Glandular Tissues Flashcards
What is the difference between exocrine and endocrine glands?
Exocrine = glands which secrete into ducts onto an epithelial surface e.g. digestive enzymes (pancreas & salivary).
Endocrine = glands which secrete directly into the bloodstream e.g. thyroid, islets of Langerhans, suprarenal gland, parathyroid.
Define a gland.
Epithelial cell(s) specialised for secretion.
Describe ways in which glands can differ.
Unicellular or multicellular. Acinar or tubular. Coiled or branched. Mucous, serous, or mixed. Merocrine, apocrine, or holocrine secretion. Control of secretion.
What is the difference between mucous and serous glands?
Mucous = mucus secretions, rich in mucins (glycosylated polypeptides) e.g. goblet cells -> H&E stains poorly
Serous = watery secretions, rich in enzymes e.g. parotid gland -> pink in H&E
Describe the mechanism of merocrine secretion.
Exocytosis of vesicles.
Plasma membrane becomes transiently larger until the membrane is retrieved, stabilising the cell surface area.
Most glands secrete in this manner.
Describe the mechanism of apocrine secretion.
Non-membrane bound molecules e.g. lipids exocytosed and plasma membrane pinches off and envelops them.
Plasma membrane transiently smaller.
e.g. lactating glands of breast.
Describe the mechanism of holocrine secretion.
Disintegration of cell to release contents which are secreted.
e.g. sebaceous glands (fill hair follicles with sebum).
How can secretion be controlled?
Nervous = e.g. sympathetic nervous stimulation of adrenal medullary cells -> release adrenaline
Endocrine = ACTH stimulates cortex of adrenal gland -> secrete hormones
Neuro-endocrine = nervous cells of hypothalamus controls ACTH secretion from pituitary gland
Negative feedback = inhibitory effect of thyroxine on TSH
What is endocytosis?
Absorption of material by engulfing (uses energy)
Solid = phago
Liquid = pino
Describe transepithelial transport.
Molecules too large to penetrate the plasma membrane can be transported through a cell by endocytosis, then through the cytoplasm through vesicles, then out of the cell by exocytosis
e.g. immunoglobulin transport.
What is exocytosis?
Secretion of molecules from the cell into the ecf by vesicles fusing with plasma membrane.
What is the definition and structure of mucous membranes, and where are they found?
Lines tubes open to the exterior.
Secretes mucus. Found in GI, respiratory, and urinary tract.
Epithelium -> Lamina Propria -> Muscularis Mucosae (GI only) CHECK
What is the definition and structure of serous membranes, and where are they found?
Lines closed body cavities.
Secrete lubricating fluid.
Includes peritoneum, pleural sacs, and pericardial sacs.
Simple squamous epithelia -> Connective tissue (blood vessels and nerves).
How does the structure of the GI tract relate to its function?
OESOPHAGUS: stratified squamous -> protects against abrasion
SMALL INTESTINE:
Epithelia contains gastric pits (secrete digestive enzymes) & mucous glands.
Plicae = permanent folds -> increases s.a. for absorption.
Villi & microvilli = finger-like extensions -> increase s.a. for absorption.
Crypts of Lieberkuhn (Large intestine) = contain goblet cells, stem cells, paneth cells (immune cells).
Simple columnar = short diffusion pathway.
How does the structure of the respiratory tract relate to its function?
TRACHEA:
- Ciliated pseudostratified epithelia -> muco-ciliary escalator (traps dust/microbes and brushes up to throat).
- Hyaline cartilage = holds lumen open
ALVEOLI:
- Simple squamous epithelia = gas exchange.
- Simple cuboidal epithelia = secretes surfactant (lowers surface tensions -> prevents osmosis from capillary to lung space.
