Endocrine System Flashcards
What is the endocrine system?
Second control system of body
Slower than nervous system
Actions mediated by hormones
What are endocrine glands?
No ducts
Secrete + release hormones directly into blood
What are hormones?
Chemical messengers
Act on target cells through specific receptors
What are the three classes of hormones?
Proteins
Steroids
Amino acid derivatives
What are exocrine glands?
Secrete outside of body e.g. skin, mouth
Development of glands:
Develop from epithelial cells
Cords of cells grow down into underlying tissue
Examples of exocrine glands:
Intestinal glands of Lieberkuhn
Sweat glands
Glands of stomach + uterus
Sebaceous glands of skin
Structure of exocrine glands:
Secretory cells arranged in alveoli
Basement membrane
Acinus
Duct
What do epithelial cells do in exocrine glands?
They form ducts to carry secretions onto epithelium surface
Characteristics of endocrine glands:
Ductless
Rich blood supply - lots of capillaries
How does the hormone travel in endocrine glands?
Hormone diffuses out of extracellular fluid into bloodstream (through capillary fenestrations)
What are paracrine secretions?
Involve paracrine factors (polypeptides) that diffuse over short distances
No blood transport
What is paracrine secretion involved with?
Cell to cell communication
Induce changes in adjacent cells (e.g. peptide neurotransmitters)
What is paracrine secretion important in?
Embryogenesis - gradients of polypeptides influence developmental change
Examples of families of different polypeptide hormones:
Fibroblast growth factor family
Hedgehog family
WnT family
TGF-B superfamily
What glands are part of endocrine system?
Pineal gland
Hypothalamus
Pituitary
Thyroid
Parathyroid
Thymus
Adrenal
Pancreas
Ovary
Testis
What does the pineal gland do?
Releases melatonin - controls sleep patterns + circadian rhythms
Where is adrenal gland positioned?
Superior poles of both kidneys
What are hormones like in the blood?
Very low concentrations
Varying concentrations - important when measuring plasma levels
How are steroid and thyroid hormones transported in the blood?
They are hydrophobic and insoluble
By specific carrier / binding proteins
Why are steroid and thyroid hormones carried by binding proteins in the blood?
Improves solubility
Increases half life
Provides reserve in blood - increases concentrations
What must hormones attached to binding proteins do before binding to receptor on target cell?
Must dissociate as not biologically active
Only free hormones are biologically active
What are the different types of receptors?
Cell membrane receptors - hydrophilic hormones bind as can’t get inside cell
Intracellular receptors in nucleus - hydrophobic hormones (steroids and thyroids) diffuse through membrane to gain access to nucleus
What are the three types of hormones?
Proteins
Steroids
Amino acid derivatives
Structure of protein hormones:
Chains of amino acids (usually injected)
What are steroids like?
Synthesised from cholesterol - basic structure
Oral administration
What are amino acid derivatives like?
Thyroid hormones
Catecholamines (adrenaline, noradrenaline, dopamine)
How does anterior pituitary develop?
Develops from epithelium of mouth
How does posterior pituitary develop?
As a downgrowth of hypothalamus
Consists of nerve fibres
What’s involved in endocrine regulation?
Endocrine axes / Cascades
Hypothalamus
Pituitary hormones
What do endocrine axes / cascades allow?
Target tissue of one hormone is another endocrine gland
Allows amplification and fine control
What does the hypothalamus do?
Secretes hormones - control secretion and release of pituitary hormones
What do pituitary glands do?
Stimulate/control many other endocrine glands
Functions of hypothalamus:
Controls release of anterior pituitary hormones via releasing hormones
Secretes hormones that are stored + released by posterior lobe of pituitary gland (oxytocin and ADH)
What’s ADH?
Antidiuretic hormone
What is the anterior lobe of pituitary gland also known as?
Adenohypophysis
What hormones do epithelial cells in anterior lobe of pituitary gland secret?
GH TSH ACTH FSH LH Prolactin
What’s GH?
Growth hormone
What’s TSH?
Thyroid stimulating hormone
What’s ACTH?
Adrenocorticotropic hormone
WWhat’s the posterior lobe of pituitary gland called?
Neurohypophysis
Structure of posterior lobe:
Consists of neural tissue
What does posterior lobe of pituitary gland do?
Stores hormones secreted by neurosecretory cells in hypothalamus
How are hormones secreted by hypothalamus transported to posterior lobe of pituitary gland?
Via neuronal axons in the stalk
What hormones does posterior lobe of pituitary gland release?
ADH
Oxytocin
What does oxytocin do?
Stimulates milk ejection
Contraction of myometrium
What does ADH do?
Acts in renal/kidney
Reduces amount of urine so body can retain water
What happens in endocrine axes / cascades?
Hypothalamus controls pituitary
Pituitary controls other endocrine glands (e.g. gonads)
Give example of an endocrine axes / cascade?
Hypothalamus secretes GnRH
GnRH stimulates secretion of FSH
FSH stimulates gonad to secrete oestrogen/testosterone
WHat’s GnRH?
Gonadotrophin Releasing Hormone
What are endocrine axes / Cascades important in?
Negative feedback
Final product of cascade inhibits hormone higher up in cascade
What’s a pituitary adenoma?
Uncontrollable release of hormone
E.g. Acromegaly - over secretion of growth hormone
Position of thyroid gland:
Anterior to trachea in neck
How does thyroid gland develop?
As down growth of epithelium of tongue
What do follicular cells within thyroid gland secrete?
Follicular cells secrete T3 and T4 - requires iodine
What’s T3
Tri-iodothyronine
What’s T4?
Thyroxine
What are hormones secreted by thyroid gland stored in?
Colloid (thyroglobulin)
What does thyroxine (T4) regulate?
Energy use - rate of metabolism
Protein production - growth + development
Regulates sensitivity of cells to other hormones
What do parafollicular cells procude in the thyroid gland?
Calcitonin - regulates calcium homeostatic + stimulates osteoblasts
Structure of parathyroid glands:
Develop from wall of pharynx
Two pairs of glands
Embedded in posterior aspect of thyroid
What do parathyroid glands do?
Produce parathyroid hormone
Regulate calcium homeostasis - stimulate osteoclasts to breakdown bone matrix
Increase blood calcium levels
What’s in the cortex of adrenal glands?
Three layers of epithelial cells
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis (innermost layer)
What’s in the medulla of adrenal glands?
Neural crest cells
What doe the adrenal cortex produce?
Steroid hormones
What does the adrenal cortex develop from?
Mesoderm of posterior abdominal wall
What does Zona glomerulosa consist of?
Mineralocorticoids e.g. aldosterone
What does Zona fasciculata consist of?
Glucocorticoids
What does Zona reticularis consist of?
Sex steroids
What does the adrenal medulla develop from?
From neuroectoderm (neural crest cells)
What does the adrenal medulla contain?
Chromaffin cells - produce catecholamines
Give examples of catecholamines:
Epinephrine (a.k.a. Adrenaline)
Norepinephrine (a.k.a. Noradrenaline)
Dopamine
What does adrenal medulla have direct connection with?
Sympathetic nervous system - controls fight or flight
What does the pancreas develop from?
As an out growth of gut tube
Closely associated with growth of gall bladder
What must happen to ducts in pancreas?
Must join before emptying into duodenum
What’s involved in the exocrine component of the pancreas?
Pancreatic acini produce pancreatic amylase
What’s involved in the endocrine component of the pancreas?
Inlets of Langerhans produce horomones
Alpha cells - glucagon
Beta cells - insulin
