Endocrine System Physiology 1 Flashcards
What do we call a chemical substance released by an endocrine gland into the blood in which it travels to another site in the body where it exerts its effect?
A hormone. Endocrine hormones are released directly into the bloodstream. Exocrine hormones are released into ducts to travel to the target tissue. Paracrine hormones act on cells within the vicinity of the secreting cell. Juxtacrine hormones act on neighboring cells. Autocrine hormones act on cells that produce the hormone.
What is the difference between an exocrine and endocrine gland?
An endocrine gland secretes substances into the bloodstream without the use of a duct. An exocrine gland uses a duct to secretes substances to a place that is external from where it resides.
What is an example of an exocrine gland?
Some examples are mammary glands, sweat glands, the pancreas, the liver, or salivary glands.
What is an example of an endocrine gland?
Some examples are the ovaries, the testes, or the adrenal glands
What are the 3 classes of hormones?
(1) Derived from amino acids
(2) Protein or peptide based
(3) Steroids
What amino acid serves as the starting point of most of the amino acid derived hormones?
Tyrosine
What 2 organs release tyrosine based hormones?
(1) Thyroid gland –> thyroxine
(2) Adrenal medulla –> Epi and Norepi
What type of receptor when bound to hormone causes an increase in cAMP?
Plasmalemma receptors
cAMP is an example of what?
Second messenger
What is the effect of an increase in cAMP?
It causes an increase in cytosolic calcium
What substances use plasmalemma receptors?
Polypeptide hormones like Norepi and Epi
What receptors use cytoplasmic receptors?
Steroids
How do steroids interact with the cytoplasmic receptor?
They bind to the receptor and the whole complex binds to DNA and induces gene expression to produce new proteins
What substances use nuclear receptors?
T3 and T4
What is the effect of T3 binding to a nuclear receptor?
Increased transcription and increased translation (production of proteins)
GH, ACTH, TSH, FSH, LH, and prolactin come from where?
Anterior pituitary
How is the hypothalamus and anterior pituitary connected?
Via portal vessels
What gland is controlled by hypothalamic releasing substances?
Anterior pituitary (adenohypophysis)
What gland is controlled by nerve signals from the hypothalamus?
Posterior pituitary (neurohypophysis)
What stimulates growth of ovum and sperm?
FSH
What stimulates the maturation and release of ovum?
LH
What stimulates the liver to release somatomedins?
Growth hormone
What promotes protein synthesis and uptake of various amino acids?
Growth hormone
What promotes increased use of fats, release of fatty acids, decreased use of carbohydrates and increased beta oxidation?
Growth hormone
Where are ADH and oxytocin released from?
Posterior pituitary
What stimulates the release of GH from the Anterior pituitary?
GHRH
What stimulates the release of GHRH from the hypothalamus?
Stress: malnutrition (especially protein), hypoglycemia, exercise, physical/mental trauma
How does the hypothalamus affect posterior pituitary?
Hormones are produced by hypothalamus and are transported down nerve endings to the posterior pituitary
What is target tissue for ADH?
Kidney collecting ducts. Collecting ducts contain lots of aquaporins and thus are highly permeable to water.
What is main stimulus for release of ADH?
Increased blood osmolarity sensed by hypothalamus
What mineral is important for synthesis of thyroid hormones?
Iodine
What is the active form of thyroid hormone?
T3 aka triiodothyroxine. T4 is the inactive form.
In what form is most of the thyroid hormone in the body?
T4/thyroxine
How is thyroxin transported in blood?
It is bound to thyroxin binding globulin, prealbumin, or albumin
What stimulates release of TRH?
Cold, emotional reactions, increased calories
What is the function of thyroid hormone?
To maintain basal metabolic rate
How does thyroid hormone maintain basal metabolic rate?
By increased activity of Na+/K+ ATPase pump
What is the effect of calcitonin on the body?
Decreases blood calcium levels
How does calcitonin decrease blood calcium?
Decreased activity of Ca2+ pump
Increased osteoblastic activity –> bone formation
Decreased osteoclastic activity –> less bone turnover
Where is calcitonin released?
Thyroid gland, C cells
What does parathyroid hormone do?
Increased calcium levels in the blood. Versus calcitonin decrease calcium levels in blood
How does PTH increase calcium levels in the blood?
Increased intestinal absorption of calcium (with Vit. D3)
Increased kidney reabsorption
Increased bone resorption
What are the two major controls of blood calcium?
PTH
Vitamin D3 (helps calcium absorption)
Where are catecholamines produced?
Adrenal medulla. Versus the adrenal cortex makes mineralocorticoids, glucocorticoids, and sex hormones.
The adrenal medulla functions most like what kind of neuron?
Post ganglionic sympathetic neuron. Adrenal medulla developed embyrologically in parallel with the sympathetic nervous system.
What four classes of hormones are released from adrenal cortex?
(1) Glucocorticoids
(2) Mineralocorticoids
(3) Androgens
(4) Estrogens and progesterones
How is cortisol transported?
Bound to globulins
Bound to albumin
Free form
The fact that we need cortisol in small levels for other hormones to work is known as what?
Permissive effect
What stimulates cortisol release?
ACTH
ACTH exhibits diurnal variations. When is it at its highest?
In the morning
What else is produced along with ACTH?
MSH - melanocyte stimulating hormone. This is why patients with Cushing’s Syndrome (hypercortisolism) may also exhibit hyperpigmentation.
What are some of the anabolic physiological activities of cortisol?
(1) Stimulates gluconeogenesis
(2) Stimulates glycogen breakdown
(3) Stimulates protein synthesis
Anabolism refers to the synthesis of molecules (from simpler ones put together).
What are some of the catabolic effects of cortisol at physiological doses?
- Increased Protein catabolism in skeletal muscle, connective tissue, and lymphoid tissue
- Increased Lipolysis
- Increased Production of rate-limiting enzymes for gluconeogenesis
Catabolism refers to the breakdown of molecules (into simpler ones).
What are some of the other roles of cortisol at physiological doses?
Weak aldosterone effect
Stimulates surfactant production in fetuses
Anti inflammatory
Enhances immune function
What stimulates crf?
Stress e.g. hypoglycemia, intense hot or cold, chronic pain, emotions, disease
What is the major mineralocorticoid?
Aldosterone
What are the target tissues for aldosterone?
Kidney
Sweat glands
Salivary glands
Colonic epithelium
What are the major effects of aldosterone?
Regulation of blood volume and blood pressure
How does aldosterone regulate blood volume and pressure?
(1) By causing an increase in Na+ reabsorption –> increased water reabsorption
(2) Increased K+ excretion
What is the long term control of aldosterone?
Angiotensin II
What are some of the other controls of aldosterone?
Increased K+ (potent regulator)
Decreased Na+
What is needed for aldosterone to work?
ACTH
What is the major adrenal androgen?
DHEA
The delta cells of the islets of Langerhans produce what hormone?
Somatostatin
What other organs produce somatostatins?
Stomach and intestines
What effects do somatostatins have on the body?
Inhibits glucagon and insulin secretion from islets of Langerhans
Inhibits GH and TSH
Inhibits G.I. secretions such as CCK and secretin
What hormone promotes fuel storage?
Insulin
What will increase insulin release?
High blood glucose
Sweet tasting food
Amino acids
What hormones increase insulin levels?
GI hormones –> cck, secretin and gastrin
Cortisol
What inhibits insulin release?
Epi and norepi and somatostatin
What are the effects of insulin?
Increased cellular uptake of glucose
Increased Glucose utilization
Increased Glycogen synthesis
Increased Fatty acid synthesis
Increased Protein synthesis
What hormone is released with low blood sugar?
Glucagon
What are the main stimuli for release of glucagon?
Main stimuli –> Decreased blood sugar
Increased Blood amino acids
Epi/Norepi
What are some of the effects of glucagon?
Increased blood glucose via:
Increased Gluconeogenesis
Increased Glycogenolysis
Increased Triglyceride breakdown in adipose tissue
Name 3 factors increase glucagon stimulation?
Low blood glucose, protein-containing meal, elevated levels of epinephrine
