Glands Flashcards
Define a gland
An epithelial cell or an aggregate (cluster) of epithelial cells that are specialised for the secretion of a substance
Define secretion
Production and release of materials by a cell or aggregate of cells
How are glands classified? (2)
Their structure
How their products are released
What are the two types of glands?
What is the key difference?
Endocrine - ductless, so secrete directly into the blood
Exocrine - ducted, so secrete into the duct
What do endocrine glands secrete?
Hormones
What do exocrine glands secrete?
Enzymes or lubricants
Give 3 examples of an endocrine gland
Pituitary gland
Thyroid gland
Parathyroid gland
Give 3 examples of an exocrine gland
Salivary gland
Pancreas
Mammary gland
Sweat glands
Sebaceous gland
Lachrymal gland
What do mammary glands secrete?
Colostrum and milk
What do sebaceous glands secrete?
Sebum onto the skin and in the ear
What do lachrymal glands secrete?
An aqueous fluid to the moisten the eye
What cells secrete hormones in endocrine glands?
All epithelial cells in the gland
What cells secrete hormones in exocrine glands?
Cells at the apex of the duct (the bottom)
What is the process in which glands develop?
Adenogenesis
What are the three steps of general gland formation?
- Growth signal received
- Proliferation of cells occurs and extracellular protein degradation enzymes produced
- Epithelial cells invade subjacent connective tissue
What does it mean when cells proliferate?
An increase in the number of cells as a result of cell growth and cell division
What happens after cells invade the space in the development of exocrine glands?
Central cells die off
A duct is produced
Branching
What happens after cells invade the space in the development of endocrine glands?
- Angiogenic factors produced - stimulates blood vessel growth
- No branching
Which type of gland is not linked to mother cells?
How is it not?
Endocrine
Broken through apoptosis
How does branching occur?
- FG10 released by immature fibroblasts
- Epithelial cells move towards the signal
If the duct doesn’t branch what would it do in response to growth factors?
Tubule elongation
What stops elongation and branching?
Sonic the hedgehog
What stimulates
Tubule elongation?
Tubule branching?
GF1 active + GF2 inactive
GF1 inactive + GF2 active
What do the two types of cells in exocrine glands do?
Line the duct
Make secretory products
What are the two types of tubular secretory structure?
Simple duct - does not branch
Compound duct - branches
What happens to some of the cells at the secretory ends of the ducts?
What is their function?
Turn into myoepithelial cells
Help eject secretions
What are the two types of secretion for salivary glands?
Mucous
Serous
What hormones stimulates the the breast to grow?
Where are they produced?
Estrogen and progesterone
Ovaries
What stimulates the production of breast secretion during pregnancy?
Prolactin
What are the four types of secretion?
Merocrine
Apocrine
Holocrine
Cytocrine
What is merocrine secretion?
Fusion of vesicle with apical membrane
(Exocytosis)
What is apocrine secretion?
Partial loss of cytoplasm
What is holocrine secretion?
Complete loss of cytoplasm
What is cytocrine secretion?
Give an example
Cells are released as a secretion
Spermatid
What are the two pathways for merocrine secretion?
Regulated
Constitutive
What are the three steps of regulated merocrine secretion?
- Vesicle migrates to cell surface along microtubules
- Membrane of vesicle fuses with plasmalemma, in the prescience of Ca2+
- Contents released to extracellular space
What does active secretion of regulated merocrine secretion require?
Ca2+
Describe constitutive secretion
How is it different from regulated?
Vesicles continuously released to the cell surface
Few or no secretory granules
Describe holocrine secretion
- Secretory cells fill up with secretory granules
- Cell organelles degenerate
- Cells die
- Plasma membrane breaks
- Contents empties
- Dead cells replaced by mitotic division of basal cells
What is the definition of glycosylation?
Covalent attachment of sugars by enzymes to proteins and lipids to form glycoproteins and glycolipids
What is the definition of glycation?
Covalent attachment of sugars WITHOUT enzymes to proteins and lipids to form glycoproteins and glycolipids
What is the purpose of glycosylation? (3)
What is the organelle that it happens to most frequently?
- aids protein folding
- prevents protein/lipid digestion by intracellular proteases/lipases
- cell recognition and cell matrix attachment
Golgi apparatus
Define exocytosis
Secretion of molecules outside the cell via a vesicle fusing to a membrane
Define endocytosis
Engulfing of molecules inside the cell via vesicle formation
Where do endocrine cells discharge their secretions?
Directly into blood vessels or lymphatic system
What are the two types of exocrine glands?
Where do they excrete their products?
Unicellular - surface of epithelium
Multicellular - into a duct
What do goblet cells secrete?
What is their secretion used for? (3)
Mucus
Lubricates the passage
Moistens the air
Entraps particles
What is the most common symptom for people with cystic fibrosis?
Why does this occur?
What can this lead to?
Thick mucus
Cannot release Cl- into lumen of duct
Water travels with Cl-, so less water in secretion
A blocked duct
What is phagocytosis?
Where does it occur mainly?
Process of phagocytes enveloping or engulfing cells or particles
Immune system
What is pinocytosis?
Where does it occur mainly?
Process of cells ingesting liquid droplets
Smooth muscle cells
What are two examples of endocytosis?
Phagocytosis
Pinocytosis
What is transepithelial transport known as?
Transcytosis
Where are the parotid glands?
Next to the ear
What are the three ways of controlling gland secretion?
Hormonal
Neural
Humoral
Explain four examples of transcytosis
By carrier proteins or counter transport processes
Aqueous channels in the intracellular junction
Through lipid cell membranes
Bind to surface receptors, by engulfed by endocytosis and then released by exocytosis
What is the function of a striated duct?
Prevent water loss
Describe how endocytosis and secretion combine to give transepithelial transport
A cell binds to cell surface receptors
The cell is engulfed by the cell membrane - endocytosis
Released inside the cell
Or expelled via membrane limited vesicles into the extracellular space - exocytosis
Describe humoral secretion control
Stimulated by changes in extracellular fluid
Describe hormonal secretion control
Hormone released
Stimulates another hormone to be released from another cell
Describe neural secretion control
Neuron releases a neurotransmitter
Binds to a cell
Stimulating hormone secretion
What are the mooring of ductless glands derivatives of?
Epithelial tissue
Describe the portal circulatory route
Blood passes through two sets of smaller vessels before returning to the heart
Blood from the first capillaries collects in portal vessels
The portal vessels branch off to supply a capillary network
The capillary network enters a series of veins, which leads to the heart
What are two key examples of portal circulatory routes?
Hypothalamus
Anterior pituitary gland
Name two functions of parafollicular cells
Where are they found?
Produce thryocalactitonin
Monitor plasma Ca2+ conc
Parathyroid glands
What is salivary secretion controlled by?
Neural
Describe how the ANS controls saliva production
Parasympathetic - large volume of watery, enzyme rich salvia
Sympathetic - small volume of thick, mucus rich saliva
What are the three different types of capillaries?
Continuous
Brain
Fenestrated
Pituitary, small intestines, kidneys
Sinusoid - have an incomplete basement membrane
Spleen, bone marrow
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