Lect 01 - Epithelial Tissue

Structure & Function

Structure & Function

Prof Kumlesh K. Dev Prof Kumlesh K. Dev D f Ph i l D f Ph i l Department of Physiology Department of Physiology

Integration

is

key

What is Structure & Function?

─

structure

and

function

requires

integration

of

physiology,

anatomy

and

biochemistry

─

you

will

understand

better

if

you

integrate

these

modules

Physiology: study of Structure and Function at all levels of biology

What is Structure & Function?

─ evolution is slow, so anatomy requires memory and recall

─ new discoveries at cellular, subcellular and molecular levels

─ anatomy needs function (connect anatomy and physiologylectures)

─ module covers from molecular to bodylevels

What is Structure & Function?

Function ─ movement of materials ─ differentiation ─ proliferation ─ support Structure

─ body (gross anatomy) ─ tissue/organs ─ cellular ─ subcellular

─ secretion ─ molecular

Molecular

Subcellular Body

Types of Structural Levels

Motor area Tissue POSTERIOR FRONTAL LOBE TEMPORAL LOBE OCCIPITAL LOBE PARIETAL LOBE ANTERIOR Prefrontal area Premotor area Cellular 1. CELLULAR

– Basic structural and functional units

Organisation of the Body

2. TISSUE

– Collection of specialised cells 3. ORGAN

– Made up of a variety of tissues 4. SYSTEMS

– Interaction of organs

1. Epithelium : lining glands, bowel, skin & organs 2 Endothelium : lining blood and lymphatic vessels

1. Cellular Levels

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. Tissue Types

2. Muscle (excitable) tissue – Skeletal (striated) muscle – Smooth muscle – Cardiac muscle 3. Nervous (excitable) tissue

– Brain – Spinal cordSpinal cord

4. Connective tissue (cells, fibres, matrix) – Loose connective tissue

– Dense fibrous tissue (Capsule, Ligament, Tendon)

– Cartilage & Bone

─ MUSCULAR : skeletal muscles, tendons

─ NERVOUS : brain, spinal cord, peripheral nerves C V S : heart blood vessels lymphatics

3. Organs and 4. Systems

─ 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 t t ll i ht h i

─ SPECIAL SENSES : taste, 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

Structure & Function

Prof Kumlesh K. Dev Prof Kumlesh K. Dev D f Ph i l D f Ph i l Department of Physiology Department of Physiology SURFACE GLANDULAR SPECIAL

EXOCRINE ENDOCRINE SENSORY

PERCEPTION REPRODUCTION SIMPLE STRATIFIED SQUAMOUS CUBOIDAL COLUMNAR SQUAMOUS CUBOIDAL COLUMNAR 1. Epithelial tissue – Lining/barrier of secretory – Skin and mucous membranes

Four Tissue Types

2. Muscle (excitable) tissue – Skeletal (striated) muscle – Smooth muscle – Cardiac muscle 3. Nervous (excitable) tissue

– Brain – Spinal cordSpinal 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?

What you should know about Epithelia?

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 ─Cell Membrane Specialisations ─ 5. How do they Proliferate? ─ 6. Pathology

─ Cells close together (minimal matrix between ll )

I. What are they?

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

II. What do they do?

g p g y

─gut - nutrients ─lungs - gases ─kidney - water, ions ─skin - water ─ Secretory cells

─secrete body fluids ─glands

─ducts

III. How are they classified?

SURFACE

GLANDULAR SPECIAL

EXOCRINE ENDOCRINE SENSORY

PERCEPTION REPRODUCTION SIMPLE STRATIFIED SIMPLE STRATIFIED SQUAMOUS CUBOIDAL COLUMNAR SQUAMOUS CUBOIDAL COLUMNAR

‘Glandular’ Epithelia

for secretion see endocrine lecture for secretion

regulate ion concentrations

see endocrine lecture series

Endocrine glands secret hormones into

Exocrine Glands: Classify by Morphology

Simple Types

─ secret hormones into bloodstream Exocrine glands ─ discharge products via duct tubular large intestine branched tubular stomach branched acinar acinar urethra coiled tubular sweat glands Compound Types Exocrine Types ─ simple / compound tubular acinar

Merocrine (eccrine) Secretion • exocytosis

Exocrine Glands: Classify by Secretion

y

• most common type of secretion Apocrine Secretion

• membrane-bound vesicles • example: breasts, sweat glands Holocrine Secretion

• rupture of secretory cells • example: sebaceous glands

‘Surface’ Epithelia

Function of ‘Surface’ Epithelium

─ covers exposed surfaces

─ lines internal passageways and chambers ─ lines internal passageways and chambers ─ highly cellular

─ avascular

─ capacity to regenerate ─ provide physical protection ─ control permeability ─ provide sensation

Morphological

1. number of cell layers ─simple (one layer, permeable)

Surface Epithelium classification

p ( y , p )

─stratified (many layers, protective)

─

2. shape of cells at free surface ─squamous (thin, flat, irregular) ─cuboidal (box-like)

─columnar (tall, slender, rectangular)

3 f i li ti (if )

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 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

Example

─blood vessels

2. Simple Cuboidal

Characteristics

─single layer of box-shaped cells

─locations: ducts and glands

collecting tubule (kidney)

locations: ducts and glands Functions

─synthesis & liberation of hormones Thyroid Gland

3. Simple Columnar

Characteristics

─single layer of tall cells Functions

─digestion (via enzymes)

─absorption (via microvilli)

─lubrication (via mucous cells) Small intestine lining of gall bladder

With Microvilli - fine extensions of surface membrane — ~1000 per cell

4. Stratified Squamous (+/- Keratin)

Characteristics

─many layers (with or without keratin) Functions

─protection

─moist surface resists dehydration

─thermoregulation and sensation

uterine Skin Oesophagus cervix (keratinised) keratin ‘flakes’ p g non-keratinised

5. Stratified Cuboidal

6. Stratified Columnar

7. Pseudostratified columnar ciliated

Characteristics

─one layer of cells

─only tall ones reach surfacey Functions

─secrete mucus (goblet cells)

─trap particles (mucus)

─move mucus (cilia)

─clean, warm, moisten (e.g. air) trachea lining of bronchus

8. Transitional epithelium

Characteristics

─many layers; all irregularly rounded

─ureter & bladder onlyureter & bladder only Functions

─permit distension i.e. increase volume to allow passage of urine

lining of bladder

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

─ two components

─ basal lamina (lamina lucida and densa)

─ fibroreticular lamina

Basement Membrane

fibroreticular lamina

─ function

Surfaces of Epithelium

Keratin Cilia Microvilli

protective role to increase surface area for nutrient exchange for movement of nutrients, particles

skin lining of bronchus lining of small intestine

Tight Junction

─ continuous band around cell ─ function:cell-cell membrane

contacts, virtually impermeable to fluids

Adherent Junction

─ continuous band around cell ─ just below tight junction ─ function:cell-cell membrane

contacts

Gap Junction

─ function:permit passage of ions & molecules between cells

Desmosome

molecules (CAMs)

─ circular patch of adherent junction ─ attached to microfilaments of cell ─ (e.g. skin) Mitosis 1. microtubules form

2 chromosomes duplicate & align at

V. Proliferation in Epithelia

2. chromosomes duplicate & align at equator (metaphase)

3. chromosomes pull apart 4. cell divides

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

Normal

VI. Pathology - Metaplasia

metaplasia

─ epithelial type may change in response to physiology due to

─ repeated damage/stress

Barrett’s Oesophagus

─ pre-cancerous

─ biggest ‘organ’ of body

─ skin epithelial cells constantly renewed by

VII. Skin & Epithelial

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)

Epithelium (epidermis) 3 cell types

• keratinocyte(forms keratin) – main cell

Skin components

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 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

Skin components

blood vessels (for exchange of nutrients & heat)

• various appendages – hair follicles – sweat glands

negative feedback

– core temperature (tc) ~37.8 °C ± 2 °C (narrow range)

th t i h th l it t f

Skin & Thermoregulation

– thermoreceptors in hypothalamus monitor temp of arterial blood

– peripheral thermoreceptors (mostly in skin) – 3 effectors: sweat glands, skin blood vessels, and

skeletal muscles. compartmentp

– 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)

Heat production and loss

(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 – skin and blood flow(skin thermoreceptors monitor

temp and change skin blood flow)

– sweatingand evaporation stimulated by sympathetic nervous system

– metabolic rate, basal metabolic rate (BMR) is ~80 kcal/h (330 kJ/h)

– cold environment(increased muscle tone, shivering; long term adjustments are made by thyroid hormones)

Pathophysiology

– hot environment(muscles relax, vasoconstriction, sweating)

– heat exhaustionin excessive sweating reduces blood volume so blood pressure drops

– heat strokeuncontrolled 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?

What you should know about Epithelia?

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 ─Cell Membrane Specialisations ─ 5. How do they Proliferate? ─ 6. Pathology

─ 7. Skin components

To be able to:

– distinguish structure and function of lining vs. glandular epithelia • protection, molecule passage vs. secretory

Learning Outcomes – Surface (Lesson 1)

– 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

i l l i t ti di ti d b ti

• e.g. simple columnar, intestine, 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

Learning Outcomes – Glandular (Lesson 2)

– 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

To be able to:

– describe general structure and function of dermis and epidermis – describe accessory cell types and functions

Learning Outcomes – Skin (Lesson 3)

y yp

– 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

Learning Outcomes – Thermoreg. (Lesson 4)

p y p g

– 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, li t h th i