Session 5 - Glands Flashcards
Define a gland
An epithelial cell or an aggregation of epithelial cells that are specialised in the secretion of a substance
How do you classify different types of glandular tissue?
1) Where the products are secreted: Endocrine or exocrine
2) What the mode of secretion is: Merocrine, Apocrine or Holocrine
Explain the differences between endocrine and exocrine glands
Endocrine glands secretes hormones directly into the blood. Exocrine glands secrete their products into a location via a duct
Define Merocrine secretion and give an example
Secretion through exocytosis. Fusion of vesicles with apical surface (insulin)
Define Apocrine secretion
The partial loss of cytoplasm due to the non-membrane bound compounds gathering at the apical surface and as such pushing on it (mammory glands)
Define Holocrine secretion
The complete loss of the cytoplasm or cell (sebaceous glands)
Define Cytocrine secretion
Cell released as secretion (spematid)
Describe how glands are formed
1) Growth signal received (FGF growth factor)
2) Proliferation of cells occurs and extracellular protein degradation enzymes are released
3) Epithelial cells invade space created
a) 4) Exocrine gland - Central cells die of to produce duct (canaliculisation). 2 Cell types produced: glandular and ductal
b) 4) Endocrine gland - Produce angiogenic factors to stimulate blood vessel growth in and around the epithelial cells
b) 5) Endocrine gland - Link to surface is broken through apoptosis
How does branching of glands occur during development?
1) tubule elongation (growth factor 1 active, 2 not)
2) tubule branching (growth factor 2 active, 1 not)
Name all 8 types of exocrine ductal morphology and give an example of each.
Simple tubular - Intestinal glands
Simple coiled tubular - sweat glands
Simple branched tubular - Gastric glands
Simple alveolar - Not common, one in end of penis
Simple branched alveolar - sebaceous glands
Compound tubular - duodenal glands of small intestine
Compound alveolar - Mammary glands
Compound tubuloalveolar glands - Salivary glands
What is a myoepithelial cell and what is their role?
Cells that feature features of both an epithelial cell and a smooth muscle cell
They help to eject secretions from the duct (by squeezing the top section)
What order do the ducts follow?
Acinus - where the product is secreted
1) Intercolated Duct
2) Striated Duct - Reabsorbs Na+ ions
3) Excretory Duct - sometimes has smooth muscle around it
4) Collecting Duct - not very common normally excretory duct is last
Explain the development of the breast
1) initial development the same as the salivary but stops until puberty
2) Puberty - oestrogen and progesterone produced by the ovaries restarts breast development
oestrogen - ductal elongation
progesterone - side branching
3) during pregnancy prolactin stimulates the production of breast secretions (colostrum and milk)
prolactin - Alveologenesis and lactogenic differentiation
What are the two modes of merocrine secretion?
Regulated - secretory granules accumulate and are released upon stimulation
Constitutive - continuously released. Vesicles often have plasma proteins associated to them to repopulate the cell membrane
Describe in detail the process of regulated merocrine secretion.
This is an active process
1) vesicles are packaged with contents
2) active secretion requires specific signal (Ca2+ ions)
3) Vesicle migrates to the cell surface along microtubules (this uses energy hense why it is an active process)
4) In the presence of Ca2+ ion, membrane of vesicles fuses with plasmalemma
5) contents released into the intercellular space
Define Glycosylation
The covalent attachment of a sugar to a protein or lipid by an enzyme. This usually occurs in the Golgi apparatus
What is the difference between phagocytosis and pinocytosis?
Phagocytosis is where cells engulf other cells or particles where as pinocytosis is the process where liquid droplets are ingested by cells. (they are both forms of endocytosis)
Name the 4 types of trans-epithelial transport.
1) paracellular - transport via aqueous channels between cells via tight junctions
2) transcellular- transport of lipid soluble molecules that pass through the membranes
3) Carrier proteins into and out of the cell
4) Endocytosis and then exocytosis
what are the 4 types of glandular control?
Humoral control - feedback loop though endocrine system
Nervous control - via innervation of nerves
Hormonal control - Hormonal secretions
Neurocrine control - eg: hypothalamus and pituitary. Neurotransmitter enters the blood stream and then travel to stimulate target cell
Why is PTH essential to life but calcitonin isn’t?
PTH is essential as it regulates the concentrations of Vitamin D for calcium absorption from the diet. If this wasn’t present I.E. no Parathyroid gland then we wouldn’t be able to absorb Calcium. Calcitonin only reduces calcium levels so is important to prevent seizures but not essential
Name the 5 major endocrine glands and tissues
Pituitary (anterior and posterior) Thyroid Parathyroid Adrenal Glands Pancreas
Where is the pituitary gland located and what does it secrete?
It is found at the base of the brain
Anterior: TSH, ACTH, Gonadotrophins (FSH, LH, GH (growth hormone)).
Posterior: ADH (vasopressin), Oxytocin
Where is the thyroid gland located and what does it secrete?
It is found anterior to the tranchea
It secretes T4 and T3
Where is the Parathyroid gland located and what does it secrete?
Dorsal to the thyroid, 4 glands 2 pairs on each lobe
PTH
Where is the adrenal gland located and what does it secrete?
It is found on the top of the kidneys
It secretes Cortex: Coticosteroids, small amounts of androgen, oestrogen and progesterone.
Medulla: Catecholamines (adrenaline and noradrenaline)
Where is the pancreas located and what does it secrete?
It is located left of and behind the stomach
It has both endo and exocrine function and so secretes
Endocrine: Islets of langerhans, Glucagon and insulin
Exocrine: digestive enzymes secreted into the duodenum
Name 4 types of hormones
Glycoproteins/Peptide hormones
Steroid hormones
Catecholamines
Thyroid hormones
Where are glycoprotein/ peptide hormones synthesised and stored. How are they transported. Where are their receptors and and what is the cellular response. Give some examples?
Synthesis and storage - made in advance (glycosylated in the Golgi apparatus) and stores in secretory vesicles
Transport in the blood - Dissolved in blood plasma
Location of receptor - Cell membrane
Response - Activation of second messenger; may activate genes
Examples - Insulin, Glucagon, Prolactin
Where are steroid hormones synthesised and stored. How are they transported. Where are their receptors and and what is the cellular response. Give some examples?
Synthesis and storage - Synthesised on demand from precursors (primarily cholestrol)
Transport in the blood - Bound to carrier proteins like albumen in the blood
Location of receptor - Cytoplasm or nucleus; some have membrane receptors too
Response - Activation of genes
Examples - Oestrogen, Androgens
Where are Catecholamine hormones synthesised and stored. How are they transported. Where are their receptors and and what is the cellular response. Give some examples?
Synthesis and storage - Made in advance and stored in vesicles
Transport in the blood - Dissolved in plasma of the blood
Location of receptor - Cell membrane
Response - Activation of the 2nd messenger systems
Examples - Adrenaline and noradrenaline
Where are thyroid hormones synthesised and stored. How are they transported. Where are their receptors and and what is the cellular response. Give some examples?
Synthesis and storage - Made in advance; precursor stored in secretory vesicle
Transport in the blood - Bound to carrier proteins
Location of receptor - Nucleus
Response - Activation of genes
Examples - T4 and T3
Give some examples of how the hypothalamus is central to homeostasis and name some hormones that are secreted
Involved in:
Thermoregulation, Plasma osmolality, heart rate, blood pressure, feeding, satiety (had enough to eat), lactation
hormones secreted: Vasopressin (ADH), Oxytocin, 6 hormones to anterior via hypothalamo-hypophyseal portal system
What are the two main lobes of the pituitary and how are they connected to the pituitary?
Anterior lobe - Connected via the portal system from the hypothalamus
Posterior lobe - connected via direct innovation from nerves. The hormone is synthesised in the hypothalamus and is transported down the nerve and as such it acts as a Neurocrine system
Define a portal system and give 2 examples
The system of blood vessels that has two distinct groups of capillary beds.
Hepatic portal
hypothalamo-hypophyseal portal system
Why is there always a small concentration of hormones from the hypothalamus and the pituitary gland in the blood?
All hormones released in here are subject to both regulated and more crucially constitutive merocrine secretion.
Describe the embryonic development of the endocrine system
Starts in week 5+
1) pituitary develops from neurohypophyseal bud and hypophyseal pouch
2) Thyroid develops from the floor of pharynx - 2nd pouch
3) Parathyroid and thymus develop from 3rd and 4th pharangeal pouches
4) pancreas from the foregut
5) Adrenals from the intermediate medoderm and neural crest
describe the thyroid and where it is found
butterfly shaped and located just below the larynx and anterior to the trachea
define hyper and hypothyroidism
high T3 or 4 = hyper
low T3 or T4 = hypo
describe how TSH levels are regulated
TRH is released from the hypothalamus and enters the portal system where it stimulated the release of TSH which in turn stimulates the release of thyroid hormones. These then increase the blood concentration which is sensed by the hypothalamus and inhibits TRH secretion and as a result TSH secretion.
What levels of TSH, T4, T3 and antibodies indicates hyperthyroidism?
Low TSH (as it’s production is being inhibited by high T3 and 4 but thyroid is over producing)
High T3 and 4
No antibodies
What levels of TSH, T4, T3 and antibodies indicates hypothyroidism?
High TSH (as it’s production is being increased by low T3 and 4 but thyroid is under producing)
Low T3 and 4
No antibodies
What levels of TSH, T4, T3 and antibodies indicates Hashimotos?
High TSH, Normal to low T4 and low T3.
Anti-TPO and Anti-TG are present in blood
What levels of TSH, T4, T3 and antibodies indicates graves?
Low TSH, Normal to high T4 and high T3.
TSI and anti-TSH present in the blood
What is the role of the parafolicular cells and where are they found?
They are found in the thyroid and release calcitonin in response to high plasma calcium levels
calcitonin:
- inhibits osteoclast activity, renal reabsorption of calcium and counteracts PTH
What is the role of the parathyroid hormone?
monitors plasma calcium levels:
- low = release of PTH which increases osteoclast activity and absorbs more calcium from GI tract
Why is Calcium important?
Calcium is important in the nervous, muscular and skeletal systems. It allows for electrical control of the muscular contraction and also is needed for bone structure. As such in high concentrations it can lead to seizure and rigor
Describe what the role of adrenal medulla is
composed of chromaffin cells and is innervated directly by presynaptic myelinated sympathetic nerves and as such when stimulated releases catecholamines such as adrenaline and noradrenanline
name the layer of the adrenal cortex in order from outside to the medulla and outline there role
Outer - Zona Glomerulosa - Aldosterone regulates blood pressure
Middle - Zona Fasciculata - Glucocorticoids mobilises fats, proteins and carbs.
Inner - Zona Reticularis - Androgen Precursors (DHEA)
Define stress
a state of real or perceived threat to homeostasis
Outline the 3 main responses in fight or flight
Ramping up blood pressure
Dumping glucose into the blood
Shutting down non-emergency services
Where are the principle stress responses localised?
Hypothalamus
anterior lobe of pituitary
adrenal gland
Describe how the adrenal gland has 2 responses to stress (short and prolonged)
Short - Hypothalamus innervates spinal cord and spinal cord innervates adrenal medulla. Which releases catecholamines
Prolonged - Hyothalamus releases CRH, anterior pituitary senses CRH and releases ACTH into blood. This targets adrenal cortex and releases mineralocorticoids and glucocorticoids
Name some endo and exocrine products of the pancreas
Endocrine - Insulin, Glucagon, Somatostatin (inhibits insulin and glucagon)
Exocrine- Trypsinogen (pro enzyme for proteases), Lipase and Amylase
