Glands

Question 1

What is a secretion?

Answer 1

The production or release of materials by a cell or aggregate of cells

Question 2

What are endocrine glands?

Answer 2

Ductless glands that secrete hormones directly into the blood flowing through them,so that the secretion function at distant parts of the body. The secretions are hormones.

• all epithelial cells secrete the hormone in endocrine glands

Question 3

What are the different examples of endocrine glands?

Answer 3

1. Pituitary gland (of the hypothalamus) it is beneath or inferior to the hypothalamus that’s why is anatomical name is hypophysis.
   - Anterior (front) pituitary gland - produces hormones that regulate most of the glands of the endocrine system e.g. prolactin- stimulates milk production in mothers; somatotropin - hormone to regulate growth of body and tissues.
   - Posterior (rear) pituitary gland - produces vasopressin (ADH) prevent water loss from the kidney and oxytocin
2. Thyroid gland: produces thyroid hormones T3 and T4 that controls metabolism an calcitonin involved in calcium homeostasis.
3. Parathyroid gland : produces parathyroid hormones, calcium homeostasis.

Question 4

What are exocrine glands?

Answer 4

These are glands with ducts and secrete into a location or region of the body through ducts, and there secretions are mostly enzymes or lubricants.

• only the cells on the apex (end of) the ducts secret the products.

Question 5

What are 5 examples of exocrine glands?

Answer 5

1. Salivary gland -secretes saliva which is needed for partial digestion of food and lubrications
2. Pancreas - secretes enzymes e.g. amylase - carbohydrates , trypsin - protein and lipase - fats.
3. Mammary glands - produces colostrum and milk in response to prolactin and oxytocin to nourish neonates
4. Sweat glands Secrete sweat to regulates body temp and for excretion
5. Sebaceous glands - secretes sebum onto the skin and ear (contributes ear wax) to protect tissues from pathogens

Question 6

What are the first steps of gland generation in utero development for both glands?

Answer 6

1. Growth of cells underneath the basal lamina as the cells receive growth signals.
2. Proliferation of the daughter cells occurs and Dow growth into the connective tissue and extracellular protein degradation enzymes produced and degrade the extracellular matrix of the connective tissue layer.
3. The epithelial cells invade the space created by the enzymes and grow downwards.

Question 7

How are exocrine glands formed?

Answer 7

• Exocrine Glands: the central cells undergo apoptosis -programmed cell death to produce a duct through the middle this is called canalicularisation.

There are 2 types of cells:

• Ductal cells which don’t secrete and are the top part of the gland
• Secretory cells/portion at the apex (end) which do secrete

Question 8

How are endocrine glands formed?

Answer 8

1. The epithelial cells produces angiogenic factors which stimulates blood vessel growth in and around the epithelial cells.
2. As the factors are being produced the link between the Mother cells are broken by apoptosis and the duct isn’t formed, instead there is an aggregate of epithelial cells with blood vessels surrounding.

Pg 9

Question 9

How are follicular endocrine glands formed (thyroid glands)?

Answer 9

1. Within in the thyroid follicular cells, the blood vessels are only made on the surrounding/outside.
2. The thyroid make thyroglobulin which is then stored in the colloid space in the middle.
3. The production of the colloid between the epithelial cells causes expansion of the follicle into a sphere and forces the blood vessels onto the edges.

Question 10

How does branching occur?

Answer 10

• Many of the ducts aren’t linear they are branched and branched in different directions.
  1. Basic FGF10 released by immature fibroblast (mesenchymal stem cells)
  2. Epithelial cells move towards the direction of the signal

3. Two different fates:
   - Tubule elongation Growth factor 1 active, GF 2 inactive
   - Tubule branching - Growth factor 1 inactive, GF 2 active

Growth factor 1 is for elongation and Growth factor 2 is the branching factor

Question 11

What are the two types of epithelial cells in the exocrine glands?

Answer 11

1. Cells lining the ducts

2. Cells that make secretory products

Question 12

What happens to some of the cells at the secretory end of the exocrine glands?

Answer 12

• The ducts change morphology and class by turning into myoepithelial cells.
• These cells have both epithelial cells and smooth muscle cells features
• when the cells contract they help to eject secretions from the duct.

Question 13

What are the different shapes of glands?and examples

Answer 13

• simple tubular - intestine glands
• simple branched tubular Stomach (gastric) glands
• Simple alveolar: no example in humans - only one found in penis
• Simple branched alveolar - sebaceous glands

Compound tubular: duodenal glands of the small intestines

• Compound alveolar - mammary glands
• Compound tubuloalveolar - salivary glands .

Acinar = alveolar

Pg 11 check the pictures .

Question 14

Information on the salivary glands?

Answer 14

Two types of fluid production

• serous
• mucous

3 types of mechanisms

• Serous only - mainly on these types there are special myoepithelial cells, they ah e the ability to contract and squeeze the content of the area in the intercalating duct out to the excretory duct
• Mucous only
• Mixture

Prebud 
Initial Bud 
Pseudograndular (intercalating ducts)
Canalicular
Terminal bud 

Check pg 12 - very important

Question 15

Information on the Breast

Answer 15

• Same process as the salivary gland development in utero except at the stage development stops until puberty.
• At puberty, estrogen and progesterone produced by the ovaries restarts breast development
• During pregnancy, Prolactin stimulates the production of breast secretions (colostrum and milk)

Question 16

What are the 6 types of ducts and their function?

Answer 16

1. Acinus - makes and releases secretions
2. Myoepithelium - ‘squeeze’ cells to release more
3. intercalating duct - connect different acini
4. Striated duct - keep the ductal system open and re-absorb NA+ ions
5. Excretory duct - sometimes surrounds smooth muscle cells
6. Main collection duct - collates all the secretions.

Question 17

What occurs in glands that undergo Merocrine secretion?

Answer 17

• It is the fusion of vesicles with the apical membrane e.g. acinar and endocrine glands of the pancreas
• a form of exocytosis

1. A cell produces a protein or product which goes through the Golgi apparatus
2. Golgi puts it into small secretory vesicles, these vesicles sit around and wait for a signal
3. Once signal is found the vesicle and contents is released into the extracellular space.

Question 18

What occurs in glands that undergo apocrine secretion?

Answer 18

• Partial loss of the apical part of the cytoplasm e.g. lactating mammary glands and sweat glands in the axilla (armpits and the external genitalia (testes and penis and vulva and labia).
  1. The production of the secretion is the same as merocrine
  2. However the amount of material near the apical surface gets bigger and bigger until the apical area of the cell gets unstable and pinches off
• it’s called apocrine because the apical surface gets pinched off

Question 19

What occurs in glands that undergo Holocrine secretions?

Answer 19

Complete loss of the cytoplasm or cell e.g. sebaceous glands (attached to hair follicles) in the skin a and tarsal glands in the eyelid.

• The mature cell dies off and becomes the secretory product.
• the nucleus and all the plasma membrane and everything is lost.

Question 20

What occurs in glands that undergo cytocrine secretion?

Answer 20

• This is a minor form of secretion.
• Cells are released as secretions e.g. spermatid (spermatozoa in the seminiferous tubule (testis) - only one found in the body.

Question 21

What are the two different pathways of Merocrine secretion?

Answer 21

Regulated secretion - Secretory granules accumulate in large vesicle and are released by exocytosis upon stimulation - needs Ca2+ ions to work.

Constitutive Secretion - The secretory product is not concentrated into granules but packaged into small vesicles and continuously released to the cells surface
- Used mainly to repopulate the plasma membrane with plasma proteins.

Pg 18 for images

Question 22

How does regulated Merocrine secretion work ?

Answer 22

• Active process - uses energy in the form of ATP

1. Contents of the vesicle can be anything within the cell
2. Active secretion requires specific signal (Ca2+ ions)
3. Vesicle migrate to the cell surface along mictotubules - reason why it uses ATP.
4. In the presence of Ca2+ ions, membrane of the vesicle fuses with the plasmalemma
5. Cargo released to extracellular space

• The vesicles need some energy applied to them, in order for proteins of the micro tubules to undergo a conformational change and move the vesicles where’ve the end of the microtubule is

Question 23

Apocrine secretion example the breast - What occurs during the neonatal period?

Answer 23

• Only fats are secreted by apocrine secretion (signet fragments.
• Fats build up in the tissue and they get bigger and build up, the top layer of the apical surface gets unstable and breaks off.
• Milk proteins are made in the RER and the free ribosomes are packed into vesicles produces by the Golgi apparatus and released by Merocrine secretion.

Pg 21

Question 24

Apocrine secretion Example, the breast - What occurs during lactation?

Answer 24

• Both fats and proteins are released by apocrine secretion.
• As the breast gets bigger as milk production starts and more demand occurs, then both fat and protein are released, everything above the Golgi is lost and ingested by the baby.

Pg 21

Question 25

How does holocrine secretion work?

Answer 25

1. The secretory cell gradually fills up with secretory granules. 2. The cell organelle degenerate 3. The cells die 4. The plasma membrane breaks and contents (secretum) empties 5. Dead cells are replaced by mitotic division of basal cells

Question 26

What is a gland that uses holocrine secretion and why?

Answer 26

- Sebaceous glands - The reason the cell dies is because there is no room for the organelles to work. - Also sebum is an oil (fat) so it doesn’t mix well with cytoplasmic proteins - So it tends to break down the cell, the cell gets bigger until the membrane breaks down on the cell and the nucleus degenerated as it goes along the whole thing is lost. Pg 22-23 - look at the stain image

Question 27

What is the role of the Golgi apparatus in Constitutive secretion?

Answer 27

1. Proteins come into the Golgi through the cis face, they are then processed in the Golgi (which has a lot of enzymes, mainly glycolytic). 2. Then package and goes to either one of the two pathways. 3. If it is not glycosylated in the Golgi, when it comes out the trans face of the Golgi it goes to the constitutive secretory pathway. 4. So the vesicle goes immediately fuses with the plasma membrane or puts protein onto the surface. E.g. white blood cells releasing interleukin

Question 28

What is the role of the Golgi in regulated secretory pathway?

Answer 28

1. Protein enters via the cis face and processed in the Golgi. 2. If the protein is glcosylated, it goes into excretory vesicles that sits close to the plasma membrane, waiting for a signal e.g. hormone or neurotransmitter 3. Calcium is mobilised and vesicle fuses with the membrane and releases the contents E.g. insulin in the beta cells or neurotransmitter in nerve endings

Question 29

What is glycosylation?

Answer 29

- The covalent attachment of sugars by enzymes to proteins and lipids to form glycoproteins and glycolipids.

Question 30

What is the role of glycosylation?

Answer 30

1. To aid protein folding 2. Prevents protein digestion by intracellular proteases 3. Prevents lipid digestion by intracellular lipases 4. Cell recognition (blood groups) 5. Role on cell to extracellular matrix attachment Pg 25

Question 31

What is Exocytosis and Endocytosis?

Answer 31

Exocytosis - Secretion of molecules outside of the cell via vesicle fusing to a membrane. Endocytosis - engulfing of molecules from outside of the cell, in the extracellular matrix inside the cell via vesicle formation Cyto - cell Osis - process

Question 32

What are the different types of endocytosis?

Answer 32

1. Phagocytosis - process by which cells (phagocytes), envelop or engulf other cells or particles. - mainly used by cells of the immune system e.g. macrophages, dendritic cells, neutrophils, basophils and eosinophils. 2. Pinocytosis - process in which liquids or lipid droplets are ingested by cells - used by cells, especially smooth muscle cells 3. Receptor mediated endocytosis is exploited in drug design - one way to transport drugs through tissues to the circulation, both forms of endocytosis

Question 33

What are the different transepithelial transport (transcytosis)?

Answer 33

1. Molecules may move (passive diffuse and be filtered with water) through aqueous channels in the intracellular junction - Paracellular transport e.g. amino acid hormone production 2. Or through lipid cell membranes - Transcellular transport. E.g. steroid hormones (oestrogen, progesterone, testosterone) 3. Molecules with appropriate characteristics may be transported by carrier proteins into and out if cells or counter-transport process e.g. thyroxine transport across thyroid follicular cell 4. Molecules that are impermeable may bind to cell surface receptors, be engulfed by cell membrane (endocytosis) and the released via membrane-limited vesicles out of the cell into the extracellular space (Exocytosis) e.g. cholesterol transport (many drugs) Pg 28 - check

Question 34

What are the three types of glandular control?

Answer 34

1. Humoral stimulus - through feedback loops most prevalent in endocrine glands 2. Neural stimulus- solely controls salivary (exocrine) gland secretion 3. Hormonal stimulus - most prevalent in endocrine glands Pg 29 & 30 - read examples

Question 35

What is a portal system?

Answer 35

- This is when blood comes in (through an artery) going through a capillary bed and then another capillary bed. - there are two types of portal systems and one is the hypothalamus - hypophyseal portal system.

Question 36

What occurs in neurocrine communication?

Answer 36

- e.g. they hypothalamus to the pituitary gland 1. A neurone produces a substance which is released and not acting on another neurone or receptor. 2. The substance is released into the blood and going to travel through the blood to its different targets Pg 31 - check picture.