Endocrine System Flashcards
Main functions of endocrine system
Maintain body homeostasis
Help body to react to stress along with nervous system
Regulate growth and development, including sexual development and reproduction
How does the endocrine system function?
Synthesis and secretion of hormones which act as chemical messengers that are released into the blood to act at specific distant receptors
What are the 4 main types of hormones?
Protein and glycoprotein hormones - insulin, parathormone
Small peptide hormones - vasopressin, oxytocin
Hormones that are derivatives of amino acids - thyroxin, adrenalin
Steroids derived from cholesterol - testosterone, cortisol
What does the endocrine system consist of?
Major endocrine organs (principal/only role is hormone production e.g. thyroid gland, adrenal gland)
Organs with a partial but significant endocrine role (pancreas, ovary, testes)
Diffuse endocrine system (scattered cells within an organ that have endocrine function e.g. enteroendocrine cells of gut)
Some major endocrine glands
Pituitary gland Hypothalamus Thyroid gland Thymus Adrenal gland Pancreas
Where is the pituitary gland?
Sella turcica of the sphenoid bone
Just below hypothalamus
What are the two lobes of the pituitary called?
Anterior - adenohypophysis
Posterior - neurohypophysis
How do the two lobes of the pituitary develop?
Neurohypophysis develops as downward growth of hypothalamus and stays attached by pituitary stalk.
Adenohypophysis develops as an upward pocket of epithelium in the roof of the oral cavity called Rathke’s pouch
How is hormone secretion in the anterior pituitary lobe controlled?
Hormones from the hypothalamus delivered by the hypothalmic-hypophyseal portal system
What does the posterior pituitary lobe secrete?
Oxytocin
ADH
What does the anterior pituitary lobe secrete?
Growth hormone Prolactin Gonadotrophins Adrenocorticotropic homrone (ACTH) Thyroid stimulating hormone (TSH)
What hormones regulate the anterior pituitary lobe?
Growth hormone-releasing hormone Somatostatin Thyrotropin-releasing hormone Corticotropin-releasing hormone Dopamine Gonadotropin-releasing hormone
What five cell types are present in the anterior pituitary lobe?
Acidophils:
- Somatotrophs
- Thyrotrophs
Basophils:
- Corticotrophs
- Lactotrophs
- Gonadotrophs
What is the pars intermedia?
The portion of the anterior lobe bordering the posterior lobe
Remnant of the lumen in Rathke’s pouch
What is the functional unit of the thyroid?
Thyroid follicle - a spherical space lined by epithelial cells that are low cuboidal when inactive but nearly columnar when active
What are the main thyroid hormones?
Triiodothyronine (T3)
Tetraiodothyronine (T4)
Where are thyroid C cells found?
Adjacent to follicular cells
Within basal lamina surrounding follicle but not in contact with the colloid
What is the secretory product of thyroid C cells?
Calcitonin
What is the function of calcitonin?
Inhibits osteoclast activity and lowers blood calcium
What are the parathyroid glands and what are their function?
4 small oval glands on posterior surface of thyroid
Produce parathyroid hormone
How does parathormone increase serum calcium?
Stimulating release of calcium from bone
Increasing renal calcium reabsorption
Increasing calcium absorption from the gut
What 3 cells are present in parathyroid glands?
Chief cells
Oxyphils
Adipose cells
What makes up the adrenal glands?
Adrenal cortex (formed of epithelial cells) Adrenal medulla (formed of neural crest cells) Both surrounded by a thick capsule with connective tissue trabeculae extending inward through the cortex
What are the 3 layers of the adrenal cortex?
Zona glomerulosa
Zona fasciulata
Zona reticularis
What 3 types of hormones does the adrenal cortex secrete?
Mineralcorticoids e.g. aldosterone (zona glomerulosa)
Glucocorticoids e.g. cortisol (zona fasciulata)
Sex hormones e.g. androgens (zona reticularis)
Function of the adrenal medulla
Reinforces action of sympathetic nervous system at times of stress
Cells contain granules of adrenaline and noradrenaline that are released into the blood in response to sympathetic stimulation
Raises blood pressure, increasing heart rate, causing bronchodilation etc
What are the 3 principal cell types in the pancreatic islets of Langerhans?
Insuling secreting cells (beta cells)
Glucagon secreting cells (alpha cells)
Somatostatin secreting cells (delta cells)
Endocrine function of testes
Leydig cells produce testosterone
Endocrine function of ovaries
Theca interna produces precursors which are converted to oestrogen by granulosa cells
