Chedy - theme 12 Flashcards
Portal venous system - what is it?
Capillary beds connected by veins, bypassing the heart.
What’s good about the portal venous system?
Allows transfer of one region’s products to another at high concentrations. Ex: products of the hypothalamus can be carried directly to the pituitary gland without getting diluted.
Origin of endocrinology:
Bucharest - pit gland and gigantism.
Early experiment on testes. Later found that pit gland controls growth hormones.
Somatotropin:
Growth hormone. Substance affecting the body.
Gigantism:
Also called giant microadenoma - enlarged pituitary gland. Good for studying, since all body systems are enlarged.
Neuroendocrine system and homeostasis:
Controls growth and development, metabolism, cardiovascular system, and reproduction.
Hypothalamus:
Links the endocrine system to the nervous system. Synthesizes and secretes neurohormones.
What is the hypothalamus responsive to?
Light, olfactory stimuli, steroids, neurally transmitted info from heart/stomach/reproductive organs, autonomic input, blood-borne stimuli, stress, thermostat.
Process of secretion from post pit gland:
Neurohormones are synthesized in the neuronal cell bodies of the hypothalamus. They travel down the axon and are stored in the neuronal terminals in the post pit gland. When the neuron is excited, the hormone is released into the post pit capillaries for distribution.
Two types of hypothalamic hormones:
Hypothalamic neurohormones: secreted by the post pit gland.
Hypothalamic-releasing neurohormones: controls secretion from ant pit gland.
Post pit hypothalamic neurohormones:
Vasopressin and oxytocin.
Vasopressin:
Also called ADH (antidiuretic hormone). Produced by supraoptic nuclei.
In nephrons of kidneys: increases water permeability of distal and collecting tubules (water retention).
In arterioles: causes vasocontriction.
Oxytocin:
Produced by paraventricular nuclei.
In uterus: stimulates uterine contraction
In mammary glands: stimulates breast milk ejection
Oxytocin and vasopressin together:
Molecularly similar. At the end of pregnancy, mother needs to retain water to produce milk.
Drinking alcohol inhibits what?
Vasopressin. Which is why you pee so much.
Process of secretion from the ant pit gland:
Hypophysiotropic hormones are secreted into the hypothalamic capillaries. They pass through the hypothalamic-hypophyseal portal system. They pass into the blood through anterior pit capillaries and control the release of ant pit hormones. The anterior pit capillaries rejoin to form a vein, through which hormones are distributed to the body.
Hypothalamic-hypophyseal portal system:
A vascular link from the hypothalamus to the anterior pit gland. Where the hypothalamic capillaries rejoin.
Hypophysiotropic hormones:
Releasing/inhibitory hormones produced by the hypothalamus for targeting to the ant pit gland.
Hormones of the ant pit gland:
Glycoproteins: TSH, pituitary gonadotropins (FSH and LH)
Proteins: GH, PRL, ACTH, endorphins
Also MSH, apparently
FSH:
Follicle-stimulating hormone. Stimulates germ cell development and sex steroid production in gonads.
LH:
Luteinizing hormone. Stimulates release of eggs and sex steroid production in gonads.
PRL:
Prolactin. Stimulates milk formation.
ACTH:
Adrenocorticotropic hormone. Stimulates adrenal cortex to produce glucocorticoids.
Hypothalamic neurohormones that control the pit gland:
CRH, GHRH, GHIH, GnRH, TRH, dopamine
CRH:
Corticotropin-releasing hormone. Stimulates ACTH synthesis.
GHRH:
Growth hormone-releasing hormone. Stimulates GH synthesis.
GHIH:
Growth hormone-inhibiting hormone. Inhibits GH synthesis. Also called somatostatin.
GnRH:
Gonadotropin-releasing hormone. Releases FSH and LH.
TRH:
Thyrotropin-releasing hormone. A tripeptide that releases TSH and PRL.
Dopamine:
Biogenic amine that inhibits PRL release.
Endorphins:
Inhibit pain in PNS
MSH:
Melanocyte-stimulating hormone. Melanocytes promote skin darkening.
How are different foods broken down for absorption?
Proteins -> AAs
Carbs -> glucose
Fats -> monoglycerides and fatty acids
What are the anabolic and catabolic processes of the components of the metabolic pool?
AAs exchange with body proteins.
Glucose exchanges with glycogen.
Fats exchange with triglycerides.
AAs can be used in the other two pathways. AAs can be disposed of through the urine as nitrogenous waste.
All three are used as metabolic fuel within cells, and the waste products can be expired.
Structure of GH:
191 AA single-chain polypeptide.
Excess GH:
Early in life: gigantism. Growth plates are not sealed, so the individual keeps growing.
Later in life: acromegaly. Due to tumours of the pit gland.
GH deficiency:
Early in life: growth failure, delayed sexual maturity
Later in life: very rare. Either caused by adenoma or a continuation of childhood deficiency.
Effects of GH:
Anabolic hormone - builds up body tissue. Increases height during childhood by stimulating cell division and multiplication of chondrocytes.
GH levels over time:
Negative exponential graph. Never reaches zero.
GH control of growth and differentiation:
GH acts on liver to produce IGF-1 (insulin-like growth factor), which stimulates osteoblast and chondrocyte activity to promote bone growth and elongation.
Gonadal hormones during puberty seal growth plates to stop bone elongation.
Metabolic effects of GH:
Increases calcium retention (for bone strength)
Increases muscle mass, bone mass, protein synthesis
Stimulates growth of internal organs
Promotes breakdown of fatty acids and glucose in blood
Regulation of GH:
Various stimuli control balance of GHRH and GHIH, which regulates GH secretion.
Stimulators of GH production:
Ghrelin - hunger protein produced mainly by fundus cells of stomach and epsilon cells of the pancreas.
Inhibitors of GH production:
Negative feedback from GH and IGF-1, hyperglycemia, glucocorticoids from adrenal cortex.
Thyroid gland: where is it? what is it?
Located in the neck under the thyroid cartilage. Consists of follicles containing thyroglobulin, which secrete thyroxine (T4) and triiodothyronine (T3)
Thyroid hormones vs CNS and PNS:
CNS will not develop properly without thyroid hormones. Conduction velocity of peripheral nerves is directly related to the availability of thyroid hormones
Thyroid hormone deficiency at birth:
May be congenital or due to maternal deficiency of iodine. 1/4000 bbs. Untreated, it can lead to stunted physical and mental growth.
Treatment of neonatal hypothyroidism:
Screening practices before birth are widely practiced. Daily dose of thyroid hormone is easy and inexpensive.
TSH:
Thyroid-stimulating hormone. Part of the glycoprotein family.
How are pituitary gland hormones differentiated?
Alpha subunits are all the same. Beta subunit determines what kind of hormone it is. The subunits get together in the ER and are glycosylated in the Golgi.
Glycoprotein family:
Gonadotropins (FSH, LH) and placental gonadotropins (human chorionic gonadotropin (hCG), equine (eCG)).
Regulation of TSH:
Positively regulated by TRH (thyrotropin releasing hormone). Negatively regulated by feedback from T4 and T3.
Goiter:
Condition where negative feedback control of TSH gets messed up.
Process of thyroid hormone secretion:
Stimulus induces hypothalamus to release TRH to the ant pit gland, which releases TSH to the thyroid gland, which releases T3 and T4.
Action of T3 and T4:
Increased metabolic rate, incread heat production, growth and CNS development, enhancement of sympathetic activity
Which of T3 / T4 controls response to cold exposure?
T4
How fast do T3 and T4 work?
Slowly, because they aren’t broken down very quickly. Response is only evident after several hours or days, and can last for days to weeks after blood concentration has gone down.
What does it mean that T3 and T4 are pleiotropic?
They have no discrete targets; they influence basically every tissue of the body.
How do thyroid hormones increase heat production?
Increasing the number of Na/K pumps increases rate of ATP hydrolysis, which produces heat as a byproduct.
__ are the most important regulator of the rate of O2 consumption and energy expenditure under resting conditions
Thyroid hormones
People with -thyroidisms:
Hyperthyroidism - sweat a lot, very thin
Hypothyroidism - cold a lot, weight gain
__% of heat produced by homeotherms is attributed to thyroid hormones.
70
Amphibians and thyroid hormones:
Thyroid hormones control metamorphosis.
