Midterm 1: Endocrine System Flashcards
Functions of Endocrine System
- regulate development, growth, and metabolism
- maintain blood composition and volume
- control digestive and reproductive activities.
Glands of the Endocrine System
Adrenal Cortex and Medulla Thymus Thyroid Parathyroid Pineal Pituitary
Organs/Tissues that contain Endocrine Cells
- Adipose
- Digestive System (stomach, small intestine, liver, pancreas)
- Gonads
- Heart
- Hypothalamus
- Kidney
- Skin
Differences between endocrine, paracrine, and autocrine receptors
Endocrine receptors has to do with hormones traveling to a distant part of the body. Paracrine is associated with local transmission of hormones. Autocrine receptors are associated with the same cell that secretes the hormone.
Circulating Hormones & examples
Hormones that travel a longer distance and bind to endocrine receptors. Ex. biogenic amines, peptides/proteins, and steroids
Local hormones & Examples
Hormones that bind with paracrine receptors and are short lived. Ex. Eicosanoids (prostaglandins, thromboxanes, leukotrienes) that are derived from arachidonic acid.
What are the 3 classes of circulating hormones?
- Biogenic amines
- peptides/proteins
- steroids
Characteristic of Biogenic amines & examples.
Water soluble (except thyroid hormone) and derived from the amino acid tyrosine.
Ex.
- Norepinephrine, epinephrine (catecholamines)
- Thyroid hormones
Characteristics of peptide/protein hormones & examples
All water soluble and derived from amino acid chains.
Ex. ADH/Vasopressin Atrial natriuretic peptide (ANP) Erythropoietin (EPO) Growth hormone Insulin/glucagon Parathyroid hormone (PTH)
Characteristics of steroids & examples
All lipid soluble and formed from cholesterol.
Ex.
- Sex hormones (testosterone, estrogen, progesterone)
- Cortisol
- Aldosterone
- Calcitrol
True or False:
All hormones that are soluble in blood are free hormones.
False. There are a few water-soluble hormones that are protein bound.
Free vs. Bound hormones
Free hormones are soluble in blood.
Water-soluble hormones (first messenger) bind to plasma membrane receptor, triggering a series of events (i.e., activation of G-proteins, second messengers) across the cell membrane that will ultimately stimulate the target cell
Bound hormones are lipid-soluble and bound to proteins. Since they are lipid soluble, they can pass through pass through the cell membrane and interact with intracellular receptors.
General description and location of thyroid gland
- Butterfly-shaped bi-lobed gland located in the anterior neck, lower cervical
- Right and left lobes connected midsagittal by the isthmus
- Positioned behind the sternohyoid and sternothyroid muscles (both are infrahyoids)
- Wraps around cricoid cartilage & superior tracheal rings
- Parathyroid glands located on posterior surface
Vasculature of thyroid
1) Superior thyroid -receives blood from the external carotid a. (first branch of the external carotid) and supplies superior-anterior portion of gland.
2) Inferior thyroid- receives blood from thyrocervical trunk (a branch of subclavian) and supplies remainder of gland
3) Superior and middle thyroid- drain into the internal jugular
4) Inferior thyroid- forms a plexus and has anastomoses with the superior and middle thyroid; typically drains into the (left) brachiocephalic v.
Autonomic innervation of the thyroid
- Sympathetic innervation via cervical ganglia
- Parasympathetic innervation via branches of the vagus n. (CN X)
Describe the glands of the thyroid.
Contain 20-30 million spherical follicles that have a cavity in the middle lined with simple cuboidal epithelium cells called follicular cells. The cavity is made up of the thyroglobulin (glycoprotein) and oxidized iodide that are secreted from the follicular cells.
Throid-stimulating hormone (TSH)
Secreted from the anterior pituitary. Stimulates secretion of T3 (most active form of thyroid hormone) and T4 (highest plasma concentration of the two)
Why is thyroglobulin important in the thyroid gland?
Thyroglobulin (specifically its tyrosine residues) and iodine are initial building blocks for the synthesis of T3 (triiodothyronine) and T4 (thyroxine)
Parafollicular cells (C cells)
Responsible for the synthesis and secretion of the peptide hormone calcitonin in response to an elevated blood calcium concentration. Larger than follicular cells and have a lighter staining nucleus.
What does calcitonin do? Where is it secreted from?
Calcitonin lowers blood calcium levels by inhibiting bone reabsorption.
General description and location of the parathyroid gland
Small, paired (superior and inferior) ovoid-shaped structures on posterior surface of thyroid
Not regulated by pituitary unlike the thyroid.
True or False:
The vasculature and the innervation of the thyroid and parathyroid are the same.
True
Describe the cells/hormones of the parathyroid and explain the role they have.
Chief (principal) cells are the most numerous cell in parathyroid and they secrete parathyroid hormone. Parathyroid hormone acts as an antagonist of calcitonin. Parathyroid hormone increases plasma calcium levels in 3 different ways.
1) increasing calcium reabsorption from bone
2) Increased reabsorption of calcium from kidneys
3) calcitrol formation in kidneys by activating enzyme. This then secretes calcitriol secretion from the kidneys which increases absorption from the small intestine.
Oxyphil (eosinophil) cells are larger than chief cells and first appear at puberty and increase with age. function is uncertain.
General description and location of Pituitary Gland
Bi-lobed gland (1cm diameter) suspended from the hypothalamus via the pituitary stalk (infundibulum).
Gland positioned within the sella turcica of the middle cranial fossa.
Carries out the functions of the hypothalamus that controls other glands and tissues in the body.
Anterior & inferior: Sphenoid sinus
Anterior only: Anterior intercavernous sinus
Posterior: Posterior intercavernous sinus; basilar artery/pons
Superior: Diaphragm sellae (dura mater deflection); optic chiasm
Lateral: Cavernous sinus
6 primary anterior pituitary hormones
FSH LH Growth hormone TSH Prolactin ACTH
Describe the anterior lobe of the pituitary gland and its interaction with the hypothalamus.
Largest lobe by volume (75%). Secretes prolactin, gonadotropins, growth hormone, thyroid stimulating hormone, and adrenocorticotropic hormone. The hypothalamus influences the anterior pituitary by secreting regulatory hormones that act on specific anterior pituitary receptors via hypothalamic-hypophyseal portal system. (not a neural influence)
Prolactin
stimulates milk production from mammary glands. Can be stimulated by estrogen and other factors
Dopamine effects on prolactin
Dopamine is prolactin’s hypothalamic regulator. It inhibits secretion.
2 types of gonadotropins and their function
1) Follicle-stimulating hormone (FSH)- drives oogenesis (female) and spermatogenesis (male)
2) Luteinizing hormone (LH): Synthesis of progesterone and androgens (testosterone) , androgens converted to estrogens (estrone and estradiol) by the aromatase enzyme
True or False;
Growth Hormone is the only hormone that stimulates growth.
False. Insulin, thyroid hormones, sex hormones, and cortisol also stimulate growth.
Describe how growth hormone works. When is secretion increased/ decreased?
GH and IGF-1 directly drives lipolysis in adipocytes where liberated glycerol can be converted to glucose in the liver for use as an energy source via gluconeogenesis and fatty acids can be utilized as an energy source in most tissues.
GH secretion greatest during non-REM sleep (earlier in sleep cycle) and during intense exercise.
GH secretion decreases with age and increases with increased nutrients in the plasma
Describe what growth hormone stimulates.
GH stimulates liver hepatocytes to secrete insulin growth factor (IGF-1), the major driver of growth secondary to the effects of GH and stimulates the conversion of glycogen to glucose (glycogenolysis) and glycerol (directed from the adipocytes after lipolysis) to glucose via gluconeogenesis for use as an energy source
Thyroid-Stimulating Hormone (TSH)
binds to external receptors of thyroid follicular cells that stimulates follicular synthesis and secretion of the thyroid hormones, T3 and T4
Adrenocorticotrophic Hormone (ACTH)
acts as regulatory hormone for glucocorticoid secretion (i.e., corticosterone, cortisol) from adrenal medulla (zona fasciculata)
Intermediate lobe & Proopiomelanocortin (POMC)
Intermediate lobe is considered part of the anterior pituitary but does not have much vascularization.
POMC is released here generates several peptides via post-translational modification including the opioids endorphins and enkephalins as well as ACTH and melanocyte-stimulating hormone (MSH)
Describe Pineal gland
Located in epithalamus immediately posterior to thalamus
Secretes hormone melatonin which regulates the body clock (Circadian rhythm)
Believed to regulate reproduction by regulating FSH and LH from the anterior pituitary
What does FSH control?
FSH controls development of ova in females and sperm in males
What does LH control?
LH stimulates ovulation in females and triggers the production of testosterone in males
What does melatonin do? What do low levels in younger people cause?
Regulate sleep cycle. Low levels delay the onset of puberty
General description and location of adrenal glands
Small, flattened endocrine glands located at the superior poles of each kidney and surrounded by a fibrous capsule.
The outer adrenal cortex is under pituitary control and secretes steroid hormones.
The inner adrenal medulla, under sympathetic control and is embryologically like the sympathetic NS.
Vasculature of adrenal glands
Arteries: Superior, middle and inferior suprarenal
Venous: Suprarenal
Adrenal cortex sections
Zona glomerulosa (outer) Zona Fasiculata Zona Reticularis (inner)
Zona glomerulosa in adrenal cortex secretes ___________.
Mineralocorticoids (Aldosterone)
Zona fasiculata in adrenal cortex secretes __________.
Glucocorticoids (Cortisol)
Zona reticularis in adrenal cortex secretes ___________.
Androgens
Adrenal Medulla composition
Comprised of specialized sympathetic neurons (that first pass through the adrenal cortex) called chromaffin cells; these cells secrete mainly epinephrine, but also secrete norepinephrine.
What do chromatin cells secrete?
secrete mainly epinephrine but also secrete norepinephrine
Where are glucocorticoids (cortisol) secreted and what are its functions?
Secreted in zona fasiculata of the adrenal cortex.
It decreases events associated with the inflammatory response such as capillary permeability and production of prostaglandins.
Suppression of the immune response.
Increased water and sodium retention.
Epinephrine/norepinephrine release from adrenal medulla.
Cortisol, as a glucocorticoid, maintains enzymes needed for glucose production in the post-absorptive state (between meals) and, therefore, is essential in maintaining plasma glucose concentration (increased gluconeogenesis and lipolysis)
Why is cortisol important for blood sugar levels?
Cortisol, as a glucocorticoid, maintains enzymes needed for glucose production in the post-absorptive state (between meals) and, therefore, is essential in maintaining plasma glucose concentration (increased gluconeogenesis and lipolysis)
What is the posterior lobe called on pituitary gland? What does it contain? Describe the hormones secreted here.
Neurohypophysis. Contains the infundibular process and stem along with the medial eminence of the hypothalamus.
Hormones secreted from this gland are mainly synthesized in the hypothalamus and stored in the posterior pituitary until their release on command.
Release hormones vasopressin/ antidiuretic hormone (ADH) and oxytocin.
Vasopressin/Antidiuretic hormone (ADH) controls blood osmolarity
Hypothalamic diabetes insipidus secondary to insufficient ADH secretion
Nephrogenic diabetes insipidus secondary to kidneys inability to respond to ADH.
Oxytocin is involved in childbirth (uterine contractions) and milk ejection from the mammary glands by contraction of myoepithelial cells around alveoli.
Arterial vasculature of the anterior pituitary.
Internal carotid artery → superior hypophyseal artery
The superior hypophyseal artery supplies arterial blood to the capillary net around hypothalamus.
This capillary net communicates with another capillary net around the anterior pituitary via a group of small veins to form the hypothalamic-hypophyseal portal system.
Arterial vasculature of the posterior pituitary.
Internal carotid artery → superior hypophyseal artery → infundibular artery → inferior hypophyseal artery.
Venous drainage of lobes in the pituitary
Same drainage for both lobes.
Anterior and posterior hypophyseal vv. → cavernous sinus
Cellular histology of pituitary gland
The anterior pituitary contains chromophils, more specifically acidophils and basophils and each cell type synthesizes and secretes specific hormones.
The posterior pituitary contain specialized glial cells called pituicytes as well as nerve fibers containing hormones stored in the nerve endings.
