Endocrine System Flashcards
Where and what do endocrine glands secrete ?
Hormones are secreted directly into the bloodstream
What is an endocrine gland ?
Ductless glands with a rich blood supply
Endo - internal, Crine - secretions
Name the 8 endocrine glands
Pineal gland
Pituitary gland
Parathyroid gland
Thyroid gland
Adrenal gland
Pancreas
Ovary
Testis
What are some functions of endocrine glands ?
Cellular metabolism
Growth and development
Sexual development
Homeostasis
Behaviour - mood/sleep
What is an exocrine gland ?
May or may not have excretory ducts
Where do exocrine glands secrete ?
Externally onto an epithelial surface
Tongue - saliva
Skin - sebum/sweat
GI tract - digestive enzymes
Name the 3 classes of hormones
Proteins/ peptides
Steroids
Amino acid derivatives
Describe the half life of proteins
They have a short half life of a few minutes, as they are not attached to a carrier protein.
Describe how proteins work ?
Note : usually water soluble, readily transported in blood
- Bind to plasma membrane receptors on target cells
- Signal transduction
- Initiate cellular changes (i.e. gene expression)
What are steroids synthesised from ?
Cholesterol
Name some examples of steroids
Testosterone
Oestrogen
Cortisol
Describe the half life of steroids
They have a longer half life than proteins, as they require specific transporter proteins in the blood.
Describe how steroids work ?
They readily diffuse across the plasma membrane
Bind to intracellular receptors/transcription factors - modify gene expression.
What are amino acid derivatives modified from ?
Tyrosine
Where are catecholamines synthesised in ?
Renal medulla
What are catecholamines ?
Neurotransmitters
Name some catecholamines
Adrenaline
Noradrenaline
Dopamine
Name some thyroid hormones
Thyroxine
Tri-iodothyronine
How do all hormones act ?
By binding to receptors
e.g. cell membrane receptors - peptides, glycoproteins and catecholamines
e.g. intracellular receptors - steroids and thyroid hormones
Episodic hormones
Released in response to physiological demand
e.g. insulin
Jagged lines
Diurnal hormones
Released in a predictable pattern over 24 hours
e.g. cortisol
Has a peak in the graph
- May also respond to episodic stimuli
Constant hormones
Fairly constant blood concentrations for normal physiological function.
e.g. thyroxine
Name the 3 types of stimuli that trigger endocrine glands to produce and release their hormones
Humoral
Neuronal
Hormonal
What is humoral stimuli ?
Circulating molecules in the blood.
SIMPLEST
i.e. critical ions or nutrients
What is neuronal stimuli ?
Stress responses
Sympathetic nervous system
e.g. Adrenaline
What is hormonal stimuli ?
In response to hormones produced by other endocrine glands
e.g. pituitary or hypothalamus
Describe the relationship between the hypothalamus and pituitary gland in the control of the endocrine system.
Hypothalamus and pituitary gland coordinate the endocrine system - orchestrate activity of other endocrine glands
Provides signal amplification - cascades and fine control
Hypothalamus secretes hormones which control release of pituitary hormones
Pituitary hormones stimulate/control many other endocrine glands
Negative feedback system
Function of the hypothalamus
Controls release of hormones from the anterior lobe of the pituitary gland
What types of hormones are released from the hypothalamus ?
Releasing hormones (GHRH)
Inhibitory hormones (GHIH)
What does the posterior pituitary do ?
Storage of hormones secreted by neurosecretory cells in the hypothalamus
Transported via neuronal axons to the posterior lobe
- ADH or Vasopressin
- Oxytocin
Results of excess growth hormones
Gigantism
Acromegaly
Adenohypophysis
(aka) Anterior pituitary
Oral ectoderm derived
Vascular connection to hypothalamus
Neurohypophysis
Posterior pituitary
Neuroectoderm derived
Direct neural link to hypothalamus
What are the 2 major lobes of the pituitary gland ?
Anterior
Posterior
Where is the pituitary located ?
Hollow of the sphenoid bone
What does the anterior lobe consist of ?
Epithelial cells
What hormones does the anterior pituitary secrete ?
Growth hormone
Thyroid stimulating hormone
Adrenocorticotropic hormone
Follicle stimulating hormone
Luteinising hormone
Prolactin
What does the posterior lobe consist of ?
Neural tissue
Where is the thyroid gland located ?
2 lobes covering the anterolateral surface of the trachea
Within the visceral compartment of the neck surrounded by the pre tracheal fascia.
What is the largest pure endocrine gland in the body ?
Thyroid gland
What are some features of the thyroid gland ?
Innervated by the SNS and PNS
Where is thyroglobulin synthesised ?
In follicular cells - stored in the follicle lumen
How is thyroid hormone generated ?
Thyroglobulin combines with iodine and endocytosed back into the follicular cells and cleaved to generate Thyroid hormone.
Name the 2 types of thyroid hormones
Tri-iodothyronine (T3) - binds 3 iodine
Thyroxine (T4) - binds 4 iodine
What does thyroxine regulate ?
Rate of metabolism – energy use
Protein production – growth & development
Sensitivity of cells to other hormones
Thyroid disorders
Hypothyroidism
Hyperthyroidism
Severe hypothyroidism
Hypothyroidism
Non-toxic goitre, endemic in particular regions
iodine poor soil/ poor diet
Hyperthyroidism
Graves disease
Severe Hypothyroidism
Due to iodine deficiency
Neurological deficits
Where is the parathyroid gland located ?
2 pairs of glands
Embedded in the posterior aspect of the thyroid gland
Develops from the wall of the pharynx
What does the parathyroid gland produce ?
Parathyroid hormone
Function of parathyroid gland
Regulates calcium homeostasis
Promotes conversion of inactive vitamin D to active form.
How does the parathyroid gland regulate calcium homeostasis ?
Stimulates osteoclasts to break down bone matrix and increase blood Ca2+ levels
Why does the parathyroid gland promote conversion of inactive vitamin D to active form ?
As Vitamin D is required for absorption of Ca2+ from diet
Where is the adrenal gland located ?
Superior to the kidneys
What is the adrenal gland comprised of ?
Cortex tissue - glandular tissue derived from mesoderm
Medulla tissue - sympathetic nervous system derived from the neural crest
Layers of the adrenal cortex
Zona :
- Glomerulosa : mineralocorticoids
- Fasciculata : glucocorticoids
- Reticularis : gonadocorticoids
Medulla
What does the adrenal cortex produce ?
Steroid hormones called corticosteroids - cholesterol is the common precursor
Mineralocorticoids
e.g. Aldosterone
Homeostasis of Na+ and K+ and water
Glucocorticoids
e.g. Cortisol
Energy metabolism and glucose availability
Gonadocorticoids
Sex steroids
Weak androgens which are converted into tissue cells to more potent forms e.g. testosterone and oestrogen
What is the cortisol feedback mechanism stimulated by ?
Stress, exercise and hypoglycaemia
Cushings syndrome
Excessive cortisol
Key effects of the adrenal medulla
Increased BP, heart and respiratory rate
Diversion of blood to muscles
Glucose mobilisation
Where are chromaffin cells found ?
Adrenal medulla
Where is the function of chromaffin cells ?
Produce :
- Epinephrine
- Norepinephrine
- Dopamine
What is the adrenal medulla the site of ?
Catecholamine synthesis and secretion
Direct connection with SNS
Where is the pancreas located ?
Partially behind the stomach
What type of gland is the pancreas ?
Endocrine and exocrine
Function of pancreas
Major role in glucose homeostasis
What hormones do the Islets of Langerhans produce ?
Glucagon - in alpha cells
Insulin - in beta cells
Diabetes mellitus
disorder of the pancreas
Gastrin
Digestive enzymes
Renin
Helps control your blood pressure and maintain healthy levels of sodium and potassium in your body.
Function of Islets of Langerhans
Essential for regulation of blood glucose
