Endocrine System Flashcards
Main Types of Hormones
Insulin and parathormone are examples of
Protein and glycoprotein hormones
Main Types of Hormones
Vasopressin and Oxytocin are examples of
Small peptide hormones
Main Types of Hormones
Thyroxin and Adrenalin are examples of
Hormones that are derivatives of amino acids
Main Types of Hormones
Testosterone and Cortisol are examples of
Steroids derived from cholesterol
Components of Endocrine System
Major endocrine organs
Principal or only role of organ is hormone production (thyroid, adrenal gland)
Components of Endocrine System
Organs with partial but significant endocrine role
Such as pancreas, ovary or testes
Components of Endocrine System
Diffuse endocrine system
Scattered cells within organs performing endocrine function, such as enteroendocrine cells of the gut working on nearby cells (paracrine)
Endocrine Tissue
Most is of what origin?
Epithelial
Endocrine Glands
Pitutary Gland
Able to regulate
Many other endocrine glands
Pitutary Gland
Location
In the sella turcica of the sphenoid bone, just below the hypothalamus
Pitutary Gland
Also called
Hypophysis
Hypothalmic-Pituitary Axis
Pituitary Gland
Two Lobes
Anterior lobe (adenohypophysis) and posterior lobe (Neurohypophysis)
Pituitary Hormone Secretion
Anterior Lobe
Controlled by hormones from the hypothalamus entering in high concentrations through the hypothalamic-hypophyseal portal system
Hypothalamic Hormones
Regulating anterior pituitary
GHRH, Somatostatin, TRH, CRH, Dopamine, GnRH
Anterior Pituitary Cell Types
Somatotrophs
Produce GH and controlled by GHRH(+) and Somatostatin (-)
Anterior Pituitary Cell Types
Thyrotrophs
Produce TSH and regulated by TRH(+) and Somatostatin(-)
Anterior Pituitary Cell Types
Corticotrophs
Produce ACTH and controlled by CRH
Anterior Pituitary Cell Types
Lactotrophs
Produce Prolactin and controlled by TRH(+) and Dopamine(-)
Anterior Pituitary Cell Types
Gonadotrophs
Produce FSH and LH, and controlled by GnRH
Anterior Pituitary
Consists of
Packed secretory cells interspersed with fenestrated edothelium-lined vascular sinuses
Anterior Pituitary
Acidophils and Basophils
Acidophils: Somatotrophs and lactotrophs
Basophils: Thyrotrophs, corticotrophs and gonadotrophs
Posterior Pituitary
Consists of
The axons of nerve cells in the supraoptic and paraventricular nuclei of the hypthalamus
Thyroid Histology
Functional Unit
Thyroid Follicle - a spherical space lined by epithelial cells that are low cuboidal when inactive but nearly columnar when active
Thyroid Function
Main thyroid hormones
T3 and T4 are the main thyroid hormones
Thyroid C Cells
Location
Found adjacent to follicular cells. Within basal lamina surrounding follicle, but not in contact with the colloid
Thyroid C Cells
Secretory Product
Calcitonin. This inhibits osteoclast activity and lowers blood calcium.
Parathyroid Glands
What are they?
Usually 4 small oval glands on posterior surface of thyroid gland. Produce parathyroid hormone which increases serum calcium.
Parathyroid Glands - Cell types
Adipose Cells
…
Parathyroid Glands - Cell types
Chief cells
Small, lightly stained cells with dark nuclei. Cells that secrete PTH.
Parathyroid Glands - Cell types
Oxyphils
Larger than chief cells. Eosinophilic. Appear at puberty becoming more numerous with age. Large numbers of mitochrondria but function unknown.
Adrenal Glands
Adrenal Cortex
Formed of epithelial cells
Adrenal Glands
Adrenal Medulla
Formed of neural crest cells. Essentially a modified sympathetic ganglion where postganglionic neurons have lost axons and release trasmitter into the blood instead
Adrenal Glands
Surrounded by
Thick capsule with connective tissue trabeculae extending inwards through the cortex
Adrenal Glands
Adrenal Cortex
Three distinct layers or zones
From outer to inner -
Zona Glomerulosa
Zona Fasciculata
Zona Reticularis
Steroid Hormones Secreted by Adrenal Cortex
Mineralocorticoids
Involved in electrolyte and fluid homeostasis. Principally aldosterone. Produced in zona glomerulosa.
Steroid Hormones Secreted by Adrenal Cortex
Glucocorticoids
Involved in many aspects of metabolism. Stored in Zona Fasciculata. Principal glucocorticoid is cortisol, whose secretion is controlled by ACTH from the anterior pituitary
Steroid Hormones Secreted by Adrenal Cortex
Sex hormones
Androgens produced in small amounts by the Zona Reticularis
Adrenal Cortex Summary
Adrenal Medulla
Function
Reinforces the action of the sympathetic nervous system at times of stress. Contain granules of adrenaline and noradrenaline which are released into the blood, preparing the body for “fight or flight” at times of stress.
Endocrine Pancreas
Consists of
About one million small, scattered, islands of tissue called islets of Langerhans. Rich blood supply to these.
Cells of the Endocrine Pancreas
Insulin Secreting Cells
About 70% of the cells. Also called B cells or ß Cells
Cells of the Endocrine Pancreas
Glucagon Secreting Cells
About 20% of the cells. Also called A or alpha cells
Cells of the Endocrine Pancreas
Somatostatin Secreting Cells
About 5-10% of cells. Also called D or delta cells
Testes
Produce
Spermatozoa, but also secrete testosterone
Testes
Leydig Cells
In the interstices between the seminiferous tubules are responsible for testosterone production in the testes
Ovaries
Produce
Ova, but also secrete the female sex hormones oestrogen and progesterone
Theca Interna
Location and function
Surrounding developing ovarian follicle. Are responsible for much of the production of female sex hormones
