Histology

Question 1

Definitions

• Cytology
• Histology

Answer 1

• Cytology: study of cell structure
• Histology: Study of tissues
  
  • looks at how specialized cells come together to form tissues

Question 2

Variety and Specialisation of cells

• Erythrocytes
• Adipocyte
• Myocyte

Answer 2

• Erythrocytes: Isolated, anucleate, flexible, abundant haemoglobin
• Adipocyte: have large lipid vacuole (main function of cell = fat storage), peripheral condensed nucleus (squished to side)
• Myocytes: Contractile filaments, respond to nerve input

Question 3

Tissues - defn

-2 parts of an organ

Answer 3

• Tissues: Collections of cell performing related functions
• Are 2 parts to tissues;
  
  1. Parenchyma: The functional cells within an organ
  2. Stroma: The supportive role within an organ

e.g. In liver, parenchyma = hepatocytes; stroma = blood vessels, liver capsule and supporting CT

Question 4

4 Tissue types (and the 5th one sometimes used)

Answer 4

1. Epithelium: Barrier b/w body and external environment
   
   • line internal and external surfaces and lining of tubes
2. Muscle: Contraction; generation of force
3. Connective Tissue: Connect, anchor, support
4. Nervous Tissue: initiate and transmit nervous impulses
5. Round cells: Cells that don’t form a coherent tissue but are individual cells that can move widely throughout body
   
   • e.g. macrophages

Question 5

Epithelia

• definition and features
• what it forms (3 things)
• where it stops

Answer 5

• Is continuous sheet-like layer of cells in combo with a thin, underlying, non-cellular basement membrane (blood vessels don’t cross)
  
  • forms barrier/active interface
  • lines hollow organs and forms glands
  • can even form more solid structures like the liver
• is supported by layer of ECM (basal lamina) -> made from type 4 collagen and other components

Question 6

5 major functional categories of Epithelia

Answer 6

1. Protective: outer surface of body and opening of cavities (oesophagus)
2. Exchange: rapid exchange of gases (is therefore a thin endothelial lining)
3. Transporting: exchange of nongaseous materials; selective (gut and kidney)
4. Ciliated: move fluid across surface (respir. airways, female reproductive tract)
5. Secretory
   i) Exocrine: Syn. and release secretory products to external environment (serous; salivary glands, pancreas)
   ii) Endocrine: secrete products into extracellular space and the bloodstream (e.g. hormones)

Question 7

Locations of Ciliated epithelia and Protective epithelia

Answer 7

• Ciliated epithelium: respiratory system and female reproductive system (move mucous coat along surface)
  - in Female; ciliated epithelia is simple
  
  • pseudostratified in Resp. system
• Protective epithelium = skin, lining mouth, oesophagus and anus
  
  • skin: stratified epithelium (cells become squamous at top)
    
    • highly keratinised (to avoid abrasion) = skin, footpad
    • Less keratinised (to moisten surfaces) = oesophagus, orgal cavity, cervix, vagina

Question 8

Layers of skin epithelia (5)

-from superficial to deep

Answer 8

• Stratum corneum (looks loose and wispy b.c. oils removed)
• Stratum lucidum
• Stratum Granulosum
• Stratum Spinuousus
• Stratum Basale

Question 9

Types of cells in exchange epithelium and transport epithelium

Answer 9

• Exchange epithelium = simple squamous (allows easy exchange)
• Transport epithelium = columnar (small intestine)

Question 10

Intracellular junctions (3 types)
   -definitions

Answer 10

• Intercellular junctions: key feature of epithelial cells
  
  • tight junctions restrict movement of material passing between transport epithelial cells
  • Anchoring junctions: cell-cell (desmosomes) and cell-basement membrane (hemidesmosomes
  • Gap junctions: cytoplasmic bridge allows electrical continuity and synchronised contraction
    - allow communication
    - cardiac myocyte have them

Question 11

Secretory epithelia - what they do

-2 types

Answer 11

• Form clusters or glands rather than sheets and secrete substances
  - may also be individual cells scattered (e.g. goblet cells
• Exocrine glands: have ducts and secrete onto internal or external surface (sweat, saliva, mammary)
• Endocrine cells: secrete into the bloodstream (e.g. Islets of Langerhans and insulin, thyroid, adrenal and pituitary)

Question 12

Gland development

Answer 12

• Exocrine glands: hollow centre forms,, creating a duct that provides passageway for secretion sot move to surface
• Endocrine glands: Lose connecting bridge of cells that link them to parent epithelium -> secretions go straight to bloodstream

Question 13

Kidney

Answer 13

• Nephron = renal coruscle + tubule
• blood filtered w/in kidney by passing along nephron
  
  • filtered material passes along tubule of nephron
  • transport epithelia found in proximal and distal convoluted tubules (and loop of Henle)
• blood enters and exits corpuscle -> filtrate forms and moves down convoluted tubule and through system
  - filtrate modified
• Proximal convoluted tubule = fuzzy surface (has tiny microvilli to increase SA for absorption)
• lining of surrounding capillaries: endothelium (flat squamous cells)
  
  • podacytes sit outside capillary -> comblike structure helps filter blood physically and electrically (has footlike structures)
• basement membrane, endothelium and podocyte = filtration system

Question 14

Epithelium in Jejunum

Answer 14

• single layer of epithelium in internal surface -> renews v. quickly (renewal occurs in crypts)
• microvilli on epithelia (to increase SA)
• columnar epithelia

Question 15

Epithelia in Liver - how cells arranged

Answer 15

• sheets of 6 sided hepatocytes arranged into lobules
  
  • bathed by sinusoidal blood on 2 sides
• b/w each row of hepatocytes are canaliculi into which bile flows (eventually become ducts)
  
  • bile helps break down fats

Question 16

Muscle tissue - 3 types

-e.g.

Answer 16

• 3 types;
  1. Skeletal (striated): voluntary contraction, often agonist/antagonist
  e. g. digphragm, tongue, extrinsic eye muscles
  2. Smooth: involuntary contraction (autonomic)
  e. g. intestinal wall w/ agonist/antagonist, blood vessels, uterus
  3. Cardiac: involuntary contraction
  
  • in heart
• contraction also important for wounds, scar tissues etc for regions to heal

Question 17

Skeletal muscles

• what composed of and basic function
• features of muscle cells
• e.g.

Answer 17

-Composed of myofilaments -> has myosin (thick) and actin (thin) fibres
-divided in sacromeres that align (z disk aligns and makes striations)
-thick heads that can move along actin if ATP available
Features;
-fused cells (so in long parallel arrangements)
-many nuclei
-peripheral nuclei
-cylindical
*can regenerate
e.g. pharynx, diaphragm, tongue, eye, oesophagus

Question 18

Skeletal muscles;

-slow vs fast twitch

Answer 18

• Slow twitch (aerobic): fatigue resistant (endurance, postural muscles)
  
  • tend to be red (like chicken leg muscle)
• Fast twitch (anaerobic): strong, precise, fatigue rapidly, sprinters, digits
  - tend to be white (like chicken breast)

Question 19

Smooth Muscle

-features and e.g.

Answer 19

Features;

• Single cells w/ one central nucleus
• often 2 layers
• perpendicular
• no striations
• spindle-shaped
• diameter varies

-e.g. arrector pili, blood vessels, iris, airways, spleen, uterine wall, bladder

Question 20

Cardiac muscle

• features
• can they regenerate?

Answer 20

Features:

• Striations
• branching
• central nucleus
• intercalated discs
• complex pattern
• can’t regenerate as post-mitotic
  e. g. Cardiac (heart)

Question 21

Connective Tissues

• functions
• definition

Answer 21

• Structural and metabolic support for tissues/organs
• mediate nutrient and metabolite exchange w/ circulation
• cells embedded in mesh of fibres (elastin/collagen) and extracellular matrix
  
  • have extensive ECM
• CT: any structure whose primary function is physical support for other structures
  - in broader sense, also encompasses fluids

Question 22

Types of CT (6)

-e.g. of each

Answer 22

1. Loose: Fibroelastic tissues that underlie epithelia (support, biological packing)
   e. g. lamina propria of intestine, surrounds blood vessels
2. Dense: tissues for strength, flexibility, biomechanical action
   
   • e.g. tendons, ligaments, muscle and nerve sheaths, basement membranes
3. Adipose tissue - fat storage (has no real matrix)
4. Cartilage: supporting tissue (ear, nose, knee menisci, joints)
5. Bone: calcified supporting tissue
6. Blood: water matrix - ions and dissolved molecules, soluble proteins

Question 23

Osteoblast, osteoclast and osteocyte

Answer 23

Osteoblast: lays new bone matrix
Osteoclast: ‘Clean’ take bone away
Osteocyte: maintain bone (are w/in lacuni)

*same pattern works for other cell types (i.e. chondrocytes)

Question 24

Chondrocytes - appearance

Answer 24

• Chondrocytes appear as cells w/in a matrix

- in cartilage, these cells appear in clusters (usu. of 2)

Question 25

Nervous Tissue - Nerve cells - Glial cells *definitions

Answer 25

- Nerve cells (neurons): specialised cells that receive, integrate and transmit info in form of electrical signals - Glial cells (astrocytes for metabolic suuport, Schwann cells and ogliodendrocytes for myelin)

Question 26

Basic neuron structure -important features

Answer 26

- Cell body = nucleus and surround cytoplasm (perikaryon) - in CNS or peripheral ganglia - 1 axon (efferent) - arises from axon hillock - ends at terminal boutons - 1 + dendrites (are afferent) *are excitable cells and are post-mitotic (don't get replaced)

Question 27

3 Types of Neurons

Answer 27

1. Multipolar Neurons: Multiple dendrites and are able to integrate input from many afferent neurons e. g. interneurons and motor neurons 2. Bipolar neurons: single dendrite located opposite the axon hillock e. g. sensory neurons of sight, smell and balance 3. Pseudounipolar neuroons: fusion of the origins of the axon and dendrite e. g. primary sensory neurons (some in eye and ear too)

Question 28

Organisation of the brain

Answer 28

- Grey matter = peripheral cortex - folded in mammals to give sulci and gyri - small foci of neuronal cell bodies form nuclei deeper w/in brain - covered in 3 layers of CT meninges (pia mater, arachnoid and dura mater (outermost tough layer) - cerebrospinal fluid fills subarachnoid space b/w arachnoid and pia mater

Question 29

Glial cells

Answer 29

- Oligodendrocytes (called Schwann cells in PNS) - Astrocytes (regulate metabolistes) - Microglia - Ependyma (simple cuboidal/columnar ciliated ep. - lines ventricles and spinal canal

Question 30

Synapses in Neurons

Answer 30

- Neurotransmitters in vesicles | - electrical signals cause release of chemical across synapse

Question 31

Neuromusclar Junction -what it is, basic features

Answer 31

- Similar to basic synapse structure - Each motor neurone innervates from 1 >1000 muscle fibres - axon ends at motor end plate, enveloped by Schwann cell - Ach is neurotransmitter that is broken down after signal sent

Question 32

Organ

Answer 32

-Organ: anatomically discrete collection of 2 or more tissue types (often 4) working together to perform a specific function

Question 33

Organ Systems

Answer 33

- More than one organ interacting | e. g. Respiratory system

Question 34

Sebaceous Gland

Answer 34

- Has hollow middle - outside gland, epithelial cells rapidly dividing, cells mature and move to middle of gland - Accumulates oily secretions (sebum) - nucleus dies and whole cell bursts onto hair follicle -> comes out and goes onto skin surface * Holocrine secretion: entire cell is shed

Question 35

Sweat gland

Answer 35

- Simple tubular gland - lined by cuboidal epithelium - discharge secretions into tube