I had some time to kill today. I hope this will help someone.
We cant talk about steroids and peptides without explaining the Endocrine system.
The endocrine system controls the Endocrine Glands
§ No ducts – secretion into fluid around cells diffuses into capillaries
§ Pituitary, thyroid, parathyroid, adrenal and pineal are examples.
§ Many organs have partial endocrine function – hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, small intestine, skin, heart.
Hormones– long distance chemical messengers that travel in blood or lymph throughout body.
Hypothalamus and Pituitary Glands
Anatomy
Hypothalamus floor and walls of third ventricle. Interfaces with ANS
Pituitary -
Anterior [adenohypophysis]
75% of gland – ectodermal origin
regulated by “releasing” hormones from hypothalamus – no neural connection – joined through hypophyseal portal system.
5 kinds of gland cells produce trophic hormones (affect other endocrine tissues).
Somatotrophs (hGH)
Thyrotrophs (TSH)
Gonadotrophs (FSH, LH)
Lactotrophs (Prolactin)
Corticotrophs (ACTH, MSH)
Posterior [neurohypophysis] – mass of neuroglia and nerve fibers.
25%, ectodermal origin; stores and releases hormones – doesn’t
make them
Ex. Oxytocin and ADH from hypothalamus
Hypothalamus Hormones
In diencephalon – integrates nervous system & hormones & controls ANS.
Synthesizes at least 9 hormones- 7 regulate the pituitary.
Regulates growth and development, metabolism, homeostasis.
Controls secretion of other hormones by other glands.
Intimately in contact with pituitary by hypophyseal portal system [primary
capillary plexus of infundibulum connected by hypophyseal portal veins with secondary capillary plexus in anterior pituitary.]
Hormones produced by the hypothalamus
A. Growth Hormone Releasing Hormone (GHRH)
Target = anterior pituitary
Effect = stimulates release of growth hormone (GH)
Regulation = Plasma levels of glucose, fatty acids, and amino
acids; sleep, ANS and other hormones.
B. Growth Hormone Inhibiting Hormone (GHIH)
Target = anterior pituitary
Effect = inhibit release of GH
Regulation = Plasma levels of glucose, fatty acids and aa's
C. Thyrotropin Releasing Hormone (TRH)
Target = anterior pituitary gland
Effect = stimulate release of Thyroid-stimulating hormone (TSH)
Regulation = plasma levels of TSH and glucose; metabolic rate
D. Corticotropin Releasing Hormone (CRH)
Target = anterior pituitary gland
Effect = stim. release of adrenocorticotropic hormone (ACTH)
Regulation = blood glucose levels, stress, interleukin -1
E. Gonadotropin Releasing Hormone (GnRH)
Target = anterior pituitary gland
Effect = stimulate release of Follicle Stimulating hormone (FSH)
and Luteinizing hormone (LH)
Regulation = Females - plasma estrogen and progesterone
Levels; Males - plasma testosterone levels
F. Prolactin Releasing Hormone (PRH)
Target = anterior pituitary gland
Effect = stim. release of prolactin (PRL)
Regulation = suckling
G. Prolactin inhibiting Hormone (PIH)
Target = anterior pituitary
Effect = inhibit PRL release
Regulation = suckling, plasma estrogen & progesterone levels
** 2 hormones are produced in the hypothalamus, and stored in special neurosecretory cells in the posterior pituitary gland.
H. Oxytocin (OT) – from paraventricular nucleus
Target = smooth muscle in uterus and breast
Effect = contraction of muscle (labor, milk ejection, sexual
arousal – “cuddle” hormone.)
Regulation = hormonal changes during pregnancy, suckling
I. Antidiuretic Hormone (ADH) – from supraoptic nucleus [=
vasopressin]
Target = kidney
Effect = decrease sweat and urine output; constrict arterioles &
increase blood pressure
Regulation = blood osmotic pressure, stress, drugs
[alcohol inhibits ADH].
Pituitary Hormones – 5 are trophic [stimulate other endocrine structures to release hormones]
A. Human Growth Hormone (hGH) or Somatotropin
Target = general [mainly bones & skeletal muscles.]
Effect = stimulates synthesis and production of insulin-like
growth factors (cause release of glucose, like insulin does.) stimulate cell growth and division; increases rate of protein synthesis and rate of fat catabolism, decreases rate of glucose catabolism (increase metab.)
Regulation = GHRH, GHIH
Also affected by stress, nutrition and sleep patterns.
B. Thyroid-stimulating Hormone (TSH)
Target = thyroid gland
Effect = stim. secretion/release of T3 and T4
Regulation = TRH
C. Adrenocorticotropic Hormone (ACTH)
Target = cortex of the adrenal gland
Effect = stimulate prod. /release of glucocorticoids
Regulation = CRH. Also affected by stress, hypoglycemia.
D. Follicle-Stimulating Hormone (FSH)
Target = gonads (ovary, testis)
Effect = stimulate production of gametes (male and
female) stimulates production of estrogen (female)
Regulation = GnRH, inhibin, estrogen (F) & testosterone (M)
E. Luteinizing Hormone (LH)
Target = gonads
Effect = (F) stimulates ovulation, formation of corpus luteum and prod. of Estrogen and Progesterone. (M) stimulates prod. of testosterone, LH also called interstitial cell stimulating hormone (ICSH) in male
Regulation = GnRH
F. Prolactin (PRL) or Lactogenic Hormone
Target = breast
Effect = milk production
Regulation = PRH, PIH, estrogen.
G. Melanocyte-Stimulating Hormone (MSH)
Target = melanocytes
Effect = increases production of melanin; CNS neurotransmitter
Regulation = MRH, MIH
Produced from pro-opiomelantocortin POMC, that also can yield 2 natural opiates, an enkephalin & endorphin.
Control of Pituitary Secretion – timing and amount of secretion are regulated by hypothalamus, brain centers & feedback from target organs.
Hypothalamus & Cerebral Control – releasing & inhibiting hormones. Brain monitors conditions and stimulates their release.
Neuroendocrine reflexes affect posterior lobe of the pituitary - in response to neurosensation [e.g., suckling].
Feedback from targets – negative feedback inhibition for the most part [note oxytocin response is positive feedback].
Other Endocrine Glands
Pineal Gland – roof of third ventricle of brain – capsule of pia mater. Decreases in size with age.
Cells = pinealocytes
Function – not clear
Produces melatonin [at night], and serotonin [by day] – may affect circadian rhythms, timing of puberty, and mood [SAD & PMS]
Thymus – over heart – functions in immunity, decreases in size with age.
Produces thymopoietin and thymosin needed for T cell maturation.
Thyroid Gland – Inferior to larynx; largest endocrine gland.
General
Lateral lobes connected by isthmus anterior to trachea
Follicles – made of follicular cells produce T3 and T4 upon TSH
stimulation
Parafollicular cells – produce calcitonin
Hormones are stored in large quantities – only gland that does this
In colloid in follicle cavity
Thyroid Hormones
T3, T4 [main]
Target – general
Effect – regulate O2 use, basal metabolic rate, growth and
development - T3 more potent than T4
Regulation – TSH from pituitary, TRH from hypothalamus
Calcitonin
Target – bone
Effect – inhibit osteoclasts, decrease Ca2+ release into blood,
increase Ca2+ uptake into bone
Regulation – Ca2+ levels
Parathyroid Glands – posterior surface of lateral lobes of thyroid – 2 per side
PTH – parathyroid hormone – in response to hypocalcemia.
Increases number and activity of osteoclasts. Most important
hormone in regulation of Ca2+ balance.
Increases bone resorption, which increases blood Ca2+ & HPO42-
Kidney changes:
Increase rate of removal of Ca2+ and Mg2+ from urine and
return to blood
Net effect – increases circulating Ca2+ and decrease HPO42-
Calcitonin is PTH antagonist
Also promotes formation of calcitriol from vitamin D, which
increases rate of Ca2+, Mg2+, and HPO42- from GI
Control – Negative feedback via blood Ca2+ levels
Adrenal Glands – 2, 1 on top of each kidney – 2 regions – cortex and medulla
Adrenal Medulla
Inner part of adrenal – not essential to life.
Chromafin cells – modified postganglionic sympathetic neurons
specialized for hormone secretion.
Produce catecholamines – epinephrine [80%] and norepinephrine – fight or flight response of sympathetic system [glycogenolysis, gluconeogenesis, glucose-sparing, etc.]
Link to cortex – under stress, catecholamine secretion stimulates corticosterone secretion.
Cortex – 80-90%
Derived from mesoderm
Produce over 2 dozen steroid hormones essential to life from cholesterol.
3 zones:
Zona glomerulosa – outer zone
Produces mineralcorticoids – affect homeostasis of Na+ and
K+ - 3 versions
Aldosterone – 95%
· Acts on kidney tubules
· Causes resorption of Na+ which also increases
resorption of Cl-, HCO3- and H2O
· Promotes secretion of K+, which increase K+ excretion
· Control – 4 mechanisms
1. Renin-angiotensin pathway
Decrease in blood volume causes decrease in blood pressure This stimulates renin secretion by the kidney, which causes Angiotensinogen to be converted to angiotensin I in the liver
This promotes conversion to angiotensin II in the lung, which causes Aldosterone secretion which increases blood volume and increase in blood pressure.
A second target for angiotensin II is arteriole walls – they constrict which further increases blood pressure.
2. Plasma Na+ and K+ concentrations – increase inhibits, decrease stimulates.
3. ACTH – in stress, causes increases in aldosterone.
4. ANP – inhibits rennin-angiotensin system.
Zona fasciculata – secretes glucocorticoids – affect glucose
Homeostasis. These regulate metabolism and resist stress
Cortisol, corticosterone, cortisone, Cortisol is 95% of what is made
Effects – stimulate:
· Protein breakdown/construction
· Gluconeogensis (formation of glucose)
· Lipolysis – breakdown of lipids
· Stress resistance – increases glucose and blood pressure
· Anti-inflammatory – reduce number of mast cells which reduces release of histamine; also decrease vessel permeability which reduces swelling, but also slows healing
· Depression of immunity – helps with organ transplants
Control – negative feedback – blood levels of glucocorticoids decrease which causes increase in CRH, which stimulates release of ACTH from the pituitary, which goes to cortex and increases glucocorticoid secretion.
Zona reticularis – produces androgens & some estrogens
This is not significant in males since the testes make more
In females – affect libido, increase axial and pubic hair,
Affect pre-pubertal growth spurt
Pancreas – endocrine and exocrine – posterior and slightly inferior to stomach
Exocrine function – 98% of total – production of digestive enzymes by
acinar cells
Endocrine function – Islets of Langerhans; 3 main types of cells
α–- produce glucagon
β – produce insulin
Δ – produce somatostatin
Hormones
Insulin
Target – general
Effect – lowers blood glucose & accelerates diffusion of glucose into cells [except kidney, liver & brain], Increases glycogenesis, increases uptake of amino acids and peptide formation (decreases gluconeogenesis), promotes glucose conversion to fat & promotes cellular respiration. Decreases glycogenolysis.
Regulation –blood levels of glucose, amino acids & fatty a’s.
Glucagon
Target – liver
We cant talk about steroids and peptides without explaining the Endocrine system.
The endocrine system controls the Endocrine Glands
§ No ducts – secretion into fluid around cells diffuses into capillaries
§ Pituitary, thyroid, parathyroid, adrenal and pineal are examples.
§ Many organs have partial endocrine function – hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, small intestine, skin, heart.
Hormones– long distance chemical messengers that travel in blood or lymph throughout body.
Hypothalamus and Pituitary Glands
Anatomy
Hypothalamus floor and walls of third ventricle. Interfaces with ANS
Pituitary -
Anterior [adenohypophysis]
75% of gland – ectodermal origin
regulated by “releasing” hormones from hypothalamus – no neural connection – joined through hypophyseal portal system.
5 kinds of gland cells produce trophic hormones (affect other endocrine tissues).
Somatotrophs (hGH)
Thyrotrophs (TSH)
Gonadotrophs (FSH, LH)
Lactotrophs (Prolactin)
Corticotrophs (ACTH, MSH)
Posterior [neurohypophysis] – mass of neuroglia and nerve fibers.
25%, ectodermal origin; stores and releases hormones – doesn’t
make them
Ex. Oxytocin and ADH from hypothalamus
Hypothalamus Hormones
In diencephalon – integrates nervous system & hormones & controls ANS.
Synthesizes at least 9 hormones- 7 regulate the pituitary.
Regulates growth and development, metabolism, homeostasis.
Controls secretion of other hormones by other glands.
Intimately in contact with pituitary by hypophyseal portal system [primary
capillary plexus of infundibulum connected by hypophyseal portal veins with secondary capillary plexus in anterior pituitary.]
Hormones produced by the hypothalamus
A. Growth Hormone Releasing Hormone (GHRH)
Target = anterior pituitary
Effect = stimulates release of growth hormone (GH)
Regulation = Plasma levels of glucose, fatty acids, and amino
acids; sleep, ANS and other hormones.
B. Growth Hormone Inhibiting Hormone (GHIH)
Target = anterior pituitary
Effect = inhibit release of GH
Regulation = Plasma levels of glucose, fatty acids and aa's
C. Thyrotropin Releasing Hormone (TRH)
Target = anterior pituitary gland
Effect = stimulate release of Thyroid-stimulating hormone (TSH)
Regulation = plasma levels of TSH and glucose; metabolic rate
D. Corticotropin Releasing Hormone (CRH)
Target = anterior pituitary gland
Effect = stim. release of adrenocorticotropic hormone (ACTH)
Regulation = blood glucose levels, stress, interleukin -1
E. Gonadotropin Releasing Hormone (GnRH)
Target = anterior pituitary gland
Effect = stimulate release of Follicle Stimulating hormone (FSH)
and Luteinizing hormone (LH)
Regulation = Females - plasma estrogen and progesterone
Levels; Males - plasma testosterone levels
F. Prolactin Releasing Hormone (PRH)
Target = anterior pituitary gland
Effect = stim. release of prolactin (PRL)
Regulation = suckling
G. Prolactin inhibiting Hormone (PIH)
Target = anterior pituitary
Effect = inhibit PRL release
Regulation = suckling, plasma estrogen & progesterone levels
** 2 hormones are produced in the hypothalamus, and stored in special neurosecretory cells in the posterior pituitary gland.
H. Oxytocin (OT) – from paraventricular nucleus
Target = smooth muscle in uterus and breast
Effect = contraction of muscle (labor, milk ejection, sexual
arousal – “cuddle” hormone.)
Regulation = hormonal changes during pregnancy, suckling
I. Antidiuretic Hormone (ADH) – from supraoptic nucleus [=
vasopressin]
Target = kidney
Effect = decrease sweat and urine output; constrict arterioles &
increase blood pressure
Regulation = blood osmotic pressure, stress, drugs
[alcohol inhibits ADH].
Pituitary Hormones – 5 are trophic [stimulate other endocrine structures to release hormones]
A. Human Growth Hormone (hGH) or Somatotropin
Target = general [mainly bones & skeletal muscles.]
Effect = stimulates synthesis and production of insulin-like
growth factors (cause release of glucose, like insulin does.) stimulate cell growth and division; increases rate of protein synthesis and rate of fat catabolism, decreases rate of glucose catabolism (increase metab.)
Regulation = GHRH, GHIH
Also affected by stress, nutrition and sleep patterns.
B. Thyroid-stimulating Hormone (TSH)
Target = thyroid gland
Effect = stim. secretion/release of T3 and T4
Regulation = TRH
C. Adrenocorticotropic Hormone (ACTH)
Target = cortex of the adrenal gland
Effect = stimulate prod. /release of glucocorticoids
Regulation = CRH. Also affected by stress, hypoglycemia.
D. Follicle-Stimulating Hormone (FSH)
Target = gonads (ovary, testis)
Effect = stimulate production of gametes (male and
female) stimulates production of estrogen (female)
Regulation = GnRH, inhibin, estrogen (F) & testosterone (M)
E. Luteinizing Hormone (LH)
Target = gonads
Effect = (F) stimulates ovulation, formation of corpus luteum and prod. of Estrogen and Progesterone. (M) stimulates prod. of testosterone, LH also called interstitial cell stimulating hormone (ICSH) in male
Regulation = GnRH
F. Prolactin (PRL) or Lactogenic Hormone
Target = breast
Effect = milk production
Regulation = PRH, PIH, estrogen.
G. Melanocyte-Stimulating Hormone (MSH)
Target = melanocytes
Effect = increases production of melanin; CNS neurotransmitter
Regulation = MRH, MIH
Produced from pro-opiomelantocortin POMC, that also can yield 2 natural opiates, an enkephalin & endorphin.
Control of Pituitary Secretion – timing and amount of secretion are regulated by hypothalamus, brain centers & feedback from target organs.
Hypothalamus & Cerebral Control – releasing & inhibiting hormones. Brain monitors conditions and stimulates their release.
Neuroendocrine reflexes affect posterior lobe of the pituitary - in response to neurosensation [e.g., suckling].
Feedback from targets – negative feedback inhibition for the most part [note oxytocin response is positive feedback].
Other Endocrine Glands
Pineal Gland – roof of third ventricle of brain – capsule of pia mater. Decreases in size with age.
Cells = pinealocytes
Function – not clear
Produces melatonin [at night], and serotonin [by day] – may affect circadian rhythms, timing of puberty, and mood [SAD & PMS]
Thymus – over heart – functions in immunity, decreases in size with age.
Produces thymopoietin and thymosin needed for T cell maturation.
Thyroid Gland – Inferior to larynx; largest endocrine gland.
General
Lateral lobes connected by isthmus anterior to trachea
Follicles – made of follicular cells produce T3 and T4 upon TSH
stimulation
Parafollicular cells – produce calcitonin
Hormones are stored in large quantities – only gland that does this
In colloid in follicle cavity
Thyroid Hormones
T3, T4 [main]
Target – general
Effect – regulate O2 use, basal metabolic rate, growth and
development - T3 more potent than T4
Regulation – TSH from pituitary, TRH from hypothalamus
Calcitonin
Target – bone
Effect – inhibit osteoclasts, decrease Ca2+ release into blood,
increase Ca2+ uptake into bone
Regulation – Ca2+ levels
Parathyroid Glands – posterior surface of lateral lobes of thyroid – 2 per side
PTH – parathyroid hormone – in response to hypocalcemia.
Increases number and activity of osteoclasts. Most important
hormone in regulation of Ca2+ balance.
Increases bone resorption, which increases blood Ca2+ & HPO42-
Kidney changes:
Increase rate of removal of Ca2+ and Mg2+ from urine and
return to blood
Net effect – increases circulating Ca2+ and decrease HPO42-
Calcitonin is PTH antagonist
Also promotes formation of calcitriol from vitamin D, which
increases rate of Ca2+, Mg2+, and HPO42- from GI
Control – Negative feedback via blood Ca2+ levels
Adrenal Glands – 2, 1 on top of each kidney – 2 regions – cortex and medulla
Adrenal Medulla
Inner part of adrenal – not essential to life.
Chromafin cells – modified postganglionic sympathetic neurons
specialized for hormone secretion.
Produce catecholamines – epinephrine [80%] and norepinephrine – fight or flight response of sympathetic system [glycogenolysis, gluconeogenesis, glucose-sparing, etc.]
Link to cortex – under stress, catecholamine secretion stimulates corticosterone secretion.
Cortex – 80-90%
Derived from mesoderm
Produce over 2 dozen steroid hormones essential to life from cholesterol.
3 zones:
Zona glomerulosa – outer zone
Produces mineralcorticoids – affect homeostasis of Na+ and
K+ - 3 versions
Aldosterone – 95%
· Acts on kidney tubules
· Causes resorption of Na+ which also increases
resorption of Cl-, HCO3- and H2O
· Promotes secretion of K+, which increase K+ excretion
· Control – 4 mechanisms
1. Renin-angiotensin pathway
Decrease in blood volume causes decrease in blood pressure This stimulates renin secretion by the kidney, which causes Angiotensinogen to be converted to angiotensin I in the liver
This promotes conversion to angiotensin II in the lung, which causes Aldosterone secretion which increases blood volume and increase in blood pressure.
A second target for angiotensin II is arteriole walls – they constrict which further increases blood pressure.
2. Plasma Na+ and K+ concentrations – increase inhibits, decrease stimulates.
3. ACTH – in stress, causes increases in aldosterone.
4. ANP – inhibits rennin-angiotensin system.
Zona fasciculata – secretes glucocorticoids – affect glucose
Homeostasis. These regulate metabolism and resist stress
Cortisol, corticosterone, cortisone, Cortisol is 95% of what is made
Effects – stimulate:
· Protein breakdown/construction
· Gluconeogensis (formation of glucose)
· Lipolysis – breakdown of lipids
· Stress resistance – increases glucose and blood pressure
· Anti-inflammatory – reduce number of mast cells which reduces release of histamine; also decrease vessel permeability which reduces swelling, but also slows healing
· Depression of immunity – helps with organ transplants
Control – negative feedback – blood levels of glucocorticoids decrease which causes increase in CRH, which stimulates release of ACTH from the pituitary, which goes to cortex and increases glucocorticoid secretion.
Zona reticularis – produces androgens & some estrogens
This is not significant in males since the testes make more
In females – affect libido, increase axial and pubic hair,
Affect pre-pubertal growth spurt
Pancreas – endocrine and exocrine – posterior and slightly inferior to stomach
Exocrine function – 98% of total – production of digestive enzymes by
acinar cells
Endocrine function – Islets of Langerhans; 3 main types of cells
α–- produce glucagon
β – produce insulin
Δ – produce somatostatin
Hormones
Insulin
Target – general
Effect – lowers blood glucose & accelerates diffusion of glucose into cells [except kidney, liver & brain], Increases glycogenesis, increases uptake of amino acids and peptide formation (decreases gluconeogenesis), promotes glucose conversion to fat & promotes cellular respiration. Decreases glycogenolysis.
Regulation –blood levels of glucose, amino acids & fatty a’s.
Glucagon
Target – liver
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