A&P II Endocrine system part 2

Describe the structure of the thyroid gland.

*Isthmus*: median mass connecting two lateral lobes *Follicles*: hollow sphere of epithelial follicular cells that produce glycoprotein thyroglobulin *Colloid*: fluid of follicle lumen containing thyroglobulin plus iodine and is precursor to thyroid hormone *Parafollicular cells*: produce hormone calcitonin

What are tropins and which hormones fall into this category?

*regulate secretion of other hormones* Thyroid-stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Follicle-stimulating hormone (FSH) Luteinizing hormone (LH)

Antidiuretic hormone (ADH)

--Hypothalamus contains osmoreceptors that monitor solute concentrations --If concentration too high, posterior pituitary triggered to secrete ADH --Targets kidney tubules to reabsorb more water to inhibit or prevent urine formation --Release also triggered by pain, low blood pressure, and drugs --Inhibited by alcohol, diuretics --High concentrations cause vasoconstriction, so also called vasopressin --To get rid of fluid --Directly effect the kidney

Oxytocin

--Strong stimulant of uterine contractions released during childbirth --Also acts as hormonal trigger for milk ejection --Both are positive feedback mechanisms --Acts as neurotransmitter in brain --Feels good hormones --Connect the baby and the mother

How is the anterior pituitary connected to the hypothalamus?

1. Anterior lobe is glandular tissue derived from an outpocketing of oral mucosa a. Vascularly connected to hypothalamus via hypophyseal portal system consisting of: i. Primary capillary plexus ii. Hypophyseal portal veins iii. Secondary capillary plexus 2. Hypothalamus secretes releasing and inhibiting hormones to anterior pituitary to regulate hormone secretion

effect of posterior pituitary gland

1. Diabetes insipidus (not producing antidiuretic hormones) a. ADH deficiency due to damage to hypothalamus or posterior pituitary b. Must keep well hydrated c. Symptoms : Dehydration and Releasing too much electrolytes 2. Syndrome of inappropriate ADH secretion (SIADH) (producing tooo much) a. Retention of fluid, headache, disorientation b. Fluid restriction; blood sodium level monitoring

Growth hormone effect

1. Hypersecretion of GH is usually caused by anterior pituitary tumor a. In children results in gigantism --Can reach heights of 8 feet b. In adults results in acromegaly --Overgrowth of hands, feet, and face 2. Hyposecretion of GH a. In children results in pituitary dwarfism --May reach height of only 4 feet b. In adults usually causes no problems

Effect of prolacton

1. Hypersecretion of prolactin is more common than hyposecretion --Hyposecretion not a problem in anyone except women who choose to nurse 2. Hyperprolactinemia is the most frequent abnormality of anterior pituitary tumors (produced milk when no baby) 3. Clinical signs include inappropriate lactation, lack of menses, infertility in females, and impotence in males

What hormones are stored in the posterior pituitary? Describe their functions and regulation.

1. Posterior pituitary consists of axon terminals of neurons from hypothalamic neurons: a. Paraventricular neurons produce oxytocin b. Supraoptic neurons produce antidiuretic hormone (ADH) 2. Oxytocin and ADH (anti-duritic hormones) a. Each composed of nine amino acids b. Almost identical but differ in two amino acids c. Produce in nuclei of the hypothalamus

Describe the steps of thyroid synthesis.

1. Thyroglobulin is synthesized and discharged into follicle lumen 2. Iodide is trapped: iodide ions (I-) are actively taken into cell and released into lumen 3. Iodide oxidized: electrons are removed, converting it to iodine (I2) 4. Iodine is attached to tyrosine: mediated by peroxidase enzymes =Monoiodotyrosine (MIT): formed if only one iodine attaches =Diiodotyrosine (DIT): formed if two iodines attach 5. Iodinated tyrosines link together to form T3 and T4 =If one MIT and one DIT link, T3 is formed =If two DITs link, T4 is formed 6. Colloid is endocytosed by follicular cells =Vesicle is then combined with a lysosome 7. Lysosomal enzymes cleave T3 and T4 from thyroglobulin =Hormones are secreted into bloodstream =Mostly T4 secreted, but T3 is also secreted =T4 must be converted to T3 at tissue level =Body will converted as need to t3 or t4

For the following anterior pituitary hormone describe the function, regulation, and the effects if too much or too little is released. Refer to table 16.1 for help. *Thyroid stimulating hormone*

1. Tropic hormone that is also called thyrotropin as it is produced by thyrotropic cells (releasing and inhabiting hormones) 2. Stimulates normal development and secretory activity of thyroid 3. Release triggered by thyrotropin-releasing hormone from hypothalamus 4. Inhibited by rising blood levels of thyroid hormones that act on both pituitary and hypothalamus -Also inhibited by GHIH

For the following anterior pituitary hormone describe the function, regulation, and the effects if too much or too little is released. Refer to table for help. *Growth hormone*

1.Also called somatotropin as it is produced by somatotropic cells 2.Has direct actions on metabolism and indirect growth-promoting actions 3. Effect mainly skeleton and muscles *4 Direct actions on metabolism* a. Glucose-sparing actions decrease rate of cellular glucose uptake and metabolism (anti-insulin effects) b. Triggers liver to break down glycogen into glucose c. Increases blood levels of fatty acids for use as fuel and encourages cellular protein synthesis *5. Indirect actions on growth:* a. GH triggers liver, skeletal muscle, and bone to produce insulin-like growth factors (IGFs) b. IGFs then stimulate: -Cellular uptake of nutrients used to synthesize DNA and proteins needed for cell division -Formation of collagen and deposition of bone matrix c. GH stimulates most cells to enlarge and divide, but major targets are bone and skeletal muscle *6. Regulation of secretion* a. GH release or inhibition chiefly regulated by hypothalamic hormones on somatotropic cells i.Growth hormone-releasing hormone (GHRH) stimulates GH release -Triggered by low blood GH or glucose, or high amino acid levels ii. Growth hormone-inhibiting hormone (GHIH) (somatostatin) inhibits release -Triggered by increase in GH and IGF levels b. Ghrelin (hunger hormone) also stimulates GH release

Where is the pituitary gland located?

=below the hypothalamus at the base of the brain =Hypothalamus is connected to pituitary gland (hypophysis) via stalk called infundibulum

Which lobe of the pituitary does not make its own hormones but is more of a storage area?

=hypothalamus hormones are stores in the posterior pituitary

Which cells of the thyroid gland produce thyroid hormone? Which cells produce calcitonin?

=thyroid gland produce by epithelial follicular cells =Calcitonin produced by parafollicular (C) cells

Describe this type of stimuli that trigger hormone release: Hormonal

By the Endocrine system

Describe this type of stimuli that trigger hormone release: Neural

Directly by nervous system

The anterior lobe of the pituitary arises from what tissue?

Glandular tissue

Chain of command

Hypothalamus Anterior pituitary Thyroid gland Target cells

What are the functions of thyroid hormone?

The function of the thyroid gland is to take iodine, found in many foods, and convert it into thyroid hormones: thyroxine (T4) and triiodothyronine (T3). Thyroid cells are the only cells in the body which can absorb iodine.

who can override the these stimuli?

The nervous system can ultimately override any of these controls.

Where is the thyroid gland located?

a butterfly-shaped gland that sits low on the front of the neck

For the following anterior pituitary hormone describe the function, regulation, and the effects if too much or too little is released. Refer to table 16.1 for help. *Adrenocorticotropic hormone*

a. Also called corticotropin as it is secreted by corticotropic cells --Precursor to corticotropin is pro-opiomelanocortin b. ACTH stimulates adrenal cortex to release corticosteroids c. Regulation of ACTH release --Triggered by hypothalamic corticotropin-releasing hormone (CRH) in daily rhythm i. Highest levels in morning --Internal and external factors that alter release of CRH include fever, hypoglycemia, and stressors

For the following anterior pituitary hormone describe the function, regulation, and the effects if too much or too little is released. Refer to table 16.1 for help. *Gonadotropins (Follicle stimulating hormone and Leutinizing hormone)*

a. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are secreted by gonadotropic cells of anterior pituitary b. FSH stimulates production of gametes (egg or sperm) c. LH promotes production of gonadal hormones --In females, LH helps mature follicles of egg, triggers ovulation and release of estrogen and progesterone --In males, LH stimulates production of testosterone d. LH and FSH both are absent from blood in prepubertal boys and girls e. Regulation of gonadotropin release --Triggered by gonadotropin-releasing hormone (GnRH) during and after puberty --Suppressed by gonadal hormones (feedback)

For the following anterior pituitary hormone describe the function, regulation, and the effects if too much or too little is released. Refer to table 16.1 for help. *Prolactin*

a. Secreted by prolactin cells of anterior pituitary b. Stimulates milk production in females; role in males not well understood c. Regulation primarily controlled by prolactin-inhibiting hormone (PIH), which is dopamine d. PIH prevents release of PRL until needed, with decreased levels leading to lactation e. Increased estrogen levels stimulate PRL --Reason behind breast swelling and tenderness during menstrual cycle f. Blood levels rise toward end of pregnancy g. Suckling stimulates PRL release and promotes continued milk production

How does the posterior pituitary maintain a neural connection with the hypothalamus?

by neurones

What is the true master endocrine gland?

hypothalamus

The posterior pituitary is derived from what tissue?

neural tissue