Endocrine System Flashcards
What is the endocrine system?
+ Second integrative control system of the body
+ Much slower to act than the nervous system
+ Actions are mediated by hormones
What regulatory systems does the endocrine system control?
+ Regulation of cellular metabolism
+ Maintenance of homeostasis (e.g. Ca++)
+Sexual development and reproduction
+ Growth and development from childhood to adulthood
+ Modulates long term behaviour (mood, sleep)
How do endocrine glands distribute hormones around the body?
They have no ducts so they secrete and release hormones directly into the bloodstream
What are hormones?
Hormones are ‘chemical messengers’ that act on target cells through specific receptors
What are the three classes of hormones?
+ Proteins
+ Steroids
+ Amino acid derivatives
Where do glands develop from?
Epithelial cells
What are exocrine glands?
+ Glands with ducts that carry secretions onto the surface of the epithelium
+ E.g salivary, sebaceous, sweat, mammary, glands open onto the skin)
+ Pancreatic duct opens into the duodenum
What are endocrine glands?
Glands that secrete their products, hormones, directly into the bloodstream rather than through ducts
What is paracrine secretion?
+ Paracrine factors (polypeptides) diffuse over short distances
+ Involves cell-cell communication: inducing changes in adjacent cells (e.g peptide neurotransmitters)
+ Important in embryogenesis where gradients of polypeptides influence developmental change
- fibroblast growth factor (FGF) family
- hedgehog family (sonic hedgehog)
- WnT family
- TGF-β superfamily
What are the major glands of the endocrine system?
\+ Hypothalamus \+ Pineal \+ Pituitary \+ Thyroid \+ Parathyroid \+ Thalamus \+ Adrenal \+ Pancreas \+ Ovaries \+ Testes
What are the features of hormones in the blood?
+ Very low concentrations
+ Concentrations vary (e.g episodic, diurnal)
- important when measuring plasma levels
+ Steroid and thyroid hormones are transported in the blood by specific carrier/binder proteins
- improves solubility
- increases half life
- provides a reserve in the blood
+ Only free hormones are biologically active
What are the conditions associated with the mechanisms of action?
+ All hormones act by binding to receptors
+ Target cells must present receptors ( lock and key)
Name types of cell membrane receptors
+ Peptides
+ Glycoproteins
+ Catecholamines
Name types of intracellular receptors in the nucleus
+ Steroids
+ Thyroid hormones
What are protein hormones?
+ Chains of amino acids
+ Usually injected
What are steroid hormones?
+ Synthesised from cholesterol
+ Oral administration
What are amino acid derivative hormones?
+ Thyroid hormones
+ Catecholamines (adrenalin, dopamine, noradrenalin)
From where does the anterior pituitary develop?
The epithelium of the mouth
How does the posterior pituitary develop?
It is a down growth of the hypothalamus (consists of nerve fibres)
What is endocrine axes/cascade?
When the target tissue of one hormone is another endocrine gland; this allows amplification and fine control
Generally, what does the hypothalamus do?
Secrete hormones that control the secretion and release of pituitary hormones
Generally, what do pituitary hormones do?
Stimulate/control many other endocrine glands (thyroid, gonads etc)
What is the function of the hypothalamus gland?
+ Controls the release of anterior pituitary hormones via releasing hormones (prolactin is controlled by a hypothalamic inhibiting factor)
+ Also secretes hormones stored and released by the posterior lobe of the pituitary gland (oxytocin and ADH)
What is another name for the anterior lobe of the pituitary gland?
Adenohypophysis
What does the anterior lobe of the pituitary gland consist of?
Epithelial cells
What 6 hormones does the anterior lobe of the pituitary gland secrete?
\+ Growth hormone (GH) \+ Thyroid stimulating hormone (TSH) \+ Adrenocorticotropic hormone (ACTH) \+ Follicle stimulating hormone (FSH) \+ Luteinising hormone (LH) \+ Prolactin
Where does TSH target in the body?
Thyroid
Where does prolactin target in the body?
The mammary glands
Where does ACTH target in the body?
Adrenoglands
Where do LH and FSH target in the body?
Ovaries and Testes
What is another name for the posterior lobe of the pituitary gland?
Neurohypophysis
What does the posterior lobe of the pituitary gland consist of?
Neural tissue
What is the function of the posterior lobe of the pituitary gland?
+ Stores hormones secreted by neurosecretory cells in the hypothalamus, which are transported via neuronal axons in the stalk to posterior lobe of the pituitary
Hormones released:
+ Antidiuretic hormone (ADH) (aka Vasopressin)
+ Oxytocin
What is ADH also known as?
Vasopressin
Where does ADH target in the body?
The kidneys
Where does oxytocin target in the body?
Breast tissue and uterus
Describe the sequence of events of the hypothalamo-hypophyseal-gonadal axis
+ Hypothalamus secretes GnRH
+ GnRH stimulates secretion of pituitary FSH (and LH?)
+ FSH stimulates the gonad to secrete oestrogen or testosterone
What is the concept of negative feedback regarding the endocrine system?
+ The final product of a cascade acts to inhibit a hormone higher up in the cascade
+ The hypothalamus is an important site of negative feedback in many hormone systems
What are pituitary adenomas?
+ Common benign tumours of the pituitary gland
+ Some tumours secrete one or more hormones in excess
Where does the thyroid gland lie?
Anterior to the trachea in the neck
How does the thyroid glands develop?
It is a down growth of the epithelium of the tongue (leaves a pit at the back of the tongue - foramen caecum)
What hormones are secreted by follicular cells in the thyroid?
+ Tri-iodothyronine (T3)
+Thyroxine (T4) - requires iodine
Where are Tri-iodothyronine (T3) and Thyroxine (T4) stored?
The colloid
What does thyroxine regulate?
+ Energy use; rate of metabolism
+ Protein production; growth and development
+ Regulates sensitivity of cells to other hormones
What do parafollicular (aka C) cells produce?
Calcitonin
What does calcitonin regulate?
It regulates calcium homeostasis and stimulates osteoblasts
From where does the parathyroid gland develop?
The wall of the pharynx
Where is the parathyroid found?
+ Embedded in the posterior aspect of the thyroid
+ Two pairs of glands
What does the parathyroid produce?
Parathyroid hormone
What does parathyroid hormone regulate?
Calcium homeostasis - stimulates osteoclasts to breakdown bone matrix and therefore increases blood calcium levels
What two regions form the adrenal glands?
+ Cortex (outside)
+ (Adrenal) medulla (inside)
What are the three layers of epithelial cells that form the cortex?
+ Zona glomerulosa
+ Zona fasciculata
+ Zona reticularis
What cells form the (adrenal) medulla?
Neural crest cells - neuroectoderm
What does the adrenal cortex produce?
Steroid hormones
What does the adrenal cortex develop from?
It develops from the mesoderm of the posterior abdominal wall
What (steroid) hormones does the zona glomerulosa produce and secrete?
Mineralocorticoids - e.g Aldosterone
What (steroid) hormones does the zona fasciculata produce and secrete?
Glucocorticoids - e.g Cortisone
What (steroid) hormones does the zona reticularis produce and secrete?
Sex steroids - e.g Androgens
What type of cells does the adrenal medulla contain?
Chromaffin cells
What do the chromaffin cells in the adrenal medulla produce?
Catecholamines:
+ Epinephrine
+ Norepinephrine
+ Dopamine
What does the adrenal medulla have a direct connection with?
The sympathetic nervous system (controlling our fight/flight response)
What kind of gland is the pancreas?
Exocrine and endocrine
How does the pancreas develop?
+ As an out growth of the gut tube
+ Closely associated with the development of the gall bladder
What forms the exocrine component of the pancreas?
Pancreatic acini
What do the pancreatic acini produce?
Pancreatic amylase
What forms the endocrine component of the pancreas?
The islets of Langerhans
What do the islets of Langerhans produce?
+ Glucagon (alpha cells)
+ Insulin (beta cells)
What hormone does the GI tract produce?
Gastrin
What hormone do the kidneys produce?
Renin
