Muscle, skin & tissue

Question 1

Tissues introduction

Answer 1

• Tissues are comprised of cells but in large numbers
• Can be classified according to their cells in terms of size, shape and function
• Four main types (with further sub-divisions)
• Epithelial – ‘protection, secretion, absorption’- line things or coats things either as a protective barrier or to secrete substances like mucus or to absorb substances like in the guts in the digestive system to absorb nutrients.
• Connective – ‘support’- holding things together and giving them shape and substance.
• Muscle – ‘movement’- that we can control such as skeletal muscles which we use to move our limbs. Or involuntary muscle such as in the heart which we don’t actively control.
• Nervous – ‘internal communication’- in our body, communicate from one thing to another.
• ‘Histology’ – study of tissues

Question 2

How Tissues Form

Answer 2

• All tissues develop from three primary germ cell layers in an embryo:
• Ectoderm (outer) – nervous, epithelial. (what eventually turns into our nervous tissue and epithelial tissue)
• Mesoderm (middle) – epithelial, muscular (what eventually turns into our muscular tissue and epithelial tissue)
• Endoderm (inner) – epithelial

Question 3

Cellular differentiation

Answer 3

• process by which cells gain their specific function/shape to form tissues
• Stem cells- have the potential to become a multiple different type of cells. It is the building block which can be used to make different types of tissues.
• Determination – of a pathway of cell types
• Differentiation – to a specific cell type

Question 4

Morphogenesis

Answer 4

– process by which cells/tissues become organised and form structures/organs
* Differentiation of cells into tissue and organisation of systems occurs within 12 weeks of gestation

Question 5

Levels of Organisation

Answer 5

Tissues
* Cells which share common aspects of morphology (shape) and function

Organs
* Structures formed from more than one tissue and with specific functions.

Systems
* Organisations of organs and structures which function in a coordinated fashion to fulfil a common goal or goals.

Question 6

Levels of organisation, example: Heart tissue

Answer 6

• Different type of cells come together to form a tissue
• Heart made up of muscle, such as an outer protective coating called the pericardium, the internal epithelial layout.
• 3 different types of tissues of the heart which make up the structure, the organ which is the heart.
• The heart works alongside the blood vessels to pump and distribute blood oxygen, carbon dioxide around the body, which makes up our cardiovascular system.

Question 7

Epithelial Tissue (Epithelium)

Answer 7

• Covers the body and lines all internal cavities (respiratory system, our gastrointestinal tract, our arteries), tubes and organs
• Also contains certain glands- A gland are a type of cell which produce a substance. For example goblet cells produce mucus (protecting body by lining and making things smooth).
• Tightly packed cells, minimal intercellular ‘matrix’ between them- meaning things can’t pass in between.
• Communicate with the external environment, protect us from them!
• Structure and function closely related:
• Protection (in a range of forms)
• Secretion
• Absorption
  Broadly divided into:
• Simple – single layer of cells
• Stratified – multiple layers

Question 8

Simple Epithelium

Answer 8

• Single layer of cells
• Bound to underlying tissue by basement membrane of connective tissue
• Roles in absorption/secretion rather than protection
• Types according to shape and function – taller in more active tissues
• include squamous, cuboidal and columnar

Question 9

Squamous

Answer 9

• Flat cells tightly packed – like paving
• Smooth lining membrane for diffusion
• Examples in blood vessels, collecting ducts of kidney and alveoli in lungs

Question 10

Cuboidal

Answer 10

• More actively involved in secretion/absorption processes
• Tubules in kidney and glands such as thyroid

Question 11

Columnar

Answer 11

• Contains adapted cells to perform specific functions in secretion/absorption
• Lines range of organs and internal tracts
• Examples include trachea and small bowel
• Adaptions include goblet cells (mucous secretion), microvilli (absorption) and cilia (propulsion of particles)

Question 12

Stratified Epithelium

Answer 12

• Layers of cells of various shapes
• Main role is protection of underlying tissues from damage
• New cells in deep layer pushed to surface and shed – continuous process
• Two types:
• Stratified squamous
• Keratinised – contain keratin; tough waterproof protein, e.g. skin
• Non-keratinised – no keratin; prevents drying out of tissues, e.g. conjunctiva of eye, mouth
• Transitional
• More rounded, allows stretching
• Found in urinary tract, e.g. bladder (so it can expand

Question 13

Tissue Membranes

Answer 13

• Thin layer or barrier surrounding and separating cells, tissues and organs
• Epithelial
• Forms outer covering of internal and external surfaces
• Layers of epithelium supported by connective tissue
• Three types:
• Mucous
• Serosal
• Skin
• Synovial
• Related to joints and tendons
• Reduces friction between structures
• Areolar (loose connective tissue) and elastic fibres
• Produce synovial fluid – lubricant and source of nutrients to cartilage

Question 14

Mucous Membrane

Answer 14

• Often referred to as mucosal layer or mucosa
• Provides a moist, slippery protective barrier/lining
• Goblet cells interspersed within epithelium produce mucous
• Protects, lubricates and captures foreign particles
• Examples include internal tracts/cavities:
• Gastrointestinal tract
• Respiratory tract
• Genitourinary tracts

Question 15

Serous Membrane

Answer 15

• Also know as ‘serosa’
• Double layer of areolar (loose) connective tissue with potential space in between
• Epithelial lining of layer produces watery ‘serous’ fluid into space
• Allows layers to glide smoothly over each other and ‘stick together’
• Layers are:
• Visceral – inner layer covering an organ
• Parietal - outer layer covering inside a cavity
• Examples include:
• Pleura – outside of lungs and inside of chest wall (thoracic cavity)
• Peritoneum – outside of abdominal organs and inside of abdominal cavity

Question 16

Nervous Tissue

Answer 16

• Brain, spinal cord and nerve
• Communication system for our body
• The nervous system is made of two types of tissue:
• Neurones
• ‘excitable’
• nerve cells
• consist of a cell body (grey matter), an axon, and dendrites (neuron processes - white matter)
• bundles of neurones form nerves
• production and transmission of signals
• cannot divide
• Glial cells
• ‘non-excitable’
• four cell types which support the neurones to do their job
• much more abundant (10x)
• Can divide

Question 17

Connective Tissue

Answer 17

• Most prevalent tissue type in body
• Cells more widely spaced – more extracellular matrix
• Matrix of ‘fibres’ which maybe elastic, fatty, spongy, or very tough
• Prominent blood supply to support functions:
• Structural support and anchoring
• Mechanical protection and repair
• Transport/storage of essential substances
• Insulation
• Found in all organs where it supports the specialised functional tissue
  Contains cells related to its function, eg. white blood cells (leukocytes), fibroblasts (produce collagen and elastic fibres),

Question 18

Important Proteins

Answer 18

• Comprise 50% of organic matter in body
• Chains of amino acids
• Structure of a protein determines function;
• Structural/fibrous proteins – connections, structure and strength of tissues, e.g.
• Collagen – most abundant in body. Connective tissues (including bone, tendons and ligaments)
• Elastin – elastic and flexible. Connective tissues
• Keratin – very strong, water resistant. Hair nails and skin
• Globular/functional – ‘do things’ massive range of vital physiological processes and cell functions
• E.g. antibodies, hormones, enzymes, transport

Question 19

Types of Connective Tissue

Answer 19

• Loose (areolar)
• Reticular
• Dense connective
• Fibrous
• Elastic
• Blood – fluid connective tissue
• Bone
• Cartilage

Question 20

Areolar (loose connective)

Answer 20

• Relatively loose matrix supported by collagen and elastic fibres
• Disorganised matrix
• Provides elasticity and strength, and support/attachment to other tissues
• Found everywhere, e.g. between the skin and muscles
• Adipose (fatty)
• Loose matrix of connective tissue with adipocytes containing large fat globules
• “fatty tissue”
• Up to 25% of body mass
• Store of energy and insulation
• Found between skin and muscle and supporting organs (protection)

Question 21

Reticular

Answer 21

• Comprised of very fine collagen fibres (reticular)
• Interspersed with large numbers of white blood cells
• Related to immune system; found in lymphatic organs
• Dense connective tissue
• More closely packed fibres, fewer other cells
• Organised matrix
• Poorer blood supply
• Fibrous – densely packed collagen fibres in bundles; Tough and strong. e.g. ligaments, periosteum of bone, muscle fascia (sheath) and tendons, covering of organs
• Elastic – elastic fibres allows stretch and recoil. e.g. walls of blood vessels and airways of lung

Question 22

Types of Connective Tissue – Cartilage

Answer 22

• Type of connective tissue; firmer than other types
• Chondrocytes (cartilage-cells) lie within varying matrix of collagen and elastic fibres
• Differences between types dependent on this matrix
• More stress/weight-bearing; more collagen, less flexible
• Avascular; vascular supply via diffusion from other tissues
• Three functions:
• Provide support/strength
• Smooth, reduced friction surface at joints
• Involved in development/growth of bones (eg physeal plates)
• Normally invisible on X-ray unless abnormal (same for all connective tissues)

Question 23

Hyaline (articular) cartilage

Answer 23

• Groups (nests) of chondrocytes in a solid/dense matrix
• Very smooth and blue/white in appearance
• Low friction
• Predominantly found:
• End of long bones in synovial/cartilaginous joints Costal cartilage joining ribs to sternum
• Forms part of the larynx, trachea, and bronchi

Question 24

Fibrocartilage

Answer 24

• Dense groups of inelastic collagen fibres interspersed with chondrocytes
• Very tough, slightly flexible connective tissue
• Predominantly found:
• Intervertebral discs
• Meniscus of the knee
• Rim of shoulder/hip joints; called a labrum- help increase strength of limbs

Question 25

Elastic fibrocartilage

Answer 25

• Not associated with joints
• Chondrocytes lie within solid matrix of elastic fibres
• Flexible tissue providing shape/support
• Predominantly found in:
• Pinna (lobe of ear)
• Epiglottis
• Tunica media (wall) of blood vessels

Question 26

Types of connective tissue – skeletal system

Answer 26

• Important in understanding the structure and function of the musculoskeletal system in particular
• Skeletal Muscle; movement/joint stabilisation
• Fibrous tissue; forms joint capsule, muscle fascia and tendons
• Tendon; continuation of muscle into bone, transmission of forces
• Ligament; binds bones together for stability. Dense fibrous connective tissue
• Cartilage:
• Hyaline
• Fibrocartilage
• Elastic

Question 27

Muscle

Answer 27

• Structure allows contraction and relaxation of fibres
• Movement – either of body or within body
• Some voluntary, some involuntary
• Requires oxygen and fuel (predominantly glucose) to function
• Different contractible cells (fibres) dependent on three types:
• Smooth
• Cardiac
• Skeletal

Question 28

Smooth Muscle

Answer 28

• Not controlled voluntarily, autonomic/hormone control – involuntary
• Spindle shape fibres with central nucleus, does not have stripes (striations) in fibres – non-striated
• Related to movement within hollow organs/movement through body – visceral
• Layers of fibres forming sheets of muscle
• Functions include:
• Propulsion (peristalsis) – e.g. gastrointestinal tract, ureters
• Excretion - e.g. bladder
• Dilation/constriction – walls of blood vessels (role in blood pressure)

Question 29

Cardiac Muscle

Answer 29

• Found only in the heart
• Not controlled voluntarily – involuntary
• Autonomic nervous system and hormones supporting internal nerve stimulation (pacemaker)
• Fibres are striated/ striped
• Each fibre has a central nucleus and ‘branches’
• Ends/branches connected by ‘intercalated discs’ or joints
• Fibres stimulated from one to next (conduction/spread), not individually

Question 30

Skeletal Muscle

Answer 30

• So called as related to movement of the skeleton
• Is under ‘conscious’ control – voluntary
• Has transverse stripes across fibres – striated
• Each cell/fibre can be very long and contains several nuclei
• Arranged in bundles (fascicles) surrounded by dense connective tissue (fascia)
• Stimulated by impulses from motor nerves in brain/spinal cord

Question 31

Skeletal Muscle – gross structure

Answer 31

• Each muscle is comprised of many tens of thousand of individual fibres
• Supported by blood vessels and nerves and extensive dense connective tissue (fascia)
• From small to large:
• Individual fibres surrounded by endomysium
• Grouped into bundles called fascicles and surrounded by perimysium
• Whole muscle encapsulated by epimysium
• Fascia extends to both ends of muscle and directly connects to bone as either:
• Tendon – more like a rope
• Aponeurosis – flat sheet
• Transmit force of muscle to points of attachment on skeleton

Question 32

Skeletal Muscle – microscopic structure

Answer 32

• Parallel dark thick (myosin) and light thin (actin) filaments run along length of muscle fibres
• Each ‘unit’ of bands know as sarcomere
• These filaments in the cytoplasm (sarcoplasm) of muscle cells run parallel to muscle fibre and are ‘contractile’
• Several nuclei due to size of cells
• Multiple mitochondria to convert oxygen/glucose to ATP (adenosine triphosphate) for energy
• Oxygen and calcium essential nutrients for muscle action so are stored in large supplies in muscle

Question 33

Skeletal Muscle – Contraction

Answer 33

1. Stimulation of muscle fibres occurs at the neuromuscular junction
2. This signal is sent through channels between muscle cells
3. Causes calcium to be released from the muscle cell and causes the adjacent mysosin and actin sections to ‘bind’ together
4. ATP provides energy for two to slide over each other, shortening the sarcomere
5. When occurs over large numbers of fibres, muscle contracts
6. Removal of nerve stimulus causes calcium to be reabsorbed, breaking bond between myosin and actin, and return to original position

Question 34

Effects on Skeletal Muscle

Answer 34

• Performance – regular training (especially anaerobic) increases muscle increases the size of muscle fibres
• Muscle fatigue – occurs when demand of oxygen and glucose (fuel) is exceeded. Causes anaerobic process to take over which release lactic acid. Takes time to recover supplies and repair damage.
• Muscle tone – to prevent muscle fatigue when maintaining posture, muscle fibres activated in groups for short periods of time

Question 35

Skeletal muscle – actions

Answer 35

• Effect of muscle contraction is force transmitted through tendons to bone
• Must be attached at both ends
• Usually arranged in antagonistic pairs
• Muscle groups arranged to work together but in opposition during movement
• Isotonic movement – increase in muscle contraction/tension to provide movement
• Isometric movement – increase in muscle contraction/tension with no movement

Question 36

Naming Muscles

Answer 36

• Named in a range of ways related to:
• Direction of muscle fibres, e.g transversus abdominus
• Shape, e.g deltoid
• Position of muscle in relation to other anatomy, e.g. tibialis anterior
• Movement it produces, e.g. flexor digitorum
• Number of attachment sites, e.g biceps brachii
• What bone it is connected to, e.g. frontalis
  Origin
• Usually more proximal attachment
• Stays in place on contraction
  Insertion
• Usually more distal attachment
• Moves on contraction

Question 37

Integumentary system

Answer 37

Whole body covering”
Functions:
* Protect the body’s systems
* Maintain temperature
* Provide sensory information on the environment; e.g touch
* Excretion and absorption
* Synthesis of vitamin D
* Define personal appearances
Consists of:
* skin
* hair /nails
* accessory glands; e.g. sweat / sebaceous
* Supporting muscles / nerves

Question 38

Why is the Skin Important in Radiography?

Answer 38

• Skin erythema has a threshold dose above which they are likely to occur
• Hair loss and erythema have been reported during prolonged scanning e.g CT brain perfusion studies and image-guided interventions
• Skin damage can be caused by cumulative dose from multiple diagnostic procedures
• Can be mistaken for allergic reactions to defibrillator pads or electrodes

Question 39

The Skin – Overview

Answer 39

• Largest body organ; average 2 square metres and 5kg (about 16%)
• Made up of different tissues with varying functions
• Ranges in thickness from 0.5mm (eyelids) to 4mm (calcaneum); average 1-2mm
• Continuous with mucosa from respiratory, digestive, urogenital systems and eyes
• Two main parts:
• Epidermis; superficial, thinner, epithelial
• Dermis; deeper, thicker, connective tissue
• Hypodermis/subcutaneous layer;
• areolar and adipose tissue
• connected to dermis and underlying tissue via connective fibres
• Storage for fat and blood vessels to skin
• Sensitive to pressure due to nerve endings (corpuscles of touch)

Question 40

Epidermis

Answer 40

• Stratified squamous epithelium
• Contains keratin (also found in hair/nails),
• insoluble tough, fibrous protein
• Protects tissues from heat, microbes, and chemicals
• Made up of four cell types:
• Keratinocytes; 90% - produce keratin and lamellar granules (waterproofing)
• Melanocytes; 8% - produce melanin granules for keratinocytes and other cells; pigment to absorb UV light and shield cell DNA. Give skin colour
• Langerhan’s cells; from red bone marrow – immune response to microbes
• Merkel cells; in deepest layer – contact with sensory neurons for touch sense
• Keratinisation:
• Process of new cells in basale layer migrating to superficial layers
• Normal organelles replaced by keratin as cells apoptoses
• Takes 4 weeks in total
• 4 layers generally; ~1mm thick

Question 41

Dermis

Answer 41

• Deeper layer of skin; connective tissue of collagen and elastic fibres
• Also contains:
• Fibroblasts, macrophages, adipocytes
• Neurovascular structures
• Sebaceous and sweat glands
• Hair follicles

Question 42

Accessory Structures

Answer 42

• Hair
• Glands:
• Sebaceous
• Sudoriferous Ceruminous
• Mammary
• Nails