETON

A. Cranium

B. Spine

C. Pelvis

D. Bone marrow

E.  Pathology

 

3.0 THE ENDOCRINE SYSTEM

A. Functions

B. Control And Regulation

C. Steroid Hormones

D. Peptide Hormones

E. Disorders

 

4.0 THE IMMUNE DEFENCE SYSTEM

A. Definitions

B. Lymphoid System/Lymphoreticular System

C. Immune Defense Mechanisms

D. Factors Modulating Immune Response

E. Disorders

 

5.0 HEMOSTASIS

A. Sites Of Hemopoiesis

B. Purpose

C. Components Of Hemostasis

D. Equilibrium

E. Disorders


1.0 SURFACES AND MEMBRANES

A. SKIN

SKIN IN THE QUR'AN:

The Qur’an was mentioned in several verses of the Qur’an (p. 279 45:50, 22:30, 39:23, 41:20-22, 70:15-16). It was mentioned in connection with punishment in hell (45:56, 22:30, 70:15-16). The skin has many sensory functions that make it an ideal organ for inflicting pain as punishment. The described the psychological and physiological reaction of the skin to mention of the name of Allah (39:23). The skin will on the last day bear witness against the person because many sinful activities involve the skin.

 

ANATOMY

The surface area of the skin is 1.6-1.85 square meters with a depth of 3-5 mm. It is 10% of body weight (Bowman p 32.l). The epidermis suffers from attrition. The average turnover of epidermal cells is 28 days. Pressure or friction serves to stimulate skin growth. A specific epidermal chalone inhibits skin growth. Its effects are stopped by trauma to the skin

 

PHYSIOLOGICAL FUNCTION

The skin plays several roles. It protects against mechanical injury. The plantar skin of the foot and pal mar skin of the hand are thicker because of their direct contact with surfaces. As long as it keeps its integrity, the skin protects against water and fluid loss as well entry of pathogenic organisms. The skin has an excretory function through sweat. It is also a sensory organ and plays part in temperature regulation. Blood flow in the skin responds to environmental temperature; it increases when the atmosphere is hot and decreases when it is cold. It also responds to the emotional state. In extreme anger more blood flows through the skin leading to change of color in fair-skinned races. The skin plays a role in immune protection. The Langhan’s cells pick up antigenic information and transmit it to lymphocytes. The skin protects the underlying tissues from the sun. Melanocytes produce melanin that protects against UV rays. Sub-cutaneous adipose tissue layer is a reserve of metabolic energy and provides thermal and mechanical protection for deeper structures. Sweat glands are of two types, exocrine and apocrine. There are 2-3.5 million exocrine glands being more in palmar and plantar surfaces. They are involved in thermo-regulation and emotional expression. Apocrine glands are fewer. Their role is not clear. They are found in the axillary, perineal, and genital regions.

 

SKIN COLOR

4 pairs of genes that among them determine dark and light skin pigmentation control skin color. Skin color is darkest when all 4 are homozygous for dark pigmentation. A fair skin color is produced when all 8 alleles code for light color. Chemically and optically, it is the melanin in the epidermis and the blood vessels in the dermis that define skin color. There are 1000-3000 melanocytes per square millimeter; the density does not differ between darker and lighter races. The difference is in the activity of cells producing melanin. Darker races have more active melanin production than lighter races. The melanocyte-stimulating hormone (MSH) from the pituitary stimulates melanocytes. The enzymes tyrosinase and alpha-dioherol oxidase in melanocytes convert tyrosine to melanin. Albinos lack the enzyme alpha-diohero oxidase and therefore cannot produce melanin that explains their pale appearance. Some parts of the skin, like the areola of the nipple and the perineum, are darker than others. Prolonged exposure to sunlight causes hypermelanization and hyperkeratosis that make the skin darker. Photosensitivity reactions may be photo allergy or may be due to skin interaction with porphyrin metabolites.

 

RADIATION

The primary purpose of melanin is to protect the skin against cosmic radiation especially ultra-violet radiation. UV radiation has different effects depending on the band. Band A (320-400 nm) causes suntan. Band B (290-320 nm) causes erythema and blistering. Band C (less than 290 nm) is harmful. Sunlight exposure can cause cancer (basal cell epithelioma, squamous cell carcinoma, keratoacanthoma, and melanoma). Lighter-pigmented persons are at higher risk of cancer because they have less melanin protection.

 

SKIN PATTERNS

Skin whorls and patterns are unique for each individual. The probability of two individuals having the same pattern is very low. This is used in criminal identification using thumbprints. The Qur’an indirectly mentioned the uniqueness of the thumb (75:4).

 

PATHOLOGY

Skin homeostasis is tested because of its continuous interaction with the outside environment. Breakdown of homeostasis results into wrinkles, hair loss, blisters and rashes. Chronic exposure leads to premature cutaneous aging, blunting of the skin immune response to antigens, pre-malignant as well as malignant lesions. Drugs may cause rashes and exanthems. Systemic diseases like diabetes mellitus, SLE, and amyloidosis have skin manifestations. Dermatologists identify several skin disorders including: pigmentation disorders, inflammatory disorders, infectious disorders, and neoplastic disorders. Disorders of pigmentation manifest as vitiligo, freckles, melasma and moles. Vitiligo is asymptomatic partial or complete loss of melanocytes affecting all races. Freckles appear seasonally. Melasma is hyper pigmentation of pregnancy. Moles are pigmented nevi that may become dysplastic and grow malignant. Neoplastic disorders may be pre-malignant lesions, benign or malignant growths. Benign epithelial tumors are seborrhoeic keratosis, acanthosis nigricans, fibro-epithelial polyps, epithelial cysts, and keratoacanthomas caused by sun exposure and that heal spontaneously. Malignant epithelial tumors are basal cell carcinoma and squamous cell carcinoma. Dermal tumors are fibrous histiocytoma, dermatofibrosarcoma protuberans, xanthomas, and vascular tumors. Acute inflammatory dermatoses are urticaria, acute eczematous dermatitis, erythema multiformis, erythema nodosum. Chronic inflammatory dermatoses are lichen planus, lupus erythromatosus, acne vulgaris, and pemphigus. Blisterous or bullous diseases are pemphigus and dermatitis herpetiformis. Common skin infections and infestations are verrucae (warts) molluscum contagiosum (due to pox virus), impetigo, superficial fungal infections, arthropod bites, and arthropod infestations.  

 

B. SEROUS MEBRANES

Serous membranes are the peritoneum, pleura, pericradium, and meninges. These membranes allow smooth movement of organs. They also play a role in immune protection by secreting lysozymes and IgA. They have phagocytes that engulf infectious organisms.  The normal flora of the membranes prevents establishment of infection by competition with pathogenic organisms.

 

C. NAILS

The Qur’an described biting nails out of anger and despair (3:119). Human nails unlike those of animals do not play a significant role in self-defense against attack. They are however used to scratch the skin and to improve grip for some small objects.

 

D. SECRETIONS

Various secretions play a role in immune protection. Tears contain lysozymes. Sweat and sebaceous secretions are acidic. Besides their anti-bacterial function, tears clean away dirt.

 

E. HAIR

There are 2 types of hair: coarse on the scalp and fine on the rest of the body. The number, size, and depth of melanin particles determine the color of hair from lack to blonde. White hair has no melanin. Red hair has iron-rich pigment. Straightness and curliness of hair of hair depend on the shape of the pit of the follicle (straight sharply curved) or shape of hair shaft (round or oval). The pattern of baldness is under genetic control. Hair is part of female beauty. Wives are not allowed to shave off their hair without permission by their husband (KS294).

 

2.0 BONY SKELETON

A. BONE TISSUE

There are 2 main types of bone cells: osteoblasts, osteocytes, and osteoclasts. Osteoblasts are formed from osteo progenitor cells and they are the bone matrix. Osteocytes control calcium and phosphate levels. Osteoclasts are responsible for bone resorption. Osteoblasts and osteoclasts work together in bone re-modeling. Bone mass is affected by age, gender, heredity, level of physical activity, muscle strength, diet, and hormonal status. Peak bone mass is attained in early adulthood. Males have a higher bone mass than females. The Qur’an has described weakness of bones, wahan al ‘idham (19:4).

 

Bone growth abnormalities manifest as: malformations, achondroplasia, and osteogenesis imperfecta. Matrix anomalies are due to muco-poly saccaridoses or osteoporosis. Primary osteoporosis is due to advancing age or estrogen deficiency in menopausal women. Secondary osteoporosis occurs in some disease conditions. Osteoclast dysfunction is found in Paget's disease (osteoitis deformans). Abnormal mineral homeostatis is found in rickets and osteomalacia.  Renal osteodystrophy are skeletal changes in chronic renal disease. Bone fractures may be complete bone separation or may be incomplete green-stick fractures common in children. Simple or closed fractures do not involve the skin. Compound fractures protrude through the skin and are more difficult to treat. Pathological fractures occur in diseased bone. Stress fractures develop in bone subjected to abnormal and repeated physical stress. Ischemia caused by fractures, thrombosis, or embolism causes osteonecrosis or avascular necrosis. Bone infection, osteomyelitis could be bacterial (pyogenic osteomyelitis), Tubeculous osteomyelitis, or due to skeletal syphilis. Bone tumors are of 2 types: bone forming or cartilage forming. The bone forming tumors are: osteoma, osteoid osteoma, osteoblastoma, and osteosarcoma. Cartilage forming tumors are osteochondroma, chondroma, chondroblastoma, and chondrosarcoma.

 

B. CRANIUM

The bony cranium protects the brain a very sensitive organ of the body.

 

C. VERTEBRAL COLUMN

The vertebral column protects the spine that passes through the vertebral canal.

 

D. THORACIC CAGE

The thoracic cage protects the important organs of the lungs, heart, and major blood vessels of the mediastinum.

 

E. PELVIC GIRDLE

The pelvic bones protect the sensitive structures of the uterus and the ovary.

 

3.0 THE ENDOCRINE SYSTEM

A. FUNCTIONS

Functions of hormones: (a) morphogenesis eg GH (b) hemostasis or metabolic regulation (c) functional integration eg sex hormones. The human hormonal system plays a major part in the flight/fight preparation involving the pituitary, thyroid, adrenal, pancreas. The problem of modern sedentary man is that the hormonal reactions are still the same but he does not have the physical stress of the hunter. The price paid is in terms of peptic ulcers.

 

B. CONTROL and REGULATION

The ultimate central control is in the hypothalamus. The hypothalamus produces the following hormones: TRH, GnRH, GRH, PRF, and RIF. The anterior pituitary produces: TSH, LH, FSH, GH, ACTH, beta-endorphin, MSH, PRC. The pituitary controls the secretion of other hormones. LH controls progesterone and testosterone secretion. FSH controls 17 beta estradiol secretion. ACTH controls cortisol secretion. Angiotensin controls aldosterone secretion. PTH controls vit D3. Equilibrium and feed-back operate to maintain balance and also deal with physiological stress. Hormone + receptor (-( hormone-receptor complex (interacts with transducing protein). The hormonal cascade refers to the chain of command and control. The flow of information is as follows: environmental signal, CNS, limbic system, hypothalamus, anterior pituitary, target organ, ultimate hormone, and systemic effects. The final hormone acts by negative feed-back on the hypothalamus, pituitary, and even CNS.

 

C. STEROID HORMONES

Steroid hormones are of two types: (a) sex hormones: progesterone, etradiol, testosterone (b) adrenal hormones: cortisol, aldosterone. They are synthesized from cholesterol. They are transported bound to specific proteins or to albumin. Progesterone prepares the uterine endometrium for implantation. It is also necessary for development of mammary glands. Testosterone in males has a role in production of sperm cells, and secondary sexual characteristics. 17 beta estradiol has different roles in males and females. In males it is involved in the negative feed-back inhibition of Leydig cell synthesis of testosterone. In females it regulates the ovarian cycle, maintains the uterine endometrium, and development of mammary glands. Cortisol is involved in stress adaptation, increase of liver glycogenolysis, killing T cells at high doses, increase of blood pressure, and increased sodium uptake. Aldosterone increased sodium uptake, blood pressure, and fluid volume.

 

D. PEPTIDE HORMONES

Peptide hormones: a single gene encodes many peptide hormones.

 

E. DISORDERS

Two parathyroid disorders occur: hypo and hyper parathyroidism. Hypo-parathyroidism is caused by: surgical removal, congenital absence as in Di Georgi syndrome, and auto-immune disease. Hypoparathyroidism has the following clinical effects: increased neuro-muscular excitability, mental changes (irritability, depression, and psychosis), calcification (in the cranium, the lens), and abnormalities of cardiac electric conductivity.

 

4.0 THE IMMUNE DEFENCE SYSTEM

A. DEFINITIONS

Immune defense is recognition and elimination on non-self (foreign) material. An antigen is a substance that is capable of provoking an immune response. Epitopes are antigenic determinants on top of the surface of the antigen. A hapten is a small molecule that becomes an antigen when covalently bound to a larger molecule. The following are cellular antigens: HL-A, autoantigens, blood group antigens (ABO & Rh). Cytokines, interleukine, interferon. Isotypes are antigenic features shared by all humans. Allotypes are antigenic features that vary by individual and are under genetic control. An antibody is an immunoglobulin that binds to foreign body to eliminate it. An antigenic determinant is a small portion of the antibody that binds antigen. Humans can produce 1 x 10E8 different antibodies. An antibody has 2 light chains and 2 heavy chains. It has constant and variable regions. Monoclonal hybridoma techniques enable production of homogenous antibodies. Complement proteins are activated by antigen-antibody complex to bind to wall of bacteria, protozoan, or tumor causing lysis. Antibodies bind antigens to form Ag-Ab complexes that are eliminated. Both B and T cells have receptors for antigens that they bind. The immune surveillance system eliminates neoplasms.

 

B. LYMPHOID SYSTEM/LYMPHORETICULAR SYSTEM

The lymphoreticular system consists of the bone marrow (WBC), thymus (T cells), spleen (antibodies and filter), lymph nodes (filter), tonsils, adenoids, and Payer’s patches. The bone marrow has multi-potent uncommitted cells. The spleen filters the blood as the lymph node filters lymph. The functions of the spleen are: filtration, manufacture of lymphoreticular cells and hematopoietic cells, and storage.

 

C. IMMUNE DEFENCE MECHANISMS

SPECIFIC AND NON-SPECIFIC

The non-specific immune mechanisms consist of phagocytosis, filtration by RES, inflammatory response (acute & chronic), and fever. Natural killer cells lyze cells that have been transformed by viruses or by malignant transformation. Non-specific immune responses can be cell mediated or humoral.

 

HUMORAL DEFENCE MECHANISMS

The human has 10E9 B cells. Each can bind an antigen and become a plasma cell. Which produces antibody. Thus a very wide range of antibodies is possible. Antibodies constitute about 20% of all plasma proteins. IgA is a mucosal secretions and is the first line of defense. IgM is in plasma and is involved in acute response.  IgG is in plasma and is involved in long-term response. The normal function of IgE is unknown.

 

CELLULAR DEFENCE MECHANISMS

Major histocompatibility genes are on chromosome #6. The most important MHC is HLA. The MHCcomplex binds peptide antigen and presents it to T cells. The T cell is specific for both the antigen and the MHC complex. Antibodies, antigens, and MHC have structural features in common which suggest a common origin from an immunological supergene family.

 

FACTORS MODULATING IMMUNE RESPONSE

Age affects immune competence. Children and the elderly have the least competent immune systems and therefore are at a higher risk for infectious and neoplastic disease. Previous exposure to an antigen creates to immunological memory such that the immune response will be faster and more effective on re-exposure to the same antigen. Malnutrition, both under and over nutrition, affects immune competence. Modern research is uncovering what empirical observation has always shown that psychological factors such as stress affect susceptibility to disease. The emerging field of psycho-neuroimmunology will unravel more of this fascinating field. Prior immunization can decrease or eliminate the risk of infection. The following types of antigens are used: killed vaccine, inactivated virus, killed parasite, non-virulent live bacterium or virus, denatured bacterial toxin.

 

DISORDERS

The common disorders of the immune system are autoimmunity, anergy and allergic reactions.

 

5.0 HEMOSTASIS

A. BLOOD AS THE ESSENCE OF MAMMALIAN LIFE

The Qur’an mentioned blood ddam (p 430 2:30,  22:37). Circulating blood is 8% of body weight. 55% of blood is plasma. Solid and liquid components: cells and plasma. RBC and Hb (adult and fetal). WBC.  Blood typing: ABO & Rh). Blood groups found in all humans indication of unity. Blood spilled as najasat. Blood is a type of connective tissue constituting 7% of body weight. It consists of aqueous plasma and particulate blood cells. Plasma is made up of water, electrolytes, proteins (albumin and globulin), and other organic solutes. The cellular elements consist of: platelets, erythrocytes, leucocytes (neutrophils, esinophils, basophils, monocytes, and lymphocytes). Plasma albumin provides the bulk of osmotic pressure (c. 25mmHg) that controls the distribution of extracellular fluid between plasma and tissue fluid spaces. Albumin also binds and transports drugs. Plasma globulins are either involved in clotting mechanisms( alpha 1, alpha 2, beta) or are immunoglobulins (gamma). The chief function of blood is transport (oxygen, carbon dioxide, nutrients, hormones, intermediary metabolites, antibodies, lymphocytes, other secretions, wastes). Blood is also a buffer and plays a role in hemostasis.

 

B. SITES OF HEMOPOIESIS

In adults the bone marrow forms RBC, WBC, and platelets. In children long bones are hemopoietic but in adults hemopoiesis is confined to the ribs and pelvis. In the fetus, the liver and spleen are hematopoietic organs. In diseases that destroy the BM, extramedullary hemopoiesis occurs.

 

C. HEMOSTASIS

The purpose of the hemostatic system is to maintain the integrity of the closed circulatory system in case of vessel rupture. The components of the hemostatic system are: the platelets, the coagulation process, and vascular smooth muscles.

 

D. EQUILIBRIUM

The fibrinolytic and coagulation systems are in a fine balance. The basic process in coagulation is the change of fibrinogen into fibrin mediated by thrombin. The basic process in the fibrinolytic system is the change of plasminogen into plasmin.

 

E. DISORDERS

Integrity of the hemostatic system is measured using bleeding time, and the capillary fragility test. At one extreme of the spectrum, there is failure of any coagulation such that blood oozes through the capillaries causing hemorrhage. On the other end of the spectrum there may be so much coagulation that emboli are formed and they cause blockage of arteries leading to infarction in essential organs. The so-called disseminated coagulopathy, coagulation factors are consumed leading to hemorrhage due to failure of hemostasis.

Professor Omar Hasan Kasule February 2001