Endocrine System Flashcards
Overview
- Includes ductless glands and endocrine tissues within other organs
- Secrete chemical signals called hormones which travel in the circulation and bind to receptors on/within target cells to initiate a change in the cell (a response)
- Target Cell = cell with receptor specific for that hormone
- No Target Cell = don’t have a receptor for hormone
What are the 3 Hormone Classes?
- Steroids
- Hormones derived from amino acids
- Peptide and protein hormones
Steroids
- Synthesized (made) from cholesterol
- Testosterone, estrogen, vitamon D
Hormones derived from amino acids
- e.g formed from tyrosine
- Thyroxine/T4
- A thyroid hormone
- Controls cellular metabolism, growth and development - Epinephrine and norepinephrine (adrenaline and noradrenaline)
- Secreated by the adrenal medulla as part of the fight or flight stress response and sexual climax (orgasm)
- Thyroxine/T4
Peptide and protein hormones
- Chains of amino acids held together by peptide bonds
- E.g. oxytocin, antidiuretic hormone (ADH), growth hormone (GH), insulin
Endocrine Glands
Glands with no other function (pure endocrine glands - their only function is to produce and secrete hormones)
How many Endocrine Glands?
- Pituitary Gland
- Thyroid Gland
- Parathyroid Glands
- Adrenal Glands
Pituitary Gland
- Suspended from hypothalamus
- In sella turcica of sphenoid bone
- 2 lobes:
- Anterior Pituitary
- Posterior Pituitary
Anterior Pituitary
- Glandular epithelial tissue
- Anterior pituitary hormone secretion regulated by hormones released by hypothalamus
- Secretes the following hormones:
- Growth Hormone (GH)
- Thyroid Stimulating Hormone (TSH)
- Adrenocorticotropic Hormone (ACTH)
- Gonadotropins - Reproductive Hormones
- Prolactin (PRL)
Growth Hormone (GH)
Affects growth and metabolism
Thyroid Stimulating Hormone (TSH)
Stimulates secretions by the thyroid gland
Adrenocorticotropic Hormone (ACTH)
Stimulates secretion of steroid hormones from the adrenal gland
Gonadotropins - Reproductive Hormones
- Luteinizing Hormone (LH)
- Stimulates ovulation and formation of corpus luteum in the ovary; stimulates testosterone production by interstitial endocrine (Leydig) cells in the testes
- Follicle Stimulating Hormone (FSH)
- Stimulates sustentocytes and follicle cells
Prolactin (PRL)
Stimulates milk production by mammary glands
Posterior Pituitary
- Nervous tissue (extension of brain structure called the hypothalamus)
- Stores and secretes hormones produced in hypothalamus, including:
- Oxytocin
- Antidiuretic Hormone (ADH, also known as vasopressin)
Oxytocin
Stimulates uterine contractions and milk ejection during suckling
Antidiuretic Hormone (ADH, also known as vasopressin)
Enhances water reabsorption by collecting duct cells of nephrons in the kidney
Thyroid Gland
- Butterfly shaped gland on anterior surface of the superior part of the trachea (inferior to larynx)
- Thyroid Histology:
- Follicles
- Parafollicular cells
Follicles
- Walls of the follicles are composed of epithelial (follicular) cells that secrete the hormone thyroxine (T4)
- Thyoxine is converted to its active form (T3) in target cells
Parafollicular cells
- Between follicles
- Secrete calcitonin
- Increase Ca++ uptake into bone (bone formation) which lowers blood Ca++
Parathyroid Glands
- 4 (usually) glands embedded in posterior thyroid
- Secrete parathyroid hormone (PTH)
- Acts on bone, kidneys to increase blood calcium levels
Adrenal Glands
- Located on the superior surface of each kidney
- Parts:
- Adrenal Cortex (outer)
- Adrenal Medulla (inner)
Adrenal Cortex (outer)
- Epithelial tissue forming glands
- Secretes only steroids
- 3 Layers ( a single class of hormones is secreted by each layer):
- Zona Glommerulosa
- Zona Fasciculata
- Zona Reticularis
Zona Glommerulosa
- Mainly secretes aldosterone
- Acts on nephrons to regulate salt balance
Zona Fasciculata
- Secretes mainly cortisol
- Regulates many body processes during long-term stress
Zona Reticularis
- Secretes androgens (sex hormones)
- Converted to testosterone or estrogens in other tissues
Adrenal Medulla (inner)
- Modified nervous tissue
- Synthesizes hormones that regulate “fight or flight” response
- Epinephrine (80%)
- Norepinephrine (20%)
Endocrine Tissues
- Hormone secreting cells or tissues located in organs that have other functions (i.e. are not stricly glands that secrete hormones):
- Pacreatic Islets of langerhans in Pancreaas
- Hypothalamus (part of the brain)
- Gonads
- Others
Hypothalamus (part of the brain)
- Produces and secretes hormones that stimulate or inhibit the secretion of hormones from the anterior pituitary
- GHRH (Growth Hormone Releasing Hormone)
- GHIH (Growth Hormone Inhibiting Hormone; also known as somatostatin)
- GnRH (Gonadotropin Rleasing Hormone) - for FSH and LH secretion
- Produces hormones that are stored and secreted by posterior pituitary
Pacreatic Islets of langerhans in Pancreaas
- 𝛼-cells
- Secrete glucagon
- Increases blood glucose concentration
- Secrete glucagon
- β-cells
- Secrete insulin
- Decreases blood glucose concentration
- Secrete insulin
Gonads
- Testes
- Interstitial endocrine (Leydig) cells - secrete testosterone
- Ovaries
- Granulosa cells of secondary and vesicular follicles secrete estrogen
- Corpus luteum secretes estrogen and progesterone
Others
- Duodenum - secretin; cholecystokinin (CCK)
- Kidney - renin, erythropoietin (EPO)
- Skin - vitamin D
- Heart - atrial natriuretic peptide (ANP)
- and others
