Lect 01 - Epithelial Tissue

Transcription

1 Structure & Function Introduction Prof Kumlesh K. Dev Department of Physiology What is Structure & Function? Integration is key structure and function requires integration of physiology, anatomy and biochemistry you will understand better if you integrate these modules What is Structure & Function? What is Structure & Function? Physiology: study of Structure and Function at all levels of biology evolution is slow, so anatomy requires memory and recall new discoveries at cellular, subcellular and molecular levels anatomy needs function (connect anatomy and physiology lectures) module covers from molecular to body levels Structure body (gross anatomy) tissue/organs cellular subcellular molecular Function movement of materials differentiation proliferation support secretion 1

2 Types of Structural Levels Organisation of the Body Molecular Subcellular Body 1. CELLULAR Basic structural and functional units 2. TISSUE Collection of specialised cells Tissue Motor area 3. ORGAN Made up of a variety of tissues Cellular Premotor area ANTERIOR POSTERIOR PARIETAL FRONTAL LOBE LOBE OCCIPITAL LOBE TEMPORAL LOBE Prefrontal area 4. SYSTEMS Interaction of organs 1. Cellular Levels 2. Tissue Types 1. Epithelium : lining glands, bowel, skin & organs 2. Endothelium : lining blood and lymphatic vessels 3. Mesothelium : lining of pleural, and pericardial spaces 4. Mesenchyme : cells filling spaces between organs, including fat, muscle, bone, cartilage and tendon cells 5. Blood cells : red/white, also those in lymph nodes & spleen 6. Neurons : conducting cells of nervous system 7. Germ cells : reproductive, sperm, oocytes 8. Stem cells : cells able to turn into one or several of above 1. Epithelial tissue Lining/barrier of secretory Skin and mucous membranes 2. Muscle (excitable) tissue Skeletal (striated) muscle Smooth muscle Cardiac muscle 3. Nervous (excitable) tissue Brain Spinal cord 4. Connective tissue (cells, fibres, matrix) Loose connective tissue Dense fibrous tissue (Capsule, Ligament, Tendon) Cartilage & Bone Blood (originate from bone marrow) 2

3 3. Organs and 4. Systems MUSCULAR : skeletal muscles, tendons NERVOUS : brain, spinal cord, peripheral nerves C.V.S. : heart, blood vessels, lymphatics SKIN : integmentary IMMUNE : lymphocyte, lymph node, tonsil, spleen RESPIRATORY : nose, pharynx, trachea, bronchi, lungs SKELETAL : bones, cartilage, ligaments G.I.T. : mouth, oesophagus, stomach, intestine SPECIAL SENSES : taste, t smell, sight, hearing REPRODUCTIVE : ovary, uterus, testes, epididymus URINARY : kidney, ureter, bladder, urethra ENDOCRINE : pituitary, thyroid, pancreas, adrenals EXOCRINE : tubular, acinar, branched, coiled glands Structure & Function Lect # 1 Epithelial tissue Prof Kumlesh K. Dev Department of Physiology GLANDULAR SURFACE SPECIAL EXOCRINE ENDOCRINE SENSORY PERCEPTION REPRODUCTION SQUAMOUS SIMPLE COLUMNAR CUBOIDAL SQUAMOUS STRATIFIED COLUMNAR CUBOIDAL Four Tissue Types What you should know about Epithelia? 1. Epithelial tissue Lining/barrier of secretory Skin and mucous membranes 2. Muscle (excitable) tissue Skeletal (striated) muscle Smooth muscle Cardiac muscle 3. Nervous (excitable) tissue Brain Spinal cord 4. Connective tissue (cells, fibres, matrix) Loose connective tissue Dense fibrous tissue (Capsule, Ligament, Tendon) Cartilage & Bone Blood (originate from bone marrow) 1. What are they? 2. What do they do? 3. How are they classified? Simple and stratified Squamous, cuboidal, columnar 4. What do they look like? Cell Membrane Specialisations 5. How do they Proliferate? 6. Pathology 7. Skin components 3

4 I. What are they? II. What do they do? Cells close together (minimal matrix between cells) Tight junctions (regulate passage of materials between cells) No nerves (except possibly at base) Absence of blood vessels (nutrition is via underlying tissue) Lining epithelia regulate passage of material in/out of body gut - nutrients lungs - gases kidney - water, ions skin - water Secretory cells secrete body fluids glands ducts III. How are they classified? Glandular Epithelia GLANDULAR SURFACE SPECIAL GLANDULAR EXOCRINE ENDOCRINE SENSORY PERCEPTION REPRODUCTION EXOCRINE ENDOCRINE SIMPLE STRATIFIED for secretion regulate ion concentrations see endocrine lecture series SQUAMOUS COLUMNAR SQUAMOUS COLUMNAR CUBOIDAL CUBOIDAL 4

5 Exocrine Glands: Classify by Morphology Exocrine Glands: Classify by Secretion Simple Types Endocrine glands secret hormones into bloodstream Merocrine (eccrine) Secretion exocytosis most common type of secretion Exocrine glands discharge products via duct tubular large intestine acinar urethra branched tubular stomach Compound Types branched acinar coiled tubular sweat glands Apocrine Secretion membrane-bound vesicles example: breasts, sweat glands Exocrine Types simple / compound Holocrine Secretion rupture of secretory cells example: sebaceous glands tubular acinar Surface Epithelia Function of Surface Epithelium SURFACE covers exposed surfaces lines internal passageways and chambers highly cellular avascular capacity to regenerate SIMPLE STRATIFIED provide physical protection control permeability SQUAMOUS COLUMNAR SQUAMOUS COLUMNAR provide sensation CUBOIDAL CUBOIDAL 5

6 Surface Epithelium classification Morphological 1. number of cell layers simple (one layer, permeable) stratified (many layers, protective) 2. shape of cells at free surface squamous (thin, flat, irregular) cuboidal (box-like) columnar (tall, slender, rectangular) 3. surface specialisation (if any) keratin, microvilli, cilia Functional 1. lining types 2. secretion/gland types 8 Types of Surface Epithelium Type Feature Example 3 Simple Types 1. Squamous Diffusion Blood vessels 2. Cuboidal Synthesis of hormones Thyroid gland 3. Columnar Digestion, absorption, lubrication Small intestine 3 Stratified Types 4. Squamous (+/- Keratin) Protection Skin 5. Cuboidal Saliva Salivary gland 6. Columnar Saliva Salivary duct 2 Special Types 7. Pseudostratified columnar Airways Trachea 8. Transitional epithelium Distention Bladder 1. Simple Squamous 2. Simple Cuboidal Example blood vessels Characteristics single layer of box-shaped cells locations: ducts and glands Functions synthesis & liberation of hormones collecting tubule (kidney) Thyroid Gland 6

7 3. Simple Columnar 4. Stratified Squamous (+/- Keratin) Characteristics single layer of tall cells Functions digestion (via enzymes) absorption (via microvilli) lubrication (via mucous cells) Characteristics many layers (with or without keratin) Functions protection moist surface resists dehydration thermoregulation and sensation Small intestine lining of gall bladder uterine Skin Oesophagus cervix (keratinised) non-keratinised keratin flakes With Microvilli - fine extensions of surface membrane ~1000 per cell 5. Stratified Cuboidal 6. Stratified Columnar Example salivary gland Example salivary gland duct 7

8 7. Pseudostratified columnar ciliated 8. Transitional epithelium Characteristics one layer of cells only tall ones reach surface Functions secrete mucus (goblet cells) trap particles (mucus) move mucus (cilia) clean, warm, moisten (e.g. air) Characteristics many layers; all irregularly rounded ureter & bladder only Functions permit distension i.e. increase volume to allow passage of urine lining of bladder trachea lining of bronchus IV. Cell Memb. Specialisations of Epithelium Type Functions Basal Surface 1. Basement membrane anchors epithelial cells to underlying tissue Free surface 1. Keratin protective 2. Cilia increase surface area & particle movement 3. Microvilli increase surface area & particle movement Intercellular junctions 1. Tight junction cell-cell contacts (virtually impermeable to fluid) 2. Adherent junction cell-cell contacts 3. Gap junction permit passage of ions & molecules between cells 4. Desmosome cell-cell contacts Basement Membrane two components basal lamina (lamina lucida and densa) fibroreticular lamina function anchors epithelial cells to underlying tissue 8

9 Surfaces of Epithelium Keratin Cilia Microvilli protective role to increase surface area for nutrient exchange for movement of nutrients, particles Tight Junction interlocking junctional proteins continuous band around cell skin lining of bronchus lining of small intestine function: cell-cell membrane contacts, virtually impermeable to fluids Adherent Junction Gap Junction adhesion belt (adhesion proteins) embedded proteins (connexons) continuous band around cell just below tight junction function: cell-cell membrane contacts protein pores function: permit passage of ions & molecules between cells 9

10 Desmosome V. Proliferation in Epithelia cell adhesion molecules (CAMs) Mitosis 1. microtubules form 2. chromosomes duplicate & align at equator (metaphase) 3. chromosomes pull apart 4. cell divides circular patch of adherent junction attached to microfilaments of cell (e.g. skin) mitoses found in lower part of intestinal Crypts metaphase arrest Vincristine (VCR) prevents formation of microtubules can be injected 3h before removal of tissues proliferation zone VI. Pathology - Metaplasia VII. Skin & Epithelial metaplasia epithelial type may change in response to physiology due to repeated damage/stress pre-cancerous Normal Barrett s Oesophagus biggest organ of body skin epithelial cells constantly renewed by proliferation of stem cells in basal layer functions of Skin protection sensation (by receptors) thermoregulation thermoregulation evaporation of sweat resists dehydration (keratin) 10

11 Skin components Skin components Epithelium (epidermis) 3 cell types keratinocyte (forms keratin) main cell melanocytes (10-20% of basal cells) produce melanin (skin colour) langerhan cells (role in immune reactions of skin; related to macrophages) 5 layers (base up, i.e. increasing age) 1. basal layer cuboidal cells: cell division occurs here 2. prickle cell layer: several cell layers tightly joined by desmosomes - prickle appearance 3. granular layer: cells contain keratohyalin (keratin precursor) 4. stratum lucidum: clear layer 5. keratin: dead cells Dermis (loose connective tissue) contains nerves blood vessels (for exchange of nutrients & heat) various appendages hair follicles sweat glands Skin & Thermoregulation Heat production and loss negative feedback core temperature (tc) ~37.8 C ± 2 C (narrow range) thermoreceptors t in hypothalamus monitor temp of arterial blood peripheral thermoreceptors (mostly in skin) 3 effectors: sweat glands, skin blood vessels, and skeletal muscles. compartment heat movement occurs from core (organs) to shell (skin) by radiation (heat loss over the skin) by conduction (contact with objects) by convection (transfer by air) by evaporation (sweating) heat production metabolism 50% efficient, muscles 25% efficient (shivering in cold heats body) brown Fat (BAT) produces heat by mitochondrial metabolism and is regulated by thyroid hormones and sympathetic nervous system heat loss skin and blood flow (skin thermoreceptors monitor temp and change skin blood flow) sweating and evaporation stimulated by sympathetic nervous system metabolic rate, basal metabolic rate (BMR) is ~80 kcal/h (330 kj/h) 11

12 Pathophysiology What you should know about Epithelia? cold environment (increased muscle tone, shivering; long term adjustments are made by thyroid hormones) hot environment (muscles relax, vasoconstriction, sweating) heat exhaustion in excessive sweating reduces blood volume so blood pressure drops heat stroke uncontrolled increase in temp leads to CNS malfunction fever due to pyrogens/pathogens which release prostaglandins onto hypothalamus 1. What are they? 2. What do they do? 3. How are they classified? Simple and stratified Squamous, cuboidal, columnar 4. What do they look like? Cell Membrane Specialisations 5. How do they Proliferate? 6. Pathology 7. Skin components Learning Outcomes Surface (Lesson 1) Learning Outcomes Glandular (Lesson 2) To be able to: distinguish structure and function of lining vs. glandular epithelia protection, molecule passage vs. secretory state the general function of lining epithelia. regulate the passage of material across them classify lining epithelia according to morphological criteria. shape of cells at free surface, no. layers, surface specialisation relate structure and function in lining epithelia (permeability/transport) more complex: e.g. mechanical protection: thick, keratin, turnover give examples of named epithelia: structure, location, function e.g. simple columnar, intestine, ti digestion and absorption. describe cell surface specialisation and functions basal surface, free surface, and junctions describe proliferation/differentiation of epithelia and relate it to function mitoses give examples of pathlogical changes in a lining epithelium metaplasia To be able to: distinguish exocrine and endocrine glands duct vs. ductless apply functional classification by secretion mucous, serous, steroid etc give examples of the different cellular mechanisms of secretion merocrine, apocrine, holocrine describe physiological/transport functional significance of ducts not only for secretion, regulate ion concentrations relate ultrastructural, LM, EM and functional properties of secretory cells 12

13 Learning Outcomes Skin (Lesson 3) Learning Outcomes Thermoreg. (Lesson 4) To be able to: describe general structure and function of dermis and epidermis describe accessory cell types and functions describe differentiation of epidermis and keratinocytes relate structure to functions of skin: sense organs, thermoregulation To be able to: describe normal and pathophysiological range of core temperature describe compensatory mechanism of temperature regulation outline mechanism of heat production and loss; thermoneutral zone explain measures of metabolism: in different activities; BMR outline role of skin thermoreceptors as a feed-forward homeostatic mechanism explain thermoregulatory responses and treatments in extreme environments, fever, hypothermia, hyperthermia give pathophysiological examples of thermoregulation: fever, malaria, malignant hyperthermia 13