Glands Flashcards
Define ‘gland’
An epithelial cell (or aggregate of cells) specialised for secretion.
What are the 2 types of glands?
Endocrine:
- Ductless
- Secrete hormones directly into blood
- ALL epithelial cells secrete hormones in the gland
- (e.g. pituitary, thyroid)
Exocrine:
- Ducted
- Secrete enzymes / lubricants
- Only cells at APEX of duct secrete
- (e.g. salivary, sweat)
What are the gland classifications by secretion method?
- MEROCRINE:
- Fusion of vesicles with apical membrane (exocytosis) - APOCRINE:
- PARTIAL loss of cytoplasm
- Pinched off section of cell is the secretion - HOLOCRINE:
- TOTAL loss of cytoplasm
- Mature cell dies and becomes the secretion
Describe the process of merocrine secretion
- Exocytosis
- Membrane bound compartment approaches cell
- Fuses with plasma membrane
- Contents dispersed by diffusion
Describe the process of apocrine secretion
- Non membrane bound structure approaches cell
- Pushes up apical membrane
- Layer of cytoplasm drapes around droplet
- Membrane surrounding droplet pinches off
Describe the process of holocrine secretion
- Cell disintegrates
- Releases contents
- Discharge of whole cell into extracellular space
State the 3 control mechanisms for hormone release
What kind of feedback loop do these use?
- Neural (nervous system)
- Hormonal (hypothalamus)
- Humoral (plasma)
Negative feedback loops
- Secretory product inhibits own secretion
Define glycosylation
Attachment of sugars, by enzymes, to proteins and lipids to form glycoproteins and glycolipids
Describe the process of glycosylation
- Vesicles from ER travel to golgi cis face
- Vesicle fuses and empties contents into lumen
- Proteins and lipids travel through golgi
- Sugar molecules added
- New glycolipids and glycoproteins tagged
- Packed in secretory vesicles at trans face
- Fuse with plasma membrane and empty outside cell
What are the 2 pathways for merocrine secretion?
REGULATED:
- Secretory granules accumulate in large vesicles
- Released by exocytosis on stimulation
- Requires Ca2+ ions
CONSTITUTIVE:
- Secretory product packaged in small vesicles
- Continuously released to cell surface
- Repopulates plasma membrane with plasma proteins
Define phagocytosis
Process by which cells engulf other cells or particles
e.g. macrophages and immune cells engulfing pathogens or infected cells
State the role of glycosylation in the golgi apparatus
- Aid protein folding
- Prevent protein / lipid digestion by intracellular enzymes
- Cell recognition (blood types)
- Role on cell to extracellular matrix attachment
Where in the cell are proteins synthesised?
Ribosomes (bound to RER)
Where in the cell are steroid hormones synthesised?
SER
Smooth endoplasmic reticulum
Briefly outline the negative feedback loop for neural control of hormone release
Nervous system > endocrine gland > target cells > action
Briefly outline the negative feedback loop for humoral control of hormone release
Change in substance level in plasma > endocrine gland > target cells > action
Briefly outline the negative feedback loop for hormonal control of hormone release
Hypothalamus > anterior pituitary > peripheral endocrine gland > target cells > action
Describe the processes of endocytosis and exocytosis.
Endocytosis:
- Bulk transport into cell
- Cell membrane pouch surrounds particles outside
- Vesicle formed
- Contents released into cytoplasm
Exocytosis:
- Bulk transport out of cell
- Vesicle moves to cell membrane - fuses
- Contents secreted as membrane smoothes.
Describe the location, structure and function of the thyroid gland
Location:
- Anterior to trachea (2 lobes)
- Butterfly shape
Secretes:
- Thyroxine (T4)
- Triodothyroinine (T3)
Describe the location, structure and function of the parathyroid gland
Location:
- Posterior surface of thyroid gland
- 4 glands, 2 pairs
- Lots of adipose tissue
Function:
- Monitor plasma calcium concentrations
- Classic negative feedback loop
Secretes:
- Parathormone (PTH) - Ca2+ resorption
Describe the location, structure and function of the adrenal glands
Location: - Top of each kidney - 2 sections (medulla = inner, cortex outer) - Right = pyramid, left = half moon
MEDULLA
Chromaffin cells
- Adrenaline 80%
- Noradrenaline 20%
CORTEX 3 zones: - (Salt, Sugar, Sex)
Zona Glomerulosa
- Mineralocorticoids
Zona Fasiculata
- Glucocorticoids
Zona Reticularis
- Glucocorticoids
- Androgens
Describe location, structure and function of pancreas
Location:
- Left of and behind stomach
Structure:
- 99% Exocrine 1% Endocrine
- Intercalated ducts
- Acinar glands (grouped into lobules)
Secretes:
EXOCRINE (Acini)
- Digestive enzymes and HCO3-
ENDOCRINE (Islet of Langerhans)
- Glucagon (alpha)
- Insulin (beta)
- Somatostatin (delta) inhibits insulin/glucagon secretion
Describe the location, structure and function of pituitary gland
Location:
- Base of brain
- 2 lobes (Anterior / Posterior)
(Neurosecretory axons from hypothalamus extend directly into PP)
Anterior (epithelial) secretes:
- Growth factor hormones
- TSH, ACTH, FSH, LH, GH, MSH, Prolactin
Posterior (nerve) secretes:
- Antidiuretic hormone (ADH) - kidney water resorption
- Oxytocin - lactation / labour
Which part of the brain is central to homeostasis?
Hypothalamus
