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Body Logistics > 4 - Glands > Flashcards

4 - Glands Flashcards

1
Q

definition of a gland

A

an epithelial cell or aggregate of cells that are specialised for the secretion of a substance

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2
Q

how can glands be classified

basics - details on seperate cards

A

based on mode of secretion
- endocrine: products released into vascular (blood) or lymphatic system
- exocrine: products released into ducts that open to organ lumen or onto skin surface

exocrine can be classified further by mode of secretion
- apocrine
- holocrine
- merocrine

by their shape
- simple/compound (unbranched/branched)
- acinar or tubular

they can also be classified by unicellular/multicellular or their type of secretion

main endocrine glands are
- adrenal
- thyroid
- parathyroid
- pancreas

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3
Q

how can glands be classified

basics - details on seperate cards

A

based on mode of secretion
- endocrine: products released into vascular (blood) or lymphatic system
- exocrine: products released into ducts that open to organ lumen or onto skin surface

exocrine can be classified further
by mode of secretion
- apocrine
- holocrine
- merocrine

by their shape
- simple (unbranched)
- compound (branched duct system)

main endocrine glands
- adrenal
- parathyroid
- thyroid
- pancreas

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4
Q

what is a merocrine mode of secretion

A

form of exocytosis
has two pathways (regulated and constituative secretion, covered on next slide)

  • membrane bounded compartment approaches cell surface
  • it fuses with the plasma membrane
  • its contents are in continuity with extracellular space and so dispersed by diffusion
  • plasma membrane transiently larger
  • membrane retrieved, stabilising cell surface area
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5
Q

merocrine secretion: regulated vs consituative secretion

A

merocrine secretion has two pathways

regulated
- active process - uses energy
- contents of vesicle can be anything within cell (eg organelle)
- secretory granules accumulate in large vesibles
- active secretion requires specific signal (Ca2+ ions)
- vesicle migrates to cell surface along microtubules
- in presence of Ca2+, membrane of vesicle fuses with plasmalemma
- cargo released to extracellular space

constituative
- the secretory product is not concentrated into granules
- the secretory product is instead packaged into small vesicles and continuously released to the cells surface
- used mainly to repopulate the plasma membrane with plasma proteins
- vesicles always moving (not waiting for signal)

note: product inside vesicle = cargo (secretion that’s released)

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6
Q

what is a apocrine mode of secretion

A
  • non membrane bounded structure (eg lipid) approaches cell surface
  • makes contact and pushes up apical membrane
  • thin layer of apical cytoplasm drapes around droplet
  • membrane surrounding droplet pinches off from cell
  • plasma membrane transiently smaller (lose the apical surface of the cell)
  • membrane added to regain original area
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7
Q

what is a holocrine method of secretion

A
  • the secretory cell gradually fills up with secretory granules
  • the cell organelles degenerate and the cells and nucleus die
  • the plasma membrane breaks and the contents (secretum) empties
  • dead cells are replaced by mitotic division of the basal cells

ie: disintergration of the cell and discharge of the whole cell into the extracellular space

note: the secretum in sebaceous glands = sebum

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8
Q

exocrine glands - unicellular vs multicellular

A

are either unicellular or multicellular

unicellular
the individual cells (eg goblet cells) of unicellular glands release their secretion (mucus) onto surface epithelium

multicellular
- have a duct system
- the glandular cells extend from the epithelial surface into underlying connective tissue
- they remain within the wall of the organ, or migrate to a distant area
- they discharge their secretory products (eg bile, digestive enzymes and saliva) into the lumen of organs via these ducts

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9
Q

what does mucus do

A
  • lubricate the passage of materials (in the digestive tract)
  • moistens the air (respiratory system)
  • entraps inhaled dust and carbon particles (respiratory tract)
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10
Q

what are the different types of multicellular exocrine glands

A
  • simple tubular eg large intestine. Secretory portion is straight tube formed by secretory goblet cells
  • simple branched tubular eg gastric glands and mucus glands of the oseophagus, tongue and duodenum
  • simple coiled tubular found in skin eg eccrine gland with secretory portion found deep in dermis. Eg merocrine sweat glands
  • simple acinar secretory portion is an outpouching of the epithelial surface
  • simple branched acinar duct is relatively short. found in stomach and also found as sebaceous (oil) glands
  • compound tubular eg duodenum
  • compound acinar alveolar shaped cells that are pyramid shaped and serous secreting eg pancreas
  • compound tubuloacinar contain elements of both acinar and tubular glands, and can produce both serous and mucinous secretions eg submandibular salivary gland
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11
Q

tubular vs acinar vs alveolar

A

tubular
- longer, thinner shape
- ducts have a thin, tubular lumen

acinar
- round shaped gland
- thin, tubular shaped lumen
- pyramid shaped cells

alveolar
- round shaped gland
- large, round shaped lumen

note: acinar and alveolar glands look the same from the outside

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12
Q

types of hormone: steroid

synthesis and storage, transport in blood, location of receptor, response to receptor-ligand binding and examples

A

synthesis and storage
synthesised on demand from precursor cholesterol

transport in blood
bound to carrier proteins (lipid like)

location of receptor
cytoplasm or nucleus - some have membrane receptors too

response to receptor-ligand binding
when bind to nucleus… activation of genes for transcription and translation; may have non genomic actions

examples
oestrogens, androgens, progesterone, cortisol, glucocorticoids

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13
Q

types of hormone: catecholamines

synthesis and storage, transport in blood, location of receptor, response to receptor-ligand binding and examples

A

type of amino acid derived hormones, with thyroid hormones

synthesis and storage
made in advance by the adrenal glands; stored in secretory vesicles

transport in blood
dissolved in plasma

location of receptor
cell membrane

response to receptor-ligand binding
activation of second messenger systems

examples
adrenaline, noradrenaline and dopamine

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14
Q

types of hormone: glycoproteins and peptide hormones

synthesis and storage, transport in blood, location of receptor, response to receptor-ligand binding and examples

A

synthesis and storage
made in advance, stored in secretory vesicles

transport in blood
dissolved in plasma

location of receptor
cell membrane, regulated

response to receptor-ligand binding
activation of second messenger systems; may activate gene expression. Alter transcription + translation of gene.

examples
insulin, glucagon, prolactin, ACTH, PTH and gastrin

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15
Q

types of hormone: thyroid hormones

synthesis and storage, transport in blood, location of receptor, response to receptor-ligand binding and examples

A

type of amino acid-derived hormone, with catecholamines

synthesis and storage
made in advance, stored in secretory vesicles

transport in blood
bound to carrier proteins

location of receptor
nucleus

response to receptor-ligand binding
activation of genes for transcription and translation

examples
thyroxine (T4), triiodothyronine (T3) and reverse T3

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16
Q

types of hormone: lipid hormones

synthesis and storage, transport in blood, location of receptor, response to receptor-ligand binding and examples

A

synthesis and storage
synthesised on demand from precursors

transport in blood
dissolved in plsama and bound to carrier proteins (as they are lipids and are therefore hydrophobic)

location of receptor
cell membrane

response to receptor-ligand binding
activation of second messenger systems

examples
thromboxanes, prostaglandins, endocannabinoids

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17
Q

name the main endocrine glands in the body

location and secretions on seperate cards

A
  • pituitary (anterior and posterior)
  • thyroid gland
  • parathyroid gland
  • adrenal gland
  • pancreas
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18
Q

endocrine gland: pituitary

location + secretions

A

location base of the brain

secretions
anterior

  • TSH thyroid-stimulating hormone
  • ACTH adrenocorticotropic hormone
  • gonadotropins: FSH + LH ★
  • GH growth hormone
  • prolactin

posterior

  • ADH antidiuretic hormone
  • vasopressin
  • oxytocin

★ FSH = follicle-stimulating hormone
LH = luteinizing hormone

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19
Q

endocrine gland: thyroid gland

location + secretions

A

location
anterior to the trachea (two lobes)

secretions
thyroxine (T4) and triodothyroinine (T3)

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20
Q

endocrine gland: parathyroid

location + secretions

A

location
lie on the dorsal surface of the thyroid gland (4 glands, 2 pairs)

secretions
parathromone (PTH)

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21
Q

endocrine gland: adrenal

location + secretions

A

location
top of each kidney (2 sections - medulla is inner and 2 cortex surrounds medulla)

secretions
cortex secretes corticosteriods (glucosteroids and minercoricoids)

small amounts of adrogen, oestrogen and progestin

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22
Q

endocrine gland: pancreas

location + secretions

A

location
left of and behind the stomach (both an exocrine and an endocrine gland)

secretions
- exocrine secretes digestive enzymes into the duodenum
- endocrine has cell clusters called islets of langerhans…

α islet cells produce glucagons
β cells secrete insulin

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23
Q

what is an example of a gland that is both endocrine and exocrine

A

the pancreas

24
Q

what does the hypothalamus do

A
  • located below the thalamus
  • main regulator for everything and is central to homeostatis
  • link between the nervous and endocrine systems

hypothalamus deals with
* thermoregulation, panting, sweating, shivering etc
* plasma osmolality via the osmoreceptors
* heart rate and blood pressure
* feeding, sateity, regulation of the GI tract
* circadian rhythms, sleep, hormones
* stimuli from the autonomic nervous system (both sympathetic and parasympathetic)
* emotion, sexual behaviour and mood
* lactation

25
Q

what are some of the main differences between endocrine and exocrine glands

A

endocrine
- ductless
- secrete directly into blood flowing through them (allows the secretion to function at distant parts of the body
- secretions are called hormones
- all epithelial cells in the gland secrete the hormones

exocrine
- ducted
- secrete into a location of the body through a duct
- secretions are mostly enzymes or lubricants
- only cell at the apex of the duct secrete the products

26
Q

describe the process of adenogenesis of exocrine glands

A
  1. growth signal recieved
  2. proliferation of daughter cells occurs and extracellular protein degradation enzymes produced
  3. epithelial cells invade space created
  4. central cells die off to produce duct aka canalicularisation
  5. link to mother cells remain
  6. significant amount of branching takes place

branching process on seperate card

27
Q

describe the process of adenogenesis of endocrine glands

A
  1. Growth signal recieved
  2. proliferation of daughter cells occurs and extracellular protein degradation enzymes produced
  3. epithelial cells invade space created
  4. produce angiogenic factors to stimulate blood vessel growth in and around epithelial cells
  5. link to mother cells broken by apoptosis
  6. virtually no branching
28
Q

how does branching occur

eg the lungs

A
  • FGF10 (fibroblast growth factor) released by immatture fibroblasts (mesenchymal stem cells)
  • epithelial cells move towards the signal
  • two different fates…
  1. Tubule elongation (growth factor 1 active, GF2 inactive)
  2. Tubule branching (GF1 inactive, GF2 active)

elongation → branching → elongation → branching → elongation etc

elongation and branching stopped by Shh (Sonic the Hedgehog)

29
Q

cells in exocrine glands

A
  1. epithelial cells lining the ducts
  2. epithelial cells that make the secretory products

some of the cell at the secretory ends of the ducts change morphology and class by turning into myoepithelial cells:

these are cells that have features of both an epithelial cell and a smooth muscle cell… these help to eject secretions from the duct, eg mucus that is sticky or in breasts to get the milk out

30
Q

structure of the golgi apparatus

A
  • stack of disc shaped cisternae
  • one end of discs are flattened, the other concave
  • discs have swellings at their edges
  • distal swellings pinch off as migratory golgi vacuoles
31
Q

golgi apparatus function

A
  • transport through the sequential golgi apparatus cisternae
  • packaging of sorted contents through condensation
  • adding sugars to proteins and lipids glycosylation

golgi product destinations…
- majority extruded in secretory vesicles
- some retained for use in the cell (eg lysosomes )
- some enters the plasma membrane (glycocalyx)

32
Q

glycosylation vs glycation

A

the covalent attachment of sugars by enzymes/without enzymes to proteins and lipids to form glycoproteins and glycolipids

glycosylation is with enzymes
glycation is without

33
Q

what is the purpose of glycosylation (or glycation)

difference between two on different card

A
  • to aid protein folding
  • prevents protein digestion by intracellular proteases
  • prevents lipid digestion by intracellular lipases
  • cell recognition (blood groups)
  • role on cell to extracellular matrix attachment

this is a critical function of the biosynthetic-secretory pathway of the endoplasmic reticulum and golgi apparatus

some disorders of glycosylation are known. all are rare and often lethal in utero

34
Q

exocytosis vs endocytosis

A

exocytosis
secretion of molecules outside the cell via a vesicle fusing to a membrane

endocytosis
engulfing of molecules inside the cell via vesicle formation

35
Q

phagocytosis vs pinocytosis

A

phagocytosis
the process by which cells (phagocytes) envelop or engulf other cells or particles. Mainly used by cells of the immune system.

pinocytosis
is the process in which lipid droplets are ingested by cells. Used by all cells, especially smooth muscle cells.

36
Q

different types of transepithelial transport

aka transcytosis

A
  1. paracellular transport molecules may move (passive fuse and be filtered with water) through aqueous channels in the intercellular junction eg amino acids for hormone production
  2. …or through lipid cell membranes transcellular transport eg steroid hormones
  3. molecules with the appropriate characteristics may be transported by carrier proetins into or out of the cells (or by a counter-transport process) eg thyroxine transport across thyroid follicular cell
  4. those that are impermeable may also bind to cell surface receptors, be engulfed by the cell membrane (endocytosis) to be released inside cell, or expelled via vesicles outside of the cell and into extracellular space (exocytosis) eg cholesterol transport
37
Q

types of glandular control

A

humoral
refers to the control of hormone release in response to changes in extracellular fluids (eg blood or the ion conc in blood)

eg a rise in blood glucose level triggers the pancreas to release insulin

hormonal
refers to the release of a hormone in response to another hormone

eg the hypothalamus produces hormones that stimulate the anterior portion of the pituitary gland, which in turn releases hormones that regulate hormone production by other endocrine glands

neural
in some cases, the nervous system directly stimulates the glands to release hormone

eg sympathetic NS directly stimulates adrenal medulla to release epinephrine and norepinephrine in response to stress

38
Q

what is neurocrine communication

A
  • neuron is a secreting cell
  • electrical signal stimulates it to release hormones into the bloodstream
  • the hormones travel through the bloodstream
  • they reach a target cell with receptors for the hormone

eg in the hypothalmo-hypophyseal portal system… where trophic hormones synthesised by the neurones in the hypothalamus are carried to the anterior pituitary via the portal vessels

39
Q

what are portal systems

A
  • occurs when a capillary bed pools into another capillary bed through veins, without first going through the heart
  • both capillary beds and the blood vessels that connect them are considered part of the portal sytem
  • differ from the typical circulatory route of arteries → arteriole → capillary bed → venule → vein

portal system goes through 2 capillary beds before returning to the heart. Only 2 portal systems in human body:

  1. hypothalmo-hypophyseal portal system
  2. the hepatic portal system
40
Q

the hypothalmo-hypophyseal portal system

A
  • portal system of blood vessels that connect the hypothalamus with the anterior pituitary
  • main function is to quickly transport and exchange hormones
  • the capillaries in the portal system are fenestrated which allows a rapid exchange between the hypothalamus and the pituitary
41
Q

development of the endocrine system

A

at 4 weeks gestation, no endocrine glands have formed, but from week 5 onwards…

  • pituitary develops from neurohypophyseal bus and hypophyseal pouch
  • thyroid develops from the floor of the pharynx (2nd pouch)
  • parathyroid and thymus develop from 3rd and 4th pharyngeal pouches
  • pancreas develops from the foregut
  • adrenals develops from intermediate mesoderm and the neural crest
42
Q

why is there always a small concentration of pituitary hormones in the blood?

short answer

A

eg TSH, GH, LH, ADH…

all of the pituitary hormones are subject to constituatice and regulated merocrine secretion

43
Q

why is there always a small concentration of pituitary hormones in the blood?

short answer

A

eg TSH, GH, LH, ADH…

all of the pituitary hormones are subject to constituative and regulated merocrine secretion

this means that there are always some hormones being released via constituative secretion (continually released without stimulation) so there are always small concentrations of these hormones in the blood.

44
Q

the pituitary gland

A

aka the hypophysis
- divided into two lobes (anterior and posterior)
- sits below the hypothalamus
- controls several of the other hormone glands
- endocrine gland

45
Q

thyroid gland

A
  • located at front of the neck
  • has a left and right lobe (like two wings of a butterfly)
  • made up of thousands of follicles that make T3 and T4
  • in between follicular cells, there are parafollicular cells that produce peptide hormone calcitonin (independent of thyroid hormone synthesis)

calcitonin
- role is to monitor plasma concentrations and decreases Ca2+ levels (counteracts the fucntion of PTH)
- major effect: inibits osteoclast activity in bone (osteoclast breaks down bone, releasing calcium into bloodstream)
- minor effect: inhibits renal calcium and phosphate re-absorbtion in the tubular cells → more calcium and phsophate extreted, causing plasma calcium levels to decrease

note: high T3 or T4 = hyperthyroidism
low T3 or T4 = hypothyroidism

46
Q

parathyroid glands

A
  • on the back of each thyroid lobe, there are two parathyroid glands (one above and one below). There are 4 parathyroid in total
  • constantly monitor the plasma calcium concentrations
  • the chief cells make parathyroid hormone (PTH) which activates osteoclasts → more calcium in bloodstream
  • PTH causes the bones to release calcium into the blood and prevents calcium loss by the kidneys; absorb more calcium from the GI tract
  • negative feedback loop (calcium reaches set point and the parathyroid glands stop making PTH)
  • fat cells are presesnt in parathyroid gland, as these provide energy
47
Q

clinical consequences of parathyroid dysfunction

A

calcium is an important element for the nervous, muscular and skeletal system
allows nerves to conduct electricity and for our muscles to contract

hyperparathyroidism
- faily common
- too much PTH
- GI: loss of appetite, nausea, vomiting and constipation
- NS: fatigue, depression and confusion
- MSK: muscle weakness and bone/joint pain
- Urinary: kidney stones, increased thirst and urination

hypoparathyroidism
- rare condition and severe effects
- paraesthesia due to NS problems: tingling sensation
- muscle cramps
- fatigue
- coarse hair and brittle nails
- dry + rough skin
- twitching facial muscles

48
Q

adrenal glands

medulla and cortex on different cards

A
  • these are just above each kidney
  • a mixed endocrine and neuroendocrine tissue
  • each adrenal gland is ade up of an outer layer called the cortex, surrounding an area called the medulla
  • the cortex can be further divided into three zones that produce hormones (more details on next cards)

the right AG: pyramidal shape
the left AG: crescent shape

adrenal glands are responsible for the stress response

49
Q

adrenal medulla

A
  • composed of parenchyma (functional part) of large, pale staining epitheliod cells called chromaffin cells
  • blood vessels are present in medulla, not cortex
  • the chromaffin cells are modified neurones
  • chromaffin cells release catecholamines (adrenaline and noradrenaline) ★
  • this area is slightly yellow due to the hormones they contain
  • numerous myelinated, pre-synaptic sympathetic nerve fibres pass directly to the chromaffin cells which release their secretory products (adrenaline and noradrenaline)
  • therefore, chromaffin cells are equivalent to post-synaptic neurones (an an example of neurocrine secretion)

★ adrenaline aka epinephrine
noradrenaline aka norepinephrine

50
Q

other names for adrenaline and noradrenaline

A

epinephrine (adrenaline)
norepinephrine (noradrenaline)

both are catecholamines

51
Q

adrenal cortex

A

THREE LAYERS

outer = zona glomerulosa
produces aldosterone, which regulates BP

middle = zona fasciculata
produces glucocorticoids (cortisone/cortisol), mobilises fats, proteins and carbohydrates

inner = zona reticularis
produces androgen precursors eg androstenedione ★, DHEA etc

★ goes onto make testosterone, progesterone etc

52
Q

stress response

A

definition: maintenance of homeostatis in the prescence of stressors that require activation of a complex range of responses involving the endocrine, nervous and immune systems

stress: a state of real or percieved threat to homeostasis

activation of the stress response initiates a number of behavioural and physiological changes that improve an individual’s chance of survival when faced with homeostatic challenges

behavioural changes
- increased awareness
- improved cognition
- euphoria
- enhanced analgesia

physiological adaptations
- increased cardiovascular tone
- increased resp rate
- increased intermediate metabolism

decreased vegetative functions such as feeding, digestion, growth, reproduction etc

the principal effectors of the stress response are localised in the hypothalamus, the anterior lobe of pituitary and the adrenal

53
Q

summary of adrenal gland responses to stress

A

adrenal medulla
SHORT TERM STRESS RESPONSE

  • inc heart rate and bp
  • liver converts glycogen → glucose released into blood
  • dilation of bronchioles
  • Δ in blood flow patterns leads to increased alterness
  • inc metabolic rate

adrenal cortex
LONG TERM STRESS RESPONSE

mineralcorticoids stimulate
- retention of sodium and water by kidneys
- inc blood vol and pressure

glucocorticoids stimulate
- proteins and fats → glucose for energy
- inc blood sugar
- suppression of immune system

54
Q

the pancreas

A
  • sits in foregut, attached to curve in duodenum
  • acinar glands grouped into lobules, and contain numerous zymogen granules
  • connect through numerous intercalated ducts to the pancreatic duct
  • pancreatic duct joins with bile duct to make common bile duct
  • intercalated duct is lined with cuboidal epithelial cells
  • consists of endocrine and exocrine components
55
Q

endocrine components of pancreas

A
  • surrounded by exocrine pancreas cells
  • α cell secretes glucagon
  • β cell secretes insulin
  • δ cell secretes somatostatin (inhibitor of glucagon and insulin)
  • islets of langerhans

other minor cells present
- PP cell: pancreatic polypeptide (inhibits bile, pancreatic enzyme and bicarbonate secretion)
- D-1 cell: vasoactive intestinal peptide (stimulates enzyme secretion and gut motility)
- EC cell: secretin (bicarb production), motilin (gastric and intestinal motility) and substance P (analgesia)
- E cell: ghrelin (increases feeding behaviour)
- G cells: gastrin (stimulates HCl production)

56
Q

main exocrine functions of pancreas

A

produces
- trypsinogen which is converted to trypsin
- chymotrypsinogen which is converted to chymotrypsin
- lipase
- amylase
- ribonuclease
- deoxyribonuclease
- gelatinase
- elastase

Body Logistics (11 decks)

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