Fundamentals of Anatomy and Histology Flashcards

1
Q

how to calculate magnification

A

Objective magnification x eyepiece magnification (eyepiece is 10x)

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2
Q

how to set up microscope (3 stages)

A
  • focus objective lens on specimen and adjust eyepieces
  • Focus condenser lens on specimen (using pencil and then blur)
  • Adjust substage iris diaphragm for optimum illumination (affects resolution)
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3
Q

frontal (coronal) plane of body

A

front and back

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4
Q

sagittal plane of body

A

left and right

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5
Q

transverse plane of body

A

top and bottom

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6
Q

anterior
posterior

superior
inferior

medial
lateral

proximal
distal

superficial
deep

A

front
back

top
bottom

towards the medium plane
away from the medium plane

towards the trunk
away from the trunk

towards the surface
towards the interior

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7
Q

terms of location embryology:

cephalic
caudal

ventral
dorsal

A

cephalic - towards head
caudal - towards bottom

ventral - towards front
dorsal - towards back

for neuroanatomy, rotate labels 90 degrees anticlockwise (dorsal on top)

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8
Q

anatomical terms of movement:

flexion
extension

abduction
adduction

medial rotation
lateral rotation

supination
pronation

dorsiflexion
plantarflexion

inversion
eversion

circumduction

opposition
repostion

protraction
retraction

elevation
depression

A

flexion - movt that decreases angle between 2 body parts
extension - movt that increases angle between 2 body parts

abduction - movt away from midline
adduction - movt towards the midline

medial rotation - rotating movt towards the midline
lateral rotation - rotating movt away from midline

supination - keep elbow/shoulder still flip hand with palm facing up
pronation - flip hand with palm facing down

dorsiflexion - flexion at ankle so foot points superiorly
plantarflexion - extension at ankle so foot points inferiorly

inversion - movt of sole towards median plane
eversion - movt of sole away from median plane

circumduction - conical movt of a limb extending from the joint, controlled

opposition - movt that bring the thumb and little finger together
repostion - movt that moves the thumb and little finger away from each other

protraction - reaching out/ protruding
retraction - picking something up/retracting

elevation - movt in superior direction
depression - movt in inferior direction

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9
Q

how many regions are there in the abdomen

A

9

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10
Q

how to process tissue for light microscopy

A
  • treat specimen with a fixative
    (halts metabolism, inactivates enzymes, renders cellular macromolecules insoluble)
  • cut tissue to 10-20um one cell thick, by freezing water or replacing water with more supportive medium (eg. wax by dehydrating with graded ethanol)
  • cut wax embedded tissue on a microtome
  • stain tissue, but stains are usually aqueous solution immiscible with wax, so rehydrate as wax no longer needed as section cut and glass support slide
  • cannot stay in aqueous phase since stain will leach out, dehydrate with graded alcohols and remove ethanol with xylene/toluene
  • protect stained section with cover slip
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11
Q

which cellular structures are shown after staining with Haematoxylin and Eosin dyes

A

Haematoxylin (dark blue)

  • basic dye
  • binds to negative charged structure such as DNA, RNA etc.

Eosin (red)

  • acidic dye
  • binds to positively charged structure (most cellular proteins)
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12
Q

which cellular structures do trichrome dyes show up

A

show nuclei and cytoplasm

help differentiate collagen from smooth muscle

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13
Q

The light microscope

A

Overall tissue organisation can be seen

Individual cells distinguished

Cell nucleus visible

Resolution 200nm-10mm

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14
Q

Scanning electron microscope

A

3D views

Resolution 0.4nm-1mm

Electron beam fired at surface and are reconstructed via a detector to produce image

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15
Q

Transmission electron microscope

A

Visualise individual cells

Resolution 0.4nm-100um

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16
Q

Human tissue act (2004)

A

Regulation of post-mortem examination, anatomical examination, public display of tissue from the deceased, removal and storage of human tissue

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17
Q

Function of Bursae and tendon synovial sheaths

A

Important in reducing friction during movement

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18
Q

Define:

Myotome

Dermatome

A

Myotome:
The complete muscle mass receiving its innervation from one cranial or spinal nerve

Dermatome:
The area of skin supplied by one cranial or spinal nerve

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19
Q

Resolutions of the microscopes

Compound light microscope
SEM
TEM

A

200nm - 10mm

  1. 4nm - 1mm
  2. 078nm - 0.1nm
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20
Q

Unobvious components of a compound light microscope

Condenser

Diaphragm

A

Focuses light through specimen

Controls the amount of light entering the condenser

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21
Q

How to distinguish the 5 types of white blood cell under a microscope (with H-E staining)

Neutrophils
Eosinophils
Basophils
Lymphocytes
Monocytes
A
  • contain nuclei with many different lobes
  • contain red or pink granules
  • contain dark blue granules
  • contain a circular nucleus that fills most of the cell
  • nucleus in the shape of kidney bean
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22
Q

Colour of staining of components using H&E staining

Nuclei
Cytoplasm
Collagen
Erythrocytes/red blood cells

A

Blue
Pink to red
Pale pink
Orange

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23
Q

Examples of artefacts

A

Degradation:
If enzymes haven’t be deactivated properly eg. Loss of cilia

Incomplete dehydration or rehydration:
General shrinkage, cracks in tissue

Folds:
When cut tissue section is placed onto slide

REMEMBER: some materials are removed by organic solvents eg. Lipid components such as cell membranes

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24
Q

Colour of staining of components using Gomori Trichrome staining

Nuclei
Collagen 
Muscle
Erythrocytes
Background
A

Blue/grey

Green

Red

Red

Blue/green

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25
Q

Features of epithelium

A
  • forms dense cellular sheets
  • no blood vessels
  • rests on a basal lamina complex
  • polarised cells (clear apical/basal aspects)
  • stain well with H&E
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26
Q

Classification of an epithelium

A

Cell shape:

  • squamous (flattened)
  • cuboidal
  • columnar

Cell arrangement:

  • simple (single layer)
  • pseudostratisfied (all cells in contact with basal lamina)
  • stratified (multiple layers)

Cell specialisation:

  • cilia (movt)
  • microvilli (absorption)
  • keratinisation (protection)
  • eg. Goblet cells
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27
Q

Microvilli

A
  • inc SA for absorption

- shape maintained by actin filaments anchored to cell membrane

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28
Q

Examples of each epithelium in the body

A

Simple squamous:
Lining surfaces involved in passive transport of gas (lungs) or liquid (endothelium of capillaries)

Simple cuboidal:
Lines small ducts and tubules

Simple columnar:
Absorptive surfaces such as small intestine and secretory surfaces

Pseudostratisfied columnar:
Upper airways (nuclei at different levels)
Stratisfied squamous (others rare)
Layers for physical protection for sites subject to mechanical abrasion
Oral cavity, pharynx, oesphagus 

Stratisfied keratinised:
Have a cornified layer of keratinised dead cells on very surface of epithelium for physical protection
Eg. Skin (prevent desiccation/waterproof)

Transitional epithelium:
Only urinary tract
Waterproof, protective from toxicity, able to distend (stretch)

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29
Q

Goblet cells

A
  • modified columnar epithelial cell that synthesises and secretes mucus
  • found particularly in respiratory/gastrointestinal tracts
  • stains poorly with H&E
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30
Q

Cilia cells

A
  • move fluid and particles along epithelia surface
  • core of 20 microtubules arranged as 9 doublets around a central pair
  • bigger than microvilli
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31
Q

Function of cell junctions in epithelial cells (2)

A

Keep epithelial sheets tightly bound (anchoring junctions)

Allow functional integrity of cells
(Selective barriers - tight junctions)
(Or for intercellular communication - gap junctions)

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32
Q

Organisation of junctions in the cell

A

Tight junction
(Seals neighbouring cells tog)
-
Adherens junction
(Joins actin bundle in one cell to another)
-
Desmosome
(Joins intermediate filaments in one cell to another)
-
Gap junction
(Allows passage of small ions and molecules)
-
Hemidesmosome
(Anchors intermediate filaments in a cell to basal lamina)

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33
Q

Desmosomes and Hemidesmosomes continued

Anchoring junctions

A
  • STRONG anchors for intermediate filaments
  • Contain membrane-spanning proteins (desmoglein & desmocolin) that allow sheets to flex without tearing, binds homophilically
  • plaque that links membrane-spanning proteins to intermediate filaments is made of plakoglobin and desmoglobin
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34
Q

Adherens junctions

Anchoring junctions

A
  • transmembrane cadherin protein dimers bind homophilically to others on adjacent cells, which are connected to actin filaments
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35
Q

Tight junctions

Non-anchoring

A
  • create seal between cells so NO molecules can get through

- tight-junction proteins that seal cells are Claudin and Occludin (homophilically)

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36
Q

Gap junctions

Non-anchoring

A
  • allow exchange of small molecules between cells via hydrophilic pore
  • protein channel gap made from 6 Connexin molecules joined together (connexon)
  • channel 1.5nm in diameter
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37
Q

Connective tissue types (2)

A

Soft connective tissue:

  • basal lamina
  • capsule for organs
  • tendons & ligaments
  • areolar tissue
  • adipose tissue

Hard connective tissue:

  • bone
  • cartilage
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38
Q

Cells of soft connective tissue

A

Permanent cells:

  • fibroblasts (synthesise collagen)
  • adipocytes/fat (largest store of energy, fill spaces between tissues)

Transient cells:

  • phagocytic
  • immunocompetent (mast, plasma, lymphocytes)
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39
Q

Non-cellular components of soft connective tissue (fibres)

COLLAGEN

A

Collagen:
- inelastic, strong, thick

  • type 1 = most abundant, forms fibres, synthesised by fibroblasts formed of 3 pp chains
  • type 2 = forms thin fibres (in hyaline & elastic cartilage)
  • type 3 = reticular fibres
  • type 4 = in basal lamina, cohere as amorphous mats
  • type 5 = small amount in basal lamina
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40
Q

Non-cellular components of soft connective tissue (fibres)

ELASTIC FIBRES

A
  • stretchable, resilient, thin
  • hydrophobic
  • cross linking
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41
Q

Non-cellular components of soft connective tissue (non fibre)

GROUND SUBSTANCE

A
  • viscous, semi-fluid gel where cells and fibres of connective tissue sit
  • contains mixture of glycoproteins and proteoglycans
  • also acts as lubricant & barrier to foreign particles
42
Q

Proteoglycans

A
  • protein core with carb side chains
  • main carbs are GAGs
  • side chain extend to occupy large volume
  • VERY hydrophilic (swell up from water intake, so extra cellular matrix can withstand compressive forces)
43
Q

Types of soft connective tissue

A

Basal lamina:

  • interface between epithelium & underlying connective tissue
  • selectively permeable
  • controls growth/specialisation

Loose:

  • component of lamina propria (digestive, respiratory, glands, skin hypodermis)
  • oval fibroblasts
  • immunocompetent cells may be present

Dense:

  • subclassified as regular or irregular depending on orientation of collagen fibres
  • irregular found in dermis of skin
  • oval fibroblasts & immunocompetent cells
  • regular found in tendons and ligaments
44
Q

Types of basic tissue (4)

A

Epithelia:
- protection, secretion, absorption

Connective tissue:

  • support to other tissues
  • divided into general connective & specialised connective

Nerve tissue:

  • sensation, control to muscles & glands
  • cells = neurons (involved in electrical signalling), neuroglia (support cells that wrap neurons)

Muscle tissue:
- movt
- tissues contain filaments which generate force and muscle contraction
- either striated (skeletal & cardiac) or non-striated (smooth)
-

45
Q

Tissues to Organs

  • liver
  • brain
  • intestines
  • heart
  • skin
A

Liver:
Mostly epithelia, little muscle

Brain:
Mostly nerve, little muscle

Intestines:
Mostly epithelia, muscle and connective tissue

Heart:
Mostly muscle

Skin:
Epithelia (epidermis) and connective tissue (dermis)

46
Q

Functions of superficial fascia

Loose connective tissue and fat

A
  • storage of water & fat
  • protection since fat & water act as cushion
  • thermal insulation from fat
  • conduction to transport nerves and blood vessels to the skin
  • metabolic function since fat is an energy store
47
Q

Functions of deep fascia

Dense connective tissue

A
  • movt of muscle (muscles wrapped in deep fascia can slide over eachother)
  • provides attachment for some muscle since it’s so thick in some places/solid surface
  • conduction, blood vessels & nerves are transported via fascias (sheaths)
  • capsule around some organs
48
Q

Serous membranes

A
  • between body wall (or tissue) and mobile organs is serous membrane
  • secretes fluid into a cavity
  • facilitates movt and reduces friction (lungs, heart, abdominal content)
  • like an organ embedding itself into semi-inflated balloon
49
Q

Basic circulatory system

A

Arteries

  • take blood away from heart
  • divide until smallest (arterioles) supply the tissue bed

Veins
- take blood to the heart

50
Q

The systemic circulation
(Blood to the systems)
(Left side of heart)

A
  • aorta pumps oxygenated blood to tissues

- veins take deoxygenated blood back via vena cava

51
Q

The pulmonary circulation
(To the lungs)
(Right side of heart)

A
  • brings deoxygenated blood to the lungs via pulmonary artery
  • veins bring oxygenated blood back to right side of heart (pulmonary veins)
52
Q

The portal system example

Largest portal system starts in digestive system

A
  • involves 2 capillary beds
  • blood passing through their capillary network ends up in the hepatic portal vein which drains into the capillary bed of the liver
  • products of digestion are removed, processed and stored
  • liver can release the nutrients when desired by releasing them into the veins of systemic circulation
53
Q

Structure of arteries

3 layers

A

INSIDE-OUT

Endothelium (epithelium)
-
Tunica media (smooth muscle)
-
Tunica externa (connective tissue)
54
Q

Systole

Diastole

A

Systole - heart contracts, systolic pressure around 120mmHg

Diastole - heart relaxes, diastolic pressure around 80mmHg

55
Q

Function of arteriovenous shunts

A

Shortcut between artery and vein (missing out capillary bed)

56
Q

Anastomoses

Inc types of artery

A

Arteries can anastomose instead of ending up as a capillary

Combine with other arteries

Anastomoses are common around joints in limbs

They form an alternative route when the main flow is obstructed eg. By movt of the joint

Types of artery:

Anatomical end artery - when an artery is the sole contributor to an capillary bed (no anastomotic connections)
(Artery heading into the gut wall)

Functional end artery - when there is more than one artery supplying tissue bed but loss of main artery still leads to tissue death, that artery is this.
(Eg. 2 coronary arteries in the heart)

57
Q

The lymphatic system

A
  • Uni-directional (valves)
  • 10% of fluid stays behind in tissue as lymph (90% goes back to venous side of circulation)
  • lymph circulated to the root of the neck (in its own system), into large veins (subclavian veins) before going back into the heart
  • on the way to the neck, lymph vessels connect to lymph nodes (packed with lymphocytes that combat pathogens found in the lymph fluid)
58
Q

Sentinel node

A

The first set of lymph nodes draining a given territory

Predict the source of the cancer/infection

59
Q

Locations of lymphatic vessels

A

Superficial (fascia) lymphatics follow veins

Deep lymphatics follow arteries

60
Q

Syncytium define

A

Single cell containing many nuclei

Formed when myoblasts fuse, proliferate and form myotubes

(Skeletal muscle)

61
Q

Propagation of action potential within muscle

A

Action potential arrives at end of motor neuron

Acetylcholine released across cleft

Impulse carried into cell via T tubules

Triggers release of Ca2+ from sad ppl admit reticulum

Calcium causes muscle fibres to contract

62
Q

Cardiac myocytes

A

Mono or bi-nucleated cells

Individual cells connected via intercalated discs

Cells have gap junctions to allow transmission of action potentials

Many mitochondria

No satellite cells

63
Q

Cartilage

A

Devoid of blood vessels

Chondrocytes make and maintain it

64
Q

Osteons

Overlapping in compact bone

A

Have central Haversian canal with blood vessels
(Which are linked transversely with volkmanns canal)

Around canal is layers of lamellae (mineralised matrix)

In this are osteocytes (connected by canniculi)

65
Q

Lamellar

A

Mineralised organic matrix

Organic: collagen type I for tensile strength
Inorganic: crystals of hydroxyapatite for compressive strength

66
Q

Trabecular bone

Spongy

A

Rods of lamellae form trabeculae (follow lines of stress for strength)
(Less mass though)

Trabeculae form vascularised cavities
(contains red marrow)

Canaliculi connect osteocytes to these cavities

67
Q

Formation of haversian systems

A

Osteoclasts tunnel through pre-existing bone

Tunnel invaded by blood vessels and osteoprogenitor cells

Osteoprogenitor cells -> osteoblasts

Osteoblasts lay down successive bone lamellae on walls of tunnel

Between new lamellae (interstitial systems) is remnants of old osteons

68
Q

Image resolution

A

Number of pixels in each direction of the image

69
Q

Aspect ratio

A

Ratio of an images width to its height

70
Q

Intensity/grey-scale

A

The number for a pixel

71
Q

Low spatial resolution

Low intensity resolution

A

Not able to resolve small objects

Not able to differentiate objects that look similar

72
Q

Volume mode visualisation

A

Involves projecting 3D data set onto 2D image

3 types:

  • MIP (maximum intensity projection)
  • surface rendering
  • volume rendering
73
Q

Most common x-day contrast agent

A

Iodine because it’s very attenuating to x-rays

Injected into circulation

74
Q

Fluoroscopy

A

Dynamic 2D x-day imaging

75
Q

For medical application, what is the x-ray target material?

A

Tungsten

76
Q

What x-ray energy is used in medical application

A

30-100 kV

77
Q

How an x-ray beam is created

A

Current passed at low voltage through filament of tungsten (cathode)

Causes heating of wire and emission of electrons

Electrons focused and formed into narrow beam and accelerated towards the anode (tungsten)

Electrons interact with the atoms on anode and produce x-ray photons

(99% of energy converted to heat, 1% to photons)

78
Q

Factors that affect the amount of x-ray transmission

A
Attenuation coefficient 
(higher atomic = higher attentuation)
(Higher attenuation = brighter image)

Thickness

79
Q

Alpha nuclear decay

A

Gives off helium atom

80
Q

Beta minus decay

A

Neutron is converted into proton

Beta(-) particle given off (fast moving e-

Anti neutrino given off (sub-atomic particle)

81
Q

Beta plus decay

Positron

A

Proton converted to neutron
Gives off a positron & neutrino

Positrons travel a few mm in space, combine with electron, annihilate and generate 2 gamma photons

82
Q

Useful types of isotopes for imaging applications

A
Gamma generators (Tc)
Positron generators
83
Q

Most common PET isotope

A

Fluorine 18

Attached to glucose to make FDG to show glucose metabolism

84
Q

Acoustic impedance (US)

A

Material property

85
Q

Attentuation

A

Combination of scattering and absorption

Scattering causes the textured image inside tissues

Higher frequency = higher absorption

86
Q

A mode vs M mode vs B mode imaging (US)

A

A mode:
A single amplitude time signal
(Amplitude)

M mode:
Have amplitude time signal and measure serially & multiple times and display in 2D image
(Movement)

B mode:
If take A mode image and move transducer across tissue to diff locations, can stack A mode images together to form 2D image

87
Q

How does MRI work

A

Person put in strong magnetic field

Person Irradiated with radio waves

Person re-emits signal, MRI localises signal using magnetic field gradients to form an image

88
Q

MRI

A

Nuclei with non-zero spin have magnetic moments

These moments typically just cancel out due to the random orientation

But when placed in external magnetic field the spins either line up with the field or against the field

Also undergo spin-top motion at Larmor frequency
(depends on strength of magnetic flux density of Bo field and the gyromagnetic ratio which is diff for each type of nucleus)

Adding radio frequency magnetic field flips some spins into anti parallel direction, reducing the size of longitudinal magnetisation

Flipped spins are put ‘in phase’ in the transverse plane, generating net transverse magnetisation

The longer the RF is applied, the more it nutates to the xy plane

89
Q

Isotope with the highest NMR sensitivity

A

H1

High natural abundance and is present in the body in large quantities - water

90
Q

Basis of contrast in MRI

A

After excitation, nuclear spins return to original energy levels

Longitudinal magnetisation recovers with relaxation time T1 (inc)

Transverse magnetisation recovers with relaxation time T2 (dec)

T1 & T2 values vary between tissues, so spins in diff tissues recover and decay at different rates

91
Q

Free induction decay signal (FID)

A

Following RF excitation, The changing transverse magnetisation induces electrical voltage in a loop of conducting wire placed nearby

92
Q

Types of hormone

A

AA derivatives (eg. Adrenalin)

Small peptides (eg. ADH)

Proteins (eg. Growth hormone, insulin)
- lots of RER, golgi, secretory vesicles

Steroids (eg. Cortisol, oestrogen)
- lots of SER, lipid droplets

93
Q

Neurohypophysis/posterior pituitary

A

Cell bodies of these neurones lie in the hypothalamus
(Supraoptic & paraventriculae nuclei):
Both polypeptides

ADH:
Inc water retention in kidney

Oxytocin:
Contract smooth muscle (especially uterus during childbirth)
Contract myoepithelial cells of mammary glands during lactation

Transported down axons to terminals

94
Q

Cell types secreting hormones

Anterior pituitary

A

Acidophils (pink):

  • somatotrophs (growth hormone)
  • mammotrophs (prolactin)

Basophils (blue):

  • Thyrotrophs (TSH)
  • corticotrophs (ACTH)
  • gonadotrophs (FSH & LH)

Chromophobes (grey)
(Reserve cells/stem cells)

95
Q

Thyroid follicular cells

A

Thyroid follicular cells take up iodide from blood

Synthesized to iodine & attached for tyrosine if thyroglobulin within the lumen of the follicle and stored (colloid)

On stimulation:
Follicular cells endocytose the iodinated thyroglobulin, break it down, release the iodinated tyrosine derivatives (T3 & T4)

96
Q

Thyroid parafollicular cells (C)

A

Secrete calcitonin

inhibits Ca++ mobilisation

97
Q

Adrenal cortex

Outside-in

A

Zona glomerulosa
secrete mineralocorticoids
(mainly aldosterone - regulates Na+ retention in distal convoluted tubule of kidney)

Zona fasciculata
Secrete glucocorticoids
(Mainly cortisol - increases glucose, lipid and protein metabolism)

Zona reticularis
Secrete some glucocorticoids and small quantities of sex steroids

98
Q

Adrenal medulla

A

Resemble axon-less ganglion cells

Recieves cholinergic input from lesser splanchnic nerves

On stimulation secrete catecholamines directly into blood

80% of cells secrete adrenaline
The rest secrete noradrenalin

99
Q

Types of islet of langerhan cells

Lining of pancreas

A

A/Alpha cells (20%):
Secrete glucagon

B/Beta cells (70%):
Secrete insulin

D/Delta cells (5-10%):
Secrete somatostatin

F/PP cells (1-2%):
Secrete pancreatic polypeptide

100
Q

Diffuse neuroendocrine system

Scattered cells especially in gut and respiratory

A

Secrete amine or peptides with hormone-like or neurotransmitter activity
(Gastrin, CCK, secretin, serotonin etc)

Secrete and act locally

101
Q

Imaging technologies

A

MRI:

  • magnetic resonance imaging
  • strong radio waves sent through body
  • (displaces nucleus of hydrogen atoms, when move back to original positions, own radio waves are emitted which the scanner picks up and turns into image)
  • pregnant or ppl with metal implant can’t have
  • more detailed than CT

CT:

  • computerized tomography scan
  • beams of X-rays from different angles sent through body, each angle provides a thin slice of area
  • 2D images onto computer are made into 3D cross sectional picture
  • contrast material taken by patient to make organs easier to see
  • uses = internal injuries, muscle and bone disorders, detect cancer
  • high resolution pictures but can inc risk of cancer / reaction to contrast (mild hives)
  • pregnant women can’t
  • faster than MRI

PET:

  • positron emission tomography
  • uses a dye with radioactive tracers
  • decay of radioactive tracers produce positrons, which react with electrons (annihilation), produces energy in the form of 2 photons in opposite directions which are detected
  • measure blood flow, oxygen use, glucose metabolism
  • can show problems at a cellular level
  • risks = exposure to radiation, allergic reaction to tracer
  • mainly used to detect cancer
  • normally used in conjunction with CT/MRI

SPECT:

  • rotate gamma camera detectors around patient and detect gamma ray emission from tracer
  • uses radioactive substance
  • primarily used to diagnose heart disease

Ultrasound:
- emir short ultrasound pulse, listen to what is reflected back

102
Q

Groups of hormones

A

Proteins/peptides:

  • majority
  • synthesized by DNA transcription/translation
  • small, long-chain, glycoproteins
  • water soluble so in blood unbound
  • therefore short half life
  • produced by hypothalamus, pituitary, parathyroids, GI tract, pancreas

Steroids:

  • sex hormones, adrenal cortex hormones
  • three 6 carbon rings, one 5 carbon ring
  • derived from cholesterol
  • synthesized in mitochondria & SER
  • lipids molecules so diffuse through membranes
  • circulate in blood bound to proteins
  • produced by adrenal gland, gonads, placenta