Intro Flashcards
What are hormones
Chemical messengers
Where are hormones secreted into
Directly into bloodstream
What are endocrine glands
They are ductless with rich blood supply. They typically act on tissues distant from source
What are exocrine glands
They may or may not have excretory ducts. They release secretions onto epithelial surface
What are the 3 main types of hormones
Proteins, steroids and amino acid derivatives
What are steroids synthesised from
Cholesterol
What are amino acid derivatives modified from
Tyrosine
What does an episodic hormone respond to
In response to physiological demand
What is a diurnal hormone
Predictable pattern over 24hr
What is a constant hormone
Fairly constant blood concentrations for normal physiological function
What are the 3 types of stimuli that trigger endocrine glands
Humoral, neuronal and hormonal
What is humoral stimuli
Circulating molecules in the blood
What is neuronal stimuli
Stress response - SNS
What is hormonal stimuli
In response to hormones produced by other endocrine glands
What endocrine glands coordinate the endocrine system
Hypothalamus and pituitary gland
What does the hypothalamus do
- Controls release of hormones from the anterior lobe of the pituitary gland
- Also synthesises hormones (oxytocin and antidiuretic hormone) which are stored in the posterior lobe of the pituitary gland
What are the 2 major lobes of the pituitary gland
- Anterior pituitary = adenohypophysis
- Posterior pituitary = neurohypophysis
What is the adenohypophysis
- Oral ectoderm derived
- Vascular connection to hypothalamus
What is the neurohypophysis
- Neuroectoderm derived
- Direct neural link to hypothalamus
Where are the lobes located
Located in a hollow of the sphenoid bone
What does the adenohypophysis consist of
Epithelial cells
What does the adenohypophysis secrete
- Growth Hormone (GH)
- Thyroid stimulating hormone (TSH)
- Adrenocorticotropic hormone (ACTH)
- Follicle stimulating hormone (FSH)
- Luteinising hormone (LH)
- Prolactin
What does the neurohypophysis consist of
Neural tissue
What does the neurohypophysis store
Hormones secreted by neurosecretory cells in the hypothalamus
How are the stored hormones transported
Via neuronal axons to the posterior lobe
What are the 2 hormones stored
- Anti-diuretic hormone (ADH) or Vasopressin
-Oxytocin
What does the thyroid gland consist of
Two lobes covering the anterolateral surface of the trachea
Where is the thyroid gland
Within the visceral compartment of the neck surrounded by the pretracheal fascia
How does the thyroid develop in the embryo
As a down growth of the tongue epithelium
Where is thyroglobulin synthesised
In follicular cells – stored in the follicle lumen
How does thyroglobulin generate hormones
Thyroglobulin combines with iodine and endocytosed back into the follicular cells and cleaved to generate Thyroid hormone:
- Tri-iodothyronine (T3)
- Thyroxine (T4)
What does thyroxine regulate
- Rate of metabolism – energy use
- Protein production – growth & development
- Sensitivity of cells to other hormones
What is the parathyroid gland
Two pairs of glands embedded in the posterior aspect of the thyroid gland
Where does the parathyroid gland develop from
The wall of the pharynx
What does parathyroid hormone do
- Regulates calcium homeostasis – stimulates osteoclasts to breakdown bone matrix and increase blood Ca++ levels
- Promotes conversion of inactive vitamin D to active form (vit D required for absorption of Ca++ from diet)
What are the adrenal glands
Paired glands situated superior to the kidneys
What are adrenal glands comprised of
- Cortex – glandular tissue derived from the mesoderm
- Medulla – sympathetic nervous system derived from the neural crest (neuroectoderm)
What does the adrenal cortex produce
Steroid hormones called corticosteroids - cholesterol is the common precursor
What are the steroid hormones produced by the adrenal complex
- Zona glomerulosa - Mineralocorticoids – e.g. Aldosterone
- Zona fasciculata - Glucocorticoids – e.g. Cortisol
- Zona reticularis - sex steroids
What is the cortisal feedback mechanism
Stimulated by stress – exercise and hypoglycaemia
Clear diurnal rhythm of activity:
- Peaks: 6 – 8 am
- Lowest: midnight – 2 am
Main effects:
- Glucose mobilisation
- Cardiovascular (blood volume)
- Sensitivity to catecholamines
What is the adrenal medulla
Direct connection with the sympathetic nervous system – primed for immediate response – fight or flight
What is the adrenal medulla the site of
Catecholamine synthesis and secretion
What do chromaffin cells produce
- Epinephrine
- Norepinephrine
- Dopamine
What do islets of Langerhans produce
- Glucagon in alpha cells
- Insulin in beta cells
