Lecture 5: gland structure and function

Question 1

what is pinocytosis?

Answer 1

process in which liquid droplets are ingested by cells
- once in cell the liquid is contained within a vesicle
- used by all cells, especially smooth muscle cells

Question 2

what are the 4 different types of trans epithelial transport?

Answer 2

1. paracellular: molecules move through aqueous channels in intercellular junctions
2. transcellular: molecules move through lipid cell membranes (through the cell)
3. carrier proteins: molecules transported by carrier proteins via counter transport process
4. endocytosis/exocytosis

Question 3

what is a gland?

Answer 3

an epithelial cell, or group of cells, specialised for the production and release of specific substances
roles:
1. signals from the CNS
2. circulating levels of hormones to other chemicals
3. local signals from neighbouring cells

Question 4

what is secretion?

Answer 4

process by which a cell, or collection of cells produce and release materials

Question 5

how are glands classified?

Answer 5

1. exocrine and endocrine glands
2. exocrine —> merocrine, apocrine, holocene (depending on the products they release)

Question 6

what are endocrine glands?

Answer 6

• secrete directly into blood that flows through them
• allows their secretions to go to distant parts of the body
• they secrete hormones
• allows their secretions epithelial cells in the gland secrete hormones

—> they do not have ducts

Question 7

what are exocrine glands?

Answer 7

• secrete into location or localised region of the body through a duct
• their secretions are mostly enzymes or lubricants
• only cells at the apex (tip) of the duct secrete products e.g salivary and sweat glands

Question 8

what are examples of endocrine glands?

Answer 8

1. thyroid glands
2. parathyroid glands
3. pituitary glands
   - anterior pituitary: FSH, TSH
   - posterior pirtuitary: oxytocin, ADH

Question 9

what are examples of exocrine glands?

Answer 9

1. salivary glands: secrete saliva
2. mammary: produces colostrum and milk in response to hormones to nourish neonates
3. sweat glands
4. sebaceous glands: secretes sebum onto skin and ear to protect from pathogens
5. lacrimal glands: aqueous fluid secreted from eye to moisten, also produces lysozyme

Question 10

how do we develop glands (foetal development)

Answer 10

1. growth signal received (top layer of cells grow/replicate down towards signal)
2. proliferation of daughter cells occurs and extracellular protein degradation enzymes produced
3. epithelial cells invade space created
   endocrine or exocrine glands produces

Question 11

how are exocrine glands developed during foetal development?

Answer 11

• central cells die off to produce duct
• link to mother cells remain
• lots of branching occurs (traced back to one single point that is linked to mother cells)

Question 12

how do endocrine glands develop during foetal development?

Answer 12

• produce angiogenic factors to stimulate blood vessel growth in and around epithelial cells
• link to mother cells broken via apoptosis
• no branching
  —> need a good blood capillary network to be able to secrete directly into blood

Question 13

how do exocrine glands branch?

Answer 13

1. growth factor released by immature fibroblasts
2. signal attracts nearby epithelial cells —> migrate towards source
3. once stimulated, epithelial cells follow 2 possible pathways
   - tube elongation: occurs when growth factor 1 is active and growth factor 2 is inactive
   - tube branching: occurs when growth factor 1 is inactive and growth factor 2 is active

—> elongation and branching stopped by Shh

Question 14

what are the different shapes of exocrine duct glands?

Answer 14

does not branch (simple = one duct)
1. simple tubular
2. simple branched tubular
3. simple alveolar
4. simple branched alveolar/acinar
does branch ( compound = many branches)
1. compound tubular
2. compound alveolar/acinar
3. compound tubuloalveolar
—> only epithelial at apex secretes products

Question 15

how do secretions pass through a salivary gland?

Answer 15

introlobular duct —> intercalated duct —> striated duct —> excretory duct

Question 16

what type of secretions do salivary glands produce?

Answer 16

mucous and serous
- myoepithelial cells are secretory ends of ducts
1. feature both epithelial cell and smooth muscle cell
2. help eject secretions from duct

Question 17

what is a merocrine gland?

Answer 17

fusion of vesicles with apical membrane (cell membrane) to release secretions
- exocytosis

Question 18

what are apocrine glands?

Answer 18

partial loss of cytoplasm lost with secretions
e.g mammary glands and sweat glands

Question 19

what are holocene glands?

Answer 19

complete loss of cytoplasm/cell
e.g sebaceous gland and tarsal gland in eye

Question 20

what are cytocrine glands?

Answer 20

cells released as secretion
e.g spermatid

Question 21

what are the 2 pathways in merocrine secretion?

Answer 21

1. regulated secretion
2. constitutive secretion
   —> both use vesicles

Question 22

what is regulated secretion?

Answer 22

• secretory granules accumulate in large vesicles
• active secretion requires specific signal (Ca2+)
• vesicle migrates to cell surface along microtubules
• if there are Ca2+, membrane of vesicle fuses with plasma membrane (at receptor)
• cargo from vesicle released into extracellular space

Question 23

what is constitutive secretion?

Answer 23

• secretory product is not concentrated in granules but packaged into small vesicles
• small vesicles continuously released to cell surface (nothing controls release)

Question 24

what is apocrine secretion?

Answer 24

neonatal period
- only fats secreted by apocrine
- milk proteins made in RER and on free ribosomes packed into vesicles by golgi (secreted by merocrine)

lactation
- both fats and proteins released by apocrine secretion

—> pinches off and pulls some cytoplasm along with it

Question 25

what is holocrine secretion?

Answer 25

1. secretory cell gradually fills up with secretory granules 2. cell organelles degenerate and cells die 3. plasma membrane breaks and contents empties 4. dead cells replaced by mitosis division of basal cells (basement membrane)

Question 26

what is glycosylation?

Answer 26

covalent attachment of sugars by enzymes to proteins and lipids to form glycoproteins and glycolipids —> occurs in the golgi

Question 27

what is the role of glycosylation of proteins and lipids?

Answer 27

1. aids protein folding 2. prevents protein digestion by intracellular proteases 3. prevents lipid digestion by intracellular lipases 4. cell recognition 5. role on cell to extracellular matrix attachment 6. glycosylation is important for pathways involved in endoplasmic reticulum and golgi

Question 28

how is secretion regulated? (3)

Answer 28

primarily negative feedback 1. hormonal 2. neural: nerves 3. humoral: substances in the blood (e.g high glucose stimulates release of insulin)

Question 29

what is a hormone?

Answer 29

chemical messenger produced by endocrine glands - released into blood stream - travel to target organs and tissues - regulate processes such as growth, reproduction, mood and immune function

Question 30

where is the pituitary gland found?

Answer 30

base of the brain

Question 31

what hormones does the anterior pirtuitary gland secrete? (6)

Answer 31

1. TSH: thyroid stimulating hormone 2. ACTH: adrenocorticotophic hormone 3. FSH and LH 4. GH: growth hormone 5. PRL: prolactin 6. MSH: melanocyte - stimulating hormone

Question 32

what hormones does the posterior pituitary gland secrete? (2)

Answer 32

1.ASH 2. oxytocin

Question 33

where is the thyroid gland found?

Answer 33

anterior to trachea (2 lobes)

Question 34

what hormones does the thyroid gland secrete? (2)

Answer 34

1. thyroxine (T4) 2. triiodothyronine (T3)

Question 35

where is the parathyroid gland found?

Answer 35

on dorsal surface of thyroid glands - 4 glands in 2 pairs

Question 36

what hormone does the parathyroid gland secrete?

Answer 36

parathyroid hormone

Question 37

where are the adrenal glands found?

Answer 37

top the superior poles of kidneys (medulla and cortex)

Question 38

what hormones are secreted in the adrenal glands doing in the inner medulla? (3)

Answer 38

catecholamines 1. adrenaline 2. noradrenaline 3. dopamine

Question 39

what hormones are secreted from adrenal glands found in the outer cortex of kidneys?

Answer 39

corticosteroids 1. glucocorticoid (cortisol and cortisone) 2. mineralocorticoids: also steroid and DHEA (dihydropiandrosterone)

Question 40

what are the 5 different types of hormones?

Answer 40

1. glycoproteins and peptide hormones 2. steroid hormones 3. amino acid derived hormones: catecholamines and thyroid hormones 4. lipid hormones

Question 41

what are glycoproteins and peptide hormones?

Answer 41

- made in advance and stored in secretory vesicles - transport in blood: dissolved in plasma - receptors for them: located on cell membrane - response to binding on receptor: activation of seconded messenger systems —> could activate gene expression examples - insulin, glucagon, ACTH

Question 42

what are steroid hormones?

Answer 42

- synthesised in demand by precursors - transport in blood: bound to carrier proteins - receptors for them: found in cytoplasm or nucleus, some have membrane receptors - response to binding on receptor: activation of genes for transcription and translation examples - oestrogen, progesterone, cortisol

Question 43

what are catecholamines? (amino acids derivative)

Answer 43

- made in advance —> stored in secretory vesicles - transport in blood: dissolved in plasma - receptors for them: found on cell membrane - response to binding on receptor: activation of secondary messenger systems examples - noradrenaline, adrenaline, dopamine

Question 44

what are thyroid hormones? (amino acid derivatives)

Answer 44

- made in advance —> stored in secretly vesicles - transport in blood: bound to carrier proteins - receptors for them: found in nucleus - response to binding to receptors: activation of genes for transcription and translation examples - thyroxine, triiodothyronine

Question 45

what are lipid hormones?

Answer 45

- synthesised on demand from precursors - transport in blood: dissolved in plasma and bound to carrier proteins - receptors for them: found on cell membrane - response to binding to receptor: activation of secondary messenger systems examples - prostaglandins, thromboxanes, endocannabinoids

Question 46

where do endocrine glands derive from?

Answer 46

epithelial tissue - epithelial tissues line the surface and cavities of organs - involved in secretion, absorption and filtration 2 main types: 1. covering or lining epithelia: forms sheets of cells that cover body surfaces or line internal cavities 2. glandular epithelia: specialised epithelial cells that produce and release substances such as enzymes, hormones or sweat

Question 47

how does epithelial tissue give rise to ductless glands during foetal development? (stage 1)

Answer 47

1. epithelial tissues fold inwards or pinch off from epithelial layers —> form glandular structures 2. thyroid glands develop from epthelial outgrowth of pharynx 3. adrenal glands originate from mesodermal epithelium 4. pirtuitary glands develop from 2 structures of epithelium: - oral ectoderm - neural ectoderm

Question 48

what is stage 2?

Answer 48

1. endocrine glands lose their ducts during development 2. the epithelial cells that would have formed a duct if it was an exocrine gland regress 3. they leave behind a cluster of hormone secreting cells surrounded by rich network of blood vessels 4. epithelial cells become more specialised for hormone production 5. arrange themselves into cords or clusters, surrounded by capillaries —> facilitates rapid hormone secretion into blood

Question 49

what type of glands does the pancreas have?

Answer 49

both exocrine (digestive enzymes) and endocrine glands (islets of langerhans: insulin and glucagon) - acinar glands grouped into lobules - contain lots of zymogen granules - connect through numerous intercalated ducts to pancreatic duct - joins with vile duct to make common bile duct - duct lines with cuboidal epithelial cells

Question 50

how is insulin regulated in merocrine secretion?

Answer 50

1. when glucose enters cell, ATP released 2. ATP causes potassium channels to open and K+ leaves cell 3. this causes an influx of Ca2+ to come into cell to balance charge inside cell 4. influx of Ca2+ causes vesicles to move and fuse with cell membrane to release insulin (glucose regulates insulin secretion)